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Re: Transatlantic response times.

  • From: Jake Khuon
  • Date: Mon Mar 25 11:01:28 2002
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### 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.":

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> figures.
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> ]======================+
 | Packet Plumber, Network Engineers     /| / [~ [~ |) | | --------------- |
 | for Effective Bandwidth Utilisation  / |/  [_ [_ |) |_| N E T W O R K S |
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