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Re: T3 Latency

  • From: Matthew F. Ringel
  • Date: Sat Feb 17 07:55:10 2001

The rule of thumb I use is that the speed of light in fiber-optic cable is 
roughly 2x10^8 m/sec.

2x10^8 m/sec = 200,000,000 m/sec = 200,000 km/sec = 200 km/msec =~ 130 mi/sec

I once worked with a customer whose first hop out was ~30ms, regardless of the
load on the line (a t3, iirc).  Sure enough, he was on a very large SONET ring 
that travelled the north-south length of the US roughly twice before his 
traffic went elsewhere.


M. F. Ringel
Network Engineer
Akamai Technologies, Inc.

On Sat, Feb 17, 2001 at 07:37:48AM +0000, Walter Prue wrote:
> Chuck,
> The question posed by Chris, "how long is your access line"?, is a rather 
> important data point before answering your question.  I have a T3 that is
> about 15 miles long.  It runs between two 7500 routers.  Its minimum ping
> round trip time with 100 byte pings is 2 ms.  It is not very heavily loaded
> with peaks of about 10 Mb/s today and the max round trip time was 21 ms.
> So that should give you some minimal bounds of what you might expect.  As
> the saying goes your mileage may vary.  Speed of light does play in here,
> if the circuit is longer.  Also intervening electronics such as a frame cloud
> or telco muxes also add latency.
> Walt

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