With 672 distinct phone channels and 45 Megabytes of Internet capacity, a T3 line has the same speed as 28 T1 lines in terms of telecoms standards. T3 connections use coax cables to transmit data, though some portions may also use fiber optic cables. A DS3 (Digital Signal Level 3) line is another name for a T3 connection.

T3 lines link telephone switching hubs to the telephone network, allowing encoded speech conversations and other data to be transmitted from one location to another. Companies also provide T3 lines for corporations, colleges, and other organizations as specialized Internet links.

The Bell Laboratories-created T-carrier system, also known as T1 and T3 lines, is a leveled digital communication system. Each version of the standard, T1 through T5, is several times quicker than the one before it. Only T1 and T3 were widely used.

T3 connections are becoming less common as a result of newer network technologies. Some Providers have completely phased out their copper wire networks because their copper wire backbone is slower than the fiber-optic connections that are replacing it.