RMT H. Mehta Internet-Draft R. Walsh Expires: January 10, 2005 Nokia J. Peltotalo S. Peltotalo Tampere University of Technology July 12, 2004 SDP Descriptors for FLUTE draft-mehta-rmt-flute-sdp-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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:// 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 January 10, 2005. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This document specifies the use of SDP to describe the parameters required to begin, join, receive data from, and end FLUTE sessions. Mehta, et al. Expires January 10, 2005 [Page 1] Internet-Draft SDP Descriptors for FLUTE July 2004 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions Used in This Document . . . . . . . . . . . . . 4 3. FLUTE Descriptors . . . . . . . . . . . . . . . . . . . . . 5 3.1 FLUTE Protocol ID . . . . . . . . . . . . . . . . . . . . . 5 3.2 IP Source Address . . . . . . . . . . . . . . . . . . . . . 6 3.3 Transport Session Identifier . . . . . . . . . . . . . . . . 6 3.4 Session Timing Parameters . . . . . . . . . . . . . . . . . 7 3.5 Channelisation Descriptors . . . . . . . . . . . . . . . . . 7 3.5.1 Number of channels . . . . . . . . . . . . . . . . . . . . . 7 3.5.2 Destination IP address and port number for channels . . . . 8 3.6 Content Description . . . . . . . . . . . . . . . . . . . . 9 3.6.1 Content Description Pointer . . . . . . . . . . . . . . . . 9 4. SDP Syntax Example . . . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . 11 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 References . . . . . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 14 Intellectual Property and Copyright Statements . . . . . . . 15 Mehta, et al. Expires January 10, 2005 [Page 2] Internet-Draft SDP Descriptors for FLUTE July 2004 1. Introduction The Session Description Protocol [5] 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 [8]) 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. FLUTE [1], SAP [9], SIP [10], email, HTTP [11] etc.). SDP [5] defines two protocol identifiers that represent unreliable connectionless protocols. These are RTP/AVP and UDP. These are appropriate choices for multimedia streams. draft-ietf-mmusic-sdp-comedia-07.txt [12] defines protocol identifiers for connection-oriented reliable transports: TCP and TCP/ TLS. RFC 3266 [6] describes SDP support for IPV6. This document defines a new protocol identifier for FLUTE and other required descriptors for initiating a FLUTE session. The formal ABNF syntax [4] is used for the descriptors. Mehta, et al. Expires January 10, 2005 [Page 3] Internet-Draft SDP Descriptors for FLUTE July 2004 2. Conventions Used in This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [2]. Mehta, et al. Expires January 10, 2005 [Page 4] Internet-Draft SDP Descriptors for FLUTE July 2004 3. FLUTE Descriptors The FLUTE specification [1] describes the optional and required parameters for a FLUTE session. This document specifies the SDP parameters for FLUTE sessions that can be used for the discovery of FLUTE download and service announcement sessions. The required parameters are: o The sender IP address o The number of channels in the session o The destination IP address and port number for each channel in the session o The Transport Session Identifier (TSI) of the session Optionally, the following parameters may be associated with the session: o The start and end time of the session o FEC Encoding ID and FEC Instance ID o Some information that tells the receiver in the first place, that the session contains files that are of interest The description of these parameters in SDP is presented in the following sections. 3.1 FLUTE Protocol ID The following is the ABNF syntax for an m= line, as specified by RFC 2327 [5]: media-field = "m=" media space port ["/" integer] space proto 1*(space fmt) CRLF We define a new value for the proto field: FLUTE/UDP. The FLUTE/UDP descriptor specifies that the session being described will use the File Delivery over Unidirectional Transport (FLUTE) protocol on top of a UDP connection. All media with this protocol ID belong to the same FLUTE session. An m= line that contains the FLUTE/UDP protocol identifier MUST further qualify the protocol using an 'fmt' [5] identifier. Mehta, et al. Expires January 10, 2005 [Page 5] Internet-Draft SDP Descriptors for FLUTE July 2004 Each complete SDP session description will describe only one FLUTE session. This arises from the limitation of SDP that no session level details can be specified after the "m=" line. 3.2 IP Source Address The LCT specification [3] requires that all the channels of a single LCT session are from the same source IP address. Hence, there MUST be exactly one IP sender address per FLUTE session, and therefore one IP address per each complete SDP description of a FLUTE session. The IP source address shall be defined according to the source-filter attribute ("a=source-filter") [5, 7], with the following exceptions: o Exactly one source address may be specified by this attribute such that exclusive-mode shall not be used and inclusive-mode shall use exactly one source address in the 'src-list'. o There shall be exactly one source-filter attribute per complete FLUTE session SDP description, and this shall be in the session part of the session description (i.e. not per media). o The * value shall be used for the 'dest-address' subfield, even when the FLUTE session employs only a single LCT (multicast) channel. An example of the use of this attribute is: a=source-filter: incl IN IP6 * 2001:210:1:2:240:96FF:FE25:8EC9 This example uses the source-filter attribute to describe an IPv6 source address. 