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# Aodv slide final

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### Aodv slide final

1. 1. Ad-hoc On-Demand Distance Vector (AODV) Routing 01001010100101011110010010100100101000101010110101010101010101010101010101010101010101010101100101001110100101010101010101010101010101010101010110101010101010101010101010101010101010101010101010101010101010101 010101 101010 11110011 101 1001 100 01010101010101010 100101111000100100 10101010101000001 1111100110101010 11101101001111101010111010011010101010100101010100 101010010101010110101010000010100000101101111111010 101001010100100101111110101100110010100110100100100
2. 2. What Does AODV Mean? <ul><li>An ad hoc network is a network with no existing infrastructure </li></ul><ul><ul><li>No routers or access points </li></ul></ul><ul><ul><li>Instead each node acts as a router </li></ul></ul><ul><li>On Demand refers to the nature the network routes information. </li></ul><ul><ul><li>it only creates and maintains routes b/w nodes as and when they are necessary and active </li></ul></ul>
3. 3. What Does AODV Mean? (cont.) <ul><li>Distance Vector refers to the way in which routes are implemented </li></ul><ul><li>Routers using distance vector protocol do not have knowledge of the full path to the destination </li></ul><ul><li>They have a routing table which dictates the next node to forward the information to and the distance to the destination </li></ul>
4. 4. What is AODV? <ul><li>It’s a routing protocol for wireless ad hoc networks </li></ul><ul><li>Provides a way for nodes to communicate w/one another </li></ul><ul><li>Can be directly from one node to another </li></ul><ul><li>Needed when nodes need to talk to nodes they are not in range with </li></ul>Node 1 Node 2 Node 3
5. 5. How Does it Work? <ul><li>Each node has a routing table </li></ul><ul><li>The table indicates routes to known destinations </li></ul><ul><ul><li>It stores: destination address, nexthop address, destination sequence number, and life time. </li></ul></ul><ul><ul><li>Life time is updated each time the route is used </li></ul></ul><ul><ul><li>If the route isn’t used in that time the info is deleted from the table </li></ul></ul>
6. 6. <ul><li>When a node wants to send a packet to another node it checks its routing table to see if it has a route </li></ul><ul><ul><li>If it does, it forwards it to the next node </li></ul></ul><ul><ul><li>If not, it sends out a Route Request (RREQ) packet </li></ul></ul><ul><li>RREQ contains: source node IP address, and current sequence number, destination IP address and sequence number, a time to live number, and a broadcast ID </li></ul><ul><ul><li>Broadcast ID and source IP address is unique to each RREQ </li></ul></ul><ul><li>The RREQ is sent to all nodes it can reach within a time limit </li></ul><ul><ul><li>Limits network congestion </li></ul></ul>
7. 7. How does it work? <ul><li>When an intermediate node receives a RREQ it logs a reverse route entry in its table </li></ul><ul><ul><li>Includes the destination, the next hop (the next node in line), the hop count (incremented 0 at the source to i=number of hops since then) </li></ul></ul><ul><li>If a neighbor of the source doesn’t know a route to the destination, it rebroadcasts the RREQ. </li></ul><ul><li>If a neighbor does know a route to the destination, it sends a route reply (RREP) back to the source. Below, Node 1 is trying to talk to node 5. </li></ul>Node 3 Node 2 Node 1 Node 4 Node 5 RREQ RREQ RREQ RREP
8. 8. How does it work? continued <ul><li>As seen in the last slide, node 4 had a route to node 5 </li></ul><ul><li>Node 5 sends node 1 a RREP along the route the RREQ came on </li></ul><ul><li>Once node 1 receives the RREP, it notes the route to node 5 and sends the packet on that route. </li></ul>Node 1 Node 4 Node 5 RREQ RREP Packet Packet
9. 9. RREQ RREP Now we can see it all in action! Node 1 Node 2 Node 3 Node 4 Node 5
10. 10. Lets get more specific! <ul><li>Sequence Number : Each message contains a sequence number, which is essentially the age of the message. This allows nodes to know how recent a message was sent, and it may allow nodes to find new, quicker routes. </li></ul><ul><li>Life Span : Each message only last the time that is specified by its life span. If the message dies before it reaches the destination, the source will resend the message with a longer life span. </li></ul>
11. 11. And more specific… <ul><li>Hello Messages : These are simple messages that nodes send at certain time intervals to all its neighbors to let them know that it is still there. If a node stops receiving hello messages from one of its neighbors, it knows that any routes through that node no longer exist. </li></ul>
12. 12. It gets complicated! <ul><li>Things get much more complicated with many nodes. This is because nodes have many neighbors so RREQ get rebroadcasted a lot! That’s why sequence numbers and life spans </li></ul><ul><li>are so key. </li></ul>
13. 13. Error Messages RERR <ul><li>RERR are used mainly when nodes get moved around and connections are lost. If a node receives a RERR, it deletes all routes associated with the new error. Error messages are sent either when a message (not RREQ or RREP) is sent to a node that has no route to the destination, or when a route becomes invalid, or if it cannot communicate with one of its neighbors. </li></ul>