[NANOG] Comcast latency

Mike Fedyk mike at reachme.com
Thu May 1 16:32:07 CDT 2008


> -----Original Message-----
> From: John Osmon [mailto:josmon at rigozsaurus.com] 
> Another time, I had a VOIP conversation fall apart once with 
> somone on a 
> Comcast link.  When the jitter finally fell into a reasonable 
> range, the call sounded *great* again -- but there was a 4 
> second latency that had been introduced.  It was wild.  I 
> kept wondering -- "where was this buffered?  Are we on a 
> satellite backup route?"  We kept the conversation going for 
> a while just for the 
> sheer novelty.

The delay was probably introduced by an adaptive jitter buffer on one of the
VoIP end points.  It is supposed to reduce the buffer as network conditions
improve.  When it "fell apart" the buffer was increased until it was long
enough to reorder all of the packets.

It would be interesting to see if a call between those same end points would
reduce the size of their buffers after the network stabalized again.

Mike





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