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Versions: (draft-taylor-pcn-cl-edge-behaviour) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 6661

Internet Engineering Task Force                                A. Charny
Internet-Draft                                             Cisco Systems
Intended status: Experimental                                   F. Huang
Expires: April 25, 2012                              Huawei Technologies
                                                          G. Karagiannis
                                                               U. Twente
                                                                M. Menth
                                                 University of Tuebingen
                                                          T. Taylor, Ed.
                                                     Huawei Technologies
                                                        October 23, 2011



    PCN Boundary Node Behaviour for the Controlled Load (CL) Mode of
                               Operation
                  draft-ietf-pcn-cl-edge-behaviour-10


Abstract


   Pre-congestion notification (PCN) is a means for protecting the
   quality of service for inelastic traffic admitted to a Diffserv
   domain.  The overall PCN architecture is described in RFC 5559.  This
   memo is one of a series describing possible boundary node behaviours
   for a PCN-domain.  The behaviour described here is that for a form of
   measurement-based load control using three PCN marking states, not-
   marked, threshold-marked, and excess-traffic-marked.  This behaviour
   is known informally as the Controlled Load (CL) PCN-boundary-node
   behaviour.


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 April 25, 2012.


Copyright Notice






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   Copyright (c) 2011 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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



























































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Table of Contents


   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  [CL-Specific] Assumed Core Network Behaviour for CL  . . . . .  9
   3.  Node Behaviours  . . . . . . . . . . . . . . . . . . . . . . .  9
     3.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  9
     3.2.  Behaviour of the PCN-Egress-Node . . . . . . . . . . . . . 10
       3.2.1.  Data Collection  . . . . . . . . . . . . . . . . . . . 10
       3.2.2.  Reporting the PCN Data . . . . . . . . . . . . . . . . 11
       3.2.3.  Optional Report Suppression  . . . . . . . . . . . . . 11
     3.3.  Behaviour at the Decision Point  . . . . . . . . . . . . . 12
       3.3.1.  Flow Admission . . . . . . . . . . . . . . . . . . . . 12
       3.3.2.  Flow Termination . . . . . . . . . . . . . . . . . . . 13
       3.3.3.  Decision Point Action For Missing
               PCN-Boundary-Node Reports  . . . . . . . . . . . . . . 14
     3.4.  Behaviour of the Ingress Node  . . . . . . . . . . . . . . 15
     3.5.  Summary of Timers and Associated Configurable Durations  . 16
       3.5.1.  Recommended Values For the Configurable Durations  . . 17
   4.  Specification of Diffserv Per-Domain Behaviour . . . . . . . . 18
     4.1.  Applicability  . . . . . . . . . . . . . . . . . . . . . . 18
     4.2.  Technical Specification  . . . . . . . . . . . . . . . . . 18
       4.2.1.  Classification and Traffic Conditioning  . . . . . . . 18
       4.2.2.  PHB Configuration  . . . . . . . . . . . . . . . . . . 19
     4.3.  Attributes . . . . . . . . . . . . . . . . . . . . . . . . 20
     4.4.  Parameters . . . . . . . . . . . . . . . . . . . . . . . . 20
     4.5.  Assumptions  . . . . . . . . . . . . . . . . . . . . . . . 20
     4.6.  Example Uses . . . . . . . . . . . . . . . . . . . . . . . 20
     4.7.  Environmental Concerns . . . . . . . . . . . . . . . . . . 20
     4.8.  Security Considerations  . . . . . . . . . . . . . . . . . 20
   5.  Operational and Management Considerations  . . . . . . . . . . 20
     5.1.  Deployment of the CL Edge Behaviour  . . . . . . . . . . . 20
       5.1.1.  Selection of Deployment Options and Global
               Parameters . . . . . . . . . . . . . . . . . . . . . . 21
       5.1.2.  Specification of Node- and Link-Specific Parameters  . 22
       5.1.3.  Installation of Parameters and Policies  . . . . . . . 23
       5.1.4.  Activation and Verification of All Behaviours  . . . . 24
     5.2.  Management Considerations  . . . . . . . . . . . . . . . . 25
       5.2.1.  Event Logging In the PCN Domain  . . . . . . . . . . . 25
         5.2.1.1.  Logging Loss and Restoration of Contact  . . . . . 25
         5.2.1.2.  Logging Flow Termination Events  . . . . . . . . . 27
       5.2.2.  Provision and Use of Counters  . . . . . . . . . . . . 28
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 29
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 29
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 30
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 30
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 31





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   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31











































































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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 (in abnormal circumstances) flow termination to decide
   whether to terminate some of the existing flows.  To achieve this,
   the overall rate of PCN-traffic is metered on every link in the PCN-
   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 PCN-boundary-nodes
   about incipient overloads before any congestion occurs (hence the
   "pre" part of "pre-congestion notification").  The level of marking
   allows decisions to be made about whether to admit or terminate PCN-
   flows.  For more details see [RFC5559].


   Section 3 of this document specifies a detailed set of algorithms and
   procedures used to implement the PCN mechanisms for the CL mode of
   operation.  Since the algorithms depend on specific metering and
   marking behaviour at the interior nodes, it is also necessary to
   specify the assumptions made about PCN-interior-node behaviour
   (Section 2).  Finally, because PCN uses DSCP values to carry its
   markings, a specification of PCN-boundary-node behaviour MUST include
   the per domain behaviour (PDB) template specified in [RFC3086],
   filled out with the appropriate content (Section 4).


   [RFC EDITOR'S NOTE: you may choose to delete the following paragraph
   and the "[CL-specific]" tags throughout this document when publishing
   it, since they are present primarily to aid reviewers.  RFCyyyy is
   the published version of draft-ietf-pcn-sm-edge-behaviour.]


   A companion document [RFCyyyy] specifies the Single Marking (SM) PCN-
   boundary-node behaviour.  This document and [RFCyyyy] have a great
   deal of text in common.  To simplify the task of the reader, the text
   in the present document that is specific to the CL PCN-boundary-node
   behaviour is preceded by the phrase: "[CL-specific]".  A similar
   distinction for SM-specific text is made in [RFCyyyy].


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].


   This document uses the following terms defined in Section 2 of
   [RFC5559]:






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   o  PCN-domain;


   o  PCN-ingress-node;


   o  PCN-egress-node;


   o  PCN-interior-node;


   o  PCN-boundary-node;


   o  PCN-flow;


   o  ingress-egress-aggregate (IEA);


   o  [CL-specific] PCN-threshold-rate;


   o  PCN-excess-rate;


   o  PCN-admissible-rate;


   o  PCN-supportable-rate;


   o  PCN-marked;


   o  [CL-specific] threshold-marked;


   o  excess-traffic-marked.


