draft-ietf-rohc-sigcomp-sip-04.txt		draft-ietf-rohc-sigcomp-sip-05.txt
	Robust Header Compression C. Bormann		Robust Header Compression C. Bormann
	Internet-Draft Universitaet Bremen TZI		Internet-Draft Universitaet Bremen TZI
	Expires: May 30, 2007 Z. Liu		Expires: September 4, 2007 Z. Liu
	Nokia Research Center		Nokia Research Center
	R. Price		R. Price
	Cogent Defence and Security		Cogent Defence and Security
	Networks		Networks
	G. Camarillo		G. Camarillo, Ed.
	Ericsson		Ericsson
	November 26, 2006		March 3, 2007
	Applying Signaling Compression (SigComp) to the Session Initiation		Applying Signaling Compression (SigComp) to the Session Initiation
	Protocol (SIP)		Protocol (SIP)
	draft-ietf-rohc-sigcomp-sip-04.txt		draft-ietf-rohc-sigcomp-sip-05.txt
	Status of this Memo		Status of this Memo
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	This Internet-Draft will expire on May 30, 2007.		This Internet-Draft will expire on September 4, 2007.
	Copyright Notice		Copyright Notice
	Copyright (C) The Internet Society (2006).		Copyright (C) The IETF Trust (2007).
	Abstract		Abstract
	This document describes some specifics that apply when Signaling		This document describes some specifics that apply when Signaling
	Compression (SigComp) is applied to the Session Initiation Protocol		Compression (SigComp) is applied to the Session Initiation Protocol
	(SIP), such as default minimum values of SigComp parameters,		(SIP), such as default minimum values of SigComp parameters,
	compartment and state management, and a few issues on SigComp over		compartment and state management, and a few issues on SigComp over
	TCP. Any implementation of SigComp for use with SIP must conform to		TCP. Any implementation of SigComp for use with SIP must conform to
	this document, in addition to SigComp and support of the SIP and		this document, in addition to SigComp and support of the SIP and
	Session Description Protocol (SDP) static dictionary.		Session Description Protocol (SDP) static dictionary.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
	3. Minimum Values of SigComp Parameters for SIP/SigComp . . . . . 3		3. Compliance with this Specification . . . . . . . . . . . . . . 3
	3.1. decompression_memory_size (DMS) for SIP/SigComp . . . . . 4		4. Minimum Values of SigComp Parameters for SIP/SigComp . . . . . 3
	3.2. state_memory_size (SMS) for SIP/SigComp . . . . . . . . . 4		4.1. decompression_memory_size (DMS) for SIP/SigComp . . . . . 4
	3.3. cycles_per_bit (CPB) for SIP/SigComp . . . . . . . . . . . 5		4.2. state_memory_size (SMS) for SIP/SigComp . . . . . . . . . 4
	3.4. SigComp_version (SV) for SIP/SigComp . . . . . . . . . . . 5		4.3. cycles_per_bit (CPB) for SIP/SigComp . . . . . . . . . . . 5
	3.5. locally available state (LAS) for SIP/SigComp . . . . . . 5		4.4. SigComp_version (SV) for SIP/SigComp . . . . . . . . . . . 5
	4. Delimiting SIP Messages and SigComp Messages on the Same		4.5. locally available state (LAS) for SIP/SigComp . . . . . . 5
			5. Delimiting SIP Messages and SigComp Messages on the Same
	Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5		Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
	5. Continuous Mode over TCP . . . . . . . . . . . . . . . . . . . 6		6. Continuous Mode over TCP . . . . . . . . . . . . . . . . . . . 6
	6. Too Large SIP Messages . . . . . . . . . . . . . . . . . . . . 6		7. Too Large SIP Messages . . . . . . . . . . . . . . . . . . . . 6
	7. SIP Retransmissions . . . . . . . . . . . . . . . . . . . . . 6		8. SIP Retransmissions . . . . . . . . . . . . . . . . . . . . . 7
	8. Compartment and State Management for SIP/SigComp . . . . . . . 7		9. Compartment and State Management for SIP/SigComp . . . . . . . 7
	8.1. Remote Application Identification . . . . . . . . . . . . 7		9.1. Remote Application Identification . . . . . . . . . . . . 7
	8.2. Identifier Comparison Rules . . . . . . . . . . . . . . . 10		9.2. Identifier Comparison Rules . . . . . . . . . . . . . . . 10
	8.3. Compartment Opening and Closure . . . . . . . . . . . . . 10		9.3. Compartment Opening and Closure . . . . . . . . . . . . . 11
	8.4. Compartment Valid During a Registration . . . . . . . . . 11		9.4. Lack of a Compartment . . . . . . . . . . . . . . . . . . 12
	8.5. Lack of a Compartment . . . . . . . . . . . . . . . . . . 12		10. Recommendations for Network Administrators . . . . . . . . . . 13
	9. Recommendations for Network Administrators . . . . . . . . . . 12		11. Private Agreements . . . . . . . . . . . . . . . . . . . . . . 13
	10. Private Agreements . . . . . . . . . . . . . . . . . . . . . . 13		12. Backwards Compatibility . . . . . . . . . . . . . . . . . . . 14
	11. Backwards Compatibility . . . . . . . . . . . . . . . . . . . 13		13. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
	12. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 13		14. Security Considerations . . . . . . . . . . . . . . . . . . . 17
	13. Security Considerations . . . . . . . . . . . . . . . . . . . 15		15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
	14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16		16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
	15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16		17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
	16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17		17.1. Normative References . . . . . . . . . . . . . . . . . . . 18
	16.1. Normative References . . . . . . . . . . . . . . . . . . . 17		17.2. Informative References . . . . . . . . . . . . . . . . . . 19
	16.2. Informative References . . . . . . . . . . . . . . . . . . 18
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
	Intellectual Property and Copyright Statements . . . . . . . . . . 20		Intellectual Property and Copyright Statements . . . . . . . . . . 21
	1. Introduction		1. Introduction
	SigComp [RFC3320] is a solution for compressing messages generated by		SigComp [RFC3320] is a solution for compressing messages generated by
	application protocols. Although its primary driver is to compress		application protocols. Although its primary driver is to compress
	SIP [RFC3261] messages, the solution itself has been intentionally		SIP [RFC3261] messages, the solution itself has been intentionally
	designed to be application agnostic so that it can be applied to any		designed to be application agnostic so that it can be applied to any
	application protocol; this is denoted as ANY/SigComp. Consequently,		application protocol; this is denoted as ANY/SigComp. Consequently,
	many application dependent specifics are left out of the base		many application dependent specifics are left out of the base
	standard. It is intended that a separate specification is used to		standard. It is intended that a separate specification is used to
	describe those specifics when SigComp is applied to a particular		describe those specifics when SigComp is applied to a particular
	application protocol.		application protocol.
