Internet Engineering Task Force A. Charny
Internet-Draft Cisco Systems
Intended status: Informational F. Huang
Expires: June 19, 2011 Huawei Technologies
G. Karagiannis
U. Twente
M. Menth
University of Tuebingen
T. Taylor, Ed.
Huawei Technologies
December 16, 2010
PCN Boundary Node Behaviour for the Controlled Load (CL) Mode of
Operation
draft-ietf-pcn-cl-edge-behaviour-08
Abstract
Pre-congestion notification (PCN) is a means for protecting the
quality of service for inelastic traffic admitted to a Diffserv
domain. The overall PCN architecture is described in RFC 5559. This
memo is one of a series describing possible boundary node behaviours
for a PCN-domain. The behaviour described here is that for a form of
measurement-based load control using three PCN marking states, not-
marked, threshold-marked, and excess-traffic-marked. This behaviour
is known informally as the Controlled Load (CL) PCN-boundary-node
behaviour.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 19, 2011.
Copyright Notice
Charny, et al. Expires June 19, 2011 [Page 1]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Charny, et al. Expires June 19, 2011 [Page 2]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. [CL-Specific] Assumed Core Network Behaviour for CL . . . . . 8
3. Node Behaviours . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2. Behaviour 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. Behaviour 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 . . . . . . . . . . . . . . 13
3.4. Behaviour of the Ingress Node . . . . . . . . . . . . . . 14
3.5. Summary of Timers . . . . . . . . . . . . . . . . . . . . 14
4. Identifying Ingress and Egress Nodes For PCN Traffic . . . . . 15
5. Specification of Diffserv Per-Domain Behaviour . . . . . . . . 15
5.1. Applicability . . . . . . . . . . . . . . . . . . . . . . 16
5.2. Technical Specification . . . . . . . . . . . . . . . . . 16
5.2.1. Classification and Traffic Conditioning . . . . . . . 16
5.2.2. PHB Configuration . . . . . . . . . . . . . . . . . . 16
5.3. Attributes . . . . . . . . . . . . . . . . . . . . . . . . 17
5.4. Parameters . . . . . . . . . . . . . . . . . . . . . . . . 17
5.5. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 18
5.6. Example Uses . . . . . . . . . . . . . . . . . . . . . . . 18
5.7. Environmental Concerns . . . . . . . . . . . . . . . . . . 19
5.8. Security Considerations . . . . . . . . . . . . . . . . . 19
6. Security Considerations . . . . . . . . . . . . . . . . . . . 19
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
9.1. Normative References . . . . . . . . . . . . . . . . . . . 19
9.2. Informative References . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
Charny, et al. Expires June 19, 2011 [Page 3]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
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].
PCN-boundary-node behaviours specify a detailed set of algorithms and
procedures used to implement the PCN mechanisms. Since the
algorithms depend on specific metering and marking behaviour at the
interior nodes, it is also necessary to specify the assumptions made
about PCN-interior-node behaviour. Finally, because PCN uses DSCP
values to carry its markings, a specification of PCN-boundary-node
behaviour MUST include the per domain behaviour (PDB) template
specified in [RFC3086], filled out with the appropriate content. The
present document accomplishes these tasks for the Controlled Load
(CL) mode of operation.
[RFC EDITOR'S NOTE: you may choose to delete the following paragraph
and the "[CL-specific]" tags throughout this document when publishing
it, since they are present primarily to aid reviewers. RFCyyyy is
the published version of draft-ietf-pcn-sm-edge-behaviour.]
A companion document [RFCyyyy] specifies the Single Marking (SM) PCN-
boundary-node behaviour. This document and [RFCyyyy] have a great
deal of text in common. To simplify the task of the reader, the text
in the present document that is specific to the CL PCN-boundary-node
behaviour is preceded by the phrase: "[CL-specific]". A similar
distinction for SM-specific text is made in [RFCyyyy].
