One document matched: draft-ietf-pcn-cl-edge-behaviour-07.xml
<?xml version="1.0" encoding="US-ASCII"?>
<!-- This template is for creating an Internet Draft using xml2rfc,
which is available here: http://xml.resource.org. -->
<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
<!-- One method to get references from the online citation libraries.
There has to be one entity for each item to be referenced.
An alternate method (rfc include) is described in the
references. -->
<!ENTITY RFC2119 SYSTEM
"http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml">
<!ENTITY RFC2474 SYSTEM
"http://xml.resource.org/public/rfc/bibxml/reference.RFC.2474.xml">
<!ENTITY RFC2475 SYSTEM
"http://xml.resource.org/public/rfc/bibxml/reference.RFC.2475.xml">
<!ENTITY RFC3086 SYSTEM
"http://xml.resource.org/public/rfc/bibxml/reference.RFC.3086.xml">
<!ENTITY RFC5559 SYSTEM
"http://xml.resource.org/public/rfc/bibxml/reference.RFC.5559.xml">
<!ENTITY RFC5670 SYSTEM
"http://xml.resource.org/public/rfc/bibxml/reference.RFC.5670.xml">
<!ENTITY RFC5696 SYSTEM
"http://xml.resource.org/public/rfc/bibxml/reference.RFC.5696.xml">
]>
<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
<!-- used by XSLT processors -->
<!-- For a complete list and description of processing instructions
(PIs), please see http://xml.resource.org/authoring/README.html.
-->
<!-- Below are generally applicable Processing Instructions (PIs)
that most I-Ds might want to use. -->
<?rfc strict="yes" ?>
<!-- give errors regarding ID-nits and DTD validation -->
<!-- control the table of contents (ToC) -->
<?rfc toc="yes"?>
<!-- generate a ToC -->
<?rfc tocdepth="4"?>
<!-- the number of levels of subsections in ToC. default: 3 -->
<!-- control references -->
<?rfc symrefs="yes"?>
<!-- use symbolic references tags, i.e, [RFC2119] instead of [1] -->
<?rfc sortrefs="yes" ?>
<!-- sort the reference entries alphabetically -->
<!-- control vertical white space
(using these PIs as follows is recommended by the RFC Editor) -->
<?rfc compact="yes" ?>
<!-- do not start each main section on a new page -->
<?rfc subcompact="no" ?>
<!-- keep one blank line between list items -->
<!-- end of list of popular I-D processing instructions -->
<rfc category="info" docName="draft-ietf-pcn-cl-edge-behaviour-07"
ipr="trust200902">
<!-- ***** FRONT MATTER ***** -->
<front>
<!-- The abbreviated title is used in the page header - it is
only necessary if the full title is longer than 39 characters
-->
<title abbrev="PCN CL Boundary Node Behaviour">PCN Boundary Node
Behaviour for the Controlled Load (CL) Mode of Operation</title>
<author fullname="Anna Charny" initials="A." surname="Charny">
<organization>Cisco Systems</organization>
<address>
<postal>
<street>300 Apollo Drive</street>
<city>Chelmsford</city>
<region>MA</region>
<code>01824</code>
<country>USA</country>
</postal>
<email>acharny@cisco.com</email>
</address>
</author>
<author fullname="Fortune Huang" initials="F.Q." surname="Huang">
<organization>Huawei Technologies</organization>
<address>
<postal>
<street>Section F, Huawei Industrial Base, </street>
<city>Bantian Longgang</city>
<region>Shenzhen</region>
<code>518129</code>
<country>P.R. China</country>
</postal>
<phone>+86 15013838060</phone>
<email>fqhuang@huawei.com</email>
</address>
</author>
<author fullname="Georgios Karagiannis" initials="G."
