[e2e] Question about propagation and queuing delays

David P. Reed dpreed at reed.com
Sun Aug 21 20:44:54 PDT 2005

I can repeatably easily measure 40 msec. coast-to-coast (Boston-LA), of 
which around 25 msec. is accounted for by speed of light in fiber (which 
is 2/3 of speed of light in vacuum, *299,792,458 m s^-1 *, because the 
refractive index of fiber is approximately 1.5 or 3/2).   So assume 2e8 
m/s as the speed of light in fiber,  1.6e3 m/mile, and you get 1.25e5 

The remaining 15 msec. can be accounted for by the fiber path not being 
straight line, or by various "buffering delays" (which include queueing 
delays, and scheduling delays in the case where frames are scheduled 
periodically and you have to wait for the next frame time to launch your 

Craig Partridge and I have debated (offline) what the breakdown might 
actually turn out to be (he thinks the total buffering delay is only 2-3 
msec., I think it's more like 10-12), and it would be quite interesting 
to get more details, but that would involve delving into the actual 
equipment deployed and its operating modes.

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