Congestion and Pre-Congestion M. Menth
Internet-Draft University of Tuebingen
Intended status: Experimental R. Geib
Expires: September 1, 2011 Deutsche Telekom
February 28, 2011
Admission Control Using PCN-Marked Signaling
draft-menth-pcn-marked-signaling-ac-00
Abstract
Pre-congestion 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 RFC5559. This memo is one
of a series describing possible boundary node behaviours for a PCN
domain.
This document proposes an admission control method. It assumes that
PCN nodes perform threshold-marking configured with the PCN-
admissible-rate on any link. The PCN marking state of an initial
signaling message of a flow is used to determine whether the flow
should be admitted or blocked.
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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material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 1, 2011.
Copyright Notice
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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Assumed Core Network Behaviour for PCN-marked signaling . . . . 3
3. Edge Node Behaviours . . . . . . . . . . . . . . . . . . . . . 4
3.1. Prerequisites . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Behavior of PCN-Ingress-Nodes . . . . . . . . . . . . . . . 4
3.3. Behavior of PCN-Egress-Nodes . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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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 flow termination to decide whether to terminate some
already admitted flows during serious congestion. To achieve this,
the overall rate of PCN-traffic is metered on every link in the
domain, and PCN-packets are appropriately remarked 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 the "pre" part of pre-
congestion notification). For more details see [RFC5559].
This document presents PCN-marked signaling as a method to perform
admission control based on PCN information. It requires that all
PCN-ingress-nodes perform threshold marking [RFC5670] configured with
the PCN-admissible-rate as reference rate, and uses the marking state
of initial signaling messages to determine whether flows should be
admitted or blocked. It neither describes a corresponding flow
termination behavior nor does it preclude flow termination.
The proposed method has several benefits: it does not require any
measurement, it blocks very quickly as soon as pre-congestion occurs
[Menth08-Sub-8], and it works well with multipath routing if
signaling messages are carried on the same path as future data
packets.
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].
The terminology defined in [RFC5559] applies.
2. Assumed Core Network Behaviour for PCN-marked signaling
Admission control using PCN-marked signaling requires that nodes of a
PCN-domain perform threshold marking [RFC5670]. The reference rate
must be set to the PCN-admissible-rate of a link. Either Baseline
Encoding [RFC5696] or 3-in-1 Encoding [I-D.ietf-pcn-3-in-1-encoding]
may be used to distinguish re-marked signaling packets from unmarked
signaling packets.
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3. Edge Node Behaviours
This section explains the behavior of PCN-ingress-nodes and PCN-
egress-nodes.
3.1. Prerequisites
PCN-marked signaling assumes that admission control is triggered by a
signaling message at the PCN-ingress-node and that this signaling
message is carried across the PCN-domain to the PCN-egress-node on
the same path as future data packets of the associated flow. These
signaling messages are processed only by PCN-ingress-nodes and PCN-
egress-nodes. An example for such a signaling is the Resource
ReServation Protocol [RFC2205]. PCN-marked signaling is relatively
simple to implement when either PCN-ingress-node or PCN-egress-node
are involved in the signaling anyway.
3.2. Behavior of PCN-Ingress-Nodes
The PCN-ingress-node re-marks signaling messages to PCN not-marked
(NM) so that they are subject to metering and re-marking by PCN-
interior-nodes. Note that signaling packets need to be marked as PCN
not-marked (NM) only as long as the flow is not yet admitted.
In case of RSVP, the PCN-ingress-node performs the following non-
standard actions. If the PCN-ingress-node receives a PATH message,
it re-marks it to NM. If the PCN-ingress-node receives an initial
RESV message, it admits the flow for the hop over the PCN domain and
forwards the RESV message to the previous RSVP-hop on the path.
3.3. Behavior of PCN-Egress-Nodes
The PCN-egress-node detects signaling messages. As long as the flow
is not yet admitted, the PCN-egress-node evaluates the PCN codepoint
of received signaling messages. If the codepoint is NM, it takes
actions so that the flow can be admitted; otherwise it takes actions
so that the flow will be blocked. Finally, the PCN-egress-node
resets the PCN codepoint to not-PCN.
In case of RSVP, the PCN-egress-node performs the following non-
standard actions. If the PCN-egress-node receives an initial not-
marked PATH message, the PCN-egress-node forwards the message as
usual. If the PCN-egress-node receives an initial re-marked PATH
message, the PCN-egress-node drops the PATH message and returns a
PATH TEAR message to the previous RSVP hop indicating insufficient
resources.
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4. IANA Considerations
This document makes no request to IANA.
