Internet Engineering Task Force (IETF) A. Charny
Request for Comments: 6661
Category: Experimental F. Huang
ISSN: 2070-1721 Huawei Technologies
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
Controlled Load (CL) 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 three PCN marking states: not-
marked, threshold-marked, and excess-traffic-marked. This behavior
is known informally as the Controlled Load (CL) 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/rfc6661.
Charny, et al. Experimental [Page 1]RFC 6661 PCN CL 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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Charny, et al. Experimental [Page 2]
RFC 6661 PCN CL Boundary-Node Behavior July 2012
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. [CL-Specific] Assumed Core Network Behavior for CL . . . . . . 8
3. Node Behaviors . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2. Behavior 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. Behavior 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 . . . . . . . . . . . . . . 15
3.4. Behavior of the Ingress Node . . . . . . . . . . . . . . . 16
3.5. Summary of Timers and Associated Configurable Durations . 16
3.5.1. Recommended Values for the Configurable Durations . . 18
4. Specification of Diffserv Per-Domain Behavior . . . . . . . . 18
4.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 18
4.2. Technical Specification . . . . . . . . . . . . . . . . . 19
4.2.1. Classification and Traffic Conditioning . . . . . . . 19
4.2.2. PHB Configuration . . . . . . . . . . . . . . . . . . 19
4.3. Attributes . . . . . . . . . . . . . . . . . . . . . . . . 19
4.4. Parameters . . . . . . . . . . . . . . . . . . . . . . . . 19
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 Behavior . . . . . . . . . . . . 20
5.1.1. Selection of Deployment Options and Global
Parameters . . . . . . . . . . . . . . . . . . . . . . 20
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 Behaviors . . . . . 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 . . . . . . . . . . . . . . . . . . . . . 30
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 30
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.1. Normative References . . . . . . . . . . . . . . . . . . . 31
9.2. Informative References . . . . . . . . . . . . . . . . . . 32
Charny, et al. Experimental [Page 3]RFC 6661 PCN CL 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 CL edge behavior;
o to evaluate the effectiveness of the CL 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 6661 PCN CL 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 CL 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 [RFC6662] specifies the Single Marking (SM) PCN-
boundary-node behavior. This document and [RFC6662] 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
behavior is preceded by the phrase "[CL-specific]". A similar
distinction for SM-specific text is made in [RFC6662].
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 [CL-specific] PCN-threshold-rate
Charny, et al. Experimental [Page 5]
RFC 6661 PCN CL Boundary-Node Behavior July 2012
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 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 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 2 of [RFC6660]:
o not-PCN codepoint;
o not-marked (NM) codepoint;
o [CL-specific] threshold-marked (ThM) 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.
Charny, et al. Experimental [Page 6]RFC 6661 PCN CL Boundary-Node Behavior July 2012
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 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.
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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.
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 Behavior for CL
This section describes the assumed behavior 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];
Charny, et al. Experimental [Page 8]RFC 6661 PCN CL Boundary-Node Behavior July 2012
o For IP transport, threshold-marking of PCN-packets uses the ThM
codepoint defined in [RFC6660]; for MPLS transport, an equivalent
marking is used as discussed in Appendix C of [RFC6660];
o For IP transport, excess-traffic-marking of PCN-packets uses the
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 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 Sections
5.2.1 and 5.2.2 of [RFC6660].
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, [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
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.
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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);
o [CL-specific] ThM-rate: octets per second of PCN-traffic in PCN-
packets that are threshold-marked (i.e., marked with the ThM
codepoint);
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.
[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
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.
Charny, et al. Experimental [Page 10]RFC 6661 PCN CL Boundary-Node Behavior July 2012
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, [CL-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.
Charny, et al. Experimental [Page 11]RFC 6661 PCN CL 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 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. 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
Charny, et al. Experimental [Page 12]RFC 6661 PCN CL Boundary-Node Behavior July 2012
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.
A performance study of this admission control method is presented in
[MeLe12].
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:
Charny, et al. Experimental [Page 13]RFC 6661 PCN CL Boundary-Node Behavior July 2012
1. [CL-specific] The sustainable aggregate rate (SAR) for the given
ingress-egress-aggregate is estimated by the sum:
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 (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. [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.
The Decision Point SHOULD log each round of termination as described
in Section 5.2.1.2.
Charny, et al. Experimental [Page 14]RFC 6661 PCN CL 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. [CL-specific] While waiting after
sending this second request, the Decision Point MAY begin selecting
flows to terminate, using ETM-rate as an estimate of the amount of
traffic to be terminated in place of the quantity specified in
Section 3.3.2:
PCN-sent-rate - SAR
Because ETM-rate will over-estimate the amount of traffic to be
terminated due to dropping of PCN-packets by interior nodes, the
Decision Point SHOULD terminate less than the full amount ETM-rate in
the first pass and recalculate the additional amount to terminate in
additional passes based on subsequent reports from the PCN-egress-
node. If the second request to the PCN-ingress-node also fails, the
Decision Point MUST select flows to terminate based on the ETM-rate
Charny, et al. Experimental [Page 15]RFC 6661 PCN CL Boundary-Node Behavior July 2012
approximation as just described and SHOULD notify management. The
log format described in Section 5.2.1.1 is also suitable for this
purpose.
