### On Mon, 25 Mar 2002 09:13:20 -0600, "Pistone, Mike"

### <Mike.Pistone@msfc.nasa.gov> casually decided to expound upon

### "'nanog@merit.edu'" <nanog@merit.edu> the following thoughts about

### "Transatlantic response times.":

I was curious if anybody would share what they consider to be average or

acceptable transatlantic ping response times over a T1.

I know there are tons of variables here, but I am looking for ballpark

figures.

Assume that utilization on the circuit is extremely low, and you are

measuring point to point across the line. You can also assume no other

bottlenecks effecting the response times (router performance, or what not).

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.

Is there any equation to estimate response times? For example, if your

circuit from A to Z has a 500ms avg response, than that equates to a circuit

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.