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rfc:rfc6662

Internet Engineering Task Force (IETF) A. Charny Request for Comments: 6662 Category: Experimental J. Zhang ISSN: 2070-1721 Cisco Systems

                                                        G. Karagiannis
                                                  University of Twente
                                                              M. Menth
                                               University of Tuebingen
                                                        T. Taylor, Ed.
                                                   Huawei Technologies
                                                             July 2012
      Pre-Congestion Notification (PCN) Boundary-Node Behavior
           for the Single Marking (SM) Mode of Operation

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 behaviors
 for a PCN-domain.  The behavior described here is that for a form of
 measurement-based load control using two PCN marking states: not-
 marked and excess-traffic-marked.  This behavior is known informally
 as the Single Marking (SM) PCN-boundary-node behavior.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for examination, experimental implementation, and
 evaluation.
 This document defines an Experimental Protocol for the Internet
 community.  This document is a product of the Internet Engineering
 Task Force (IETF).  It represents the consensus of the IETF
 community.  It has received public review and has been approved for
 publication by the Internet Engineering Steering Group (IESG).  Not
 all documents approved by the IESG are a candidate for any level of
 Internet Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6662.

Charny, et al. Experimental [Page 1] RFC 6662 PCN SM Boundary-Node Behavior July 2012

Copyright Notice

 Copyright (c) 2012 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 Simplified BSD License.

Charny, et al. Experimental [Page 2] RFC 6662 PCN SM Boundary-Node Behavior July 2012

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
 2.  [SM-Specific] Assumed Core Network Behavior for SM . . . . . .  8
 3.  Node Behaviors . . . . . . . . . . . . . . . . . . . . . . . .  9
   3.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  9
   3.2.  Behavior of the PCN-Egress-Node  . . . . . . . . . . . . .  9
     3.2.1.  Data Collection  . . . . . . . . . . . . . . . . . . .  9
     3.2.2.  Reporting the PCN Data . . . . . . . . . . . . . . . . 10
     3.2.3.  Optional Report Suppression  . . . . . . . . . . . . . 10
   3.3.  Behavior at the Decision Point . . . . . . . . . . . . . . 11
     3.3.1.  Flow Admission . . . . . . . . . . . . . . . . . . . . 11
     3.3.2.  Flow Termination . . . . . . . . . . . . . . . . . . . 12
     3.3.3.  Decision Point Action for Missing
             PCN-Boundary-Node Reports  . . . . . . . . . . . . . . 14
   3.4.  Behavior of the Ingress Node . . . . . . . . . . . . . . . 15
   3.5.  Summary of Timers and Associated Configurable Durations  . 15
     3.5.1.  Recommended Values for the Configurable Durations  . . 17
 4.  Specification of Diffserv Per-Domain Behavior  . . . . . . . . 17
   4.1.  Applicability  . . . . . . . . . . . . . . . . . . . . . . 17
   4.2.  Technical Specification  . . . . . . . . . . . . . . . . . 18
     4.2.1.  Classification and Traffic Conditioning  . . . . . . . 18
     4.2.2.  PHB Configuration  . . . . . . . . . . . . . . . . . . 18
   4.3.  Attributes . . . . . . . . . . . . . . . . . . . . . . . . 18
   4.4.  Parameters . . . . . . . . . . . . . . . . . . . . . . . . 18
   4.5.  Assumptions  . . . . . . . . . . . . . . . . . . . . . . . 19
   4.6.  Example Uses . . . . . . . . . . . . . . . . . . . . . . . 19
   4.7.  Environmental Concerns . . . . . . . . . . . . . . . . . . 19
   4.8.  Security Considerations  . . . . . . . . . . . . . . . . . 19
 5.  Operational and Management Considerations  . . . . . . . . . . 19
   5.1.  Deployment of the SM Edge Behavior . . . . . . . . . . . . 19
     5.1.1.  Selection of Deployment Options and Global
             Parameters . . . . . . . . . . . . . . . . . . . . . . 19
     5.1.2.  Specification of Node- and Link-Specific Parameters  . 21
     5.1.3.  Installation of Parameters and Policies  . . . . . . . 22
     5.1.4.  Activation and Verification of All Behaviors . . . . . 23
   5.2.  Management Considerations  . . . . . . . . . . . . . . . . 24
     5.2.1.  Event Logging in the PCN-Domain  . . . . . . . . . . . 24
       5.2.1.1.  Logging Loss and Restoration of Contact  . . . . . 24
       5.2.1.2.  Logging Flow Termination Events  . . . . . . . . . 26
     5.2.2.  Provision and Use of Counters  . . . . . . . . . . . . 27
 6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 28
 7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28
 8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
   8.1.  Normative References . . . . . . . . . . . . . . . . . . . 29
   8.2.  Informative References . . . . . . . . . . . . . . . . . . 30