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
This document uses the following terms defined in Section 2 of
[RFC5559]:
Charny, et al. Expires June 19, 2011 [Page 4]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
o PCN-domain;
o PCN-ingress-node;
o PCN-egress-node;
o PCN-interior-node;
o PCN-boundary-node;
o PCN-flow;
o ingress-egress-aggregate (IEA);
o [CL-specific] PCN-threshold-rate;
o PCN-excess-rate;
o PCN-admissible-rate;
o PCN-supportable-rate;
o PCN-marked;
o [CL-specific] threshold-marked;
o excess-traffic-marked.
It also uses the following terms, for which the definition is
repeated from [RFC5559] because of their importance to the
understanding of the text that follows:
PCN-traffic, PCN-packets, PCN-BA
A PCN-domain carries traffic of different Diffserv behaviour
aggregates (BAs) [RFC2474]. The PCN-BA uses the PCN mechanisms to
carry PCN-traffic, and the corresponding packets are PCN-packets.
The same network will carry traffic of other Diffserv BAs. The
PCN-BA is distinguished by a combination of the Diffserv codepoint
and ECN fields.
This document uses the following terms from [RFC5670]:
o [CL-specific] threshold-meter;
o excess-traffic-meter.
To complete the list of borrowed terms, this document reuses the
following terms and abbreviations defined in Section 3 of [RFC5696]:
Charny, et al. Expires June 19, 2011 [Page 5]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
o not-PCN codepoint;
o Not-marked (NM) codepoint;
o PCN-marked (PM) codepoint;
o EXP (experimental) [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. Regardless of the
location of the Decision Point, the PCN-ingress-node is the point
where the decisions are enforced.
NM-rate
The rate of not-marked PCN-traffic received at a PCN-egress-node
for a given ingress-egress-aggregate in octets per second. For
further details see Section 3.2.1.
[CL-specific] ThM-rate
The rate of threshold-marked PCN-traffic received at a PCN-egress-
node for a given ingress-egress-aggregate in octets per second.
For further details see Section 3.2.1.
ETM-rate
The rate of excess-traffic-marked PCN-traffic received at a PCN-
egress-node for a given ingress-egress-aggregate in octets per
second. For further details see Section 3.2.1.
PCN-sent-rate
The rate of PCN-traffic received at a PCN-ingress-node and
destined for a given ingress-egress-aggregate in octets per
second. For further details see Section 3.4.
Congestion level estimate (CLE)
A value derived from the measurement of PCN-packets received at a
PCN-egress-node for a given ingress-egress-aggregate, representing
the ratio of marked to total PCN-traffic (measured in octets)
received over a short period. The CLE is used to derive the PCN-
admission-state (Section 3.3.1) and also by the report suppression
procedure (Section 3.2.3) if report suppression is activated.
Charny, et al. Expires June 19, 2011 [Page 6]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
PCN-admission-state
The state ("admit" or "block") derived by the Decision Point for a
given ingress-egress-aggregate based on PCN packet marking
statistics. The Decision Point decides to admit or block new
flows offered to the aggregate based on the current value of the
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 admitted to
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 in order to
derive the PCN-admission-state for a given ingress-egress-
aggregate. For further details, see Section 3.3.1.
T-meas
An interval, the value of which is configurable, defining the
measurement period at the PCN-egress-node during which statistics
relating to PCN-traffic marking are collected. At the end of the
interval the values NM-rate, [CL-specific] ThM-rate, and ETM-rate
as defined above are calculated and a report is sent to the
Decision Point, subject to the operation of the report suppression
feature. For further details see Section 3.2.
T-maxsuppress
An interval, the value of which is configurable, 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 is used as a keep-alive mechanism for
signalling between the PCN-egress-node and the Decision Point when
report suppression is activated. For further details, see
Section 3.2.3.
Charny, et al. Expires June 19, 2011 [Page 7]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
T-fail
An interval, the value of which is configurable, 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.
