RIPT: A Receiver-initiated Reservation-based Protocol for Underwater Acoustic Networks

1. RIPT: A Receiver-initiated Reservation-based Protocol for Underwater Acoustic Networks Nitthita Chirdchoo, Wee-Seng Soh, Kee Chaing Chua IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 26, NO. 9, DECEMBER 2008

2. Outline • Introduction • Receiver Initiated Packet Train (RIPT) Protocol • Simulation and Results • Conclusion

3. Introduction • In terrestrial, typically assume the propagation delay is negligible • busy signal, handshaking mechanism • In contrast, underwater communication resulting in • propagation delay and narrow available bandwidth • may not be practical to set aside a separate frequency band for transmitting busy signals

4. RIPT Protocol Overview • Long propagation delay, node takes much longer to receive control packets • higher collision rate, and again, low throughput • It appears that receiver-initiated reservations are better • because a receiver knows exactly when the current handshake will end • Utilized a receiver-initiated 4-way (RTR/SIZE/ORDER/DATA) handshake

5. 4-Way Handshaking

6. Initiated by RTR Packet • It contains • receiver’s ID and number of data slots reserved at the receiver (Mtrain) • inter-node propagation delay from itself to each of its neighbors • a flag to indicate whether the receiver has any DATA packet to broadcast • Nodes have same propagation delay • granting priority to node with smaller node ID

7. Transmission Time of SIZE Packet Receive RTR

8. First Hop Neighbor Calculate

9. ORDER Packet • It contains the total slots assigned to each neighboring, and the order of transmission • Each of the neighboring nodes is assigned a unique priority randomly • Mtrain = 4

10. Broadcast Packet (Nb) • Receiver resends the information on broadcast packets • Improve the chances of its neighbors to be ready for them • After ORDER packet transmitting, receiver transmits its broadcast packets, if any

11. DATA Train Transmission

12. Adaptive Train Size • If the receiver finds that its Mtrain is not large enough • increases Mtrain by 2 for the next round • If it finds that there are sufficient slot requests to fill up its Mtrain • decreases Mtrain by 1 • There should be a maximum limit for Mtrain, • avoid any receiver from capturing the channel for too long

13. When to Initiate an RTR Packet • The timing of initiating RTR packets is an important issue • Pick the exponential distribution for the time between RTR-initiations

14. Fairness Bit • To avoid same node acting as a receiver before other neighboring • fairness bit • If a node has released from a handshaking loop while acting as a receiver • set bit to ‘0’, and will not initiate any RTR packet • reset once only the node has served as sender • if a node has set ‘0’ for longer than tlimit,it will reset back to ‘1’

15. Simulation and Results

16. The effect of Mtrain and Tavg offered load per node = 0.07

17. Throughput

18. Transmission and Collision

19. Delay

20. Conclusion • They proposed and studied a new MAC protocol for multi-hop underwater acoustic networks – RIPT • Random access handshaking protocol that addresses long propagation delay • utilizing receiver-initiated reservations