Joined: 25 Apr 2006
|Posted: Sun Jan 04, 2009 11:56 am Post subject: T1s
T-1 (or T-carrier) is a generic designator for telecommunications carrier systems that transmit digitized data through a series of channels, or a multiplex system.
The T-carrier system is entirely digital, using pulse code modulation and time-division multiplexing (TDM). The system uses four wires and provides duplex capability (two wires for receiving and two for sending at the same time). The T1 digital stream consists of 24 64-Kbps channels that are multiplexed. (The standardized 64 Kbps channel is based on the bandwidth required for a voice conversation.) The four wires were originally a pair of twisted pair copper wires, but can now also include coaxial cable, optical fiber, digital microwave, and other media. A number of variations on the number and use of channels are possible.
In the T1 system, voice signals are sampled 8,000 times a second, with each sample digitized into an 8-bit word. With 24 channels being digitized at the same time, a 192-bit frame (24 channels each with an 8-bit word) is thus being transmitted 8,000 times a second. Each frame is separated from the next by a single bit, making a 193-bit block. The 192 bit frame multiplied by 8,000 and the additional 8,000 framing bits make up the T1's 1.544 Mbps data rate. The signaling bits are the least significant bits per frame.
Standard T-1 can transmit data at a rate of 1,544,000 kilobits-per-second (1.5 Mbps).
A T-3 (a.k.a. DS-3) is the equivalent to twenty eight T1 lines. It can transmit data at a rate of 44,736,00 bits-per-second (45 Mbps). Typically used to transfer high quality full screen video feeds.