Internet Engineering Task Force G. Karagiannis
Internet-Draft University of Twente
Intended status: Informational T. Taylor
Expires: April 20, 2011 K. Chan
Huawei Technologies
M. Menth
University of Wurzburg
October 20, 2010
Requirements for Signaling of (Pre-) Congestion Information in a
DiffServ Domain
draft-ietf-pcn-signaling-requirements-01
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: PCN feedback is carried from the PCN-egress-node to the
decision point and the decision point may demand for the measurement
and delivery of the PCN rate sent at the PCN-ingress-node. The
decision point may be either collocated with the PCN-ingress-node or
a centralized node.
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
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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 April 18, 2011.
Copyright Notice
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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
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(http://trustee.ietf.org/license-info) in effect on the date of
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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
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Signaling Requirements between PCN-egress-nodes and
Decision Point . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 PCN Reporting Frequency . . . . . . . . .. . . . . . . . . . . 4
2.2 Signaled PCN egress Feedback . . . . . . .. . . . . . . . . . .5
2.3 Signaling Requirements . . . . . . . . . .. . . . . . . . . . .6
2.3.1 Priority of Signaling Messages . . . . . . . . . . . . . . 6
2.3.2 Local Information Exchange. . . . . . . . . . . . . . . . .6
2.3.3 Carry Identification of PCN edge Nodes . . . . . . . . . .6
2.3.4 Carry Identification of ingress-egress-aggregates . . . . 6
2.3.5 Signaling Load. . . . . . .. . . . . . . . . . . . . . . . 6
2.3.6 Reliability. . . . . . .. . . . . . . . . . . . . . . . . 7
2.3.7 Security. . . . . . .. . . . . . . . . . . . . . . . . . 7
2.4. Filter Specifications . . . . . . . . . . . . . . . . . . . . 7
3. Signaling Requirements between Decision Point and
PCN-ingress-nodes . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1 Signaled PCN ingress Feedback. . . . . . . . . . . . . . . . . 8
3.2 Signaled Decision Point Trigger. . . . . . . . . . . . . . . . 8
3.3 Signaling Requirements . . . . . . . . . .. . . . . . . . . . .8
4. Security Considerations . . . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
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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 as so-called PCN feedback 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-07],
[draft-ietf-pcn-sm-edge-behaviour-04].
Thus, signaling is needed to transport PCN feedback from PCN-egress-
nodes towards the decision point. Moreover, signaling is needed that
the decision point can trigger the PCN-ingress-node to measure the
PCN traffic rate and send these measurement results to the decision
point.
This memo briefly describes the signaled content and specifies the
requirements that have to be satisfied by the signaling protocols.
1.1. Terminology
In addition to the terms defined in [RFC5559], this document uses the
following terms:
Decision Point:
The node that makes the decision about which flows to admit and to
terminate. In a given network deployment, this may be the ingress
node or a centralized control node. Of course, regardless of the
location of the decision point, the ingress node is the point
where the decisions are enforced.
PCN egress feedback:
Content used by the PCN-egress-node to report and inform the
decision point about measurements required during flow
admission and flow termination decisions.
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PCN ingress feedback:
Content used by the PCN-ingress-node to report and inform the
decision point about measurements required during flow termination
decisions.
ingress rate request:
A message sent by the decision point towards the PCN-ingress-node
to request the PCN-ingress-node to measure and report the value of
the rate of admitted PCN traffic for a given
ingress-egress-aggregate.
Congestion level estimate (CLE)
A value derived from the measurement of PCN packets calculated 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. For further details see
[draft-ietf-pcn-cl-edge-behaviour-07] and [draft-ietf-pcn-sm-edge-
behaviour-04].
2. Signaling requirements between PCN-egress-nodes and
Decision Point
The PCN-egress-node measures the rates of differently marked PCN
traffic in regular intervals and signals them as PCN egress feedback
to the decision point.