Charny, et al. Experimental [Page 3] RFC 6662 PCN SM Boundary-Node Behavior July 2012

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].
 This document describes an experimental edge-node behavior to
 implement PCN in a network.  The experiment may be run in a network
 in which a substantial proportion of the traffic carried is in the
 form of inelastic flows and where admission control of micro-flows is
 applied at the edge.  For the effects of PCN to be observable, the
 committed bandwidth (i.e., level of non-best-effort traffic) on at
 least some links of the network should be near or at link capacity.
 The amount of effort required to prepare the network for the
 experiment (see Section 5.1) may constrain the size of network to
 which it is applied.  The purposes of the experiment are:
 o  to validate the specification of the SM edge behavior;
 o  to evaluate the effectiveness of the SM edge behavior in
    preserving quality of service for admitted flows; and
 o  to evaluate PCN's potential for reducing the amount of capital and
    operational costs in comparison to alternative methods of assuring
    quality of service.
 For the first two objectives, the experiment should run long enough
 for the network to experience sharp peaks of traffic in at least some
 directions.  It would also be desirable to observe PCN performance in
 the face of failures in the network.  A period on the order of a
 month or two in busy season may be enough.  The third objective is
 more difficult and could require observation over a period long
 enough for traffic demand to grow to the point where additional
 capacity must be provisioned at some points in the network.

Charny, et al. Experimental [Page 4] RFC 6662 PCN SM Boundary-Node Behavior July 2012

 Section 3 of this document specifies a detailed set of algorithms and
 procedures used to implement the PCN mechanisms for the SM mode of
 operation.  Since the algorithms depend on specific metering and
 marking behavior at the interior nodes, it is also necessary to
 specify the assumptions made about PCN-interior-node behavior
 (Section 2).  Finally, because PCN uses Diffserv codepoint (DSCP)
 values to carry its markings, a specification of PCN-boundary-node
 behavior must include the per-domain behavior (PDB) template
 specified in [RFC3086], filled out with the appropriate content
 (Section 4).
 Note that the terms "block" or "terminate" actually translate to one
 or more of several possible courses of action, as discussed in
 Section 3.6 of [RFC5559].  The choice of which action to take for
 blocked or terminated flows is a matter of local policy.
 A companion document [RFC6661] specifies the Controlled Load (CL)
 PCN-boundary-node behavior.  This document and [RFC6661] 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 SM PCN-boundary-node
 behavior is preceded by the phrase "[SM-specific]".  A similar
 distinction for CL-specific text is made in [RFC6661].

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]:
 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
 o  PCN-excess-rate

Charny, et al. Experimental [Page 5] RFC 6662 PCN SM Boundary-Node Behavior July 2012

 o  PCN-admissible-rate
 o  PCN-supportable-rate
 o  PCN-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 behavior
    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 term from [RFC5670]:
 o  excess-traffic-meter.
 To complete the list of borrowed terms, this document reuses the
 following terms and abbreviations defined in Section 2 of [RFC6660]:
 o  not-PCN codepoint;
 o  not-marked (NM) codepoint;
 o  excess-traffic-marked (ETM) 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.

Charny, et al. Experimental [Page 6] RFC 6662 PCN SM Boundary-Node Behavior July 2012

 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 statistics about PCN-
    packet marking.  The Decision Point decides to admit or block new
    flows offered to the aggregate based on the current value of the
    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.

Charny, et al. Experimental [Page 7] RFC 6662 PCN SM Boundary-Node Behavior July 2012

 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 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.
 T_crit
    A configurable interval used in the calculation of T_fail.  For
    further details, see Section 3.3.3.

