draft-ietf-sipping-early-disposition-03.txt		rfc3959.txt
	SIPPING Working Group G. Camarillo		Network Working Group G. Camarillo
	Internet-Draft Ericsson		Request for Comments: 3959 Ericsson
	Expires: December 15, 2004 June 16, 2004		Category: Standards Track December 2004
	The Early Session Disposition Type for the Session Initiation
	Protocol (SIP)
	draft-ietf-sipping-early-disposition-03.txt
	Status of this Memo
	By submitting this Internet-Draft, I certify that any applicable
	patent or other IPR claims of which I am aware have been disclosed,
	and any of which I become aware will be disclosed, in accordance with
	RFC 3668.
	Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF), its areas, and its working groups. Note that other
	groups may also distribute working documents as Internet-Drafts.
	Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."
	The list of current Internet-Drafts can be accessed at http://		The Early Session Disposition Type for
	www.ietf.org/ietf/1id-abstracts.txt.		the Session Initiation Protocol (SIP)
	The list of Internet-Draft Shadow Directories can be accessed at		Status of This Memo
	http://www.ietf.org/shadow.html.
	This Internet-Draft will expire on December 15, 2004.		This document specifies an Internet standards track protocol for the
			Internet community, and requests discussion and suggestions for
			improvements. Please refer to the current edition of the "Internet
			Official Protocol Standards" (STD 1) for the standardization state
			and status of this protocol. Distribution of this memo is unlimited.
	Copyright Notice		Copyright Notice
	Copyright (C) The Internet Society (2004). All Rights Reserved.		Copyright (C) The Internet Society (2004).
	Abstract		Abstract
	This document defines a new disposition type (early-session) for the		This document defines a new disposition type (early-session) for the
	Content-Disposition header field in SIP. The treatment of		Content-Disposition header field in the Session Initiation Protocol
	"early-session" bodies is similar to the treatment of "session"		(SIP). The treatment of "early-session" bodies is similar to the
	bodies. That is, they follow the offer/answer model. Their only		treatment of "session" bodies. That is, they follow the offer/answer
	difference is that session descriptions whose disposition type is		model. Their only difference is that session descriptions whose
	"early-session" are used to establish early media sessions within		disposition type is "early-session" are used to establish early media
	early dialogs, as opposed to regular sessions within regular dialogs.		sessions within early dialogs, as opposed to regular sessions within
			regular dialogs.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
	3. Issues Related to Early Media Session Establishment . . . . 3		3. Issues Related to Early Media Session Establishment . . . . . 2
	4. The Early Session Disposition Type . . . . . . . . . . . . . 4		4. The Early Session Disposition Type . . . . . . . . . . . . . . 4
	5. Preconditions . . . . . . . . . . . . . . . . . . . . . . . 5		5. Preconditions . . . . . . . . . . . . . . . . . . . . . . . . 4
	6. Option tag . . . . . . . . . . . . . . . . . . . . . . . . . 5		6. Option tag . . . . . . . . . . . . . . . . . . . . . . . . . . 5
	7. Example . . . . . . . . . . . . . . . . . . . . . . . . . . 6		7. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
	8. Security Considerations . . . . . . . . . . . . . . . . . . 8		8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
	9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 9		9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
	10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9		10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10		11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
	11.1 Normative References . . . . . . . . . . . . . . . . . . . 10		11.1. Normative References . . . . . . . . . . . . . . . . . . 9
	11.2 Informational References . . . . . . . . . . . . . . . . . 10		11.2. Informational References . . . . . . . . . . . . . . . . 9
	Author's Address . . . . . . . . . . . . . . . . . . . . . . 10		Author's Address . . . . . . . . . . . . . . . . . . . . . . . 10
	Intellectual Property and Copyright Statements . . . . . . . 11		Full Copyright Statement . . . . . . . . . . . . . . . . . . . 11
	1. Introduction		1. Introduction
	Early media refers to media (e.g., audio and video) that is exchanged		Early media refers to media (e.g., audio and video) that is exchanged
	before a particular session is accepted by the called user. Within a		before a particular session is accepted by the called user. Within a
	dialog, early media occurs from the moment the initial INVITE is sent		dialog, early media occurs from the moment the initial INVITE is sent
	until the UAS generates a final response. It may be unidirectional or		until the User Agent Server (UAS) generates a final response. It may
	bidirectional, and can be generated by the caller, the callee, or		be unidirectional or bidirectional, and can be generated by the
	both. Typical examples of early media generated by the callee are		caller, the callee, or both. Typical examples of early media
	ringing tone and announcements (e.g., queuing status). Early media		generated by the callee are ringing tone and announcements (e.g.,
	generated by the caller typically consists of voice commands or DTMF		queuing status). Early media generated by the caller typically
	tones to drive IVRs.		consists of voice commands or dual tone multi-frequency (DTMF) tones
			to drive interactive voice response (IVR) systems.
