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MAE clarifications: Full Duplex FDDI, Congestion

  • From: Steve Feldman
  • Date: Mon Dec 09 14:47:29 1996

There's been a flurry of information about the MAEs over the weekend, and I'd
like to clear up a few points:

Full Duplex FDDI

The DEC Gigaswitch supports full duplex FDDI by default, and MFS has *not*
disabled this feature.  At least one provider has already plugged in a
Full Duplex capable interface and seen it work without any intervention
on our part.  There's no additional charge for use of full duplex FDDI,
and there's nothing anyone has to do to "sign up" for it.  I would ask that
you notify me so I can watch more closely for difficulties, however.

Cisco's full duplex FDDI interface is a module for the VIP2 card, which I
believe is only supported on the 75xx and 70xx/RSP (but not 70xx "classic")
platforms.  I don't know of any other router vendors supporting full duplex
FDDI, but they don't always check with me first!

MAE Congestion

There have been problems at both MAE East and West recently with apparent
packet loss on trunks between Gigaswitches.  In both cases, the links
themselves were not full, but the packets were being dropped on ingress to
one of the Gigaswitches.  The apparent reason is head-of-line blocking in
that switch (Giga1 at MAE East, the Ames switch at MAE West) caused by one
or more providers filling their FDDI access links.

In both cases, we have been working with those providers to find ways to
relieve pressure on their attachment ports, and have made some configuration
changes to reduce the amount of packet drops.

We are also working with DEC to find solutions for the head-of-line problems.

	Steve Feldman
	MFS
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