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Wireless Routing (2)

Wireless Routing (2). Philippe Jacquet. Reactive protocols. Ad hoc On Demand distance Vector (AODV) Routing tables contains only active routes Route discovery on demand based on wireless flooding Route recovery procedure after route failure. Distance vector revisited.

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Wireless Routing (2)

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  1. Wireless Routing (2) Philippe Jacquet

  2. Reactive protocols • Ad hoc On Demand distance Vector (AODV) • Routing tables contains only active routes • Route discovery on demand based on wireless flooding • Route recovery procedure after route failure

  3. Distance vector revisited • Count to infinity and routing loops • Use of a route sequence number • Incremented at each new demand or recovery • The « good » route has the highest seq number

  4. On demand routing • A node S with a packet to a new destination D • If routing table lookup fails then • 1. Starts a route discovery • 2. Waits for new route notification • 3. Insert new entry in routing table • 4 forwards packet • Meanwhile keeps packet to X in buffer. • No best prefix routing. • entries in routing table • Expires if inactive • Removed on route error notification • Changed on updated seq(D) D Next relay dist Seq(D)

  5. Route discovery • Two main control packets • Route REQuest (RREQ) packet • Route REPly (RREP) packet • A third control packets • Route ERRor (RERR) packet • A node sequence number seq(X)

  6. Route discovery • RREQ from S for a route to D contains (after IP headers) • route originator ID (S), • route destination ID (D) • Hop count (set at zero on source) • Seq(S) +1 • Eseq(D) (last known seq(D) +1)

  7. Basic Route Discovery • The RREQ packet is flooded in the network • Each node retransmits once the RREQ • Excepted the route destination • Upon first reception of RREQ: on fly reverse route update • Route entry to S updated • Hop count updated S Last relay hop Seq(S) S D A B C (S:S,0) (S:S,1) (S:A,2) (S:B,3) (S:C,4)

  8. Basic Route Discovery • Upon reception of RREQ • Destination increments its own seq(S) • Generates and send to D a RREP • Use reverse route (using routing table) • RREP contains • A RREP hop count set to zero • Current seq(S)

  9. Basic Route Discovery • RREP forwarding • Update route to D • Forward RREP • Routing table updated only on route nodes D Last relay hop Seq(D) S D A B C (S:S,0) (S:S,1) (S:A,2) (S:B,3) (S:C,4) (D:A,4) (D:B,3) (D:C,2) (D:D,1) (D:D,0)

  10. 2 3 1 1 3 2 1 4 1 1 5 2 On demand Distance vector

  11. Route failure • If a link breaks on an active route • upward node sends a RERR packets • To all nodes that are on the active route. • Contains the list of unreachable destination. • Active sources will generate new RREQ • Possibility of local repair. S D A B C RERR(D) RERR(D) RERR(D)

  12. Route discovery optimization • Wireless flooding consumes too much resource. • 1. S Sends RREQ only to neighbor (TTL=1) • 2. If neighbor X has route to D • X sends RREP for D with hop count set to dist • (optional) forwards RREP to D for reverse route to S. S D A B C (S:S,0) (S:S,1) (S:A,2) (S:B,3) (S:C,4) (D:A,4) (D:B,3) (D:C,2) (D:D,1) (D:D,0)

  13. Route discovery cost Source Destination

  14. Route discovery optimization • Expanding ring search • First try with TTL=1 • With TTL=2 • With TTL=4…

  15. 1 2 3 5 1 Route optimization • Hop count can be any metric • Basic route discovery does not give shortest path • Improvement: upon reception of a RREQ copy with shorter metric • Update route to D • Sends a new RREP if destination. 2 6

  16. 1 2 3 5 1 Route optimization • Fails on 2 7 6 7

  17. Super-flooding • Retransmit RREQ when hop count is shorter • Node may retransmit RREQ several times • Hop count: • number of retransmissions may be quadratic • General metric: • Number of retransmissions may be exponential

  18. 1 2 3 5 1 Super-flooding 4 2 7 6 3 7 4

  19. Further optimization • MultiPoint Relay flooding • RREQ flooded via MPRs • Reduces flooding cost

  20. Overhead in routing protocols • Preliminary points • Network: n mobile nodes in an area density • Radio: average range R: average neighborhood per node • Routing: average number of hops between two random nodes • Mobility: typical node speed s, average link creation/termination rate • For uniform independent random walk

  21. Classic BGP • Topology dissemination • Overall link rate creation and failure • Message link state average size M • Dissemination overhead per link change • Total overhead • With wireless flooding

  22. OLSR • Average multipoint relay subset size • Average link state TC message size: • Dissemination overhead • Total overhead

  23. Basic AODV • Average route length • Route failure rate • Number of active routes per node • Dissemination overhead N • Ratio with OLSR

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