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Re: Transatlantic response times.
- From: Jake Khuon
- Date: Mon Mar 25 11:01:28 2002
### On Mon, 25 Mar 2002 09:13:20 -0600, "Pistone, Mike"
### <Mike.Pistone@msfc.nasa.gov> casually decided to expound upon
### "'firstname.lastname@example.org'" <email@example.com> the following thoughts about
### "Transatlantic response times.":
MP> I was curious if anybody would share what they consider to be average or
MP> acceptable transatlantic ping response times over a T1.
MP> I know there are tons of variables here, but I am looking for ballpark
MP> Assume that utilization on the circuit is extremely low, and you are
MP> measuring point to point across the line. You can also assume no other
MP> bottlenecks effecting the response times (router performance, or what not).
MP> Should you see a ~150ms trip? 250ms? 450ms???
Well, I've been seeing around 70ms (+/- 5ms) RTT pings from NYC to LON
across AC-1 (Global Crossing) as normal. Granted this is on an OC-48 but
bandwidth should not matter much to RTT if the load is light and all you're
measuring is ICMP ping.
MP> Is there any equation to estimate response times? For example, if your
MP> circuit from A to Z has a 500ms avg response, than that equates to a circuit
MP> distance of aprox. 5000 miles or something?
Assuming you exclude switching latency in the hardware, latency induced by
regenerators, etc... spead of light in a medium is a simple
distance-rate-time equation with a slight twist: c = nL/t, where n is the
refractive index, L is the length, and t is the transmission time difference
(double this for RTT). The rest is just simple math. So expected one way
time should be: t = nL/c
Note -- I believe most fiber optic cables have a refractive index somewhere
on the order of 1.4.
/*===================[ Jake Khuon <khuon@NEEBU.Net> ]======================+
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