2. [CL-Specific] Assumed Core Network Behaviour for CL
This section describes the assumed behaviour for nodes of the PCN-
domain when acting in their role as PCN-interior-nodes. The CL mode
of operation assumes that:
o PCN-interior-nodes perform both threshold-marking and excess-
traffic-marking of packets, according to the rules specified in
[RFC5670];
o excess-traffic-marking of packets uses the PCN-Marked (PM)
codepoint defined in [RFC5696];
o threshold-marking of packets uses the EXP codepoint defined in
[RFC5696];
o the PCN-domain satisfies the conditions specified in [RFC5696];
o on each link the reference rate for the threshold-meter is
configured to be equal to the PCN-admissible-rate for the link;
o on each link the reference rate for the excess-traffic-meter is
configured to be equal to the PCN-supportable-rate for the link;
o the set of valid codepoint transitions is as shown in Section 4.2
of [RFC5696].
3. Node Behaviours
3.1. Overview
This section describes the behaviour of the PCN-ingress-node, PCN-
egress-node, and the Decision Point (which MAY be collocated with the
PCN-ingress-node).
The PCN-egress-node collects the rates of not-marked, [CL-specific]
threshold-marked, and excess-traffic-marked PCN-traffic for each
ingress-egress-aggregate and reports them to the Decision Point.
[CL-specific] It MAY also identify and report PCN-flows that have
Charny, et al. Expires June 19, 2011 [Page 8]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
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.
3.2. Behaviour of the PCN-Egress-Node
3.2.1. Data Collection
The PCN-egress-node MUST meter received PCN-traffic in order to
derive periodically the following rates for each ingress-egress-
aggregate passing through it:
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 PM
codepoint);
o [CL-specific] ETM-rate: octets per second of PCN-traffic in PCN-
packets that are excess-traffic-marked (i.e., marked with the EXP
codepoint).
The PCN-traffic SHOULD be metered continuously and the measurement
intervals themselves SHOULD be of equal length, to minimize the
statistical variance introduced by the measurement process itself.
The starting and ending times of the measurement intervals for
different ingress-egress-aggregates MAY be the same or MAY be
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. 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
Charny, et al. Expires June 19, 2011 [Page 9]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
excess-traffic-marking helps to avoid termination of PCN-flows not
contributing to congestion.
3.2.2. Reporting the PCN Data
If the report suppression option described in the next sub-section is
not 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 so configured (e.g., because multipath routing is
being used, as explained in the previous section), the PCN-egress-
node MUST also report the set of flow identifiers of PCN-flows for
which excess-traffic-marking was observed in the most recent
measurement interval. If this set is large, the PCN-egress-node MAY
report only the most recently excess-traffic-marked PCN-flows rather
than the complete set.
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. T-maxsuppress functions as a
keep-alive mechanism for signalling between the PCN-egress-node and
the Decision Point.
If the report suppression option is enabled, the PCN-egress-node MUST
apply the following procedure to decide whether to send a report to
the Decision Point, rather than sending a report automatically at the
end of each measurement interval.
1. As well as the quantities NM-rate, [CLE-specific] ThM-rate, and
ETM-rate, the PCN-egress-node MUST calculate the congestion level
estimate (CLE) for each measurement interval. The CLE is
computed as:
[CL-specific]
CLE = (ThM-rate + ETM-rate) / (NM-rate + ThM-rate + ETM-rate)
if any PCN-traffic was observed, or CLE = 0 if all the rates are
zero.
2. If the calculated CLE for the latest measurement interval is
greater than the CLE-reporting-threshold and/or the calculated
CLE 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
Charny, et al. Expires June 19, 2011 [Page 10]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
described below.
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 so configured, the PCN-
egress-node MUST also report the set of flow identifiers of PCN-flows
for which excess-traffic-marking was observed in the most recent
measurement interval.
The above procedure ensures that at least one report is sent per
interval (T-maxsuppress + T-meas). This provides some protection
against loss of egress reports and also demonstrates to the Decision
Point that both the PCN-egress-node and the communication path
between that node and the Decision Point are in operation.
3.3. Behaviour at the Decision Point
Operators can choose to use PCN procedures just for flow admission,
or just for flow termination, or for both. A compliant Decision
Point MUST implement both mechanisms, but configurable options MUST
be provided to activate or deactivate PCN-based flow admission and
flow termination independently of each other at a given Decision
Point.
