[Docs] [txt|pdf] [draft-ietf-policy...] [Diff1] [Diff2]

PROPOSED STANDARD

Network Working Group                                           B. Moore
Request for Comments: 3670                               IBM Corporation
Category: Standards Track                                      D. Durham
                                                                   Intel
                                                            J. Strassner
                                                        INTELLIDEN, Inc.
                                                           A. Westerinen
                                                           Cisco Systems
                                                                W. Weiss
                                                                Ellacoya
                                                            January 2004


                   Information Model for Describing
                Network Device QoS Datapath Mechanisms

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

   The purpose of this document is to define an information model to
   describe the quality of service (QoS) mechanisms inherent in
   different network devices, including hosts.  Broadly speaking, these
   mechanisms describe the properties common to selecting and
   conditioning traffic through the forwarding path (datapath) of a
   network device.  This selection and conditioning of traffic in the
   datapath spans both major QoS architectures: Differentiated Services
   and Integrated Services.

   This document should be used with the QoS Policy Information Model
   (QPIM) to model how policies can be defined to manage and configure
   the QoS mechanisms (i.e., the classification, marking, metering,
   dropping, queuing, and scheduling functionality) of devices.
   Together, these two documents describe how to write QoS policy rules
   to configure and manage the QoS mechanisms present in the datapaths
   of devices.





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   This document, as well as QPIM, are information models.  That is,
   they represent information independent of a binding to a specific
   type of repository.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
       1.1.  Policy Management Conceptual Model . . . . . . . . . . .  6
       1.2.  Purpose and Relation to Other Policy Work. . . . . . . .  7
       1.3.  Typical Examples of Policy Usage . . . . . . . . . . . .  7
   2.  Approach . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
       2.1.  Common Needs Of DiffServ and IntServ . . . . . . . . . .  8
       2.2.  Specific Needs Of DiffServ . . . . . . . . . . . . . . .  9
       2.3.  Specific Needs Of IntServ. . . . . . . . . . . . . . . .  9
   3.  Methodology. . . . . . . . . . . . . . . . . . . . . . . . . . 10
       3.1.  Level of Abstraction for Expressing QoS Policies . . . . 10
       3.2.  Specifying Policy Parameters . . . . . . . . . . . . . . 11
       3.3.  Specifying Policy Services . . . . . . . . . . . . . . . 12
       3.4.  Level of Abstraction for Defining QoS Attributes and
             Classes. . . . . . . . . . . . . . . . . . . . . . . . . 13
       3.5.  Characterization of QoS Properties . . . . . . . . . . . 14
       3.6.  QoS Information Model Derivation . . . . . . . . . . . . 15
       3.7.  Attribute Representation . . . . . . . . . . . . . . . . 16
       3.8.  Mental Model . . . . . . . . . . . . . . . . . . . . . . 17
             3.8.1.  The QoSService Class . . . . . . . . . . . . . . 17
             3.8.2.  The ConditioningService Class. . . . . . . . . . 18
             3.8.3.  Preserving QoS Information from Ingress to
                     Egress . . . . . . . . . . . . . . . . . . . . . 19
       3.9.  Classifiers, FilterLists, and Filter Entries . . . . . . 21
       3.10. Modeling of Droppers . . . . . . . . . . . . . . . . . . 23
             3.10.1. Configuring Head and Tail Droppers . . . . . . . 23
             3.10.2. Configuring RED Droppers . . . . . . . . . . . . 24
       3.11. Modeling of Queues and Schedulers. . . . . . . . . . . . 25
             3.11.1. Simple Hierarchical Scheduler. . . . . . . . . . 25
             3.11.2. Complex Hierarchical Scheduler . . . . . . . . . 27
             3.11.3. Excess Capacity Scheduler. . . . . . . . . . . . 29
             3.11.4. Hierarchical CBQ Scheduler . . . . . . . . . . . 31
   4.  The Class Hierarchy. . . . . . . . . . . . . . . . . . . . . . 33
       4.1.  Associations and Aggregations. . . . . . . . . . . . . . 33
       4.2.  The Structure of the Class Hierarchies . . . . . . . . . 34
       4.3.  Class Definitions. . . . . . . . . . . . . . . . . . . . 38
             4.3.1.  The Abstract Class ManagedElement. . . . . . . . 38
             4.3.2.  The Abstract Class ManagedSystemElement. . . . . 39
             4.3.3.  The Abstract Class LogicalElement. . . . . . . . 39
             4.3.4.  The Abstract Class Service . . . . . . . . . . . 39
             4.3.5.  The Class ConditioningService. . . . . . . . . . 39
             4.3.6.  The Class ClassifierService. . . . . . . . . . . 40
             4.3.7.  The Class ClassifierElement. . . . . . . . . . . 41



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             4.3.8.  The Class MeterService . . . . . . . . . . . . . 42
             4.3.9.  The Class AverageRateMeterService. . . . . . . . 44
             4.3.10. The Class EWMAMeterService . . . . . . . . . . . 44
             4.3.11. The Class TokenBucketMeterService. . . . . . . . 46
             4.3.12. The Class MarkerService. . . . . . . . . . . . . 47
             4.3.13. The Class PreambleMarkerService. . . . . . . . . 47
             4.3.14. The Class ToSMarkerService . . . . . . . . . . . 48
             4.3.15. The Class DSCPMarkerService. . . . . . . . . . . 49
             4.3.16. The Class 8021QMarkerService . . . . . . . . . . 49
             4.3.17. The Class DropperService . . . . . . . . . . . . 50
             4.3.18. The Class HeadTailDropperService . . . . . . . . 52
             4.3.19. The Class REDDropperService. . . . . . . . . . . 52
             4.3.20. The Class QueuingService . . . . . . . . . . . . 54
             4.3.21. The Class PacketSchedulingService. . . . . . . . 55
             4.3.22. The Class NonWorkConservingSchedulingService . . 56
             4.3.23. The Class QoSService . . . . . . . . . . . . . . 57
             4.3.24. The Class DiffServService. . . . . . . . . . . . 58
             4.3.25. The Class AFService. . . . . . . . . . . . . . . 59
             4.3.26. The Class FlowService. . . . . . . . . . . . . . 60
             4.3.27. The Class DropThresholdCalculationService. . . . 60
             4.3.28. The Abstract Class FilterEntryBase . . . . . . . 61
             4.3.29. The Class IPHeaderFilter . . . . . . . . . . . . 62
             4.3.30. The Class 8021Filter . . . . . . . . . . . . . . 62
             4.3.31. The Class PreambleFilter . . . . . . . . . . . . 62
             4.3.32. The Class FilterList . . . . . . . . . . . . . . 63
             4.3.33. The Abstract Class ServiceAccessPoint. . . . . . 63
             4.3.34. The Class ProtocolEndpoint . . . . . . . . . . . 63
             4.3.35. The Abstract Class Collection. . . . . . . . . . 65
             4.3.36. The Abstract Class CollectionOfMSEs. . . . . . . 65
             4.3.37. The Class BufferPool . . . . . . . . . . . . . . 65
             4.3.38. The Abstract Class SchedulingElement . . . . . . 65
             4.3.39. The Class AllocationSchedulingElement. . . . . . 66
             4.3.40. The Class WRRSchedulingElement . . . . . . . . . 67
             4.3.41. The Class PrioritySchedulingElement. . . . . . . 69
             4.3.42. The Class BoundedPrioritySchedulingElement . . . 70
       4.4.  Association Definitions. . . . . . . . . . . . . . . . . 70
             4.4.1.  The Abstract Association Dependency. . . . . . . 71
             4.4.2.  The Association ServiceSAPDependency . . . . . . 71
             4.4.3.  The Association
                     IngressConditioningServiceOnEndpoint . . . . . . 71
             4.4.4.  The Association
                     EgressConditioningServiceOnEndpoint. . . . . . . 72
             4.4.5.  The Association HeadTailDropQueueBinding . . . . 72
             4.4.6.  The Association CalculationBasedOnQueue. . . . . 73
             4.4.7.  The Association ProvidesServiceToElement . . . . 74
             4.4.8.  The Association ServiceServiceDependency . . . . 74
             4.4.9.  The Association CalculationServiceForDropper . . 75
             4.4.10. The Association QueueAllocation. . . . . . . . . 75



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             4.4.11. The Association ClassifierElementUsesFilterList. 76
             4.4.12. The Association AFRelatedServices. . . . . . . . 77
             4.4.13. The Association NextService. . . . . . . . . . . 78
             4.4.14. The Association
                     NextServiceAfterClassifierElement. . . . . . . . 79
             4.4.15. The Association NextScheduler. . . . . . . . . . 80
             4.4.16. The Association FailNextScheduler. . . . . . . . 81
             4.4.17. The Association NextServiceAfterMeter. . . . . . 82
             4.4.18. The Association QueueToSchedule. . . . . . . . . 83
             4.4.19. The Association SchedulingServiceToSchedule. . . 84
             4.4.20. The Aggregation MemberOfCollection . . . . . . . 85
             4.4.21. The Aggregation CollectedBufferPool. . . . . . . 85
             4.4.22. The Abstract Aggregation Component . . . . . . . 86
             4.4.23. The Aggregation ServiceComponent . . . . . . . . 86
             4.4.24. The Aggregation QoSSubService. . . . . . . . . . 86
             4.4.25. The Aggregation QoSConditioningSubService. . . . 87
             4.4.26. The Aggregation
                     ClassifierElementInClassifierService . . . . . . 88
             4.4.27. The Aggregation EntriesInFilterList. . . . . . . 89
             4.4.28. The Aggregation ElementInSchedulingService . . . 90
   5.  Intellectual Property Statement. . . . . . . . . . . . . . . . 91
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 91
   7.  Security Considerations. . . . . . . . . . . . . . . . . . . . 91
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 92
       8.1. Normative References. . . . . . . . . . . . . . . . . . . 92
       8.2. Informative References  . . . . . . . . . . . . . . . . . 92
   9.  Appendix A:  Naming Instances in a Native CIM Implementation . 94
       9.1. Naming Instances of the Classes Derived from Service. . . 94
       9.2. Naming Instances of Subclasses of FilterEntryBase . . . . 94
       9.3. Naming Instances of ProtocolEndpoint. . . . . . . . . . . 94
       9.4. Naming Instances of BufferPool. . . . . . . . . . . . . . 95
             9.4.1.  The Property CollectionID. . . . . . . . . . . . 95
             9.4.2.  The Property CreationClassName . . . . . . . . . 95
       9.5. Naming Instances of SchedulingElement . . . . . . . . . . 95
   10. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 96
   11. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 97

1. Introduction

   The purpose of this document is to define an information model to
   describe the quality of service (QoS) mechanisms inherent in
   different network devices, including hosts.  Broadly speaking, these
   mechanisms describe the attributes common to selecting and
   conditioning traffic through the forwarding path (datapath) of a
   network device.  This selection and conditioning of traffic in the
   datapath spans both major QoS architectures: Differentiated Services
   (see [R2475]) and Integrated Services (see [R1633]).




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   This document is intended to be used with the QoS Policy Information
   Model [QPIM] to model how policies can be defined to manage and
   configure the QoS mechanisms (i.e., the classification, marking,
   metering, dropping, queuing, and scheduling functionality) of
   devices.  Together, these two documents describe how to write QoS
   policy rules to configure and manage the QoS mechanisms present in
   the datapaths of devices.

   This document, as well as [QPIM], are information models.  That is,
   they represent information independent of a binding to a specific
   type of repository.  A separate document could be written to provide
   a mapping of the data contained in this document to a form suitable
   for implementation in a directory that uses (L)DAP as its access
   protocol.  Similarly, a document could be written to provide a
   mapping of the data in [QPIM] to a directory. Together, these four
   documents (information models and directory schema mappings) would
   then describe how to write QoS policy rules that can be used to store
   information in directories to configure device QoS mechanisms.

   The approach taken in this document defines a common set of classes
   that can be used to model QoS in a device datapath. Vendors can then
   map these classes, either directly or using an intervening format
   like a COP-PR PIB, to their own device-specific implementations.
   Note that the admission control element of Integrated Services is not
   included in the scope of this model.

   The design of the class, association, and aggregation hierarchies
   described in this document is influenced by the Network QoS submodel
   defined by the Distributed Management Task Force (DMTF) - see [CIM].
   These hierarchies are not derived from the Policy Core Information
   Model [PCIM].  This is because the modeling of the QoS mechanisms of
   a device is separate and distinct from the modeling of policies that
   manage those mechanisms.  Hence, there is a need to separate QoS
   mechanisms (this document) from their control (specified using the
   generic policy document [PCIM] augmented by the QoS Policy document
   [QPIM]).

   While it is not a policy model per se, this document does have a
   dependency on the Policy Core Information Model Extensions document
   [PCIME].  The device-level packet filtering, through which a
   Classifier splits a traffic stream into multiple streams, is based on
   the FilterEntryBase and FilterList classes defined in [PCIME].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14, RFC 2119
   [R2119].




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1.1.  Policy Management Conceptual Model

   The Policy Core Information Model [PCIM] describes a general
   methodology for constructing policy rules.  PCIM Extensions [PCIME]
   updates and extends the original PCIM.  A policy rule aggregates a
   set of policy conditions and an ordered set of policy actions.  The
   semantics of a policy rule are such that if the set of conditions
   evaluates to TRUE, then the set of actions are executed.

   Policy conditions and actions have two principal components: operands
   and operators.  Operands can be constants or variables. To specify a
   policy, it is necessary to specify:

   o  the operands to be examined (also known as state variables);

   o  the operands to be changed (also known as configuration
      variables);

   o  the relationships between these two sets of operands.

   Operands can be specified at a high-level, such as Joe (a user) or
   Gold (a service).  Operands can also be specified at a much finer
   level of detail, one that is much closer to the operation of the
   device.  Examples of the latter include an IP Address or a queue's
   bandwidth allocation.  Implicit in the use of operands is the binding
   of legal values or ranges of values to an operand.  For example, the
   value of an IP address cannot be an integer.  The concepts of
   operands and their ranges are defined in [PCIME].

   The second component of policy conditions and actions is a set of
   operators.  Operators can express both relationships (greater than,
   member of a set, Boolean OR, etc.) and assignments.  Together,
   operators and operands can express a variety of conditions and
   actions, such as:

      If Bob is an Engineer...
      If the source IP address is in the Marketing Subnet...
      Set Joe's IP address to 192.0.2.100
      Limit the bandwidth of application x to 10 Mb

   We recognize that the definition of operator semantics is critical to
   the definition of policies.  However, the definition of these
   operators is beyond the scope of this document.  Rather, this
   document (with [QPIM]) takes the first steps in identifying and
   standardizing a set of properties (operands) for use in defining
   policies for Differentiated and Integrated Services.





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1.2.  Purpose and Relation to Other Policy Work

   This model establishes a canonical model of the QoS mechanisms of a
   network device (e.g., a router, switch, or host) that is independent
   of any specific type of network device.  This enables traffic
   conditioning to be described using a common set of abstractions,
   modeled as a set of services and sub-services.

   When the concepts of this document are used in conjunction with the
   concepts of [QPIM], one is able to define policies that bind the
   services in a network to the needs of applications using that
   network.  In other words, the business requirements of an
   organization can be reflected in one set of policies, and those
   policies can be translated to a lower-level set of policies that
   control and manage the configuration and operation of network
   devices.

1.3.  Typical Examples of Policy Usage

   Policies could be implemented as low-level rules using the
   information model described in this specification.  For example, in a
   low-level policy, a condition could be represented as an evaluation
   of a specific attribute from this model.  Therefore, a condition such
   as "If filter = HTTP" would be interpreted as a test determining
   whether any HTTP filters have been defined for the device.  A high-
   level policy, such as "If protocol = HTTP, then mark with
   Differentiated Services Code Point (DSCP) 24," would be expressed as
   a series of actions in a low-level policy using the classes and
   attributes described below:

   1.  Create HTTP filter
   2.  Create DSCP marker with the value of 24
   3.  Bind the HTTP filter to the DSCP marker

   Note that unlike "mark with DSCP 24," these low-level actions are not
   performed on a packet as it passes through the device. Rather, they
   are configuration actions performed on the device itself, to make it
   ready to perform the correct action(s) on the correct packet(s).  The
   act of moving from a high-level policy rule to the correct set of
   low-level device configuration actions is an example of what
   [POLTERM] characterizes as "policy translation" or "policy
   conversion".









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2.  Approach

   QoS activities in the IETF have mainly focused in two areas,
   Integrated Services (IntServ) and Differentiated Services (DiffServ)
   (see [POLTERM], [R1633] and [R2475]).  This document focuses on the
   specification of QoS properties and classes for modeling the datapath
   where packet traffic is conditioned. However, the framework defined
   by the classes in this document has been designed with the needs of
   the admission control portion of IntServ in mind as well.

2.1.  Common Needs Of DiffServ and IntServ

   First, let us consider IntServ.  IntServ has two principal
   components.  One component is embedded in the datapath of the
   networking device.  Its functions include the classification and
   policing of individual flows, and scheduling admitted packets for the
   outbound link.  The other component of IntServ is admission control,
   which focuses on the management of the signaling protocol (e.g., the
   PATH and RESV messages of RSVP).  This component processes
   reservation requests, manages bandwidth, outsources decision making
   to policy servers, and interacts with the Routing Table manager.

   We will consider RSVP when defining the structure of this information
   model.  As this document focuses on the datapath, elements of RSVP
   applicable to the datapath will be considered in the structure of the
   classes.  The complete IntServ device model will, as we have
   indicated earlier, be addressed in a subsequent document.

   This document models a small subset of the QoS policy problem, in
   hopes of constructing a methodology that can be adapted for other
   aspects of QoS in particular, and of policy construction in general.
   The focus in this document is on QoS for devices that implement
   traffic conditioning in the datapath.

   DiffServ operates exclusively in the datapath.  It has all of the
   same components of the IntServ datapath, with two major differences.
   First, DiffServ classifies packets based solely on their DSCP field,
   whereas IntServ examines a subset of a standard flow's addressing 5-
   tuple.  The exception to this rule occurs in a router or host at the
   boundary of a DiffServ domain.  A device in this position may examine
   a packet's DSCP, its addressing 5-tuple, other fields in the packet,
   or even information wholly outside the packet, in determining the
   DSCP value with which to mark the packet prior to its transfer into
   the DiffServ domain.  However, routers in the interior of a DiffServ
   domain will only need to classify based on the DSCP field.






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   The second difference between IntServ and DiffServ is that the
   signaling protocol used in IntServ (e.g., RSVP) affects the
   configuration of the datapath in a more dynamic fashion.  This is
   because each newly admitted RSVP reservation requires a
   reconfiguration of the datapath.  In contrast, DiffServ requires far
   fewer changes to the datapath after the Per Hop Behaviors (PHBs) have
   been configured.

   The approach advocated in this document for the creation of policies
   that control the various QoS mechanisms of networking devices is to
   first identify the attributes with which policies are to be
   constructed.  These attributes are the parameters used in expressions
   that are necessary to construct policies.  There is also a parallel
   desire to define the operators, relations, and precedence constructs
   necessary to construct the conditions and actions that constitute
   these policies.  However, these efforts are beyond the scope of this
   document.

2.2.  Specific Needs Of DiffServ

   DiffServ-specific rules focus on two particular areas: the core and
   the edges of the network.  As explained in the DiffServ Architecture
   document [R2475], devices at the edge of the network classify traffic
   into different traffic streams.  The core of the network then
   forwards traffic from different streams by using a set of Per Hop
   Behaviors (PHBs).  A DSCP identifies each PHB. The DSCP is part of
   the IP header of each packet (as described in [R2474]).  This enables
   multiple traffic streams to be aggregated into a small number of
   aggregated traffic streams, where each aggregate traffic stream is
   identified by a particular DSCP, and forwarded using a particular
   PHB.

   The attributes used to manipulate QoS capabilities in the core of the
   network primarily address the behavioral characteristics of each
   supported PHB.  At the edges of the DiffServ network, the additional
   complexities of flow classification, policing, RSVP mappings,
   remarkings, and other factors have to be considered. Additional
   modeling will be required in this area.  However, first, the
   standards for edges of the DiffServ network need more detail - to
   allow the edges to be incorporated into the policy model.

2.3.  Specific Needs Of IntServ

   This document focuses exclusively on the forwarding aspects of
   network QoS.  Therefore, while the forwarding aspects of IntServ are
   considered, the management of IntServ is not considered. This topic
   will be addressed in a future document.




