--- 1/draft-ietf-mmusic-sdp-comedia-07.txt 2006-02-05 00:28:23.000000000 +0100 +++ 2/draft-ietf-mmusic-sdp-comedia-08.txt 2006-02-05 00:28:23.000000000 +0100 @@ -1,20 +1,20 @@ MMUSIC Working Group D. Yon Internet-Draft Dialout.Net, Inc -Expires: December 10, 2004 G. Camarillo +Expires: January 14, 2005 G. Camarillo Ericsson - June 11, 2004 + July 16, 2004 Connection-Oriented Media Transport in the Session Description Protocol (SDP) - draft-ietf-mmusic-sdp-comedia-07.txt + draft-ietf-mmusic-sdp-comedia-08.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 @@ -24,21 +24,21 @@ 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:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. - This Internet-Draft will expire on December 10, 2004. + This Internet-Draft will expire on January 14, 2005. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This document describes how to express media transport over connection-oriented protocols using the Session Description Protocol (SDP). It defines the SDP TCP protocol identifier, the SDP setup @@ -47,153 +47,163 @@ Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Protocol Identifier . . . . . . . . . . . . . . . . . . . . . 3 4. Setup Attribute . . . . . . . . . . . . . . . . . . . . . . . 4 4.1 The Setup Attribute in the Offer/answer Model . . . . . . 4 5. The Connid Attribute . . . . . . . . . . . . . . . . . . . . . 5 5.1 Offerer Behaviour . . . . . . . . . . . . . . . . . . . . 6 - 5.2 Answerer Behaviour . . . . . . . . . . . . . . . . . . . . 6 + 5.2 Answerer Behaviour . . . . . . . . . . . . . . . . . . . . 7 6. Connection Management . . . . . . . . . . . . . . . . . . . . 7 7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7.1 Passive/Active . . . . . . . . . . . . . . . . . . . . . . 8 - 7.2 Passive/Active with Connection Reestablishment . . . . . . 8 + 7.2 Passive/Active with Connection Reestablishment . . . . . . 9 7.3 Actpass/Passive . . . . . . . . . . . . . . . . . . . . . 9 - 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 + 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 11.1 Normative References . . . . . . . . . . . . . . . . . . . . 10 - 11.2 Informational References . . . . . . . . . . . . . . . . . . 10 + 11.2 Informative References . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 11 - Intellectual Property and Copyright Statements . . . . . . . . 12 + Intellectual Property and Copyright Statements . . . . . . . . 13 1. Introduction The Session Description Protocol [3] provides a general-purpose format for describing multimedia sessions in announcements or invitations. SDP uses an entirely textual data format (the US-ASCII - subset of UTF-8 [5]) to maximize portability among transports. SDP + subset of UTF-8 [10]) to maximize portability among transports. SDP does not define a protocol, but only the syntax to describe a multimedia session with sufficient information to participate in that session. Session descriptions may be sent using arbitrary existing - application protocols for transport (e.g., SAP [9], SIP [10], RTSP - [6], email, HTTP [8], etc.). + application protocols for transport (e.g., SAP [8], SIP [9], RTSP + [5], email, HTTP [7], etc.). SDP [3] defines two protocol identifiers: RTP/AVP and UDP, both of which represent unreliable connectionless protocols. While these transports are appropriate choices for multimedia streams, there are applications for which connection-oriented transports, such as TCP, - are more appropriate. We define a new protocol identifier, TCP, to - describe TCP connetions in SDP. + are more appropriate. This document defines a new protocol + identifier, TCP, to describe TCP connetions in SDP. Connection-oriented protocols introduce two new factor when describing a session: how and when should end points perform the - connection setup procedure. We define two new attributes to describe - connection setups: setup and connid. + connection setup procedure. This document defines two new attributes + to describe connection setups: setup and connid. 2. Terminology In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119 [2] and indicate requirement levels for compliant implementations. 3. Protocol Identifier The following is the ABNF for an m= line, as specified by RFC 2327 [3]. media-field = "m=" media space port ["/" integer] space proto 1*(space fmt) CRLF - We define a new values for the proto field: TCP. + This document defines a new value for the proto field: TCP. The TCP protocol identifier is similar to the UDP protocol identifier in that it only describes the transport protocol, and not the upper-layer protocol. An m= line that specifies "TCP" MUST further qualify the application-layer protocol using an fmt identifier. Media lines with the TCP protocol identifier are carried using TCP [1]. It is RECOMMENDED that documents defining new SDP protocol identifiers that involve extra protocol layers between TCP and the - media itself (e.g., TLS [7] over TCP) start with the string "TCP/" + media itself (e.g., TLS [6] over TCP) start with the string "TCP/" (e.g., TCP/TLS). The following sections define the setup and the connid attributes. - While they are applicable to m= lines that use the TCP protocol - identifier, they are not limited to them. These attributes SHOULD be - used in any m= line which uses a connection-oriented transport + While both attributes are applicable to m= lines that use the TCP + protocol identifier, they are not limited to them. These attributes + MAY be used in any m= line which uses a connection-oriented transport protocol, even if the protocol identifier of the m= line is not TCP. 4. Setup Attribute The