If PCN-based flow termination is enabled but PCN-based flow admission
is not, flow termination operates as specified in this document.
Logically, some other system of flow admission control is in
operation, but the description of such a system is out of scope of
this document and depends on local arrangements.
3.3.1. Flow Admission
The Decision Point determines the PCN-admission-state for a given
ingress-egress-aggregate each time it receives a report from the
egress node. It makes this determination on the basis of the
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. Expires June 19, 2011 [Page 11]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
[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".
[CL-specific] The outcome of the comparison is not very sensitive
to the value of the CLE-limit in practice, because when threshold-
marking occurs it tends to persist long enough that threshold-
marked traffic becomes a large proportion of the received traffic
in a given interval.
If the PCN-admission-state for a given ingress-egress-aggregate is
"admit", the Decision Point SHOULD allow new flows to be admitted to
that aggregate. If the PCN-admission-state for a given ingress-
egress-aggregate is "block", the Decision Point SHOULD NOT allow new
flows to be admitted to that aggregate. These actions MAY be
modified by policy in specific cases, but such policy intervention
risks defeating the purpose of using PCN.
3.3.2. Flow Termination
[CL-specific] When the report from the PCN-egress-node includes a
non-zero value of the ETM-rate for some ingress-egress-aggregate, the
Decision Point MUST request the PCN-ingress-node to provide an
estimate of the rate (PCN-sent-rate) at which the PCN-ingress-node is
receiving PCN-traffic that is destined for the given ingress-egress-
aggregate.
If the Decision Point is collocated with the PCN-ingress-node, the
request and response are internal operations.
The Decision Point MUST then wait, for both the requested rate from
the PCN-ingress-node and the next report from the PCN-egress-node for
the ingress-egress-aggregate concerned. If this next egress node
report also includes a non-zero value for the ETM-rate, the Decision
Point MUST determine an amount of flow to terminate using the
following steps:
1. [CL-specific] The sustainable aggregate rate (SAR) for the given
ingress-egress-aggregate is estimated by the sum:
Charny, et al. Expires June 19, 2011 [Page 12]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
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.
If the difference calculated in the second step is positive, the
Decision Point SHOULD select PCN-flows to terminate, until it
determines that the PCN-traffic admission rate will no longer be
greater than the estimated sustainable aggregate rate. If the
Decision Point knows the bandwidth required by individual PCN-flows
(e.g., from resource signalling used to establish the flows), it MAY
choose to complete its selection of PCN-flows to terminate in a
single round of decisions.
Alternatively, the Decision Point MAY spread flow termination over
multiple rounds to avoid over-termination. If this is done, it is
RECOMMENDED that enough time elapse between successive rounds of
termination to allow the effects of previous rounds to be reflected
in the measurements upon which the termination decisions are based
(see [IEEE-Satoh] and sections 4.2 and 4.3 of [MeLe10]).
In general, the selection of flows for termination MAY be guided by
policy. [CL-specific] If the egress node has supplied a list of
identifiers of PCN-flows that experienced excess-traffic-marking
(Section 3.2), the Decision Point SHOULD first consider terminating
PCN-flows in that list.
3.3.3. Decision Point Action For Missing PCN-Boundary-Node Reports
If the Decision Point fails to receive any report from a given PCN-
egress-node for a configurable interval T-fail, it SHOULD raise an
alarm to management. A Decision Point collocated with a PCN-ingress-
node SHOULD cease to admit PCN-flows to the ingress-egress-aggregate
passing from the PCN-ingress-node to the given PCN-egress-node, until
it again receives a report from that node. A centralized Decision
Point MAY cease to admit PCN-flows to all ingress-egress-aggregates
destined to the PCN-egress-node concerned, until it again receives a
report from that node.
If a centralized Decision Point fails to receive a reply within a
reasonable period of time to a request for a PCN-sent-rate value sent
to a given PCN-ingress-node, it SHOULD raise an alarm to management.
