draft-ietf-pcn-baseline-encoding-01.txt		draft-ietf-pcn-baseline-encoding-02.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 17, 2009 BT & UCL		Expires: August 14, 2009 BT & UCL
	M. Menth		M. Menth
	University of Wuerzburg		University of Wuerzburg
	October 14, 2008		February 10, 2009
	Baseline Encoding and Transport of Pre-Congestion Information		Baseline Encoding and Transport of Pre-Congestion Information
	draft-ietf-pcn-baseline-encoding-01		draft-ietf-pcn-baseline-encoding-02
	Status of This Memo		Status of This Memo
	By submitting this Internet-Draft, each author represents that any		This Internet-Draft is submitted to IETF in full conformance with the
	applicable patent or other IPR claims of which he or she is aware		provisions of BCP 78 and BCP 79.
	have been or will be disclosed, and any of which he or she becomes
	aware will be disclosed, in accordance with Section 6 of BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF), its areas, and its working groups. Note that		Task Force (IETF), its areas, and its working groups. Note that
	other groups may also distribute working documents as Internet-		other groups may also distribute working documents as Internet-
	Drafts.		Drafts.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	The list of current Internet-Drafts can be accessed at		The list of current Internet-Drafts can be accessed at
	http://www.ietf.org/ietf/1id-abstracts.txt.		http://www.ietf.org/ietf/1id-abstracts.txt.
	The list of Internet-Draft Shadow Directories can be accessed at		The list of Internet-Draft Shadow Directories can be accessed at
	http://www.ietf.org/shadow.html.		http://www.ietf.org/shadow.html.
	This Internet-Draft will expire on April 17, 2009.		This Internet-Draft will expire on August 14, 2009.
			Copyright Notice
			Copyright (c) 2009 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
			publication of this document. Please review these documents
			carefully, as they describe your rights and restrictions with respect
			to this document.
	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 extended to provide more encoding states		It is designed to be easily extended to provide more encoding 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 . . . . . . . . . . . . . . . . 5		4. Encoding two PCN States in IP . . . . . . . . . . . . . . . . 5
	4.1. Rationale for Encoding . . . . . . . . . . . . . . . . . . 5		4.1. Rationale for Encoding . . . . . . . . . . . . . . . . . . 6
	4.2. PCN-Compatible DiffServ Codepoints . . . . . . . . . . . . 6		4.2. PCN-Compatible DiffServ Codepoints . . . . . . . . . . . . 7
	5. Rules for Experimental Encoding Schemes . . . . . . . . . . . 6		5. Rules for Experimental Encoding Schemes . . . . . . . . . . . 7
	6. Backwards Compatibility . . . . . . . . . . . . . . . . . . . 6		6. Backwards Compatibility . . . . . . . . . . . . . . . . . . . 8
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 7		8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
	9. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 7		9. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 8
	10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7		10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
	11. Comments Solicited . . . . . . . . . . . . . . . . . . . . . . 8		11. Comments Solicited . . . . . . . . . . . . . . . . . . . . . . 9
	12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8		12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
	12.1. Normative References . . . . . . . . . . . . . . . . . . . 8		12.1. Normative References . . . . . . . . . . . . . . . . . . . 9
	12.2. Informative References . . . . . . . . . . . . . . . . . . 8		12.2. Informative References . . . . . . . . . . . . . . . . . . 9
	Appendix A. Tunnelling Constraints . . . . . . . . . . . . . . . 9		Appendix A. PCN Deployment Considerations . . . . . . . . . . . . 10
	Appendix B. PCN Node Behaviours . . . . . . . . . . . . . . . . . 10		A.1. Choice of Suitable DSCPs . . . . . . . . . . . . . . . . . 10
	Appendix C. Deployment Scenarios for PCN Using Baseline		A.2. Rationale for Using ECT(0) for Not Marked . . . . . . . . 10
	Encoding . . . . . . . . . . . . . . . . . . . . . . 10
	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 markings		nodes of the PCN-domain. [pcn-arch] describes how PCN packet markings
	can be used to assure the QoS of inelastic flows within a single		can be used to assure the QoS of inelastic flows within a single
	skipping to change at page 3, line 29		skipping to change at page 3, line 29
	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. In order to ensure		which can build on the baseline encoding. In order to ensure
	backward compatibility any alternative encoding schemes that claim		backward compatibility any alternative encoding schemes that claim
	compliance with PCN standards MUST extend this baseline scheme.		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 -01 to -02:
			Removed Appendix A and replaced with reference to [ecn-tunneling]
			Moved Appendix B into main body of text.
