Unformatted text preview: he source node must have fairly comprehensive information about the network
environment. However, the routing decision process is efficient because the
intermediate nodes need not make any routing decision. A drawback of the
method is that the path cannot be changed after the packet has left the source node,
rendering the method susceptible to component failures.
2. Hop-by-hop routing. In this method, each node along the path decides only
the next node for the path. That is, each node maintains information about the
status of all its outgoing channels and the adjacent nodes and then selects a
suitable adjacent node for the packet and transmits it to that node. The routing
decisions are typically based on the channel availability and the readiness of the
adjacent nodes to receive and relay the packet. The method requires that each
node must maintain a routing table of some sort. However, as compared to the
source routing method, this method makes more efficient use of network
bandwidth and provides resilience to failures because alternative paths can be used
for packet transmissions.
3. Hybrid routing. This method combines the first two methods in the sense that
the source node specifies only certain major intermediate nodes of the complete
path, and the subpaths between any two of the specified nodes are decided by the
method of hop-by-hop routing.
Static and Dynamic Routing
Depending on when the information used for making routing decisions is specified
and how frequently it is modified, routing algorithms are classified into the
following two types [Reprinted, with permission, from the book titled Distributed
Operating Systems: Concepts and Design by Pradeep K. Sinha. © 1997 IEEE]:
1. Static routing. In this method, routing tables (stored at the nodes) are set once
and do not change for very long periods of time. They are changed only when the
network undergoes major modifications. Static routing is also known as fixed or
deterministic routing. Static routing is simple and easy to implement. However, it
makes poor use of...
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This document was uploaded on 04/07/2014.
- Spring '14