	The basic SIP specification (RFC 3261 [2]) only supports very simple		The basic SIP specification (RFC 3261 [2]) only supports very simple
	early media mechanisms. These simple mechanisms have a number of		early media mechanisms. These simple mechanisms have a number of
	problems which relate to forking and security, and do not satisfy the		problems related to forking and security, and do not satisfy the
	requirements of most applications. RFC xxxx [8] goes beyond the		requirements of most applications. RFC 3960 [8] goes beyond the
	mechanisms defined in RFC 3261 [2] and describes two models to		mechanisms defined in RFC 3261 [2] and describes two models of early
	implement early media using SIP: the gateway model and the		media using SIP: the gateway model and the application server model.
	application server model.
	Although both early media models described in RFC xxxx [8] are		Although both early media models described in RFC 3960 [8] are
	superior to the one specified in RFC 3261 [2], the gateway model		superior to the one specified in RFC 3261 [2], the gateway model
	still presents a set of issues. In particular, the gateway model does		still presents a set of issues. In particular, the gateway model
	not work well with forking. Nevertheless, the gateway model is needed		does not work well with forking. Nevertheless, the gateway model is
	because some SIP entities (in particular, some gateways) cannot		needed because some SIP entities (in particular, some gateways)
	implement the application server model.		cannot implement the application server model.
	The application server model addresses some of the issues present in		The application server model addresses some of the issues present in
	the gateway model. This model uses the early-session disposition		the gateway model. This model uses the early-session disposition
	type, which is specified in this document.		type specified in this document.
	2. Terminology		2. Terminology
	In this document, the key words "MUST", "MUST NOT", "REQUIRED",		In this document, the key words "MUST", "MUST NOT", "REQUIRED",
	"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT		"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
	RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as		RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
	described in BCP 14, RFC 2119 [1] and indicate requirement levels for		described in BCP 14, RFC 2119 [1] and indicate requirement levels for
	compliant implementations.		compliant implementations.
	3. Issues Related to Early Media Session Establishment		3. Issues Related to Early Media Session Establishment
	Traditionally, early media sessions have been established in the same		Traditionally, early media sessions have been established in the same
	way as regular sessions. That is, using an offer/answer exchange		way as regular sessions. That is, using an offer/answer exchange
	where the disposition type of the session descriptions is "session".		where the disposition type of the session descriptions is "session".
	Application servers perform an offer/answer exchange with the UAC to		Application servers perform an offer/answer exchange with the User
	exchange early media exclusively, while UASs use the same offer/		Agent Client (UAC) to exchange early media exclusively, while UASs
	answer exchange, first to exchange early media, and once the regular		use the same offer/answer exchange, first to exchange early media,
	dialog is established, to exchange regular media. This way of		and once the regular dialog is established, to exchange regular
	establishing early media sessions is known as the gateway model [8],		media. This way of establishing early media sessions is known as the
	which presents some issues which relate to forking and security.		gateway model [8], which presents some issues related to forking and
	These issues exist when this model is used by either an application		security. These issues exist when this model is used by either an
	server or by a UAS.		application server or by a UAS.