			Changed Appendix C to give deployment advice.
			Minor changes throughout including checking consistency of
			capitalisation of defined terms.
			Clarified that LU was deliberately excluded from encoding.
	From -00 to -01:		From -00 to -01:
	Added section on restrictions for extension encoding schemes.		Added section on restrictions for extension encoding schemes.
	Included table in Appendix showing encoding transitions at		Included table in Appendix showing encoding transitions at
	different PCN nodes.		different PCN nodes.
	Checked for consistency of terminology.		Checked for consistency of terminology.
	Minor language changes for clarity.		Minor language changes for clarity.
	skipping to change at page 4, line 40		skipping to change at page 5, line 6
	"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-enabled.		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
			[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. By definition packets carrying such codepoints are
			PCN-packets.
	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 than [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:
	+---------------+-------------+-------------+-------------+---------+		+---------------+-------------+-------------+-------------+---------+
	| ECN codepoint | not-ECT | ECT(0) (10) | ECT(1) (01) | CE (11) |		| ECN codepoint | Not-ECT | ECT(0) (10) | ECT(1) (01) | CE (11) |
	| | (00) | | | |		| | (00) | | | |
	+---------------+-------------+-------------+-------------+---------+		+---------------+-------------+-------------+-------------+---------+
	| DSCP n | not-PCN | NM | EXP | PM |		| DSCP n | Not-PCN | NM | EXP | PM |
	+---------------+-------------+-------------+-------------+---------+		+---------------+-------------+-------------+-------------+---------+
	Where DSCP n is a PCN-compatible 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. N.B. we deliberately
			reserve this codepoint for experimental use only (and not local use)
			to prevent any possible future compatability issues.
	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. To conserve DSCPs, DiffServ Codepoints SHOULD be		Codepoint. To conserve DSCPs, DiffServ Codepoints SHOULD be
	chosen that are already defined for use with admission controlled		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]. Guidelines for mixing traffic-types within a PCN-		[voice-admit]. Guidelines for mixing traffic-types within a PCN-
	domain are given in [pcn-marking-behaviour].		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 equal to 00.		field equal to 00.
			The following table sets out the valid and invalid codepoint
			transitions at PCN-nodes for this baseline encoding. Extension
			encodings may have different rules regarding the validity of the
			transitions. Note that this table assumes there is a functional
			separation between a PCN-boundary-node and a PCN-interior-node such
			that PCN-boundary-nodes do not perform packet metering or marking
			functions. PCN-nodes MUST follow the encoding transition rules set
			out in this table (e.g. they MUST NOT set invalid codepoints on
			packets they forward). This table only applies to PCN-packets.
			+-----------+-------------+-----------------+-----------------------+
			| PCN node | Codepoint | Valid codepoint | Invalid codepoint out |
			| type | in | out | |
			+-----------+-------------+-----------------+-----------------------+
			| ingress | Any | NM (or Not-PCN) | PM |
			| interior | NM | NM or PM | Not-PCN or EXP |
			| interior | EXP + | EXP or PM | Not-PCN |
			| interior | Not-PCN | Not-PCN | Any other codepoint |
			| interior | PM | PM | Any other codepoint |
			| egress | Any | 00 | Any other codepoint * |
			+-----------+-------------+-----------------+-----------------------+
			+ This SHOULD cause an alarm to be raised at a higher layer. The
			packet MUST be treated as if it were NM.
