Proactive protocols - OLSR

A proactive approach to MANET routing seeks to maintain a constantly updated topology understanding. The whole network should, in theory, be known to all nodes. This results in a constant overhead of routing traffic, but no initial delay in communication.

The Optimized Link State routing(OLSR) is described in RFC3626[23]. It is a table-driven pro-active protocol. As the name suggests, it uses the link-state scheme in an optimized manner to diffuse topology information. In a classic link-state algorithm, link-state information is flooded throughout the network. OLSR uses this approach as well, but since the protocol runs in wireless multi-hop scenarios the message flooding in OLSR is optimized to preserve bandwidth. The optimization is based on a technique called MultiPoint Relaying. The MPR technique is studied further in chapter 3.

Being a table-driven protocol, OLSR operation mainly consists of updating and maintaining information in a variety of tables. The data in these tables is based on received control traffic, and control traffic is generated based on information retrieved from these tables. The route calculation itself is also driven by the tables.

OLSR defines three basic types of control messages all of which will be studied in detail in chapter 3:

HELLO - HELLO messages are transmitted to all neighbors. These messages are used for neighbor sensing and MPR calculation.

TC - Topology Control messages are the link state signaling done by OLSR. This messaging is optimized in several ways using MPRs.

MID - Multiple Interface Declaration messages are transmitted by nodes running OLSR on more than one interface. These messages lists all IP addresses used by a node.

OLSR is further studied in chapters 3 and 4.