North American Network Operators Group

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Re: latency vs. packet loss

  • From: Jon Zeeff
  • Date: Thu Jan 14 09:22:17 1999

True, one can certainly think of and even find many situations where 
they don't correlate, but in real world measurements, it looks like in 
perhaps 90% of the cases, packet loss between randomly choosen places 
on the Internet is accompanied by greater than typical latency.  I suppose 
this suggests that saturated links (where the router/switch adds latency by 
buffering) are a commmon cause of Internet packet loss (vs line 
errors, etc which would not show this correlation).  

As a single example, connectivity from here to a popular NSP web site
is 40 msec in the morning with no packet loss and 500 msec with
20% packet loss in the afternoon.  Routing is the same (through mae-east :-)).

> > How well does latency correlate to packet loss on the Internet?  For 
> > example, if one were to pick one of several randomly placed sites on 
> > the net based on lowest latency to/from point x, what percentage of 
> > this time would this also yield the site with the lowest packet loss 
> > to/from point x?  My guess is that the correlation is high (due to 
> > typical buffer sizes).  
> Remember latency is also affected by other things, like distance
> (you won't get less than 70ms RTT NY<->Lon even on an empty STM-1),
> Also note there are some conditions which cause packet loss which
> won't cause ICMP latency (line errors, various IXP overload conditions