--- 1/draft-ietf-mmusic-sdp-comedia-06.txt 2006-02-05 00:28:23.000000000 +0100 +++ 2/draft-ietf-mmusic-sdp-comedia-07.txt 2006-02-05 00:28:23.000000000 +0100 @@ -1,20 +1,20 @@ MMUSIC Working Group D. Yon Internet-Draft Dialout.Net, Inc -Expires: November 12, 2004 G. Camarillo +Expires: December 10, 2004 G. Camarillo Ericsson - May 14, 2004 + June 11, 2004 Connection-Oriented Media Transport in the Session Description Protocol (SDP) - draft-ietf-mmusic-sdp-comedia-06.txt + draft-ietf-mmusic-sdp-comedia-07.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 @@ -24,461 +24,436 @@ 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 November 12, 2004. + This Internet-Draft will expire on December 10, 2004. 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 two new protocol identifiers: TCP and TCP/TLS. It - also defines the SDP setup attribute, which describes the connection - setup procedure, and the SDP reconnect attribute. + (SDP). It defines the SDP TCP protocol identifier, the SDP setup + attribute, which describes the connection setup procedure, and the + SDP connid attribute, which provides a connection identifier. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 - 3. Protocol Identifiers . . . . . . . . . . . . . . . . . . . . . 3 - 3.1 TCP . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 - 3.2 TCP/TLS . . . . . . . . . . . . . . . . . . . . . . . . . 4 + 3. Protocol Identifier . . . . . . . . . . . . . . . . . . . . . 3 4. Setup Attribute . . . . . . . . . . . . . . . . . . . . . . . 4 4.1 The Setup Attribute in the Offer/answer Model . . . . . . 4 - 4.2 Multiple-Connection Avoidance when Using Actpass . . . . . 5 - 5. The Reconnect Attribute . . . . . . . . . . . . . . . . . . . 6 - 6. Connection Lifetime . . . . . . . . . . . . . . . . . . . . . 7 - 6.1 Session Renegotiation . . . . . . . . . . . . . . . . . . 7 + 5. The Connid Attribute . . . . . . . . . . . . . . . . . . . . . 5 + 5.1 Offerer Behaviour . . . . . . . . . . . . . . . . . . . . 6 + 5.2 Answerer Behaviour . . . . . . . . . . . . . . . . . . . . 6 + 6. Connection Management . . . . . . . . . . . . . . . . . . . . 7 7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7.1 Passive/Active . . . . . . . . . . . . . . . . . . . . . . 8 - 7.2 Passive/Active with Reconnect . . . . . . . . . . . . . . 9 - 7.3 Actpass . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 + 7.2 Passive/Active with Connection Reestablishment . . . . . . 8 + 7.3 Actpass/Passive . . . . . . . . . . . . . . . . . . . . . 9 + 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 - 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 - 11.1 Normative References . . . . . . . . . . . . . . . . . . . . 11 - 11.2 Informational References . . . . . . . . . . . . . . . . . . 11 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 12 - Intellectual Property and Copyright Statements . . . . . . . . 13 + 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 + 11.1 Normative References . . . . . . . . . . . . . . . . . . . . 10 + 11.2 Informational References . . . . . . . . . . . . . . . . . . 10 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 11 + Intellectual Property and Copyright Statements . . . . . . . . 12 1. Introduction - The Session Description Protocol [4] provides a general-purpose + 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 [6]) to maximize portability among transports. SDP + subset of UTF-8 [5]) 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 - [7], email, HTTP [8], etc.). + [6], email, HTTP [8], etc.). - SDP [4] defines two protocol identifiers: RTP/AVP and UDP, both of + 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 two new protocol identifiers: TCP and - TCP/TLS. Both represent connection-oriented reliable transports. + 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. - Connection-oriented protocols introduce a new factor when describing - a session: how should end points perform the connection setup - procedure. We define two new attributes to describe connection setup: - setup and reconnect. + 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. 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 Identifiers +3. Protocol Identifier The following is the ABNF for an m= line, as specified by RFC 2327 - [4]. + [3]. media-field = "m=" media space port ["/" integer] space proto 1*(space fmt) CRLF - We define two new values for the proto field: TCP and TCP/TLS. - -3.1 TCP + We define a new values 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]. - -3.2 TCP/TLS + qualify the application-layer protocol using an fmt identifier. Media + lines with the TCP protocol identifier are carried using TCP [1]. - The TCP/TLS protocol identifier specifies that the session will use - the Transport Layer Security (TLS) protocol [3] on top on a TCP [1] - connection. + 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/" + (e.g., TCP/TLS). - An m= line that contain the TCP/TLS protocol identifier MUST further - qualify the protocol using a fmt identifier. + 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 + 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" Active: The endpoint will initiate an outgoing connection. Passive: The endpoint will accept an incoming connection. - ActPass: The endpoint will both accept an incoming connection and - will initiate an outgoing connection. - - The default value of the setup attribute is actpass. That is, an m= - line without an associated setup line is considered to be actpass. + ActPass: The endpoint is willing to accept an incoming connection + or to initiate an outgoing connection. 