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3.  Methodology

   There is a clear need to define attributes and behavior that together
   define how traffic should be conditioned.  This document defines a
   set of classes and relationships that represent the QoS mechanisms
   used to condition traffic; [QPIM] is used to define policies to
   control the QoS mechanisms defined in this document.

   However, some very basic issues need to be considered when combining
   these documents.  Considering these issues should help in
   constructing a schema for managing the operation and configuration of
   network QoS mechanisms through the use of QoS policies.

3.1.  Level of Abstraction for Expressing QoS Policies

   The first issue requiring consideration is the level of abstraction
   at which QoS policies should be expressed.  If we consider policies
   as a set of rules used to react to events and manipulate attributes
   or generate new events, we realize that policy represents a continuum
   of specifications that relate business goals and rules to the
   conditioning of traffic done by a device or a set of devices.  An
   example of a business level policy might be: from 1:00 pm PST to 7:00
   am EST, sell off 40% of the network capacity on the open market.  In
   contrast, a device-specific policy might be: if the queue depth grows
   at a geometric rate over a specified duration, trigger a potential
   link failure event.

   A general model for this continuum is shown in Figure 1 below.

   +---------------------+
   | High-Level Business |    Not directly related to device
   |     Policies        |    operation and configuration details
   +---------------------+
             |
             |
   +---------V-----------+
   | Device-Independent  |    Translate high-level policies to
   |       Policies      |    generic device operational and
   +---------------------+    configuration information
             |
             |
   +---------V-----------+
   |   Device-Dependent  |    Translate generic device information
   |       Policies      |    to specify how particular devices
   +---------------------+    should operate and be configured

   Figure 1.  The Policy Continuum




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   High-level business policies are used to express the requirements of
   the different applications, and prioritize which applications get
   "better" treatment when the network is congested.  The goal, then, is
   to use policies to relate the operational and configuration needs of
   a device directly to the business rules that the network
   administrator is trying to implement in the network that the device
   belongs to.

   Device-independent policies translate business policies into a set of
   generalized operational and configuration policies that are
   independent of any specific device, but dependent on a particular set
   of QoS mechanisms, such as random early detection (RED) dropping or
   weighted round robin scheduling.  Not only does this enable different
   types of devices (routers, switches, hosts, etc.) to be controlled by
   QoS policies, it also enables devices made by different vendors that
   use the same types of QoS mechanisms to be controlled.  This enables
   these different devices to each supply the correct relative
   conditioning to the same type of traffic.

   In contrast, device-dependent policies translate device-independent
   policies into ones that are specific for a given device.  The reason
   that a distinction is made between device-independent and device-
   dependent policies is that in a given network, many different devices
   having many different capabilities need to be controlled together.
   Device-independent policies provide a common layer of abstraction for
   managing multiple devices of different capabilities, while device-
   dependent policies implement the specific conditioning that is
   required.  This document provides a common set of abstractions for
   representing QoS mechanisms in a device-independent way.

   This document is focused on the device-independent representation of
   QoS mechanisms.  QoS mechanisms are modeled in sufficient detail to
   provide a common device-independent representation of QoS policies.
   They can also be used to provide a basis for specialization, enabling
   each vendor to derive a set of vendor-specific classes that represent
   how traffic conditioning is done for that vendor's set of devices.

3.2.  Specifying Policy Parameters

   Policies are a function of parameters (attributes) and operators
   (boolean, arithmetic, relational, etc.).  Therefore, both need to be
   defined as part of the same policy in order to correctly condition
   the traffic.  If the parameters of the policy are specified too
   narrowly, they will reflect the individual implementations of QoS in
   each device.  As there is currently little consensus in the industry
   on what the correct implementation model for QoS is, most defined
   attributes would only be applicable to the unique characteristics of
   a few individual devices.  Moreover, standardizing all of these



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   potential implementation alternatives would be a never-ending task as
   new implementations continued to appear on the market.

   On the other hand, if the parameters of the policy are specified too
   broadly, it is impossible to develop meaningful policies. For
   example, if we concentrate on the so-called Olympic set of policies,
   a business policy like "Bob gets Gold Service," is clearly
   meaningless to the large majority of existing devices. This is
   because the device has no way of determining who Bob is, or what QoS
   mechanisms should be configured in what way to provide Gold service.

   Furthermore, Gold service may represent a single service, or it may
   identify a set of services that are related to each other. In the
   latter case, these services may have different conditioning
   characteristics.

   This document defines a set of parameters that fit into a canonical
   model for modeling the elements in the forwarding path of a device
   implementing QoS traffic conditioning.  By defining this model in a
   device-independent way, the needed parameters can be appropriately
   abstracted.

3.3.  Specifying Policy Services

   Administrators want the flexibility to be able to define traffic
   conditioning without having to have a low-level understanding of the
   different QoS mechanisms that implement that conditioning.
   Furthermore, administrators want the flexibility to group different
   services together, describing a higher-level concept such as "Gold
   Service".  This higher-level service could be viewed as providing the
   processing to deliver "Gold" quality of service.

   These two goals dictate the need for the following set of
   abstractions:

   o  a flexible way to describe a service

   o  must be able to group different services that may use different
      technologies (e.g., DiffServ and IEEE 802.1Q) together

   o  must be able to define a set of sub-services that together make up
      a higher-level service

   o  must be able to associate a service and the set of QoS mechanisms
      that are used to condition traffic for that service

   o  must be able to define policies that manage the QoS mechanisms
      used to implement a service.



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   This document addresses this set of problems by defining a set of
   classes and associations that can represent abstract concepts like
   "Gold Service," and bind each of these abstract services to a
   specific set of QoS mechanisms that implement the conditioning that
   they require.  Furthermore, this document defines the concept of
   "sub-services," to enable Gold Service to be defined either as a
   single service or as a set of services that together should be
   treated as an atomic entity.

   Given these abstractions, policies (as defined in [QPIM]) can be
   written to control the QoS mechanisms and services defined in this
   document.

3.4.  Level of Abstraction for Defining QoS Attributes and Classes

   This document defines a set of classes and properties to support
   policies that configure device QoS mechanisms.  This document
   concentrates on the representation of services in the datapath that
   support both DiffServ (for aggregate traffic conditioning) and
   IntServ (for flow-based traffic conditioning).  Classes and
   properties for modeling IntServ admission control services may be
   defined in a future document.

   The classes and properties in this document are designed to be used
   in conjunction with the QoS policy classes and properties defined in
   [QPIM].  For example, to preserve the delay characteristics committed
   to an end-user, a network administrator may wish to create policies
   that monitor the queue depths in a device, and adjust resource
   allocations when delay budgets are at risk (perhaps as a result of a
   network topology change).  The classes and properties in this
   document define the specific services and mechanisms required to
   implement those services. The classes and properties defined in
   [QPIM] provide the overall structure of the policy that manages and
   configures this service.

   This combination of low-level specification (using this document) and
   high-level structuring (using [QPIM]) of network services enables
   network administrators to define new services required of the
   network, that are directly related to business goals, while ensuring
   that such services can be managed.  However, this goal (of creating
   and managing service-oriented policies) can only be realized if
   policies can be constructed that are capable of supporting diverse
   implementations of QoS.  The solution is to model the QoS
   capabilities of devices at the behavioral level. This means that for
   traffic conditioning services realized in the datapath, the model
   must support the following characteristics:

   o  modeling of a generic network service that has QoS capabilities



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   o  modeling of how the traffic conditioning itself is defined

   o  modeling of how statistics are gathered to monitor QoS traffic
      conditioning services - this facet of the model will be added in a
      future document.

   This document models a network service, and associates it with one or
   more QoS mechanisms that are used to implement that service.  It also
   models in a canonical form the various components that are used to
   condition traffic, such that standard as well as custom traffic
   conditioning services may be described.

3.5.  Characterization of QoS Properties

   The QoS properties and classes will be described in more detail in
   Section 4.  However, we should consider the basic characteristics of
   these properties, to understand the methodology for representing
   them.

   There are essentially two types of properties, state and
   configuration.  Configuration properties describe the desired state
   of a device, and include properties and classes for representing
   desired or proposed thresholds, bandwidth allocations, and how to
   classify traffic.  State properties describe the actual state of the
   device.  These include properties to represent the current
   operational values of the attributes in devices configured via the
   configuration properties, as well as properties that represent state
   (queue depths, excess capacity consumption, loss rates, and so
   forth).

   In order to be correlated and used together, these two types of
   properties must be modeled using a common information model.  The
   possibility of modeling state properties and their corresponding
   configuration settings is accomplished using the same classes in this
   model - although individual instances of the classes would have to be
   appropriately named or placed in different containers to distinguish
   current state values from desired configuration settings.

   State information is addressed in a very limited fashion by QDDIM.
   Currently, only CurrentQueueDepth is proposed as an attribute on
   QueuingService.  The majority of the model is related to
   configuration.  Given this fact, it is assumed that this model is a
   direct memory map into a device.  All manipulation of model classes
   and properties directly affects the state of the device.  If it is
   desired to also use these classes to represent desired configuration,
   that is left to the discretion of the implementor.





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   It is acknowledged that additional properties are needed to
   completely model current state.  However, many of the properties
   defined in this document represent exactly the state variables that
   will be configured by the configuration properties.  Thus, the
   definition of the configuration properties has an exact
   correspondence with the state properties, and can be used in modeling
   both actual (state) and desired/proposed configuration.

3.6.  QoS Information Model Derivation

   The question of context also leads to another question: how does the
   information specified in the core and QoS policy models ([PCIM],
   [PCIME], and [QPIM], respectively) integrate with the information
   defined in this document?  To put it another way, where should
   device-independent concepts that lead to device-specific QoS
   attributes be derived from?

   Past thinking was that QoS was part of the policy model.  This view
   is not completely accurate, and it leads to confusion.  QoS is a set
   of services that can be controlled using policy.  These services are
   represented as device mechanisms.  An important point here is that
   QoS services, as well as other types of services (e.g., security),
   are provided by the mechanisms inherent in a given device.  This
   means that not all devices are indeed created equal.  For example,
   although two devices may have the same type of mechanism (e.g., a
   queue), one may be a simple implementation (i.e., a FIFO queue)
   whereas one may be much more complex and robust (e.g., class-based
   weighted fair queuing (CBWFQ)).  However, both of these devices can
   be used to deliver QoS services, and both need to be controlled by
   policy.  Thus, a device-independent policy can instruct the devices
   to queue certain traffic, and a device-specific policy can be used to
   control the queuing in each device.

   Furthermore, policy is used to control these mechanisms, not to
   represent them.  For example, QoS services are implemented with
   classifiers, meters, markers, droppers, queues, and schedulers.
   Similarly, security is also a characteristic of devices, as
   authentication and encryption capabilities represent services that
   networked devices perform (irrespective of interactions with policy
   servers).  These security services may use some of the same
   mechanisms that are used by QoS services, such as the concepts of
   filters.  However, they will mostly require different mechanisms than
   the ones used by QoS, even though both sets of services are
   implemented in the same devices.

   Thus, the similarity between the QoS model and models for other
   services is not so much that they contain a few common mechanisms.
   Rather, they model how a device implements their respective services.



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   As such, the modeling of QoS should be part of a networking device
   schema rather than a policy schema.  This allows the networking
   device schema to concentrate on modeling device mechanisms, and the
   policy schema to focus on the semantics of representing the policy
   itself (conditions, actions, operators, etc.).  While this document
   concentrates on defining an information model to represent QoS
   services in a device datapath, the ultimate goal is to be able to
   apply policies that control these services in network devices.
   Furthermore, these two schemata (device and policy) must be tightly
   integrated in order to enable policy to control QoS services.

3.7.  Attribute Representation

   The last issue to be considered is the question of how attributes are
   represented.  If QoS attributes are represented as absolute numbers
   (e.g., Class AF2 gets 2 Mbs of bandwidth), it is more difficult to
   make them uniform across multiple ports in a device or across
   multiple devices, because of the broad variation in link capacities.
   However, expressing attributes in relative or proportional terms
   (e.g., Class AF2 gets 5% of the total link bandwidth) makes it more
   difficult to express certain types of conditions and actions, such
   as:

      (If ConsumedBandwidth = AssignedBandwidth Then ...)

   There are really three approaches to addressing this problem:

   o  Multiple properties can be defined to express the same value in
      various forms.  This idea has been rejected because of the
      difficulty in keeping these different properties synchronized
      (e.g., when one property changes, the others all have to be
      updated).

   o  Multi-modal properties can be defined to express the same value,
      in different terms, based on the access or assignment mode.  This
      option was rejected because it significantly complicates the model
      and is impossible to express in current directory access protocols
      (e.g., (L)DAP).

   o  Properties can be expressed as "absolutes", but the operators in
      the policy schema would need to be more sophisticated.  Thus, to
      represent a percentage, division and multiplication operators are
      required (e.g., Class AF2 gets .05 * the total link bandwidth).
      This is the approach that has been taken in this document.







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3.8.  Mental Model

   The mental model for constructing this schema is based on the work
   done in the Differentiated Services working group.  This schema is
   based on information provided in the current versions of the DiffServ
   Informal Management Model [DSMODEL], the DiffServ MIB [DSMIB], the
   PIB [PIB], as well as on information in the set of RFCs that
   constitute the basic definition of DiffServ itself ([R2475], [R2474],
   [R2597], and [R3246]).  In addition, a common set of terminology is
   available in [POLTERM].

   This model is built around two fundamental class hierarchies that are
   bound together using a set of associations.  The two class
   hierarchies derive from the QoSService and ConditioningService base
   classes.  A set of associations relate lower-level QoSService
   subclasses to higher-level QoS services, relate different types of
   conditioning services together in processing a traffic class, and
   relate a set of conditioning services to a specific QoS service.
   This combination of associations enables us to view the device as
   providing a set of services that can be configured, in a modular
   building block fashion, to construct application-specific services.
   Thus, this document can be used to model existing and future standard
   as well as application-specific network QoS services.

3.8.1.  The QoSService Class

   The first of the classes defined here, QoSService, is used to
   represent higher-level network services that require special
   conditioning of their traffic.  An instance of QoSService (or one of
   its subclasses) is used to bring together a group of conditioning
   services that, from the perspective of the system manager, are all
   used to deliver a common service.  Thus, the set of classifiers,
   markers, and related conditioning services that provide premium
   service to the "selected" set of user traffic may be grouped together
   into a premium QoS service.

   QoSService has a set of subclasses that represent different
   approaches to delivering IP services.  The currently defined set of
   subclasses are a FlowService for flow-oriented QoS delivery and a
   DiffServService for DiffServ aggregate-oriented QoS service delivery.

   The QoS services can be related to each other as peers, or they can
   be implemented as subservient services to each other.  The
   QoSSubService aggregation indicates that one or more QoSService
   objects are subservient to a particular QoSService object.  For
   example, this enables us to define Gold Service as a combination of
   two DiffServ services, one for high quality traffic treatment, and
   one for servicing the rest of the traffic.  Each of these



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   DiffServService objects would be associated with a set of
   classifiers, markers, etc, such that the high quality traffic would
   get EF marking and appropriate queuing.

   The DiffServService class itself has an AFService subclass.  This
   subclass is used to represent the specific notion that several
   related markings within the AF PHB Group work together to provide a
   single service.  When other DiffServ PHB Groups are defined that use
   more than one code point, these will be likely candidates for
   additional DiffServService subclasses.

   Technology-specific mappings of these services, representing the
   specific use of PHB marking or 802.1Q marking, are captured within
   the ConditioningService hierarchy, rather than in the subclasses of
   QoSService.

   These concepts are depicted in Figure 2.  Note that both of the
   associations are aggregations: a QoSService object aggregates both
   the set of QoSService objects subservient to it, and the set of
   ConditioningService objects that realize it.  See Section 4 for class
   and association definitions.

                /\______
           0..1 \/      |
   +--------------+     | QoSSubService     +---------------+
   |              |0..n |                   |               |
   |  QoSService  |-----                    | Conditioning  |
   |              |                         |   Service     |
   |              |                         |               |
   |              |0..n                 0..n|               |
   |              | /\______________________|               |
   |              | \/  QoSConditioning     |               |
   +--------------+       SubService        +---------------+

   Figure 2.  QoSService and its Aggregations

3.8.2.  The ConditioningService Class

   The goal of the ConditioningService classes is to describe the
   sequence of traffic conditioning that is applied to a given traffic
   stream on the ingress interface through which it enters a device, and
   then on the egress interface through which it leaves the device.
   This is done using a set of classes and relationships.  The routing
   decision in the device core, which selects which egress interface a
   particular packet will use, is not represented in this model.

   A single base class, ConditioningService, is the superclass for a set
   of subclasses representing the mechanisms that condition traffic.



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   These subclasses define device-independent conditioning primitives
   (including classifiers, meters, markers, droppers, queues, and
   schedulers) that together implement the conditioning of traffic on an
   interface.  This model abstracts these services into a common set of
   modular building blocks that can be used, regardless of device
   implementation, to model the traffic conditioning internal to a
   device.

   The different conditioning mechanisms need to be related to each
   other to describe how traffic is conditioned.  Several important
   variations of how these services are related together exist:

   o  A particular ingress or egress interface may not require all the
      types of ConditioningServices.

   o  Multiple instances of the same mechanism may be required on an
      ingress or egress interface.

   o  There is no set order of application for the ConditioningServices
      on an ingress or egress interface.

   Therefore, this model does not dictate a fixed ordering among the
   subclasses of ConditioningService, or identify a subclass of
   ConditioningService that must appear first or last among the
   ConditioningServices on an ingress or egress interface.  Instead,
   this model ties together the various ConditioningService instances on
   an ingress or egress interface using the NextService,
   NextServiceAfterMeter, and NextServiceAfterConditioningElement
   associations.  There are also separate associations, called
   IngressConditioningServiceOnEndpoint and
   EgressConditioningServiceOnEndpoint, which, respectively, tie an
   ingress interface to its first ConditioningService, and tie an egress
   interface to its last ConditioningService(s).

3.8.3.  Preserving QoS Information from Ingress to Egress

   There is one important way in which the QDDIM model diverges from the
   [DSMODEL].  In [DSMODEL], traffic passes through a network device in
   three stages:

   o  It comes in on an ingress interface, where it may receive QoS
      conditioning.

   o  It traverses the routing core, where logic outside the scope of
      QoS determines which egress interface it will use to leave the
      device.





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   o  It may receive further QoS conditioning on the selected egress
      interface, and then it leaves the device.

   In this model, no information about the QoS conditioning that a
   packet receives on the ingress interface is communicated with the
   packet across the routing core to the egress interface.

   The QDDIM model relaxes this restriction, to allow information about
   the treatment that a packet received on an ingress interface to be
   communicated along with the packet to the egress interface.  (This
   relaxation adds a capability that is present in many network
   devices.)  QDDIM represents this information transfer in terms of a
   packet preamble, which is how many devices implement it.  But
   implementations are free to use other mechanisms to achieve the same
   result.

       +---------+
       | Meter-A |
    a  |         | b      d
   --->|      In-|---PM-1--->
       |         | c      e
       |     Out-|---PM-2--->
       +---------+

   Figure 3:  Meter Followed by Two Preamble Markers

   Figure 3 shows an example in which meter results are captured in a
   packet preamble.  The arrows labeled with single letters represent
   instances of either the NextService association (a, d, and e), or of
   its peer association NextServiceAfterMeter (b and c).  PreambleMarker
   PM-1 adds to the packet preamble an indication that the packet exited
   Meter A as conforming traffic. Similarly, PreambleMarker PM-2 adds to
   the preambles of packets that come through it indications that they
   exited Meter A as nonconforming traffic.  A PreambleMarker appends
   its information to whatever is already present in a packet preamble,
   as opposed to overwriting what is already there.

   To foster interoperability, the basic format of the information
   captured by a PreambleMarker is specified.  (Implementations, of
   course, are free to represent this information in a different way
   internally - this is just how it is represented in the model.) The
   information is represented by an ordered, multi-valued string
   property FilterItemList, where each individual value of the property
   is of the form "<type>,<value>".  When a PreambleMarker "appends" its
   information to the information that was already present in a packet
   preamble, it does so by adding additional items of the indicated
   format to the end of the list.




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   QDDIM provides a limited set of <type>'s that a PreambleMarker may
   use:

   o  ConformingFromMeter: the value is the name of the meter.

   o  PartConformingFromMeter: the value is the name of the meter.

   o  NonConformingFromMeter: the value is the name of the meter.

   o  VlanId: the value is the virtual LAN identifier (VLAN ID).

