draft-ietf-pce-of-00.txt   draft-ietf-pce-of-01.txt 
Network Working Group J.L. Le Roux Network Working Group J.L. Le Roux
Internet Draft France Telecom Internet Draft France Telecom
Category: Standard Track Category: Standard Track
Expires: March 2008 J.P. Vasseur Expires: May 2008 J.P. Vasseur
Cisco System Inc. Cisco System Inc.
Y. Lee Y. Lee
Huawei Huawei
September 2007 November 2007
Encoding of Objective Functions in Path Computation Element (PCE) Encoding of Objective Functions in Path Computation Element
communication and discovery protocols communication Protocol (PCEP)
draft-ietf-pce-of-00.txt draft-ietf-pce-of-01.txt
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Abstract Abstract
The computation of one or a series of Traffic Engineering Label The computation of one or a series of Traffic Engineering Label
Switched Paths (TE LSP) in MultiProtocol Label Switching (MPLS) and Switched Paths (TE LSPs) in MultiProtocol Label Switching (MPLS) and
Generalized MPLS (GMPLS) networks, is subject to a set of one or more Generalized MPLS (GMPLS) networks, is subject to a set of one or more
specific optimization criteria(s), referred to as an objective specific optimization criteria(s), referred to as an objective
function (e.g. minimum cost path, widest path, etc.). A Path function (e.g. minimum cost path, widest path, etc.). A Path
Computation Element (PCE) may support one or multiple objective Computation Element (PCE) may support one or multiple objective
functions, and it is desired for a Path Computation Client (PCC) to functions, and it is desired for a Path Computation Client (PCC) to
automatically discover the set of objective functions supported by a automatically discover the set of objective functions supported by a
PCE. Furthermore, it may be useful for a PCC to specify in a path PCE. Furthermore, it may be useful for a PCC to specify in a path
computation request the required objective function used by the PCE computation request the required objective function to be used by the
to compute a TE LSP or a set of TE LSPs. Thus the aim of this PCE to compute a TE LSP or a set of TE LSPs. Thus the aim of this
document is to define extensions to the PCE Discovery (PCED) TLV document is to define extensions to the PCE communication Protocol
carried within the IS-IS Router Capability TLV and the OSPF Router (PCEP) in order to allow a PCC to discover the set of objective
Information LSA so as to allow a PCC to discover the set of objective functions supported by a PCE as well as to allow a PCC to indicate in
functions supported by a PCE. Extensions to the PCE communication a path computation request the required objective function and a PCE
Protocol (PCEP) are also specified allowing a PCC to indicate in a to indicate in a path computation reply the objective function that
path computation request the required objective function and a PCE to was used for path computation.
indicate in a path computation reply the objective function actually
applied.
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 this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119. document are to be interpreted as described in RFC-2119.
Table of Contents Table of Contents
1. Terminology.................................................3 1. Terminology.................................................3
2. Introduction................................................4 2. Introduction................................................3
3. PCE Discovery Extensions....................................5 3. Discovery of PCE Objective Functions........................5
3.1. IS-IS PCED Extensions.......................................5 3.1. OF-List TLV.................................................5
3.1.1. IS-IS OF-List sub-TLV.......................................5 3.2. Elements of procedure.......................................6
3.1.2. Elements of Procedure.......................................6 4. Objective Function in PCEP Path Computation request and
3.2. OSPF PCED Extensions........................................6 reply messages..............................................6
3.2.1. OSPF OF-List sub-TLV........................................6 4.1. OF Object...................................................6
3.2.2. Elements of procedure.......................................7 4.1.1. Elements of Procedure.......................................7
4. PCEP Extensions.............................................7 4.2. Carrying the OF object in a PCEP message....................8
4.1. OF Object...................................................8 4.3. New RP object flag.........................................10
4.1.1. Elements of procedure.......................................8 4.3.1. Elements of procedure......................................10
4.2. Carrying the OF object in a PCEP message....................9 5. Objective Functions definition.............................10
4.3. New RP object flag.........................................11 6. IANA Considerations........................................12
4.3.1. Elements of procedure......................................11 6.1. PCE Objective Function registry............................12
5. Objective Functions definition.............................11 6.2. PCEP code points...........................................13
6. IANA Considerations........................................13 6.2.1. OF Object..................................................13
6.1. PCE Objective Function registry............................13 6.2.2. OF-List TLV................................................13
6.2. PCEP code points...........................................14 6.2.3. PCEP Error values..........................................13
6.2.1. OF Object..................................................14 6.2.4. RP Object flag.............................................14
6.2.2. OF Object TLV Space........................................14 7. Security Considerations....................................14
6.2.3. PCEP Error values..........................................14 8. Manageability Considerations...............................14
6.2.4. RP Object flag.............................................15 8.1. Control of Function and Policy.............................14
6.3. IS-IS OF-List sub-TLV......................................15 8.2. Information and Data Models................................14
6.4. OSPF OF-List sub-TLV.......................................15 8.3. Liveness Detection and Monitoring..........................15
7. Security Considerations....................................16 8.4. Verify Correct Operations..................................15
8. Manageability Considerations...............................16 8.5. Requirements on other protocols............................15
8.1. Control of Function and Policy.............................16 8.6. Impact on network operations...............................15
8.2. Information and Data Models................................16 9. Acknowledgments............................................15
8.3. Liveness Detection and Monitoring..........................16 10. References.................................................15
8.4. Verify Correct Operations..................................16 10.1. Normative references.......................................15
8.5. Requirements on other protocols............................17 10.2. Informative references.....................................16
8.6. Impact on network operations...............................17 11. Author's Addresses:........................................16
9. Acknowledgments............................................17 12. Intellectual Property Statement............................17
10. References.................................................17
10.1. Normative references.......................................17
10.2. Informative references.....................................18
11. Author's Addresses:........................................18
12. Intellectual Property Statement............................18
1. Terminology 1. Terminology
Terminology used in this document Terminology used in this document
IGP: Interior Gateway Protocol: Either of the two routing
protocols Open Shortest Path First (OSPF) or Intermediate System
to Intermediate system (IS-IS).
