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                   RSVP Extensions for PCN-based CL          June 2006



   Internet Draft                                  Francois Le Faucheur
                                                            Anna Charny
                                                    Cisco Systems, Inc.

                                                            Bob Briscoe
                                                           Phil Eardley
                                                                     BT

                                                            Joe Barbiaz
                                                           Kwok-Ho Chan
                                                                 Nortel
   draft-lefaucheur-rsvp-ecn-01.txt
   Expires: December 2006                                     June 2006

                   RSVP Extensions for Admission Control
           over Diffserv using Pre-congestion Notification (PCN)


Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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Abstract

   This document specifies the extensions to RSVP for support of the
   Controlled Load (CL) service over a Diffserv cloud using Pre-
   Congestion Notification as defined in [CL-DEPLOY].




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Copyright Notice
      Copyright (C) The Internet Society (2006)


Specification of Requirements

   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 [RFC2119].


1.  Introduction

   [RSVP] defines the Resource reSerVation Protocol which can be used by
   applications to request resources from the network. The network
   responds by explicitely admitting or rejecting these RSVP requests.
   Certain applications that have quantifiable resource requirements
   express these requirements using Intserv parameters as defined in the
   appropriate Intserv service specifications ([RFC2212], [RFC2211]).
   Controlled Load (CL) service is a quality of service (QoS) closely
   approximating the QoS that the same flow would receive from a lightly
   loaded network element [RFC2211]. CL is useful for inelastic flows
   such as those for real-time media.

   [CL-DEPLOY] describes a deployment model to achieve a Controlled Load
   (CL) service ([RFC2211]) by using distributed measurement-based
   admission control edge-to-edge, i.e. within a particular region of
   the Internet. The measurement made is of CL packets that have their
   Congestion Experienced (CE) codepoint set as they travel across the
   edge-to-edge region. Setting the CE codepoint, which is under the
   control of a new Pre-congestion Marking behaviour, provides an "early
   warning" of potential congestion. This information is used by the
   ingress node of the edge-to-edge region to decide whether to admit a
   new CL microflow.

   [CL-DEPLOY] also describes how the framework uses rate-based pre-
   emption to maintain the CL service to as many admitted microflows as
   possible even after localised failure and routing changes in the
   interior of the edge-to-edge region.

   The edge-to-edge architecture of [CL-DEPLOY] is a building block in
   delivering an end-to-end CL service. The approach is similar to that
   described in [INTSERV-DIFFERV] for Integrated services operation over
   Diffserv networks. Like [INTSERV-DIFFERV], an IntServ class (CL in
   our case) is achieved end-to-end, with a CL-region viewed as a single
   reservation hop in the total end-to-end path. Interior nodes of the
   CL-region do not process flow signalling nor do they hold state.




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   [CL-DEPLOY] assumes that the end-to-end signalling mechanism is RSVP.
   This document specifies the extensions to RSVP for support of the
   Controlled Load (CL) service over a Diffserv cloud using Pre-
   Congestion Notification as defined in [CL-DEPLOY].


2.  Definitions

   For readability, a number of definitions from [CL-DEPLOY] are
   repeated here:

   o ingress edge (or ingress gateway): router at an ingress to the CL-
      region. A CL-region may have several ingress gateways.

   o egress edge (or egress gateway): router at an egress from the CL-
      region. A CL-region may have several egress gateways.

   o Interior router: a router which is part of the CL-region, but is
      not an ingress or egress gateway.

   o CL-region: A region of the Internet in which all traffic
      enters/leaves through an ingress/egress gateway and all routers
      run Pre-Congestion Notification marking. A CL-region is a
      DiffServ region (a DiffServ region is either a single DiffServ
      domain or set of contiguous DiffServ domains), but note that the
      CL-region does not use the traffic conditioning agreements (TCAs)
      of the (informational) DiffServ architecture.

   o CL-region-aggregate: all the microflows between a specific pair of
      ingress and egress gateways. Note there is no field in the flow
      packet headers that uniquely identifies the aggregate.

   o Congestion-Level-Estimate: the number of bits in CL packets that
      are admission marked (or pre-emption marked), divided by the
      number of bits in all CL packets. It is calculated as an
      exponentially weighted moving average. It is calculated by an
      egress gateway for the CL packets from a particular ingress
      gateway, i.e. there is a Congestion-Level-Estimate for each CL-
      region-aggregate.

   o  Sustainable-Aggregate-Rate: the rate of traffic that the network
      can actually support for a specific CL-region-aggregate. So it is
      measured by an egress gateway for the CL packets from a particular
      ingress gateway.



