< draft-ietf-sip-ice-option-tag-01.txt		draft-ietf-sip-ice-option-tag-02.txt >
	SIP J. Rosenberg		SIP J. Rosenberg
	Internet-Draft Cisco		Internet-Draft Cisco
	Intended status: Standards Track March 5, 2007		Intended status: Standards Track June 19, 2007
	Expires: September 6, 2007		Expires: December 21, 2007
	Indicating Support for Interactive Connectivity Establishment (ICE) in		Indicating Support for Interactive Connectivity Establishment (ICE) in
	the Session Initiation Protocol (SIP)		the Session Initiation Protocol (SIP)
	draft-ietf-sip-ice-option-tag-01		draft-ietf-sip-ice-option-tag-02
	Status of this Memo		Status of this Memo
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	applicable patent or other IPR claims of which he or she is aware		applicable patent or other IPR claims of which he or she is aware
	have been or will be disclosed, and any of which he or she becomes		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.		aware will be disclosed, in accordance with Section 6 of BCP 79.
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	Task Force (IETF), its areas, and its working groups. Note that		Task Force (IETF), its areas, and its working groups. Note that
	skipping to change at page 1, line 35 ¶		skipping to change at page 1, line 35 ¶
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
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	This Internet-Draft will expire on September 6, 2007.		This Internet-Draft will expire on December 21, 2007.
	Copyright Notice		Copyright Notice
	Copyright (C) The IETF Trust (2007).		Copyright (C) The IETF Trust (2007).
	Abstract		Abstract
	This specification defines a media feature tag and an option tag for		This specification defines a media feature tag and an option tag for
	use with the Session Initiation Protocol (SIP). The media feature		use with the Session Initiation Protocol (SIP). The media feature
	tag allows a UA to communicate to its registrar that it supports ICE.		tag allows a UA to communicate to its registrar that it supports ICE.
	skipping to change at page 4, line 7 ¶		skipping to change at page 4, line 7 ¶
	that do and do not support ICE. In order to facilitate deployment of		that do and do not support ICE. In order to facilitate deployment of
	ICE, it is anticipated that domains will make use of gateways which		ICE, it is anticipated that domains will make use of gateways which
	act as ICE agents on one side, an non-ICE agents on the other side.		act as ICE agents on one side, an non-ICE agents on the other side.
	This would allow a call from domain A into domain B to make use of		This would allow a call from domain A into domain B to make use of
	ICE, even if the device in domain B does not itself yet support ICE.		ICE, even if the device in domain B does not itself yet support ICE.
	However, when domain B receives a call, it will need to know whether		However, when domain B receives a call, it will need to know whether
	the call needs to pass through such a gateway, or whether it can go		the call needs to pass through such a gateway, or whether it can go
	to the terminating UA directly.		to the terminating UA directly.
	In order to make such a determination, this specification defines a		In order to make such a determination, this specification defines a
	media feature tag, sip.ice, which can be included in the Contact		media feature tag, "sip.ice", which can be included in the Contact
	header field of a REGISTER request [4]. This allows the registrar to		header field of a REGISTER request [4]. This allows the registrar to
	track whether a UA supports ICE or not. This information can be		track whether a UA supports ICE or not. This information can be
	accessed by a proxy in order to determine whether a call needs to		accessed by a proxy in order to determine whether a call needs to
	route through a gateway or not.		route through a gateway or not.
	3.2. Mandating Support for ICE		3.2. Mandating Support for ICE
	Although ICE provides a built in fall back to non-ICE operation when		Although ICE provides a built in fall back to non-ICE operation when
	the answerer doesn't support it, there are cases where the offerer		the answerer doesn't support it, there are cases where the offerer
	would rather abort the call rather than proceed without ICE.		would rather abort the call rather than proceed without ICE.
	Typically, this is because they would like to choose a different m/c-		Typically, this is because they would like to choose a different m/c-
	line address for a non-ICE peer than they would for an ICE capable		line address for a non-ICE peer than they would for an ICE capable
	peer.		peer.
	To do this, the "ice" SIP option tag can be included in the Require		To do this, the "ice" SIP option tag can be included in the Require
	header field of an INVITE request.		header field of an INVITE request.
	4. Media Feature Tag Definition		4. Media Feature Tag Definition
	The sip.ice media feature tag indicates support for ICE. An agent		The "sip.ice" media feature tag indicates support for ICE. An agent
	supports ICE if it is either a lite or full implementation, and		supports ICE if it is either a lite or full implementation, and
	consequently, is capable of including candidate attributes in an SDP		consequently, is capable of including candidate attributes in an SDP
	offer or answer for at least one transport protocol. An agent that		offer or answer for at least one transport protocol. An agent that
	supports ICE SHOULD include this media feature tag in the Contact		supports ICE SHOULD include this media feature tag in the Contact
	header field of its REGISTER requests and OPTION responses.		header field of its REGISTER requests and OPTION responses.
	An agent MAY include the media feature tag in the Contact header		An agent MAY include the media feature tag in the Contact header
	field of an INVITE or INVITE response; however, doing so is redundant		field of an INVITE or INVITE response; however, doing so is redundant
	with ICE attributes in the SDP which indicate the same thing. In		with ICE attributes in the SDP which indicate the same thing. In
	cases where an INVITE omits an offer, the lack or presence of the		cases where an INVITE omits an offer, the lack or presence of the
	media feature tag in the Contact header field cannot be used by the		media feature tag in the Contact header field cannot be used by the
	callee (which will be the offerer) to determine whether the caller		callee (which will be the offerer) to determine whether the caller
	supports ICE. In cases of third party call control [8], the caller		supports ICE. In cases of third party call control [8], the caller
	may be a controller that supports (or doesn't) ICE, while the		may be a controller that supports (or doesn't) ICE, while the
	answerer may be an agent which does (or doesn't) support ICE.		answerer may be an agent which does (or doesn't) support ICE.
	5. Option Tag Definition		5. Option Tag Definition
	This "ice" OPTION tag SHOULD NOT be used in conjunction with the		This "ice" OPTION tag SHOULD NOT be used in conjunction with the
	Supported header field. The media feature tag is used as the one and		Supported header field (this SHOULD NOT includes responses to OPTIONS
	only mechanism for indicating support for ICE. The option tag is		requests) The media feature tag is used as the one and only mechanism
	meant to be used only with the Require header field. When placed in		for indicating support for ICE. The option tag is meant to be used
	the Require header field of an INVITE request, it indicates that the		only with the Require header field. When placed in the Require
	UAS must support ICE in order to process the call. An agent supports		header field of an INVITE request, it indicates that the UAS must
	ICE if it is either a full or lite implementation, and consequently,		support ICE in order to process the call. An agent supports ICE if
	is capable of including candidate attributes in an SDP offer or		it is either a full or lite implementation, and consequently, is
	answer for at least one transport protocol.		capable of including candidate attributes in an SDP offer or answer
			for at least one transport protocol.
	6. Security Considerations		6. Security Considerations
	A malicious intermediary might attempt to modify a SIP message by		A malicious intermediary might attempt to modify a SIP message by
	inserting a Require header field containing the "ice" option tag. If		inserting a Require header field containing the "ice" option tag. If
	ICE were not supported on the UAS, this would cause the call to fail		ICE were not supported on the UAS, this would cause the call to fail
	when it would otherwise succeed. Of course, this attack is not		when it would otherwise succeed. Of course, this attack is not
	specific to ICE, and can be done using any option tag. This attack		specific to ICE, and can be done using any option tag. This attack
	is prevented by usage of the SIPS mechanism as defined in RFC 3261.		is prevented by usage of the SIPS mechanism as defined in RFC 3261.
	Similarly, an intermediary might attempt to remove the media feature		Similarly, an intermediary might attempt to remove the media feature
	tag from a REGISTER request or OPTIONS request, which might cause a		tag from a REGISTER request or OPTIONS request, which might cause a
	call to skip ICE processing when it otherwise might make use of it.		call to skip ICE processing when it otherwise might make use of it.
	This attack is also prevented using the SIP mechanism.		This attack is also prevented using the SIPS mechanism.
	7. IANA Considerations		7. IANA Considerations
	This specification defines a new media feature tag and SIP option		This specification defines a new media feature tag and SIP option
	tag.		tag.
	7.1. Option Tag		7.1. Option Tag
	This section defines a new SIP option tag per the guidelines in		This section defines a new SIP option tag per the guidelines in
	Section 27.1 of RFC 3261.		Section 27.1 of RFC 3261.
End of changes. 7 change blocks.
	15 lines changed or deleted		16 lines changed or added
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