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Re: trans-Atlantic latency?

  • From: Majdi S. Abbas
  • Date: Thu Jun 28 20:24:46 2007 
On Thu, Jun 28, 2007 at 06:20:31PM -0500, Neal R wrote:
>   I have a customer with IP transport from Sprint and McLeod and fiber
> connectivity to Sprint in the Chicago area. The person making the
> decisions is not a routing guy but is very sharp overall. He is
> currently examining the latency on trans-Atlantic links and has fixed on
> the idea that he needs 40ms or less to London through whatever carrier
> he picks. He has spoken to someone at Cogent about a point to point link.

	Chicago to London: ~3950 mi
	New York to London: ~3470 mi

	c == 186,282 mi/sec (in a vacuum)

	0.66 * c == 122,946 mi/sec

	CHI-LON: 32.128 ms
	NYC-LON: 28.224 ms

	That is one way, absolute best case, and the cables never run quite
the way you want them to.  If he's looking for 40 ms RTT, he is not going to
get it.  If he just needs 40 ms one way to London, it is possibly doable,
even from Chicago.

	I couldn't readily find lengths for the individual segments of
TAT-14, so as a representative example, we'll use TAT-12/13.  From RI to
the UK: 3,674 mi.

	( 3674 / (0.66 * c) ) * 1000 == 29.883 ms, doubled for 59.766 ms
RTT.

	Real world numbers seem to suggest many carriers run between 70 and 
80 ms RTT from NYC to London, and I just measured around 100 ms RTT from
Chicago to a host in the UK.

	--msa