draft-ietf-pcn-baseline-encoding-00.txt   draft-ietf-pcn-baseline-encoding-01.txt 
Congestion and Pre Congestion T. Moncaster Congestion and Pre Congestion T. Moncaster
Internet-Draft BT Internet-Draft BT
Intended status: Standards Track B. Briscoe Intended status: Standards Track B. Briscoe
Expires: April 3, 2009 BT & UCL Expires: April 17, 2009 BT & UCL
M. Menth M. Menth
University of Wuerzburg University of Wuerzburg
September 30, 2008 October 14, 2008
Baseline Encoding and Transport of Pre-Congestion Information Baseline Encoding and Transport of Pre-Congestion Information
draft-ietf-pcn-baseline-encoding-00 draft-ietf-pcn-baseline-encoding-01
Status of this Memo Status of This Memo
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skipping to change at page 1, line 37 skipping to change at page 1, line 37
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Abstract Abstract
Pre-congestion notification (PCN) provides information to support Pre-congestion notification (PCN) provides information to support
admission control and flow termination in order to protect the admission control and flow termination in order to protect the
Quality of Service of inelastic flows. It does this by marking Quality of Service of inelastic flows. It does this by marking
packets when traffic load on a link is approaching or has exceeded a packets when traffic load on a link is approaching or has exceeded a
threshold below the physical link rate. This document specifies how threshold below the physical link rate. This document specifies how
such marks are to be encoded into the IP header. The baseline such marks are to be encoded into the IP header. The baseline
encoding described here provides for only two PCN encoding states. encoding described here provides for only two PCN encoding states.
It is designed to be easily extensible to provide more encoding It is designed to be easily extended to provide more encoding states
states but such schemes will be described in other documents. but such schemes will be described in other documents.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements notation . . . . . . . . . . . . . . . . . . . . 4 2. Requirements notation . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Encoding two PCN States in IP . . . . . . . . . . . . . . . . 4 4. Encoding two PCN States in IP . . . . . . . . . . . . . . . . 5
4.1. Rationale for Encoding . . . . . . . . . . . . . . . . . . 5 4.1. Rationale for Encoding . . . . . . . . . . . . . . . . . . 5
4.2. PCN-Compatible DiffServ Codepoints . . . . . . . . . . . . 6 4.2. PCN-Compatible DiffServ Codepoints . . . . . . . . . . . . 6
5. Backwards Compatability . . . . . . . . . . . . . . . . . . . 6 5. Rules for Experimental Encoding Schemes . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 6. Backwards Compatibility . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 7 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 9. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 7
10. Comments Solicited . . . . . . . . . . . . . . . . . . . . . . 7 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 11. Comments Solicited . . . . . . . . . . . . . . . . . . . . . . 8
11.1. Normative References . . . . . . . . . . . . . . . . . . . 7 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
11.2. Informative References . . . . . . . . . . . . . . . . . . 8 12.1. Normative References . . . . . . . . . . . . . . . . . . . 8
12.2. Informative References . . . . . . . . . . . . . . . . . . 8
Appendix A. Tunnelling Constraints . . . . . . . . . . . . . . . 9 Appendix A. Tunnelling Constraints . . . . . . . . . . . . . . . 9
Appendix B. PCN Node Behvaiours . . . . . . . . . . . . . . . . . 9 Appendix B. PCN Node Behaviours . . . . . . . . . . . . . . . . . 10
B.1. Valid and Invalid Encoding Transitions at a PCN Node . . . 10
Appendix C. Deployment Scenarios for PCN Using Baseline Appendix C. Deployment Scenarios for PCN Using Baseline
Encoding . . . . . . . . . . . . . . . . . . . . . . 10 Encoding . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . . . 12
1. Introduction 1. Introduction
Pre-congestion notification (PCN) provides information to support Pre-congestion notification (PCN) provides information to support
admission control and flow termination in order to protect the admission control and flow termination in order to protect the
quality of service (QoS) of inelastic flows. This is achieved by quality of service (QoS) of inelastic flows. This is achieved by
marking packets according to the level of pre-congestion at nodes marking packets according to the level of pre-congestion at nodes
within a PCN-domain. These markings are evaluated by the egress within a PCN-domain. These markings are evaluated by the egress
nodes of the PCN-domain. [PCN-arch] describes how PCN packet nodes of the PCN-domain. [pcn-arch] describes how PCN packet markings
markings can be used to assure the QoS of inelastic flows within a can be used to assure the QoS of inelastic flows within a single
single DiffServ domain. DiffServ domain.