			* Except where the egress node knows that other marks may be safely
			exposed outside the PCN-domain (e.g. [PCN-3-enc-state]).
			Table 2: Valid and Invalid Codepoint Transitions for
			PCN-packets at PCN-nodes
			If a pcn-interior-node compliant with this baseline encoding receives
			a
	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]. One of		by existing IETF RFCs, in particular [RFC3168], [RFC4301] and
	the tightest constraints was the need for any PCN encoding to survive		[RFC4774]. One of the tightest constraints was the need for any PCN
	being tunnelled through either an IP in IP tunnel or an IPSec Tunnel.		encoding to survive being tunnelled through either an IP in IP tunnel
	Appendix A explains this in detail. The main effect of this		or an IPSec Tunnel. [ecn-tunneling] explains this in more detail.
	constraint is that any PCN marking has to carry the 11 codepoint in		The main effect of this constraint is that any PCN marking has to
	the ECN field. If the packet is being tunneled then only the 11		carry the 11 codepoint in the ECN field. If the packet is being
	codepoint gets copied into the inner header upon decapsulation. An		tunneled then only the 11 codepoint gets copied into the inner header
	additional constraint is the need to minimise the use of DiffServ		upon decapsulation. An additional constraint is the need to minimise
	codepoints as there is a limited supply of standards track codepoints		the use of DiffServ codepoints as there is a limited supply of
	remaining. Section 4.2 explains how we have minimised this still		standards track codepoints remaining. Section 4.2 explains how we
	further by reusing pre-existing Diffserv codepoint(s) such that non-		have minimised this still further by reusing pre-existing Diffserv
	PCN traffic can still be distinguished from PCN traffic. There are a		codepoint(s) such that non-PCN traffic can still be distinguished
	number of factors that were considered before deciding to set 10 as		from PCN traffic. There are a number of factors that were considered
	the NM state. These included similarity to ECN, presence of tunnels		before deciding to set 10 as the NM state. These included similarity
	within the domain, leakage into and out of PCN-domain and incremental		to ECN, presence of tunnels within the domain, leakage into and out
	deployment.		of PCN-domain and incremental deployment.
	The encoding scheme above seems to meet all these constraints and		The encoding scheme above seems to meet all these constraints and
	ends up looking very similar to ECN. This is perhaps not surprising		ends up looking very similar to ECN. This is perhaps not surprising
	given the similarity in architectural intent between PCN and ECN.		given the similarity in architectural intent between PCN 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 certain Diffserv codepoints. This document defines		be enabled for certain Diffserv codepoints. This document defines
	the term "PCN-compatible Diffserv codepoint" for such a DSCP.		the term "PCN-compatible Diffserv codepoint" for such a DSCP.
	Enabling PCN for a DSCP switches on PCN marking behaviour for packets		Enabling PCN for a DSCP switches on PCN marking behaviour for packets
	with that DSCP, but only if those packets also have their ECN field		with that DSCP, but only if those packets also 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]). All traffic scheduling and conditioning		introduced in [RFC3168]). All traffic scheduling and conditioning
	behaviours are discussed in [pcn-marking-behaviour].		behaviours are discussed in [pcn-marking-behaviour]. This ensures
			compliance with the BCP guidance set out in [RFC4774].
	5. Rules for Experimental Encoding Schemes		5. Rules for Experimental Encoding Schemes
	Any experimental encoding scheme MUST follow these rules to ensure		Any experimental encoding scheme MUST follow these rules to ensure
	backward compatibility with this baseline scheme:		backward compatibility with this baseline scheme:
	o The 00 codepoint in the ECN field MUST mean not-PCN.		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		o The 11 codepoint in the ECN field MUST mean PCN-marked (though
	this doesn't exclude other codepoints from carrying the same		this doesn't exclude other codepoints from carrying the same
	meaning).		meaning).
	o Once set the 11 codepoint in the ECN field MUST NOT be changed to		o Once set the 11 codepoint in the ECN field MUST NOT be changed to
	any other codepoint.		any other codepoint.
			o Any experimental scheme MUST include details of all valid and
			invalid codepoint transitions at any PCN nodes.
