Designing Reliable Delivery for Mobile Ad-hoc Networks in Robots BJ Tiemessen Advisor: Dr. Dan Massey Department of Computer Science Colorado State University

Motivation Autonomous robots used to perform search and rescue Autonomous robots used to perform search and rescue Need reliable data communications Need reliable data communications

The Robots Evolution Robotics ER1 Evolution Robotics ER1 Use standard laptop Use standard laptop USB camera USB camera wireless card wireless card

Ad-hoc Network No central infrastructure No central infrastructure Each node may act as a sender or receiver Each node may act as a sender or receiver Each node may also need to act as a router Each node may also need to act as a router

Mobile Ad-hoc Network In a Mobile Ad-hoc Network (MANET) each node is free to move aroundIn a Mobile Ad-hoc Network (MANET) each node is free to move around MANET presents new challengesMANET presents new challenges Topology may be constantly changingTopology may be constantly changing Nodes may move out of range of other nodesNodes may move out of range of other nodes

Transmission Control Protocol (TCP) More than 90% of all traffic in the Internet is TCPMore than 90% of all traffic in the Internet is TCP Without TCPWithout TCP packets may be delivered out of orderpackets may be delivered out of order packets may be lostpackets may be lost

How 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

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

Methodology Network Simulator (ns2)Network Simulator (ns2) Single TCP flowSingle TCP flow Ad-Hoc On-Demand Distance Vector (AODV) routingAd-Hoc On-Demand Distance Vector (AODV) routing Maximum node speed.5 m/sMaximum node speed.5 m/s

Topology 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 Changes As the mobile node moves The topology changes The route from sender to receiver changes

TCP Throughput

TCP 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 Window

Changing Packet Size

Conclusion Changing the TCP window and packet size reduces the number of dropped packets and increases the throughput Changing the TCP window and packet size reduces the number of dropped packets and increases the throughput

Future Work Look at TCP timeout during route changes Look at TCP timeout during route changes Adaptive packet size and window size depending on number of hops to destination Adaptive packet size and window size depending on number of hops to destination

Questions?