	This document binds SigComp and SIP; this is denoted as SIP/SigComp.		This document binds SigComp and SIP; this is denoted as SIP/SigComp.
	Any SigComp implementation that is used for the compression of SIP
	messages must conform to this document, as well as to [RFC3320].
	Additionally, it must support the SIP/SDP static dictionary as
	specified in [RFC3485] and the mechanism for discovering SigComp
	support at the SIP layer as specified in [RFC3486].
	2. Terminology		2. Terminology
	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 BCP 14 [RFC2119].		document are to be interpreted as described in RFC 2119 [RFC2119].
	3. Minimum Values of SigComp Parameters for SIP/SigComp		3. Compliance with this Specification
			Any SigComp implementation that is used for the compression of SIP
			messages MUST conform to this document, as well as to [RFC3320].
			Additionally, it must support the SIP/SDP static dictionary, as
			specified in [RFC3485], and the mechanism for discovering SigComp
			support at the SIP layer, as specified in [RFC3486].
			4. Minimum Values of SigComp Parameters for SIP/SigComp
	In order to support a wide range of capabilities among endpoints		In order to support a wide range of capabilities among endpoints
	implementing SigComp, SigComp defines a few parameters to describe		implementing SigComp, SigComp defines a few parameters to describe
	SigComp behavior (see section 3.3 of [RFC3320]). For each parameter,		SigComp behavior (see section 3.3 of [RFC3320]). For each parameter,
	[RFC3320] specifies a minimum value that any SigComp endpoint MUST		[RFC3320] specifies a minimum value that any SigComp endpoint MUST
	support for ANY/SigComp. Those minimum values were determined with		support for ANY/SigComp. Those minimum values were determined with
	the consideration of all imaginable devices in which SigComp may be		the consideration of all imaginable devices in which SigComp may be
	implemented. Scalability was also considered as a key factor.		implemented. Scalability was also considered as a key factor.
	However, some of the minimum values specified in [RFC3320] are too		However, some of the minimum values specified in [RFC3320] are too
	small to allow good performance for SIP message compression.		small to allow good performance for SIP message compression.
	Therefore, they are increased for SIP/SigComp as specified in the		Therefore, they are increased for SIP/SigComp as specified in the
	following sections. For completeness, those parameters that are the		following sections. For completeness, those parameters that are the
	same for SIP/SigComp as they are for ANY/SigComp are also listed.		same for SIP/SigComp as they are for ANY/SigComp are also listed.
	Note: the new minimum values are specific to SIP/SigComp. They do		The new minimum values are specific to SIP/SigComp and, thus, do not
	not apply to any other application protocols.		apply to any other application protocols. A SIP/SigComp endpoint MAY
			offer additional resources over and above the minimum values
	Note: a SigComp endpoint MAY offer additional resources if available;		specified in this document if available; these resources can be
	these resources can be advertised to remote endpoints as described in		advertised to remote endpoints as described in section 9.4.9 of
	section 9.4.9 of [RFC3320].		[RFC3320].
	3.1. decompression_memory_size (DMS) for SIP/SigComp		4.1. decompression_memory_size (DMS) for SIP/SigComp
	Minimum value for ANY/SigComp: 2048 bytes, as specified in section		Minimum value for ANY/SigComp: 2048 bytes, as specified in section
	3.3.1 of [RFC3320].		3.3.1 of [RFC3320].
	Minimum value for SIP/SigComp: 8192 bytes.		Minimum value for SIP/SigComp: 8192 bytes.
	Reason: a DMS of 2048 bytes is too small for SIP message compression		Reason: a DMS of 2048 bytes is too small for SIP message compression
	as it seriously limits the compression ratio and even makes		as it seriously limits the compression ratio and even makes
	compression impossible for certain messages. For example, the		compression impossible for certain messages. For example, the
	condition set by [RFC3320] for SigComp over UDP means: C + 2*B + R +		condition set by [RFC3320] for SigComp over UDP means: C + 2*B + R +
	2*S + 128 < DMS (each term is described below). On the other hand,		2*S + 128 < DMS (each term is described below). Therefore, if DMs is
	8KB additional memory should not cause any problem for an endpoint		too small, at least one of C, B, R, or S will be severely restricted.
	that already implements SIP, SigComp, and applications that use SIP		On the other hand, DMS is memory that is only temporarily needed
	as DMS is memory only temporarily needed during decompression of a		during decompression of a SigComp message (the memory can be
	SigComp message (the memory can be reclaimed when the message has		reclaimed when the message has been decompressed). Therefore, a
	been decompressed).		requirement of 8 KB should not cause any problem for an endpoint that
			already implements SIP, SigComp, and applications that use SIP.
	C size of compressed application message, depending on R		C size of compressed application message, depending on R
	B size of bytecode. Note: two copies -- one as part of the SigComp		B size of bytecode. Note: two copies -- one as part of the SigComp
	message and one in UDVM (Universal Decompressor Virtual Machine)		message and one in UDVM (Universal Decompressor Virtual Machine)
	memory.		memory.
	R size of ring buffer in UDVM memory		R size of circular buffer in UDVM memory
	S any additional state uploaded other than that created from the		S any additional state uploaded other than that created from the
	content of the ring buffer at the end of decompression (similar to		content of the circular buffer at the end of decompression
	B, two copies of S are needed)		(similar to B, two copies of S are needed)
	128 the smallest address in UDVM memory to copy bytecode to		128 the smallest address in UDVM memory to copy bytecode to
	3.2. state_memory_size (SMS) for SIP/SigComp		4.2. state_memory_size (SMS) for SIP/SigComp
	Minimum value for ANY/SigComp: 0 (zero) bytes, as specified in		Minimum value for ANY/SigComp: 0 (zero) bytes, as specified in
	section 3.3.1 of [RFC3320].		section 3.3.1 of [RFC3320].
	Minimum value for SIP/SigComp: 2048 bytes.		Minimum value for SIP/SigComp: 2048 bytes.
	Reason: a non-zero SMS allows an endpoint to upload a state in the		Reason: a non-zero SMS allows an endpoint to upload a state in the
	first SIP message sent to a remote endpoint without the uncertainty		first SIP message sent to a remote endpoint without the uncertainty
	of whether or not it can be created in the remote endpoint. A non-		of whether the remote endpoint will have enough memory to store such
	zero SMS obviously requires the SIP/SigComp implementation to keep		a state. A non-zero SMS obviously requires the SIP/SigComp
	state. Based on the observation that there is little gain from		implementation to keep state. Based on the observation that there is
	stateless SigComp compression, the assumption is that purely		little gain from stateless SigComp compression, the assumption is
	stateless SIP implementations are unlikely to provide a SigComp		that purely stateless SIP implementations are unlikely to provide a
	function. Stateful implementations should have little problem to		SigComp function. Stateful implementations should have little
	keep 2K additional state for each compartment (see Section 8).		problem to keep 2K additional state for each compartment (see
			Section 9).
