Browse Prior Art Database

CSMA/CD Baseband Network Collision Detection

IP.com Disclosure Number: IPCOM000036569D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 5 page(s) / 182K

Publishing Venue

IBM

Related People

Bischoff, RA: AUTHOR [+4]

Abstract

This article describes a circuit arrangement which utilizes a differential voltage discriminator (DVD) to detect the voltage surge that occurs during a collision in a carrier sense multiple access (CSMA)/collision detection (CD) baseband network; then use this result to assure detection with the conventional detection method which is a cyclic redundancy check (CRC).

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CSMA/CD Baseband Network Collision Detection

This article describes a circuit arrangement which utilizes a differential voltage discriminator (DVD) to detect the voltage surge that occurs during a collision in a carrier sense multiple access (CSMA)/collision detection (CD) baseband network; then use this result to assure detection with the conventional detection method which is a cyclic redundancy check (CRC).

When more than one station (node) on a CSMA/CD local area network (LAN) transmits data at the same time, it will result in a data collision. In a personal computer (PC) baseband LAN adapter, as shown in block diagram in Fig. 1, the collision detection is accomplished in the LAN controller (Intel 82588) by either comparing the corresponding CRC results of the transmitted data and of the received data at a specific interval during transmission or detecting the CRC error at the end of the transmission.

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However, when baseband network stations are connected in a daisy chain configuration, due to the strong signal overriding weak signal effect, sometimes the data collision for some nodes may escape undetected. The circuit disclosed herein is an effective way to detect the data collision on such a daisy chain configuration.

Fig. 2 is a block diagram of the circuit implementation of the PC baseband LAN network daisy chain configuration with a multi-drop bus topology of this disclosure. SN75172 is chosen as the media driver. It is an RS-422 three-state output differential line driver which has the capability to drive for 100 ohms terminated transmission line. When data collision occurs, more than one station is transmitting data. The load impedance to the transmission node media driver is changed, which results in a media driver output voltage level surge (increase). By adding a DVD (level comparator) to...