SOLUTIONS MANUAL-DATA AND COMPUTER COMMUNICATIONS Seventh Edition-WILLIAM STALLINGS-part 2

SOLUTIONS MANUAL-DATA AND COMPUTER COMMUNICATIONS Seventh Edition-WILLIAM STALLINGS-part 2

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-56- A A NSWERS TO NSWERS TO Q Q UESTIONS UESTIONS 12.1 The average load expected over the course of the busiest hour of use during the course of a day. 12.2 The tradeoff is between efficiency and resilience. 12.3 A static routing strategy does not adapt to changing conditions on the network but uses a fixed strategy developed ahead of time. With alternate routing, there are a number of alternate routes between source and destination and a dynamic choice of routes is made. 12.4 Correctness, simplicity, robustness, stability, fairness, optimality, and efficiency. 12.5 For fixed routing, a single, permanent route is configured for each source- destination pair of nodes in the network. 12.6 With flooding, a packet is forwarded to all other switches so that eventually all routes between source and destination are traversed. 12.7 Advantages: (1) An adaptive routing strategy can improve performance, as seen by the network user. (2) An adaptive routing strategy can aid in congestion control. Because an adaptive routing strategy tends to balance loads, it can delay the onset of severe congestion. Disadvantages: (1) The routing decision is more complex; therefore, the processing burden on network nodes increases. (2) In most cases, adaptive strategies depend on status information that is collected at one place but used at another. There is a tradeoff here between the quality of the information and the amount of overhead. The more information that is exchanged, and the more frequently it is exchanged, the better will be the routing decisions that each node makes. On the other hand, this information is itself a load on the constituent networks, causing a performance degradation. (3) An adaptive strategy may react too quickly, causing congestion-producing oscillation, or too slowly, being irrelevant. 12.8 Given a network of nodes connected by bidirectional links, where each link has a cost associated with it in each direction, define the cost of a path between two nodes as the sum of the costs of the links traversed. For each pair of nodes, find a path with the least cost. 12.9 The Bellman-Ford algorithm uses only on information from its neighbors and knowledge of its link costs, to update it costs and paths. Dijkstra's algorithm requires that each node must have complete topological information about the network; that is, each node must know the link costs of all links in the network. C HAPTER 12 R OUTING IN S WITCHED N ETWORKS
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-57- A A NSWERS TO NSWERS TO P P ROBLEMS ROBLEMS 12.1 The number of hops is one less than the number of nodes visited. a. The fixed number of hops is 2. b. The furthest distance from a station is half-way around the loop. On average, a station will send data half this distance. For an N-node network, the average number of hops is (N/4) 1. c. 1. 12.2 The mean node-node path is twice the mean node-root path. Number the levels of the tree with the root as 1 and the deepest level as N. The path from the root to level N requires N 1 hops and 0.5 of the nodes are at this level. The path from the root to level N 1 has 0.25 of the nodes and a length of N 2 hops.
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SOLUTIONS MANUAL-DATA AND COMPUTER COMMUNICATIONS Seventh Edition-WILLIAM STALLINGS-part 2

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