draft-ietf-pcn-3-state-encoding-01.txt   draft-ietf-pcn-3-state-encoding-02.txt 
Congestion and Pre Congestion B. Briscoe Congestion and Pre Congestion T. Moncaster
Internet-Draft BT & UCL Internet-Draft University of Cambridge
Intended status: Experimental T. Moncaster Intended status: Historic B. Briscoe
Expires: August 14, 2010 BT Expires: September 13, 2012 BT
M. Menth M. Menth
University of Wuerzburg University of Tuebingen
February 10, 2010 March 12, 2012
A PCN encoding using 2 DSCPs to provide 3 or more states A PCN encoding using 2 DSCPs to provide 3 or more states
draft-ietf-pcn-3-state-encoding-01 draft-ietf-pcn-3-state-encoding-02
Abstract Abstract
Pre-congestion notification (PCN) is a mechanism designed to protect Pre-congestion notification (PCN) is a mechanism designed to protect
the Quality of Service of inelastic flows within a controlled domain. the Quality of Service of inelastic flows within a controlled domain.
It does this by marking packets when traffic load on a link is It does this by marking packets when traffic load on a link is
approaching or has exceeded a threshold below the physical link rate. approaching or has exceeded a threshold below the physical link rate.
This experimental encoding scheme specifies how three encoding states This experimental encoding scheme specifies how three encoding states
can be carried in the IP header using a combination of two DSCPs and can be carried in the IP header using a combination of two DSCPs and
the ECN bits. The Basic scheme only allows for three encoding the ECN bits. The Basic scheme only allows for three encoding
states. The Full scheme provides 6 states, enough for limited end- states. The Full scheme provides 6 states, enough for limited end-
to-end support for ECN as well. to-end support for ECN as well.
Status
Since its original publication, the baseline encoding (RFC5696) on
which this document depends has become obsolete. The PCN working
Group has chosen to publish this as a historical document to preserve
the details of the encoding and to allow it to be cited in other
documents.
Status of this Memo Status of this Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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Copyright Notice Copyright Notice
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Copyright (c) 2012 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Changes from Previous Drafts (to be removed by the RFC 1.1. Changes from Previous Drafts (to be removed by the RFC
Editor) . . . . . . . . . . . . . . . . . . . . . . . . . 3 Editor) . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Requirements notation . . . . . . . . . . . . . . . . . . . . 4 2. Requirements notation . . . . . . . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. The Requirement for Three PCN Encoding States . . . . . . . . 5 4. The Requirement for Three PCN Encoding States . . . . . . . . 6
5. Adding Limited End-to-End ECN Support to PCN . . . . . . . . . 5 5. Adding Limited End-to-End ECN Support to PCN . . . . . . . . . 7
6. Encoding Three PCN States in IP . . . . . . . . . . . . . . . 6 6. Encoding Three PCN States in IP . . . . . . . . . . . . . . . 7
6.1. Basic Three State Encoding . . . . . . . . . . . . . . . . 6 6.1. Basic Three State Encoding . . . . . . . . . . . . . . . . 8
6.2. Full Three State Encoding . . . . . . . . . . . . . . . . 6 6.2. Full Three State Encoding . . . . . . . . . . . . . . . . 8
6.3. Common Diffserv Per-Hop Behaviour . . . . . . . . . . . . 7 6.3. Common Diffserv Per-Hop Behaviour . . . . . . . . . . . . 9
6.4. Valid and invalid codepoint transitions at 6.4. Valid and invalid codepoint transitions at
PCN-ingress-nodes . . . . . . . . . . . . . . . . . . . . 8 PCN-ingress-nodes . . . . . . . . . . . . . . . . . . . . 9
6.5. Valid and invalid codepoint transitions at 6.5. Valid and invalid codepoint transitions at
PCN-interior-nodes . . . . . . . . . . . . . . . . . . . . 8 PCN-interior-nodes . . . . . . . . . . . . . . . . . . . . 10
6.6. Forwarding traffic out of the PCN-domain . . . . . . . . . 9 6.6. Forwarding traffic out of the PCN-domain . . . . . . . . . 10
7. PCN-domain support for the PCN extension encoding . . . . . . 9 7. PCN-domain support for the PCN extension encoding . . . . . . 11
7.1. End-to-End transport behaviour compliant with the PCN 7.1. End-to-End transport behaviour compliant with the PCN
extension encoding . . . . . . . . . . . . . . . . . . . . 10 extension encoding . . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