   It also uses the terms PCN-traffic and PCN-packet, for which the
   definition is repeated from [RFC5559] because of their importance to
   the understanding of the text that follows:


   PCN-traffic, PCN-packets, PCN-BA
      A PCN-domain carries traffic of different Diffserv behaviour
      aggregates (BAs) [RFC2474].  The PCN-BA uses the PCN mechanisms to
      carry PCN-traffic, and the corresponding packets are PCN-packets.
      The same network will carry traffic of other Diffserv BAs.  The
      PCN-BA is distinguished by a combination of the Diffserv codepoint
      and the ECN field.


   This document uses the following terms from [RFC5670]:


   o  [CL-specific] threshold-meter;


   o  excess-traffic-meter.


   To complete the list of borrowed terms, this document reuses the
   following terms and abbreviations defined in Section 3 of [RFC5696]:





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   o  not-PCN codepoint;


   o  Not-marked (NM) codepoint;


   o  PCN-marked (PM) codepoint;


   o  [CL-specific] Experimental (EXP) codepoint.


   This document defines the following additional terms:


   Decision Point
      The node that makes the decision about which flows to admit and to
      terminate.  In a given network deployment, this can be the PCN-
      ingress-node or a centralized control node.  In either case, the
      PCN-ingress-node is the point where the decisions are enforced.


   NM-rate
      The rate of not-marked PCN-traffic received at a PCN-egress-node
      for a given ingress-egress-aggregate in octets per second.  For
      further details see Section 3.2.1.


   [CL-specific] ThM-rate
      The rate of threshold-marked PCN-traffic received at a PCN-egress-
      node for a given ingress-egress-aggregate in octets per second.
      For further details see Section 3.2.1.


   ETM-rate
      The rate of excess-traffic-marked PCN-traffic received at a PCN-
      egress-node for a given ingress-egress-aggregate in octets per
      second.  For further details see Section 3.2.1.


   PCN-sent-rate
      The rate of PCN-traffic received at a PCN-ingress-node and
      destined for a given ingress-egress-aggregate in octets per
      second.  For further details see Section 3.4.


   Congestion level estimate (CLE)
      The ratio of PCN-marked to total PCN-traffic (measured in octets)
      received for a given ingress-egress-aggregate during a given
      measurement period.  The CLE is used to derive the PCN-admission-
      state (Section 3.3.1) and is also used by the report suppression
      procedure (Section 3.2.3) if report suppression is activated.


   PCN-admission-state
      The state ("admit" or "block") derived by the Decision Point for a
      given ingress-egress-aggregate based on PCN packet marking
      statistics.  The Decision Point decides to admit or block new
      flows offered to the aggregate based on the current value of the





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      PCN-admission-state.  For further details see Section 3.3.1.


   Sustainable aggregate rate (SAR)
      The estimated maximum rate of PCN-traffic that can be carried in a
      given ingress-egress-aggregate at a given moment without risking
      degradation of quality of service for the admitted flows.  The
      intention is that if the PCN-sent-rate of every ingress-egress-
      aggregate passing through a given link is limited to its
      sustainable aggregate rate, the total rate of PCN-traffic flowing
      through the link will be limited to the PCN-supportable-rate for
      that link.  An estimate of the sustainable aggregate rate for a
      given ingress-egress-aggregate is derived as part of the flow
      termination procedure, and is used to determine how much PCN-
      traffic needs to be terminated.  For further details see
      Section 3.3.2.


   CLE-reporting-threshold
      A configurable value against which the CLE is compared as part of
      the report suppression procedure.  For further details, see
      Section 3.2.3.


   CLE-limit
      A configurable value against which the CLE is compared to
      determine the PCN-admission-state for a given ingress-egress-
      aggregate.  For further details, see Section 3.3.1.


   T-meas
      A configurable time interval that defines the measurement period
      over which the PCN-egress-node collects statistics relating to
      PCN-traffic marking.  At the end of the interval the PCN-egress-
      node calculates the values NM-rate, [CL-specific] ThM-rate, and
      ETM-rate as defined above and sends a report to the Decision
      Point, subject to the operation of the report suppression feature.
      For further details see Section 3.2.


   T-maxsuppress
      A configurable time interval after which the PCN-egress-node MUST
      send a report to the Decision Point for a given ingress-egress-
      aggregate regardless of the most recent values of the CLE.  This
      mechanism provides the Decision Point with a periodic confirmation
      of liveness when report suppression is activated.  For further
      details, see Section 3.2.3.


   T-fail
      An interval after which the Decision Point concludes that
      communication from a given PCN-egress-node has failed if it has
      received no reports from the PCN-egress-node during that interval.
      For further details see Section 3.3.3.





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   T-crit
      A configurable interval used in the calculation of T-fail.  For
      further details see Section 3.3.3.



2.  [CL-Specific] Assumed Core Network Behaviour for CL


   This section describes the assumed behaviour for PCN-interior-nodes
   in the PCN-domain.  The CL mode of operation assumes that:


   o  PCN-interior-nodes perform both threshold-marking and excess-
      traffic-marking of PCN-packets, according to the rules specified
      in [RFC5670];


   o  excess-traffic-marking of PCN-packets uses the PCN-Marked (PM)
      codepoint defined in [RFC5696];


   o  threshold-marking of PCN-packets uses the EXP codepoint defined in
      [RFC5696];


   o  the PCN-domain satisfies the conditions specified in [RFC5696];


   o  on each link the reference rate for the threshold-meter is
      configured to be equal to the PCN-admissible-rate for the link;


   o  on each link the reference rate for the excess-traffic-meter is
      configured to be equal to the PCN-supportable-rate for the link;


   o  the set of valid codepoint transitions is as shown in Section 4.2
      of [RFC5696].



3.  Node Behaviours


3.1.  Overview


   This section describes the behaviour of the PCN-ingress-node, PCN-
   egress-node, and the Decision Point (which MAY be collocated with the
   PCN-ingress-node).


   The PCN-egress-node collects the rates of not-marked, [CL-specific]
   threshold-marked, and excess-traffic-marked PCN-traffic for each
   ingress-egress-aggregate and reports them to the Decision Point.
   [CL-specific] It MAY also identify and report PCN-flows that have
   experienced excess-traffic-marking.  For a detailed description, see
   Section 3.2.


   The PCN-ingress-node enforces flow admission and termination





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   decisions.  It also reports the rate of PCN-traffic sent to a given
   ingress-egress-aggregate when requested by the Decision Point.  For
   details, see Section 3.4.


   Finally, the Decision Point makes flow admission decisions and
   selects flows to terminate based on the information provided by the
   PCN-ingress-node and PCN-egress-node for a given ingress-egress-
   aggregate.  For details, see Section 3.3.


