Reversing the Collision Avoidance Handshake in Wireless Networks

1. Reversing the Collision Avoidance Handshake in Wireless Networks J.J. Garcia-Luna-Aceves and Makis Tzamaloukas (jj,jamal@cse.ucsc.edu)Computer and Communications Research Group (CCRG)http://www.cse.ucsc.edu/research/ccrg Computer Engineering DepartmentJack Baskin School of EngineeringUniversity of CaliforniaSanta Cruz, CA 95064

2. Presentation Outline • Sender-Initiated Collision Avoidance Protocols • Motivation • Polling Issues • Correct Collision Avoidance • RIMA protocols • Throughput and Delay Analysis • Conclusions JJ. Garcia-Luna-Aceves and A. Tzamaloukas

3. Sender-Initiated Protocols • SRMA (Kleinrock and Tobagi, August ‘76) • MACA (Karn, April ‘90) • MACAW (Bharghavan, Demers, Shenker and Zhang, August ‘94) • FAMA (Garcia-Luna-Aceves and Fullmer, September ‘97) • IEEE 802.11 (July ‘97) JJ. Garcia-Luna-Aceves and A. Tzamaloukas

4. Motivation • The recipient of data packet is the point of interest • Recast the collision avoidance dialogues so that the receiver, sender or both can have control of the dialogue • Provide equal or better throughput than any sender-initiated IEEE 802.11-like MAC protocol • Be applicable to multi-channel frequency-hopping or direct-sequence spread-spectrum radios • To date no receiver-initiated MAC protocol ensures correct collision avoidance • The receivers poll the senders JJ. Garcia-Luna-Aceves and A. Tzamaloukas

5. Ensuring Correct Collision Avoidance • First receiver-initiated MAC protocol was MACA-BI (Talucci and Gerla): • a node sends a DATA packet if it has previously received an RTR • a polled node can send a DATA packet either to the polling node or to any other neighbor • does not guarantee correct floor acquisition JJ. Garcia-Luna-Aceves and A. Tzamaloukas

6. Ensuring Correct Collision Avoidance • At time t0, nodes a and d send RTRs to b and e; at time t1 both b and e send DATA to c resulting in a collision d a b c e t0 RTR to b RTR to e t1 DATA to c DATA to c JJ. Garcia-Luna-Aceves and A. Tzamaloukas

7. Ensuring Correct Collision Avoidance • At time t0, node a sends an RTR to b; at time t1, b sends DATA to a; at time t2 < t1 + , c sends an RTR to d; at time t3, d sends DATA to c; if data packets last longer than  + 3 the DATA from b and d collide at c a b c d t0 RTR t1 DATA t2 RTR t3 DATA JJ. Garcia-Luna-Aceves and A. Tzamaloukas

8. Ensuring Correct Collision Avoidance • With RIMA-SP correct floor acquisition is guaranteed: • the polled node transmits a DATA packet only to the polling node • a collision avoidance period of  seconds is required at a polled node prior to answering an RTR; we have shown that  =  • an additional control signal is introduced; we call this signal No-Transmission-Request (NTR) JJ. Garcia-Luna-Aceves and A. Tzamaloukas

9. RIMA-SP illustrated RTR RTR Successful handshake RTR data X Z X Z RTR RTR RTR BACKOFF RTR RTR Colliding RTRs X Z X Z RTR RTR RTR RTR RTR NTR NTR RTR X Z Hidden node interference NTR X Z data NTR RTR NTR RTR JJ. Garcia-Luna-Aceves and A. Tzamaloukas

10. RIMA-SP timing diagrams Waiting period X RTR DATA Node X sends an RTR and after  seconds receives a DATA packet Z X RTR Nodes X and Z send RTRs within  seconds and therefore a collision occurs Z RTR channel collision BACKOFF Noise detected at Z X RTR NTR BACKOFF Due to interference from node Z, node X sends an NTR to stop the handshake Z interference JJ. Garcia-Luna-Aceves and A. Tzamaloukas

11. Polling Issues • When to poll: whether or not the polling rate is independent of the data rate at polling nodes • independent polling • data driven polling • To whom: whether the poll is sent to a particular neighbor or to all neighbors; for dense networks a schedule must be provided to the poll recipients • How: whether the polling packet asks for permission to transmit as well JJ. Garcia-Luna-Aceves and A. Tzamaloukas

