Optimized Link State Routing Protocol

OLSR stands for Optimized Link State Routing Protocol. In this, each node periodically floods status of its links. Each node re-broadcasts link state information received from its neighbors. Each node keeps track of link state information received from other nodes. Each node uses above information to determine next hope to each destination. It is proactive and table-driven.

Link State Routing :

  • Each node expands a spanning tree.
  • Each node can obtain the whole network topology.

Example :

TC(6) = <4, 5, 7>
  • Node 6 generates a TC message advertising nodes in MS(6) = {4, 5, 7}.
  • Node 4 forwards TC(6) from Node 6 and Node 3 forwards TC(6) from Node 4.
  • After nodes 3, 4 and 6 have generated TC messages, all nodes have link-state information to route to any node.

It utilizes a technique to reduce message flooding – MultiPoint Relaying (MPR).



In this, each node N in the network selects a set of neighbor nodes as multipoint relays, MPR(N), that retransmit control packets from N- Neighbors not in MPR(N) process control packets from N, but they do not forward the packets. MPR(N) is selected such that all two-hops neighbors of N are covered by (one-hop neighbors) of MPR(N).

Advantages of OLSR :

  • OLSR has less average end-to-end delay therefore it is used for applications which needs minimum delay.
  • The OLSR implementation is more user friendly and worked with fewer headaches than other protocols.
  • It is also a flat routing protocol.
  • It does not need a central administrative system to handle its routing process.
  • It increases protocol’s suitability for an ad hoc network with the rapid changes of the source and destination pairs.
  • It does not require the link which is reliable in controlling messages, since the messages are sent periodically and the delivery does not have to be sequential.

Disadvantages of OLSR :

  • It maintains routing table for all the possible routes.
  • When the number of mobile hosts increases, then the overhead from the control messages also increases.
  • It needs considerable time to re-discover a broken link.
  • It requires more processing power than other protocols when discovering an alternate route.

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