[nm-wg] treatment of lost packets when measuring delay

[stanislav shalunov <shalunov@internet2.edu>]

Loukik Kudarimoti <loukik.kudarimoti@dante.org.uk> writes:

> During the TPM workshop, we realized that there is a need to come to a
> common understanding of OWD data representation ( esp. treatment of
> packet loss ).

For what it's worth, the OWAMP specification is written so that send
times of all packets are known with fair precision to the receiver
(despite the element of pseudo-randomness in the timings).  Then, if a
packet does not arrive within a specified timeout, it is considered
lost; the send timestamp of such a packet is known and reported.

When interpreting the results, lost packets simply have infinite
delay, don't they?  This makes certain statistics meaningless (such as
mean delay), but if a value of an estimator becomes undefined because
of the presence of a small number of infinite values, the estimator is
not robust, and, therefore, should probably be avoided anyway.
Percentiles in general do not suffer from this problem.  (Harmonic
average works fine with infinite numbers, too, if one wanted to insist
on using non-robust---but more robust than mean---averaging
mechanisms.)

-- 
Stanislav Shalunov		http://www.internet2.edu/~shalunov/