Re: packet reordering at exchange points

["Stephen Sprunk" <ssprunk () cisco com>]

Thus spake "Iljitsch van Beijnum" <iljitsch () muada com>
> But how is packet reordering on two parallell gigabit interfaces
> ever going to translate into reordered packets for individual
> streams?

Think of a large FTP between two well-connected machines.  Such flows tend
to generate periodic clumps of packets; split one of these clumps across two
pipes and the clump will arrive out of order at the other end.  The
resulting mess will create a clump of retransmissions, then another bigger
clump of new data, ...

> Packets for streams that are subject to header compression or
> for voice over IP or even Mbone are nearly always transmitted
> at relatively large intervals, so they can't travel down parallell
> paths simultaneously.

RTP reordering isn't a problem in my experience, probably since RTP has an
inherent resequencing mechanism.  The problem with RTP is that if the
packets don't follow a deterministic path, the header compression scheme is
severely trashed.  Also, non-deterministic paths tend to increase jitter,
requiring more bufferring at endpoints.

S