3.  Overview of RSVP extensions and Operations



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3.1.  Overall QoS Architecture

    The overall QoS architecture is described in [CL-DEPLOY]. For
    readability, the Figure of [CL-DEPLOY] illustrating this QoS
    architecture is reproduced below in Figure 1.

   ----   -----  -----------------------------------------  -----  -----
   |   |  |   |  |                                       |  |   |  |   |
   |   |  |   |  |Ingress         Interior         Egress|  |   |  |   |
   |   |  |   |  |gateway         routers         gateway|  |   |  |   |
   |   |  |   |  |-------+  +-------+  +-------+  +------|  |   |  |   |
   |   |  |   |  | PCN-  |  | PCN-  |  | PCN-  |  |      |  |   |  |   |
   |   |..|   |..|marking|..|marking|..|marking|..| Meter|..|   |..|   |
   |   |  |   |  |-------+  +-------+  +-------+  +------|  |   |  |   |
   |   |  |   |  |  \                                 /  |  |   |  |   |
   |   |  |   |  |   \                               /   |  |   |  |   |
   |   |  |   |  |    \  Congestion-Level-Estimate  /    |  |   |  |   |
   |   |  |   |  |     \  (for admission control)  /     |  |   |  |   |
   |   |  |   |  |      --<-----<----<----<-----<--      |  |   |  |   |
   |   |  |   |  |      Sustainable-Aggregate-Rate       |  |   |  |   |
   |   |  |   |  |        (for flow pre-emption)         |  |   |  |   |
   |   |  |   |  |                                       |  |   |  |   |
   ----   -----  -----------------------------------------  -----  -----
   Sx     Access               CL-region                   Access    Rx
   End    Network                                          Network   End
   Host
   Host
                   <------ edge-to-edge signalling ----->
                 (for admission control & flow pre-emption)

   <-------------------end-to-end QoS signalling protocol-------------->


                   Figure 1: Overall QoS Architecture


3.2.  Overview of Procedures for Admission Control of New Reservations

   As mentioned earlier, [CL-DEPLOY] describes a framework to achieve a
   Controlled Load (CL) service by using distributed measurement-based
   admission control edge-to-edge, i.e. within a particular region of
   the Internet. This section describes RSVP operations to support such
   an admission control scheme relying on Pre-Congestion Notification in
   the eddge-to-edge region.

   When a new Path message is received by Ingress Edge, the Ingress Edge
   does regular RSVP processing (including updating the RSVP PHOP) and
   forwards the Path towards destination.



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   All the PCN-capable Interior nodes are not RSVP-capable (or have RSVP
   processing disabled) and thus simply ignore the Path message.

   When the Path message arrives at the Egress Edge, the Egress Edge
   processes it as per regular RSVP processing, augmented with the
   following rules:

      1) The Egress Edge does NOT perform the RSVP-TTL vs IP TTL-check
         and does NOT update the ADspec Break bit. This is because the
         whole CL-region is effectively handled by RSVP as a virtual
         "link" on which Integrated Service is indeed supported (and
         admission control performed) so that the Break bit MUST not be
         set.

      2) The Egress Edge MAY check, at the time of initial Path
         processing, whether it has a valid value for the corresponding
         Congestion-Level-Estimate and if not it MAY send a PathErr
         message to the Ingress Edge with a new "CL-PCN Probes
         Required" Error Code. This minimizes call set up time as it
         allows probes to be generated by the Ingress Edge and measured
         by the Egress Edge while the Path is traveling towards the
         receiver and while the Resv travels back from the receiver.


   Then the Egress Edge forwards the Path message towards the receiver.

   [Editor Note: discussion on Adspec update to be added]

   When the Resv message is received by the Egress Edge (from the
   downstream side), the Egress Edge performs regular RSVP processing
   (including performing admission control for the segment downstream of
   the Egress Edge) augmented with the procedures described in this
   section.

   The Egress Edge MUST include the new CL-PCN object in the Resv
   message transmitted to the RSVP PHOP (which is the Ingress Edge). The
   CL-PCN object MUST convey the current Pre-Congestion Notification
   Congestion-Level-Estimate as measured by the Egress Edge from the
   corresponding Ingress Edge to itself. Details for computing the
   Congestion-Level-estimate can be found in [CL-DEPLOY] and [PCN-
   MARKING].