surname="Karagiannis">
<organization>U. Twente</organization>
<address>
<postal>
<street> </street>
<city></city>
<region></region>
<code></code>
<country></country>
</postal>
<phone></phone>
<email>karagian@cs.utwente.nl</email>
</address>
</author>
<author fullname="Michael Menth" initials="M." surname="Menth">
<organization>University of Wuerzburg</organization>
<address>
<postal>
<street>Am Hubland</street>
<city>Wuerzburg</city>
<code>D-97074</code>
<country>Germany</country>
</postal>
<phone>+49-931-888-6644</phone>
<email>menth@informatik.uni-wuerzburg.de</email>
</address>
</author>
<author fullname="Tom Taylor" initials="T." role="editor"
surname="Taylor">
<organization>Huawei Technologies</organization>
<address>
<postal>
<street>1852 Lorraine Ave</street>
<city>Ottawa</city>
<region>Ontario</region>
<country>Canada</country>
<code>K1H 6Z8</code>
</postal>
<phone>+1 613 680 2675</phone>
<email>tom111.taylor@bell.net</email>
</address>
</author>
<date year="2010"/>
<!-- Meta-data Declarations -->
<area>Transport</area>
<workgroup>Internet Engineering Task Force</workgroup>
<keyword>PCN</keyword>
<keyword>controlled load</keyword>
<keyword>CL</keyword>
<keyword>boundary node behaviour</keyword>
<abstract>
<t>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. </t>
</abstract>
</front>
<middle>
<section anchor="intro" title="Introduction">
<t> The objective of Pre-Congestion Notification (PCN) is to protect
the quality of service 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 on whether to admit or terminate PCN-flows. For
more details see <xref target="RFC5559"/>. </t>
<t>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
<xref target="RFC3086"/>, filled out with the appropriate content. The
present document accomplishes these tasks for the controlled load (CL)
mode of operation. </t>
<section anchor="terms" title="Terminology">
<t>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 [RFC2119].</t>
<t>In addition to the terms defined in <xref target="RFC5559"/>,
this document uses the following terms:
<list style="hanging" hangIndent="3">
<t hangText="Decision Point">
<vspace blankLines="0" />
The node that makes the decision about which flows to admit and to
terminate. In a given network deployment, this may be the
PCN-ingress-node or a centralized control node. Regardless of the
location of the Decision Point, the ingress node is the point where
the decisions are enforced.</t>
<t hangText="NM-rate">
<vspace blankLines="0" />
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 <xref target="egrColl"/>.</t>
<t hangText="ThM-rate">
<vspace blankLines="0" />
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 <xref target="egrColl"/>.</t>
<t hangText="ETM-rate">
<vspace blankLines="0" />
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 <xref target="egrColl"/>.</t>
<t hangText="PCN-sent-rate">
<vspace blankLines="0" />
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 <xref target="ingrBehav"/>.</t>
<t hangText="Congestion level estimate (CLE)">
<vspace blankLines="0"/>
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) over a short period. The CLE is used to derive the
PCN-admission-state (<xref target="decisAdmit"/>) and also by the
report suppression procedure (<xref target="repSuppress"/>) if
report suppression is activated.</t>
<t hangText="PCN-admission-state">
<vspace blankLines="0" />
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 <xref target="decisAdmit"/>.</t>
<t hangText="Sustainable aggregate rate (SAR)">
<vspace blankLines="0" />
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 must
be terminated. For further details see <xref target="decisTerm"/>.</t>
<t hangText="CLE-reporting-threshold">
<vspace blankLines="0" />
A configurable value against which the CLE is compared as part of the
report suppression procedure. For further details, see
<xref target="repSuppress"/>.</t>
<t hangText="CLE-limit">
<vspace blankLines="0" />
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 <xref target="decisAdmit"/>.</t>
<t hangText="T-meas">
<vspace blankLines="0" />
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, 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
<xref target="egressBehav"/>.</t>
<t hangText="T-maxsuppress">
<vspace blankLines="0" />
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 <xref target="repSuppress"/>.</t>
<t hangText="T-fail">
<vspace blankLines="0" />
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 <xref target="decisSig"/>.</t>
</list>
</t>
</section><!-- terms -->
</section><!-- intro -->
<section anchor="coreAssum" title="Assumed Core Network Behaviour for CL">
<t> 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:
<list style="symbols">
<t> PCN-interior-nodes perform threshold-marking and excess-traffic-marking
of packets according to the rules specified in <xref target="RFC5670"/>, and
any additional rules specified in the applicable encoding extension document;
</t>
<t> encoding of PCN status within individual packets is based on
<xref target="RFC5696"/>, extended to provide a third PCN encoding state.
