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RFC 3317

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Differentiated Services Quality of Service Policy Information Base

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Network Working Group                                            K. Chan
Request for Comments: 3317                               Nortel Networks
Category: Informational                                        R. Sahita
                                                                 S. Hahn
                                                           K. McCloghrie
                                                           Cisco Systems
                                                              March 2003

  Differentiated Services Quality of Service Policy Information Base

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.


   This document describes a Policy Information Base (PIB) for a device
   implementing the Differentiated Services Architecture.  The
   provisioning classes defined here provide policy control over
   resources implementing the Differentiated Services Architecture.
   These provisioning classes can be used with other none Differentiated
   Services provisioning classes (defined in other PIBs) to provide for
   a comprehensive policy controlled mapping of service requirement to
   device resource capability and usage.

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Table of Contents

   Conventions used in this document...................................3
   1. Glossary.........................................................3
   2. Introduction.....................................................3
   3. Relationship to the DiffServ Informal Management Model...........3
     3.1. PIB Overview.................................................4
   4. Structure of the PIB.............................................6
     4.1. General Conventions..........................................6
     4.2. DiffServ Data Paths..........................................7
       4.2.1. Data Path PRC............................................7
     4.3. Classifiers..................................................8
       4.3.1. Classifier PRC...........................................9
       4.3.2. Classifier Element PRC...................................9
     4.4. Meters.......................................................9
       4.4.1. Meter PRC...............................................10
       4.4.2. Token-Bucket Parameter PRC..............................10
     4.5. Actions.....................................................10
       4.5.1. DSCP Mark Action PRC....................................11
     4.6. Queueing Elements...........................................11
       4.6.1. Algorithmic Dropper PRC.................................11
       4.6.2. Random Dropper PRC......................................12
       4.6.3. Queues and Schedulers...................................14
     4.7. Specifying Device Capabilities..............................16
   5. PIB Usage Example...............................................17
     5.1. Data Path Example...........................................17
     5.2. Classifier and Classifier Element Example...................18
     5.3. Meter Example...............................................21
     5.4. Action Example..............................................21
     5.5. Dropper Examples............................................22
       5.5.1. Tail Dropper Example....................................22
       5.5.2. Single Queue Random Dropper Example.....................23
       5.5.3. Multiple Queue Random Dropper Example...................23
     5.6.   Queue and Scheduler Example...............................26
   6. Summary of the DiffServ PIB.....................................27
   7. PIB Operational Overview........................................28
   8. PIB Definition..................................................29
   9. Acknowledgments.................................................90
   10. Security Considerations........................................90
   11. Intellectual Property Considerations...........................91
   12. IANA Considerations............................................91
   13. Normative References...........................................92
   14. Authors' Addresses.............................................95
   15. Full Copyright Statement.......................................96

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Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

1.  Glossary

   PRC    Provisioning Class.  A type of policy data.  See [POLTERM].
   PRI    Provisioning Instance.  An instance of a PRC.  See [POLTERM].
   PIB    Policy Information Base.  The database of policy information.
          See [POLTERM].
   PDP    Policy Decision Point. See [RAP-FRAMEWORK].
   PEP    Policy Enforcement Point. See [RAP-FRAMEWORK].
   PRID   Provisioning Instance Identifier. Uniquely identifies an
          instance of a PRC.

2.  Introduction

   [SPPI] describes a structure for specifying policy information that
   can then be transmitted to a network device for the purpose of
   configuring policy at that device.  The model underlying this
   structure is one of well-defined provisioning classes and instances
   of these classes residing in a virtual information store called the
   Policy Information Base (PIB).

   This document specifies a set of provisioning classes specifically
   for configuring QoS Policy for Differentiated Services [DSARCH].

   One way to provision policy is by means of the COPS protocol [COPS],
   with the extensions for provisioning [COPS-PR].  This protocol
   supports multiple clients, each of which may provision policy for a
   specific policy domain such as QoS.  The PRCs defined in this
   DiffServ QoS PIB are intended for use by the COPS-PR diffServ client
   type.  Furthermore, these PRCs are in addition to any other PIBs that
   may be defined for the diffServ client type in the future, as well as
   the PRCs defined in the Framework PIB [FR-PIB].

3.  Relationship to the DiffServ Informal Management Model

   This PIB is designed according to the Differentiated Services
   Informal Management Model documented in [MODEL].  The model describes
   the way that ingress and egress interfaces of a 'n'-port router are
   modeled.  It describes the configuration and management of a DiffServ
   interface in terms of a Traffic Conditioning Block (TCB) which
   contains, by definition, zero or more classifiers, meters, actions,
   algorithmic droppers, queues and schedulers.  These elements are

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   arranged according to the QoS policy being expressed, and are always
   in that order.  Traffic may be classified; classified traffic may be
   metered; each stream of traffic identified by a combination of
   classifiers and meters may have some set of actions performed on it;
   it may have dropping algorithms applied and it may ultimately be
   stored into a queue before being scheduled out to its next
   destination, either onto a link or to another TCB.  When the
   treatment for a given packet must have any of those elements repeated
   in a way that breaks the permitted sequence {classifier, meter,
   action, algorithmic dropper, queue, scheduler}, this must be modeled
   by cascading multiple TCBs.

   The PIB represents this cascade by following the "Next" attributes of
   the various elements.  They indicate what the next step in DiffServ
   processing will be, whether it be a classifier, meter, action,
   algorithmic dropper, queue, scheduler or a decision to now forward a

   The PIB models the individual elements that make up the TCBs.  The
   higher level concept of a TCB is not required in the parameterization
   or in the linking together of the individual elements, hence it is
   not used in the PIB itself and is only mentioned in the text for
   relating the PIB with the [MODEL].  The actual distinguishing of
   which TCB a specific element is a part of is not needed for the
   instrumentation of a device to support the functionalities of
   DiffServ, but it is useful for conceptual reasons.  By not using the
   TCB concept, this PIB allows any grouping of elements to construct
   TCBs, using rules indicated by the [MODEL].  This will minimize
   changes to this PIB if rules in [MODEL] change.

   The notion of a Data Path is used in this PIB to indicate the
   DiffServ processing a packet may experience.  This Data Path is
   distinguished based on the Role Combination, Capability Set, and the
   Direction of the flow the packet is part of.  A Data Path Table Entry
   indicates the first of possibly multiple elements that will apply
   DiffServ treatment to the packet.

3.1.  PIB Overview

   This PIB is structured based on the need to configure the sequential
   DiffServ treatments being applied to a packet, and the
   parameterization of these treatments.  These two aspects of the
   configuration are kept separate throughout the design of the PIB, and
   are fulfilled using separate tables and data definitions.

   In addition, the PIB includes tables describing the capabilities and
   limitations of the device using a general extensible framework.

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   These tables are reported to the PDP and assist the PDP with the
   configuration of functional elements that can be realized by the

   This capabilities and limitations exchange allows a single or
   multiple devices to support many different variations of a functional
   datapath element.  Allowing diverse methods of providing a general
   functional datapath element.

   In this PIB, the ingress and egress portions of a router are
   configured independently but in the same manner.  The difference is
   distinguished by an attribute in a table describing the start of the
   data path.  Each interface performs some or all of the following
   high-level functions:

   - Classify each packet according to some set of rules.

   - Determine whether the data stream the packet is part of is within
     or outside its metering parameters.

   - Perform a set of resulting actions such as counting and marking of
     the traffic with a Differentiated Services Code Point (DSCP) as
     defined in [DSFIELD].

   - Apply the appropriate drop policy, either simple or complex
     algorithmic drop functionality.

   - Enqueue the traffic for output in the appropriate queue, whose
     scheduler may shape the traffic or simply forward it with some
     minimum rate or maximum latency.

   The PIB therefore contains the following elements:

   Data Path Table
      This describes the starting point of DiffServ data paths within a
      single DiffServ device.  This class describes interface role
      combination and interface direction specific data paths.

   Classifier Tables
      A general extensible framework for specifying a group of filters.

   Meter Tables
      A general extensible framework and one example of a
      parameterization table - TBParam table, applicable for Simple
      Token Bucket Meter, Average Rate Meter, Single Rate Three Color
      Meter, Two Rate Three Color Meter, and Sliding Window Three Color

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   Action Tables
      A general extensible framework and example of parameterization
      tables for Mark action.  The "multiplexer" and "null" actions
      described in [MODEL] are accomplished implicitly by means of the
      Prid structures of the other elements.

   Algorithmic Dropper Tables
      A general extensible framework for describing the dropper
      functional datapath element.  This includes the absolute dropper
      and other queue measurement dependent algorithmic droppers.

   Queue and Scheduler Tables
      A general extensible framework for parameterizing queuing and
      scheduler systems.  Notice Shaper is considered as a type of
      scheduler and is included here.

   Capabilities Tables
      A general extensible framework for defining the capabilities and
      limitations of the elements listed above.  The capability tables
      allow intelligent configuration of the elements by a PDP.

4.  Structure of the PIB

4.1.  General Conventions

   The PIB consists of PRCs that represent functional elements in the
   data path (e.g., classifiers, meters, actions), and classes that
   specify parameters that apply to a certain type of functional element
   (e.g., a Token Bucket meter or a Mark action).  Parameters are
   typically specified in a separate PRC to enable the use of parameter
   classes by multiple policies.

   Functional element PRCs use the Prid TC (defined in [SPPI]) to
   indicate indirection.  A Prid is an object identifier that is used to
   specify an instance of a PRC in another table.  A Prid is used to
   point to parameter PRC that applies to a functional element, such as
   which filter should be used for a classifier element.  A Prid is also
   used to specify an instance of a functional element PRC that
   describes what treatment should be applied next for a packet in the
   data path.

   Note that the use of Prids to specify parameter PRCs allows the same
   functional element PRC to be extended with a number of different
   types of parameter PRC's.  In addition, using Prids to indicate the
   next functional datapath element allows the elements to be ordered in
   any way.

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4.2.  DiffServ Data Paths

   This part of the PIB provides instrumentation for connecting the
   DiffServ Functional Elements within a single DiffServ device.  Please
   refer to [MODEL] for discussions on the valid sequencing and grouping
   of DiffServ Functional Elements.  Given some basic information, e.g.,
   the interface capability, role combination and direction, the first
   DiffServ Functional Element is determined.  Subsequent DiffServ
   Functional Elements are provided by the "Next" pointer attribute of
   each entry of data path tables.  A description of how this "Next"
   pointer is used in each table is provided in their respective
   DESCRIPTION clauses.

4.2.1.  Data Path PRC

   The Data Path PRC provides the DiffServ treatment starting points for
   all packets of this DiffServ device.  Each instance of this PRC
   specifies the interface capability, role combination and direction
   for the packet flow.  There should be at most two entries for each
   instance (interface type, role combination, interface capability),
   one for ingress and one for egress.  Each instance provides the first
   DiffServ Functional Element that each packet, at a specific interface
   (identified by the roles assigned to the interface) traveling in a
   specific relative direction, should experience.  Notice this class is
   interface specific, with the use of interface type capability set and
   RoleCombination.  To indicate explicitly that there are no DiffServ
   treatments for a particular interface type capability set, role
   combination and direction, an instance of the Data Path PRC can be
   created with zeroDotZero in the dsDataPathStart attribute.  This
   situation can also be indicated implicitly by not supplying an
   instance of a Data Path PRC for that particular interface type
   capability set, role combination and direction.  The
   explicit/implicit selection is up to the implementation.  This means
   that the PEP should perform normal IP device processing when
   zeroDotZero is used in the dsDataPathStart attribute, or when the
   entry does not exist.  Normal IP device processing will depend on the
   device; for example, this can be forwarding the packet.

   Based on implementation experience of network devices where data path
   functional elements are implemented in separate physical processors
   or application specific integrated circuits, separated by switch
   fabric, it seems that more complex notions of data path are required
   within the network device to correlate the different physically
   separate data path functional elements.  For example, ingress
   processing may have determined a specific ingress flow that gets
   aggregated with other ingress flows at an egress data path functional
   element.  Some of the information determined at the ingress data path
   functional element may need to be used by the egress data path

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   functional element.  In numerous implementations, such information
   has been carried by adding it to the frame/memory block used to carry
   the flow within the network device; some implementers have called
   such information a "preamble" or a "frame descriptor".  Different
   implementations use different formats for such information.
   Initially, one may think such information has implementation details
   within the network device that does not need to be exposed outside of
   the network device.  But from Policy Control point of view, such
   information will be very useful in determining network resource usage
   feedback from the network device to the policy server.  This is
   accomplished by using the Internal Label Marker and Filter PRCs
   defined in [FR-PIB].

4.3.  Classifiers

   The classifier and classifier element tables determine how traffic is
   sorted out.  They identify separable classes of traffic, by reference
   to appropriate filters, which may select anything from an individual
   micro-flow to aggregates identified by DSCP.

   The classification is used to send these separate streams to
   appropriate Meter, Action, Algorithmic Dropper, Queue and Scheduler
   elements.  For example, to indicate a multi-stage meter, sub-classes
   of traffic may be sent to different meter stages: e.g., in an
   implementation of the Assured Forwarding (AF) PHB [AF-PHB], AF11
   traffic might be sent to the first meter, AF12 traffic might be sent
   to the second and AF13 traffic sent to the second meter stage's out-
   of-profile action.