   Implementations may recognize other <type>'s in addition to these.
   If collisions of implementation-specific <type>'s become a problem,
   it is possible that <type>'s may become an IANA-administered range in
   a future revision of this document.

   To make use of the information that a PreambleMarker stores in a
   packet preamble, a specific subclass PreambleFilter of
   FilterEntryBase is defined, to match on the "<type>,<value>" strings.
   To simplify the case where there's just a single level of metering in
   a device, but different individual meters on each ingress interface,
   PreambleFilter allows a wildcard "any" for the <value> part of the
   three meter-related filters.  With this wildcard, an administrator
   can specify a Classifier to select all packets that were found to be
   conforming (or partially conforming, or non-conforming) by their
   respective meters, without having to name each meter individually in
   a separate ClassifierElement.

   Once a meter result has been stored in a packet preamble, it is
   available for any subsequent Classifier to use.  So while the
   motivation for this capability has been described in terms of
   preserving QoS conditioning information from an ingress interface to
   an egress interface, a prior meter result may also be used for
   classifying packets later in the datapath on the same interface where
   the meter resides.

3.9.  Classifiers, FilterLists, and Filter Entries

   This document uses a number of classes to model the classifiers
   defined in [DSMODEL]: ClassifierService, ClassifierElement,
   FilterList, FilterEntryBase, and various subclasses of
   FilterEntryBase.  There are also two associations involved:
   ClassifierElementUsesFilterList and EntriesInFilterList.  The QDDIM
   model makes no use of CIM's FilterEntry class.

   In [DSMODEL], a single traffic stream coming into a classifier is
   split into multiple traffic streams leaving it, based on which of an
   ordered set of filters each packet in the incoming stream matches.  A



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   filter matches either a field in the packet itself, or possibly other
   attributes associated with the packet.  In the case of a multi-field
   (MF) classifier, packets are assigned to output streams based on the
   contents of multiple fields in the packet header.  For example, an MF
   classifier might assign packets to an output stream based on their
   complete IP-addressing 5-tuple.

   To optimize the representation of MF classifiers, subclasses of
   FilterEntryBase are introduced, which allow multiple related packet
   header fields to be represented in a single object.  These subclasses
   are IPHeaderFilter and 8021Filter.  With IPHeaderFilter, for example,
   criteria for selecting packets based on all five of the IP 5-tuple
   header fields and the DiffServ DSCP can be represented by a
   FilterList containing one IPHeaderFilter object.  Because these two
   classes have applications beyond those considered in this document,
   they, as well as the abstract class FilterEntryBase, are defined in
   the more general document [PCIME] rather than here.

   The FilterList object is always needed, even if it contains only one
   filter entry (that is, one FilterEntryBase subclass) object. This is
   because a ClassifierElement can only be associated with a Filter
   List, as opposed to an individual FilterEntry.  FilterList is also
   defined in [PCIME].

   The EntriesInFilterList aggregation (also defined in [PCIME]) has a
   property EntrySequence, which in the past (in CIM) could be used to
   specify an evaluation order on the filter entries in a FilterList.
   Now, however, the EntrySequence property supports only a single
   value: '0'.  This value indicates that the FilterEntries are ANDed
   together to determine whether a packet matches the MF selector that
   the FilterList represents.

   A ClassifierElement specifies the starting point for a specific
   policy or data path.  Each ClassifierElement uses the
   NextServiceAfterClassifierElement association to determine the next
   conditioning service to apply for packets to.

   A ClassifierService defines a grouping of ClassifierElements. There
   are certain instances where a ClassifierService actually specifies an
   aggregation of ClassifierServices.  One practical case would be where
   each ClassifierService specifies a group of policies associated with
   a particular application and another ClassifierService groups the
   application-specific ClassifierService instances.  In this particular
   case, the application-specific ClassifierService instances are
   specified once, but unique combinations of these ClassifierServices
   are specified, as needed, using other ClassifierService instances.
   ClassifierService instances grouping other ClassifierService
   instances may not specify a FilterList using the



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   ClassifierElementUsesFilterList association.  This special use of
   ClassifierService serves just as a Classifier collecting function.

3.10.  Modeling of Droppers

   In [DSMODEL], a distinction is made between absolute droppers and
   algorithmic droppers.  In QDDIM, both of these types of droppers are
   modeled with the DropperService class, or with one of its subclasses.
   In both cases, the queue from which the dropper drops packets is tied
   to the dropper by an instance of the NextService association.  The
   dropper always plays the PrecedingService role in these associations,
   and the queue always plays the FollowingService role.  There is
   always exactly one queue from which a dropper drops packets.

   Since an absolute dropper drops all packets in its queue, it needs no
   configuration beyond a NextService tie to that queue. For an
   algorithmic dropper, however, further configuration is needed:

   o  a specific drop algorithm;

   o  parameters for the algorithm (for example, token bucket size);

   o  the source(s) of input(s) to the algorithm;

   o  possibly per-input parameters for the algorithm.

   The first two of these items are represented by properties of the
   DropperService class, or properties of one of its subclasses. The
   last two, however, involve additional classes and associations.

3.10.1.  Configuring Head and Tail Droppers

   The HeadTailDropQueueBinding is the association that identifies the
   inputs for the algorithm executed by a tail dropper.  This
   association is not used for a head dropper, because a head dropper
   always has exactly one input to its drop algorithm, and this input is
   always the queue from which it drops packets.  For a tail dropper,
   this association is defined to have a many-to-many cardinality.
   There are, however, two distinct cases:

   One dropper bound to many queues: This represents the case where the
   drop algorithm for the dropper involves inputs from more than one
   queue.  The dropper still drops from only one queue, the one to which
   it is tied by a NextService association.  But the drop decision may
   be influenced by the state of several queues.  For the classes
   HeadTailDropper and HeadTailDropQueueBinding, the rule for combining
   the multiple inputs is simple addition: if the sum of the lengths of
   the monitored queues exceeds the dropper's QueueThreshold value, then



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   packets are dropped.  This rule for combining inputs may, however, be
   overridden by a different rule in subclasses of one or both of these
   classes.

   One queue bound to many droppers: This represents the case where the
   state of one queue (which is typically also the queue from which
   packets are dropped) provides an input to multiple droppers' drop
   algorithms.  A use case here is a classifier that splits a traffic
   stream into, say, four parts, representing four classes of traffic.
   Each of the parts goes through a separate HeadTailDropper, then
   they're re-merged onto the same queue.  The net is a single queue
   containing packets of four traffic types, with, say, the following
   drop thresholds:

      o    Class 1 - 90% full
      o    Class 2 - 80% full
      o    Class 3 - 70% full
      o    Class 4 - 50% full

   Here the percentages represent the overall state of the queue. With
   this configuration, when the queue in question becomes 50% full,
   Class 4 packets will be dropped rather than joining the queue, when
   it becomes 70% full, Class 3 and 4 packets will be dropped, etc.

   The two cases described here can also occur together, if a dropper
   receives inputs from multiple queues, one or more of which are also
   providing inputs to other droppers.

3.10.2.  Configuring RED Droppers

   Like a tail dropper, a RED dropper, represented by an instance of the
   REDDropperService class, may take as its inputs the states of
   multiple queues.  In this case, however, there is an additional step:
   each of these inputs may be smoothed before the RED dropper uses it,
   and the smoothing process itself must be parameterized. Consequently,
   in addition to REDDropperService and QueuingService, a third class,
   DropThresholdCalculationService, is introduced, to represent the
   per-queue parameterization of this smoothing process.













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   The following instance diagram illustrates how these classes work
   with each other:

           RDSvc-A
           |  |  |
     +-----+  |  +-----+
     |        |        |
   DTCS-1   DTCS-2   DTCS-3
     |        |        |
    Q-1      Q-2      Q-3

   Figure 4. Inputs for a RED Dropper

   So REDDropperService-A (RDSvc-A) is using inputs from three queues to
   make its drop decision.  (As always, RDSvc-A is linked to the queue
   from which it drops packets via the NextService association.)  For
   each of these three queues, there is a
   (DropThresholdCalculationService) DTCS instance that represents the
   smoothing weight and time interval to use when looking at that queue.
   Thus each DTCS instance is tied to exactly one queue, although a
   single queue may be examined (with different weight and time values)
   by multiple DTCS instances.  Also, a DTCS instance and the queue
   behind it can be thought of as a "unit of reusability".  So a single
   DTCS can be referred to by multiple RDSvc's.

   Unless it is overridden by a different rule in a subclass of
   REDDropperService, the rule that a RED dropper uses to combine the
   smoothed inputs from the DTCS's to create a value to use in making
   its drop decision is simple addition.

3.11.  Modeling of Queues and Schedulers

   In order to appreciate the rationale behind this rather complex model
   for scheduling, we must consider the rather complex nature of
   schedulers, as well as the extreme variations in algorithms and
   implementations.  Although these variations are broad, we have
   identified four examples that serve to test the model and justify its
   complexity.

3.11.1.  Simple Hierarchical Scheduler

   A simple, hierarchical scheduler has the following properties. First,
   when a scheduling opportunity is given to a set of queues, a single,
   viable queue is determined based on some scheduling criteria, such as
   bandwidth or priority.  The output of the scheduler is the input to
   another scheduler that treats the first scheduler (and its queues) as
   a single logical queue.  Hence, if the first scheduler determined the
   appropriate packet to release based on a priority assigned to each



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   queue, the second scheduler might specify a bandwidth
   limit/allocation for the entire set of queues aggregated by the first
   scheduler.

   +----------+                              NextService
   |QueuingSvc+----------------------------------------------+
   | Name=EF1 |                                              |
   |          | QueueTo    +--------------+ ElementSched     |
   |          +------------+PrioritySched +---------------+  |
   +----------+ Schedule   |Element       | Service       |  |
                           | Name=EF1-Pri |               |  v
                           | Priority=1   |    +-----------+-+-+
                           +--------------+    |SchedulingSvc  +
                                               | Name=PriSched1+
                           +--------------+    +----------+--+-+
                           |PrioritySched | ElementSched  |  ^
   +----------+            |Element       +---------------+  |
   |QueuingSvc| QueueTo    | Name=AF1x-Pri| Service          |
   | Name=AF1x+------------+ Priority=2   |                  |
   |          | Schedule   +--------------+                  |
   |          |                              NextService     |
   |          +----------------------------------------------+
   +----------+
   :
   +---------------+            NextScheduler
   |SchedulingSvc  +--------------------------------------------+
   | Name=PriSched1|                                            |
   +-------+-------+       +--------------------+ElementSchedSvc|
           | SchedToSched  |AllocationScheduling+--------+      |
           +---------------+Element             |        |      |
                           | Name=PriSched1-Band|        |      |
                           | Units=Bytes        |        |      v
                           | Bandwidth=100      | +------+------+--+
                           +--------------------+ |SchedulingSvc   |
                                                  | Name=BandSched1|
                           +--------------------+ +------+------+--+
                           |AllocationScheduling|        |      ^
   +---------------+       |Element             +--------+      |
   |QueuingService |       | Name=BE-Band       |ElementSchedSvc|
   | Name=BE       |QueueTo+ Units=Bytes        |               |
   |               |-------+ Bandwidth=50       |               |
   |               |Sched  +--------------------+               |
   |               |                             NextService    |
   |               +--------------------------------------------+
   +---------------+

   Figure 5. Example 1: Simple Hierarchical Scheduler




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   Figure 5 illustrates the example and how it would be instantiated
   using the model.  In the figure, NextService determines the first
   scheduler after the queue.  NextScheduler determines the
   subsequent ordering of schedulers.  In addition, the
   ElementSchedulingService association determines the set of
   scheduling parameters used by a specific scheduler.  Scheduling
   parameters can be bound either to queues or to schedulers.  In
   the case of the SchedulingElement EF1-Pri, the binding is to a
   queue, so the QueueToSchedule association is used.  In the case
   of the SchedulingElement PriSched1-Band, the binding is to
   another scheduler, so the SchedulerToSchedule association is
   used.  Note that due to space constraints of the document, the
   SchedulingService PRISched1 is represented twice, to show how it
   is connected to all the other objects.

3.11.2.  Complex Hierarchical Scheduler

   A complex, hierarchical scheduler has the same characteristics as
   a simple scheduler, except that the criteria for the second
   scheduler are determined on a per queue basis rather than on an
   aggregate basis.  One scenario might be a set of bounded priority
   schedulers.  In this case, each queue is assigned a relative
   priority.  However, each queue is also not allowed to exceed a
   bandwidth allocation that is unique to that queue.  In order to
   support this scenario, the queue must be bound to two separate
   schedulers.  Figure 6 illustrates this situation, by describing
   an EF queue and a best effort (BE) queue both pointing to a
   priority scheduler via the NextService association.  The
   NextScheduler association between the priority scheduler and the
   bandwidth scheduler in turn defines the ordering of the
   scheduling hierarchy.  Also note that each scheduler has a
   distinct set of scheduling parameters that are bound back to each
   queue.  This demonstrates the need to support two or more
   parameter sets on a per queue basis.

















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   +----------------+
   |QueuingService  |
   | Name=EF        |
   |                |QueueTo   +----------------+ElementSchedSvc
   |                +----------+AllocationSched +--------+
   ++---+-----------+Schedule  |Element         |        |
    |   |                      | Name=BandEF    |        |
    |   |QueueTo               | Units=Bytes    |        |
    |   |Schedule              | Bandwidth=100  |        |
    |   |                      +----------------+ +------+---------+
    |   |                                         |SchedulingSvc   |
    |   |      +------------------+               | Name=BandSched |
    |   +------+PriorityScheduling|               +------------+--++
    |          |Element           |                            ^  |
    |          | Name=PriEF       |ElementSchedSvc             |  |
    |          | Priority=1       +---------------------+      |  |
    |          +------------------+                     |      |  |
    |NextService                                        |      |  |
    +-------------------------------------------------+ |      |  |
                                                      | |      |  |
     NextService                                      | |      |  |
    +-----------------------------------------------+ | |      |  |
    |                                               | | |      |  |
    |          +------------------+ElementSchedSvc  | | |      |  |
    |          |PriorityScheduling+--------+        | | |      |  |
    |          |Element           |        |        | | |      |  |
    |          | Name=PriBE       |        |        v v |      |  |
    |   +------+ Priority=2       |    +---+--------+-+-+-+Next|  |
    |   |      +------------------+    |SchedulingService +----+  |
    |   |                              | Name=PriSched    |Sched  |
    |   |                              +------------------+       |
    |   |QueueTo                                                  |
    |   |Schedule              +----------------+                 |
    |   |                      |AllocationSched |ElementSchedSvc  |
   +----+---------+            |Element         +-----------------+
   |QueuingService|QueueTo     | Name=BandBE    |
   | Name=BE      +------------+ Units=Bytes    |
   |              |Schedule    | Bandwidth=50   |
   |              |            +----------------+
   +--------------+

   Figure 6. Example 2: Complex Hierarchical Scheduler









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3.11.3.  Excess Capacity Scheduler

   An excess capacity scheduler offers a similar requirement to support
   two scheduling parameter sets per queue.  However, in this scenario
   the reasons are a little different.  Suppose a set of queues have
   each been assigned bandwidth limits to ensure that no traffic class
   starves out another traffic class.  The result may be that one or
   more queues have exceeded their allocation while the queues that
   deserve scheduling opportunities are empty.

   The question then is how is the excess (idle) bandwidth allocated.
   Conceivably, the scheduling criteria for excess capacity are
   completely different from the criteria that determine allocations
   under uniform load.  This could be supported with a scheduling
   hierarchy.  However, the problem is that the criteria for using the
   subsequent scheduler are different from those in the last two cases.
   Specifically, the next scheduler should only be used if a scheduling
   opportunity exists that was passed over by the prior scheduler.

   When a scheduler chooses to forgo a scheduling decision, it is
   behaving as a non-work conserving scheduler.  Work conserving
   schedulers, by definition, will always take advantage of a scheduling
   opportunity, irrespective of which queue is being serviced and how
   much bandwidth it has consumed in the past. This point leads to an
   interesting insight.  The semantics of a non-work conserving
   scheduler are equivalent to those of a meter, in that if a packet is
   in profile it is given the scheduling opportunity, and if it is out
   of profile it does not get a scheduling opportunity.  However, with
   meters there are semantics that determine the next action behavior
   when the packet is in profile and when the packet is out of profile.
   Similarly, with the non-work conserving scheduler, there needs to be
   a means for determining the next scheduler when a scheduler chooses
   not to utilize a scheduling opportunity.

   Figure 7 illustrates this last scenario.  It appears very similar to
   Figure 6, except that the binding between the allocation scheduler
   and the WRR scheduler is using a FailNextScheduler association.  This
   association is explicitly indicating the fact that the only time the
   WRR scheduler would be used is when there are non-empty queues that
   the allocation scheduler rejected for scheduling consideration.  Note
   that Figure 7 is incomplete, in that typically there would be several
   more queues that are bound to an allocation scheduler and a WRR
   scheduler.








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   +------------+
   |QueuingSvc  |
   | Name=EF    |
   |            |
   |            |
   ++-+---------+
    | |
    | |QueueTo
    | |Schedule                                     +--------------+
    | |                                             |SchedulingSvc |
    | |      +------------------+                   | Name=WRRSched|
    | +------+AllocationSched   |                   +----------+-+-+
    |        |Element           |                              ^ |
    |        | Name=BandEF      |ElementSchedSvc               | |
    |        | Units=Bytes      +--------------------+         | |
    |        | Bandwidth=100    |                    |         | |
    |        +------------------+                    |         | |
    |NextService                                     |         | |
    +----------------------------------------------+ |         | |
                                                   | |         | |
     NextService                                   | |         | |
    +--------------------------------------------+ | |         | |
    |                                            | | |         | |
    |        +------------------+ElementSchedSvc | | |         | |
    |        |AllocationSched   +--------+       | | |         | |
    |        |Element           |        |       | | |         | |
    |        | Name=BandwidthAF1|        |       | | |         | |
    |        | Units=Bytes      |        |       v v |         | |
    | +------+ Bandwidth=50     |  +--+----------+-+-++FailNext| |
    | |      +------------------+  |SchedulingService +--------+ |
    | |QueueTo                     | Name=BandSched   |Scheduler |
    | |Schedule                    +------------------+          |
    | |                                                          |
    | |                       +---------------------+            |
   ++-+-----------+           | WRRSchedulingElement|            |
   |QueuingService|QueueTo    | Name=WRRBE          +------------+
   | Name=BE      +-----------+ Weight=30           |ElementSchedSvc
   +--------------+Schedule   +---------------------+

   Figure 7.  Example 3: Excess Capacity Scheduler











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3.11.4.  Hierarchical CBQ Scheduler

   A hierarchical class-based queuing (CBQ) scheduler is the fourth
   scenario to be considered.  In hierarchical CBQ, each queue is
   allocated a specific bandwidth allocation.  Queues are grouped
   together into a logical scheduler.  This logical scheduler in turn
   has an aggregate bandwidth allocation that equals the sum of the
   queues it is scheduling.  In turn, logical schedulers can be
   aggregated into higher-level logical schedulers.  Changing
   perspectives and looking top down, the top-most logical scheduler has
   100% of the link capacity.  This allocation is parceled out to
   logical schedulers below it such that the sum of the allocations is
   equal to 100%.  These second tier schedulers may in turn parcel out
   their allocation across a third tier of schedulers and so forth until
   the lowest tier that parcels out their allocations to specific queues
   representing relatively fine-grained classes of traffic.  The unique
   aspect of hierarchical CBQ is that when there is insufficient
   bandwidth for a specific allocation, schedulers higher in the tree
   are tested to see if another portion of the tree has capacity to
   spare.

   Figure 8 demonstrates this example with two tiers.  The example is
   split in half because of space constraints, resulting in the CBQTier1
   scheduling service instance being represented twice. Note that the
   total allocation at the top tier is 50 Mb.  The voice allocation is
   22 Mb.  The remaining 23 Mb is split between FTP and Web.  Hence, if
   Web traffic is actually consuming 20 Mb (5 Mb in excess of the
   allocation).  If FTP is consuming 5 Mb, then it is possible for the
   CBQTier1 scheduler to offer 3Mb of its allocation to Web traffic.
   However, this is not enough, so the FailNextScheduler association
   needs to be traversed to determine if there is any excess capacity
   available from the voice class.  If the voice class is only consuming
   15 Mb of its 22 Mb allocation, there are sufficient resources to
   allow the web traffic through.  Note that FailNextScheduler is used
   as the association.  The reason is because the CBQTier1 scheduler in
   fact failed to schedule a packet because of insufficient resources.
   It is conceivable that a variant of hierarchical CBQ allows a
   hierarchy for successful scheduling as well.  Hence, both
   associations are necessary.

   Note that due to space constraints of the document, the
   SchedulingService CBQTier1 is represented twice, to show how it is
   connected to all the other objects.








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   +-----------+                        NextService
   |QueuingSvc +-------------------------------------------+
   | Name=Web  |                                           |
   |           |QueueTo+----------------+ ElementSchedSvc  |
   |           +-------+AllocationSched +----------------+ |
   +-----------+Sched  |Element         |                | |
                       | Name=Web-Alloc |                | v
                       | Bandwidth=15   |    +-----------+-+-+
                       +----------------+    |SchedulingSvc  +
                                             | Name=CBQTier1 +
                       +----------------+    +-----------+-+-+
                       |AllocationSched | ElementSchedSvc| ^
   +-----------+       |Element         +----------------+ |
   |QueuingSvc |QueueTo| Name=FTP-Alloc |                  |
   | Name=FTP  +-------+ Bandwidth=8    |                  |
   |           |Sched  +----------------+                  |
   |           |                        NextService        |
   |           +-------------------------------------------+
   +-----------+
   :

   +---------------+                    FailNextScheduler
   |SchedulingSvc  +---------------------------------------------+
   | Name=CBQTier1 |                                             |
   +-------+-------+       +---------------------+ElementSchedSvc|
           | SchedToSched  |AllocationScheduling +--------+      |
           +---------------+Element              |        |      |
                           | Name=LowPri-Alloc   |        |      |
                           | Bandwidth=23        |        |      v
                           +---------------------+  +-----+------+-+
                                                    |SchedulingSvc |
                                                    | Name=CBQTop  |
                        +---------------------+     +----------+-+-+
                        |AllocationScheduling |ElementSchedSvc | ^
   +------------+       |Element              +----------------+ |
   |QueuingSvc  |QueueTo| Name=BE-Band        |                  |
   | Name=Voice +-------+ Bandwidth=22        |                  |
   |            |Sched  +---------------------+                  |
   |            |                       NextService              |
   |            +------------------------------------------------+
   +------------+

   Figure 8.  Example 4: Hierarchical CBQ Scheduler








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4.  The Class Hierarchy

   The following sections present the class and association hierarchies
   that together comprise the information model for modeling QoS
   capabilities at the device level.

4.1.  Associations and Aggregations

   Associations and aggregations are a means of representing
   relationships between two (or theoretically more) objects.
   Dependency, aggregation, and other relationships are modeled as
   classes containing two (or more) object references.  It should be
   noted that aggregations represent either "whole-part" or "collection"
   relationships.  For example, aggregation can be used to represent the
   containment relationship between a system and the components that
   constitute the system.

   Since associations and aggregations are classes, they can benefit
   from all of the object-oriented features that other non-relationship
   classes have.  For example, they can contain properties and methods,
   and inheritance can be used to refine their semantics such that they
   represent more specialized types of their superclasses.

   Note that an association (or an aggregation) object is treated as an
   atomic unit (individual instance), even though it relates/collects/is
   comprised of multiple objects.  This is a defining feature of an
   association (or an aggregation) - although the individual elements
   that are related to other objects have their own identities, the
   association (or aggregation) object that is constructed using these
   objects has its own identity and name as well.

   It is important to note that associations and aggregations form an
   inheritance hierarchy that is separate from the class inheritance
   hierarchy.  Although associations and aggregations are typically bi-
   directional, there is nothing that prevents higher order associations
   or aggregations from being defined. However, such associations and
   aggregations are inherently more complex to define, understand, and
   use.  In practice, associations and aggregations of orders higher
   than binary are rarely used, because of their greatly increased
   complexity and lack of generality.  All of the associations and
   aggregations defined in this model are binary.

   Note also that by definition, associations and aggregations cannot be
   unary.







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   Finally, note that associations and aggregations that are defined
   between two classes do not affect the classes themselves.  That is,
   the addition or deletion of an association or an aggregation does not
   affect the interfaces of the classes that it is connecting.

4.2.  The Structure of the Class Hierarchies

   The structure of the class, association, and aggregation class
   inheritance hierarchies for managing the datapaths of QoS devices is
   shown, respectively, in Figure 9, Figure 10, and Figure 11. The
   notation (CIMCORE) identifies a class defined in the CIM Core model.
   Please refer to [CIM] for the definitions of these classes.
   Similarly, the notation [PCIME] identifies a class defined in the
   Policy Core Information Model Extensions document. This model has
   been influenced by [CIM], and is compatible with the Directory
   Enabled Networks (DEN) effort.

   +--ManagedElement (CIMCORE)
      |
      +--ManagedSystemElement (CIMCORE)
      |  |
      |  +--LogicalElement (CIMCORE)
      |     |
      |     +--Service (CIMCORE)
      |     |  |
      |     |  +--ConditioningService
      |     |  |  |
      |     |  |  +--ClassifierService
      |     |  |  |  |
      |     |  |  |  +--ClassifierElement
      |     |  |  |
      |     |  |  +--MeterService
      |     |  |  |  |
      |     |  |  |  +--AverageRateMeterService
      |     |  |  |  |
      |     |  |  |  +--EWMAMeterService
      |     |  |  |  |
      |     |  |  |  +--TokenBucketMeterService
      |     |  |  |
      |     |  |  +--MarkerService
      |     |  |  |  |
      |     |  |  |  +--PreambleMarkerService
      |     |  |  |  |
      |     |  |  |  +--TOSMarkerService
      |     |  |  |  |
      |     |  |  |  +--DSCPMarkerService
      |     |  |  |  |




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   (continued from previous page;
    the first four elements are repeated for convenience)

   +--ManagedElement (CIMCORE)
      |
      +--ManagedSystemElement (CIMCORE)
      |  |
      |  +--LogicalElement (CIMCORE)
      |     |
      |     +--Service (CIMCORE)
      |     |  |  |  +--8021QMarkerService
      |     |  |  |
      |     |  |  +--DropperService
      |     |  |  |  |
      |     |  |  |  +--HeadTailDropperService
      |     |  |  |  |
      |     |  |  |  +--RedDropperService
      |     |  |  |
      |     |  |  +--QueuingService
      |     |  |  |
      |     |  |  +--PacketSchedulingService
      |     |  |     |
      |     |  |     +--NonWorkConservingSchedulingService
      |     |  |
      |     |  +--QoSService
      |     |  |  |
      |     |  |  +--DiffServService
      |     |  |  |   |
      |     |  |  |   +--AFService
      |     |  |  |
      |     |  |  +--FlowService
      |     |  |
      |     |  +--DropThresholdCalculationService
      |     |
      |     +--FilterEntryBase [PCIME]
      |     |  |
      |     |  +--IPHeaderFilter [PCIME]
      |     |  |
      |     |  +--8021Filter [PCIME]
      |     |  |
      |     |  +--PreambleFilter
      |     |
      |     +--FilterList [PCIME]
      |     |
      |     +--ServiceAccessPoint (CIMCORE)
      |        |
      |        +--ProtocolEndpoint




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   (continued from previous page;
    the first four elements are repeated for convenience)

   +--ManagedElement (CIMCORE)
      |
      +--ManagedSystemElement (CIMCORE)
      |  |
      |  +--LogicalElement (CIMCORE)
      |     |
      |     +--Service (CIMCORE)
      |
      +--Collection (CIMCORE)
      |  |
      |  +--CollectionOfMSEs (CIMCORE)
      |     |
      |     +--BufferPool
      |
      +--SchedulingElement
         |
         +--AllocationSchedulingElement
         |
         +--WRRSchedulingElement
         |
         +--PrioritySchedulingElement
            |
            +--BoundedPrioritySchedulingElement

   Figure 9.  Class Inheritance Hierarchy























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   The inheritance hierarchy for the associations defined in this
   document is shown in Figure 10.

   +--Dependency (CIMCORE)
   |  |
   |  +--ServiceSAPDependency (CIMCORE)
   |  |  |
   |  |  +--IngressConditioningServiceOnEndpoint
   |  |  |
   |  |  +--EgressConditioningServiceOnEndpoint
   |  |
   |  +--HeadTailDropQueueBinding
   |  |
   |  +--CalculationBasedOnQueue
   |  |
   |  +--ProvidesServiceToElement (CIMCORE)
   |  |  |
   |  |  +--ServiceServiceDependency (CIMCORE)
   |  |     |
   |  |     +--CalculationServiceForDropper
   |  |
   |  +--QueueAllocation
   |  |
   |  +--ClassifierElementUsesFilterList
   |
   +--AFRelatedServices
   |
   +--NextService
   |  |
   |  +--NextServiceAfterClassifierElement
   |  |
   |  +--NextScheduler
   |    |
   |    +--FailNextScheduler
   |
   +--NextServiceAfterMeter
   |
   +--QueueToSchedule
   |
   +--SchedulingServiceToSchedule

   Figure 10.  Association Class Inheritance Hierarchy









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   The inheritance hierarchy for the aggregations defined in this
   document is shown in Figure 11.

   +--MemberOfCollection (CIMCORE)
   |  |
   |  +--CollectedBufferPool
   |
   +--Component (CIMCORE)
   |  |
   |  +--ServiceComponent (CIMCORE)
   |  |  |
   |  |  +--QoSSubService
   |  |  |
   |  |  +--QoSConditioningSubService
   |  |  |
   |  |  +--ClassifierElementInClassifierService
   |  |
   |  +--EntriesInFilterList [PCIME]
   |
   +--ElementInSchedulingService

   Figure 11.  Aggregation Class Inheritance Hierarchy

4.3.  Class Definitions

   This section presents the classes and properties that make up the
   Information Model for describing QoS-related functionality in network
   devices, including hosts.  These definitions are derived from
   definitions in the CIM Core model [CIM].  Only the QoS-related
   classes are defined in this document.  However, other classes drawn
   from the CIM Core model, as well as from [PCIME], are described
   briefly.  The reader is encouraged to look at [CIM] and at [PCIME]
   for further information.  Associations and aggregations are defined
   in Section 4.4.

4.3.1.  The Abstract Class ManagedElement

   This is an abstract class defined in the Core Model of CIM.  It is
   the root of the entire class inheritance hierarchy in CIM. Among the
   associations that refer to it are two that are subclassed in this
   document: Dependency and MemberOfCollection, which is an aggregation.
   ManagedElement's properties are Caption and Description.  Both are
   free-form strings to describe an instantiated object.  Please refer
   to [CIM] for the full definition of this class.







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4.3.2.  The Abstract Class ManagedSystemElement

   This is an abstract class defined in the Core Model of CIM; it is a
   subclass of ManagedElement.  ManagedSystemElement serves as the base
   class for the PhysicalElement and LogicalElement class hierarchies.
   LogicalElement, in turn, is the base class for a number of important
   CIM hierarchies, including System.  Any distinguishable component of
   a System is a candidate for inclusion in this class hierarchy,
   including physical components (e.g., chips and cards) and logical
   components (e.g., software components, services, and other objects).

   None of the associations in which this class participates is used
   directly in the QoS device state model.  However, the aggregation
   Component, which relates one ManagedSystemElement to another, is the
   base class for the two aggregations that form the core of the QoS
   device state model: QoSSubService and QoSConditioningSubService.
   Similarly, the association ProvidesServiceToElement, which relates a
   ManagedSystemElement to a Service, is the base class for the model's
   CalculationServiceForDropper association.

   Please refer to [CIM] for the full definition of this class.

4.3.3.  The Abstract Class LogicalElement

   This is an abstract class defined in the Core Model of CIM.  It is a
   subclass of the ManagedSystemElement class, and is the base class for
   all logical components of a managed System, such as Files, Processes,
   or system capabilities in the form of Logical Devices and Services.
   None of the associations in which this class participates is relevant
   to the QoS device state model. Please refer to [CIM] for the full
   definition of this class.

4.3.4.  The Abstract Class Service

   This is an abstract class defined in the Core Model of CIM.  It is a
   subclass of the LogicalElement class, and is the base class for all
   objects that represent a "service" or functionality in a System.  A
   Service is a general-purpose object that is used to configure and
   manage the implementation of functionality.  As noted above in
   section 4.3.2, this class participates in the
   ProvidesServiceToElement association.  Please refer to [CIM] for the
   full definition of this class.

4.3.5.  The Class ConditioningService

   This is a concrete subclass of the CIM Core class Service; it
   represents the ability to define how traffic is conditioned in the
   data-forwarding path of a device.  The subclasses of



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   ConditioningService define the particular types of conditioning that
   are done.  Six fundamental types of conditioning are defined in this
   document.  These are the services performed by a classifier, a meter,
   a marker, a dropper, a queue, and a scheduler.  Other, more
   sophisticated types of conditioning may be defined in future
   documents.

   ConditioningService is a concrete class because at the time it was
   defined in CIM, its superclass was concrete.  While this class can be
   instantiated, an instance of it would not accomplish anything,
   because the nature of the conditioning, and the parameters that
   control it, are specified only in the subclasses of
   ConditioningService.

   Two associations in which ConditioningService participates are
   critical to its usage in QoS - QoSConditioningSubService and
   NextService.  QoSConditioningSubService aggregates
   ConditioningServices into a particular QoS service (such as AF), to
   describe the specific conditioning functionality that underlies that
   QoS service in a particular device.  NextService indicates the
   subsequent conditioning service(s) for different traffic streams.

   The class definition is as follows:

      NAME                ConditioningService
      DESCRIPTION         A concrete class to define how traffic
                          is conditioned in the data forwarding
                          path of a host or network device.
      DERIVED FROM        Service
      TYPE                Concrete
      PROPERTIES          (none)

4.3.6.  The Class ClassifierService

   The concept of a Classifier comes from [DSMODEL]. ClassifierService
   is a concrete class that represents a logical entity in an ingress or
   egress interface of a device, that takes a single input stream, and
   sorts it into one or more output streams.  The sorting is done by a
   set of filters that select packets based on the packet contents, or
   possibly based on other attributes associated with the packet.  Each
   output stream is the result of matching a particular filter.

   The representation of classifiers in QDDIM is closely related to that
   presented in [DSMIB] and [DSMODEL].  Rather than being linked
   directly to its FilterLists, a classifier is modeled here as an
   aggregation of ClassifierElements.  Each of these ClassifierElements
   is then linked to a single FilterList, by the association
   ClassifierElementUsesFilterList.



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   A Classifier is modeled as a subclass of ConditioningService so that
   it can be aggregated into a QoSService (using the
   QoSConditioningSubService aggregation), and can use the NextService
   association to identify the subsequent ConditioningService objects
   for the different traffic streams.

   ClassifierService is designed to allow hierarchical classification.
   When hierarchical classification is used, a ClassifierElement may
   point to another ClassifierService.  When used for this purpose, the
   ClassifierElement must not use the ClassifierElementUsesFilterList
   association.

   The class definition is as follows:

      NAME                ClassifierService
      DESCRIPTION         A concrete class describing how an input
                          traffic stream is sorted into multiple
                          output streams using one or more
                          filters.
      DERIVED FROM        ConditioningService
      TYPE                Concrete
      PROPERTIES          (none)

4.3.7.  The Class ClassifierElement

   The concept of a ClassifierElement comes from [DSMIB].  This concrete
   class represents the linkage, within a single ClassifierService,
   between a FilterList that specifies a set of criteria for selecting
   packets from the stream of packets coming into the ClassifierService,
   and the next ConditioningService to which the selected packets go
   after they leave the ClassifierService.  ClassifierElement has no
   properties of its own.  It is present to serve as the anchor for an
   aggregation with its classifier, and for associations with its
   FilterList and its next ConditioningService.

   When a ClassifierElement is associated with a ClassifierService
   through the NextServiceAfterClassifierElement association, the
   ClassifierElement may not use the ClassifierElementUsesFilterList
   association.  Further, when a ClassifierElement is associated with a
   ClassifierService as described above, the order of processing of the
   associated ClassifierService is a function of the ClassifierOrder
   property of the ClassifierElementInClassifierService aggregation.
   For example, lets assume the following:

   1. ClassifierService (C1) aggregates ClassifierElements (E1), (E2)
      and (E3), with relative ClassifierOrder values of 1, 2, and 3.





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   2. ClassifierElements (E1) and (E3) associations to FilterLists (F1)
      and (F3) respectively using the ClassifierElementUsesFilterList
      association.

   3. (E1) & (E3) are associated with Meters (M1) and (M3) through their
      respective NextServiceAfterClassifierElement associations.

   4. (E2) is associated with ClassifierService (C2) through its
      NextServiceAfterClassifierElement association.

   5. ClassifierService (C2) aggregates ClassifierElements (E4) and (E5)
      with relative ClassifierOrder values of 1 and 2.

   6. ClassifierElements (E4) and (E5) have associations to FilterLists
      (F4) and (F5) respectively using the
      ClassifierElementUsesFilterList association.

   In this example, packet processing would match FilterLists in the
   order of (F1), (F4), (F5), and (F3).

   The class definition is as follows:

      NAME                ClassifierElement
      DESCRIPTION         A concrete class representing
                          the process by which a classifier
                          uses a filter to select packets
                          to forward to a specific next
                          conditioning service.
      DERIVED FROM        ClassifierService
      TYPE                Concrete
      PROPERTIES          (none)

4.3.8.  The Class MeterService

   This is a concrete class that represents the metering of network
   traffic.  Metering is the function of monitoring the arrival times of
   packets of a traffic stream, and determining the level of conformance
   of each packet with respect to a pre-established traffic profile.  A
   meter has the ability to invoke different ConditioningServices for
   conforming and non-conforming traffic. Traffic leaving a meter may be
   further conditioned (e.g., dropped or queued) by routing the packet
   to another conditioning element. Please see [DSMODEL] for more
   information on metering.

   This class is the base class for defining different types of meters.
   As such, it contains common properties that all meter subclasses
   share.  It is modeled as a ConditioningService so that it can be
   aggregated into a QoSService (using the QoSConditioningSubService



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   association), to indicate that its functionality underlies that QoS
   service.  MeterService also participates in the NextServiceAfterMeter
   association, to identify the subsequent ConditioningService objects
   for conforming and non-conforming traffic.

   The class definition is as follows:

      NAME                MeterService
      DESCRIPTION         A concrete class describing the
                          monitoring of traffic with respect to a
                          pre-established traffic profile.
      DERIVED FROM        ConditioningService
      TYPE                Concrete
      PROPERTIES          MeterType, OtherMeterType,
                          ConformanceLevels

   Note: The MeterType property and the MeterService subclasses provide
   similar information.  The MeterType property is defined for query
   purposes and for future expansion.  It is possible that not all
   MeterServices will require a subclass to define them.  In these
   cases, MeterService will be instantiated directly, and the MeterType
   property will provide the only way of identifying the type of the
   meter.

4.3.8.1.  The Property MeterType

   This property is an enumerated 16-bit unsigned integer that is used
   to specify the particular type of meter represented by an instance of
   MeterService.  The following enumeration values are defined:

      1 - Other
      2 - Average Rate Meter
      3 - Exponentially Weighted Moving Average Meter
      4 - Token Bucket Meter

   Note: if the value of MeterType is not one of these four values, it
   SHOULD be interpreted as if it had the value '1' (Other).

4.3.8.2.  The Property OtherMeterType

   This is a string property that defines a vendor-specific description
   of a type of meter.  It is used when the value of the MeterType
   property in the instance is equal to 1.








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4.3.8.3.  The Property ConformanceLevels

   This property is a 16-bit unsigned integer.  It indicates the number
   of conformance levels supported by the meter.  For example, when only
   "in profile" versus "out of profile" metering is supported,
   ConformanceLevels is equal to 2.

4.3.9.  The Class AverageRateMeterService

   This is a concrete subclass of MeterService that represents a simple
   meter, called an Average Rate Meter.  This type of meter measures the
   average rate at which packets are submitted to it over a specified
   time.  Packets are defined as conformant if their average arrival
   rate does not exceed the specified measuring rate of the meter.  Any
   packet that causes the specified measuring rate to be exceeded is
   defined to be non-conforming.  For more information, please see
   [DSMODEL].

   The class definition is as follows:

      NAME                AverageRateMeterService
      DESCRIPTION         A concrete class classifying traffic as
                          either conforming or non-conforming,
                          depending on whether the arrival of a
                          packet causes the average arrival rate
                          to exceed a pre-determined value.
      DERIVED FROM        MeterService
      TYPE                Concrete
      PROPERTIES          AverageRate, DeltaInterval

4.3.9.1.  The Property AverageRate

   This is an unsigned 32-bit integer that defines the rate used to
   determine whether admitted packets are in conformance or not. The
   value is specified in kilobits per second.

4.3.9.2.  The Property DeltaInterval

   This is an unsigned 64-bit integer that defines the time period over
   which the average measurement should be taken.  The value is
   specified in microseconds.

4.3.10.  The Class EWMAMeterService

   This is a concrete subclass of the MeterService class that represents
   an exponentially weighted moving average meter.  This meter is a
   simple low-pass filter that measures the rate of incoming packets




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   over a small, fixed sampling interval.  Any admitted packet that
   pushes the average rate over a pre-defined limit is defined to be
   non-conforming.  Please see [DSMODEL] for more information.

   The class definition is as follows:

      NAME                EWMAMeterService
      DESCRIPTION         A concrete class classifying admitted
                          traffic as either conforming or non-
                          conforming, depending on whether the
                          arrival of a packet causes the average
                          arrival rate in a small fixed
                          sampling interval to exceed a
                          pre-determined value or not.
      DERIVED FROM        MeterService
      TYPE                Concrete
      PROPERTIES          AverageRate, DeltaInterval, Gain

4.3.10.1.  The Property AverageRate

   This property is an unsigned 32-bit integer that defines the average
   rate against which the sampled arrival rate of packets should be
   measured.  Any packet that causes the sampled rate to exceed this
   rate is deemed non-conforming.  The value is specified in kilobits
   per second.

4.3.10.2.  The Property DeltaInterval

   This property is an unsigned 64-bit integer that defines the sampling
   interval used to measure the arrival rate.  The calculated rate is
   averaged over this interval and checked against the AverageRate
   property.  All packets whose computed average arrival rate is less
   than the AverageRate are deemed conforming.

   The value is specified in microseconds.

4.3.10.3.  The Property Gain

   This property is an unsigned 32-bit integer representing the
   reciprocal of the time constant (e.g., frequency response) of what is
   essentially a simple low-pass filter.  For example, the value 64 for
   this property represents a time constant value of 1/64.









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4.3.11.  The Class TokenBucketMeterService

   This is a concrete subclass of the MeterService class that represents
   the metering of network traffic using a token bucket meter.  Two
   types of token bucket meters are defined using this class - a simple,
   two-parameter bucket meter, and a multi-stage meter.

   A simple token bucket usually has two parameters, an average token
   rate and a burst size, and has two conformance levels: "conforming"
   and "non-conforming".  This class also defines an excess burst size,
   which enables the meter to have three conformance levels
   ("conforming", "partially conforming", and "non-conforming").  In
   this case, packets that exceed the excess burst size are deemed non-
   conforming, while packets that exceed the smaller burst size but are
   less than the excess burst size are deemed partially conforming.
   Operation of these meters is described in [DSMODEL].

   The class definition is as follows:

      NAME                TokenBucketMeterService
      DESCRIPTION         A concrete class classifying admitted
                          traffic with respect to a token bucket.
                          Either two or three levels of
                          conformance can be defined.
      DERIVED FROM        MeterService
      TYPE                Concrete
      PROPERTIES          AverageRate, PeakRate,
                          BurstSize, ExcessBurstSize

4.3.11.1.  The Property AverageRate

   This property is an unsigned 32-bit integer that specifies the
   committed rate of the meter.  The value is expressed in kilobits per
   second.

4.3.11.2.  The Property PeakRate

   This property is an unsigned 32-bit integer that specifies the peak
   rate of the meter.  The value is expressed in kilobits per second.

4.3.11.3.  The Property BurstSize

   This property is an unsigned 32-bit integer that specifies the
   maximum number of tokens available for the committed rate (specified
   by the AverageRate property).  The value is expressed in kilobytes.






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4.3.11.4.  The Property ExcessBurstSize

   This property is an unsigned 32-bit integer that specifies the
   maximum number of tokens available for the peak rate (specified by
   the PeakRate property).  The value is expressed in kilobytes.

4.3.12.  The Class MarkerService

   This is a concrete class that represents the general process of
   marking some field in a network packet with some value. Subclasses of
   MarkerService identify particular fields to be marked, and introduce
   properties to represent the values to be used in marking these
   fields.  Markers are usually invoked as a result of a preceding
   classifier match.  Operation of markers of various types is described
   in [DSMODEL].

   MarkerService is a concrete class because at the time it was defined
   in CIM, its superclass was concrete.  While this class can be
   instantiated, an instance of it would not accomplish anything,
   because both the field to be marked and the value to be used to mark
   it are specified only in subclasses of MarkerService.

   MarkerService is modeled as a ConditioningService so that it can be
   aggregated into a QoSService (using the QoSConditioningSubService
   association) to indicate that its functionality underlies that QoS
   service.  It participates in the NextService association to identify
   the subsequent ConditioningService object that acts on traffic after
   it has been marked by the marker.

   The class definition is as follows:

      NAME                MarkerService
      DESCRIPTION         A concrete class representing the
                          general process of marking a selected
                          field in a packet with a specified
                          value.  Packets are marked in order
                          to control the conditioning that
                          they will subsequently receive.
      DERIVED FROM        ConditioningService
      TYPE                Concrete
      PROPERTIES          (none)

4.3.13.  The Class PreambleMarkerService

   This is a concrete class that models the storing of traffic-
   conditioning results in a packet preamble.  See Section 3.8.3 for a
   discussion of how, and why, QDDIM models the capability to store
   these results in a packet preamble.  An instance of



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   PreambleMarkerService appends to a packet preamble a two-part string
   of the form "<type>,<value>".  Section 3.8.3 provides a list of the
   <type> strings defined by QDDIM.  Implementations may support other
   <type>'s in addition to these.

   The class definition is as follows:

      NAME                PreambleMarkerService
      DESCRIPTION         A concrete class representing the saving
                          of traffic-conditioning results in a
                          packet preamble.
      DERIVED FROM        MarkerService
      TYPE                Concrete
      PROPERTIES          FilterItemList[ ]

4.3.13.1.  The Multi-valued Property FilterItemList

   This property is an ordered list of strings, where each string has
   the format "<type>,<value>".  See Section 3.8.3 for a list of
   <type>'s defined in QDDIM, and the nature of the associated <value>
   for each of these types.

4.3.14.  The Class ToSMarkerService

   This is a concrete class that represents the marking of the ToS field
   in the IPv4 packet header [R791].  Following common practice, the
   value to be written into the field is represented as an unsigned 8-
   bit integer.

   The class definition is as follows:

      NAME                ToSMarkerService
      DESCRIPTION         A concrete class representing the
                          process of marking the type of service
                          (ToS) field in the IPv4 packet header
                          with a specified value.  Packets are
                          marked in order to control the
                          conditioning that they will subsequently
                          receive.
      DERIVED FROM        MarkerService
      TYPE                Concrete
      PROPERTIES          ToSValue









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4.3.14.1.  The Property ToSValue

   This property is an unsigned 8-bit integer, representing a value to
   be used for marking the type of service (ToS) field in the IPv4
   packet header.  The ToS field is defined to be a complete octet, so
   the range for this property is 0..255.  Some implementations,
   however, require that the lowest-order bit in the ToS field always be
   '0'.  Such an implementation is consequently unable to support an odd
   TosValue.

4.3.15.  The Class DSCPMarkerService

   This is a concrete class that represents the marking of the
   differentiated services codepoint (DSCP) within the DS field in the
   IPv4 and IPv6 packet headers, as defined in [R2474]. Following common
   practice, the value to be written into the field is represented as an
   unsigned 8-bit integer.

   The class definition is as follows:

      NAME                DSCPMarkerService
      DESCRIPTION         A concrete class representing the
                          process of marking the DSCP field
                          in a packet with a specified
                          value.  Packets are marked in order
                          to control the conditioning that
                          they will subsequently receive.
      DERIVED FROM        MarkerService
      TYPE                Concrete
      PROPERTIES          DSCPValue

4.3.15.1.  The Property DSCPValue

   This property is an unsigned 8-bit integer, representing a value to
   be used for marking the DSCP within the DS field in an IPv4 or IPv6
   packet header.  Since the DSCP consists of 6 bits, the values for
   this property are limited to the range 0..63.  When the DSCP is
   marked, the remaining two bit in the DS field are left unchanged.

4.3.16.  The Class 8021QMarkerService

   This is a concrete class that represents the marking of the user
   priority field defined in the IEEE 802.1Q specification [IEEE802Q].
   Following common practice, the value to be written into the field is
   represented as an unsigned 8-bit integer.






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   The class definition is as follows:

      NAME                8021QMarkerService
      DESCRIPTION         A concrete class representing the
                          process of marking the Priority
                          field in an 802.1Q-compliant frame
                          with a specified value.  Frames are
                          marked in order to control the
                          conditioning that they will
                          subsequently receive.
      DERIVED FROM        MarkerService
      TYPE                Concrete
      PROPERTIES          PriorityValue

4.3.16.1.  The Property PriorityValue

   This property is an unsigned 8-bit integer, representing a value to
   be used for marking the Priority field in the 802.1Q header. Since
   the Priority field consists of 3 bits, the values for this property
   are limited to the range 0..7.  When the Priority field is marked,
   the remaining bits in its octet are left unchanged.

4.3.17.  The Class DropperService

   This is a concrete class that represents the ability to selectively
   drop network traffic, or to invoke another ConditioningService for
   further processing of traffic that is not dropped.  This is the base
   class for different types of droppers. Droppers are distinguished by
   the algorithm that they use to drop traffic.  Please see [DSMODEL]
   for more information about the various types of droppers.  Note that
   this class encompasses both Absolute Droppers and Algorithmic
   Droppers from [DSMODEL].

   DropperService is modeled as a ConditioningService so that it can be
   aggregated into a QoSService (using the QoSConditioningSubService
   association) to indicate that its functionality underlies that QoS
   service.  It participates in the NextService association to identify
   the subsequent ConditioningService object that acts on any remaining
   traffic that is not dropped.

   NextService has special semantics for droppers, in addition to the
   general "what happens next" semantics that apply to all
   ConditioningServices.  The queue(s) from which a particular dropper
   drops packets are identified by following chain(s) of NextService
   associations "rightwards" from the dropper until they reach a queue.






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   The class definition is as follows:

      NAME                DropperService
      DESCRIPTION         A concrete base class describing the
                          common characteristics of droppers.
      DERIVED FROM        ConditioningService
      TYPE                Concrete
      PROPERTIES          DropperType, OtherDropperType, DropFrom

   Note: The DropperType property and the DropperService subclasses
   provide similar information.  The DropperType property is defined for
   query purposes, as well as for those cases where a subclass of
   DropperService is not needed to model a particular type of dropper.
   For example, the Absolute Dropper defined in [DSMODEL] is modeled as
   an instance of the DropperService class with its DropperType set to
   '4' ("Absolute Dropper").

4.3.17.1.  The Property DropperType

   This is an enumerated 16-bit unsigned integer that defines the type
   of dropper.  Values include:

      1 - Other
      2 - Random
      3 - HeadTail
      4 - Absolute Dropper

   Note: if the value of DropperType is not one of these four values, it
   SHOULD be interpreted as if it had the value '1' (Other).

4.3.17.2.  The Property OtherDropperType

   This string property is used in conjunction with the DropperType
   property.  When the value of DropperType is '1' (i.e., Other), then
   the name of the type of dropper appears in this property.

4.3.17.3.  The Property DropFrom

   This is an unsigned 16-bit integer enumeration that indicates the
   point in the associated queue from which packets should be dropped.
   Defined enumeration values are:

      o  unknown(0)
      o  head(1)
      o  tail(2)






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   Note: if the value of DropFrom is '0' (unknown), or if it is not one
   of the three values listed here, then packets MAY be dropped from any
   location in the associated queue.

4.3.18.  The Class HeadTailDropperService

   This is a concrete class that represents the threshold information of
   a head or tail dropper.  The inherited property DropFrom indicates
   whether a particular instance of this class represents a head dropper
   or a tail dropper.

   A head dropper always examines the same queue from which it drops
   packets, and this queue is always related to the dropper as the
   following service in the NextService association.

   The class definition is as follows:

      NAME                HeadTailDropperService
      DESCRIPTION         A concrete class used to describe
                          a head or tail dropper.
      DERIVED FROM        DropperService
      TYPE                Concrete
      PROPERTIES          QueueThreshold

4.3.18.1.  The Property QueueThreshold

   This is an unsigned 32-bit integer that indicates the queue depth at
   which traffic will be dropped.  For a tail dropper, all newly
   arriving traffic is dropped.  For a head dropper, packets at the
   front of the queue are dropped to make room for new packets, which
   are added at the end.  The value is expressed in bytes.

4.3.19.  The Class REDDropperService

   This is a concrete class that represents the ability to drop network
   traffic using a Random Early Detection (RED) algorithm. This
   algorithm is described in [RED].  The purpose of a RED algorithm is
   to avoid congestion (as opposed to managing congestion).  Instead of
   waiting for the queues to fill up, and then dropping large numbers of
   packets, RED works by monitoring the average queue depth.  When the
   queue depth exceeds a minimum threshold, packets are randomly
   discarded.  These discards cause TCP to slow its transmission rate
   for those connections that experienced the packet discards.  Other
   TCP connections are not affected by these discards.  Please see
   [DSMODEL] for more information about a dropper.






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   A RED dropper always drops packets from a single queue, which is
   related to the dropper as the following service in the NextService
   association.  The queue(s) examined by the drop algorithm are found
   by following the CalculationServiceForDropper association to find the
   dropper's DropThresholdCalculationService, and then following the
   CalculationBasedOnQueue association(s) to find the queue(s) being
   watched.

   The class definition is as follows:

      NAME                REDDropperService
      DESCRIPTION         A concrete class used to describe
                          dropping using the RED algorithm (or
                          one of its variants).
      DERIVED FROM        DropperService
      TYPE                Concrete
      PROPERTIES          MinQueueThreshold, MaxQueueThreshold,
                          ThresholdUnits, StartProbability,
                          StopProbability

   NOTE:  In [DSMIB], there is a single diffServRandomDropTable, which
   represents the general category of random dropping.  (RED is one type
   of random dropping, but there are also types of random dropping
   distinct from RED.)  The REDDropperService class corresponds to the
   columns in the table that apply to the RED algorithm in particular.

4.3.19.1.  The Property MinQueueThreshold

   This is an unsigned 32-bit integer that defines the minimum average
   queue depth at which packets are subject to being dropped.  The units
   are identified by the ThresholdUnits property.  The slope of the drop
   probability function is described by the Start/StopProbability
   properties.

4.3.19.2.  The Property MaxQueueThreshold

   This is an unsigned 32-bit integer that defines the maximum average
   queue length at which packets are subject to always being dropped,
   regardless of the dropping algorithm and probabilities being used.
   The units are identified by the ThresholdUnits property.

4.3.19.3.  The Property ThresholdUnits

   This is an unsigned 16-bit integer enumeration that identifies the
   units for the MinQueueThreshold and MaxQueueThreshold properties.
   Defined enumeration values are:





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      o    bytes(1)
      o    packets(2)

   Note: if the value of ThresholdUnits is not one of these two values,
   it SHOULD be interpreted as if it had the value '1' (bytes).

4.3.19.4.  The Property StartProbability

   This is an unsigned 32-bit integer; in conjunction with the
   StopProbability property, it defines the slope of the drop
   probability function.  This function governs the rate at which
   packets are subject to being dropped, as a function of the queue
   length.

   This property expresses a drop probability in drops per thousand
   packets.  For example, the value 100 indicates a drop probability of
   100 per 1000 packets, that is, 10%.  Min and max values are 0 to
   1000.

4.3.19.5.  The Property StopProbability

   This is an unsigned 32-bit integer; in conjunction with the
   StartProbability property, it defines the slope of the drop
   probability function.  This function governs the rate at which
   packets are subject to being dropped, as a function of the queue
   length.

   This property expresses a drop probability in drops per thousand
   packets.  For example, the value 100 indicates a drop probability of
   100 per 1000 packets, that is, 10%.  Min and max values are 0 to
   1000.

4.3.20.  The Class QueuingService

   This is a concrete class that represents the ability to queue network
   traffic, and to specify the characteristics for determining long-term
   congestion.  Please see [DSMODEL] for more information about queuing
   functionality.

   QueuingService is modeled as a ConditioningService so that it can be
   aggregated into a QoSService (using the QoSConditioningSubService
   association) to indicate that its functionality underlies that QoS
   service.








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   The class definition is as follows:

      NAME                QueuingService
      DESCRIPTION         A concrete class describing the ability
                          to queue network traffic and to specify
                          the characteristics for determining
                          long-term congestion.
      DERIVED FROM        ConditioningService
      TYPE                Concrete
      PROPERTIES          CurrentQueueDepth, DepthUnits

4.3.20.1.  The Property CurrentQueueDepth

   This is an unsigned 32-bit integer, which functions as a (read-only)
   gauge representing the current depth of this one queue.  This value
   may be important in diagnosing unexpected behavior by a
   DropThresholdCalculationService.

4.3.20.2.  The Property DepthUnits

   This is an unsigned 16-bit integer enumeration that identifies the
   units for the CurrentQueueDepth property.  Defined enumeration values
   are:

      o    bytes(1)
      o    packets(2)

   Note: if the value of DepthUnits is not one of these two values, it
   SHOULD be interpreted as if it had the value '1' (bytes).  The

4.3.21.  Class PacketSchedulingService

   This is a concrete class that represents a scheduling service, which
   is a process that determines when a queued packet should be removed
   from a queue and sent to an output interface.  Note that output
   interfaces can be physical network interfaces or interfaces to
   components internal to systems, such as crossbars or back planes.  In
   either case, if multiple queues are involved, schedulers are used to
   provide access to the interface.

   Each instance of a PacketSchedulingService describes a scheduler from
   the perspective of the queues that it is servicing.  Please see
   [DSMODEL] for more information about a scheduler.

   PacketSchedulingService is modeled as a ConditioningService so that
   it can be aggregated into a QoSService (using the
   QoSConditioningSubService association) to indicate that its
   functionality underlies that QoS service.  It participates in the



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   NextService association to identify the subsequent
   ConditioningService object, if any, that acts on traffic after it has
   been processed by the scheduler.

   The class definition is as follows:

      NAME                PacketSchedulingService
      DESCRIPTION         A concrete class used to determine when
                          a packet should be removed from a
                          queue and sent to an output interface.
      DERIVED FROM        ConditioningService
      TYPE                Concrete
      PROPERTIES          SchedulerType, OtherSchedulerType

4.3.21.1.  The Property SchedulerType

   This property is an enumerated 16-bit unsigned integer, and defines
   the type of scheduler.  Values are:

      1 - Other
      2 - FIFO
      3 - Priority
      4 - Allocation
      5 - Bounded Priority
      6 - Weighted Round Robin Packet

   Note: if the value of SchedulerType is not one of these six values,
   it SHOULD be interpreted as if it had the value '2' (FIFO).

4.3.21.2.  The Property OtherSchedulerType

   This string property is used in conjunction with the SchedulerType
   property.  When the value of SchedulerType is 1 (i.e., Other), then
   the type of scheduler is specified in this property.

4.3.22.  The Class NonWorkConservingSchedulingService

   This class does not add any properties beyond those it inherits from
   its superclass, PacketSchedulingService.  It does, however,
   participate in one additional association, FailNextScheduler.











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   The class definition is as follows:

      NAME                NonWorkConservingSchedulingService
      DESCRIPTION         A concrete class representing a
                          scheduler that is capable of operating
                          in a non-work conserving manner.
      DERIVED FROM        PacketSchedulingService
      TYPE                Concrete
      PROPERTIES          (none)

4.3.23.  The Class QoSService

   This is a concrete class that represents the ability to conceptualize
   a QoS service as a set of coordinated sub-services. This enables the
   network administrator to map business rules to the network, and the
   network designer to engineer the network such that it can provide
   different functions for different traffic streams.