	Note: SMS is a parameter that applies to each individual compartment.		Note: SMS is a parameter that applies to each individual compartment.
	An endpoint MAY offer different SMS values for different compartments		An endpoint MAY offer different SMS values for different compartments
	as long as the SMS value is not less than 2048 bytes.		as long as the SMS value is not less than 2048 bytes.
	3.3. cycles_per_bit (CPB) for SIP/SigComp		4.3. cycles_per_bit (CPB) for SIP/SigComp
	Minimum value for ANY/SigComp: 16, as specified in section 3.3.1 of		Minimum value for ANY/SigComp: 16, as specified in section 3.3.1 of
	[RFC3320].		[RFC3320].
	Minimum value for SIP/SigComp: 16 (same as above)		Minimum value for SIP/SigComp: 16 (same as above)
	3.4. SigComp_version (SV) for SIP/SigComp		4.4. SigComp_version (SV) for SIP/SigComp
	For ANY/SigComp: 0x01, as specified in section 3.3.2 of [RFC3320].		For ANY/SigComp: 0x01, as specified in section 3.3.2 of [RFC3320].
	For SIP/SigComp: >= 0x02 (at least SigComp + NACK)		For SIP/SigComp: >= 0x02 (at least SigComp + NACK)
	3.5. locally available state (LAS) for SIP/SigComp		4.5. locally available state (LAS) for SIP/SigComp
	Minimum LAS for ANY/SigComp: none, see section 3.3.3 of [RFC3320].		Minimum LAS for ANY/SigComp: none, see section 3.3.3 of [RFC3320].
	Minimum LAS for SIP/SigComp: the SIP/SDP static dictionary as defined		Minimum LAS for SIP/SigComp: the SIP/SDP static dictionary as defined
	in [RFC3485].		in [RFC3485].
	4. Delimiting SIP Messages and SigComp Messages on the Same Port		Note that, since support for the static SIP/SDP dictionary is
			mandatory, it does not need to be advertised.
			5. Delimiting SIP Messages and SigComp Messages on the Same Port
	In order to limit the number of ports required by a SigComp-aware		In order to limit the number of ports required by a SigComp-aware
	endpoint, it is possible to allow both SigComp messages and 'vanilla'		endpoint, it is possible to allow both SigComp messages and 'vanilla'
	SIP messages (i.e. uncompressed SIP messages with no SigComp header)		SIP messages (i.e. uncompressed SIP messages with no SigComp header)
	to arrive on the same port.		to arrive on the same port.
	For a message-based transport such as UDP or SCTP, this can be done		For a message-based transport such as UDP or SCTP, distinguishing
	per message. The receiving endpoint checks the first octet of the		between SigComp and non-SigComp messages can be done per message.
	UDP/SCTP payload to determine whether the message has been compressed		The receiving endpoint checks the first octet of the UDP/SCTP payload
	using SigComp. If the MSBs (Most Significant Bits) of the octet are		to determine whether the message has been compressed using SigComp.
	"11111" then the message is considered to be a SigComp message and is		If the MSBs (Most Significant Bits) of the octet are "11111" then the
	parsed as per [RFC3320]. If the MSBs of the octet take any other		message is considered to be a SigComp message and is parsed as per
	value, then the message is assumed to be an uncompressed SIP message,
	and is passed directly to the application with no further effect on
	the SigComp layer.
	For a stream-based transport such as TCP, the distinction is per
	connection. The receiving endpoint checks the first octet of the TCP
	data stream to determine whether the stream has been compressed using
	SigComp. If the MSBs of the octet are "11111" then the stream is
	considered to contain SigComp messages and is parsed as per
	[RFC3320]. If the MSBs of the octet take any other value, then the		[RFC3320]. If the MSBs of the octet take any other value, then the
	stream is assumed to contain uncompressed SIP messages, and is passed		message is assumed to be an uncompressed SIP message, and is passed
	directly to the application with no further effect on the SigComp		directly to the application with no further effect on the SigComp
	layer. Note that SigComp message delimiters MUST NOT be used if the		layer.
	stream contains uncompressed SIP messages.
			For a stream-based transport such as TCP, distinguishing between
			SigComp and non-SigComp messages has to be done per connection. The
			receiving endpoint checks the first octet of the TCP data stream to
			determine whether the stream has been compressed using SigComp. If
			the MSBs of the octet are "11111" then the stream is considered to
			contain SigComp messages and is parsed as per [RFC3320]. If the MSBs
			of the octet take any other value, then the stream is assumed to
			contain uncompressed SIP messages, and is passed directly to the
			application with no further effect on the SigComp layer. Note that
			SigComp message delimiters MUST NOT be used if the stream contains
			uncompressed SIP messages.
	Applications MUST NOT mix SIP messages and SigComp messages on a		Applications MUST NOT mix SIP messages and SigComp messages on a
	single TCP connection. If the TCP connection is used to carry		single TCP connection. If the TCP connection is used to carry
	SigComp messages then all messages sent over the connection MUST have		SigComp messages then all messages sent over the connection MUST have
	a SigComp header and be delimited by the use of 0xFFFF as described		a SigComp header and be delimited by the use of 0xFFFF as described
	in [RFC3320].		in [RFC3320].
	[I-D.ietf-rohc-sigcomp-impl-guide] shows how to send uncompressed		[I-D.ietf-rohc-sigcomp-impl-guide] shows how to send uncompressed
	messages in a SigComp structured TCP connection using a "well-known		messages in a SigComp-structured TCP connection using a "well-known
	shim header". Should it for any reason not be desirable to set up		shim header". Should it for any reason not be desirable to set up
	more than one TCP connection to a SIP implementation, but the		more than one TCP connection to a SIP implementation, but the
	flexibility to send both compressed and uncompressed SIP messages be		flexibility to send both compressed and uncompressed SIP messages be
	required, the compressor can set up a SigComp structured connection		required, the compressor can set up a SigComp-structured connection
	and send any uncompressed SIP messages using the well-known shim		and send any uncompressed SIP messages using the well-known shim
	header.		header.
	5. Continuous Mode over TCP		6. Continuous Mode over TCP
	Continuous Mode is a special feature of SigComp, which is designed to		Continuous Mode is a special feature of SigComp, which is designed to
	improve the overall compression ratio for long-lived connections.		improve the overall compression ratio for long-lived connections.
	Its use requires pre-agreement between the SigComp compressor and		Its use requires pre-agreement between the SigComp compressor and
	decompressor. Continuous mode is not used with SIP/SigComp.		decompressor. Continuous mode is not used with SIP/SigComp.
