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Re: Is latency equivalent to RTT?

  • From: Henk Uijterwaal (RIPE-NCC)
  • Date: Wed May 14 11:23:20 2003

On Wed, 14 May 2003 [email protected] 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?

The problem is buying and installing the equipment, even if you buy an off
the shelf product like RIPE NCC's TTM :-).  Once installed, these products
will just provide you with the numbers.

> 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?

If you are sure that the path taken for A-B-A is equal to B-A-B, then no,
measuring only A-B-A is sufficient.


Henk Uijterwaal                             Email: [email protected]
RIPE Network Coordination Centre            WWW:
P.O.Box 10096          Singel 258           Phone: +31.20.5354414
1001 EB Amsterdam      1016 AB Amsterdam    Fax: +31.20.5354445
The Netherlands        The Netherlands      Mobile: +31.6.55861746

That problem that we weren't having yesterday, is it better? (Big ISP NOC)