12. RIMA Protocols • Polling done with RTR (Request-To-Receive) packet • Three Receiver Initiated Medium Access (RIMA) protocols defined based on the type of polling: • RIMA-SP: A simple poll receiver initiated protocol (only the receiver sends data in a successful busy period) • RIMA-DP: A dual poll receiver initiated protocol (2 data packets are sent in the same successful busy period) • RIMA-BP: A broadcast poll receiver initiated protocol (the RTR is sent to everybody) JJ. Garcia-Luna-Aceves and A. Tzamaloukas

13. data data RTR RTR RTR CTS data X Z X Z X Z RTR data RTR data RIMA-DP illustrated RTR RTR data data RTR X Z data X Z Success 1 data X Z RTR RTR data data Success 2 RTR RTR NTR RTR RTR BACKOFF NTR RTR RTR X Z NTR X Z X Z X Z Failure 2 Failure 1 RTR data NTR RTR NTR RTR RTR RTR JJ. Garcia-Luna-Aceves and A. Tzamaloukas

14. RIMA-DP timing diagrams Waiting period X RTR DATA Node X sends an RTR and after  seconds receives a DATA packet and then sends its DATA DATA Z Waiting period RTR DATA X Node X sends an RTR and node Z replies with a CTS; node X sends its DATA Z CTS X RTR Nodes X and Z send RTRs within  seconds and therefore a collision occurs Z RTR channel collision BACKOFF Noise detected at Z X RTR NTR BACKOFF Due to interference from node Z, node X sends an NTR to stop the handshake Z interference JJ. Garcia-Luna-Aceves and A. Tzamaloukas

15. RIMA-BP illustrated RTR RTR RTR RTS data X Z X Z X Z Success 1 RTR RTR Y Y RTS RTR RTR RTS NTR NTR RTS X Z RTR X Z Failure 1 NTR X Z RTR RTR NTR NTR RTR RTR BACKOFF X Z RTR X Z Failure 2 RTR RTR RTR JJ. Garcia-Luna-Aceves and A. Tzamaloukas

16. RIMA-BP timing diagrams Waiting period RTR X Node X sends an RTR; node Z responds with a RTS and after  seconds sends its DATA Z RTS DATA collision RTR X NTR Node X sends an RTR; nodes Z and Y send an RTS within  seconds; node X sends an NTR to stop the handshake Z RTS Y RTS X RTR Nodes X and Z send RTRs within  seconds and therefore a collision occurs Z RTR channel collision BACKOFF JJ. Garcia-Luna-Aceves and A. Tzamaloukas

17. Throughput Analysis Model • fully-connected network of N nodes • single, unslotted channel, error-free • the size for an RTR, RTS and CTS is  seconds; the size for a data packet is  seconds • the turn-around time is considered to be part of the duration of control and data packet • the propagation delay of the channel is  seconds • a polled node receiving an RTR always has a data packet to send • the probability that the packet is addressed to the polling node is 1/N JJ. Garcia-Luna-Aceves and A. Tzamaloukas

18. Throughput Analysis • 500 Byte data packets; 1Mbps network speed; maximum distance between nodes is 1 mile; on the left a 10 node network; on the right a 50 node network JJ. Garcia-Luna-Aceves and A. Tzamaloukas

19. Delay Analysis 500 Byte data packets; 1Mbps network speed; maximum distance between nodes is 1 mile JJ. Garcia-Luna-Aceves and A. Tzamaloukas

20. Heavy Traffic Approximation • MACA-BI analysis assumes that there is always a DATA packet after a successful poll • To present a fair comparison between MACA-BI and RIMA protocols we analyze a heavy load approximation where there is always a DATA packet to be sent after receiving an RTR JJ. Garcia-Luna-Aceves and A. Tzamaloukas

21. Throughput Analysis • 500 Byte data packets; 1Mbps network speed; maximum distance between nodes is 1 mile; network of 50 nodes; heavy load approximation throughput: any polled node always has data to send to any polling node JJ. Garcia-Luna-Aceves and A. Tzamaloukas

22. Conclusions • RIMA protocols provide correct collision avoidance in the presence of hidden terminals • The throughput achieved with RIMA-DP is higher than any other sender initiated MAC protocol for fully connected networks • RIMA-DP achieves higher throughput than all other collision avoidance protocols in fully-connected networks under heavy load approximation • Relative differences in performance remain the same in networks with hidden terminals JJ. Garcia-Luna-Aceves and A. Tzamaloukas

23. Simulation Results Base N1 N1 N1 N2 (b) Base (a) N1 N1 (c) B2 B1 JJ. Garcia-Luna-Aceves and A. Tzamaloukas

24. Simulation Results JJ. Garcia-Luna-Aceves and A. Tzamaloukas