2. [SM-Specific] Assumed Core Network Behavior for SM

 This section describes the assumed behavior for PCN-interior-nodes in
 the PCN-domain.  The SM mode of operation assumes that:
 o  PCN-interior-nodes perform excess-traffic-marking of PCN-packets
    according to the rules specified in [RFC5670].
 o  For IP transport, excess-traffic-marking of PCN-packets uses the
    excess-traffic-marked (ETM) codepoint defined in [RFC6660]; for
    MPLS transport, an equivalent marking is used as discussed in
    Appendix C of [RFC6660].
 o  On each link, the reference rate for the excess-traffic-meter is
    configured to be equal to the PCN-admissible-rate for the link.
 o  The set of valid codepoint transitions is as shown in Sections
    5.2.1 and 5.2.3.1 of [RFC6660].

Charny, et al. Experimental [Page 8] RFC 6662 PCN SM Boundary-Node Behavior July 2012

3. Node Behaviors

3.1. Overview

 This section describes the behavior 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 and excess-
 traffic-marked PCN-traffic for each ingress-egress-aggregate and
 reports them to the Decision Point.  For a detailed description, see
 Section 3.2.
 The PCN-ingress-node enforces flow admission and termination
 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.
 Specification of a signaling protocol to report rates to the Decision
 Point is out of scope of this document.  If the PCN-ingress-node is
 chosen as the Decision Point, [RSVP-PCN] specifies an appropriate
 signaling protocol.
 Section 5.1.2 describes how to derive the filters by means of which
 PCN-ingress-nodes and PCN-egress-nodes are able to classify incoming
 packets into ingress-egress-aggregates.

3.2. Behavior of the PCN-Egress-Node

3.2.1. Data Collection

 The PCN-egress-node needs to 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.  For further information,
 see Section 3.5.
 o  NM-rate: octets per second of PCN-traffic in PCN-packets that are
    not-marked (i.e., marked with the NM codepoint);

Charny, et al. Experimental [Page 9] RFC 6662 PCN SM Boundary-Node Behavior July 2012

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

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 and ETM-rate to the Decision Point each time that it calculates
 them.

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 and ETM-rate, the PCN-egress-
     node MUST calculate the congestion level estimate (CLE) for each
     measurement interval.  The CLE is computed as:
        [SM-specific]
        CLE = ETM-rate / (NM-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.

Charny, et al. Experimental [Page 10] RFC 6662 PCN SM Boundary-Node Behavior July 2012

        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 the 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, ETM-rate, and CLE
 that were calculated for the most recent measurement interval.
 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. Behavior at the Decision Point

 Operators can choose to use PCN procedures just for flow admission,
 or just for flow termination, or for both.  Decision Points 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
 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:

Charny, et al. Experimental [Page 11] RFC 6662 PCN SM Boundary-Node Behavior July 2012

    [SM-specific]
    CLE = ETM-rate / (NM-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.
 A performance study of this admission control method is presented in
 [MeLe12].

3.3.2. Flow Termination

 [SM-specific] When the PCN-admission-state computed on the basis of
 the CLE is "block" for the given 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.  [SM-specific] The sustainable aggregate rate (SAR) for the given
     ingress-egress-aggregate is estimated using the formula:
        SAR = U * NM-Rate

Charny, et al. Experimental [Page 12] RFC 6662 PCN SM Boundary-Node Behavior July 2012

     for the latest reported interval, where U is a configurable
     factor greater than one and is the same for all ingress-egress-
     aggregates.  In effect, the value of the PCN-supportable-rate for
     each link is approximated by the expression
        U * PCN-admissible-rate
     rather than being calculated explicitly.
 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 (traffic
 rate to be terminated), the Decision Point SHOULD select PCN-flows
 for termination.  To that end, the Decision Point MAY use upper rate
 limits for individual PCN-flows (known, e.g., from resource signaling
 used to establish the PCN-flows) and select a set of PCN-flows whose
 sum of upper rate limits is up to the traffic rate to be terminated.
 Then, these PCN-flows are terminated.  The use of upper limits on
 PCN-flow rates avoids over-termination.
 Termination may be continuously needed after consecutive measurement
 intervals for various reasons, e.g., if the used upper rate limits
 overestimate the actual flow rates.  For such cases it is RECOMMENDED
 that enough time elapses between successive termination events to
 allow the effects of previous termination events to be reflected in
 the measurements upon which the termination decisions are based;
 otherwise, over-termination may occur.  See [Satoh10] and Sections
 4.2 and 4.3 of [MeLe10].
 In general, the selection of flows for termination MAY be guided by
 policy.
 The Decision Point SHOULD log each round of termination as described
 in Section 5.2.1.2.

