Subject: [MMUSIC] draft-garcia-mmusic-sdp-misc-cap-00. About "icap"

From: "Miguel A. Garcia" <[email-masked]>
Date: Tue, 18 Nov 2008 10:06:11 +0100

Yesterday we had a discussion about the Miscellaneous Capabilities draft, 
and there was a question about the "icap" capability. I was listening to 
the audio stream and posted some comments on the chat room, but let me 
try to clarify the issue.

The "icap" capability allows to express media "i" lines as capabilities. 
Bear in mind that the "i" line is intended for human consumption, so, 
there are no semantics added to it, other than provide a human readable 
description of the media stream. If we wanted to get a user agent to 
consume the information, we should be using the "label" attribute 
specified in RFC 4574.

So, considering that the i line is for human consumption, people would 
ask whether there is a need for expressing it as a capability. The 
authors discussed this issue and came up with a use case where a user 
would offer several alternative media streams and could indicate in the 
i/icap line some information about what is in that media stream. For 
example, one could indicate that a video stream contains a close-up of 
the presenter versus a general room, or an audio stream could contain the 
original movie audio track versus the director's commentary. This could 
help the answerer to select the appropriate alternative media stream.

Obviously this require the endpoint to be able to present this 
information to the end user. Honestly, I don't know of any endpoint that 
allows the user to write an i line, or which displays it to the end user. 
  That might be the weakest selling point of this idea. But technically 
it makes sense.

What do people think? What should we do in the next revision of the 
document, should we keep the icap line (and add the use case 
description), or should we remove it?

Thanks,

         Miguel
-- 
Miguel A. Garcia
+34-91-339-3608
Ericsson Spain
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---

From: "Krishna Prasad Kalluri" <[email-masked]>
Date: Tue, 18 Nov 2008 11:06:13 +0100

Hi Miguel,

I have difficulties to understand icap. I just try to illustrate with an
example. You can correct me or provide a better example to understand
this. May be you can give an example to show how it looks with just i=
(media title) and the same example with 'icap'

m=video 52000 RTP/AVP 31
a=rtpmap:31 H261/90000

a=icap:1 video
a=icap:2 video close-up

a=tcap:1 RTP/SAVPF RTP/SAVP RTP/AVPF

a=acap:1 key-mgmt:mikey AQAFgM0XflABAAAAAAAAAAAAAAsAyO...
a=acap:2 crypto:1 AES_CM_128_HMAC_SHA1_32
         inline:NzB4d1BINUAvLEw6UzF3WSJ+PSdFcGdUJShpX1Zj|2^20|1:32
a=acap:3 crypto:1 AES_CM_128_HMAC_SHA1_80
         inline:d0RmdmcmVCspeEc3QGZiNWpVLFJhQX1cfHAwJSoj|2^20|1:32
a=acap:4 rtcp-fb:* nack

a=pcfg:1 t=1 a=1,4|3,4 i=1|2
a=pcfg:2 t=2 a=1|3 i=1
a=pcfg:3 t=3 a=4  i=2

>From sdp-misc-cap-00 section 3.1.3.1, Each potential capability
configuration contains a single information capability attribute number.
So this can as well be expressed with just i= xyz at the media stream
level. If you have multiple m lines you can write an 'i' line for each
'm' line and express multiple labels. May be I miss understood :(

Regards
Krishna

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf
Of Miguel A. Garcia
Sent: den 18 november 2008 10:06
To: mmusic
Cc: Joerg Ott
Subject: [MMUSIC] draft-garcia-mmusic-sdp-misc-cap-00. About "icap"

Yesterday we had a discussion about the Miscellaneous Capabilities
draft, and there was a question about the "icap" capability. I was
listening to the audio stream and posted some comments on the chat room,
but let me try to clarify the issue.

So, considering that the i line is for human consumption, people would
ask whether there is a need for expressing it as a capability. The
authors discussed this issue and came up with a use case where a user
would offer several alternative media streams and could indicate in the
i/icap line some information about what is in that media stream. For
example, one could indicate that a video stream contains a close-up of
the presenter versus a general room, or an audio stream could contain
the original movie audio track versus the director's commentary. This
could help the answerer to select the appropriate alternative media
stream.

