the ad hoc on-demand distance vector routing protocol

The Ad hoc On-Demand Distance Vector Routing Protocol

Elizabeth M. RoyerElectrical and Computer Engineering Department

University of California, Santa Barbara

[email protected]://alpha.ece.ucsb.edu/~eroyer

Elizabeth M. Royer AODV 2

Why Go Wireless?

Mobile wireless networks...• Free the user from cumbersome wires• Enable anytime/anywhere connectivity• Allow “instantaneous” network setup • Bring computer communication to

areas without existing infrastructure


Wireless Networks

• Infrastructured Networks– Wired backbone– Mobile nodes communicate with access point– Handoff between access points as nodes move– Suitable for buildings, campuses

• Infrastructureless Networks– No wired backbone– Mobile nodes communicate directly with other nodes– All nodes are routers– Suitable for search-and-rescue, field operations


Ad hoc Networks

• Infrastructureless networks• All nodes capable of movement• Links appear and disappear dynamically• May need several hops to reach destination• Special constraints:

– limited bandwidth– limited power– high error rates

• Protocol needed to create and maintain routes– Conventional routing protocols not applicable


Desired Characteristics

• Unicast, broadcast, and multicast routing ability • Ability to find multi-hop paths• Dynamic topology maintenance• Ability to self-start• Loop-freedom and rapid route convergence• Low consumption of memory, bandwidth• Scalable to large ( 1000) numbers of nodes• Minimal control overhead; no data overhead

≥


Ad hoc Routing Protocols

Two basic approaches:• Table-driven

– Each node discovers and maintains routes to every other node in network

– All movement and broken link information propagated across network

– High bandwidth consumption and processing overhead– DSDV, WRP

• On-demand source-initiated– Routes established and maintained only when needed– Lower bandwidth consumption, processing overhead– Higher route acquisition latency– DSR, TORA, ODMRP, CAMP


Ad hoc On-Demand Distance Vector Routing

• Primary Objectives– Provide unicast, broadcast, and multicast capability– Initiate forward route discovery only on demand– Disseminate changes in local connectivity to those

neighboring nodes likely to need the information• Characteristics

– On-demand route creation• Effect of topology changes is localized• Control traffic is minimized

– Two dimensional routing metric: <Seq#, HopCount>– Storage of routes in Route Table


Route Table

• Fields:– Destination IP Address– Destination Sequence Number– HopCount– Next Hop IP Address– Precursor Nodes– Expiration Time

• Each time a route entry is used to transmit data, the expiration time is updated to current_time + active_route_timeout

Next Hop

Source

Source

APrecursor Nodes

Destination


Forward Path Setup

• Destination, or intermediate node with current route to destination,unicasts Route Reply (RREP) to source<Flags, HopCnt, Dst_Addr,

Dst_Seq#, Src_Addr, Lifetime>• Nodes along path create

forward route• Source begins sending data

when it receives first RREP

Source

Destination

Forward Path Formation


Path Maintenance

• Movement of nodes not along active path does not trigger protocol action• If source node moves, it can reinitiate route discovery• When destination or intermediate node moves,

node upstream of break broadcasts Route Error (RERR) message• RERR contains list of all destinations no longer reachable due to link break• RERR propagated until node with no precursors for destination is reached

Source

Destination1

2

3

4

3’

Source

Destination1

24

3’


Multicast Overview

• Utilizes same RREQ/RREP message cycle as unicast route discovery

• Shared tree composed of group members and connecting nodes is formed

• Dynamic group membership• Group Leader

– Maintains and distributes group sequence number– Not a central point of failure

• Multicast group members are also routers for the multicast tree

• Multicast routing information maintained in Multicast Route Table


Multicast Routing TableFields:

– Multicast Group IP Address– Group Leader IP Address– Group Sequence Number– HopCount to Group Leader– Next Hops

• Next Hop IP Address• Activated Flag• Link Direction

A

A’s Next Hops

Group Leader

Activated flag set after reception of Multicast Activation (MACT) message


Multicast Route Discovery

• Source node broadcasts RREQ• Indicates whether wants to

join group• Nodes receiving RREQ

set up reverse route entry• If no reply received, rebroadcast

RREQ up to rreq_retriesadditional attempts

• After rreq_retries attempts, become group leader

Group Leader

Non-Tree MemberMulticast Tree MemberMulticast Group MemberProspective Group Member

