T1/E1 Today: An Essential Building BlockFrom its roots as a telco inter-office connectivity device, T1/E1 has settled in as a core building-block for voice, data, and video delivery. In the early 1980's, T1/E1 migrated to the local loop - also known as the last mile. The local loop is the distance between the local telco office and the end user, usually about 2.5 miles or about 4 km, and it is in this capacity, as a customer access vehicle for both public and private networks, that T1/E1 is most commonly used. At present, it is estimated that in excess of 700,000 T1 lines have been installed in the U.S. and approximately 80 percent of those lines have been implemented with copper. Outside the U.S. and Canada, except for Japan and a few other countries, the standard for transmission of digital information, E1, is expected to reach similar levels of usage as deregulation of public telephone companies continues around the world and competition increases.In large urban areas, heavy user concentration and sophisticated communications requirements have mandated the use of fiber - though as a prerequisite in this setting, many customers must be located within hundreds of feet from the end of a fiber optic line. In these instances - and only when significant bandwidth (multiple T1/E1 lines) is an absolute necessity - fiber plants have been installed and represent a cost-effective way to achieve local public and private network connectivity. In the majority of cases, however, particularly in rural areas, or more typical cityscapes, the use of fiber can't be cost justified. As a result, economics dictate the use of existing copper cable plants.
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