setup attribute indicates which of the end points should initiate the connection establishment (e.g., send the initial TCP SYN). The setup attribute is charset-independent and can be a session-level or a media-level attribute. The following is the ABNF of the setup attribute: setup-attr = "a=setup:" role role = "active" / "passive" / "actpass" + / "holdconn" Active: The endpoint will initiate an outgoing connection. + Passive: The endpoint will accept an incoming connection. + ActPass: The endpoint is willing to accept an incoming connection or to initiate an outgoing connection. + Holdconn: The endpoint does not want the connection to be + established for the time being. + 4.1 The Setup Attribute in the Offer/answer Model The offer/answer model, defined in RFC 3264 [4], provides endpoints with a means to obtain shared view of a session. Some session parameters are negotiated (e.g., codecs to use), while others are simply communicated from one endpoint to the other (e.g., IP addresses). The value of the setup attribute falls into the first category. That is, both endpoints negotiate its value using the offer/answer model. The negotiation of the value of the setup attribute takes places as - follows. The offerer states which role or roles is willing to perform - and the answerer, taking the offerer's willingness into + follows. The offerer states which role or roles it is willing to + perform and the answerer, taking the offerer's willingness into consideration, chooses which roles both endpoints will actually perform during connection establishment. The following are the values that the setup attribute can take in an offer/answer exchange: Offer Answer - _______________ - active passive - passive active - actpass active / passive + ________________ + active passive / holdconn + passive active / holdconn + actpass active / passive / holdconn + holdconn holdconn - The value active indicates that the endpoint SHOULD initiate a - connection to the port number on the m= line of the other endpoint. - The port number on its own m= line is irrelevant, and the opposite - endpoint MUST NOT attempt to initiate a connection to the port number - specified there. Nevertheless, since the m= line must contain a valid - port number, the endpoint specifying using the value active SHOULD - specify a port number of 9 (the discard port) on its m= line. The - endpoint MUST NOT specify a port number of zero, except to denote an - m= line that has been or is being refused. + The active endpoint SHOULD initiate a connection to the port number + on the m= line of the other endpoint. The port number on its own m= + line is irrelevant, and the opposite endpoint MUST NOT attempt to + initiate a connection to the port number specified there. + Nevertheless, since the m= line must contain a valid port number, the + endpoint specifying using the value active SHOULD specify a port + number of 9 (the discard port) on its m= line. The endpoint MUST NOT + specify a port number of zero, except to denote an m= line that has + been or is being refused. - The value passive indicates that the endpoint SHOULD be ready to - accept a connection on the port number specified in the m= line. + The passive endpoint SHOULD be ready to accept a connection on the + port number specified in the m= line. - The value actpass indicates that the offerer can either initiate a + A value of actpass indicates that the offerer can either initiate a connection to the port number on the m= line in the answer or accept a connection on the port number specified in the m= line in the offer. That is, the offerer has no preference as to whether it accepts or initiates the connection and, so, is letting the answerer choose. + A value of holdconn indicates that the connection should not be + established for the time being. + The default value of the setup attribute in an offer/answer exchange is active in the offer and passive in the answer. 5. The Connid Attribute The preceding description of the setup attribute has been in the context of using SDP to initiate a session. Still, SDP may be exchanged between endpoints at various stages of a session to accomplish tasks such as terminating a session, redirecting media to a new endpoint, or renegotiating the media parameters for a session. @@ -234,22 +244,23 @@ m= line, the offerer MUST use the same connid value for the m= line. If, on the other hand, the offerer wants to establish a new transport-layer connection for the m= line, it MUST use a new connid value. This new connid value MUST be different from the current connid value in use and SHOULD be different than any connid value used previously in the same m= line. The connid value in an offer is only compared with the connid value currently in use. So, having a connid value different than the one in use is enough to trigger the establishment of a new - connection. Still, we recommend to use a value different than all - the previous ones used in the m= line to make debugging easier. + connection. Still, it is recommended to use a value different than + all the previous ones used in the m= line to make debugging + easier. Note that, according to the rules in this section, an offer that changes the transport address (IP address plus port number) of an m= line will have a new connid value for this m=line. 5.2 Answerer Behaviour The connid value for an m= line is negotiated using the offer/answer model. The resulting connid value after an offer/answer exchange is the connid value in the answer. @@ -261,51 +272,52 @@ the offer contains the connid value in use but the answerer wishes to establish a new transport-layer