This document specifies how these PCN marks are encoded into the IP This document specifies how these PCN marks are encoded into the IP
header. It also describes how packets are identified as belonging to header. It also describes how packets are identified as belonging to
a PCN flow. Some deployment models require two PCN encoding states, a PCN flow. Some deployment models require two PCN encoding states,
others require more. The baseline encoding described here only others require more. The baseline encoding described here only
provides for two PCN encoding states. An extension of the baseline provides for two PCN encoding states. An extension of the baseline
encoding described in [PCN-3-enc-state] provides for three PCN encoding described in [PCN-3-enc-state] provides for three PCN
encoding states. Other extensions have also been suggested all of encoding states. Other extensions have also been suggested all of
which can build on the baseline encoding. which can build on the baseline encoding. In order to ensure
backward compatibility any alternative encoding schemes that claim
compliance with PCN standards MUST extend this baseline scheme.
Changes from previous drafts (to be removed by the RFC Editor): Changes from previous drafts (to be removed by the RFC Editor):
From -02 to -03: From -00 to -01:
Added section on restrictions for extension encoding schemes.
Included table in Appendix showing encoding transitions at
different PCN nodes.
Checked for consistency of terminology.
Minor language changes for clarity.
Changes from previous filename
Filename changed from draft-moncaster-pcn-baseline-encoding.
Terminology changed for clarity (PCN-compatible DSCP and PCN-
enabled packet).
Minor changes throughout. Minor changes throughout.
Modified meaning of ECT(1) state to EXP. Modified meaning of ECT(1) state to EXP.
Moved text relevant to behaviour of nodes into appendix for later Moved text relevant to behaviour of nodes into appendix for later
transfer to new document on edge behaviours transfer to new document on edge behaviours.
From -01 to -02: From draft-moncaster -01 to -02:
Minor changes throughout including tightening up language to Minor changes throughout including tightening up language to
remain consistent with the PCN Architecture terminology remain consistent with the PCN Architecture terminology
From -00 to -01: From draft-moncaster -00 to -01:
Change of title from "Encoding and Transport of (Pre-)Congestion Change of title from "Encoding and Transport of (Pre-)Congestion
Information from within a DiffServ Domain to the Egress" Information from within a DiffServ Domain to the Egress"
Extensive changes to Introduction and abstract. Extensive changes to Introduction and abstract.
Added a section on the implications of re-using a DSCP. Added a section on the implications of re-using a DSCP.
Added appendix listing possible operator scenarios for using this Added appendix listing possible operator scenarios for using this
baseline encoding. baseline encoding.
skipping to change at page 4, line 20 skipping to change at page 4, line 37
2. Requirements notation 2. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Terminology 3. Terminology
The following terms are used in this document: The following terms are used in this document:
o Not-PCN - packets that are not PCN capable. o Not-PCN - packets that are not PCN-enabled.
o PCN-marked - codepoint indicating packets that have been marked at o PCN-marked - codepoint indicating packets that have been marked at
a PCN-interior-node using some PCN marking behaviour. Also PM. a PCN-interior-node using some PCN marking behaviour. Also PM.
o Not-Marked - codepoint indicating packets that are PCN capable but o Not-marked - codepoint indicating packets that are PCN-capable but
are not PCN-marked. Also NM. are not PCN-marked. Also NM.
o PCN-enabled codepoints - collective term for all the NM and PM o PCN-enabled codepoints - collective term for all the NM and PM
codepoints. codepoints.
o PCN-compatible Diffserv codepoint - a Diffserv codepoint for which o PCN-compatible Diffserv codepoint - a Diffserv codepoint for which
the ECN field is used to carry PCN markings rather thatn [RFC3168] the ECN field is used to carry PCN markings rather than [RFC3168]
markings. markings.
In addition the document uses the terminology defined in [PCN-arch]. In addition the document uses the terminology defined in [pcn-arch].
4. Encoding two PCN States in IP 4. Encoding two PCN States in IP
The PCN encoding states are defined using a combination of the DSCP The PCN encoding states are defined using a combination of the DSCP
and ECN fields within the IP header. The baseline PCN encoding and ECN fields within the IP header. The baseline PCN encoding
closely follows the semantics of ECN [RFC3168]. It allows the closely follows the semantics of ECN [RFC3168]. It allows the
encoding of two PCN states: Not-Marked and PCN-Marked. It also encoding of two PCN states: Not-Marked and PCN-Marked. It also
allows for traffic that is not PCN capable to be marked as such (not- allows for traffic that is not PCN capable to be marked as such (not-
PCN). Given the scarcity of codepoints within the IP header the PCN). Given the scarcity of codepoints within the IP header the
baseline encoding leaves one codepoint free for experimental use. baseline encoding leaves one codepoint free for experimental use.
The following table defines how to encode these states in IP: The following table defines how to encode these states in IP:
+---------------------+------------+-----------+-----------+--------+ +---------------+-------------+-------------+-------------+---------+
| DSCP \ RFC3168 ECN | not-ECT | ECT(0) | ECT(1) | CE | | ECN codepoint | not-ECT | ECT(0) (10) | ECT(1) (01) | CE (11) |
| codepoint | (00) | (10) | (01) | (11) | | | (00) | | | |
+---------------------+------------+-----------+-----------+--------+ +---------------+-------------+-------------+-------------+---------+
| DSCP n | not-PCN | NM | EXP | PM | | DSCP n | not-PCN | NM | EXP | PM |
+---------------------+------------+-----------+-----------+--------+ +---------------+-------------+-------------+-------------+---------+
Where DSCP n is a PCN-enabled DiffServ codepoint (see Section 4.2) Where DSCP n is a PCN-compatible DiffServ codepoint (see Section 4.2)
and EXP means available for Experimental use. and EXP means available for Experimental use.
Table 1: Encoding PCN in IP Table 1: Encoding PCN in IP
The following rules apply to all PCN traffic: The following rules apply to all PCN traffic:
o PCN traffic MUST be marked with a PCN-compatible DiffServ o PCN-traffic MUST be marked with a PCN-compatible DiffServ
Codepoint. That is a DiffServ codepoint that indicates that PCN Codepoint. To conserve DSCPs, DiffServ Codepoints SHOULD be
could be enabled by setting the appropriate value in the ECN chosen that are already defined for use with admission controlled
field. To conserve DSCPs, DiffServ Codepoints SHOULD be chosen
that are already defined for use with admission controlled
traffic, such as the Voice-Admit codepoint defined in traffic, such as the Voice-Admit codepoint defined in
[voice-admit]. [voice-admit]. Guidelines for mixing traffic-types within a PCN-
domain are given in [pcn-marking-behaviour].
o Any packet that is not PCN-enabled (not-PCN) but which shares the o Any packet that is not PCN-enabled (not-PCN) but which shares the
same DiffServ codepoint as PCN-enabled traffic MUST have the ECN same DiffServ codepoint as PCN-enabled traffic MUST have the ECN
field set to 00. field equal to 00.
4.1. Rationale for Encoding 4.1. Rationale for Encoding
The exact choice of encoding was dictated by the constraints imposed The exact choice of encoding was dictated by the constraints imposed
by existing IETF RFCs, in particular [RFC3168] and [RFC4774]. Full by existing IETF RFCs, in particular [RFC3168] and [RFC4774]. One of
details are contained in [pcn-enc-compare]. One of the tightest the tightest constraints was the need for any PCN encoding to survive
constraints was the need for any PCN encoding to survive being being tunnelled through either an IP in IP tunnel or an IPSec Tunnel.
tunnelled through either an IP in IP tunnel or an IPSec Tunnel.