   The concept of a classifier is the same as described in [MODEL].  The
   structure of the classifier and classifier element tables, is the
   same as the classifier described in [MODEL].  Classifier elements
   have an associated precedence order solely for the purpose of
   resolving ambiguity between overlapping filters.  A filter with
   higher values of precedence are compared first; the order of tests
   for entries of the same precedence is unimportant.

   A datapath may consist of more than one classifier.  There may be an
   overlap of filter specification between filters of different
   classifiers.  The first classifier functional datapath element
   encountered, as determined by the sequencing of diffserv functional
   datapath elements, will be used first.

   An important form of classifier is "everything else": the final stage
   of the classifier i.e., the one with the lowest precedence, must be
   "complete" since the result of an incomplete classifier is not
   necessarily deterministic - see [MODEL] section 4.1.2.

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   When a classifier PRC is instantiated at the PEP, it should always
   have at least one classifier element table entry, the "everything
   else" classifier element, with its filter matching all IP packets.
   This "everything else" classifier element should be created by the
   PDP as part of the classifier setup.  The PDP has full control of all
   classifier PRIs instantiated at the PEP.

   The definition of the actual filter to be used by the classifier is
   referenced via a Prid: this enables the use of any sort of filter
   table that one might wish to design, standard or proprietary.  No
   filters are defined in this PIB.  However, standard filters for IP
   packets are defined in the Framework PIB [FR-PIB].

4.3.1.  Classifier PRC

   Classifiers, used in various ingress and egress interfaces, are
   organized by the instances of the Classifier PRC.  A data path entry
   points to a classifier entry.  A classifier entry identifies a list
   of classifier elements.  A classifier element effectively includes
   the filter entry, and points to a "next" classifier entry or some
   other data path functional element.

4.3.2.  Classifier Element PRC

   Classifier elements point to the filters which identify various
   classes of traffic.  The separation between the "classifier element"
   and the "filter" allows us to use many different kinds of filters
   with the same essential semantics of "an identified set of traffic".
   The traffic matching the filter corresponding to a classifier element
   is given to the "next" data path functional element identified in the
   classifier element.

   An example of a filter that may be pointed to by a Classifier Element
   PRI is the frwkIpFilter PRC, defined in [FR-PIB].

4.4.  Meters

   A meter, according to [MODEL] section 5, measures the rate at which
   packets composing a stream of traffic pass it, compares this rate to
   some set of thresholds, and produces some number (two or more) of
   potential results.  A given packet is said to "conform" to the meter
   if, at the time the packet is being looked at, the stream appears to
   be within the meter's profile.  PIB syntax makes it easiest to define
   this as a sequence of one or more cascaded pass/fail tests, modeled
   here as if-then-else constructs.  It is important to understand that
   this way of modeling does not imply anything about the implementation
   being "sequential": multi-rate/multi-profile meters, e.g., those
   designed to support [SRTCM], [TRTCM], or [TSWTCM] can still be

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   modeled this way even if they, of necessity, share information
   between the stages: the stages are introduced merely as a notational
   convenience in order to simplify the PIB structure.

4.4.1.  Meter PRC

   The generic meter PRC is used as a base for all more specific forms
   of meter.  The definition of parameters specific to the type of meter
   used is referenced via a pointer to an instance of a PRC containing
   those specifics.  This enables the use of any sort of specific meter
   table that one might wish to design, standard or proprietary. One
   specific meter table is defined in this PIB module.  Other meter
   tables may be defined in other PIB modules.

4.4.2.  Token-Bucket Parameter PRC

   This is included as an example of a common type of meter.  Entries in
   this class are referenced from the dsMeterSpecific attributes of
   meter PRC instances.  The parameters are represented by a rate
   dsTBParamRate, a burst size dsTBParamBurstSize, and an interval
   dsTBparamInterval.  The type of meter being parameterized is
   indicated by the dsTBParamType attribute.  This is used to determine
   how the rate, burst, and rate interval parameters are used.
   Additional meter parameterization classes can be defined in other
   PIBs when necessary.

4.5.  Actions

   Actions include "no action", "mark the traffic with a DSCP" or
   "specific action".  Other tasks such as "shape the traffic" or "drop
   based on some algorithm" are handled in other functional datapath
   elements rather than in actions.  The "multiplexer", "replicator",
   and "null" actions described in [MODEL] are accomplished implicitly
   through various combinations of the other elements.

   This PIB uses the Action PRC dsActionTable to organize one Action's
   relationship with the element(s) before and after it.  It allows
   Actions to be cascaded to enable that multiple Actions be applied to
   a single traffic stream by using each entry's dsActionNext attribute.
   The dsActionNext attribute of the last action entry in the chain
   points to the next element in the TCB, if any, e.g., a Queueing
   element.  It may also point at a next TCB.

   The parameters needed for the Action element will depend on the type
   of Action to be taken.  Hence the PIB allows for specific Action
   Tables for the different Action types.  This flexibility allows
   additional Actions to be specified in other PIBs and also allows for
   the use of proprietary Actions without impact on those defined here.

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   One may consider packet dropping as an Action element.  Packet
   dropping is handled by the Algorithmic Dropper datapath functional

4.5.1.  DSCP Mark Action PRC

   This Action is applied to traffic in order to mark it with a DiffServ
   Codepoint (DSCP) value, specified in the dsDscpMarkActTable.

4.6.  Queueing Elements

   These include Algorithmic Droppers, Queues and Schedulers, which are
   all inter-related in their use of queueing techniques.

4.6.1.  Algorithmic Dropper PRC

   Algorithmic Droppers are represented in this PIB by instances of the
   Algorithmic Dropper PRC.  An Algorithmic Dropper is assumed to
   operate indiscriminately on all packets that are presented at its
   input; all traffic separation should be done by classifiers and
   meters preceding it.

   Algorithmic Dropper includes many types of droppers, from the simple
   always dropper to the more complex random dropper.  This is indicated
   by the dsAlgDropType attribute.

   Algorithmic Droppers have a close relationship with queuing; each
   Algorithmic Dropper Table entry contains a dsAlgDropQMeasure
   attribute, indicating which queue's state affects the calculation of
   the Algorithmic Dropper.  Each entry also contains a dsAlgDropNext
   attribute that indicates to which queue the Algorithmic Dropper sinks
   its traffic.

   Algorithmic Droppers may also contain a pointer to a specific detail
   of the drop algorithm, dsAlgDropSpecific.  This PIB defines the
   detail for three drop algorithms:  Tail Drop, Head Drop, and Random
   Drop; other algorithms are outside the scope of this PIB module, but
   the general framework is intended to allow for their inclusion via
   other PIB modules.

