RMT R. Walsh
Internet-Draft Nokia
Expires: May 12, 2006 J. Peltotalo
S. Peltotalo
Tampere University of Technology
H. Mehta
I. Curcio
Nokia
November 8, 2005
SDP Descriptors for FLUTE
draft-mehta-rmt-flute-sdp-04
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
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 May 12, 2006.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document specifies the use of SDP to describe the parameters
required to begin, join, receive data from, and/or end FLUTE
sessions.
Walsh, et al. Expires May 12, 2006 [Page 1]
Internet-Draft SDP Descriptors for FLUTE November 2005
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
3. FLUTE Descriptors . . . . . . . . . . . . . . . . . . . . . . 5
3.1. FLUTE Protocol Identifier . . . . . . . . . . . . . . . . 5
3.2. Composite Session Semantics . . . . . . . . . . . . . . . 6
3.3. Source IP Address . . . . . . . . . . . . . . . . . . . . 8
3.4. Transport Session Identifier . . . . . . . . . . . . . . . 9
3.5. Session Timing Parameters . . . . . . . . . . . . . . . . 9
3.6. Channelisation Descriptors . . . . . . . . . . . . . . . . 9
3.6.1. Number of Channels . . . . . . . . . . . . . . . . . . 10
3.6.2. Destination IP Address and Port Number for Channels . 11
3.7. FEC Object Transmission Information . . . . . . . . . . . 12
3.8. Content Description Pointer . . . . . . . . . . . . . . . 14
3.9. Bandwidth Specification . . . . . . . . . . . . . . . . . 15
4. SDP Syntax Examples . . . . . . . . . . . . . . . . . . . . . 16
5. Security Considerations . . . . . . . . . . . . . . . . . . . 19
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
6.1. Transport Protocol . . . . . . . . . . . . . . . . . . . . 20
6.1.1. Media formats ("fmt") . . . . . . . . . . . . . . . . 20
6.2. Attribute Names . . . . . . . . . . . . . . . . . . . . . 20
6.3. Composite Session Token to Differentiate FLUTE Sessions . 21
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 23
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 24
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.1. Normative References . . . . . . . . . . . . . . . . . . . 25
9.2. Informative References . . . . . . . . . . . . . . . . . . 26
Appendix A. Use of FEC attributes with RTP sessions
(informative) . . . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28
Intellectual Property and Copyright Statements . . . . . . . . . . 29
Walsh, et al. Expires May 12, 2006 [Page 2]
Internet-Draft SDP Descriptors for FLUTE November 2005
1. Introduction
The Session Description Protocol (SDP) [6] 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 [9]) 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 [14], SIP
[15], RTSP [19], HTTP [16], email etc.).
SDP defines two protocol identifiers that represent unreliable
connectionless protocols. These are RTP/AVP and UDP. These are
appropriate choices for multimedia streams. [17] defines protocol
identifiers for connection-oriented reliable transports: TCP and TCP/
TLS. RFC 3266 [7] describes SDP support for IPv6.
This document defines a new protocol identifier for File Delivery
over Unidirectional Transport (FLUTE) protocol [1] and other required
SDP attributes for initiating a FLUTE session. The formal ABNF
syntax [5] is used for the attributes. This SDP syntax is
independent of Any Source Multicast (ASM) or Source Specific
Multicast (SSM) is used to route the media.
Walsh, et al. Expires May 12, 2006 [Page 3]
Internet-Draft SDP Descriptors for FLUTE November 2005
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].
Walsh, et al. Expires May 12, 2006 [Page 4]
Internet-Draft SDP Descriptors for FLUTE November 2005
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/or service announcement sessions.
The required parameters are:
o The source 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
o The start time and end time of the session
Optionally, the following parameters may be associated with the
session:
o FEC Object Transmission Information
o Some information that tells receiver in the first place, that the
session contains files that are of interest
o Bandwidth specification
The description of these parameters in SDP is presented in the
following sections. Note also that "v=", "o=" and "s=" lines are
mandatory for SDP descriptions [6].
The semantics of a FLUTE session within an SDP description differ
slightly from that of the well-establish RTP session descriptions. A
FLUTE session includes one or more FLUTE channels which are each a
distinct media flow. Generally, each RTP media is recognised as a
distinct RTP session. Hence, to preserve harmony with the de facto
understanding of RTP sessions within SDP descriptions, the optional
Composite Session mechanism is specified, using a the grouping
framework [13].
