Designing Reliable Delivery for Mobile Ad-hoc

Networks in Robots

BJ TiemessenBJ TiemessenAdvisor: Dr. Dan MasseyAdvisor: Dr. Dan Massey

Department of Computer ScienceDepartment of Computer Science

Colorado State UniversityColorado State University

MotivationMotivation

• Autonomous robots used to Autonomous robots used to perform search and rescueperform search and rescue

• Need reliable data Need reliable data communicationscommunications

The RobotsThe Robots

• Evolution Evolution Robotics ER1Robotics ER1

• Use standard Use standard laptoplaptop

• USB cameraUSB camera• 802.11 wireless 802.11 wireless

cardcard

Ad-hoc NetworkAd-hoc Network

• No central No central infrastructureinfrastructure

• Each node may Each node may act as a sender act as a sender or receiveror receiver

• Each node may Each node may also need to act also need to act as a routeras a router

Mobile Ad-hoc NetworkMobile Ad-hoc Network

• In a Mobile Ad-hoc Network In a Mobile Ad-hoc Network (MANET) each node is free to (MANET) each node is free to move aroundmove around

• MANET presents new challengesMANET presents new challenges• Topology may be constantly changingTopology may be constantly changing• Nodes may move out of range of Nodes may move out of range of

other nodesother nodes

Transmission Control Transmission Control Protocol (TCP)Protocol (TCP)• More than 90% of all traffic in the More than 90% of all traffic in the

Internet is TCPInternet is TCP• Without TCPWithout TCP

• packets may be delivered out of packets may be delivered out of orderorder

• packets may be lostpackets may be lost

How TCP WorksHow TCP Works

• Sending node sends a data packet

• Receiving node sends an acknowledgment packet once data packet is received

• Sending node sends next data packet once acknowledgment packet is received

PurposePurpose

• Improve TCP performance in Improve TCP performance in mobile ad-hoc networks mobile ad-hoc networks

MethodologyMethodology

• Network Simulator (ns2)Network Simulator (ns2)• Single TCP flowSingle TCP flow• Ad-Hoc On-Demand Distance Vector Ad-Hoc On-Demand Distance Vector

(AODV) routing(AODV) routing• Maximum node speed .5 m/sMaximum node speed .5 m/s

TopologyTopology

•15 stationary nodes in a chain topology

•1 mobile node that moves past all nodes

•Mobile node 15 sends data to node 0, the first node in the chain

Routing ChangesRouting Changes

• As the mobile node moves • The topology changes

• The route from sender to receiver changes

TCP ThroughputTCP Throughput

TCP WindowTCP Window

• TCP window is number of data packets that are sent every time an acknowledgement is received

• Each time the sender receives an ack it can send 2 packets

• When 3 duplicate acks are received, cut send window in half

• If no ack is heard after timeout interval set window to 1

Changing TCP WindowChanging TCP Window

Changing Packet SizeChanging Packet Size

ConclusionConclusion

• Changing the TCP window and Changing the TCP window and packet size reduces the number of packet size reduces the number of dropped packets and increases the dropped packets and increases the throughputthroughput

Future WorkFuture Work

• Look at TCP timeout during route Look at TCP timeout during route changeschanges

• Adaptive packet size and window Adaptive packet size and window size depending on number of hops size depending on number of hops to destinationto destination

Questions?Questions?