Appendix A explains this in detail. The main effect of this Appendix A explains this in detail. The main effect of this
constraint is that any PCN marking has to use the ECN field set to 11 constraint is that any PCN marking has to carry the 11 codepoint in
(CE codepoint). If the packet is being tunneled then only the CE the ECN field. If the packet is being tunneled then only the 11
codepoint gets copied into the inner header upon decapsulation. An codepoint gets copied into the inner header upon decapsulation. An
additional constraint is the need to minimise the use of DiffServ additional constraint is the need to minimise the use of DiffServ
codepoints as these are in increasingly short supply. Section 4.2 codepoints as there is a limited supply of standards track codepoints
explains how we have minimised this still further by reusing pre- remaining. Section 4.2 explains how we have minimised this still
existing Diffserv codepoint(s) such that non-PCN traffic can still be further by reusing pre-existing Diffserv codepoint(s) such that non-
distinguished from PCN traffic. PCN traffic can still be distinguished from PCN traffic. There are a
number of factors that were considered before deciding to set 10 as
the NM state. These included similarity to ECN, presence of tunnels
within the domain, leakage into and out of PCN-domain and incremental
deployment.
The encoding scheme (Table 1) that best addresses the above The encoding scheme above seems to meet all these constraints and
constraints ends up looking very similar to ECN. This is perhaps not ends up looking very similar to ECN. This is perhaps not surprising
surprising given the similarity in architectural intent between PCN given the similarity in architectural intent between PCN and ECN.
and ECN.
4.2. PCN-Compatible DiffServ Codepoints 4.2. PCN-Compatible DiffServ Codepoints
Equipment complying with the baseline PCN encoding MUST allow PCN to Equipment complying with the baseline PCN encoding MUST allow PCN to
be enabled for a certain Diffserv codepoint or codepoints. This be enabled for certain Diffserv codepoints. This document defines
document defines the term "PCN-Compatible Diffserv Codepoint" for the term "PCN-compatible Diffserv codepoint" for such a DSCP.
such a DSCP. Enabling PCN for a DSCP switches on PCN marking Enabling PCN for a DSCP switches on PCN marking behaviour for packets
behaviour for packets with that DSCP, but only if those packets also with that DSCP, but only if those packets also have their ECN field
have their ECN field set to indicate a codepoint other than not-PCN. set to indicate a codepoint other than not-PCN.
Enabling PCN marking behaviour disables any other marking behaviour Enabling PCN marking behaviour disables any other marking behaviour
(e.g. enabling PCN disables the default ECN marking behaviour (e.g. enabling PCN disables the default ECN marking behaviour
introduced in [RFC3168]). The scheduling behaviour is discussed in introduced in [RFC3168]). All traffic scheduling and conditioning
[pcn-marking-behaviour]. behaviours are discussed in [pcn-marking-behaviour].
5. Backwards Compatability 5. Rules for Experimental Encoding Schemes
Any experimental encoding scheme MUST follow these rules to ensure
backward compatibility with this baseline scheme:
o The 00 codepoint in the ECN field MUST mean not-PCN.
o The 11 codepoint in the ECN field MUST mean PCN-marked (though
this doesn't exclude other codepoints from carrying the same
meaning).
o Once set the 11 codepoint in the ECN field MUST NOT be changed to
any other codepoint.
6. Backwards Compatibility
BCP 124 [RFC4774] gives guidelines for specifying alternative BCP 124 [RFC4774] gives guidelines for specifying alternative
semantics for the ECN field. It sets out a number of factors that semantics for the ECN field. It sets out a number of factors to be
must be taken into consideration. It also suggests various taken into consideration. It also suggests various techniques to
techniques to allow the co-existence of default ECN and alternative allow the co-existence of default ECN and alternative ECN semantics.
ECN semantics. The baseline encoding specified in this document The baseline encoding specified in this document defines PCN-
defines PCN-compatible DiffServ Codepoints as no longer supporting compatible DiffServ codepoints as no longer supporting the default
the default ECN semantics. As such this document is compatible with ECN semantics. As such this document is compatible with BCP 124. It
BCP 124. should be noted that this baseline encoding blocks end-to-end ECN
except where mechanisms are put in place to tunnel such traffic
across the PCN-domain.
6. IANA Considerations 7. IANA Considerations
This document makes no request to IANA. This document makes no request to IANA.
