Hi,
Just to emphasis Colin email.
If raptorfec
is a the payload format you want to standardize than it can have parameters
specified for this payload type and conveyed in fmtp line.
The first example is using the generic SDP parameters approach and you will need to specify the semantics for session and media level usage of the parameters. I noticed that it is different from draft-begen-fecframe-sdp-elements-00. This solution will need to register the parameter and I assume they will relate to a registered scheme id as specified in the begen draft.
Both will work and it depends what approach you are using.
Roni Even
From:
avt-bounces at ietf.org [mailto:avt-bounces at ietf.org] On Behalf Of Colin
Perkins
Sent: Tuesday, December 09, 2008 8:18 PM
To: Mark Watson
Cc: avt at ietf.org; fecframe at ietf.org
Subject: Re: [AVT] [Fecframe] Question from FECFRAME about RTP Payload
Format Parameters
Mark,
RTP payload formats are named using media subtypes, which
have associated media subtype parameters. Those parameters are conveyed
in SDP using the "a=fmtp:" line. If you're designing an RTP
payload format, it should use that standard mechanism for naming the format and
conveying its parameters. The FEC-scheme-specific information would be one of
those parameters, I assume, carried in the "a=fmtp:" line.
On 17 Nov 2008, at 18:21, Mark Watson wrote:
All,
The following question was discussed at FECFRAME and it was suggested to take
this to AVT as well.
FECFRAME has defined an SDP attribute to carry information about FEC repair
flows which is specific to the particular FEC Scheme being used. This attribute
contains an ‘opaque’ container which contains FEC-Scheme-specific
information that is supposed to be handled by the FEC scheme. This is a generic
mechanism which could be applied whether the FEC repair data is carried over
RTP or directly over UDP.
In the case that RTP is used for repair data, then RTP Payload Format must be
defined for the FEC Scheme in the usual way. In this context we have the
possibility to define RTP Payload Format parameters which would then be carried
in the a=fmtp SDP parameter.
The question under discussion is whether we should define RTP Payload Format
parameters at all, or whether we can use the FEC Framework SDP attribute in the
RTP context just as it is used for repair data carried over UDP.
The advantage of defining RTP Payload Format Parameters is that this is the
standard and recognised way of communicating parameters which are needed to
process data carried in an RTP Payload.
The disadvantage of defining RTP Payload Format Parameters is that we
essentially end up with two mechanisms for carrying the same information and
this causes additional implementation work and potential for confusion about
which mechanism should be used when.
An example of SDP using the FECFRAME attribute would be:
v=0
o=ali 1122334455 1122334466 IN
IP4 fec.example.com
t=0 0
a=group:FEC S1 R1
m=video 30000 RTP/AVP 100
c=IN IP4 224.1.1.1/127
a=rtpmap:100 MP2T/90000
a=mid:S1
m=application 30000 RTP/AVP 110
c=IN IP4 224.1.2.1/127
a=rtpmap:110 raptorfec/90000
a=fec-repair-flow:
encoding-id=0; fssi=4W5S6X
a=repair-window: 200 ms
a=mid:R1
And an example using RTP Payload Format Parameters would be:
v=0
o=ali 1122334455 1122334466 IN
IP4 fec.example.com
t=0 0
a=group:FEC S1 R1
m=video 30000 RTP/AVP 100
c=IN IP4 224.1.1.1/127
a=rtpmap:100 MP2T/90000
a=mid:S1
m=application 30000 RTP/AVP 110
c=IN IP4 224.1.2.1/127
a=rtpmap:110 raptorfec/90000
a=fmtp:110 sbl=1231;
symbol-size=96; repair-window=200ms
a=mid:R1
FECFRAME would like to hear opinions from AVT on this question.
Regards,
Mark Watson
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