   One generally-applicable parameter of a dropper is the specification
   of a queue-depth threshold at which some drop action is to start.
   This is represented in this PIB, as a base attribute,
   dsAlgDropQThreshold, of the Algorithmic Dropper entry.  The
   attribute, dsAlgDropQMeasure, specifies which queue's depth
   dsAlgDropQThreshold is to be compared against.

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   o  An Always Dropper drops every packet presented to it.  This type
      of dropper does not require any other parameter.

   o  A Tail Dropper requires the specification of a maximum queue depth
      threshold:  when the queue pointed at by dsAlgDropQMeasure reaches
      that depth threshold, dsAlgDropQThreshold, any new traffic
      arriving at the dropper is discarded.  This algorithm uses only
      parameters that are part of the dsAlgDropEntry.

   o  A Head Dropper requires the specification of a maximum queue depth
      threshold:  when the queue pointed at by dsAlgDropQMeasure reaches
      that depth threshold, dsAlgDropQThreshold, traffic currently at
      the head of the queue is discarded.  This algorithm uses only
      parameters that are part of the dsAlgDropEntry.

   o  Random Droppers are recommended as a way to control congestion, in
      [QUEUEMGMT] and called for in the [AF-PHB].  Various
      implementations exist, that agree on marking or dropping just
      enough traffic to communicate with TCP-like protocols about
      congestion avoidance, but differ markedly on their specific
      parameters.  This PIB attempts to offer a minimal set of controls
      for any random dropper, but expects that vendors will augment the
      PRC with additional controls and status in accordance with their
      implementation.  This algorithm requires additional parameters on
      top of those in dsAlgDropEntry; these are discussed below.

   A Dropper Type of other is provided for the implementation of dropper
   types not defined here.  When the Dropper Type is other, its full
   specification will need to be provided by another PRC referenced by
   dsAlgDropSpecific.  A Dropper Type of Multiple Queue Random Dropper
   is also provided; please reference section 5.5.3 of this document for
   more details.

4.6.2.  Random Dropper PRC

   One example of a random dropper is a RED-like dropper.  An example of
   the representation chosen in this PIB for this element is shown in
   Figure 1.

   Random droppers often have their drop probability function described
   as a plot of drop probability (P) against averaged queue length (Q).
   (Qmin, Pmin) then defines the start of the characteristic plot.
   Normally Pmin=0, meaning that with average queue length below Qmin,
   there will be no drops.  (Qmax, Pmax) defines a "knee" on the plot,
   after which point the drop probability become more progressive
   (greater slope).  (Qclip, 1) defines the queue length at which all

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   packets will be dropped.  Notice this is different from Tail Drop
   because this uses an averaged queue length.  Although it is possible
   for Qclip = Qmax.

   In the PIB module, dsRandomDropMinThreshBytes and
   dsRandomDropMinThreshPkts represent Qmin.  dsRandomDropMaxThreshBytes
   and dsRandomDropMaxThreshPkts represent Qmax.  dsAlgDropQThreshold
   represents Qclip.  dsRandomDropProbMax represents Pmax.  This PIB
   does not represent Pmin (assumed to be zero unless otherwise

   In addition, since message memory is finite, queues generally have
   some upper bound above which they are incapable of storing additional
   traffic.  Normally this number is equal to Qclip, specified by

   Each random dropper specification is associated with a queue.  This
   allows multiple drop processes (of same or different types) to be
   associated with the same queue, as different PHB implementations may
   require.  This also allows for sequences of multiple droppers if

         +-----------------+                    +-------+
         |AlgDrop          |                    |Queue  |
     --->| Next   ---------+-+----------------->| Next -+-->
         | QMeasure -------+-+                  | ...   |
         | QThreshold      |                    +-------+
         | Type=randomDrop |   +----------------+
         | Specific -------+-->|RandomDrop      |
         +-----------------+   | MinThreshBytes |
                               | MaxThreshBytes |
                               | ProbMax        |
                               | Weight         |
                               | SamplingRate   |

       Figure 1: Example Use of the RandomDropTable for Random Droppers

   The calculation of a smoothed queue length may also have an important
   bearing on the behavior of the dropper:  parameters may include the
   sampling interval or rate, and the weight of each sample.  The
   performance may be very sensitive to the values of these parameters
   and a wide range of possible values may be required due to a wide
   range of link speeds.  Most algorithms include a sample weight,
   represented here by dsRandomDropWeight.  The availability of
   dsRandomDropSamplingRate as readable is important; the information
   provided by the Sampling Rate is essential to the configuration of
   dsRandomDropWeight.  Having the Sampling Rate be configurable is also

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   helpful, because as line speed increases, the ability to have queue
   sampling be less frequent than packet arrival is needed.  Note
   however that there is ongoing research on this topic, see e.g.,

   Additional parameters may be added in an enterprise PIB module, e.g.,
   by using AUGMENTS on this class, to handle aspects of random drop
   algorithms that are not standardized here.

   NOTE:  Deterministic Droppers can be viewed as a special case of
   Random Droppers with the drop probability restricted to 0 and 1.
   Hence Deterministic Droppers might be described by a Random Dropper
   with Pmin = 0, Pmax = 1, Qmin = Qmax = Qclip, the averaged queue
   length at which dropping occurs.

4.6.3.  Queues and Schedulers

   The Queue PRC models simple FIFO queues, as described in [MODEL]
   section 7.1.1.  The Scheduler PRC allows flexibility in constructing
   both simple and somewhat more complex queueing hierarchies from those
   queues.  Of course, since TCBs can be cascaded multiple times on an
   interface, even more complex hierarchies can be constructed that way

   Queue PRC instances are pointed at by the "next" attributes of the
   upstream elements e.g., dsMeterSucceedNext.  Note that multiple
   upstream elements may direct their traffic to the same Queue PRI.
   For example, the Assured Forwarding PHB suggests that all traffic
   marked AF11, AF12, or AF13 be placed in the same queue after
   metering, without reordering.  This would be represented by having
   the dsMeterSucceedNext of each upstream meter point at the same Queue

   NOTE:  Queue and Scheduler PRIs are for data path description; they
   both use Scheduler Parameterization Table entries for diffserv
   treatment parameterization.

   A Queue Table entry specifies the scheduler it wants service from by
   use of its Next pointer.

   Each Scheduler Table entry represents the algorithm in use for
   servicing the one or more queues that feed it.  [MODEL] section 7.1.2
   describes a scheduler with multiple inputs:  this is represented in
   the PIB by having the scheduling parameters be associated with each
   input.  In this way, sets of Queues can be grouped together as inputs
   to the same Scheduler.  This class serves to represent the example
   scheduler described in the [MODEL]:  other more complex
   representations might be created outside of this PIB.