3.2.  Behaviour of the PCN-Egress-Node


3.2.1.  Data Collection


   The PCN-egress-node MUST meter the PCN-traffic it receives in order
   to calculate the following rates for each ingress-egress-aggregate
   passing through it.  These rates SHOULD be calculated at the end of
   each measurement period based on the PCN-traffic observed during that
   measurement period.  The duration of a measurement period is equal to
   the configurable value T-meas.


   o  NM-rate: octets per second of PCN-traffic in PCN-packets that are
      not-marked (i.e., marked with the NM codepoint);


   o  [CL-specific] ThM-rate: octets per second of PCN-traffic in PCN-
      packets that are threshold-marked (i.e., marked with the EXP
      codepoint);


   o  ETM-rate: octets per second of PCN-traffic in PCN-packets that are
      excess-traffic-marked (i.e., marked with the PM codepoint).


   Informative note: metering the PCN-traffic continuously and using
   equal-length measurement intervals minimizes the statistical variance
   introduced by the measurement process itself.  On the other hand, the
   operation of PCN is not affected if the starting and ending times of
   the measurement intervals for different ingress-egress-aggregates are
   different.


   [CL-specific] As a configurable option, the PCN-egress-node MAY
   record flow identifiers of the PCN-flows for which excess-traffic-
   marked packets have been observed during this measurement interval.
   If this set is large (e.g., more than 20 flows), the PCN-egress-node
   MAY record only the most recently excess-traffic-marked PCN-flow
   identifiers rather than the complete set.


      These can be used by the Decision Point when it selects flows for
      termination.  In networks using multipath routing it is possible
      that congestion is not occurring on all paths carrying a given
      ingress-egress-aggregate.  Assuming that specific PCN-flows are





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      routed via specific paths, identifying the PCN-flows that are
      experiencing excess-traffic-marking helps to avoid termination of
      PCN-flows not contributing to congestion.


3.2.2.  Reporting the PCN Data


   Unless the report suppression option described in Section 3.2.3 is
   activated, the PCN-egress-node MUST report the latest values of NM-
   rate, [CL-specific] ThM-rate, and ETM-rate to the Decision Point each
   time that it calculates them.


   [CL-specific] If the PCN-egress-node recorded a set of flow
   identifiers of PCN-flows for which excess-traffic-marking was
   observed in the most recent measurement interval, then it MUST also
   include these identifiers in the report.


3.2.3.  Optional Report Suppression


   Report suppression MUST be provided as a configurable option, along
   with two configurable parameters, the CLE-reporting-threshold and the
   maximum report suppression interval T-maxsuppress.  The default value
   of the CLE-reporting-threshold is zero.  The CLE-reporting-threshold
   MUST NOT exceed the CLE-limit configured at the Decision Point.  For
   further information on T-maxsuppress see Section 3.5.


   If the report suppression option is enabled, the PCN-egress-node MUST
   apply the following procedure to decide whether to send a report to
   the Decision Point, rather than sending a report automatically at the
   end of each measurement interval.


   1.  As well as the quantities NM-rate, [CLE-specific] ThM-rate, and
       ETM-rate, the PCN-egress-node MUST calculate the congestion level
       estimate (CLE) for each measurement interval.  The CLE is
       computed as:


          [CL-specific]
          CLE = (ThM-rate + ETM-rate) / (NM-rate + ThM-rate + ETM-rate)


       if any PCN-traffic was observed, or CLE = 0 if all the rates are
       zero.


   2.  If the CLE calculated for the latest measurement interval is
       greater than the CLE-reporting-threshold and/or the CLE
       calculated for the immediately previous interval was greater than
       the CLE-reporting-threshold, then the PCN-egress-node MUST send a
       report to the Decision Point.  The contents of the report are
       described below.






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          The reason for taking into account the CLE of the previous
          interval is to ensure that the Decision Point gets immediate
          feedback if the CLE has dropped below CLE-reporting-threshold.
          This is essential if the Decision Point is running the flow
          termination procedure and observing whether (further) flow
          termination is needed.  See Section 3.3.2.


   3.  If an interval T-maxsuppress has elapsed since the last report
       was sent to the Decision Point, then the PCN-egress-node MUST
       send a report to the Decision Point regardless of the CLE value.


   4.  If neither of the preceding conditions holds, the PCN-egress-node
       MUST NOT send a report for the latest measurement interval.


   Each report sent to the Decision Point when report suppression has
   been activated MUST contain the values of NM-rate, [CL-specific] ThM-
   rate, ETM-rate, and CLE that were calculated for the most recent
   measurement interval.  [CL-specific] If the PCN-egress-node recorded
   a set of flow identifiers of PCN-flows for which excess-traffic-
   marking was observed in the most recent measurement interval, then it
   MUST also include these identifiers in the report.


   The above procedure ensures that at least one report is sent per
   interval (T-maxsuppress + T-meas).  This demonstrates to the Decision
   Point that both the PCN-egress-node and the communication path
   between that node and the Decision Point are in operation.


3.3.  Behaviour at the Decision Point


   Operators can choose to use PCN procedures just for flow admission,
   or just for flow termination, or for both.  A compliant Decision
   Point MUST implement both mechanisms, but configurable options MUST
   be provided to activate or deactivate PCN-based flow admission and
   flow termination independently of each other at a given Decision
   Point.


   If PCN-based flow termination is enabled but PCN-based flow admission
   is not, flow termination operates as specified in this document.


      Logically, some other system of flow admission control is in
      operation, but the description of such a system is out of scope of
      this document and depends on local arrangements.


3.3.1.  Flow Admission


   The Decision Point determines the PCN-admission-state for a given
   ingress-egress-aggregate each time it receives a report from the
   egress node.  It makes this determination on the basis of the





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   congestion level estimate (CLE).  If the CLE is provided in the
   egress node report, the Decision Point SHOULD use the reported value.
   If the CLE was not provided in the report, the Decision Point MUST
   calculate it based on the other values provided in the report, using
   the formula:


      [CL-specific]
      CLE = (ThM-rate + ETM-rate) / (NM-rate + ThM-rate + ETM-rate)


   if any PCN-traffic was observed, or CLE = 0 if all the rates are
   zero.


   The Decision Point MUST compare the reported or calculated CLE to a
   configurable value, the CLE-limit.  If the CLE is less than the CLE-
   limit, the PCN-admission-state for that aggregate MUST be set to
   "admit"; otherwise it MUST be set to "block".


   If the PCN-admission-state for a given ingress-egress-aggregate is
   "admit", the Decision Point SHOULD allow new flows to be admitted to
   that aggregate.  If the PCN-admission-state for a given ingress-
   egress-aggregate is "block", the Decision Point SHOULD NOT allow new
   flows to be admitted to that aggregate.  These actions MAY be
   modified by policy in specific cases, but such policy intervention
   risks defeating the purpose of using PCN.


