From: ack@Ingres.COM (David Ackerman)
Subject: Problems with Cabletron 10BaseT hubs and DEC XMI Ethernet cards?
Followup-To: comp.dcom.lans.ethernet
Summary: DEC's XMI card doesn't seem to work with Cabletron's 10BaseT hubs
Keywords: 10BaseT
Reply-To: ack@Ingres.COM (David Ackerman)
Organization: Ingres, 1080 Marina Village Parkway, Alameda CA 94501
Date: 27 Aug 92 00:14:13 GMT

Is anyone out there using Cabletron 10BaseT hubs with a DEC XMI Ethernet
card? We are, and we have experienced the following problem:

We have a DEC VAX 6000-540 which uses a DEC XMI Ethernet card. When it is
hooked to a Cabletron 10BaseT hub, over 50% of the transmissions on the port
it is connected to are errors. The approximate breakdown of these errors is
as follows: 10% CRC errors, 40% runt packets and 50% frame alignment errors.
The Cabletron hub is an MMAC5 chassis, TPMIM-34 10BaseT card connected to a
Cabletron TPT-4 10BaseT transceiver on the VAX, and an IRM2 management card.
The statistics are from the IRM2 management card in the hub.

The workaround we arrived at through experimentation is to put a Cabletron
MT-800 (a multiport transceiver) between the hub and the VAX. The TPT-4 from
the hub connects to the network port on the MT-800, and a short AUI cable
connects the VAX to one of the transceiver ports on the MT-800. When the
VAX is connected to the hub in this manner, there are no errors.

The 10BaseT connection itself was thoroughly tested and works fine with
other systems. We have had only one other problem of this type with the
Cabletron 10BaseT hubs: a few of our Pyramids have old Ethernet cards that
only support level 1 Ethernet (not 802.3). They are also front-ended with
a DEC Delni, which works fine. I can understand an incompatibility problem
with crusty old equipment like that, but the XMI card is supposed to be
DEC's latest and greatest.

The story from both vendors is typical. Cabletron says they meet the 802.3
spec so it must be the card. DEC came out and did their usual repair and
troubleshooting method of swapping every possible piece of the VAX that has
to do with the card, including the card itself 3 times. They concluded that
since nothing changed during the process of swapping everything, it must be
the Cabletron hub.

My theory at this point is that it's a design flaw in the XMI card. Since
the MT-800 supplies its own power and the TPT-4 doesn't, it may be a problem
with the XMI board not supplying enough power to the transceiver (the
voltage checks out OK). Or it may be some other type of problem with the
card. At any rate, I am more inclined to believe it is a problem with the
card rather than the hub since the exact same TPT-4 on the exact same hub
port works fine on other systems. I will be able to test further in about
three weeks, and Cabletron has offered to come out with more extensive
diagnostic equipment to help me test.

So, the basic question is: has anyone else experienced this problem? If
so, what did you do about it? Have you used Cabletron (or other vendors')
10BaseT hubs connecting directly to DEC VAXen with XMI cards and *not*
had problems? Thanks in advance for any light you can shed on this.


         +-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-+
        /  David Ackerman               |  ack@ingres.com             \
       |   Network Administrator        |  (510) 748-2637     (voice)  |
       |   Ingres                       |  (510) 748-2688     (FAX)    |
       |   1080 Marina Village Parkway  |                              |
        \  Alameda, CA 94501            |  #include <cute-saying.h>   /
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