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Dynamic Source Routing andDynamic Source Routing andAssociativityAssociativity--Based RoutingBased Routing

Nil UnerdemE6768, Professor Maxemchuk

May 2, 2002

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OutlineOutline

Overview of DSR, Route Discovery,Route Maintenance

ABR Characteristics

ABR Protocol

Differences and Comparison Issues

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DSR OverviewDSR Overview

Uses source routing, every node has acache of source routes

Phases: route discovery, routemaintenance

No periodic messaging

Multiple routes available Promiscuous mode

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Route DiscoveryRoute Discovery

If a mobile node wants to send a packet, itfirst checks its route cache.

Route discovery is initiated by broadcasting a

route requestpacket. Aroute requestcontains the address of destination, theaddress of the source, and a unique ID.

Each node checks for a route, if not, it addsits own address to the route recordof thepacket.

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Route Discovery continuedRoute Discovery continued

To limit route requests, the mobile onlyforwards if it is new and if the address is notalready in its route record.

Aroute replyis generated when thedestination is reached or when there is anintermediate node with an unexpired route tothe destination in its cache.

The route recordnow contains the sequenceof hops. It reverses the path or generates itsown route discovery and piggybacks route

replyon a new route request.

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Route MaintenanceRoute Maintenance

Accomplished through the use ofroute errorpackets and acknowledgements.

Route errorpackets are generated at a node

when there is a link failure. The source is interrupted, the hop error is

removed from the route cache and all routeswith error are truncated.

Acknowledgments also verify link operation,passive acknowledgments as well.

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AssociativityAssociativity--Based RoutingBased Routing

Associativity is related to the spatial,temporal, and connection stability of a MH.Stability in ABR refers to associativity ticks,signal strength, and power life.

Assumption: a MH will spend some dormanttime at a location before moving again.

New routing metrics besides fast adaptability,

minimum-hop, prop. delay, loop avoidance,and link capacity:

longevity of a route (not shortest path)

fair route relaying load (congestion).

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AssociativityAssociativity TicksTicks

Each MH transmits beacons to identify itselfand constantly updates its associativity ticksbased on its neighbors.

The threshold where associativity transitionstake place is defined. If ticks>Athreshold,stable link, stable route (may not be shortestpath).Adepends on trans. range, speed, and

beaconing interval. Low associativity ticks = high state of mobility

for MH.

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ABR Protocol DescriptionABR Protocol Description

Route discovery when a source needsa route.

Route reconstruction when links

change due to source, destination,intermediate, or subnet-bridging MHmigration.

Route deletion when a source nolonger needs a route.

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Route DiscoveryRoute Discovery

Broadcast query (BQ) and an await replycycle by the SRC. BQ has a sequence numberand is broadcast only once.

All INs check to see if they are the DEST. Ifnot, IN re-broadcasts and appends:- MH address - link prop. Delay

- associativity ticks - remaining power life

- route relaying load - route hop count

DEST receives multiple BQs, selects bestroute, sends REPLY back to SRC via route.

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Route Reconstruction (RRC)Route Reconstruction (RRC)PhasePhase

RRC is invoked to cope with mobility.ABR attempts to locate an alternative route

quickly without resorting to a BQ unlessnecessary.

Phases: Partial route discovery

Invalid route erasure

Valid route update

New route discovery (worst case)

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RRC continuedRRC continued

Any moves by SRC will cause routeinitialization via BQ packet.

Any moves by DEST cause a localized query

(LQ) process at upstream neighbor. If thisfails, a route notification (RN) causes new BQfrom SRC.

Any moves by an IN invokes LQ, route erasetowards DEST, either partial route or no. ofbacktracks exceeds route length (delay).

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MultipleMultiple RRCsRRCs

Concurrent movements by SRC, DEST,and IN cause multiple RRCs.

Only one RRC succeeds. LQs have asequence number and if nodesprocessing LQs hear a BQ, the LQ

process is aborted.

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Route Deletion PhaseRoute Deletion Phase

When a discovered route is no longerdesired, a route delete (RD) broadcastis initiated by the SRC so that all INs

will update their routing table entries. Route entries may also be invalidated

upon time out if there is no traffic.

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ABR Headers and TablesABR Headers and Tables

Each data packet header contains only theneighboring node route information, not allnodes in the route (unlike DSR).

Routing table contains neighbor information,hop count to DEST, and route relaying load(updated by the data-link layer protocol).

Neighboring table interprets beacons and

updates associativity ticks.Seen tables for duplicate BQ,RD, or LQ.

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ABR/DSR Main DifferencesABR/DSR Main Differences

Source routing(source initiated)

No beaconing

Shortest pathoptimal

No partial routediscovery, multipleroutes (SRC routerebuilding)

Hop by hop routing(source initiated)

Associativitybeacons and QoS

Long lived, stableroutes optimal

Partial routediscovery (IN routerebuilding)

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Comparison IssuesComparison Issues

Periodic beaconing at each MH in ABR maylead to power consumption problems.

Multiple route overhead (and stale routes) inDSR compared with partial route discoverytime in ABR (RRC and more BQs).

Source routing overhead in DSR (scalability),not in ABR.

Stability (load and power) and long livedroutes (ABR) vs. shortest path routes (DSR).

The signaling traffic grows with increasing

mobility of active routes in ABR.

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ReferencesReferences

Toh, C.-K., Ad-Hoc Mobile Wireless Networks:Protocols and Systems, 2002

Johnson, David B. and Maltz, David A., DynamicSource Routing in Ad Hoc Wireless Networks, 1996

Toh, C.-K.,A Novel Distributed Routing Protocol ToSupport Ad-Hoc Mobile Computing, 1996

Royer, Elizabeth M.,A Review of Current RoutingProtocols for Ad Hoc Wireless Networks, 1999

Perkins, Charles E., Performance Comparison of TwoOn-Demand Routing Protocols for Ad Hoc Networks,2001