[e2e] Re: crippled Internet

Randy Bush randy at psg.com
Thu Apr 26 06:30:32 PDT 2001

> 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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