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Internet Engineering Task Force                           G. Karagiannis
Internet-Draft                                      University of Twente
Intended status: Informational                                 T. Taylor
Expires: September 8, 2010                                       K. Chan
                                                     Huawei Technologies
                                                                M. Menth
                                                  University of Wurzburg
                                                           March 8, 2010






    Requirements for Signaling of (Pre-) Congestion Information in a
                           DiffServ Domain
                  draft-karagiannis-pcn-signaling-requirements-01

Abstract

   Precongestion notification (PCN) is a means for protecting quality of
   service for inelastic traffic admitted to a Diffserv domain. The
   overall PCN architecture is described in RFC 5559. This memo
   describes the requirements for the signaling applied within the PCN
   domain: PCN feedback is carried from the PCN-egress-node to the
   decision point and the decision point may demand for the measurement
   and delivery of the PCN rate sent at the PCN-ingress-node. The
   decision point may be either collocated with the PCN-ingress-node or
   a centralized node.


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on September 8, 2010.


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Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.



Requirements Language

   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 [RFC2119].

Table of Contents
1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
2.  Signaling requirements between PCN-egress-nodes and
    Decision Point . . . . . . . . . . . . . . . . . . . . . . . . . . 4
    2.1 PCN Reporting Frequency . . . . . . . . .. . . . . . . . . . . 4
    2.2 Signaled PCN egress Feedback . . . . . . .. . . . . . . . . . .4
    2.3 Signaling requirements . . . . . . . . . .. . . . . . . . . . .5
      2.3.1 Priority of signaling messages . . . . . . . . . . . . . . 5
      2.3.2 Local information exchange. . . . . . . . . . . . . . . . .5
      2.3.3 Carry identification of PCN edge nodes  . . . . . . . . . .5
      2.3.4 Carry identification of ingress-egress-aggregates  . . . . 5
      2.3.5 Signaling load. . . . . . .. . . . . . . . . . . . . . . . 6
      2.3.6 Reliability. . . . . . .. . . . . . . . . . . . . . . . .  6
    2.4. Filter specifications . . . . . . . . . . . . . . . . . . . . 6
3. Signaling Requirements between Decision Point and
   PCN-ingress-nodes . . . . . . . . . . . . . . . . . . . . . . . . . 7
    3.1 Signaled PCN ingress Feedback. . . . . . . . . . . . . . . . . 7
    3.2 Signaled decision point trigger. . . . . . . . . . . . . . . . 7
    3.3 Signaling requirements . . . . . . . . . .. . . . . . . . . . .7
4.  Security Considerations . . . . . . . . . . . . . . . . . . . . .  8
5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . .  8
6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . .   8
7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
    7.1.  Normative References . . . . . . . . . . . . . . . . . . . . 8
    7.2.  Informative References . . . . . . . . . . . . . . . . . . . 8
    Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9


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1.  Introduction


   The main objective of Pre-Congestion Notification (PCN) is to support
   the quality of service (QoS) of inelastic flows within a Diffserv
   domain in a simple, scalable, and robust fashion.  Two mechanisms
   are used: admission control and flow termination. Admission control
   is used to decide whether to admit or block a new flow request while
   flow termination is used in abnormal circumstances to decide
   whether to terminate some of the existing flows.  To support these
   two features, the overall rate of PCN-traffic is metered on every
   link in the domain, and PCN-packets are appropriately marked when
   certain configured rates are exceeded.  These configured rates are
   below the rate of the link thus providing notification to boundary
   nodes about overloads before any congestion occurs (hence "pre-
   congestion" notification). The PCN-egress-nodes measure the rates of
   differently marked PCN traffic in periodic intervals and report these
   rates as so-called PCN feedback to the decision points for admission
   control and flow termination based on which they take their
   decisions.The decision points may be collocated with the PCN-ingress-
   nodes or their function may be implemented in a centralized node.

   For more details see[RFC5559, [draft-ietf-pcn-cl-edge-behaviour-02],
   [draft-ietf-pcn-sm-edge-behaviour-02].

   Thus, signaling is needed to transport PCN feedback from PCN-egress-
   nodes towards the decision point. Moreover, signaling is needed that
   the decision point can trigger the PCN-ingress-node to measure the
   PCN traffic rate and send these measurement results to the decision
   point.

