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Versions: (draft-chan-tsvwg-diffserv-class-aggr) 00 01 02 03 04 05 06 07 RFC 5127

TSVWG                                                            K. Chan
Internet-Draft                                                J. Babiarz
Intended status: Informational                           Nortel Networks
Expires: April 23, 2007                                         F. Baker
                                                           Cisco Systems
                                                        October 20, 2006


                Aggregation of DiffServ Service Classes
                draft-ietf-tsvwg-diffserv-class-aggr-01

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   In the core of a high capacity network, service differentiation is
   still needed to support applications' utilization of the network.
   Applications with similar traffic characteristics and performance
   requirements are mapped into diffserv service classes based on end-
   to-end behavior requirements of the applications as indicated by
   Diffserv Service Classes [5].  However, some network segments may be



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   configured in such a way that a single forwarding treatment may
   satisfy the traffic characteristics and performance requirements of
   two or more service classes.  In these cases, it may be desirable to
   aggregate two or more Diffserv Service Classes [5] into a single
   forwarding treatment.  This document provides guidelines for the
   aggregation of Diffserv Service Classes [5] into forwarding
   treatments.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Requirements Notation  . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Overview of Service Class Aggregation  . . . . . . . . . . . .  5
   4.  Service Classes to Treatment Aggregate Mapping . . . . . . . .  6
     4.1.  Mapping Service Classes into Four Treatment Aggregates . .  6
       4.1.1.  Network Control Treatment Aggregate  . . . . . . . . .  8
       4.1.2.  Real Time Treatment Aggregate  . . . . . . . . . . . .  9
       4.1.3.  Assured Elastic Treatment Aggregate  . . . . . . . . .  9
       4.1.4.  Elastic Treatment Aggregate  . . . . . . . . . . . . . 10
   5.  Using MPLS for Treatment Aggregates  . . . . . . . . . . . . . 11
     5.1.  Network Control Treatment Aggregate with E-LSP . . . . . . 13
     5.2.  Real Time Treatment Aggregate with E-LSP . . . . . . . . . 13
     5.3.  Assured Elastic Treatment Aggregate with E-LSP . . . . . . 13
     5.4.  Elastic Treatment Aggregate with E-LSP . . . . . . . . . . 13
     5.5.  Treatment Aggregates and L-LSP . . . . . . . . . . . . . . 14
   6.  Treatment Aggregates and Inter-Provider Relationships  . . . . 14
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 15
     10.2. Informative References . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
   Intellectual Property and Copyright Statements . . . . . . . . . . 18















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1.  Introduction

   In the core of a high capacity network, it is common for the network
   to be engineered in such a way that a major link, switch, or router
   can fail and the result will be a routed network that still meets
   ambient SLAs.  The implication of this is that there is sufficient
   capacity on any given link such that all SLAs sold can be
   simultaneously supported at their respective maximum rates, and that
   this remains true after re-routing (either IP re-routing or MPLS
   protection-mode switching) has occurred.

   Over-provisioning is generally considered to meet the requirements of
   all traffic without further QoS treatment, and in the general case
   that is true in high capacity backbones.  However, as the process of
   network convergence continues, and with the increasing speed of the
   access networks, certain services still have issues.  Delay, jitter,
   and occasional loss are perfectly acceptable for elastic
   applications.  However, sub-second surges that occur in the best-
   designed of networks [14] affect real-time applications.  Moreover,
   DOS loads, worms, and network disruptions such as that of 11
   September 2001 affect routing [15].  Our objective is to prevent
   disruption to routing (which in turn affects all services), and
   jitter-sensitive services that may be revenue-bearing.

   The document "Diffserv Service Classes" [5] defines the basic
   diffserv classes from the points of view of the application requiring
   specific end-to-end behaviors from the network.  The service classes
   are differentiated based on the traffic-payload's tolerance to packet
   loss, delay, and delay variation (jitter).  Different degrees of
   these criterions form the foundation for supporting the needs of
   real-time and elastic traffic.  The "Diffserv Service Classes" [5]
   document also provides recommendations for the treatment method of
   these service classes.  But, at some network segments of the end-to-
   end path, the number of levels of network treatment differentiation
   may be less than the number of service classes that the network
   segment needs to support.  In such a situation, that network segment
   may use the same treatment to support more than one service class.
   In this document we provide guidelines on how multiple service
   classes may be aggregated into a forwarding treatment aggregate.
   Note that in a given domain, we may recommend that the supported
   service classes be aggregated into forwarding treatment aggregates;
   however, this does not mean all service classes need to be supported
   and hence not all forwarding treatment aggregates need to be
   supported.  Which service classes and which forwarding treatment
   aggregates are supported by a domain is up to the domain
   administration and may be influenced by business reasons.

