英语论文网

zed Link State Routing (OLSR)
Topology Dissemination Based on Reverse-Path Forwarding

2.2 MANET routing protocols:

As mentioned earlier, three proposed protocols have been accepted as experimental RFCs by the IETF and two of them have been presented here. Both of them are based on widely used algorithms from Internet routing. AODV uses the principals from Distance Vector routing (used in RIP) and OLSR uses principals from Link State routing (used in OSPF). The 3rd approach known as Hybrid Protocol combines the strength of both proactive and reactive schemes.

2.2.1 Reactive protocols - AODV

Reactive protocols seek to set up routes on-demand as in advance the route is not known. In the same way as mentioned above, the whole network is not known to all nodes in advance. So when a node wants to communicate with an-other node to which the route is not defined. Then the route to the destination node is established by the routing protocol. There can be a delay at the start of communication. Where the delay is not desirable one should not use the Reactive routing protocol e-g military applications etc. However, it preserves the precious node battery.

The AODV routing protocol was described in RFC 3561. The idea in AODV is like all reactive protocols, is that it transmits the topology information by node but only on-demand. When a node wants to communicate to the host and if it has no route then the route request “RREQ” will be generated by it and it will be flooded in a limited way to other nodes. It will result in an initial delay and causes the control traffic overhead to be dynamic when initiating this kind of communication. When the RREQ message reaches to the destination or to the intermediate node that have valid route entry for the destination then the route is considered found. AODV remains passive as long as a route
Mobile Ad-hoc Working Group: Charles E. Perkins, Elizabeth M. Belding-Royer and Samir A. Das, “Ad-hoc On demand distance Vector Routing”.

There is a problem in the classical distance vector algorithm that is “counting to infinity” by using sequence numbers for all the routes, AODV avoids that. In the counting to infinity problem the nodes are updated by each other in a loop. Consider nodes N1, N2, N3 and N4 making up a MANET as illustrated in figure 2-2. N1 is not updated on the fact that its route to N4 via N3 is broken. This means that N1 has a registered route, with a metric of N2, to N4. N3 has registered that the link to N4 is down, so once node N2 is updated on the link breakage between N3 and N4, it will calculate the shortest path to N4 to be via N1 using a metric of 3. N3 receives information that N2 can reach N4 in 3 hops and updates its metric to 4 hops. N1 then registers an update in hop-count for its route to N4 via N3 and updates the metric to 5. So in this way they continue to increment the metric in a loop. This is the way that is avoided in AODV, for the example described, is by N2 noticing that N1’s route to N4 is old based on a sequence number. N2 will then discard the route and N3 will be the node with the most recent routing information by which N2 will update its routing table.

Mobile Ad-hoc Working Group: Charles E. Perkins, Elizabeth M. Belding-Royer and Samir A. Das, “Ad-hoc On demand distance Vector Routing”.

For flooding these messages AODV uses an expanding ring techni本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。