Associativity-Based Routing ABR

1. Associativity-Based Routing ABR

2. Associativity-Based Routing ABR • Invented& developed by C.-K. Toh at Cambridge University (1996) • Source-initiated: no need for periodic route updates • ABR selects routes based on the temporal stability of the links • The temporal stability=> counting the number of beacons

3. Every node generates periodic beacons to signify its existence to the neighbors (beacon-based) • This beacons are used to update the associativity table of each node • Each node classifies each neighbor link as stable or unstable • The fundamental objective of ABR: find longer-lived routes

5. A B C D

6. Associativity-Based Routing ABRMetrics • ABR takes up a few metrics such as: • Link delay • Signal strength • Power life (battery) • Route relaying load • Period of presence

7. Associativity-Based Routing ABR3 Phases • 3 Phases: • Route Discovery • Route Repair/Reconstruction RRC • Route Delete RD

8. Associativity-Based Routing ABRRoute Discovery1/3 • If no route in cache, the source floods Route Request messages in search of nodes that have a route to the destination • All intermediate nodes forward the Route Request message only once • On receiving a Route Request message, the intermediate nodes append their address& associativity ticks to the packet

9. Associativity-BasedRoutingABRRoute Discovery2/3 • After a time period, the target can select the best route by examining the associativity ticks along each path • If more paths have the same over all degree of association stability, then the shortest route with less hops is selected • Once the route as been chosen, the targets ends a Reply packet back to the source along the same path

10. 3 routes possible from1 to 15: 1.1-5-10-14-15 2.1-5-4-12-15 3.1-2-4-8-13-15 ABR selects route 3:highest percentage of stable links

11. Associativity-BasedRoutingABRRoute Repair/Reconstruction 1/3 Node closer to the source initiates a local route repair process Repair process: The node broadcasts a Route Repair packet named local query LQ with a limited TTL Broken link is by passed locally without flodding a new broadcast query

12. Associativity-BasedRoutingABRRoute Repair/Reconstruction 2/3- Broken path: 8-13-15 -Node8 initiates the LQ broadcast -New path: 8-12-15

13. Associativity –Based Routing ABRRoute Repair/Reconstruction 3/3 Case: Node is moving First the last node before the destination erases its route Then a LQ process is initiated to check if the node is still reachable If the target is reachable, it selects the best partial route and replies Otherwise the LQ process is forwarded to the next upstream node A Route Notification message is sent to the next upstream node to erase the invalid route and inform this node that it should take over the LQ process If this process results in backtracking more than halfway to the source, the LQ process is discontinued and the source initiates a new broadcast query process

14. Associativity-BasedRoutingABRRoute Delete • If a discovered route is no longer needed, the source node initiates a Route Delete RD broadcast • Every node on this route will then delete the route entry from their routing cache.

15. Associativity-BasedRoutingABRAdvantages& Disadvantages • Stable routes have a higher preference compared to shorter routes • => fewer paths will break which reduces flooding • A broken link is «repaired» locally • Stability informationsare only used during the route selection process • Chosen path may be longer than the shortest path, because of the preference given to stable paths • LQ broadcasts may resulting high delays during the route repair