A possible extension is documented in <xref target="ID.PCN3in1"/>; </t>
<t> the PCN-domain satisfies the conditions specified in the applicable
encoding extension document; </t>
<t> on each link the reference rate for the threshold-meter is configured
to be equal to the PCN-admissible-rate for the link; </t>
<t> on each link the reference rate for the excess traffic meter is
configured to be equal to the PCN-supportable-rate for the link; </t>
</list>
</t>
<t> According to <xref target="RFC5696"/>, the encoding extension documents
should specify the allowable transitions between marking states. However, to
be absolutely clear, these allowable transitions are specified here. At any
interior node, the only permitted transitions are these:
<list style="symbols">
<t>a PCN-packet that is not-marked (NM) MAY be threshold-marked (ThM)
or excess-traffic-marked (ETM);</t>
<t>a PCN-packet that is threshold-marked (ThM) MAY be
excess-traffic-marked (ETM).</t>
</list>
An interior node MUST NOT perform any of the following:
<list style="symbols">
<t>re-mark a packet from PCN to non-PCN, or from non-PCN to PCN;</t>
<t>re-mark a PCN-packet from threshold-marked (ThM) to not-marked (NM);</t>
<t>re-mark a PCN-packet from excess-traffic-marked (ETM) to not-marked (NM)
or threshold-marked (ThM).</t>
</list>
</t>
</section><!-- coreAssum -->
<section anchor="behaviours" title="Node Behaviours">
<section anchor="overBehav" title="Overview">
<t>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). </t>
<t>The PCN-egress-node collects the rates of not-marked, threshold-marked,
and excess-traffic-marked PCN-traffic for each ingress-egress-aggregate and
reports them to the Decision Point. It may also identify PCN-flows that have
experienced excess-traffic-marking. For a detailed description, see
<xref target="egressBehav"/>.</t>
<t>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
<xref target="ingrBehav"/>.</t>
<t>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
<xref target="decisBehav"/>.</t>
</section><!-- overBehav -->
<section anchor="egressBehav" title="Behaviour of the PCN-Egress-Node">
<section anchor="egrColl" title="Data Collection">
<t>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:
<list style="symbols">
<t>NM-rate: octets per second of PCN-traffic in PCN-packets that are
not-marked;</t>
<t>ThM-rate: octets per second of PCN-traffic in PCN-packets that are
threshold-marked;</t>
<t>ETM-rate: octets per second of PCN-traffic in PCN-packets that are
excess-traffic-marked.</t>
</list>
It is RECOMMENDED that the measurement interval, T-meas, between successive
calculations of these quantities be in the range 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>
<t>The PCN-traffic SHOULD be metered continuously and the 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.</t>
<t>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.
<list style="empty">
<t>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.</t>
</list>
</t>
</section><!-- egrColl -->
<section anchor="egrSig" title="Reporting the PCN Data">
<t>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,
ThM-rate, and ETM-rate to the Decision Point each time that it calculates
them.</t>
<t>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. </t>
</section><!-- egrSig -->
<section anchor="repSuppress" title="Optional Report Suppression">
<t>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 is discussed further at the
end of this sub-section, but functions as a keep-alive mechanism for
signalling between the PCN-egress-node and the Decision Point.</t>
<t>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.
<list style="numbers">
<t>As well as the quantities NM-rate, ThM-rate, and ETM-rate, the
PCN-egress-node MUST calculate the congestion level estimate (CLE) for
each measurement interval. The CLE is equal to the ratio:
<list style="empty">
<t>(ThM-rate + ETM-rate) / (NM-rate + ThM-rate + ETM-rate)</t>
</list>
if any PCN-traffic was observed, or zero otherwise.
</t>
<t>If the calculated CLE for the latest measurement interval or for the
immediately previous interval is 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.</t>
<t>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. </t>
<t>If neither of the preceding conditions holds, the PCN-egress-node MUST
NOT send a report for the latest measurement interval.</t>
</list>
</t>
<t>Each report sent to the Decision Point when report suppression has been
activated MUST contain the values of NM-rate, ThM-rate, ETM-rate, and CLE
that were calculated for the most recent measurement interval. 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.</t>
<t>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 the two nodes are in
operation. However, depending on the transport used for reporting, the
operator may choose to set T-maxsuppress to an effectively infinite value.