3.3.2.  Flow Termination


   [CL-specific] When the report from the PCN-egress-node includes a
   non-zero value of the ETM-rate for some ingress-egress-aggregate, the
   Decision Point MUST request the PCN-ingress-node to provide an
   estimate of the rate (PCN-sent-rate) at which the PCN-ingress-node is
   receiving PCN-traffic that is destined for the given ingress-egress-
   aggregate.


      If the Decision Point is collocated with the PCN-ingress-node, the
      request and response are internal operations.


   The Decision Point MUST then wait, for both the requested rate from
   the PCN-ingress-node and the next report from the PCN-egress-node for
   the ingress-egress-aggregate concerned.  If this next egress node
   report also includes a non-zero value for the ETM-rate, the Decision
   Point MUST determine the amount of PCN-traffic to terminate using the
   following steps:


   1.  [CL-specific] The sustainable aggregate rate (SAR) for the given
       ingress-egress-aggregate is estimated by the sum:








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          SAR = NM-rate + ThM-rate


       for the latest reported interval.


   2.  The amount of traffic to be terminated is the difference:


          PCN-sent-rate - SAR,


       where PCN-sent-rate is the value provided by the PCN-ingress-
       node.


   See Section 3.3.3 for a discussion of appropriate actions if the
   Decision Point fails to receive a timely response to its request for
   the PCN-sent-rate.


   If the difference calculated in the second step is positive, the
   Decision Point SHOULD select PCN-flows to terminate, until it
   determines that the PCN-traffic admission rate will no longer be
   greater than the estimated sustainable aggregate rate.  If the
   Decision Point knows the bandwidth required by individual PCN-flows
   (e.g., from resource signalling used to establish the flows), it MAY
   choose to complete its selection of PCN-flows to terminate in a
   single round of decisions.


   Alternatively, the Decision Point MAY spread flow termination over
   multiple rounds to avoid over-termination.  If this is done, it is
   RECOMMENDED that enough time elapse between successive rounds of
   termination to allow the effects of previous rounds to be reflected
   in the measurements upon which the termination decisions are based.
   (See [IEEE-Satoh] and sections 4.2 and 4.3 of [MeLe10].)


   In general, the selection of flows for termination MAY be guided by
   policy.  [CL-specific] If the egress node has supplied a list of
   identifiers of PCN-flows that experienced excess-traffic-marking
   (Section 3.2), the Decision Point SHOULD first consider terminating
   PCN-flows in that list.


3.3.3.  Decision Point Action For Missing PCN-Boundary-Node Reports


   The Decision Point SHOULD start a timer t-recvFail when it receives a
   report from the PCN-egress-node. t-recvFail is reset each time a new
   report is received from the PCN-egress-node. t-recvFail expires if it
   reaches the value T-fail.  T-fail is calculated according to the
   following logic:


   a.  T-fail = the configurable duration T-crit, if report suppression
       is not deployed;






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   b.  T-fail = T-crit also if report suppression is deployed and the
       last report received from the PCN-egress-node contained a CLE
       value greater than CLE-reporting-threshold (Section 3.2.3);


   c.  T-fail = 3 * T-maxsuppress (Section 3.2.3) if report suppression
       is deployed and the last report received from the PCN-egress-node
       contained a CLE value less than or equal to CLE-reporting-
       threshold.


   If timer t-recvFail expires for a given PCN-egress-node, the Decision
   Point SHOULD notify management.  A Decision Point collocated with a
   PCN-ingress-node SHOULD cease to admit PCN-flows to the ingress-
   egress-aggregate associated with the given PCN-egress-node, until it
   again receives a report from that node.  A centralized Decision Point
   MAY cease to admit PCN-flows to all ingress-egress-aggregates
   destined to the PCN-egress-node concerned, until it again receives a
   report from that node.


   A centralized Decision Point SHOULD start a timer t-sndFail when it
   sends a request for the estimated value of PCN-sent-rate to a given
   PCN-ingress-node.  If the Decision Point fails to receive a response
   from the PCN-ingress-node before t-sndFail reaches the configurable
   value T-crit, the Decision Point SHOULD repeat the request but MAY
   also use ETM-rate as an estimate of the amount of traffic to be
   terminated in place of the quantity


      PCN-sent-rate - SAR


   specified in Section 3.3.2.  Because this will over-estimate the
   amount of traffic to be terminated due to dropping of PCN-packets by
   interior nodes, the Decision Point SHOULD use multiple rounds of
   termination under these circumstances.  If the second request to the
   PCN-ingress-node also fails, the Decision Point SHOULD notify
   management.


      The use of T-crit is an approximation.  A more precise limit would
      be of the order of two round-trip times, plus an allowance for
      processing at each end, plus an allowance for variance in these
      values.


   See Section 3.5 for suggested values of the configurable durations
   T-crit and T-maxsuppress.


3.4.  Behaviour of the Ingress Node


   The PCN-ingress-node MUST provide the estimated current rate of PCN-
   traffic received at that node and destined for a given ingress-
   egress-aggregate in octets per second (the PCN-sent-rate) when the





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   Decision Point requests it.  The way this rate estimate is derived is
   a matter of implementation.


      For example, the rate that the PCN-ingress-node supplies MAY be
      based on a quick sample taken at the time the information is
      required.


3.5.  Summary of Timers and Associated Configurable Durations


   Here is a summary of the timers used in the procedures just
   described:


   t-meas


         Where used: PCN-egress-node.


         Used in procedure: data collection (Section 3.2.1).


         Incidence: one per ingress-egress-aggregate.


         Reset: immediately on expiry.


         Expiry: when it reaches the configurable duration T-meas.


         Action on expiry: calculate NM-rate, [CL-specific] ThM-rate,
         and ETM-rate and proceed to the applicable reporting procedure
         (Section 3.2.2 or Section 3.2.3).


   t-maxsuppress


         Where used: PCN-egress-node.


         Used in procedure: report suppression (Section 3.2.3).


         Incidence: one per ingress-egress-aggregate.


         Reset: when the next report is sent, either after expiry or
         because the CLE has exceeded the reporting threshold.


         Expiry: when it reaches the configurable duration
         T-maxsuppress.


         Action on expiry: send a report to the Decision Point the next
         time the reporting procedure (Section 3.2.3) is invoked,
         regardless of the value of CLE.









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   t-recvFail


         Where used: Decision Point.


         Used in procedure: failure detection (Section 3.3.3).


         Incidence: one per ingress-egress-aggregate.


         Reset: when a report is received for the ingress-egress-
         aggregate.


         Expiry: when it reaches the calculated duration T-fail.  As
         described in Section 3.3.3, T-fail is equal either to the
         configured duration T-crit or to the calculated value 3 *
         T-maxsuppress, where T-maxsuppress is a configured duration.


         Action on expiry: notify management, and possibly other
         actions.


   t-sndFail


         Where used: centralized Decision Point.


