Differences Between DSL & T1 Lines

In the United States, telephones are traditionally connected to a service provider's network through a local loop -- a pair of twisted copper wires. Human voices have a frequency range of 0 to 3,400 hertz, but copper telephone wires have the ability to handle frequencies up to several million hertz. DSL technology transfers digital data in frequency ranges higher than 3,400 hertz, allowing a regular copper telephone line to be used for both voice and data transfer.

High speed T1 connections, delivered over dedicated four-wire fiber access, are able to carry larger packets of data than a traditional telephone line. A T1 line combines 24 channels, each with a speed of 64 Kbps, to transmit data at a speed of 1.54 Mbps.

Multiple DSL phone lines are connected to a DSL access multiplexor (DSLAM), which is connected to the Internet through a single port. When many users are competing for bandwidth, there may be a bottleneck at the DSLAM, slowing DSL connection speeds. T1 lines establish a direct connection to the Internet through a dedicated 1.5 Mbps port, which allows a T1 line to deliver a consistent 1.54 MBps connection speed.

Data signals moving through traditional telephone wiring degrade with distance. The further a customer is from their carrier, the slower the connection speed. T1 lines offer consistent and dependable connection speeds of 1.54 Mbps, regardless of distance from the service provider.

Modern telephone installations may include a fiber-optic transmission system known as fiber-in-the-loop (FITL). DSL signals are only passed through copper wiring, so DSL will not be available in areas where a portion of the telephone circuit comes through fiber-optic cables. T1 service is delivered through a dedicated line that can be installed almost anywhere.

Asymmetric DSL (ADSL) is the type most commonly used in homes and small businesses. ADSL has fast download speeds but significantly slower upload speeds. Symmetric DSL (SDSL) has matching upload and download speeds, but is generally only marketed as a premium business service. A T1 line is 1.54 Mbps for both uploads and downloads.

The most noticeable difference between DSL and T1 lines is the price. T1 subscription prices can be as much as 10 times more than ADSL subscription prices. In addition, laying a T1 line to a service location costs considerably more than installing DSL on a pre-existing phone line.