9. Security Considerations . . . . . . . . . . . . . . . . . . . 10 9. Security Considerations . . . . . . . . . . . . . . . . . . . 12
10. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 11 10. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 12
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
12. Comments Solicited . . . . . . . . . . . . . . . . . . . . . . 11 12. Comments Solicited . . . . . . . . . . . . . . . . . . . . . . 13
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
13.1. Normative References . . . . . . . . . . . . . . . . . . . 11 13.1. Normative References . . . . . . . . . . . . . . . . . . . 13
13.2. Informative References . . . . . . . . . . . . . . . . . . 12 13.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction 1. Introduction
The objective of Pre-Congestion Notification (PCN) [RFC5559] is to The objective of Pre-Congestion Notification (PCN) [RFC5559] is to
protect the quality of service (QoS) of inelastic flows within a protect the quality of service (QoS) of inelastic flows within a
Diffserv domain, in a simple, scalable and robust fashion. The Diffserv domain, in a simple, scalable and robust fashion. The
overall rate of the PCN-traffic is metered on every link in the PCN- overall rate of the PCN-traffic is metered on every link in the PCN-
domain, and PCN-packets are appropriately marked when certain domain, and PCN-packets are appropriately marked when certain
configured rates are exceeded. These configured rates are below the configured rates are exceeded. These configured rates are below the
rate of the link thus providing notification before any congestion rate of the link thus providing notification before any congestion
skipping to change at page 4, line 42 skipping to change at page 4, line 42
doing it are discussed in Section 5. doing it are discussed in Section 5.
As in the baseline encoding, this extension encoding re-uses the ECN As in the baseline encoding, this extension encoding re-uses the ECN
bits within the IP header within a controlled PCN-domain. This bits within the IP header within a controlled PCN-domain. This
extension requires the use of two DSCPs as described later in this extension requires the use of two DSCPs as described later in this
document. This experimental scheme is one of three that are being document. This experimental scheme is one of three that are being
proposed within the PCN working group. The aim is to allow proposed within the PCN working group. The aim is to allow
implementors to decide which scheme is most suitable for possible implementors to decide which scheme is most suitable for possible
future standardisation. future standardisation.
Following the publication of new rules relating to the tunnelling of
ECN marks [RFC6040], the PCN workign group decided to obsolete
[RFC5696] in favour of the 3-in-1 encoding
[I-D.ietf-pcn-3-in-1-encoding]. A side-effect of this decision was
to make the encoding described in this document obsolete. However
the PCN working group feels it is useful to have a formal historical
record of this encoding. This ensures details of the encoding are
not lost and also allows it to be cited in other documents.
1.1. Changes from Previous Drafts (to be removed by the RFC Editor) 1.1. Changes from Previous Drafts (to be removed by the RFC Editor)
From draft-ietf-pcn-3-state-encoding-01 to 02:
o Changed the document from teh experimental to the historic track
o Added notes to the Introduciton and Abstract explaining the change
to historical
o Updated refs
From draft-ietf-pcn-3-state-encoding-00 to 01: From draft-ietf-pcn-3-state-encoding-00 to 01:
o Removed text implying the two DSCPs have different priority and o Removed text implying the two DSCPs have different priority and
added Section 6.3 specifying they must both have the same PHB. added Section 6.3 specifying they must both have the same PHB.
o Made IANA considerations text more precise. o Made IANA considerations text more precise.
o Changed variable names for DSCP 1 & DSCP 2 to DSCP n & DSCP m to o Changed variable names for DSCP 1 & DSCP 2 to DSCP n & DSCP m to
be consistent with baseline encoding. be consistent with baseline encoding.
skipping to change at page 6, line 12 skipping to change at page 6, line 32
represents a PCN capable packet that has no PCN marking but which represents a PCN capable packet that has no PCN marking but which
arrived with the ECN bits set to congestion experienced. arrived with the ECN bits set to congestion experienced.
