Pstn Essay

1233 words - 5 pages

PUBLIC SWITCHED TELEPHONE NETWORK The Public Switched Telephone Network (PSTN) is a variety of companies and government agencies that are linked by interconnected data transmission systems. Although the PSTN has changed with time, its functionality has remained constant. The main function of the PSTN is to transmit information, whether it is voice or data. The PSTN is now a part of just about everyone's lives and continues to expand with the popularity and growth of the Internet, cell phones and satellites.The PSTN has many components including drop wires, terminals, computers, switches, central offices, LEC's, local loops, inside wire, trunk lines and of course the telephone. The components of the PSTN are rapidly changing to increase the speed at which information can be transmitted.An overview of how the PSTN works, starting from the outside plant. Basically the outside plant consist of several components, poles, conduit, fiber, copper cables that all work in unison to connect the Central Office to the Subscriber (paying customer). All these components come together to create the Local Loop.There are five different classes of Central Offices (1-5). Class 5 offices are the local exchange offices. These are the offices that serve the end users. Class 4 offices are tandem toll centers, which serve to interconnect Class 5 offices that are not directly connected. As the lowest class of toll center, these also serve as the first point of entry of the long distance, or toll, network. Class 3 offices, or primary toll centers, are higher-order toll centers, generally serving to connect Class 4 offices for intrastate toll calling. Class 2 offices, or sectional toll centers, serve to interconnect primary toll centers, largely for interstate calling within a geographical region. Class 1 office, or regional toll centers, serve to interconnect sectional toll centers in support of interregional calling.( ) A Central Office (CO) services several areas, which are then broken up to one or more smaller locations. CO's are placed about every 16 miles. Each CO handles roughly 41,000 subscriber lines. Originally "Every subscriber line location in a CO switch is assigned a seven-digit number. The first three digits represent the exchange and identify which CO switch serves that particular telephone. The last four digits identify the individual line number, which is a circuit physically connected from the CO to the subscriber. A CO switch can handle one or more exchanges, and each exchange can handle up to 10,000 subscriber lines, numbered 0000 to 9999". ( ) CO's are connected via Trunk lines. These trunk lines are used to support the calls that need to get from one area to another. There are CO's that do not have enough traffic going between them to have direct Trunk lines they would then use a Tandem office to route calls to the different CO's. A Tandem office is when you have two or more other CO's that are not directly connected, they would use a centralized...

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