7. Security Considerations 8. Security Considerations
Packets claim entitlement to be PCN marked by carrying a PCN-enabled Packets claim entitlement to be PCN marked by carrying a PCN-
DSCP and a PCN-Capable ECN codepoint. This encoding document is Compatible DSCP and a PCN-Enabled ECN codepoint. This encoding
intended to stand independently of the architecture used to determine document is intended to stand independently of the architecture used
whether specific packets are authorised to be PCN marked, which will to determine whether specific packets are authorised to be PCN
be described in a future separate document on PCN edge-node behaviour marked, which will be described in a future separate document on PCN
(see Appendix B). edge-node behaviour (see Appendix B).
The PCN working group has initially been chartered to only consider a The PCN working group has initially been chartered to only consider a
PCN-domain to be entirely under the control of one operator, or a set PCN-domain to be entirely under the control of one operator, or a set
of operators who trust each other [PCN-charter]. However there is a of operators who trust each other [PCN-charter]. However there is a
requirement to keep inter-domain scenarios in mind when defining the requirement to keep inter-domain scenarios in mind when defining the
PCN encoding. One way to extend to multiple domains would be to PCN encoding. One way to extend to multiple domains would be to
concatenate PCN-domains and use PCN-boundary-nodes back to back at concatenate PCN-domains and use PCN-boundary-nodes back to back at
borders. Then any one domain's security against its neighbours would borders. Then any one domain's security against its neighbours would
be described as part of the edge-node behaviour document as above. be described as part of the proposed edge-node behaviour document.
One proposal on the table allows one to extend PCN across multiple One proposal on the table allows one to extend PCN across multiple
domains without PCN-boundary-nodes back-to-back at borders [re-PCN]. domains without PCN-boundary-nodes back-to-back at borders [re-PCN].
It is believed that the encoding described here would be compatible It is believed that the encoding described here would be compatible
with the security framework described there. with the security framework described there.
8. Conclusions 9. Conclusions
This document defines the baseline PCN encoding utilising a This document defines the baseline PCN encoding utilising a
combination of a PCN-enabled DSCP and the ECN field in the IP header. combination of a PCN-enabled DSCP and the ECN field in the IP header.
This baseline encoding allows the existence of two PCN encoding This baseline encoding allows the existence of two PCN encoding
states, not-Marked and PCN-Marked. It also allows for the co- states, not-Marked and PCN-Marked. It also allows for the co-
existence of traffic that is not PCN-capable within the same DSCP so existence of competing traffic within the same DSCP so long as that
long as theat traffic doesn't require end-to-end ECN support. The traffic doesn't require end-to-end ECN support. The encoding scheme
encoding scheme is conformant with [RFC4774]. is conformant with [RFC4774].
9. Acknowledgements 10. Acknowledgements
This document builds extensively on work done in the PCN working This document builds extensively on work done in the PCN working
group by Kwok Ho Chan, Georgios Karagiannis, Philip Eardley and group by Kwok Ho Chan, Georgios Karagiannis, Philip Eardley, Anna
others. Full details of the alternative schemes that were considered Charny, Joe Babiarz and others. Thanks to Ruediger Geib for
for adoption can be found in the document [pcn-enc-compare]. Thanks providing detailed comments on this document.
to Ruediger Geib for providing detailed comments on this document.
10. Comments Solicited 11. Comments Solicited
Comments and questions are encouraged and very welcome. They can be Comments and questions are encouraged and very welcome. They can be
addressed to the IETF congestion and pre-congestion working group addressed to the IETF congestion and pre-congestion working group
mailing list <pcn@ietf.org>, and/or to the authors. mailing list <pcn@ietf.org>, and/or to the authors.
11. References 12. References
11.1. Normative References 12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to
Requirement Levels", BCP 14, RFC 2119, March 1997. Indicate Requirement Levels", BCP 14,
RFC 2119, March 1997.
[RFC4774] Floyd, S., "Specifying Alternate Semantics for the [RFC4774] Floyd, S., "Specifying Alternate Semantics
Explicit Congestion Notification (ECN) Field", BCP 124, for the Explicit Congestion Notification
RFC 4774, November 2006. (ECN) Field", BCP 124, RFC 4774,
November 2006.
11.2. Informative References [pcn-arch] Eardley, P., "Pre-Congestion Notification
(PCN) Architecture",
draft-ietf-pcn-architecture-07 (work in
progress), September 2008.
