draft-ietf-forces-model-03.txt   draft-ietf-forces-model-04.txt 
Internet Draft L. Yang Internet Draft L. Yang
Expiration: July 2004 Intel Corp. Expiration: August 2005 Intel Corp.
File: draft-ietf-forces-model-03.txt J. Halpern File: draft-ietf-forces-model-04.txt J. Halpern
Working Group: ForCES Megisto Systems Working Group: ForCES Megisto Systems
R. Gopal R. Gopal
Nokia Nokia
A. DeKok A. DeKok
IDT Inc. Infoblox, Inc.
Z. Haraszti Z. Haraszti
Clovis Solutions
S. Blake S. Blake
Ericsson Modular Networks
E. Deleganes E. Deleganes
Intel Corp. Intel Corp.
August 2005
ForCES Forwarding Element Model ForCES Forwarding Element Model
draft-ietf-forces-model-03.txt draft-ietf-forces-model-04.txt
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Abstract Abstract
This document defines the forwarding element (FE) model used in the This document defines the forwarding element (FE) model used in the
Forwarding and Control Element Separation (ForCES) protocol. The Forwarding and Control Element Separation (ForCES) protocol. The
model represents the capabilities, state and configuration of model represents the capabilities, state and configuration of
forwarding elements within the context of the ForCES protocol, so forwarding elements within the context of the ForCES protocol, so
that control elements (CEs) can control the FEs accordingly. More that control elements (CEs) can control the FEs accordingly. More
specifically, the model describes the logical functions that are specifically, the model describes the logical functions that are
present in an FE, what capabilities these functions support, and present in an FE, what capabilities these functions support, and how
how these functions are or can be interconnected. This FE model is these functions are or can be interconnected. This FE model is
intended to satisfy the model requirements specified in the ForCES intended to satisfy the model requirements specified in the ForCES
requirements draft [1]. A list of the basic logical functional requirements draft, RFC 3564 [1]. A list of the basic logical
blocks (LFBs) is also defined in the LFB class library to aid the functional blocks (LFBs) is also defined in the LFB class library to
effort in defining individual LFBs. aid the effort in defining individual LFBs.
Table of Contents Table of Contents
Abstract.........................................................1 Abstract...........................................................2
1. Definitions...................................................4 1. Definitions.....................................................4
2. Introduction..................................................5 2. Introduction....................................................5
2.1. Requirements on the FE model.............................6 2.1. Requirements on the FE model...............................6
2.2. The FE Model in Relation to FE Implementations...........6 2.2. The FE Model in Relation to FE Implementations.............6
2.3. The FE Model in Relation to the ForCES Protocol..........7 2.3. The FE Model in Relation to the ForCES Protocol............7
2.4. Modeling Language for the FE Model.......................7 2.4. Modeling Language for the FE Model.........................7
2.5. Document Structure.......................................8 2.5. Document Structure.........................................8
3. FE Model Concepts.............................................8 3. FE Model Concepts...............................................8
3.1. FE Capability Model and State Model......................9 3.1. FE Capability Model and State Model........................9
3.2. LFB (Logical Functional Block) Modeling.................11 3.2. LFB (Logical Functional Block) Modeling...................11
3.2.1. LFB Outputs........................................13 3.2.1. LFB Outputs..........................................13
3.2.2. LFB Inputs.........................................16 3.2.2. LFB Inputs...........................................16
3.2.3. Packet Type........................................19 3.2.3. Packet Type..........................................19
3.2.4. Metadata...........................................20 3.2.4. Metadata.............................................19
3.2.5. LFB Versioning.....................................27 3.2.5. LFB Versioning.......................................26
3.2.6. LFB Inheritance....................................27 3.2.6. LFB Inheritance......................................27
3.3. FE Datapath Modeling....................................28 3.3. FE Datapath Modeling......................................28
3.3.1. Alternative Approaches for Modeling FE Datapaths...29 3.3.1. Alternative Approaches for Modeling FE Datapaths.....28
3.3.2. Configuring the LFB Topology.......................33 3.3.2. Configuring the LFB Topology.........................32
4. Model and Schema for LFB Classes.............................37 4. Model and Schema for LFB Classes...............................36
4.1. Namespace...............................................37 4.1. Namespace.................................................36
4.2. <LFBLibrary> Element....................................37 4.2. <LFBLibrary> Element......................................36
4.3. <load> Element..........................................39 4.3. <load> Element............................................38
4.4. <frameDefs> Element for Frame Type Declarations.........39 4.4. <frameDefs> Element for Frame Type Declarations...........38
4.5. <dataTypeDefs> Element for Data Type Definitions........40 4.5. <dataTypeDefs> Element for Data Type Definitions..........39
4.5.1. <typeRef> Element for Aliasing Existing Data Types.42 4.5.1. <typeRef> Element for Aliasing Existing Data Types...41
4.5.2. <atomic> Element for Deriving New Atomic Types.....42 4.5.2. <atomic> Element for Deriving New Atomic Types.......42
4.5.3. <array> Element to Define Arrays...................43 4.5.3. <array> Element to Define Arrays.....................42
4.5.4. <struct> Element to Define Structures..............45 4.5.4. <struct> Element to Define Structures................46
4.5.5. <union> Element to Define Union Types..............46 4.5.5. <union> Element to Define Union Types................47
4.5.6. Augmentations......................................46 4.5.6. Augmentations........................................49
4.6. <metadataDefs> Element for Metadata Definitions.........47 4.6. <metadataDefs> Element for Metadata Definitions...........50
4.7. <LFBClassDefs> Element for LFB Class Definitions........48 4.7. <LFBClassDefs> Element for LFB Class Definitions..........51
4.7.1. <derivedFrom> Element to Express LFB Inheritance...49 4.7.1. <derivedFrom> Element to Express LFB Inheritance.....52
4.7.2. <inputPorts> Element to Define LFB Inputs..........49 4.7.2. <inputPorts> Element to Define LFB Inputs............53
4.7.3. <outputPorts> Element to Define LFB Outputs........52 4.7.3. <outputPorts> Element to Define LFB Outputs..........55
4.7.4. <attributes> Element to Define LFB Operational 4.7.4. <attributes> Element to Define LFB Operational
Attributes................................................54 Attributes..................................................57
4.7.5. <capabilities> Element to Define LFB Capability 4.7.5. <capabilities> Element to Define LFB Capability
Attributes................................................57 Attributes..................................................60
4.7.6. <description> Element for LFB Operational 4.7.6. <description> Element for LFB Operational Specification
Specification.............................................58 ............................................................61
4.8. XML Schema for LFB Class Library Documents..............58 4.8. XML Schema for LFB Class Library Documents................61
5. FE Attributes and Capabilities...............................67 5. FE Attributes and Capabilities.................................71
5.1. XML Schema for FE Attribute Documents...................68 5.1. XML for FEObject Class definition.........................72
5.2. FEDocument..............................................72 5.2. FE Capabilities...........................................80
5.2.1. FECapabilities.....................................72 5.2.1. ModifiableLFBTopology................................80
5.2.2. FEAttributes.......................................75 5.2.2. SupportedLFBs and SupportedLFBType...................80
5.3. Sample FE Attribute Document............................77 5.2.3. SupportedAttributeType...............................82
6. LFB Class Library............................................80 5.3. FEAttributes..............................................83
6.1. Port LFB................................................80 5.3.1. FEStatus.............................................83
6.2. L2 Interface LFB........................................81 5.3.2. LFBSelectors and LFBSelectorType.....................83
6.3. IP interface LFB........................................82 5.3.3. LFBTopology and LFBLinkType..........................83
6.4. Classifier LFB..........................................84 5.3.4. FENeighbors an FEConfiguredNeighborType..............84
6.5. Next Hop LFB............................................85 6. Satisfying the Requirements on FE Model........................85
6.6. Rate Meter LFB..........................................87 6.1. Port Functions............................................86
6.7. Redirector (de-MUX) LFB.................................87 6.2. Forwarding Functions......................................86
6.8. Packet Header Rewriter LFB..............................88 6.3. QoS Functions.............................................86
6.9. Counter LFB.............................................88 6.4. Generic Filtering Functions...............................86
6.10. Dropper LFB............................................89 6.5. Vendor Specific Functions.................................86
6.11. IPv4 Fragmenter LFB....................................89 6.6. High-Touch Functions......................................87
6.12. L2 Address Resolution LFB..............................90 6.7. Security Functions........................................87
6.13. Queue LFB..............................................90 6.8. Off-loaded Functions......................................87
6.14. Scheduler LFB..........................................91 6.9. IPFLOW/PSAMP Functions....................................87
6.15. MPLS ILM/Decapsulation LFB.............................91 7. Using the FE model in the ForCES Protocol......................88
6.16. MPLS Encapsulation LFB.................................92 7.1. FE Topology Query.........................................90
6.17. Tunnel Encapsulation/Decapsulation LFB.................92 7.2. FE Capability Declarations................................91
6.18. Replicator LFB.........................................93 7.3. LFB Topology and Topology Configurability Query...........91
7. Satisfying the Requirements on FE Model......................93 7.4. LFB Capability Declarations...............................91
7.1. Port Functions..........................................94 7.5. State Query of LFB Attributes.............................92
7.2. Forwarding Functions....................................94 7.6. LFB Attribute Manipulation................................93
7.3. QoS Functions...........................................94 7.7. LFB Topology Re-configuration.............................93
7.4. Generic Filtering Functions.............................95 8. Acknowledgments................................................93
7.5. Vendor Specific Functions...............................95 9. Security Considerations........................................94
7.6. High-Touch Functions....................................95 10. Normative References..........................................94
7.7. Security Functions......................................95 11. Informative References........................................94
7.8. Off-loaded Functions....................................95 12. Authors' Addresses............................................95
7.9. IPFLOW/PSAMP Functions..................................96 13. Intellectual Property Right...................................96
8. Using the FE model in the ForCES Protocol....................96 14. IANA consideration............................................96
8.1. FE Topology Query.......................................98 15. Copyright Statement...........................................96
8.2. FE Capability Declarations..............................99
8.3. LFB Topology and Topology Configurability Query.........99
8.4. LFB Capability Declarations............................100
8.5. State Query of LFB Attributes..........................101
8.6. LFB Attribute Manipulation.............................101
8.7. LFB Topology Re-configuration..........................102
9. Acknowledgments.............................................102
10. Security Considerations....................................102
11. Normative References.......................................102
12. Informative References.....................................103
13. Authors' Addresses.........................................103
14. Intellectual Property Right................................104
15. IANA consideration.........................................105
Conventions used in this document Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
this document are to be interpreted as described in [RFC-2119]. document are to be interpreted as described in [RFC-2119].
1. Definitions 1.
Definitions
Terminology associated with the ForCES requirements is defined in Terminology associated with the ForCES requirements is defined in
[1] and is not copied here. The following list of terminology is RFC 3564 [1] and is not copied here. The following list of
relevant to the FE model defined in this document. terminology relevant to the FE model is defined in this section.
FE Model -- The FE model is designed to model the logical FE Model -- The FE model is designed to model the logical processing
processing functions of an FE. The FE model proposed in this functions of an FE. The FE model proposed in this document includes
document includes three components: the modeling of individual three components: the modeling of individual logical functional
logical functional blocks (LFB model), the logical interconnection blocks (LFB model), the logical interconnection between LFBs (LFB
between LFBs (LFB topology) and the FE level attributes, including topology) and the FE level attributes, including FE capabilities.
FE capabilities. The FE model provides the basis to define the The FE model provides the basis to define the information elements
information elements exchanged between the CE and the FE in the exchanged between the CE and the FE in the ForCES protocol.
ForCES protocol.
Datapath -- A conceptual path taken by packets within the Datapath -- A conceptual path taken by packets within the forwarding
forwarding plane inside an FE. Note that more than one datapath plane inside an FE. Note that more than one datapath can exist
can exist within an FE. within an FE.
LFB (Logical Function Block) class (or type) -- A template LFB (Logical Functional Block) Class (or type) -- A template
representing a fine-grained, logically separable and well-defined representing a fine-grained, logically separable and well-defined
packet processing operation in the datapath. LFB classes are the packet processing operation in the datapath. LFB classes are the
basic building blocks of the FE model. basic building blocks of the FE model.
LFB (Logical Function Block) Instance -- As a packet flows through LFB Instance -- As a packet flows through an FE along a datapath, it
an FE along a datapath, it flows through one or multiple LFB flows through one or multiple LFB instances, where each LFB is an
instances, where each LFB implements an instance of a specific LFB instance of a specific LFB class. Multiple instances of the same
class. Multiple instances of the same LFB class can be present in LFB class can be present in an FE's datapath. Note that we often
an FE's datapath. Note that we often refer to LFBs without refer to LFBs without distinguishing between an LFB class and LFB
distinguishing between an LFB class and LFB instance when we instance when we believe the implied reference is obvious for the
believe the implied reference is obvious for the given context. given context.
LFB Model -- The LFB model describes the content and structures in LFB Model -- The LFB model describes the content and structures in
an LFB, plus the associated data definition. Four types of an LFB, plus the associated data definition. Four types of
information are defined in the LFB model. The core part of the LFB information are defined in the LFB model. The core part of the LFB
model is the LFB class definitions; the other three types define model is the LFB class definitions; the other three types define the
the associated data including common data types, supported frame associated data including common data types, supported frame formats
formats and metadata. and metadata.
LFB Metadata -- Metadata is used to communicate per-packet state LFB Metadata -- Metadata is used to communicate per-packet state
from one LFB to another, but is not sent across the network. The from one LFB to another, but is not sent across the network. The FE
FE model defines how such metadata is identified, produced and model defines how such metadata is identified, produced and consumed
consumed by the LFBs, but not how the per-packet state is by the LFBs, but not how the per-packet state is implemented within
implemented within actual hardware. actual hardware.
LFB Attribute -- Operational parameters of the LFBs that must be LFB Attribute -- Operational parameters of the LFBs that must be
visible to the CEs are conceptualized in the FE model as the LFB visible to the CEs are conceptualized in the FE model as the LFB
attributes. The LFB attributes include: flags, single parameter attributes. The LFB attributes include: flags, single parameter
arguments, complex arguments, and tables that the CE can read arguments, complex arguments, and tables that the CE can read or/and
or/and write via the ForCES protocol. write via the ForCES protocol.
LFB Topology -- A representation of the logical interconnection and LFB Topology -- A representation of the logical interconnection and
the placement of LFB instances along the datapath within one FE. the placement of LFB instances along the datapath within one FE.
Sometimes this representation is called intra-FE topology, to be Sometimes this representation is called intra-FE topology, to be
distinguished from inter-FE topology. LFB topology is outside of distinguished from inter-FE topology. LFB topology is outside of
the LFB model, but is part of the FE model. the LFB model, but is part of the FE model.
FE Topology -- A representation of how multiple FEs within a single FE Topology -- A representation of how multiple FEs within a single
NE are interconnected. Sometimes this is called inter-FE topology, NE are interconnected. Sometimes this is called inter-FE topology,
to be distinguished from intra-FE topology (i.e., LFB topology). to be distinguished from intra-FE topology (i.e., LFB topology). An
An individual FE might not have the global knowledge of the full FE individual FE might not have the global knowledge of the full FE
topology, but the local view of its connectivity with other FEs is topology, but the local view of its connectivity with other FEs is
considered to be part of the FE model. The FE topology is considered to be part of the FE model. The FE topology is
discovered by the ForCES base protocol or some other means. discovered by the ForCES base protocol or by some other means.
Inter-FE Topology -- See FE Topology. Inter-FE Topology -- See FE Topology.
Intra-FE Topology -- See LFB Topology. Intra-FE Topology -- See LFB Topology.
LFB class library -- A set of LFB classes that has been identified LFB class library -- A set of LFB classes that has been identified
as the most common functions found in most FEs and hence should be as the most common functions found in most FEs and hence should be
defined first by the ForCES Working Group. defined first by the ForCES Working Group.
2. Introduction 2.
[2] specifies a framework by which control elements (CEs) can Introduction
configure and manage one or more separate forwarding elements (FEs)
within a networking element (NE) using the ForCES protocol. The RFC 3746 [2] specifies a framework by which control elements (CEs)
ForCES architecture allows Forwarding Elements of varying can configure and manage one or more separate forwarding elements
(FEs) within a networking element (NE) using the ForCES protocol.
The ForCES architecture allows Forwarding Elements of varying
functionality to participate in a ForCES network element. The functionality to participate in a ForCES network element. The
implication of this varying functionality is that CEs can make only implication of this varying functionality is that CEs can make only
minimal assumptions about the functionality provided by FEs in an minimal assumptions about the functionality provided by FEs in an
NE. Before CEs can configure and control the forwarding behavior NE. Before CEs can configure and control the forwarding behavior of
of FEs, CEs need to query and discover the capabilities and states FEs, CEs need to query and discover the capabilities and states of
of their FEs. [1] mandates that the capabilities, states and their FEs. RFC 3654 [1] mandates that the capabilities, states and
configuration information be expressed in the form of an FE model. configuration information be expressed in the form of an FE model.
RFC 3444 [11] observed that information models (IMs) and data RFC 3444 [11] observed that information models (IMs) and data models
models (DMs) are different because they serve different purposes. (DMs) are different because they serve different purposes. "The
"The main purpose of an IM is to model managed objects at a main purpose of an IM is to model managed objects at a conceptual
conceptual level, independent of any specific implementations or level, independent of any specific implementations or protocols
protocols used". "DMs, conversely, are defined at a lower level of used". "DMs, conversely, are defined at a lower level of
abstraction and include many details. They are intended for abstraction and include many details. They are intended for
implementors and include protocol-specific constructs." Sometimes implementors and include protocol-specific constructs." Sometimes
it is difficult to draw a clear line between the two. The FE model it is difficult to draw a clear line between the two. The FE model
described in this document is primarily an information model, but described in this document is primarily an information model, but
also includes some aspects of a data model, such as explicit also includes some aspects of a data model, such as explicit
definitions of the LFB class schema and FE schema. It is expected definitions of the LFB class schema and FE schema. It is expected
that this FE model will be used as the basis to define the payload that this FE model will be used as the basis to define the payload
for information exchange between the CE and FE in the ForCES for information exchange between the CE and FE in the ForCES
protocol. protocol.
2.1. Requirements on the FE model 2.1. Requirements on the FE model
[1] defines requirements that must be satisfied by a ForCES FE RFC 3654 [1] defines requirements that must be satisfied by a ForCES
model. To summarize, an FE model must define: FE model. To summarize, an FE model must define:
. Logically separable and distinct packet forwarding operations . Logically separable and distinct packet forwarding operations
in an FE datapath (logical functional blocks or LFBs); in an FE datapath (logical functional blocks or LFBs);
. The possible topological relationships (and hence the sequence . The possible topological relationships (and hence the sequence
of packet forwarding operations) between the various LFBs; of packet forwarding operations) between the various LFBs;
. The possible operational capabilities (e.g., capacity limits, . The possible operational capabilities (e.g., capacity limits,
constraints, optional features, granularity of configuration) constraints, optional features, granularity of configuration)
of each type of LFB; of each type of LFB;
. The possible configurable parameters (i.e., attributes) of . The possible configurable parameters (i.e., attributes) of each
each type of LFB; type of LFB;
. Metadata that may be exchanged between LFBs. . Metadata that may be exchanged between LFBs.
2.2. The FE Model in Relation to FE Implementations 2.2. The FE Model in Relation to FE Implementations
The FE model proposed here is based on an abstraction of distinct The FE model proposed here is based on an abstraction of distinct
logical functional blocks (LFBs), which are interconnected in a logical functional blocks (LFBs), which are interconnected in a
directed graph, and receive, process, modify, and transmit packets directed graph, and receive, process, modify, and transmit packets
along with metadata. The FE model should be designed such that along with metadata. The FE model should be designed such that
different implementations of the forwarding datapath can be different implementations of the forwarding datapath can be
logically mapped onto the model with the functionality and sequence logically mapped onto the model with the functionality and sequence
of operations correctly captured. However, the model itself does of operations correctly captured. However, the model is not
not directly address how a particular implementation maps to an LFB intended to directly address how a particular implementation maps to
topology. It is left to the forwarding plane vendors to define how an LFB topology. It is left to the forwarding plane vendors to
the FE functionality is represented using the FE model. Our goal define how the FE functionality is represented using the FE model.
is to design the FE model such that it is flexible enough to
accommodate most common implementations.
The LFB topology model for a particular datapath implementation Our goal is to design the FE model such that it is flexible enough
MUST correctly capture the sequence of operations on the packet. to accommodate most common implementations.
Metadata generation (by certain LFBs) must always precede any use
of that metadata (by subsequent LFBs in the topology graph); this The LFB topology model for a particular datapath implementation MUST
is required for logically consistent operation. Further, correctly capture the sequence of operations on the packet.
modification of packet fields that are subsequently used as inputs Metadata generation by certain LFBs must always precede any use of
for further processing must occur in the order specified in the that metadata by subsequent LFBs in the topology graph; this is
model for that particular implementation to ensure correctness. required for logically consistent operation. Further, modification
of packet fields that are subsequently used as inputs for further
processing must occur in the order specified in the model for that
particular implementation to ensure correctness.
2.3. The FE Model in Relation to the ForCES Protocol 2.3. The FE Model in Relation to the ForCES Protocol
The ForCES base protocol is used by the CEs and FEs to maintain the The ForCES base protocol is used by the CEs and FEs to maintain the
communication channel between the CEs and FEs. The ForCES protocol communication channel between the CEs and FEs. The ForCES protocol
may be used to query and discover the inter-FE topology. The may be used to query and discover the inter-FE topology. The
details of a particular datapath implementation inside an FE, details of a particular datapath implementation inside an FE,
including the LFB topology, along with the operational capabilities including the LFB topology, along with the operational capabilities
and attributes of each individual LFB, are conveyed to the CE and attributes of each individual LFB, are conveyed to the CE within
within information elements in the ForCES protocol. The model of information elements in the ForCES protocol. The model of an LFB
an LFB class should define all of the information that needs to be class should define all of the information that needs to be
exchanged between an FE and a CE for the proper configuration and exchanged between an FE and a CE for the proper configuration and
management of that LFB. management of that LFB.
Specifying the various payloads of the ForCES messages in a Specifying the various payloads of the ForCES messages in a
systematic fashion is difficult without a formal definition of the systematic fashion is difficult without a formal definition of the
objects being configured and managed (the FE and the LFBs within). objects being configured and managed (the FE and the LFBs within).
The FE Model document defines a set of classes and attributes for The FE Model document defines a set of classes and attributes for
describing and manipulating the state of the LFBs within an FE. describing and manipulating the state of the LFBs within an FE.
These class definitions themselves will generally not appear in the These class definitions themselves will generally not appear in the
ForCES protocol. Rather, ForCES protocol operations will reference ForCES protocol. Rather, ForCES protocol operations will reference
classes defined in this model, including relevant attributes (and classes defined in this model, including relevant attributes and the
the defined operations). defined operations.
Section 8 provides more detailed discussion on how the FE model Section 7 provides more detailed discussion on how the FE model
should be used by the ForCES protocol. should be used by the ForCES protocol.
2.4. Modeling Language for the FE Model 2.4. Modeling Language for the FE Model
Even though not absolutely required, it is beneficial to use a Even though not absolutely required, it is beneficial to use a
formal data modeling language to represent the conceptual FE model formal data modeling language to represent the conceptual FE model
described in this document. Use of a formal language can help to described in this document. Use of a formal language can help to
enforce consistency and logical compatibility among LFBs. A full enforce consistency and logical compatibility among LFBs. A full
specification will be written using such a data modeling language. specification will be written using such a data modeling language.
The formal definition of the LFB classes has the potential to The formal definition of the LFB classes may facilitate the eventual
facilitate the eventual automation of some part of the code automation of some of the code generation process and the functional
generation process and the functional validation of arbitrary LFB validation of arbitrary LFB topologies.
topologies.
Human readability was the most important factor considered when Human readability was the most important factor considered when
selecting the specification language. Encoding, decoding and selecting the specification language, whereas encoding, decoding and
transmission performance was not a selection factor for the transmission performance was not a selection factor. The encoding
language because the encoding method for over the wire transport is method for over the wire transport is not dependent on the
an issue independent of the specification language chosen. It is specification language chosen and is outside the scope of this
outside the scope of this document and up to the ForCES protocol to document and up to the ForCES protocol to define.
define.
XML was chosen as the specification language in this document, XML was chosen as the specification language in this document,
because XML has the advantage of being both human and machine because XML has the advantage of being both human and machine
readable with widely available tools support. readable with widely available tools support.
2.5. Document Structure 2.5. Document Structure
Section 3 provides a conceptual overview of the FE model, laying Section 3 provides a conceptual overview of the FE model, laying the
the foundation for the more detailed discussion and specifications foundation for the more detailed discussion and specifications in
in the sections that follow. Section 4 and 5 constitute the core the sections that follow. Section 4 and 5 constitute the core of
of the FE model, detailing the two major components in the FE the FE model, detailing the two major components in the FE model:
model: LFB model and FE level attributes including capability and LFB model and FE level attributes including capability and LFB
LFB topology. Section 6 presents a list of LFB classes in the LFB topology. Section 6 directly addresses the model requirements
class library that will be further specified in separate documents imposed by the ForCES requirement draft [1] while Section 7 explains
according to the FE model presented in Sections 4 and 5. Section 7 how the FE model should be used in the ForCES protocol.
directly addresses the model requirements imposed by the ForCES
requirement draft [1] while Section 8 explains how the FE model
should be used in the ForCES protocol.
3. FE Model Concepts 3.
FE Model Concepts
Some of the important concepts used throughout this document are Some of the important concepts used throughout this document are
introduced in this section. Section 3.1 explains the difference introduced in this section. Section 3.1 explains the difference
between a state model and a capability model, and how the two can between a state model and a capability model, and describes how the
be combined in the FE model. Section 3.2 introduces the concept of two can be combined in the FE model. Section 3.2 introduces the
LFBs (Logical Functional Blocks) as the basic functional building concept of LFBs (Logical Functional Blocks) as the basic functional
blocks in the FE model. Section 3.3 discusses the logical inter- building blocks in the FE model. Section 3.3 discusses the logical
connection and ordering between LFB instances within an FE, that inter-connection and ordering between LFB instances within an FE,
is, the LFB topology. that is, the LFB topology.
The FE model proposed in this document is comprised of two major The FE model proposed in this document is comprised of two major
components: LFB model and FE level attributes, including FE components: the LFB model and FE level attributes, including FE
capabilities and LFB topology. The LFB model provides the content capabilities and LFB topology. The LFB model provides the content
and data structures to define each individual LFB class. FE and data structures to define each individual LFB class. FE
attributes provide information at the FE level particularly the attributes provide information at the FE level, particularly the
capabilities of the FE at a coarse level. Part of the FE level capabilities of the FE at a coarse level. Part of the FE level
information is the LFB topology, which expresses the logical inter- information is the LFB topology, which expresses the logical inter-
connection between the LFB instances along the datapath(s) within connection between the LFB instances along the datapath(s) within
the FE. Details of these components are described in Section 4 and the FE. Details of these components are described in Section 4 and
5. The intent of this section is to discuss these concepts at the 5. The intent of this section is to discuss these concepts at the
high level and lay the foundation for the detailed description in high level and lay the foundation for the detailed description in
the following sections. the following sections.
3.1. FE Capability Model and State Model 3.1. FE Capability Model and State Model
The ForCES FE model must describe both a capability and a state The ForCES FE model must describe both a capability and a state
model. The FE capability model describes the capabilities and model. The FE capability model describes the capabilities and
capacities of an FE by specifying the variation in functions capacities of an FE by specifying the variation in functions
supported and any limitations. The FE state model describes the supported and any limitations. The FE state model describes the
current state of the FE, that is, the instantaneous values or current state of the FE, that is, the instantaneous values or
operational behavior of the FE. operational behavior of the FE.
Conceptually, the FE capability model tells the CE which states are Conceptually, the FE capability model tells the CE which states are
allowed on an FE, with capacity information indicating certain allowed on an FE, with capacity information indicating certain
quantitative limits or constraints. Thus, the CE has general quantitative limits or constraints. Thus, the CE has general
knowledge about which configurations are applicable to a particular knowledge about configurations that are applicable to a particular
FE and which ones are not. For example, an FE capability model may FE. For example, an FE capability model may describe the FE at a
describe the FE at a coarse level such as: coarse level such as:
. this FE can handle IPv4 and IPv6 forwarding; . this FE can handle IPv4 and IPv6 forwarding;
. this FE can perform classification on the following fields: . this FE can perform classification on the following fields:
source IP address, destination IP address, source port number, source IP address, destination IP address, source port number,
destination port number, etc; destination port number, etc;
. this FE can perform metering; . this FE can perform metering;
. this FE can handle up to N queues (capacity); . this FE can handle up to N queues (capacity);
. this FE can add and remove encapsulating headers of types . this FE can add and remove encapsulating headers of types
including IPSec, GRE, L2TP. including IPSec, GRE, L2TP.
While one could try and build an object model to fully represent While one could try and build an object model to fully represent the
the FE capabilities, other efforts found this to be a significant FE capabilities, other efforts found this to be a significant
undertaking. The main difficulty arises in describing detailed undertaking. The main difficulty arises in describing detailed
limits, such as the maximum number of classifiers, queues, buffer limits, such as the maximum number of classifiers, queues, buffer
pools, and meters the FE can provide. We believe that a good pools, and meters the FE can provide. We believe that a good
balance between simplicity and flexibility can be achieved for the balance between simplicity and flexibility can be achieved for the
FE model by combining the coarse level capability reporting with an FE model by combining coarse level capability reporting with an
error reporting mechanism. That is, if the CE attempts to instruct error reporting mechanism. That is, if the CE attempts to instruct
the FE to set up some specific behavior it cannot support, the FE the FE to set up some specific behavior it cannot support, the FE
will return an error indicating the problem. Examples of similar will return an error indicating the problem. Examples of similar
approaches include DiffServ PIB [4] and Framework PIB [5]. approaches include DiffServ PIB [4] and Framework PIB [5].
The FE state model presents the snapshot view of the FE to the CE. The FE state model presents the snapshot view of the FE to the CE.
For example, using an FE state model, an FE may be described to its For example, using an FE state model, an FE may be described to its
corresponding CE as the following: corresponding CE as the following:
. on a given port, the packets are classified using a given . on a given port, the packets are classified using a given
classification filter; classification filter;
. the given classifier results in packets being metered in a . the given classifier results in packets being metered in a
certain way, and then marked in a certain way; certain way, and then marked in a certain way;
. the packets coming from specific markers are delivered into a . the packets coming from specific markers are delivered into a
shared queue for handling, while other packets are delivered shared queue for handling, while other packets are delivered to
to a different queue; a different queue;
. a specific scheduler with specific behavior and parameters . a specific scheduler with specific behavior and parameters will
will service these collected queues. service these collected queues.
