trans-Atlantic latency?

Jay Hennigan jay at
Fri Jun 29 00:59:01 UTC 2007

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.

Paging Scotty, warp factor 4 please!

>     What is a reasonable latency to see on a link of that distance? I
> get the impression he is shopping for something that involves dilithium
> crystal powered negative latency inducers, wormhole technology, or an
> ethernet to tachyon bridge, but its been a long time (9/14/2001, to be
> exact) since I've had a trans-Atlantic circuit under my care and things
> were different back then.

The speed of light hasn't changed much.

Propagation delay alone, assuming a 3000 mile straight-line path 
(probably on the short side) and 0.7 velocity factor in the transport 
medium is around 45 milliseconds round trip. Chicago to the East coast 
is about another 1000 miles or 15 ms, so 60ms. is probably a bit on the 
low side.

Serialization delay depends on bit rate and packet size, easy enough to 

Switching delay, probably minimal.

>       Anyone care to enlighten me on what these guys can reasonably
> expect on such a link? My best guess is he'd like service from Colt
> based on the type of customer he is trying to reach, but its a big
> muddle and I don't get to talk to all of the players ...

Jay Hennigan - CCIE #7880 - Network Engineering - jay at
Impulse Internet Service  -
Your local telephone and internet company - 805 884-6323 - WB6RDV

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