Subject: RTP Packetization

From: Ramana Yarlagadda <[email-masked]>
Date: Sat, 13 Nov 1999 09:39:16

Hi all,

In section 6.2.1/H225v2 it is mentioned as :
For audio algorithms such as G.723 which use more than one size of audio

frame, audio frame boundaries within each packet shall be signalled
in-band to the audio channel.

If we consider it from RTP point of view, then in a RTP packet
there can be various combinations of the silence and voice frames.
Let's consider one RTP packet like this:
<voice><voice><SID><voice><SID>.
so, audio frame boundaries can be
1. between two voice frames or
2. between voice frame and a non-voice frame.
3. or both 1 and 2.
My question is exactely which of the above mentioned audio boundaries,
according to the section 6.2.1/h225v2 needs to be signalled in the RTP
packet?

And, the boubndaries are to be signalled in-band, it means we have to
add the boundary signalling in the RTP payload itself.
am I correct?

If we are going to put the boundary signalling inside the RTP payload,
and this sort of signalling is H323 specific thing. then I think it will
create some interoperability problems with RTP implementations other
than
H323.

-Thanks in advance.
-ramana

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From: Larry Cox <[email-masked]>
Date: Mon, 15 Nov 1999 10:58:19 -0700

At 09:39 AM 11/13/99 +0000, you wrote:
> ...

I may have missed something here. Doesn't "in-band" indicate that the
packet boundaries are to be part of the G.723 data stream and are not to be
identified in the RTP part of the frames? As I understand it, this means
that RTP is not to be involved in the management of the audio packet
framing process. This is to be the responsibility of the G.723 compression
process exclusively. Otherwise there would be a need to update the RTP
definition each time an additional compression protocol is added to the
library.

Larry

======================================

Larry Cox
Senior Software Engineer

Hypercom Network Systems Inc.
2851 West Kathleen Road
Phoenix, AZ 85053
USA

Phone: (602) 504-4657
Fax: (602) 504-4711
Web: www.hypercom.com

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From: Fantolino Luca <[email-masked]>
Date: Tue, 16 Nov 1999 09:30:10 +0100

I guess section 6.2.1/H225v2 means that G.723 payload reports information
sufficent to identify frame boudaries.
In fact the length of a G.723 frame (which may be 4, 20 or 24 bytes) can be
determined by the least significant two bits of the first octet of the frame
(see draft-ietf-avt-profile-new-07.txt).

bye
Luca

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Luca Fantolino                 tel: +39 011 2287543
CSELT (Telecom Italia Group)   fax: +39 011 2285069
via G. Reiss Romoli, 274       [email-masked]
10148 Torino
ITALY
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> ----------
> From: 	Larry Cox[SMTP:[email-masked]]
> Sent: 	lunedì 15 novembre 1999 18:58
> To: 	[email-masked]
> Subject: 	Re: RTP Packetization
> 

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