3.1. FLUTE Protocol Identifier
The following is the ABNF syntax for an "m=" line, as specified by
RFC 2327 [6]:
Walsh, et al. Expires May 12, 2006 [Page 5]
Internet-Draft SDP Descriptors for FLUTE November 2005
media-field = "m=" media SP port ["/" integer] SP
proto 1*(SP fmt) CRLF
We define a new value for the "proto" sub-field: FLUTE/UDP. The
FLUTE/UDP protocol identifier specifies that the session being
described will use the FLUTE [1] protocol on top of a UDP connection.
Without additional grouping of media lines, the default behaviour of
a host is to group all media of a single SDP with the FLUTE/UDP
protocol identifier as belonging to the same single FLUTE session.
As described below, more than one FLUTE session may be described by a
single SDP using the Composite Session mechanism.
The fmt (format) list may be ignored for FLUTE. The fmt list of
FLUTE "m=" lines MAY contain a single "*" character to indicate that
miscellaneous and unspecified MIME types (file formats) are contained
in the FLUTE session. Use of any other values (MIME types) in a
FLUTE fmt list is out of scope of this specification. "0" is known to
be used in the fmt list to represent the same as "*", in a non
standard way, and so implementers may take this into account. An
example of FLUTE/UDP protocol identifier is shown in section 4.
FLUTE is a general file delivery protocol and so it is not considered
necessary to identify a list of media types per FLUTE session or
channel in the session description.
3.2. Composite Session Semantics
The Composite Session mechanism enables the grouping of FLUTE/UDP
media lines in to distinct FLUTE sessions. This provides an
unambiguous way to define multiple FLUTE sessions as distinct from
multiple the media-sessions semantics of RTP. It is only useful for
describing more than one FLUTE session in an SDP instance and so its
use and support are OPTIONAL.
To support simple applications, as well as ensure harmony with FLUTE
SDP standards outside of the IETF [20], when the Composite Session
mechanism is not used for media of the UDP/FLUTE protocol, exactly
one FLUTE session is specified within the SDP description and all
UDP/FLUTE media that SDP description belong to the same FLUTE session
(this is known as the Default Behaviour).
The Composite Session mechanism SHOULD NOT be used where the target
clients are expected to include simpler FLUTE SDP parsers, such as in
3GPP MBMS [20].
The Composite Session mechanism inherits the "group" and "mid"
attributes from the SDP grouping framework [13] and introduces the
Walsh, et al. Expires May 12, 2006 [Page 6]
Internet-Draft SDP Descriptors for FLUTE November 2005
"CS" (Composite Session) token. When a complete SDP description
specifies only one FLUTE session, using the Composite Session
mechanism is OPTIONAL. When a complete SDP description specifies
more than one FLUTE session, using the Composite Session mechanism is
REQUIRED.
When the Composite Session mechanism is used: the SDP grouping
framework [13] MUST be used (and requirements from that are
inherited); and the "CS" token MUST be used with the "group"
attribute to indicate a Composite Session grouping. The SDP grouping
framework declares groups at session-level and labels media (with the
"mid" attribute) at media-level. Hence, all media identified by
their "mid" values by a group:CS line belong to the same Composite
Session group and inherit the grouping specified for that value at
session-level.
A partial example of using the Composite Session mechanism is shown
below.
<other session-level attributes>
a=group:CS 1 2
a=group:CS 3
m=application 12345 FLUTE/UDP *
a=mid:1
<other media-level attributes>
m=application 12346 FLUTE/UDP *
a=mid:2
<other media-level attributes>
m=application 56789 FLUTE/UDP *
a=mid:3
<other media-level attributes>
The first media line declared for a Composite Session group is the
Primary Media (mid values 1 and 3 for the two groups in the example).
Just as session-level attributes are inherited to media-level
declarations (unless specifically overwritten by an additional media-
level attribute), Primary Media attributes SHALL be inherited to all
media of a particular Composite Session group and these MAY be
overwritten these where an attribute syntax allows. (As in the
example, the media with mid value "2" inherits attributes of the
media with mid value "1".) Several of the attributes subsequently
specified in this document use this feature of Primary Media
inheritance to all media of a Composite Session.
The Composite Session mechanism is specified to solve the problem of
describing multiple FLUTE sessions in a single SDP instance.
However, this does not place any restrictions on the use of the
Composite Session mechanism with transport protocols other than
Walsh, et al. Expires May 12, 2006 [Page 7]
Internet-Draft SDP Descriptors for FLUTE November 2005
FLUTE/UDP, nor on whether a complete SDP would include media of other
transport protocols too. Specification of semantics beyond the use
of FLUTE sessions is outside the scope of this document.
