Subject: Re: Concerns about exported numbers 12/2 1/02/96 14:52:

From: [email-masked] (Christian Huitema)
Date: Wed, 3 Jan 1996 11:34:26 +0100

Roch,

Yes, some switches are equipped with very large buffers.  This is related
to their "customer target", i.e. high-bandwidth TCP flows.  Van Jacobson
argued that, due to the end-to-end nature of TCP controls, one can only get
a stable service if the switch memory is at least the switch bandwidth
times the network delay.  It follows that the maximum jitter introduced by
such a switch can be as large as the average network delay, which does not
bode well for real time services.

But then, there are some very simple solutions, e.g. to mark the real-time
packets so that the switches schedule them according to a general "care for
delay" category.  The "priority" bits of IPv6 already allow this; we could
probably declare that the IPv4 "delay" TOS has the same effect.  The
switches would then implement two queuing disciplines, one for real-time
with short queues, short delays, possibly high loss rates, and another for
batch with long delays but less losses.

The bottom line is the need to keep the network simple. Juha formulated
this very well: isolated flows with guaranteed minimum bandwidth, the
default bandwidth being nil. There may be further requirements for specific
applications, but why not start with a simple 95% solution ?

Christian Huitema