         Used in procedure: failure detection (Section 3.3.3).


         Incidence: only as required, one per outstanding request to a
         PCN-ingress-node.


         Started: when a request for the value of PCN-sent-traffic for a
         given ingress-egress-aggregate is sent to the PCN-ingress-node.


         Terminated without action: when a response is received before
         expiry.


         Expiry: when it reaches the configured duration T-crit.


         Action on expiry: repeat the request, but use an approximation
         for the estimate of amount of traffic to terminate.  After two
         failures, notify management and stop repeating the request.


3.5.1.  Recommended Values For the Configurable Durations


   The timers just described depend on three configurable durations,
   T-meas, T-maxsuppress, and T-crit.  The recommendations given below
   for the values of these durations are all related to the intended PCN
   reaction time of 1 to 3 seconds.  However, they are based on
   judgement rather than operational experience or mathematical
   derivation.





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   The value of T-meas is RECOMMENDED to be of the order of 100 to 500
   ms to provide a reasonable tradeoff between demands on network
   resources (PCN-egress-node and Decision Point processing, network
   bandwidth) and the time taken to react to impending congestion.


   The value of T-maxsuppress is RECOMMENDED to be on the order of 3 to
   6 seconds, for similar reasons to those for the choice of T-meas.


   The value of T-crit SHOULD NOT be less than 3 * T-meas.  Otherwise it
   could cause too many management notifications due to transient
   conditions in the PCN-egress-node or along the signalling path.  A
   reasonable upper bound on T-crit is in the order of 3 seconds.



4.  Specification of Diffserv Per-Domain Behaviour


   This section provides the specification required by [RFC3086] for a
   per-domain behaviour.


4.1.  Applicability


   This section quotes [RFC5559].


   The PCN CL boundary node behaviour specified in this document is
   applicable to inelastic traffic (particularly video and voice) where
   quality of service for admitted flows is protected primarily by
   admission control at the ingress to the domain.


   In exceptional circumstances (e.g., due to rerouting as a result of
   network failures) already-admitted flows MAY be terminated to protect
   the quality of service of the remaining flows.  [CL-specific] The
   performance results in, e.g., [MeLe10], indicate that the CL boundary
   node behaviour provides better service outcomes under such
   circumstances than the SM boundary node behaviour described in
   [RFCyyyy], because CL is less likely to terminate PCN-flows
   unnecessarily.


   [RFC EDITOR'S NOTE: please replace RFCyyyy above by the reference to
   the published version of draft-ietf-pcn-sm-edge-behaviour.]


4.2.  Technical Specification


4.2.1.  Classification and Traffic Conditioning


   This section paraphrases the applicable portions of Sections 3.6 and
   4.2 of [RFC5559].


   Packets at the ingress to the domain are classified as either PCN or





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   non-PCN.  Non-PCN packets MAY share the network with PCN packets
   within the domain.  Because the encoding specified in [RFC5696] and
   used in this document requires the use of the ECN fields, PCN-
   ingress-nodes MUST prevent ECN-capable traffic that uses the same
   DSCP as PCN from entering the PCN-domain directly.  The PCN-ingress-
   node can accomplish this in three ways.  The choice between these
   depends on local policy.


   o  ECN-capable traffic MAY be dropped.  This policy is NOT
      RECOMMENDED, since it prevents the proper operation of end-to-end
      ECN as a means of controlling congestion.


   o  ECN-capable traffic MAY be assigned a different DSCP from PCN
      traffic.  This could mean that it is relegated to a lower-priority
      behaviour aggregate.


   o  ECN-capable traffic MAY be tunneled across the PCN-domain.  If
      this is done, the PCN-ingress-node MUST mark packets as either
      not-PCN or PCN-not-marked only after the encapsulation of the
      packet, including any initial setting of the ECN field, has been
      completed.


   PCN packets are further classified as belonging or not belonging to
   an admitted flow.  PCN packets not belonging to an admitted flow are
   dropped.  Packets belonging to an admitted flow are policed to ensure
   that they adhere to the rate or flowspec that was negotiated during
   flow admission.


4.2.2.  PHB Configuration


   The PCN CL boundary node behaviour is a metering and marking
   behaviour rather than a scheduling behaviour.  As a result, while the
   encoding uses a single DSCP value, that value MAY vary from one
   deployment to another.  The PCN working group suggests using
   admission control for the following service classes (defined in
   [RFC4594]):


   o  Telephony (EF)


   o  Real-time interactive (CS4)


   o  Broadcast Video (CS3)


   o  Multimedia Conferencing (AF4)


   For a fuller discussion, see Section A.1 of Appendix A of [RFC5696].








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4.3.  Attributes


   The purpose of this per-domain behaviour is to achieve low loss and
   jitter for the target class of traffic.  The design requirement for
   PCN was that recovery from overloads through the use of flow
   termination SHOULD happen within 1-3 seconds.  PCN probably performs
   better than that.


4.4.  Parameters


   The set of parameters that needs to be configured at each PCN-node
   and at the Decision Point is described in Section 5.1.


4.5.  Assumptions


   It is assumed that a specific portion of link capacity has been
   reserved for PCN-traffic.


4.6.  Example Uses


   The PCN CL behaviour MAY be used to carry real-time traffic,
   particularly voice and video.


4.7.  Environmental Concerns


   The PCN CL per-domain behaviour can interfere with the use of end-to-
   end ECN due to reuse of ECN bits for PCN marking.  See Appendix B of
   [RFC5696] for details.


4.8.  Security Considerations


   Please see the security considerations in [RFC5559] as well as those
   in [RFC2474] and [RFC2475].



5.  Operational and Management Considerations


5.1.  Deployment of the CL Edge Behaviour


   Deployment of the PCN Controlled Load edge behaviour requires the
   following steps:


   o  selection of deployment options and global parameter values;


   o  derivation of per-node and per-link information;


   o  installation, but not activation, of parameters and policies at
      all of the nodes in the PCN domain;





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   o  activation and verification of all behaviours.


5.1.1.  Selection of Deployment Options and Global Parameters


   The first set of decisions affects the operation of the network as a
   whole.  To begin with, the operator needs to make basic design
   decisions such as whether the Decision Point is centralized or
   collocated with the PCN-ingress-nodes, and whether per-flow and
   aggregate resource signalling as described in [I-D.tsvwg-rsvp-pcn] is
   deployed in the network.  After that, the operator needs to decide:


   o  whether PCN packets will be forwarded unencapsulated or in tunnels
      between the PCN-ingress-node and the PCN-egress-node.
      Encapsulation preserves incoming ECN settings and simplifies the
      PCN-egress-node's job when it comes to relating incoming packets
      to specific ingress-egress-aggregates, but lowers the path MTU and
      imposes the extra labour of encapsulation/decapsulation on the
      PCN-edge-nodes.


   o  which service classes will be subject to PCN control and what
      Diffserv code point (DSCP) will be used for each.  (See [RFC5696]
      Appendix A.1 for advice on this topic.)


   o  the markings to be used at all nodes in the PCN domain to indicate
      Not-Marked (NM), [CL-specific] Threshold-Marked (ThM), and Excess-
      Traffic-Marked (ETM) PCN packets;


   o  The marking rules for re-marking PCN-traffic leaving the PCN
      domain;


   o  whether PCN-based flow admission is enabled;


   o  whether PCN-based flow termination is enabled.


