Internet Engineering Task Force G. Karagiannis
Internet-Draft University of Twente
Intended status: Informational T. Taylor
Expires: December 15, 2011 K. Chan
Huawei Technologies
M. Menth
University of Tuebingen
P. Eardley
BT
June 15, 2011
Requirements for Signaling of (Pre-) Congestion Information in a
DiffServ Domain
draft-ietf-pcn-signaling-requirements-05
Abstract
Precongestion notification (PCN) is a means for protecting quality of
service for inelastic traffic admitted to a Diffserv domain. The
overall PCN architecture is described in RFC 5559. This memo
describes the requirements for the signaling applied within the PCN
domain: (1) PCN-feedback-information is carried from the PCN-egress-
node to the decision point;(2) the decision point may ask the PCN-
ingress-node to measure, and report back, the rate of sent PCN-
traffic between that PCN-ingress-node and PCN-egress-node. The
decision point may be either collocated with the PCN-ingress-node or
a centralized node (in the latter case, (2) is not required). The
signaling requirements pertain in particular to two edge behaviours,
"controlled load (CL)" and "single marking (SM)"
[draft-ietf-pcn-cl-edge- behaviour-08],
[draft-ietf-pcn-sm-edge-behaviour-05].
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
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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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 15, 2011.
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Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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.
Requirements Language
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 RFC 2119 [RFC2119].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Signaling Requirements for Messages from the PCN-Egress-Nodes to
Decision Point(s) . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Specification of PCN-Flow Identifiers . . . . . . . . . . . 4
3. Signaling Requirements for Messages between Decision Point(s) and
PCN-Ingress-Nodes . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
The main objective of Pre-Congestion Notification (PCN) is to support
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 and flow termination. Admission control
is used to decide whether to admit or block a new flow request while
flow termination is used in abnormal circumstances to decide
whether to terminate some of the existing flows. To support these
two features, the overall rate of PCN-traffic is metered on every
link in the 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 boundary
nodes about overloads before any congestion occurs (hence "pre-
congestion" notification). The PCN-egress-nodes measure the rates of
differently marked PCN traffic in periodic intervals and report these
rates to the decision points for admission control and flow
termination, based on which they take their decisions. The decision
points may be collocated with the PCN-ingress-nodes or their function
may be implemented in a centralized node.
For more details see [RFC5559],
[draft-ietf-pcn-cl-edge-behaviour-08],
[draft-ietf-pcn-sm-edge-behaviour-05].
This memo specifies the requirements on signaling protocols:
o to carry reports from a PCN-egress-node to the decision point,
o to carry requests, from the decision point to a PCN-ingress-node,
that trigger the PCN-ingress-node to measure the PCN-sent-rate,
o to carry reports, from a PCN-ingress-node to the decision
point.
The latter two messages are only needed if the decision point and
PCN-ingress-node are not collocated.
2. Signaling Requirements for Messages from the PCN-Egress-Nodes to
Decision Point(s)
The PCN-egress-node measures- per ingress-egress-aggregate the rates
of differently marked PCN-traffic in regular intervals. The
measurement intervals are recommended to take a fixed value between
100 ms and 500 ms, see [draft-ietf-pcn-cl-edge-behaviour-08],
[draft-ietf-pcn-sm-edge-behaviour-05]. At the end of each measurement
interval, the PCN-egress-node calculates the congestion-level-
estimate (CLE) based on these quantities. The PCN-egress-node MAY be
configured to record a set of identifiers of PCN-flows for which it
received excess-traffic-marked packets during the last measurement
interval. The latter may be useful to perform flow termination in
networks with multipath routing.
At the end of each measurement interval, or less frequently if
"optional report suppression" is activated, see
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[draft-ietf-pcn-cl-edge-behaviour-08], [draft-ietf-pcn-sm-edge-
behaviour-05], the PCN-egress-node sends a report to the decision
point.
For the SM edge behaviour, the report MUST contain:
o the identifier of the PCN-ingress-node and the identifier of the
PCN-egress-node (typically their IP addresses); together they
specify the ingress-egress-aggregate to which the report refers,
o the rate of not-marked PCN-traffic (NM-rate) in octets/second,
o rate of PCN-marked traffic in octets/second,
o the congestion-level-estimate, which is a number between zero and
one.
For the CL edge behaviour, the report MUST contain:
o the identifier of the PCN-ingress-node and the identifier of the
PCN-egress-node (typically their IP addresses); together they
specify the ingress-egress-aggregate to which the report refers,
o the rate of threshold-marked PCN traffic (ThM-rate) in
octets/second,
o rate of excess-traffic-marked traffic (ETM-rate) in octets/second,
o the congestion-level-estimate, which is a number between zero and
one.
The number format and the rate units used by the signalling protocol
will limit the maximum rate that PCN can use. If signalling space is
tight it might be reasonable to impose a limit, but any such limit
may impose unnecessary constraints in future.
For both CL and SM edge behaviours, the report MAY also contain:
o a set of PCN-flow identifiers (see Section 2.1).