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   Both the Queue PRC and the Scheduler PRC use instances of the
   Scheduler Parameterization PRC to specify diffserv treatment
   parameterization.  Scheduler Parameter PRC instances are used to
   parameterize each input that feeds into a scheduler.  The inputs can
   be a mixture of Queue PRI's and Scheduler PRI's.  Scheduler Parameter
   PRI's can be used/reused by one or more Queue and/or Scheduler Table

   For representing a Strict Priority scheduler, each scheduler input is
   assigned a priority with respect to all the other inputs feeding the
   same scheduler, with default values for the other parameters.  A
   higher-priority input which contains traffic that is not being
   delayed for shaping will be serviced before a lower-priority input.

   For Weighted Scheduling methods e.g., WFQ, WRR, the "weight" of a
   given scheduler input is represented with a Minimum Service Rate
   leaky-bucket profile that provides a guaranteed minimum bandwidth to
   that input, if required.  This is represented by a rate
   dsMinRateAbsolute; the classical weight is the ratio between that
   rate and the interface speed, or perhaps the ratio between that rate
   and the sum of the configured rates for classes.  Alternatively, the
   rate may be represented by a relative value, as a fraction of the
   interface's current line rate, dsMinRateRelative to assist in cases
   where line rates are variable or where a higher-level policy might be
   expressed in terms of fractions of network resources.  The two rate
   parameters are inter-related and changes in one may be reflected in
   the other.

   For weighted scheduling methods, one can say loosely, that WRR
   focuses on meeting bandwidth sharing, without concern for relative
   delay amongst the queues, where WFQ control both queue service order
   and amount of traffic serviced, providing meeting bandwidth sharing
   and relative delay ordering amongst the queues.

   A queue or scheduled set of queues (which is an input to a scheduler)
   may also be capable of acting as a non-work-conserving [MODEL]
   traffic shaper:  this is done by defining a Maximum Service Rate
   leaky-bucket profile in order to limit the scheduler bandwidth
   available to that input.  This is represented by a rate
   dsMaxRateAbsolute; the classical weight is the ratio between that
   rate and the interface speed, or perhaps the ratio between that rate
   and the sum of the configured rates for classes.  Alternatively, the
   rate may, be represented by a relative value, as a fraction of the
   interface's current line rate, dsMaxRateRelative.  There was
   discussion in the working group about alternative modeling
   approaches, such as defining a shaping action or a shaping element.
   We did not take this approach because shaping is in fact something a
   scheduler does to its inputs, (which we model as a queue with a

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   maximum rate or a scheduler whose output has a maximum rate) and we
   felt it was simpler and more elegant to simply describe it in that
   context.  Additionally, multi-rate shaper [SHAPER] can be represented
   by the use of multiple dsMaxRateTable entries.

   Other types of priority and weighted scheduling methods can be
   defined using existing parameters in dsMinRateEntry.  NOTE:
   dsSchedulerMethod uses AutonomousType syntax, with the different
   types of scheduling methods defined as OBJECT-IDENTITY.  Future
   scheduling methods may be defined in other PIBs.  This requires an
   OBJECT-IDENTITY definition, a description of how the existing objects
   are reused, if they are, and any new objects they require.

   NOTE:  Hierarchical schedulers can be parameterized using this PIB by
   having Scheduler Table entries feeds into Scheduler Table entry.

4.7.  Specifying Device Capabilities

   The DiffServ PIB uses the Base PRC classes frwkPrcSupportTable and
   frwkCompLimitsTable defined in [FR-PIB] to specify what PRC's are
   supported by a PEP and to specify any limitations on that support.
   The PIB also uses the capability PRC's frwkCapabilitySetTable and
   frwkIfRoleComboTable defined in [FR-PIB] to specify the device's
   capability sets, interface types, and role combinations.  Each
   instance of the capability PRC frwkCapabilitySetTable contains an OID
   that points to an instance of a PRC that describes some capability of
   that interface type.  The DiffServ PIB defines several of these
   capability PRCs, that assist the PDP with the configuration of
   DiffServ functional elements that can be implemented by the device.
   Each of these capability PRCs contains a direction attribute that
   specifies the direction for which the capability applies.  This
   attribute is defined in a base capability PRC, which is extended by
   each specific capability PRC.

   Classification capabilities, which specify the information elements
   the device can use to classify traffic, are reported using the
   dsIfClassificationCaps PRC.  Metering capabilities, which indicate
   what the device can do with out-of-profile packets, are specified
   using the dsIfMeteringCaps PRC.  Scheduling capabilities, such as the
   number of inputs supported, are reported using the dsIfSchedulingCaps
   PRC.  Algorithmic drop capabilities, such as the types of algorithms
   supported, are reported using the dsIfAlgDropCaps PRC.  Queue
   capabilities, such as the maximum number of queues, are reported
   using the dsIfQueueCaps PRC.  Maximum Rate capabilities, such as the
   maximum number of max rate Levels, are reported using the
   dsIfMaxRateCaps PRC.

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   Two PRC's are defined to allow specification of the element linkage
   capabilities of the PEP.  The dsIfElmDepthCaps PRC indicates the
   maximum number of functional datapath elements that can be linked
   consecutively in a datapath.  The dsIfElmLinkCaps PRC indicates what
   functional datapath elements may follow a specific type of element in
   a datapath.

   The capability reporting classes in the DiffServ and Framework PIB
   are meant to allow the PEP to indicate some general guidelines about
   what the device can do.  They are intended to be an aid to the PDP
   when it constructs policy for the PEP.  These classes do not
   necessarily allow the PEP to indicate every possible configuration
   that it can or cannot support.  If a PEP receives a policy that it
   cannot implement, it must notify the PDP with a failure report.
   Currently [COPS-PR] error handling mechanism as specified in [COPS-
   PR] sections 4.4, 4.5, and 4.6 completely handles all known error
   cases of this PIB; hence no additional methods or PRCs need to be
   specified here.

5.  PIB Usage Example

   This section provides some examples on how the different table
   entries of this PIB may be used together for a DiffServ Device.  The
   usage of each individual attribute is defined within the PIB module
   itself.  For the figures, all the PIB table entry and attribute names
   are assumed to have "ds" as their first common initial part of the
   name, with the table entry name assumed to be their second common
   initial part of the name.  "0.0" is being used to mean zeroDotZero.
   And for Scheduler Method "= X" means "using the OID of

5.1.  Data Path Example

   Notice Each entry of the DataPath table is used for a specific
   interface type handling a flow in a specific direction for a specific
   functional role-combination.  For our example, we just define one
   such entry.

      |DataPath             |
      | CapSetName ="IfCap1"|
      | Roles = "A+B"       |
      | IfDirection=Ingress |    +---------+
      | Start --------------+--->|Clfr     |
      +---------------------+    | Id=Dept |

                        Figure 2: DataPath Usage Example

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   In Figure 2, we are using IfCap1 to indicate interface type with
   capability set 1 handling ingress flow for functional roles of "A+B".
   We are using classifier for departments to lead us into the
   Classifier Example below.