   In this document, we've provided:



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   o  definitions for terminology we use in this document,

   o  requirements for performing this aggregation,

   o  an example of performing this aggregation over MPLS using E-LSP.

   The treatment aggregate recommendations are designed to aggregate the
   service classes [5] in such a manner as to protect real-time traffic
   and routing, on the assumption that real-time sessions are protected
   from each other by admission at the edge.

   An example of aggregation over MPLS networks using E-LSP, EXP
   Inferred PHB Scheduling Class (PSC) Label Switched Path (LSP), to
   realize the treatment aggregates is provided.  Note that the MPLS
   E-LSP is just an example; this document does not exclude the use of
   other methods.

1.1.  Requirements Notation

   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 RFC 2119 [3].


2.  Terminology

   This document assumes the reader is familiar with the terms used in
   differentiated services.  This document provides the definitions for
   new terms introduced by this document and referencing information for
   existing none differentiated services terms defined in existing RFCs.

   For new terms introduced by this document, we provide the definition
   here:

   o  Treatment Aggregate.  This term is used here to indicate the
      aggregate of DiffServ service classes.  This is different from
      Behavior Aggregate and Traffic Aggregate because Treatment
      Aggregate is only concerned with the treatment of the aggregated
      traffic.  It does not concern itself with how the aggregated
      traffic is marked, and hence does not put a restriction on the
      aggregated traffic having a single diffserv codepoint that have a
      single PHB.

   For terms from existing RFCs, we provide the reference to the
   appropriate section of the relevant RFC that contain the definition:

   o  Real-Time and Elastic Applications and their traffic.  Section 3.1
      of RFC 1633 [6].



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   o  Diffserv Service Class.  Section 1.3 of
      draft-ietf-tsvwg-diffserv-service-classes-02.txt [5].

   o  MPLS E-LSP, EXP Inferred PHB Scheduling Class (PSC) Label Switched
      Path (LSP).  Section 1.2 of RFC 3270 [8].

   o  MPLS L-LSP, Label Only Inferred PHB Scheduling Class (PSC) Label
      Switched Path (LSP).  Section 1.3 of RFC 3270 [8].


3.  Overview of Service Class Aggregation

   In diffserv domains where less granular traffic treatment
   differentiation is provided, aggregation of the different service
   classes [5] may be required.

   These aggregations have the following requirements:

   1.  The end-to-end network performance characteristic required by the
       application must be supported.  This performance characteristic
       is represented by the use of Diffserv Service Classes [5].

   2.  The treatment aggregate must exhibit the strictest requirement of
       its member service classes.

   3.  The treatment aggregate should only contain member service
       classes with similar traffic characteristic and performance
       requirements.

   4.  The notion of the individual end-to-end service classes must not
       be destroyed when aggregation is performed.  Each domain along
       the end-to-end path may perform aggregation differently, based on
       the original end-to-end service classes.  We recommend an easy
       way to accomplish this by not altering the DSCP used to indicate
       the end-to-end service class.  But some administrative domains
       may require the use of their own marking; when this is needed,
       the original end-to-end service class indication must be restored
       upon exiting such administrative domains.

   5.  Each treatment aggregate has limited resources, hence traffic
       conditioning and/or admission control must be performed for each
       service class aggregated into the treatment aggregate.

   with the following suggestions:

   1.  The treatment aggregate and assigned resources may consider
       historical traffic patterns and the variability of these
       patterns.  For example, a point-point service (e.g., pseudowire)



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       may have a very predictable pattern, while a multipoint service
       (e.g., VPLS) may have a much less predictable pattern.  Even the
       traffic patterns within the Internet may vary widely.

   2.  In addition to Diffserv, other controls are available to
       influence the traffic level offered to a particular traffic
       aggregate.  These include adjustment of routing metrics, usage of
       MPLS-based traffic engineering techniques.


