History

• The invention of the telephone drove the building of a global network of copper wires, each capable of carrying a single connection or voice conversation. As the number of phone users continued to grow, the growth and support of this massive physical network became difficult to maintain. An increase in the number of lines required to support long-distance calling, as well as degradation of call quality over distance, became formidable obstacles.
  
  Both of these issues were mitigated in 1962 by American Telephone &Telegraph (AT&T) with the creation of the T1 standard. Also called DS-1 (digital signal-1) protocol, T1 combines the data transmission capabilities of 24 DS-0 lines, each of which can carry 64 kilobits per second of voice or data. Originally developed for voice transmission, carriers began transmitting digital data using this protocol in the early 1980s. Almost all new T1 installations are designed to support data networking, namely access to the Internet.
  
  

Specifications

• The strength of the T1 protocol is that it can be used to transmit data at high speeds with a minimum use of physical resources. This is accomplished by two wire pairs, each carrying data in a specific direction, managed by a framing system to control the bits of data. This is one framing data bit accompanied by 24 channels (or streams) of data 8 bits in size. The size of the "packet" of data traveling across the channel equals 193 bits per frame.
  
  

Data Encoding Standards

• Several methods are used to encode (securely protect and transmit) data, including High Density Bipolar Three Code (HDB3) and Alternate Mark Inversion (AMI). These dictate the uses, patterns and values of each "0" and "1" transmitted to comprise a data packet, allowing the sender to determine the pattern of data sent across the line. The receiving program looks for the specific pattern being transmitted and reassembles the data into the original format for use.
  
  

Control Protocols

• Each data stream must be controlled and segregated to retain signal and content quality. The protocol is managed by specific control and alarm standards coded as blue, yellow and red, with red being the most local indicator of signal quality issues.
  
  For example, if there is a local failure of the signal, a red alarm sounds on equipment tracking software. This generates a general signal to the connected networks that a problem or local failure exists (yellow). A blue alarm indicates a total signal failure, resulting in the start of a data synchronization signal of repeated "1's" until the issue is resolved.
  
  

Summary

• The strength of the T1 data transmission protocol, although originally designed to resolve voice data networking capacity and quality, is its ability to transmit data in a variety of encoded patterns over a global system that is both high speed and reliable. This allows users to access the Internet simultaneously to access and share vast amounts of information in a variety of formats.