re:AppleTalk broadcast addr on FDDI

["Ben (B.T.) Schmidt" <[e-mail]>]

In msg "AppleTalk broadcast addr on FDDI", '[e-mail]' writes:

>Could someone please tell me what is the AppleTalk broadcast address
>on FDDI. Is it 0x090007ffffff or 0xffffffffffff? I thought it was the
>former one but I saw the FDDITalk that came with the Impulse Technologies'
>FDDI cards use 0xffffffffffff for AppleTalk broadcast.

I'd agree with your first "impulse". :)  rgds, ben  <[e-mail]>

PS. No chance that was an IP broadcast coming from the FDDI-attached Mac?

--->forwarded msg
Date: Thu, 27 Feb 1992 08:54:56 -0800
To: [e-mail] (Mississipi Mud)
From: [e-mail]
Subject: Re: fdditalk
Cc: [e-mail]

The following is the text of the document FDDITalk that is found on
AppleLink.  I hope this helps.  John Veizades...

------------------------------------------------------------

FDDITalk: Preliminary Proposal
Apple Computer, Inc.
March 8, 1991

This document represents a proposed definition for how AppleTalk protocols
should be implemented on FDDI (that is, for "FDDITalk").  This proposal
should be considered as highly preliminary and subject to change.  Apple
will be publishing an official definition of FDDITalk at some point in the
near future.

The proposed definition of FDDITalk is simple and easy to state: FDDITalk
is precisely the same as EtherTalk Phase 2.  Although this is a slight
oversimplification, it is true from an overall point of view.  To be more
accurate, FDDITalk packet formats, at the 802.2 level, are precisely the
same as those used by EtherTalk.  Specifically, AppleTalk data packets and
AppleTalk Address Resolution Protocol (AARP) packets on FDDI have exactly
the same format as those on Ethernet (802.3) when looked at from the LLC
level (MAC headers will of course be different).

FDDITalk packets, like EtherTalk packets, are encapsulated in SNAP headers.
 AppleTalk data packets use SNAP type $080007809B.  AARP packets use SNAP
type $00000080F3.  The AppleTalk broadcast address used by FDDITalk is the
same as that used by EtherTalk, $090007FFFFFF.  The zone multicast
addresses are also the same, $090007000000 through $0900070000FC.  Finally,
the AARP hardware type used by FDDITalk is the same as that used by
EtherTalk, one (1).

At this time, it has not been decided whether AARP timeouts on FDDITalk
will remain the same as those on EtherTalk or not.  The issue of AARP
timeouts on FDDI is currently under investigation.

It is important to note that the actual AppleTalk data (i.e. the DDP
packet) is encapsulated in the FDDITalk packet (that is in the SNAP frame)
in the same way as it is encapsulated in EtherTalk packets.  This means
that the maximum size packets used by AppleTalk on FDDI is in the 600 byte
range (600 bytes plus SNAP, LLC and MAC headers).  The FDDI data link,
however, provides the ability to transmit multiple back-to-back packets on
one token, up to the limit placed by the "token hold timer" (a
MAC-layer-settable parameter).  Through judicious use of this feature, it
should be possible to achievement end-to-end AppleTalk throughput on FDDI
roughly equivalent to that which could be achieved through use of much
larger packets.

FDDITalk is being defined to be the same as EtherTalk due to the emergence
of FDDI-to-Ethernet "transparent" bridges.  These bridges make possible
communication between Ethernet (802.3) and FDDI, at the data link level.
Although communication at this level may or may not be desirable (routing
is often be a better approach), this communication may be necessary in some
environments. Specifically, environments which already have FDDI-Ethernet
bridges installed may desire communication between AppleTalk nodes on both
media without requiring the installation of a router.