Charny, et al. Experimental [Page 13] RFC 6662 PCN SM Boundary-Node Behavior July 2012

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;
 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 log format is defined for that
 purpose in Section 5.2.1.1.  Other actions depend on local policy,
 but MAY include blocking of new flows destined for the PCN-egress-
 node concerned until another report is received from it.  Termination
 of already admitted flows is also possible, but could be triggered by
 "Destination unreachable" messages received at the PCN-ingress-node.
 If a centralized Decision Point sends a request for the estimated
 value of PCN-sent-rate to a given PCN-ingress-node and fails to
 receive a response in a reasonable amount of time, the Decision Point
 SHOULD repeat the request once.  [SM-specific] If the second request
 to the PCN-ingress-node also fails, the Decision Point SHOULD notify
 management.  The log format defined in Section 5.2.1.1 is also
 suitable for this case.
    The response timer t_sndFail with upper bound T_crit is specified
    in Section 3.5.  The use of T_crit is an approximation.  A more
    precise limit would be on 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.

Charny, et al. Experimental [Page 14] RFC 6662 PCN SM Boundary-Node Behavior July 2012

3.4. Behavior 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
 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 can 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 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.

Charny, et al. Experimental [Page 15] RFC 6662 PCN SM Boundary-Node Behavior July 2012

       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.
 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: as described in Section 3.3.3.

Charny, et al. Experimental [Page 16] RFC 6662 PCN SM Boundary-Node Behavior July 2012

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.
 The value of T_meas is RECOMMENDED to be on the order of 100 to 500
 ms to provide a reasonable trade-off 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 signaling path.  A
 reasonable upper bound on T_crit is on the order of 3 seconds.

4. Specification of Diffserv Per-Domain Behavior

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

4.1. Applicability

 This section quotes [RFC5559].
 The PCN SM boundary-node behavior 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.  [SM-specific] The
 performance results in, e.g., [MeLe10], indicate that the SM boundary
 node behavior is more likely to terminate too many flows under such
 circumstances than the CL boundary-node behavior described in
 [RFC6661].

Charny, et al. Experimental [Page 17] RFC 6662 PCN SM Boundary-Node Behavior July 2012

4.2. Technical Specification

4.2.1. Classification and Traffic Conditioning

 Packet classification and treatment at the PCN-ingress-node is
 described in Section 5.1 of [RFC6660].
 PCN packets are further classified as belonging or not belonging to
 an admitted flow.  PCN packets not belonging to an admitted flow are
 "blocked".  (See Section 1 for an understanding of how this term is
 interpreted.)  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 SM boundary-node behavior is a metering and marking behavior
 rather than a scheduling behavior.  As a result, while the encoding
 uses a single DSCP value, that value can 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 Appendix A of [RFC6660].

4.3. Attributes

 The purpose of this per-domain behavior 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.

Charny, et al. Experimental [Page 18] RFC 6662 PCN SM Boundary-Node Behavior July 2012

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 SM behavior may be used to carry real-time traffic,
 particularly voice and video.

4.7. Environmental Concerns

 The PCN SM per-domain behavior could theoretically interfere with the
 use of end-to-end ECN due to reuse of ECN bits for PCN marking.
 Section 5.1 of [RFC6660] describes the actions that can be taken to
 protect ECN signaling.  Appendix B of that document provides further
 discussion of how ECN and PCN can coexist.

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 SM Edge Behavior

 Deployment of the PCN Single Marking edge behavior 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;
 o  activation and verification of all behaviors.

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 signaling as described in [RSVP-PCN] is deployed
 in the network.  After that, the operator needs to decide:

Charny, et al. Experimental [Page 19] RFC 6662 PCN SM Boundary-Node Behavior July 2012

 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 labor of encapsulation/decapsulation on the PCN-
    edge-nodes.
 o  which service classes will be subject to PCN control and what DSCP
    will be used for each.  (See [RFC6660] Appendix A for advice on
    this topic.)
 o  the markings to be used at all nodes in the PCN-domain to indicate
    not-marked (NM) 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.
    [SM-specific] It is RECOMMENDED that the CLE-limit for SM be set
    fairly low, on the order of 5%.
 o  the value of the collection interval T_meas.  For a recommended
    range of values, see Section 3.5.1 above.
 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  [SM-specific] The factor U that is used in the flow termination
    procedure (Section 3.3.2).  An operational definition for U is
    given in that section, but it may be thought of as a contingency
    factor providing a buffer to handle flow peaks above the aggregate

Charny, et al. Experimental [Page 20] RFC 6662 PCN SM Boundary-Node Behavior July 2012

    levels expected when flows are admitted.  A reasonable value for U
    is between 1.2 and 2.  Larger values of U tend to cause more over-
    termination of traffic during peaks, but raise the average link
    utilization level.

