# A Survey on Parameters Affecting MANET Performance
## 2 Routing in MANETs
### DSR Routing Protocol  
DSR is an efficient reactive routing protocol for MANETs. Each data packet contains a header that carries the IP address of all intermediate nodes between a source node and a destination node. The DSR header holds the sequence of hops to reach the destination [19]. In DSR, each node holds a cache memory to store the routing information needed for all MANET nodes; a source node can also cache multiple routes to the same destination. This mechanism allows the routing of data packets to be much more rapid in comparison to other MANETs' routing protocols. There is no need for periodic packets in DSR to minimize network overhead [20]. The DSR protocol is divided into two mechanisms: route discovery and route maintenance [21]. The route discovery mechanism is initiated when a source node does not hold the needed routing information to reach the destination node. The source node broadcasts a RREQ message to all neighbors within the source's wireless range to initiate a route discovery. The RREQ message contains the following information:  
1. source node identifier;
2. destination node identifier;
3. route request identifier;
4. record listing the address of all intermediate nodes. \begin{table}
\begin{tabular}{c c} \hline \hline
**AODV Parameter** & **Default Value** \\ \hline NetworkDiameter & 35 hops \\ NodeTransversalTime & 40 ms \\ NetworkTransversalTime & 1400 ms \\ RouteRequestRetry & 2 retries \\ BlackListTimeout & 2800 ms \\ RouteRequestRateLimits & 10 packets/s \\ ActiveRoutTimeout & 3000 ms \\ HelloInterval & 1000 ms \\ AllowedHelloLoss & 2 times \\ Delete Period Constant & 5 s \\ \hline \hline \end{tabular}
\end{table} 
Table 2: AODV parameters’ default values. A route maintenance mechanism is issued when the cached route to a destination is no longer valid. When a link to the destination node is broken, the source node can try using another cached route to this destination or it can initiate a route discovery mechanism to find new routes and update the cache. Figure 4 depicts the DSR routing protocol flowchart. When the destination node receives a RREQ, it examines the route back again to the source node, then it returns a RREP message that holds the accumulated record list back again to the initiator. If the examination of the reverse path to reach the source node fails, the destination node should broadcast a route discovery and then send the RREP message after updating the cached route. The DSR protocol contains a set of configuration parameters that could affect routing in MANETs as follows [22]:  
* Discovery hop limit: The discovery hop limit value is defined as the limit to the route request re-broadcast. If the first attempt of RREQ does not reach the destination node, the default value of the discovery hop limit is 255 hops, and the minimum value is one hop. * Broadcast jitter: The destination node should delay the RREP message by a random value that does not exceed the broadcast jitter's maximum delay time. The broadcast jitter default value is ten milliseconds. * Route cache timeout: The route cache timeout is associated with each route entry in the cache [23]. When the timeout is reached, this means that the related route is not used and needs to be deleted from the node's cache. Route cache timeout default value is three hundred milliseconds. Figure 4: The DSR routing protocol flowchart. * Send buffer timeout: When a packet cannot be transmitted to the next-hop node, this packet is queued inside a buffer to try sending it when possible. Send buffer timeout is the maximum time associated with a packet to be sent before being removed from the send buffer. The default value for send buffer timeout is 30 s.
* Max request period: After a route discovery attempt fails to find a route to the destination node, the time between successive route discovery attempts doubles until the maximum request period is reached.