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Simulation of MAC protocols in high-speed networks

This experiment focuses on simulating and comparing different MAC protocols (ALOHA, CSMA, CSMA/CD) in high-speed networks, analyzing their throughput and delay performance under various offered loads and node configurations. The experiment also investigates the effect of bandwidth on maximum throughput.

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Simulation of MAC protocols in high-speed networks

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  1. 實驗三媒體存取協定模擬 教師： 助教： 1998/10/19 High Speed Network Lab. Department of Computer Information Science, NCTU

  2. Outline • Background • Why simulation ? • MAC Protocols • Throughput v.s. Offered load • Investigated topics • Experiment steps • Experiment records

  3. Classification of MAC protocols Note : Some systems use a combination of above schemes.

  4. ALOHA • Transmit whenever it wants • Listen to know if it’s a success or collision • Wait a random time to retx, if collided Vulnerable period : 2 frame times S (throughput) = G P0 = G e-2G Smax = 0.5 e-1 = 18.4 % (G = 0.5) • Slotted ALOHA S = G e-G Smax=1 e-1 =36.8 % (G =1)

  5. CSMA/CD constant or random delay non-persistent : tx if idle otherwise, delay and try again channel busy 1-persistent: tx when channel goes idle if collision, backoff exponentially p-persistent: tx when channel goes idle with prob. p otherwise, delay one slot and repeat ready

  6. Approximate Analysis of CSMA/CD Assume infinite population (i.e. very large number of stations) and Poisson arrival with rate G arrivals/slot S = G e-G Smax= 1 e-1= 1/e (i.e. one success every e slots) max (throughput) = = where  = end-to-end propagation delay b = packet length B= bandwidth Note : Efficiency drops as BL increases. succ      succ     succ 2 p

  7. Simulation Principle • Mathematics Model v.s. Simulation Model • Preciseness v.s. Cost • CACI COMNET III

  8. Summary of MAC protocols • ALOHA • No listen • CSMA • Persistent CSMA (wait it to be idle and Tx) • Non-persistent CSMA (randomly see the channel) • P-persistent CSMA (slotted randomly see with Tx prob. p) • CSMA/CD • Collision Detection • Binary exponential backoff

  9. Two Definitions

  10. Throughput vs. Offered-load Slotted ALOHA 0.2 Throughput ALOHA 0.1 0 1/4 1/3 1/2 1 2 3 Offered load

  11. Investigated Topics • Offered-load v.s. throughput • throughput & delay comparison • ALOHA • CSMA • CSMA/CD • same offered-load • (throughput) v.s. (# of node) • (bandwidth) v.s. (max throughput)

  12. Experiment Steps • Build network topology • Set traffic parameters • Set link parameters • Choose report format • Initialize simulator and run

  13. Step 1: Building the Topology

  14. Step 1: Building the Topology

  15. Step 2: Setting Traffic Parameters

  16. Step 3: Setting Link Parameters

  17. Example: Link Parameters

  18. Step 4: Choose Report Format

  19. Step 4: Choose Report Format CACI COMNET III RELEASE 1.1r Thu Oct 29 20:04:45 1998 PAGE 1 test11 LINK DELAYS AND UTILIZATION REPLICATION 1 FROM 0.0 TO 60.0 SECONDS FRAMES TRANSMISSION DELAY (MS) % LINK DELIVERED RESENT AVERAGE STD DEV MAXIMUM UTIL _____________________ _________ ______ _________ _________ _________ _____ Link11 599 0 880.570 1943.065 17312.537 99.87 CACI COMNET III RELEASE 1.1r Thu Oct 29 20:04:45 1998 PAGE 2

  20. Experiment Records • Throughput and Delay : CSMA/CD, CSMA, and ALOHA under 1, 1/2, 1/3, and 1/4 offered-load • Throughput : different # Nodes under the same offered-load • Max throughput : different bandwidth (high-bandwidth v.s. low-bandwidth)

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