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Ad hoc
- 1. AD-HOC Protocols (AODV) Ali Forooghie UMZ 1397
- 2. What is AD-HOC ? • Direct transmission with neighboring nodes • Each node can be router and so it can relay traffic • B relays packet from A to C • Self‐configuration , Self‐healing
- 4. Proactive Protocols • Proactive • maintain routing information independently of need for communication • Update messages send throughout the network periodically or when network topology changes • Low latency , suitable for real-time traffic • Determine routes independent of traffic pattern • Based on periodic updates = High routing overhead • Example: OLSR , OSDV
- 5. • Reactive • discover route only when you need it • Saves energy and bandwidth during inactivity • Can be bursty cause congestion during high activity • Good for light loads, collapse in large loads • Example: DSR (dynamic source routing) Reactive Protocols
- 6. Hybrid Protocols • Proactive for neighborhood, Reactive for far away (Zone Routing Protocol, Haas group) • Proactive for long distance, Reactive for neighborhood (Safari) • Attempts to strike balance between the two • Example : ZRP , Safari
- 7. Hierarchical Protocols • Nodes are organized in clusters • Cluster head “controls” cluster • Trade off • Overhead and confusion for leader election • Scalability: intra-cluster vs intercluster • One or Multiple levels of hierarchy
- 8. Geographical Protocols • Nodes know their geo coordinates (GPS) • Route to move packet closer to end point • Propagate geo info by flooding (decrease frequency for long distances) • Example : DREAM, GPSR, LAR
- 9. Castings • Unicasting • The routing we have discussed so far is mainly point-to-point routing • A source node wants to send a message to a destination node • Multicasting • In many situations a node wants to send a message to a group of nodes in the network • This is called multicasting and the group is called a multicast group • Broadcasting • Broadcasting is a special case of multicasting when all the nodes in the network is in the multicast group
- 10. Multicasting Support • DSDV and DSR mainly support unicast routing • If multicasting is required, a node must establish unicast routes to each node in the multicast group • A more efficient approach will maintain multicast routing trees for each multicast group
- 11. AODV I • The AODV(Ad-Hoc-On-Demand-Distance-Vector) protocol is both an on-demand and a table-driven protocol • AODV supports multicasting and unicasting within a uniform framework • One of the most popular routing protocols
- 12. AODV II • Each route has a Lifetime after which the route expires if it is not used • A route is maintained only when it is used and hence old and expired routes are never used • AODV maintains only one route between a source-destination pair
- 13. AODV III • This protocols uses two types of messages : • Route request (RREQ) and route reply (RREP) • Route Error (RERR) • We use sequence numbers to keep track of recent routes. Every time a node sends a new message, it uses a new sequence number which increases monotonically
- 14. AODV IV • RREQ • When node S wants to send a message to node D, S searches its route table for a route to D • If there is no route, S initiates a RREQ message with the following components : • The IP addresses of S and D • The current sequence number of S and the last known sequence number of D • A broadcast ID from S. This broadcast ID is incremented each time S sends a RREQ message.
- 15. AODV V • RREQ Process • The <broadcast ID, IP address> pair of the source S forms a unique identifier for the RREQ • Suppose a node P receives the RREQ from S. P first checks whether it has received this RREQ before • Each node stores the <broadcast ID, IP address> pairs for all the recent RREQs it has received
- 16. AODV VI • RREQ Process • If P has seen this RREQ from S already, P discards the RREQ. Otherwise, P processes the RREQ : • P sets up a reverse route entry in its route table for the source S. • This entry contains the IP address and current sequence number of S, number of hops to S and the address of the neighbors from whom P got the RREQ. S Q P D
- 17. AODV VII B A E F H J C G I K M N L D S B A E F H J C G I K M N L S D Represents a node that has received RREQ for D from S Represents transmission of RREQ
- 18. AODV VIII B A E F H J C G I K M N L S D B A E F H J C G I K M N L S D Forward links are setup when RREP travels along the reverse path Represents a link on the forward path Represents links on Reverse Path
- 19. AODV IX • Performance • AODV does not retransmit data packets that are lost and hence does not guarantee packet delivery. • The packet delivery percentage is close to 100 with relatively small number of nodes. • The packet delivery percentage drops with increased mobility.
- 20. AODV X • SUMMARY • Routes need not be included in packet headers • Nodes maintain routing tables containing entries only for routes that are in active use • Sequence numbers are used to avoid old/broken routes • Sequence numbers prevent formation of routing loops • Unused routes expire even if topology does not change