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Improving NFS Performance Over Wireless Links

Improving NFS Performance Over Wireless Links. Rohit Dube, Cynthia D. Rais,and Satish K.Tripathi.Fellow,IEEE. 報告人 : 蔡昭明 學號 :492515265. Introduction (1). 1.Now:Mobile computing→The performance ◎currently limited by low bandwidth ◎high error rates ◎temporary disconnect

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Improving NFS Performance Over Wireless Links

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  1. Improving NFS Performance Over Wireless Links Rohit Dube, Cynthia D. Rais,and Satish K.Tripathi.Fellow,IEEE 報告人:蔡昭明 學號:492515265

  2. Introduction (1) • 1.Now:Mobile computing→The performance ◎currently limited by low bandwidth ◎high error rates ◎temporary disconnect ◎high latencies ◎limited disk space ◎ fetch files from severs on the wired network via wireless links

  3. Introduction (2) • 2.Testbed Conditions: ◎ Limited wireless LAN networks (bandwidths on the order of 1 Mbps ). • ◎ NFS is designed (on the order of 10 Mbps) • 3.This Paper:improve response time by up to 62%,which brings the performance to whithin 5% of that obtained in zero error conditions

  4. Solution Approach(1) • 1. Modifications to the mobile NFS client • 2. Modifications the wireless device drivers. 3.Test Method: ◎ NFS uses block sizes ( From 8.192 to→1024bytes) ◎ Physiacl link→Maximum Transmission Unit (1500bytes)

  5. Solution Approach(2)

  6. Solution Approach(3) 1.Poor performance on the NFS client: ◎ Few losses will be retransmitted (Add the timeout period) ◎ Exponentially increasing timeout values.

  7. Solution Approach(4) • 1.Solution: ◎Use simpler mechanisms withmodifications only to the mobile NFS client and the wireless device drivers.

  8. Markov error model (1) • Mobile host Base-station

  9. Markov error model (2) • Results:Implement a temporal model by using a distribution for the period spent in the good and bad states: ─Distribution with a good period mean of 1 sec. ─Distribution with a bad period means between 0 and 160 ms. (1 MB files and 10 times)

  10. Effect of Block Size (1)

  11. Effect of Block Size (2)

  12. Effect of Block Size (3) • NFS use block size. • The best performace is expected between the two extremes of 1,024 and 8,192 bytes • ─ A large block sizes increases the probability of loss.(fragment number ↑) ─ A small block sizes increases in request and acknowledgment messages. ─ 4,096 bytes is the best on the testbed evironment .

  13. Effect of Hybrid Linear Back-off Algorithm (1) • R is the number of retransmissions of the current packet. • a equals the number of times linear back-off • c and Initial are small constants

  14. Effect of Hybrid Linear Back-off Algorithm (2) • Modified NFS client uses a hybrid of linear and exponential algorithms. • ─The first few timeouts value are calcaulated by hybrid of linear algorithms • ─The next few timeouts value are calcaulated by exponential algorithms

  15. Effect of Hybrid Linear Back-off Algorithm (3)

  16. Effect of Hybrid Linear Back-off Algorithm (4)

  17. Performance with Multiple Mobile Hosts(1) Modified system

  18. Performance with Multiple Mobile Hosts(2) Modified system

  19. Performance with Multiple Mobile Hosts(3) Modified system

  20. Conclusion • 1.Experiment results:improve response time by up to 62%(corresponding to a 160% increase in throughput) • Brings the performance to whithin 5% of the”zero error on the wireless link” case

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