5.2.  Classifier and Classifier Element Example

   We want to show how a multilevel classifier can be built using the
   classifier tables provided by this PIB.  Notice we didn't go into
   details on the filters because they are not defined by this PIB.
   Continuing in the Data Path example from the previous section, lets
   say we want to perform the following classification functionality to
   do flow separation based on department and application type:

      if (Dept1) then take Dept1-action
        if (Appl1) then take Dept1-Appl1-action.
        if (Appl2) then take Dept1-Appl2-action.
        if (Appl3) then take Dept1-Appl3-action.

      if (Dept2) then take Dept2-action
        if (Appl1) then take Dept2-Appl1-action.
        if (Appl2) then take Dept2-Appl2-action.
        if (Appl3) then take Dept2-Appl3-action.
      if (Dept3) then take Dept3-action
        if (Appl1) then take Dept3-Appl1-action.
        if (Appl2) then take Dept3-Appl2-action.
        if (Appl3) then take Dept3-Appl3-action.

   The above classification logic is translated into the following PIB
   table entries, with two levels of classifications.

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   First for department:

   |Clfr     |
   | Id=Dept |

   +-------------+      +-----------+
   |ClfrElement  |  +-->|Clfr       |
   | Id=Dept1    |  |   | Id=D1Appl |
   | ClfrId=Dept |  |   +-----------+
   | Preced=NA   |  |
   | Next -------+--+   +------------+
   | Specific ---+----->|Filter Dept1|
   +-------------+      +------------+

   +-------------+      +-----------+
   |ClfrElement  |  +-->|Clfr       |
   | Id=Dept2    |  |   | Id=D2Appl |
   | ClfrId=Dept |  |   +-----------+
   | Preced=NA   |  |
   | Next -------+--+   +------------+
   | Specific ---+----->|Filter Dept2|
   +-------------+      +------------+

   +-------------+      +-----------+
   |ClfrElement  |  +-->|Clfr       |
   | Id=Dept3    |  |   | Id=D3Appl |
   | ClfrId=Dept |  |   +-----------+
   | Preced=NA   |  |
   | Next -------+--+   +------------+
   | Specific ---+----->|Filter Dept3|
   +-------------+      +------------+

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   Second for application:

   |Clfr       |
   | Id=D1Appl |

   +---------------+                     +--------------+
   |ClfrElement    |  +----------------->|Meter         |
   | Id=D1Appl1    |  |                  | Id=D1A1Rate1 |
   | ClfrId=D1Appl |  |                  | SucceedNext -+--->...
   | Preced=NA     |  |                  | FailNext ----+--->...
   | Next ---------+--+  +------------+  | Specific ----+--->...
   | Specific -----+---->|Filter Appl1|  +--------------+
   +---------------+     +------------+

   +---------------+                     +--------------+
   |ClfrElement    |  +----------------->|Meter         |
   | Id=D1Appl2    |  |                  | Id=D1A2Rate1 |
   | ClfrId=D1Appl |  |                  | SucceedNext -+--->...
   | Preced=NA     |  |                  | FailNext ----+--->...
   | Next ---------+--+  +------------+  | Specific ----+--->...
   | Specific -----+---->|Filter Appl2|  +--------------+
   +---------------+     +------------+

   +---------------+                     +--------------+
   |ClfrElement    |  +----------------->|Meter         |
   | Id=D1Appl3    |  |                  | Id=D1A3Rate1 |
   | ClfrId=D1Appl |  |                  | SucceedNext -+--->...
   | Preced=NA     |  |                  | FailNext ----+--->...
   | Next ---------+--+  +------------+  | Specific ----+--->...
   | Specific -----+---->|Filter Appl3|  +--------------+
   +---------------+     +------------+

                    Figure 3: Classifier Usage Example

   The application classifiers for department 2 and 3 will be very much
   like the application classifier for department 1 shown above.  Notice
   in this example, Filters for Appl1, Appl2, and Appl3 are reusable
   across the application classifiers.

   This classifier and classifier element example assume the next
   differentiated services functional datapath element is Meter and
   leads us into the Meter Example section.

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5.3.  Meter Example

   A single rate simple Meter may be easy to envision, hence we will do
   a Two Rate Three Color [TRTCM] example, using two Meter table entries
   and two TBParam table entries.

   +--------------+    +---------+     +--------------+    +----------+
   |Meter         | +->|Action   |  +->| Meter        | +->|Action    |
   | Id=D1A1Rate1 | |  | Id=Green|  |  | Id=D1A1Rate2 | |  | Id=Yellow|
   | SucceedNext -+-+  +---------+  |  | SucceedNext -+-+  +----------+
   | FailNext ----+-----------------+  | FailNext ----+--+  +-------+
   | Specific -+  |                    | Specific -+  |  +->|Action |
   +-----------+--+                    +-----------+--+     | Id=Red|
               |                                   |        +-------+
               |  +------------+                   |  +------------+
               +->|TBParam     |                   +->|TBParam     |
                  | Type=TRTCM |                      | Type=TRTCM |
                  | Rate       |                      | Rate       |
                  | BurstSize  |                      | BurstSize  |
                  | Interval   |                      | Interval   |
                  +------------+                      +------------+

                       Figure 4: Meter Usage Example

   For [TRTCM], the first level TBParam entry is used for Committed
   Information Rate and Committed Burst Size Token Bucket, and the
   second level TBParam entry is used for Peak Information Rate and Peak
   Burst Size Token Bucket.

   The other meters needed for this example will depend on the service
   class each classified flow uses.  But their construction will be
   similar to the example given here.  The TBParam table entries can be
   shared by multiple Meter table entries.

   In this example the differentiated services functional datapath
   element following Meter is Action, detailed in the following section.

5.4.  Action Example

   Typically, Mark Action will be used; we will continue using the
   "Action, Id=Green" branch off the Meter example.

   Recall this is the D1A1Rate1 SucceedNext branch, meaning the flow
   belongs to Department 1 Application 1, within the committed rate and
   burst size limits for this flow.  We would like to Mark this flow
   with a specific DSCP and also with a device internal label.