LSR: Label Switching Router. LSR: Label Switching Router.
OF: Objective Function: A set of one or more optimization OF: Objective Function: A set of one or more optimization
criteria(s) used for the computation of a single path (e.g. path criteria(s) used for the computation of a single path (e.g. path
cost minimization), or the synchronized computation of a set of cost minimization), or the synchronized computation of a set of
paths (e.g. aggregate bandwidth consumption minimization, etc.). paths (e.g. aggregate bandwidth consumption minimization, etc.).
PCC: Path Computation Client: Any client application requesting a PCC: Path Computation Client: Any client application requesting a
path computation to be performed by a Path Computation Element. path computation to be performed by a Path Computation Element.
PCE: Path Computation Element: An entity (component, application, PCE: Path Computation Element: An entity (component, application,
or network node) that is capable of computing a network path or or network node) that is capable of computing a network path or
route based on a network graph, and applying computational route based on a network graph, and applying computational
constraints. constraints.
PCED: PCE Discovery: Generic term to refer to a PCE Discovery
Mechanism.
IS-IS PCED: IS-IS based PCE Discovery.
OSPF PCED: OSPF based PCE Discovery.
PCEP: Path Computation Element communication Protocol. PCEP: Path Computation Element communication Protocol.
TE LSP: Traffic Engineered Label Switched Path. TE LSP: Traffic Engineered Label Switched Path.
2. Introduction 2. Introduction
The PCE-based network architecture [RFC4655] defines a Path The PCE-based network architecture [RFC4655] defines a Path
Computation Element (PCE) as an entity capable of computing TE LSP Computation Element (PCE) as an entity capable of computing TE LSP
paths based on a network graph, and applying computational paths based on a network graph, and applying computational
constraints. A PCE serves path computation requests sent by Path constraints. A PCE serves path computation requests sent by Path
Computation Clients (PCC). Computation Clients (PCC).
The PCE communication Protocol (PCEP), defined in [PCEP], allows for The PCE communication Protocol (PCEP), defined in [PCEP], allows for
communication between a PCC and a PCE or between two PCEs, in communication between a PCC and a PCE or between two PCEs, in
compliance with requirements and guidelines set forth in [RFC4657]. compliance with requirements and guidelines set forth in [RFC4657].
Such interactions include path computation requests and path Such interactions include path computation requests and path
computation replies. computation replies.
The IS-IS based PCE Discovery and OSPF based PCE Discovery mechanisms
defined respectively in [ISIS-PCED] and [OSPF-PCED], allow a PCC to
automatically discover a set of PCEs as well as some information
required for PCE selection, in compliance with requirements set forth
in [RFC4674].
The computation of one or a set of TE LSPs is subject to a set of one The computation of one or a set of TE LSPs is subject to a set of one
or more optimization criteria(s), called an objective function. An or more optimization criteria(s), called an objective function. An
objective function is used by the PCE, when it computes a path or a objective function is used by the PCE, when it computes a path or a
set of paths, in order to select the "best" candidate path(s). There set of paths, in order to select the "best" candidate path(s). There
is a variety of objective functions: an objective function could is a variety of objective functions: an objective function could
apply either to a set of non synchronized path computation requests, apply either to a set of non synchronized path computation requests,
or to a set of synchronized path computation requests. In the former or to a set of synchronized path computation requests. In the former
case, the objective function refers to an individual path computation case, the objective function refers to an individual path computation
request (e.g. computation of the shortest constrained path where the request (e.g. computation of the shortest constrained path where the
metric is the IGP metric, computation of the least loaded constrained metric is the IGP metric, computation of the least loaded constrained
path, etc.). Conversely in the latter case, the objective function path, etc.). Conversely in the latter case, the objective function
applies to a set of path computation requests the computation of refers to a set of path computation requests the computation of which
which is synchronized (e.g. minimize the aggregate bandwidth is synchronized (e.g. minimize the aggregate bandwidth consumption of
consumption of all links, minimize the sum of the delays for two all LSPs, minimize the sum of the delays for two diverse paths, or
diverse paths, or the delta between those delays, etc.). Moreover, the delta between those delays, etc.). Moreover, some objective
some objective functions relate to the optimization of a single functions relate to the optimization of a single metric and others to
metric and others to the optimization of a set of metrics (organized the optimization of a set of metrics (organized in a hierarchical
in a hierarchical manner, using a weighted function, etc.). manner, using a weighted function, etc.).
As spelled out in [RFC4674], it may be useful for a PCC to discover As spelled out in [RFC4674], it may be useful for a PCC to discover
the set of objective functions supported by a PCE. For that purpose the set of objective functions supported by a PCE. Furthermore,
this document specifies PCE Discovery (PCED) extensions in order to [RFC4657] requires the ability for a PCC to indicate in a path
allow a PCE advertising a list of supported objective functions.
As spelled out in [RFC4657], a PCC must be able to indicate in a path
computation request a required/desired objective function, as well as computation request a required/desired objective function, as well as
optional function parameters. For that purpose this document extends optional function parameters.
the PCE communication Protocol (PCEP), so as to carry the objective
function as well as function parameters. It thus complements the PCEP
specification.
