Computer Science

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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 commonly called an interexchange carrier (IXC). As the LECs move into the long distance market and IXCs move into the local telephone market, this distinction may disappear. 3. Explain how cloud architecture works.

Cloud architecture is represented as a cloud with connection points. Users of circuit switched services lease the connection points (e.g., telephone lines) into the common carrier’s network, which is called the cloud. This architecture is very flexible and hides its internal details. Circuits can be established as needed between any computers attached to the cloud at any point. However, data can only be transmitted while a circuit is established, and only to the one location it connects to. These designs are simpler for the organization because they hide the common carrier’s burner of network design and management inside the cloud. Network managers do not need to worry about the amount of traffic sent between each computer, they just need to specify the amount of traffic entering and leaving each computer and buy the appropriate size and number of connections into the PSTN. Cloud-based designs can be more expensive because users must pay for each connection into the network and pay based on the amount of time each circuit is used. Cloud-based designs are often used when network managers are uncertain of network demand, particularly in a new or rapidly growing network.

9. Compare and contrast circuit-switched services, dedicated circuit services, and packet-switched services. For both circuit switched and dedicated circuit networks, a circuit is established between the two communicating computers. This circuit provides a guaranteed data transmission capability that was available for use by only those two computers and is assigned solely to that transmission. No other transmission is possible until the circuit is closed. In contrast, packet switched services enable multiple connections to exist simultaneously between computers over the same physical circuit or even over different physical circuits. In the POTS and ISDN circuit switched networks each connection goes through the regular telephone network on a different circuit. These circuits may vary in quality, meaning that while one connection will be fairly clear, the next call may be noisy. The data transmission rates on these circuits are usually low. Usually, transmission rates range from 28.8 Kbps to 56 Kbps for dialed POTS circuits to 128 Kbps to 1.5 Mbps for ISDN circuits. You usually pay per use for circuit switched services. With a dedicated circuit network, you lease from common carriers for their exclusive use twenty-four hours per day, seven days per week. All connections are point to point, from one building in one city to another building in the same or a different city. The carrier installs the circuit connections at the two end points to the circuit and makes the connection between them. The circuit still runs through the common carrier’s cloud, but the network behaves as if you have your own physical circuit running from one point to another. Dedicated circuits are billed at a flat fee per month and the user has unlimited use of...
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