3.3 Transport Session Identifier The combination of the TSI and the IP source address identifies the session. Each TSI MUST uniquely identify a FLUTE session for a given IP source address during the time that the session is active and also for a large time before and after the active session time. This requirement is also specified by [3]. There MUST be exactly one occurence of the TSI SDP descriptor in a complete SDP FLUTE session description and it MUST appear at the session level. The ABNF syntax for the TSI descriptor is given below: sdp-flute-tsi-line = "a=flute-tsi:" value CRLF Mehta, et al. Expires January 10, 2005 [Page 6] Internet-Draft SDP Descriptors for FLUTE July 2004 where value = %d 3.4 Session Timing Parameters The SDP timing field "t=" [5] may be optionally used to indicate the FLUTE session start and end times. 3.5 Channelisation Descriptors This section specifies the description of the channel(s) used within a FLUTE session. The required parameters for channel description are: o Number of channels o Destination IP address and port number for channels 3.5.1 Number of channels The FLUTE specification allows for the use of multiple LCT channels (multicast groups) to transport the files of a single FLUTE session. This is referred to as FLUTE session channelisation in this document. FLUTE session channelisation is defined according to a new SDP attribute at session level as specified in this document. Details of each channel are defined by SDP media level information also described in this document. The multiple channel attribute describes the number of channels used by the sender to transmit. It may also be used to check the number of channels against the SDP "m=" lines. The syntax for the attribute in ABNF is as follows: sdp-flute-channel-line = "a=flute-ch:" value CRLF where value = %d, value is the number of channels used by the sender to transmit data in a FLUTE session. This parameter indicates to the receiver that the sender is using multiple channels in the FLUTE session to transmit data. This also indicates the number of channels used by the sender. The value specified by this descriptor can be used by the receiver to check that it has received all the m-lines describing the destinations. For example, if the value of this parameter is 2, then there should be 2 channels specified by the m-lines. An example is given in section 4. In the absence of this descriptor, a receiver shall understand that Mehta, et al. Expires January 10, 2005 [Page 7] Internet-Draft SDP Descriptors for FLUTE July 2004 exactly one FLUTE channel is used for the FLUTE session. 3.5.2 Destination IP address and port number for channels One or more channels MUST be described by the media-level channel descriptors. The number of channels shall be inferred from the channel parameters. These channel parameters shall be per channel: o IP destination address o Destination port number The IP destination address shall be defined according to the connection data field ("c=") of SDP [5]. The destination port number shall be defined according to the "port" sub-field of the media announcement field ("m=") of SDP [5]. Although it is generally recommended that multiple channels are differentiated by IP destination address, in the case that the same destination IP address is used for all the channels of a session and only the destination port number differentiates channels, the IP destination address may be given by the connection data field at session-level for all channels (if so, the connection data field shall not be used at media-level). Exactly one destination port MUST be used per FLUTE channel. When more than one session channel is used, it is recommended that the channels are differentiated based on destination/group IP address (other parameters may vary too, but channel differentiation based on destination port with the same destination address is considered unnecessary, complex and potentially harmful). Thus, it is recommended that the "number of ports" option in the SDP "m" line is not used (or used only with a value of 1). If the value is greater than 1, this indicates that number of FLUTE channels. For per channel description of the IP destination address, IP destination address values must be given at media-level, i.e. following an "m=" descriptor. The sequence of multiple channels shall be determined by the order in which their media descriptions are defined in the session description (i.e. the first media description gives the first channel in the sequence). In the case of the slash notation usage for specifying multiple destination addresses or ports, the order of the channel sequence shall be lowest value first and highest last; and in the case of slash notation for both destination address and port of a media-level description the channel sequence will be from the lowest address value and incremented through the range. Mehta, et al. Expires January 10, 2005 [Page 8] Internet-Draft SDP Descriptors for FLUTE July 2004 Also we need to indicate the presence of a FLUTE session on a certain channel. This is done by using the "m=" line in the SDP description as shown in the following example: m=application 12345 FLUTE/UDP 0 c=IN IP6 FF1E:03AD::7F2E:172A:1E24/1 In the above SDP attributes, the "m" line indicates the media used and the c-line indicates the corresponding channel. Thus, in the above example, the m-line indicates that the media is transported on a channel that uses FLUTE over UDP. Further, the c-line indicates the channel address, which, in this case, is an IPv6 address. 