3.3. Source IP Address
The Asynchronous Layered Coding (ALC) [3] and the Layered Coding
Transport (LCT) [4] specifications require that all the channels of a
single ALC/LCT session are from the same source IP address. Hence,
there MUST be exactly one source IP address per FLUTE session, and
therefore one source IP address per each description of a FLUTE
session description. Default behaviour is one source IP address per
each complete SDP. Where multiple FLUTE sessions are described
within one SDP instance this means one source IP address per each
Composite Session.
The source IP address MUST be defined according to the source-filter
attribute ("a=source-filter") [8], with the following exceptions:
o The source-filter attribute MUST be included in any SDP describing
FLUTE per FLUTE session described.
o The number of source-filter attributes in any SDP describing FLUTE
must be exactly equal to the number of FLUTE sessions described in
that SDP.
o In the default behaviour of only one FLUTE session description in
an SDP and no use of the Composite Session mechanism: The source-
filter attribute MUST be in the session part of the session
description and MUST NOT be given per media. Note, the
requirement that there must not be more than a single source-
filter attribute in the session part is inherited from [8].
o Where the Composite Session mechanism is used: The source-filter
attribute MUST be in the media part of Primary Media of each
distinct FLUTE session, and MUST NOT be given in other media
declarations but these, nor in the session-level part of the SDP.
o Exactly one source address is specified by any instance of this
attribute. Exactly one source address MUST be given in an
inclusive-mode "src-list". Exclusive-mode MUST NOT be used.
o The "*" value MUST be used for the "dest-address" sub-field, even
when the FLUTE session employs only a single channel (e.g. a
multicast group).
An example of the use of this attribute is:
Walsh, et al. Expires May 12, 2006 [Page 8]
Internet-Draft SDP Descriptors for FLUTE November 2005
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.
3.4. Transport Session Identifier
The combination of the TSI and the source IP address identifies a
FLUTE session. Each TSI MUST uniquely identify a FLUTE session for a
given source IP 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 [4]. The TSI MUST be described
by the "flute-tsi" attribute.
There MUST be exactly one occurrence of the "flute-tsi" attribute per
FLUTE session description of a SDP description.
o The number of flute-tsi attributes in any SDP describing FLUTE
must be exactly equal to the number of FLUTE sessions described in
that SDP.
o In the default behaviour of only one FLUTE session description in
an SDP and no use of the Composite Session mechanism: The flute-
tsi attribute MUST be in the session part of the session
description and MUST NOT be given per media.
o Where the Composite Session mechanism is used: The flute-tsi
attribute MUST be in the media part of Primary Media of each
distinct FLUTE session, and MUST NOT be given in other media
declarations but these, nor in the session-level part of the SDP.
The syntax for the attribute in ABNF is given below:
flute-tsi-line = "a=flute-tsi:" tsi CRLF
tsi = 1*DIGIT
3.5. Session Timing Parameters
The SDP timing field "t=" [6] MUST be used to indicate the FLUTE
session start and end times. This value applies to all FLUTE and
transport sessions defined in a single SDP instance and, thus, FLUTE
sessions of different timing values need to be declared in different
SDP instances.
3.6. Channelisation Descriptors
This section specifies the description of the channel(s) used within
a FLUTE session. The required parameters for channelisation
Walsh, et al. Expires May 12, 2006 [Page 9]
Internet-Draft SDP Descriptors for FLUTE November 2005
description are:
o Number of channels
o Destination IP address and port number for channels
3.6.1. Number of Channels
The FLUTE specification allows the use of multiple channels (e.g.
multicast groups) to transport the files of a single FLUTE session.
This is referred to as FLUTE session channelisation in this document.
A FLUTE channel is equivalent to an ALC/LCT channel. An ALC/LCT
channel is defined by the combination of a sender and an address
associated with the channel by the sender. Details of each channel
are defined by SDP media-level information also described in this
document. The number of channels is calculated by summing the number
of unique destination IP address and port number pairs for a certain
FLUTE session (assignment of media to FLUTE sessions is done with
presence of absence of the Composite Session grouping).
The OPTIONAL "flute-ch" attribute describes the number of channels
used by the source to transmit the FLUTE session. When present, it
is used to validate the channel number calculation based on the
number of destination address/port pairs, and it is expected to be
used where SDP proxies and other automatic and manual editing that
introduces errors would cause bad failure conditions at the client.
When the "flute-ch" attribute is used:
o The number of flute-ch attributes in any SDP describing FLUTE MUST
be exactly equal to the number of FLUTE sessions described in that
SDP. A client SHOULD discard all of an SDP instance if this
condition is not met. Alternative behaviour, such as retries at
delivery, error reporting and partial use of SDP instances known
to include errors, are allowed but beyond the scope of this
document.
o In the default behaviour of only one FLUTE session description in
an SDP and no use of the Composite Session mechanism: The flute-ch
attribute MUST be in the session part of the session description
and MUST NOT be given per media.
o Where the Composite Session mechanism is used: The flute-ch
attribute MUST be in the media part of Primary Media of each
distinct FLUTE session, and MUST NOT be given in other media
declarations but these, nor in the session-level part of the SDP.