Figure 1 shows the concepts of FE state, capabilities and Figure 1 shows the concepts of FE state, capabilities and
configuration in the context of CE-FE communication via the ForCES configuration in the context of CE-FE communication via the ForCES
protocol. protocol.
+-------+ +-------+ +-------+ +-------+
| | FE capabilities: what it can/cannot do. | | | | FE capabilities: what it can/cannot do. | |
| |<-----------------------------------------| | | |<-----------------------------------------| |
| | | | | | | |
| CE | FE state: what it is now. | FE | | CE | FE state: what it is now. | FE |
| |<-----------------------------------------| | | |<-----------------------------------------| |
| | | | | | | |
| | FE configuration: what it should be. | | | | FE configuration: what it should be. | |
| |----------------------------------------->| | | |----------------------------------------->| |
+-------+ +-------+ +-------+ +-------+
Figure 1. Illustration of FE state, capabilities and configuration Figure 1. Illustration of FE state, capabilities and configuration
exchange in the context of CE-FE communication via ForCES. exchange in the context of CE-FE communication via ForCES.
The concepts relating to LFB, particularly capability at the LFB The concepts relating to LFBs, particularly capability at the LFB
level, and LFB topology will be discussed in the rest of this level and LFB topology will be discussed in the rest of this
section. section.
Capability information at the LFB level is an integral part of the Capability information at the LFB level is an integral part of the
LFB model, and is modeled the same way as the other operational LFB model, and is modeled the same way as the other operational
parameters inside an LFB. For example, certain features of an LFB parameters inside an LFB. For example, when certain features of an
class may be optional, in which case it must be possible for the CE LFB class are optional, it must be possible for the CE to determine
to determine whether or not an optional feature is supported by a whether those optional features are supported by a given LFB
given LFB instance. Such capability information can be modeled as instance. Such capability information can be modeled as a read-only
a read-only attribute in the LFB instance, see Section 4.7.5 for attribute in the LFB instance, see Section 4.7.5 for details.
details.
Capability information at the FE level may describe the LFB classes Capability information at the FE level may describe the LFB classes
the FE can instantiate; the number of instances of each that can be that the FE can instantiate; the number of instances of each that
created; the topological (i.e., linkage) limitations between these can be created; the topological (linkage) limitations between these
LFB instances, etc. Section 5 defines the FE level attributes LFB instances, etc. Section 5 defines the FE level attributes
including capability information. including capability information.
Once the FE capability is described to the CE, the FE state Once the FE capability is described to the CE, the FE state
information can be represented by two levels. The first level is information can be represented by two levels. The first level is
the logically separable and distinctive packet processing the logically separable and distinct packet processing functions,
functions, called Logical Functional Blocks (LFBs). The second called Logical Functional Blocks (LFBs). The second level of
level of information describes how these individual LFBs are information describes how these individual LFBs are ordered and
ordered and placed along the datapath to deliver a complete placed along the datapath to deliver a complete forwarding plane
forwarding plane service. The interconnection and ordering of the service. The interconnection and ordering of the LFBs is called LFB
LFBs is called LFB Topology. Section 3.2 discusses high level Topology. Section 3.2 discusses high level concepts around LFBs,
concepts around LFBs, whereas Section 3.3 discusses LFB topology whereas Section 3.3 discusses LFB topology issues.
issues.
3.2. LFB (Logical Functional Block) Modeling 3.2. LFB (Logical Functional Block) Modeling
Each LFB performs a well-defined action or computation on the Each LFB performs a well-defined action or computation on the
packets passing through it. Upon completion of such a function, packets passing through it. Upon completion of its prescribed
either the packets are modified in certain ways (e.g., function, either the packets are modified in certain ways (e.g.,
decapsulator, marker), or some results are generated and stored, decapsulator, marker), or some results are generated and stored,
often in the form of metadata (like a classifier). Each LFB often in the form of metadata (e.g., classifier). Each LFB
typically performs a single action. Classifiers, shapers, meters typically performs a single action. Classifiers, shapers and meters
are all examples of such LFBs. Modeling LFBs at such a fine are all examples of such LFBs. Modeling LFBs at such a fine
granularity allows us to use a small number of LFBs to express the granularity allows us to use a small number of LFBs to express the
higher-order FE functions (such as an IPv4 forwarder) precisely, higher-order FE functions (such as an IPv4 forwarder) precisely,
which in turn can describe more complex networking functions and which in turn can describe more complex networking functions and
vendor implementations of software and hardware. Section 6 vendor implementations of software and hardware. These LFBs will be
provides a list of useful LFBs with such granularity. defined in detail in one or more documents.
An LFB has one or more inputs, each of which takes a packet P, and An LFB has one or more inputs, each of which takes a packet P, and
optionally metadata M; and produces one or more outputs, each of optionally metadata M; and produces one or more outputs, each of
which carries a packet P', and optionally metadata M'. Metadata is which carries a packet P', and optionally metadata M'. Metadata is
data associated with the packet in the network processing device data associated with the packet in the network processing device
(router, switch, etc.) and is passed from one LFB to the next, but (router, switch, etc.) and is passed from one LFB to the next, but
is not sent across the network. In general, multiple LFBs are is not sent across the network. In general, multiple LFBs are
contained in one FE, as shown in Figure 2, and all the LFBs share contained in one FE, as shown in Figure 2, and all the LFBs share
the same ForCES protocol termination point that implements the the same ForCES protocol termination point that implements the
ForCES protocol logic and maintains the communication channel to ForCES protocol logic and maintains the communication channel to and
and from the CE. from the CE.
+-----------+ +-----------+
| CE | | CE |
+-----------+ +-----------+
^ ^
| Fp reference point | Fp reference point
| |
+--------------------------|-----------------------------------+ +--------------------------|-----------------------------------+
| FE | | | FE | |
| v | | v |
skipping to change at page 12, line 35 skipping to change at page 12, line 35
| (P,M) | |Attributes| |(P',M') | |Attributes| |(P",M") | | (P,M) | |Attributes| |(P',M') | |Attributes| |(P",M") |
| | +----------+ | | +----------+ | | | | +----------+ | | +----------+ | |
| +--------------+ +--------------+ | | +--------------+ +--------------+ |
| | | |
+--------------------------------------------------------------+ +--------------------------------------------------------------+
Figure 2. Generic LFB Diagram Figure 2. Generic LFB Diagram
An LFB, as shown in Figure 2, has inputs, outputs and attributes An LFB, as shown in Figure 2, has inputs, outputs and attributes
that can be queried and manipulated by the CE indirectly via an Fp that can be queried and manipulated by the CE indirectly via an Fp
reference point (defined in [2]) and the ForCES protocol reference point (defined in RFC 3746 [2]) and the ForCES protocol
termination point. The horizontal axis is in the forwarding plane termination point. The horizontal axis is in the forwarding plane
for connecting the inputs and outputs of LFBs within the same FE. for connecting the inputs and outputs of LFBs within the same FE.
The vertical axis between the CE and the FE denotes the Fp The vertical axis between the CE and the FE denotes the Fp reference
reference point where bidirectional communication between the CE point where bidirectional communication between the CE and FE
and FE occurs: the CE to FE communication is for configuration, occurs: the CE to FE communication is for configuration, control and
control and packet injection while FE to CE communication is used packet injection while FE to CE communication is used for packet re-
for packet re-direction to the control plane, monitoring and direction to the control plane, monitoring and accounting
accounting information, errors, etc. Note that the interaction information, errors, etc. Note that the interaction between the CE
between the CE and the LFB is only abstract and indirect. The and the LFB is only abstract and indirect. The result of such an
result of such an interaction is for the CE to indirectly interaction is for the CE to indirectly manipulate the attributes of
manipulate the attributes of the LFB instances. the LFB instances.
A namespace is used to associate a unique name or ID with each LFB A namespace is used to associate a unique name or ID with each LFB
class. The namespace must be extensible so that a new LFB class class. The namespace must be extensible so that a new LFB class can
can also be added later to accommodate future innovation in the be added later to accommodate future innovation in the forwarding
forwarding plane. plane.
LFB operation must be specified in the model to allow the CE to LFB operation must be specified in the model to allow the CE to
understand the behavior of the forwarding datapath. For instance, understand the behavior of the forwarding datapath. For instance,
the CE must understand at what point in the datapath the IPv4 the CE must understand at what point in the datapath the IPv4 header
header TTL is decremented (i.e., it needs to know if a control TTL is decremented. That is, the CE needs to know if a control
packet could be delivered to the CE either before or after this packet could be delivered to it either before or after this point in
point in the datapath). In addition, the CE must understand where the datapath. In addition, the CE must understand where and what
and what type of header modifications (e.g., tunnel header append type of header modifications (e.g., tunnel header append or strip)
or strip) are performed by the FEs. Further, the CE must verify are performed +by the FEs. Further, the CE must verify that the
that the various LFBs along a datapath within an FE are compatible various LFBs along a datapath within an FE are compatible to link
to link together. together.
There is value to vendors if the operation of LFB classes can be There is value to vendors if the operation of LFB classes can be
expressed in sufficient detail so that physical devices expressed in sufficient detail so that physical devices implementing
implementing different LFB functions can be integrated easily into different LFB functions can be integrated easily into an FE design.
an FE design. Therefore, a semi-formal specification is needed; Therefore, a semi-formal specification is needed; that is, a text
that is, a text description of the LFB operation (human readable), description of the LFB operation (human readable), but sufficiently
but sufficiently specific and unambiguous to allow conformance specific and unambiguous to allow conformance testing and efficient
testing and efficient design (i.e., eliminate guess-work), so that design, so that interoperability between different CEs and FEs can
interoperability between different CEs and FEs can be achieved. be achieved.
The LFB class model specifies information such as: The LFB class model specifies information such as:
. number of inputs and outputs (and whether they are . number of inputs and outputs (and whether they are
configurable) configurable)
. metadata read/consumed from inputs; . metadata read/consumed from inputs;
. metadata produced at the outputs; . metadata produced at the outputs;
. packet type(s) accepted at the inputs and emitted at the . packet type(s) accepted at the inputs and emitted at the
outputs; outputs;
. packet content modifications (including encapsulation or . packet content modifications (including encapsulation or
decapsulation); decapsulation);
. packet routing criteria (when multiple outputs on an LFB are . packet routing criteria (when multiple outputs on an LFB are
present); present);
. packet timing modifications; . packet timing modifications;
. packet flow ordering modifications; . packet flow ordering modifications;
. LFB capability information; . LFB capability information;
. LFB operational attributes, etc. . LFB operational attributes, etc.
Section 4 of this document provides a detailed discussion of the Section 4 of this document provides a detailed discussion of the LFB
LFB model with a formal specification of LFB class schema. The model with a formal specification of LFB class schema. The rest of
rest of Section 3.2 only intends to provide a conceptual overview Section 3.2 only intends to provide a conceptual overview of some
of some important issues in LFB modeling, without covering all the important issues in LFB modeling, without covering all the specific
specific details. details.
3.2.1. LFB Outputs 3.2.1. LFB Outputs
An LFB output is a conceptual port on an LFB that can send An LFB output is a conceptual port on an LFB that can send
information to another LFB. The information is typically a packet information to another LFB. The information is typically a packet
and its associated metadata, although in some cases it might and its associated metadata, although in some cases it might consist
consist of only metadata, i.e., with no packet data. of only metadata, i.e., with no packet data.
A single LFB output can be connected to only one LFB input. This A single LFB output can be connected to only one LFB input. This is
is required to make the packet flow through the LFB topology required to make the packet flow through the LFB topology
unambiguously. unambiguously.
Some LFBs will have a single output, as depicted in Figure 3.a. Some LFBs will have a single output, as depicted in Figure 3.a.
+---------------+ +-----------------+ +---------------+ +-----------------+
| | | | | | | |
| | | OUT +--> | | | OUT +-->
... OUT +--> ... | ... OUT +--> ... |
| | | EXCEPTIONOUT +--> | | | EXCEPTIONOUT +-->
| | | | | | | |
skipping to change at page 14, line 41 skipping to change at page 14, line 39
+---------------+ | OUT:n +--> +---------------+ | OUT:n +-->
+-----------------+ +-----------------+
c. One output group d. One output and one output group c. One output group d. One output and one output group
Figure 3. Examples of LFBs with various output combinations. Figure 3. Examples of LFBs with various output combinations.
To accommodate a non-trivial LFB topology, multiple LFB outputs are To accommodate a non-trivial LFB topology, multiple LFB outputs are
needed so that an LFB class can fork the datapath. Two mechanisms needed so that an LFB class can fork the datapath. Two mechanisms
are provided for forking: multiple singleton outputs and output are provided for forking: multiple singleton outputs and output
groups (the two concepts can be also combined in the same LFB groups, which can be combined in the same LFB class.
class).
Multiple separate singleton outputs are defined in an LFB class to Multiple separate singleton outputs are defined in an LFB class to
model a pre-determined number of semantically different outputs. model a pre-determined number of semantically different outputs.
That is, the number of outputs is known when the LFB class is That is, the number of outputs must be known when the LFB class is
defined. Additional singleton outputs cannot be created at LFB defined. Additional singleton outputs cannot be created at LFB
instantiation time, nor can they be created on the fly after the instantiation time, nor can they be created on the fly after the LFB
LFB is instantiated. is instantiated.
For example, an IPv4 LPM (Longest-Prefix-Matching) LFB may have one For example, an IPv4 LPM (Longest-Prefix-Matching) LFB may have one
output(OUT) to send those packets for which the LPM look-up was output(OUT) to send those packets for which the LPM look-up was
successful (passing a META_ROUTEID as metadata); and have another successful, passing a META_ROUTEID as metadata; and have another
output (EXCEPTIONOUT) for sending exception packets when the LPM output (EXCEPTIONOUT) for sending exception packets when the LPM
look-up failed. This example is depicted in Figure 3.b. Packets look-up failed. This example is depicted in Figure 3.b. Packets
emitted by these two outputs not only require different downstream emitted by these two outputs not only require different downstream
treatment, but they are a result of two different conditions in the treatment, but they are a result of two different conditions in the
LFB, plus they also carry different metadata. This concept assumes LFB and each output carries different metadata. This concept
that the number of distinct outputs is known when the LFB class is assumes the number of distinct outputs is known when the LFB class
defined. For each singleton output, the LFB class definition is defined. For each singleton output, the LFB class definition
defines what types of frames and metadata the output emits. defines the types of frames and metadata the output emits.
An output group, on the other hand, is used to model the case where An output group, on the other hand, is used to model the case where
a flow of seemingly similar packets with an identical set of a flow of similar packets with an identical set of metadata needs to
metadata needs to be split into multiple paths, and where the be split into multiple paths. In this case, the number of such paths
number of such paths is not known when the LFB class is defined is not known when the LFB class is defined because it is not an
(i.e., because it is not an inherent property of the LFB class). inherent property of the LFB class. An output group consists of a
An output group consists of a number of outputs (called the output number of outputs, called the output instances of the group, where
instances of the group), all sharing the same frame and metadata all output instances share the same frame and metadata emission
emission definitions (see Figure 3.c). Each output instance can definitions (see Figure 3.c). Each output instance can connect to a
connect to a different downstream LFB, just as if they were different downstream LFB, just as if they were separate singleton
separate singleton outputs. But the number of output instances can outputs, but the number of output instances can differ between LFB
be different between one instance of the LFB class and another. instances of the same LFB class. The class definition may include a
The class definition may include a lower and/or an upper limit on lower and/or an upper limit on the number of outputs. In addition,
the number of output instances. In addition, for configurable FEs, for configurable FEs, the FE capability information may define
the FE capability information may include further limits on the further limits on the number of instances in specific output groups
number of instances in specific output groups for certain LFBs. for certain LFBs. The actual number of output instances in a group
The actual number of output instances in a group is an attribute of is an attribute of the LFB instance, which is read-only for static
the LFB instance, which is read-only for static topologies, and topologies, and read-write for dynamic topologies. The output
read-write for dynamic topologies. The output instances in a group instances in a group are numbered sequentially, from 0 to N-1, and
are numbered sequentially, from 0 to N-1, and are addressable from are addressable from within the LFB. The LFB has a built-in
within the LFB. The LFB has a built-in mechanism to select one mechanism to select one specific output instance for each packet.
specific output instance for each packet. This mechanism is This mechanism is described in the textual definition of the class
described in the textual definition of the class and is typically and is typically configurable via some attributes of the LFB.
configurable via some attributes of the LFB.
For example, consider a re-director LFB, whose sole purpose is to For example, consider a re-director LFB, whose sole purpose is to
direct packets to one of N downstream paths based on one of the direct packets to one of N downstream paths based on one of the
metadata associated with each arriving packet. Such an LFB is metadata associated with each arriving packet. Such an LFB is
fairly versatile and can be used in many different places in a fairly versatile and can be used in many different places in a
topology. For example, a redirector can be used to divide the data topology. For example, a redirector can be used to divide the data
path into an IPv4 and an IPv6 path based on a FRAMETYPE metadata path into an IPv4 and an IPv6 path based on a FRAMETYPE metadata
(N=2), or to fork into color specific paths after metering using (N=2), or to fork into color specific paths after metering using the
the COLOR metadata (red, yellow, green; N=3), etc. COLOR metadata (red, yellow, green; N=3), etc.
Using an output group in the above LFB class provides the desired Using an output group in the above LFB class provides the desired
flexibility to adapt each instance of this class to the required flexibility to adapt each instance of this class to the required
operation. The metadata to be used as a selector for the output operation. The metadata to be used as a selector for the output
instance is a property of the LFB. For each packet, the value of instance is a property of the LFB. For each packet, the value of
the specified metadata may be used as a direct index to the output the specified metadata may be used as a direct index to the output
instance. Alternatively, the LFB may have a configurable selector instance. Alternatively, the LFB may have a configurable selector
table that maps a metadata value to output instance. table that maps a metadata value to output instance.
Note that other LFBs may also use the output group concept to build Note that other LFBs may also use the output group concept to build
in similar adaptive forking capability. For example, a classifier in similar adaptive forking capability. For example, a classifier
LFB with one input and N outputs can be defined easily by using the LFB with one input and N outputs can be defined easily by using the
output group concept. Alternatively, a classifier LFB with one output group concept. Alternatively, a classifier LFB with one
singleton output in combination with an explicit N-output re- singleton output in combination with an explicit N-output re-
director LFB models the same processing behavior. The decision of director LFB models the same processing behavior. The decision of
whether to use the output group model for a certain LFB class is whether to use the output group model for a certain LFB class is
left to the LFB class designers. left to the LFB class designers.
The model allows the output group be combined with other singleton The model allows the output group be combined with other singleton
output(s) in the same class, as demonstrated in Figure 3.d. The output(s) in the same class, as demonstrated in Figure 3.d. The LFB
LFB here has two types of outputs, OUT, for normal packet output, here has two types of outputs, OUT, for normal packet output, and
and EXCEPTIONOUT for packets that triggered some exception. The EXCEPTIONOUT for packets that triggered some exception. The normal
normal OUT has multiple instances, i.e., it is an output group. OUT has multiple instances, thus, it is an output group.
In summary, the LFB class may define one output, multiple singleton In summary, the LFB class may define one output, multiple singleton
outputs, one or more output groups, or a combination of the latter outputs, one or more output groups, or a combination thereof.
two. Multiple singleton outputs should be used when the LFB must Multiple singleton outputs should be used when the LFB must provide
provide for forking the datapath, and at least one of the following for forking the datapath, and at least one of the following
conditions hold: conditions hold:
- the number of downstream directions are inherent from the . the number of downstream directions are inherent from the
definition of the class (and hence fixed); definition of the class and hence fixed;
- the frame type and set of metadata emitted on any of the outputs . the frame type and set of metadata emitted on any of the
are substantially different from what is emitted on the other outputs are substantially different from what is emitted on
outputs (i.e., they cannot share frame-type and metadata the other outputs (i.e., they cannot share frame-type and
definitions); metadata definitions);
An output group is appropriate when the LFB must provide for An output group is appropriate when the LFB must provide for forking
forking the datapath, and at least one of the following conditions the datapath, and at least one of the following conditions hold:
hold: . the number of downstream directions is not known when the LFB
- the number of downstream directions is not known when the LFB
class is defined; class is defined;
- the frame type and set of metadata emitted on these outputs are . the frame type and set of metadata emitted on these outputs are
sufficiently similar or ideally identical, such they can share the sufficiently similar or ideally identical, such they can share
same output definition. the same output definition.
3.2.2. LFB Inputs 3.2.2. LFB Inputs
An LFB input is a conceptual port on an LFB where the LFB can An LFB input is a conceptual port on an LFB where the LFB can
receive information from other LFBs. The information is typically receive information from other LFBs. The information is typically a
a packet and associated metadata, although in some cases it might packet and associated metadata, although in some cases it might
consist of only metadata, i.e., with no packet data. consist of only metadata, without any packet data.
For LFB instances that receive packets from more than one other LFB For LFB instances that receive packets from more than one other LFB
instance (fan-in), there are three ways to model fan-in, all instance (fan-in). There are three ways to model fan-in, all
supported by the LFB model: supported by the LFB model and can be combined in the same LFB:
- Implicit multiplexing via a single input . Implicit multiplexing via a single input
- Explicit multiplexing via multiple singleton inputs . Explicit multiplexing via multiple singleton inputs
- Explicit multiplexing via a group of inputs (input group) . Explicit multiplexing via a group of inputs (input group)
The above modes can be combined in the same LFB.
The simplest form of multiplexing uses a singleton input (Figure The simplest form of multiplexing uses a singleton input (Figure
4.a). Most LFBs will have only one singleton input. Multiplexing 4.a). Most LFBs will have only one singleton input. Multiplexing
into a single input is possible because the model allows for more into a single input is possible because the model allows more than
than one LFB output to connect to the same input of an LFB. This one LFB output to connect to the same LFB input. This property
property applies to any LFB input without any special provisions in applies to any LFB input without any special provisions in the LFB
the LFB class. Multiplexing into a single input is applicable when class. Multiplexing into a single input is applicable when the
the packets from the upstream LFBs are similar (in frame-type and packets from the upstream LFBs are similar in frame-type and
accompanying metadata) and require similar processing. Note that accompanying metadata, and require similar processing. Note that
this model does not address how potential contention is handled this model does not address how potential contention is handled when
when multiple packets arrive simultaneously. If this needs to be multiple packets arrive simultaneously. If contention handling
explicitly modeled, one of the other two modeling solutions must be needs to be explicitly modeled, one of the other two modeling
used. solutions must be used.
The second method to model fan-in uses individually defined The second method to model fan-in uses individually defined
singleton inputs (Figure 4.b). This model is meant for situations singleton inputs (Figure 4.b). This model is meant for situations
where the LFB needs to handle distinct types of packet streams, where the LFB needs to handle distinct types of packet streams,
requiring input-specific handling inside the LFB, and where the requiring input-specific handling inside the LFB, and where the
number of such distinct cases is known when the LFB class is number of such distinct cases is known when the LFB class is
defined. For example, a Layer 2 Decapsulation/Encapsulation LFB defined. For example, a Layer 2 Decapsulation/Encapsulation LFB may
may have two inputs, one for receiving Layer 2 frames for have two inputs, one for receiving Layer 2 frames for decapsulation,
decapsulation, and one for receiving Layer 3 frames for and one for receiving Layer 3 frames for encapsulation. This LFB
encapsulation. This LFB type expects different frames (L2 vs. L3) type expects different frames (L2 vs. L3) at its inputs, each with
at its inputs, each with different sets of metadata, and would thus different sets of metadata, and would thus apply different
apply different processing on frames arriving at these inputs. processing on frames arriving at these inputs. This model is
This model is capable of explicitly addressing packet contention, capable of explicitly addressing packet contention by defining how
i.e., by defining how the LFB class handles the contending packets. the LFB class handles the contending packets.
+--------------+ +------------------------+ +--------------+ +------------------------+
| LFB X +---+ | | | LFB X +---+ | |
+--------------+ | | | +--------------+ | | |
| | | | | |
+--------------+ v | | +--------------+ v | |
| LFB Y +---+-->|input Meter LFB | | LFB Y +---+-->|input Meter LFB |
+--------------+ ^ | | +--------------+ ^ | |
| | | | | |
+--------------+ | | | +--------------+ | | |
skipping to change at page 18, line 42 skipping to change at page 18, line 28
| | | | | |
+--------------+ +-->|in:0 \ | +--------------+ +-->|in:0 \ |
| Queue LFB #2 +------>|in:1 | input group | | Queue LFB #2 +------>|in:1 | input group |
+--------------+ |... | | +--------------+ |... | |
+-->|in:N-1 / | +-->|in:N-1 / |
... | | | ... | | |
+--------------+ | | | +--------------+ | | |
| Queue LFB #N |---+ | Scheduler LFB | | Queue LFB #N |---+ | Scheduler LFB |
+--------------+ +------------------------+ +--------------+ +------------------------+
(c) A Scheduler LFB uses an input group to differentiate which (c) A Scheduler LFB uses an input group to differentiate which queue
queue LFB packets are coming from. LFB packets are coming from.
Figure 3. Input modeling concepts (examples). Figure 3. Input modeling concepts (examples).
The third method to model fan-in uses the concept of an input The third method to model fan-in uses the concept of an input group.
group. The concept is similar to the output group introduced in The concept is similar to the output group introduced in the
the previous section, and is depicted in Figure 4.c. An input previous section, and is depicted in Figure 4.c. An input group
group consists of a number of input instances, all sharing the consists of a number of input instances, all sharing the properties
properties (same frame and metadata expectations). The input (same frame and metadata expectations). The input instances are
instances are numbered from 0 to N-1. From the outside, these numbered from 0 to N-1. From the outside, these inputs appear as
inputs appear as normal inputs, i.e., any compatible upstream LFB normal inputs, i.e., any compatible upstream LFB can connect its
can connect its output to one of these inputs. When a packet is output to one of these inputs. When a packet is presented to the
presented to the LFB at a particular input instance, the index of LFB at a particular input instance, the index of the input where the
the input where the packet arrived is known to the LFB and this packet arrived is known to the LFB and this information may be used
information may be used in the internal processing. For example, in the internal processing. For example, the input index can be
the input index can be used as a table selector, or as an explicit used as a table selector, or as an explicit precedence selector to
precedence selector to resolve contention. As with output groups, resolve contention. As with output groups, the number of input
the number of input instances in an input group is not defined in instances in an input group is not defined in the LFB class.
the LFB class. However, the class definition may include However, the class definition may include restrictions on the range
restrictions on the range of possible values. In addition, if an of possible values. In addition, if an FE supports configurable
FE supports configurable topologies, it may impose further topologies, it may impose further limitations on the number of
limitations on the number of instances for a particular port instances for a particular port group(s) of a particular LFB class.
group(s) of a particular LFB class. Within these limitations,
different instances of the same class may have a different number Within these limitations, different instances of the same class may
of input instances. The number of actual input instances in the have a different number of input instances. The number of actual
group is an attribute of the LFB class, which is read-only for input instances in the group is an attribute of the LFB class, which
static topologies, and is read-write for configurable topologies. is read-only for static topologies, and is read-write for
configurable topologies.
As an example for the input group, consider the Scheduler LFB As an example for the input group, consider the Scheduler LFB
depicted in Figure 3.c. Such an LFB receives packets from a number depicted in Figure 3.c. Such an LFB receives packets from a number
of Queue LFBs via a number of input instances, and uses the input of Queue LFBs via a number of input instances, and uses the input
index information to control contention resolution and scheduling. index information to control contention resolution and scheduling.
In summary, the LFB class may define one input, multiple singleton In summary, the LFB class may define one input, multiple singleton
inputs, one or more input groups, or a combination thereof. Any inputs, one or more input groups, or a combination thereof. Any
input allows for implicit multiplexing of similar packet streams input allows for implicit multiplexing of similar packet streams via
via connecting multiple outputs to the same input. Explicit connecting multiple outputs to the same input. Explicit multiple
multiple singleton inputs are useful when either the contention singleton inputs are useful when either the contention handling must
handling must be handled explicitly, or when the LFB class must be handled explicitly, or when the LFB class must receive and
receive and process a known number of distinct types of packet process a known number of distinct types of packet streams. An
streams. An input group is suitable when the contention handling input group is suitable when contention handling must be modeled
must be modeled explicitly, but the number of inputs are not explicitly, but the number of inputs are not inherent from the class
inherent from the class (and hence not known when the class is (and hence is not known when the class is defined), or when it is
defined), or when it is critical for LFB operation to know exactly critical for LFB operation to know exactly on which input the packet
on which input the packet was received. was received.
3.2.3. Packet Type 3.2.3. Packet Type
When LFB classes are defined, the input and output packet formats When LFB classes are defined, the input and output packet formats
(e.g., IPv4, IPv6, Ethernet, etc.) must be specified: these are the (e.g., IPv4, IPv6, Ethernet, etc.) must be specified. These are the
types of packets a given LFB input is capable of receiving and types of packets a given LFB input is capable of receiving and
processing, or a given LFB output is capable of producing. This processing, or a given LFB output is capable of producing. This
requires that distinct packet types be uniquely labeled with a requires distinct packet types be uniquely labeled with a symbolic
symbolic name and/or ID. name and/or ID.
Note that each LFB has a set of packet types that it operates on, Note that each LFB has a set of packet types that it operates on,
but does not care about whether the underlying implementation is but does not care whether the underlying implementation is passing a
passing a greater portion of the packets. For example, an IPv4 LFB greater portion of the packets. For example, an IPv4 LFB might only
might only operate on IPv4 packets, but the underlying operate on IPv4 packets, but the underlying implementation may or
implementation may or may not be stripping the L2 header before may not be stripping the L2 header before handing it over -- whether
handing it over -- whether that is happening or not is opaque to that is happening or not is opaque to the CE.
the CE.
3.2.4. Metadata 3.2.4. Metadata
Metadata is the per-packet state that is passed from one LFB to Metadata is the per-packet state that is passed from one LFB to
another. The metadata is passed with the packet to assist another. The metadata is passed with the packet to assist subsequent
subsequent LFBs to process that packet. The ForCES model captures LFBs to process that packet. The ForCES model captures how the per-
how the per-packet state information is propagated from one LFB to packet state information is propagated from one LFB to other LFBs.
other LFBs. Practically, such metadata propagation can happen Practically, such metadata propagation can happen within one FE, or
within one FE, or cross the FE boundary between two interconnected cross the FE boundary between two interconnected FEs. We believe
FEs. We believe that the same metadata model can be used for both that the same metadata model can be used for either situation;
situations, however, our focus here is for intra-FE metadata. however, our focus here is for intra-FE metadata.