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.
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, [CL-specific] ThM-rate,
and ETM-rate and proceed to the applicable reporting procedure
(Section 3.2.2 or Section 3.2.3).
Charny, et al. Experimental [Page 16]RFC 6661 PCN CL Boundary-Node Behavior July 2012
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.
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.
Charny, et al. Experimental [Page 17]RFC 6661 PCN CL Boundary-Node Behavior July 2012
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.
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 CL 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. [CL-specific] The
performance results in, e.g., [MeLe10], indicate that the CL boundary
node behavior provides better service outcomes under such
Charny, et al. Experimental [Page 18]RFC 6661 PCN CL Boundary-Node Behavior July 2012
circumstances than the SM boundary node behavior described in
[RFC6662], because CL is less likely to terminate PCN-flows
unnecessarily.
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 CL 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 19]
RFC 6661 PCN CL 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 CL behavior may be used to carry real-time traffic,
particularly voice and video.
4.7. Environmental Concerns
The PCN CL 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 CL Edge Behavior
Deployment of the PCN Controlled Load 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 20]RFC 6661 PCN CL 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), [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] In practice, the operation of flow admission is not
very sensitive to the value of the CLE-limit, 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.
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.
Charny, et al. Experimental [Page 21]RFC 6661 PCN CL Boundary-Node Behavior July 2012
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
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.
Charny, et al. Experimental [Page 22]RFC 6661 PCN CL Boundary-Node Behavior July 2012
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
values for the PCN-admissible-rate and [CL-specific] PCN-supportable-
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.
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, new objects may need to be defined at the PCN-
interior-nodes to represent the metering algorithms for threshold-
marking and packet-size-independent excess-traffic-marking.
Values for the PCN-admissible-rate and [CL-specific] PCN-supportable-
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 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 [CL-specific] whether specific flow identifiers must be captured
when excess-traffic-marked packets are observed;
o whether report suppression is to be applied;
Charny, et al. Experimental [Page 23]RFC 6661 PCN CL Boundary-Node Behavior July 2012
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.
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 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.
Charny, et al. Experimental [Page 24]RFC 6661 PCN CL Boundary-Node Behavior July 2012
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.
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.
Charny, et al. Experimental [Page 25]RFC 6661 PCN CL Boundary-Node Behavior July 2012
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.
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. 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:
Charny, et al. Experimental [Page 26]RFC 6661 PCN CL Boundary-Node Behavior July 2012
o PRI changes to 117, indicating a Facility value of (14) "log
alert" and a Severity of (5) "Notice: normal but significant
condition".
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. 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
Charny, et al. Experimental [Page 27]RFC 6661 PCN CL Boundary-Node Behavior July 2012
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.
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 [CL-specific] total PCN packets and octets re-marked to threshold-
marked;
o total PCN packets and octets re-marked to excess-traffic-marked.
Charny, et al. Experimental [Page 28]RFC 6661 PCN CL Boundary-Node Behavior July 2012
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;
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 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.
Charny, et al. Experimental [Page 29]RFC 6661 PCN CL Boundary-Node Behavior July 2012
7. IANA Considerations
IANA has added the following entries to the "syslog Structured Data
ID Values" registry.
Structured Data ID: PCNNode OPTIONAL
Structured Data Parameter: ID MANDATORY
Structured Data Parameter: Rtyp MANDATORY
Reference: RFC 6661
Structured Data ID: PCNTerm OPTIONAL
Structured Data Parameter: IngrID MANDATORY
Structured Data Parameter: EgrID MANDATORY
Structured Data Parameter: TermRate MANDATORY
Structured Data Parameter: FCnt MANDATORY
Reference: RFC 6661
8. Acknowledgements
The content of this memo bears a family resemblance to [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 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.
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).
Charny, et al. Experimental [Page 30]RFC 6661 PCN CL Boundary-Node Behavior July 2012
As part of the broader review process, the document saw further
improvements as a result of comments by Joel Halpern, Brian
Carpenter, Stephen Farrell, Sean Turner, and Pete Resnick.
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.
[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 31]RFC 6661 PCN CL Boundary-Node Behavior July 2012
9.2. Informative References
[Briscoe-CL] Briscoe, B., Eardley, P., Songhurst, D., Le Faucheur,
F., Charny, A., Babiarz, J., Chan, K., Dudley, S.,
Karagiannis, G., Bader, A., and L. Westberg, "An edge-
to-edge Deployment Model for Pre-Congestion
Notification: Admission Control over a DiffServ
Region", Work in Progress, October 2006.
[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.
[RFC6662] Charny, A., Zhang, J., Karagiannis, G., Menth, M., and
T. Taylor, Ed., "Pre-Congestion Notification (PCN)
Boundary Node Behavior for the Single Marking (SM) Mode
of Operation", RFC 6662, 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 32]RFC 6661 PCN CL Boundary-Node Behavior July 2012
Authors' Addresses
Anna Charny
USA
EMail: anna@mwsm.com
Fortune Huang
Huawei Technologies
Section F, Huawei Industrial Base,
Bantian Longgang, Shenzhen 518129
P.R. China
Phone: +86 15013838060
EMail: huangfuqing@huawei.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 33]
