Digital Signal 1
T1-DS1 is a PCM-based framing and signaling standard for digital voice and data transmission widely used in telecommunications in North America, South Korea and Japan (E1 is the preferred scheme instead of T1 in the rest of the world). Technically, DS1 (Digital Signal 1) is the logical bit pattern (frame format) used over a physical T1 line; however, the terms "DS1" and "T1" They are often used interchangeably.
When digital transmission began to be a feasible technology compared to analog transmission of information, the CCITT was unable to reach an agreement on an international standard for pulse coding modulation (PCM). This led to the use of several incompatible schemes in different countries around the world.
The T-Carrier (T-Carrier) system, introduced by the Bell System in the United States in the 1960s was the first successful system that supported digitized voice transmission. The original transmission rate (1544 kbit/s) on the T-1 line is commonly used today in Internet Service Provider (ISP) connections to the Internet. At another level, a T-3 line provides 44736 kbit/s, which is also commonly used by Internet Service Providers. Another commonly installed service is a fractional T-1, which is the rental of a certain portion of the 24 channels on a T-1 line, with the other channels not being used.
The T-carrier system is entirely digital, using pulse code modulation and time division multiplexing. The system uses four threads and provides two-way capability (two threads to receive and two to send at the same time). The T-1 digital stream consists of 24 multiplexed 64-kbit/s channels (the standard 64-kbit/s channel is based on the bandwidth needed for a voice conversation.) The four wires were originally a pair of stranded copper, but now can also include coaxial cable, fiber optics, digital microwave and other media. A number of variations in the number and use of channels are possible.
Bandwidth
In the T-1 system, voice signals are sampled 8000 times per second and each sample is digitized into an 8-bit word. With 24 channels being converted to digital at the same time, a 192-bit frame (24 channels each with an 8-bit word) is thus being transmitted 8000 times per second. Each frame is separated from the next by a single bit, making a 193-bit block. The 192-bit frame was multiplied by 8,000, and the 8,000 framing bits grow the T-1's data rate to 1,544 kbit/s. The signaling bits are the least significant for each frame. This is calculated as follows:
