Internet Engineering Task Force G. Karagiannis
Internet-Draft University of Twente
Intended status: Informational T. Taylor
Expires: August 08, 2012 Huawei
K. Chan
Consultant
M. Menth
University of Tuebingen
P. Eardley
BT
February 08, 2012
Requirements for Signaling of (Pre-) Congestion Information in a
DiffServ Domain
draft-ietf-pcn-signaling-requirements-08
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 first case, (2) is not required). The
signaling requirements pertain in particular to two edge behaviors,
"controlled load (CL)" and "single marking (SM)".
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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material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 08, 2012.
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Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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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
3. Signaling Requirements for Messages between Decision Point(s) and
PCN-Ingress-Nodes . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 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-11],
[draft-ietf-pcn-sm-edge-behaviour-08].
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-11],
[draft-ietf-pcn-sm-edge-behaviour-08]. 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.
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At the end of each measurement interval, or less frequently if
"optional report suppression" is activated, see
[draft-ietf-pcn-cl-edge-behaviour-11], [draft-ietf-pcn-sm-edge-
behaviour-08], the PCN-egress-node sends a report to the decision
point.
For the SM edge behavior, the report MUST contain:
o 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 rate of not-marked PCN-traffic (NM-rate) in octets/second,
o rate of PCN-marked traffic (PM-rate) in octets/second,
For the CL edge behavior, the report MUST contain:
o 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 rate of not-marked PCN-traffic (NM-rate) in octets/second,
o rate of threshold-marked PCN traffic (ThM-rate) in
octets/second,
o rate of excess-traffic-marked traffic (ETM-rate) in octets/second,
The number format and the rate units used by the signaling protocol
will limit the maximum rate that PCN can use. If signaling space is
tight it might be reasonable to impose a limit, but any such limit
may impose unnecessary constraints in future.
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.
As described in [draft-ietf-pcn-cl-edge-behaviour-11], PCN reports
from the PCN-egress-node to the decision point may contain flow
identifiers for individual flows within an ingress-egress-
aggregate that have recently experienced excess-marking. Hence,
the PCN report messages used by the PCN CL edge behavior MUST be
capable of carrying sequences of octet strings constituting such
identifiers."
Signaling messages SHOULD have a higher priority and a lower drop
precedence than PCN-packets, see [RFC5559], 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).
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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
decision point(s) are needed, see [draft-ietf-pcn-cl-edge-behaviour-
-11], [draft-ietf-pcn-sm-edge-behaviour-08].
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.
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, a lower
drop precedence than PCN-packets, and reliably, because they are sent
only when flow termination is needed, which is an urgent action.
Note that a complete system description for a PCN domain with
centralized Decision Point includes the signaling from Decision Point
to the PCN-ingress-nodes to control flow admission and termination.
However, this is a known problem whose solutions were given by,
for example, [RFC3084] or [RFC5431], and it lies outside the scope of
the present document.
4. Security Considerations
[RFC5559] provides a general description of the security
considerations for PCN. This memo relies on the security related
requirements on the PCN signaling, provided in [RFC5559]. In
particular, the signaling between the PCN-boundary-nodes must be
protected from attacks. For example, the recipient needs to
validate that the message is indeed from the node that claims to have
sent it. Possible measures include digest authentication and
protection against replay and man-in-the-middle attacks.
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For the generic aggregate RSVP protocol, specifically, additional
protection methods against security attacks are described in
[RFC4860].
5. IANA Considerations
This memo includes no request to IANA.
6. Acknowledgments
We would like to acknowledge the members of the PCN working group for
the discussions that produced the contents of this memo.
7. References
7.1. Normative References
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5559] P., Eardley, "Pre-Congestion Notification (PCN)
Architecture", RFC 5559, June 2009.
[draft-ietf-pcn-cl-edge-behaviour-11] 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 2011.
[draft-ietf-pcn-sm-edge-behaviour-08] 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 2011.
7.2. Informative References
[RFC3084] K. Chan, J. Seligson, D. Durham, S. Gai, K. McCloghrie, S.
Herzog, F. Reichmeyer, R. Yavatkar, A. Smith, "COPS Usage
for Policy Provisioning (COPS-PR)", RFC 3084, March 2001.
[RFC4860] F. Le Faucheur, B. Davie, P. Bose, C. Christou, M.
Davenport, "Generic Aggregate Resource ReSerVation
Protocol (RSVP) Reservations", RFC 4860, May 2007.
[RFC5431] D. Sun, "Diameter ITU-T Rw Policy Enforcement Interface
Application", RFC 5431, March 2009.
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Authors' Addresses
Georgios Karagiannis
University of Twente
P.O. Box 217
7500 AE Enschede,
The Netherlands
EMail: g.karagiannis@utwente.nl
Tom Taylor
Huawei Technologies
1852 Lorraine Ave.
Ottawa, Ontario K1H 6Z8
Canada
Phone: +1 613 680 2675
Email: tom.taylor.stds@gmail.com
Kwok Ho Chan
Consultant
Email: khchan.work@gmail.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
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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