	Application servers may not be able to generate an answer for an		Application servers may not be able to generate an answer for an
	offer received in the INVITE. The UAC created the offer for the UAS,		offer received in the INVITE. The UAC created the offer for the UAS,
	and so, it may have applied end-to-end encryption or have included		and so, it may have applied end-to-end encryption or have included
	information (e.g., related to key management) that the application		information (e.g., related to key management) that the application
	server is not supposed to use. Therefore, application servers need a		server is not supposed to use. Therefore, application servers need a
	means to perform an offer/answer exchange with the UAC which is		means to perform an offer/answer exchange with the UAC that is
	independent from the offer/answer exchange between both UAs.		independent from the offer/answer exchange between both UAs.
	UASs using the offer/answer exchange that will carry regular media to		UASs using the offer/answer exchange that will carry regular media
	send and receive early media can cause media clipping, as described		for sending and receiving early media can cause media clipping, as
	in Section 2.1.1 of [8]. Some UACs cannot receive early media from		described in Section 2.1.1 of [8]. Some UACs cannot receive early
	different UASs at the same time. So, when an INVITE forks and several		media from different UASs at the same time. So, when an INVITE forks
	UASs start sending early media, the UAC mutes all the UASs but one		and several UASs start sending early media, the UAC mutes all the
	(which is usually randomly chosen). If the UAS that accepts the		UASs but one (which is usually chosen at random). If the UAS that
	INVITE (i.e., sends a 200 OK) was muted, a new offer/answer exchange		accepts the INVITE (i.e., sends a 200 OK) was muted, a new
	is needed to unmute it. This usually causes media clipping.		offer/answer exchange is needed to unmute it. This usually causes
	Therefore, UASs need a means to perform an offer/answer exchange with		media clipping. Therefore, UASs need a means of performing an
	the UAC to exchange early media which is independent from the offer/		offer/answer exchange with the UAC to exchange early media that is
	answer exchanged used to exchange regular media.		independent from the offer/answer exchanged used to exchange regular
			media.
	A potential solution to this need would be to establish a different		A potential solution to this need would be to establish a different
	dialog using a globally routable URI to perform an independent offer/		dialog using a globally routable URI to perform an independent
	answer exchange. This dialog would be labelled as a dialog for early		offer/answer exchange. This dialog would be labelled as a dialog for
	media and would be related to the original dialog somehow at the UAC.		early media and would be somehow related to the original dialog at
	However, performing all the offer/answer exchanges within the		the UAC. However, performing all the offer/answer exchanges within
	original dialog has many advantages:		the original dialog has many advantages:
	o It is simpler.		o It is simpler.
	o It does not have synchronization problems, because all the early		o It does not have synchronization problems, because all the early
	dialogs are terminated when the session is accepted.		dialogs are terminated when the session is accepted.
	o It does not require globally routable URIs.		o It does not require globally routable URIs.
	o It does not introduce service interaction issues related to		o It does not introduce service interaction issues related to
	services that may be wrongly applied to the new dialog.		services that may be wrongly applied to the new dialog.
	o It makes firewall management easier.		o It makes firewall management easier.
	This way of performing offer/answer exchanges for early media is		This way of performing offer/answer exchanges for early media is
	referred to as the application server model [8]. This model uses the		referred to as the application server model [8]. This model uses the
	early-session disposition type, which we define in the following		early-session disposition type defined in the following section.
	section.
	4. The Early Session Disposition Type		4. The Early Session Disposition Type
	We define a new disposition type for the Content-Disposition header		We define a new disposition type for the Content-Disposition header
	field: early-session. User agents MUST use early-session bodies to		field: early-session. User agents MUST use early-session bodies to
	establish early media sessions in the same way as they use session		establish early media sessions in the same way as they use session
	bodies to establish regular sessions, as described in RFC 3261 [2]		bodies to establish regular sessions, as described in RFCs 3261 [2]
	and in RFC 3264 [3]. Particularly, early-session bodies MUST follow		and 3264 [3]. Particularly, early-session bodies MUST follow the
	the offer/answer model and MAY appear in the same messages as session		offer/answer model and MAY appear in the same messages as session
	bodies do with the exceptions of 2xx responses for an INVITE and		bodies do with the exceptions of 2xx responses for an INVITE and
	ACKs. Nevertheless, it is NOT RECOMMENDED to include early offers in		ACKs. Nevertheless, it is NOT RECOMMENDED that early offers in
	INVITEs because they can fork, and the UAC could receive multiple		INVITEs be included because they can fork, and the UAC could receive
	early answers establishing early media streams at roughly the same		multiple early answers establishing early media streams at roughly
	time. It is also NOT RECOMMENDED to use the same transport address		the same time. Also, the use of the same transport address (IP
	(IP address plus port) in a session body and in an early-session		address plus port) in a session body and in an early-session body is
	body. Using different transport addresses (e.g., different ports) to		NOT RECOMMENDED. Using different transport addresses (e.g.,
	receive early and regular media makes it easy to detect the start of		different ports) to receive early and regular media makes it easy to
	the regular media.		detect the start of the regular media.