3.6 Content Description In the context of a FLUTE session, two forms of content description are important: o The out-of-band URI or content description pointer that may signal to the receiver that the FLUTE session is transmitting something of interest, and, o The media type(s) of the files being transmitted during the FLUTE session. 3.6.1 Content Description Pointer The syntax of the information that tells receiver, in the first place, that the session contains files that are of interest is out of scope of this document. However, the SDP may include a Content description pointer to enable efficient linkage to such information. The content descriptor pointer attribute describes how the sender indicates to the receiver the URI where the content description is stored. The content descriptor pointer shall be defined according to the following SDP descriptor. The syntax in ABNF is given below: sdp-content-desc-line = "a=content-desc:" URI-reference CRLF where URI-reference = as defined in RFC 2396 URI is a valid URI for the Content Description. The URI may be of an XML definition, such as one defined according to the FDT Instance schema (as described in [1]). Mehta, et al. Expires January 10, 2005 [Page 9] Internet-Draft SDP Descriptors for FLUTE July 2004 4. SDP Syntax Example This section gives an example of the use of SDP attributes to describe a FLUTE session. v=0 o=user123 2890844526 2890842807 IN IP6 2201:056D::112E:144A:1E24 s=File delivery session example i=More information t=2873397496 2873404696 a=source-filter: incl IN IP6 * 2001:210:1:2:240:96FF:FE25:8EC9 a=flute-tsi: 3 a=flute-ch: 2 m=data 12345 FLUTE/UDP 0 c=IN IP6 FF1E:03AD::7F2E:172A:1E24/1 m=data 12346 FLUTE/UDP 0 c=IN IP6 FF1E:03AD::7F2E:172A:1E30/1 The sender indicates in the above example that it will transmit data in the FLUTE session on two channels (a=flute-ch:2). The sender then specifies the channels. These channels are indicated in the line c=IN IP6 FF1E:03AD::7F2E:172A:1E30/1. This also shows to the receivers that the channels are two (maybe more in other cases) consecutive channels. The attribute TSI defined in the line a=flute-tsi:3 describes the TSI (Transmission Session Identifier) for the session. The line m=data 12345 FLUTE/UDP indicates the media used for the channel. In this example, there are two 'm' lines for the two channels described. The a ttribute defined in the line a=source-filter: incl IN IP6 * 2001:210:1:2:240:96FF:FE25:8EC9 describes a source filter. In this example the sender indicates that the receivers should include the given IP address (2001:210:1:2:240:96FF:FE25:8EC9) into the session. This pair of the (source IP address, TSI) together uniquely identifies a session. It should be noted that although other possibilities may be used, in this case only the incl and * attributes may be used in the above descriptor. The line m=data 12345 FLUTE/UDP indicates the media used for the channel. In this example, there are two 'm' lines for the two channels described. Mehta, et al. Expires January 10, 2005 [Page 10] Internet-Draft SDP Descriptors for FLUTE July 2004 5. Security Considerations FLUTE implementations are subject to security considerations mentioned in [1]. There are no additional security considerations resulting from the testing guidelines mentioned in this draft. Mehta, et al. Expires January 10, 2005 [Page 11] Internet-Draft SDP Descriptors for FLUTE July 2004 6. Acknowledgements The authors would like to thank Juha-Pekka Luoma for his contributions and feedback on this document. Mehta, et al. Expires January 10, 2005 [Page 12] Internet-Draft SDP Descriptors for FLUTE July 2004 References [1] Paila, T., Luby, M., Lehtonen, R. and V. Roca, "FLUTE - File Delivery over Unidirectional Transport", draft-ietf-rmt-flute-08 (work in progress), June 2004. [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, BCD 14, March 1997. [3] Luby, M., Gemmell, J., Vicisano, L., Rizzo, L., Handley, M. and J. Crowcroft, "Layered Coding Transport (LCT) Building Block", RFC 3451, December 2002. [4] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [5] Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998. [6] Olson, S., Camarillo, G. and A. Roach, "Support for IPv6 in Session Description Protocol (SDP)", RFC 3266, June 2002. [7] Quinn, B. and R. Finlayson, "Session Description Protocol (SDP) Source Filters", draft-ietf-mmusic-sdp-srcfilter-05 (work in progress), May 2003. [8] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC 3629, November 2003. [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, "Session Initiation Protocol", RFC 3261, June 2002. [11] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., Berners-Lee, T. and E. Schooler, "Hypertext Tansfer Protocol -- HTTP/1.1", RFC 3261, June 2002. [12] Yon, D. and G. Camarillo, "Connection-Oriented Media Transport in the Session Descript Protocol (SDP)", draft-ietf-mmusic-sdp-comedia-07.txt (work in progress), December 2004. Mehta, et al. Expires January 10, 2005 [Page 13] Internet-Draft SDP Descriptors for FLUTE July 2004 Authors' Addresses Harsh Mehta Nokia P.O. Box 100 (Visiokatu 1) Tampere FIN-33721 Finland EMail: harsh.mehta@nokia.com Rod Walsh Nokia P.O. Box 100 (Visiokatu 1) Tampere FIN-33721 Finland EMail: rod.walsh@nokia.com Jani Peltotalo Tampere University of Technology P.O. Box 553 (Korkeakoulunkatu 1) Tampere FIN-33101 Finland EMail: jani.peltotalo@tut.fi Sami Peltotalo Tampere University of Technology P.O. Box 553 (Korkeakoulunkatu 1) Tampere FIN-33101 Finland EMail: sami.peltotalo@tut.fi Mehta, et al. Expires January 10, 2005 [Page 14] Internet-Draft SDP Descriptors for FLUTE July 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. 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