Introduction to Data Communications
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36c. IEEE 802.3 10Base5

Coaxial Cable

Uses double shielded 0.4 inch diameter RG8 coaxial cable about the size of a garden hose. The cable is not flexible and difficult to work with. The cable has a characteristic impedance of 50 ohms.

Connection to the workstation is made with a MAU - Medium Attachment Unit or Transceiver. The MAU physically and electrically attaches to the coaxial cable by a cable tap. The cable is pierced and a connection is made by a screw to the center conductor.

The MAU is connected to the NIC (Network Interface Card) by the AUI (Attachment Unit Interface) cable. The AUI port on a NIC and a MAU is a DB15 connector. Maximum AUI cable length is 50 m.

Cable Termination and Connector

The standard termination is 50 +/-2 ohms. The end connector on the RG-8 cable is an "N" type connector. The cable is externally terminated with a resistor inside an N connector.

Grounding

To minimize noise on the segment, the cable is grounded at the termination at only one end.

Maximum Nodes on a cable segment

On any 1 cable segment, the maximum allowed number of nodes or MAUs is 100.

Minimum Distance between nodes

Minimum distance between nodes or MAUs is 2.5 m or 8 feet.

Velocity of propagation

The speed of the signal through the cable is 0.77c. ("c" is equal to the speed of light - 300,000,000 m/sec). The velocity of propagation for 10Base5 specification cable is equal to 0.77 x 300,000,000 m/sec. This is determined by cable capacitance. Maximum coaxial cable segment length 500 m

The maximum segment length is 500 m or a maximum 2.165 uSec propagation delay. Propagation delay is what actually determines the maximum length of the segment.

Introduction to Data Communications
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