1. The Effect of Exerting Adequate Persistence in Collision Avoidance Protocols 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 Department Jack Baskin School of Engineering University of California Santa Cruz, CA 95064

2. MOMUC '99, November 15-17 JJ. Garcia-Luna-Aceves and A. E. Tzamaloukas2 Presentation Outline n Non-persistent collision avoidance protocols n Motivation n Limited persistence issues n Limited persistence protocols: – FAMA-LCS, RIMA-SPL, RIMA-DPL n Throughput analysis n Conclusions

3. MOMUC '99, November 15-17 JJ. Garcia-Luna-Aceves and A. E. Tzamaloukas3 Non-persistent MAC Protocols n SRMA (Kleinrock and Tobagi, August ‘76) n MACA (Karn, April ‘90) n MACAW (Bharghavan, Demers, Shenker and Zhang, August ‘94) n FAMA (Garcia-Luna-Aceves and Fullmer, September ‘97) n IEEE 802.11 (July ‘97) n RIMA (Garcia-Luna-Aceves and Tzamaloukas, August ‘99)

4. MOMUC '99, November 15-17 JJ. Garcia-Luna-Aceves and A. E. Tzamaloukas4 Motivation n Improve performance achieved with non-persistent protocols at light-moderate loads: – reduced number of times a single node with a packet to send after sensing the channel busy must back off – smaller idle periods n Modify traditional persistent strategies: – node persists to transmit a packet only for a limited amount of time – reduced amount of contention when the channel becomes idle

5. MOMUC '99, November 15-17 JJ. Garcia-Luna-Aceves and A. E. Tzamaloukas5 1-Persistent Carrier Sensing n Definition: Any node that has a local DATA packet to send will persist to sense the channel until no carrier is detected. At that time, with probability 1 the node will transmit the packet n Claim: Persisting over an entire DATA packet limits throughput ongoing transmission collision

6. MOMUC '99, November 15-17 JJ. Garcia-Luna-Aceves and A. E. Tzamaloukas6 Limited Persistence Carrier Sensing DEFINITION: persistent carrier sensing up to  seconds after detecting carrier to limit contention n FAMA-LCS (Floor Acquisition Multiple Access with Limited-persistence Carrier Sensing) n RIMA-SPL (Receiver Initiated Multiple Access with Single Poll and Limited-persistence carrier sensing) n RIMA-DPL (Receiver Initiated Multiple Access with Dual Poll and Limited-persistence carrier sensing)

7. MOMUC '99, November 15-17 JJ. Garcia-Luna-Aceves and A. E. Tzamaloukas7 FAMA-LCS

8. MOMUC '99, November 15-17 JJ. Garcia-Luna-Aceves and A. E. Tzamaloukas8 RIMA-SPL

9. MOMUC '99, November 15-17 JJ. Garcia-Luna-Aceves and A. E. Tzamaloukas9 RIMA-DPL

10. MOMUC '99, November 15-17 JJ. Garcia-Luna-Aceves and A. E. Tzamaloukas10 Throughput Analysis Model n All the assumptions made for the analysis of non persistent protocols are valid here as well n Divide time into transmission periods (TP) n The type of a TP that follows another TP depends on the number of those persistent users waiting for the current TP to end TP1 TP0TP2 TP0 BusyIdle Busy 

11. MOMUC '99, November 15-17 JJ. Garcia-Luna-Aceves and A. E. Tzamaloukas11 Throughput Analysis Model n Since we assume Poisson arrivals, what occurs in a given TP depends only on what happens in the previous TP n Define the state of the system at the beginning of a TP to be the type of that TP (i.e. state 0 is TP0) n These states correspond to a three-state Markov chain embedded at the beginning of the TP 0 2 1 P 00 01 P P P P P P P 10 21 12 22 11 20

12. MOMUC '99, November 15-17 JJ. Garcia-Luna-Aceves and A. E. Tzamaloukas12 Throughput Analysis Model n fully-connected network of N nodes n single, unslotted channel, error-free n the size for an RTR, RTS and CTS is  seconds; the size for a data packet is  seconds n the turn-around time is considered to be part of the duration of control and data packet n the propagation delay of the channel is  seconds n a polled node receiving an RTR always has a data packet to send n the probability that the packet is addressed to the polling node is 1/N

13. MOMUC '99, November 15-17 JJ. Garcia-Luna-Aceves and A. E. Tzamaloukas13 Throughput results n Throughput vs. offered load for 1Mbps channel and 500 bytes DATA packets; network of 10 nodes FAMARIMA-SP

14. MOMUC '99, November 15-17 JJ. Garcia-Luna-Aceves and A. E. Tzamaloukas14 Throughput results n Throughput vs. offered load for 1Mbps channel and 500 bytes DATA packets for RIMA-DP; network of 10 nodes

15. MOMUC '99, November 15-17 JJ. Garcia-Luna-Aceves and A. E. Tzamaloukas15 Conclusions n We present a first approach of limited persistence in collision- avoidance protocols n Variations of well-known non-persistent sender and receiver- initiated protocols were proposed to demonstrate the effects of applying limited persistence n Our performance analysis results showed considerable benefits when adopting a limited carrier sensing approach n Since all the protocols considered provide correct floor acquisition our results can be extrapolated to networks with hidden terminals