The syntax for the attribute in ABNF is given below:
Walsh, et al. Expires May 12, 2006 [Page 10]
Internet-Draft SDP Descriptors for FLUTE November 2005
flute-channel-line = "a=flute-ch:" ch CRLF
ch = integer
;integer is as defined in [6].
value is the number of channels used by the source to transmit data
in a FLUTE session.
3.6.2. Destination IP Address and Port Number for Channels
SDP media-level information describes one or more channels. The
channel parameters MUST be given per channel and are:
o Destination IP address
o Destination port number
The destination IP address MUST be defined according to the
connection data field ("c=") of SDP [6]. The destination port number
MUST be defined according to the "port" sub-field of the media
description field ("m=") of SDP [6].
A "c=" line can describe multiple addresses by using "number of
addresses" sub-field, and also an "m=" line can describe multiple
ports by using "number of ports" sub-field. So multiple channels can
be described by using one "c=" line and one "m=" line (slash
notation).
When more than one channel is used in a multicast FLUTE session, it
is RECOMMENDED that the channels are differentiated based on
destination IP address, and channels are not differentiated based on
destination port (although those ports could be same or different for
each channels). When more than one channel is used in a unicast
FLUTE session, the channels have to be differentiated based on
destination ports, as only one destination IP address could be used.
Whenever channels are differentiated based on destination port number
they must use the same IP destination address for that FLUTE session.
In the case (always with a unicast session) where the same
destination IP address is used for all the channels of the session
and only the destination port number differentiates channels, the
destination IP address MAY be given by the connection data field at
session-level for all channels (if so, the connection data field MUST
NOT be used at media-level).
In the case where each channel has a different destination IP
address, the destination IP addresses MUST be given at media-level,
i.e. following an "m=" line.
Walsh, et al. Expires May 12, 2006 [Page 11]
Internet-Draft SDP Descriptors for FLUTE November 2005
The sequence of multiple channels MUST 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). This applies individually to each FLUTE session of an SDP
whether one or more FLUTE sessions are described. In the case of the
slash notation usage for specifying multiple destination addresses or
ports, the order of the channel sequence MUST be lowest value first
and highest last. (Note, slash notation for both IP destination
address and port would be incompatible with requirement to not use
both IP destination address and port to differentiate channels in a
FLUTE session and thus slash notation for both IP destination address
and port is not allowed for a single media.)
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 *
c=IN IP6 FF1E:03AD::7F2E:172A:1E24
In the above SDP attributes, the "m=" line indicates the media used
and the "c=" line together with "m=" line's "port" sub-field
indicates the corresponding channel's address and port respectively.
Thus, in the above example, the media is transported on a channel
that uses FLUTE over UDP. Further, the "c=" line indicates the
channel's address, which, in this case, is an IPv6 address, and "m="
line indicates the channel's port (12345).
Note, the value of the IP destination address implicitly indicated
whether a multicast media belongs to an ASM or a SSM group as
described by [18].
3.7. FEC Object Transmission Information
An SDP description for a FLUTE session MAY include FEC Object
Transmission Information (FEC-OTI) [12]. FEC parameters can be
placed either at session-level or at media-level, although it is
RECOMMENDED to place them at session-level. Furthermore, if FEC
parameters are placed at media level (contrary to the recommendation)
and the Composite Session mechanism is used, they should only be
placed in the Primary Media for any FLUTE session description. If
FEC declarations on both session and media level use the same
reference number (fec-ref) then the media level declaration takes
precedence for that media component. FEC parameters include:
o FEC Encoding ID
Walsh, et al. Expires May 12, 2006 [Page 12]
Internet-Draft SDP Descriptors for FLUTE November 2005
o FEC Instance ID (for FEC Encoding IDs 128-255)
Where FEC-OTI is given, FEC parameters MUST be described in a "FEC-
declaration" attribute. Multiple instances of this attribute MAY
exist both at session-level and media-level. If an instance exists
at session-level (or in a Primary Media), a reference to it MAY be
used at media-level, and an attribute "FEC" MUST be defined for this
purpose. The absence of a both a "FEC-declaration" and a "FEC"
attribute at media-level MUST be interpreted as the default FEC
(Compact No-Code FEC [11] for FLUTE).