[PCN-3-enc-state] 12.2. Informative References
Moncaster, T., Briscoe, B., and M. Menth, "A three state
extended PCN encoding scheme",
draft-moncaster-pcn-3-state-encoding-00 (work in
progress), June 2008.
[PCN-arch] [PCN-3-enc-state] Moncaster, T., Briscoe, B., and M. Menth, "A
Eardley, P., "Pre-Congestion Notification Architecture", three state extended PCN encoding scheme",
draft-ietf-pcn-architecture-03 (work in progress), draft-moncaster-pcn-3-state-encoding-00
February 2008. (work in progress), June 2008.
[PCN-charter] [PCN-charter] IETF, "IETF Charter for Congestion and Pre-
IETF, "IETF Charter for Congestion and Pre-Congestion Congestion Notification Working Group".
Notification Working Group".
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black,
of Explicit Congestion Notification (ECN) to IP", "The Addition of Explicit Congestion
RFC 3168, September 2001. Notification (ECN) to IP", RFC 3168,
September 2001.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the [RFC4301] Kent, S. and K. Seo, "Security Architecture
Internet Protocol", RFC 4301, December 2005. for the Internet Protocol", RFC 4301,
December 2005.
[ecn-tunnelling] [ecn-tunnelling] Briscoe, B., "Layered Encapsulation of
Briscoe, B., "Layered Encapsulation of Congestion Congestion Notification",
Notification", draft-briscoe-tsvwg-ecn-tunnel-01 (work in draft-briscoe-tsvwg-ecn-tunnel-01 (work in
progress), July 2008. progress), July 2008.
[pcn-enc-compare] [pcn-marking-behaviour] Eardley, P., "Marking behaviour of PCN-
Chan, K., Karagiannis, G., Moncaster, T., Menth, M., nodes", draft-ietf-pcn-marking-behaviour-00
Eardley, P., and B. Briscoe, "Pre-Congestion Notification (work in progress), October 2008.
Encoding Comparison",
draft-chan-pcn-encoding-comparison-03 (work in progress),
February 2008.
[pcn-marking-behaviour]
Eardley, P., "Marking behaviour of PCN-nodes",
draft-eardley-pcn-marking-behaviour-01 (work in progress),
June 2008.
[re-PCN] Briscoe, B., "Emulating Border Flow Policing using Re-ECN [re-PCN] Briscoe, B., "Emulating Border Flow Policing
on Bulk Data", draft-briscoe-re-pcn-border-cheat-00 (work using Re-ECN on Bulk Data",
draft-briscoe-re-pcn-border-cheat-00 (work
in progress), July 2007. in progress), July 2007.
[voice-admit] [voice-admit] Baker, F., Polk, J., and M. Dolly, "DSCPs
Baker, F., Polk, J., and M. Dolly, "DSCPs for Capacity- for Capacity-Admitted Traffic",
Admitted Traffic", draft-ietf-tsvwg-admitted-realtime-dscp-04
draft-ietf-tsvwg-admitted-realtime-dscp-04 (work in (work in progress), February 2008.
progress), February 2008.
Appendix A. Tunnelling Constraints Appendix A. Tunnelling Constraints
The rules that govern the behaviour of the ECN field for IP-in-IP The rules that govern the behaviour of the ECN field for IP-in-IP
tunnels were defined in [RFC3168]. This allowed for two tunnel tunnels were defined in [RFC3168]. This allowed for two tunnel
modes. The limited functionality mode sets the outer header to not- modes. The limited functionality mode sets the outer header to not-
ECT, regardless of the value of the inner header, in other words ECT, regardless of the value of the inner header, in other words
disabling ECN within the tunnel. The full functionality mode copies disabling ECN within the tunnel. The full functionality mode copies
the inner ECN field into the outer header if the inner header is not- the inner ECN field into the outer header if the inner header is not-
ECT or either of the 2 ECT codepoints. If the inner header is CE ECT or either of the 2 ECT codepoints. If the inner header is CE
skipping to change at page 9, line 29 skipping to change at page 9, line 41
stated reason for blocking CE from being copied to the outer header stated reason for blocking CE from being copied to the outer header
was to prevent this from being used as a covert channel through IPSec was to prevent this from being used as a covert channel through IPSec
tunnels. tunnels.