Extensions to IS-IS and OSPF based PCE Discovery ([ISIS-PCED], [OSPF- For these purposes, this document extends the PCE communication
PCED]) are defined in section 3. A new sub-TLV, the OF-List sub-TLV Protocol (PCEP). It defines PCEP extensions allowing a PCE
is defined, to be carried within the PCED TLV. It allows advertising advertising a list of supported objective functions, as well as
the list of objective functions supported by a PCE. extensions so as to carry the objective function in PCEP request and
reply messages. It thus complements the PCEP base specification
[PCEP].
Extensions to PCEP ([PCEP]) are defined in section 4. A new PCEP Note that IS-IS and OSPF based PCE Discovery mechanisms are defined
object, the OF object is defined, to be carried within a PCReq in ([ISIS-PCED], [OSPF-PCED]). These mechanisms are dedicated to the
message to indicate the required/desired objective function to be discovery of a few generic parameters while more detailed PCE
applied by a PCE or in a PCRep message to indicate the objective parameters should rather be discovered using the PCE communication
function that was actually applied by the PCE. Protocol. Objective functions pertain to this second category; thus
the Objective Function discovery procedure is handled by PCEP.
A common PCE Objective Function code point registry is defined for A new PCEP TLV, named the OF-List TLV is defined in section 3. The
both PCEP and PCED protocols, to be managed by IANA. OF-List TLV is carried in the PCEP OPEN object and allows a PCE
advertising to a PCEP peer, during PCEP session setup phase, the list
of objective functions that it supports.
A new PCEP object, the OF object, is defined in section 4. The OF
object is carried within a PCReq message to indicate the
required/desired objective function to be applied by a PCE or in a
PCRep message to indicate the objective function that was used for
path computation.
Six mandatory objective functions that must be supported by PCEP are Six mandatory objective functions that must be supported by PCEP are
listed in [RFC4657]. This document provides a definition of these six listed in [RFC4657]. This document provides a definition of these six
mandatory objective functions. Additional objective functions may be mandatory objective functions. Additional objective functions may be
defined in other documents. defined in other documents. Note that additional objective functions
are defined for PCE Global Concurrent Optimization (GCO) application,
3. PCE Discovery Extensions in [PCE-GCO].
3.1. IS-IS PCED Extensions
3.1.1. IS-IS OF-List sub-TLV
The IS-IS Objective Function List (OF-List) sub-TLV is a new sub-TLV
carried within the IS-IS PCED sub-TLV defined in [ISIS-PCED]. It
allows advertising the list of objective functions supported by a
PCE.
The OF-List sub-TLV is an optional sub-TLV. It MAY be present
within the PCED sub-TLV. It MUST NOT be present more than once.
If present more than once, all instances except the first one MUST be
ignored.
The format of the IS-IS OF-List sub-TLV is the identical to the TLV
format used by the Traffic Engineering Extensions to IS-IS [RFC3784].
That is, the TLV is composed of 1 octet for the type, 1 octet
specifying the TLV length, and a value field. The Length field
defines the length of the value portion in octets.
The IS-IS OF-List sub-TLV has the following format:
TYPE: To be assigned by IANA (suggested value = 6)
LENGTH: N * 2 (where N is the number of objective functions)
VALUE: list of 2-bytes objective function code points,
identifying the supported objective functions.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OF Code #1 | OF Code #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OF Code # N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OF Code (2 bytes): Objective Function Identifier
The IANA is requested to manage the PCE objective function code point
registry (see IANA section).
3.1.2. Elements of Procedure
The OF-List sub-TLV is advertised within an IS-IS PCED sub-TLV
defined in [ISIS-PCED]. As such, elements of procedures are inherited
from those defined in [ISIS-PCED].
The OF-List sub-TLV is OPTIONAL. A PCE MAY include an OF-List sub-TLV 3. Discovery of PCE Objective Functions
within the PCED sub-TLV so as to advertise a set of one or more
objective functions. When a PCED sub-TLV does not contain any OF-List
sub-TLV this means that the supported objective functions of that PCE
are unknown.
3.2. OSPF PCED Extensions This section defines PCEP extensions (see [PCEP]) so as to support
the advertisement of the objective functions supported by a PCE.
3.2.1. OSPF OF-List sub-TLV A new PCEP OF-List (Objective Function list) TLV is defined. The PCEP
OF-List TLV is carried within an OPEN object, in order for a PCE to
advertise to a PCEP peer the list of objective functions it supports,
during PCEP session setup phase.
The OSPF Objective Function List (OF-List) sub-TLV is a new sub-TLV 3.1. OF-List TLV
carried within the OSPF PCED TLV defined in [OSPF-PCED]. It allows
advertising the objective functions supported by a PCE. It includes a
list of 2-bytes objective function identifiers.
The OF-List sub-TLV is an optional TLV. It MAY be present The PCEP OF-List TLV is optional. It MAY be carried within an OPEN
within the PCED TLV. It MUST NOT be present more than once. object sent by a PCE in an Open message to a PCEP peer, so as to
If present more than once, all instances except the first one MUST be indicate the list of supported objective functions.
ignored.
The format of the OSPF OF-List sub-TLV is the identical to the TLV The OF-List TLV format is compliant with the PCEP TLV format defined
format used by the Traffic Engineering Extensions to OSPF in [PCEP]. That is, the TLV is composed of 2 octets for the type, 2
[RFC3630]. That is, the TLV is composed of 2 octets for the type, 2
octets specifying the TLV length, and a value field. The Length field octets specifying the TLV length, and a value field. The Length field
defines the length of the value portion in octets. The TLV is padded defines the length of the value portion in octets. The TLV is padded
to four-octet alignment; padding is not included in the Length field to four-octet alignment and padding is not included in the Length
(so a two octet value would have a length of two, but the total size field (e.g. a three octet value would have a length of three, but the
of the TLV would be eight octets). total size of the TLV would be eight octets).
