Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!wuarchive!zaphod.mps.ohio-state.edu!mips!sgi!vjs@rhyolite.wpd.sgi.com
From: vjs@rhyolite.wpd.sgi.com (Vernon Schryver)
Newsgroups: comp.dcom.lans
Subject: Re: Multi-protocol router scorecard
Summary: FDDI nits
Message-ID: <68398@sgi.sgi.com>
Date: 2 Sep 90 21:44:54 GMT
References: <90245.110408HANK@BARILVM.BITNET>
Sender: guest@sgi.sgi.com
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 34

In article <90245.110408HANK@BARILVM.BITNET>, HANK@BARILVM.BITNET (Hank Nussbacher) writes:
> ...
>     - FDDI             | 2x100Mb      | Rel 5.5 (d)  |               |
>       - DAS (Dual)  (e)| Yes          | Yes          |               |
>       - SAS (Single)   | Yes          | No           |               |
> ...
>  e. Dual is also known as Type A and Single is also known as Type B.
> ...


On the chance that "Dual" and "DAS" refer to the FDDI things defined
by X3T9.5, I have some nits.

You can always attach a Dual Attachment Station ("DAS") as if it were a
Single Attachment Station ("SAS") simply by plugging in an S cable
(connected on its other end to the M port of a concentrator), to
the B port of the DAS.  The MIC keying allows this.  SMT is happy.  (see
section 5.2.4 in SMT 6.2.)  The only caveat is that I do not think the
standards completely define who does what to and with WA_Withhold, so
that connecting both A and B ports of a DAS to a concentrator ("tree
connection with redundancy") is too likely to both not work and to trash
the ring.

In FDDI-speak, a DAS has two ports, an "A" port and a "B" port.  Please
note that each "port" has two fibers, one for receiving and one for
transmitting.  Each SAS has one port, an "S" or "slave" port.  Each
concentrator has one or more "M" or "master" ports for its slaves, and
either an S port if it is a Single Attachment Concentrator or both an A and
a B if it is a Dual Attachment Concentrator to connect to the rest of the
ring.


Vernon Schryver
vjs@sgi.com