3.2.4.1. Metadata Vocabulary 3.2.4.1. Metadata Vocabulary
Metadata has historically been understood to mean "data about Metadata has historically been understood to mean "data about data".
data". While this definition is a start, it is inadequate to While this definition is a start, it is inadequate to describe the
describe the multiple forms of metadata, which may appear within a multiple forms of metadata, which may appear within a complex
complex network element. Our discussion here categorizes forms of network element. The discussion here categorizes forms of metadata
metadata by two orthogonal axes. by two orthogonal axes.
The first axis is "internal" versus "external", which describes The first axis is "internal" versus "external", which describes
where the metadata exists in the network model or implementation. where the metadata exists in the network model or implementation.
For example, a particular vendor implementation of an IPv4 For example, a particular vendor implementation of an IPv4 forwarder
forwarder may make decisions inside of a chip that are not visible may make decisions inside of a chip that are not visible externally.
externally. Those decisions are metadata for the packet that is Those decisions are metadata for the packet that is "internal" to
"internal" to the chip. When a packet is forwarded out of the the chip. When a packet is forwarded out of the chip, it may be
chip, it may be marked with a traffic management header. That marked with a traffic management header. That header, which is
header, which is metadata for the packet, is visible outside of the metadata for the packet, is visible outside of the chip, and is
chip, and is therefore called "external" metadata. therefore called "external" metadata.
The second axis is "implicit" versus "explicit", which describes The second axis is "implicit" versus "expressed", which specifies
whether or not the metadata has a visible physical representation. whether or not the metadata has a visible physical representation.
For example, the traffic management header described in the For example, the traffic management header described in the previous
previous paragraph may be represented as a series of bits in some paragraph may be represented as a series of bits in some format, and
format, and that header is associated with the packet. Those bits that header is associated with the packet. Those bits have physical
have physical representation, and are therefore "explicit" representation, and are therefore "expressed" metadata. If the
metadata. In situations where the metadata is not physically metadata does not have a physical representation, it is called
represented, it is called "implicit" metadata. This situation "implicit" metadata. This situation occurs, for example, when a
occurs, for example, when a particular path through a network particular path through a network device is intended to be traversed
device is intended to be traversed only by particular kinds of only by particular kinds of packets, such as an IPv4 router. An
packets, such as an IPv4 router. An implementation may not mark implementation may not mark every packet along this path as being of
every packet along this path as being of type "IPv4", but the type "IPv4", but the intention of the designers is that every packet
intention of the designers is that every packet is of that type. is of that type. This understanding can be thought of as metadata
This understanding can be thought of as metadata about the packet, about the packet, which is implicitly attached to the packet through
which is implicitly attached to the packet through the intent of the intent of the designers.
the designers.
In the ForCES model, we do NOT discuss or represent metadata In the ForCES model, we do NOT discuss or represent metadata
"internal" to vendor implementations of LFBs. Our focus is solely "internal" to vendor implementations of LFBs. Our focus is solely
on metadata "external" to the LFBs, and therefore visible in the on metadata "external" to the LFBs, and therefore visible in the
ForCES model. The metadata discussed within this model may, or may ForCES model. The metadata discussed within this model may, or may
not, be visible outside of the particular FE implementing the LFB not, be visible outside of the particular FE implementing the LFB
model. In this regard, the scope of the metadata within ForCES is model. In this regard, the scope of the metadata within ForCES is
very narrowly defined. very narrowly defined.
Note also that while we define metadata within this model, it is Note also that while we define metadata within this model, it is
only a model. There is no requirement that vendor implementations only a model. There is no requirement that vendor implementations
of ForCES use the exact metadata representations described in this of ForCES use the exact metadata representations described in this
document. The only implementation requirement is that vendors document. The only implementation requirement is that vendors
implement the ForCES protocol, not the model. implement the ForCES protocol, not the model.
3.2.4.2. Metadata lifecycle within the ForCES model 3.2.4.2. Metadata lifecycle within the ForCES model
Each metadata can be conveniently modeled as a <label, value> pair, Each metadata can be conveniently modeled as a <label, value> pair,
where the label identifies the type of information, (e.g., where the label identifies the type of information, (e.g., "color"),
"color"), and its value holds the actual information (e.g., "red"). and its value holds the actual information (e.g., "red"). The tag
The tag here is shown as a textual label, but it can be replaced or here is shown as a textual label, but it can be replaced or
associated with a unique numeric value (identifier). associated with a unique numeric value (identifier).
The metadata life-cycle is defined in this model using three types The metadata life-cycle is defined in this model using three types
of events: "write", "read" and "consume". The first "write" of events: "write", "read" and "consume". The first "write"
initializes the value of the metadata (implicitly creating and/or implicitly creates and initializes the value of the metadata, and
initializing the metadata), and hence starts the life-cycle. The hence starts the life-cycle. The explicit "consume" event
explicit "consume" event terminates the life-cycle. Within the terminates the life-cycle. Within the life-cycle, that is, after a
life-cycle, that is, after a "write" event, but before the next "write" event, but before the next "consume" event, there can be an
"consume" event, there can be an arbitrary number of "write" and arbitrary number of "write" and "read" events. These "read" and
"read" events. These "read" and "write" events can be mixed in an "write" events can be mixed in an arbitrary order within the life-
arbitrary order within the life-cycle. Outside of the life-cycle cycle. Outside of the life-cycle of the metadata, that is, before
of the metadata, that is, before the first "write" event, or the first "write" event, or between a "consume" event and the next
between a "consume" event and the next "write" event, the metadata "write" event, the metadata should be regarded non-existent or non-
should be regarded non-existent or non-initialized. Thus, reading initialized. Thus, reading a metadata outside of its life-cycle is
a metadata outside of its life-cycle is considered an error. considered an error.
To ensure inter-operability between LFBs, the LFB class To ensure inter-operability between LFBs, the LFB class
specification must define what metadata the LFB class "reads" or specification must define what metadata the LFB class "reads" or
"consumes" on its input(s) and what metadata it "produces" on its "consumes" on its input(s) and what metadata it "produces" on its
output(s). For maximum extensibility, this definition should output(s). For maximum extensibility, this definition should
neither specify which LFBs the metadata is expected to come from neither specify which LFBs the metadata is expected to come from for
for a consumer LFB, nor which LFBs are expected to consume metadata a consumer LFB, nor which LFBs are expected to consume metadata for
for a given producer LFB. a given producer LFB.
While it is important to define the metadata types passing between While it is important to define the metadata types passing between
LFBs, it is not appropriate to define the exact encoding mechanism LFBs, it is not appropriate to define the exact encoding mechanism
used by LFBs for that metadata. Different implementations are used by LFBs for that metadata. Different implementations are
allowed to use different encoding mechanisms for metadata. For allowed to use different encoding mechanisms for metadata. For
example, one implementation may store metadata in registers or example, one implementation may store metadata in registers or
shared memory, while another implementation may encode metadata in- shared memory, while another implementation may encode metadata in-
band as a preamble in the packets. band as a preamble in the packets.
At any link between two LFBs, the packet is marked with a finite At any link between two LFBs, the packet is marked with a finite set
set of active metadata, where active means the metadata is within of active metadata, where active means the metadata is within its
its life-cycle. (i.e., the metadata has been properly initialized life-cycle. There are two corollaries of this model:
and has not been consumed yet.) There are two corollaries of this
model:
1. No uninitialized metadata exists in the model. 1. No un-initialized metadata exists in the model.
2. No more than one occurrence of each metadata tag can be 2. No more than one occurrence of each metadata tag can be
associated with a packet at any given time. associated with a packet at any given time.
3.2.4.3. LFB Operations on Metadata 3.2.4.3. LFB Operations on Metadata
When the packet is processed by an LFB (i.e., between the time it When the packet is processed by an LFB (i.e., between the time it is
is received and forwarded by the LFB), the LFB may perform read, received and forwarded by the LFB), the LFB may perform read, write
write and/or consume operations on any active metadata associated and/or consume operations on any active metadata associated with the
with the packet. If the LFB is considered to be a black box, one packet. If the LFB is considered to be a black box, one of the
of the following operations is performed on each active metadata. following operations is performed on each active metadata.
- IGNORE: ignores and forwards the metadata . IGNORE: ignores and forwards the metadata
- READ: reads and forwards the metadata . READ: reads and forwards the metadata
- READ/RE-WRITE: reads, over-writes and forwards the metadata . READ/RE-WRITE: reads, over-writes and forwards the metadata
- WRITE: writes and forwards the metadata . WRITE: writes and forwards the metadata
(can also be used to create new metadata) (can also be used to create new metadata)
- READ-AND-CONSUME: reads and consumes the metadata . READ-AND-CONSUME: reads and consumes the metadata
- CONSUME consumes metadata without reading . CONSUME consumes metadata without reading
The last two operations terminate the life-cycle of the metadata, The last two operations terminate the life-cycle of the metadata,
meaning that the metadata is not forwarded with the packet when the meaning that the metadata is not forwarded with the packet when the
packet is sent to the next LFB. packet is sent to the next LFB.
In our model, a new metadata is generated by an LFB when the LFB In our model, a new metadata is generated by an LFB when the LFB
applies a WRITE operation into a metadata type that was not present applies a WRITE operation to a metadata type that was not present
when the packet was received by the LFB. Such implicit creation when the packet was received by the LFB. Such implicit creation may
may be unintentional by the LFB, that is, the LFB may apply the be unintentional by the LFB, that is, the LFB may apply the WRITE
WRITE operation without knowing or caring if the given metadata operation without knowing or caring if the given metadata existed or
existed or not. If it existed, the metadata gets over-written; if not. If it existed, the metadata gets over-written; if it did not
it did not exist, the metadata is created. exist, the metadata is created.
For source-type LFBs (i.e., an LFB that inserts packets into the For LFBs that insert packets into the model, WRITE is the only
model), WRITE is the only meaningful metadata operation. meaningful metadata operation.
Sink-type LFBs (i.e., an LFB that removes the packet from the For LFBs that remove the packet from the model, they may either
model), may either READ-AND-CONSUME (read) or CONSUME (ignore) each READ-AND-CONSUME (read) or CONSUME (ignore) each active metadata
active metadata associated with the packet. associated with the packet.
3.2.4.4. Metadata Production and Consumption 3.2.4.4. Metadata Production and Consumption
For a given metadata on a given packet path, there must be at least For a given metadata on a given packet path, there must be at least
one producer LFB that creates that metadata and should be at least one producer LFB that creates that metadata and should be at least
one consumer LFB that needs the metadata. In this model, the one consumer LFB that needs that metadata. In this model, the
producer and consumer LFBs of a metadata are not required to be producer and consumer LFBs of a metadata are not required to be
adjacent. There may be multiple consumers for the same metadata adjacent. In addition, there may be multiple producers and
and there may be multiple producers of the same metadata. When a consumers for the same metadata. When a packet path involves
packet path involves multiple producers of the same metadata, then multiple producers of the same metadata, then subsequent producers
subsequent producers overwrite that metadata value. overwrite that metadata value.
The metadata that is produced by an LFB is specified by the LFB The metadata that is produced by an LFB is specified by the LFB
class definition on a per output port group basis. A producer may class definition on a per output port group basis. A producer may
always generate the metadata on the port group, or may generate it always generate the metadata on the port group, or may generate it
only under certain conditions. We call the former an only under certain conditions. We call the former an
"unconditional" metadata, whereas the latter is a "conditional" "unconditional" metadata, whereas the latter is a "conditional"
metadata. In the case of conditional metadata, it should be metadata. In the case of conditional metadata, it should be
possible to determine from the definition of the LFB when a possible to determine from the definition of the LFB when a
"conditional" metadata is produced. "conditional" metadata is produced.
The consumer behavior of an LFB, that is, the metadata that the LFB The consumer behavior of an LFB, that is, the metadata that the LFB
needs for its operation, is defined in the LFB class definition on needs for its operation, is defined in the LFB class definition on a
a per input port group basis. An input port group may "require" a per input port group basis. An input port group may "require" a
given metadata, or may treat it as "optional" information. In the given metadata, or may treat it as "optional" information. In the
latter case, the LFB class definition must explicitly define what latter case, the LFB class definition must explicitly define what
happens if an optional metadata is not provided. One approach is happens if an optional metadata is not provided. One approach is to
to specify a default value for each optional metadata, and assume specify a default value for each optional metadata, and assume that
that the default value is used if the metadata is not provided with the default value is used if the metadata is not provided with the
the packet. packet.
When a consumer requires a given metadata, it has dependencies on When a consumer LFB requires a given metadata, it has dependencies
its up-stream LFBs. That is, the consumer LFB can only function if on its up-stream LFBs. That is, the consumer LFB can only function
there is at least one producer of that metadata and no intermediate if there is at least one producer of that metadata and no
LFB consumes the metadata. intermediate LFB consumes the metadata.
The model should expose this inter-dependency. Furthermore, it The model should expose these inter-dependencies. Furthermore, it
should be possible to take this inter-dependency into consideration should be possible to take inter-dependencies into consideration
when constructing LFB topologies, and also that the dependency can when constructing LFB topologies, and also that the dependencies can
be verified when validating topologies. be verified when validating topologies.
For extensibility reasons, the LFB specification should define what For extensibility reasons, the LFB specification should define what
metadata the LFB requires without specifying which LFB(s) it metadata the LFB requires without specifying which LFB(s) it expects
expects a certain metadata to come from. Similarly, LFBs should a certain metadata to come from. Similarly, LFBs should specify
specify what metadata they produce without specifying which LFBs what metadata they produce without specifying which LFBs the
the metadata is meant for. metadata is meant for.
When specifying the metadata tags, some harmonization effort must When specifying the metadata tags, some harmonization effort must be
be made so that the producer LFB class uses the same tag as its made so that the producer LFB class uses the same tag as its
intended consumer(s), or vice versa. intended consumer(s), or vice versa.
3.2.4.5. Fixed, Variable and Configurable Tag 3.2.4.5. Fixed, Variable and Configurable Tag
When the produced metadata is defined for a given LFB class, most When the produced metadata is defined for a given LFB class, most
metadata will be specified with a fixed tag. For example, a Rate metadata will be specified with a fixed tag. For example, a Rate
Meter LFB will always produce the "Color" metadata. Meter LFB will always produce the "Color" metadata.
A small subset of LFBs need to have the capability to produce one A small subset of LFBs need the capability to produce one or more of
or more of their metadata with tags that are not fixed in the LFB their metadata with tags that are not fixed in the LFB class
class definition, but instead can be selected per LFB instance. An definition, but instead can be selected per LFB instance. An
example of such an LFB class is a Generic Classifier LFB. We call example of such an LFB class is a Generic Classifier LFB. We call
this variable tag metadata production. If an LFB produces metadata this capability "variable tag metadata production". If an LFB
with a variable tag, a corresponding LFB attribute--called the tag produces metadata with a variable tag, the corresponding LFB
selector--specifies the tag for each such metadata. This mechanism attribute, called the tag selector, specifies the tag for each such
is to improve the versatility of certain multi-purpose LFB classes, metadata. This mechanism improves the versatility of certain multi-
since it allows the same LFB class be used in different topologies, purpose LFB classes, since it allows the same LFB class to be used
producing the right metadata tags according to the needs of the in different topologies, producing the right metadata tags according
topology. to the needs of the topology.
Depending on the capability of the FE, the tag selector can be a Depending on the capability of the FE, the tag selector can be
read-only or a read-write attribute. In the former case, the tag either a read-only or a read-write attribute. If the selector is
cannot be modified by the CE. In the latter case the tag can be read-only, the tag cannot be modified by the CE. If the selector is
configured by the CE, hence we call this "configurable tag metadata read-write, the tag can be configured by the CE, hence we call this
production." (Note that in this definition configurable tag "configurable tag metadata production." Note that using this
metadata production is a subset of variable tag metadata definition, configurable tag metadata production is a subset of
production.) variable tag metadata production.
Similar concepts can be introduced for the consumer LFBs to satisfy Similar concepts can be introduced for the consumer LFBs to satisfy
the different metadata needs. Most LFB classes will specify their different metadata needs. Most LFB classes will specify their
metadata needs using fixed metadata tags. For example, a Next Hop metadata needs using fixed metadata tags. For example, a Next Hop
LFB may always require a "NextHopId" metadata; but the Redirector LFB may always require a "NextHopId" metadata; but the Redirector
LFB may need to use a "ClassID" metadata in one instance, and a LFB may need a "ClassID" metadata in one instance, and a
"ProtocolType" metadata in another instance as a basis for "ProtocolType" metadata in another instance as a basis for selecting
selecting the right output port. In this case, an LFB attribute is the right output port. In this case, an LFB attribute is used to
used to provide the required metadata tag at run-time. This provide the required metadata tag at run-time. This metadata tag
metadata tag selector attribute may be read-only or read-write, selector attribute may be read-only or read-write, depending on the
depending on the capabilities of the LFB instance and the FE. capabilities of the LFB instance and the FE.
3.2.4.6. Metadata Usage Categories 3.2.4.6. Metadata Usage Categories
Depending on the role and usage of a metadata, various amount of Depending on the role and usage of a metadata, various amounts of
encoding information must be provided when the metadata is defined, encoding information must be provided when the metadata is defined,
and some cases offer less flexibility in the value selection than where some cases offer less flexibility in the value selection than
others. others.
There are three types of metadata related to metadata usage: There are three types of metadata related to metadata usage:
- Relational (or binding) metadata . Relational (or binding) metadata
- Enumerated metadata . Enumerated metadata
- Explicit/external value metadata . Explicit/external value metadata
The purpose of the relational metadata is to refer in one LFB The purpose of the relational metadata is to refer in one LFB
instance (producer LFB) to a "thing" in another downstream LFB instance (producer LFB) to a "thing" in another downstream LFB
instance (consumer LFB), where the "thing" is typically an entry in instance (consumer LFB), where the "thing" is typically an entry in
a table attribute of the consumer LFB. a table attribute of the consumer LFB.
For example, the Prefix Lookup LFB executes an LPM search using its For example, the Prefix Lookup LFB executes an LPM search using its
prefix table and resolves to a next-hop reference. This reference prefix table and resolves to a next-hop reference. This reference
needs to be passed as metadata by the Prefix Lookup LFB (producer) needs to be passed as metadata by the Prefix Lookup LFB (producer)
to the Next Hop LFB (consumer), and must refer to a specific entry to the Next Hop LFB (consumer), and must refer to a specific entry
in the next-hop table within the consumer. in the next-hop table within the consumer.
Expressing and propagating such a binding relationship is probably Expressing and propagating such a binding relationship is probably
the most common usage of metadata. One or more objects in the the most common usage of metadata. One or more objects in the
producer LFB are related (bound) to a specific object in the producer LFB are bound to a specific object in the consumer LFB.
consumer LFB. Such a relationship is established by the CE very Such a relationship is established by the CE explicitly by properly
explicitly, i.e., by properly configuring the attributes in both configuring the attributes in both LFBs. Available methods include
LFBs. Available methods include the following: the following:
The binding may be expressed by tagging the involved objects in The binding may be expressed by tagging the involved objects in both
both LFBs with the same unique (but otherwise arbitrary) LFBs with the same unique, but otherwise arbitrary, identifier. The
identifier. The value of the tag is explicitly configured (written value of the tag is explicitly configured by the CE by writing the
by the CE) into both LFBs, and this value is also carried by the value into both LFBs, and this value is also carried by the metadata
metadata between the LFBs. between the LFBs.
Another way of setting up binding relations is to use a naturally Another way of setting up binding relations is to use a naturally
occurring unique identifier of the consumer's object (for example, occurring unique identifier of the consumer's object as a reference
the array index of a table entry) as a reference (and as a value of and as a value of the metadata (e.g., the array index of a table
the metadata). In this case, the index is either read or inferred entry). In this case, the index is either read or inferred by the
by the CE by communicating with the consumer LFB. Once the CE CE by communicating with the consumer LFB. Once the CE obtains the
obtains the index, it needs to write it into the producer LFB to index, it needs to write it into the producer LFB to establish the
establish the binding. binding.
Important characteristics of the binding usage of metadata are: Important characteristics of the binding usage of metadata are:
- The value of the metadata shows up in the CE-FE communication for . The value of the metadata shows up in the CE-FE communication
BOTH the consumer and the producer. That is, the metadata value for BOTH the consumer and the producer. That is, the metadata
must be carried over the ForCES protocol. Using the tagging value must be carried over the ForCES protocol. Using the
technique, the value is WRITTEN to both LFBs. Using the other tagging technique, the value is WRITTEN to both LFBs. Using
technique, the value is WRITTEN to only the producer LFB and may be the other technique, the value is WRITTEN to only the producer
READ from the consumer LFB. LFB and may be READ from the consumer LFB.
- The metadata value is irrelevant to the CE, the binding is simply . The metadata value is irrelevant to the CE, the binding is
expressed by using the SAME value at the consumer and producer simply expressed by using the SAME value at the consumer and
LFBs. producer LFBs.
- Hence the definition of the metadata is not required to include . Hence the metadata definition is not required to include value
value assignments. The only exception is when some special assignments. The only exception is when some special value(s)
value(s) of the metadata must be reserved to convey special events. of the metadata must be reserved to convey special events.
Even though these special cases must be defined with the metadata Even though these special cases must be defined with the
specification, their encoded values can be selected arbitrarily. metadata specification, their encoded values can be selected
For example, for the Prefix Lookup LFB example, a special value may arbitrarily. For example, for the Prefix Lookup LFB example, a
be reserved to signal the NO-MATCH case, and the value of zero may special value may be reserved to signal the NO-MATCH case, and
be assigned for this purpose. the value of zero may be assigned for this purpose.
The second class of metadata is the enumerated type. An example is The second class of metadata is the enumerated type. An example is
the "Color" metadata that is produced by a Meter LFB. As the name the "Color" metadata that is produced by a Meter LFB. As the name
suggests, enumerated metadata has a relatively small number of suggests, enumerated metadata has a relatively small number of
possible values, each with a very specific meaning. All of the possible values, each with a specific meaning. All possible cases
possible cases must be enumerated when defining this class of must be enumerated when defining this class of metadata. Although a
metadata. Although a value encoding must be included in the value encoding must be included in the specification, the actual
specification, the actual values can be selected arbitrarily (e.g., values can be selected arbitrarily (e.g., <Red=0, Yellow=1, Green=2>
<Red=0, Yellow=1, Green=2> and <Red=3, Yellow=2, Green 1> would be and <Red=3, Yellow=2, Green 1> would be both valid encodings, what
both valid encodings, what is important is that an encoding is is important is that an encoding is specified).
specified).
The value of the enumerated metadata may or may not be conveyed via The value of the enumerated metadata may or may not be conveyed via
the ForCES protocol between the CE and FE. the ForCES protocol between the CE and FE.
The third class of metadata is the explicit type. This refers to The third class of metadata is the explicit type. This refers to
cases where the value of the metadata is explicitly used by the cases where the metadata value is explicitly used by the consumer
consumer LFB to change some packet header fields. In other words, LFB to change some packet header fields. In other words, the value
its value has a direct and explicit impact on some field and will has a direct and explicit impact on some field and will be visible
be visible externally when the packet leaves the NE. Examples are: externally when the packet leaves the NE. Examples are: TTL
TTL increment given to a Header Modifier LFB, and DSCP value for a increment given to a Header Modifier LFB, and DSCP value for a
Remarker LFB. For explicit metadata, the value encoding must be Remarker LFB. For explicit metadata, the value encoding must be
explicitly provided in the metadata definition, the values cannot explicitly provided in the metadata definition. The values cannot
be selected arbitrarily, but rather they should conform to what is be selected arbitrarily and should conform to what is commonly
commonly expected. For example, a TTL increment metadata should be expected. For example, a TTL increment metadata should be encoded
encoded as zero for the no increment case, one for the single as zero for the no increment case, one for the single increment
increment case, etc. A DSCP metadata should use 0 to encode case, etc. A DSCP metadata should use 0 to encode DSCP=0, 1 to
DSCP=0, 1 to encode DSCP=1, etc. encode DSCP=1, etc.
3.2.5. LFB Versioning 3.2.5. LFB Versioning
LFB class versioning is a method to enable incremental evolution of LFB class versioning is a method to enable incremental evolution of
LFB classes. In general, an FE is not allowed to contain an LFB LFB classes. In general, an FE is not allowed to contain an LFB
instance for more than one version of a particular class. instance for more than one version of a particular class.
Inheritance (discussed next in Section 3.2.6) has special rules. If Inheritance (discussed next in Section 3.2.6) has special rules. If
an FE datapath model containing an LFB instance of a particular an FE datapath model containing an LFB instance of a particular
class C also simultaneously contains an LFB instance of a class C' class C also simultaneously contains an LFB instance of a class C'
inherited from class C; C could have a different version than C'. inherited from class C; C could have a different version than C'.
LFB class versioning is supported by requiring a version string in LFB class versioning is supported by requiring a version string in
the class definition. CEs may support backwards compatibility the class definition. CEs may support multiple versions of a
between multiple versions of a particular LFB class, but FEs are particular LFB class to provide backward compatibility, but FEs are
not allowed to support more than one single version of a particular not allowed to support more than one version of a particular class.
class.
3.2.6. LFB Inheritance 3.2.6. LFB Inheritance
LFB class inheritance is supported in the FE model as a method to LFB class inheritance is supported in the FE model as a method to
define new LFB classes. This also allows FE vendors to add vendor- define new LFB classes. This also allows FE vendors to add vendor-
specific extensions to standardized LFBs. An LFB class specific extensions to standardized LFBs. An LFB class
specification MUST specify the base class (with version number) it specification MUST specify the base class and version number it
inherits from (with the default being the base LFB class). inherits from (the default is the base LFB class). Multiple-
Multiple-inheritance is not allowed, though, to avoid the inheritance is not allowed, however, to avoid unnecessary
unnecessary complexity. complexity.
Inheritance should be used only when there is significant reuse of Inheritance should be used only when there is significant reuse of
the base LFB class definition. A separate LFB class should be the base LFB class definition. A separate LFB class should be
defined if little or no reuse is possible between the derived and defined if little or no reuse is possible between the derived and
the base LFB class. the base LFB class.
An interesting issue related to class inheritance is backward An interesting issue related to class inheritance is backward
compatibility (between a descendant and an ancestor class). compatibility between a descendant and an ancestor class. Consider
Consider the following hypothetical scenario where a standardized the following hypothetical scenario where a standardized LFB class
LFB class "L1" exists. Vendor A builds an FE that implements LFB "L1" exists. Vendor A builds an FE that implements LFB "L1" and
"L1" and vendor B builds a CE that can recognize and operate on LFB vendor B builds a CE that can recognize and operate on LFB "L1".
"L1". Suppose that a new LFB class, "L2", is defined based on the Suppose that a new LFB class, "L2", is defined based on the existing
existing "L1" class (for example, by extending its capabilities in "L1" class by extending its capabilities incrementally. Let us
some incremental way). Lets first examine the FE backward examine the FE backward compatibility issue by considering what
compatibility issue by considering what would happen if vendor B would happen if vendor B upgrades its FE from "L1" to "L2" and
upgrades its FE from "L1" to "L2" while vendor C's CE is not vendor C's CE is not changed. The old L1-based CE can interoperate
changed. The old L1-based CE can interoperate with the new L2- with the new L2-based FE if the derived LFB class "L2" is indeed
based FE if the derived LFB class "L2" is indeed backward backward compatible with the base class "L1".
compatible with the base class "L1".
The reverse scenario is a much less problematic case, i.e., when CE The reverse scenario is a much less problematic case, i.e., when CE
vendor B upgrades to the new LFB class "L2", but the FE is not vendor B upgrades to the new LFB class "L2", but the FE is not
upgraded. Note that as long as the CE is capable of working with upgraded. Note that as long as the CE is capable of working with
older LFB classes, this problem does not affect the model; hence we older LFB classes, this problem does not affect the model; hence we
will use the term "backward compatibility" to refer to the first will use the term "backward compatibility" to refer to the first
scenario concerning FE backward compatibility. scenario concerning FE backward compatibility.
Backward compatibility can be designed into the inheritance model Backward compatibility can be designed into the inheritance model by
by constraining LFB inheritance to require the derived class be a constraining LFB inheritance to require the derived class be a
functional superset of the base class (i.e. the derived class can functional superset of the base class (i.e. the derived class can
only add functions to the base class, but not remove functions). only add functions to the base class, but not remove functions).
Additionally, the following mechanisms are required to support FE Additionally, the following mechanisms are required to support FE
backward compatibility: backward compatibility:
1) When detecting an LFB instance of an LFB type that is 1. When detecting an LFB instance of an LFB type that is unknown
unknown to the CE, the CE MUST be able to query the base to the CE, the CE MUST be able to query the base class of such
class of such an LFB from the FE. an LFB from the FE.
2) The LFB instance on the FE SHOULD support a backward
2. The LFB instance on the FE SHOULD support a backward
compatibility mode (meaning the LFB instance reverts itself compatibility mode (meaning the LFB instance reverts itself
back to the base class instance), and the CE SHOULD be able back to the base class instance), and the CE SHOULD be able to
to configure the LFB to run in such a mode. configure the LFB to run in such a mode.
3.3. FE Datapath Modeling 3.3. FE Datapath Modeling
Packets coming into the FE from ingress ports generally flow Packets coming into the FE from ingress ports generally flow through
through multiple LFBs before leaving out of the egress ports. How multiple LFBs before leaving out of the egress ports. How an FE
an FE treats a packet depends on many factors, such as type of the treats a packet depends on many factors, such as type of the packet
packet (e.g., IPv4, IPv6 or MPLS), actual header values, time of (e.g., IPv4, IPv6 or MPLS), actual header values, time of arrival,
arrival, etc. The result of the operation of an LFB may have an etc. The result of LFB processing may have an impact on how the
impact on how the packet is to be treated in further (downstream) packet is to be treated in downstream LFBs. This differentiation of
LFBs and this differentiation of packet treatment downstream can be packet treatment downstream can be conceptualized as having
conceptualized as having alternative datapaths in the FE. For alternative datapaths in the FE. For example, the result of a 6-
example, the result of a 6-tuple classification (performed by a tuple classification performed by a classifier LFB could control
classifier LFB) could control which rate meter is applied to the which rate meter is applied to the packet by a rate meter LFB in a
packet (by a rate meter LFB) in a later stage in the datapath. later stage in the datapath.
LFB topology is a directed graph representation of the logical LFB topology is a directed graph representation of the logical
datapaths within an FE, with the nodes representing the LFB datapaths within an FE, with the nodes representing the LFB
instances and the directed link the packet flow direction from one instances and the directed link depicting the packet flow direction
LFB to the next. Section 3.3.1 discusses how the FE datapaths can from one LFB to the next. Section 3.3.1 discusses how the FE
be modeled as LFB topology; while Section 3.3.2 focuses on issues datapaths can be modeled as LFB topology; while Section 3.3.2
around LFB topology reconfiguration. focuses on issues related to LFB topology reconfiguration.
