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. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
Full Copyright Statement
Copyright (C) The Internet Society (2004). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assignees.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
Mehta, et al. Expires January 10, 2005 [Page 15]
Internet-Draft SDP Descriptors for FLUTE July 2004
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Mehta, et al. Expires January 10, 2005 [Page 16]