	If a UA needs to refuse an early-session offer, it MUST to so by		If a User Agent (UA) needs to refuse an early-session offer, it MUST
	refusing all the media streams in it. When SDP [7] is used, this is		do so by refusing all the media streams in it. When SDP [7] is used,
	done by setting the port number of all the media streams to zero.		this is done by setting the port number of all the media streams to
			zero.
	This is the same mechanism that UACs use to refuse regular offers		This is the same mechanism that UACs use to refuse regular offers
	that arrive in a response to an empty INVITE.		that arrive in a response to an empty INVITE.
	An early media session established using early-session bodies MUST be		An early media session established using early-session bodies MUST be
	terminated when its corresponding early dialog is terminated or it		terminated when its corresponding early dialog is terminated or it
	transitions to a regular dialog.		transitions to a regular dialog.
	It is RECOMMENDED that UAs generating regular and early session		It is RECOMMENDED that UAs generating regular and early session
	descriptions use, as long as it is possible, the same codecs in both.		descriptions use, as long as it is possible, the same codecs in both.
	This way, the remote UA does not need to change codecs when the early		This way, the remote UA does not need to change codecs when the early
	session transitions to a regular session.		session transitions to a regular session.
	5. Preconditions		5. Preconditions
	RFC 3312 [4] defines a framework for preconditions for SDP.		RFC 3312 [4] defines a framework for preconditions for SDP. Early-
	Early-sessions MAY contain preconditions, which are treated in the		sessions MAY contain preconditions, which are treated in the same way
	same way as preconditions in regular sessions. That is, the UAs do		as preconditions in regular sessions. That is, the UAs do not
	not exchange media and the called user is not alerted until the		exchange media, and the called user is not alerted until the
	preconditions are met.		preconditions are met.
	6. Option tag		6. Option Tag
	We define an option tag to be used in Require and Supported header		We define an option tag to be used in Require and Supported header
	fields. Its name is early-session. A UA adding the early-session		fields: early-session. A UA adding the early-session option tag to a
	option tag to a message indicates that it understands the		message indicates that it understands the early-session disposition
	early-session disposition type.		type.
	7. Example		7. Example
	Figure 1 shows the message flow between two UAs. INVITE (1) has an		Figure 1 shows the message flow between two UAs. INVITE (1) has an
	early-session option tag in its Supported header field and the body		early-session option tag in its Supported header field and the body
	shown in Figure 2. The UAS sends back a response with two body parts,		shown in Figure 2. The UAS sends back a response with two body
	as shown in Figure 3; one of disposition type session and the other		parts, as shown in Figure 3: one of disposition type session and the
	early-session. The session body part is the answer to the offer in		other early-session. The session body part is the answer to the
	the INVITE. The early-session body part is an offer to establish an		offer in the INVITE. The early-session body part is an offer to
	early media session. When the UAC receives the 183 (Session Progress)		establish an early media session. When the UAC receives the 183
	response, it sends the answer to the early-session offer in a PRACK,		(Session Progress) response, it sends the answer to the early-session
	as shown in Figure 4. This early media session is terminated when the		offer in a PRACK, as shown in Figure 4. This early media session is
	early dialog transitions to a regular dialog. That is, when the UAS		terminated when the early dialog transitions to a regular dialog.
	sends the (5) 200 (OK) response for the INVITE.		That is, when the UAS sends the (5) 200 (OK) response for the INVITE.
