From: koning@koning.enet.dec.com (Paul Koning)
Newsgroups: comp.dcom.lans.fddi
Subject: Re: SMT Standard
Date: 13 Apr 92 18:13:28 GMT
Reply-To: koning@koning.enet.dec.com
Organization: Digital Equipment Co., distributed systems architecture


In article <1992Apr9.132017.3551@doug.cae.wisc.edu>, wittmann@engr.wisc.edu (art wittmann) writes:

|>So what does this mean for Joe Average NetManager?  Should one wait for 7.X
|>complient adaptors, hubs & routers?  Is SMT typically implemented in 
|>firmware/software or in hardware?  As I understand it, and my understanding
|>is pretty limited, there should be only one SMT entity per device (i.e. not
|>per connection).  To me that implies that SMT would often be implemented in
|>a driver on host computers since a single host could have more than one
|>ring connection.  Is that true, and therefore would imply that only certain
|>drivers would have to be upgraded?  In the case of routers & hubs, can
|>any similar statements be made?
|>
|>So many questions, so little knowledge (on my part).
|>
|>Thanks,
|>Art
|>
|>=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
|>Art Wittmann                                  Phone: (608) 263-1748
|>Network Manager                               Email: wittmann@engr.wisc.edu
|>Computer Aided Engineering Center                or: wittmann@cae.wisc.edu
|>University of Wisconsin, Madison

Couple of comments...

There's one SMT entity per STATION.  That's not really an answer, it's really
more a definition of what a station is.  So what is a station?  Ignoring
obscure cases, it's a thing with either an S port or an A/B port pair, plus
optionally (i.e., if it's a concentrator) some M ports.  A station usually
has a MAC or sometimes two.  Think of them as similar to an Ethernet station,
though with a bunch of complexity added.

So, if you look at a router and see four ports, two A and two B, then there
are two stations in that box.  If the four ports are all S ports, then there
are FOUR stations in the box.  Doesn't matter much; the higher layer is
really only concerned with the MAC.  The router cares how many MACs there
are but not particularly about what's holding them together.

As for waiting for 7.x, if you are otherwise ready to install FDDI, I'd 
suggest (a) don't want, but (b) select products that are easy to upgrade.

The only really crucual part of SMT is CMT -- the part that allows stations
to connect to the ring.  I'm sure Vern can think of some eloquent phrases
to describe the rest...  Anyway, CMT hasn't changed significantly in a LONG
time, so there is no reason to wait; current implementations will get you
a perfectly useable network.

In the long run, however, you will want to get the latest SMT, if only to
conform to the standard as it actually gets approved.  So what is SMT?  In
most implementations, it's a mix of things, but much of it tends to be
"firmware".  In traditional designs you'd find that in ROMs that would have
to be swapped.  Some suppliers (the one I work for is one) have moved the
firmware into writable memory, so you can "down line upgrade" it without
having to do surgery on all your boxes.  Ease-of-upgrade features along those
lines are useful -- the state of SMT is only one of the arguments for this
(and not even the strongest, I'd say).

	paul