R

R

R


Group Hello Messages

• First member of mulitcast group becomes leader for that group

• Initializes, maintains, disseminates group sequence number• Broadcasts Group Hello every

group_hello_interval seconds<Flags, HopCnt, GrpLdr_Addr, MGrp_Addr, MGrp_Seq#>

• Used by multicast tree members to update current distance to group leader


Unicast Simulation Environment

• All simulations executed in GloMoSim• Random waypoint mobility model• Simulated Length of Time: 600 seconds• IEEE 802.11 DCF• Data rate: 1.0 Mbit/sec• Data packet size: 64 bytes• Room Size: 1000m x 1000m• Transmission Radius: 250m• Objectives

– AODV route establishment is quick and accurate– Investigate amount of control overhead generated


Unicast Packet Delivery Ratio

• High Packet Delivery Ratio for both network sizes• Slightly decreased for 100 Node simulation

– Higher node degree– More collisions

90

92

94

96

98

100

0 0.2 0.4 0.6 0.8 1

Speed (m/s)

Pac

ket D

eliv

ery

Rat

io (%

)

50 Nodes

100 Nodes


Unicast Control Overhead

• Small increase in number of RREQs, RERRs• Large Increase in RREPs

– Expanding Ring Search– Query Localization

100 Nodes

020406080

100120140160180200

0 0.2 0.4 0.6 0.8 1

Speed (m/s)

Nu

mb

er

of

Me

ss

ag

es

RREQRREPRERR

50 Nodes

020406080

100120140160180200

0 0.2 0.4 0.6 0.8 1

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Multicast Simulation Environment

• All simulations executed in GloMoSim• Random waypoint mobility model• Simulated Length of Time: 300 seconds• IEEE 802.11 DCF• Data rate: 2.0 Mbit/sec• Data packet size: 64 bytes• Room Size: 1000m x 1000m, 1500m x 300m• Transmission Radius: 200m - 500m• Objectives

– AODV builds and maintains multicast trees– Determine effect of transmission radius on performance


Packet Delivery Ratio

• Both networks show high packet delivery ratio• Speed has smaller effect on 1500m x 300m network• Increase in power increase packet delivery ratio

1000m x 1000m

80

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0 0.2 0.4 0.6 0.8 1Speed (m/s)

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1500m x 300m

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⇒

TransmissionRange


Control Overhead1000m x 1000m

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1500m x 300m

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• Increase in power reduction in control overhead• Initialization overhead approximately constant for all ranges• 1500m x 300m control less affected by speed

⇒

TransmissionRange


Distance to Multicast Group Leader

• Number of hops decreases for increasing transmission radius

• Distance to group leader indicates – Size of tree– Number of hops data packets must traverse

1000m x 1000m

0

1

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ps

1500m x 300m

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ps

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TransmissionRange


Number of Repairs to Multicast Tree

• Number of repairs – Inversely proportional to transmission range– Increases for increasing speed

• 1500m x 300m network requires fewer repairs

1000m x 1000m

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1500m x 300m

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TransmissionRange


Conclusion

AODV Main features• Unicast, Broadcast, and Multicast communication• On-demand route establishment with small delay• Multicast trees connecting group members maintained for

lifetime of multicast group• Link breakages in active routes efficiently repaired• Routes are always loop-free through use of sequence

numbersAODV is an effective and efficient routing protocol forall forms of ad-hoc mobile communication


For More Information...

Elizabeth Royerhttp://alpha.ece.ucsb.edu/[email protected]

http://alpha.ece.ucsb.edu/~eroyer/aodv.html

ftp://ftp.ietf.org/internet-drafts/draft-ietf-manet-aodv-04.txt


Future Work

• Linux Implementation• Continue simulations with varying channel models• Security• Reliable delivery• Quality of Service• Interoperate with Mobile IP

the ad hoc on-demand distance vector routing protocol

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