This section describes the PCN egress feedback and the requirements
that apply to signaling protocols used for the transport of PCN
feedback from PCN-egress-nodes to decision points.
Note that if the decision point and the PCN-ingress-node are
collocated, then the signaling requirements described in this section
apply to the signaling between PCN-egress-nodes and PCN-ingress-
nodes.
2.1 PCN Reporting Frequency
The specification of PCN-based admission control and flow termination
in [draft-ietf-pcn-cl-edge-behaviour-07], [draft-ietf-pcn-sm-edge-
behaviour-04] suggest measurement and reporting intervals at the PCN-
egress-nodes of 100 to 500 ms. The PCN reporting frequency can
provide some level of reliability. Therefore, it is considered that
for regularly reported information, additional reliability mechanisms
are not needed, see Section 2.3.6. The following PCN contents are
sent regularly: rate of not-marked PCN traffic, rate of threshold-
marked PCN traffic, rate of excess-traffic-marked PCN traffic, CLE.
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2.2 Signaled PCN egress Feedback
The PCN-egress-node measures per ingress-egress-aggregate the
following rates
o rate of not-marked PCN traffic;
o rate of threshold-marked PCN traffic, which applies to CL edge
behaviour only;
o rate of excess-traffic-marked PCN traffic.
o Congestion level estimate (CLE)
The rate values are reported in octets/second to the decision point
each time that the PCN-egress-node calculates them and when this is
supported via configuration. CLE is only reported to the decision
point when this is supported via configuration.
In particular (see [draft-ietf-pcn-cl-edge-behaviour-07],
[draft-ietf-pcn-sm-edge-behaviour-04]:
o) if the report suppression option is not activated, the PCN-
egress-node MUST report the latest values of rate of not-marked
PCN traffic, rate of threshold-marked PCN traffic and rate of
excess-traffic-marked PCN traffic, to the Decision Point each
time that it calculates them.
o) otherwise, if the report suppression option is activated, then
each PCN feedback report sent to the Decision Point MUST contain
the values of rate of not-marked PCN traffic, rate of threshold-
marked PCN traffic and rate of excess-traffic-marked PCN traffic
and CLE that were calculated for the most recent measurement
interval.
If so configured (e.g., because multipath routing is being used), the
PCN-egress-node MUST also include in the PCN feedback and report the
set of flow identifiers of PCN-flows for which excess-traffic-marking
was observed in the most recent measurement interval.
The representation of a flow ID depends on the surrounding
environment, e.g., "pure IP", MPLS, GMPLS, etc. Examples of such flow
ID representations can be found in [RFC2205], [RFC3175] [RFC3209],
[RFC3473]. The list SHOULD be a concatenation of flow IDs associated
with the flows that are candidates for termination. The format of a
list containing flow ID_1 to flow ID_n SHOULD be:
list flow IDs = <flow ID_1> <flow ID_2> ... <flow_ID_n>.
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.
For more details see [draft-ietf-pcn-cl-edge-behaviour-07], [draft-
ietf-pcn-sm-edge-behaviour-04].
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2.3 Signaling Requirements
This section describes the requirements for signaling protocols that
are used to carry the PCN egress feedback from PCN-egress-nodes to
the decision point.
2.3.1 Priority of Signaling Messages
Signaling messages SHOULD have a higher priority than data packets.
This is needed to avoid as much as possible the situations that
during severe overload cases the signaling messages are dropped
within the PCN domain.
2.3.2 Local Information Exchange
Signaling messages MUST be able to carry the PCN egress feedback from
the PCN-egress-node to the decision point.
2.3.3 Carry Identification of PCN edge Nodes
The signaling protocol MUST be able to carry identification
(address information) of the PCN edge nodes.
This is required due to the fact that the decision point needs to be
able to associate the received signaling message with the PCN edge
node that sent this message.
However, the identification of the PCN edge nodes
MUST NOT be visible to non-PCN nodes outside the PCN domain.
