T-span

Digital Signal 1 (DS1, sometimes DS-1) is a T-carrier signaling scheme devised by Bell Labs. DS1 is the primary digital telephone standard used in the United States and Japan and is able to transmit up to 24 multiplexed voice and data calls over telephone lines. E-carrier is used in place of T-carrier outside the United States, Japan, and South Korea. DS1 is the logical bit pattern used over a physical T1 line; in practice, the terms "DS1" and "T1" are often used interchangeably.

T1 refers to the primary digital telephone carrier system used in North America. T1 is one line type of the PCM T-carrier hierarchy. T1 describes the cabling, signal type, and signal regeneration requirements of the carrier system.

Source: Fiber Optics Standard Dictionary; T1 Overview (Motorola, 1996)

The signal transmitted on a T1 line, referred to as the DS1 signal, consists of serial bits transmitted at the rate of 1.544 Mbps. The type of line code used is called Alternate Mark Inversion (AMI). Digital Signal Designation is the classification of digital bit rates in the digital multiplex hierarchy used in transport of telephone signals from one location to another. DS-1 is a for multiplexing the bitstreams of up to 24 telephone calls, along with two special bits: a framing bit (for frame synchronization) and a maintenance-signaling bit, transmitted over a digital circuit called T1. T1's maximum data transmission rate is 1.544 megabits per second.

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