Obviously this require the endpoint to be able to present this
information to the end user. Honestly, I don't know of any endpoint that
allows the user to write an i line, or which displays it to the end
user. 
  That might be the weakest selling point of this idea. But technically
it makes sense.

Thanks,

         Miguel

---

From: "Miguel A. Garcia" <[email-masked]>
Date: Tue, 18 Nov 2008 15:34:52 +0100

Hi Krishna:

Your example got lost in the jungle of Audio-Video Profiles. And I didn't 
succeed even myself in trying to give you an example where one can 
indicate two mutually exclusive media streams, where only the port number 
changes. I am not sure how to encode it.

But let me give you another example for which I am more familiar with. 
Assume I can offer you two audio streams, one is narrow bandwidth over 
the PSTN (with codec number 3 (GSM low bandwidth) and the other is 
wideband stereo over IP (codec 10, L16 2 channels). I want to describe 
these options in clear written language (icap line). The potential 
configuration 1 selects the narrowband channel whereas the potential 
configuration 2 selects the wideband channel. This would be the SDP 
(relevant lines).

    m=audio 49170 RTP/AVP 3
    c=IN IP4 192.0.2.1
    a=creq:med-v0,pstn-v0
    a=mcap:1 GSM/8000/1
    a=mcap:2 L16/48000/2
    a=tcap:1 RTP/AVP PSTN
    a=ccap:1 IN IP4 192.0.2.1
    a=ccap:2 PSTN E164 +15551234
    a=icap:1 telephony quality audio
    a=icap:2 high quality stereo audio
    a=pcfg:1 t=1 m=1 c=1 i=1
    a=pcfg:2 t=2 m=2 c=2 i=2

/Miguel

---

From: "Krishna Prasad Kalluri" <[email-masked]>
Date: Tue, 18 Nov 2008 16:18:14 +0100

Hi Miguel,

OK Thanks for the clarification. Now I see the usage. Minor issue with
the example I guess the correct pcfgs are 

   a=pcfg:1 t=1 m=2 c=1 i=2
   a=pcfg:2 t=2 m=1 c=2 i=1

I think the document can be improved with examples and it will be easy
to grasp the concept.

Regards
Krishna

-----Original Message-----
From: Miguel Garcia A 
Sent: den 18 november 2008 15:35
To: Krishna Prasad Kalluri
Cc: mmusic; Joerg Ott
Subject: Re: [MMUSIC] draft-garcia-mmusic-sdp-misc-cap-00. About "icap"

Hi Krishna:

Your example got lost in the jungle of Audio-Video Profiles. And I
didn't succeed even myself in trying to give you an example where one
can indicate two mutually exclusive media streams, where only the port
number changes. I am not sure how to encode it.

    m=audio 49170 RTP/AVP 3
    c=IN IP4 192.0.2.1
    a=creq:med-v0,pstn-v0
    a=mcap:1 GSM/8000/1
    a=mcap:2 L16/48000/2
    a=tcap:1 RTP/AVP PSTN

/Miguel

Krishna Prasad Kalluri wrote:
> Hi Miguel,
> 
> I have difficulties to understand icap. I just try to illustrate with 
> an example. You can correct me or provide a better example to 
> understand this. May be you can give an example to show how it looks 
> with just i= (media title) and the same example with 'icap'
> 
> m=video 52000 RTP/AVP 31
> a=rtpmap:31 H261/90000
> 
> a=icap:1 video
> a=icap:2 video close-up
> 

> From: [email-masked] [mailto:[email-masked]] On 
> Behalf Of Miguel A. Garcia
> listening to the audio stream and posted some comments on the chat 
> room, but let me try to clarify the issue.
> 
> there are no semantics added to it, other than provide a human 
> readable description of the media stream. If we wanted to get a user 
> agent to consume the information, we should be using the "label" 
> attribute specified in RFC 4574.
> 

> would offer several alternative media streams and could indicate in 
> the i/icap line some information about what is in that media stream. 
> For example, one could indicate that a video stream contains a 
> close-up of the presenter versus a general room, or an audio stream 
> could contain the original movie audio track versus the director's 
> commentary. This could help the answerer to select the appropriate 
> alternative media stream.
> 
> information to the end user. Honestly, I don't know of any endpoint 
> that allows the user to write an i line, or which displays it to the 
> end user.
>   That might be the weakest selling point of this idea. But 
> technically it makes sense.
>