Reliable Transport for Wireless Sensor Networks

Abstract

Wireless sensor networks (WSNs) are ad-hoc wireless networks of small form-factor embedded nodes with limited memory, processing, and energy resources. Certain applications, like security and art monitoring,require reliable data transport. Current work for WSNs only provides stochastic reliability or guaranteed reliability for bulk transfer. This thesis describes the design, implementation, and evaluation of Reliable Transport AODV (RT-AODV). RT-AODV is a protocol that provides guaranteed reliability for individual messages. Both routing and reliable transport are covered in this work. End-to-end positive acknowledgements with timeouts and retransmissions are used to provide guaranteed reliability. NST-AODV, an existing any-to-any routing protocol, is used to route the data and acknowledgement messages through the network. To enhance the stability and quality of NST-AODV some adjustments are done: the hardware specifc Link Quality Indicator (LQI) is replaced by a statistical link estimator, and a loop detection mechanism and route quality monitoring are added. A proof of concept implementation has been done on the Embedded Software group's testbed. Experiments of larger scale and longer duration were done in TOSSIM simulations. For evaluation, Reliable Transport AODV (RT-AODV) is compared to the Collection Tree Protocol (CTP) and NST-AODV. Results show that RT-AODV performs well compared to both NST-AODV and CTP. A serious cost increase (in terms of transmissions) is involved with using end-to- end acknowledgements. The strength of RT-AODV is not pure delivery ratio. For larger networks, it performs slightly less than NST-AODV. However, RT-AODV guarantees that a message is delivered to its destination if an acknowledgement is received. The work described in this thesis shows that using end-to-end acknowledgements and any-to-any routing in wireless sensor networks is certainly viable.