From: my@dunkin.nsc.com (Mike Yip)
Newsgroups: comp.dcom.lans.fddi
Subject: Re: Minimal MAC/LLC
Date: 19 Nov 92 05:05:09 GMT
Reply-To: my@dunkin.nsc.com
Organization: National Semiconductor Corp.

In article 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.

Go ask Vernon.  He did that also. ;-)
You don't even need SMT to run FDDI.  I ran a good size
FDDI ring without SMT when our chips first come out.  But if you want
some SMT functionality, then you can probably pick the part that you need.
For example, you can use (all or part of) RMT and CMT in your ring.  If you 
just want to "connect" to the "standard" FDDI ring, you can probably get by
with only PCM and some sort of real simple RMT/CFM.  The problem comes when
something goes wrong.  When the ring is not working right, SMT can help you
to detect and recover from some or most errors.  Do you really need
any of the frame services?  May be not.  But then someone will tell you
that they cannot manage those stations (tell them to get lost or use SNMP ;-)

>
>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.

Well I don't speak for NPI (and I don't even speak for National), but I think
that NPI has a 100% complete 6.2 SMT.  I don't think that they implemented
all the optional SMT stuffs.  After all, those are optional, right?

All the MAC protocols and more are implement on the National chipset.
The NPI "SMT processor" on board implements the CMT and RMT and possibly some
portion of the frame driver.  The rest runs on the system driver.  

Along the same line, I really don't think that one should associate the 
size of the program with the completeness, robustness, etc., of the program.
But then again, if you prefer to have huge driver to make you feel better, 
you can always patch their code with white space.  ;)  They need to spend
extra time to make the driver small so that it will work in the PC, especially
DOS (or DOG ;-).

---
| Michael Yip			Email: my@berlioz.nsc.com
| National Semiconductor Corp	Voice: (408) 721-5148
| 
| Of course, this is my own opinion!