[Asterisk-Users] Re: Horrible MeetMe performance

[qrss]

In my experience, several seconds of delay becomes apparent over time when
using an internal clock source.  Seems its a clocking/timer issue. 
Certainly we are dealing with clocking differences over time and unsynced
samples are being significantly buffered and then replayed later.  What
are you using as a clock source? I think that basically we are looking at
50 packets/sec at 20ms each packet for alaw/ulaw voip. That is - 1 second
of speech.  Now, zaptel seems to time from whatever hardware clock is
available and almost assumes that the clock will be precisely 8000 samples
per second or 1000 interrupts/second (also 1 second of speech).  It seems
that the voip clock is slightly faster than the hardware clock that zaptel
is timing from.  The extra samples/second must be being buffered.  Of
course, this buffering would add up over time until the point that a VOIP
sample is played back several seconds out of phase.  Seems that either the
zaptel clock source must be brought to closer tolerance, or the extra data
that is being buffered must be thrown away in order to stay in sync. Any
thoughts?

-----Original Message-----
From: Tony Mountifield
Sent: Sun, June 26, 2005 5:35 pm

In article <9FEE3E56D424E243B7CA76B875B07326045F6B at sbserver.ABBCO.inner>,
Dan Morin <DMorin at ABBCOInc.com> wrote:
> Make sure that if you're using anything other than zaptel hardware, it
> is running uLaw as the codec.  Anything else will produce ever
> increasing delays.

Hey, now that's a snippet of information I hadn't seen before!

All my work with SIP and MeetMe is using aLaw, since I'm in the UK.

Do you know why it causes ever increasing delays? I would have thought
that a transcoding would just introduce a contstant (small) delay, not
an accumulating one. So if you're right, then it ought to be fixable,
once the mechanism is understood.

Cheers
Tony
--
Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org
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