4.1 The Setup Attribute in the Offer/answer Model - The offer/answer model, defined in RFC 3264 [5], provides endpoints + 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 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 / actpass + actpass active / passive 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, as that carries - other semantics in SDP. + 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 value actpass indicates that the endpoint SHOULD initiate a - connection to the port number on the m= line of the other endpoint - and that the endpoint SHOULD be ready to accept a connection on the - port number specified in the m= line. It is RECOMMENDED that, if - possible, endpoints set the port number on their m= line to the - source port number which they will use to establish the connection - towards the remote endpoint. This way, the transport-layer protocol - (e.g., TCP) can take care of simultaneous opens. - - Endpoints typically use the actpass value for the following reasons: - 1. The offerer has no preference as to whether it accepts or - initiates the connection and, so, is letting the answerer choose. - 2. The endpoints intend to use a single connection to transport the - media, but it is not known whether NAT (Network Address - Translator) issues will prevent either endpoint from initiating - or accepting the connection. So, both endpoints will attempt to - initiate a connection hoping that at least one will succeed. - -4.2 Multiple-Connection Avoidance when Using Actpass - - When an offer/answer exchange results in actpass, each endpoint - attempts to establish a transport connection towards the other - endpoint. If only one of the connections succeeds, this connection is - used to transfer media. Nevertheless, if both connections succeed, - one of them needs to be terminated so that both endpoints exchange - data over a single connection. In this section, we provide rules to - choose which of the two connections should be terminated (or not even - initiated). - - First of all, if the endpoints follow the recommendation of setting - the port number in their m= line to the source port number which they - will use to establish the connection towards the remote endpoint, the - transport layer should take care of simultaneous opens (at least if - TCP is the transport protocol). If, for some reason, any of the - endpoints does not follow this recommendation, both endpoints should - follow the rules below. - - If an endpoint is notified about a connection establishment attempt - from the other endpoint before performing its own connection attempt, - it SHOULD behave as a passive endpoint and SHOULD NOT attempt to - establish any other connection. - - In case two connections are established, if an endpoint receives data - (i.e., media) over one of the connections before having sent any data - on any of the connections, the endpoint SHOULD terminate the - connection that has not carried any data. - - When two connections are established and both endpoints start sending - data before receiving anything from the other endpoint, it may happen - that each of the endpoints choose a different connection to send - data. If the answerer receives data over a connection after having - sent data on the other connection, it SHOULD continue sending data on - the other connection until an application-layer data boundary. At - that point, the answerer SHOULD terminate this connection and start - using the connection on which the offerer was sending data. + The value 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. - Note that different applications may define application-layer - boundaries in different ways. A typical suitable point for the - answerer to change connections is the end of an application-layer - message and the beginning of the next one. + The default value of the setup attribute in an offer/answer exchange + is active in the offer and passive in the answer. -5. The Reconnect Attribute +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. After the initial session has been established, it may be ambiguous as to whether subsequent SDP exchange represents a confirmation that the endpoint is to continue using the current media connection unchanged, or is a request to make a new media connection. The - reconnect attribute, which is charset-independent and can be a - session-level or a media-level attribute, is used to disambiguate - these two scenarios. The following is the ABNF of the reconnect - attribute: + media-level connid attribute, which is charset-independent, is used + to disambiguate these two scenarios. The following is the ABNF of the + connid attribute: - reconnect-attr = "a=reconnect" + connid = "a=connid:" connection-identifier + connection-identifier = token - On reception of an m= line with a reconnect attribute, the endpoints - SHOULD close the existing connection, in case it was still up, and - SHOULD establish a new connection according to the setup attribute in - the m= line. + The connid attribute provides an identifier for the transport-layer + connection used by the m= line. Connid values are meaningful in the + context of a particular m= line. So, different m= lines in the same + session description MAY have the same connid value. - Either the offerer or the answerer can include a reconnect attribute - in an m= line. In any event, if the offer contained this attribute, - the answer MUST contain it as well. +5.1 