   This class has two main purposes.  First, it serves as a common base
   class for defining the various sub-services needed to build higher-
   level QoS services.  Second, it serves as a way to consolidate the
   relationships between different types of QoS services and different
   types of ConditioningServices.

   For example, Gold Service may be defined as a QoSService which
   aggregates two QoS services together.  Each of these QoS services
   could be represented by an instance of the class DiffServService, one
   for servicing of very high demand packets (represented by an instance
   of DiffServService itself), and one for the service given to most of
   the packets, represented by an instance of AFService, which is a
   subclass of DiffServService.  The high demand DiffServService
   instance will then use the QoSConditioningSubService aggregation to
   aggregate together the necessary classifiers to indicate which
   traffic it applies to, and the appropriate meters for contract
   limits, the marker to mark the EF PHB in the packets, and the
   queuing-related conditioning services.  The AFService instance will
   also use the QoSConditioningSubService aggregation, to aggregate its
   classifiers and meters, the several markers used to mark the
   different AF PHBs in the packets, and the queuing-related
   conditioning services needed to deliver the packet treatment.

   QoSService is modeled as a type of Service, which is used as the
   anchor point for defining a set of sub-services that implement the
   desired conditioning characteristics for different types of flows.
   It will direct the specific type of conditioning services to be used
   in order to implement this service.





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   The class definition is as follows:

      NAME                QoSService
      DESCRIPTION         A concrete class used to represent a QoS
                          service or set of services, as defined
                          by a network administrator.
      DERIVED FROM        Service
      TYPE                Concrete
      PROPERTIES          (none)

4.3.24.  The Class DiffServService

   This is a concrete class representing the use of standard or custom
   DiffServ services to implement a (higher-level) QoS service.  Note
   that a DiffServService object may be just one of a set of coordinated
   QoSSubServices objects that together implement a higher-level QoS
   service.

   DiffServService is modeled as a subclass of QoSService.  This enables
   it to be related to a higher-level QoS service via QoSSubService, as
   well as to specific ConditioningService objects (e.g., metering,
   dropping, queuing, and others) via QoSConditioningSubService.

   The class definition is as follows:

      NAME                DiffServService
      DESCRIPTION         A concrete class used to represent a
                          DiffServ service associated with a
                          particular Per Hop Behavior.
      DERIVED FROM        QoSService
      TYPE                Concrete
      PROPERTIES          PHBID

4.3.24.1.  The Property PHBID

   This property is a 16-bit unsigned integer, which identifies a
   particular per hop behavior, or family of per hop behaviors.  The
   value here is a Per Hop Behavior Identification Code, as defined in
   [R3140].  Note that as defined, these identification codes use the
   default, recommended, code points for PHBs as part of their
   structure.  These values may well be different from the actual value
   used in the marker, as the marked value is a domain-dependent value.
   The ability to indicate the PHB Identification Code associated with a
   service is helpful for tying the QoS Service to reference documents,
   and for inter-domain coordination and operation.






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4.3.25.  The Class AFService

   This is a concrete class that represents a specialization of the
   general concept of forwarding network traffic, by adding specific
   semantics that characterize the operation of the Assured Forwarding
   (AF) Service ([R2597]).

   [R2597] defines four different AF classes, to represent four
   different treatments of traffic.  A different amount of forwarding
   resources, such as buffer space and bandwidth, are allocated to each
   AF class.  Within each AF class, IP packets are marked with one of
   three possible drop precedence values.  The drop precedence of a
   packet determines the relative importance of that packet compared to
   other packets within the same AF class, if congestion occurs.  A
   congested interface will try to avoid dropping packets marked with a
   lower drop precedence value, by instead discarding packets marked
   with a higher drop precedence value.

   Note that [R2597] defines 12 DSCPs that together represent the AF Per
   Hop Behavior (PHB) group.  Implementations are free to extend this
   (e.g., add more classes and/or drop precedences).

   The AFService class is modeled as a specialization of
   DiffServService, which is in turn a specialization of QoSService.
   This enables it to be related to higher-level QoS services, as well
   as to lower-level conditioning sub-services (e.g., classification,
   metering, dropping, queuing, and others).

   The class definition is as follows:

      NAME                AFService
      DESCRIPTION         A concrete class for describing the
                          common characteristics of differentiated
                          services that are used to affect
                          traffic forwarding, using the AF
                          PHB Group.
      DERIVED FROM        DiffServService
      TYPE                Concrete
      PROPERTIES          ClassNumber, DropperNumber

4.3.25.1.  The Property ClassNumber

   This property is an 8-bit unsigned integer that indicates the number
   of AF classes that this AF implementation uses.  Among the instances
   aggregated using the QoSConditioningSubService aggregation with an
   instance of AFService, one SHOULD find markers with as many distinct
   values as the ClassNumber of the AFService instance.




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4.3.25.2.  The Property DropperNumber

   This property is an 8-bit unsigned integer that indicates the number
   of drop precedence values that this AF implementation uses.  The
   number of drop precedence values is the number PER AF CLASS.  The
   corresponding droppers will be found in the collection of
   conditioning services aggregated with the QoSConditioningSubService
   aggregation.

4.3.26.  The Class FlowService

   This class represents a service that supports a particular microflow.
   The microflow is identified by the string-valued property FlowID.  In
   some implementations, an instance of this class corresponds to an
   entry in the implementation's flow table.

   The class definition is as follows:

      NAME                FlowService
      DESCRIPTION         A concrete class representing a
                          microflow.
      DERIVED FROM        QoSService
      TYPE                Concrete
      PROPERTIES          FlowID

4.3.26.1.  The Property FlowID

   This property is a string containing an identifier for a microflow.

4.3.27.  The Class DropThresholdCalculationService

   This class represents a logical entity that calculates an average
   queue depth for a queue, based on a smoothing weight and a sampling
   time interval.  It does this calculation on behalf of a RED dropper,
   to allow the dropper to make its decisions whether to drop packets
   based on a smoothed average queue depth for the queue.















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   The class definition is as follows:

      NAME                DropThresholdCalculationService
      DESCRIPTION         A concrete class representing a logical
                          entity that calculates an average queue
                          depth for a queue, based on a smoothing
                          weight and a sampling time interval.
                          The latter are properties of this
                          Service, describing how it operates and
                          its necessary parameters.
      DERIVED FROM        Service
      TYPE                Concrete
      PROPERTIES          SmoothingWeight, TimeInterval

4.3.27.1.  The Property SmoothingWeight

   This property is a 32-bit unsigned integer, ranging between 0 and
   100,000 - specified in thousandths.  It defines the weighting of past
   history in affecting the calculation of the current average queue
   depth.  The current queue depth calculation uses the inverse of this
   value as its factor, and one minus that inverse as the factor for the
   historical average.  The calculation takes the form:

      average = (old_average*(1-inverse of SmoothingWeight))
           + (current_queue_depth*inverse of SmoothingWeight)

   Implementations may choose to limit the acceptable set of values to a
   specified set, such as powers of 2.

   Min and max values are 0 and 100000.

4.3.27.2.  The Property TimeInterval

   This property is a 32-bit unsigned integer, defining the number of
   nanoseconds between each calculation of average/smoothed queue depth.
   If this property is not specified, the CalculationService may
   determine an appropriate interval.

4.3.28.  The Abstract Class FilterEntryBase

   FilterEntryBase is the abstract base class from which all filter
   entry classes are derived.  It serves as the endpoint for the
   EntriesInFilterList aggregation, which groups filter entries into
   filter lists.  Its properties include CIM naming properties and an
   IsNegated boolean property (to easily "NOT" the match information
   specified in an instance of one of its subclasses).





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   Because FilterEntryBase has general applicability, it is defined in
   [PCIME].  See [PCIME] for the definition of this class.

4.3.29.  The Class IPHeaderFilter

   This concrete class makes it possible to represent an entire IP
   header filter in a single object.  A property IpVersion identifies
   whether the IP addresses in an instance are IPv4 or IPv6 addresses.
   (Since the source and destination IP addresses come from the same
   packet header, they will always be of the same type.)

   See [PCIME] for the definition of this class.

4.3.30.  The Class 8021Filter

   This concrete class allows 802.1.source and destination MAC
   addresses, as well as the 802.1 protocol ID, priority, and VLAN
   identifier fields, to be expressed in a single object

   See [PCIME] for the definition of this class.

4.3.31.  The Class PreambleFilter

   This is a concrete class that models classifying packets using
   traffic-conditioning results stored in a packet preamble by a
   PreambleMarkerService.  See Section 3.8.3 for a discussion of how,
   and why, QDDIM models the capability to store these results in a
   packet preamble.  An instance of PreambleFilter is used to select
   packets based on a two-part string identifying a specific result.
   The logic for this match is "at least one".  That is, a packet with
   multiple results in its preamble matches a filter if at least one of
   these results matches the filter.

   The class definition is as follows:

      NAME                PreambleFilter
      DESCRIPTION         A concrete class representing criteria
                          for selecting packets based on prior
                          traffic-conditioning results stored in
                          a packet preamble.
      DERIVED FROM        FilterEntryBase
      TYPE                Concrete
      PROPERTIES          FilterItemList[ ]








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4.3.31.1.  The Multi-valued Property FilterItemList

   This property is an ordered list of strings, where each string has
   the format "<type>,<value>".  See Section 3.8.3 for a list of
   <type>'s defined in QDDIM, and the nature of the associated <value>
   for each of these types.

   Note that there are two parallel terminologies for characterizing
   meter results.  The enumeration value "conforming(1)" is sometimes
   described as "in profile," and the value "nonConforming(3)" is
   sometimes described as "out of profile".

4.3.32.  The Class FilterList

   This is a concrete class that aggregates instances of (subclasses of)
   FilterEntryBase via the aggregation EntriesInFilterList.  It is
   possible to aggregate different types of filters into a single
   FilterList - for example, packet header filters (represented by the
   IPHeaderFilter class) and security filters (represented by subclasses
   of FilterEntryBase defined by IPsec).

   The aggregation property EntriesInFilterList.EntrySequence is always
   set to 0, to indicate that the aggregated filter entries are ANDed
   together to form a selector for a class of traffic.

   See [PCIME] for the definition of this class.

4.3.33.  The Abstract Class ServiceAccessPoint

   This is an abstract class defined in the Core Model of CIM.  It is a
   subclass of the LogicalElement class, and is the base class for all
   objects that manage access to CIM_Services.  It represents the
   management of utilizing or invoking a Service. Please refer to [CIM]
   for the full definition of this class.

4.3.34.  The Class ProtocolEndpoint

   This is a concrete class derived from ServiceAccessPoint, which
   describes a communication point from which the services of the
   network or the system's protocol stack may be accessed.  Please refer
   to [CIM] for the full definition of this class.










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4.3.35.  The Abstract Class Collection

   This is an abstract class defined in the Core Model of CIM.  It is
   the superclass for all classes that represent groupings or bags, and
   that carry no status or "state".  (The latter would be more correctly
   modeled as ManagedSystemElements.)  Please refer to [CIM] for the
   full definition of this class.

4.3.36.  The Abstract Class CollectionOfMSEs

   This is an abstract class defined in the Core Model of CIM.  It is a
   subclass of the Collection superclass, restricting the contents of
   the Collection to ManagedSystemElements.  Please refer to [CIM] for
   the full definition of this class.

4.3.37.  The Class BufferPool

   This is a concrete class that represents the collection of buffers
   used by a QueuingService.  (The association QueueAllocation
   represents this usage.)  The existence and management of individual
   buffers may be modeled in a future document.  At the current level of
   abstraction, modeling the existence of the BufferPool is necessary.
   Long term, it is not sufficient.

   In implementations where there are multiple buffer sizes, an instance
   of BufferPool should be defined for each set of buffers with
   identical or similar sizes.  These instances of buffer pools can then
   be grouped together using the CollectedBuffersPool aggregation.

   Note that this class is derived from CollectionOfMSEs, and not from
   Forwarding or ConditioningService.  A BufferPool is only a collection
   of storage, and is NOT a Service.

   The class definition is as follows:

      NAME                BufferPool
      DESCRIPTION         A concrete class representing
                          a collection of buffers.
      DERIVED FROM        CollectionOfMSEs
      TYPE                Concrete
      PROPERTIES          Name, BufferSize, TotalBuffers,
                          AvailableBuffers, SharedBuffers

4.3.37.1.  The Property Name

   This property is a string with a maximum length of 256 characters.
   It is the common name or label by which the object is known.




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4.3.37.2.  The Property BufferSize

   This property is a 32-bit unsigned integer, identifying the
   approximate number of bytes in each buffer in the buffer pool. An
   implementation will typically group buffers of roughly the same size
   together, to reduce the number of buffer pools it needs to manage.
   This model does not specify the degree to which buffers in the same
   buffer pool may differ in size.

4.3.37.3.  The Property TotalBuffers

   This property is a 32-bit unsigned integer, reporting the total
   number of individual buffers in the pool.

4.3.37.4.  The Property AvailableBuffers

   This property is a 32-bit unsigned integer, reporting the number of
   buffers in the Pool that are currently not allocated to any instance
   of a QueuingService.  Buffers allocated to a QueuingService could
   either be in use (that is, currently contain packet data), or be
   allocated to a queue pending the arrival of new packet data.

4.3.37.5.  The Property SharedBuffers

   This property is a 32-bit unsigned integer, reporting the number of
   buffers in the Pool that have been simultaneously allocated to
   multiple instances of QueuingService.

4.3.38.  The Abstract Class SchedulingElement

   This is an abstract class that represents the configuration
   information that a PacketSchedulingService has for one of the
   elements that it is scheduling.  The scheduled element is either a
   QueuingService or another PacketSchedulingService.

   Among the subclasses of this class, some are defined in such a way
   that all of their instances are work conserving.  Other subclasses,
   however, may have instances that either are or are not work
   conserving.  In this class, the boolean property WorkConserving
   indicates whether an instance is or is not work conserving.  The
   range of values for WorkConserving is restricted to TRUE in the
   subclasses that are inherently work conserving, since instances of
   these classes cannot be anything other than work conserving.








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   The class definition is as follows:

      NAME                SchedulingElement
      DESCRIPTION         An abstract class representing the
                          configuration information that a
                          PacketSchedulingService has for one of
                          the elements that it is scheduling.
      DERIVED FROM        ManagedElement
      TYPE                Abstract
      PROPERTIES          WorkConserving

4.3.38.1.  The Property WorkConserving

   This boolean property indicates whether the PacketSchedulingService
   tied to this instance by the ElementInSchedulingService aggregation
   is treating the input tied to this instance by the QueueToSchedule or
   SchedulingServiceToSchedule association in a work-conserving manner.
   Note that this property is writable, indicating that an administrator
   can change the behavior of the SchedulingElement - but only for those
   elements that can operate in a non-workconserving mode.

4.3.39.  The Class AllocationSchedulingElement

   This class is a subclass of the abstract class SchedulingElement. It
   introduces five new properties to support bandwidth-based scheduling.
   As is the case with all subclasses of SchedulingElement, the input
   associated with an instance of AllocationSchedulingElement is of one
   of two types: either a queue, or another scheduler.

   The class definition is as follows:

      NAME                AllocationSchedulingElement
      DESCRIPTION         A concrete class containing parameters
                          for controlling bandwidth-based
                          scheduling.

      DERIVED FROM        SchedulingElement
      TYPE                Concrete
      PROPERTIES          AllocationUnits, BandwidthAllocation,
                          BurstAllocation, CanShare,
                          WorkFlexible










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4.3.39.1.  The Property AllocationUnits

   This property is a 16-bit unsigned integer enumeration that
   identifies the units in which the BandwidthAllocation and
   BurstAllocation properties are expressed.  The following values are
   defined:

      o bytes(1)
      o packets(2)
      o cells(3)       -- fixed-size, for example, ATM

   Note: if the value of AllocationUnits is not one of these three
   values, it SHOULD be interpreted as if it had the value '1' (bytes).

4.3.39.2.  The Property BandwidthAllocation

   This property is a 32-bit unsigned integer that defines the number of
   units/second that should be allocated to the associated input.  The
   units are identified by the AllocationUnits property.

4.3.39.3.  The Property BurstAllocation

   This property is a 32-bit unsigned integer that specifies the amount
   of temporary or short-term bandwidth (in units per second) that can
   be allocated to an input, beyond the amount of bandwidth allocated
   through the BandwidthAllocation property.  If the maximum actual
   bandwidth allocation for the input were to be measured, it would be
   the sum of the BurstAllocation and the BandwidthAllocation
   properties.  The units are identified by the AllocationUnits
   property.

4.3.39.4.  The Property CanShare

   This is a boolean property that, if TRUE, enables unused bandwidth
   from the associated input to be allocated to other inputs serviced by
   the Scheduler.

4.3.39.5.  The Property WorkFlexible

   This is a boolean property that, if TRUE, indicates that the behavior
   of the scheduler relative to this input can be altered by changing
   the value of the inherited property WorkConserving.

4.3.40.  The Class WRRSchedulingElement

   This class is a subclass of the abstract class SchedulingElement,
   representing a weighted round robin (WRR) scheduling discipline. It
   introduces a new property WeightingFactor, to give some inputs a



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   higher probability of being serviced than other inputs.  It also
   introduces a property Priority, to serve as a tiebreaker to be used
   when inputs have equal weighting factors.  As is the case with all
   subclasses of SchedulingElement, the input associated with an
   instance of WRRSchedulingElement is of one of two types: either a
   queue, or another scheduler.

   Because scheduling of this type is always work conserving, the
   inherited boolean property WorkConserving is restricted to the value
   TRUE in this class.

   The class definition is as follows:

      NAME              WRRSchedulingElement
      DESCRIPTION       This class specializes the
                        SchedulingElement class to add
                        a per-input weight.  This is used
                        by a weighted round robin packet
                        scheduler when it handles its
                        associated inputs.  It also adds a
                        second property to serve as a tie-breaker
                        in the case where multiple inputs have
                        been assigned the same weight.
      DERIVED FROM      SchedulingElement
      TYPE              Concrete
      PROPERTIES        WeightingFactor, Priority

4.3.40.1.  The Property WeightingFactor

   This property is a 32-bit unsigned integer, which defines the
   weighting factor that offers some inputs a higher probability of
   being serviced than other inputs.  This property represents this
   probability.  Its minimum value is 0, its maximum value is 100000,
   and its units are in thousandths.

4.3.40.2.  The Property Priority

   This property is a 16-bit unsigned integer, which serves as a
   tiebreaker, in the event that two or more inputs have equal weights.
   A larger value represents a higher priority.  If this property is
   specified for any of the WRRSchedulingElements associated with a
   PacketSchedulingService, then it must be specified for all
   WRRSchedulingElements for that PacketSchedulingService, and the
   property values for these WRRSchedulingElements must all be
   different.






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   While this condition may not occur in some implementations of a
   weighted round-robin scheduler, many implementations require a
   priority to resolve an equal-weight condition.  In instances where
   this behavior is not necessary or is undesirable, this property may
   be left unspecified.

4.3.41.  The Class PrioritySchedulingElement

   This class is a subclass of the abstract class SchedulingElement. It
   indicates that a scheduler is taking packets from a set of inputs
   using the priority scheduling discipline.  As is the case with all
   subclasses of SchedulingElement, the input associated with an
   instance of PrioritySchedulingElement is of one of two types: either
   a queue, or another scheduler.  The property Priority in
   PrioritySchedulingElement represents the priority for an input,
   relative to the priorities of all the other inputs to which the
   scheduler that aggregates this PrioritySchedulingElement is
   associated.  Inputs to which the scheduler is related via other
   scheduling disciplines do not figure in this prioritization.

   Because scheduling of this type is always work conserving, the
   inherited boolean property WorkConserving is restricted to the value
   TRUE in this class.

   The class definition is as follows:

      NAME             PrioritySchedulingElement
      DESCRIPTION      A concrete class that specializes the
                       SchedulingElement class to add a
                       Priority property.  This property is
                       used by a SchedulingService that is doing
                       priority scheduling for a set of  inputs.

      DERIVED FROM     SchedulingElement
      TYPE             Concrete
      PROPERTIES       Priority

4.3.41.1.  The Property Priority

   This property is a 16-bit unsigned integer that indicates the
   priority level of a scheduler input relative to the other inputs
   serviced by this PacketSchedulingService.  A larger value represents
   a higher priority.








