Seongwon Han, Youngtae Noh, Max Ohlendorf , Mario Gerla University of California, Los Angeles

1. MDOTS: A Multi-session Delay-aware Opportunistic MAC protocol for Underwater Sensor Networks Seongwon Han, Youngtae Noh, Max Ohlendorf , Mario Gerla University of California, Los Angeles {swhan, ytnoh, maxo, gerla}@cs.ucla.edu • GOAL: Achieve better channel utilization while providing fairness • Alleviates limitations caused by the long propagation delay • Harnessing temporal/spatial reuse • Providing naïve frame rescheduling SEA Swarm Architecture • Our Solution: • Allow each node to have multiple sessions • Each node maintains a delay map through passive listening to the channel to avoid collision • Collision Detection: • A Delay map contains informations • source: the sender of the observed MAC frame • destination: the intended destination for the observed MAC frame • timestamp: the time at which the observed MAC frame was sent • src-dest delay: the estimated propagation delay between the source and the destination DOTS [1] MDOTS • Whenever a node initiates a communication or overhears an RTS or CTS transmission from its neighbors, the node calculates timing information for all future transmissions and receptions in the sequence. The node creates entries in its delay map for each of the calculated times. Before sending an RTS for a new session, the node inspects its delay map to verify that: • the associated RTS and DATA tx durations for this session do not conflict with its existing tx and rx schedules. • the subsequent CTS and ACK rx durations for this session do not conflict with its existing tx and rx schedules. • any impending RTS and DATA tx durations do not interfere with neighbors' rx schedules. Results: Randomly deployed 10 nodes : throughput as a function of offered load with fixed data size (128 bytes) Jain’s Fairness Index for the four protocols [2] Reference [1] Y. Noh, P. Wang, U. Lee, D. Torres and M. Gerla, DOTS: A Propagation delay-aware opportunistic MAC Protocol for Underwater Sensor Networks, In ICNP 2010. [2] R Jain, D. Chiu, and W. Hawe, A quantitative measure of fairness and discrimination for resource allocation in shared computer system, DEC Research, Tech. Rep., 1984.