The OSPF OF-List sub-TLV has the following format: The OSPF OF-List TLV has the following format:
TYPE: To be assigned by IANA (suggested value = 6) TYPE: To be assigned by IANA (suggested value = 4 )
LENGTH: N * 2 (where N is the number of objective functions) LENGTH: N * 2 (where N is the number of objective functions)
VALUE: list of 2-bytes objective function code points, VALUE: list of 2-bytes objective function code points,
identifying the supported objective functions. identifying the objective functions supported by the
sender of the Open message.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OF Code #1 | OF Code #2 | | OF Code #1 | OF Code #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// // // //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OF Code #N | | | OF Code #N | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OF Code (2 bytes): Objective Function code point identifier.
OF Code (2 bytes): Objective Function Identifier IANA is requested to manage the PCE objective function code point
The IANA is requested to manage the PCE objective function code point
registry (see IANA section). registry (see IANA section).
3.2.2. Elements of procedure 3.2. Elements of procedure
The OF-List sub-TLV is advertised within an OSPF PCED TLV defined in A PCE MAY include and OF-List TLV within an OPEN object in an Open
[OSPF-PCED]. As such, elements of procedures are inherited from those message sent to a PCEP peer, to advertise a set of one or more
defined in [OSPF-PCED]. objective functions. The OF-List TLV MUST NOT appear more than once
in an OPEN object. The absence of the OF-List TLV in an OPEN object
must be interpreted as an absence of information on the list of
supported objective functions by the PCE.
The OF-List sub-TLV is OPTIONAL. A PCE MAY include an OF-List sub-TLV As specified in [PCEP], a PCEP peer that does not recognize the OF-
within the PCED TLV so as to advertise a set of one or more objective List TLV will silently ignore it.
functions. When a PCED TLV does not contain any OF-List sub-TLV this
means that the supported objective functions of that PCE are unknown.
4. PCEP Extensions 4. Objective Function in PCEP Path Computation request and reply
messages
This section defines extensions to PCEP ([PCEP]) so as to support the This section defines PCEP extensions ([PCEP]) so as to support the
communication of objective functions. A new PCEP OF (Objective communication of objective functions in PCEP path computation request
Function) object is defined, to be carried within a PCReq message in and reply messages. A new PCEP OF (Objective Function) object is
order for the PCC to indicate the required/desired objective function defined, to be carried within a PCReq message in order for the PCC to
and within a PCRep message in order for the PCE to indicate the indicate the required/desired objective function.
objective function that has actually been applied by the PCE. A new
flag is defined in the RP object, so as to indicate in a PCRep The PCEP OF Object may also be carried within a PCRep message in
message that the inclusion of the objective function actually applied order for the PCE to indicate the objective function that was used by
by the PCE is required in the response. Also new PCEP error type and the PCE.
value are defined.
A new flag is defined in the RP object, so as to indicate in a PCReq
message that the PCE MUST provide in the PCRep message the objective
function that was used during path computation.
Also new PCEP error type and value are defined.
4.1. OF Object 4.1. OF Object
The PCEP OF (Objective Function) object is optional. It MAY be The PCEP OF (Objective Function) object is optional. It MAY be
carried within a PCReq message so as to indicate the desired/required carried within a PCReq message so as to indicate the desired/required
objective function to be applied by the PCE during path computation, objective function to be applied by the PCE during path computation,
or within a PCRep message so as to indicate the objective function or within a PCRep message so as to indicate the objective function
that has been actually applied by the PCE. that was used by the PCE during path computation.
The OF object format is compliant with the PCEP object format defined The OF object format is compliant with the PCEP object format defined
in [PCEP]. in [PCEP].
The OF Object-Class is to be assigned by IANA (recommended value=18). The OF Object-Class is to be assigned by IANA (recommended value=21).
The OF Object-Types is to be assigned by IANA (recommended value=1). The OF Object-Types is to be assigned by IANA (recommended value=1).
The format of the OF object body is: The format of the OF object body is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Objective Function Code(IANA) | Reserved | |Objective Function Code(IANA) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
skipping to change at page 8, line 43 skipping to change at page 7, line 28
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Objective Function Code (2 bytes): The identifier of the Objective Objective Function Code (2 bytes): The identifier of the Objective
Function. The IANA is requested to manage the PCE objective function Function. The IANA is requested to manage the PCE objective function
code point registry (see IANA section). code point registry (see IANA section).
Reserved (2 bytes): This field MUST be set to zero on transmission Reserved (2 bytes): This field MUST be set to zero on transmission
and MUST be ignored on receipt. and MUST be ignored on receipt.
Optional TLVs may be defined so as to encode objective function Optional TLVs may be defined so as to encode objective function
parameters. The IANA is requested to create a registry for this TLVs' parameters.
name space.
4.1.1. Elements of procedure 4.1.1. Elements of Procedure
To specify an objective function to be applied by a PCE, a PCC MUST To request the use of a specific objective function to be used by the
include an OF object in the PCReq message. PCE a PCC MUST include an OF object in the PCReq message.
A bit flag referred to as the P bit is defined in the common header [PCEP] specifies a bit flag referred to as the P bit in a PCEP
of each PCEP object that can be set by a PCC to enforce a PCE to take common header that can be set by a PCC to enforce a PCE to take into
into account the related information during the path computation. If account the related information during the path computation. If the
the objective function is mandatory (required objective function), objective function is mandatory (required objective function), the P
the P bit in the OF object MUST be set, else if it is optional bit in the OF object MUST be set, else if it is optional (desired
(desired objective function) the P bit MUST be cleared. objective function) the P bit MUST be cleared.