The syntax for the attributes in ABNF is given below:
fec-declaration-line = "a=FEC-declaration:" fec-ref SP
fec-enc-id [";" SP fec-inst-id] CRLF
fec-ref = 1*3DIGIT
;value is the SDP-internal identifier for FEC-declaration
fec-enc-id = "encoding-id=" enc-id
enc-id = 1*DIGIT
;value is the FEC Encoding ID used
fec-inst-id = "instance-id=" inst-id
inst-id = 1*DIGIT
;value is the FEC Instance ID used
fec-line = "a=FEC:" fec-ref CRLF
Examples of FEC-OTI are shown in section 4.
The FEC parameters are for capabilities description for the session.
(Note, any "FDT-like" fuller description of files in the session
could give the FEC parameters per file). FLUTE's FDT syntax (and
codepoint header field usage) allows complete specification of these
FEC parameters in-band with FLUTE (per file). Thus machine
configuration can be performed using FLUTE alone.
There are five main reasons that the FEC Encoding and Instance IDs
are optional capabilities descriptions:
1. It is not always necessary to explicitly describe the FEC
capabilities in advance of the session - e.g. for simple (and
short) sessions it can be more elegant to discover this from the
session (FDT) itself (even when some mechanism for machine-
readable session parameters, such as IP addresses and ports, is
wanted in advance).
Walsh, et al. Expires May 12, 2006 [Page 13]
Internet-Draft SDP Descriptors for FLUTE November 2005
2. There may be some other out-of-band discovery of FEC capability
requirements (e.g. well known-FEC/standardised capabilities for a
certain application, verbal agreement between a group, etc.) that
provides the FEC capability information. This document does not
want to prevent this, and in this case repeating the information
in SDP would be unnecessary and wasteful (and probably result in
implementations not following the flute-sdp specification).
3. FLUTE defaults to Compact No-Code FEC [11] and support for this
is mandatory for FLUTE anyway so it is a given (capability
requirement) which does not need to be described by the SDP. In
cases where only Compact No-Code FEC is required, there is no use
in specifying any FEC Encoding (and Instance) IDs in the SDP
(though it is allowed).
4. In cases where a FLUTE session description (SDP file) is not
defined once for all time, it is possible that the FEC usage is
not known in advance and the FEC capabilities would only be added
to the SDP in a later version of that SDP file when the FEC codes
have been selected (e.g. a larger audience may suggest stronger
FEC to make FLUTE delivery more reliable, whereas additional bi-
directional messages may be scalable for smaller groups).
5. Also, in cases where a FLUTE session description (SDP file) is
very static (e.g. once for all time for that session), it is
possible that the FEC usage is not known in advance and it needs
to be left to some other mechanism (e.g. FDT) to discover any
FEC capability requirements set closer to the session
transmission - with the same examples as in (4).
Also, in a complex case of very many FEC codes being used in the
session giving a full list in SDP is not seen as being reasonable
(but this is likely to be a rare case anyway).
The identification and description of any congestion control (CC)
instance related to layered media (multiple FLUTE channels) is
orthogonal to the FEC declarations and other aspects of this
document. Hence, CC descriptions are not in scope of this document.
3.8. 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 at the session-level and/or media-level
(including Primary Media of composite Sessions) to enable efficient
linkage to such information.
Walsh, et al. Expires May 12, 2006 [Page 14]
Internet-Draft SDP Descriptors for FLUTE November 2005
The content description pointer attribute describes to the
receiver(s) the URI where the content description is stored. The
content description pointer MUST be defined according to the
"content-desc" attribute.
The syntax for the attribute in ABNF is given below:
content-desc-line = "a=content-desc:" URI-reference CRLF
;URI-reference is as defined in [10].
An example of content description pointer is shown in section 4.
3.9. Bandwidth Specification
The specification of bandwidth (data rate) is optional and where
included in the SDP it shall adhere to the following rules. The
maximum bit-rate required by this FLUTE session shall be specified
using the "AS" bandwidth modifier [6] on session level. The maximum
bit-rate required by a particular FLUTE media-line (one or more FLUTE
channels, depending on the usage or IP address and port ranges) shall
be specified using the "AS" bandwidth modifier [1] on media level.
The Application Specific (AS) bandwidth shall be the largest sum of
the sizes of all packets transmitted during any one second long
period of the session or media-line, depending on which level it is
being used, expressed as kilobits. The size of the packet shall be
the complete packet, i.e. IP, UDP and FLUTE headers, and the data
payload.