4. The Requirement for Three PCN Encoding States 4. The Requirement for Three PCN Encoding States
The PCN Marking Behaviours document [RFC5670] describes proposed PCN The PCN Marking Behaviours document [RFC5670] describes proposed PCN
schemes that require traffic to be metered and marked using both schemes that require traffic to be metered and marked using both
Threshold and Excess Traffic schemes. In order to achieve this it is Threshold and Excess Traffic schemes. In order to achieve this it is
necessary to allow for three PCN encoding states. The constraints necessary to allow for three PCN encoding states. The constraints
imposed by the way tunnels process the ECN field severely limit how imposed by the way tunnels process the ECN field severely limit how
to encode these states as explained in [RFC5696] and to encode these states as explained in [RFC5696] and [RFC6040]. The
[I-D.ietf-tsvwg-ecn-tunnel]. The obvious way to provide one more obvious way to provide one more encoding state than the base encoding
encoding state than the base encoding is through the use of an is through the use of an additional PCN-compatible DiffServ
additional PCN-compatible DiffServ codepoint. codepoint.
One aim of this document is to allow for experiments to show whether One aim of this document is to allow for experiments to show whether
such schemes are better than those that only employ two PCN encoding such schemes are better than those that only employ two PCN encoding
states. As such, the additional DSCP will be taken from the EXP/LU states. As such, the additional DSCP will be taken from the EXP/LU
pools defined in [RFC2474]. If the experiments demonstrate that PCN pools defined in [RFC2474]. If the experiments demonstrate that PCN
schemes employing three encoding states are significantly better than schemes employing three encoding states are significantly better than
those only employing two, then at a later date IANA might be asked to those only employing two, then at a later date IANA might be asked to
assign a new PCN enabled DSCP from pool 1. Note that there are other assign a new PCN enabled DSCP from pool 1. Note that there are other
experimental encoding schemes being considered which only use one experimental encoding schemes being considered which only use one
DSCP but require either alternative tunnel semantics DSCP but require either alternative tunnel semantics
([I-D.ietf-pcn-3-in-1-encoding]) or additional signalling ([I-D.ietf-pcn-3-in-1-encoding]) or additional signalling
([I-D.ietf-pcn-psdm-encoding])in order to work. ([I-D.ietf-pcn-psdm-encoding])in order to work.
5. Adding Limited End-to-End ECN Support to PCN 5. Adding Limited End-to-End ECN Support to PCN
[I-D.sarker-pcn-ecn-pcn-usecases] suggests a number of use-cases There are a number of use-cases where explicit preservation of end-
where explicit preservation of end-to-end ECN semantics might be to-end ECN semantics might be needed across a PCN domain. One of the
needed across a PCN domain. One of the use-cases suggests that the use-cases suggests that the end-nodes might be running rate-adaptive
end-nodes might be running rate-adaptive codecs that would respond to codecs that would respond to ECN marks by reducing their transmission
ECN marks by reducing their transmission rate. If the sending rate. If the sending transport sets the ECT codepoint, the setting
transport sets the ECT codepoint, the setting of the ECN field as it of the ECN field as it arrives at the PCN ingress node will need to
arrives at the PCN ingress node will need to be re-instated as it be re-instated as it leaves the PCN egress node.
leaves the PCN egress node.
If a PCN region is starting to suffer pre-congestion then it may make If a PCN region is starting to suffer pre-congestion then it may make
sense to expose marks generated within the PCN region by forwarding sense to expose marks generated within the PCN region by forwarding
CE marks from the PCN egress to such a rate-adaptive endpoint. They CE marks from the PCN egress to such a rate-adaptive endpoint. They
would be in addition to any CE marks generated elsewhere on the end- would be in addition to any CE marks generated elsewhere on the end-
to-end path. This would allow the endpoints to reduce the traffic to-end path. This would allow the endpoints to reduce the traffic
rate. This will in turn help to alleviate the pre-congestion, rate. This will in turn help to alleviate the pre-congestion,
potentially averting any need for call blocking or termination. potentially averting any need for call blocking or termination.
