  In this paper, we study and improve the recovery properties of single and
multipath routing strategies when facing network failure situations. In
particular, we focus our study on two MANET routing protocols: OLSR and its
multipath extension MP-OLSR. In various wireless multi-hop network
environments, especially in multiple chain topologies, we define and seek to
evaluate the latency introduced by these protocols to find a new path after a
link failure. Theoretical estimations and simulation results show that, under
dual chain-topologies, this latency can be too long and incompatible with the
needs of loss and delay constrained applications. As the source nodes cannot
detect link failures immediately because of the delay incurred by the
well-known nature of link state protocols in general, and of OLSR Topology
Control (TC) messages in particular, these nodes keep sending packets along
broken paths. We thus study the inconsistencies between the actual network
topology and the nodes' own representation. After analyzing the consequences of
this long latency, we seek to alleviate these problems with the introduction of
adapted mechanisms. We propose three new different schemes and accordingly
extend the original OLSR and MP-OLSR protocols in order to decrease the
expected latency and improve the protocol performance. Simulation results show
a steep decrease of the latency when using these new schemes in dual
chain-topologies. We also discuss these results in terms of packet loss,
end-to-end delay and overhead.