3.3.1. Alternative Approaches for Modeling FE Datapaths 3.3.1. Alternative Approaches for Modeling FE Datapaths
There are two basic ways to express the differentiation in packet There are two basic ways to express the differentiation in packet
treatment within an FE, one represents the datapath directly and treatment within an FE, one represents the datapath directly and
graphically (topological approach) and the other utilizes metadata graphically (topological approach) and the other utilizes metadata
(the encoded state approach). (the encoded state approach).
. Topological Approach . Topological Approach
Using this approach, differential packet treatment is expressed Using this approach, differential packet treatment is expressed by
by splitting the LFB topology into alternative paths. In other splitting the LFB topology into alternative paths. In other
words, if the result of an LFB must control how the packet is words, if the result of an LFB must control how the packet is
further processed, then such an LFB will have separate output further processed, then such an LFB will have separate output
ports (one for each alternative treatment) connected to separate ports, one for each alternative treatment, connected to separate
sub-graphs (each expressing the respective treatment sub-graphs, each expressing the respective treatment downstream.
downstream).
. Encoded State Approach . Encoded State Approach
An alternative way of expressing differential treatment is using An alternate way of expressing differential treatment is by using
metadata. The result of the operation of an LFB can be encoded metadata. The result of the operation of an LFB can be encoded in
in a metadata, which is passed along with the packet to a metadata, which is passed along with the packet to downstream
downstream LFBs. A downstream LFB, in turn, can use the LFBs. A downstream LFB, in turn, can use the metadata and its
metadata (and its value, e.g., as an index into some table) to value (e.g., as an index into some table) to determine how to
decide how to treat the packet. treat the packet.
Theoretically, the two approaches can substitute for each other, so Theoretically, either approach could substitute for the other, so
one could consider using a single pure approach to describe all one could consider using a single pure approach to describe all
datapaths in an FE. However, neither model by itself is very datapaths in an FE. However, neither model by itself results in the
useful for all practically relevant cases. For a given FE with best representation for all practically relevant cases. For a given
certain logical datapaths, applying the two different modeling FE with certain logical datapaths, applying the two different
approaches result in very different looking LFB topology graphs. A modeling approaches will result in very different looking LFB
model using only the topological approach may require a very large topology graphs. A model using only the topological approach may
graph with many links (i.e., paths) and nodes (i.e., LFB instances) require a very large graph with many links or paths, and nodes
to express all alternative datapaths. On the other hand, a model (i.e., LFB instances) to express all alternative datapaths. On the
using only the encoded state model would be restricted to a string other hand, a model using only the encoded state model would be
of LFBs, which makes it unintuitive to describe different datapaths restricted to a string of LFBs, which is not an intuitive way to
(such as MPLS and IPv4). Therefore, a mix of these two approaches describe different datapaths (such as MPLS and IPv4). Therefore, a
will likely be used for a practical model. In fact, as we mix of these two approaches will likely be used for a practical
illustrate below, the two approaches can be mixed even within the model. In fact, as we illustrate below, the two approaches can be
same LFB. mixed even within the same LFB.
Using a simple example of a classifier with N classification Using a simple example of a classifier with N classification outputs
outputs followed by other LFBs, Figure 5(a) shows what the LFB followed by other LFBs, Figure 5(a) shows what the LFB topology
topology looks like by using the pure topological approach. Each looks like when using the pure topological approach. Each output
output from the classifier goes to one of the N LFBs where no from the classifier goes to one of the N LFBs where no metadata is
metadata is needed. The topological approach is simple, needed. The topological approach is simple, straightforward and
straightforward and graphically intuitive. However, if N is large graphically intuitive. However, if N is large and the N nodes
and N nodes following the classifier (LFB#1, LFB#2, ..., LFB#N) all following the classifier (LFB#1, LFB#2, ..., LFB#N) all belong to
belong to the same LFB type (for example, meter), but each has its the same LFB type (e.g., meter), but each has its own independent
own independent attributes, the encoded state approach gives a much attributes, the encoded state approach gives a much simpler topology
simpler topology representation, as shown in Figure 5(b). The representation, as shown in Figure 5(b). The encoded state approach
encoded state approach requires that a table of N rows of meter requires that a table of N rows of meter attributes is provided in
attributes is provided in the Meter node itself, with each row the Meter node itself, with each row representing the attributes for
representing the attributes for one meter instance. A metadata M one meter instance. A metadata M is also needed to pass along with
is also needed to pass along with the packet P from the classifier the packet P from the classifier to the meter, so that the meter can
to the meter, so that the meter can use M as a look-up key (index) use M as a look-up key (index) to find the corresponding row of the
to find the corresponding row of the attributes that should be used attributes that should be used for any particular packet P.
for any particular packet P.
What if those N nodes (LFB#1, LFB#2, ..., LFB#N) are not of the same
type? For example, if LFB#1 is a queue while the rest are all
meters, what is the best way to represent such datapaths? While it
is still possible to use either the pure topological approach or the
pure encoded state approach, the natural combination of the two
appears to be the best option. Figure 5(c) depicts two different
functional datapaths using the topological approach while leaving
the N-1 meter instances distinguished by metadata only, as shown in
Figure 5(c).
Now what if all the N nodes (LFB#1, LFB#2, ..., LFB#N) are not of
the same type? For example, if LFB#1 is a queue while the rest are
all meters, what is the best way to represent such datapaths?
While it is still possible to use either the pure topological
approach or the pure encoded state approach, the natural
combination of the two appears to be the best option. Figure 5(c)
depicts two different functional datapaths using the topological
approach while leaving the N-1 meter instances distinguished by
metadata only, as shown in Figure 5(c).
+----------+ +----------+
P | LFB#1 | P | LFB#1 |
+--------->|(Attrib-1)| +--------->|(Attrib-1)|
+-------------+ | +----------+ +-------------+ | +----------+
| 1|------+ P +----------+ | 1|------+ P +----------+
| 2|---------------->| LFB#2 | | 2|---------------->| LFB#2 |
| classifier 3| |(Attrib-2)| | classifier 3| |(Attrib-2)|
| ...|... +----------+ | ...|... +----------+
| N|------+ ... | N|------+ ...
+-------------+ | P +----------+ +-------------+ | P +----------+
skipping to change at page 31, line 24 skipping to change at page 30, line 49
| N| | (Attrib-2) | | N| | (Attrib-2) |
+-------------+ | ... | +-------------+ | ... |
| (Attrib-N) | | (Attrib-N) |
+-------------+ +-------------+
5(c) Using a combination of the two, if LFB#1, LFB#2, ..., and 5(c) Using a combination of the two, if LFB#1, LFB#2, ..., and
LFB#N are of different types (e.g., queue and meter). LFB#N are of different types (e.g., queue and meter).
Figure 5. An example of how to model FE datapaths Figure 5. An example of how to model FE datapaths
From this example, we demonstrate that each approach has distinct From this example, we demonstrate that each approach has a distinct
advantages depending on the situation. Using the encoded state advantage depending on the situation. Using the encoded state
approach, fewer connections are typically needed between a fan-out approach, fewer connections are typically needed between a fan-out
node and its next LFB instances of the same type, because each node and its next LFB instances of the same type because each packet
packet carries metadata the following nodes can interpret and hence carries metadata the following nodes can interpret and hence invoke
invoke a different packet treatment. For those cases, a pure a different packet treatment. For those cases, a pure topological
topological approach forces one to build elaborate graphs with many approach forces one to build elaborate graphs with many more
more connections and often results in an unwieldy graph. On the connections and often results in an unwieldy graph. On the other
other hand, a topological approach is intuitive and most useful for hand, a topological approach is the most intuitive for representing
representing functionally different datapaths. functionally different datapaths.
For complex topologies, a combination of the two is the most useful For complex topologies, a combination of the two is the most
and flexible. A general design guideline is provided to indicate flexible. A general design guideline is provided to indicate which
which approach is best used for a particular situation. The approach is best used for a particular situation. The topological
topological approach should primarily be used when the packet approach should primarily be used when the packet datapath forks to
datapath forks into areas with distinct LFB classes (not just distinct LFB classes (not just distinct parameterizations of the
distinct parameterizations of the same LFB class), and when the same LFB class), and when the fan-outs do not require changes, such
fan-outs do not require changes (adding/removing LFB outputs) or as adding/removing LFB outputs, or require only very infrequent
require only very infrequent changes. Configuration information changes. Configuration information that needs to change frequently
that needs to change frequently should be expressed by the internal should be expressed by using the internal attributes of one or more
attributes of one or more LFBs (and hence using the encoded state LFBs (and hence using the encoded state approach).
approach).
+---------------------------------------------+ +---------------------------------------------+
| | | |
+----------+ V +----------+ +------+ | +----------+ V +----------+ +------+ |
| | | | |if IP-in-IP| | | | | | | |if IP-in-IP| | |
---->| ingress |->+----->|classifier|---------->|Decap.|---->---+ ---->| ingress |->+----->|classifier|---------->|Decap.|---->---+
| ports | | |----+ | | | ports | | |----+ | |
+----------+ +----------+ |others+------+ +----------+ +----------+ |others+------+
| |
V V
skipping to change at page 32, line 28 skipping to change at page 31, line 46
--->|ingress|-->|classifier1|----------->|Decap.|-->+classifier2|-> --->|ingress|-->|classifier1|----------->|Decap.|-->+classifier2|->
| ports | | |----+ | | | | | ports | | |----+ | | | |
+-------+ +-----------+ |others +------+ +-----------+ +-------+ +-----------+ |others +------+ +-----------+
| |
V V
(b) The LFB topology without the loop utilizing two (b) The LFB topology without the loop utilizing two
independent classifier instances. independent classifier instances.
Figure 6. An LFB topology example. Figure 6. An LFB topology example.
It is important to point out that the LFB topology described here It is important to point out that the LFB topology described here is
is the logical topology, not the physical topology (e.g. how the FE the logical topology, not the physical topology of how the FE
hardware is actually laid out). Nevertheless, the actual hardware is actually laid out. Nevertheless, the actual
implementation may still influence how the functionality is mapped implementation may still influence how the functionality is mapped
to the LFB topology. Figure 6 shows one simple FE example. In to the LFB topology. Figure 6 shows one simple FE example. In this
this example, an IP-in-IP packet from an IPSec application like VPN example, an IP-in-IP packet from an IPSec application like VPN may
may go to the classifier first and have the classification done go to the classifier first and have the classification done based on
based on the outer IP header; upon being classified as an IP-in-IP the outer IP header; upon being classified as an IP-in-IP packet,
packet, the packet is then sent to a decapsulator to strip off the the packet is then sent to a decapsulator to strip off the outer IP
outer IP header, followed by a classifier again to perform header, followed by a classifier again to perform classification on
classification on the inner IP header. If the same classifier the inner IP header. If the same classifier hardware or software is
hardware or software is used for both outer and inner IP header used for both outer and inner IP header classification with the same
classification with the same set of filtering rules, a logical loop set of filtering rules, a logical loop is naturally present in the
is naturally present in the LFB topology, as shown in Figure 6(a). LFB topology, as shown in Figure 6(a). However, if the
However, if the classification is implemented by two different classification is implemented by two different pieces of hardware or
pieces of hardware or software with different filters (i.e., one software with different filters (i.e., one set of filters for the
set of filters for outer IP header while another set for inner IP outer IP header and another set for the inner IP header), then it is
header), then it is more natural to model them as two different more natural to model them as two different instances of classifier
instances of classifier LFB, as shown in Figure 6(b). LFB, as shown in Figure 6(b).
To distinguish multiple instances of the same LFB class, each LFB To distinguish between multiple instances of the same LFB class,
instance has its own LFB instance ID. One way to encode the LFB each LFB instance has its own LFB instance ID. One way to encode
instance ID is to encode it as x.y where x is the LFB class ID the LFB instance ID is to encode it as x.y where x is the LFB class
while y is the instance ID within each LFB class. ID and y is the instance ID within each LFB class.
3.3.2. Configuring the LFB Topology 3.3.2. Configuring the LFB Topology
While there is little doubt that the individual LFB must be While there is little doubt that an individual LFB must be
configurable, the configurability question is more complicated for configurable, the configurability question is more complicated for
LFB topology. Since LFB topology is really the graphic LFB topology. Since the LFB topology is really the graphic
representation of the datapaths within an FE, configuring the LFB representation of the datapaths within an FE, configuring the LFB
topology means dynamically changing the datapaths, including topology means dynamically changing the datapaths, including
changes to the LFBs along the datapaths on an FE (e.g., creating, changing the LFBs along the datapaths on an FE (e.g., creating,
instantiating or deleting LFBs), setting up or deleting instantiating or deleting LFBs) and setting up or deleting
interconnections between outputs of upstream LFBs to inputs of interconnections between outputs of upstream LFBs to inputs of
downstream LFBs. downstream LFBs.
Why would the datapaths on an FE ever change dynamically? The Why would the datapaths on an FE ever change dynamically? The
datapaths on an FE is set up by the CE to provide certain data datapaths on an FE are set up by the CE to provide certain data
plane services (e.g., DiffServ, VPN, etc.) to the Network Element's plane services (e.g., DiffServ, VPN, etc.) to the Network Element's
(NE) customers. The purpose of reconfiguring the datapaths is to (NE) customers. The purpose of reconfiguring the datapaths is to
enable the CE to customize the services the NE is delivering at run enable the CE to customize the services the NE is delivering at run
time. The CE needs to change the datapaths when the service time. The CE needs to change the datapaths when the service
requirements change (e.g., when adding a new customer, or when an requirements change, such as adding a new customer or when an
existing customer changes their service). However, note that not existing customer changes their service. However, note that not all
all datapath changes result in changes in the LFB topology graph. datapath changes result in changes in the LFB topology graph.
Changes in the graph are dependent on the approach used to map the Changes in the graph are dependent on the approach used to map the
datapaths into LFB topology. As discussed in 3.3.1, the datapaths into LFB topology. As discussed in 3.3.1, the topological
topological approach and encoded state approach can result in very approach and encoded state approach can result in very different
different looking LFB topologies for the same datapaths. In looking LFB topologies for the same datapaths. In general, an LFB
general, an LFB topology based on a pure topological approach is topology based on a pure topological approach is likely to
likely to experience more frequent topology reconfiguration than experience more frequent topology reconfiguration than one based on
one based on an encoded state approach. However, even an LFB an encoded state approach. However, even an LFB topology based
topology based entirely on an encoded state approach may have to entirely on an encoded state approach may have to change the
change the topology at times, for example, to bypass some LFBs or topology at times, for example, to bypass some LFBs or insert new
insert new LFBs. Since a mix of these two approaches is used to LFBs. Since a mix of these two approaches is used to model the
model the datapaths, LFB topology reconfiguration is considered an datapaths, LFB topology reconfiguration is considered an important
important aspect of the FE model. aspect of the FE model.
We want to point out that allowing a configurable LFB topology in We want to point out that allowing a configurable LFB topology in
the FE model does not mandate that all FEs must have this the FE model does not mandate that all FEs must have this
capability. Even if an FE supports configurable LFB topology, it capability. Even if an FE supports configurable LFB topology, the
is expected there will be FE-specific limitations on what can FE may impose limitations on what can actually be configured.
actually be configured. Performance-optimized hardware Performance-optimized hardware implementations may have zero or very
implementations may have zero or very limited configurability, limited configurability, while FE implementations running on network
while FE implementations running on network processors may provide processors may provide more flexibility and configurability. It is
more flexibility and configurability. It is entirely up to the FE entirely up to the FE designers to decide whether or not the FE
designers to decide whether or not the FE actually implements actually implements reconfiguration and if so, how much. Whether a
reconfiguration and if so, how much. Whether it is a simple simple runtime switch is used to enable or disable (i.e., bypass)
runtime switch to enable or disable (i.e., bypass) certain LFBs, or certain LFBs, or more flexible software reconfiguration is used, is
more flexible software reconfiguration is all implementation detail implementation detail internal to the FE and outside of the scope of
internal to the FE and outside of the scope of FE model. In either FE model. In either case, the CE(s) must be able to learn the FE's
case, the CE(s) must be able to learn the FE's configuration configuration capabilities. Therefore, the FE model must provide a
capabilities. Therefore, the FE model must provide a mechanism for mechanism for describing the LFB topology configuration capabilities
describing the LFB topology configuration capabilities of an FE. of an FE. These capabilities may include (see Section 5 for full
These capabilities may include (see Section 5 for full details): details):
. What LFB classes can the FE instantiate . Which LFB classes the FE can instantiate
. Maximum number of instance of the same LFB class that can be . Maximum number of instances of the same LFB class that can be
created created
. Any topological limitations, For example: . Any topological limitations, For example:
o The maximum number of instances of the same class or any o The maximum number of instances of the same class or any
class that can be created on any given branch of the class that can be created on any given branch of the graph
graph
o Ordering restrictions on LFBs (e.g., any instance of LFB o Ordering restrictions on LFBs (e.g., any instance of LFB
class A must be always downstream of any instance of LFB class A must be always downstream of any instance of LFB
class B). class B).
Note that even when the CE is allowed to configure LFB topology for Note that even when the CE is allowed to configure LFB topology for
the FE, the CE is not expected to be able to interpret an arbitrary the FE, the CE is not expected to be able to interpret an arbitrary
LFB topology and determine which specific service or application LFB topology and determine which specific service or application
(e.g. VPN, DiffServ, etc.) is supported by the FE. However, once (e.g. VPN, DiffServ, etc.) is supported by the FE. However, once
the CE understands the coarse capability of an FE, it is the the CE understands the coarse capability of an FE, it is the
responsibility of the CE to configure the LFB topology to implement responsibility of the CE to configure the LFB topology to implement
the network service the NE is supposed to provide. Thus, the the network service the NE is supposed to provide. Thus, the
mapping the CE has to understand is from the high level NE service mapping the CE has to understand is from the high level NE service
to a specific LFB topology, not the other way around. The CE is not to a specific LFB topology, not the other way around. The CE is not
expected to have the ultimate intelligence to translate any high expected to have the ultimate intelligence to translate any high
level service policy into the configuration data for the FEs. level service policy into the configuration data for the FEs.
However, it is conceivable that within a given network service However, it is conceivable that within a given network service
domain (such as DiffServ), a certain amount of intelligence can be domain, a certain amount of intelligence can be programmed into the
programmed into the CE to give the CE a general understanding of CE to give the CE a general understanding of the LFBs involved to
the LFBs involved to allow the translation from a high level allow the translation from a high level service policy to the low
service policy to the low level FE configuration to be done level FE configuration to be done automatically. Note that this is
automatically. Note that this is considered an implementation considered an implementation issue internal to the control plane and
issue internal to the control plane and outside the scope of the FE outside the scope of the FE model. Therefore, it is not discussed
model. Therefore, it is not discussed any further in this draft. any further in this draft.
+----------+ +-----------+ +----------+ +-----------+
---->| Ingress |---->|classifier |--------------+ ---->| Ingress |---->|classifier |--------------+
| | |chip | | | | |chip | |
+----------+ +-----------+ | +----------+ +-----------+ |
v v
+-------------------------------------------+ +-------------------------------------------+
+--------+ | Network Processor | +--------+ | Network Processor |
<----| Egress | | +------+ +------+ +-------+ | <----| Egress | | +------+ +------+ +-------+ |
+--------+ | |Meter | |Marker| |Dropper| | +--------+ | |Meter | |Marker| |Dropper| |
skipping to change at page 36, line 42 skipping to change at page 35, line 42
accepted by the FE accepted by the FE
Figure 7. An example of configuring LFB topology. Figure 7. An example of configuring LFB topology.
Figure 7 shows an example where a QoS-enabled router has several Figure 7 shows an example where a QoS-enabled router has several
line cards that have a few ingress ports and egress ports, a line cards that have a few ingress ports and egress ports, a
specialized classification chip, a network processor containing specialized classification chip, a network processor containing
codes for FE blocks like meter, marker, dropper, counter, queue, codes for FE blocks like meter, marker, dropper, counter, queue,
scheduler and Ipv4 forwarder. Some of the LFB topology is already scheduler and Ipv4 forwarder. Some of the LFB topology is already
fixed and has to remain static due to the physical layout of the fixed and has to remain static due to the physical layout of the
line cards. For example, all the ingress ports might be hard-wired line cards. For example, all of the ingress ports might be hard-
into the classification chip and so all packets must flow from the wired into the classification chip so all packets must flow from the
ingress port into the classification engine. On the other hand, ingress port into the classification engine. On the other hand, the
the LFBs on the network processor and their execution order are LFBs on the network processor and their execution order are
programmable. However, certain capacity limits and linkage programmable. However, certain capacity limits and linkage
constraints could exist between these LFBs. Examples of the constraints could exist between these LFBs. Examples of the capacity
capacity limits might be: 8 meters; 16 queues in one FE; the limits might be: 8 meters; 16 queues in one FE; the scheduler can
scheduler can handle at most up to 16 queues; etc. The linkage handle at most up to 16 queues; etc. The linkage constraints might
constraints might dictate that the classification engine may be dictate that the classification engine may be followed by a meter,
followed by a meter, marker, dropper, counter, queue or IPv4 marker, dropper, counter, queue or IPv4 forwarder, but not a
forwarder, but not a scheduler; queues can only be followed by a scheduler; queues can only be followed by a scheduler; a scheduler
scheduler; a scheduler must be followed by the IPv4 forwarder; the must be followed by the IPv4 forwarder; the last LFB in the datapath
last LFB in the datapath before going into the egress ports must be before going into the egress ports must be the IPv4 forwarder, etc.
the IPv4 forwarder, etc.
Once the FE reports these capabilities and capacity limits to the Once the FE reports these capabilities and capacity limits to the
CE, it is now up to the CE to translate the QoS policy into a CE, it is now up to the CE to translate the QoS policy into a
desirable configuration for the FE. Figure 7(a) depicts the FE desirable configuration for the FE. Figure 7(a) depicts the FE
capability while 7(b) and 7(c) depict two different topologies that capability while 7(b) and 7(c) depict two different topologies that
the FE might be asked to configure to. Note that both the ingress the CE may request the FE to configure. Note that both the ingress
and egress are omitted in (b) and (c) to simplify the and egress are omitted in (b) and (c) to simplify the
representation. The topology in 7(c) is considerably more complex representation. The topology in 7(c) is considerably more complex
than 7(b) but both are feasible within the FE capabilities, and so than 7(b) but both are feasible within the FE capabilities, and so
the FE should accept either configuration request from the CE. the FE should accept either configuration request from the CE.
4. Model and Schema for LFB Classes 4.
Model and Schema for LFB Classes
The main goal of the FE model is to provide an abstract, generic, The main goal of the FE model is to provide an abstract, generic,
modular, implementation-independent representation of the FEs. modular, implementation-independent representation of the FEs. This
This is facilitated using the concept of LFBs, which are is facilitated using the concept of LFBs, which are instantiated
instantiated from LFB classes. LFB classes and associated from LFB classes. LFB classes and associated definitions will be
definitions will be provided in a collection of XML documents. The provided in a collection of XML documents. The collection of these
collection of these XML documents is called a LFB class library, XML documents is called a LFB class library, and each document is
and each document is called an LFB class library document (or called an LFB class library document (or library document, for
library document, for short). Each of the library documents will short). Each of the library documents will conform to the schema
conform to the schema presented in this section. The root element presented in this section. The root element of the library document
of the library document is the <LFBLibrary> element. is the <LFBLibrary> element.
It is not expected that library documents will be exchanged between It is not expected that library documents will be exchanged between
FEs and CEs "over-the-wire". But the model will serve as an FEs and CEs "over-the-wire". But the model will serve as an
important reference for the design and development of the CEs important reference for the design and development of the CEs
(software) and FEs (mostly the software part). It will also serve (software) and FEs (mostly the software part). It will also serve
as a design input when specifying the ForCES protocol elements for as a design input when specifying the ForCES protocol elements for
CE-FE communication. CE-FE communication.
4.1. Namespace 4.1. Namespace
skipping to change at page 38, line 10 skipping to change at page 37, line 10
4.2. <LFBLibrary> Element 4.2. <LFBLibrary> Element
The <LFBLibrary> element serves as a root element of all library The <LFBLibrary> element serves as a root element of all library
documents. It contains one or more of the following main blocks: documents. It contains one or more of the following main blocks:
. <frameTypeDefs> for the frame declarations; . <frameTypeDefs> for the frame declarations;
. <dataTypeDefs> for defining common data types; . <dataTypeDefs> for defining common data types;
. <metadataDefs> for defining metadata, and . <metadataDefs> for defining metadata, and
. <LFBClassDefs> for defining LFB classes. . <LFBClassDefs> for defining LFB classes.
Each block is optional, that is, one library may contain only Each block is optional, that is, one library document may contain
metadata definitions, another may contain only LFB class only metadata definitions, another may contain only LFB class
definitions, yet another may contain all of the above. definitions, yet another may contain all of the above.
In addition to the above main blocks, a library document can import In addition to the above main blocks, a library document can import
other library documents if it needs to refer to definitions other library documents if it needs to refer to definitions
contained in the included document. This concept is similar to the contained in the included document. This concept is similar to the
"#include" directive in C. Importing is expressed by the <load> "#include" directive in C. Importing is expressed by the <load>
elements, which must precede all the above elements in the elements, which must precede all the above elements in the document.
document. For unique referencing, each LFBLibrary instance For unique referencing, each LFBLibrary instance document has a
document has a unique label defined in the "provide" attribute of unique label defined in the "provide" attribute of the LFBLibrary
the LFBLibrary element. element.
The <LFBLibrary> element also includes an optional <description> The <LFBLibrary> element also includes an optional <description>
element, which can be used to provide textual description about the element, which can be used to provide textual description about the
library. library document.
The following is a skeleton of a library document: The following is a skeleton of a library document:
<?xml version="1.0" encoding="UTF-8"?> <?xml version="1.0" encoding="UTF-8"?>
<LFBLibrary xmlns="http://ietf.org/forces/1.0/lfbmodel" <LFBLibrary xmlns="http://ietf.org/forces/1.0/lfbmodel"
provides="this_library"> provides="this_library">
<description> <description>
... ...
</description> </description>
skipping to change at page 39, line 18 skipping to change at page 38, line 21
<!¨LFB CLASS DEFINITIONS (optional) --> <!¨LFB CLASS DEFINITIONS (optional) -->
<LFBCLassDefs> <LFBCLassDefs>
... ...
</LFBCLassDefs> </LFBCLassDefs>
</LFBLibrary> </LFBLibrary>
4.3. <load> Element 4.3. <load> Element
This element is used to refer to another LFB library document. This element is used to refer to another LFB library document.
Similar to the "include" directive in C, this makes the objects Similar to the "#include" directive in C, this makes the objects
(metadata types, data types, etc.) defined in the referred library (metadata types, data types, etc.) defined in the referred library
available for referencing in the current document. document available for referencing in the current document.
The load element must contain the label of the library to be The load element must contain the label of the library document to
included and may contain a URL to specify where the library can be be included and may contain a URL to specify where the library can
retrieved. The load element can be repeated unlimited times. be retrieved. The load element can be repeated unlimited times.
Three examples for the <load> elements: Three examples for the <load> elements:
<load library="a_library"/> <load library="a_library"/>
<load library="another_library" location="another_lib.xml"/> <load library="another_library" location="another_lib.xml"/>
<load library="yetanother_library" <load library="yetanother_library"
location="http://www.petrimeat.com/forces/1.0/lfbmodel/lpm.xml"/> location="http://www.petrimeat.com/forces/1.0/lfbmodel/lpm.xml"/>
4.4. <frameDefs> Element for Frame Type Declarations 4.4. <frameDefs> Element for Frame Type Declarations
Frame names are used in the LFB definition to define the types of Frame names are used in the LFB definition to define the types of
skipping to change at page 40, line 31 skipping to change at page 39, line 31
<synopsis>IPv6 packet</synopsis> <synopsis>IPv6 packet</synopsis>
<description> <description>
This frame type refers to an IPv6 packet. This frame type refers to an IPv6 packet.
</description> </description>
</frameDef> </frameDef>
... ...
</frameDefs> </frameDefs>
4.5. <dataTypeDefs> Element for Data Type Definitions 4.5. <dataTypeDefs> Element for Data Type Definitions
The (optional) <dataTypeDefs> element can be used to define The (optional) <dataTypeDefs> element can be used to define commonly
commonly used data types. It contains one or more <dataTypeDef> used data types. It contains one or more <dataTypeDef> elements,
elements, each defining a data type with a unique name. Such data each defining a data type with a unique name. Such data types can be
types can be used in several places in the library documents, used in several places in the library documents, including:
including:
. Defining other data types . Defining other data types
. Defining metadata . Defining metadata
. Defining attributes of LFB classes . Defining attributes of LFB classes
This is similar to the concept of having a common header file for This is similar to the concept of having a common header file for
shared data types. shared data types.
Each <dataTypeDef> element contains a unique name (NMTOKEN), a Each <dataTypeDef> element contains a unique name (NMTOKEN), a brief
brief synopsis, an optional longer description, and a type synopsis, an optional longer description, and a type definition
definition element. The name must be unique among all data types element. The name must be unique among all data types defined in
defined in the same library document and in any directly or the same library document and in any directly or indirectly included
indirectly included library documents. For example: library documents. For example:
<dataTypeDefs> <dataTypeDefs>
<dataTypeDef> <dataTypeDef>
<name>ieeemacaddr</name> <name>ieeemacaddr</name>
<synopsis>48-bit IEEE MAC address</synopsis> <synopsis>48-bit IEEE MAC address</synopsis>
... type definition ... ... type definition ...
</dataTypeDef> </dataTypeDef>
<dataTypeDef> <dataTypeDef>
<name>ipv4addr</name> <name>ipv4addr</name>
<synopsis>IPv4 address</synopsis> <synopsis>IPv4 address</synopsis>
... type definition ... ... type definition ...
</dataTypeDef> </dataTypeDef>
... ...
</dataTypeDefs> </dataTypeDefs>
There are two kinds of data types: atomic and compound. Atomic There are two kinds of data types: atomic and compound. Atomic data
data types are appropriate for single-value variables (e.g. types are appropriate for single-value variables (e.g. integer,
integer, ASCII string, byte array). ASCII string, byte array).
