Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!amdcad!sdjmc
From: sdjmc@amdcad.AMD.COM (John McCool)
Newsgroups: comp.dcom.lans
Subject: Re: Starlan/Ethernet compatibility
Message-ID: <26111@amdcad.AMD.COM>
Date: 24 Jun 89 20:39:47 GMT
References: <2009@wasatch.utah.edu> <2230006@hprnd.HP.COM> <26097@amdcad.AMD.COM> <36666@sgi.SGI.COM>
Reply-To: sdjmc@amdcad.UUCP (John McCool)
Organization: Advanced Micro Devices
Lines: 38

In article <36666@sgi.SGI.COM> vjs@rhyolite.wpd.sgi.com (Vernon Schryver) writes:
>
>However, after the votes for less than compelling changes taken in the
>X3T9.5 FDDI SMT meeting on Wednesday, I am a little puzzled by someone from
>AMD defending the standards process.  Can the FORMAC capture the 6 byte
>info field in the newly required "directed beacon"?  If not, how might one
>build a network manager with the "SUPERNET Family for FDDI"?  (I understand
>the FORMAC can at least send them, unlike the silicon of a big computer
>computer vendor.)

I would like to clarify the operation of FDDI rings during recovery to 
avoid confusion. The short answer to Vernon's question is Yes.

Here's the long answer:


AMD's SUPERNET chipset for FDDI is capable of sending
directed beacons during ring recovery. In addition, the chip set WILL  
receive beacons in buffer memory if the destination address
matches the node's address (or is a broadcast).

The FDDI MAC State Machines, however, may
prevent reception of ANY FRAME during the ring recovery process. During
ring recovery, the token passing protocol for transmission no longer holds.
Several stations on the ring may be transmitting (beacons, claims,
etc.) Under these conditions, an FDDI station will stop transmission on
reception of a beacon frame. Subsequent directed beacons arriving before TMAX 
time will be received and repeated.

Note that normal 'failed claim' beacons are not
received by stations as their destination address = null. This is done
to prevent buffer overflows during non-fatal physical layer reconfigurations.

John McCool
Advanced Micro Devices
802.3 Network Products   
(408)749-2302