Walsh, et al. Expires May 12, 2006 [Page 15]
Internet-Draft SDP Descriptors for FLUTE November 2005
4. SDP Syntax Examples
This section gives examples 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:1
a=flute-ch:2
a=FEC-declaration:0 encoding-id=0
a=FEC-declaration:1 encoding-id=128; instance-id=0
a=content-desc:http://www.example.com/flute-sessions/session001
m=application 12345 FLUTE/UDP *
c=IN IP6 FF1E:03AD::7F2E:172A:1E24
a=FEC:0
m=application 12346 FLUTE/UDP *
c=IN IP6 FF1E:03AD::7F2E:172A:1E25
a=FEC:1
Figure 1: An SDP for FLUTE Session with Two Channels
Figure 1 shows an example SDP description for FLUTE session with two
channels.
The attribute 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 source indicates that the receiver(s) should include the
given IP address (2001:210:1:2:240:96FF:FE25:8EC9) into the 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
attribute.
The attribute defined in the line "a=flute-tsi:3" describes the
Transport Session Identifier for the session. The pair made of the
source IP address and the TSI together uniquely identifies a FLUTE
session.
The source indicates in the above example that it will transmit data
in the FLUTE session on two channels (a=flute-ch:2). The source then
specifies the channels.
The "a=FEC-declaration" lines describes two different FEC schemes
used in the FLUTE session.
Walsh, et al. Expires May 12, 2006 [Page 16]
Internet-Draft SDP Descriptors for FLUTE November 2005
The "a=content-desc" line describes the URI where the content
description is stored.
The line "m=application 12345 FLUTE/UDP *" indicates the media used
for the channel. In this example, there are two "m=" lines for the
two channels described.
The destination addresses for the channels are given in the "c="
lines. These also show to the receiver(s) that the channels are two
(maybe more in other cases) consecutive channels.
The "a=FEC" lines at media-level reference FEC declarations at
session-level ("a=FEC-declaration").
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:2
a=flute-ch:1
m=application 12345 FLUTE/UDP *
c=IN IP6 FF1E:03AD::7F2E:172A:1E24
a=FEC-declaration:0 encoding-id=128; instance-id=0
Figure 2: An SDP for FLUTE Session with One Channel
Figure 2 shows an example SDP description for FLUTE session with one
channel.
Walsh, et al. Expires May 12, 2006 [Page 17]
Internet-Draft SDP Descriptors for FLUTE November 2005
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=FEC-declaration:0 encoding-id=0
a=FEC-declaration:1 encoding-id=128; instance-id=0'
a=group:CS 1 2
a=group:CS 3 4
m=application 12345 FLUTE/UDP *
c=IN IP6 FF1E:03AD::7F2E:172A:1E24
a=flute-tsi:1
a=FEC:0
a=mid:1
m=application 12346 FLUTE/UDP *
c=IN IP6 FF1E:03AD::7F2E:172A:1E25
a=mid:2
m=application 12347 FLUTE/UDP *
c=IN IP6 FF1E:03AD::7F2E:172A:1E26
a=flute-tsi:2
a=FEC:1
a=mid:3
m=application 12348 FLUTE/UDP *
c=IN IP6 FF1E:03AD::7F2E:172A:1E27
a=mid:4
Figure 3: An SDP for composite FLUTE session
Figure 3 shows an example SDP description for composite FLUTE
session.
Walsh, et al. Expires May 12, 2006 [Page 18]
Internet-Draft SDP Descriptors for FLUTE November 2005
5. Security Considerations
See [6] for security considerations specific to the Session
Description Protocol in general. See also [8] for security
consideration related to source address filters.
Walsh, et al. Expires May 12, 2006 [Page 19]
Internet-Draft SDP Descriptors for FLUTE November 2005
6. IANA Considerations
6.1. Transport Protocol
The "proto" sub-field of the media description field ("m=") describes
the transport protocol used. This document registers one value:
"FLUTE/UDP" is a reference to FLUTE [1] running over UDP/IP.
6.1.1. Media formats ("fmt")
FLUTE media using the "FLUTE/UDP" proto value may use the character
"*" as their "fmt" value. The "*" character represents a wild card
which indicates that miscellaneous and unspecified MIME types are
contained in the FLUTE session. Alternatively a list of MIME types
(file formats) may be given in the "fmt" list. These formats SHOULD
be registered. Use of an existing MIME subtype for the format is
encouraged. If no MIME subtype exists, it is RECOMMENDED that a
suitable one is registered through the IETF process (RFC 2048).