On receipt of a PCReq message with an OF object, a PCE has to proceed On receipt of a PCReq message with an OF object, a PCE MUST proceed
as follows: as follows:
- If the OF object is unknown/unsupported, the PCE MUST follow - If the OF object is unknown/unsupported, the PCE MUST follow
procedures defined in [PCEP], that is if the P bit is set, it procedures defined in [PCEP], that is if the P bit is set, it
sends a PCErr message with error type unknown/unsupported sends a PCErr message with error type unknown/unsupported
object (type 3 and 4) else if the P bit is cleared it is free object (type 3 and 4) and the related path computation request
MUST be discarded. If the P bit is cleared it is free
to ignore the object. to ignore the object.
- If the objective function is unknown / unsupported and the P - If the objective function is unknown / unsupported and the P
bit is set, the PCE MUST send a PCErr message with a new PCEP bit is set, the PCE MUST send a PCErr message with a new PCEP
error type "objective function error" and error value error type "objective function error" and error value
"unknown/unsupported objective function" (defined in this "unknown/unsupported objective function" (defined in this
document), and the related path computation request MUST be document), and the related path computation request MUST be
discarded. discarded.
- If the objective function is unknown / unsupported and the P - If the objective function is unknown / unsupported and the P
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- If the objective function is supported but policy does not - If the objective function is supported but policy does not
allow applying it, and the P bit is cleared, the PCE SHOULD allow applying it, and the P bit is cleared, the PCE SHOULD
apply another (default) objective function. apply another (default) objective function.
- If the objective function is supported and policy allows - If the objective function is supported and policy allows
applying it, then if the P bit is set the PCE MUST apply the applying it, then if the P bit is set the PCE MUST apply the
requested objective function, else if the P bit is cleared the requested objective function, else if the P bit is cleared the
PCE is free to apply any other objective function. PCE is free to apply any other objective function.
The default objective function may be locally configured.
4.2. Carrying the OF object in a PCEP message 4.2. Carrying the OF object in a PCEP message
The OF object MAY be carried within a PCReq message. An OF object The OF object MAY be carried within a PCReq message. An OF object
specifying an objective function that applies to a set of specifying an objective function that applies to a set of
synchronized path computation requests MUST be carried just after the synchronized path computation requests MUST be carried just after the
corresponding SVEC object, and MUST NOT be repeated for each corresponding SVEC object, and MUST NOT be repeated for each
elementary request. elementary request.
An OF object specifying an objective function that applies to an An OF object specifying an objective function that applies to an
individual path computation request (non synchronized case) MUST individual path computation request (non synchronized case) MUST
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[<BANDWIDTH>] [<BANDWIDTH>]
[<metric-list>] [<metric-list>]
[<RRO>] [<RRO>]
[<IRO>] [<IRO>]
[<LOAD-BALANCING>] [<LOAD-BALANCING>]
where: where:
<metric-list>::=<METRIC>[<metric-list>] <metric-list>::=<METRIC>[<metric-list>]
The OF object MAY be carried within a PCRep message to indicate the The OF object MAY be carried within a PCRep message to indicate the
objective function that was actually applied by the PCE. objective function used by the PCE during path computation.
When the PCE wants to indicate to the PCC the objective function that
was used for the synchronized computation of a set of paths, the
PCRep message MUST include the corresponding SVEC object directly
followed by the OF object, which MUST NOT be repeated for each
elementary request.
An OF object specifying an objective function used for an individual
path computation (non synchronized case) MUST follow the RP object
for which it applies.
The format of the PCRep message is updated as follows: The format of the PCRep message is updated as follows:
<PCRep Message> ::= <Common Header> <PCRep Message> ::= <Common Header>
[<SVEC-list>]
<response-list> <response-list>
where: where:
<svec-list> ::=<SVEC>
[<OF>]
[<svec-list>]
<response-list>::=<response>[<response-list>] <response-list>::=<response>[<response-list>]
<response>::=<RP> <response>::=<RP>
[<NO-PATH>] [<NO-PATH>]
[<path-list>] [<path-list>]
<path-list>::=<path>[<path-list>] <path-list>::=<path>[<path-list>]
<path>::= <ERO> <path>::= <ERO>
[<OF>] [<OF>]
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<path-list>::=<path>[<path-list>] <path-list>::=<path>[<path-list>]
<path>::= <ERO> <path>::= <ERO>
[<OF>] [<OF>]
[<LSPA>] [<LSPA>]
[<BANDWIDTH>] [<BANDWIDTH>]
[<metric-list>] [<metric-list>]
[<IRO>] [<IRO>]
where: where:
<metric-list>::=<METRIC>[<metric-list>] <metric-list>::=<METRIC>[<metric-list>]
4.3. New RP object flag 4.3. New RP object flag
In some cases, where no objective function is specified in the In some cases, where no objective function is specified in the
request, or an optional objective function is desired (P bit cleared request, or an optional objective function is desired (P flag cleared
in the OF object header) but the PCE does not follow the in the OF object common header) but the PCE does not follow the
recommendation, the PCC may desire to know the objective function recommendation, the PCC may desire to know the objective function
actually applied by the PCE. For that purpose, a new flag is defined that was used by the PCE during path computation. To that end, a new
in the RP object, the OF flag, allowing a PCC to request for the flag is defined in the RP object, named the OF flag, allowing a PCC
inclusion in the reply of the objective function actually applied by to request for the inclusion in the path computation reply of the
the PCE. objective function that was used by the PCE during path computation.
The following new bit flag of the RP object is defined: The following new bit flag of the RP object is defined:
Objective Function (OF) flag (1 bit): 0x200 (suggested value, to be Objective Function (OF) flag (1 bit): 0x200 (bit number 16)
assigned by IANA). When set in a PCReq message, this indicates that (suggested value, to be assigned by IANA). When set in a PCReq
the PCE must provide the applied objective function (should a path message, this indicates that the PCE has to provide the applied
satisfying the constraints be found) in the PCRep message. When set objective function (should a path satisfying the constraints be found)
in a PCRep message this indicates that the Objective Function applied in the PCRep message. When set in a PCRep message this indicates that
by the PCE is included. the Objective Function that was used during path computation is
included.
