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ASCENT Design When a neighbor receive a help message, it decides to join the network or not If the node joins, it becomes an active neighbor and signals the existence of a new active neighbor to other passive neighbors by sending a neighbor announcement message It continues until the number of active nodes stabilizes on a certain value and the cycle stops When the process is completed, the newly joined nodes participate in the data delivery process from source to sink more reliably The process will be repeated in the case of network event (e.g., node failure) or environmental effect (e.g., new obstacle) causes message loss
Neighbor Announcements Messages Data Message Source Source Sink Sink (b) Self-configuration transition (c) Final State ASCENT
ASCENT State Transactions Test
neighbors < NT and loss > LT loss < LT & help after Tt Active neighbors > NT (high ID for ties); or loss > loss T0 after Tp Passive Sleep after Ts NT: neighbor threshold LT: loss threshold T?: state timer values (p: passive, s: sleep, t: test) DL: Data loss rate ASCENT
ASCENT State Transactions Initially, a random timer turns on the nodes to avoid synchronization Node initializes to test state: Sends data and routing control messages Sets up a timer, Tt and sends neighbor announcement messages Moves into passive state if the conditions are met before Tt expires When Tt expires, it enters to active state The reasoning behind the test state is to probe the network to decide whether the addition of a new node would improve connectivity On entering the passive state, node: Sets up a timer Tp and when Tp expires, it enters to sleep state If before Tp expires, it enters to test state only if the conditions are met Nodes in passive state can hear all packets transmitted, but no routing or data packets are forwarded in this state since this is listen-only state ASCENT
ASCENT State Transactions The reasoning behind the passive state is to gather information about the state of the network without causing interference with other nodes Nodes in passive and test states update the number of active neighbors and data loss rates In passive states, the nodes still consume energy since the radio is on The nodes in sleep state turns the radio off, sets up timer Ts and goes to sleep When Ts expires, the nodes moves into passive state A node in the active state continuous to forward data and routing packets until it runs out of energy ASCENT
ASCENT Parameters Tuning ASCENT has many parameters and the choices are left to the applications such as a particular application may trade energy savings for greater sensing coverage Neighbor Threshold (NT): Determines the average connectivity if the network Tradeoff between energy consumed and/or level of interference (packet loss) vs. desired sensing coverage Determines the maximum amount of data loss an application can tolerate before requesting help to improve network connectivity This value is highly application dependent Determines the maximum time a node remains in test, passive, sleep states Tradeoff between power consumption vs. decision quality Loss Threshold (LT): Test timer (Tt), Passive timer (Tp), Sleep timer (Ts): References
[Basagni+ 2001] S. Basagni, D. Turgut, and S.K. Das, Mobility-Adaptive Protocols for Managing Large Ad hoc Networks, Proceedings of IEEE International Conference on Communications (ICC), Helsinki, Finland, June 11-14, 2001, pp. 1539-1543. [Chen+ 2002] B. Chen, K. Jamieson, R. Morris, and H. Balakrishnan, SPAN: An Energy-Efficient Coordination Algorithm for Maintenance in Ad hoc Wireless Networks, To appear in ACM Wireless Networks Journal, Vol. 8, No. 5, September 2002. [Cerpa+ 2002] A. Cerpa and D. Estrin, ASCENT: Adaptive Self-Configuring Sensor Networks Topologies, Proceedings of the Twenty First International Annual Joint Conference of the IEEE Computer and Communications Societies (INFOCOM 2002), New York, NY, USA, June 23-27 2002....
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This note was uploaded on 08/25/2011 for the course EEL 5937 taught by Professor Staff during the Spring '08 term at University of Central Florida.
- Spring '08