For example, the transport may include its own keep-alive signalling at a
frequency such that PCN keep-alive signalling is redundant. </t>
</section><!-- repSuppress -->
</section><!-- egressBehav -->
<section anchor="decisBehav" title="Behaviour at the Decision Point">
<t>Operators may choose to use PCN procedures just for flow admission, or just
for flow termination, or for both. The 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.</t>
<t>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 must be in operation, but the description of
such a system is out of scope of this document and depends on local
arrangements.</t>
<section anchor="decisAdmit" title="Flow Admission">
<t>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
<list style="empty">
<t>CLE = (ThM-rate + ETM-rate) / (NM-rate + ThM-rate + ETM-rate)</t>
</list>
if any PCN-traffic was observed, or CLE = 0 if all the rates are zero.</t>
<t>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".
<list style="empty">
<t>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.</t>
</list>
</t>
<t>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. </t>
</section><!-- decisAdmit -->
<section anchor="decisTerm" title="Flow Termination">
<t>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.
<list style="empty">
<t>If the Decision Point is collocated with the PCN-ingress-node, the
request and response are internal operations.</t>
</list>
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 the 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:
<list style="numbers">
<t>The sustainable aggregate rate (SAR) for the given
ingress-egress-aggregate is estimated by the sum:
<list style="empty">
<t>SAR = NM-rate + ThM-rate</t>
</list>
for the latest reported interval.</t>
<t>The amount of traffic that should be terminated is the difference:
<list style="empty">
<t>PCN-sent-rate - SAR,</t>
</list>
where PCN-sent-rate is the value provided by the PCN-ingress-node.
</t>
</list>
</t>
<t>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.</t>
<t>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 <xref target="IEEE-Satoh"/>
and sections 4.2 and 4.3 of <xref target="Menth08-sub-9"/>).</t>
<t>If the egress node has supplied a list of PCN-flow identifiers
(<xref target="egressBehav"/>), the Decision Point SHOULD first consider
terminating PCN-flows in that list. In general, the selection of flows for
termination MAY be guided by policy.</t>
</section><!-- decisTerm -->
<section anchor="decisSig" title="Decision Point Action For Missing
PCN-Boundary-Node Reports">
<t>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.</t>
<t>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.</t>
</section><!-- decisSig -->
</section><!-- decisBehav -->
<section anchor="ingrBehav" title="Behaviour of the Ingress Node">
<t>The PCN-ingress-node MUST provide the estimated 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.
<list style="empty">
<t>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 30
PCN-packets to achieve reasonable statistical reliability. </t>
</list>
</t>
</section><!-- ingrBehav -->
<section anchor="timers" title="Summary of Timers">
<t><xref target="tab_Timers"/> summarizes the timers implied by the preceding
procedures. The three 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.</t>
<texttable anchor="tab_Timers" title="Timers Used For the CL Boundary Node
Behaviour">
<ttcol>Timer</ttcol>
<ttcol>Location</ttcol>
<ttcol>Incidence</ttcol>
<ttcol>Limit</ttcol>
<ttcol>Action on Expiry</ttcol>
<c>t-meas</c>
<c>Egress node</c>
<c>One per node</c>
<c>T-meas</c>
<c>Calculate and possibly report NM-rate, ThM-rate, ETM-rate and
conditionally CLE for each IEA.</c>
<c>-</c>
<c>-</c>
<c>-</c>
<c>-</c>
<c>-</c>
<c>t-maxsuppress</c>
<c>Egress node</c>
<c>One per IEA if report suppression is enabled.</c>
<c>T-maxsuppress</c>
<c>Send a report for that IEA at the next expiry of T-meas.</c>
<c>-</c>
<c>-</c>
<c>-</c>
<c>-</c>
<c>-</c>
<c>t-fail</c>
<c>Decision point</c>
<c>One per egress node</c>
<c>T-fail</c>
<c>Assume failure and cease to admit flows passing through that egress
node.</c>
<postamble>IEA = ingress-egress-aggregate</postamble>
</texttable>