The IPSec protocol [RFC4301] changed the ECN tunnelling rule to allow The IPSec protocol [RFC4301] changed the ECN tunnelling rule to allow
IPSec tunnels to simply copy the inner header into the outer header. IPSec tunnels to simply copy the inner header into the outer header.
On decapsulation the outer header is discarded and the ECN field is On decapsulation the outer header is discarded and the ECN field is
only copied down if it is set to CE. only copied down if it is set to CE.
Because of the possible existence of tunnels, only CE (11) can be Because of the possible existence of tunnels, only CE (11) can be
used as a PCN marking as it is the only mark that will survive used as a PCN marking as it is the only mark that will always survive
decapsulation. However there is a need for caution with all decapsulation. However there is a need for caution with all
tunneling within the PCN-domain. RFC3168 full functionality IP in IP tunneling within the PCN-domain. RFC3168 full functionality IP in IP
tunnels are expected to set the ECN field to ECT(0) if the inner ECN tunnels are expected to set the ECN field to ECT(0) if the inner ECN
field is set to CE. This leads to the possibility that some packets field is set to CE. This leads to the possibility that some packets
within the PCN-domain that have already been marked may have that within the PCN-domain that have already been marked may have that
mark concealed further into the domain. This is undesirable for many mark concealed further into the domain. This is undesirable for many
PCN schemes and thus standard IP in IP tunnels SHOULD NOT be used PCN schemes and thus the PCN working group needs to decide whether to
within a PCN-domain. Further work is needed within the Transport advise against the use of full functionality RFC3168 IP in IP tunnels
within a PCN-domain to support the ongoing work within the Transport
Area to rationalise the behaviour of IP in IP tunnels in respect to Area to rationalise the behaviour of IP in IP tunnels in respect to
the ECN field and bring them in line with the behaviour of IPSec the ECN field and bring them in line with the behaviour of IPSec
tunnels [ecn-tunnelling]. tunnels [ecn-tunnelling].
Appendix B. PCN Node Behvaiours Appendix B. PCN Node Behaviours
Any packet that belongs to a PCN capable flow MUST have the ECN field
set to indicate a NM state at the PCN-ingress-node.
Any packet that is PCN capable and has been PCN-marked by a PCN-
interior-node MUST have the ECN field set to indicate a PM state.
Any packet leaving the PCN-domain SHOULD have the ECN field reset to
00. The only exception is where the egress node knows the end-hosts
will react safely to any PCN marks they receive.
B.1. Valid and Invalid Encoding Transitions at a PCN Node
o PCN-interior-nodes MUST NOT change not-PCN to another codepoint The following table of valid and invalid transitions, while necessary
and they SHOULD NOT change a PCN-Capable codepoint to not-PCN for the correct functioning of PCN they is not strictly part of the
except where they need to downgrade the packet to a lower class of encoding scheme. The PCN working group needs to decide whether to
service. include this in this baseline encoding or whether to transfer it to
an alternative document.
o PCN-interior-nodes that are in a pre-congestion state above the +-----------+-------------+-----------------+-----------------------+
configured level MUST set a PM codepoint as defined in Table 1 or | PCN node | Codepoint | Valid codepoint | Invalid codepoint out |
in any local/experimental scheme running within the PCN-domain. | type | in | out | |
+-----------+-------------+-----------------+-----------------------+
| ingress | Any | NM (or Not-PCN) | PM |
| interior | NM | NM or PM | not-PCN |
| interior | Not-PCN | Not-PCN | Any other codepoint |
| egress | Any | 00 | Any other codepoint * |
+-----------+-------------+-----------------+-----------------------+
* Except where the egress node knows that other marks may be safely
exposed outside the PCN-domain (e.g. [PCN-3-enc-state]).
o Packets carrying the 01 ECT(1) codepoint are for local/ Table 2: Valid and Invalid Transitions at PCN nodes
experimental use only and their unexpected presence SHOULD cause
an alarm to be raised at the management level. However, to allow
for the possibility of misconfiguration they SHOULD be treated as
NM packets.
o The PM codepoint MUST NOT be changed to NM. It is also necessary to define a safe behaviour for baseline-
compliant nodes to follow should they unexpectedly encounter a packet
carrying the EXP (01) codepoint. The obvious safe behaviour would be
to treat this as if it were a NM packet but to raise an alarm at a
higher layer to check why the packet was there. An alternative safe
approach is to treat it as a not-PCN packet but this might jeopardise
partial deployment of any future experimental encoding scheme.
