03-08-2012, 12:03 PM
IMPLEMENTING AND COMPARING DSR AND DSDV ROUTING PROTOCOLS FOR MOBILE AD HOC NETWORKING
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ABSTRACT
Ad hoc networking allows portable devices to establish communication independent of a central infrastructure. However, the fact that there is no central Infrastructure and that the devices can move randomly gives rise to various kind of problems, such as routing and security. In this thesis the problem of routing is considered. This thesis addresses issues pertaining to Destination Sequenced Distance vector (DSDV) and Dynamic Source Routing (DSR) protocols, which are used for efficient routing under different scenarios in Mobile Ad-hoc Network (MANET), which plays a critical role in places where wired network are neither available nor economical to deploy. My objective was to implement the two routing protocols using Network Simulators and run it for different number of nodes. Then I compared the two routing protocols for different network parameters and studied the efficient protocol under a particular scenario on the basis of two metrics.
INTRODUCTION
Wireless cellular systems have been in use since 1980s. We have seen their evolutions to first, second and third generation's wireless systems. Wireless systems operate with the aid of a centralized supporting structure such as an access point. These access points assist the wireless users to keep connected with the wireless system, when they roam from one place to the other.
The presence of a fixed supporting structure limits the adaptability of wireless systems. In other words, the technology cannot work effectively in places where there is no fixed infrastructure. Future generation wireless systems will require easy and quick deployment of wireless networks. This quick network deployment is not possible with the existing structure of current wireless systems.
PROACTIVE GATEWAY DISCOVERY
All the proactive approach algorithms are based on traditional distance vector and link state protocols developed for use in wireless approach. The primary
characteristic of proactive approach is that each node in the maintenance of network is to maintain a route to every other node in the network all the times regardless of whether or not these routes are needed. In order to maintain correct route information, a node must periodically send control messages. Updates to route table are triggered or by certain events which caused in manipulation of other nodes (neighboring) route table. Link addition and removal can trigger an event triggered updation of routing table. In proactive approach the main advantage is that the rout to each node is instantly found because the table contains all the nodal address. Source only need to check the routing table and transfer a packet. The major disadvantage of proactive approach is that each node is prone to rapid movement. So the overhead of maintaining .
REACTIVE GATEWAY DISCOVERY
Reactive routing technique is also known as on-demand routing. It takes a different approach of routing which overcomes the disadvantages of proactive routing. In reactive approaches those nodes which require connectivity to the Internet reactively find Internet gateways by means of broadcasting some kind of solicitation within the entire ad hoc network. This approach reduces the overhead of maintaining the route table as that of proactive. The node dynamically checks the route table, and if it does not find an entry for its destination or it finds an outdated entry it performs route discovery to find the path to its destination. [5]
The signaling overhead is reduced in this method, particularly in networks with low to moderate traffic loads. However it has a drawback of route acquisition latency. That is when corresponding entry is not found the route discovery mechanism occurs which takes a very large amount of time, and for that time the packet waits for updation of the table.
DSR
The Dynamic Source Routing protocol (DSR) is a simple and efficient routing protocol designed specifically for use in multi-hop wireless ad hoc networks of mobile nodes. DSR allows the network to be completely self-organizing and self-configuring, without the need for any existing network infrastructure or administration. Dynamic Source Routing, DSR, is a reactive routing protocol that uses source routing to send packets. It uses source routing which means that the source must know the complete hop sequence to the destination.
Route Discovery
Route Discovery is used whenever a source node desires a route to a destination node. First, the source node looks up its route cache to determine if it already contains a route to the destination. If the source finds a valid route to the destination, it uses this route to send its data packets. If the node does not have a valid route to the destination, it initiates the route discovery process by broadcasting a route request message. The route request message contains the address of the source and the destination, and a unique identification number.
An intermediate node that receives a route request message searches its route cache for a route to the destination. If no route is found, it appends its address to the route record of the message and forwards the message to its neighbors. The message propagates through the network until it reaches either the destination or an intermediate node with a route to the destination. Then a route reply message, containing the proper hop sequence for reaching the destination, is generated and unicast back to the source node. [6]
Route maintenance
Route Maintenance is used to handle route breaks. When a node encounters a fatal transmission problem at its data link layer, it removes the route from its route cache and generates a route error message. The route error message is sent to each node that has sent a packet routed over the broken link. When a node receives a route error message, it removes the hop in error from its route cache.
Acknowledgment messages are used to verify the correct operation of the route links. In wireless networks acknowledgments are often provided as e.g. an existing standard part of the MAC protocol in use, such as the link-layer acknowledgment frame defined by IEEE 802.11. If a built-in acknowledgment mechanism is not available, the node transmitting the message can explicitly request a DSR-specific software acknowledgment to be returned by the next node along the route.