4.  Service Classes to Treatment Aggregate Mapping

   The service class and DSCP selection in "Diffserv Service Classes"
   [5] has been defined to allow, in many instances, mapping of two or
   possibly more service classes into a single forwarding treatment
   aggregate.  Notice that there is a relationship/trade-off between
   link speed, queue depth, delay, and jitter.  The degree of
   aggregation and hence the number of treatment aggregates will depend
   on whether the speed of the links and scheduler behavior, being used
   to implement the aggregation, can minimize the affects of mixing
   traffic with different packet sizes and transmit rates on queue
   depth.  And their impacts on loss, delay, and jitter.  A general
   rule-of-thumb is that higher link speeds allow for more aggregation/
   smaller number of treatment aggregates.

4.1.  Mapping Service Classes into Four Treatment Aggregates

   This section explains one way of performing this aggregation by using
   four treatment aggregates.  The use of four treatment aggregates
   assumes that the resources allocated to each treatment aggregate is
   sufficient to honor the required behavior of each service class [5]
   in each of the four treatment aggregates.  We use the performance
   requirement (tolerance to loss, delay, and jitter) from the
   application/end-user as a guide on how to map the service classes
   into treatment aggregates.  We have also used Section 3.1 of RFC 1633
   [6] to provide us with guidance on the definition of Real-Time and
   Elastic applications.  An overview of the mapping between service
   classes and the four treatment aggregates is provided by Figure 1,
   with the mapping being based on performance requirements.  In Figure
   1, the right side columns of "Service Class", "Tolerance to Loss/
   Delay/Jitter" are from Figure 2 of Diffserv Service Classes [5].

   It is recommended that certain service classes be mapped into
   specific treatment aggregates.  But this does not mean that all the
   service classes recommended for that treatment aggregate need to be
   supported.  Hence, for a given domain, a treatment aggregate may
   contain only a subset of the service classes recommended in this
   document, they being the service classes supported by that domain.  A



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   domain's treatment of non-supported service classes should be based
   on the domain's local policy.  This local policy may be influenced by
   its agreement with its customers.  Such treatment may use the Elastic
   Treatment Aggregate, dropping the packets, or some other
   arrangements.

  ---------------------------------------------------------------------
 |Treatment |    Tolerance to    ||Service Class  |    Tolerance to    |
 |Aggregate | Loss |Delay |Jitter||               | Loss |Delay |Jitter|
 |==========+======+======+======++===============+======+======+======|
 | Network  | Low  | Low  | Yes  || Network       |  Low |  Low | Yes  |
 | Control  |      |      |      || Control       |      |      |      |
 |==========+======+======+======++===============+======+======+======|
 | Real     | Very | Very | Very ||  Telephony    | VLow | VLow | VLow |
 | Time     | Low  | Low  | Low  ||---------------+------+------+------|
 |          |      |      |      ||   Signaling   | Low  | Low  | Yes  |
 |          |      |      |      ||---------------+------+------+------|
 |          |      |      |      ||  Multimedia   |Low - | Very | Low  |
 |          |      |      |      || Conferencing  |Medium| Low  |      |
 |          |      |      |      ||---------------+------+------+------|
 |          |      |      |      ||   Real-time   | Low  | Very | Low  |
 |          |      |      |      ||  Interactive  |      | Low  |      |
 |          |      |      |      ||---------------+------+------+------|
 |          |      |      |      ||   Broadcast   | Very |Medium| Low  |
 |          |      |      |      ||     Video     | Low  |      |      |
 |==========+======+======+======++===============+======+======+======|
 | Assured  | Low  |Low - | Yes  ||  Multimedia   |Low - |Medium| Yes  |
 | Elastic  |      |Medium|      ||   Streaming   |Medium|      |      |
 |          |      |      |      ||---------------+------+------+------|
 |          |      |      |      ||  Low Latency  | Low  |Low - | Yes  |
 |          |      |      |      ||      Data     |      |Medium|      |
 |          |      |      |      ||---------------+------+------+------|
 |          |      |      |      ||      OAM      | Low  |Medium| Yes  |
 |          |      |      |      ||---------------+------+------+------|
 |          |      |      |      ||High Throughput| Low  |Medium| Yes  |
 |          |      |      |      ||      Data     |      |- High|      |
 |==========+======+======+======++===============+======+======+======|
 | Elastic  |  Not Specified     ||   Standard    |  Not Specified     |
 |          |      |      |      ||---------------+------+------+------|
 |          |      |      |      || Low Priority  | High | High | Yes  |
 |          |      |      |      ||      Data     |      |      |      |
  ---------------------------------------------------------------------

        Figure 1: Treatment Aggregate and Service Class Performance
                               Requirements

   As we are recommending to preserve the notion of the individual end-
   to-end service classes, we also recommend that the original DSCP



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   field marking not be changed when treatment aggregates are used.
   Instead, classifiers that select packets based on the contents of the
   DSCP field should be used to direct packets from the member DiffServ
   Service Classes into the queue that handles each of the treatment
   aggregates, without remarking the DSCP field of the packets.  This is
   summarized in Figure 2, which shows the behavior each Treatment
   Aggregate should have, and the DSCP field marking of the packets that
   should be classified into each of the treatment aggregates.