	Reason: continuous mode requires the transport itself to provide a		Reason: continuous mode requires the transport itself to provide a
	certain level of protection against denial of service attacks. TCP		certain level of protection against denial of service attacks. TCP
	alone is not considered to provide enough protection.		alone is not considered to provide enough protection.
	6. Too Large SIP Messages		7. Too Large SIP Messages
	SigComp does not support the compression of messages larger than 64k.		SigComp does not support the compression of messages larger than 64k.
	Therefore, if a SIP application sending compressed SIP messages to		Therefore, if a SIP application sending compressed SIP messages to
	another SIP application over a transport connection (e.g., a TCP		another SIP application over a transport connection (e.g., a TCP
	connection) needs to send a SIP message larger than 64k, the SIP		connection) needs to send a SIP message larger than 64k, the SIP
	application SHOULD establish a new transport connection and send the		application SHOULD establish a new transport connection and send the
	(uncompressed) SIP message over the new connection.		(uncompressed) SIP message over the new connection.
	7. SIP Retransmissions		8. SIP Retransmissions
	SIP retransmissions need to be compressed again before being sent.		SIP retransmissions need to be compressed again before being sent.
	That is, SIP applications MUST NOT retransmit already-compressed		That is, SIP applications MUST NOT retransmit already-compressed
	information.		information.
	The reason for this behavior is that it is impossible to know whether		The reason for this behavior is that it is impossible to know whether
	the failure causing the retransmission occurred to the message being		the failure causing the retransmission occurred on the message being
	retransmitted or to the response to that message. If the loss		retransmitted or on the response to that message. If the response
	occurred to the response, any state changes effected by the first		was lost, any state changes effected by the first instance of the
	instance of the retransmitted message would already have taken place.		retransmitted message would already have taken place. If these state
	If these state changes removed a state that the previously-		changes removed a state that the previously-transmitted message
	transmitted message relied upon, then retransmission of the same		relied upon, then retransmission of the same compressed message would
	compressed message would lead to a decompression failure.		lead to a decompression failure.
	8. Compartment and State Management for SIP/SigComp		9. Compartment and State Management for SIP/SigComp
	An application exchanging compressed traffic with a remote		An application exchanging compressed traffic with a remote
	application has a compartment that contains state information needed		application has a compartment that contains state information needed
	to compress outgoing messages and to decompress incoming messages.		to compress outgoing messages and to decompress incoming messages.
	To increase the compression efficiency, the application must assign		To increase the compression efficiency, the application must assign
	distinct compartments to distinct remote applications.		distinct compartments to distinct remote applications.
	8.1. Remote Application Identification		9.1. Remote Application Identification
	SIP/SigComp applications identify remote applications by their SIP/		SIP/SigComp applications identify remote applications by their SIP/
	SigComp identifiers. Each SIP/SigComp application MUST have a SIP/		SigComp identifiers. Each SIP/SigComp application MUST have a SIP/
	SigComp identifier URN (Uniform Resource Name) that uniquely		SigComp identifier URN (Uniform Resource Name) that uniquely
	identifies the application. Usage of a URN provides a persistent and		identifies the application. Usage of a URN provides a persistent and
	unique name for the SIP/SigComp identifier. It also provides an easy		unique name for the SIP/SigComp identifier. It also provides an easy
	way to guarantee uniqueness. This URN MUST be persistent as long as		way to guarantee uniqueness. This URN MUST be persistent as long as
	the application stores compartment state related to other SIP/SigComp		the application stores compartment state related to other SIP/SigComp
	applications.		applications.
	skipping to change at page 9, line 10		skipping to change at page 9, line 21
	appear in '+sip.instance' Contact header field parameters, and not		appear in '+sip.instance' Contact header field parameters, and not
	in SIP URI parameters. We have chosen to define 'sigcomp-id' as a		in SIP URI parameters. We have chosen to define 'sigcomp-id' as a
	SIP URI parameter to be consistent with the use of the already-in-		SIP URI parameter to be consistent with the use of the already-in-
	use 'comp=sigcomp' parameter, which is a SIP URI parameter as		use 'comp=sigcomp' parameter, which is a SIP URI parameter as
	well.		well.
	The following is an example of a 'sigcomp-id' SIP URI parameter:		The following is an example of a 'sigcomp-id' SIP URI parameter:
	sigcomp-id=urn%3auuid%3a0C67446E-F1A1-11D9-94D3-000A95A0E128		sigcomp-id=urn%3auuid%3a0C67446E-F1A1-11D9-94D3-000A95A0E128
			The following is an example of a REGISTER request that carries
			'sigcomp-id' parameters in a Via entry and in the Contact header
			field. Additionally, it also carries a '+sip.instance' Contact
			header field parameter.
			REGISTER sip:example.net SIP/2.0
			Via: SIP/2.0/UDP 192.0.2.247:2078;branch=z9hG4bK-et736vsjirav;
			rport;sigcomp-id="urn:uuid:2e5fdc76-00be-4314-8202-1116fa82a473"
			From: "Joe User" <sip:2145550500@example.net>;tag=6to4gh7t5j
			To: "Joe User" <sip:2145550500@example.net>
			Call-ID: 3c26700c1adb-lu1lz5ri5orr
			CSeq: 215196 REGISTER
			Max-Forwards: 70
			Contact: <sip:2145550500@192.0.2.247:2078;
			sigcomp-id=urn%3auuid%3a2e5fdc76-00be-4314-8202-1116fa82a473>;
			q=1.0; expires=3600;
			+sip.instance="<urn:uuid:2e5fdc76-00be-4314-8202-1116fa82a473>"
			Content-Length: 0
	SIP messages are matched with remote application identifiers as		SIP messages are matched with remote application identifiers as
	follows.		follows.
	Outgoing requests: the remote application identifier is the SIP/		Outgoing requests: the remote application identifier is the SIP/
	SigComp identifier of the URI to which the request is sent. If		SigComp identifier of the URI to which the request is sent. If
	the URI does not contain a SIP/SigComp identifier, the remote		the URI does not contain a SIP/SigComp identifier, the remote
	application identifier is the IP address plus port of the datagram		application identifier is the IP address plus port of the datagram
	carrying the request for connection-less transport protocols, and		carrying the request for connection-less transport protocols, and
	the transport connection (e.g., a TCP connection) carrying the		the transport connection (e.g., a TCP connection) carrying the
	request for connection-oriented transport protocols (this is to		request for connection-oriented transport protocols (this is to
	support legacy SIP/SigComp applications).		support legacy SIP/SigComp applications).
	Incoming responses: the remote application identifier is the same as		Incoming responses: the remote application identifier is the same as
	the one of the previously-sent request that initiated the		that of the previously-sent request that initiated the transaction
	transaction the response belongs to.		to which the response belongs.
