The Impact of Node´s Mobility on Link-Detection Based on Routing Hello Messages

Several routing protocols for Mobile Ad Hoc Networks (MANETS), including the well known Ad hoc On-Demand Distance Vector Routing (AODV) and Optimized Link State Routing (OLSR), propose the use of periodic messages (Hello messages) to detect neighbor nodes. After receiving the first Hello message from one of its neighbors, a node starts the link sensing task by setting up a sensing timer. Each time a new Hello message is received from the same neighbor, the sensing timer is restarted and the link duration is prolonged. If the sensing timer expires, it indicates a long time interval without receiving an Hello message and, consequently, the link is considered broken. The transmission frequency of the Hello messages and the expiration value of the sensing timer truly depends on node´s mobility: if the nodes are moving quickly and the Hello messages are rarely transmitted, the neighbor nodes can be in communication range but they are not detected; in the same scenario, if the expiration value of the sensing timer is too high, a link is sensed broken too late. In this paper, we consider a MANET under the Random Waypoint mobility model. We investigate the relationship between the transmission frequency of the Hello messages and the sensing timer expiration value with the network node´s mobility. We formally deduce the probability of link existence after β periods of transmission of the Hello message. The probability is later used to define the sensing timer expiration value, considering a given probability that the Hello message transmission fails. Finally, we evaluate our study through both numerically analysis and simulations, which confirms the effectiveness and accuracy of our approach.