60 ms cross-continent

Tim Požár pozar at lns.com
Sat Jun 20 17:07:08 UTC 2020


Besides the refractive index of glass that makes like go about 2/3rds it 
can in a vacuum, "Stuff" also includes many other things like 
modulation/demodulation, buffers, etc.  I did a quora answer on this you 
can find at:

https://www.quora.com/How-can-one-describe-the-delay-characteristics-of-ping-and-traceroute-commands/answer/Tim-Pozar

On 6/20/20 9:29 AM, Joe Greco wrote:
> On Sat, Jun 20, 2020 at 09:24:11AM -0700, William Herrin wrote:
>> Howdy,
>>
>> Why is latency between the east and west coasts so bad? Speed of light
>> accounts for about 15ms each direction for a 30ms round trip. Where
>> does the other 30ms come from and why haven't we gotten rid of it?
>>
>> c = 186,282 miles/second
>> 2742 miles from Seattle to Washington DC mainly driving I-90
>>
>> 2742/186282 ~= 0.015 seconds
> 
> Speed of light in a fiber is more like 124K miles per second.  It
> depends on the refractive index.  And of course amplifiers and stuff.
> 
> ... JG
> 


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