	Incoming requests: the remote application identifier is the SIP/		Incoming requests: the remote application identifier is the SIP/
	SigComp identifier of the top-most Via entry. If the Via header		SigComp identifier of the top-most Via entry. If the Via header
	field does not contain a SIP/SigComp identifier, the remote		field does not contain a SIP/SigComp identifier, the remote
	application identifier is the source IP address plus port of the		application identifier is the source IP address plus port of the
	datagram carrying the request for connection-less transport		datagram carrying the request for connection-less transport
	protocols, and the transport connection (e.g., a TCP connection)		protocols, and the transport connection (e.g., a TCP connection)
	carrying the request for connection-oriented transport protocols		carrying the request for connection-oriented transport protocols
	(this is to support legacy SIP/SigComp applications).		(this is to support legacy SIP/SigComp applications).
	Outgoing responses: the remote application identifier is the same as		Outgoing responses: the remote application identifier is the same as
	the previously-received request that initiated the transaction the		that of the previously-received request that initiated the
	response belongs to. Note that, due to standard SIP Via header		transaction to which the response belongs. Note that, due to
	field processing, this identifier will be present in the top-most		standard SIP Via header field processing, this identifier will be
	Via entry in such responses (as long as it was present in the top-		present in the top-most Via entry in such responses (as long as it
	most Via entry of the previously-received request).		was present in the top-most Via entry of the previously-received
			request).
	A SIP/SigComp application placing its URI with the 'comp=sigcomp'		A SIP/SigComp application placing its URI with the 'comp=sigcomp'
	parameter in a header field MUST add a 'sigcomp-id' parameter with		parameter in a header field MUST add a 'sigcomp-id' parameter with
	its SIP/SigComp identifier to that URI.		its SIP/SigComp identifier to that URI.
	A SIP/SigComp application generating its own Via entry containing the		A SIP/SigComp application generating its own Via entry containing the
	'comp=sigcomp' parameter MUST add a 'sigcomp-id' parameter with its		'comp=sigcomp' parameter MUST add a 'sigcomp-id' parameter with its
	SIP/SigComp identifier to that Via entry.		SIP/SigComp identifier to that Via entry.
	A given remote application identifier is mapped to a particular		A given remote application identifier is mapped to a particular
	SigComp compartment ID following the rules given in Section 8.3 and		SigComp compartment ID following the rules given in Section 9.3.
	Section 8.4.
	8.2. Identifier Comparison Rules		9.2. Identifier Comparison Rules
	Equality comparisons between SIP/SigComp identifiers are performed		Equality comparisons between SIP/SigComp identifiers are performed
	using the rules for URN equality that are specific to the scheme in		using the rules for URN equality that are specific to the scheme in
	the URN. If the element performing the comparisons does not		the URN. If the element performing the comparisons does not
	understand the URN scheme, it performs the comparisons using the		understand the URN scheme, it performs the comparisons using the
	lexical equality rules defined in RFC 2141 [RFC2141]. Lexical		lexical equality rules defined in RFC 2141 [RFC2141]. Lexical
	equality may result in two URNs being considered unequal when they		equality may result in two URNs being considered unequal when they
	are actually equal. In this specific usage of URNs, the only element		are actually equal. In this specific usage of URNs, the only element
	which provides the URN is the SIP/SigComp application identified by		which provides the URN is the SIP/SigComp application identified by
	that URN. As a result, the SIP/SigComp application SHOULD provide		that URN. As a result, the SIP/SigComp application SHOULD provide
	lexically equivalent URNs in each registration it generates. This is		lexically equivalent URNs in each registration it generates. This is
	likely to be normal behavior in any case; applications are not likely		likely to be normal behavior in any case; applications are not likely
	to modify the value of their SIP/SigComp identifiers so that they		to modify the value of their SIP/SigComp identifiers so that they
	remain functionally equivalent yet lexigraphically different from		remain functionally equivalent yet lexigraphically different from
	previous identifiers.		previous identifiers.
	8.3. Compartment Opening and Closure		9.3. Compartment Opening and Closure
	SIP applications need to know when to open a new compartment and when		SIP applications need to know when to open a new compartment and when
	to close it. The lifetime of SIP/SigComp compartments is linked to		to close it. The lifetime of SIP/SigComp compartments is linked to
	registration state. Compartments are opened at SIP registration time		registration state. Compartments are opened at SIP registration time
	and are typically closed when the registration expires or is		and are typically closed when the registration expires or is
	canceled.		canceled.
	Previous revisions of this document also defined compartments		Previous revisions of this document also defined compartments
	valid during a SIP transaction or a SIP dialog. It was decided to		valid during a SIP transaction or a SIP dialog. It was decided to
	eliminate those types of compartments because the complexity they		eliminate those types of compartments because the complexity they
	skipping to change at page 10, line 51		skipping to change at page 11, line 34
	(same) state.		(same) state.
	A SigComp endpoint may offer to keep a state created upon request		A SigComp endpoint may offer to keep a state created upon request
	from a SigComp peer endpoint beyond the default lifetime of a		from a SigComp peer endpoint beyond the default lifetime of a
	compartment (i.e., beyond the duration of its associated		compartment (i.e., beyond the duration of its associated
	registration). This may be used to improve compression efficiency of		registration). This may be used to improve compression efficiency of
	subsequent SIP messages generated by the same remote application at		subsequent SIP messages generated by the same remote application at
	the SigComp peer endpoint. To indicate that such state will continue		the SigComp peer endpoint. To indicate that such state will continue
	to be available, the SigComp endpoint can inform its peer SigComp		to be available, the SigComp endpoint can inform its peer SigComp
	endpoint by announcing the (partial) state ID in the returned SigComp		endpoint by announcing the (partial) state ID in the returned SigComp
	parameters at the end of the registration, dialog, or transaction		parameters at the end of the registration that was supposed to limit
	that was supposed to limit the lifetime of the SigComp state. That		the lifetime of the SigComp state. That signals the state will be
	signals the state will be maintained. The mandatory support for the		maintained. The mandatory support for the SigComp Negative
	SigComp Negative Acknowledgement (NACK) Mechanism [RFC4077] in SIP/		Acknowledgement (NACK) Mechanism [RFC4077] in SIP/SigComp ensures
	SigComp ensures that it is possible to recover from synchronization		that it is possible to recover from synchronization errors regarding
	errors regarding comparment lifetimes.		compartment lifetimes.
	As an operational concern, bugs in the compartment management		As an operational concern, bugs in the compartment management
	implementation are likely to lead to sporadic, hard to diagnose		implementation are likely to lead to sporadic, hard to diagnose
	failures. Decompressors may therefore want to cache old state and,		failures. Decompressors may therefore want to cache old state and,
	if still available, allow access while logging diagnostic		if still available, allow access while logging diagnostic
	information. Both compressors and decompressors use the SigComp		information. Both compressors and decompressors use the SigComp
	Negative Acknowledgement (NACK) Mechanism [RFC4077] to recover from		Negative Acknowledgement (NACK) Mechanism [RFC4077] to recover from
	situations where such old state may no longer be available.		situations where such old state may no longer be available.
