Ref: 08260006
Title: Running 3+Open on ARCNET or Other Media
Date: 9/28/90

Copyright 3Com Corporation, 1991.  All rights reserved.

Note: this tip assumes the reader is somewhat familiar with NDIS
(Network Driver Interface Specification) architecture and technology.
For a good overview of both, see the article "Exploring NDIS,"
LAN Magazine, October 1989.

It is well-known that 3Com's 3+Open runs on both Ethernet and Token Ring
media.  But some customers have a large installed base of Arcnet (or other
media) adapters, and they also want to benefit from the features of the
client-server model as implemented by 3+Open/LAN Manager.  Can they do
this?  If so, how?

First, let's understand how it is possible to run the same 3+Open protocol
drivers on either Ethernet or Token Ring adapters, without modification.

All 3+Open protocols use a common method of accessing network adapters
for transmitting and receiving frames, initialization, and control.  The
methodology is based on the NDIS.  The NDIS interface requires that the
protocol create the portion of the MAC-level frame that is to be transmitted,
starting at the frame header and ending with the user data.

The frame header includes the destination and source addresses and certain
other frame control information that varies from media to media.  The
Ethernet frame header is different than Token Ring, which is different from
Arcnet.

The protocol can create the appropriate header because the MAC driver below
it recognized the media on which it is running.  The MAC exposes this
information in a shared data structure called the MAC Service-Specific
Characteristics table.  The protocol looks at this data structure to learn
which type of MAC it is binding to at initialization time, and subsequently
creates (and expects to receive) all frames in the specified format.

Currently, all 3+Open protocols process only Ethernet and Token Ring frame
headers.  However, it is possible for 3+Open protocols to run on other media
that use neither Ethernet nor Token Ring frame headers.  The MAC driver can
be written to translate the native media frame headers to and from either the
Ethernet or Token Ring types.  It can then advertise itself in the
MAC Service-Specific Characteristics table as being of type Ethernet or Token
Ring accordingly.  Doing this would produce an insignificant penalty in
performance and it would allow new capabilities, such as 3+Open running on
Arcnet.

Note:  Any version of NDIS drivers (including drivers written to the new
NDIS 2.0.1 spec) will run with any version of LAN Manager, including LAN
Manager 2.0.
