T1 Line Definition | The Interactive Glossary

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The T1 line was developed in 1962 by AT&T Bell Laboratories as the first in a series of hardware specifications for digital transmission of telephone calls. The original T1 specification is capable of carrying 24 transmissions, each carrying a single voice or data stream. The T1 line was originally developed to serve as a trunk line to connect to hubs on a network. However, just a few years after the release of the T1 line, bandwidth demands were such that bundles of T1 lines and upgraded lines were necessary.

A single T1 line is capable of transmission speeds of approximately 1.5 megabits per second (mbps). T1 lines can be bonded together, with each additional line boosting the connection speed by an additional 1.5 mbps. While a single T1 line is quite slow when compared to typical broadband connection speeds, bonded T1 lines are a popular option for businesses for a few reasons:

• T1 lines provide the same “always on” peformance of other broadband connections.
• T1 lines can be bonded to provide speeds comparable to other broadband connections.
• A T1 connection establishes a dedicated point-to-point connection between the connected network, the Internet service provider (ISP), and the Internet, resulting in more reliable service and fewer connectivity issues than broadband connections.
• T1 lines are typically backed by a Service Level Agreement (SLA) that provides a financial incentive for the ISP to provide 100% uptime, and financial renumeration in the event that connectivity issues are experienced.

Also See: T3 Line, Broadband, Bandwidth, Ethernet

Frequently Asked Questions

Is a T1 line fast enough for my business?

A single T1 line provides 1.5 Mbps of bandwidth. In the early days of the Internet, that qualified as a blazing fast connection. However, today it's likely that you'd quickly grow frustrated by a single T1 connection when attempting to view streaming video, upload large files to cloud storage, or perform anything more demanding than simple web browsing. For this reason, T1 lines are now rarely sold unbundled. A business that needs the dependability of a physical point-to-point connection with an ISP will typically purchase several bundled T1 lines to have a rock-solid Internet connection backbone, and then add supplementary bandwidth with an Ethernet connection for fast speeds during typical day-to-day operation.

Why are T1 lines expensive to install?

Since T1 connections establish a point-to-point connection between an ISP and the organization purchasing the connection, it is often necessary to install new physical lines between the entity purchasing the connection, and the nearest direct connection point to the ISPs network. As a result, establishing a T1 connection may be quite expensive if doing so involves the installation of a lot of physical cables.

Is a T1 connection always carried over the hardware developed by AT&T in the 1960s?

When an ISP offers a T1 or DS1 connection today, quite often they are planning on delivering that connection using hardware technology that represents and upgrade over the T1 line developed decades ago by AT&T. In today's IT world, T1 is usually used to define a connection that is offered in 1.5 Mbps increments, provides a direct point-to-point connection with the ISP, and is backed by an SLA.