Subject: [AVT] AMR IF 2

From: "Yuval Nissan" <[email-masked]>
Date: Mon, 27 Feb 2006 10:53:06 +0200

Hi,

I would like to know if there is standard/draft that defines how to
transport AMR IF 2 (described in 3GPP TS 26.101 Annex A) over RTP. RFC
3267 uses only AMR IF 1.

Also can someone advise where this format is used and why? 

Regards,

Yuval 

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Audio/Video Transport Working Group
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From: Magnus Westerlund <[email-masked]>
Date: Mon, 27 Feb 2006 11:21:17 +0100

> transport AMR IF 2 (described in 3GPP TS 26.101 Annex A) over RTP. RFC

Actually, RFC 3267 doesn't use IF1 either, only the speech data bits are 
ordered the same way as for IF1. The RTP payload format for AMR 
maintains most of the functionality of IF1, however the order of the 
fields and their bit-location is different.

> Also can someone advise where this format is used and why? 

IF2 is used in for example 324M where the framework provides with CRC 
and other ways of carrying the codec mode request. The lack of frame 
quality indicator may be its biggest weakness.

But I don't know of an RTP payload format for AMR IF2. I would also 
recommend against it. Please use RFC 3267 and do the necessary 
bit-shuffling in any gateway. That way we avoid splintering the 
transport of AMR over RTP, causing interoperability issues.

Cheers

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
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