<t>The value of T-meas SHOULD be configurable, and is RECOMMENDED to be of
the order of 100 to 500 ms.</t>
<t>t-maxsuppress is active only when report suppression is enabled. The value
of T-maxsuppress SHOULD be configurable. The appropriate value depends on the
transport used to carry the egress node reports. For unreliable transport,
T-maxsuppress is RECOMMENDED to be of the order of one second.</t>
<t>The value of T-fail MUST be configurable. When unreliable transport is
used, the value of T-fail is RECOMMENDED to be of the order of
3 * T-maxsuppress if report suppression is enabled, and of the order of
3 * T-meas if report suppression is not enabled. When reliable transport is
used, the operator may choose to provide similar values for T-fail or may
choose to disable report timing by setting an effectively infinite value for
T-fail.</t>
</section><!-- timers -->
</section><!-- behaviours -->
<section anchor="aggregates" title="Identifying Ingress and Egress
Nodes for PCN Traffic">
<t>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.</t>
<t>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.</t>
</section><!-- aggregates -->
<section anchor="PDBSpec" title="Specification of Diffserv Per-Domain Behaviour">
<t>This section provides the specification required by <xref target="RFC3086"/>
for a per-domain behaviour.</t>
<section anchor="PDBApplic" title="Applicability">
<t>This section draws heavily upon points made in the PCN architecture document,
<xref target="RFC5559"/>. </t>
<t>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. The CL boundary node behaviour is less likely to terminate
too many flows under such circumstances than the SM boundary node behaviour
(<xref target="I-D.SM-edge-behaviour"/>).</t>
</section><!-- PDBApplic -->
<section anchor="PDBTechSpec" title="Technical Specification">
<t>The technical specification of the PCN CL per domain behaviour is provided
by the contents of <xref target="RFC5559"/>, <xref target="RFC5696"/>,
<xref target="RFC5670"/>, the specification of the encoding extension
(e.g., <xref target="ID.PCN3in1"/>), and the present document. </t>
</section><!-- PDBTechSpec -->
<section anchor="PDBAttrib" title="Attributes">
<t>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.</t>
</section><!-- PDBAttrib -->
<section anchor="PDBParms" title="Parameters">
<t>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.</t>
<t>Parameters at the PCN-ingress-node: <vspace blankLines="0"/>
-----------------------------------
<list style="symbols">
<t>Filters for distinguishing PCN from non-PCN inbound traffic.</t>
<t>The markings to be applied to PCN-traffic.</t>
<t>Reference rates on each inward link for the PCN-threshold-rate and
PCN-excess-rate; see <xref target="coreAssum"/>.</t>
<t>The information needed to distinguish PCN-traffic belonging to a given
ingress-egress-aggregate.</t>
</list>
</t>
<t>Parameters at the PCN-egress-node: <vspace blankLines="0"/>
----------------------------------
<list style="symbols">
<t>The measurement interval T-meas. </t>
<t>Whether report suppression is enabled and, if so, the values of the
CLE-reporting-threshold and T-maxsuppress.</t>
<t>Whether individual flow identifiers must be reported for
excess-traffic-marked PCN-traffic.</t>
<t>The information needed to distinguish PCN-traffic belonging to a given
ingress-egress-aggregate.</t>
<t>The marking rules for re-marking PCN-traffic leaving the PCN domain.</t>
</list>
</t>
<t>Parameters at each interior node: <vspace blankLines="0"/>
---------------------------------
<list style="symbols">
<t>Reference rates on each link for the PCN-threshold-rate and
PCN-excess-rate; see <xref target="coreAssum"/>.</t>
<t>The markings to be applied to PCN-traffic, including the identification
of PCN-packets and the encodings to indicate threshold-marking and
excess-traffic-marking..</t>
</list>
</t>
<t>Parameters at the Decision Point: <vspace blankLines="0"/>
---------------------------------
<list style="symbols">
<t>Activation/deactivation of PCN-based flow admission.</t>
<t>Activation/deactivation of PCN-based flow termination.</t>
<t>The value of CLE-limit.</t>
<t>The maximum interval T-fail between reports from a given PCN-egress-node,