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4.3.42.  The Class BoundedPrioritySchedulingElement

   This class is a subclass of the class PrioritySchedulingElement,
   which is itself derived from the abstract class SchedulingElement.
   As is the case with all subclasses of SchedulingElement, the input
   associated with an instance of BoundedPrioritySchedulingElement is of
   one of two types: either a queue, or another scheduler.
   BoundedPrioritySchedulingElement adds an upper bound (in kilobits per
   second) on how much traffic can be handled from an input.  This data
   is specific to that one input.  It is needed when bounded strict
   priority scheduling is performed.

   This class inherits from its superclass PrioritySchedulingElement the
   restriction of the inherited boolean property WorkConserving to the
   value TRUE.

   The class definition is as follows:

      NAME              BoundedPrioritySchedulingElement
      DESCRIPTION       This concrete class specializes the
                        PrioritySchedulingElement class to add
                        a BandwidthBound property.  This property
                        bounds the rate at which traffic from the
                        associated input can be handled.

      DERIVED FROM      PrioritySchedulingElement
      TYPE              Concrete
      PROPERTIES        BandwidthBound

4.3.42.1.  The Property BandwidthBound

   This property is a 32-bit unsigned integer that defines the upper
   limit on the amount of traffic that can be handled from the input.
   This is not a shaped upper bound, since bursts can occur. It is a
   strict bound, limiting the impact of the input.  The units are
   kilobits per second.

4.4.  Association Definitions

   This section details the QoS device datapath associations, including
   the aggregations, which were shown earlier in Figures 4 and 5.  These
   associations are defined as classes in the Information Model.  Each
   of these classes has two properties referring to instances of the two
   classes that the association links.  Some of the association classes
   have additional properties as well.






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4.4.1.  The Abstract Association Dependency

   This abstract association defines two object references (named
   Antecedent and Dependent) that establish general dependency
   relationships between different managed objects in the information
   model.  The Antecedent reference identifies the independent object in
   the association, while the Dependent reference identifies the entity
   that IS dependent.

   The association's cardinality is many to many.

   The association is defined in the Core Model of CIM.  Please refer to
   [CIM] for the full definition of this class.

4.4.2.  The Association ServiceSAPDependency

   This association defines two object references that establish a
   general dependency relationship between a Service object and a
   ServiceAccessPoint object.  This relationship indicates that the
   referenced Service uses the ServiceAccessPoint of ANOTHER Service.
   The Service is the Dependent reference, relying on the
   ServiceAccessPoint to gain access to another Service.

   The association's cardinality is many to many.

   The association is defined in the Core Model of CIM.  Please refer to
   [CIM] for the full definition of this class.

4.4.3.  The Association IngressConditioningServiceOnEndpoint

   This association is derived from the association
   ServiceSAPDependency, and represents the binding, in the ingress
   direction, between a protocol endpoint and the first
   ConditioningService that processes packets received via that protocol
   endpoint.  Since there can only be one "first" ConditioningService
   for a protocol endpoint, the cardinality for the Dependent object
   reference is narrowed from 0..n to 0..1. Since, on the other hand, a
   single ConditioningService can be the first to process packets
   received via multiple protocol endpoints, the cardinality of the
   Antecedent object reference remains 0..n.











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   The class definition is as follows:

      NAME              IngressConditioningServiceOnEndpoint
      DESCRIPTION       An association that establishes a
                        dependency relationship between a protocol
                        endpoint and the first conditioning
                        service that processes traffic arriving
                        via that protocol endpoint.
      DERIVED FROM      ServiceSAPDependency
      ABSTRACT          False
      PROPERTIES        Antecedent[ref ProtocolEndpoint[0..n]],
                        Dependent[ref ConditioningService[0..1]]

4.4.4.  The Association EgressConditioningServiceOnEndpoint

   This association is derived from the association
   ServiceSAPDependency, and represents the binding, in the egress
   direction, between a protocol endpoint and the last
   ConditioningService that processes packets before they leave a
   network device via that protocol endpoint.  (This "last"
   ConditioningService is ordinarily a scheduler, but it doesn't have to
   be.)  Since there can be multiple "last" ConditioningServices for a
   protocol endpoint in the case of a fallback scheduler, the
   cardinality for the Dependent object reference remains 0..n.  Since,
   however, a single ConditioningService cannot be the last one to
   process packets for multiple protocol endpoints, the cardinality of
   the Antecedent object reference is narrowed from 0..n to 0..1.

   The class definition is as follows:

      NAME              EgressConditioningServiceOnEndpoint
      DESCRIPTION       An association that establishes a
                        dependency relationship between a protocol
                        endpoint and the last conditioning
                        service(s) that process traffic to be
                        transmitted via that protocol endpoint.
      DERIVED FROM      ServiceSAPDependency
      ABSTRACT          False
      PROPERTIES        Antecedent[ref ProtocolEndpoint[0..1]],
                        Dependent[ref ConditioningService[0..n]]

4.4.5.  The Association HeadTailDropQueueBinding

   This association is a subclass of Dependency, describing the
   association between a head or tail dropper and a queue that it
   monitors to determine when to drop traffic.  The referenced queue is
   the one whose queue depth is compared against the Dropper's
   threshold.  The cardinality is 1..n on the queue side, since a



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   head/tail dropper must monitor at least one queue.  For the classes
   HeadTailDropper and HeadTailDropQueueBinding, the rule for combining
   the inputs from multiple queues is simple addition: if the sum of the
   lengths of the monitored queues exceeds the dropper's QueueThreshold
   value, then packets are dropped.  This rule for combining inputs may,
   however, be overridden by a different rule in subclasses of one or
   both of these classes.

   The class definition is as follows:

      NAME              HeadTailDropQueueBinding
      DESCRIPTION       A generic association used to establish a
                        dependency relationship between a
                        head or tail dropper and a queue that it
                        monitors.
      DERIVED FROM      Dependency
      ABSTRACT          False
      PROPERTIES        Antecedent[ref QueuingService[1..n]],
                        Dependent[ref
                           HeadTailDropperService [0..n]]

4.4.6.  The Association CalculationBasedOnQueue

   This association is a subclass of Dependency, which defines two
   object references that establish a dependency relationship between a
   QueuingService and an instance of the DropThresholdCalculationService
   class.  The queue's current depth is used by the calculation service
   in calculating an average queue depth.

   The class definition is as follows:

      NAME              CalculationBasedOnQueue
      DESCRIPTION       A generic association used to establish a
                        dependency relationship between a
                        QueuingService object and a
                        DropThresholdCalculationService object.
      DERIVED FROM      ServiceServiceDependency
      ABSTRACT          False
      PROPERTIES        Antecedent[ref QueuingService[1..1]],
                        Dependent[ref
                           DropThresholdCalculationService [0..n]]










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4.4.6.1.  The Reference Antecedent

   This property is inherited from the Dependency association, and
   overridden to serve as an object reference to a QueuingService object
   (instead of to the more general ManagedElement).  This reference
   identifies the queue that the DropThresholdCalculationService will
   use in its calculation of average queue depth.

4.4.6.2.  The Reference Dependent

   This property is inherited from the Dependency association, and
   overridden to serve as an object reference to a
   DropThresholdCalculationService object (instead of to the more
   general ManagedElement).  This reference identifies a
   DropThresholdCalculationService that uses the referenced queue's
   current depth as one of the inputs to its calculation of average
   queue depth.

4.4.7.  The Association ProvidesServiceToElement

   This association defines two object references that establish a
   dependency relationship in which a ManagedSystemElement depends on
   the functionality of one or more Services.  The association's
   cardinality is many to many.

   The association is defined in the Core Model of CIM.  Please refer to
   [CIM] for the full definition of this class.

4.4.8.  The Association ServiceServiceDependency

   This association defines two object references that establish a
   dependency relationship between two Service objects.  The particular
   type of dependency is represented by the TypeOfDependency property;
   typical examples include that one Service is required to be present
   or required to have completed for the other Service to operate.

   This association is very similar to the ServiceSAPDependency
   relationship.  For the latter, the Service is dependent on an
   AccessPoint to get at another Service.  In this relationship, it
   directly identifies its Service dependency.  Both relationships
   should not be instantiated, since their information is repetitive.

   The association's cardinality is many to many.

   The association is defined in the Core Model of CIM.  Please refer to
   [CIM] for the full definition of this class.





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4.4.9.  The Association CalculationServiceForDropper

   This association is a subclass of ServiceServiceDependency, which
   defines two object references that represent the reliance of a
   REDDropperService on a DropThresholdCalculationService - calculating
   an average queue depth based on the observed depths of one or more
   queues.

   The class definition is as follows:

      NAME              CalculationServiceForDropper
      DESCRIPTION       A generic association used to establish a
                        dependency relationship between a
                        calculation service and a
                        REDDropperSrevice for which it performs
                        average queue depth calculations
      DERIVED FROM      ServiceServiceDependency
      ABSTRACT          False
      PROPERTIES        Antecedent[ref
                           DropThresholdCalculationService[1..n]],
                        Dependent[ref REDDropperService[0..n]]
4.4.9.1.  The Reference Antecedent

   This property is inherited from the ServiceServiceDependency
   association, and overridden to serve as an object reference to a
   DropThresholdCalculationService object (instead of to the more
   general Service object).  The cardinality of the object reference is
   1..n, indicating that a RED dropper may be served by one or more
   calculation services.

4.4.9.2.  The Reference Dependent

   This property is inherited from the ServiceServiceDependency
   association, and overridden to serve as an object reference to a
   REDDropperService object (instead of to the more general Service
   object).  This reference identifies a RED dropper served by a
   DropThresholdCalculationService.

4.4.10.  The Association QueueAllocation

   This association is a subclass of Dependency, which defines two
   object references that establish a dependency relationship between a
   QueuingService and a BufferPool that provides storage space for the
   packets in the queue.







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   The class definition is as follows:

      NAME              QueueAllocation
      DESCRIPTION       A generic association used to establish a
                        dependency relationship between a
                        QueuingService object and a BufferPool
                        object.
      DERIVED FROM      Dependency
      ABSTRACT          False
      PROPERTIES        Antecedent[ref BufferPool[0..n]],
                        Dependent[ref QueuingService[0..n]]
                        AllocationPercentage

4.4.10.1.  The Reference Antecedent

   This property is inherited from the Dependency association, and
   overridden to serve as an object reference to a BufferPool object.
   This reference identifies the BufferPool in which packets on the
   QueuingService's queue are stored.

4.4.10.2.  The Reference Dependent

   This property is inherited from the Dependency association, and
   overridden to serve as an object reference to a QueuingService
   object.  This reference identifies the QueuingService whose packets
   are being stored in the BufferPool's buffers.

4.4.10.3.  The Property AllocationPercentage

   This property is an 8-bit unsigned integer with minimum value of zero
   and maximum value of 100.  It defines the percentage of the
   BufferPool that should be allocated to the referenced QueuingService.
   If absolute sizes are desired, this would be accomplished by defining
   individual BufferPools of the specified sizes, with
   QueueAllocation.AllocationPercentages set to 100.

4.4.11.  The Association ClassifierElementUsesFilterList

   This association is a subclass of the Dependency association.  It
   relates one or more ClassifierElements with a FilterList representing
   the criteria for selecting packets for each of the ClassifierElements
   to process.

   In the QDDIM model, a classifier is always modeled as a
   ClassifierService that aggregates a set of ClassifierElements. When
   ClassifierElements use the NextServiceAfterClassifierElement





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   association to bind to another ClassifierService (to construct a
   hierarchical classifier), the ClassifierElementUsesFilterList
   association must not be specified.

   The class definition is as follows:

      NAME              ClassifierElementUsesFilterList
      DESCRIPTION       An association relating a
                        ClassifierElement to the FilterList
                        representing the criteria for selecting
                        packets for that
                        ClassifierElement to process.
      DERIVED FROM      Dependency
      ABSTRACT          False
      PROPERTIES        Antecedent[ref FilterList [0..1]],
                        Dependent[ref ClassifierElement [0..n]]

4.4.11.1.  The Reference Antecedent

   This property is inherited from the Dependency association, and
   overridden to serve as an object reference to a FilterList object,
   instead of to the more general ManagedElement object. Also, its
   cardinality is restricted to 0 and 1, indicating that a
   ClassifierElement uses either one FilterList to select packets for it
   or no FilterList when the ClassifierElement uses the
   NextServiceAfterClassifierElement association to bind to another
   ClassifierService to form a hierarchical classifier.

4.4.11.2.  The Reference Dependent

   This property is inherited from the Dependency association, and
   overridden to serve as an object reference to a ClassifierElement
   object, instead of to the more general ManagedElement object. This
   reference identifies a ClassifierElement that depends on the
   associated FilterList object to represent its packet-selection
   criteria.

4.4.12.  The Association AFRelatedServices

   This association defines two object references that establish a
   dependency relationship between two AFService objects.  This
   dependency is the precedence of the individual AF drop-related
   Services within an AF IP packet-forwarding class.








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   The class definition is as follows:

      NAME              AFRelatedServices
      DESCRIPTION       An association used to establish
                        a dependency relationship between two
                        AFService objects.
      DERIVED FROM      Nothing
      ABSTRACT          False
      PROPERTIES        AFLowerDropPrecedence[ref
                          AFService[0..1]],
                        AFHigherDropPrecedence[ref
                          AFService[0..n]]

4.4.12.1.  The Reference AFLowerDropPrecedence

   This property serves as an object reference to an AFService object
   that has the lower probability of dropping packets.

4.4.12.2.  The Reference AFHigherDropPrecedence

   This property serves as an object reference to an AFService object
   that has the higher probability of dropping packets.

4.4.13.  The Association NextService

   This association defines two object references that establish a
   predecessor-successor relationship between two ConditioningService
   objects.  This association is used to indicate the sequence of
   ConditioningServices required to process a particular type of
   traffic.

   Instances of this dependency describe the various relationships
   between different ConditioningServices (such as classifiers, meters,
   droppers, etc.) that are used collectively to condition traffic.
   Both one-to-one and more complicated fan-in and/or fan-out
   relationships can be described.  The ConditioningServices may feed
   one another directly, or they may be mapped to multiple "next"
   Services based on the characteristics of the packet.













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   The class definition is as follows:

      NAME              NextService
      DESCRIPTION       An association used to establish
                        a predecessor-successor relationship
                        between two ConditioningService objects.
      DERIVED FROM      Nothing
      ABSTRACT          False
      PROPERTIES        PrecedingService[ref
                          ConditioningService[0..n]],
                        FollowingService[ref
                          ConditioningService[0..n]]

4.4.13.1.  The Reference PrecedingService

   This property serves as an object reference to a ConditioningService
   object that occurs earlier in the processing sequence for a given
   type of traffic.

4.4.13.2.  The Reference FollowingService

   This property serves as an object reference to a ConditioningService
   object that occurs later in the processing sequence for a given type
   of traffic, immediately after the ConditioningService identified by
   the PrecedingService object reference.

4.4.14.  The Association NextServiceAfterClassifierElement

   This association refines the definition of its superclass, the
   NextService association, in two ways:

   o  It restricts the PrecedingService object reference to the class
      ClassifierElement.

   o  It restricts the cardinality of the FollowingService object
      reference to exactly 1.

   The class definition is as follows:

      NAME              NextServiceAfterClassifierElement
      DESCRIPTION       An association used to establish
                        a predecessor-successor relationship
                        between a single ClassifierElement within
                        a Classifier and the next
                        ConditioningService object that is
                        responsible for further processing of
                        the traffic selected by that
                        ClassifierElement.



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      DERIVED FROM      NextService
      ABSTRACT          False
      PROPERTIES        PrecedingService
                          [ref ClassifierElement[0..n]],
                        FollowingService
                          [ref ConditioningService[1..1]

4.4.14.1.  The Reference PrecedingService

   This property is inherited from the NextService association.  It is
   overridden in this subclass to restrict the object reference to a
   ClassifierElement, as opposed to the more general ConditioningService
   defined in the NextService superclass.

   This property serves as an object reference to a ClassifierElement,
   which is a component of a single ClassifierService.  Packets selected
   by this ClassifierElement are always passed to the
   ConditioningService identified by the FollowingService object
   reference.

4.4.14.2.  The Reference FollowingService

   This property is inherited from the NextService association.  It is
   overridden in this subclass to restrict the cardinality of the
   reference to exactly 1.  This reflects the requirement that the
   behavior of a DiffServ classifier must be deterministic: the packets
   selected by a given ClassifierElement in a given ClassifierService
   must always go to one and only one next ConditioningService.

4.4.15.  The Association NextScheduler

   This association is a subclass of NextService, and defines two object
   references that establish a predecessor-successor relationship
   between PacketSchedulingServices.  In a hierarchical queuing
   configuration where a second scheduler treats the output of a first
   scheduler as a single, aggregated input, the two schedulers are
   related via the NextScheduler association.

   The class definition is as follows:

      NAME              NextScheduler
      DESCRIPTION       An association used to establish
                        predecessor-successor relationships
                        between PacketSchedulingService objects
                        for simple hierarchical scheduling.
      DERIVED FROM      NextService
      ABSTRACT          False




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      PROPERTIES        PrecedingService[ref
                           PacketSchedulingService[0..n]],
                        FollowingService[ref
                           PacketSchedulingService[0..1]]

4.4.15.1.  The Reference PrecedingService

   This property is inherited from the NextService association, and
   overridden to serve as an object reference to a
   PacketSchedulingService object (instead of to the more general
   ConditioningService object).  This reference identifies a scheduler
   whose output is being treated as a single, aggregated input by the
   scheduler identified by the FollowingService reference.  The [0..n]
   cardinality indicates that a single FollowingService scheduler may
   bring together the aggregated outputs of multiple prior schedulers.

4.4.15.2.  The Reference FollowingService

   This property is inherited from the NextService association, and
   overridden to serve as an object reference to a
   PacketSchedulingService object (instead of to the more general
   ConditioningService object).  This reference identifies a scheduler
   that includes among its inputs the aggregated outputs of one or more
   PrecedingService schedulers.

4.4.16.  The Association FailNextScheduler

   This association is a subclass of the NextScheduler association.
   FailNextScheduler represents the relationship between two schedulers
   when the first scheduler passes up a scheduling opportunity (thereby
   behaving in a non-work conserving manner), and makes the resulting
   bandwidth available to the second scheduler for its use.  See
   Sections 3.11.3 and 3.11.4 for examples of where this association
   might be used.

   The class definition is as follows:

      NAME              FailNextScheduler
      DESCRIPTION       This association specializes the
                        NextScheduler association.  It
                        establishes a relationship between a
                        non-work-conserving scheduler and a
                        second scheduler to which it makes
                        available the bandwidth that it elects
                        not to use.
      DERIVED FROM      NextScheduler
      ABSTRACT          False




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      PROPERTIES        PrecedingService[ref
                         NonWorkConservingSchedulingService[0..n]]

4.4.16.1.  The Reference PrecedingService

   This property is inherited from the NextScheduler association, and
   overridden to serve as an object reference to a
   NonWorkConservingSchedulingService object (instead of to the more
   general PacketSchedulingService object).  This reference identifies a
   non-work-conserving scheduler whose excess bandwidth is being made
   available to the scheduler identified by the FollowingService
   reference.  The [0..n] cardinality indicates that a single
   FollowingService scheduler may have the opportunity to use the unused
   bandwidth of multiple prior non-work-conserving schedulers.

4.4.17.  The Association NextServiceAfterMeter

   This association describes a predecessor-successor relationship
   between a MeterService and one or more ConditioningService objects
   that process traffic from the meter.  For example, for devices that
   implement preamble marking, the FollowingService reference (after the
   meter) is a PreambleMarkerService, to record the results of the
   metering in the preamble.

   It might be expected that the NextServiceAfterMeter association would
   subclass from NextService.  However, meters are 1:n fan-out elements,
   and require a mechanism to distinguish between the different
   results/outputs of the meter.  Therefore, this association defines a
   new key property, MeterResult, which is used to record the result and
   identify the output through which this traffic left the meter.
   Because of this additional key, NextServiceAfterMeter cannot be a
   subclass of NextService.

   The class definition is as follows:

      NAME              NextServiceAfterMeter
      DESCRIPTION       An association used to establish
                        a predecessor-successor relationship
                        between a particular output of a
                        MeterService and the next
                        ConditioningService object that is
                        responsible for further processing of
                        the traffic.
      DERIVED FROM      Nothing
      ABSTRACT          False






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      PROPERTIES        PrecedingService[ref MeterService[0..n]],
                        FollowingService[ref
                          ConditioningService[0..n]],
                        MeterResult

4.4.17.1.  The Reference PrecedingService

   The preceding MeterService, 'earlier' in the processing sequence for
   a packet.  Since Meters are 1:n fan-out devices, this relationship
   associates a particular output of a MeterService (identified by the
   MeterResult property) to the next ConditioningService that is used to
   further process the traffic.

