Browse Prior Art Database

Standard PC-NET Adapter and Software CSMA or CSMA/CA on Non-traditional Media

IP.com Disclosure Number: IPCOM000109213D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 4 page(s) / 217K

Publishing Venue

IBM

Related People

Cato, RT: AUTHOR

Abstract

The Wireless-LAN (Wireless-Local Area Network) area of technology is presently booming with many offerings available and more on the way. Wireless-LANs (WL-LANs) include RF-LANs, power line communication LANs, and Infrared-LANs. By far and large, the WL-LANs only use a form of Carrier Sense Multiple Access (CSMA) communication protocol (listen before talk), because of the difficulty in detecting collisions. There is usually some relatively simple form of collision avoidance used as well so that the protocol is sometimes known as CSMA/CA.

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Standard PC-NET Adapter and Software CSMA or CSMA/CA on Non-traditional Media

       The Wireless-LAN (Wireless-Local Area Network) area of
technology is presently booming with many offerings available and
more on the way.  Wireless-LANs (WL-LANs) include RF-LANs, power line
communication LANs, and Infrared-LANs.  By far and large, the WL-LANs
only use a form of Carrier Sense Multiple Access (CSMA) communication
protocol (listen before talk), because of the difficulty in detecting
collisions.  There is usually some relatively simple form of
collision avoidance used as well so that the protocol is sometimes
known as CSMA/CA.

      The IBM PC-NET local area network uses CSMA/CD (carrier sense
multiple access with collision detection) communication protocol.
There is extensive software available that supports PC-NET and its
place in the OSI stack.  There is also a PC adapter that is involved
in the PC-NET protocol, and which also interfaces to the "physical
layer" hardware that connects to the actual wires or coax.  The
"physical layer" hardware is on a daughter card on the adapter card.
Different daughter cards enable a single PC-NET card to support
either base-band or broad-band PC-NET.  This article describes how
new daughter cards could be designed that would allow standard PC-NET
adapter cards and software to fully function, including collision
detection, on radio, infrared, power line, or other appropriate
non-traditional (not wire or coax) mediums.

      WL-LANs were developed to provide a simple, inexpensive way to
connect digital devices together.  Eliminating the wires produces a
significant cost and convenience advantage. Essentially, all WL-LANs
were developed using a form of CSMA communication protocol because it
was understood, mostly standardized, relatively simple, and provided
the much desired peer to peer communications.

      The PC-NET protocol is CSMA/CD, which is CSMA with collision
detection.  A common problem with radio and other non-traditional
mediums is that a station can only hear itself transmitting while it
is transmitting.  Being able to hear other stations' transmissions is
critical to collision detection.  Thus, all radio systems known to
the author do not detect collisions.  This article describes how the
PC-NET CSMA/CD protocol can be "fooled" into acting like either zero
persistent CSMA or CSMA/CA.

      The easiest way to use RF with PC-NET is to design the
"physical layer" hardware so that the signal to be transmitted is
also fed directly back into the PC-NET protocol hardware (on its
receive line) when the station is transmitting.  This could be done
with an AND/OR circuit on the daughter card (see Fig. 1).  Since the
PC-NET protocol hardware will never hear any other station
transmitting while it is transmitting, no collision will ever be
detected.  This would defeat or eliminate the collision detection
function of PC-NET.  Since PC-NET stations waiting for access t...