   If the Egress Edge does not have a current value for the Congestion-
   Level-estimate for the corresponding Ingress Edge (because there was
   no traffic received by the Egress Edge from that Ingress Edge) and it
   has not already requested the Ingress Edge to generate CL-PCN probes,
   the Egress Edge:

      1) triggers a timer and puts the Resv message processing on hold


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      2) sends a PathErr message towards the Ingress Edge with the new
         Error Code of "CL-PCN Probes Required" specified in this
         document, in order to instruct the Ingress Edge to generate
         the necessary probe traffic to enable the Egress Edge to
         compute the Congestion-Level-Estimate from that Ingress Edge

      3) When timer expires the Resv processing resumes. Assuming the
         Congestion-Level-Estimate is now available, the Egress Edge
         can include it in the CL-PCN object and complete Resv
         processing. If the Congestion-Level-Estimate is still
         available, the Egress Edge may loop again a few times through
         step 1) and 2). After a given number of times, the Egress Edge
         MUST send a ResvErr towards the receiver with existing
         ErrorCode "Admission Control Failure"

   [Editor note: approach in previous paragraph may be revisited to try
   avoid having to "put Resv message processing on hold".]

   The Egress Edge will then forward the Resv message to the PHOP
   signaled earlier in the Path message and which identifies the Ingress
   Edge. Since the Resv message is directly addressed to the Ingress
   Edge and does not carry the Router Alert option (as per regular RSVP
   Resv procedures), the Resv message is hidden from the Interior nodes
   which handle the E2E Resv message as a regular IP packet.

   When receiving the Resv message, the Ingress Edge processes the Resv
   message as per regular RSVP with the following exceptions:

      1) if the CL-PCN object is absent from the Resv message, this
         means that the RSVP Next Hop is not CL-PCN capable and hence
         proper admission control can not be achieved for that
         reservation over the PCN cloud. Thus, the Ingress Edge MUST
         send a ResvErr message towards the receiver with an new Error
         Code "Inconsistent Admission Control Behaviour across Ingress
         and Egress Edge" and an Error Value of "Egress Edge Router not
         CL-PCN capable". The Ingress Edge MAY also generate an alarm
         to the network operator.
         Note that in the case where the RSVP Next Hop is not CL-PCN
         capable, this RSVP hop would have (most probably) performed
         the RSVP-TTL vs IP-TTL check when processing the initial Path
         message and as a result would have set the Break bit in the
         Adspec (assuming there is at least one Interior node on the
         path from the Ingress Edge to the RSVP Next Hop). Thus, the
         sender would already have been notified in the first place
         that the QoS could not be guaranteed end-to-end.

      2) The Ingress Edge MUST carry out the admission control decision
         (for admission of the reservation over the path from Ingress


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         Edge to Egress Edge through the PCN cloud) taking into account
         the congestion information provided in the CL-PCN object of
         the Resv message in accordance with the procedures of [CL-
         DEPLOY] and [PCN-MARKING]. For example, if the Congestion
         Level Estimate conveyed in the CL-PCN object exceeds a
         configured threshold, the Ingress Edge may decide to reject
         this new reservation. Once the admission control decision is
         taken by the Ingress Edge, regular RSVP procedures are
         followed to either proceed with the reservation (and forward
         the Resv towards the sender) or tear down the reservation (and,
         in particular, send a ResvErr towards the receiver with
         existing Error Code "Admission Control failure".

      3) In case the Ingress Edge forwards the Resv message upstream,
         the Ingress Edge MUST remove the CL-PCN object

   When generating a refresh for a Resv message towards the Ingress Edge,
   the Egress Edge SHOULD NOT include the current value of the
   Congestion-Level-Estimate in the CL-PCN object, but rather SHOULD
   include the value which was included in the previous refresh. This is
   for implementation reasons, to facilitate detection by the Ingress
   Edge that this message is a mere refresh even if the value of the
   actual Congestion-Level-Estimate has changed since the previous
   refresh.

   When receiving a PathErr message with the new Error Code of "CL-PCN
   Probes Required", the Ingress Edge MUST generate CL-PCN probes as
   described in [CL-DEPLOY] towards the Egress Edge which sent the
   PathErr Message, and MUST not propagate the PathErr message further
   upstream.


   [Editor Note: discuss RSVP Authentication between ingress and egress
   edges]


3.3.  Removal of E2E reservations

   E2E reservations are removed in the usual RSVP way via PathTear,
   ResvTear, timeout, or as the result of an error condition. This does
   not directly affect CL-PCN operations.


3.4.  Overview of Procedures for Preemption of Existing Reservations

   As mentioned earlier, [CL-DEPLOY] describes how rate-based pre-
   emption can be used to maintain the CL service to as many admitted
   microflows as possible, even after localised failure and routing
   changes in the interior of the edge-to-edge region. The solution


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   involves the egress edge alerting the ingress edge of the CL-region-
   aggregate that preemption may be needed and conveying to the ingress
   edge the measured Sustainable-Aggregate-Rate. [CL-DEPLOY] also
   identifies that this information needs to be transferred reliably.
   This section describes the corresponding RSVP extensions.

   Section 3.2.1 "Alerting the Ingress Edge that pre-emption may be

   Let us assume that a number of reservations are established and
   transit through a given Ingress Edge Ei and a given Egress Edge Ee.
   Let us now assume that Ee is alerted that preemption may be needed
   and that Ee has measured the Sustainable-Aggregate-Rate for the CL-
   region-aggregate from Ei to Ee.

   Then, Ee MUST arbitrarily select one of the reservations whose
   Previous Hop is Ei and address to Ei a Resv message for that
   reservation with a CL-PCN object containing the current Sustainable-
   Aggregate-Rate for the relevant CL-region-aggregate.

   To avoid the risk that this Resv message gets lost and in turn that
   the Ingress Edge is not made aware in a timely manner that preemption
   may be needed, the RSVP reliable messaging procedures specified in
   [RSVP-REFRESH] SHOULD be used.

   Note that, even when reliable messaging is used, there is a very
   small risk that the alert that preemption may be needed does not make
   it to the Ingress Edge. For example, this could happen because there
   could be a race condition whereby the corresponding RSVP reservation
   may get torn down around the same time where the Resv message with
   the CL-PCN object is transmitted, resulting in the Ingress Edge
   ignoring the whole Resv message. However, the probability for this to
   occur is low and could also be mitigated by the Egress Edge sending
   the alert on more than one reservation.

   [Editor Note: optional use of a Notify message will be investigated.
   Can this solve the race condition problem mentioned above?]

   On receipt of the Resv message Ei will detect that this message is
   not just a refresh because the content of the CL-PCN object has
   changed and will immediately trigger its preemption logic. This will
   assess whether some reservations need to be dropped in accordance
   with the [CL-DEPLOY] and [PCN-MARKING] scheme. In case some do, those
   will be torn down as per regular RSVP procedures (in particular a
   ResvErr message is then sent to the receiver).


4.  RSVP Object and Error Code Definition

   This document defines a new object and two new error codes.


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4.1.  CL-PCN Object

   o      Class = To be allocated by IANA
          C-Type = 1

       0           7 8          15 16            25 26       31
      +-------------+-------------+-------------+-------------+
      |                Congestion-Level-Estimate              |
      +-------------+-------------+-------------+-------------+
      |                 Sustainable-Aggregate-Rate                |
      +-------------+-------------+-------------+-------------+


   The CL-PCN Object may only be used in Resv messages.

   Let us refer:
      - to the Egress Edge which generated the Resv message containing
        the CL-PCN object as Ee
      - to the RSVP Previous HOP (Ingres Edge) for the corresponding
        reservation as Ei.

   CL-PCN Congestion-Level-Estimate:
   This contains the value of the Congestion-Level-Estimate (defined in
   [CL-DEPLOY] and [PCN-MARKING]) computed by Ee for the CL-region-
   aggregate from Ei to Ee. When generating a refresh for a Resv message
   towards the Ingress Edge, the Egress Edge SHOULD NOT include the
   current value of the Congestion-Level-Estimate in the CL-PCN object,
   but rather SHOULD include the value which was included in the
   previous refresh.
   [Editor Note: Encoding details to be added]

   Sustainable-Aggregate-Rate:
   This contains:
      - When Ee is not alerted that preemption is needed for the CL-
        region-aggregate from Ei to Ee, this field is set to 0,
      - When Ee is alerted that preemption is (or may be) needed for
        the CL-region-aggregate from Ei to Ee, the Sustainable-
        Aggregate-Rate  for the relevant CL-region-aggregate (defined
        in [CL-DEPLOY] and [PCN-MARKING]) computed by Ee for this CL-
        region-aggregate.
   [Editor Note: Encoding details to be added]


4.2.  "CL-PCN Probes Required" Error Code

   The "CL-PCN Probes Required" Error Code may appear only in PathErr
   messages.



