Strategies for Finding Stable Routes in Ad-hoc Networks - Abstract

ABSTRACT 

            Ad-hoc networks are expected to play an important role in future commercial and military communications systems. As such, scalable routing strategies capable of supporting greater user mobility and a wide range of applications are needed. A mobile ad hoc network (MANET) is an infrastructure less and highly dynamic network. Routes in such a network may fail frequently because of node mobility or other issues. Stability therefore can be an important element in the design of routing protocols. Stable routes, also called the long-lived routes, can be discovered and used to reduce the overhead resulted from route maintenance in ad hoc networks. Since mobility may cause radio links to break frequently, one pivotal issue for routing in mobile ad-hoc networks is how to select a reliable path that can last longer. Several metrics have been proposed in previous literature, including link persistence, link duration, link availability, link residual time, and their path equivalent. Here we are going to propose a technique to find stable route in mobile ad-hoc network.

   

INTRODUCTION:

In the past years, a vast number of routing protocols for mobile wireless ad hoc networks has been introduced. One reason for the considerable effort in this area is that routing in such networks is a very challenging task, since network topology changes occur frequently. Each time this happens, an established route may break. If this is the case, data packets must be re-routed quickly, which potentially involves a high amount of control traffic and yet may not be able to avoid interruptions perceived by the users of real-time applications. Therefore, the re-routing of existing connections should be carried out as seldom as possible; in other words, routes should be established along “stable”, i.e. durable paths. In the design of most ad hoc routing protocols, this issue has not been addressed. E.g., DSR simply tries to establish any shortest path in order to save bandwidth. AODV establishes the path along which the RREQ was propagated with the lowest delay, which is likely to be a path with generally low delay and hop count. Only a few protocols aim at establishing stable routes) and these either depend on specific hardware features or on unverified assumptions.

Link duration and Path duration

            Mobility changes the connectivity graph, which in turn affects the performance. The metrics that are useful to predict this behavior are link duration and path duration. Link duration is the amount of time a node has an active link to its neighbor (a node within the communication range of another). If a node wants to send a packet that is too long to its neighbor, the neighbor should be in the communication range until the communication is complete. If a premature disconnection occurs than the receiving node losses part of its data. In a multihop scenario, the underlying routing protocol finds a route to its destination either by table driven or demand. Both these techniques find a path irrespective of how long a path is available. This period of time that the route is available is called route duration or path duration. Hence the route that becomes invalid will effect the ongoing communication and increases the overhead of routing protocol as well. Path durations actually the minimum link duration along the path. Since the path and link duration affects the performance of routing protocol, it affects the throughput and overhead in the network as well. Having the knowledge of average link and path duration in the network it helps in finding TTL value for routing protocol. It can be used to determine the appropriate packet length for successful communication to minimize the packet loss. In order to overcome the above mentioned problems, prediction of how long a payh will exit will be a useful metrics for design of routing protocol. But the prediction of path is not so easy as it depends upon the unknown parameters such as position of relay nodes, velocity, direction of movement etc. such a perdiction would be easy for GPS but very few MANETs use GPS. The widely used routing proti=ocols in MANET such as DSR, AODV do not select a path considering the duration of the path.

Link stability estimation

            Link stability indicates how stable the link is and how long it can support communication between two nodes. We can estimate link stability using many parameters. Signal strength was used in SSA, and pilot signals were used in ABR. Relative speed between two nodes or remaining battery power of a node can be used also. Link stability between mobile nodes is basically dependent on the distance between mobile nodes. Buffer zone effect, presented in SSA, shows the relationship between the distance and the link stability. However, if nodes have long pause time, the relationship between the distance and the link stability is broken. If two nodes with long pause time are located at the edge of radio transmission range, they can communicate during long pause time. Though, the bit error rate of the link is high, the link would not be broken. This makes the estimation of the link stability as a hard problem

• Signal strength based link stability estimation model (SBM)

            SSA uses signal strength as link stability estimation. All nodes monitor signals from its neighbor nodes. If the strength of signal received from neighbor node beyond threshold, the link from the neighbor node is considered as strong stability link. Signal strength values can be obtained from radio device and strength regulator averages strength values. In simulation, we assume free space radio propagation model and used a distance between two nodes, instead.