T-Carrier and E-Carrier
AT&T designed its T-carrier system to allow the grouping of individual channels together into larger units. A T2 line, for example, consists of four aggregated T1 lines. Similarly, a T3 line consists of 28 T1 lines. The system defined five levels — T1 through T5:
Leased Line Internet Service
Some internet providers offer T-carrier lines for businesses to use as dedicated connections to other geographically separated offices and to the internet. Businesses use leased line internet services to offer T1, T3 or fractional T3 levels of performance because those are the most cost-effective options.
More About T1 Lines and T3 Lines
Owners of small businesses, apartment buildings, and hotels once relied on T1 lines as their primary method of internet access before business-class DSL became prevalent. T1 and T3 leased lines are high-priced business solutions that are not suitable for residential users, especially now that so many other high-speed options are available to homeowners. A T1 line does not have nearly enough capacity to support significant demand for internet usage nowadays.
Besides being used for long-distance internet traffic, T3 lines are often used to build the core of a business network at its headquarters. T3 line costs are proportionately higher than those for T1 lines. So-called “fractional T3” lines allow subscribers to pay for a lesser number of channels than a full T3 line, lowering leasing costs somewhat.
