Introduction to Data Communications
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36e. IEEE 802.3i 10BaseT

10BaseT uses unshielded twisted pair (UTP) cable. The cable is flexible and easy to work with. The cable has a characteristic impedance of 100 ohms. There are 2 pairs of twisted wires used with 10BaseT. Separate Rx (receive) and Tx (transmit) pairs are used. The lines are balanced lines to minimize noise and there are a Rx+ & Rx- pair and a Tx+ & Tx- pair.

The nodes are connected to a MPR (multiport repeater) also called a Concentrator or Hub. The cables are wired as straight-through cables meaning the Node's Rx & Tx lines connect directly to the Hub's Rx & Tx lines respectively.

Two nodes can be directly connected together bypassing the Hub by using a Cross-over (X-over) cable. In a X-over cable, the Tx and Rx lines are crossed so that one node's Tx lines go to the other nodes Rx lines and vice versa.

Cable Termination and Connector

The standard termination is 100 ohms. The end connector is an "RJ45" quick disconnect connector. The cable is internally terminated at the NIC and Hub.

Grounding

To minimize noise on the segment, the cable is a balanced line with Rx- & Rx+ and Tx- & Tx+. There is no shielding and any noise that appears on the Rx+ wire will appear on the Rx- wire. When the 2 signals are combined, the noise cancels due to Rx- & Rx+ being 180 degrees out of phase.

Maximum Nodes

For 10BaseT, the maximum allowed number of nodes is 128 on one segment.

Maximum Distance between Nodes & Hub

Maximum distance between nodes & Hub is 100 m.

Velocity of propagation

The speed of the signal through the cable is 0.59c. ("c" is equal to the speed of light - 300,000,000 m/sec). The minimum velocity of propagation for 10Base5 specification cable is equal to 0.59 x 300,000,000 m/sec. This is determined by cable capacitance.

Maximum cable segment length 100 m

The maximum segment length is 100 m or a maximum 0.565 uSec propagation delay. Propagation delay not distance is what actually determines the maximum length of the segment. Propagation delay (units are seconds) is calculated by:

What is the propagation delay for a 100 m length of 10BaseT cable?

Introduction to Data Communications
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