    ------------------------------------------------------------
   |Treatment |Treatment || DSCP                                |
   |Aggregate |Aggregate ||                                     |
   |          |Behavior  ||                                     |
   |==========+==========++=====================================|
   | Network  | CS       || CS6                                 |
   | Control  |(RFC 2474)||                                     |
   |==========+==========++=====================================|
   | Real     | EF       || EF, CS5, AF41, AF42, AF43, CS4, CS3 |
   | Time     |(RFC 3246)||                                     |
   |==========+==========++=====================================|
   | Assured  | AF       || CS2, AF31, AF21, AF11               |
   | Elastic  |(RFC 2597)||-------------------------------------|
   |          |          || AF32, AF22, AF12                    |
   |          |          ||-------------------------------------|
   |          |          || AF33, AF23, AF13                    |
   |==========+==========++=====================================|
   | Elastic  | Default  || Default, (CS0)                      |
   |          |(RFC 2474)||-------------------------------------|
   |          |          || CS1                                 |
    ------------------------------------------------------------

                  Figure 2: Treatment Aggregate Behavior

4.1.1.  Network Control Treatment Aggregate

   The Network Control Treatment Aggregate aggregates all service
   classes that are functionally necessary for the survival of a network
   during a DOS attack or other high traffic load interval.  The theory
   is that whatever else is true, the network must protect itself.  This
   includes the traffic that "Diffserv Service Classes" [5]
   characterizes as being included in the Network Control Service Class.

   The DSCPs of the original service class remain an important
   consideration and should be preserved during aggregation.  Traffic in
   the Network Control treatment aggregate should be carried in a common
   queue or class with a PHB as described in RFC 2474 [4] section
   4.2.2.2.  This treatment aggregate should have a lower probability of
   packet loss, bearing a relatively deep target mean queue depth (min-



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   threshold if RED is being used).

4.1.2.  Real Time Treatment Aggregate

   The Real Time Treatment Aggregate aggregates all real-time
   (inelastic) service classes.  The theory is that real-time traffic is
   admitted under some model and controlled by a SLA managed at the edge
   of the network prior to aggregation.  As such, there is a predictable
   and enforceable upper bound on the traffic that can enter such a
   queue, and to provide predictable variation in delay it must be
   protected from bursts of elastic traffic.  The predictability of
   traffic level may be based upon admission control for a well known
   community of interest (e.g., a point-point service) and/or based upon
   historical measurements.

   This treatment aggregate may include the following service classes
   from the Diffserv Service Classes [5], in addition to other locally
   defined classes: Telephony, Signaling, Multimedia Conferencing, Real-
   time Interactive, Broadcast Video.

   Traffic in each service class that is going to be aggregated into the
   treatment aggregate should be conditioned prior to aggregation.  It
   is recommended that per service class admission control procedures be
   used followed by per service class policing so that any individual
   service class does not generate more than what it is allowed.
   Furthermore, additional admission control and policing may be used on
   the sum of all service classes aggregated.

   The DSCPs of the original service classes remain an important
   consideration and should be preserved during aggregation.  Traffic
   bearing these DSCPs is carried in a common queue or class with a PHB
   as described in RFC 3246 [11] and RFC 3247 [12].

4.1.3.  Assured Elastic Treatment Aggregate

   The Assured Elastic Treatment Aggregate aggregates all elastic
   traffic that uses the Assured Forwarding model as described in RFC
   2597 [10].  The premise of such a service is that a SLA is negotiated
   which includes a "committed rate" and the ability to exceed that rate
   (and perhaps a second "excess rate") in exchange for a higher
   probability of loss using AQM [9] or ECN flagging [13] for the
   portion of traffic deemed to be in excess.

   This treatment aggregate may include the following service classes
   from the Diffserv Service Classes [5], in addition to other locally
   defined classes: Multimedia Streaming, Low Latency Data, OAM, High
   Throughput Data.