	8.4. Compartment Valid During a Registration
	A REGISTER transaction causes an application to open a new		A REGISTER transaction causes an application to open a new
	compartment to be valid for the duration of the registration		compartment to be valid for the duration of the registration
	established by the REGISTER transaction.		established by the REGISTER transaction.
	A SIP application that needs to send a compressed SIP REGISTER (i.e.,		A SIP application that needs to send a compressed SIP REGISTER (i.e.,
	a user agent generating a REGISTER or a proxy server relaying one to		a user agent generating a REGISTER or a proxy server relaying one to
	its next hop) SHOULD open a compartment for the request's remote		its next hop) SHOULD open a compartment for the request's remote
	application identifier. A SIP application that receives a compressed		application identifier. A SIP application that receives a compressed
	SIP REGISTER (i.e., the registrar or a proxy relaying the REGISTER to		SIP REGISTER (i.e., the registrar or a proxy relaying the REGISTER to
	its next-hop) SHOULD open a compartment for the request's remote		its next-hop) SHOULD open a compartment for the request's remote
	skipping to change at page 12, line 4		skipping to change at page 12, line 33
	initial REGISTER transaction. The path the REGISTER transaction		initial REGISTER transaction. The path the REGISTER transaction
	follows is typically determined by configuration data. The path		follows is typically determined by configuration data. The path
	subsequent requests traverse is determined by the Path [RFC3327]		subsequent requests traverse is determined by the Path [RFC3327]
	and the Service-Route [RFC3308] header fields in the REGISTER		and the Service-Route [RFC3308] header fields in the REGISTER
	transaction and by the Record-Route and the Route header fields in		transaction and by the Record-Route and the Route header fields in
	dialog-creating transactions. Previous revisions of this document		dialog-creating transactions. Previous revisions of this document
	supported the use of different paths for different types of		supported the use of different paths for different types of
	traffic. However, for simplicity reasons, this document now		traffic. However, for simplicity reasons, this document now
	assumes that networks using compression are configured so that		assumes that networks using compression are configured so that
	subsequent requests follow the same path as the initial REGISTER		subsequent requests follow the same path as the initial REGISTER
	transaction. Section 9 provides network administrators with		transaction. Section 10 provides network administrators with
	recommendations so that they configure they networks properly.		recommendations so that they can configure they networks properly.
	If following the previous rules, a SIP application is supposed to		If, following the rules above, a SIP application is supposed to open
	open a compartment for a remote application identifier for which it		a compartment for a remote application identifier for which it
	already has a compartment, the SIP application MUST use the already		already has a compartment, the SIP application MUST use the already
	existing compartment. That is, the SIP application MUST NOT open a		existing compartment. That is, the SIP application MUST NOT open a
	new compartment.		new compartment.
	8.5. Lack of a Compartment		9.4. Lack of a Compartment
	The use of stateless compression (i.e., compression without a		The use of stateless compression (i.e., compression without a
	compartment) is not typically worthwhile and may even result in		compartment) is not typically worthwhile and may even result in
	message expansion. Therefore, if a SIP application does not have a		message expansion. Therefore, if a SIP application does not have a
	compartment for a message it needs to send, it SHOULD NOT compress it		compartment for a message it needs to send, it MAY choose not to
	even in the presence of the comp=sigcomp parameter. Note that RFC		compress it even in the presence of the comp=sigcomp parameter. Note
	3486 [RFC3486] states the following:		that RFC 3486 [RFC3486] states the following:
	"If the next-hop URI contains the parameter comp=sigcomp, the		"If the next-hop URI contains the parameter comp=sigcomp, the
	client SHOULD compress the request using SigComp"		client SHOULD compress the request using SigComp"
	Experience since RFC 3486 [RFC3486] was written has shown that		Experience since RFC 3486 [RFC3486] was written has shown that
	stateless compression is not worthwhile. That is why now it is not		stateless compression is, in most cases, not worthwhile. That is why
	recommended to use it any longer.		now it is not recommended to use it any longer.
	9. Recommendations for Network Administrators		10. Recommendations for Network Administrators
	Network administrators can configure their networks so that the		Network administrators can configure their networks so that the
	compression efficiency achieved is increased. The following		compression efficiency achieved is increased. The following
	recommendations help network administrators perform their task.		recommendations help network administrators perform their task.
	For a given user agent, the route sets for incoming requests (created		For a given user agent, the route sets for incoming requests (created
	by a Path header field) and for outgoing requests (created by a		by a Path header field) and for outgoing requests (created by a
	Service-Route header field) are typically the same. However,		Service-Route header field) are typically the same. However,
	registrars can, if they wish, insert proxies in the latter route that		registrars can, if they wish, insert proxies in the latter route that
	do not appear in the former route and vice versa. It is RECOMMENDED		do not appear in the former route and vice versa. It is RECOMMENDED
	skipping to change at page 13, line 13		skipping to change at page 13, line 42
	inside dialogs.		inside dialogs.
	When a user agent's registration expires, proxy servers performing		When a user agent's registration expires, proxy servers performing
	compression may close their associated SIP/SigComp compartment. If		compression may close their associated SIP/SigComp compartment. If
	the user agent is involved in a dialog that was established before		the user agent is involved in a dialog that was established before
	the registration expired, subsequent requests within the dialog may		the registration expired, subsequent requests within the dialog may
	not be compressed any longer. In order to avoid this situation, it		not be compressed any longer. In order to avoid this situation, it
	is RECOMMENDED that user agents are registered as long as they are		is RECOMMENDED that user agents are registered as long as they are
	involved in a dialog.		involved in a dialog.
	10. Private Agreements		11. Private Agreements
	SIP/SigComp implementations that are subject to private agreements		SIP/SigComp implementations that are subject to private agreements
	MAY deviate from this specification, if the private agreements		MAY deviate from this specification, if the private agreements
	unambiguously specify so. Plausible candidates for such deviations		unambiguously specify so. Plausible candidates for such deviations
	include:		include:
	o Minimum values (Section 3).		o Minimum values (Section 4).
	o Use of continuous mode (Section 5).		o Use of continuous mode (Section 6).
	o Compartment definition (Section 8).		o Compartment definition (Section 9).
