Delay jitter, measurements etc. (was: RE: [e2e] Re: crippled
cannara at attglobal.net
Thu Apr 26 18:46:44 PDT 2001
This sounds very reasonable Vilho. One other reason for jitter concern is for
videophone, where one doesn't want the lips much out of sync with the sound.
vilho.raisanen at nokia.com wrote:
> I'll throw in my two (euro) cents on VoIP characteristics.
> Further sources for VoIP quality classifications: TIA, ETSI EP TIPHON.
> Generally, one-way mouth-to-ear delays larger than 400 ms are regarded to
> lead to walkie-talkie-style conversation. This is generally deemed the limit
> of "acceptable" delay. Below 400 ms, the classification limits vary
> according to source.
> As for delay jitter from endpoint perspective, a sensible-looking approach
> to delay jitter goes as follows:
> 1) one picks the maximum target value end-to-end delay
> 2) End-to-end delays is partitioned into terminal and network delay budgets.
> >From this, the maximum size of jitter buffer is determined
> 3) delay variations that can not be handled by jitter buffer thusly sized
> are packet losses.
> Audible effects are caused by correlations of packet losses. Modern codecs
> typically can handle single packet losses.
> This argument suggests that the size of jitter buffer size depends on the
> usage scenario.
> As for measurements, ETSI EP TIPHON has standardized a measurement method
> designed for VoIP and other periodic real-time streams. IETF is still
> considering whether a similar method would be a good idea. The underlying
> idea in this kind of measurement is to emulate VoIP media stream as to
> packet sizes and packet transmission intervals.
> -- Vilho
Menlo Park, Calif.
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