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   The DSCP values belonging to the AF PHB group of the original service
   classes remain an important consideration and should be preserved
   during aggregation.  This treatment aggregate should maintain the AF
   PHB group marking of the original packet.  For example, AF3x marked
   packets should remain AF3x marked within this treatment aggregate.
   Traffic bearing these DSCPs is carried in a common queue or class
   with a PHB as described in RFC 2597 [10].  In effect, appropriate
   target rate thresholds have been applied at the edge, dividing
   traffic into AFn1 (committed, for any value of n), AFn2, and AFn3
   (excess).  The service should be engineered so that AFn1 marked
   packet flows have sufficient bandwidth in the network to provide high
   assurance of delivery.  Since the traffic is elastic and responds
   dynamically to packet loss, Active Queue Management [9] should be
   used primarily to reduce the forwarding rate to the minimum assured
   rate at congestion points.  The probability of loss of AFn1 traffic
   must not exceed the probability of loss of AFn2 traffic, which in
   turn must not exceed the probability of loss of AFn3 traffic.

   If RED [9] is used as an AQM algorithm, the min-threshold specifies a
   target queue depth for each of AFn1, AFn2, AFn3, and the max-
   threshold specifies the queue depth above which all traffic with such
   a DSCP is dropped or ECN marked.  Thus, in this Treatment Aggregate,
   the following inequalities should hold in queue configurations:

   o  min-threshold AFn3 < max-threshold AFn3

   o  max-threshold AFn3 <= min-threshold AFn2

   o  min-threshold AFn2 < max-threshold AFn2

   o  max-threshold AFn2 <= min-threshold AFn1

   o  min-threshold AFn1 < max-threshold AFn1

   o  max-threshold AFn1 <= memory assigned to the queue

   Note: This configuration tends to drop AFn3 traffic before AFn2 and
   AFn2 before AFn1.  Many other AQM algorithms exist and are used; they
   should be configured to achieve a similar result.

4.1.4.  Elastic Treatment Aggregate

   The Elastic Treatment Aggregate aggregates all remaining elastic
   traffic.  The premise of such a service is that there is no intrinsic
   SLA differentiation of traffic, but that AQM [9] or ECN flagging [13]
   is appropriate for such traffic.

   This treatment aggregate may include the following service classes



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   from the Diffserv Service Classes [5], in addition to other locally
   defined classes: Standard, Low Priority Data.

   The DSCPs of the original service classes remain an important
   consideration and should be preserved during aggregation.  Traffic
   bearing these DSCPs is carried in a common queue or class with a PHB
   as described in RFC 2474 [4] section 4.1: A Default PHB.  The AQM
   thresholds for Elastic traffic MAY be separately set, so that Low
   Priority Data traffic is dropped before Standard traffic, but this is
   not a requirement.


5.  Using MPLS for Treatment Aggregates

   RFC 2983 on DiffServ and Tunnels [7] and RFC 3270 on MPLS Support of
   DiffServ [8] provide a very good background on this topic.  This
   document provides an example of using the E-LSP, EXP Inferred PHB
   Scheduled Class (PSC) Label Switched Path (LSP), defined by MPLS
   Support of DiffServ [8] for realizing the Treatment Aggregates.

   When Treatment Aggregates are represented in MPLS using EXP Inferred
   PSC LSP, we recommend the following usage of the MPLS EXP field for
   Treatment Aggregates.




























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    -------------------------------------------
   |Treatment || MPLS ||  DSCP   |   DSCP      |
   |Aggregate || EXP  ||  name   |   value     |
   |==========++======++=========|=============|
   | Network  || 110  ||  CS6    |   110000    |
   | Control  ||      ||         |             |
   |==========++======++=========|=============|
   | Real     || 100  ||  EF     |   101110    |
   | Time     ||      ||---------|-------------|
   |          ||      ||  CS5    |   101000    |
   |          ||      ||---------|-------------|
   |          ||      ||AF41,AF42|100010,100100|
   |          ||      ||  AF43   |   100110    |
   |          ||      ||---------|-------------|
   |          ||      ||  CS4    |   100000    |
   |          ||      ||---------|-------------|
   |          ||      ||  CS3    |   011000    |
   |==========++======++=========|=============|
   | Assured  || 010* ||  CS2    |   010000    |
   | Elastic  ||      ||  AF31   |   011010    |
   |          ||      ||  AF21   |   010010    |
   |          ||      ||  AF11   |   001010    |
   |          ||------||---------|-------------|
   |          || 011* ||  AF32   |   011100    |
   |          ||      ||  AF22   |   010100    |
   |          ||      ||  AF12   |   001100    |
   |          ||      ||  AF33   |   011110    |
   |          ||      ||  AF23   |   010110    |
   |          ||      ||  AF13   |   001110    |
   |==========++======++=========|=============|
   | Elastic  || 000* || Default |   000000    |
   |          ||      || (CS0)   |             |
   |          ||------||---------|-------------|
   |          || 001* ||  CS1    |   001000    |
    -------------------------------------------

