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5.2 10BASE-T Components

Twisted-Pair Patch Cables

A common error when connecting a computer to a twisted-pair segment is to make the connection with the widely available "silver satin" patch cable typically used to connect telephones to a telephone jack. The problem is that the typical silver satin patch cable used for telephones does not have twisted wire pairs in it. This lack of twisted pairs results in excessive signal crosstalk and can cause "phantom collisions." This occurs because collisions are detected in twisted-pair Ethernet by the simultaneous occurrence of signals on the transmit and receive wire pairs. Excessive crosstalk signals can look like simultaneous traffic and can falsely trigger the collision detect circuit.

This can result in "late collisions," which are collisions that occur too late in the transmission of an Ethernet frame. A normal collision results in the immediate retransmission of a frame by the Ethernet interface. However, a late collision results in a lost frame that must be detected and retransmitted by the application software. Retransmission by the application is a lot slower and can lead to a severe loss of application performance over the network. This problem can be avoided by using only twisted-pair patch cables rated for use in twisted-pair Ethernet systems.

Quick Reference Guide to 10BASE-T Twisted-Pair Ethernet - 04 SEP 95

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