5. Security Considerations
Please see the security considerations in [RFC2205], [RFC2474], and
[RFC2475]. [RFC5559] provides a general description of the security
considerations for PCN.
6. Conclusions
The PCN-based admission control method proposed in this document has
several benefits. It does not require any measurement and does not
require any parameters except for threshold metering and re-marking.
Implicit probing blocks very quickly as soon as pre-congestion occurs
[Menth08-Sub-8] and leads to less over-admission than PCN-based
admission control that calculates congestion level estimates per
ingress-egress aggregate to derive admission decisions. Moreover,
Implicit Probing works well with multipath routing when the signaling
message is carried on the same path as future data packets
[Menth08-Sub-8]. Admission control using PCN-marked signaling as
proposed in this document is simple provided that the admission of
flows is requested by a path-coupled signaling protocol (e.g. RSVP).
In contrast to other approaches [I-D.ietf-pcn-cl-edge-behaviour],
[I-D.ietf-pcn-sm-edge-behaviour] PCN-egress-nodes neither need to
measure PCN traffic nor need to signal PCN-feedback. In particular,
pcn-egress-nodes no longer need to map packets to corresponding
ingress-egress-aggregates. Moreover, the presented method blocks
very quickly as soon as pre-congestion occurs [Menth08-Sub-8],
minimizing over-admission. It also works well with multipath routing
if signaling messages are carried on the same path as future data
packets [Menth08-Sub-8], minimizing under-admission.
7. Acknowledgements
Joe Babiarz presented the idea documented in this memo for the first
time in [I-D.babiarz-pcn-3sm]. It was further developed to be useful
for restricted tunneling rules which called for a special encoding
[I-D.ietf-pcn-psdm-encoding], [I-D.menth-pcn-psdm-deployment],
[Menth09f].
8. References
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8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[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.
[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.
8.2. Informative References
[I-D.babiarz-pcn-3sm]
Babiarz, J., Liu, X., Chan, K., and M. Menth, "Three State
PCN Marking", draft-babiarz-pcn-3sm-01 (work in progress),
November 2007.
[I-D.ietf-pcn-3-in-1-encoding]
Briscoe, B., Moncaster, T., and M. Menth, "Encoding 3 PCN-
States in the IP header using a single DSCP",
draft-ietf-pcn-3-in-1-encoding-04 (work in progress),
January 2011.
[I-D.ietf-pcn-cl-edge-behaviour]
Charny, A., Huang, F., Karagiannis, G., Menth, M., and T.
Taylor, "PCN Boundary Node Behaviour for the Controlled
Load (CL) Mode of Operation",
draft-ietf-pcn-cl-edge-behaviour-08 (work in progress),
December 2010.
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[I-D.ietf-pcn-psdm-encoding]
Menth, M., Babiarz, J., Moncaster, T., and B. Briscoe,
"PCN Encoding for Packet-Specific Dual Marking (PSDM
Encoding)", draft-ietf-pcn-psdm-encoding-01 (work in
progress), March 2010.
[I-D.ietf-pcn-sm-edge-behaviour]
Charny, A., Karagiannis, G., Menth, M., and T. Taylor,
"PCN Boundary Node Behaviour for the Single Marking (SM)
Mode of Operation", draft-ietf-pcn-sm-edge-behaviour-05
(work in progress), December 2010.
[I-D.menth-pcn-psdm-deployment]
Menth, M., "Deployment Models for PCN-Based Admission
Control and Flow Termination Using Packet-Specific Dual
Marking (PSDM)", draft-menth-pcn-psdm-deployment-00 (work
in progress), October 2008.
[Menth08-Sub-8]
Menth, M. and F. Lehrieder, "Performance of PCN-Based
Admission Control", currently under submission, University
of Wuerzburg, Germany, 2011.
[Menth09f]
Menth, M., Babiarz, J., and P. Eardley, "Pre-Congestion
Notification Using Packet-Specific Dual Marking",
in Proceedings of the International Workshop on the
Network of the Future (Future-Net), IEEE, Dresden,
Germany, June 2009.
Authors' Addresses
Michael Menth
University of Tuebingen
Department of Computer Science
Chair of Communication Networks
Sand 13
Tuebingen 72076
Germany
Phone: +49 7071 29 70505
Email: menth@informatik.uni-tuebingen.de
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Ruediger Geib
Deutsche Telekom
Heinrich-Hertz-Strasse 3-7
Darmstadt 64295
Germany
Phone: +49 6151 628 2747
Email: ruediger.geib@telekom.de
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