However, the 'leaking' of CE marks out of the PCN region is However, the 'leaking' of CE marks out of the PCN region is
potentially dangerous and could violate [RFC4774] if the end hosts potentially dangerous and could violate [RFC4774] if the end hosts
skipping to change at page 8, line 21 skipping to change at page 8, line 43
(where DSCP n is a PCN-compatible DiffServ codepoint (see [RFC5696]) (where DSCP n is a PCN-compatible DiffServ codepoint (see [RFC5696])
and DSCP m is a PCN-compatible DSCP from the EXP/LU pools as defined and DSCP m is a PCN-compatible DSCP from the EXP/LU pools as defined
in [RFC2474]) in [RFC2474])
Table 2: Encoding three PCN states in IP Table 2: Encoding three PCN states in IP
The four different Not-marked (NM) states allow for the addition of The four different Not-marked (NM) states allow for the addition of
limited end-to-end ECN support as explained in the previous section. limited end-to-end ECN support as explained in the previous section.
Warning WARNING: In order to comply with this encoding all the nodes within
the PCN-domain MUST be configured with this encoding scheme.
In order to comply with this encoding all the nodes within the PCN- However there may be operators who choose not to be fully
domain MUST be configured with this encoding scheme. However there compliant with the scheme. If an operator chooses to leave some
may be operators who choose not to be fully compliant with the PCN-interior-nodes that only support two marking states (the
scheme. If an operator chooses to leave some PCN-interior-nodes that baseline encoding [RFC5696]), then they must be aware of the
only support two marking states (the baseline encoding [RFC5696]), following: Ideally such nodes would be configured to indicate pre-
then they must be aware of the following: Ideally such nodes would be congestion or congestion using the ETM state since this would
configured to indicate pre-congestion or congestion using the ETM ensure they could notify worst-case congestion, however this is
state since this would ensure they could notify worst-case not possible since it requires the packets to be re-marked to DSCP
congestion, however this is not possible since it requires the m (hence altering the baseline encoding). This means that such
packets to be re-marked to DSCP m (hence altering the baseline nodes will only be able to indicate ThM traffic.
encoding). This means that such nodes will only be able to indicate
ThM traffic.
6.3. Common Diffserv Per-Hop Behaviour 6.3. Common Diffserv Per-Hop Behaviour
Packets carrying Diffserv codepoint 'DSCP n' or 'DSCP m' MUST all be Packets carrying Diffserv codepoint 'DSCP n' or 'DSCP m' MUST all be
treated with the same Diffserv PHB [RFC2474]. The choice of PHB is treated with the same Diffserv PHB [RFC2474]. The choice of PHB is
discussed in [RFC5559] and [RFC5696]. discussed in [RFC5559] and [RFC5696].
Two DSCPs are merely used to provide sufficient PCN encoding states, Two DSCPs are merely used to provide sufficient PCN encoding states,
there is no need or intention to provide different scheduling or drop there is no need or intention to provide different scheduling or drop
preference for each row in the table of PCN codepoints. preference for each row in the table of PCN codepoints.
skipping to change at page 13, line 16 skipping to change at page 13, line 35
[RFC5670] Eardley, P., "Metering and Marking Behaviour of PCN- [RFC5670] Eardley, P., "Metering and Marking Behaviour of PCN-
Nodes", RFC 5670, November 2009. Nodes", RFC 5670, November 2009.
[RFC5696] Moncaster, T., Briscoe, B., and M. Menth, "Baseline [RFC5696] Moncaster, T., Briscoe, B., and M. Menth, "Baseline
Encoding and Transport of Pre-Congestion Information", Encoding and Transport of Pre-Congestion Information",
RFC 5696, November 2009. RFC 5696, November 2009.
13.2. Informative References 13.2. Informative References
[I-D.ietf-pcn-3-in-1-encoding] [I-D.ietf-pcn-3-in-1-encoding]
Briscoe, B. and T. Moncaster, "PCN 3-State Encoding Briscoe, B., Moncaster, T., and M. Menth, "Encoding 3 PCN-
Extension in a single DSCP", States in the IP header using a single DSCP",
draft-ietf-pcn-3-in-1-encoding-01 (work in progress), draft-ietf-pcn-3-in-1-encoding-09 (work in progress),
February 2010. March 2012.
