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TopThe Proposed Protocol
Optimized link state routing (OLSR) (Clausen and Jaquet, 2003), is one of the most important proactive routing protocols designed for MANET. Each node uses OLSR in order to perform periodic exchange of messages to get information about network topology. The key concept of OLSR is the use of multipoint relay (MPR) to ensure efficient flooding.
To detect its neighbors with whom it has a direct link, each node, at regular intervals (Hello Interval seconds) broadcasts hello messages, containing the list of known neighbors and their link status (symmetric, asymmetric, Multi-Point Relay or Lost).These messages are broadcasted by all nodes and heard only by immediate neighbors; they are never relayed any further, i.e. these packets have a Time-To-Live (TTL) value of 1.
In addition to information about neighbor nodes, periodic exchange of HELLO messages allows each node to maintain information describing each link between neighbor nodes and those who are two hops away. Based on these information’s, each node selects independently its own set of Multi-Point Relay (MPR) among its one-hop neighbors so that the MPR covers all two-hop neighbors.
Topology Control (TC) messages are also broadcasted by MPR-nodes at regular intervals (TC_Interval second). Thus, a TC message contains the list of neighbors that have selected the sender node as a MPR (MPR Selector Set). Furthermore, an Advertized Neighbor Sequence Number (ANSN), is used by nodes in order to verify if information contained in TC messages is up-to-date. TC messages are flooded to all nodes and take advantage of the existence of Multi-Point Relay to reduce the number of retransmissions.