for detecting failure of communications with that node.</t>
<t>The information needed to map between each ingress-egress-aggregate and the
corresponding PCN-ingress-node and PCN-egress-node. </t>
</list>
</t>
</section><!-- PDBParms -->
<section anchor="PDBAssum" title="Assumptions">
<t>Assumed that a specific portion of link capacity has been reserved for
PCN-traffic. </t>
</section><!-- PDBAssum -->
<section anchor="PDBExamp" title="Example Uses">
<t>The PCN CL behaviour may be used to carry real-time traffic, particularly
voice and video.</t>
</section><!-- PDBExamp -->
<section anchor="PDBEnv" title="Environmental Concerns">
<t>The PCN CL per-domain behaviour may interfere with the use of end-to-end
ECN due to reuse of ECN bits for PCN marking. See the applicable PCN marking
specifications for details.</t>
</section><!-- PDBEnv -->
<section anchor="PDBSec" title="Security Considerations">
<t>Please see the security considerations in <xref target="secur"/> as well
as those in <xref target="RFC2474"/> and <xref target="RFC2475"/>.</t>
</section><!-- PDBSec -->
</section><!-- PDBSpec -->
<section anchor="secur" title="Security Considerations">
<t><xref target="RFC5559"/> provides a general description of the security
considerations for PCN. This memo introduces no new considerations.</t>
</section><!-- secur -->
<section anchor="iana" title="IANA Considerations">
<t>This memo includes no request to IANA.</t>
</section><!-- iana -->
<section anchor="Acknowledgements" title="Acknowledgements">
<t>The content of this memo bears a family resemblance to
<xref target="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.</t>
<t>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.</t>
<t>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.</t>
</section><!-- Acknowledgements -->
</middle>
<!-- *****BACK MATTER ***** -->
<back>
<references title="Normative References">
&RFC2119;
&RFC2474;
&RFC2475;
&RFC5559;
&RFC5670;
&RFC5696;
</references>
<references title="Informative References">
&RFC3086;
<reference anchor="ID.briscoe-CL">
<front>
<title>An edge-to-edge Deployment Model for Pre-Congestion Notification:
Admission Control over a DiffServ Region (expired Internet Draft)</title>
<author initials="B." surname="Briscoe">
<organization>BT & UCL</organization>
</author>
<date year="2006" />
</front>
</reference>
<reference anchor="ID.PCN3in1">
<front>
<title>PCN 3-State Encoding Extension in a single DSCP (Work in progress)
</title>
<author initials="B." surname="Briscoe">
<organization>BT & UCL</organization>
</author>
<date year="2010" month="July" />
</front>
</reference>
<reference anchor="Menth08-sub-9"
target="http://www3.informatik.uni-wuerzburg.de/
~menth/Publications/papers/Menth08-Sub-9.pdf">
<front>
<title>PCN-Based Measured Rate Termination</title>
<author initials="M." surname="Menth">
<organization>U. Wuerzburg</organization>
</author>
<author initials="F." surname="Lehrieder">
<organization>U. Wuerzburg</organization>
</author>
<date year="2009" month="July"/>
</front>
<format type="PDF" target="http://www3.informatik.uni-wuerzburg.de/
~menth/Publications/papers/Menth08-Sub-9.pdf" />
</reference>
<reference anchor="I-D.SM-edge-behaviour">
<front>
<title>PCN Boundary Node Behaviour for the Single Marking (SM)
Mode of Operation (Work in progress)</title>
<author initials="A." surname="Charny">
<organization>Cisco</organization>
</author>
<author initials="J." surname="Zhang">
<organization>Cisco</organization>
</author>
<author initials="G." surname="Karagiannis">
<organization>U. Twente</organization>
</author>
<author initials="M." surname="Menth">
<organization>U. Wuerzburg</organization>
</author>
<author initials="T." surname="Taylor">
<organization>Huawei Technologies</organization>
</author>
<date year="2010" month="June"/>
</front>
</reference>
<reference anchor="IEEE-Satoh">
<front>
<title>"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</title>
<author initials="D." surname="Satoh">
<organization>NTT-AT</organization>
</author>
<author initials="H." surname="Ueno">
<organization>NTT-AT</organization>
</author>
<date month="June" year="2010" />
</front>
</reference>
</references>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-23 09:22:23 |