   The following parameters affect the operation of PCN itself.  The
   operator needs to choose:


   o  the value of CLE-limit if PCN-based flow admission is enabled.
      [CL-specific] The operation of flow admission is not very
      sensitive to the value of the CLE-limit in practice, because when
      threshold-marking occurs it tends to persist long enough that
      threshold-marked traffic becomes a large proportion of the
      received traffic in a given interval.


   o  the value of the collection interval T-meas.  For a recommended
      range of values see Section 3.5.1 above.








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   o  whether report suppression is to be enabled at the PCN-egress-
      nodes and if so, the values of CLE-reporting-threshold and
      T-maxsuppress.  It is reasonable to leave CLE-reporting-threshold
      at its default value (zero, as specified in Section 3.2.3).  For a
      recommended range of values of T-maxsuppress see Section 3.5.1
      above.


   o  the value of the duration T-crit, which the Decision Point uses in
      deciding whether communications with a given PCN-edge-node have
      failed.  For a recommended range of values of T-crit see
      Section 3.5.1 above.


   o  [CL-specific] Activation/deactivation of recording of individual
      flow identifiers when excess-traffic-marked PCN-traffic is
      observed.  Reporting these identifiers has value only if PCN-based
      flow termination is activated and Equal Cost Multi-Path (ECMP)
      routing is enabled in the PCN-domain.


5.1.2.  Specification of Node- and Link-Specific Parameters


   Each PCN-ingress-node needs filters to classify incoming PCN packets
   according to ingress-egress-aggregate, both to satisfy Decision Point
   requests for sent traffic rates and, if applicable, to support
   encapsulation.  If PCN packets are being tunneled to the PCN-egress-
   nodes (encapsulation), the PCN-ingress-node also needs the address of
   the PCN-egress-node for each ingress-egress-aggregate.


   Each PCN-egress-node needs filters to classify incoming PCN packets
   by ingress-egress-aggregate, in order to gather measurements on a
   per-aggregate basis.  The PCN-egress-node also needs to know the
   address of the Decision Point to which it sends reports for each
   ingress-egress-aggregate.


   If [I-D.tsvwg-rsvp-pcn] is deployed and the Decision Points are
   collocated with the PCN-ingress-nodes, this information can be built
   up dynamically from the contents of the end-to-end RSVP signalling
   and does not have to be pre-configured.  Otherwise the filters have
   to be derived from the routing tables in use in the domain, and the
   address of the peer at the other end of each ingress-egress-aggregate
   has to be tabulated for each PCN-edge-node.


   A centralized Decision Point needs to have the address of the PCN-
   ingress-node corresponding to each ingress-egress-aggregate.
   Security considerations require that information also be prepared for
   a centralized Decision Point and each PCN-edge-node to allow them to
   authenticate each other.


   Turning to link-specific parameters, the operator needs to derive





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   values for the PCN-supportable-rate and [CL-specific] PCN-admissible-
   rate on each link in the network.  The first two paragraphs of
   Section 5.2.2 of [RFC5559] discuss how these values may be derived.
   (For "PCN-excess-rate" in [RFC5559] read "PCN-supportable-rate", and
   [CL-specific] for "PCN-threshold-rate" read "PCN-admissible-rate".)


5.1.3.  Installation of Parameters and Policies


   As discussed in the previous two sections, every PCN node needs to be
   provisioned with a number of parameters and policies relating to its
   behaviour in processing incoming packets.  The Diffserv MIB [RFC3289]
   can be useful for this purpose, although it needs to be extended in
   some cases.  This MIB covers packet classification, metering,
   counting, policing and dropping, and marking.  The required
   extensions specifically include objects for re-marking the ECN field
   at the PCN-ingress-node and an extension to the classifiers to
   include the ECN field at PCN-interior and PCN-egress-nodes.  In
   addition, the MIB has to be extended to include a potential
   encapsulation action following re-classification by ingress-egress-
   aggregate.  Finally, new metering algorithms may need to be defined
   at the PCN-interior-nodes to handle threshold-marking and packet-
   size-independent excess-traffic-marking.


   Values for the PCN-supportable-rate and [CL-specific] PCN-admissible-
   rate on each link on a node appear as metering parameters.  Operators
   should take note of the need to deploy meters of a given type
   (threshold or excess-traffic) either on the ingress side or the
   egress of each interior link, but not both (Appendix B.2 of
   [RFC5670].


   The following additional information has to be configured by other
   means (e.g., additional MIBs, NETCONF models).


   At the PCN-egress-node:


   o  the measurement interval T-meas (units of ms, range 50 to 1000);


   o  whether specific flow identifiers must be captured when excess-
      traffic-marked packets are observed;


   o  whether report suppression is to be applied;


   o  if so, the interval T-maxsuppress (units of 100 ms, range 1 to
      100) and the CLE-reporting-threshold (units of tenths of one
      percent, range 0 to 1000, default value 0);


   o  the address of the PCN-ingress-node for each ingress-egress-
      aggregate, if the Decision Point is collocated with the PCN-





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      ingress-node and [I-D.tsvwg-rsvp-pcn] is not deployed.


   o  the address of the centralized Decision Point to which it sends
      its reports, if there is one.


   At the Decision Point:


   o  whether PCN-based flow admission is enabled;


   o  whether PCN-based flow termination is enabled.


   o  the value of CLE-limit (units of tenths of one percent, range 0 to
      1000);


   o  the value of the interval T-crit (units of 100 ms, range 1 to
      100);


   o  whether report suppression is to be applied;


   o  if so, the interval T-maxsuppress (units of 100 ms, range 1 to
      100) and the CLE-reporting-threshold (units of tenths of one
      percent, range 0 to 1000, default value 0).  These MUST be the
      same values that are provisioned in the PCN-egress-nodes;


   o  if the Decision Point is centralized, the address of the PCN-
      ingress-node (and any other information needed to establish a
      security association) for each ingress-egress-aggregate.


   Depending on the testing strategy, it may be necessary to install the
   new configuration data in stages.  This is discussed further below.


5.1.4.  Activation and Verification of All Behaviours


   It is certainly not within the scope of this document to advise on
   testing strategy, which operators undoubtedly have well in hand.
   Quite possibly an operator will prefer an incremental approach to
   activation and testing.  Implementing the PCN marking scheme at PCN-
   ingress-nodes, corresponding scheduling behaviour in downstream
   nodes, and re-marking at the PCN-egress-nodes is a large enough step
   in itself to require thorough testing before going further.