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   +-----------+                     +-----------+  +--->AlgDropAF11
   |Action     |  +----------------->|Action     |  |
   | Next -----+--+  +------------+  | Next -----+--+ +-------------+
   | Specific -+---->|DscpMarkAct |  | Specific -+--->|ILabelMarker |
   +-----------+     | Dscp=AF11  |  +-----------+    | ILabel=D1A1 |
                     +------------+                   +-------------+

                      Figure 5: Action Usage Example

   This example uses the frwkILabelMarker PRC defined in [FR-PIB],
   showing the device internal label being used to indicate the micro
   flow that feeds into the aggregated AF flow.  This device internal
   label may be used for flow accounting purposes and/or other data path

5.5.  Dropper Examples

   The Dropper examples below will continue from the Action example
   above for AF11 flow.  We will provide three different dropper setups,
   from simple to complex.  The examples below may include some queuing
   structures; they are here only to show the relationship of the
   droppers to queuing and are not complete.  Queuing examples are
   provided in later sections.

5.5.1.  Tail Dropper Example

   The Tail Dropper is one of the simplest.  For this example we just
   want to drop part of the flow that exceeds the queue's buffering
   capacity, 2 Mbytes.

   +--------------------+       +------+
   |AlgDrop             |    +->|Q AF1 |
   | Id=AF11            |    |  +------+
   | Type=tailDrop      |    |
   | Next --------------+-+--+
   | QMeasure ----------+-+
   | QThreshold=2Mbytes |
   | Specific=0.0       |

                   Figure 6: Tail Dropper Usage Example

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5.5.2.  Single Queue Random Dropper Example

   The use of Random Dropper will introduce the usage of
   dsRandomDropEntry as in the example below.

   +-----------------+       +------+
   |AlgDrop          |    +->|Q AF1 |
   | Id=AF11         |    |  +------+
   | Type=randomDrop |    |
   | Next -----------+-+--+
   | QMeasure -------+-+
   | QThreshold      |   +----------------+
   | Specific -------+-->|RandomDrop      |
   +-----------------+   | MinThreshBytes |
                         | MinThreshPkts  |
                         | MaxThreshBytes |
                         | MaxThreshPkts  |
                         | ProbMax        |
                         | Weight         |
                         | SamplingRate   |

            Figure 7: Single Queue Random Dropper Usage Example

   Notice for Random Dropper, dsAlgDropQThreshold contains the maximum
   average queue length, Qclip, for the queue being measured as
   indicated by dsAlgDropQMeasure, the rest of the Random Dropper
   parameters are specified by dsRandomDropEntry as referenced by
   dsAlgDropSpecific.  In this example, both dsAlgDropNext and
   dsAlgDropQMeasure references the same queue.  This is the simple case
   but dsAlgDropQMeasure may reference another queue for PEP
   implementation supporting this feature.

5.5.3.  Multiple Queue Random Dropper Example

   When network device implementation requires measuring multiple queues
   in determining the behavior of a drop algorithm, the existing PRCs
   defined in this PIB will be sufficient for the simple case, as
   indicated by this example.

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   +-------------+                                         +------+
   |AlgDrop      | +----------------+-------------------+->|Q_AF1 |
   | Id=AF11     | |                |                   |  +------+
   | Type=mQDrop | |                |                   |
   | Next -------+-+ +------------+ |    +------------+ |
   | QMeasure ---+-->|MQAlgDrop   | | +->|MQAlgDrop   | |
   | QThreshold  |   | Id=AF11A   | | |  | Id=AF11B   | |
   | Specific    |   | Type       | | |  | Type       | |
   +-------------+   | Next ------+-+ |  | Next ------+-+
                     | ExceedNext +---+  | ExceedNext |   +------+
                     | QMeasure --+-+    | QMeasure --+-->|Q_AF2 |
                     | QThreshold | |    | QThreshold |   +------+
                     | Specific + | |    | Specific + |
                     +----------+-+ |    +----------+-+
                                |   |           +---+
                         +------+   |  +------+ |
                         |          +->|Q_AF1 | |
                         |             +------+ |
                         |                      |
                         |  +----------------+  |  +----------------+
                         +->|RandomDrop      |  +->|RandomDrop      |
                            | MinThreshBytes |     | MinThreshBytes |
                            | MinThreshPkts  |     | MinThreshPkts  |
                            | MaxThreshBytes |     | MaxThreshBytes |
                            | MaxThreshPkts  |     | MaxThreshPkts  |
                            | ProbMax        |     | ProbMax        |
                            | Weight         |     | Weight         |
                            | SamplingRate   |     | SamplingRate   |
                            +----------------+     +----------------+

           Figure 8: Multiple Queue Random Dropper Usage Example

   For this example, we have two queues, Q_AF1 and Q_AF2, sharing the
   same buffer resources.  We want to make sure the common buffer
   resource is sufficient to service the AF11 traffic, and we want to
   measure the two queues for determining the drop algorithm for AF11
   traffic feeding into Q_AF1.  Notice mQDrop is used for dsAlgDropType
   of dsAlgDropEntry to indicate Multiple Queue Dropping Algorithm.

   The common shared buffer resource is indicated by the use of
   dsAlgDropEntry, with their attributes used as follows:

   - dsAlgDropType indicates the algorithm used, mQDrop.
   - dsAlgDropNext is used to indicate the next functional data path
     element to handle the flow when no drop occurs.
   - dsAlgDropQMeasure is used as the anchor for the list of
     dsMQAlgDropEntry, one for each queue being measured.

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   - dsAlgDropQThreshold is used to indicate the size of the shared
     buffer pool.
   - dsAlgDropSpecific can be used to reference instances of additional
     PRC (not defined in this PIB) if more parameters are required to
     describe the common shared buffer resource.

   For this example, there are two subsequent dsMQAlgDropEntrys, one for
   each queue being measured, with its attributes used as follows:

   - dsMQAlgDropType indicates the algorithm used, for this example,
     both dsMQAlgDropType uses randomDrop.
   - dsMQAlgDropQMeasure indicates the queue being measured.
   - dsMQAlgDropNext indicates the next functional data path element
     to handle the flow when no drop occurs.
   - dsMQAlgDropExceedNext is used to indicate the next queue's
     dsMQAlgDropEntry.  With the use of zeroDotZero to indicate the
     last queue.
   - dsMQAlgDropQMeasure is used to indicate the queue being measured.
     For this example, Q_AF1 and Q_AF2 are the two queues used.
   - dsAlgDropQThreshold is used as in single queue Random Dropper.
   - dsAlgDropSpecific is used to reference the PRID that describes
     the dropper parameters as in its normal usage.  For this example
     both dsAlgDropSpecifics reference dsRandomDropEntrys.