4.3.1. Elements of procedure 4.3.1. Elements of procedure
If the PCC wants to know the objective function actually applied by a If the PCC wants to know the objective function used by the PCE
PCE for a given request, it MUST set the OF flag in the RP object. during path computation for a given request, it MUST set the OF flag
in the RP object.
On receipt of a PCReq message with the OF flag in the RP object set, On receipt of a PCReq message with the OF flag in the RP object set,
the PCE has to proceed as follows: the PCE has to proceed as follows:
- If policy permits it MUST include in the PCRep message an OF - If policy permits it MUST include in the PCRep message an OF
object indicating the objective function it actually applied. object indicating the objective function it used during path
computation.
- If policy does not permit, it MUST send a PCErr message with - If policy does not permit, it MUST send a PCErr message with
the PCEP error code "policy-violation" (type 5) and a new the PCEP error code "policy-violation" (type 5) and a new
error value "objective function indication not allowed" error value "objective function indication not allowed"
(defined in this document). (defined in this document).
5. Objective Functions definition 5. Objective Functions definition
Six objective functions that must be supported by PCEP are listed in Six objective functions that must be supported by PCEP are listed in
[RFC4657]. Objective function codes should be assigned by IANA and [RFC4657]. Objective function codes should be assigned by IANA and
are suggested below. are suggested below.
Objective functions are formulated using the following terminology: Objective functions are formulated using the following terminology:
- a network comprises a set of N links {Li, (i=1N)} - a network comprises a set of N links {Li, (i=1...N)}
- a path P is a list of K links {Lpi,(i=1K)} - a path P is a list of K links {Lpi,(i=1...K)}
- Metric of link L is noted M(L), this can be the IGP metric the - metric of link L is noted M(L), this can be the IGP metric the
TE metric or any other metric. TE metric or any other metric.
- The cost of a path P is noted C(P), - the cost of a path P is noted C(P),
C(P) = sum {M(Lpi), (i=1K)}. C(P) = sum {M(Lpi), (i=1...K)}.
- Residual bandwidth on link L is noted R(L) - residual bandwidth on link L is noted r(L)
- Speed of link L is noted B(L) - maximum reservable bandwidth on link L is noted R(L).
There are three objective functions that apply to the computation of There are three objective functions that apply to the computation of
a single path: a single path:
Objective Function Code: 1 (suggested value, to be assigned by IANA) Objective Function Code: 1 (suggested value, to be assigned by IANA)
Name: Minimum Cost Path (MCP) Name: Minimum Cost Path (MCP)
Description: Find a path P such that C(P) is minimized. Description: Find a path P such that C(P) is minimized.
Objective Function Code: 2 (suggested value, to be assigned by IANA) Objective Function Code: 2 (suggested value, to be assigned by IANA)
Name: Minimum Load Path (MLP) Name: Minimum Load Path (MLP)
Description: Find a path P such that ( Max {(B(Lpi) - R(Lpi)) / Description: Find a path P such that ( Max {(R(Lpi) - r(Lpi)) /
B(Lpi), i=1K } ) is minimized R(Lpi), i=1...K } ) is minimized
Objective Function Code: 3 (suggested value, to be assigned by IANA) Objective Function Code: 3 (suggested value, to be assigned by IANA)
Name: Maximum residual Bandwidth Path (MBP) Name: Maximum residual Bandwidth Path (MBP)
Description: Find a path P such that ( Min { R(Lpi)), i=1K } ) is Description: Find a path P such that ( Min { r(Lpi)), i=1...K } ) is
maximized. maximized.
There are three objective functions that apply to a set of path There are three objective functions that apply to a set of path
computation requests the computation of which is synchronized: computation requests the computation of which is synchronized:
Objective Function Code: 4 (suggested value, to be assigned by IANA) Objective Function Code: 4 (suggested value, to be assigned by IANA)
Name: Minimize aggregate Bandwidth Consumption (MBC) Name: Minimize aggregate Bandwidth Consumption (MBC)
Description: Find a set of paths such that ( Sum {B(Li) - R(Li), Description: Find a set of paths such that ( Sum {R(Li) - r(Li),
i=1N} ) is minimized. i=1...N} ) is minimized.
Objective Function Code: 5 (suggested value, to be assigned by IANA) Objective Function Code: 5 (suggested value, to be assigned by IANA)
Name: Minimize the Load of the most loaded Link (MLL) Name: Minimize the Load of the most loaded Link (MLL)
Description: Find a set of paths such that ( Max { B(Li) - R(Li)) / Description: Find a set of paths such that ( Max { (R(Li) - r(Li)) /
B(Li), i=1N}) is minimized. R(Li), i=1...N}) is minimized.
Objective Function Code: 6 (suggested value, to be assigned by IANA) Objective Function Code: 6 (suggested value, to be assigned by IANA)
Name: Minimize the Cumulative Cost of a set of paths (MCC) Name: Minimize the Cumulative Cost of a set of paths (MCC)
Description: Find a set of paths {P1Pm} such that (Sum { C(Pi), Description: Find a set of paths {P1...Pm} such that (Sum { C(Pi),
i=1m}) is minimized. i=1...m}) is minimized.
Other objective functions may be defined in separate documents. Other objective functions may be defined in separate documents.
