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Re: VoIP QOS best practices
From: "Petri Helenius" <pete () he iki fi>
Date: Tue, 11 Feb 2003 00:51:23 +0200



Reordering per se doesn't affect VoIP at all since RTP has an inherent
resync mechanism.

Most VoIP implementations don´t care about storing out-of-order packets
because they think that 20ms or 30ms late packets should be thrown
away in any case.

Reordering is also unlikely, since each packet is sent 20ms or more apart;
I'm not aware of any network devices that reorder on that scale.

Most "core" routers, at least from vendors C and J have enough packet
memory to keep packets for hundreds of milliseconds. Apply sufficent
per packet load balancing (which would be stupid but doable) to this,
and you´ll arrive at the end result.

Our observations tell us that reordering does not happen too much but
there are periods from a few minutes to an hour where reordering from
specific AS´s skyrocket to return to normal, in many cases even without
observable path change. (MPLS in action?)

Pete


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