Charny, et al. Expires June 19, 2011 [Page 13]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
3.4. Behaviour of the Ingress Node
The PCN-ingress-node MUST provide the estimated current rate of PCN-
traffic received at that node and destined for a given ingress-
egress-aggregate in octets per second (the PCN-sent-rate) when the
Decision Point requests it. The way this rate estimate is derived is
a matter of implementation.
For example, the rate that the PCN-ingress-node supplies MAY be
based on a quick sample taken at the time the information is
required. It is RECOMMENDED that such a sample be based on
observation of at least thirty PCN-packets to achieve reasonable
statistical reliability.
3.5. Summary of Timers
Table 1 summarizes the timers implied by the preceding procedures.
The three configurable limits T-meas, T-maxsuppress, and T-fail apply
to the three timers t-meas, t-maxsuppress, and t-fail respectively.
t-meas and t-maxsuppress are reset upon expiry. t-fail is reset by
management action or by receipt of a report from the PCN-egress-node
concerned.
IEA = ingress-egress-aggregate.
+---------------+----------+---------------+------------------------+
| Limit | Where | Incidence | Action on Expiry |
+---------------+----------+---------------+------------------------+
| T-meas | Egress | One per node | Calculate and possibly |
| | node | | report NM-rate, |
| | | | ThM-rate*, ETM-rate |
| | | | and CLE for each IEA. |
| - | - | - | - |
| T-maxsuppress | Egress | One per IEA | Send a report for that |
| | node | if report | IEA at the next expiry |
| | | suppression | of t-meas. |
| | | is enabled. | |
| - | - | - | - |
| T-fail | Decision | One per | Assume failure and |
| | Point | egress node | cease to admit flows |
| | | | passing through that |
| | | | egress node. |
+---------------+----------+---------------+------------------------+
* ThM-rate is [CL-specific].
Table 1: Timers Used For the CL Boundary Node Behaviour
Charny, et al. Expires June 19, 2011 [Page 14]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
The value of T-meas SHOULD be configurable, and is RECOMMENDED to be
of the order of 100 to 500 ms to provide a reasonable tradeoff
between signalling demands on the network and the time taken to react
to impending congestion.
t-maxsuppress is active only when report suppression is enabled. The
value of T-maxsuppress SHOULD be configurable. The appropriate value
for T-maxsuppress depends on whether the transport protocol between
the PCN-egress-node and the Decision Point is reliable, and whether
it implements its own keep-alive procedures. At the time of writing,
that transport protocol has not yet been specified. This
specification therefore requires that any transport protocol
specification for carrying PCN reports MUST specify an appropriate
default value for T-maxsuppress.
The value of T-fail MUST be configurable. As for T-maxsuppress, the
appropriate value of T-fail depends on the transport protocol between
the PCN-boundary-nodes and the Decision Point. It is RECOMMENDED
that the default value for T-fail be three times the default value
for T-maxsuppress as proposed by the transport protocol
specification. The transport protocol specification MAY propose a
different default value for T-fail in view of the particular
characteristics of that protocol.
4. Identifying Ingress and Egress Nodes For PCN Traffic
The operation of PCN depends on the ability of the PCN-ingress-node
to identify the ingress-egress-aggregate to which each new PCN-flow
belongs and the ability of the egress node to identify the ingress-
egress-aggregate to which each received PCN-packet belongs. If the
Decision Point is collocated with the PCN-ingress-node, the PCN-
egress-node also needs to associate each ingress-egress-aggregate
with the address of the PCN-ingress-node to which it MUST send its
reports.
The means by which this is done depends on the packet routing
technology in use in the network. The procedure to provide the
required information is out of the scope of this document.
5. Specification of Diffserv Per-Domain Behaviour
This section provides the specification required by [RFC3086] for a
per-domain behaviour.
Charny, et al. Expires June 19, 2011 [Page 15]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
5.1. Applicability
This section draws heavily upon points made in the PCN architecture
document, [RFC5559].
The PCN CL boundary node behaviour specified in this document is
applicable to inelastic traffic (particularly video and voice) where
quality of service for admitted flows is protected primarily by
admission control at the ingress to the domain. In exceptional
circumstances (e.g., due to network failures) already-admitted flows
MAY be terminated to protect the quality of service of the remaining
flows. [CL-specific] The CL boundary node behaviour is less likely
to terminate too many flows under such circumstances than the SM
boundary node behaviour [RFCyyyy].