The following built-in atomic data types are provided, but The following built-in atomic data types are provided, but
additional atomic data types can be defined with the <typeRef> and additional atomic data types can be defined with the <typeRef> and
<atomic> elements: <atomic> elements:
<name> Meaning <name> Meaning
---- ------- ---- -------
char 8-bit signed integer char 8-bit signed integer
uchar 8-bit unsigned integer uchar 8-bit unsigned integer
int16 16-bit signed integer int16 16-bit signed integer
uint16 16-bit unsigned integer uint16 16-bit unsigned integer
int32 32-bit signed integer int32 32-bit signed integer
uint32 32-bit unsigned integer uint32 32-bit unsigned integer
int64 64-bit signed integer int64 64-bit signed integer
uint64 64-bit unisgned integer uint64 64-bit unisgned integer
boolean A true / false value where
0 = false, 1 = true
string[N] ASCII null-terminated string with string[N] ASCII null-terminated string with
buffer of N characters (string max buffer of N characters (string max
length is N-1) length is N-1)
byte[N] A byte array of N bytes byte[N] A byte array of N bytes
octetstring[N] A buffer of N octets, which may
contain fewer than N octets. Hence
the encoded value will always have
a length.
float16 16-bit floating point number float16 16-bit floating point number
float32 32-bit IEEE floating point number float32 32-bit IEEE floating point number
float64 64-bit IEEE floating point number float64 64-bit IEEE floating point number
These built-in data types can be readily used to define metadata or These built-in data types can be readily used to define metadata or
LFB attributes, but can also be used as building blocks when LFB attributes, but can also be used as building blocks when
defining new data types. defining new data types. The boolean data type is defined here
because it is so common, even though it can be built by sub-ranging
the uchar data type.
Compound data types can build on atomic data types and other Compound data types can build on atomic data types and other
compound data types. There are four ways that compound data types compound data types. Compound data types can be defined in one of
can be defined. They may be defined as an array of elements of four ways. They may be defined as an array of elements of some
some compound or atomic data type. They may be a structure of compound or atomic data type. They may be a structure of named
named elements of compound or atomic data types (ala C structures). elements of compound or atomic data types (ala C structures). They
They may be a union of named elements of compound or atomic data may be a union of named elements of compound or atomic data types
types (ala C unions). They may also be defined as augmentations (ala C unions). They may also be defined as augmentations
(explained below in 4.5.6) of existing compound data types. (explained below in 4.5.6) of existing compound data types.
Given that the FORCES protocol will be getting and setting Given that the FORCES protocol will be getting and setting attribute
attribute values, all atomic data types used here must be able to values, all atomic data types used here must be able to be conveyed
be conveyed in the FORCES protocol. Further, the FORCES protocol in the FORCES protocol. Further, the FORCES protocol will need a
will need a mechanism to convey compound data types. However, the mechanism to convey compound data types. However, the details of
details of such representations are for the protocol document, not such representations are for the protocol document to define, not
the model documents. the model document.
For the definition of the actual type in the <dataTypeDef> element, For the definition of the actual type in the <dataTypeDef> element,
the following elements are available: <typeRef>, <atomic>, <array>, the following elements are available: <typeRef>, <atomic>, <array>,
<struct>, and <union>. <struct>, and <union>.
The predefined type alias is somewhere between the atomic and
compound data types. It behaves like a structure, one element of
which has special behavior. Given that the special behavior is tied
to the other parts of the structure, the compound result is treated
as a predefined construct.
[EDITOR: How to support augmentation is for further study.] [EDITOR: How to support augmentation is for further study.]
4.5.1. <typeRef> Element for Aliasing Existing Data Types 4.5.1. <typeRef> Element for Aliasing Existing Data Types
The <typeRef> element refers to an existing data type by its name. The <typeRef> element refers to an existing data type by its name.
The referred data type must be defined either in the same library The referred data type must be defined either in the same library
document, or in one of the included library documents. If the document, or in one of the included library documents. If the
referred data type is an atomic data type, the newly defined type referred data type is an atomic data type, the newly defined type
will also be regarded as atomic. If the referred data type is a will also be regarded as atomic. If the referred data type is a
compound type, the new type will also be a compound. Some usage compound type, the new type will also be compound. Some usage
examples: examples follow:
<dataTypeDef> <dataTypeDef>
<name>short</name> <name>short</name>
<synopsis>Alias to int16</synopsis> <synopsis>Alias to int16</synopsis>
<typeRef>int16</typeRef> <typeRef>int16</typeRef>
</dataTypeDef> </dataTypeDef>
<dataTypeDef> <dataTypeDef>
<name><name>ieeemacaddr</name> <name>ieeemacaddr</name>
<synopsis>48-bit IEEE MAC address</synopsis> <synopsis>48-bit IEEE MAC address</synopsis>
<typeRef>byte[6]</typeRef> <typeRef>byte[6]</typeRef>
</dataTypeDef> </dataTypeDef>
4.5.2. <atomic> Element for Deriving New Atomic Types 4.5.2. <atomic> Element for Deriving New Atomic Types
The <atomic> element allows the definition of a new atomic type
from an existing atomic type, applying range restrictions and/or The <atomic> element allows the definition of a new atomic type from
providing special enumerated values. Note that the <atomic> an existing atomic type, applying range restrictions and/or
element can only use atomic types as base types, and its result is providing special enumerated values. Note that the <atomic> element
always another atomic type. can only use atomic types as base types, and its result is always
another atomic type.
For example, the following snippet defines a new "dscp" data type: For example, the following snippet defines a new "dscp" data type:
<dataTypeDef> <dataTypeDef>
<name>dscp</name> <name>dscp</name>
<synopsis>Diffserv code point.</synopsis> <synopsis>Diffserv code point.</synopsis>
<atomic> <atomic>
<baseType>uchar</baseType> <baseType>uchar</baseType>
<rangeRestriction> <rangeRestriction>
<allowedRange min="0" max="63"/> <allowedRange min="0" max="63"/>
skipping to change at page 43, line 34 skipping to change at page 42, line 48
</specialValue> </specialValue>
... ...
</specialValues> </specialValues>
</atomic> </atomic>
</dataTypeDef> </dataTypeDef>
4.5.3. <array> Element to Define Arrays 4.5.3. <array> Element to Define Arrays
The <array> element can be used to create a new compound data type The <array> element can be used to create a new compound data type
as an array of a compound or an atomic data type. The type of the as an array of a compound or an atomic data type. The type of the
array entry can be specified either by referring to an existing array entry can be specified either by referring to an existing type
type (using the <typeRef> element) or defining an unnamed type (using the <typeRef> element) or defining an unnamed type inside the
inside the <array> element using any of the <atomic>, <array>, <array> element using any of the <atomic>, <array>, <struct>, or
<struct>, or <union> elements. <union> elements.
The array can be "fixed-size" or "variable-size", which is The array can be "fixed-size" or "variable-size", which is specified
specified by the "type" attribute of the <array> element. The by the "type" attribute of the <array> element. The default is
default is "variable-size". For variable size arrays, an optional "variable-size". For variable size arrays, an optional "max-length"
"max-length" attribute can specify the maximum allowed length. This attribute specifies the maximum allowed length. This attribute
attribute should be used to encode semantic limitations, and not should be used to encode semantic limitations, not implementation
implementation limitations. The latter should be handled by limitations. The latter should be handled by capability attributes
capability attributes of LFB classes, and should never be included of LFB classes, and should never be included in data type
in data type definitions. If the "max-length" attribute is not definitions. If the "max-length" attribute is not provided, the
provided, the array is regarded as of unlimited-size. array is regarded as of unlimited-size.
For fixed-size arrays, a "length" attribute must be provided that For fixed-size arrays, a "length" attribute must be provided that
specifies the constant size of the array. specifies the constant size of the array.
The result of this construct is always a compound type, even if the The result of this construct is always a compound type, even if the
array has a fixed size of 1. array has a fixed size of 1.
Arrays can only be subscripted by integers, and will be presumed to Arrays can only be subscripted by integers, and will be presumed to
start with index 0. start with index 0.
In addition to their subscripts, arrays may be declared to have
content keys. Such a declaration has several effects:
. Any declared key can be used in the ForCES protocol to select
an element for operations (for details, see the protocol).
. In any instance of the array, each declared key must be unique
within that instance. No two elements of an array may have the
same values on all the fields which make up a key.
Each key is declared with a keyID for use in the protocol, where the
unique key is formed by combining one or more specified key fields.
To support the case where an array of an atomic type with unique
values can be referenced by those values, the key field identifier
may be "*" (i.e., the array entry is the key). If the value type of
the array is a structure or an array, then the key is one or more
fields, each identified by name. Since the field may be an element
of the structure, the element of an element of a structure, or
further nested, the field name is actually a concatenated sequence
of part identifiers, separated by decimal points (˘.÷). The syntax
for key field identification is given following the array examples.
The following example shows the definition of a fixed size array The following example shows the definition of a fixed size array
with pre-defined data type as array elements: with a pre-defined data type as the array elements:
<dataTypeDef> <dataTypeDef>
<name>dscp-mapping-table</name> <name>dscp-mapping-table</name>
<synopsys> <synopsis>
A table of 64 DSCP values, used to re-map code space. A table of 64 DSCP values, used to re-map code space.
</synopsis> </synopsis>
<array type="fixed-size" length="64"> <array type="fixed-size" length="64">
<typeRef>dscp</typeRef> <typeRef>dscp</typeRef>
</array> </array>
</dataTypeDef> </dataTypeDef>
The following example defines a variable size array with an upper The following example defines a variable size array with an upper
limit on its size: limit on its size:
<dataTypeDef> <dataTypeDef>
<name>mac-alias-table </name> <name>mac-alias-table </name>
<synopsys>A table with up to 8 IEEE MAC addresses</synopsis> <synopsis>A table with up to 8 IEEE MAC addresses</synopsis>
<array type="variable-size" max-length="8"> <array type="variable-size" max-length="8">
<typeRef>ieeemacaddr</typeRef> <typeRef>ieeemacaddr</typeRef>
</array> </array>
</dataTypeDef> </dataTypeDef>
The following example shows the definition of an array with local The following example shows the definition of an array with a local
(unnamed) type definition: (unnamed) type definition:
<dataTypeDef> <dataTypeDef>
<name>classification-table</name> <name>classification-table</name>
<synopsys> <synopsis>
A table of classification rules and result opcodes. A table of classification rules and result opcodes.
</synopsis> </synopsis>
<array type="variable-size"> <array type="variable-size">
<struct> <struct>
<element> <element elementID=÷1÷>
<name>rule</name> <name>rule</name>
<synopsis>The rule to match</synopsis> <synopsis>The rule to match</synopsis>
<typeRef>classrule</typeRef> <typeRef>classrule</typeRef>
</element> </element>
<element> <element ˘elementID=÷2÷>
<name>opcode</name> <name>opcode</name>
<synopsis>The result code</synopsis> <synopsis>The result code</synopsis>
<typeRef>opcode</typeRef> <typeRef>opcode</typeRef>
</element> </element>
</struct> </struct>
</array> </array>
</dataTypeDef> </dataTypeDef>
In the above example each entry of the array is a <struct> of two In the above example, each entry of the array is a <struct> of two
fileds ("rule" and "opcode"). fields ("rule" and "opcode").
The following example shows a table of IP Prefix information that
can be accessed by a multi-field content key on the IP Address and
prefix length. This means that in any instance of this table, no
two entries can have the same IP address and prefix length.
<dataTypeDef>
<name>ipPrefixInfo_table</name>
<synopsis>
A table of information about known prefixes
</synopsis>
<array type=÷variable-size÷>
<struct>
<element elementID=÷1÷>
<name>address-prefix</name>
<synopsis>the prefix being described</synopsis>
<typeRef>ipv4Prefix</typeRef>
</element>
<element elementID=÷2÷>
<name>source</name>
<synopsis>where is this from</synopsis>
<typeRef>uint16</typeRef>
</element>
<element elementID=÷3÷>
<name>prefInfo</name>
<synopsis>the information we care about</synopsis>
<typeRef>hypothetical-info-type</typeRef>
</element>
</struct>
<key keyID=÷1÷>
<keyField> address-prefix.ipv4addr </keyField>
<keyField> address-prefix.prefixlen </keyField>
<keyField> source </keyField>
</key>
</array>
</dataTypeDef>
Note that the keyField elements could also have been simply address-
prefix and source, since all of the fields of address-prefix are
being used.
4.5.3.1 Key Field References
In order to use key declarations, one must refer to fields that are
potentially nested inside other fields in the array. If there are
nested arrays, one might even use an array element as a key (but
great care would be needed to ensure uniqueness.)
The key is the combination of the values of each field declared in a
keyField element.
Therefore, the value of a keyField element is defined as a
concatenated Sequence of field identifiers, separated by a "."
(period) character. Whitespace is permitted and ignored.
A valid string for a single field identifier within a keyField
depends upon the current context. Initially, in an array key
declaration, the context is the type of the array. Progressively,
the context is whatever type is selected by the field identifiers
processed so far in the current key field declaration.
When the current context is an array, (e.g., when declaring a key
for an array whose content is an array) then the only valid value
for the field identifier is an explicit number.
When the current context is a structure, the valid values for the
field identifiers are the names of the elements of the structure.
In the special case of declaring a key for an array containing an
atomic type, where that content is unique and is to be used as a
key, the value "*" can be used as the single key field identifier.
4.5.4. <struct> Element to Define Structures 4.5.4. <struct> Element to Define Structures
A structure is comprised of a collection of data elements. Each A structure is comprised of a collection of data elements. Each
data element has a data type (either an atomic type or an existing data element has a data type (either an atomic type or an existing
compound type) and is assigned a name unique within the scope of compound type) and is assigned a name unique within the scope of the
the compound data type being defined. These serve the same compound data type being defined. These serve the same function as
function as "struct" in C, etc. "struct" in C, etc.
The actual type of the field can be defined by referring to an The actual type of the field can be defined by referring to an
existing type (using the <typeDef> element), or can be a locally existing type (using the <typeDef> element), or can be a locally
defined (unnamed) type created by any of the <atomic>, <array>, defined (unnamed) type created by any of the <atomic>, <array>,
<struct>, or <union> elements. <struct>, or <union> elements.
A structure definition is a series of element declarations. Each
element carries an elementID for use by the ForCES protocol. In
addition, the element contains the name, a synopsis, an optional
description, an optional declaration that the element itself is
optional, and the typeRef declaration that specifies the element
type.
For a dataTypeDefinition of a struct, the structure definition may
be inherited from, and augment, a previously defined structured type.
This is indicated by including the derivedFrom attribute on the
struct declaration.
The result of this construct is always regarded a compound type, The result of this construct is always regarded a compound type,
even if the <struct> contains only one field. even when the <struct> contains only one field.
An example: An example:
<dataTypeDef> <dataTypeDef>
<name>ipv4prefix</name> <name>ipv4prefix</name>
<synopsis> <synopsis>
IPv4 prefix defined by an address and a prefix length IPv4 prefix defined by an address and a prefix length
</synopsis> </synopsis>
<struct> <struct>
<element> <element elementID=÷1÷>
<name>address</name> <name>address</name>
<synopsis>Address part</synopsis> <synopsis>Address part</synopsis>
<typeRef>ipv4addr</typeRef> <typeRef>ipv4addr</typeRef>
</element> </element>
<element> <element elementID=÷2÷>
<name>prefixlen</name> <name>prefixlen</name>
<synopsis>Prefix length part</synopsis> <synopsis>Prefix length part</synopsis>
<atomic> <atomic>
<baseType>uchar</baseType> <baseType>uchar</baseType>
<rangeRestriction> <rangeRestriction>
<allowedRange min="0" max="32"/> <allowedRange min="0" max="32"/>
</rangeRestriction> </rangeRestriction>
</atomic> </atomic>
</element> </element>
</struct> </struct>
</dataTypeDef> </dataTypeDef>
4.5.5. <union> Element to Define Union Types 4.5.5. <union> Element to Define Union Types
Similar to the union declaration in C, this construct allows the Similar to the union declaration in C, this construct allows the
definition of overlay types. Its format is identical to the definition of overlay types. Its format is identical to the
<struct> element. <struct> element.
The result of this construct is always regarded a compound type, The result of this construct is always regarded a compound type,
even if the union contains only one element. even when the union contains only one element.
4.5.6 <alias> Element
It is sometimes necessary to have an element in an LFB or structure
refer to information in other LFBs. The <alias> declaration creates
the constructs for this. An <alias> element creates a structure
with fields to control the alias and a field to access the aliased
information.
An <alias> declaration is used wherever a type reference can occur,
just like a <struct> or <array>. A typical alias usage would look
like:
<dataTypeDef>
<name>anAliasedVariable</name>
<synopsis>a reference to something, somewhere</synopsis>
<alias>the-underlying-type</alias>
</dataTypeDef>
This definition declares a type to be used for an alias to things of
type ˘the-underlying-type÷. This would more likely occur inside a
structure rather than directly in a dataTypeDef.
An alias is a complex structure in order to hold the pieces
necessary to make it useful. If "alias" was an actual declared
structure, and if "tiedReference" was a usable type, the structure
declaration would look like:
<dataTypeDef>
<name>alias</name>
<synopsis>a reference to information in another LFB</synopsis>
<struct>
<element elementID=÷1÷>
<name>referenceClass</name>
<synopsis>
The class of LFB this alias is currently pointing to
</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID=÷2÷>
<name>referenceInstance</name>
<synopsis>
The LFB Instance this alias is currently pointing to
</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID=÷3÷>
<name>referencePath</name>
<synopsis>
The path to the LFB field this alias is currently
pointing to
</synopsis>
<typeRef)octetString[128]</typeRef>
</element>
<element elementID=÷4÷>
<name>referenceClass</name>
<synopsis>
The element to use to follow the alias
</synopsis>
<typeRef>tiedReference</typeRef>
</element>
</struct>
</dataTypeDef>
The referencePath is the identifier in the form used by the ForCES
protocol for the actual field being referenced. Its type must be
the same as the type declared for the alias. (And the FE MUST ensure
the types are the same on any effort to set the referenceClass,
referenceInstance, or referencePath elements). Note that "128" is
the length limit for paths in the ForCES protocol.) Thus, by
setting the three control fields, the CE controls which LFB and the
field in that LFB, the alias data points to. Typically, this will
be information needed by the LFB containing the element with an
<alias> declaration.
4.5.6. Augmentations 4.5.6. Augmentations
Compound types can also be defined as augmentations of existing Compound types can also be defined as augmentations of existing
compound types. If the existing compound type is a structure, compound types. If the existing compound type is a structure,
augmentation may add new elements to the type. The type of an augmentation may add new elements to the type. The type of an
existing element can only be replaced with an augmentation derived existing element can only be replaced with an augmentation derived
from the current type, an existing element cannot be deleted. If from the current type, an existing element cannot be deleted. If
the existing compound type is an array, augmentation means the existing compound type is an array, augmentation means
augmentation of the array element type. augmentation of the array element type.
skipping to change at page 46, line 47 skipping to change at page 49, line 49
compatibility rules for subclasses. compatibility rules for subclasses.
For example, consider a simple base LFB class A that has only one For example, consider a simple base LFB class A that has only one
attribute (attr1) of type X. One way to derive class A1 from A can attribute (attr1) of type X. One way to derive class A1 from A can
be by simply adding a second attribute (of any type). Another way be by simply adding a second attribute (of any type). Another way
to derive a class A2 from A can be by replacing the original to derive a class A2 from A can be by replacing the original
attribute (attr1) in A of type X with one of type Y, where Y is an attribute (attr1) in A of type X with one of type Y, where Y is an
augmentation of X. Both classes A1 and A2 are backward compatible augmentation of X. Both classes A1 and A2 are backward compatible
with class A. with class A.
[EDITOR: How to support the concept of augmentation in the XML The syntax for augmentations is to include a derivedFrom attribute
schema is for further study.] in a structure definition, indicating what structure type is being
augmented. Element names and element IDs within the augmentation
must not be the same as those in the structure type being augmented.
[EDITOR: This is a preliminary proposal for handling augmentation of
structures.]
4.6. <metadataDefs> Element for Metadata Definitions 4.6. <metadataDefs> Element for Metadata Definitions
The (optional) <metadataDefs> element in the library document The (optional) <metadataDefs> element in the library document
contains one or more <metadataDef> elements. Each <metadataDef> contains one or more <metadataDef> elements. Each <metadataDef>
element defines a metadata. element defines a metadata.
Each <metadataDef> element contains a unique name (NMTOKEN). Each <metadataDef> element contains a unique name (NMTOKEN).
Uniqueness is defined over all metadata defined in this library Uniqueness is defined to be over all metadata defined in this
document and in all directly or indirectly included library library document and in all directly or indirectly included library
documents. The <metadataDef> element also contains a brief documents. The <metadataDef> element also contains a brief
synopsis, an optional detailed description, and a compulsory type synopsis, an optional detailed description, and a compulsory type
definition information. Only atomic data types can be used as value definition information. Only atomic data types can be used as value
types for metadata. types for metadata.
Two forms of type definitions are allowed. The first form uses the Two forms of type definitions are allowed. The first form uses the
<typeRef> element to refer to an existing atomic data type defined <typeRef> element to refer to an existing atomic data type defined
in the <dataTypeDefs> element of the same library document or in in the <dataTypeDefs> element of the same library document or in one
one of the included library documents. The usage of the <typeRef> of the included library documents. The usage of the <typeRef>
element is identical to how it is used in the <dataTypeDef> element is identical to how it is used in the <dataTypeDef>
elements, except here it can only refer to atomic types. elements, except here it can only refer to atomic types.
[EDITOR: The latter restriction is not yet enforced by the XML [EDITOR: The latter restriction is not yet enforced by the XML
schema.] schema.]
The second form is an explicit type definition using the <atomic> The second form is an explicit type definition using the <atomic>
element. This element is used here in the same way as in the element. This element is used here in the same way as in the
<dataTypeDef> elements. <dataTypeDef> elements.
skipping to change at page 48, line 20 skipping to change at page 51, line 25
</metadataDef> </metadataDef>
</metadataDefs> </metadataDefs>
4.7. <LFBClassDefs> Element for LFB Class Definitions 4.7. <LFBClassDefs> Element for LFB Class Definitions
The (optional) <LFBClassDefs> element can be used to define one or The (optional) <LFBClassDefs> element can be used to define one or
more LFB classes using <LFBClassDef> elements. Each <LFBClassDef> more LFB classes using <LFBClassDef> elements. Each <LFBClassDef>
element defines an LFB class and includes the following elements: element defines an LFB class and includes the following elements:
. <name> provides the symbolic name of the LFB class. Example: . <name> provides the symbolic name of the LFB class. Example:
"ipv4lpm" "ipv4lpm"
. <synopsis> provides a short synopsis of the LFB class. . <synopsis> provides a short synopsis of the LFB class. Example:
Example: "IPv4 Longest Prefix Match Lookup LFB" "IPv4 Longest Prefix Match Lookup LFB"
. <version> is the version indicator . <version> is the version indicator
. <derivedFrom> is the inheritance indicator . <derivedFrom> is the inheritance indicator
. <inputPorts> lists the input ports and their specifications . <inputPorts> lists the input ports and their specifications
. <outputPorts> lists the output ports and their specifications . <outputPorts> lists the output ports and their specifications
. <attributes> defines the operational attributes of the LFB . <attributes> defines the operational attributes of the LFB
. <capabilities> defines the capability attributes of the LFB . <capabilities> defines the capability attributes of the LFB
. <description> contains the operational specification of the . <description> contains the operational specification of the LFB
LFB . The LFBClassID attribute of the LFBClassDef element defines the
ID for this class. These must be globally unique.
[EDITOR: LFB class names should be unique not only among classes [EDITOR: LFB class names should be unique not only among classes
defined in this document and in all included documents, but also defined in this document and in all included documents, but also
unique across a large collection of libraries. Obviously some unique across a large collection of libraries. Obviously some global
global control is needed to ensure such uniqueness. This subject control is needed to ensure such uniqueness. This subject requires
requires further study.] further study. The uniqueness of the class IDs also requires further
study.]
Here is a skeleton of an example LFB class definition: Here is a skeleton of an example LFB class definition:
<LFBClassDefs> <LFBClassDefs>
<LFBClassDef> <LFBClassDef LFBClassID=÷12345÷>
<name>ipv4lpm</name> <name>ipv4lpm</name>
<synopsis>IPv4 Longest Prefix Match Lookup LFB</synopsis> <synopsis>IPv4 Longest Prefix Match Lookup LFB</synopsis>
<version>1.0</version> <version>1.0</version>
<derivedFrom>baseclass</derivedFrom> <derivedFrom>baseclass</derivedFrom>
<inputPorts> <inputPorts>
... ...
</inputPorts> </inputPorts>
<outputPorts> <outputPorts>
... ...
</outputPorts> </outputPorts>
<attributes> <attributes>
... ...
</attributes> </attributes>
<capabilities> <capabilities>
... ...
skipping to change at page 49, line 27 skipping to change at page 52, line 33
This LFB represents the IPv4 longest prefix match lookup This LFB represents the IPv4 longest prefix match lookup
operation. operation.
The modeled behavior is as follows: The modeled behavior is as follows:
Blah-blah-blah. Blah-blah-blah.
</description> </description>
</LFBClassDef> </LFBClassDef>
... ...
</LFBClassDefs> </LFBClassDefs>
Note that the <name>, <synopsis>, and <version> elements, all other The individual attributes and capabilities will have elementIDs for
elements are optional in <LFBClassDef>. However, when they are use by the ForCES protocol. These parallel the elementIDs used in
present, they must occur in the above order. structs, and are used the same way. Attribute and capability
elementIDs must be unique within the LFB class definition.
Note that the <name>, <synopsis>, and <version> elements are
required, all other elements are optional in <LFBClassDef>. However,
when they are present, they must occur in the above order.
4.7.1. <derivedFrom> Element to Express LFB Inheritance 4.7.1. <derivedFrom> Element to Express LFB Inheritance
The optional <derivedFrom> element can be used to indicate that The optional <derivedFrom> element can be used to indicate that this
this class is a derivative of some other class. The content of class is a derivative of some other class. The content of this
this element must be the unique name (<name>) of another LFB class. element must be the unique name (<name>) of another LFB class. The
The referred LFB class must be defined in the same library document referred LFB class must be defined in the same library document or
or in one of the included library documents. in one of the included library documents.
[EDITOR: The <derivedFrom> element will likely need to specify the [EDITOR: The <derivedFrom> element will likely need to specify the
version of the ancestor, which is not included in the schema yet. version of the ancestor, which is not included in the schema yet.
The process and rules of class derivation are still being studied.] The process and rules of class derivation are still being studied.]
It is assumed that the derived class is backwards compatible with It is assumed that the derived class is backwards compatible with
the base class. the base class.
4.7.2. <inputPorts> Element to Define LFB Inputs 4.7.2. <inputPorts> Element to Define LFB Inputs
The optional <inputPorts> element is used to define input ports. The optional <inputPorts> element is used to define input ports. An
An LFB class may have zero, one, or more inputs. If the LFB class LFB class may have zero, one, or more inputs. If the LFB class has
has no input ports, the <inputPorts> element must be omitted. The no input ports, the <inputPorts> element must be omitted. The
<inputPorts> element can contain one or more <inputPort> elements, <inputPorts> element can contain one or more <inputPort> elements,
one for each port or port-group. We assume that most LFBs will one for each port or port-group. We assume that most LFBs will have
have exactly one input. Multiple inputs with the same input type exactly one input. Multiple inputs with the same input type are
are modeled as one input group. Input groups are defined the same modeled as one input group. Input groups are defined the same way
way as input ports by the <inputPort> element, differentiated only as input ports by the <inputPort> element, differentiated only by an
by an optional "group" attribute. optional "group" attribute.
Multiple inputs with different input types should be avoided if Multiple inputs with different input types should be avoided if
possible (see discussion in Section 3.2.1). Some special LFBs will possible (see discussion in Section 3.2.1). Some special LFBs will
have no inputs at all. For example, a packet generator LFB does have no inputs at all. For example, a packet generator LFB does not
not need an input. need an input.
Single input ports and input port groups are both defined by the Single input ports and input port groups are both defined by the
<inputPort> element, they are differentiated by only an optional <inputPort> element, they are differentiated by only an optional
"group" attribute. "group" attribute.
The <inputPort> element contains the following elements: The <inputPort> element contains the following elements:
. <name> provides the symbolic name of the input. Example: "in". . <name> provides the symbolic name of the input. Example: "in".
Note that this symbolic name must be unique only within the Note that this symbolic name must be unique only within the scope
scope of the LFB class. of the LFB class.
. <synopsis> contains a brief description of the input. Example: . <synopsis> contains a brief description of the input. Example:
"Normal packet input". "Normal packet input".
. <expectation> lists all allowed frame formats. Example: {"ipv4" . <expectation> lists all allowed frame formats. Example: {"ipv4"
and "ipv6"}. Note that this list should refer to names and "ipv6"}. Note that this list should refer to names specified
specified in the <frameDefs> element of the same library in the <frameDefs> element of the same library document or in any
document or in any included library documents. The included library documents. The <expectation> element can also
<expectation> element can also provide a list of required provide a list of required metadata. Example: {"classid",
metadata. Example: {"classid", "vifid"}. This list should "vifid"}. This list should refer to names of metadata defined in
refer to names of metadata defined in the <metadataDefs> element the <metadataDefs> element in the same library document or in any
in the same library document or in any included library included library documents. For each metadata, it must be
documents. For each metadata, it must be specified whether the specified whether the metadata is required or optional. For each
metadata is required or optional. For each optional metadata, a optional metadata, a default value must be specified, which is
default value must be specified, which is used by the LFB if the used by the LFB if the metadata is not provided with a packet.
metadata is not provided with a packet.
In addition, the optional "group" attribute of the <inputPort> In addition, the optional "group" attribute of the <inputPort>
element can specify if the port can behave as a port group, i.e., element can specify if the port can behave as a port group, i.e., it
it is allowed to be instantiated. This is indicated by a "yes" is allowed to be instantiated. This is indicated by a "yes" value
value (the default value is "no"). (the default value is "no").
An example <inputPorts> element, defining two input ports, the An example <inputPorts> element, defining two input ports, the
second one being an input port group: second one being an input port group:
<inputPorts> <inputPorts>
<inputPort> <inputPort>
<name>in</name> <name>in</name>
<synopsis>Normal input</synopsis> <synopsis>Normal input</synopsis>
<expectation> <expectation>
<frameExpected> <frameExpected>
skipping to change at page 51, line 21 skipping to change at page 54, line 34
<ref>vifid</ref> <ref>vifid</ref>
<ref dependency="optional" defaultValue="0">vrfid</ref> <ref dependency="optional" defaultValue="0">vrfid</ref>
</metadataExpected> </metadataExpected>
</expectation> </expectation>
</inputPort> </inputPort>
<inputPort group="yes"> <inputPort group="yes">
... another input port ... ... another input port ...
</inputPort> </inputPort>
</inputPorts> </inputPorts>
For each <inputPort>, the frame type expectations are defined by For each <inputPort>, the frame type expectations are defined by the
the <frameExpected> element using one or more <ref> elements (see <frameExpected> element using one or more <ref> elements (see
example above). When multiple frame types are listed, it means example above). When multiple frame types are listed, it means that
that "one of these" frame types are expected. A packet of any "one of these" frame types are expected. A packet of any other
other frame type is regarded as incompatible with this input port frame type is regarded as incompatible with this input port of the
of the LFB class. The above example list two frames as expected LFB class. The above example list two frames as expected frame
frame types: "ipv4" and "ipv6". types: "ipv4" and "ipv6".