	A B		A B
	| |		| |
	|--------(1) INVITE-------->|		|--------(1) INVITE-------->|
	| offer |		| offer |
	| |		| |
	|<--(2) Session Progress----|		|<--(2) Session Progress----|
	| early-offer |		| early-offer |
	| answer |		| answer |
	| |		| |
	skipping to change at page 8, line 19		skipping to change at page 7, line 19
	s=		s=
	c=IN IP4 192.0.2.1		c=IN IP4 192.0.2.1
	t=0 0		t=0 0
	m=audio 20002 RTP/AVP 0		m=audio 20002 RTP/AVP 0
	Figure 4: Early answer		Figure 4: Early answer
	8. Security Considerations		8. Security Considerations
	The security implications of using early-session bodies in SIP are		The security implications of using early-session bodies in SIP are
	the same as the ones of using session bodies; they are part of the		the same as when using session bodies; they are part of the
	offer/answer model.		offer/answer model.
	SIP uses the offer/answer model [3] to establish early sessions in		SIP uses the offer/answer model [3] to establish early sessions in
	both the gateway and the application server models. User Agents (UAs)		both the gateway and the application server models. User Agents
	generate a session description, which contains the transport address		(UAs) generate a session description, which contains the transport
	(i.e., IP address plus port) where they want to receive media, and		address (i.e., IP address plus port) where they want to receive
	send it to their peer in a SIP message. When media packets arrive at		media, and send it to their peer in a SIP message. When media
	this transport address, the UA assumes that they come from the		packets arrive at this transport address, the UA assumes that they
	receiver of the SIP message carrying the session description.		come from the receiver of the SIP message carrying the session
	Nevertheless, attackers may attempt to gain access to the contents of		description. Nevertheless, attackers may attempt to gain access to
	the SIP message and send packets to the transport address contained		the contents of the SIP message and send packets to the transport
	in the session description. To prevent this situation, UAs SHOULD		address contained in the session description. To prevent this
	encrypt their session descriptions (e.g., using S/MIME).		situation, UAs SHOULD encrypt their session descriptions (e.g., using
			S/MIME).
	Still, even if a UA encrypts its session descriptions, an attacker		Still, even if a UA encrypts its session descriptions, an attacker
	may try to guess the transport address used by the UA and send media		may try to guess the transport address used by the UA and send media
	packets to that address. Guessing such a transport address is		packets to that address. Guessing such a transport address is
	sometimes easier than it may seem because many UAs always pick up the		sometimes easier than it may seem because many UAs always pick up the
	same initial media port. To prevent this situation, UAs SHOULD use		same initial media port. To prevent this situation, UAs SHOULD use
	media-level authentication mechanisms (e.g., SRTP [6]). In addition,		media-level authentication mechanisms (e.g., Secure Realtime
	UAs that wish to keep their communications confidential SHOULD use		Transport Protocol (SRTP)[6]). In addition, UAs that wish to keep
	media-level encryption mechanisms (e.g, SRTP [6]).		their communications confidential SHOULD use media-level encryption
			mechanisms (e.g, SRTP [6]).
	Attackers may attempt to make a UA send media to a victim as part of		Attackers may attempt to make a UA send media to a victim as part of
	a DoS attack. This can be done by sending a session description with		a DoS attack. This can be done by sending a session description with
	the victim's transport address to the UA. To prevent this attack,		the victim's transport address to the UA. To prevent this attack,
	the UA SHOULD engage in a handshake with the owner of the transport		the UA SHOULD engage in a handshake with the owner of the transport
	address received in a session descriptions (just verifying		address received in a session description (just verifying willingness
	willingness to receive media) before sending a large amount of data		to receive media) before sending a large amount of data to the
	to the transport address. This check can be performed by using a		transport address. This check can be performed by using a connection
	connection oriented transport protocol, by using STUN [5] in an		oriented transport protocol, by using Simple Traversal of the UDP
	end-to-end fashion, or by the key exchange in SRTP [6].		Protocol through NAT (STUN)[5] in an end-to-end fashion, or by the
			key exchange in SRTP [6].
