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[ippm] Re: need of sync of clocks in dup metric def

Hi Emile,

The methodology (section 2.6) of the draft refers to section 2.6 of
RFC2680 which speaks about sync of clocks:

Is the sync of clocks really needed for detecting packet
duplication? 
No, actually this is one of the things that suprised me as well in
RFC2680.  Does anybody remember why this is in 2680?


My understanding of the philosophy of RFCs 2679 & 80 is that a packet
arriving very very late is an excellent packet lost. Seriously, the
definition of the packet loss requires the time the packet is sent
because there is not any local (on the receiver) event available to
start the timeout timer.

Packet duplication differs. The reference of time for waiting a copy is
the arrival of a first image of the packet. So it does rely on any
remote time.


I assume you mean "does not rely" otherwise the question whether we need
sync'd clocks would be moot.

Under that assumption: loss is defined as send a packet at time T, wait
for it to arrive or not in some interval [T,T+delta].  I have defined
duplication in the same manner: send a time T, count the number of
copies that arrive in an interval [T, T+delta], with delta set to
be such that the packet actual has a chance to arrive, and such that
the receipient of a real application could still use the packet.
This makes the two definitions compatible.

Your idea would be: send packet at time T, wait for the first copy
to arrive, count the number of additional copies, in other words,
arrive in the interval [T+OWD, T+OWD+delta].  That could work too but
makes the definition somewhat incompatible with the loss definition.

Henk

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