6.2. Attribute Names
As recommended by [6], the new attribute names "flute-tsi",
"flute-ch", "FEC-declaration", "FEC", "FEC-OTI-extension" and
"content-desc" should be registered with IANA, as follows:
The following contact information shall be used for all registrations
included here:
Contact: Rod Walsh
EMail: rod.walsh (at) nokia.com
SDP Attribute ("att-field"):
Attribute name: flute-tsi
Long form: FLUTE Transport Session Identifier
Type of name: att-field
Type of attribute: Session level or media level
Subject to charset: No
Purpose: See this document
Reference: This document
Values: See this document
SDP Attribute ("att-field"):
Attribute name: flute-ch
Long form: Number of Channels in a FLUTE Session
Type of name: att-field
Type of attribute: Session level or media level
Subject to charset: No
Purpose: See this document
Walsh, et al. Expires May 12, 2006 [Page 20]
Internet-Draft SDP Descriptors for FLUTE November 2005
Reference: This document
Values: See this document
SDP Attribute ("att-field"):
Attribute name: FEC-declaration
Long form: Forward Error Correction Declaration
Type of name: att-field
Type of attribute: Session level or media level
Subject to charset: No
Purpose: See this document
Reference: This document
Values: See this document
SDP Attribute ("att-field"):
Attribute name: FEC
Long form: A Reference to FEC Declaration
Type of name: att-field
Type of attribute: Media level
Subject to charset: No
Purpose: See this document
Reference: This document
Values: See this document
SDP Attribute ("att-field"):
Attribute name: FEC-OTI-extension
Long form: FEC Object Transmission Information extension
Type of name: att-field
Type of attribute: Session level or media level
Subject to charset: No
Purpose: See this document
Reference: This document
Values: See this document
SDP Attribute ("att-field"):
Attribute name: content-desc
Long form: Content Description Pointer
Type of name: att-field
Type of attribute: Session level or media level
Subject to charset: No
Purpose: See this document
Reference: This document
Values: See this document
6.3. Composite Session Token to Differentiate FLUTE Sessions
IANA needs to register the following new 'semantics' attribute for
the SDP grouping framework [13]:
Walsh, et al. Expires May 12, 2006 [Page 21]
Internet-Draft SDP Descriptors for FLUTE November 2005
Semantics Token Reference
--------------------------------- ----- ---------
Composite Session CS [RFCxxxx]
It should be registered in the SDP parameters registry
(http://www.iana.org/assignments/sdp-parameters) under Semantics for
the "group" SDP Attribute.
Walsh, et al. Expires May 12, 2006 [Page 22]
Internet-Draft SDP Descriptors for FLUTE November 2005
7. Acknowledgements
The authors would like to thank all the people who gave feedback on
this document.
Walsh, et al. Expires May 12, 2006 [Page 23]
Internet-Draft SDP Descriptors for FLUTE November 2005
8. Contributors
Magnus Westerlund
Ericsson Research
Ericsson AB
SE-164 80 Stockholm
Sweden
EMail: Magnus.Westerlund (at) ericsson.com
Joerg Ott
Helsinki University of Technology
Otakaari 5A
FIN-02150 Espoo
Finland
EMail: jo (at) netlab.hut.fi
Walsh, et al. Expires May 12, 2006 [Page 24]
Internet-Draft SDP Descriptors for FLUTE November 2005
9. References
9.1. Normative References
[1] Paila, T., Luby, M., Lehtonen, R., Roca, V., and R. Walsh,
"FLUTE - File Delivery over Unidirectional Transport",
draft-ietf-rmt-flute-revised-00 (work in progress),
October 2004.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, BCP 14, March 1997.
[3] Luby, M., Gemmell, J., Vicisano, L., Rizzo, L., and J.
Crowcroft, "Asynchronous Layered Coding (ALC) Protocol
Instantiation", draft-ietf-rmt-pi-alc-revised-00 (work in
progress), July 2005.
[4] Luby, M., Gemmell, J., Vicisano, L., Rizzo, L., Handley, M.,
and J. Crowcroft, "Layered Coding Transport (LCT) Building
Block", draft-ietf-rmt-bb-lct-revised-00 (work in progress),
July 2005.
[5] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[6] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998.
[7] Olson, S., Camarillo, G., and A. Roach, "Support for IPv6 in
Session Description Protocol (SDP)", RFC 3266, June 2002.
[8] Quinn, B. and R. Finlayson, "Session Description Protocol (SDP)
Source Filters", draft-ietf-mmusic-sdp-srcfilter-10 (work in
progress), September 2005.
[9] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
RFC 3629, November 2003.
[10] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[11] Watson, M., "Basic Forward Error Correction (FEC) Schemes",
draft-ietf-rmt-bb-fec-basic-schemes-revised-01 (work in
progress), October 2005.
[12] Watson, M., Luby, M., and L. Vicisano, "Forward Error
Correction (FEC) Building Block",
Walsh, et al. Expires May 12, 2006 [Page 25]
Internet-Draft SDP Descriptors for FLUTE November 2005
draft-ietf-rmt-fec-bb-revised-01 (work in progress),
September 2005.
