[NANOG] Comcast latency

John Osmon josmon at rigozsaurus.com
Wed Apr 30 18:31:48 CDT 2008


On Wed, Apr 30, 2008 at 09:46:38AM -0400, Jim Popovitch wrote:
> Looks can sometimes be deceiving. ;-)  I've seen Comcast drop packets
> left and right, but show 8Mbs/2Mbs on speed test sites.   Other times
> I've seen the opposite, zero PL but extremely high latency (seconds,
> double digits!)... all the while non-dynamic web pages (probably
> cached upstream) loaded just fine.

I had mrt running across a Comcast connection that indicated a
14000 ms RTT for one packet out of several hundred.  I wasn't sure 
that was a trustworthy measurement, but it sure suprised me.

Another time, I had a VOIP conversation fall apart once with somone on a 
Comcast link.  When the jitter finally fell into a reasonable
range, the call sounded *great* again -- but there was a
4 second latency that had been introduced.  It was wild.  I kept
wondering -- "where was this buffered?  Are we on a satellite
backup route?"  We kept the conversation going for a while just for the 
sheer novelty.

Overall, my data points on Comcast point to a pretty solid
service -- but the outliers are pretty impressive in their
own right.




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