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Ad-Hoc Routing Protocols

Ad-Hoc Routing Protocols. Distance Vector Destination Sequenced Distance Vector. Outline. Routing Protocol Overview Distance Vector (DV) Route Table in Node Route Update Loop Problem Destination Sequenced Distance Vector (DSDV) Route Table in Node

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Ad-Hoc Routing Protocols

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  1. Ad-Hoc Routing Protocols Distance Vector Destination Sequenced Distance Vector

  2. Outline • Routing Protocol Overview • Distance Vector (DV) Route Table in Node Route Update Loop Problem • Destination Sequenced Distance Vector (DSDV) Route Table in Node Route Update ( Sequence Number ) Damping of fluctuations

  3. Classification of routing protocol Ad-Hoc Mobile Routing Protocols Table-Driven Proactive Hybrid On-Demand-Driven Reactive ZRP DSDV WRP AODV DSR TROA ABR CGSR SSR

  4. Table V.S On-Demand • Proactive • Advantage • No latency in route discovery • May be appropriate for real time communication • Disadvantage • Large network capacity to keep information to update • Most routing information may never be used

  5. Table V.S On-Demand • Reactive • Advantage • Route discovery by global search • Small network capacity to keep information to update • Disadvantage • Bottleneck due to latency of route discovery • May be not appropriate for real time communication

  6. Distance Vector (DV) • Basic Routing Protocol • known also as Distributed Bellman-Ford or RIP • Periodically send table to all neighbors to maintain topology • Bi-directional links are required

  7. Distance Vector Table Entry • Every node maintains a routing table • all available destinations • the next node to reach to destination • the number of hops to reach the destination 1 2 A B C

  8. DV Routing Table Update Form 1 2 1 A B C D

  9. Distance Vector Routing Update B broadcasts the new routing information to his neighbors Routing table is updated (A, 1) (B, 0) (C, 1) (A, 1) (B, 0) (C, 1) 1 2 1 A B C 2 1 1 2

  10. Distance VectorCount-to-Infinite Problem [D,4] [D,4] [D,3] [D,2] [D,2] 1 1 1 A B C D 4 B ∞ 3

  11. Destination Sequenced Distance Vector (DSDV) • Based on bellman-ford algorithm (DV) • A Table Driven protocol • Every node maintains a routing table • Each node periodically broadcast routing updates • Guarantees loop freedom • Each entry of the table marked with a sequencenumber assigned by the destination node

  12. DSDV Table Entry (1/2) 1 2 1 A B C D Node A Routing Table

  13. DSDV Table Entry (2/2) • Seq.No : Sequence number originated from destination • Ensures loop freeness • Install Time: Time when the entry was made • Used to delete stale entries • Stable Data: Pointer to a table holding information on how stable a route is • Used to dampen fluctuations in network

  14. DSDV Routing Table Update Form 1 2 1 A B C D Advertised route table by A

  15. DSDV Route Advertisement (A, 1, A-552) (B, 0, B-102) (C, 1, C-588) • B increases Seq. No from 100 => 102 (A, 2, A-552) (B, 1, B-102) (C, 0, C-588) (A, 1, A-550) (B, 0, B-102) (C, 1, C-588) (A, 1, A-550) (B, 0, B-102) (C, 1, C-588) 1 2 1 A B C A-552 A-552 2 A-552 B-102 B-102 1 B-102 2 1 C-588 C-588 C-588

  16. DSDV Loop Handling 1. Node C detects broken Link: - Increase Seq. No by 1(only case where not the destination sets the sequence number - odd number) 2. B broadcasts=> no affect on C : higher seq. no => no loop -> no count to infinity [D,2, D-100] [D,2, D-100] 1 1 1 A B C D ∞ D-101

  17. DSDVDamping Routing Changes • Routing update occasion • Periodicity • Immediate • Routing update method • Full dump • Incremental packet

  18. DSDV Route Update Immediately • DSDV adopts triggered updates to make route convergence faster • Send an immediate routing update when a significant change is noticed: • Link to a neighbor has broken. • A routing entry with higher sequence number and an infinity metric is received. • Newly recorded routes. • Improved metric for same route or larger sequence number.

  19. DSDV Route Update Periodically • Routing update changes are not immediately propagated • Waiting some settling time

  20. DSDV Fluctuations Problem D,Q,14,D-100 D,P,15,D-102 D,Q,14,D-102 Entry for D in A: [D, Q, 14, D-100] A P Q D makes Broadcast with Seq. Nr. D-102 A receives from P Update (D, 15, D-102)-> Entry for D in A: [D, P, 15, D-102] 11 Hops 10 Hops A must propagate this route immediately. A receives from Q Update (D, 14, D-102)-> Entry for D in A: [D, Q, 14, D-102]A must propagate this route immediately. (D,0,D-102) D

  21. DSDVSolving the Fluctuations Problem • Damping of fluctuations from triggered updates: • Settling Time: Destination address Last settling time Average settling time • Delay sending triggered updates when things seem likely to change again based on past experience.

  22. DSDVFull/Incremental Update • Full Update: Send all routing information from own table. • Incremental Update: Send only entries that has changed.

  23. Reference • C. P. . P. Bhagwat, “Highly Dynamic Destination-Sequenced Distance Vector Routing (DSDV) for Mobile Computer,” in Proceedings of ACM SIGCOMM 94, pp.234-244, September 1994.

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