6. IANA Considerations 6. IANA Considerations
6.1. PCE Objective Function registry 6.1. PCE Objective Function registry
This document defines a 16-bit PCE Objective Function identifier to This document defines a 16-bit PCE Objective Function identifier to
be carried within the PCEP OF object, as well as the ISIS and OSPF be carried within the PCEP OF object, as well as the PCEP OF-List TLV.
OF-List sub-TLVs.
The IANA is requested to create and manage the 16-bit "PCE Objective IANA is requested to create and manage the 16-bit "PCE Objective
Function" code point registry, starting from 1 and continuing through Function" code point registry, starting from 1 and continuing through
32767, as follows: 32767, as follows:
- Objective Function code point value - Objective Function code point value
- Objective Function name - Objective Function name
- Defining RFC - Defining RFC
The same registry is applicable to the PCEP OF object and the ISIS The same registry is applicable to the OF object and the OF-List TLV
and OSPF OF-List sub-TLVs defined in this document. defined in this document.
The guidelines (using terms defined in [RFC2434]) for the The guidelines (using terms defined in [RFC2434]) for the
assignment of objective function code point values are as follows: assignment of objective function code point values are as follows:
- Function code value 0 is reserved. - Function code value 0 is reserved.
- Function code value in the range 1-32767 are to be assigned as - Function code value in the range 1-32767 are to be assigned as
follows: follows:
- Function code values 1 through 1023 are to be assigned by - Function code values 1 through 1023 are to be assigned by
IANA using the "IETF Consensus" policy. IANA using the "IETF Consensus" policy.
- Function code values 1024 through 32767 are to be - Function code values 1024 through 32767 are to be
skipping to change at page 14, line 18 skipping to change at page 13, line 18
The IANA has been requested to manage the PCEP Objects code point The IANA has been requested to manage the PCEP Objects code point
registry (see [PCEP]). registry (see [PCEP]).
This document defines a new PCEP object, the OF object, to be This document defines a new PCEP object, the OF object, to be
carried in PCReq and PCRep messages. The IANA is requested to make carried in PCReq and PCRep messages. The IANA is requested to make
the following allocation (suggested value): the following allocation (suggested value):
Object Name Object Name Reference Object Name Object Name Reference
Class Type Class Type
18 OF 1 Objective (this document) 21 OF 1 Objective (this document)
Function Function
6.2.2. OF Object TLV Space 6.2.2. OF-List TLV
The new PCEP OF object referenced above includes optional TLVs that
encode objective function parameters. Each TLV includes a 16-bit type
identifier.
The IANA is requested to create a new registry, the "PCEP OF TLV"
registry, and manage TLV type identifiers as follows:
- TLV Type value
- TLV Name
- Defining RFC
Type values in the range 1-32767 are to be assigned as follows: IANA is requested to manage the PCEP TLV code point registry (see
- Values 1 through 1023 are to be assigned by IANA using the [PCEP]).
"IETF Consensus" policy. This document defines a new PCEP TLV, the OF-List TLV, to be carried
- Values 1024 through 32767 are to be assigned by IANA, using the in the OPEN object. The IANA is requested to make the following
"First Come First Served" policy. allocation (suggested value):
Type values in the range 32768-65535 are for "Private Use". Type TLV name References
----- -------- ----------
4 OF-List (This document)
6.2.3. PCEP Error values 6.2.3. PCEP Error values
A new PCEP Error-Type is defined in this document, with two error A new PCEP Error-Type is defined in this document, with two error
values (Error-Type and Error-value to be assigned by IANA): values (Error-Type and Error-value to be assigned by IANA):
Error-type Meaning and error values Reference Error-type Meaning and error values Reference
14 Objective Function Error (this doc) 14 Objective Function Error (this doc)
Error-value=1: unknown objective function Error-value=1: unknown objective function
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6.2.4. RP Object flag 6.2.4. RP Object flag
A new flag of the RP object (specified in [PCEP]) is defined in this A new flag of the RP object (specified in [PCEP]) is defined in this
document. The IANA is requested to make the following allocation document. The IANA is requested to make the following allocation
(suggested value): (suggested value):
Bit Hex Name Reference Bit Hex Name Reference
Number Number
08 0x200 OF (this document) 16 0x200 OF (this document)
When set, this indicates that the PCC requests the inclusion, in the
PCRep message, of the objective function actually used to compute the
path.
6.3. IS-IS OF-List sub-TLV
Once a registry for the IS-IS PCED sub-TLV defined in [ISIS-PCED]
will have been assigned, IANA will assign a new sub-TLV code-point
for the OF-List sub-TLV carried in the PCED sub-TLV. Here is the
suggested value:
Value TLV name References
----- -------- ----------
6 OF-List (This document)
6.4. OSPF OF-List sub-TLV
Once a registry for the OSPF PCED TLV defined in [OSPF-PCED] will
have been assigned, IANA will assign a new sub-TLV code-point for the
OF-List sub-TLV carried in the PCED TLV. Here is the suggested value:
Value TLV name References
----- -------- ----------
6 OF-List (This document)
7. Security Considerations 7. Security Considerations
Mechanisms discussed in [ISIS-PCED] and [OSPF-PCED] to secure the PCED Mechanisms discussed in [PCEP] to secure a PCEP session can be used
TLV can be used to secure the PCED sub-TLV as well. to secure the PCEP OF object and OF list TLV as well.
Mechanisms discussed in [PCEP] to secure a PCEP session can be used to
secure the PCEP OF object as well.
8. Manageability Considerations 8. Manageability Considerations
8.1. Control of Function and Policy 8.1. Control of Function and Policy
It MUST be possible to configure the activation/deactivation of It MUST be possible to configure the activation/deactivation of
Objective Function Discovery in the PCED protocol. Objective Function Discovery in PCEP.
