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
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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
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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.
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