Offerer Behaviour -6. Connection Lifetime + Offerers and answerers use the connid attribute to decide whether a + new transport connection needs to be established or, on the other + hand, the existing transport connection should still be used. - An endpoint that intends to initiate the connection SHOULD initiate - the connection immediately after it has sufficient information to do - so, even if it does not intend to immediately begin sending media to - the remote endpoint. This allows media to flow from the remote - endpoint. An endpoint SHOULD NOT close the connection until the - session has expired, been explicitly terminated, or the media stream - is redirected to a different address or port. + When an offerer generates an m= line which uses a connection-oriented + transport, it SHOULD provide such an m= line with a connection + identifier using a connid attribute, unless the application using the + m= line has other means to deal with connection reestablishment. The + connid attribute in an initial offer (i.e., no transport connection + has been established yet) can take any value. This value identifies + the initial connection that the endpoints will attempt to establish. - If the endpoint determines that the connection has been closed, it - MAY attempt to re-establish the connection. The decision to do so is - application and context dependant. + After the initial offer/answer exchange, any of the endpoints can + generate a new offer to change some characteristics of the session + (e.g., the direction attribute). If such an offerer wants to continue + using the previously-established transport-layer connection for the + 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. -6.1 Session Renegotiation + 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. + 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. - There are scenarios where SDP is sent by an endpoint in order to - renegotiate an existing session. These include muting/unmuting a - session, renegotiating the attributes of the media used by the - session, or extending the length of a session about to expire. - Connection-oriented media introduces some ambiguities into session - renegotiation as to when the direction attribute must be obeyed and - when it is ignored. +5.2 Answerer Behaviour - The scenario of extending the duration of an existing session is a - good example: in order to extend an existing session, endpoints will - typically resend the original SDP with updated time information. In - connectionless media the result is no change to the existing media - streams. The problem with connection oriented media is that the - original SDP will contain a setup attribute which can be considered - as a request to create a new connection, as opposed to a request to - maintain steady state. The following rule help avoid this ambiguity: + 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. - If the transport section (the c= and m= lines) of an SDP - description describes an existing connection between two endpoints - and the m= line does not contain a reconnect attribute, the - endpoints SHOULD use that connection to carry the media described - in the remainder of the message. The endpoints SHOULD NOT attempt - to set up a new connection, regardless of what is specified in the - setup attribute. - Note that if the port number in the m= line changes, there is no - need to use the reconnect attribute because the new port will - trigger the establishment of a new connection anyway. + For an m= line, if the offer contains a new connid value (i.e., + different from the one in use) the answerer MUST use this value in + the answer. If the offer contains the connid value in use and the + answerer wishes to continue using the existing transport-layer + connection, the answerer MUST use this connid value in the answer. If + 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. -7. Examples + 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. - What follows are a number of examples that show the most common usage - of the setup attribute combined with TCP-based media descriptions. - For the purpose of brevity, the main portion of the session - description is omitted in the examples and is assumed to be the - following: + 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. - v=0 - o=me 2890844526 2890842807 IN IP4 10.1.1.2 - s=Call me using TCP - t=3034423619 3042462419 + 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 + 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 + 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. + +7. Examples + + The following examples show the most common usage of the setup + attribute combined with TCP-based media descriptions. For the purpose + of brevity, the main portion of the session description is omitted in + the examples, which only show m= lines and their attributes + (including c= lines). 