What Is a T1 Communications Line?

by Herb Kirchhoff

A T1 communications line is a dedicated digital, high-speed phone line that is 24 times faster than a standard phone line, according to TechTarget.com. T1 has a transmission capacity of 1.544 million bits per second, or mbps, as compared to a phone line's 64,000 bits per second. Provided over copper wire, fiber optic lines or by wireless connections, a T1 line can be subdivided electronically into 24 standard phone lines or used as a single 1.544 mbps channel.


T1 lines are used mainly by businesses, colleges, Internet access providers and government agencies with high volumes of communications traffic, says TechTarget.com. T1 service is too expensive for home or small-business use, although some telephone companies sell fractional T1 service for small businesses at half or a quarter the capacity of a full T1 line.


The history of the T1 line is actually a long one. T1 lines are part of a digital T-carrier system introduced in the old AT&T; Bell System in the 1960s. T-carriers were the first successful implementation of digitized voice transmission, said TechTarget.


T-1 lines can reach out about a mile without being boosted. Longer distances require a booster device known as a repeater. T-carriers are used over short distances, less than 15,000 feet. For longer hauls across town or between cities, the phone companies interconnect T1 lines with ultra-high-speed, fiber-optic-backbone telecommunications networks that link America's cities and states to each other.

Analog Conversion

T1 carrier systems work with legacy analog voice systems seamlessly. T1 systems convert analog voice to digital bits by sampling the analog signal 8,000 times a second and converting each sample into an 8-bit word, said TechTarget. If digitizing 24 channels at once, each sample becomes a 192-bit frame. The system transmits 8,000 frames each second, with each frame separated by a single bit. Other countries use different digital-carrier sampling and format standards, but the general conversion idea is the same.

When to Switch to T1

In general, a business should consider T1 service when it needs reliable high-speed Internet access for 20 or more employees, or if the office hosts email or a Web server, said the experts at T1Link.com. Alternatives such as cable or DSL are shared services that can slow down during peak usage hours, but a T1 line never slows down because it is dedicated exclusively to one business. In addition to reliable Internet access, a T1 line also can reduce voice service charges. T1 service in most cities is highly competitive, so comparing prices among competing vendors is wise.

About the Author

Herb Kirchhoff has more than three decades of hands-on experience as an avid garden hobbyist and home handyman. Since retiring from the news business in 2008, Kirchhoff takes care of a 12-acre rural Michigan lakefront property and applies his experience to his vegetable and flower gardens and home repair and renovation projects.

Photo Credits

  • photo_camera telephone terminal image by Vonora from Fotolia.com