Computer Science

1693 Words Feb 27th, 2013 7 Pages
Part-1
1. What are common carriers, local exchange carriers, and interexchange carriers? A common carrier is a private company that sells or leases communication services and facilities to the public. Common carriers are profit-oriented, and their primary products are services for voice and data transmissions, both over traditional wired circuits as well as cellular services. Common carriers often supply a broad range of computer-based services, such as the manufacturing and marketing of specialized communication hardware and software. A common carrier that provides local telephone services (e.g., BellSouth) is commonly called a local exchange carrier (LEC), while one that provides long distance services (e.g., MCI) is
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Therefore, dedicated circuits require more care in network design than switched circuits both in terms of locations and the amount of capacity you purchase. With packet switched services, the user again buys a connection into the common carrier cloud. The user pays a fixed fee for the connection into the network depending upon the type and capacity of the service and is charged for the number of packets transmitted.
13. Distinguish among T1, T2, T3, and T4 circuits. T1 circuit is sometimes called a DS-1 circuit. It provides a data rate of 1.544 Mbps. T1 circuits can be used to transmit data, but often are used to transmit both data and voice. In this case, a time division multiplexer (TDM) provides 24 64-Kbps circuits. Digitized voice using pulse code modulation (PCM) requires a 64 Kbps circuit so T1 circuit enables 24 simultaneous voice channels. T2 circuit transmits data at a rate of 6.312 Mbps. Basically; it is a multiplexed bundle of four T1 circuits. T3 circuits allow transmission at a rate of 44.376 Mbps, although most articles refer to this rate as 45 megabits per second. This is equal to the capacity of 28 T1 circuits. T3 circuits are becoming popular as the transmission medium for corporate MANs and WANs because of their higher data rates. At low speed, these T3 circuits can be used as 672 different 64 Kbps channels or voice channels. A T4 circuit transmits at
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