[AVT] Clock skew and RTP

[Dominique Fober <[e-mail]>]

I would like to know if there is any mecanism and/or payload defined 
to take account of the clock skew problem.  To be more explicit, here is 
a brief description of what I mean by 'clock skew problem':

Clocks on different stations are not running at the same frequency
(we have commonly measured clock deviations up to 1 per 10000 ms).
For real-time transmissions, it results in a problem similar to a 
consumer / producer problem. 
Let's take an example with a sender host A (the producer) and a receiver 
host B (the consumer):
if the consumer consumes the events faster than produced (the B clock is
running faster than the A clock), it will unavoidably lack data in a 
given delay,
if the consumer consumes the events slower than produced, (the B clock is
running slower than the A clock) it will unavoidably accummulate more and 
more data, resulting sooner or later in storage capacity problems.

Real-time streaming multimedia applications are generally buffering 
up to several seconds of data in order to make up for the transport 
latency variations. Therefore side effects of the clock skew aren't
noticeable unless the transmission lasts several hours.

What's the common way to solve this problem (if there is one) ? 
are there any mecanism and/or payload defined in RTP ?

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Dominique Fober               <[e-mail]>
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GRAME - Centre National de Creation Musicale -
9 rue du Garet  69001 Lyon France
tel:[phone] fax:[phone]
http://www.grame.fr


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