data communications
CHAPTER 12
ROUTING IN SWITCHED NETWORKS
A NSWERS
TO
Q 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 sourcedestination 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,
ROUTING IN SWITCHED NETWORKS
A NSWERS
TO
Q 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 sourcedestination 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,