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Re: Is latency equivalent to RTT?

  • From: Stephen J. Wilcox
  • Date: Wed May 14 10:16:30 2003


On Wed, 14 May 2003 Michael.Dillon@radianz.com wrote:

> 
> Has it become common usage to define latency in an IP network as the round 
> trip time in that network?
> 
> I've always considered latency to be a one-way measure of delay and RTT to 
> be the sum of the latencies in both directions. When I tried to find 
> something to back up this view, I discovered that a number of companies 
> define latency as equivalent to RTT in their SLAs.
> 
> Assuming that one has measuring devices in every PoP, do you think it is 
> harder to measure a full matrix of one way latency compared to measuring a 
> full matrix of RTT? 
> 
> Does it even make sense to measure a full matrix of RTT when the 
> measurement of A to B to A should be equivalent to the measurement of B to 
> A to B?

Ah but its not is it, so much of the Internet is asymmetric now this is 
important especially for troubleshooting

But generally performance relates to how well say your web pages download from a 
site which is a 2 way tcp connection to you may as well do rtt and get both 
directions.

Your problem with 1-way is finding a way to do it thats reliable, for rtt ping 
is about as simple as you can get and works a treat but for 1-way you have to be 
a bit more creative....

Steve