Re: [AVT] Re: draft-jones-avt-audio-t38-04.txt

["Paul E. Jones" <paulej at packetizer.com>]

Magnus,

> I can't find anywhere that you define the RTP TS field. The timestamp
> must also be defined by a RTP payload format. If you do not use it for
> any purpose, then you should at least define it as being the timestamp
> at the time of the sending so that the RTCP jitter measurements work.

I suppose that it was felt that it did not need explanation.  The timestamp
field will be adjusted according to the clockrate specified in SDP.  I
cannot say why it was left out, but it is something that should be
documented in T.38.

> > It is strange as defined. What I would prefer is that devices would just
> > use
> > the same value they use for audio codecs, which is typically 8000.
> > Since
> > the usage of this MIME type will be with TDM circuits, it is probably
> > reasonable to just set it to 8000, though I'd prefer it to match the
> > voice
> > codec-- perhaps the voice codec rate is 16000.  I'm open to suggestions.
> >
>
> I don't see a problem with defining 8 kHz as default, and then recommend
> that in any gateway cases the RTP TS rate is equal to the audio RTP TS
> rates used in the same session.

OK.  How is this?
   rate: The RTP timestamp clock rate, which SHOULD be 8000Hz by
   default. The clock frequency MAY be set to any value, but SHOULD
   be set to the same value as for any audio packets in the same RTP
   stream in order to avoid RTP timestamp rate switching.

Paul


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