Metadata expectations are specified by the <metadataExpected> Metadata expectations are specified by the <metadataExpected>
element. In its simplest form, this element can contain a list of element. In its simplest form, this element can contain a list of
<ref> elements, each referring to a metadata. When multiple <ref> elements, each referring to a metadata. When multiple
instances of metadata are listed by <ref> elements, it means that instances of metadata are listed by <ref> elements, it means that
"all of these" metadata must be received with each packet (except "all of these" metadata must be received with each packet (except
metadata that are marked as "optional" by the "dependency" metadata that are marked as "optional" by the "dependency" attribute
attribute of the corresponding <ref> element). For a metadata that of the corresponding <ref> element). For a metadata that is
is specified "optional", a default value must be provided using the specified "optional", a default value must be provided using the
"defaultValue" attribute. The above example lists three metadata "defaultValue" attribute. The above example lists three metadata as
as expected metadata, two of which are mandatory ("classid" and expected metadata, two of which are mandatory ("classid" and
"vifid"), and one being optional ("vrfid"). "vifid"), and one being optional ("vrfid").
[EDITOR: How to express default values for byte[N] atomic types is [EDITOR: How to express default values for byte[N] atomic types is
yet to be defined.] yet to be defined.]
The schema also allows for more complex definitions of metadata The schema also allows for more complex definitions of metadata
expectations. For example, using the <one-of> element, a list of expectations. For example, using the <one-of> element, a list of
metadata can be specified to express that at least one of the metadata can be specified to express that at least one of the
specified metadata must be present with any packet. For example: specified metadata must be present with any packet. For example:
skipping to change at page 52, line 26 skipping to change at page 55, line 39
<ref>classid</ref> <ref>classid</ref>
<ref>vifid</ref> <ref>vifid</ref>
<ref dependency="optional" defaultValue="0">vrfid</ref> <ref dependency="optional" defaultValue="0">vrfid</ref>
<one-of> <one-of>
<ref>prefixmask</ref> <ref>prefixmask</ref>
<ref>prefixlen</ref> <ref>prefixlen</ref>
</one-of> </one-of>
</metadataExpected> </metadataExpected>
Although the schema is constructed to allow even more complex Although the schema is constructed to allow even more complex
definition of metadata expectations, we do not discuss these here. definitions of metadata expectations, we do not discuss those here.
4.7.3. <outputPorts> Element to Define LFB Outputs 4.7.3. <outputPorts> Element to Define LFB Outputs
The optional <outputPorts> element is used to define output ports. The optional <outputPorts> element is used to define output ports.
An LFB class may have zero, one, or more outputs. If the LFB class An LFB class may have zero, one, or more outputs. If the LFB class
has no output ports, the <outputPorts> element must be omitted. has no output ports, the <outputPorts> element must be omitted. The
The <outputPorts> element can contain one or more <outputPort> <outputPorts> element can contain one or more <outputPort> elements,
elements, one for each port or port-group. If there are multiple one for each port or port-group. If there are multiple outputs with
outputs with the same output type, we model them as an output port the same output type, we model them as an output port group. Some
group. Some special LFBs may have no outputs at all (e.g., special LFBs may have no outputs at all (e.g., Dropper).
Dropper).
Single output ports and output port groups are both defined by the Single output ports and output port groups are both defined by the
<outputPort> element; they are differentiated by only an optional <outputPort> element; they are differentiated by only an optional
"group" attribute. "group" attribute.
The <outputPort> element contains the following elements: The <outputPort> element contains the following elements:
. <name> provides the symbolic name of the output. Example: . <name> provides the symbolic name of the output. Example: "out".
"out". Note that the symbolic name must be unique only within Note that the symbolic name must be unique only within the scope
the scope of the LFB class. of the LFB class.
. <synopsis> contains a brief description of the output port. . <synopsis> contains a brief description of the output port.
Example: "Normal packet output". Example: "Normal packet output".
. <product> lists the allowed frame formats. Example: {"ipv4", . <product> lists the allowed frame formats. Example: {"ipv4",
"ipv6"}. Note that this list should refer to symbols specified "ipv6"}. Note that this list should refer to symbols specified in
in the <frameDefs> element in the same library document or in the <frameDefs> element in the same library document or in any
any included library documents. The <product> element may also included library documents. The <product> element may also
contain the list of emitted (generated) metadata. Example: contain the list of emitted (generated) metadata. Example:
{"classid", "color"}. This list should refer to names of {"classid", "color"}. This list should refer to names of metadata
metadata specified in the <metadataDefs> element in the same specified in the <metadataDefs> element in the same library
library document or in any included library documents. For each document or in any included library documents. For each generated
generated metadata, it should be specified whether the metadata metadata, it should be specified whether the metadata is always
is always generated or generated only in certain conditions. generated or generated only in certain conditions. This
This information is important when assessing compatibility information is important when assessing compatibility between
between LFBs. LFBs.
In addition, the optional "group" attribute of the <outputPort> In addition, the optional "group" attribute of the <outputPort>
element can specify if the port can behave as a port group, i.e., element can specify if the port can behave as a port group, i.e., it
it is allowed to be instantiated. This is indicated by a "yes" is allowed to be instantiated. This is indicated by a "yes" value
value (the default value is "no"). (the default value is "no").
The following example specifies two output ports, the second being The following example specifies two output ports, the second being
an output port group: an output port group:
<outputPorts> <outputPorts>
<outputPort> <outputPort>
<name>out</name> <name>out</name>
<synopsis>Normal output</synopsis> <synopsis>Normal output</synopsis>
<product> <product>
<frameProduced> <frameProduced>
skipping to change at page 54, line 19 skipping to change at page 57, line 29
inside the <product> element in each <outputPort>. Within the inside the <product> element in each <outputPort>. Within the
<product> element, the list of frame types the port produces is <product> element, the list of frame types the port produces is
listed in the <frameProduced> element. When more than one frame is listed in the <frameProduced> element. When more than one frame is
listed, it means that "one of" these frames will be produced. listed, it means that "one of" these frames will be produced.
The list of metadata that is produced with each packet is listed in The list of metadata that is produced with each packet is listed in
the optional <metadataProduced> element of the <product>. In its the optional <metadataProduced> element of the <product>. In its
simplest form, this element can contain a list of <ref> elements, simplest form, this element can contain a list of <ref> elements,
each referring to a metadata type. The meaning of such a list is each referring to a metadata type. The meaning of such a list is
that "all of" these metadata are provided with each packet, except that "all of" these metadata are provided with each packet, except
those that are listed with the optional "availability" attribute those that are listed with the optional "availability" attribute set
set to "conditional". Similar to the <metadataExpected> element of to "conditional". Similar to the <metadataExpected> element of the
the <inputPort>, the <metadataProduced> element supports more <inputPort>, the <metadataProduced> element supports more complex
complex forms, which we do not discuss here further. forms, which we do not discuss here further.
4.7.4. <attributes> Element to Define LFB Operational Attributes 4.7.4. <attributes> Element to Define LFB Operational Attributes
Operational parameters of the LFBs that must be visible to the CEs Operational parameters of the LFBs that must be visible to the CEs
are conceptualized in the model as the LFB attributes. These are conceptualized in the model as the LFB attributes. These
include, for example, flags, single parameter arguments, complex include, for example, flags, single parameter arguments, complex
arguments, and tables. Note that the attributes here refer to only arguments, and tables. Note that the attributes here refer to only
those operational parameters of the LFBs that must be visible to those operational parameters of the LFBs that must be visible to the
the CEs. Other variables that are internal to LFB implementation CEs. Other variables that are internal to LFB implementation are
are not regarded as LFB attributes and hence are not covered. not regarded as LFB attributes and hence are not covered.
Some examples for LFB attributes are: Some examples for LFB attributes are:
. Configurable flags and switches selecting between operational . Configurable flags and switches selecting between operational
modes of the LFB modes of the LFB
. Number of inputs or ouputs in a port group . Number of inputs or outputs in a port group
. Metadata CONSUME vs. PROPAGATE mode selectors . Metadata CONSUME vs. PROPAGATE mode selectors
. Various configurable lookup tables, including interface . Various configurable lookup tables, including interface tables,
tables, prefix tables, classification tables, DSCP mapping prefix tables, classification tables, DSCP mapping tables, MAC
tables, MAC address tables, etc. address tables, etc.
. Packet and byte counters . Packet and byte counters
. Various event counters . Various event counters
. Number of current inputs or outputs for each input or output . Number of current inputs or outputs for each input or output
group group
. Metadata CONSUME/PROPAGATE mode selector . Metadata CONSUME/PROPAGATE mode selector
There may be various access permission restrictions on what the CE There may be various access permission restrictions on what the CE
can do with an LFB attribute. The following categories may be can do with an LFB attribute. The following categories may be
supported: supported:
. No-access attributes. This is useful when multiple access . No-access attributes. This is useful when multiple access
modes maybe defined for a given attribute to allow some modes maybe defined for a given attribute to allow some
flexibility for different implementations. flexibility for different implementations.
. Read-only attributes. . Read-only attributes.
. Read-write attributes. . Read-write attributes.
. Write-only attributes. This could be any configurable data . Write-only attributes. This could be any configurable data for
for which read capability is not provided to the CEs. (e.g., which read capability is not provided to the CEs. (e.g., the
the security key information) security key information)
. Read-reset attributes. The CE can read and reset this . Read-reset attributes. The CE can read and reset this
resource, but cannot set it to an arbitrary value. Example: resource, but cannot set it to an arbitrary value. Example:
Counters. Counters.
. Firing-only attributes. A write attempt to this resource will . Firing-only attributes. A write attempt to this resource will
trigger some specific actions in the LFB, but the actual value trigger some specific actions in the LFB, but the actual value
written is ignored. written is ignored.
The LFB class may define more than one possible access mode for a The LFB class may define more than one possible access mode for a
given attribute (for example, "write-only" and "read-write"), in given attribute (for example, "write-only" and "read-write"), in
which case it is left to the actual implementation to pick one of which case it is left to the actual implementation to pick one of
the modes. In such cases a corresponding capability attribute must the modes. In such cases, a corresponding capability attribute must
inform the CE about the access mode the actual LFB instance inform the CE about the access mode the actual LFB instance supports
supports (see next subsection on capability attributes). (see next subsection on capability attributes).
The attributes of the LFB class are listed in the <attributes> The attributes of the LFB class are listed in the <attributes>
element. Each attribute is defined by an <attribute> element. An element. Each attribute is defined by an <attribute> element. An
<attribute> element contains the following elements: <attribute> element contains the following elements:
. <name> defines the name of the attribute. This name must be . <name> defines the name of the attribute. This name must be
unique among the attributes of the LFB class. Example: unique among the attributes of the LFB class. Example:
"version". "version".
. <synopsis> should provide a brief description of the purpose . <synopsis> should provide a brief description of the purpose of
of the attribute. the attribute.
. <optional/> indicates that this attribute is optional.
. The data type of the attribute can be defined either via a . The data type of the attribute can be defined either via a
reference to a predefined data type or providing a local reference to a predefined data type or providing a local
definition of the type. The former is provided by using the definition of the type. The former is provided by using the
<typeRef> element, which must refer to the unique name of an <typeRef> element, which must refer to the unique name of an
existing data type defined in the <dataTypeDefs> element in existing data type defined in the <dataTypeDefs> element in the
the same library document or in any of the included library same library document or in any of the included library
documents. When the data type is defined locally (unnamed documents. When the data type is defined locally (unnamed
type), one of the following elements can be used: <atomic>, type), one of the following elements can be used: <atomic>,
<array>, <struct>, and <union>. Their usage is identical to <array>, <struct>, and <union>. Their usage is identical to how
how they are used inside <dataTypeDef> elements (see Section they are used inside <dataTypeDef> elements (see Section 4.5).
4.5). . The optional <defaultValue> element can specify a default value
. The optional <defaultValue> element can specify a default for the attribute, which is applied when the LFB is initialized
value for the attribute, which is applied when the LFB is or reset. [EDITOR: A convention to define default values for
initialized or reset. [EDITOR: A convention to define default compound data types and byte[N] atomic types is yet to be
values for compound data types and byte[N] atomic types is yet defined.]
to be defined.]
The attribute element also has a mandatory elementID attribute,
which is a numeric value used by the ForCES protocol.
In addition to the above elements, the <attribute> element includes In addition to the above elements, the <attribute> element includes
an optional "access" attribute, which can take any of the following an optional "access" attribute, which can take any of the following
values or even a list of these values: "read-only", "read-write", values or even a list of these values: "read-only", "read-write",
"write-only", "read-reset", and "trigger-only". The default access "write-only", "read-reset", and "trigger-only". The default access
mode is "read-write". mode is "read-write".
The following example defines two attributes for an LFB: The following example defines two attributes for an LFB:
<attributes> <attributes>
<attribute access="read-only"> <attribute access="read-only" elementID=÷1÷>
<name>foo</name> <name>foo</name>
<synopsis>number of things</synopsis> <synopsis>number of things</synopsis>
<typeRef>uint32</typeRef> <typeRef>uint32</typeRef>
</attribute> </attribute>
<attribute access="read-write write-only"> <attribute access="read-write write-only" elementID=÷2÷>
<name>bar</name> <name>bar</name>
<synopsis>number of this other thing</synopsis> <synopsis>number of this other thing</synopsis>
<atomic> <atomic>
<baseType>uint32</baseType> <baseType>uint32</baseType>
<rangeRestriction> <rangeRestriction>
<allowedRange min="10" max="2000"/> <allowedRange min="10" max="2000"/>
</rangeRestriction> </rangeRestriction>
</atomic> </atomic>
<defaultValue>10</defaultValue> <defaultValue>10</defaultValue>
</attribute> </attribute>
</attributes> </attributes>
The first attribute ("foo") is a read-only 32-bit unsigned integer, The first attribute ("foo") is a read-only 32-bit unsigned integer,
defined by referring to the built-in "uint32" atomic type. The defined by referring to the built-in "uint32" atomic type. The
second attribute ("bar") is also an integer, but uses the <atomic> second attribute ("bar") is also an integer, but uses the <atomic>
element to provide additional range restrictions. This attribute element to provide additional range restrictions. This attribute has
has two possible access modes, "read-write" or "write-only". A two possible access modes, "read-write" or "write-only". A default
default value of 10 is provided. value of 10 is provided.
Note that not all attributes are likely to exist at all times in a Note that not all attributes are likely to exist at all times in a
particular implementation. While the capabilities will frequently particular implementation. While the capabilities will frequently
indicate this non-existence, CEs may attempt to reference non- indicate this non-existence, CEs may attempt to reference non-
existent or non-permitted attributes anyway. The FORCES protocol existent or non-permitted attributes anyway. The FORCES protocol
mechanisms should include appropriate error indicators for this mechanisms should include appropriate error indicators for this
case. case.
The mechanism defined above for non-supported attributes can also The mechanism defined above for non-supported attributes can also
apply to attempts to reference non-existent array elements or to apply to attempts to reference non-existent array elements or to set
set read-only elements. read-only elements.
4.7.5. <capabilities> Element to Define LFB Capability Attributes 4.7.5. <capabilities> Element to Define LFB Capability Attributes
The LFB class specification will provide some flexibility for the The LFB class specification will provide some flexibility for the FE
FE implementation regarding how the LFB class is implemented. For implementation regarding how the LFB class is implemented. For
example, the class may define some optional features, in which case example, the class may define some optional features, in which case
the actual implementation may or may not provide the given feature. the actual implementation may or may not provide the given feature.
In these cases the CE must be able to query the LFB instance about In these cases the CE must be able to query the LFB instance about
the availability of the feature. In addition, the instance may the availability of the feature. In addition, the instance may have
have some limitations that are not inherent from the class some limitations that are not inherent from the class definition,
definition, but rather the result of some implementation but rather the result of some implementation limitations. For
limitations. For example, an array attribute may be defined in the example, an array attribute may be defined in the class definition
class definition as "unlimited" size, but the physical as "unlimited" size, but the physical implementation may impose a
implementation may impose a hard limit on the size of the array. hard limit on the size of the array.
Such capability related information is expressed by the capability Such capability related information is expressed by the capability
attributes of the LFB class. The capability attributes are always attributes of the LFB class. The capability attributes are always
read-only attributes, and they are listed in a separate read-only attributes, and they are listed in a separate
<capabilities> element in the <LFBClassDef>. The <capabilities> <capabilities> element in the <LFBClassDef>. The <capabilities>
element contains one or more <capability> elements, each defining element contains one or more <capability> elements, each defining
one capability attribute. The format of the <capability> element one capability attribute. The format of the <capability> element is
is almost the same as the <attribute> element, it differs in two almost the same as the <attribute> element, it differs in two
aspects: it lacks the access mode attribute (because it is always aspects: it lacks the access mode attribute (because it is always
read-only), and it lacks the <defaultValue> element (because read-only), and it lacks the <defaultValue> element (because default
default value is not applicable to read-only attributes). value is not applicable to read-only attributes).
Some examples of capability attributes: Some examples of capability attributes:
. The version of the LFB class that this LFB instance complies . The version of the LFB class that this LFB instance complies
with; with;
. Supported optional features of the LFB class; . Supported optional features of the LFB class;
. Maximum number of configurable outputs for an output group; . Maximum number of configurable outputs for an output group;
. Metadata pass-through limitations of the LFB; . Metadata pass-through limitations of the LFB;
. Maximum size of configurable attribute tables; . Maximum size of configurable attribute tables;
. Additional range restriction on operational attributes; . Additional range restriction on operational attributes;
. Supported access modes of certain attributes (if the access . Supported access modes of certain attributes (if the access
mode of an operational attribute is specified as a list of two mode of an operational attribute is specified as a list of two
or mode modes). or mode modes).
The following example lists two capability attributes: The following example lists two capability attributes:
<capabilities> <capabilities>
<capability> <capability elementID="3">
<name>version</name> <name>version</name>
<synopsis> <synopsis>
LFB class version this instance is compliant with. LFB class version this instance is compliant with.
</synopsis> </synopsis>
<typeRef>version</typeRef> <typeRef>version</typeRef>
</capability> </capability>
<capability> <capability elementID="4">
<name>limitBar</name> <name>limitBar</name>
<synopsis> <synopsis>
Maximum value of the "bar" attribute. Maximum value of the "bar" attribute.
</synopsis> </synopsis>
<typeRef>uint16</typeRef> <typeRef>uint16</typeRef>
</capability> </capability>
</capabilities> </capabilities>
4.7.6. <description> Element for LFB Operational Specification 4.7.6. <description> Element for LFB Operational Specification
skipping to change at page 60, line 13 skipping to change at page 63, line 25
<xsd:element ref="description" minOccurs="0"/> <xsd:element ref="description" minOccurs="0"/>
<xsd:group ref="typeDeclarationGroup"/> <xsd:group ref="typeDeclarationGroup"/>
</xsd:sequence> </xsd:sequence>
</xsd:complexType> </xsd:complexType>
</xsd:element> </xsd:element>
</xsd:sequence> </xsd:sequence>
</xsd:complexType> </xsd:complexType>
<!-- <!--
Predefined (built-in) atomic data-types are: Predefined (built-in) atomic data-types are:
char, uchar, int16, uint16, int32, uint32, int64, uint64, char, uchar, int16, uint16, int32, uint32, int64, uint64,
string[N], byte[N], string[N], byte[N], boolean,
float16, float32, float64 float16, float32, float64
--> -->
<xsd:group name="typeDeclarationGroup"> <xsd:group name="typeDeclarationGroup">
<xsd:choice> <xsd:choice>
<xsd:element name="typeRef" type="typeRefNMTOKEN"/> <xsd:element name="typeRef" type="typeRefNMTOKEN"/>
<xsd:element name="atomic" type="atomicType"/> <xsd:element name="atomic" type="atomicType"/>
<xsd:element name="array" type="arrayType"/> <xsd:element name="array" type="arrayType"/>
<xsd:element name="struct" type="structType"/> <xsd:element name="struct" type="structType"/>
<xsd:element name="union" type="structType"/> <xsd:element name="union" type="structType"/>
<xsd:element name=÷alias÷ type="typeRefNMTOKEN"/>
</xsd:choice> </xsd:choice>
</xsd:group> </xsd:group>
<xsd:simpleType name="typeRefNMTOKEN"> <xsd:simpleType name="typeRefNMTOKEN">
<xsd:restriction base="xsd:token"> <xsd:restriction base="xsd:token">
<xsd:pattern value="\c+"/> <xsd:pattern value="\c+"/>
<xsd:pattern value="string\[\d+\]"/> <xsd:pattern value="string\[\d+\]"/>
<xsd:pattern value="byte\[\d+\]"/> <xsd:pattern value="byte\[\d+\]"/>
</xsd:restriction> </xsd:restriction>
</xsd:simpleType> </xsd:simpleType>
<xsd:complexType name="atomicType"> <xsd:complexType name="atomicType">
skipping to change at page 61, line 22 skipping to change at page 64, line 35
<xsd:element ref="synopsis"/> <xsd:element ref="synopsis"/>
</xsd:sequence> </xsd:sequence>
<xsd:attribute name="value" type="xsd:token"/> <xsd:attribute name="value" type="xsd:token"/>
</xsd:complexType> </xsd:complexType>
</xsd:element> </xsd:element>
</xsd:sequence> </xsd:sequence>
</xsd:complexType> </xsd:complexType>
<xsd:complexType name="arrayType"> <xsd:complexType name="arrayType">
<xsd:sequence> <xsd:sequence>
<xsd:group ref="typeDeclarationGroup"/> <xsd:group ref="typeDeclarationGroup"/>
<xsd:element name="key" maxOccurs="unbounded">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="keyField" maxOccurs="unbound"
type="xsd:string"/>
</xsd:sequence>
<xsd:attribute name="keyID" use="required"
type="xsd:integer"/>
</xsd:complexType>
</xsd:element>
</xsd:sequence> </xsd:sequence>
<xsd:attribute name="type" use="optional" <xsd:attribute name="type" use="optional"
default="variable-size"> default="variable-size">
<xsd:simpleType> <xsd:simpleType>
<xsd:restriction base="xsd:string"> <xsd:restriction base="xsd:string">
<xsd:enumeration value="fixed-size"/> <xsd:enumeration value="fixed-size"/>
<xsd:enumeration value="variable-size"/> <xsd:enumeration value="variable-size"/>
</xsd:restriction> </xsd:restriction>
</xsd:simpleType> </xsd:simpleType>
</xsd:attribute> </xsd:attribute>
<xsd:attribute name="length" type="xsd:integer" use="optional"/> <xsd:attribute name="length" type="xsd:integer" use="optional"/>
<xsd:attribute name="maxLength" type="xsd:integer" <xsd:attribute name="maxLength" type="xsd:integer"
use="optional"/> use="optional"/>
<!¨declare keys to have unique IDs -->
<xsd:key name="keyID">
<xsd:selector xpath="lfb:key"/>
<xsd:field xpath="@keyID"/>
</xsd:key>
</xsd:complexType> </xsd:complexType>
<xsd:complexType name="structType"> <xsd:complexType name="structType">
<xsd:sequence> <xsd:sequence>
<xsd:element name="element" maxOccurs="unbounded"> <xsd:element name="element" maxOccurs="unbounded">
<xsd:complexType> <xsd:complexType>
<xsd:sequence> <xsd:sequence>
<xsd:element name="name" type="xsd:NMTOKEN"/> <xsd:element name="name" type="xsd:NMTOKEN"/>
<xsd:element ref="synopsis"/> <xsd:element ref="synopsis"/>
<xsd:element name="optional" minOccurs="0"/>
<xsd:group ref="typeDeclarationGroup"/> <xsd:group ref="typeDeclarationGroup"/>
</xsd:sequence> </xsd:sequence>
<xsd:attribute name="elementID" use="required"
type="xsd:integer"/>
</xsd:complexType> </xsd:complexType>
</xsd:element> </xsd:element>
</xsd:sequence> </xsd:sequence> <xsd:attribute name="derivedFrom" use="optional"
type="typeRefNMTOKEN"/>
<!-- key declaration to make elementIDs unique in a struct -->
<xsd:key name="structElementID">
<xsd:selector xpath="lfb:element"/>
<xsd:field xpath="@elementID"/>
</xsd:key>
</xsd:complexType> </xsd:complexType>
<xsd:complexType name="metadataDefsType"> <xsd:complexType name="metadataDefsType">
<xsd:sequence> <xsd:sequence>
<xsd:element name="metadataDef" maxOccurs="unbounded"> <xsd:element name="metadataDef" maxOccurs="unbounded">
<xsd:complexType> <xsd:complexType>
<xsd:sequence> <xsd:sequence>
<xsd:element name="name" type="xsd:NMTOKEN"/> <xsd:element name="name" type="xsd:NMTOKEN"/>
<xsd:element ref="synopsis"/> <xsd:element ref="synopsis"/>
<xsd:element ref="description" minOccurs="0"/> <xsd:element ref="description" minOccurs="0"/>
<xsd:choice> <xsd:choice>
skipping to change at page 62, line 39 skipping to change at page 66, line 29
<xsd:element name="inputPorts" type="inputPortsType" <xsd:element name="inputPorts" type="inputPortsType"
minOccurs="0"/> minOccurs="0"/>
<xsd:element name="outputPorts" type="outputPortsType" <xsd:element name="outputPorts" type="outputPortsType"
minOccurs="0"/> minOccurs="0"/>
<xsd:element name="attributes" type="LFBAttributesType" <xsd:element name="attributes" type="LFBAttributesType"
minOccurs="0"/> minOccurs="0"/>
<xsd:element name="capabilities" <xsd:element name="capabilities"
type="LFBCapabilitiesType" minOccurs="0"/> type="LFBCapabilitiesType" minOccurs="0"/>
<xsd:element ref="description" minOccurs="0"/> <xsd:element ref="description" minOccurs="0"/>
</xsd:sequence> </xsd:sequence>
<xsd:attribute name="LFBClassID" use="required"
type="xsd:integer"/>
</xsd:complexType> </xsd:complexType>
<!-- Key constraint to ensure unique attribute names within <!-- Key constraint to ensure unique attribute names within
a class: a class:
--> -->
<xsd:key name="attributes"> <xsd:key name="attributes">
<xsd:selector xpath="lfb:attributes/lfb:attribute"/> <xsd:selector xpath="lfb:attributes/lfb:attribute"/>
<xsd:field xpath="lfb:name"/> <xsd:field xpath="lfb:name"/>
</xsd:key> </xsd:key>
<xsd:key name="capabilities"> <xsd:key name="capabilities">
<xsd:selector xpath="lfb:capabilities/lfb:capability"/> <xsd:selector xpath="lfb:capabilities/lfb:capability"/>
<xsd:field xpath="lfb:name"/> <xsd:field xpath="lfb:name"/>
</xsd:key> </xsd:key>
<! í does the above ensure that attributes and capabilities
have different names?
If so, the following is the elementID constraint .
<xsd:key name="attributeIDs">
<xsd:selector xpath="lfb:attributes/lfb:attribute"/>
<xsd:field xpath="@elementID"/>
</xsd:key>
<xsd:key name="capabilityIDs">
<xsd:selector xpath="lfb:attributes/lfb:capability"/>
<xsd:field xpath="@elementID"/>
</xsd:key>
</xsd:element> </xsd:element>
</xsd:sequence> </xsd:sequence>
</xsd:complexType> </xsd:complexType>
<xsd:simpleType name="versionType"> <xsd:simpleType name="versionType">
<xsd:restriction base="xsd:NMTOKEN"> <xsd:restriction base="xsd:NMTOKEN">
<xsd:pattern value="[1-9][0-9]*\.([1-9][0-9]*|0)"/> <xsd:pattern value="[1-9][0-9]*\.([1-9][0-9]*|0)"/>
</xsd:restriction> </xsd:restriction>
</xsd:simpleType> </xsd:simpleType>
<xsd:complexType name="inputPortsType"> <xsd:complexType name="inputPortsType">
<xsd:sequence> <xsd:sequence>
skipping to change at page 66, line 19 skipping to change at page 70, line 22
</xsd:simpleContent> </xsd:simpleContent>
</xsd:complexType> </xsd:complexType>
<xsd:complexType name="LFBAttributesType"> <xsd:complexType name="LFBAttributesType">
<xsd:sequence> <xsd:sequence>
<xsd:element name="attribute" maxOccurs="unbounded"> <xsd:element name="attribute" maxOccurs="unbounded">
<xsd:complexType> <xsd:complexType>
<xsd:sequence> <xsd:sequence>
<xsd:element name="name" type="xsd:NMTOKEN"/> <xsd:element name="name" type="xsd:NMTOKEN"/>
<xsd:element ref="synopsis"/> <xsd:element ref="synopsis"/>
<xsd:element ref="description" minOccurs="0"/> <xsd:element ref="description" minOccurs="0"/>
<xsd:element name="optional" minOccurs="0"/>
<xsd:group ref="typeDeclarationGroup"/> <xsd:group ref="typeDeclarationGroup"/>
<xsd:element name="defaultValue" type="xsd:token" <xsd:element name="defaultValue" type="xsd:token"
minOccurs="0"/> minOccurs="0"/>
</xsd:sequence> </xsd:sequence>
<xsd:attribute name="access" use="optional" <xsd:attribute name="access" use="optional"
default="read-write"> default="read-write">
<xsd:simpleType> <xsd:simpleType>
<xsd:list itemType="accessModeType"/> <xsd:list itemType="accessModeType"/>
</xsd:simpleType> </xsd:simpleType>
</xsd:attribute> </xsd:attribute>
<xsd:attribute name="elementID" use="required"
type="xsd:integer"/>
</xsd:complexType> </xsd:complexType>
</xsd:element> </xsd:element>
</xsd:sequence> </xsd:sequence>
</xsd:complexType> </xsd:complexType>
<xsd:simpleType name="accessModeType"> <xsd:simpleType name="accessModeType">
<xsd:restriction base="xsd:NMTOKEN"> <xsd:restriction base="xsd:NMTOKEN">
<xsd:enumeration value="read-only"/> <xsd:enumeration value="read-only"/>
<xsd:enumeration value="read-write"/> <xsd:enumeration value="read-write"/>
<xsd:enumeration value="write-only"/> <xsd:enumeration value="write-only"/>
<xsd:enumeration value="read-reset"/> <xsd:enumeration value="read-reset"/>
skipping to change at page 66, line 50 skipping to change at page 71, line 9
</xsd:restriction> </xsd:restriction>
</xsd:simpleType> </xsd:simpleType>
<xsd:complexType name="LFBCapabilitiesType"> <xsd:complexType name="LFBCapabilitiesType">
<xsd:sequence> <xsd:sequence>
<xsd:element name="capability" maxOccurs="unbounded"> <xsd:element name="capability" maxOccurs="unbounded">
<xsd:complexType> <xsd:complexType>
<xsd:sequence> <xsd:sequence>
<xsd:element name="name" type="xsd:NMTOKEN"/> <xsd:element name="name" type="xsd:NMTOKEN"/>
<xsd:element ref="synopsis"/> <xsd:element ref="synopsis"/>
<xsd:element ref="description" minOccurs="0"/> <xsd:element ref="description" minOccurs="0"/>
<xsd:element name="optional" minOccurs="0"/>
<xsd:group ref="typeDeclarationGroup"/> <xsd:group ref="typeDeclarationGroup"/>
</xsd:sequence> </xsd:sequence>
<xsd:attribute name="elementID" use="required"
type="xsd:integer"/>
</xsd:complexType> </xsd:complexType>
</xsd:element> </xsd:element>
</xsd:sequence> </xsd:sequence>
</xsd:complexType> </xsd:complexType>
<xsd:simpleType name="booleanType"> <xsd:simpleType name="booleanType">
<xsd:restriction base="xsd:string"> <xsd:restriction base="xsd:string">
<xsd:enumeration value="yes"/> <xsd:enumeration value="yes"/>
<xsd:enumeration value="no"/> <xsd:enumeration value="no"/>
</xsd:restriction> </xsd:restriction>
</xsd:simpleType> </xsd:simpleType>
</xsd:schema> </xsd:schema>
5. FE Attributes and Capabilities 5.
FE Attributes and Capabilities
A ForCES forwarding element handles traffic on behalf of a ForCES A ForCES forwarding element handles traffic on behalf of a ForCES
control element. While the standards will describe the protocol control element. While the standards will describe the protocol and
and mechanisms for this control, different implementations and mechanisms for this control, different implementations and different
different instances will have different capabilities. The CE needs instances will have different capabilities. The CE needs to be able
to be able to determine what each instance it is responsible for is to determine what each instance it is responsible for is actually
actually capable of doing. As stated previously, this is an capable of doing. As stated previously, this is an approximation.
approximation. The CE is expected to be prepared to cope with The CE is expected to be prepared to cope with errors in requests
errors in requests and variations in detail not captured by the and variations in detail not captured by the capabilities
capabilities information about an FE. information about an FE.
