21-01-2013, 04:39 PM
A Mobile Ad-hoc Network (MANET)
1A Mobile Ad-hoc.doc (Size: 40 KB / Downloads: 29)
INTRODUCTION
A Mobile Ad-hoc Network (MANET) is a self-configuring infrastructure less network of mobile devices connected by wireless links. The topology of the MANET may change uncertainly and rapidly due to the high mobility of the independent mobile nodes, and because of the network decentralization, each node in the MANET will act as a router to discover the topology and maintain the network connectivity.
The following are the advantages of MANETs:
They provide access to information and services regardless of geographic position.
These networks can be set up at any place and time.
The set of applications for MANETs is diverse, ranging from large-scale, mobile, highly dynamic networks, to small, static networks that are constrained by power sources. Besides the legacy applications that move from traditional infrastructure environment into the adhoc context, a great deal of new services can and will be generated for the new environment.
Some of the applications of MANETs are
Military or police exercises.
Disaster relief operations.
Mine cite operations.
Urgent Business meetings.
Due to the error prone wireless channel and the dynamic network topology, reliable data delivery in MANETs, especially in challenged environments with high mobility remains an issue. Traditional topology based MANET’s routing protocols are quite susceptible to node mobility. Owing to the constantly and even fast changing network topology, it is very difficult to maintain a deterministic route. The discovery and recovery procedures are also time and energy consuming. Once the path breaks, data packets will get lost or be delayed for a long time until the reconstruction of the route, causing transmission interruption. No end-to-end routes need to be maintained, leading to high efficiency and scalability. The neighbor which is relatively far away from the sender is chosen as the next hop. If the node moves out of the network the transmission will fails. There will be n number of candidates among the network, if the best candidate does not forward the packet in certain time slots, suboptimal Candidates will take turn to forward the packet according to a locally formed order.
Geographic routing
Geographic routing(GR) uses location information to forward data packets, in a hop-by-hop routing fashion.. Greedy forwarding is used to select next hop forwarder with the largest positive progress towards the destination while void handling mechanism is triggered to route around communication voids .No end-toend routes need to be maintained, leading to Geographic Routing high efficiency and scalability. However, Geographic Routing is very sensitive to the inaccuracy of location information .In the operation of greedy forwarding, the neighbor which is relatively far away from the sender is chosen as the next hop. If the node moves out of the sender’s coverage area, the transmission will fail.
Greedy Perimeter Stateless Routing
In Greedy Perimeter Stateless Routing (a very famous geographic routing protocol), the MAC-layer failure feedback is used to offer the packet another chance to reroute. However, our simulation reveals that it is still incapable of keeping up with the performance when node mobility increases.
Ad hoc On-Demand Multipath Distance Vector Routing
AOMDV shares several characteristics with AODV.It is based on the distance vector concept and uses hop-by-hop routing approach. Moreover, AOMDV also finds routes on demand using a route discovery procedure. The main difference lies in the number of routes found in each route discovery. In AOMDV, RREQ propagation from the source towards the destination establishes multiple reverse paths both at intermediate nodes as well as the destination.Multiple RREPs traverse these reverse paths back to form multiple forward paths to the destination at the source and intermediate nodes. Note that AOMDV also provides intermediate nodes with alternate paths as they are found to be useful in reducing route discovery frequency [9].The core of the AOMDV protocol lies in ensuring that multiple paths discovered are loop-free and disjoint, and in efficiently finding such paths using a flood-based route discovery. AOMDV route update rules, applied locally at each node, play a key role in maintaining loop-freedom and disjointness properties. Here we discuss the main ideas to achieve these two desired properties. Next subsection deals with incorporating those ideas into the AOMDV protocol including detailed description of route update rules used at each node and the multipath route discovery procedure.