The average load expected over the course of the busiest hour of use during the
course of a day.
The tradeoff is between efficiency and resilience.
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.
Correctness, simplicity, robustness, stability, fairness, optimality, and efficiency.
For fixed routing, a single, permanent route is configured for each source-
destination pair of nodes in the network.
With flooding, a packet is forwarded to all other switches so that eventually all
routes between source and destination are traversed.
An adaptive routing strategy can improve performance, as seen
by the network user.
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.
The routing decision is more
complex; therefore, the processing burden on network nodes increases.
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.
An adaptive strategy
may react too quickly, causing congestion-producing oscillation, or too slowly,
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.
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.