[58449] in North American Network Operators' Group
Re: Is latency equivalent to RTT?
daemon@ATHENA.MIT.EDU (Henk Uijterwaal (RIPE-NCC))
Wed May 14 11:22:02 2003
Date: Wed, 14 May 2003 17:17:55 +0200 (CEST)
From: "Henk Uijterwaal (RIPE-NCC)" <henk@ripe.net>
To: Michael.Dillon@radianz.com
Cc: nanog@merit.edu
In-Reply-To: <OFE25C62FB.D3D121A6-ON80256D26.004C5DB8-80256D26.004D0174@radianz.com>
Errors-To: owner-nanog-outgoing@merit.edu
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?
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
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