In addition to its capabilities, an FE will have some information In addition to its capabilities, an FE will have attribute
(attributes) that can be used in understanding and controlling the information that can be used in understanding and controlling the
forwarding operations. Some of the attributes will be read only, forwarding operations. Some of the attributes will be read only,
while others will also be writeable. while others will also be writeable.
The ForCES protocol will define the actual mechanism for getting In order to make the FE attribute information easily accessible, the
and setting attribute information. This model defines the starting information will be stored in an LFB. This LFB will have a class,
set of information that will be available. This definition FEObject. The LFBClassID for this class is 1. Only one instance of
includes the semantics and the structuring of the information. It this class will ever be present, and the instance ID of that
also provides for extensions to this information. instance in the protocol is 1. Thus, by referencing the elements of
class:1, instance:1 a CE can get all the information about the FE.
In order to crisply define the attribute information and structure, For model completeness, this LFB Class is described in this section.
this document describes the attributes as information in an
abstract XML document. Conceptually, each FE contains such a
document. The document structure is defined by the XML Schema
contained in this model. Operationally, the ForCES protocol refers
to information contained in that document in order to read or write
FE attributes and capabilities. This document is an abstract
representation of the information. There is no requirement that
such a document actually exist in memory. Unless the ForCES
protocol calls for transfer of the information in XML, the
information is not required to ever be represented in the FE in
XML. The XML schema serves only to identify the elements and
structure of the information.
The subsections in this part of the document provide the details on There will also be an FEProtocol LFB Class. LFBClassID 2 is
this aspect of the FE model. 5.1 gives the XML schema for the reserved for that class. There will be only one instance of that
abstract FE attribute document. 5.2 elaborates on each of the class as well. Details of that class are defined in the ForCES
defined attributes of the FE, following the hierarchy of the protocol document.
schema. 5.3 provides an example XML FE attribute document to
clarify the meaning of 5.1 and 5.2.
5.1. XML Schema for FE Attribute Documents 5.1. XML for FEObject Class definition
<?xml version="1.0" encoding="UTF-8"?> <?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <LFBLibrary xmlns="http://ietf.org/forces/1.0/lfbmodel"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
<xsd:annotation> xsi:schemaLocation="http://ietf.org/forces/1.0/lfbmodel
<xsd:documentation xml:lang="en"> provides="FEObject">
Schema for the Abstract FE Attributes and Capabilities Document <dataTypeDefs>
</xsd:documentation> <dataTypeDef>
</xsd:annotation> <name>LFBAdjacencyLimitType</name>
<synopsis>Describing the Adjacent LFB</synopsis>
<xsd:element name="FEDocument"> <struct>
<xsd:complexType> <element elementID="1">
<xsd:sequence> <name>NeighborLFB</name>
<xsd:element name="FECapabilities" type="FECapabilitiesType" <synopsis>ID for that LFB Class</synopsis>
minOccurs="0" maxOccurs="1"/> <typeRef>uint32</typeRef>
<xsd:element name="FEAttributes" type="FEAttributesType" </element>
minOccurs="0" maxOccurs="1"/> <element elementID="2">
</xsd:sequence> <name>ViaPorts</name>
</xsd:complexType> <synopsis>
</xsd:element> the ports on which we can connect
</synopsis>
<xsd:complexType name="FECapabilitiesType"> <array type="variable-size">
<xsd:sequence> <!-- It is necessary to define the length limit
<xsd:element name="ModifiableLFBTopology" type="xsd:boolean" This should be whatever we define elsewhere as the
minOccurs="0" maxOccurs="1"/> limit of a port name
<xsd:element name="SupportedLFBs" minOccurs="0" maxOccurs="1"> -->
<xsd:complexType> <typeRef>String[40]</typeRef>
<xsd:sequence> </array>
<xsd:element name="SupportedLFB" type="SupportedLFBType" </element>
minOccurs="1" maxOccurs="unbounded"/> </struct>
</xsd:sequence> </dataTypeDef>
</xsd:complexType> <dataTypeDef>
</xsd:element> <name>PortGroupLimitType</name>
<xsd:element name="SupportedAttributes" <synopsis>
type="SupportedAttributesType" Limits on the number of ports in a given group
minOccurs="0" maxOccurs="1"/> </synopsis>
</xsd:sequence> <struct>
</xsd:complexType> <element elementID="1">
<name>PortGroupName</name>
<xsd:complexType name="SupportedLFBType"> <synopsis>Group Name</synopsis>
<xsd:sequence> <!-- Again, a length limit is needed -->
<!-- the name of a supported LFB --> <typeRef>String[4]</typeRef>
<xsd:element name="LFBName" type="xsd:NMTOKEN"/> </element>
<!-- how many of this LFB class can exist --> <element elementID="2">
<xsd:element name="LFBOccurrenceLimit" <name>MinPortCount</name>
type="xsd:nonNegativeInteger" minOccurs="0" maxOccurs="1"/> <synopsis>Minimum Port Count</synopsis>
<optional/>
<typeRef>uint32</typeRef>
</element>
<element elementID="3">
<name>MaxPortCount</name>
<synopsis>Max Port Count</synopsis>
<optional/>
<typeRef>uint32</typeRef>
</element>
</struct>
</dataTypeDef>
<dataTypeDef>
<name>SupportedLFBType</name>
<synopsis>table entry for supported LFB</synopsis>
<struct>
<element elementID="1">
<name>LFBName</name>
<synopsis>
The name of a supported LFB Class
</synopsis>
<!-- again with the length limit -->
<typeRef>string[40]</typeRef>
</element>
<element elementID="2">
<name>LFBClassID</name>
<synopsis>the id of a supported LFB Class</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID="3">
<name>LFBOccurrenceLimit</name>
<synopsis>
the upper limit of instances of LFBs of this class
</synopsis>
<optional/>
<typeRef>uint32</typeRef>
</element>
<!-- For each port group, how many ports can exist --> <!-- For each port group, how many ports can exist -->
<xsd:element name="PortGroupLimits" minOccurs="0" maxOccurs="1"> <element elementID="4">
<xsd:complexType> <name>PortGroupLimits</name>
<xsd:sequence> <synopsis>Table of Port Group Limits</synopsis>
<xsd:element name="PortGroupLimit" minOccurs="0" <optional/>
maxOccurs="unbounded"> <array type="variable-size">
<xsd:complexType> <typeRef>PortGroupLimitType</typeRef>
<xsd:sequence> </array>
<xsd:element name="PortGroupName" type="xsd:NMTOKEN"/> </element>
<xsd:element name="MinPortCount"
type="xsd:nonNegativeInteger"
minOccurs="0" maxOccurs="1"/>
<xsd:element name="MaxPortCount"
type="xsd:nonNegativeInteger"
minOccurs="0" maxOccurs="1"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<!-- for the named LFB Class, the LFB Classes it may follow --> <!-- for the named LFB Class, the LFB Classes it may follow -->
<xsd:element name="CanOccurAfters" minOccurs="0" maxOccurs="1"> <element elementID="5">
<xsd:complexType> <name>CanOccurAfters</name>
<xsd:sequence> <synopsis>
<xsd:element name="CanOccurAfter" List of LFB Classes that this LFB class can follow
type="LFBAdjacencyLimitType" </synopsis>
minOccurs="0" maxOccurs="unbounded"/> <optional/>
</xsd:sequence> <array type="variable-size">
</xsd:complexType> <typeRef>LFBAdjacencyLimitType</typeRef>
</xsd:element> </array>
</element>
<!-- for the named LFB Class, which LFB Classes may follow --> <!-- for the named LFB Class, the LFB Classes that may follow it
<xsd:element name="CanOccurBefores" minOccurs="0" maxOccurs="1"> -->
<xsd:complexType> <element elementID="6">
<xsd:sequence> <name>CanOccurBefores</name>
<xsd:element name="CanOccurBefore" <synopsis>
type="LFBAdjacencyLimitType" List of LFB Classes that can follow this LFB class
minOccurs="0" maxOccurs="unbounded"/> </synopsis>
</xsd:sequence> <optional/>
</xsd:complexType> <array type="variable-size">
</xsd:element> <typeRef>LFBAdjacencyLimitType</typeRef>
<!-- information defined by the Class Definition --> </array>
<xsd:element name="LFBClassCapabilities" type="xsd:anyType" </element>
minOccurs="0" maxOccurs="1"/> </struct>
</xsd:sequence> </dataTypeDef>
</xsd:complexType> <dataTypeDef>
<name>FEStatusValues</name>
<xsd:complexType name="LFBAdjacencyLimitType"> <synopsis>The possible values of status</synopsis>
<xsd:sequence> <atomic>
<xsd:element name="NeighborLFB" type="xsd:NMTOKEN"/> <baseType>uchar</baseType>
<xsd:element name="viaPort" type="xsd:NMTOKEN" <specialValues>
minOccurs="0" maxOccurs="unbounded"/> <specialValue value="0">
</xsd:sequence> <name> AdminDisable </name>
</xsd:complexType> <synopsis>
FE is administratively disabled
<xsd:complexType name="SupportedAttributesType"> </synopsis>
<xsd:sequence> </specialValue>
<xsd:element name="SupportedAttribute" <specialValue value="1">
minOccurs="0" maxOccurs="unbounded"> <name>OperDisable</name>
<xsd:complexType> <synopsis>FE is operatively disabled</synopsis>
<xsd:sequence> </specialValue>
<xsd:element name="AttributeName" type="xsd:NMTOKEN"/> <specialValue value="2">
<xsd:element name="AccessModes" type="xsd:NMTOKEN"/> <name> Operenable </name>
</xsd:sequence> <synopsis>FE is operating</synopsis>
</xsd:complexType> </specialValue>
</xsd:element> </specialValues>
</xsd:sequence> </atomic>
</xsd:complexType> </dataTypeDef>
<dataTypeDef>
<xsd:complexType name="FEAttributesType"> <name>FEConfiguredNeighborType</name>
<xsd:sequence> <synopsis>Details of the FE's Neighbor</synopsis>
<xsd:element name="Vendor" type="xsd:string" minOccurs="0"/> <struct>
<xsd:element name="Model" type="xsd:string" minOccurs="0"/> <element elementID="1">
<xsd:element name="FEStatus" type="FEStateType" minOccurs="0"/> <name>NeighborID</name>
<xsd:element name="LFBInstances" minOccurs="0" maxOccurs="1"> <synopsis>Neighbors FEID</synopsis>
<xsd:complexType> <typeRef>uint32</typeRef>
<xsd:sequence> </element>
<xsd:element name="LFBInstance" minOccurs="0" <element elementID="2">
maxOccurs="unbounded"> <name>interfaceToNeighbor</name>
<xsd:complexType> <synopsis>
<xsd:sequence> FE's interface that connects to this neighbor
<xsd:element name="LFBClassName" type="xsd:NMTOKEN"/>"> </synopsis>
<xsd:element name="LFBInstanceID" type="xsd:NMTOKEN"/>"> <optional/>
</xsd:sequence> <!-- the length here is the length of interface name.
</xsd:complexType> It is unfortunate to have to limit it, since it has
</xsd:element> nothing to do with the model
</xsd:sequence> -->
</xsd:complexType> <typeRef>String[20]</typeRef>
</xsd:element> </element>
<xsd:element name="LFBTopology" type="LFBTopologyType" <element elementID="3">
minOccurs="0" maxOccurs="1"/> <name>neighborNetworkAddress</name>
<xsd:element name="FEConfiguredNeighbors" minOccurs="0" <synopsis>The network layer address of the neighbor
maxOccurs="1"> Presumably, the network type can be
<xsd:complexType> determined from the interface information
<xsd:sequence> </synopsis>
<xsd:element name="FEConfiguredNeighbor" <typeRef>OctetSting[16]</typeRef>
type="FEConfiguredNeighborType" </element>
minOccurs="0" maxOccurs="unbounded"/> <element elementID="4">
</xsd:sequence> <name>neighborMACAdddress</name>
</xsd:complexType> <synopsis>the media access control address of
</xsd:element> the neighbor. Again, it is presumed
</xsd:sequence> the type can be determined
</xsd:complexType> from the interface information
</synopsis>
<xsd:complexType name="LFBTopologyType"> <typeRef>OctetString[8]</typeRef>
<xsd:sequence> </element>
<xsd:element name="LFBLink" minOccurs="0" maxOccurs="unbounded"> </struct>
<xsd:complexType> </dataTypeDef>
<xsd:sequence> <dataTypeDef>
<xsd:element name="FromLFBID" type="xsd:NMTOKEN"/> <name>AccessPermissionValues</name>
<xsd:element name="FromPortGroup" type="xsd:NMTOKEN"/> <synopsis>
<xsd:element name="FromPortIndex" The possible values of attribute access permission
type="xsd:nonNegativeInteger"/> </synopsis>
<xsd:element name="ToLFBID" type="xsd:NMTOKEN"/> <!-- can this use the access from the schema somehow? -->
<xsd:element name="ToPortGroup" type="xsd:NMTOKEN"/> <atomic>
<xsd:element name="ToPortIndex" <baseType>uchar</baseType>
type="xsd:nonNegativeInteger"/> <specialValues>
</xsd:sequence> <specialValue value="0">
</xsd:complexType> <name>None</name>
</xsd:element> <synopsis>Access is prohibited</synopsis>
</xsd:sequence> </specialValue>
</xsd:complexType> <specialValue value="1">
<name> Read-Only </name>
<xsd:complexType name="FEConfiguredNeighborType"> <synopsis>Access is read only</synopsis>
<xsd:sequence> </specialValue>
<xsd:element name="NeighborID" type="xsd:anyType"/> <specialValue value="2">
<xsd:element name="NeighborInterface" type="xsd:anyType"/> <name>Write-Only</name>
<xsd:element name="NeighborNetworkAddress" type="xsd:anyType" <synopsis>
minOccurs="0" maxOccurs="1"/> The attribute may be written, but not read
<xsd:element name="NeighborMACAddress" type="xsd:anyType" </synopsis>
minOccurs="0" maxOccurs="1"/> </specialValue>
</xsd:sequence> <specialValue value="3">
</xsd:complexType> <name>Read-Write</name>
<synopsis>
<!-- The values for the simple state attribute --> The attribute may be read or written
<!-- These should probably be directly encodable in the --> </synopsis>
<!-- protocol so they may end up numeric instead of strings --> </specialValue>
<xsd:simpleType name="FEStateType"> </specialValues>
<xsd:restriction base="xsd:NMTOKEN"> </atomic>
<xsd:enumeration value="AdminDisable"/> </dataTypeDef>
<xsd:enumeration value="OperDisable"/> <dataTypeDef>
<xsd:enumeration value="OperEnable"/> <name>SupportedAttributeType</name>
</xsd:restriction> <synopsis>
</xsd:simpleType> Mapping between attributes and access modes
</synopsis>
</xsd:schema> <struct>
<element elementID="1">
5.2. FEDocument <name>AttributeName</name>
<synopsis>
An instance of this document captures the capabilities and FE level Name of referenced Attribute
attribute / state information about a given FE. Currently, two </synopsis>
elements are allowed in the FEDocument, FECapabilities and <!-- the length limit issue again -->
FEAttributes. <typeRef>String[40]</typeRef>
</element>
At the moment, all capability and attribute information in this <element elementID=÷2÷>
abstract document is defined as optional. We may wish to mandate <name>AttributeID</name>
support for some capability and/or attribute information. <synopsis>
The ID in the FE Object of the attribute
If a protocol using binary encoding of this information is adopted </synopsis>
by the ForCES working group, then each relevant element defined in <typeRef>uint32</typeRef>
the schema will have a "ProtocolEncoding" attribute added, with a </element>
"Fixed" value providing the value that is used in the protocol for <element elementID="3">
that element, so that the XML and the on the wire protocol can be <name>AccessModes</name>
correlated. <synopsis>Access Modes</synopsis>
<typeRef>AccessPermissionValues</typeRef>
</element>
</struct>
</dataTypeDef>
<dataTypeDef>
<name>LFBSelectorType</name>
<synopsis>
Unique identification of a LFB class-instance
</synopsis>
<struct>
<element elementID="1">
<name>LFBClassID</name>
<synopsis>LFB Class Identifier</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID="2">
<name>LFBInstanceID</name>
<synopsis>LFB Instance ID</synopsis>
<typeRef>uint32</typeRef>
</element>
</struct>
</dataTypeDef>
<dataTypeDef>
<name>LFBLinkType</name>
<synopsis>
Link between two LFB instances of topology
</synopsis>
<struct>
<element elementID="1">
<name>FromLFBID</name>
<synopsis>LFB src</synopsis>
<typeRef>LFBSelector</typeRef>
</element>
<element elementID="2">
<name>FromPortGroup</name>
<synopsis>src port group</synopsis>
<!-- again the length limit on strings pops up -->
<typeRef>String[4]</typeRef>
</element>
<element elementID="3">
<name>FromPortIndex</name>
<synopsis>src port index</synopsis>
<typeRef>uint32</typeRef>
</element>
<element elementID="4">
<name>ToLFBID</name>
<synopsis>dst LFBID</synopsis>
<typeRef>LFBSelector</typeRef>
</element>
<element elementID="5">
<name>ToPortGroup</name>
<synopsis>dst port group</synopsis>
<!-- again the string length limit -->
<typeRef>String[40]</typeRef>
</element>
<element elementID="6">
<name>ToPortIndex</name>
<synopsis>dst port index</synopsis>
<typeRef>uint32</typeRef>
</element>
</struct>
</dataTypeDef>
</dataTypeDefs>
<LFBClassDefs>
<LFBClassDef LFBClassID="1">
<name>FEObject</name>
<synopsis>Core LFB: FE Object</synopsis>
<capabilities>
<capability elementID="30">
<name>ModifiableLFBTopology</name>
<synopsis>
Whether Modifiable LFB is supported
</synopsis>
<optional/>
<typeRef>boolean</typeRef>
</capability>
<capability elementID="31">
<name>SupportedLFBs</name>
<synopsis>List of all supported LFBs</synopsis>
<optional/>
<array type="variable-size">
<typeRef>SupportedLFBType</typeRef>
</array>
</capability>
<capability elementID="32">
<synopsis>List of attribute ACLs</synopsis>
<optional/>
<array type="variable-size">
<typeRef>SupportedAttributeType</typeRef>
</array>
</capability>
</capabilities>
<attributes>
<attribute access="read-write" elementID="1">
<name>LFBTopology</name>
<synopsis>the table of known Topologies</synopsis>
<array type="variable-size">
<typeRef>LFBLinkType</typeRef>
</array>
</attribute>
<attribute access="read-write" elementID="2">
<name>LFBSelectors</name>
<synopsis>
table of known active LFB classes and
instances
</synopsis>
<array type="variable-size">
<typeRef>LFBSelectorType</typeRef>
</array>
</attribute>
<attribute access="read-write" elementID="3">
<name>FEName</name>
<synopsis>name of this FE</synopsis>
<typeRef>string[40]</typeRef>
</attribute>
<attribute access="read-write" elementID="4">
<name>FEID</name>
<synopsis>ID of this FE</synopsis>
<typeRef>uint32</typeRef>
</attribute>
<attribute access="read-only" elementID="5">
<name>FEVendor</name>
<synopsis>vendor of this FE</synopsis>
<typeRef>string[40]</typeRef>
</attribute>
<attribute access="read-only" elementID="6">
<name>FEModel</name>
<synopsis>model of this FE</synopsis>
<typeRef>string[40]</typeRef>
</attribute>
<attribute access="read-only" elementID="7">
<name>FEState</name>
<synopsis>model of this FE</synopsis>
<typeRef>FEStatusValues</typeRef>
</attribute>
<attribute access="read-write" elementID="8">
<name>FENeighbors</name>
<synopsis>table of known neighbors</synopsis>
<array type="variable-size">
<typeRef>FEConfiguredNeighborType</typeRef>
</array>
</attribute>
</attributes>
</LFBClassDef>
</LFBClassDefs>
</LFBLibrary>
5.2.1. FECapabilities 5.2. FE Capabilities
This element, if it occurs, must occur only once and contains all The FE Capability information is contained in the capabilities
the capability related information about the FE. Capability element of the class definition. As described elsewhere, capability
information is always considered to be read-only. information is always considered to be read-only.
The currently defined elements allowed within the FECapabilities The currently defined capabilities are ModifiableLFBTopology,
element are ModifiableLFBTopology, LFBsSupported, SupportedLFBs and SupportedAttributeType.
WriteableAttributes and ReadableAttributes.
5.2.1.1. ModifiableLFBTopology 5.2.1. ModifiableLFBTopology
This element has a boolean value. This element indicates whether
the LFB topology of the FE may be changed by the CE. If the This element has a boolean value that indicates whether the LFB
element is absent, the default value is assumed to be true, and the topology of the FE may be changed by the CE. If the element is
CE presumes the LFB topology may be changed. If the value is absent, the default value is assumed to be true, and the CE presumes
present and set to false, the LFB topology of the FE is fixed. In the LFB topology may be changed. If the value is present and set to
that case, the LFBs supported clause may be omitted, and the list false, the LFB topology of the FE is fixed. If the topology is
of supported LFBs is inferred by the CE from the LFB topology fixed, the LFBs supported clause may be omitted, and the list of
supported LFBs is inferred by the CE from the LFB topology
information. If the list of supported LFBs is provided when information. If the list of supported LFBs is provided when
ModifiableLFBTopology is false, the CanOccurBefore and ModifiableLFBTopology is false, the CanOccurBefore and CanOccurAfter
CanOccurAfter information should be omitted. information should be omitted.
5.2.1.2. SupportedLFBs and SupportedLFB 5.2.2. SupportedLFBs and SupportedLFBType
One capability that the FE should include is the list of supported One capability that the FE should include is the list of supported
LFB classes. The SupportedLFBs element, which occurs at most once, LFB classes. The SupportedLFBs element, is an array that contains
serves as a wrapper for the list of LFB classes supported. Each the information about each supported LFB Class. The array structure
class is described in a SupportedLFB element. type is defined as the SupportedLFBType dataTypeDef.
Each occurrence of the SupportedLFB element describes an LFB class Each occurrence of the SupportedLFBs array element describes an LFB
that the FE supports. In addition to indicating that the FE class that the FE supports. In addition to indicating that the FE
supports the class, FEs with modifiable LFB topology should include supports the class, FEs with modifiable LFB topology should include
information about how LFBs of the specified class may be connected information about how LFBs of the specified class may be connected
to other LFBs. This information should describe which LFB classes to other LFBs. This information should describe which LFB classes
the specified LFB class may succeed or precede in the LFB topology. the specified LFB class may succeed or precede in the LFB topology.
The FE should include information as to which port groups may be The FE should include information as to which port groups may be
connected to the given adjacent LFB class. If port group connected to the given adjacent LFB class. If port group
information is omitted, it is assumed that all port groups may be information is omitted, it is assumed that all port groups may be
used. used.
5.2.1.2.1. LFBName 5.2.2.1. LFBName
This element has as its value the name of the LFB being described. This element has as its value the name of the LFB being described.
5.2.1.2.2. LFBOccurrenceLimit 5.2.2.2. LFBOccurrenceLimit
This element, if present, indicates the largest number of instances This element, if present, indicates the largest number of instances
of this LFB class the FE can support. For FEs that do not have the of this LFB class the FE can support. For FEs that do not have the
capability to create or destroy LFB instances, this can either be capability to create or destroy LFB instances, this can either be
omitted or be the same as the number of LFB instances of this class omitted or be the same as the number of LFB instances of this class
contained in the LFB list attribute. contained in the LFB list attribute.
5.2.1.2.3. PortGroupLimits and PortGroupLimit 5.2.2.3. PortGroupLimits and PortGroupLimitType
The PortGroupLimits element is the wrapper to hold information The PortGroupLimits element is an array of information about the
about the port groups supported by the LFB class. It holds port groups supported by the LFB class. The structure of the port
multiple occurrences of the PortGroupLimit element. group limit information is defined by the PortGroupLimitType
dataTypeDef.
Each occurrence of the PortGroupLimit element contains the port Each PortGroupLimits array element contains information describing a
occurrence information for a single port group of the LFB class. single port group of the LFB class. Each array element contains the
Each occurrence has the name of the port group in the PortGroupName name of the port group in the PortGroupName element, the fewest
element, the fewest number of ports that can exist in the group in number of ports that can exist in the group in the MinPortCount
the MinPortCount element, and the largest number of ports that can element, and the largest number of ports that can exist in the group
exist in the group in the MaxPortCount element. in the MaxPortCount element.
5.2.1.2.4.CanOccurAfters and CanOccurAfter 5.2.2.4.CanOccurAfters and LFBAdjacencyLimitType
The CanOccurAfters element is a wrapper to hold the multiple The CanOccurAfters element is an array that contains the list of
occurrences of the CanOccurAfter permissible placement information. LFBs the described class can occur after. The array elements are
defined in the LFBAdjacencyLimitType dataTypeDef.
The CanOccurAfter element describes a permissible positioning of The array elements describe a permissible positioning of the
the SupportedLFB. Specifically, it names an LFB that can described LFB class, referred to here as the SupportedLFB.
topologically precede the SupportedLFB. That is, the SupportedLFB Specifically, each array element names an LFB that can topologically
can have an input port connected to an output port of the LFB that precede that LFB class. That is, the SupportedLFB can have an input
it CanOccurAfter. The LFB class that the SupportedLFB can follow port connected to an output port of an LFB that appears in the
is identified by the NeighborLFB element of the CanOccurAfter CanOccurAfters array. The LFB class that the SupportedLFB can
element. If this neighbor can only be connected to a specific set follow is identified by the NeighborLFB element of the
of input port groups, then the viaPort element is included. This LFBAdjacencyLimitType array element. If this neighbor can only be
element occurs once for each input port group of the SupportedLFB connected to a specific set of input port groups, then the viaPort
that can be connected to an output port of the NeighborLFB. element is included. This element occurs once for each input port
group of the SupportedLFB that can be connected to an output port of
the NeighborLFB.
[e.g., Within a SupportedLFB element, each CanOccurAfter element [e.g., Within a SupportedLFBs element, each array element of the
must have a unique NeighborLFB, and within each CanOccurAfter CanOccurAfters array must have a unique NeighborLFB, and within each
element each viaPort must represent a unique and valid input port array element each viaPort must represent a distinct and valid input
group of the SupportedLFB. The "unique" clauses for this have not port group of the SupportedLFB. The LFB Class definition schema
yet been added to the schema.] does not yet support uniqueness declarations]
5.2.1.2.5. CanOccurBefores and CanOccurBefore 5.2.2.5. CanOccurBefores and LFBAdjacencyLimitType
The CanOccurBefores element is a wrapper to hold the multiple The CanOccurBefores array holds the information about which LFB
occurrences of the CanOccurBefore permissible placement classes can follow the described class. Structurally this element
information. parallels CanOccurAfters, and uses the same type definition for the
array element.
The CanOccurBefore element similarly lists those LFB classes that The array elements list those LFB classes that the SupportedLFB may
the SupportedLFB may precede in the topology. In this element, the precede in the topology. In this element, the
viaPort element represents the output port group of the viaPort element of the array value represents the output port group
SupportedLFB that may be connected to the NeighborLFB. As with of the SupportedLFB that may be connected to the NeighborLFB. As
CanOccurAfter, viaPort may occur multiple times if multiple output with CanOccurAfters, viaPort may occur multiple times if multiple
ports may legitimately connect to the given NeighborLFB class. output ports may legitimately connect to the given NeighborLFB
class.
[And a similar set of uniqueness constraints apply to the [And a similar set of uniqueness constraints apply to the
CanOccurBefore clauses, even though an LFB may occur both in CanOccurBefore clauses, even though an LFB may occur both in
CanOccurAfter and CanOccurBefore.] CanOccurAfter and CanOccurBefore.]
5.2.1.2.6. LFBClassCapabilities
5.2.2.6. LFBClassCapabilities
This element contains capability information about the subject LFB This element contains capability information about the subject LFB
class whose structure and semantics are defined by the LFB class class whose structure and semantics are defined by the LFB class
definition. definition.
5.2.1.3. SupportedAttributes [Note: Important Omissions]
However, this element does not appear in the definition, because the
author can not figure out how to write it.
5.2.3. SupportedAttributeType
This element serves as a wrapper to hold the information about This element serves as a wrapper to hold the information about
attributed related capabilities. Specifically, attributes should attributed related capabilities. Specifically, attributes should be
be described in this element if: described in this element if:
a) they are optional elements in the standard and are supported a) they are optional elements in the standard and are supported by
by the FE, or the FE, or
b) the standard allows for a range of access permissions (for b) the standard allows for a range of access permissions (for
example, read-only or read-write). example, read-only or read-write).
