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# Aodv slide final

## on Apr 28, 2010

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## Aodv slide finalPresentation Transcript

• Ad-hoc On-Demand Distance Vector (AODV) Routing 01001010100101011110010010100100101000101010110101010101010101010101010101010101010101010101100101001110100101010101010101010101010101010101010110101010101010101010101010101010101010101010101010101010101010101 010101 101010 11110011 101 1001 100 01010101010101010 100101111000100100 10101010101000001 1111100110101010 11101101001111101010111010011010101010100101010100 101010010101010110101010000010100000101101111111010 101001010100100101111110101100110010100110100100100
• What Does AODV Mean?
• An ad hoc network is a network with no existing infrastructure
• No routers or access points
• Instead each node acts as a router
• On Demand refers to the nature the network routes information.
• it only creates and maintains routes b/w nodes as and when they are necessary and active
• What Does AODV Mean? (cont.)
• Distance Vector refers to the way in which routes are implemented
• Routers using distance vector protocol do not have knowledge of the full path to the destination
• They have a routing table which dictates the next node to forward the information to and the distance to the destination
• What is AODV?
• It’s a routing protocol for wireless ad hoc networks
• Provides a way for nodes to communicate w/one another
• Can be directly from one node to another
• Needed when nodes need to talk to nodes they are not in range with
Node 1 Node 2 Node 3
• How Does it Work?
• Each node has a routing table
• The table indicates routes to known destinations
• It stores: destination address, nexthop address, destination sequence number, and life time.
• Life time is updated each time the route is used
• If the route isn’t used in that time the info is deleted from the table
• When a node wants to send a packet to another node it checks its routing table to see if it has a route
• If it does, it forwards it to the next node
• If not, it sends out a Route Request (RREQ) packet
• 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
• Broadcast ID and source IP address is unique to each RREQ
• The RREQ is sent to all nodes it can reach within a time limit
• Limits network congestion
• How does it work?
• When an intermediate node receives a RREQ it logs a reverse route entry in its table
• 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)
• If a neighbor of the source doesn’t know a route to the destination, it rebroadcasts the RREQ.
• 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.
Node 3 Node 2 Node 1 Node 4 Node 5 RREQ RREQ RREQ RREP
• How does it work? continued
• As seen in the last slide, node 4 had a route to node 5
• Node 5 sends node 1 a RREP along the route the RREQ came on
• Once node 1 receives the RREP, it notes the route to node 5 and sends the packet on that route.
Node 1 Node 4 Node 5 RREQ RREP Packet Packet
• RREQ RREP Now we can see it all in action! Node 1 Node 2 Node 3 Node 4 Node 5
• Lets get more specific!
• 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.
• 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.
• And more specific…
• 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.
• It gets complicated!
• 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
• are so key.
• Error Messages RERR
• 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.