	6. Backwards Compatibility		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 to be		semantics for the ECN field. It sets out a number of factors to be
	taken into consideration. It also suggests various techniques to		taken into consideration. It also suggests various techniques to
	allow the co-existence of default ECN and alternative ECN semantics.		allow the co-existence of default ECN and alternative ECN semantics.
	The baseline encoding specified in this document defines PCN-		The baseline encoding specified in this document defines PCN-
	compatible DiffServ codepoints as no longer supporting the default		compatible DiffServ codepoints as no longer supporting the default
	ECN semantics. As such this document is compatible with BCP 124. It		ECN semantics. As such this document is compatible with BCP 124. It
	should be noted that this baseline encoding blocks end-to-end ECN		should be noted that this baseline encoding effectively disables end-
	except where mechanisms are put in place to tunnel such traffic		to-end ECN except where mechanisms are put in place to tunnel such
	across the PCN-domain.		traffic across the PCN-domain.
	7. IANA Considerations		7. IANA Considerations
	This document makes no request to IANA.		This document makes no request to IANA.
	8. Security Considerations		8. Security Considerations
	Packets claim entitlement to be PCN marked by carrying a PCN-		Packets claim entitlement to be PCN marked by carrying a PCN-
	Compatible DSCP and a PCN-Enabled ECN codepoint. This encoding		Compatible DSCP and a PCN-Enabled ECN codepoint. This encoding
	document is intended to stand independently of the architecture used		document is intended to stand independently of the architecture used
	to determine whether specific packets are authorised to be PCN		to determine whether specific packets are authorised to be PCN
	marked, which will be described in a future separate document on PCN		marked, which will be described in a future separate document on PCN
	edge-node behaviour (see Appendix B).		edge-node behaviour.
	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 proposed edge-node behaviour document.		be described as part of the proposed edge-node behaviour document.
	skipping to change at page 8, line 24		skipping to change at page 9, line 32
	[RFC2119] Bradner, S., "Key words for use in RFCs to		[RFC2119] Bradner, S., "Key words for use in RFCs to
	Indicate Requirement Levels", BCP 14,		Indicate Requirement Levels", BCP 14,
	RFC 2119, March 1997.		RFC 2119, March 1997.
	[RFC4774] Floyd, S., "Specifying Alternate Semantics		[RFC4774] Floyd, S., "Specifying Alternate Semantics
	for the Explicit Congestion Notification		for the Explicit Congestion Notification
	(ECN) Field", BCP 124, RFC 4774,		(ECN) Field", BCP 124, RFC 4774,
	November 2006.		November 2006.
	[pcn-arch] Eardley, P., "Pre-Congestion Notification
	(PCN) Architecture",
	draft-ietf-pcn-architecture-07 (work in
	progress), September 2008.
	12.2. Informative References		12.2. Informative References
	[PCN-3-enc-state] Moncaster, T., Briscoe, B., and M. Menth, "A		[PCN-3-enc-state] Moncaster, T., Briscoe, B., and M. Menth, "A
	three state extended PCN encoding scheme",		three state extended PCN encoding scheme",
	draft-moncaster-pcn-3-state-encoding-00		draft-moncaster-pcn-3-state-encoding-00
	(work in progress), June 2008.		(work in progress), June 2008.
	[PCN-charter] IETF, "IETF Charter for Congestion and Pre-		[PCN-charter] IETF, "IETF Charter for Congestion and Pre-
	Congestion Notification Working Group".		Congestion Notification Working Group".
	[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black,		[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black,
	"The Addition of Explicit Congestion		"The Addition of Explicit Congestion
	Notification (ECN) to IP", RFC 3168,		Notification (ECN) to IP", RFC 3168,
	September 2001.		September 2001.