2.3.4 Carry Identification of ingress-egress-aggregates
The signaling protocol MUST be able to carry identification
(address information) of the ingress-egress-aggregates. It is
proposed to identify them using the addresses of the PCN-ingress-node
and PCN-egress-node between which they pass. If each of the edge
nodes do not have unique addresses, then other identifiers could be
used.
2.3.5 Signaling Load
The load generated by the signaling protocol to carry the PCN egress
Feedback from the PCN-egress-nodes to the decision point SHOULD be
minimized as much as possible.
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2.3.6 Reliability
There are situations that messages need to be received in a
reliable way. There are different ways of achieving reliability. The
specification of a mandatory solution of achieving this reliability
is out of the scope of this document. It can be however considered,
that when information is received on a regular fashion, additional
reliability measures Should Not be required.
2.3.7 Security
The signaling support may need security protection against replay
attacks. The security services to be supported are:
o) Message authentication and integrity: an attacker could cause
denial of service using impersonation. Moreover, an attacker
could cause a denial of service by modifying message contents.
Therefore, message authentication and integrity SHOULD be
supported.
o) Message confidentiality: There could be situations where the PCN
signaling messages should not be visible to non authorised nodes.
In such cases, PCN message confidentiality MAY be supported.
2.4. Filter Specifications
In PCN the ingress and egress nodes should be able to identify the
ingress-egress-aggregate to which each flow belongs.
Moreover, the egress node also needs to associate an aggregate with
the address of the ingress node for receiving reports, if the ingress
node is the decision point.The filter specification at the PCN-
egress-nodes depends on the surrounding environment, e.g., pure IP,
MPLS, GMPLS.
In this document, a possible IP filter spec for pure IP is given as
an example. In this case the filter spec should be able to identify a
flow using (all or 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.
o IP address of PCN-ingress-node
o IP address of PCN-egress-node
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3. Signaling Requirements between Decision Point and PCN-ingress-nodes
The decision point monitors and uses the PCN egress feedback sent by
the PCN-egress-node. There are situations that the decision point
must obtain an estimate of the rate at which PCN-traffic is being
admitted to the aggregate from the PCN-ingress-node.
In order to receive this information the decision point has to
request from the PCN-ingress-node to send the value of the PCN
traffic admitted to a certain aggregate.
Note that if the decision point and the PCN-ingress-node are
collocated, then the information exchanges between the decision point
and PCN-ingress-node are internal operations.
3.1 Signaled PCN ingress Feedback
The PCN-ingress-node measures per ingress-egress-aggregate the
following rate
o rate of admitted PCN traffic
This value is reported in octets/second to the decision point as
soon as possible after receiving the request from the decision
point. .
3.2 Signaled Decision Point Trigger
The decision point uses the "ingress rate request" to request from
the PCN-ingress-node to send for a certain ingress-egress-aggregate,
the value of the admitted PCN traffic rate.
The "ingress rate request" message identifies the ingress-egress-
aggregate for which the admitted PCN traffic rate is required.The
only difference is the fact that these signaling requirements apply
for the signaling messages that have to be sent between the decision
point and PCN-ingress-nodes. Moreover, since the "ingress rate
request" message sent by the decision point towards the PCN-ingress-
node and the admitted PCN traffic rate sent by the PCN-ingress-node
towards the decision point are not sent regularly, they SHOULD be
delivered reliably.
3.3 Signaling Requirements
The same signaling requirements described in Section 2.3 apply for
this situation.
4. Security Considerations
[RFC5559] provides a general description of the security
considerations for PCN. This memo introduces the additional security
considerations described in Section 2.3.7.
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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-07] 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)", September 2010.
[draft-ietf-pcn-sm-edge-behaviour-04] 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)", September 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.
[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.
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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 Wurzburg
Institute of Computer Science
Room B206
Am Hubland, Wuerzburg D-97074
Germany
Email: menth@informatik.uni-wuerzburg.de
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