RE: [AVT] RE: avt Digest, Vol 28, Issue 21

["Ingemar Johansson S \(LU/EAB\)" <ingemar.s.johansson at ericsson.com>]

Hi

Reply below.
Ingemar 

> -----Original Message-----
> From: David R Oran [mailto:oran at cisco.com] 
> Sent: den 29 augusti 2006 20:58
> To: Desineni, Harikishan
> Cc: Ingemar Johansson S (LU/EAB); avt at ietf.org; Colin 
> Perkins; roni.even at polycom.co.il
> Subject: Re: [AVT] RE: avt Digest, Vol 28, Issue 21
> 
> 
> On Aug 29, 2006, at 2:41 PM, Desineni, Harikishan wrote:
> 
> >
> >
> >> -----Original Message-----
> >> From: Ingemar Johansson S (LU/EAB)
> >> [mailto:ingemar.s.johansson at ericsson.com]
> >> Sent: Tuesday, August 29, 2006 2:27 AM
> >> To: avt at ietf.org
> >> Cc: roni.even at polycom.co.il
> >> Subject: [AVT] RE: avt Digest, Vol 28, Issue 21
> >>
> >> Hi
> >>
> >> The problem is not limited to a specific speech codec, it 
> is more a 
> >> general problem that all speech codecs have. The proposed 
> solution is
> > to
> >> (by using inband signaling) being able to request redundant
> > transmission
> >> and/or frame aggregation in order to enable an efficient channel 
> >> adaptation strategy as the one proposed in the draft
> >>
> > (http://www.ietf.org/internet-drafts/draft-johansson-avt-rtp-
> > shim-00.txt
> >> )
> >>
> >> Reason why I propose inband signaling for this is because RTCP is
> > bulky
> >> and bursty and does not fit well with optimized cellular networks
> > (this
> >> is copy pasted from a previous post).
> Stupid question. What if the audio is going one way and there 
> IS NO RTP packet to piggyback the feedback on going in the 
> reverse direction? Lots of cases for this, e.g. VAD, MOH, 
> playing voicemail, etc.
> 
> Seems like you need the RTCP machinery anyway.

 VAD (I assume that you mean DTX, correct me if I am wrong here) the
case is that silence descriptor packets are transmitted with regular
intervals, for AMR the interval is typically 160ms, this interval is
however a requirement from a circuit switched cellular network
perspective and for packet switced networks 500ms is sufficient.
 Music on hold: Not 100% sure here but in todays cellular networks I
belive that both directions are active despite music on hold, however
DTX will be used in one direction due to speech inactivity.
 Voicemail is a special case and is not meant to be covered by the
proposed adaptation strategy (at least not my intention).

As stated in the draft, the intention is not to replace RTCP, RTCP is
needed for other purposes such as sychronization of speech and video in
a videophone session. For a speech only situation the situation for RTCP
is however less certain as the burstyness causes some potential problems
in optimized cellular networks.

Ingemar

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