Each attribute so described is contained in the SupportedAttributes Each attribute so described is contained in the
element. That element contains an AttributeName element whose SupportedAttributeType element. That element contains an
value is the name of the element being described and an AccessModes AttributeName element whose value is the name of the element being
element, whose value is the list of permissions. described, and AttributeID element whose value is the ID in the FE
Object of the Attribute, and an AccessModes element whose value is
the list of permissions.
5.2.2. FEAttributes 5.3.FEAttributes
The FEAttributes element contains the attributes of the FE that are The attributes element is included if the class definition contains
not considered "capabilities". Some of these attributes are the attributes of the FE that are not considered "capabilities".
writeable, and some are read-only, which should be indicated by the Some of these attributes are writeable, and some are read-only,
capability information. At the moment, the set of attributes is which should be indicated by the capability information.
woefully incomplete. Each attribute is identified by a unique
element tag, and the value of the element is the value of the
attribute.
5.2.2.1. FEStatus [Editors note - At the moment, the set of attributes is woefully
incomplete.]
5.3.1. FEStatus
This attribute carries the overall state of the FE. For now, it is This attribute carries the overall state of the FE. For now, it is
restricted to the strings AdminDisable, OperDisable and OperEnable. restricted to the strings AdminDisable, OperDisable and OperEnable.
5.2.2.2.LFBInstances and LFBInstance 5.3.2. LFBSelectors and LFBSelectorType
The LFBInstances element serves as a wrapper to hold the multiple The LFBSelectors element is an array of information about the LFBs
occurrences of the LFBInstance information about individual LFB currently accessible via ForCES in the FE. The structure of the LFB
instances on the FE. information is defined by the LFBSelectorType.
Each occurrence of the LFBInstance element describes a single LFB Each entry in the array describes a single LFB instance in the FE.
instance. Each element contains an LFBClassName indicating what The array element contains the numeric class ID of the class of the
class this instance has, and an LFBInstanceID indicating the ID LFB instance and the numeric instance ID for this instance.
used for referring to this instance. For now, the ID uses the
NMTOKEN construction. Further protocol work is likely to replace
this with a range restricted integer.
5.2.2.3. LFBTopology and LFBLink 5.3.3. LFBTopology and LFBLinkType
This optional element contains the information about each inter-LFB The optional LFBTopology element contains information about each
link inside the FE. Each link is described in an LFBLink element. inter-LFB link inside the FE, where each link is described in an
This element contains sufficient information to identify precisely LFBLinkType element. The LFBLinkType element contains sufficient
the end points of a link. The FromLFBID and ToLFBID fields information to identify precisely the end points of a link. The
indicate the LFB instances at each end of the link, and must FromLFBID and ToLFBID fields specify the LFB instances at each end
reference LFBs in the LFB instance table. The FromPortGroup and of the link, and must reference LFBs in the LFB instance table. The
ToPortGroup must identify output and input port groups defined in FromPortGroup and ToPortGroup must identify output and input port
the LFB classes of the LFB instances identified by the FromLFBID groups defined in the LFB classes of the LFB instances identified by
and ToLFBID. The FromPortIndex and ToPortIndex fields select the FromLFBID and ToLFBID. The FromPortIndex and ToPortIndex fields
elements from the port groups that this link connects. All links select the elements from the port groups that this link connects.
are uniquely identified by the FromLFBID, FromPortGroup, and
FromPortIndex fields. Multiple links may have the same ToLFBID,
ToPortGroup, and ToPortIndex as this model supports fan in of
inter-LFB links but not fan out.
5.2.2.4. FEConfiguredNeighbors an FEConfiguredNeighbor All links are uniquely identified by the FromLFBID, FromPortGroup,
and FromPortIndex fields. Multiple links may have the same ToLFBID,
ToPortGroup, and ToPortIndex as this model supports fan in of inter-
LFB links but not fan out.
The FEConfiguredNeighbors element is a wrapper to hold the 5.3.4. FENeighbors an FEConfiguredNeighborType
configuration information that one or more FEConfiguredNeighbor
elements convey about the configured FE topology.
The FEConfiguredNeighbor element occurs once for each configured FE The FENeighbors element is an array of information about manually
neighbor the FE knows about. It should not be filled in based on configured adjacencies between this FE and other FEs. The content
FE level protocol operations. In general, neighbor discovery of the array is defined by the FEConfiguredNeighborType element.
operation on the FE should be represented and manipulated as an
LFB. However, for FEs that include neighbor discovery and do not This array is intended to capture information that may be configured
have such an LFB, it is permitted to fill in the information in on the FE and is needed by the CE, where one array entry corresponds
this table based on such protocols. to each configured neighbor. Note that this array is not intended
to represent the results of any discovery protocols, as those will
have their own LFBs.
Similarly, the MAC address information in the table is intended to Similarly, the MAC address information in the table is intended to
be used in situations where neighbors are configured by MAC be used in situations where neighbors are configured by MAC address.
address. Resolution of network layer to MAC address information Resolution of network layer to MAC address information should be
should be captured in ARP LFBs, not duplicated in this table. Note captured in ARP LFBs and not duplicated in this table. Note that
that the same neighbor may be reached through multiple interfaces the same neighbor may be reached through multiple interfaces or at
or at multiple addresses. There is no uniqueness requirement of multiple addresses. There is no uniqueness requirement of any sort
any sort on occurrences of the FEConfiguredNeighbor element. on occurrences of the FENeighbors element.
Information about the intended forms of exchange with a given Information about the intended forms of exchange with a given
neighbor is not captured here, only the adjacency information is neighbor is not captured here, only the adjacency information is
included. included.
5.2.2.4.1.NeighborID 5.3.4.1.NeighborID
This is the ID in some space meaningful to the CE for the neighbor. This is the ID in some space meaningful to the CE for the neighbor.
If this table remains, we probably should add an FEID from the same If this table remains, we probably should add an FEID from the same
space as an attribute of the FE. space as an attribute of the FE.
5.2.2.4.2.NeighborInterface 5.3.4.2.NeighborInterface
This identifies the interface through which the neighbor is This identifies the interface through which the neighbor is reached.
reached.
[Editors note: As the port structures become better defined, the [Editors note: As the port structures become better defined, the
type for this should be filled in with the types necessary to type for this should be filled in with the types necessary to
reference the various possible neighbor interfaces, include reference the various possible neighbor interfaces, include physical
physical interfaces, logical tunnels, virtual circuits, etc.] interfaces, logical tunnels, virtual circuits, etc.]
5.2.2.4.3. NeighborNetworkAddress
5.3.4.3. NeighborNetworkAddress
Neighbor configuration is frequently done on the basis of a network Neighbor configuration is frequently done on the basis of a network
layer address. For neighbors configured in that fashion, this is layer address. For neighbors configured in that fashion, this is
where that address is stored. where that address is stored.
5.2.2.4.4.NeighborMacAddress 5.3.4.4.NeighborMacAddress
Neighbors are sometimes configured using MAC level addresses Neighbors are sometimes configured using MAC level addresses
(Ethernet MAC address, circuit identifiers, etc.) If such (Ethernet MAC address, circuit identifiers, etc.) If such addresses
addresses are used to configure the adjacency, then that are used to configure the adjacency, then that information is stored
information is stored here. Note that over some ports such as here. Note that over some ports such as physical point to point
physical point to point links or virtual circuits considered as links or virtual circuits considered as individual interfaces, there
individual interfaces, there is no need for either form of address. is no need for either form of address.
5.3. Sample FE Attribute Document
<?xml version="1.0">
<fm:FEDocument xmlns:fm="http://www.ietf.org/...theschema...">
<fm:FECapabilities>
<fm:ModifiableLFBTopology> true </fm:ModifiableLFBTopology>
<fm:SupportedLFBs>
<fm:SupportedLFB>
<!-- A simple single-input multi-output classifier -->
<fm:LFBName> Classifier </fm:LFBName>
<fm:LFBOccurrenceLimit> 3 </fm:LFBOccurrenceLimit>
<fm:PortGroupLimits>
<fm:PortGroupLimit>
<!-- The input port -->
<fm:PortGroupName> InputPortGroup </fm:PortGroupName>
<fm:MinPortCount> 1 </fm:MinPortCount>
<fm:MaxPortCount> 1 </fm:MaxPortCount>
</fm:PortGroupLimit>
<fm:PortGroupLimit>
<!--The normal output ports -->
<fm:PortGroupName> OutputPortGroup </fm:PortGroupName>
<fm:MinPortCount> 0 </fm:MinPortCount>
<fm:MaxPortCount> 32 </fm:MaxPortCount>
</fm:PortGroupLimit>
<fm:PortGroupLimit>
<!-- The optional error port -->
<fm:PortGroupName> ErrorPortGroup </fm:PortGroupName>
<fm:MinPortCount> 0 </fm:MinPortCount>
<fm:MaxPortCount> 1 </fm:MaxPortCount>
</fm:PortGroupLimit>
</fm:PortGroupLimits>
<fm:CanOccurAfters>
<fm:CanOccurAfter>
<fm:NeighborLFB> Port </fm:NeighborLFB>
<!-- omitted viaPort -->
</fm:CanOccurAfter>
<fm:CanOccurAfter
<fm:NeighborLFB> InternalSource </fm:NeighborLFB>
<!-- omitted viaPort -->
</fm:CanOccurAfter>
</fm:CanOccurAfters>
<fm:CanOccurBefores>
<fm:CanOccurBefore>
<fm:NeighborLFB> Marker </fm:NeighborLFB>
<!-- omitted viaPort -->
</fm:CanOccurBefore>
</fm:CanOccurBefores>
</fm:SupportedLFB>
<!-- then Supported LFB elements for Port, InternalSource -->
<!-- Marker, ... -->
</fm:SupportedLFBs>
<fm:SupportedAttributes>
<fm:SupportedAttribute>
<fm:AttributeName> FEStatus </fm:AttributeName>
<fm:AccessModes> read write </fm:AccessModes>
</fm:SupportedAttribute>
<fm:SupportedAttribute>
<fm:AttributeName> Vendor </fm:AttributeName>
<fm:AccessModes> read </fm:AccessModes>
</fm:SupportedAttribute
<fm:SupportedAttribute>
<fm:AttributeName> Model </fm:AttributeName>
<fm:AccessModes> read </fm:AccessModes>
</fm:SupportedAttribute>
</fm:SupportedAttributes>
</fm:FECapabilities>
<fm:FEAttributes>
<fm:Vendor> World Wide Widgets </fm:Vendor>
<fm:Model> Foo Forward Model 6 </fm:Model>
<fm:FEStatus> OperEnable </fm:FEStatus>
<fm:LFBInstances>
<fm:LFBInstance>
<fm:LFBClassName> Classifier </fm:LFBClassName>
<fm:LFBInstanceID> Inst5 </fm:LFBInstanceID>
</fm:LFBInstance>
<fm:LFBInstance>
<fm:LFBClassName> Interface </fm:LFBClassName>
<fm:LFBInstanceID> Inst11 </fm:LFBInstanceID>
</fm:LFBInstance>
<fm:LFBInstance>
<fm:LFBClassName> Meter </fm:LFBClassName>
<fm:LFBInstanceID> Inst17 </fm:LFBInstanceID>
</fm:LFBInstance>
</fm:LFBIntances>
<fm:LFBTopology>
<fm:LFBLink>
<fm:FromLFBID> Inst11 </fm:fromLFBID>
<fm:FromPortGroup> IFOnwardGroup </fm:FromPortGroup>
<fm:FromPortIndex> 1 </fm:FromPortIndex>
<fm:ToLFBID> Inst5 </fm:ToLFBID>
<fm:ToPortGroup> InputPortGroup </fm:ToPortGroup>
<fm:ToPortIndex> 1 </fm:ToPortIndex>
</fm:LFBLink>
<fm:LFBLink>
<fm:FromLFBID> Inst5 </fm:fromLFBID>
<fm:FromPortGroup> OutputGroup </fm:FromPortGroup>
<fm:FromPortIndex> 1 </fm:FromPortIndex>
<fm:ToLFBID> Inst17 </fm:ToLFBID>
<fm:ToPortGroup> InMeterGroup </fm:ToPortGroup>
<fm:ToPortIndex> 1 </fm:ToPortIndex>
</fm:LFBLink>
</fm:LFBTopology>
</fm:FEAttributes>
</fm:FEDocument>
6. LFB Class Library
A set of initial LFB classes are identified here in the LFB class
library as necessary to build common FE functions. Some of the LFB
classes described here are abstract base classes from which
specific LFB sub-classes will be derived. Hence, the base classes
may not be used directly in a particular FE's model, but the sub-
classes (yet to be defined) could be. This initial list attempts
to describe LFB classes at the expected level of granularity. This
list is neither exhaustive nor sufficiently detailed.
Several working groups in the IETF have already done some relevant
work in modeling the provisioning policy data for some of the
functions we are interested in, for example, the DiffServ
(Differentiated Services) PIB [4] and IPSec PIB [8]. Whenever
possible, we have tried to reuse the work done elsewhere.
6.1. Port LFB
A Port LFB is used to model physical I/O ports on the FE. It is
both a source of data "received" by the FE and a sink of data
"transmitted" by the FE. The Port LFB contains a number of static
attributes, which may include, but are not limited to, the
following items:
. the number of physical ports on this LFB
. physical port type
. physical port link speed (may be variable; e.g., 10/100/1000
Ethernet).
In addition, the Port LFB contains a number of configurable
attributes, including:
. physical port current status (up or down)
. physical port loopback
. physical port mapping to L2 interface.
The Port LFB can be sub-classed into technology specific LFB
classes, with additional static and configurable attributes.
Examples of possible sub-classes include:
. Ethernet
. Packet-over-SONET OC-N
. ATM-over-SONET/SDN OC-N
. T3
. E3
. T1
. E1
. CSIX-L1 switching fabric port (Fi interface)
. CE-FE port (for Fp interface).
LFB class inheritance can be used to sub-class derived LFB classes
with additional properties, such as TDM channelization.
The Port LFB "receives" (sources) and "transmits" (sinks) frames in
technology specific formats (described in the respective LFB class
definition but not otherwise modeled) into/out of the FE. Packets
"received" from a physical port are sourced on (one of) the LFB's
output port(s), while packets to be "transmitted" on a physical
port are sinked on (one of) the LFB's input port(s). The Port LFB
is unique among LFB classes in that packets accepted on a LFB input
port are not emitted back out on an LFB output port (except in the
case of physical port loopback operation).
The Port LFB transmits technology specific L2 frames to
topologically adjacent LFB instances (i.e., no frame
decapsulation/encapsulation is modeled in this LFB class). When
transmitting a frame to an adjacent downstream LFB, the Port LFB
provides two items of metadata: the frame length and the L2
interface identifier. When receiving frames from an adjacent
upstream LFB, the frame is accompanied by two items of metadata:
frame length and outgoing port identifier.
Statistics are not maintained by the Port LFB; statistics
associated with a particular port may be maintained by an L2
interface LFB (see Section 6.2).
6.2. L2 Interface LFB
The L2 Interface LFB models L2 protocol termination. The L2
Interface LFB performs two sets of functions: decapsulation and
demultiplexing as needed on the receive side of an FE, and
encapsulation and multiplexing as needed on the transmit side.
Hence the LFB has two distinct sets of inputs and outputs tailored
for these separate functions. The L2 Interface LFB is not modeled
as two separate (receive/transmit) LFBs because there are shared
attributes between the decapsulation and encapsulation functions.
On the decapsulation input(s), the LFB accepts an L2 protocol
specific frame, along with frame length and L2 interface metadata.
The LFB decapsulates the L2 frame by removing any L2
header/trailers (while simultaneously applying any checksum/CRC
functions), determines the L2 or L3 protocol type of the next-layer
packet (based on a PID or Ethertype within the L2 frame header),
adjusts the frame length metadata, and uses the L2 interface
metadata to select an L2 interface attribute. The L2 interface
attribute supports a number of additional attributes, including:
. L2 MTU
. supported next-layer L2 or L3 protocols
. L2-specific receive counters (byte, packet)
. counting mode
. L2 or L3 interface metadata for next-layer packet
. LFB output port.
The LFB may support multiple decapsulation output ports within two
output groups; one for normal forwarding, and one for exception
packets. The LFB emits the decapsulated packet along with the
modified frame length metadata, an L2 or L3 protocol type metadata,
and an L2 or L3 interface metadata.
On the encapsulation input(s), the LFB accepts a packet along with
frame length, protocol type, and L2 interface metadata. The L2
interface metadata is used to select an L2 interface attribute,
which supports a number of additional attributes, including:
. L2-specific transmit counters (byte, packet)
. counting mode (may be taken from receive counters mode)
. L2 or L3 interface metadata for next-layer frame (we assume
that L2 protocols could be layered on top of an L3 protocol;
e.g., L2TP or PWE3), or port metadata.
. LFB output port
The LFB encapsulates the packet using the appropriate L2
header/trailer and protocol type information (calculating
checksums/CRCs as necessary), and provides the frame to the next
LFB along with incremented frame length metadata, updated protocol
type metadata, and updated interface (or port) metadata, on a
configurable LFB encapsulation output.
As in the case of the Port LFB, technology specific variants of the
L2 interface LFB will be sub-classes of the L2 Interface LFB.
Example sub-classes include:
. Ethernet/802.1Q
. PPP
. ATM AAL5.
Each sub-class will likely support static and configurable
attributes specific to the L2 technology; for example the
Ethernet/802.1Q Interface LFB will support a per-interface MAC
address attribute. Note that each technology specific sub-class
may require additional metadata. For example, the Ethernet/802.1Q
Interface LFB requires an outgoing MAC destination address to
generate an outgoing Ethernet header.
The L2 interface management function is separated into a distinct
LFB from the Port LFB because L2 encapsulations can be nested
within frames; e.g., PPP-over-Ethernet-over-ATM AAL5 (PPPoEoA).
6.3. IP interface LFB
The IP Interface LFB models a container for IP interface-specific
attributes. These may include:
. IP protocols supported (IPv4 and/or IPv6)
. IP MTU
. interface MIB counters
. table metadata for associated forwarding tables (LPM,
multicast)
. table metadata for associated classification tables.
The IP Interface LFB also performs basic protocol-specific packet
header validation functions (e.g., IP version, IPv4 header length,
IPv4 header checksum, MTU, TTL=0, etc.). The IP Interface LFB
class supports three different L3 protocols: IPv4, IPv6, and MPLS,
although individual LFB instances might support a subset of these
protocols, configurable on each interface attribute.
As with the L2 Interface LFB, the IP Interface LFB supports two
modes of operation: one needed on the receive side of an FE, and
one on the transmit side, using separate sets of LFB inputs and
outputs. In the first mode of operation (for FE receive
processing), the IP Interface LFB accepts IP packets along with
frame length, L3 protocol type, and interface metadata (possibly
including additional metadata items such as L2-derived class
metadata). The interface metadata is used to select an interface
attribute, and the protocol type is checked against the protocols
supported for this interface. Error checks are applied, including
whether the particular protocol type is supported on this
interface, and if no errors occur, the appropriate counters are
incremented and the protocol type is used to select the outgoing
LFB output from a set dedicated to the first mode of operation.
The IP header protocol type/next header field may also be used to
select an LFB output; for example, IPv4 packets with AH header may
be directed to a particular next LFB, or IPv6 packets with Hop-by-
Hop Options. If errors do occur, the appropriate error counters
are incremented, and the error type is used to select a specific
exception LFB output.
In the second mode of operation (for FE transmit processing), the
IP Interface LFB accepts an IP packet along with frame length,
protocol type, and interface metadata. Again, the interface
metadata is used to select an interface attribute. The interface
attribute stores the outgoing L2 or IP interface (e.g., tunnel)
interface metadata. The IP MTU of the outgoing interface is
checked, along with the protocol type of the packet. If no errors
occur, the appropriate counters are incremented, and the next level
interface metadata may be used to select an IP Interface LFB output
dedicated to the second mode of operation. Otherwise, the
appropriate error counters are incremented, and the error type is
used to select an exception output.
Because the IP Interface LFB is the repository for the interface
MIB counters, two special pairs of inputs are provided for packets
which have been selected to be discarded further downstream (one
each for the receive and transmit counters). Packets arriving on
these LFB inputs must be accompanied by frame length and L3
interface metadata. An exception output on the LFB should be
connected to a dropper LFB.
6.4. Classifier LFB
The function of classification is to logically partition packets
into one of N different classes, based on some sequence of one or
more mathematical operations applied to the packet and its
associated metadata. Various LFBs perform an intrinsic
classification function. Where this function is a well-defined
protocol operation, a separate LFB may be defined (e.g., IP
Interface LFB, which performs header verification).
Several common applications need to classify packets using a
particular mathematical operation (e.g., longest prefix match (LPM)
or ternary match) against a fixed set of fields in a packet's
header plus metadata, or an easily recognized part of the packet
payload. Two example applications are classification for
Differentiated Services or for security processing. Typically the
packet is evaluated against a potentially large set of rules
(called "filters"), which are processed in a particular order to
ensure a deterministic result. This sort of classification
functionality is modeled by the Classifier LFB.
The Classifier LFB accepts an input packet and metadata, and
produces the unmodified packet along with a class metadata, which
may be used to map the packet to a particular LFB output.
The Classifier LFB supports multiple classifier attributes. Each
classifier is parameterized by one or more filters. Classification
is performed by selecting the classifier to use on a particular
packet (e.g., by metadata lookup on a configurable metadata item),
and by evaluating the selected contents of the accepted packet
against that classifier's filters. A filter decides if the input
packet satisfies particular criteria. According to [DiffServ], "a
filter consists of a set of conditions on the component values of a
packet's classification key (the header values, contents, and
attributes relevant for classification)".
Note that other LFBs may perform simple classification on the
packet or its metadata. The purpose of the Classifier LFB is to
model an LFB that "digests" large amounts of input data (packet,
metadata), to produce a "summary" of the classification results, in
the form of additional (or modified) metadata. Other LFBs can then
use this summary information to quickly and simply perform trivial
classification operations.
The Classifier LFB can be sub-classed into several function-
specific LFB classes which perform common classification functions.
These may include:
. Longest Prefix Match (LPM)
. IP Multicast lookup (S,G)
. Multifield Exact Match
. Multifield Ternary Match.
6.5. Next Hop LFB
The Next Hop LFB is used to resolve next hop information following
a forwarding lookup. Next Hop information normally includes the
outgoing interface (or interfaces, in the case of multicast), as
well as the outgoing IP address(es). This next hop information
associated with a forwarding prefix or classification rule is often
separated into a separate data structure in implementations to
allow the two pieces of information to be decoupled, because there
is frequently a fan-in relationship between forwarding prefix/rule
entries and next hop information, and decoupling them can permit
more efficient data structure management.
The Next Hop LFB maintains next hop attributes organized into
multiple next hop tables. The relevant table for a packet is
selected based on next hop table metadata. A set of one or more
next hop attributes is selected based on next hop index metadata.
Each next hop attribute stores the following information:
. a list of one or more outgoing interfaces
. next hop IP addresses, or, an index to a table of this
information
. that is maintained at a downstream LFB
. a list of outgoing MTUs
. TTL decrement value
The Next Hop LFB has two primary operations. The first is to map
the incoming next hop table and next hop index metadata into a
configurable next hop attribute. This mapping may be direct (one
metadata pair to one next hop attribute). If the next hop index
metadata selects a set of next hop attributes, final attribute
resolution depends on a selection algorithm that uses some
additional metadata, or an internal classification operation, to
select among a set of possible next hop attributes. One example is
weighted next hop selection, where individual packets are mapped to
particular next hop attributes in the set according to weights and
to some flow order-preserving function (e.g., such as an address
pair hash). Another alternative is class-based next hop selection,
based on some class metadata.
The second operation is a derivative of the first. The next hop
table and next hop index metadata are used to select a set of one
or more next hop attributes. Then the outgoing interface values
stored in those attributes are compared against the incoming
interface metadata provided to the Next Hop LFB, to determine
whether the incoming interface is in the set. This operation, in
combination with a IP source address forwarding lookup (which
provides the next hop table/index metadata), can be used to perform
a reverse path forwarding (RPF) check.
The Next Hop LFB has two inputs: one for normal next hop
resolution, and one for the incoming interface metadata test (e.g.,
RPF). The LFB requires incoming interface, frame length, next hop
table, and next hop index metadata. There are two normal output
groups, one for the normal next hop resolution, and another for the
RPF check. No additional metadata is produced for the latter, but
for the former, the following metadata may be produced:
. outgoing interface(s)
. next hop IP address(es)
. TTL decrement value (if TTL decrement is not performed by the
Next Hop LFB)
An alternative mode of operation produces index metadata instead of
outgoing interface and next hop IP address metadata. This index
metadata is used to access a cache of the outgoing interface and
next hop IP address that may be stored on the egress FE (this
permits more efficient communication across the FE interface).
This index metadata can also be used as input metadata to a MPLS
Encapsulation LFB.
The Next Hop LFB supports an exception output port group.
Exception conditions include:
. RPF test failed
. No route to host
. No route to network
. Packet too big
. TTL expired
The mapping between exception conditions and exception outputs is
configurable, and an exception code metadata is produced on these
outputs.
6.6. Rate Meter LFB
The Rate Meter LFB is used to meter the packet flow through the LFB
according to a rate- and time-dependent function. Packets are
provided to the Rate Meter LFB along with packet length metadata
(and optional color metadata) and are associated with a meter
attribute either statically (based on LFB input) or via some other
configurable metadata item. The metering algorithm of the
associated meter attribute is applied to the packet, using the
packet length and the current time as inputs, along with previous
state maintained by the attribute. A color metadata is associated
with the packet in accordance with the metering algorithm used.
The color metadata is optionally emitted with the packet, or used
to map the packet to a particular LFB output. Color-aware metering
algorithms use color metadata if provided with the packet (e.g., by
a Classifier LFB), or assume a default color value.
The Rate Meter LFB supports a number of static attributes,
including:
. supported metering algorithms
. maximum number of meter attributes
The Rate Meter LFB supports a number of configurable attributes,
including:
. number of LFB inputs
. number of LFB outputs
. mapping of LFB input to meter attribute (when mapped
statically)
. metadata item to select for mapping to meter attribute
. mapping of metadata value to meter attribute
. default meter attribute (when not mapped statically or via
correct
. metadata)
. per-attribute metering algorithm
. per-attribute metering parameters, including:
. minimum rate
. maximum rate
. burst size
. color metadata enable
. mapping of packet color to LFB output
A Rate Meter LFB can be used to implement a policing function, by
connecting a LFB output directly to a Dropper LFB, and mapping non-
conforming (e.g., "red") traffic to that output.
6.7. Redirector (de-MUX) LFB
The Redirector LFB is used to select between alternative datapaths
based on the value of some metadata item. The Redirector LFB
accepts an input packet P, and uses associated metadata item M to
demultiplex that packet onto one of N outputs; e.g., unicast
forwarding, multicast, or broadcast. Configurable attributes
include:
. number of LFB output ports (N)
. metadata item to demultiplex on (M)
. mapping of metadata value to output port
. default output port (for un-matched input metadata values).
Note that other LFBs may include demultiplexing functionality
(i.e., if they have multiple outputs in an output group). The
Redirector LFB is especially useful for demultiplexing based on
metadata items that are not generated or modified by an immediate
upstream LFB.
6.8. Packet Header Rewriter LFB
The Packet Header Rewriter LFB is used to re-write fields in a
packet's header. Function-specific sub-classes of the Packet
Header Rewriter LFB may be specified as sub-classes of the Modifier
LFB. These may include:
. IPv4 TTL/IPv6 Hop Count
. IPv4 header checksum
. DSCP
. IPv4 NAT
The precise means by which the packet header rewriting functions
will be specified is TBD.
6.9. Counter LFB
The Counter LFB is used to maintain packet and/or byte statistics
on the packet flow through the LFB. Packets are provided to the
Counter LFB on an LFB input along with packet length metadata and
are associated with a count attribute either statically (based on
the LFB input) or via some other configurable metadata item. The
Counter LFB modifies neither the packet nor any associated
metadata.
The Counter LFB supports a number of static attributes, including:
. supported counting modes (e.g., byte, packet, both)
. supported logging modes (e.g., last recorded packet time)
. maximum number of count attributes
The Counter LFB supports a number of configurable attributes,
including:
. number of LFB inputs
. mapping of LFB input to count attribute (when mapped
statically)
. metadata item to select for mapping to count attribute
. mapping of metadata value to count attribute
. default count attribute (when not mapped statically or via
correct
. metadata)
. counting mode per-attribute
. logging mode per-attribute
The Counter LFB does not perform any time-dependent counting. The
time at which a count is made may, however, be logged as part of
the count attribute.
Other LFBs may maintain internal statistics (e.g., interface LFBs).
The Counter LFB is especially useful to maintain counts associated
with QoS policy.
6.10. Dropper LFB
A Dropper LFB has one input, and no outputs. It discards all
packets that it accepts without any modification or examination of
those packets.
The purpose of a Dropper LFB is to allow the description of "sinks"
within the model, where those sinks do not result in the packet
being sent into any object external to the model.
The Dropper LFB has no configurable attributes.
6.11. IPv4 Fragmenter LFB
The IPv4 Fragmenter LFB fragments IPv4 packets according to the MTU
of the outgoing interface. The IPv4 Fragmenter LFB accepts packets
with frame length and MTU metadata, and produces a sequence of one
or more valid IPv4 packets properly fragmented, each along with
corrected frame length metadata.
The source of the outgoing interface MTU is TBD. The IPv4
fragmentation function is not incorporated into the IP Interface
LFB because forwarding implementations may include additional
forwarding functions between fragmentation and final output
interface processing.
6.12. L2 Address Resolution LFB
The L2 Address Resolution LFB is used to map a next hop IP address
into an L2 address. The LFB accepts packets with output L2
interface and next hop IP address metadata, and produces the packet
along with the correct L2 destination address. The L2 Address
Resolution LFB maintains multiple address resolution table
attributes accessed by the output L2 interface metadata. Each
table attribute maintains a set of configurable L2 address
attributes, accessed by the next hop IP address.
The L2 Address Resolution LFB has a normal output group, which
produces the L2 destination address metadata as well as an
exception output. This exception output can be used to divert the
packet to another LFB (e.g., an ARP/ND Protocol LFB, or a Port LFB
used to reach the CE) for address resolution.
6.13. Queue LFB
The Queue LFB is used to represent queueing points in the packet
datapath. It is always used in combination with one or more
Scheduler LFBs. The Queue LFB manages one or more FIFO packet
queues as configurable attributes. The Queue LFB provides one or
more LFB inputs, and packets are mapped from LFB inputs to queues,
either statically, or via queue metadata. Each queue attribute is
mapped one-to-one with a scheduling input on a downstream Scheduler
LFB. The Queue LFB provides one or more LFB outputs, along with
optional scheduling input metadata.