🚀 go-pugleaf

In article <GAH.92Nov18150548@HP370T.trc.mew.mei.co.jp>, gah@trc.mew.mei.co.jp (Gary A. Hildebrand) writes:
> 
> Let's imagine a hypothetical case.  You want to implement minimal data
> transport over FDDI, with just enough MAC/SMT support for somewhat robust
> LLC, and nothing more.  You don't care about MIB management or SRF's at
> this point.  Anyone who's read through the FDDI standards can tell you what
> is perscribed as mandatory and what is optional, but how much can you
> really get away with?  In a real implementation, are any SMT frame services
> absolutely essential for keeping the ring up?  NIF frames immediately come
> to mind.  What about the many different types of CMT services and
> functions?  I would suppose that most nodes would cause trouble if they
> didn't all implement full RMT and PCM support in or out of the MAC
> chip/software layer.

All you need to play with other standard-conforming FDDI stations
and concentrators is CMT signalling.  You need none of the frame
management stuff including NIF's.  The ring will work just fine even
if other stations' ring maps are bogus.

By "play", I mean just that.  You can't sell a real product that does
not do all of the mandatory stuff in SMT 6.x.  Too many of your biggest
potential customers would run screaming.

> This case is actually not so hypothetical.  I'm wondering about PC FDDI
> interface cards such as the one from Network Periperals.  Does the small
> NDIS driver loaded and/or firmware on the board actually implement all the
> ANSI-draft-standard mandatory components of the MAC/SMT protocols that are
> not covered by the National chipset, or just a bare minimum functional
> subset?  Unfortunately, this board comes with little or no technical
> information.

For many reasons, from the people involved to their evident intention
to make a profitable product to the test beds their systems have been
seen on, I would be very surprised if NPI's products failed to
implement more than just the mandatory part of SMT 6.x or if they do
not soon conform to SMT 7.2.

As you say, there are a lot of messy SMT frames.  I think a case can be
made that handling the SMT frames is about as complicated as doing
TCP/IP.  Fortunately, a straight forward implementation of the
mandatory SMT frames (or of TCP/IP) is not hard, at least for computers
of this decade.  That's shown by the nearly universal support of SNMP
in FDDI concentrators and even ethernet twisted pair hubs.

Ironically, some in ANSI X3T9.5 justified much of the SMT frame based
stuff on the grounds that most stations and concentrators could not
afford TCP or TP4 stacks and so could not use SNMP or CMOT.  The
company that pushed that view hardest was in the business of selling
SMT implementations to other vendors.  Most ironically, that company
was soon seen at test beds with SNMP managed products.


Vernon Schryver,  vjs@sgi.com