Dynamic Source Routingin ad hoc wireless networks

Alexander StojanovicIST Lisabon 1

Outline

■ Introduction

■ Assumptions■ Basic Operation

Route Discovery

Route Maintenance

■ Optimizations■ Performance Evaluation■ Conclusion

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Introduction (1/3)

Ad hoc network A collection of mobile hosts with wireless network interfaces may

form a temporary network

Without the aid of any established infrastructure or centralizedadministration

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Introduction (2/2)

Dynamic Source Routing The sender of a packet determines the complete sequence of

nodes through which to forward the packet

The sender explicitly lists this route in the packet’s header

DSR offers a number of advantages Uses no periodic routing advertisement messages

Network bandwidth overhead

Battery power

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Assumptions

n Each host should be willing to forward packets for other hosts

The diameter of the ad hoc network may be greater than one

Hosts move at any time without notice, but the speed withwhich hosts move is moderate

Hosts can enable a promiscuous receive mode on theirwireless network interface hardware

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Basic Operation

The sender constructs a source route in the packet’s header

Each host in the ad hoc network maintains a route cache

When a host sends a packet to another host A route is found

Use this route to transmit the packet

Use the route discovery

No route is found

The route should fail The correct operation of a route in use we call route maintenance

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Basic Operation – Route Discovery (1/3)

A host initiating a route discovery Broadcasts a route request packet

Each route request packet contains Route record

Initiator address Request id

If the route discovery is successful The Initiating host receives a route reply packet

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Basic Operation – Route Discovery (2/3)

When any host receives a route request packet, it processesthe request according to the following steps: If <initiator address, request id> is found in this host

Discard the route request packet

If this host’s address is already listed in the route record

Discard the route request packet

If the target of the request matches this host’s address

Return a copy of this route in a route reply packet to the initiator

Otherwise, append this host’s address to the route record, andre-broadcast the request

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Basic Operation – Route Discovery (3/3)

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Basic Operation – Route Maintenance (1/2)

Conventional routing protocols integrate route discovery withroute maintenance by continuously sending periodic routingupdates

There are no periodic message of any kind from any of themobile hosts

It monitors the operation of the route and inform the sender ofany routing errors

The host sends a route error packet to the original sender

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Basic Operation – Route Maintenance (2/2)

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OptimizationsFull Use of the Route Cache (1/2)

A host can add entries to its route cache any time it learns anew route

A host may use its route cache to avoid propagating a routerequest packet received from another host

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OptimizationsFull Use of the Route Cache (2/2)

There are two problems can occur

Collision

Delay for a period of d

d=Hx(h – 1 + r)

h : the length of network hops for the route to be returned

r : a random number between 0 and 1

H : a small constant delay to be introduced per hop (4 msec)

Loop The host instead discards the request if the route in its reply

would contain a loop

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OptimizationsReflecting Shorter Routes

While two hosts are communicating with each other usingcached routes it is desirable for the hosts to begin using shorter routes if the

hosts move sufficiently closer together

Network interfaces operate in promiscuous receive mode

Use an unsolicited route reply packet

It has not yet added this method to simulator

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OptimizationsImproved Handling of Errors

Use promiscuous receive mode

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Performance Evaluation (1/3)

The Simulation The area in which the host move is square, 9 meters on a side

Each host moves with a velocity between 0.3 ~ 0.7 meters / s Each transceiver has a range of 3 meters Packet lengths

70% of the packets are long packets (1000 bytes)

The remainder are short packets (32 bytes)

Transmissions to a host that is out of range always fail whiletransmissions to a host in range fail with a probability of 5%

The bandwidth for transmitting data is 100 Kbytes / s

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Performance Evaluation (2/3)

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Performance Evaluation (3/3)

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Conclusion

This presentation has presented a protocol for routing packetsbetween wireless mobile hosts in an ad hoc network.

Future work

Security

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