Highly Dynamic Destination- Sequenced Distance-Vector Routing Protocol (DSDV) for Mobile Computers Charles E. Perkins Pravin Bhagwat Mobile Computing, 1996

Outline Introduction of ad hoc network Overview of routing methods Goal of this paper DSDV protocol Property of the DSDV protocol Summary

Introduction of Ad Hoc Network Properties of ad-hoc networks Dynamic and self-starting network No administrative intervention required Battery-powered

Overview of Routing Methods Link-State algorithm Distance-Vector algorithm

Distance-Vector Every node maintains a routing table all available destinations the next node to reach to destination the number of hops to reach the destination Periodically exchanges route table with all neighbors to keep routing data up to date

Problems of Distance Vector Loops C 11 BA D 1 Dest.NextMetric … ……… DB3 Dest.NextMetric … ……… DC2 Dest.NextMetric … ……… DB 3 Dest.NextMetric … ……… DD∞ Dest.NextMetric … ……… DD1

Problems of Distance Vector Counting-to-infinity (D,2) (D,4) (D,3) (D,5) (D,2) (D,4) 11 D 1 CBA Dest.NextMetric … ……… DB3, 5, … Dest.NextMetric … ……… DC2, 4, 6 … Dest.NextMetric … ……… DB 3, 5, …

Goal Design a routing method Preserves the simplicity of RIP Avoids the looping problem

DSDV Protocol DV-based routing protocol Sequence number attached route table Route advertisement Route updates Problem of fluctuations

DSDV Protocol DV-based routing protocol Sequence number attached route table Route advertisement Responding to topology change Route selection criteria Problem of fluctuations

Route Table Entry Structure Forwarding table (for routing) Advertised table (for update) Destination Next HopMetric Sequence Number Install Time Stable Data AA0S550_AT001_APtr_A BB1S102_BT001_APtr_B CB3S588_CT002 _APtr_C DB4S312_DT001_APtr_D DestinationMetric Sequence Number A0S550_A B1S102_B C3S588_C D4S312_D

Route Advertisement Advertise to each neighbor own routing information Advertised table Rules to set sequence number Advertisement increase own destination sequence number (use only even numbers) Broken link increase sequence number of this node by 1 (odd sequence number) set metric = 

Route Advertisement (A, 1, A-500) (B, 0, B-102) (C, 1, C-588) (A, 1, A-500) (B, 0, B-102) (C, 1, C-588) CBA B increases Seq. from 100 -> 102 B broadcasts routing information to Neighbors A, C including destination sequence numbers 11 Dest.NextMetricSeq AA0A-550 BB1B-102 CB2C-588 Dest.NextMetricSeq AA1A-550 BB0B-102 CC1C-588 Dest.NextMetricSeq. AB2A-550 BB1B-102 CC0C-588

Responding to Topology Change Immediate advertisements New routes, broken links, metric changes Full/Incremental Update Full Update: Send all routing information from own table. Incremental Update: Send only entries that has changed.

1.New Node CBA Dest.NextMetricSeq. AA0A-550 BB1B-104 CB2C-590 Dest.NextMetricSeq. AA1A-550 BB0B-104 CC1C-590 Dest.NextMetricSeq. AB2A-550 BB1B-104 CC0C-590 DD1D-000 D (D, 0, D-000) 1. D broadcast for first time Send Sequence number D Insert entry for D with sequence number D-000 Then immediately broadcast own table (A, 2, A-550) (B, 1, B-102) (C, 0, C-592) (D, 1, D-000) (A, 2, A-550) (B, 1, B-102) (C, 0, C-592) (D, 1, D-000) 3. C increases its sequence number to C-592 then broadcasts its new table. ……… 4. B gets this new information and updates its table……. Dest.NextMetricSeq. AB2A-550 BB1B-104 CC0C-590

2.Broken Link CBA D (D, 2, D-100) 2. B does its broadcast -> no affect on C (C knows that B has stale information because C has higher seq. number for destination D) -> no loop -> no count to infinity 1. Node C detects broken Link: -> Increase Seq. Nr. by 1 (only case where not the destination sets the sequence number -> odd number) Dest.NextMetricSeq. ……… DB3D-100 Dest.NextMetricSeq. ……… DC2D-100 Dest.NextMetricSeq. ……… DD  D-101

3.Broken Link - Immediate Advertisement Dest.NextMetricSeq. ………... DB 3 D-100 DB  D-101 Dest.NextMetricSeq. ………... DC 2 D-100 DC  D-101 Dest.NextMetricSeq. ……… DD 1 D-100 DD  D-101 CBA D (D, , D-101) 3. Immediate propagation B to A: (update information has higher Seq. Nr. -> replace table entry) (D, , D-101) 2. Immediate propagation C to B: (update information has higher Seq. Nr. -> replace table entry) 1. Node C detects broken Link: -> Increase Seq. Nr. by 1 (only case where not the destination sets the sequence number -> odd number)

Route Selection Criteria Update information is compared to own routing table 1. Higher destination sequence number 2. Better metric when sequence numbers are equal.

Problem of Fluctuations Two routes with identical sequence numbers are received in the wrong order Leads to unnecessary route advertisements

Problem of Fluctuations

Damping Fluctuations Settling time: time between arrival of first route and the best route with a given sequence number Last settling time Average settling time Delay: Average_Settling_Time × 2

Summary Advantages Simple Loop free No latency caused by route discovery Disadvantages Overheads in maintaining route table routing information may never be used