   Notice the anchoring dsAlgDropEntry and the two dsMQAlgDropEntrys
   all have their Next attribute pointing to Q_AF1.  This indicates:

   - If the packet does not need to be checked with the individual
     queue's drop processing because of abundance of common shared
     buffer resources, then the packet is sent to Q_AF1.
   - If the packet is not dropped due to current Q_AF1 conditions, then
     it is sent to Q_AF1.
   - If the packet is not dropped due to current Q_AF2 conditions, then
     it is sent to Q_AF1.

   This example also uses two dsRandomDropEntrys for the two queues it
   measures.  Their attribute usage is the same as if for single queue
   random dropper.

   Other more complex result combinations can be achieved by specifying
   a new PRC and referencing this new PRC with the dsAlgDropSpecific of
   the anchoring dsAlgDropEntry.  A more simple usage can also be
   achieved when a single set of drop parameters are used for all queues
   being measured.  This, again, can be referenced by the anchoring of
   dsAlgDropSpecific.  These are not defined in this PIB.

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5.6.  Queue and Scheduler Example

   The queue and scheduler example will continue from the dropper
   example in the previous section, concentrating in the queue and
   scheduler DiffServ datapath functional elements.  Notice a shaper is
   constructed using queue and scheduler with MaxRate parameters.

        +------------+                           +-----------------+
   ---->|Q           |                        +->|Scheduler        |
        | Id=EF      |                        |  | Id=DiffServ     |
        | Next ------+------------------------+  | Next=0.0        |
        | MinRate ---+--+                     |  | Method=Priority |
        | MaxRate -+ |  |   +----------+      |  | MinRate=0.0     |
        +----------+-+  +-->|MinRate   |      |  | MaxRate=0.0     |
                   |        | Priority |      |  +-----------------+
        +----------+        | Absolute |      |
        |                   | Relative |      |
        |  +-----------+    +----------+      |
        +->|MaxRate    |                      |
           | Level     |                      |
           | Absolute  |                      |
           | Relative  |                      |
           | Threshold |                      |
           +-----------+                      +-------------+
        +----------+                        +------------+  |
   ---->|Q         |                    +-->|Scheduler   |  |
        | Id=AF1   |                    |   | Id=AF      |  |
        | Next ----+--------------------+   | Next ------+--+
        | MinRate -+-+                  |   | Method=WRR |
        | MaxRate  | |  +----------+    |   | MinRate -+ |
        +----------+ +->|MinRate   |    |   | MaxRate  | |
                        | Priority |    |   +----------+-+
                        | Absolute |    |              |
                        | Relative |    |   +----------+
                        +----------+    |   |
        +----------+                    |   |  +------------+
   ---->|Q         |                    |   +->|MinRate     |
        | Id=AF2   |                    |      | Priority   |
        | Next ----+--------------------+      | Absolute   |
        | MinRate -+-+                  |      | Relative   |
        | MaxRate  | |  +----------+    |      +------------+
        +----------+ +->|MinRate   |    |
                        | Priority |    |
                        | Absolute |    |
                        | Relative |    |
                        +----------+    |

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        +----------+                    |
   ---->|Q         |                    |
        | Id=AF3   |                    |
        | Next ----+--------------------+
        | MinRate -+-+
        | MaxRate  | |  +----------+
        +----------+ +->|MinRate   |
                        | Priority |
                        | Absolute |
                        | Relative |

                Figure 9: Queue and Scheduler Usage Example

   This example shows the queuing system for handling EF, AF1, AF2, and
   AF3 traffic.  It is assumed that AF11, AF12, and AF13 traffic feeds
   into Queue AF1.  And likewise for AF2x and AF3x traffic.

   The AF1, AF2, and AF3 Queues are serviced by the AF Scheduler using a
   Weighed Round Robin method.  The AF Scheduler will service each of
   the queues feeding into it based on the minimum rate parameters of
   each queue.

   The AF and EF traffic are serviced by the DiffServ Scheduler using a
   Strict Priority method.  The DiffServ Scheduler will service each of
   its inputs based on their priority parameter.

   Notice there is an upper bound to the servicing of EF traffic by the
   DiffServ Scheduler.  This is accomplished with the use of maximum
   rate parameters.  The DiffServ Scheduler uses both the maximum rate
   and priority parameters when servicing the EF Queue.

   The DiffServ Scheduler is the last DiffServ datapath functional
   element in this datapath.  It uses zeroDotZero in its Next attribute.

6.  Summary of the DiffServ PIB

   The DiffServ PIB consists of one module containing the base PRCs for
   setting DiffServ policy, queues, classifiers, meters, etc., and also
   contains capability PRC's that allow a PEP to specify its device
   characteristics to the PDP.  This module contains two groups that are
   summarized in this section.

   DiffServ Capabilities Group
      This group consists of PRCs to indicate to the PDP the types of
      interface supported on the PEP in terms of their DiffServ
      capabilities and PRCs that the PDP can install in order to
      configure these interfaces (queues, scheduling parameters, buffer

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      sizes, etc.) to affect the desired policy.  This group describes
      capabilities in terms of the types of interfaces and takes
      configuration in terms of interface types and role combinations
      [FR-PIB]; it does not deal with individual interfaces on the

   DiffServ Policy Group
      This group contains configurations of the functional elements that
      comprise the DiffServ policy that applies to an interface and the
      specific parameters that describe those elements.  This group
      contains classifiers, meters, actions, droppers, queues and
      schedulers.  This group also contains the PRC that associates the
      datapath elements with role combinations.

7.  PIB Operational Overview

   This section provides an operational overview of configuring DiffServ
   QoS policy.

   After the initial PEP to PDP communication setup, using [COPS-PR] for
   example, the PEP will provide to the PDP the PIB Provisioning classes
   (PRCs), interface types, and interface type capabilities it supports.

   The PRCs supported by the PEP are reported to the PDP in the PRC
   Support Table, frwkPrcSupportTable, defined in the framework PIB
   [FR-PIB].  Each instance of the frwkPrcSupportTable indicates a PRC
   that the PEP understands and for which the PDP can send class
   instances as part of the policy information.

   The capabilities of interface types the PEP supports are described by
   rows in the capability set table, frwkCapabilitySetTable.  Each row,
   or instance of this class contains a pointer to an instance of a PRC
   that describes the capabilities of the interface type.  The
   capability objects may reside in the dsIfClassifierCapsTable, the
   dsIfMeteringCapsTable, the dsIfSchedulerCapsTable, the
   dsIfElmDepthCapsTable, the dsIfElmLinkCapsTable, or in a table
   defined in another PIB.

   The PDP, with knowledge of the PEP's capabilities, then provides the
   PEP with administrative domain and interface-type-specific policy

   Instances of the dsDataPathTable are used to specify the first
   element in the set of functional elements applied to an interface
   type.  Each instance of the dsDataPathTable applies to an interface
   type defined by its roles and direction (ingress or egress).

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