	[RFC4301] Kent, S. and K. Seo, "Security Architecture		[RFC4301] Kent, S. and K. Seo, "Security Architecture
	for the Internet Protocol", RFC 4301,		for the Internet Protocol", RFC 4301,
	December 2005.		December 2005.
	[ecn-tunnelling] Briscoe, B., "Layered Encapsulation of		[RFC5127] Chan, K., Babiarz, J., and F. Baker,
			"Aggregation of DiffServ Service Classes",
			RFC 5127, February 2008.
			[ecn-tunneling] Briscoe, B., "Layered Encapsulation of
	Congestion Notification",		Congestion Notification",
	draft-briscoe-tsvwg-ecn-tunnel-01 (work in		draft-ietf-tsvwg-ecn-tunnel-01 (work in
	progress), July 2008.		progress), October 2008.
			[pcn-arch] Eardley, P., "Pre-Congestion Notification
			(PCN) Architecture",
			draft-ietf-pcn-architecture-07 (work in
			progress), September 2008.
	[pcn-marking-behaviour] Eardley, P., "Marking behaviour of PCN-		[pcn-marking-behaviour] Eardley, P., "Marking behaviour of PCN-
	nodes", draft-ietf-pcn-marking-behaviour-00		nodes", draft-ietf-pcn-marking-behaviour-01
	(work in progress), October 2008.		(work in progress), October 2008.
	[re-PCN] Briscoe, B., "Emulating Border Flow Policing		[re-PCN] Briscoe, B., "Emulating Border Flow Policing
	using Re-ECN on Bulk Data",		using Re-ECN on Bulk Data",
	draft-briscoe-re-pcn-border-cheat-00 (work		draft-briscoe-re-pcn-border-cheat-00 (work
	in progress), July 2007.		in progress), July 2007.
	[voice-admit] Baker, F., Polk, J., and M. Dolly, "DSCPs		[voice-admit] Baker, F., Polk, J., and M. Dolly, "DSCP for
	for Capacity-Admitted Traffic",		Capacity-Admitted Traffic",
	draft-ietf-tsvwg-admitted-realtime-dscp-04		draft-ietf-tsvwg-admitted-realtime-dscp-05
	(work in progress), February 2008.		(work in progress), November 2008.
	Appendix A. Tunnelling Constraints
	The rules that govern the behaviour of the ECN field for IP-in-IP
	tunnels were defined in [RFC3168]. This allowed for two tunnel
	modes. The limited functionality mode sets the outer header to not-
	ECT, regardless of the value of the inner header, in other words
	disabling ECN within the tunnel. The full functionality mode copies
	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
	then the outer header is set to ECT(0). On decapsulation, if the CE
	codepoint is set on the outer header then this is copied into the
	inner header. Otherwise the inner header is left unchanged. The
	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
	tunnels.
	The IPSec protocol [RFC4301] changed the ECN tunnelling rule to allow
	IPSec tunnels to simply copy the inner header into the outer header.
	On decapsulation the outer header is discarded and the ECN field is
	only copied down if it is set to CE.
	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 always survive
	decapsulation. However there is a need for caution with all
	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
	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
	mark concealed further into the domain. This is undesirable for many
	PCN schemes and thus the PCN working group needs to decide whether to
	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
	the ECN field and bring them in line with the behaviour of IPSec
	tunnels [ecn-tunnelling].
	Appendix B. PCN Node Behaviours
	The following table of valid and invalid transitions, while necessary		Appendix A. PCN Deployment Considerations
	for the correct functioning of PCN they is not strictly part of the
	encoding scheme. The PCN working group needs to decide whether to
	include this in this baseline encoding or whether to transfer it to
	an alternative document.
	+-----------+-------------+-----------------+-----------------------+		A.1. Choice of Suitable DSCPs
	| PCN node | Codepoint | Valid codepoint | Invalid codepoint out |
	| 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]).
