packet reordering at exchange points

Wed Apr 10 15:06:49 UTC 2002

On Wed, 10 Apr 2002 15:48:36 +0100
"Peter Galbavy" <peter.galbavy at knowtion.net> wrote:

> I am still waiting (after many years) for anyone to explain to me the
> issue of buffering. It appears to be completely unneccesary in a
> router.

OK, what I am missing?  Unless I'm misunderstanding your question, this
seems relatively simplistic and the need for buffers on routes is
actually quite obvious.

Imagine a router with more than 2 interfaces, each interface being of
the same speed.  Packets arrive on 2 or more interfaces and each need to
be forwarded onto the same outbound interface.  Imagine packets arrive
at exactly or roughly the same time.  Since the bits are going out
serially, you're gonna need to buffer packets one behind the others on
the egress interface.

Similar scenarios occur when egress interface capacity is less than some
rate or aggregate rate wanting to exit via that interface.

John