Appendix C. Deployment Scenarios for PCN Using Baseline Encoding Appendix C. Deployment Scenarios for PCN Using Baseline Encoding
This appendix illustrates possible PCN deployment scenarios where the This appendix illustrates possible PCN deployment scenarios where the
baseline encoding can be used and also explain a case for which baseline encoding can be used and also explain a case for which
baseline encoding is not sufficient. {Note this appendix is provided baseline encoding is not sufficient. {Note this appendix is provided
for information only}. for information only}.
1. An operator may wish to use PCN-based admission control only. To 1. an operator requires only admission control. Then admission
that end, threshold marking based on admissible rates might be control is triggered from PCN-packets that are threshold-marked
used as the only PCN metering and marking algorithm. As a and this baseline encdoding scheme suffices.
consequence, the PM marks on the packets are interpreted as
meaning the ingress should stop admitting new traffic.
2. An operator may wish to use PCN-based flow termination only. To 2. an operator requires only flow termination. Then flow
that end, excess rate marking based on supportable rates might be termination is triggered from PCN-packets that are excess-
used as the only PCN metering and marking algorithm. As a traffic-marked and this baseline encdoding scheme suffices.
consequence, the PM marks on the packets are interpreted as
meaning the ingress shoudl start terminating appropriate flows.
3. An operator may wish to use both PCN-based admission control and 3. an operator requires both admission control and flow termination.
flow termination. To that end, excess rate marking based on If both admission control and flow termination are triggered from
admissible rates might be used as the only PCN metering and PCN-packets that are excess-traffic-marked then this baseline
marking algorithm. The level of marks will be used to determine encoding scheme suffices.
when the ingress shoudl stop admitting new traffic and whether
the ingress should terminate any flows.
4. An operator may wish to implement admission control based on 4. an operator requires both admission control triggered by packets
threshold marking at admissible rates and flow termination based that are threshold-marked and flow termination triggered by
on excess rate marking at supportable rates because these methods packets that are excess-traffic-marked. In this case the
are believed to work better with small ingress-egress aggregates. baseline encoding provides insufficient encoding states to
Then two different markings are needed. Such a deployment achieve this.
scenario is not supported by the PCN baseline encoding.
Authors' Addresses Authors' Addresses
Toby Moncaster Toby Moncaster
BT BT
B54/70, Adastral Park B54/70, Adastral Park
Martlesham Heath Martlesham Heath
Ipswich IP5 3RE Ipswich IP5 3RE
UK UK
Phone: +44 1473 648734 Phone: +44 1473 648734
Email: toby.moncaster@bt.com EMail: toby.moncaster@bt.com
Bob Briscoe Bob Briscoe
BT & UCL BT & UCL
B54/77, Adastral Park B54/77, Adastral Park
Martlesham Heath Martlesham Heath
Ipswich IP5 3RE Ipswich IP5 3RE
UK UK
Phone: +44 1473 645196 Phone: +44 1473 645196
Email: bob.briscoe@bt.com EMail: bob.briscoe@bt.com
Michael Menth Michael Menth
University of Wuerzburg University of Wuerzburg
room B206, Institute of Computer Science room B206, Institute of Computer Science
Am Hubland Am Hubland
Wuerzburg D-97074 Wuerzburg D-97074
Germany Germany
Phone: +49 931 888 6644 Phone: +49 931 888 6644
Email: menth@informatik.uni-wuerzburg.de EMail: menth@informatik.uni-wuerzburg.de
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2008). Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
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such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Acknowledgment Acknowledgement
This document was produced using xml2rfc v1.33 (of This document was produced using xml2rfc v1.33 (of
http://xml.resource.org/) from a source in RFC-2629 XML format. http://xml.resource.org/) from a source in RFC-2629 XML format.
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