Wireless Ad Hoc and Sensor Networks

Optimized Energy and Delay-Based Routing 4198.10.2.2 Routing PacketsThe routing aspects of the OEDSR protocol have been implemented onthe 8051 platform with an 802.15.4 radio module. Five types of messageshave been considered:• BEAM packet: The BS broadcasts BEAM packets to the wholenetwork to wake-up nodes and initiates data transmission. RSSIis retrieved by the receiving nodes and used to estimate the distanceto the BS.• HELLO packet: The node while searching for a route to the BS,broadcasts HELLO packets to neighbors periodically until ACKis received, or until timeout. The distance to BS is included sothat the receiving node can determine the closest node to the BS.• Acknowledgment (ACK) packet: ACK is sent as a response to theHELLO packet when the node’s distance to BS is smaller than therequesting node’s distance. Also, ACK contains the node’sremaining energy and distance to the BS. The HELLO source nodereceives ACK packet and calculates a transmission delay. The linkcost is calculated and temporarily stored to compare it with laterresponses.• SELECT packet: When HELLO/ACK timeout elapses, the nodeselects the route based on the link costs from the stored ACKinformation. Subsequently, the SELECT packet is sent to theselected node to indicate route selection. The receiving node startsroute discovery toward BS by sending a HELLO packet.• DATA packet: The DATA packet conveys application specific datato the BS.8.10.2.3 Traffic CasesFigure 8.51 presents a block diagram of the routing implementation. Thehandling of the received message starts at the RX block, where the typeof the packet is determined. Next, the processing proceeds depending onthe packet type.8.10.2.4 Memory LimitationsMemory limitations are incurred by the hardware. The routing protocolrequires a particular amount of memory to store the routing table andtemporary information from ACK. The number of routing table entriesdepends on expected number of active CHs. Moreover, the routing tablesstore only a link cost value, calculated from HELLO-ACK exchange. Furthermore,to reduce memory requirements, periodically inactive sourcesare purged from the routing table.