[e2e] Re: crippled Internet
J.Crowcroft at cs.ucl.ac.uk
Thu Apr 26 09:26:52 PDT 2001
actualyl ,i dont claim it works well scalably yet, but that it will
tend to get better and better - its stil limportant to consider fancy
queueing for weak points in the net and its still important to
consider mechanisms to remove phase correlation so that we dont get
these occasionaly HUGE delays which we all have seen (but can't find
the really good experimental evidence for yet unelss i missed a
In message <E14slqq-000BiY-00 at rip.psg.com>, Randy Bush typed:
>>> experience with actually using audio tools is that generally the net
>>> is not the main problem so long as neither end is dial up and both
>>> ends haev good analog audio setups - can cite lots of papers pointing
>>> at the problems mostly being with mikes and speakers - typical tier 1
>>> and 2 paths are fine when there isnt inter-provider congestion.
>>this makes sense. thank you!
>>scott called me voice to apply a clue-by-four.
>> o voip packets are time-stamped, so the receiver can filter some jitter.
>> (i like that relative stamping is sufficient. the absoloute needed to
>> measure one-way delay/jitter is a pain in the operational butt. you
>> try getting a gps antenna on the roof of a bunker-style pop)
>> o there can be echo through analog gear at an end, or because mic and
>> earpiece are air-coupled. so echo cancellation is relevant.
>> o codecs can introduce *significant* delay. but, as i said, a network
>> operator i can't do much about delay.
>>[ and craig and a few others also passed on useful clue ]
>>a whole lot of folk have written to tell me that voip actually works and
>>that i don't need to get too upset that i can't really deploy qos because
>>it is not clear it is a critical need.
>>so my interest remains in the distribution of jitter in time and in jitter
>>clumping. there are issues i have yet to understand here:
>> o have folk characterized what is good/acceptable/bad?
>> o do we have good ippm-style techniques to measure on those dimensions?
>>the point was raised that folk do see occasional very large queuing delays.
>>i have seen single-hop delays (i.e. routing has nothing to do with it)
>>going into the multi-second range. because of the bandwidth delay product
>>on trans-oceanic links, routers have *really* big buffers, so they can
>>have gawdawful queues. but folk are still chasing *why* they have these
>>sudden exciting spurts of scary long queues.
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