[RFC EDITOR'S NOTE: please replace RFCyyyy above by the reference to
the published version of draft-ietf-pcn-sm-edge-behaviour.]
5.2. Technical Specification
5.2.1. Classification and Traffic Conditioning
This section paraphrases the applicable portions of Sections 3.6 and
4.2 of [RFC5559].
Packets at the ingress to the domain are classified as either PCN or
non-PCN. Non-PCN packets MAY share the network with PCN packets
within the domain. Because the encoding specified in [RFC5696] and
used in this document requires the use of the ECN fields, PCN-
ingress-nodes MUST block ECN-capable traffic that uses the same DSCP
as PCN from entering the PCN-domain directly. "Blocking" means it is
dropped or downgraded to a lower-priority behaviour aggregate.
Alternatively such traffic MAY be tunnelled through the PCN-domain.
PCN packets are further classified as belonging or not belonging to
an admitted flow. PCN packets not belonging to an admitted flow are
dropped. (This assumes that requests for flow admission are
signalled in advance of the arrival of the flows themselves.)
Packets belonging to an admitted flow are policed to ensure that they
adhere to the agreed rate or flowspec.
5.2.2. PHB Configuration
The PCN SM and CL boundary node behaviours are metering and marking
behaviours rather than scheduling behaviours. As a result, they are
not tied to the selection of a specific DSCP value. The PCN working
group suggests using admission control for the following service
classes (defined in [RFC4594]):
Charny, et al. Expires June 19, 2011 [Page 16]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
o Telephony (EF)
o Real-time interactive (CS4)
o Broadcast Video (CS3)
o Multimedia Conferencing (AF4)
For a fuller discussion, see Section A.1 of Appendix A of [RFC5696].
5.3. Attributes
The purpose of this per-domain behaviour is to achieve low loss and
jitter for the target class of traffic. The design requirement for
PCN was that recovery from overloads through the use of flow
termination SHOULD happen within 1-3 seconds. PCN probably performs
better than that.
5.4. Parameters
In the list that follows, note that most PCN-ingress-nodes are also
PCN-egress-nodes, and vice versa. Furthermore, the PCN-ingress-nodes
MAY be collocated with Decision Points.
Parameters at the PCN-ingress-node:
-----------------------------------
o Filters for distinguishing PCN from non-PCN inbound traffic.
o The markings to be applied to PCN-traffic.
o Reference rates on each inward link for the [CL-specific]
threshold-meter and the excess-traffic-meter; see Section 2.
o The information needed to distinguish PCN-traffic belonging to a
given ingress-egress-aggregate.
Parameters at the PCN-egress-node:
----------------------------------
o The measurement interval T-meas.
o Whether report suppression is enabled and, if so, the values of
the CLE-reporting-threshold and T-maxsuppress.
o [CL-specific] Whether individual flow identifiers will be reported
for excess-traffic-marked PCN-traffic.
Charny, et al. Expires June 19, 2011 [Page 17]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
o The information needed to distinguish PCN-traffic belonging to a
given ingress-egress-aggregate.
o The marking rules for re-marking PCN-traffic leaving the PCN
domain.
Parameters at each interior node:
---------------------------------
o Reference rates on each link for the [CL-specific] threshold-meter
and the excess-traffic-meter; see Section 2.
o The markings to be applied to PCN-traffic, including the
identification of PCN-packets and the encodings to indicate [CL-
specific] threshold-marking and excess-traffic-marking.
Parameters at the Decision Point:
---------------------------------
o Activation/deactivation of PCN-based flow admission.
o Activation/deactivation of PCN-based flow termination.
o The value of CLE-limit.
o The maximum interval T-fail between reports from a given PCN-
egress-node, for detecting failure of communications with that
node.
o The information needed to map between each ingress-egress-
aggregate and the corresponding PCN-ingress-node and PCN-egress-
node.