	In any event, note that the previous security considerations are not		In any event, note that the previous security considerations are not
	early media specific, but apply to the usage of the offer/answer		early media specific, but apply to the usage of the offer/answer
	model in SIP to establish sessions in general.		model in SIP to establish sessions in general.
	Additionally, an early media-specific risk (roughly speaking, an		Additionally, an early media-specific risk (roughly speaking, an
	equivalent to forms of "toll fraud" in the PSTN) attempts to exploit		equivalent to forms of "toll fraud" in the Public Switched Telephone
	the different charging policies some operators apply to early and to		Network (PSTN)) attempts to exploit the different charging policies
	regular media. When UAs are allowed to exchange early media for free,		some operators apply to early and to regular media. When UAs are
	but are required to pay for regular media sessions, rogue UAs may try		allowed to exchange early media for free, but are required to pay for
	to establish a bidirectional early media session and never send a 2xx		regular media sessions, rogue UAs may try to establish a
	response for the INVITE.		bidirectional early media session and never send a 2xx response for
			the INVITE.
	On the other hand, some application servers (e.g., Interactive Voice		On the other hand, some application servers (e.g., Interactive Voice
	Response systems) use bidirectional early media to obtain information		Response systems) use bidirectional early media to obtain information
	from the callers (e.g., the PIN code of a calling card). So, we do		from the callers (e.g., the Personal Identification Number (PIN) code
	not recommend that operators disallow bidirectional early media.		of a calling card). So, we do not recommend that operators disallow
	Instead, operators should consider a remedy of charging early media		bidirectional early media. Instead, operators should consider a
	exchanges that last too long, or stopping them at the media level		remedy of charging early media exchanges that last too long, or
	(according to the operator's policy).		stopping them at the media level (according to the operator's
			policy).
	9. IANA Considerations		9. IANA Considerations
	This document defines a new Content-Disposition header field		This document defines a new Content-Disposition header field
	disposition type (early-session) in Section 4. This value should be		disposition type (early-session) in Section 4. This value has been
	registered in the IANA registry for Content-Dispositions with the		registered in the IANA registry for Content-Dispositions with the
	following description:		following description:
	early-session the body describes an early communications		early-session The body describes an early communications
	session, for example, an RFC 2327 SDP body		session, for example, an RFC 2327 SDP body
	This document defines a SIP option tag (early-session) in Section 6.		This document defines a SIP option tag (early-session) in Section 6.
	It should be registered in the SIP parameters registry (http://		It has been registered in the SIP parameters registry
	www.iana.org/assignments/sip-parameters) under "Option Tags", with		(http://www.iana.org/assignments/sip-parameters) under "Option Tags",
	the following description.		with the following description.
	A UA adding the early-session option tag to a message indicates		early-session A UA adding the early-session option tag to a
	that it understands the early-session content disposition.		message indicates that it understands the early-
			session content disposition.
	10. Acknowledgements		10. Acknowledgements
	Francois Audet, Christer Holmberg, and Allison Mankin provided useful		Francois Audet, Christer Holmberg, and Allison Mankin provided useful
	comments on this document.		comments on this document.
	11. References		11. References
	11.1 Normative References		11.1. Normative References
	[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement		[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
	Levels", BCP 14, RFC 2119, March 1997.		Levels", BCP 14, RFC 2119, March 1997.
	[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,		[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
	Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:		Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
	Session Initiation Protocol", RFC 3261, June 2002.		Session Initiation Protocol", RFC 3261, June 2002.
	[3] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with		[3] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
	Session Description Protocol (SDP)", RFC 3264, June 2002.		Session Description Protocol (SDP)", RFC 3264, June 2002.
	[4] Camarillo, G., Marshall, W. and J. Rosenberg, "Integration of		[4] Camarillo, G., Marshall, W., and J. Rosenberg, "Integration of
	Resource Management and Session Initiation Protocol (SIP)", RFC		Resource Management and Session Initiation Protocol (SIP)", RFC
	3312, October 2002.		3312, October 2002.
