T1 (also referred to as DS1) is a standard for digital transmission over phone lines at 1.544 Mbps.
It is split into 24 channels of 64Kbps each. In the original standard, signalling was inband (robbed bit signalling). Now T1s are often "clear channel" and all bits are available for data.

Each 64Kbps channel (also known as a DS0) can carry data or voice traffic, and two or more channels can be combined into one higher speed data channel.

T1s are often used to deliver phone connections to a PBX in blocks of 24 lines.
ISDN Primary Rate PRI lines are delivered over T1 circuits in the USA.

A channelbank can convert a T1 to 24 analog phone lines.

T1s are also used to deliver high-speed data service.

A T1 connection is established by providing a "loop" or wire from the users premises to the CO where the service provider has equipment.

Once the connection reaches the "CO" it can access the carriers network and reach any destination.

A good overview on the fundamentals of digital telephony, digital voice, basic TDM, and T-1 and E-1 applications is the T-1/E-1 Technology Primer, published by Intel Corporation in 2001.

See Also

• DSx Digital Signal X
• T1 over IP transport T1 circuits over an IP network
• E1: The European standard used as a replacement for T1
• T1 Crossover Cable T1 null modem cables
• All You Wanted to Know About T1 But Were Afraid to Ask

Commercial Vendors (T1 lines)

• Alfaintercom T1
• Bandwidtht1 T1