	11. Backwards Compatibility		12. Backwards Compatibility
	SigComp has a number of parameters that can be configured per		SigComp has a number of parameters that can be configured per
	endpoint. This document specifies a profile for SigComp when used		endpoint. This document specifies a profile for SigComp when used
	for SIP compression that further constrains the range that some of		for SIP compression that further constrains the range that some of
	these parameters may take. Examples of this are Decompressor Memory		these parameters may take. Examples of this are Decompressor Memory
	Size, State Memory Size, and SigComp Version (support for NACK).		Size, State Memory Size, and SigComp Version (support for NACK).
	Additionally, this document specifies how SIP/SigComp applications		Additionally, this document specifies how SIP/SigComp applications
	should perform compartment mapping.		should perform compartment mapping.
	When this document was written, there already were a few existing		When this document was written, there already were a few existing
	SIP/SigComp deployments. The rules in this document have been		SIP/SigComp deployments. The rules in this document have been
	designed to maximize interoperability with those legacy SIP/SigComp		designed to maximize interoperability with those legacy SIP/SigComp
	implementations. Nevertheless, implementers should be aware that		implementations. Nevertheless, implementers should be aware that
	legacy SIP/SigComp implementations may not conform to this		legacy SIP/SigComp implementations may not conform to this
	specification. Examples of problems with legacy applications would		specification. Examples of problems with legacy applications would
	be smaller DMS than mandated in this document, lack of NACK support,		be smaller DMS than mandated in this document, lack of NACK support,
	or a different comparment mapping.		or a different compartment mapping.
	12. Example		13. Example
	Figure 1 shows an example message flow where the user agent and the		Figure 1 shows an example message flow where the user agent and the
	outbound proxy exchange compressed SIP traffic. Compressed messages		outbound proxy exchange compressed SIP traffic. Compressed messages
	are marked with a (c).		are marked with a (c).
	User Agent Outbound Proxy Registrar		User Agent Outbound Proxy Registrar
	|(1) REGISTER (c) | |		|(1) REGISTER (c) | |
	|---------------->| |		|---------------->| |
	| |(2) REGISTER |		| |(2) REGISTER |
	skipping to change at page 14, line 40		skipping to change at page 15, line 40
	| |------------------------------>		| |------------------------------>
	| |(13) 200 OK |		| |(13) 200 OK |
	| |<------------------------------		| |<------------------------------
	|(14) 200 OK (c) | |		|(14) 200 OK (c) | |
	|<----------------| |		|<----------------| |
	Figure 1: Example message flow		Figure 1: Example message flow
	The user agent in Figure 1 is initialy configured (e.g., using the		The user agent in Figure 1 is initialy configured (e.g., using the
	SIP configuration framework [I-D.ietf-sipping-config-framework]) with		SIP configuration framework [I-D.ietf-sipping-config-framework]) with
	the URI of its outbound proxy. That URI contains the outbound's		the URI of its outbound proxy. That URI contains the outbound
	proxy SIP/SigComp identifier, referred to as 'Outbound-id', in a		proxy's SIP/SigComp identifier, referred to as 'Outbound-id', in a
	'sigcomp-id' parameter.		'sigcomp-id' parameter.
	When the user agent sends an initial REGISTER request (1) to the		When the user agent sends an initial REGISTER request (1) to the
	outbound proxy's URI, the user agent opens a new compartment for		outbound proxy's URI, the user agent opens a new compartment for
	'Outbound-id'. This compartment will be valid, at least, for the		'Outbound-id'. This compartment will be valid, at least, for the
	duration of the registration.		duration of the registration.
	On receiving this REGISTER request (1), the outbound proxy opens a		On receiving this REGISTER request (1), the outbound proxy opens a
	new compartment for the SIP/SigComp identifier that appears in the		new compartment for the SIP/SigComp identifier that appears in the
	'sigcomp-id' parameter of the top-most Via entry. This identifier,		'sigcomp-id' parameter of the top-most Via entry. This identifier,
	skipping to change at page 15, line 17		skipping to change at page 16, line 17
	'Outbound-id' SIP/SigComp identifier, to the REGISTER request and		'Outbound-id' SIP/SigComp identifier, to the REGISTER request and
	relays it to the registrar (2).		relays it to the registrar (2).
	When the registrar receives the REGISTER request (2), it constructs		When the registrar receives the REGISTER request (2), it constructs
	the route future incoming requests (to the user agent) will follow		the route future incoming requests (to the user agent) will follow
	using the Contact and the Path header fields. Future incoming		using the Contact and the Path header fields. Future incoming
	requests will traverse the outbound proxy before reaching the user		requests will traverse the outbound proxy before reaching the user
	agent.		agent.
	The registrar also constructs the route future outgoing requests		The registrar also constructs the route future outgoing requests
	(from the user agent) and places it in a Service-Route header field		(from the user agent) will follow and places it in a Service-Route
	in a 200 (OK) response (3). Future outgoing requests will always		header field in a 200 (OK) response (3). Future outgoing requests
	traverse the outbound proxy. The registrar has ensured that the		will always traverse the outbound proxy. The registrar has ensured
	outbound proxy performing compression handles both incoming and		that the outbound proxy performing compression handles both incoming
	outgoing requests.		and outgoing requests.
	When the outbound proxy receives a 200 (OK) response (3), it inspects		When the outbound proxy receives a 200 (OK) response (3), it inspects
	the top-most Via entry. This entry's SIP/SigComp identifier 'UA-id'		the top-most Via entry. This entry's SIP/SigComp identifier 'UA-id'
	matches that of the compartment created before. Therefore, the		matches that of the compartment created before. Therefore, the
	outbound proxy uses that compartment to compress it and relay it to		outbound proxy uses that compartment to compress it and relay it to
	the user agent.		the user agent.
	On receiving the 200 (OK) response (4), the user agent stores the		On receiving the 200 (OK) response (4), the user agent stores the
	Service-Route header field in order to use it to send future outgoing		Service-Route header field in order to use it to send future outgoing
	requests. The Service-Route header field contains the outbound		requests. The Service-Route header field contains the outbound
	skipping to change at page 15, line 49		skipping to change at page 17, line 5
	the INVITE request.		the INVITE request.
	On receiving the INVITE request (5), the outbound proxy Record Routes		On receiving the INVITE request (5), the outbound proxy Record Routes
	and relays the INVITE request (6) forward. The outbound proxy Record		and relays the INVITE request (6) forward. The outbound proxy Record
	Routes to ensure that all SIP messages related to this new dialog are		Routes to ensure that all SIP messages related to this new dialog are
	routed through the outbound proxy.		routed through the outbound proxy.
	Finally the dialog is terminated by a BYE transaction (11) that also		Finally the dialog is terminated by a BYE transaction (11) that also
	traverses the outbound proxy.		traverses the outbound proxy.