5.1.2. Specification of Node- and Link-Specific Parameters

 Filters are required at both the PCN-ingress-node and the PCN-egress-
 node to classify incoming PCN packets by ingress-egress-aggregate.
 Because of the potential use of multipath routing in domains upstream
 of the PCN-domain, it is impossible to do such classification
 reliably at the PCN-egress-node based on the packet header contents
 as originally received at the PCN-ingress-node.  (Packets with the
 same header contents could enter the PCN-domain at multiple PCN-
 ingress-nodes.)  As a result, the only way to construct such filters
 reliably is to tunnel the packets from the PCN-ingress-node to the
 PCN-egress-node.
 The PCN-ingress-node needs filters in order to place PCN packets into
 the right tunnel in the first instance, and also to satisfy requests
 from the Decision Point for admission rates into specific ingress-
 egress-aggregates.  These filters select the PCN-egress-node, but not
 necessarily a specific path through the network to that node.  As a
 result, they are likely to be stable even in the face of failures in
 the network, except when the PCN-egress-node itself becomes
 unreachable.  If all PCN packets will be tunneled, the PCN-ingress-
 node also needs to know the address of the peer PCN-egress-node
 associated with each filter.
 Operators may wish to give some thought to the provisioning of
 alternate egress points for some or all ingress-egress-aggregates in
 case of failure of the PCN-egress-node.  This could require the
 setting up of standby tunnels to these alternate egress points.
 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.  If tunneling is used, these filters are
 constructed on the basis of the identifier of the tunnel from which
 the incoming packet has emerged (e.g., the source address in the
 outer header if IP encapsulation is used).  The PCN-egress-node also
 needs to know the address of the Decision Point to which it sends
 reports for each ingress-egress-aggregate.
 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.

Charny, et al. Experimental [Page 21] RFC 6662 PCN SM Boundary-Node Behavior July 2012

 Turning to link-specific parameters, the operator needs to derive a
 value for the 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.  ([SM-specific] Confusingly, "PCN-admissible-
 rate" in the present context corresponds to "PCN-threshold-rate" in
 the cited paragraphs.)

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
 behavior 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, dropping, and marking.  The required extensions
 specifically include an encapsulation action following
 reclassification by ingress-egress-aggregate.  In addition, the MIB
 has to be extended to include objects for marking the ECN field in
 the outer header at the PCN-ingress-node and an extension to the
 classifiers to include the ECN field at PCN-interior and PCN-egress-
 nodes.  Finally, a new object may need to be defined at the PCN-
 interior-nodes to represent the packet-size-independent excess-
 traffic-marking metering algorithm.
 The value for the PCN-admissible-rate on each link on a node appears
 as a metering parameter.  Operators should take note of the need to
 deploy excess-traffic meters either on the ingress or the egress side
 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 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-
    ingress-node and [RSVP-PCN] is not deployed;
 o  the address of the centralized Decision Point to which it sends
    its reports, if there is one.

Charny, et al. Experimental [Page 22] RFC 6662 PCN SM Boundary-Node Behavior July 2012

 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  [SM-specific] the value of the factor U used in the flow
    termination procedure;
 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 Behaviors

 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 behavior 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.

Charny, et al. Experimental [Page 23] RFC 6662 PCN SM Boundary-Node Behavior July 2012

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.
 The field names (e.g., HOSTNAME, STRUCTURED-DATA) used in the
 following subsections are defined in [RFC5424].

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-ingress-node or PCN-
 egress-node MUST include the following content:
 o  The HOSTNAME field MUST identify the Decision Point issuing the
    log.

Charny, et al. Experimental [Page 24] RFC 6662 PCN SM Boundary-Node Behavior July 2012

 o  A STRUCTURED-DATA element MUST be present, containing parameters
    identifying the node for which an expected report has not been
    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" (without the quotes), which has been registered
    with IANA (see [RFC6661] for more information).  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 (14)
    "log alert" and a Severity level of (3) "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 Facility value of (14) "log
 alert" and a Severity value of (1) "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 Facility value of (14) "log
    alert" and a Severity of (5) "Notice: normal but significant
    condition".

