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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

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
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


Introduction 2
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


Solution approach 1
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)



Solution approach 3
Solution Approach(3)

1.Poor performance on the NFS client:

◎ Few losses will be retransmitted

(Add the timeout period)

◎ Exponentially increasing timeout values.


Solution approach 4
Solution Approach(4)

  • 1.Solution:

    ◎Use simpler mechanisms withmodifications only to the mobile NFS client and the wireless device drivers.


Markov error model 1
Markov error model (1)

  • Mobile host Base-station


Markov error model 2
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)




Effect of block size 3
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 .


Effect of hybrid linear back off algorithm 1
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


Effect of hybrid linear back off algorithm 2
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







Conclusion
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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