Introduction to Data Communications
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36d. IEEE 802.3a 10Base2

Uses RG-58A/U coaxial cable, 0.2 inch in diameter. The cable is flexible and easy to work with. The cable has a characteristic impedance of 50 ohms.

Connection to the workstation is made with either a MAU - Medium Attachment Unit/Transceiver or directly to the NIC using a BNC TEE.

Most NICs have the MAU built-in for 10Base2. The 3C509 card in the lab have built-in MAUs for Coax (10Base2) and Twisted Pair (10BaseT). They also have a AUI connection for an external MAU such as used in 10Base5. You can buy MAUs for 10Base2 and 10BaseT if your NIC does not have them already built-in.

Cable Termination and Connector

The standard termination is 50 +/-2 ohms. The end connector is an "BNC" twist and lock type connector. The cable is externally terminated with a special terminating BNC connector. BNC stands for Bayonet Navy Connector.

Grounding

To minimize noise on the segment, the cable is floating. The IEEE 802.3a specifications calls for all BNC connectors and TEEs to be insulated. A common problem with 10Base2 is having the barrel of the BNC connector touching a heating duct or computer chassis. The shield should be floating, it is not connected to electrical ground.

Introduction to Data Communications
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