   Testing will probably involve the injection of packets at individual
   nodes and tracking of how the node processes them.  This work can
   make use of the counter capabilities included in the Diffserv MIB.
   The application of these capabilities to the management of PCN is
   discussed in the next section.








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5.2.  Management Considerations


   This section focuses on the use of event logging and the use of
   counters supported by the Diffserv MIB [RFC3289] for the various
   monitoring tasks involved in management of a PCN network.


5.2.1.  Event Logging In the PCN Domain


   It is anticipated that event logging using SYSLOG [RFC5424] will be
   needed for fault management and potentially for capacity management.
   Implementations MUST be capable of generating logs for the following
   events:


   o  detection of loss of contact between a Decision Point and a PCN-
      edge-node, as described in Section 3.3.3;


   o  successful receipt of a report from a PCN-egress-node, following
      detection of loss of contact with that node;


   o  flow termination events.


   All of these logs are generated by the Decision Point.  There is a
   strong likelihood in the first and third cases that the events are
   correlated with network failures at a lower level.  This has
   implications for how often specific event types should be reported,
   so as not to contribute unnecessarily to log buffer overflow.
   Recommendations on this topic follow for each event report type.


5.2.1.1.  Logging Loss and Restoration of Contact


   Section 3.3.3 describes the circumstances under which the Decision
   Point may determine that it has lost contact, either with a PCN-
   ingress-node or a PCN-egress-node, due to failure to receive an
   expected report.  Loss of contact with a PCN-ingress-node is a case
   primarily applicable when the Decision Point is in a separate node.
   However, implementations MAY implement logging in the collocated case
   if the implementation is such that non-response to a request from the
   Decision Point function can occasionally occur due to processor load
   or other reasons.


   The log reporting the loss of contact with a PCN-egress-node MUST
   include the following content:


   o  The HOSTNAME field MUST identify the Decision Point issuing the
      log.


   o  A STRUCTURED-DATA element MUST be present, containing parameters
      identifying the node for which an expected report has not been





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      received and the type of report lost (ingress or egress).  It is
      RECOMMENDED that the SD-ID for the STRUCTURED-DATA element have
      the form "PCNnode@nnn" (without the quotes, where nnn is the
      operator enterprise number as described in Section 6.3.2 of
      [RFC5424]).  The node identifier PARAM-NAME is RECOMMENDED to be
      "ID" (without the quotes).  The identifier itself is subject to
      the preferences expressed in Section 6.2.4 of [RFC5424] for the
      HOSTNAME field.  The report type PARAM-NAME is RECOMMENDED to be
      "RTyp" (without the quotes).  The PARAM-VALUE for the RTyp field
      MUST be either "ingr" or "egr".


   The following values are also RECOMMENDED for the indicated fields in
   this log, subject to local practice:


   o  PRI initially set to 115, representing a Facility value of "log
      alert" and a Severity level of "Error Condition".  Note that loss
      of contact with a PCN-egress-node implies that no new flows will
      be admitted to one or more ingress-egress-aggregates until contact
      is restored.  The reason a higher severity level (lower value) is
      not proposed for the initial log is because any corrective action
      would probably be based on alerts at a lower subsystem level.


   o  APPNAME set to "PCN" (without the quotes).


   o  MSGID set to "LOST" (without the quotes).


   If contact is not regained with a PCN-egress-node in a reasonable
   period of time (say, one minute), the log SHOULD be repeated, this
   time with a PRI value of 113, implying a Severity value of "Alert:
   action must be taken immediately".  The reasoning is that by this
   time, any more general conditions should have been cleared, and the
   problem lies specifically with the PCN-egress-node concerned and the
   PCN application in particular.


   Whenever a loss-of-contact log is generated for a PCN-egress-node, a
   log indicating recovery SHOULD be generated when the Decision Point
   next receives a report from the node concerned.  The log SHOULD have
   the same content as just described for the loss-of-contact log, with
   the following differences:


   o  PRI changes to 117, indicating a Severity of "Notice: normal but
      significant condition".


   o  MSGID changes to "RECVD" (without the quotes).











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5.2.1.2.  Logging Flow Termination Events


   Section 3.3.2 describes the process whereby the Decision Point
   decides that flow termination is required for a given ingress-egress-
   aggregate, calculates how much flow to terminate, and selects flows
   for termination.  This section describes a log that SHOULD be
   generated each time such an event occurs.  (In the case where
   termination occurs in multiple rounds, one log SHOULD be generated
   per round.)  The log may be useful in fault management, to indicate
   the service impact of a fault occuring in a lower-level subsystem.
   In the absence of network failures, it may also be used as an
   indication of an urgent need to review capacity utilization along the
   path of the ingress-egress-aggregate concerned.


   The log reporting a flow termination event MUST include the following
   content:


   o  The HOSTNAME field MUST identify the Decision Point issuing the
      log.


   o  A STRUCTURED-DATA element MUST be present, containing parameters
      identifying the ingress and egress nodes for the ingress-egress-
      aggregate concerned, indicating the total amount of flow being
      terminated, and giving the number of flows terminated to achieve
      that objective. [***PTT***: identifying the flows could be helpful
      for complaint follow-up, but I'm worried about the size of the
      resulting log.]


      It is RECOMMENDED that the SD-ID for the STRUCTURED-DATA element
      have the form: "PCNterm@nnn" (without the quotes, where nnn is the
      operator enterprise number as described in Section 6.3.2 of
      [RFC5424]).  The parameter identifying the ingress node for the
      ingress-egress-aggregate is RECOMMENDED to have PARAM-NAME
      "IngrID" (without the quotes).  This parameter MAY be omitted if
      the Decision Point is collocated with that PCN-ingress-node.  The
      parameter identifying the egress node for the ingress-egress-
      aggregate is RECOMMENDED to have PARAM-NAME "EgrID" (without the
      quotes).  Both identifiers are subject to the preferences
      expressed in Section 6.2.4 of [RFC5424] for the HOSTNAME field.


      The parameter giving the total amount of flow being terminated is
      RECOMMENDED to have PARAM-NAME "TermRate" (without the quotes).
      The PARAM-VALUE MUST be the target rate as calculated according to
      the procedures of Section 3.3.2, as an integer value in millions
      of octets per second.  The parameter giving the number of flows
      selected for termination is RECOMMENDED to have PARAM-NAME "FCnt"
      (without the quotes).  The PARAM-VALUE for this parameter MUST be
      an integer, the number of flows selected.