          Figure 3: Treatment Aggregate and MPLS EXP Field Usage

   Notes *: For Assured Elastic (and Elastic) Treatment Aggregate, the
   usage of 010 or 011 (000 or 001) as EXP field value depends on the
   drop probability.  Packets in the LSP with EXP field of 011 (001)
   have a higher probability of being dropped than packets with an EXP
   field of 010 (000).

   The above table indicates the recommended usage of EXP fields for
   Treatment Aggregates.  Because many deployments of MPLS are on a per
   domain basis, each domain has total control of its EXP usage and each
   domain may use a different EXP field allocation for the domain's



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   supported Treatment Aggregates.

5.1.  Network Control Treatment Aggregate with E-LSP

   The usage of E-LSP for Network Control Treatment Aggregate needs to
   adhere to the recommendations indicated in section 4.1.1 of this
   document and section 3.2 of "Diffserv Service Classes" [5].
   Reinforcing these recommendations, there should be no drop precedence
   associated with the MPLS PSC used for Network Control Treatment
   Aggregate because dropping of Network Control Treatment Aggregate
   traffic should be prevented.

5.2.  Real Time Treatment Aggregate with E-LSP

   In addition to the recommendations provided in section 4.1.2 of this
   document and in member service classes' sections of "Diffserv Service
   Classes" [5], we want to indicate that Real Time Treatment Aggregate
   traffic should not be dropped, as some of the applications whose
   traffic is carried in the Real Time Treatment Aggregate do not react
   well to dropped packets.  As indicated in section 4.1.2 of this
   document, admission control should be performed on each Service Class
   contributing to the Real Time Treatment Aggregate to prevent packet
   loss due to insufficient resources allocated to Real Time Treatment
   Aggregate.  Further, admission control and policing may also be
   applied on the sum of all traffic aggregated into this treatment
   aggregate.

5.3.  Assured Elastic Treatment Aggregate with E-LSP

   EXP field markings of 010 and 011 are used for the Assured Elastic
   Treatment Aggregate.  The two encodings are used to provide two
   levels of drop precedence indications, with 010 encoded traffic
   having a lower probability of being dropped than 011 encoded traffic.
   This provides for the mapping of CS2, AF31, AF21, and AF11 into EXP
   010; and AF32, AF22, AF12 and AF33, AF23, AF13 into EXP 011.

5.4.  Elastic Treatment Aggregate with E-LSP

   EXP field markings of 000 and 001 are used for the Elastic Treatment
   Aggregate.  The two encodings are used to provide two levels of drop
   precedence indications, with 000 encoded traffic having a lower
   probability of being dropped than 001 encoded traffic.  This provides
   for the mapping of Default/CS0 into 000; and CS1 into 001.  Notice
   that with this mapping, during congestion, CS1 marked traffic may be
   starved.






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5.5.  Treatment Aggregates and L-LSP

   Because L-LSP (Label Only Inferred PSC LSP) supports a single PSC per
   LSP, the support of each Treatment Aggregate is on a per LSP basis.
   This document does not further specify any additional recommendation
   (beyond what has been indicated in section 4 of this document) for
   Treatment Aggregate to L-LSP mapping, leaving this to each individual
   MPLS domain administrations.


6.  Treatment Aggregates and Inter-Provider Relationships

   When Treatment Aggregates are used at provider boundaries, we
   recommend that the Inter-Provider Relationship be based on Diffserv
   Service Classes [5].  This allows the admission control into each
   Treatment Aggregate of a provider domain to be based on the admission
   control of traffic into the supported Service Classes, as indicated
   by the discussion in section 4 of this document.

   If the Inter-Provider Relationship needs to be based on Treatment
   Aggregates specified by this document, then the exact Treatment
   Aggregate content and representation must be agreed to by the peering
   providers.