	Table 2: Valid and Invalid Transitions at PCN nodes		The choice of which DSCP is most suitable for the PCN-domain is
			dependant on the nature of the traffic entering that domain and the
			link rates of all the links making up that domain. In PCN-domains
			with uniformly high link rates, the appropriate DSCPs would currently
			be those for the Real Time Traffic Class [RFC5127]. If the PCN
			domain includes lower speed links it would also be appropriate to use
			the DSCPs of the other traffic classes that [voice-admit] defines for
			use with admission control, such as the three video classes CS4, CS3
			and AF4 and the Admitted Telephony Class.
	It is also necessary to define a safe behaviour for baseline-		A.2. Rationale for Using ECT(0) for Not Marked
	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		The choice of which ECT codepoint to use for the Not Marked state was
			based on the following considerations:
	This appendix illustrates possible PCN deployment scenarios where the		o [RFC3168] full functionality tunnel within PCN-domain: Either ECT
	baseline encoding can be used and also explain a case for which		is safe.
	baseline encoding is not sufficient. {Note this appendix is provided
	for information only}.
	1. an operator requires only admission control. Then admission		o Leakage of traffic into PCN-domain: ECT(1) is less often correct.
	control is triggered from PCN-packets that are threshold-marked
	and this baseline encdoding scheme suffices.
	2. an operator requires only flow termination. Then flow		o Leakage of traffic out of PCN-domainL Either ECT is equally unsafe
	termination is triggered from PCN-packets that are excess-		(since this would incorrectly indicate the traffic was ECN capable
	traffic-marked and this baseline encdoding scheme suffices.		outside the controlled PCN-domain).
	3. an operator requires both admission control and flow termination.		o Incremental deployment: Either ECT is suitable as long as they are
	If both admission control and flow termination are triggered from		used consistently.
	PCN-packets that are excess-traffic-marked then this baseline
	encoding scheme suffices.
	4. an operator requires both admission control triggered by packets		o Conceptual consistency with other schemes: ECT(0) is conceptually
	that are threshold-marked and flow termination triggered by		consistent with [RFC3168].
	packets that are excess-traffic-marked. In this case the
	baseline encoding provides insufficient encoding states to
	achieve this.
	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
	skipping to change at page 12, line 4		skipping to change at line 506
	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
	Copyright (C) The IETF Trust (2008).
	This document is subject to the rights, licenses and restrictions
	contained in BCP 78, and except as set forth therein, the authors
	retain all their rights.
	This document and the information contained herein are provided on an
	"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
	OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
	THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
	OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
	THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
	WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
	Intellectual Property
	The IETF takes no position regarding the validity or scope of any
	Intellectual Property Rights or other rights that might be claimed to
	pertain to the implementation or use of the technology described in
	this document or the extent to which any license under such rights
	might or might not be available; nor does it represent that it has
	made any independent effort to identify any such rights. Information
	on the procedures with respect to rights in RFC documents can be
	found in BCP 78 and BCP 79.
	Copies of IPR disclosures made to the IETF Secretariat and any
	assurances of licenses to be made available, or the result of an
	attempt made to obtain a general license or permission for the use of
	such proprietary rights by implementers or users of this
	specification can be obtained from the IETF on-line IPR repository at
	http://www.ietf.org/ipr.
	The IETF invites any interested party to bring to its attention any
	copyrights, patents or patent applications, or other proprietary
	rights that may cover technology that may be required to implement
	this standard. Please address the information to the IETF at
	ietf-ipr@ietf.org.
	Acknowledgement
	This document was produced using xml2rfc v1.33 (of
	http://xml.resource.org/) from a source in RFC-2629 XML format.
End of changes. 38 change blocks.
	149 lines changed or deleted		157 lines changed or added
This html diff was produced by rfcdiff 1.35. The latest version is available from http://tools.ietf.org/tools/rfcdiff/