Charny, et al. Experimental [Page 25] RFC 6662 PCN SM Boundary-Node Behavior July 2012

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

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 occurring 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.
    It is RECOMMENDED that the SD-ID for the STRUCTURED-DATA element
    have the form: "PCNTerm" (without the quotes), which has been
    registered with IANA (see [RFC6661] for more information).  The
    parameter identifying the ingress node for the ingress-egress-
    aggregate is RECOMMENDED to have PARAM-NAME "IngrID" (without the
    quotes).  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 thousands
    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.

Charny, et al. Experimental [Page 26] RFC 6662 PCN SM Boundary-Node Behavior July 2012

 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 (14)
    "log alert" and a Severity level of (4) "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 that were received for that ingress-
    egress-aggregate but were 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  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.
 o  total not-marked PCN packets and octets received;

Charny, et al. Experimental [Page 27] RFC 6662 PCN SM Boundary-Node Behavior July 2012

 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 one new consideration,
 related to the use of a centralized Decision Point.  The Decision
 Point itself is a trusted entity.  However, its use implies the
 existence of an interface on the PCN-ingress-node through which
 communication of policy decisions takes place.  That interface is a
 point of vulnerability that must be protected from denial-of-service
 attacks.

7. Acknowledgements

 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.

Charny, et al. Experimental [Page 28] RFC 6662 PCN SM Boundary-Node Behavior July 2012

 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).
 Finally, reviews by Joel Halpern and Brian Carpenter helped to
 clarify how ingress-egress-aggregates are distinguished (Joel) and
 handling of packets that cannot be carried successfully as PCN-
 packets (Brian).  They also made other suggestions to improve the
 document, as did Stephen Farrell, Sean Turner, and Pete Resnick.

8. References

8.1. 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.
 [RFC6660]   Briscoe, B., Moncaster, T., and M. Menth, "Encoding Three
             Pre-Congestion Notification (PCN) States in the IP Header
             Using a Single Diffserv Codepoint (DSCP)", RFC 6660,
             July 2012.

Charny, et al. Experimental [Page 29] RFC 6662 PCN SM Boundary-Node Behavior July 2012

8.2. Informative References

 [MeLe10]    Menth, M. and F. Lehrieder, "PCN-Based Measured Rate
             Termination", Computer Networks Journal (Elsevier), vol.
             54, no. 13, pp. 2099-2116, September 2010.
 [MeLe12]    Menth, M. and F. Lehrieder, "Performance of PCN-Based
             Admission Control under Challenging Conditions", IEEE/
             ACM Transactions on Networking, vol. 20, no. 2,
             April 2012.
 [RFC4594]   Babiarz, J., Chan, K., and F. Baker, "Configuration
             Guidelines for DiffServ Service Classes", RFC 4594,
             August 2006.
 [RFC6661]   Charny, A., Huang, F., Karagiannis, G., Menth, M., and T.
             Taylor, Ed., "Pre-Congestion Notification (PCN) Boundary-
             Node Behavior for the Controlled Load (CL) Mode of
             Operation", RFC 6661, July 2012.
 [RSVP-PCN]  Karagiannis, G. and A. Bhargava, "Generic Aggregation of
             Resource ReSerVation Protocol (RSVP) for IPv4 And IPv6
             Reservations over PCN domains", Work in Progress,
             July 2012.
 [Satoh10]   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.

Charny, et al. Experimental [Page 30] RFC 6662 PCN SM Boundary-Node Behavior July 2012

Authors' Addresses

 Anna Charny
 USA
 EMail: anna@mwsm.com
 Xinyan (Joy) Zhang
 Cisco Systems
 300 Apollo Drive
 Chelmsford, MA  01824
 USA
 EMail: joyzhang@cisco.com
 Georgios Karagiannis
 University of Twente
 P.O. Box 217
 7500 AE Enschede,
 The Netherlands
 Phone: +31 53 4894099
 EMail: g.karagiannis@utwente.nl
 Michael Menth
 University of Tuebingen
 Sand 13
 72076 Tuebingen
 Germany
 Phone: +49-7071-2970505
 EMail: menth@uni-tuebingen.de
 Tom Taylor (editor)
 Huawei Technologies
 Ottawa
 Canada
 EMail: tom.taylor.stds@gmail.com

Charny, et al. Experimental [Page 31]

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