7.  Security Considerations

   This document discusses the policy of using Differentiated Services
   and its service classes.  If implemented as described, it should
   require that the network do nothing that the network has not already
   allowed.  If that is the case, no new security issues should arise
   from the use of such a policy.

   It is possible for the policy to be applied incorrectly, or for a
   wrong policy to be applied in the network for the defined
   aggregation.  In that case, a policy issue exists that the network
   must detect, assess, and deal with.  This is a known security issue
   in any network dependent on policy-directed behavior.

   A well known flaw appears when bandwidth is reserved or enabled for a
   service (for example, voice transport) and another service or an
   attacking traffic stream uses it.  This possibility is inherent in
   DiffServ technology, which depends on appropriate packet markings.
   When bandwidth reservation or a priority queuing system is used in a
   vulnerable network, the use of authentication and flow admission is
   recommended.  To the best of the authors' knowledge, there is no
   known technical way to respond to or act upon a data stream that has
   been admitted for service but that it is not intended for



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   authenticated use.


8.  IANA Considerations

   This document does not request any IANA considerations.


9.  Acknowledgements

   This document has benefited from discussions with numerous people,
   especially Shane Amante, Brian Carpenter, and Dave McDysan.  It has
   also benefited from detailed reviews by David Black and Marvin Krym.


10.  References

10.1.  Normative References

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

   [2]   Bradner, S., "The Internet Standards Process -- Revision 3",
         BCP 9, RFC 2026, October 1996.

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

   [4]   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.

   [5]   Babiarz, J., Chan, K., and F. Baker, "Configuration Guidelines
         for DiffServ Service Classes", RFC 4594, August 2006.

   [6]   Braden, B., Clark, D., and S. Shenker, "Integrated Services in
         the Internet Architecture: an Overview", RFC 1633, June 1994.

   [7]   Black, D., "Differentiated Services and Tunnels", RFC 2983,
         October 2000.

   [8]   Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen, P.,
         Krishnan, R., Cheval, P., and J. Heinanen, "Multi-Protocol
         Label Switching (MPLS) Support of Differentiated Services",
         RFC 3270, May 2002.

   [9]   Braden, B., Clark, D., Crowcroft, J., Davie, B., Deering, S.,
         Estrin, D., Floyd, S., Jacobson, V., Minshall, G., Partridge,



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         C., Peterson, L., Ramakrishnan, K., Shenker, S., Wroclawski,
         J., and L. Zhang, "Recommendations on Queue Management and
         Congestion Avoidance in the Internet", RFC 2309, April 1998.

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

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

   [12]  Charny, A., Bennet, J., Benson, K., Boudec, J., Chiu, A.,
         Courtney, W., Davari, S., Firoiu, V., Kalmanek, C., and K.
         Ramakrishnan, "Supplemental Information for the New Definition
         of the EF PHB (Expedited Forwarding Per-Hop Behavior)",
         RFC 3247, March 2002.

   [13]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition of
         Explicit Congestion Notification (ECN) to IP", RFC 3168,
         September 2001.

10.2.  Informative References

   [14]  Choi, B., Moon, S., Zhang, Z., Papagiannaki, K., and C. Diot,
         "Analysis of Point-To-Point Packet Delay in an Operational
         Network", INFOCOMM 2004, March 2004,
         <http://www.ieee-infocom.org/2004/Papers/37_4.PDF>.

   [15]  Ogielski, A. and J. Cowie, "Internet Routing Behavior on 9/11",
         March 2002, <http://www.renesys.com/tech/presentations/pdf/
         renesys-030502-NRC-911.pdf>.


Authors' Addresses

   Kwok Ho Chan
   Nortel Networks
   600 Technology Park Drive
   Billerica, MA  01821
   US

   Phone: +1-978-288-8175
   Fax:   +1-978-288-8700
   Email: khchan@nortel.com






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   Jozef Z. Babiarz
   Nortel Networks
   3500 Carling Avenue
   Ottawa, Ont.  K2H 8E9
   Canada

   Phone: +1-613-763-6098
   Fax:   +1-613-768-2231
   Email: babiarz@nortel.com


   Fred Baker
   Cisco Systems
   1121 Via Del Rey
   Santa Barbara, CA  93117
   US

   Phone: +1-408-526-4257
   Fax:   +1-413-473-2403
   Email: fred@cisco.com































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Full Copyright Statement

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