   This memo briefly describes the signaled content and specifies the
   requirements that have to be satisfied by the signaling protocols.


1.1.  Terminology

   In addition to the terms defined in [RFC5559], this document uses the
   following terms:

   Decision Point:

      The node that makes the decision about which flows to admit and to
      terminate.  In a given network deployment, this may be the ingress
      node or a centralized control node.  Of course, regardless of the
      location of the decision point, the ingress node is the point
      where the decisions are enforced.






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   PCN egress feedback:

      Content used by the PCN-egress-node to report and inform the
      decision point about measurements required during flow
      admission and flow termination decisions.

   PCN ingress feedback:

      Content used by the PCN-ingress-node to report and inform the
      decision point about measurements required during flow termination
      decisions.

   ingress rate request:

      A message sent by the decision point towards the PCN-ingress-node
      to request the PCN-ingress-node to measure and report the value of
      the rate of admitted PCN traffic for a given
      ingress-egress-aggregate.


2.  Signaling requirements between PCN-egress-nodes and
    Decision Point

   The PCN-egress-node measures the rates of differently marked PCN
   traffic in regular intervals and signals them as PCN egress feedback
   to the decision point.
   This section describes the PCN egress feedback and the requirements
   that apply to signaling protocols used for the transport of PCN
   feedback from PCN-egress-nodes to decision points.
   Note that if the decision point and the PCN-ingress-node are
   collocated, then the signaling requirements described in this section
   apply to the signaling between PCN-egress-nodes and PCN-ingress-
   nodes.


2.1 PCN Reporting Frequency

   The specification of PCN-based admission control and flow termination
   in [draft-ietf-pcn-cl-edge-behaviour-02], [draft-ietf-pcn-sm-edge-
   behaviour-02] suggest measurement and reporting intervals at the PCN-
   egress-nodes of 100 to 500 ms.


2.2 Signaled PCN egress Feedback

   The PCN-egress-node measures per ingress-egress-aggregate the
   following rates
      o rate of not-marked PCN traffic;
      o rate of threshold-marked PCN traffic, which applies to CL edge
        behaviour only;
      o rate of excess-traffic-marked PCN traffic.


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   These values are reported in octets/second to the decision point at
   the end of each measurement interval.

   If multipath routing is enabled, the PCN-egress-node tracks a list of
   flows for which it has recently received excess-traffic-marked
   packets. The list of these flow IDs is included in the PCN feedback
   because these flows are candidates for termination.
   The representation of a flow ID depends on the surrounding
   environment, e.g., "pure IP", MPLS, GMPLS, etc. For the
   representation of a flow ID in a "pure IP" surrounding environment,
   see Section 2.4.


2.3 Signaling requirements

   This section describes the requirements for signaling protocols that
   are used to carry the PCN egress feedback from PCN-egress-nodes to
   the decision point.


2.3.1 Priority of signaling messages

   Signaling messages SHOULD have a higher priority than data packets.
   This is needed to avoid as much as possible the situations that
   during severe overload cases the signaling messages are dropped
   within the PCN domain.


2.3.2 Local information exchange

   Signaling messages MUST be able to carry the PCN egress feedback from
   the PCN-egress-node to the decision point.


2.3.3 Carry identification of PCN edge nodes

   The signaling protocol MUST be able to carry identification
   (address information) of the PCN edge nodes.
   However, the identification of the PCN edge nodes
   MUST NOT be visible outside the PCN domain.


2.3.4 Carry identification of ingress-egress-aggregates

   The signaling protocol MUST be able to carry identification
   (address information) of the ingress-egress-aggregates. It is
   proposed to identify them using the addresses of the PCN-ingress-node
   and PCN-egress-node between which they pass. If each of the edge
   nodes do not have unique addresses, then other identifiers could be
   used.



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2.3.5 Signaling load

   The load generated by the signaling protocol to carry the PCN egress
   Feedback from the PCN-egress-nodes to the decision point SHOULD be
   minimized as much as possible.


2.3.6 Reliability

   There are situations that messages need to be sent in a
   reliable way, meaning that the PCN-egress-node MUST be acknowledged
   that the sent message is successfully received by the
   decision point. It is considered that the PCN egress feedback that
   is sent in a regular fashion SHOULD NOT be sent reliably.