The signaling report can either be sent directly to the decision
point or it can "piggy-back", i.e., be included within some other
message that passes through the PCN-egress-node and then reaches the
decision point.
Signaling messages SHOULD have a higher priority than data packets to
deliver them quickly and to avoid that they are dropped in case of
overload.
The load generated by the signaling protocol SHOULD be minimized. We
give three examples that may help to achieve that goal:
o piggy-backing the reports by the PCN-egress-nodes to the decision
point(s) onto other signaling messages that are already in place,
o reducing the amount of reports to be sent by optional report
suppression,
o combining reports for different ingress-egress-aggregates in a
single message (if they are for the same decision point).
As PCN reports are sent regularly, additional reliability mechanisms
are not needed. This also holds in the presence of optional report
suppression as reports are sent periodically if actions by the
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decision point(s) are needed, see [draft-ietf-pcn-cl-edge-behaviour-
-08], [draft-ietf-pcn-sm-edge-behaviour-05].
2.1 Specification of PCN-Flow Identifiers
The representation of a PCN-flow identifier depends on the
surrounding environment, e.g., pure IP, MPLS, GMPLS, etc.
Examples of such PCN-flow identifier representations can be found in
[RFC2205], [RFC3175] [RFC3209], [RFC3473], [RFC4804].
In pure IP networks, the identifier may consist of a subset of the
following information:
o source IP address;
o destination IP address
o protocol identifier and higher layer (port) addressing
o flow label (typical for IPv6)
o SPI field for IPsec encapsulated data
o DSCP/TOS field
Note, where a PCN-flow consists of a collection of microflows, then
the PCN-flow is identified by the PCN-ingress-node's and PCN-egress-
node's identifiers (typically their IP addresses), which are already
part of the report.
3. Signaling Requirements for Messages between Decision Point(s) and
PCN-Ingress-Nodes
Through request-response signaling between the decision point and
PCN-ingress-node, the decision point requests and in response the
PCN-ingress-node measures and reports the PCN-sent-rate for a
specific ingress-egress-aggregate. Signaling is needed only if the
decision point and PCN-ingress-node are not collocated.
The request MUST contain:
o the identifier of the PCN-ingress-node and the identifier of the
PCN-egress-node; together they determine the ingress-egress-
aggregate for which the PCN-sent-rate is requested,
o the identifier of the decision point that requests the PCN-sent-
rate.
The report MUST contain:
o the PCN-sent-rate in octets/second,
o the identifier of the PCN-ingress-node and the identifier of the
PCN-egress-node.
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The request MUST be addressed to the PCN-ingress-node, and the report
MUST be addressed to the decision point that requested it.
The request and the report SHOULD be sent with high priority and
reliably, because they are sent only when flow termination is needed,
which is an urgent action.
4. Security Considerations
[RFC5559] provides a general description of the security
considerations for PCN. This memo does not introduce additional
security considerations.
5. IANA Considerations
This memo includes no request to IANA.
6. Acknowledgements
We would like to acknowledge the members of the PCN working group for
the discussions that generated the contents of this memo.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5559] Eardley, P., "Pre-Congestion Notification (PCN)
Architecture", RFC 5559, June 2009.
[draft-ietf-pcn-cl-edge-behaviour-08] T. Taylor, A, Charny,
F. Huang, G. Karagiannis, M. Menth, "PCN Boundary Node
Behaviour for the Controlled Load (CL) Mode of Operation
(Work in progress)", December 2010.
[draft-ietf-pcn-sm-edge-behaviour-05] A. Charny, J. Zhang,
G. Karagiannis, M. Menth, T. Taylor, "PCN Boundary Node
Behaviour for the Single Marking (SM) Mode of Operation
(Work in progress)", December 2010.
7.2. Informative References
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
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[RFC3175] Baker, F., Iturralde, C. Le Faucher, F., Davie, B.,
"Aggregation of RSVP for IPv4 and IPv6 Reservations",
RFC 3175, 2001.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473,
January 2003.
[RFC4804] F. Le Faucheur, "Aggregation of Resource ReSerVation
Protocol (RSVP) Reservations over MPLS TE/DS-TE Tunnels",
RFC 4804, February 2007.
Authors' Addresses
Georgios Karagiannis
University of Twente
P.O. Box 217
7500 AE Enschede,
The Netherlands
EMail: g.karagiannis@ewi.utwente.nl
Tom Taylor
Huawei Technologies
1852 Lorraine Ave.
Ottawa, Ontario K1H 6Z8
Canada
Phone: +1 613 680 2675
Email: tom111.taylor@bell.net
Kwok Ho Chan
Huawei Technologies
125 Nagog Park
Acton, MA 01720
USA
Email: khchan@huawei.com
Michael Menth
University of Tuebingen
Department of Computer Science
Chair of Communication Networks
Sand 13
72076 Tuebingen
Germany
Phone: +49 7071 29 70505
Email: menth@informatik.uni-tuebingen.de
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Philip Eardley
BT
B54/77, Sirius House Adastral Park Martlesham Heath
Ipswich, Suffolk IP5 3RE
United Kingdom
EMail: philip.eardley@bt.com
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