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			Group has chosen to publish this as a historical document to preserve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
	This Internet-Draft is submitted to IETF in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
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	The list of current Internet-Drafts can be accessed at		This Internet-Draft will expire on September 13, 2012.
	http://www.ietf.org/ietf/1id-abstracts.txt.
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	This Internet-Draft will expire on August 14, 2010.
	Copyright Notice		Copyright Notice
	Copyright (c) 2010 IETF Trust and the persons identified as the
			Copyright (c) 2012 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
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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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