connection, the answerer MUST use a new connid value in the answer. If the connid value for an m= line resulting from an offer/answer exchange is different than the connid in use so far, the endpoints SHOULD establish a new transport-layer connection as indicated by the setup attribute. If a previous connection is still up, the endpoint responsible for establishing the new connection performing the active role SHOULD close it as soon as the offer/answer exchange is - completed. + completed. It is up to the application to ensure proper data + synchornization between the two connections. If the connid value for an m= line resulting from an offer/answer exchange is the same as the connid in use so far, the endpoints SHOULD continue using the existing connection. In the past, it was proposed to use the presence of a media-level SDP attribute as a flag to indicate that a new connection needed - to be established. We chose not to follow the flag approach + to be established. It was decided not to follow the flag approach because an offerer whose intent was to signal "no changes" in a session would need to issue a different offer than the previous one (i.e., it would need to remove the flag from the m= line). By using the connid attribute instead, an offerer signals "no changes" in a session by issuing an identical offer to the one in use. 6. Connection Management An endpoint that according to an offer/answer exchange is supposed to initiate a new connection SHOULD initiate it as soon as the offer/ answer exchange is completed, even if the endpoint does not intend to immediately begin sending media to the remote endpoint. This allows media to flow from the remote endpoint if needed. Typically, endpoints do not close the connection until the session has expired, been explicitly terminated, or a new connid value has been provided for the m= line. Additionaly, specific applications can describe further scenarios where an end-point may close a given connection. In case the session is explicitly terminated by one of - the endpoints (e.g., the endpoint sends a SIP [10] BYE), the end - point terminating the session is responsible for closing the + the endpoints (e.g., the endpoint sends a SIP [9] BYE), the end point + terminating the session is responsible for closing the transport-connection. If an endpoint determines that the transport-connection for an m= line has been closed and it should be reestablished, it SHOULD perform a new offer/answer exchange using a new connid value for this m= line. Note that the SDP direction attribute (e.g., a=sendonly) deals with the media sent over the transport-connection, but has no impact on the transport-connection itself. @@ -381,27 +394,28 @@ a=connid:3 This will cause the offerer (at 192.0.2.2) to initiate a connection to port 54321 at 192.0.2.1. 8. Security Considerations See RFC 2327 [3] for security and other considerations specific to the Session Description Protocol in general. - An attacker may attempt to modify the values of the connid attributes - to have endpoints reestablish connections unnecesaryly. So, it is - STRONGLY RECOMMENDED that integrity protection be applied to the SDP - session descriptions. For session descriptions carried in SIP [10], - S/MIME is the natural choice to provide such end-to-end integrity - protection, as described in RFC 3261 [10]. Other applications MAY use - a different form of integrity protection. + An attacker may attempt to modify the values of the connid and setup + attributes to have endpoints reestablish connections unnecesaryly or + to keep them from establishing a connection. So, it is STRONGLY + RECOMMENDED that integrity protection be applied to the SDP session + descriptions. For session descriptions carried in SIP [9], S/MIME is + the natural choice to provide such end-to-end integrity protection, + as described in RFC 3261 [9]. Other applications MAY use a different + form of integrity protection. 9. IANA Considerations This document defines two session and media level SDP attributes: setup and connid. Their formats are defined in Section 4 and Section 5 respectively. These two attributes should be registered by the IANA on http://www.iana.org/assignments/sdp-parameters @@ -429,52 +443,51 @@ [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [3] Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998. [4] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002. - [5] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD - 63, RFC 3629, November 2003. - -11.2 Informational References +11.2 Informative References - [6] Schulzrinne, H., Rao, A. and R. Lanphier, "Real Time Streaming + [5] Schulzrinne, H., Rao, A. and R. Lanphier, "Real Time Streaming Protocol (RTSP)", RFC 2326, April 1998. - [7] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC + [6] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 2246, January 1999. - [8] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., + [7] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. - [9] Handley, M., Perkins, C. and E. Whelan, "Session Announcement + [8] Handley, M., Perkins, C. and E. Whelan, "Session Announcement Protocol", RFC 2974, October 2000. - [10] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., + [9] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. + [10] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD + 63, RFC 3629, November 2003. + Authors' Addresses David Yon Dialout.Net, Inc One Indian Head Plaza Nashua, NH 03060 USA EMail: yon@dialout.net - Gonzalo Camarillo Ericsson Hirsalantie 11 Jorvas 02420 Finland EMail: Gonzalo.Camarillo@ericsson.com Intellectual Property Statement