Link state declaration

Link state routing protocols are based on nodes flooding the network with information about their local links. In protocols like ISIS[65] this information is mostly links to subnets, since these protocols are highly based on aggregation of networks. OLSR uses host based flat routing, so the link state emitted describes links to neighbor nodes. This is done using Topology Control(TC) messages. The format of a TC message is shown in figure 3.13.

Figure: the OLSR Topology Control message format.

TC messages are flooded using the MPR optimization. This is done on a regular interval, but TC messages are also generated immediately when changes are detected in the MPR selector set. In OLSR the flooding process itself is optimized by the usage of MPRs, but as explained in section 3.4.3, the MPR technique introduces two link-state declaration optimizations as well. As we will see in the Auxiliary functionality chapter, OLSR nodes can also be tuned to send more than just its MPR selector set. One should notice that more robust routing could be achieved by announcing more than the MPR selector set.

The MPR functionality introduces two optimizations to TC messaging: