ssprunk at cisco.com
Mon Nov 18 20:24:47 UTC 2002
Thus spake "Jere Retzer" <retzerj at ohsu.edu>
> Stephen Sprunk wrote:
> >>>Any point in the US is within 25ms RTT (or less) of a major exchange;
eliminating this 25ms of latency will have no effect on VoIP unless you're
already near the 250ms RTT limit for other reasons.<<<
Can you please upgrade to a MUA with standard quoting semantics?
> 25 MS is assuming that the only delay is due to the speed of light.
No. I'm asserting that every populated area in the U.S. is within 25ms ping
time of a major exchange, absent congested pipes.
> Add equipment, especially routers or other gear that requires manipulating
> packets and the delays add up quickly.
If your router(s), switch(es), or firewall(s) need more than 1ms to forward a
packet, it's time to select a new vendor.
It's 20 hops between my home and work box, including 2900mi of fiber, a couple
firewalls, and a DSL link -- and that's only 80-90ms. We clearly don't need an
exchange for every 100km2 to get acceptable RTT. What we need are uncongested
> I once read that the most people wil tolerate on a regular basis is around
> 150-180 ms. I think that is much too high for regular use
ITU G.113 says users won't even notice the latency until it his 250ms. Do you
have scientific studies that show 150-180ms is problematic? I'm sure the ITU
(and a few hundred telcos) will be interested.
Business experience shows users will tolerate over 1000ms latency if there's an
economic incentive. There are many companies doing voice-over-internet that
operate networks this way, and they're making a lot of money doing it.
More information about the NANOG