	13. Security Considerations		14. Security Considerations
	The same security considerations as described in [RFC3320] apply to		The same security considerations as described in [RFC3320] apply to
	this document. Note that keeping SigComp states longer than the		this document. Note that keeping SigComp states longer than the
	duration of a SIP dialog should not pose new security risks for two		duration of a SIP dialog should not pose new security risks for two
	reasons: a) the state has been allowed to be created in the first		reasons: a) the state has been allowed to be created in the first
	place; and b) this is on voluntary basis and a SigComp endpoint can		place; and b) this is on voluntary basis and a SigComp endpoint can
	choose not to offer it.		choose not to offer it.
	14. IANA Considerations		15. IANA Considerations
	The IANA is requested to register the 'sigcomp-id' Via header field		The IANA is requested to register the 'sigcomp-id' Via header field
	parameter, which is defined in Section 8.1, under the Header Field		parameter, which is defined in Section 9.1, under the Header Field
	Parameters and Parameter Values subregistry within the SIP Parameters		Parameters and Parameter Values subregistry within the SIP Parameters
	registry:		registry:
	Predefined		Predefined
	Header Field Parameter Name Values Reference		Header Field Parameter Name Values Reference
	---------------------------- --------------- --------- ---------		---------------------------- --------------- --------- ---------
	Via sigcomp-id No [RFCxxxx]		Via sigcomp-id No [RFCxxxx]
	The IANA is requested to register the 'sigcomp-id' SIP URI parameter,		The IANA is requested to register the 'sigcomp-id' SIP URI parameter,
	which is defined in Section 8.1, under the SIP/SIPS URI Parameters		which is defined in Section 9.1, under the SIP/SIPS URI Parameters
	subregistry within the SIP Parameters registry:		subregistry within the SIP Parameters registry:
	Parameter Name Predefined Values Reference		Parameter Name Predefined Values Reference
	-------------- ----------------- ---------		-------------- ----------------- ---------
	sigcomp-id No [RFCxxxx]		sigcomp-id No [RFCxxxx]
	Note to the RFC Editor: please, substitute RFCxxxx with the RFC		Note to the RFC Editor: please, substitute RFCxxxx with the RFC
	number this document will get.		number this document will get.
	15. Acknowledgements		16. Acknowledgements
	The authors would like to thank the following people for their		The authors would like to thank the following people for their
	comments and suggestions: Jan Christoffersson, Joerg Ott, Mark West,		comments and suggestions: Jan Christoffersson, Joerg Ott, Mark West,
	Pekka Pessi, Robert Sugar, Jonathan Rosenberg, and Robert Sparks.		Pekka Pessi, Robert Sugar, Jonathan Rosenberg, and Robert Sparks.
	Abigail Surtees and Adam Roach performed thorough reviews of this		Abigail Surtees and Adam Roach performed thorough reviews of this
	document.		document.
	16. References		17. References
	16.1. Normative References		17.1. Normative References
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.		Requirement Levels", BCP 14, RFC 2119, March 1997.
	[RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997.		[RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997.
	[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,		[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
	A., Peterson, J., Sparks, R., Handley, M., and E.		A., Peterson, J., Sparks, R., Handley, M., and E.
	Schooler, "SIP: Session Initiation Protocol", RFC 3261,		Schooler, "SIP: Session Initiation Protocol", RFC 3261,
	June 2002.		June 2002.
	skipping to change at page 17, line 50		skipping to change at page 18, line 50
	[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally		[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
	Unique IDentifier (UUID) URN Namespace", RFC 4122,		Unique IDentifier (UUID) URN Namespace", RFC 4122,
	July 2005.		July 2005.
	[RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax		[RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
	Specifications: ABNF", RFC 4234, October 2005.		Specifications: ABNF", RFC 4234, October 2005.
	[I-D.ietf-sip-outbound]		[I-D.ietf-sip-outbound]
	Jennings, C. and R. Mahy, "Managing Client Initiated		Jennings, C. and R. Mahy, "Managing Client Initiated
	Connections in the Session Initiation Protocol (SIP)",		Connections in the Session Initiation Protocol (SIP)",
	draft-ietf-sip-outbound-04 (work in progress), June 2006.		draft-ietf-sip-outbound-07 (work in progress),
			January 2007.
	[I-D.ietf-rohc-sigcomp-impl-guide]		[I-D.ietf-rohc-sigcomp-impl-guide]
	Surtees, A., "Implementer's Guide for SigComp",		Surtees, A., "Implementer's Guide for SigComp",
	draft-ietf-rohc-sigcomp-impl-guide-06 (work in progress),		draft-ietf-rohc-sigcomp-impl-guide-10 (work in progress),
	March 2006.		January 2007.
	16.2. Informative References		17.2. Informative References
	[I-D.ietf-sipping-config-framework]		[I-D.ietf-sipping-config-framework]
	Petrie, D., "A Framework for Session Initiation Protocol		Petrie, D. and S. Channabasappa, "A Framework for Session
	User Agent Profile Delivery",		Initiation Protocol User Agent Profile Delivery",
	draft-ietf-sipping-config-framework-08 (work in progress),		draft-ietf-sipping-config-framework-10 (work in progress),
	March 2006.		January 2007.
	Authors' Addresses		Authors' Addresses
	Carsten Bormann		Carsten Bormann
	Universitaet Bremen TZI		Universitaet Bremen TZI
	Postfach 330440		Postfach 330440
	Bremen D-28334		Bremen D-28334
	Germany		Germany
	Phone: +49 421 218 7024		Phone: +49 421 218 7024
	skipping to change at page 19, line 35		skipping to change at page 20, line 4
	Richard Price		Richard Price
	Cogent Defence and Security Networks		Cogent Defence and Security Networks
	Queensway Meadows Industrial Estate		Queensway Meadows Industrial Estate
	Meadows Road		Meadows Road
	Newport, Gwent NP19 4SS		Newport, Gwent NP19 4SS
	Phone: +44 (0)1794 833681		Phone: +44 (0)1794 833681
	Email: richard.price@cogent-dsn.com		Email: richard.price@cogent-dsn.com
	URI: http://www.cogent-dsn.com		URI: http://www.cogent-dsn.com
			Gonzalo Camarillo (editor)
	Gonzalo Camarillo
	Ericsson		Ericsson
	Hirsalantie 11		Hirsalantie 11
	Jorvas 02420		Jorvas 02420
	Finland		Finland
	Email: Gonzalo.Camarillo@ericsson.com		Email: Gonzalo.Camarillo@ericsson.com
	Intellectual Property Statement		Full Copyright Statement
			Copyright (C) The IETF Trust (2007).
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			contained in BCP 78, and except as set forth therein, the authors
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			THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
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	skipping to change at page 20, line 29		skipping to change at page 21, line 45
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	Copyright Statement
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	Acknowledgment		Acknowledgment
	Funding for the RFC Editor function is currently provided by the		Funding for the RFC Editor function is provided by the IETF
	Internet Society.		Administrative Support Activity (IASA).
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