4.4.17.2.  The Reference FollowingService

   The 'next' or following ConditioningService.

4.4.17.3.  The Property MeterResult

   This property is an enumerated 16-bit unsigned integer, and
   represents information describing the result of the metering. Traffic
   is distinguished as being conforming, non-conforming, or partially
   conforming.  More complicated metering can be built either by
   extending the enumeration or by cascading meters.

   The enumerated values are: "Unknown" (0), "Conforming" (1),
   "PartiallyConforming" (2), "NonConforming" (3).

4.4.18.  The Association QueueToSchedule

   This is a top-level association, representing the relationship
   between a queue (QueuingService) and a SchedulingElement.  The
   SchedulingElement, in turn, represents the information in a packet
   scheduling service that is specific to this queue, such as relative
   priority or allocated bandwidth.

   It cannot be expressed formally with the association cardinalities,
   but there is an additional constraint on participation in this
   association.  A particular instance of (a subclass of)
   SchedulingElement always participates either in exactly one instance
   of this association, or in exactly one instance of the association
   SchedulingServiceToSchedule.









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   The class definition is as follows:

      NAME              QueueToSchedule
      DESCRIPTION       This association relates a queue to
                        the SchedulingElement containing
                        information specific to the queue.
      DERIVED FROM      Nothing
      ABSTRACT          False
      PROPERTIES        Queue[ref QueuingService[0..1]],
                        SchedElement[ref
                           SchedulingElement[0..n]]

4.4.18.1.  The Reference Queue

   This property serves as an object reference to a QueuingService
   object.  A QueuingService object may be associated 0 or more
   SchedulingElement objects.

4.4.18.2.  The Reference SchedElement

   This property serves as an object reference to a SchedulingElement
   object.  A SchedulingElement is always associated either with exactly
   one QueuingService or with exactly one upstream scheduler
   (PacketSchedulingService).

4.4.19.  The Association SchedulingServiceToSchedule

   This is a top-level association, representing the relationship
   between a scheduler (PacketSchedulingService) and a
   SchedulingElement, in a configuration involving cascaded schedulers.
   The SchedulingElement, in turn, represents the information in a
   subsequent packet scheduling service that is specific to this
   scheduler, such as relative priority or allocated bandwidth.

   It cannot be expressed formally with the association cardinalities,
   but there is an additional constraint on participation in this
   association.  A particular instance of (a subclass of)
   SchedulingElement always participates either in exactly one instance
   of this association, or in exactly one instance of the association
   QueueToSchedule.

   The class definition is as follows:

      NAME              SchedulingServiceToSchedule
      DESCRIPTION       This association relates a scheduler to
                        the SchedulingElement in a subsequent
                        scheduler containing information specific
                        to this scheduler.



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      DERIVED FROM      Nothing
      ABSTRACT          False
      PROPERTIES        SchedService[ref
                           PacketSchedulingService[0..1]],
                        SchedElement[ref
                           SchedulingElement[0..n]]

4.4.19.1.  The Reference SchedService

   This property serves as an object reference to a
   PacketSchedulingService object.  A PacketSchedulingService object may
   be associated 0 or more SchedulingElement objects.

4.4.19.2.  The Reference SchedElement

   This property serves as an object reference to a SchedulingElement
   object.  A SchedulingElement is always associated either with exactly
   one QueuingService or with exactly one upstream scheduler
   (PacketSchedulingService).

4.4.20.  The Aggregation MemberOfCollection

   This aggregation is a generic relationship used to model the
   aggregation of a set of ManagedElements in a generalized Collection
   object.  The aggregation's cardinality is many to many.

   MemberOfCollection is defined in the Core Model of CIM.  Please refer
   to [CIM] for the full definition of this class.

4.4.21.  The Aggregation CollectedBufferPool

   This aggregation models the ability to treat a set of buffers as a
   pool, or collection, that can in turn be contained in a "higher-
   level" buffer pool.  This class overrides the more generic
   MemberOfCollection aggregation to restrict both the aggregate and the
   part component objects to be instances only of the BufferPool class.

   The class definition for the aggregation is as follows:

      NAME              CollectedBufferPool
      DESCRIPTION       A generic association used to aggregate
                        a set of related buffers into a
                        higher-level buffer pool.
      DERIVED FROM      MemberOfCollection
      ABSTRACT          False
      PROPERTIES        Collection[ref BufferPool[0..1]],
                        Member[ref BufferPool[0..n]]




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4.4.21.1.  The Reference Collection

   This property represents the parent, or aggregate, object in the
   relationship.  It is a BufferPool object.

4.4.21.2.  The Reference Member

   This property represents the child, or lower level pool, in the
   relationship.  It is one of the set of BufferPools that together make
   up the higher-level pool.

4.4.22.  The Abstract Aggregation Component

   This abstract aggregation is a generic relationship used to establish
   "part-of" relationships between managed objects (named GroupComponent
   and PartComponent).  The association's cardinality is many to many.

   The association is defined in the Core Model of CIM.  Please refer to
   [CIM] for the full definition of this class.

4.4.23.  The Aggregation ServiceComponent

   This aggregation is used to model a set of subordinate Services that
   are aggregated together to form a higher-level Service. This
   aggregation is derived from the more generic Component superclass to
   restrict the types of objects that can participate in this
   relationship.  The association's cardinality is many to many.

   The association is defined in the Core Model of CIM.  Please refer to
   [CIM] for the full definition of this class.

4.4.24.  The Aggregation QoSSubService

   This aggregation represents a set of subordinate QoSService objects
   (that is, a set of instances of subclasses of the QoSService class)
   that are aggregated together to form a higher-level QoSService.  A
   QoSService is a specific type of Service that conceptualizes QoS
   functionality as a set of coordinated sub-services.

   This aggregation is derived from the more generic ServiceComponent
   superclass to restrict the types of objects that can participate in
   this relationship to QoSService objects, instead of a more generic
   Service object.  It also restricts the cardinality of the aggregate
   to 0-or-1 (instead of the more generic 0-or-more).







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   The class definition for the aggregation is as follows:

      NAME              QoSSubService
      DESCRIPTION       A generic association used to establish
                        "part-of" relationships between a
                        higher-level QoSService object and the
                        set of lower-level QoSServices that
                        are aggregated to create/form it.
      DERIVED FROM      ServiceComponent
      ABSTRACT          False
      PROPERTIES        GroupComponent[ref QoSService[0..1]],
                        PartComponent[ref QoSService[0..n]]

4.4.24.1.  The Reference GroupComponent

   This property is overridden in this aggregation to represent an
   object reference to a QoSService object (instead of to the more
   generic Service object defined in its superclass).  This object
   represents the parent, or aggregate, object in the relationship.

4.4.24.2.  The Reference PartComponent

   This property is overridden in this aggregation to represent an
   object reference to a QoSService object (instead of to the more
   generic Service object defined in its superclass).  This object
   represents the child, or "component", object in the relationship.

4.4.25.  The Aggregation QoSConditioningSubService

   This aggregation identifies the set of conditioning services that
   together condition traffic for a particular QoS service.

   This aggregation is derived from the more generic ServiceComponent
   superclass; it restricts the types of objects that can participate in
   it to ConditioningService and QoSService objects, instead of the more
   generic Service objects.

   The class definition for the aggregation is as follows:

      NAME              QoSConditioningSubService
      DESCRIPTION       A generic aggregation used to establish
                        "part-of" relationships between a set
                        of ConditioningService objects and the
                        particular QoSService object(s) that they
                        provide traffic conditioning for.
      DERIVED FROM      ServiceComponent
      ABSTRACT          False




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      PROPERTIES        GroupComponent[ref QoSService[0..n]],
                        PartComponent[ref
                          ConditioningService[0..n]]

4.4.25.1.  The Reference GroupComponent

   This property is overridden in this aggregation to represent an
   object reference to a QoSService object (instead of to the more
   generic Service object defined in its superclass).  The cardinality
   of the reference remains 0..n, to indicate that a given
   ConditioningService may provide traffic conditioning for 0, 1, or
   more than 1 QoSService objects.

   This object represents the parent, or aggregate, object in the
   association.  In this case, this object represents the QoSService
   that aggregates one or more ConditioningService objects to implement
   the appropriate traffic conditioning for its traffic.

4.4.25.2.  The Reference PartComponent

   This property is overridden in this aggregation to represent an
   object reference to a ConditioningService object (instead of to the
   more generic Service object defined in its superclass).  This object
   represents the child, or "component", object in the relationship.  In
   this case, this object represents one or more ConditioningService
   objects that together indicate how traffic for a specific QoSService
   is conditioned.

4.4.26.  The Aggregation ClassifierElementInClassifierService

   This aggregation represents the relationship between a classifier and
   the classifier elements that provide the fan-out function for the
   classifier.  A classifier typically aggregates multiple classifier
   elements.  A classifier element, however, is aggregated only by a
   single classifier.  See [DSMODEL] and [DSMIB] for more about
   classifiers and classifier elements.

   The class definition for the aggregation is as follows:

      NAME              ClassifierElementInClassifierService
      DESCRIPTION       An aggregation representing the
                        relationship between a classifier
                        and its classifier elements.
      DERIVED FROM      ServiceComponent
      ABSTRACT          False






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      PROPERTIES        GroupComponent[ref
                           ClassifierService[1..1]],
                        PartComponent[ref
                           ClassifierElement[0..n],
                        ClassifierOrder

4.4.26.1.  The Reference GroupComponent

   This property is overridden in this aggregation to represent an
   object reference to a ClassifierService object (instead of to the
   more generic Service object defined in its superclass).  It also
   restricts the cardinality of the aggregate to 1..1 (instead of the
   more generic 0-or-more), representing the fact that a
   ClassifierElement always exists within the context of exactly one
   ClassifierService.

4.4.26.2.  The Reference PartComponent

   This property is overridden in this aggregation to represent an
   object reference to a ClassifierElement object (instead of to the
   more generic Service object defined in its superclass).  This object
   represents a single traffic selector for the classifier. A
   ClassifierElement usually has an association to a FilterList that
   provides selection criteria for packets from the traffic stream
   coming into the classifier, and to a ConditioningService to which
   packets selected by these criteria are next forwarded.

4.4.26.3.  The Property ClassifierOrder

   Because the filters for a classifier can overlap, it is necessary to
   specify the order in which the ClassifierElements aggregated by a
   ClassifierService are presented with packets coming into the
   classifier.  This property is an unsigned 32-bit integer representing
   this order.  Values are represented in ascending order: first '1',
   then '2', and so on.  Different values MUST be assigned for each of
   the ClassifierElements aggregated by a given ClassifierService.

4.4.27.  The Aggregation EntriesInFilterList

   This aggregation is a specialization of the Component aggregation; it
   is used to define a set of filter entries (subclasses of
   FilterEntryBase) that are aggregated by a FilterList.

   The cardinalities of the aggregation itself are 0..1 on the
   FilterList end, and 0..n on the FilterEntryBase end.  Thus in the
   general case, a filter entry can exist without being aggregated into





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   any FilterList.  However, the only way a filter entry can figure in
   the QoS Device model is by being aggregated into a FilterList by this
   aggregation.

   See [PCIME] for the definition of this aggregation.

4.4.28.  The Aggregation ElementInSchedulingService

   This concrete aggregation represents the relationship between a
   PacketSchedulingService and the set of SchedulingElements that tie it
   to its inputs.

   The class definition for the aggregation is as follows:

      NAME              ElementInSchedulingService
      DESCRIPTION       An aggregation used to tie a
                        PacketSchedlingService to the
                        configuration information for one of
                        the elements (either a QueuingService or
                        another PacketSchedulingService) that it
                        schedules.
      DERIVED FROM      Component
      ABSTRACT          False
      PROPERTIES        GroupComponent[ref
                          PacketSchedulingService[0..1]],
                        PartComponent[ref
                           SchedulingElement[1..n]

4.4.28.1.  The Reference GroupComponent

   This property is overridden in this aggregation to represent an
   object reference to a PacketSchedulingService object (instead of to
   the more generic Service object defined in its superclass). It also
   restricts the cardinality of the aggregate to 0..1 (instead of the
   more generic 0-or-more), representing the fact that a
   SchedulingElement exists within the context of at most one
   PacketSchedulingService.

4.4.28.2.  The Reference PartComponent

   This property is overridden in this aggregation to represent an
   object reference to a SchedulingElement object (instead of to the
   more generic Service object defined in its superclass).  This object
   represents a single scheduling element for the scheduler. It also
   restricts the cardinality of the SchedulingElement to 1..n (instead
   of the more generic 0-or-more), representing the fact that a
   PacketSchedulingService always includes at least one
   SchedulingElement.



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5.  Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights. Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.

   Copies of claims of rights made available for publication and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive
   Director.

6.  Acknowledgements

   The authors wish to thank the participants of the Policy Framework
   and Differentiated Services working groups for their many helpful
   comments and suggestions.  Special thanks to Joel Halpern, who
   provided some key technical direction during the latter stages of the
   document's development.

7.  Security Considerations

   Like [PCIM] and [PCIME], this document defines an information model
   that cannot be implemented directly.  Consequently, security issues
   do not arise until it is mapped to an actual, implementable data
   model such as a MIB, PIB, or LDAP schema.  See [PCIM] for a general
   discussion of security considerations for information models.  See
   also [DSMIB] (which in fact is a data model that corresponds to a
   large extent with the QDDIM information model), for a discussion of
   the security implications of specific objects in the model.










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8.  References

8.1.  Normative References

   [CIM]      Common Information Model (CIM) Schema, version 2.5.
              Distributed Management Task Force, Inc., available at
              http://www.dmtf.org/standards/cim_schema_v25.php.

   [IEEE802Q] Virtual Bridged Local Area Networks, ANSI/IEEE std 802.1Q,
              1998 edition.  Approved December 8, 1998

   [PCIM]     Moore, B., Ellesson, E., Strassner, J. and A. Westerinen,
              "Policy Core Information Model - Version 1 Specification",
              RFC 3060, February 2001.

   [PCIME]    Moore, B., Ed., "Policy Core Information Model (PCIM)
              Extensions", RFC 3460, January 2003.

   [R791]     Postel, J., "Internet Protocol", STD 5, RFC 791, September
              1981.

   [R2119]    Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [R2474]    Nichols, K., Blake, S., Baker, F. and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474, December
              1998.

   [R2597]    Heinanen, J., Baker, F., Weiss, W. and J. Wroclawski,
              "Assured Forwarding PHB Group", RFC 2597, June 1999.

   [R3140]    Black, D., Brim, S., Carpenter, B. and F. Le Faucheur,
              "Per Hop Behavior Identification Codes", RFC 3140, June
              2001.

8.2.  Informative References

   [DSMIB]    Baker, F., Chan, K. and A. Smith, "Management Information
              Base for the Differentiated Services Architecture", RFC
              3289, May 2002.

   [DSMODEL]  Bernet, Y., Blake, S., Grossman, D. and A. Smith, "An
              Informal Management Model for DiffServ Routers", RFC 3290,
              May 2002.






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   [PIB]      Chan, K., Sahita, R., Hahn, S. and K. McCloghrie,
              "Differentiated Services Quality of Service Policy
              Information Base", RFC 3317, March 2003.

   [POLTERM]  Westerinen, A., Schnizlein, J., Strassner, J., Scherling,
              M., Quinn, B., Herzog, S., Huynh, A., Carlson, M., Perry,
              J. and S. Waldbusser, "Terminology for Policy-Based
              Management", RFC 3198, November 2001.

   [QPIM]     Snir, Y., Ramberg, Y., Strassner, J., Cohen, R. and B.
              Moore, "Policy Quality of Service (QoS) Information
              Model", RFC 3644, November 2003.

   [R1633]    Braden, R., Clark, D. and S. Shenker, "Integrated Services
              in the Internet Architecture: An Overview",  RFC 1633,
              June 1994.

   [R2475]    Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.
              and W. Weiss, "An Architecture for Differentiated
              Service", RFC 2475, December 1998.

   [R3246]    Davie, B., Charny, A., Bennet, J.C.R., Benson, K., Le
              Boudec, J.Y., Courtney, W., Davari, S., Firoiu, V. and D.
              Stiliadis, "An Expedited Forwarding PHB (Per-Hop
              Behavior)", RFC 3246, March 2002.

   [RED]      See http://www.aciri.org/floyd/red.html
























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9.  Appendix A:  Naming Instances in a Native CIM Implementation

   Following the precedent established in [PCIM], this document has
   placed the details of how to name instances of its classes in a
   native CIM implementation here in an appendix.  Since Appendix A in
   [PCIM] has a lengthy discussion of the general principles of CIM
   naming, this appendix does not repeat that information here.  Readers
   interested in a more global discussion of how instances are named in
   a native CIM implementation should refer to [PCIM].

9.1.  Naming Instances of the Classes Derived from Service

   Most of the classes defined in this model are derived from the CIM
   class Service.  Although Service is an abstract class, it
   nevertheless has key properties included as part of its definition.
   The purpose of including key properties in an abstract class is to
   have instances of all of its instantiable subclasses named in the
   same way.  Thus, the majority of the classes in this model name their
   instances in exactly the same way: with the two key properties
   CreationClassName and Name that they inherit from Service.

9.2.  Naming Instances of Subclasses of FilterEntryBase

   Like Service, FilterEntryBase (defined in [PCIME]) is an abstract
   class that includes key properties in its definition.
   FilterEntryBase has four key properties.  Two of them,
   SystemCreationClassName and SystemName, are propagated to it via the
   weak association FilterEntryInSystem.  The other two,
   CreationClassName and Name, are native to FilterEntryBase.

   Thus, instances of all of the subclasses of FilterEntryBase,
   including the PreambleFilter class defined here, are named in the
   same way: with the four key properties they inherit from
   FilterEntryBase.

9.3.  Naming Instances of ProtocolEndpoint

   The class ProtocolEndpoint inherits its key properties from its
   superclass, ServiceAccessPoint.  These key properties provide the
   same naming structure that we've seen before: two propagated key
   properties SystemCreationClassName and SystemName, plus two native
   key properties CreationClassName and Name.









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9.4.  Naming Instances of BufferPool

   Unlike the other classes in this model, BufferPool is not derived
   from Service.  Consequently, it does not inherit its key properties
   from Service.  Instead, it inherits one of its key properties,
   CollectionID, from its superclass Collection, and adds its other key
   property, CreationClassName, in its own definition.

9.4.1.  The Property CollectionID

   CollectionID is a string property with a maximum length of 256
   characters.  It identifies the buffer pool.  Note that this property
   is defined in the BufferPool class's superclass, CollectionOfMSEs,
   but not as a key property.  It is overridden in BufferPool, to make
   it part of this class's composite key.

9.4.2.  The Property CreationClassName

   This property is a string property of with a maximum length of 256
   characters.  It is set to "CIM_BufferPool" if this class is directly
   instantiated, or to the class name of the BufferPool subclass that is
   created.

9.5.  Naming Instances of SchedulingElement

   This class has not yet been incorporated into the CIM model, so it
   does not have any CIM naming properties yet.  If the normal pattern
   is followed, however, instances will be named with two properties
   CreationClassName and Name.






















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10.  Authors' Addresses

   Bob Moore
   P. O. Box 12195, BRQA/B501/G206
   3039 Cornwallis Rd.
   Research Triangle Park, NC  27709-2195

   Phone: (919) 254-4436
   EMail: remoore@us.ibm.com


   David Durham
   Intel
   2111 NE 25th Avenue
   Hillsboro, OR 97124

   Phone: (503) 264-6232
   EMail: david.durham@intel.com


   John Strassner
   INTELLIDEN, Inc.
   90 South Cascade Avenue
   Colorado Springs, CO  80903

   Phone: (719) 785-0648
   EMail: john.strassner@intelliden.com


   Andrea Westerinen
   Cisco Systems, Bldg 20
   725 Alder Drive
   Milpitas, CA 95035

   EMail: andreaw@cisco.com


   Walter Weiss
   Ellacoya Networks
   7 Henry Clay Dr.
   Merrimack, NH 03054

   Phone: (603) 879-7364
   EMail: walterweiss@attbi.com







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11.  Full Copyright Statement

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assignees.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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