[13] Camarillo, G., Holler, J., Eriksson, G., and H. Schulzrinne,
"Grouping of Media Lines in the Session Description Protocol
(SDP)", RFC 3388, December 2002.
9.2. Informative References
[14] Handley, M., Perkins, C., and E. Whelan, "Session Announcement
Protocol", RFC 2974, October 2000.
[15] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler,
"Session Initiation Protocol", RFC 3261, June 2002.
[16] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
Leach, P., Berners-Lee, T., and E. Schooler, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 3261, June 2002.
[17] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the
Session Description Protocol (SDP)", RFC 4145, September 1998.
[18] Holbrook, H. and B. Cain, "Source-Specific Multicast for IP",
draft-ietf-ssm-arch-07 (work in progress), October 2005.
[19] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming
Protocol (RTSP)", RFC 2326, April 1998.
[20] "3GPP TS 26.346 V6.2.0 (2005-09), 3rd Generation Partnership
Project; Technical Specification Group Services and System
Aspects; Multimedia Broadcast/Multicast Service (MBMS);
Protocols and codecs(Release 6)", September 2005.
<Note to RFC Editor: if sdp-new goes to RFC it supersedes references
6 and 7>
<Note to RFC Editor: reference 8 needs correct RFC number when known>
Walsh, et al. Expires May 12, 2006 [Page 26]
Internet-Draft SDP Descriptors for FLUTE November 2005
Appendix A. Use of FEC attributes with RTP sessions (informative)
The "FEC-declaration" and "FEC" attributes provide general FEC-OTI
information in FEC Encoding ID and FEC Instance ID values. These may
also be used for RTP sessions employing same FEC Building Block (as
is done for 3GPP MBMS [20]). However semantics of RTP are different
from FLUTE (FEC is per session not per object) and RTP does not have
in-band mechanism to signal FEC OTI extensions. Thus, RTP FEC
declarations are expected to be used for machine configuration as
well as capability requirements specification (for FLUTE it is
generally only the latter).
Hence the FLUTE SDP, defined in this document, may be extended using
a "FEC-OTI-extension" attribute, depending on the configuration needs
of the FEC decoder used and the lack of an alternative means to
signal the extended OTI information. The purpose of extended FEC-OTI
information define FEC code/instance-specific OTI required for
receiver FEC payload configuration. The contents of such an
extension would be FEC code- specific and exact specification, beyond
adherence to the ABNF below, needs to be specified by any FEC code
using this attribute, and hence is outside the scope of this
Appendix.
A "FEC-OTI-extension" attribute must be immediately preceded by its
associated "FEC-declaration" attribute and so the full FEC-OTI,
including extension, will be found in two neighbouring attribute
lines. The fec-ref value binds a "FEC-OTI-extension" and "FEC-
declaration attribute" pair.
The syntax for the attribute in ABNF is given below:
fec-oti-extension-line = "a=FEC-OTI-extension:" fec-ref SP
oti-extension CRLF
oti-extension = base64
base64 = *base64-unit [base64-pad]
base64-unit = 4base64-char
base64-pad = 2base64-char "==" / 3base64-char "="
base64-char = ALPHA / DIGIT / "+" / "/"
Walsh, et al. Expires May 12, 2006 [Page 27]
Internet-Draft SDP Descriptors for FLUTE November 2005
Authors' Addresses
Rod Walsh
Nokia
P.O. Box 100 (Visiokatu 1)
Tampere FIN-33721
Finland
Email: rod.walsh (at) nokia.com
Jani Peltotalo
Tampere University of Technology
P.O. Box 553 (Korkeakoulunkatu 1)
Tampere FIN-33101
Finland
Email: jani.peltotalo (at) tut.fi
Sami Peltotalo
Tampere University of Technology
P.O. Box 553 (Korkeakoulunkatu 1)
Tampere FIN-33101
Finland
Email: sami.peltotalo (at) tut.fi
Harsh Mehta
Nokia
P.O. Box 100 (Visiokatu 1)
Tampere FIN-33721
Finland
Email: harsh.mehta (at) nokia.com
Igor D.D. Curcio
Nokia
P.O. Box 88 (Tieteenkatu 1)
Tampere FIN-33721
Finland
Email: igor.curcio (at) nokia.com
Walsh, et al. Expires May 12, 2006 [Page 28]
Internet-Draft SDP Descriptors for FLUTE November 2005
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights 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; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat 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 implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
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 (2005). 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
Funding for the RFC Editor function is currently provided by the
Internet Society.
Walsh, et al. Expires May 12, 2006 [Page 29]
