Hierarchical OLSR - a scalable proactive routing protocol for heterogeneous ad hoc networks

The IETF's mobile ad hoc networks (MANET) working group has designated the optimized link state routing (OLSR) as being one of four base routing protocols for use in ad hoc networks. Ad hoc routing protocols in general, including OLSR, do not scale well in heterogeneous networks, as they do not differentiate between the transmission capabilities of various member nodes, nor the channel access control scheme used by nodes when performing routing computations, even though many of the protocols support nodes having multiple interfaces. Under OLSR, for example, the control messages are sent to all interfaces, generating a very high overhead. In this paper, we propose optimizations to OLSR in order to limit the amount of control traffic generated and to make more efficient use of the higher capacity links found in heterogeneous wireless networks. Using OPNET simulations, we introduce a hierarchical mechanism to OLSR, and demonstrate that the hierarchical OLSR (HOLSR) greatly reduces the required protocol overhead, which improves protocol scalability in large size heterogeneous networks. To our knowledge, this paper represents the first attempt made to address in-dept scalability issues of the OLSR protocol on heterogeneous wireless ad hoc networks.