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   Error Code = To be allocated by IANA


4.3.  "Inconsistent Admission Control Behaviour across Ingress and
    Egress Edge" Error Code

   The "Inconsistent Admission Control Behaviour across Ingress and
   Egress Edge" may appear only in ResvErr messages.
   [Editor note: should we allow it in PathErr messages too so that
   notification can also be provided to the sender?]

   Error Code for "Inconsistent Admission Control Behaviour across
   Ingress and Egress Edge"= To be allocated by IANA

   Error Value for "Egress Edge Router not CL-PCN capable"= To be
   allocated by IANA


5.  Security Considerations

   To be added


6.  IANA Considerations

   This document makes the following requests to the IANA:
      - allocate a new Object Class (CL-PCN Object)
      - allocate a new Error Code ("CL-PCN Probes Required") and manage
   the corresponding Error Value range
      - allocate a new Error Code ("Inconsistent Admission Control
   Behaviour across Ingress and Egress Edge"), manage the corresponding
   Error Value range, and allocate the "Egress Edge Router not CL-PCN
   capable" under that range.


7.  Acknowledgments

   We would like to thank Carol Iturralde for her input into this
   document.


8.  Normative References

   [RSVP] Braden, R., ed., et al., "Resource ReSerVation Protocol
   (RSVP)- Functional Specification", RFC 2205, September 1997.

   [CL-DEPLOY] B. Briscoe, P. Eardley, D. Songhurst, F. Le Faucheur, A.
   Charny, S. Dudley, J. Babiarz, K. Chan, G. Karagiannis, A. Bader., L
   Westberg. "A Deployment Model for Admission Control over DiffServ


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   using Pre-Congestion Notification, draft-briscoe-tsvwg-cl-
   architecture-03.txt", (work in progress), June 2006

   [RFC2998] Bernet, Y., Yavatkar, R., Ford, P., Baker, F., Zhang, L.,
   Speer, M., Braden, R., Davie, B., Wroclawski, J. and E. Felstaine, "A
   Framework for Integrated Services Operation Over DiffServ Networks",
   RFC 2998, November 2000.

   [PCN-MARKING] B. Briscoe, P. Eardley, D. Songhurst, F. Le Faucheur, A.
   Charny, S. Dudley, J. Babiarz, K. Chan, G. Karagiannis, A. Bader., L
   Westberg. "Pre-Congestion Notification marking"
   draft-briscoe-tsvwg-cl-phb-02.txt (work in progress), June 2006.

   [RSVP-REFRESH] Burger et al, "RSVP Refresh Overhead Reduction
   Extensions", RFC2961, April 2001

   [RFC2211] J. Wroclawski, Specification of the Controlled-Load Network
   Element Service, September 1997

   [RFC2212] S. Shenker et al., Specification of Guaranteed Quality of
   Service, September 1997


9.  Informative References

   [RFC2211] J. Wroclawski, Specification of the Controlled-Load Network
   Element Service, September 1997

   [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z. and
   W. Weiss, "A framework for Differentiated Services", RFC 2475,
   December 1998.


10.  Authors' Address

   Francois Le Faucheur
   Cisco Systems, Inc.
   Village d'Entreprise Green Side - Batiment T3
   400, Avenue de Roumanille
   06410 Biot Sophia-Antipolis
   France
   Email: flefauch@cisco.com

   Anna Charny
   Cisco Systems
   300 Apollo Drive
   Chelmsford, MA 01824
   USA
   EMail: acharny@cisco.com


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   Bob Briscoe
   BT Research
   B54/77, Sirius House
   Adastral Park
   Martlesham Heath
   Ipswich, Suffolk
   IP5 3RE
   United Kingdom
   Email: bob.briscoe@bt.com

   Philip Eardley
   BT Research
   B54/77, Sirius House
   Adastral Park
   Martlesham Heath
   Ipswich, Suffolk
   IP5 3RE
   United Kingdom
   Email: philip.eardley@bt.com

   Kwok Ho Chan
   Nortel Networks
   600 Technology Park Drive
   Billerica, MA  01821
   USA
   Email: khchan@nortel.com

   Jozef Z. Babiarz
   Nortel Networks
   3500 Carling Avenue
   Ottawa, Ont  K2H 8E9
   Canada
   Email: babiarz@nortel.com


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Appendix A - Example RSVP Signaling Flow for Admission Control

   To be added. Shows RSVP message flow in case of admission control of
   new reservations.


Appendix B - Example Signaling Flow for Preemption

   To be added. Shows RSVP message flow in case of preemption of
   existing reservations.










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