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Contrast this technology with circuit switching, in which a dedicated path from sender to receiver is established and maintained throughout the conversation.

T-Series Connections

The T-series connections are digital connections that you can lease from the telephone company. They can use regular copper pairs like regular phone lines, or they can be brought in as part of a backbone (also called a trunk line). At this point, T-series connections use time division multiplexing (TDM) to divide the bandwidth into 24 channels plus a control line.

The T-series connection types are rated by the letter T plus a number. Each connection type differs primarily in its speed. Table 7.2 lists some of the T-series connections and their maximum data rates. The most commonly used T-series lines are T1 and T3.

TABLE 7.2 T-Series Connections


Maximum Speed











The T1 Connection

A T1 is a 1.544Mbps digital connection that is typically carried over two pairs of UTP wires. This 1.544Mbps connection is divided into 24 discrete, 64Kbps channels (called DS0 channels). Each channel can carry either voice or data. In the POTS world, T1 lines are used to bundle analog phone conversations over great distances, using much less wiring than would be needed if each pair carried only one call. This splitting into channels allows a company to combine voice and data over one T1 connection. You can also order a fractional T1 channel that uses fewer than the 24 channels of a full T1.

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