5.5. Assumptions
Assumed that a specific portion of link capacity has been reserved
for PCN-traffic. Assumed that the Decision Point receives requests
for admission of PCN-flows before the packets in the PCN-flows
arrive. This is not a critical assumption, but in its absence,
packets will be dropped by the PCN-ingress-node until it obtains the
admission decision from the Decision Point.
5.6. Example Uses
The PCN CL behaviour MAY be used to carry real-time traffic,
particularly voice and video.
Charny, et al. Expires June 19, 2011 [Page 18]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
5.7. Environmental Concerns
The PCN CL per-domain behaviour can interfere with the use of end-to-
end ECN due to reuse of ECN bits for PCN marking. See Appendix B of
[RFC5696] for details.
5.8. Security Considerations
Please see the security considerations in Section 6 as well as those
in [RFC2474] and [RFC2475].
6. Security Considerations
[RFC5559] provides a general description of the security
considerations for PCN. This memo introduces no new considerations.
7. IANA Considerations
This memo includes no request to IANA.
8. Acknowledgements
The content of this memo bears a family resemblance to
[ID.briscoe-CL]. The authors of that document were Bob Briscoe,
Philip Eardley, and Dave Songhurst of BT, Anna Charny and Francois Le
Faucheur of Cisco, Jozef Babiarz, Kwok Ho Chan, and Stephen Dudley of
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.
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.
Charny, et al. Expires June 19, 2011 [Page 19]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
[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.
[RFC5559] Eardley, P., "Pre-Congestion Notification (PCN)
Architecture", RFC 5559, June 2009.
[RFC5670] Eardley, P., "Metering and Marking Behaviour of PCN-
Nodes", RFC 5670, November 2009.
[RFC5696] Moncaster, T., Briscoe, B., and M. Menth, "Baseline
Encoding and Transport of Pre-Congestion Information",
RFC 5696, November 2009.
9.2. Informative References
[ID.briscoe-CL]
Briscoe, B., "An edge-to-edge Deployment Model for Pre-
Congestion Notification: Admission Control over a DiffServ
Region (expired Internet Draft)", 2006.
[IEEE-Satoh]
Satoh, D. and H. Ueno, ""Cause and Countermeasure of
Overtermination for PCN-Based Flow Termination",
Proceedings of IEEE Symposium on Computers and
Communications (ISCC '10), pp. 155-161, Riccione, Italy",
June 2010.
[MeLe10] Menth, M. and F. Lehrieder, "PCN-Based Measured Rate
Termination", Computer Networks Journal (Elsevier) vol.
54, no. 13, pages 2099 - 2116, September 2010.
[RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration
Guidelines for DiffServ Service Classes", RFC 4594,
August 2006.
[RFCyyyy] Charny, A., Zhang, J., Karagiannis, G., Menth, M., and T.
Taylor, "PCN Boundary Node Behaviour for the Single
Marking (SM) Mode of Operation (Work in progress)",
Charny, et al. Expires June 19, 2011 [Page 20]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
December 2010.
Authors' Addresses
Anna Charny
Cisco Systems
300 Apollo Drive
Chelmsford, MA 01824
USA
Email: acharny@cisco.com
Fortune Huang
Huawei Technologies
Section F, Huawei Industrial Base,
Bantian Longgang, Shenzhen 518129
P.R. China
Phone: +86 15013838060
Email: fqhuang@huawei.com
Georgios Karagiannis
U. Twente
Phone:
Email: karagian@cs.utwente.nl
Michael Menth
University of Tuebingen
Sand 13
Tuebingen D-97074
Germany
Phone: +49-7071-2970505
Email: menth@informatik.uni-tuebingen.de
Charny, et al. Expires June 19, 2011 [Page 21]
Internet-Draft PCN CL Boundary Node Behaviour December 2010
Tom Taylor (editor)
Huawei Technologies
1852 Lorraine Ave
Ottawa, Ontario K1H 6Z8
Canada
Phone: +1 613 680 2675
Email: tom111.taylor@bell.net
Charny, et al. Expires June 19, 2011 [Page 22]