[I-D.ietf-pcn-encoding-comparison] [I-D.ietf-pcn-encoding-comparison]
Chan, K., Karagiannis, G., Moncaster, T., Menth, M., Karagiannis, G., Chan, K., Moncaster, T., Menth, M.,
Eardley, P., and B. Briscoe, "Pre-Congestion Notification Eardley, P., and B. Briscoe, "Overview of Pre-Congestion
Encoding Comparison", Notification Encoding",
draft-ietf-pcn-encoding-comparison-01 (work in progress), draft-ietf-pcn-encoding-comparison-09 (work in progress),
October 2009. March 2012.
[I-D.ietf-pcn-psdm-encoding] [I-D.ietf-pcn-psdm-encoding]
Menth, M., Babiarz, J., Moncaster, T., and B. Briscoe, Menth, M., Babiarz, J., Moncaster, T., and B. Briscoe,
"PCN Encoding for Packet-Specific Dual Marking (PSDM)", "PCN Encoding for Packet-Specific Dual Marking (PSDM
draft-ietf-pcn-psdm-encoding-00 (work in progress), Encoding)", draft-ietf-pcn-psdm-encoding-01 (work in
June 2009. progress), March 2010.
[I-D.ietf-tsvwg-ecn-tunnel]
Briscoe, B., "Tunnelling of Explicit Congestion
Notification", draft-ietf-tsvwg-ecn-tunnel-06 (work in
progress), December 2009.
[I-D.sarker-pcn-ecn-pcn-usecases]
Sarker, Z. and I. Johansson, "Usecases and Benefits of end
to end ECN support in PCN Domains",
draft-sarker-pcn-ecn-pcn-usecases-01 (work in progress),
May 2008.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS "Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, Field) in the IPv4 and IPv6 Headers", RFC 2474,
December 1998. December 1998.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP", of Explicit Congestion Notification (ECN) to IP",
RFC 3168, September 2001. RFC 3168, September 2001.
[RFC3540] Spring, N., Wetherall, D., and D. Ely, "Robust Explicit [RFC3540] Spring, N., Wetherall, D., and D. Ely, "Robust Explicit
Congestion Notification (ECN) Signaling with Nonces", Congestion Notification (ECN) Signaling with Nonces",
RFC 3540, June 2003. RFC 3540, June 2003.
[RFC5559] Eardley, P., "Pre-Congestion Notification (PCN) [RFC5559] Eardley, P., "Pre-Congestion Notification (PCN)
Architecture", RFC 5559, June 2009. Architecture", RFC 5559, June 2009.
[RFC6040] Briscoe, B., "Tunnelling of Explicit Congestion
Notification", RFC 6040, November 2010.
Authors' Addresses Authors' Addresses
Bob Briscoe Toby Moncaster
BT & UCL University of Cambridge
B54/77, Adastral Park Computer Laboratory
Martlesham Heath JJ Thomson Avenue
Ipswich IP5 3RE Cambridge CB3 0FD
UK UK
Phone: +44 1473 645196 Phone: +44 1223 763654
Email: bob.briscoe@bt.com Email: toby@moncaster.com
Toby Moncaster Bob Briscoe
BT BT
B54/70, Adastral Park B54/77, Adastral Park
Martlesham Heath Martlesham Heath
Ipswich IP5 3RE Ipswich IP5 3RE
UK UK
Phone: +44 1473 648734 Phone: +44 1473 645196
Email: toby.moncaster@bt.com Email: bob.briscoe@bt.com
URI: http://www.cs.ucl.ac.uk/staff/B.Briscoe/ URI: http://www.bobbriscoe.net
Michael Menth Michael Menth
University of Wuerzburg University of Tuebingen
room B206, Institute of Computer Science Department of Computer Science
Am Hubland Sand 13
Wuerzburg D-97074 Tuebingen D-72076
Germany Germany
Phone: +49 931 888 6644 Phone: +49 07071 29 70505
Email: menth@informatik.uni-wuerzburg.de Email: menth@informatik.uni-tuebingen.de
URI: http://www.kn.inf.uni-tuebingen.de
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