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Congestion and Pre-Congestion                                   M. Menth
Internet-Draft                                   University of Wuerzburg
Intended status: Experimental                                    R. Geib
Expires: January 6, 2011                                Deutsche Telekom
                                                            July 5, 2010


           PCN-Based Admission Control Using Implicit Probing
                  draft-menth-pcn-implicit-probing-00

Abstract

   Pre-congestion 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 RFC5559.  This memo is one
   of a series describing possible boundary node behaviours for a PCN
   domain.

   This document proposes an admission control method.  It assumes that
   PCN nodes perform threshold-marking configured with the PCN-
   admissible-rate on any link.  The decision point uses the PCN marking
   state of an initial signaling message of a flow to determine whether
   the flow should be admitted or blocked.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 6, 2011.

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



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   (http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Assumed Core Network Behaviour for Implicit Probing . . . . . . 4
   3.  Node Behaviours . . . . . . . . . . . . . . . . . . . . . . . . 4
     3.1.  Prerequisites . . . . . . . . . . . . . . . . . . . . . . . 4
     3.2.  Behavior of PCN-Ingress-Nodes . . . . . . . . . . . . . . . 4
     3.3.  Behavior of PCN-Egress-Nodes  . . . . . . . . . . . . . . . 4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   6.  Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7

























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1.  Introduction

   The objective of Pre-Congestion Notification (PCN) is to protect 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, to decide whether to admit or block a new flow
   request, and flow termination to decide whether to terminate some
   already admitted flows during serious congestion.  To achieve this,
   the overall rate of PCN-traffic is metered on every link in the
   domain, and PCN-packets are appropriately remarked 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 the "pre" part of pre-
   congestion notification).  For more details see [RFC5559].

   This document presents Implicit Probing as a method to perform
   admission control based on PCN information.  It requires that all
   PCN-ingress-nodes perform threshold marking [RFC5670] configured with
   the PCN-admissible-rate as reference rate, and uses the marking state
   of an initial signaling message of a flow to determine whether a flow
   should be admitted or blocked.  It neither describes a corresponding
   flow termination behavior nor does it preclude flow termination.

   The proposed method has several benefits: it does not require any
   measurement, it blocks very quickly as soon as pre-congestion occurs
   [Menth08-Sub-8], and it works well with multipath routing when the
   signaling message is carried on the same paths as future data
   packets.

1.1.  Terminology

   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].

   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.  Regardless
      of the location of the Decision Point, the ingress node is the
      point where the decisions are enforced.








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2.  Assumed Core Network Behaviour for Implicit Probing

   Implicit Probing requires that nodes of a PCN-domain perform
   threshold marking [RFC5670].  The reference rate must be set to the
   PCN-admissible-rate of a link.  Either Baseline Encoding [RFC5696] or
   3-in-1 Encoding [I-D.ietf-pcn-3-in-1-encoding] or another encoding,
   e.g., [Menth09f], may be used to distinguish re-marked signaling
   packets from unmarked signaling packets.


3.  Node Behaviours

   This section explains the behavior of PCN-ingress-nodes and PCN-
   egress-nodes.

3.1.  Prerequisites

   Implicit Probing assumes that admission control is triggered by a
   signaling message at the PCN-ingress-node and that this signaling
   message is carried across the PCN domain to the PCN-egress-node on
   the same path as future data packets of the associated flow.  These
   signaling messages are processed only by PCN-ingress-nodes and PCN-
   egress-nodes.  An example for such a signaling is the Resource
   ReServation Protocol [RFC2205].  Implicit Probing is relatively
   simple to implement when either PCN-ingress-node or PCN-egress-node
   are Decision Points as they are involved in the signaling anyway.

3.2.  Behavior of PCN-Ingress-Nodes

   The PCN-ingress-node re-marks signaling messages to not-marked so
   that they are subject to metering and re-marking by the PCN-interior-
   nodes.

   In case of RSVP, the PCN-ingress-node performs the following non-
   standard actions.  If the PCN-ingress-node receives a PATH message,
   it re-marks it to not-marked.  If the PCN-ingress-node receives an
   initial RESV message, it admits the flow for the hop over the PCN
   domain and forwards the RESV message to the previous RSVP-hop on the
   path.

