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Transmission Code for CSMA/CD

IP.com Disclosure Number: IPCOM000034243D
Original Publication Date: 1989-Jan-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Haas, LC: AUTHOR

Abstract

The detection of transmission collisions between stations using a CSMA/CD access method is important and difficult. In order to perform the collision detection function many systems require careful balancing of the signals by controlling the path loss and/or the transmitted signal. Other CSMA/CD systems must add additional equipment that performs or aids the detection of collisions but does not otherwise increase the transmission performance. This transmission code provides for the detection of collisions, eliminating the need to match transmission levels and does not require additional monitoring equipment. In addition, no increase in bandwidth is required. The signal is baseband, and removes any DC from the NRZI (non-return to zero invert) input data stream.

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Transmission Code for CSMA/CD

The detection of transmission collisions between stations using a CSMA/CD access method is important and difficult. In order to perform the collision detection function many systems require careful balancing of the signals by controlling the path loss and/or the transmitted signal. Other CSMA/CD systems must add additional equipment that performs or aids the detection of collisions but does not otherwise increase the transmission performance. This transmission code provides for the detection of collisions, eliminating the need to match transmission levels and does not require additional monitoring equipment. In addition, no increase in bandwidth is required. The signal is baseband, and removes any DC from the NRZI (non-return to zero invert) input data stream. The transmission code is as follows: There are three voltage levels (for example: +5

V, 0 V, and -5 V).

Coding is as follows:

- A positive transition from 0 to 1 is

sent as a positive pulse.

- A negative transition from 1 to 0 is

sent as a negative pulse.

- A bit of the same value as the previous

bit is sent as a zero voltage level. This code is ideally suited for data which is transmitted in the NRZI format with the incorporation of zero-bit stuffing as in SDLC or HDLC. Long runs of a steady up or down level do not occur when the NRZI with bit-stuffing format is used. The drawing illustrates possible sample waveforms. Collision detection is done by card logic which detects err...