7.1 Passive/Active An offerer at 192.0.2.2 signals its availability for a T.38 fax session at port 54111: - c=IN IP4 192.0.2.2 m=image 54111 TCP t38 + c=IN IP4 192.0.2.2 a=setup:passive + a=connid:1 An answerer at 192.0.2.1 receiving this offer responds with the following answer: c=IN IP4 192.0.2.1 m=image 9 TCP t38 a=setup:active + a=connid:1 The endpoint at 192.0.2.1 then initiates the TCP connection to port 54111 at 192.0.2.2. -7.2 Passive/Active with Reconnect +7.2 Passive/Active with Connection Reestablishment Continuing the preceding example, consider the scenario where the TCP connection fails and the endpoints wish to reestablish the connection for the session. The endpoint at 192.0.2.2 signals this intent with the following SDP: - c=IN IP4 192.0.2.2 m=image 54111 TCP t38 + c=IN IP4 192.0.2.2 a=setup:passive - a=reconnect - - The reconnect attribute informs the endpoint at 192.0.2.1 that this - SDP represents the intent to establish a new connection for media - transport, rather than continuing with the original connection. - Because the endpoint at 192.0.2.1 may not yet be aware that the TCP - connection has failed, this eliminates any ambiguity. If 192.0.2.1 - agrees to continue the session using a new connection, it responds - with: + a=connid:2 + The new connid value informs the endpoint at 192.0.2.1 that this SDP + represents the intent to establish a new connection for media + transport, rather than continuing with the original connection. If + 192.0.2.1 agrees to continue the session using a new connection, it + responds with: - c=IN IP4 192.0.2.1 m=image 9 TCP t38 - a=setup:active IN IP4 - a=reconnect + c=IN IP4 192.0.2.1 + a=setup:active + a=connid:2 -7.3 Actpass +7.3 Actpass/Passive - An offerer at 192.0.2.2 signals its availability for a T.38 fax - session at TCP port 54111. Additionally, this offerer is also willing - to set up the media stream by initiating the TCP connection: + In another example, an offerer at 192.0.2.2 signals its availability + for a T.38 fax session at TCP port 54111. Additionally, this offerer + is also willing to set up the media stream by initiating the TCP + connection: - c=IN IP4 192.0.2.2 m=image 54111 TCP t38 + c=IN IP4 192.0.2.2 a=setup:actpass + a=connid:3 The endpoint at 192.0.2.1 responds with the following description: - c=IN IP4 192.0.2.1 m=image 54321 TCP t38 - a=setup:actpass + c=IN IP4 192.0.2.1 + a=setup:passive + 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 and the answerer (at 192.0.2.1) to - initiate a connection to port 54111 at 192.0.2.2. Ideally, the - offerer would use 192.0.2.2:5411 as the source of its connection - attempt and the answerer would use 192.0.2.1:54321 as its. + to port 54321 at 192.0.2.1. 8. Security Considerations - See RFC 2327 [4] for security and other considerations specific to + See RFC 2327 [3] for security and other considerations specific to the Session Description Protocol in general. - An attacker may attempt to substitute TCP/TLS with only TCP in a - session description. 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. - - This document touches upon NAT traversal. Implementers should be - aware of some issues that relate to the use of private IP addresses - within the offer/answer model (i.e., they are not specific to this - document). - - When an endpoint receives a session description with a private IP - address that belongs to a different address space, in most of the - cases, the endpoint will not be able to reach such an address. - Nevertheless, if this particular address also exists in the - endpoint's address space, the endpoint may end up reaching a - different peer than the one that generated the session description. - It is RECOMMENDED that endpoints authenticate their peer somehow - (e.g., using TLS [3]) or that they encrypt their media. + 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. 9. IANA Considerations This document defines two session and media level SDP attributes: - setup and reconnect. 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 under - "att-field (both session and media level)". + setup and connid. Their formats are defined in Section 4 and Section + 5 respectively. These two attributes should be registered by the IANA + on - This document defines two proto values: TCP and TCP/TLS. Their - formats are defined in Section 3.1 and Section 3.2 respectively. - These two proto values should be registered by the IANA on http:// - www.iana.org/assignments/sdp-parameters under "proto". + http://www.iana.org/assignments/sdp-parameters + + under "att-field (both session and media level)". + + This document defines a proto values: TCP. Its format is defined in + Section 3. This proto value should be registered by the IANA on + + http://www.iana.org/assignments/sdp-parameters + + under "proto". 10. Acknowledgements - The authors would like to thank Jonathan Rosenberg, Rohan Mahy, - Anders Kristensen, Joerg Ott, Paul Kyzivat, Robert - Fairlie-Cuninghame, and Colin Perkins for their valuable insights and - contributions. + Jonathan Rosenberg, Rohan Mahy, Anders Kristensen, Joerg Ott, Paul + Kyzivat, Robert Fairlie-Cuninghame, Colin Perkins, and Christer + Holmberg provided valuable insights and contributions. 11. References 11.1 Normative References [1] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981. [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. - [3] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC - 2246, January 1999. - - [4] Handley, M. and V. Jacobson, "SDP: Session Description + [3] Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998. - [5] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with + [4] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002. - [6] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD + [5] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. 11.2 Informational References - [7] Schulzrinne, H., Rao, A. and R. Lanphier, "Real Time Streaming + [6] 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 + 2246, January 1999. + [8] 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 Protocol", RFC 2974, October 2000. [10] 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.