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   The following values are also RECOMMENDED for the indicated fields in
   this log, subject to local practice:


   o  PRI initially set to 116, representing a Facility value of "log
      alert" and a Severity level of "Warning: warning conditions".


   o  APPNAME set to "PCN" (without the quotes).


   o  MSGID set to "TERM" (without the quotes).


5.2.2.  Provision and Use of Counters


   The Diffserv MIB [RFC3289] allows for the provision of counters along
   the various possible processing paths associated with an interface
   and flow direction.  It is RECOMMENDED that the PCN-nodes be
   instrumented as described below.  It is assumed that the cumulative
   counts so obtained will be collected periodically for use in
   debugging, fault management, and capacity management.


   PCN-ingress-nodes SHOULD provide the following counts for each
   ingress-egress-aggregate.  Since the Diffserv MIB installs counters
   by interface and direction, aggregation of counts over multiple
   interfaces may be necessary to obtain total counts by ingress-egress-
   aggregate.  It is expected that such aggregation will be performed by
   a central system rather than at the PCN-ingress-node.


   o  total PCN packets and octets received for that ingress-egress-
      aggregate but dropped;


   o  total PCN packets and octets admitted to that aggregate.


   PCN-interior-nodes SHOULD provide the following counts for each
   interface, noting that a given packet MUST NOT be counted more than
   once as it passes through the node:


   o  total PCN packets and octets dropped;


   o  total PCN packets and octets forwarded without re-marking;


   o  [CL-specific] total PCN packets and octets re-marked to Threshold-
      Marked;


   o  total PCN packets and octets re-marked to Excess-Traffic-Marked.


   PCN-egress-nodes SHOULD provide the following counts for each
   ingress-egress-aggregate.  As with the PCN-ingress-node, so with the
   PCN-egress-node it is expected that any necessary aggregation over
   multiple interfaces will be done by a central system.





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   o  total Not-Marked PCN packets and octets received;


   o  [CL-specific] total Threshold-Marked PCN packets and octets
      received;


   o  total Excess-Traffic-Marked PCN packets and octets received.


   The following continuously cumulative counters SHOULD be provided as
   indicated, but require new MIBs to be defined.  If the Decision Point
   is not collocated with the PCN-ingress-node, the latter SHOULD
   provide a count of the number of requests for PCN-sent-rate received
   from the Decision Point and the number of responses returned to the
   Decision Point.  The PCN-egress-node SHOULD provide a count of the
   number of reports sent to each Decision Point.  Each Decision Point
   SHOULD provide the following:


   o  total number of requests for PCN-sent-rate sent to each PCN-
      ingress-node with which it is not collocated;


   o  total number of reports received from each PCN-egress-node;


   o  total number of loss-of-contact events detected for each PCN-
      boundary-node;


   o  total cumulative duration of "block" state in hundreds of
      milliseconds for each ingress-egress-aggregate;


   o  total number of rounds of flow termination exercised for each
      ingress-egress-aggregate.



6.  Security Considerations


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



7.  IANA Considerations


   This memo includes no request to IANA.



8.  Acknowledgements


   The content of this memo bears a family resemblance to
   [ID.briscoe-CL].  The authors of that document were Bob Briscoe,
   Philip Eardley, and Dave Songhurst of BT, Anna Charny and Francois Le
   Faucheur of Cisco, Jozef Babiarz, Kwok Ho Chan, and Stephen Dudley of





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   Nortel, Giorgios Karagiannis of U. Twente and Ericsson, and Attila
   Bader and Lars Westberg of Ericsson.


   Ruediger Geib, Philip Eardley, and Bob Briscoe have helped to shape
   the present document with their comments.  Toby Moncaster gave a
   careful review to get it into shape for Working Group Last Call.


   Amongst the authors, Michael Menth deserves special mention for his
   constant and careful attention to both the technical content of this
   document and the manner in which it was expressed.


   Finally, David Harrington's careful AD review resulted not only in
   necessary changes throughout the document, but also the addition of
   the operations and management considerations (Section 5).



9.  References


9.1.  Normative References


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


   [RFC3086]  Nichols, K. and B. Carpenter, "Definition of
              Differentiated Services Per Domain Behaviors and Rules for
              their Specification", RFC 3086, April 2001.


   [RFC3289]  Baker, F., Chan, K., and A. Smith, "Management Information
              Base for the Differentiated Services Architecture",
              RFC 3289, May 2002.


   [RFC5424]  Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009.


   [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.






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


9.2.  Informative References


   [I-D.tsvwg-rsvp-pcn]
              Karagiannis, G. and A. Bhargava, "Generic Aggregation of
              Resource ReSerVation Protocol (RSVP) for IPv4 And IPv6
              Reservations over PCN domains", July 2011.


   [ID.briscoe-CL]
              Briscoe, B., "An edge-to-edge Deployment Model for Pre-
              Congestion Notification: Admission Control over a DiffServ
              Region (expired Internet Draft)", 2006.


   [IEEE-Satoh]
              Satoh, D. and H. Ueno, ""Cause and Countermeasure of
              Overtermination for PCN-Based Flow Termination",
              Proceedings of IEEE Symposium on Computers and
              Communications (ISCC '10), pp. 155-161, Riccione, Italy",
              June 2010.


   [MeLe10]   Menth, M. and F. Lehrieder, "PCN-Based Measured Rate
              Termination", Computer Networks Journal (Elsevier) vol.
              54, no. 13, pages 2099 - 2116, September 2010.


   [RFC4594]  Babiarz, J., Chan, K., and F. Baker, "Configuration
              Guidelines for DiffServ Service Classes", RFC 4594,
              August 2006.


   [RFC6040]  Briscoe, B., "Tunnelling of Explicit Congestion
              Notification", RFC 6040, November 2010.


   [RFCyyyy]  Charny, A., Zhang, J., Karagiannis, G., Menth, M., and T.
              Taylor, "PCN Boundary Node Behaviour for the Single
              Marking (SM) Mode of Operation (Work in progress)",
              December 2010.




















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Authors' Addresses


   Anna Charny
   Cisco Systems
   300 Apollo Drive
   Chelmsford, MA  01824
   USA


   Email: acharny@cisco.com



   Fortune Huang
   Huawei Technologies
   Section F, Huawei Industrial Base,
   Bantian Longgang, Shenzhen  518129
   P.R. China


   Phone: +86 15013838060
   Email: fqhuang@huawei.com



   Georgios Karagiannis
   U. Twente



   Phone:
   Email: karagian@cs.utwente.nl



   Michael Menth
   University of Tuebingen
   Sand 13
   Tuebingen  D-72076
   Germany


   Phone: +49-7071-2970505
   Email: menth@informatik.uni-tuebingen.de



   Tom Taylor (editor)
   Huawei Technologies
   1852 Lorraine Ave
   Ottawa, Ontario  K1H 6Z8
   Canada


   Phone: +1 613 680 2675
   Email: tom111.taylor@bell.net






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