	[5] Rosenberg, J., Weinberger, J., Huitema, C. and R. Mahy, "STUN -		[5] Rosenberg, J., Weinberger, J., Huitema, C., and R. Mahy,
	Simple Traversal of User Datagram Protocol (UDP) Through Network		"STUN - Simple Traversal of User Datagram Protocol (UDP) Through
	Address Translators (NATs)", RFC 3489, March 2003.		Network Address Translators (NATs)", RFC 3489, March 2003.
	[6] Baugher, M., McGrew, D., Naslund, M., Carrara, E. and K.		[6] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
	Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC		Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC
	3711, March 2004.		3711, March 2004.
	11.2 Informational References		11.2. Informational References
	[7] Handley, M. and V. Jacobson, "SDP: Session Description		[7] Handley, M. and V. Jacobson, "SDP: Session Description
	Protocol", RFC 2327, April 1998.		Protocol", RFC 2327, April 1998.
	[8] Camarillo, G. and H. Schulzrinne, "Early Media and Ringback Tone		[8] Camarillo, G. and H. Schulzrinne, "Early Media and Ringing Tone
	Generation in the Session Initiation Protocol",		Generation in the Session Initiation Protocol (SIP)", RFC 3960,
	draft-camarillo-sipping-early-media-02 (work in progress), July		December 2004.
	2003.
	Author's Address		Author's Address
	Gonzalo Camarillo		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 Internet Society (2004).
			This document is subject to the rights, licenses and restrictions
			contained in BCP 78, and except as set forth therein, the authors
			retain all their rights.
			This document and the information contained herein are provided on an
			"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
			OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
			ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
			INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
			INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
			WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
			Intellectual Property
	The IETF takes no position regarding the validity or scope of any		The IETF takes no position regarding the validity or scope of any
	Intellectual Property Rights or other rights that might be claimed to		Intellectual Property Rights or other rights that might be claimed to
	pertain to the implementation or use of the technology described in		pertain to the implementation or use of the technology described in
	this document or the extent to which any license under such rights		this document or the extent to which any license under such rights
	might or might not be available; nor does it represent that it has		might or might not be available; nor does it represent that it has
	made any independent effort to identify any such rights. Information		made any independent effort to identify any such rights. Information
	on the IETF's procedures with respect to rights in IETF Documents can		on the IETF's procedures with respect to rights in IETF Documents can
	be found in BCP 78 and BCP 79.		be found in BCP 78 and BCP 79.
	Copies of IPR disclosures made to the IETF Secretariat and any		Copies of IPR disclosures made to the IETF Secretariat and any
	assurances of licenses to be made available, or the result of an		assurances of licenses to be made available, or the result of an
	attempt made to obtain a general license or permission for the use of		attempt made to obtain a general license or permission for the use of
	such proprietary rights by implementers or users of this		such proprietary rights by implementers or users of this
	specification can be obtained from the IETF on-line IPR repository at		specification can be obtained from the IETF on-line IPR repository at
	http://www.ietf.org/ipr.		http://www.ietf.org/ipr.
	The IETF invites any interested party to bring to its attention any		The IETF invites any interested party to bring to its attention any
	copyrights, patents or patent applications, or other proprietary		copyrights, patents or patent applications, or other proprietary
	rights that may cover technology that may be required to implement		rights that may cover technology that may be required to implement
	this standard. Please address the information to the IETF at		this standard. Please address the information to the IETF at ietf-
	ietf-ipr@ietf.org.		ipr@ietf.org.
	Disclaimer of Validity
	This document and the information contained herein are provided on an
	"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
	OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
	ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
	INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
	INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
	WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
	Copyright Statement
	Copyright (C) The Internet Society (2004). This document is subject
	to the rights, licenses and restrictions contained in BCP 78, and
	except as set forth therein, the authors retain all their rights.
	Acknowledgment		Acknowledgement
	Funding for the RFC Editor function is currently provided by the		Funding for the RFC Editor function is currently provided by the
	Internet Society.		Internet Society.
End of changes.
This html diff was produced by rfcdiff 1.25, available from http://www.levkowetz.com/ietf/tools/rfcdiff/