ReviewCS447

ReviewCS447 - Computer Networks and Data Communications...

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Computer Networks and Data Communications CS642/CS447, Fall 2006 Review Problems The Medium Access Control Sub-layer: 1- Based on the subjects discussed in this unit of the course, give a comparison between Point-to-point network and Broadcast network in terms of the network structure, properties, and the design issues to be considered. Broadcast Network: Uses a single communication channel that is used by all the machines on the network. Short messages are sent to all machines, and only accepted by the destination node when the address is matched. Allows two modes of operation: broadcasting and multicasting. In broadcasting, the message is received and processed by all machines. In multicasting, the message is only sent to a subnet of the machines. Point-to-Point Network: Uses many possible connections between individual pairs of machines. The message has to travel from node to node until destination is reached, routing is essential to find the shortest route. Used mainly in large networks, while broadcast networks is suitable for small networks. 2- Compare between Persistent and Non-persistent CSMA protocols in terms of the basic idea, advantages, and disadvantages. Persistent CSMA Protocol: When a station is ready to send data, it listens to the channel if it's being used at that moment or not. If the channel is busy, it waits until it becomes idle. When the channel detects an idle channel, it transmits the frame. Collision might occur if at least two stations are ready to transmit at the same time. If a collision occurs, the station waits a random time and retransmits the frame. Advantages: Provides better performance than ALOHA protocol. Disadvantages: Long propagation delay causes other stations to sense that the channel is idle and transmit at the same time. Performance decreases as load increases. Non-persistent CSMA Protocol: When a station is ready to send data, it listens to the channel if it's being used at that moment or not. If the channel is busy, it will wait a random amount of time and repeats the algorithm
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ReviewCS447 - Computer Networks and Data Communications...

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