SUBSCRIBER SYSTEMS

Subscriber-type systems are available that use the same operations as those systems that operate in the telephone network. These systems are also software programmable for voice and data circuits. The main difference is that one terminal is located in the central office while the other is in the field near or on the customer's location (see Figure A-6). They also may be referred to as a pair gain system, a digital loop carrier, or a subscriber loop carrier. Some of them can also extend a leased digital link to the customer premise for his/her own use.

Subscriber-type systems support a wide variety of applications by various operating companies. One of the more popular uses is providing service to developing areas for new subdivisions where an existing cable plant is insufficient. A system can provide the service immediately and permanently, or it can be moved to another location (if growth in the area eventually justifies a central office). Regardless of whether the service is permanent or temporary, a subscriber system is easy to engineer and install on short notice. An example would be a new industrial park experiencing sudden and unexpected growth, resulting in demands for service exceeding available loop plant. The system can be installed and operating within a few weeks. Also, many companies use these systems to provide for temporary service to large functions such as business conventions or sporting events.

There are other reasons to justify the placement of a subscriber loop carrier in the loop plant. First, the copper pairs serving the subscribers will be much shorter, thus overcoming distance limitations in providing the newer services. Second, shortening the customer loop decreases the exposure to power-line interference with its resultant degradation and noise impact on these circuits. Third, electronics allow the future ability to provide new services quickly. The distance from the central office to the remote terminal is limited only by the copper span line performance. Today, most of these systems employ fiber optics, so there is very little distance limitation.