In addition to the parameters already listed in section 8.1 of [PCEP], In addition to the parameters already listed in section 8.1 of [PCEP],
a PCEP implementation SHOULD allow configuring on a PCE a list of a PCEP implementation SHOULD allow configuring on a PCE a list of
authorized objective functions. This may apply to any session the authorized objective functions. This may apply to any session the
PCEP speaker participates in, to a specific session with a given PCEP PCEP speaker participates in, to a specific session with a given PCEP
peer or to a specific group of sessions with a specific group of PCEP peer or to a specific group of sessions with a specific group of PCEP
peers. peers.
Note that an implementation may support the specification of the OF Note that it is not mandatory for an implementation to support all
to be used in PCEP without supporting the discovery of the set of objective functions defined in section 5.
OF via the IGP.
Also note that it is not mandatory for an implementation to support It MUST be possible to configure a default objective function used
all objective functions defined in section 5. for path computation when a path request is received that requests to
use an optional objective function.
8.2. Information and Data Models 8.2. Information and Data Models
The PCED MIB Module defined in [PCED-MIB] MUST be extended to include
Objective Functions.
The PCEP MIB Module defined in [PCEP-MIB] MUST be extended to include The PCEP MIB Module defined in [PCEP-MIB] MUST be extended to include
Objective Functions. Objective Functions.
8.3. Liveness Detection and Monitoring 8.3. Liveness Detection and Monitoring
Mechanisms defined in this document do not imply any new liveness Mechanisms defined in this document do not imply any new liveness
detection and monitoring requirements in addition to those already detection and monitoring requirements in addition to those already
listed in [PCEP], [ISIS-PCED] and [OSPF-PCED]. listed in [PCEP].
8.4. Verify Correct Operations 8.4. Verify Correct Operations
Mechanisms defined in this document do not imply any new operation Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already verification requirements in addition to those already listed in
listed in [PCEP], [ISIS-PCED] and [OSPF-PCED]. [PCEP].
8.5. Requirements on other protocols 8.5. Requirements on other protocols
Mechanisms defined in this draft do not imply any requirements on Mechanisms defined in this document do not imply any requirements on
other protocols in addition to those already listed in [PCEP], [ISIS- other protocols in addition to those already listed in [PCEP].
PCED] and [OSPF-PCED].
8.6. Impact on network operations 8.6. Impact on network operations
Mechanisms defined in this document do not imply any impact on Mechanisms defined in this document do not have any impact on network
network operations in addition to those already listed in [PCEP], operations in addition to those already listed in [PCEP].
[ISIS-PCED] and [OSPF-PCED].
9. Acknowledgments 9. Acknowledgments
The authors would like to thank Jerry Ash for his useful comments. The authors would like to thank Jerry Ash for his useful comments.
10. References 10. References
10.1. Normative references 10.1. Normative references
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
skipping to change at page 17, line 44 skipping to change at page 16, line 5
[RFC3784] Li, T., Smit, H., "IS-IS extensions for Traffic [RFC3784] Li, T., Smit, H., "IS-IS extensions for Traffic
Engineering", RFC 3784, June 2004. Engineering", RFC 3784, June 2004.
[RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation [RFC4655] Farrel, A., Vasseur, J.P., Ash, J., "Path Computation
Element (PCE)-based Architecture", RFC4655, august 2006. Element (PCE)-based Architecture", RFC4655, august 2006.
[PCEP] Vasseur, Le Roux, et al., "Path Computation Element (PCE) [PCEP] Vasseur, Le Roux, et al., "Path Computation Element (PCE)
communication Protocol (PCEP)", draft-ietf-pce-pcep, work in communication Protocol (PCEP)", draft-ietf-pce-pcep, work in
progress. progress.
10.2. Informative references
[RFC4657] Ash, J., Le Roux, J.L., " PCE Communication Protocol
Generic Requirements", RFC4657, September 2006.
[RFC4674] Le Roux, J.L., et al. "Requirements for PCE discovery",
RFC4674, October 2006.
[ISIS-PCED] Le Roux, Vasseur, et al. "IS-IS protocol extensions for [ISIS-PCED] Le Roux, Vasseur, et al. "IS-IS protocol extensions for
Path Computation Element (PCE) Discovery", draft-ietf-pce-disco- Path Computation Element (PCE) Discovery", draft-ietf-pce-disco-
proto-isis, work in progress. proto-isis, work in progress.
[OSPF-PCED] Le Roux, Vasseur, et al. "OSPF protocol extensions for [OSPF-PCED] Le Roux, Vasseur, et al. "OSPF protocol extensions for
Path Computation Element (PCE) Discovery", draft-ietf-pce-disco- Path Computation Element (PCE) Discovery", draft-ietf-pce-disco-
proto-ospf, work in progress. proto-ospf, work in progress.
10.2. Informative references [PCE-GCO] Y. Lee, J.L. Le Roux, D. King, and E. Oki, "Path
Computation Element Communication Protocol (PCECP) Requirements and
[RFC4657] Ash, J., Le Roux, J.L., " PCE Communication Protocol Protocol Extensions In Support of Global Concurrent Optimization",
Generic Requirements", RFC4657, September 2006. draft-ietf-pce-global-concurrent-optimization-01.txt, work in
progress
[RFC4674] Le Roux, J.L., et al. "Requirements for PCE discovery",
RFC4674, October 2006.
11. Author's Addresses: 11. Author's Addresses:
Jean-Louis Le Roux Jean-Louis Le Roux
France Telecom France Telecom
2, avenue Pierre-Marzin 2, avenue Pierre-Marzin
22307 Lannion Cedex 22307 Lannion Cedex
FRANCE FRANCE
Email: jeanlouis.leroux@orange-ftgroup.com Email: jeanlouis.leroux@orange-ftgroup.com
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