[34715] in North American Network Operators' Group
Re: T3 Latency
daemon@ATHENA.MIT.EDU (Matthew F. Ringel)
Sat Feb 17 07:53:23 2001
Date: Sat, 17 Feb 2001 07:50:56 -0500
From: "Matthew F. Ringel" <ringel@akamai.com>
To: nanog@merit.edu
Message-ID: <20010217075056.A15283@crabcake.kendall.akamai.com>
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In-Reply-To: <200102170737.HAA07490@i-14.isi.edu>; from prue@ISI.EDU on Sat, Feb 17, 2001 at 07:37:48AM +0000
Errors-To: owner-nanog-outgoing@merit.edu
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.
......Matthew
----------
M. F. Ringel
Network Engineer
Akamai Technologies, Inc.
ringel@akamai.com
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
>