3.3.  Behavior of PCN-Egress-Nodes

   The PCN-egress-node detects signaling messages.  As long as the flow
   is not yet admitted, the PCN-egress-node evaluates the PCN codepoint
   of received signaling messages.  If the codepoint is not-marked, it
   takes an action so that the flow will be admitted; otherwise it takes
   an action so that the flow will be blocked.  Finally, the PCN-egress-
   node resets the PCN codepoint to not-PCN.



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   In case of RSVP, the PCN-egress-node performs the following non-
   standard actions.  If the PCN-egress-node receives an initial not-
   marked PATH message, the PCN-egress-node forwards the message as
   usual.  If the PCN-egress-node receives an initial re-marked PATH
   message, the PCN-egress-node drops the PATH message and returns a
   PATH TEAR message to the previous RSVP hop indicating insufficient
   resources.


4.  IANA Considerations

   This document makes no request to IANA.


5.  Security Considerations

   Please see the security considerations in [RFC2205], [RFC2474], and
   [RFC2475].  [RFC5559] provides a general description of the security
   considerations for PCN.


6.  Conclusions

   The PCN-based admission control method proposed in this document has
   several benefits.  It does not require any measurement and does not
   require any parameters except for threshold metering and re-marking.
   Implicit probing blocks very quickly as soon as pre-congestion occurs
   [Menth08-Sub-8] and leads to less over-admission than PCN-based
   admission control that calculates congestion level estimates per
   ingress-egress aggregate to derive admission decisions.  Moreover,
   Implicit Probing works well with multipath routing when the signaling
   message is carried on the same path as future data packets
   [Menth08-Sub-8].


7.  Acknowledgements

   Joe Babiarz presented the idea documented in this memo for the first
   time in [I-D.babiarz-pcn-3sm].  It was further developed to be useful
   for restricted tunneling rules which called for a special encoding
   [I-D.ietf-pcn-psdm-encoding], [I-D.menth-pcn-psdm-deployment],
   [Menth09f].


8.  References






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8.1.  Normative References

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

   [RFC2205]  Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, September 1997.

   [RFC2474]  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.

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

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

   [RFC5670]  Eardley, P., "Metering and Marking Behaviour of PCN-
              Nodes", RFC 5670, November 2009.

   [RFC5696]  Moncaster, T., Briscoe, B., and M. Menth, "Baseline
              Encoding and Transport of Pre-Congestion Information",
              RFC 5696, November 2009.

8.2.  Informative References

   [I-D.babiarz-pcn-3sm]
              Babiarz, J., Liu, X., Chan, K., and M. Menth, "Three State
              PCN Marking", draft-babiarz-pcn-3sm-01 (work in progress),
              November 2007.

   [I-D.ietf-pcn-3-in-1-encoding]
              Briscoe, B. and T. Moncaster, "PCN 3-State Encoding
              Extension in a single DSCP",
              draft-ietf-pcn-3-in-1-encoding-02 (work in progress),
              March 2010.

   [I-D.ietf-pcn-psdm-encoding]
              Menth, M., Babiarz, J., Moncaster, T., and B. Briscoe,
              "PCN Encoding for Packet-Specific Dual Marking (PSDM
              Encoding)", draft-ietf-pcn-psdm-encoding-01 (work in
              progress), March 2010.

   [I-D.menth-pcn-psdm-deployment]



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              Menth, M., "Deployment Models for PCN-Based Admission
              Control and Flow Termination Using  Packet-Specific Dual
              Marking (PSDM)", draft-menth-pcn-psdm-deployment-00 (work
              in progress), October 2008.

   [Menth08-Sub-8]
              Menth, M. and F. Lehrieder, "Pre-Congestion Notification
              Using Packet-Specific Dual Marking", currently under
              submission, University of Wuerzburg, Germany, 2009.

   [Menth09f]
              Menth, M., Babiarz, J., and P. Eardley, "Pre-Congestion
              Notification Using Packet-Specific Dual Marking",
              in Proceedings of the International Workshop on the
              Network of the Future (Future-Net), IEEE, Dresden,
              Germany, June 2009.


Authors' Addresses

   Michael Menth
   University of Wuerzburg
   room B206, Institute of Computer Science
   Am Hubland
   Wuerzburg  97074
   Germany

   Phone: +49 931 31 86644
   Email: menth@informatik.uni-wuerzburg.de


   Ruediger Geib
   Deutsche Telekom
   Heinrich-Hertz-Strasse 3-7
   Darmstadt  64295
   Germany

   Phone: +49 6151 628 2747
   Email: ruediger.geib@telekom.de












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