2.4. Filter specifications

   In PCN the ingress and egress nodes should be able to identify the
   ingress-egress-aggregate to which each flow belongs. Moreover, the
   egress node also needs to associate an aggregate with the address of
   the ingress node for receiving reports, if the ingress node is the
   decision point. The filter specification at the PCN-egress-nodes
   depends on the surrounding environment, e.g., pure IP, MPLS, GMPLS.
   In this document, only the pure IP filter spec is given as an
   example. In this case the filter spec should be able to identify a
   flow using (all or a subset of the) following information:

   o  source IP address;

   o  destination IP address;

   o  protocol identifier and higher layer (port) addressing;

   o  flow label (typical for IPv6);

   o  SPI field for IPsec encapsulated data;

   o  DSCP/TOS field.

   o  IP address of PCN-ingress-node

   o  IP address of PCN-egress-node

   o  IP address of decision point







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3. Signaling Requirements between Decision Point and PCN-ingress-nodes

   The decision point monitors and uses the PCN egress feedback sent by
   the PCN-egress-node. There are situations that the decision point
   must obtain an estimate of the rate at which PCN-traffic is being
   admitted to the aggregate from the PCN-ingress-node.
   In order to receive this information the decision point has to
   request from the PCN-ingress-node to send the value of the PCN
   traffic admitted to a certain aggregate.
   Note that if the decision point and the PCN-ingress-node are
   collocated, then the signaling required between the decision point
   and PCN-ingress-node are internal operations.


3.1 Signaled PCN ingress Feedback

   The PCN-ingress-node measures per ingress-egress-aggregate the
   following rate
      o rate of admitted PCN traffic

   This value is reported in octets/second to the decision point as
   soon as possible after receiving the request from the decision
   point. .


3.2 Signaled decision point trigger

   The decision point uses the "ingress rate request" to request from
   the PCN-ingress-node to send for a certain ingress-egress-aggregate,
   the value of the admitted PCN traffic rate. The "ingress rate
   request" message identifies the ingress-egress-aggregate for which
   the admitted PCN traffic rate is required.


3.3 Signaling requirements

   The same signaling requirements described in Section 2.3 apply for
   this situation. The only difference is the fact that these signaling
   requirements apply for the signaling messages that have to be sent
   between the decision point and PCN-ingress-nodes. Moreover, since the
   "ingress rate request" message sent by the decision point towards
   the PCN-ingress-node and the admitted PCN traffic rate sent by the
   PCN-ingress-node towards the decision point are not sent regularly,
   they SHOULD be delivered reliably.








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4.  Security Considerations

   [RFC5559] provides a general description of the security
   considerations for PCN.  This memo introduces no new considerations.


5.  IANA Considerations

   This memo includes no request to IANA.


6.  Acknowledgements

   We would like to acknowledge the members of the PCN working group for
   the discussions that generated the contents of this memo.


7.  References


7.1.  Normative References


   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.


   [RFC5559]  Eardley, P., "Pre-Congestion Notification (PCN)
              Architecture", RFC 5559, June 2009.


   [draft-ietf-pcn-cl-edge-behaviour-02] T. Taylor, A, Charny,
              F. Huang, G. Karagiannis, M. Menth, "PCN Boundary Node
              Behaviour for the Controlled Load (CL) Mode of Operation
              (Work in progress)", March 2010.


   [draft-ietf-pcn-sm-edge-behaviour-02] A. Charny, J. Zhang,
              G.  Karagiannis, M. Menth, T. Taylor, "PCN Boundary Node
              Behaviour for the Single Marking (SM) Mode of Operation
              (Work in progress)", March 2010.


7.2.  Informative References








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Authors' Addresses

   Georgios Karagiannis
   University of Twente
   P.O. Box 217
   7500 AE Enschede,
   The Netherlands
   EMail: g.karagiannis@ewi.utwente.nl

   Tom Taylor
   Huawei Technologies
   1852 Lorraine Ave.
   Ottawa, Ontario  K1H 6Z8
   Canada
   Phone: +1 613 680 2675
   Email: tom111.taylor@bell.net


   Kwok Ho Chan
   Huawei Technologies
   125 Nagog Park
   Acton, MA  01720
   USA
   Email: khchan@huawei.com


   Michael Menth
   University of Wurzburg
   Institute of Computer Science
   Room B206
   Am Hubland, Wuerzburg  D-97074
   Germany
   Email: menth@informatik.uni-wuerzburg.de




















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