1 / 30

Fault Tolerant Design and Analysis for Access Points in Public WLAN

Fault Tolerant Design and Analysis for Access Points in Public WLAN. 公眾無線區域網路擷取點容錯技術之設計與分析. Outline. Introduction Background Proposed approach Comparison Evaluation Simulation Conclusion References. Introduction. What is public WLAN (public Wireless Local Access Network).

bethany-watts
Télécharger la présentation

Fault Tolerant Design and Analysis for Access Points in Public WLAN

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Fault Tolerant Design and Analysisfor Access Points in Public WLAN 公眾無線區域網路擷取點容錯技術之設計與分析

  2. Outline • Introduction • Background • Proposed approach • Comparison • Evaluation • Simulation • Conclusion • References

  3. Introduction • What is public WLAN (public Wireless Local Access Network)

  4. Introduction • Motivation

  5. Introduction • Traditional fault tolerance in public WLAN • Based on the hardware or network planning support. • Goal • Propose a new approach to tolerating the AP failure in a public WLAN. • No extra hardware required. • No pre-planned network required. • The vicinity and overloading are simultaneously considered.

  6. Background • Network model

  7. Background • Previous approaches: • Access-point replication • Overlapping coverage • Link multiplexing

  8. Background • Previous approaches: • Access-point replication [DSN’03] • Overlapping coverage • Link multiplexing Hardware cost Hardware compatibility Fault-tolerant capability

  9. Background • Previous approaches: • Access-point replication • Overlapping coverage [ICC’04, WMCSA’03, MONET’02, COMCON’01, WCNC’99] • Link multiplexing Network planning AP overloading Fault-tolerant capability

  10. Background • Previous approaches: • Access-point replication • Overlapping coverage • Link multiplexing [WORDS’03] Network planning Hardware cost Software support Fault-tolerant capability

  11. Proposed Approach • Basic idea • If an AP fails, some working (survival) APs still exist in the system. • If the failure-affected MSs can move to the coverage ranges of the survival APs, their wireless connectivity can be resumed.

  12. Proposed Approach • Basic idea (Cont.) • The public WLAN is usually deployed in indoor environment. • A failure-affected MS can find a survival AP without moving too far. • The main idea of the proposed approach: • To give each failure-affected MS a direction to guide it how to move.

  13. Proposed Approach • Problems for achieving the basic idea • How to select preferable survival AP as the fault-tolerant AP ? • How to avoid the preferable AP being an overloading AP or a faulty AP ? • How to forcefully direct to the coverage range of fault-tolerant AP ?

  14. Proposed Approach • First problem • To make each failure-affected MS quickly resume the wireless connectivity with the least cost.

  15. Proposed Approach Failure-tolerant AP set Faulty AP list AP - 2 , 3 , 5 , 7 , 9 , 10 AP - 6  AP - 3 , 4 , 10 , 11 AP - 6 , 7    • Second problem • To enhance the fault-tolerant AP selection with the state consideration.

  16. Proposed Approach • Third problem • To make each failure-affected MS follow the given direction without randomly moving. • To prevent inter-AP interference: • The channels used by neighboring APs be separated by at least five channels • To set failure-affected MS: • Scanning mode: Active mode. • Scanning channel: Same as fault-tolerant AP.

  17. Proposed Approach • System architecture • Data Structures: • SNMP Server: AP deployment map and AP location table with loading information • AP: Overloading record • MS: AP deployment map and AP location table • Procedures: • SNMP Server: The loading inquiry routine and the fault-tolerant AP recommendation procedure • AP: The loading control procedure • MS: The fault-tolerant procedure and the map direction procedure

  18. Proposed Approach loading of APs Request new fault tolerant AP Response new fault tolerant AP   Overloading record ( recommending AP & lifetime )  Extended probe response with new fault tolerant AP Probe request Normal probe response (ACCEPT)       New fault tolerant AP Fault tolerant AP works   Fault tolerant AP fails Fault tolerant AP  • System architecture (Cont.)

  19. Comparison

  20. Evaluation • The increase of collision probability (DCF mode): • The increase of transmission waiting interval (PCF mode):

  21. Simulation • Simulation model • Software: • NS-2 2.27(Network Simulator version 2) on Linux • Topology: [Huan-Yun Wei et al., "Co-DRR: An Integrated Uplink and Downlink Scheduler for Bandwidth Management over Wireless LANs"]

  22. Simulation • Simulation model (Cont.) • Parameters: • The arrivals of MSs to an AP follow a Poisson distribution. • The association time of an MS with an AP is random. • The MS intensity ( ) is controlled to be 10, 30, 60, and 90. • The max. number of MSs associated with an AP is set to 100. • The overloading threshold of an AP is set to 90. • Each MS in an AP randomly issues a data service to an application server, and the service time is also random. • The ratio between the failure rate and recovery rate of an AP is set to 0.0033. [D. Chen et al., "Dependability Enhancement for IEEE 802.11 Wireless LAN with Redundancy Techniques"]

  23. Simulation • Performance metrics concerned • Failure-free overhead • The cost of downloading the map and table • The cost of the loading inquiry routine • Fault-tolerant overhead • The cost of the two-stage fault-tolerant procedure • The performance affection on a survival AP • The increase of collision probability (DCF mode) • The increase of transmission waiting interval (PCF mode)

  24. Simulation • Simulation results • The cost of downloading the AP deployment map (32KB) and AP location table (4KB): • 1.17 second • The cost of the loading inquiry routine: • 0.027 second

  25. Simulation • Simulation results (Cont.) • The cost of the two-stage fault-tolerant procedure Number of simultaneous AP failures = 1 Number of simultaneous AP failures = 2 Number of simultaneous AP failures = 4 Number of simultaneous AP failures = 8

  26. Simulation • Simulation results (Cont.) • The performance affection on a survival AP DCF mode PCF mode

  27. Conclusion • An efficient approach to tolerating AP failures in a public WLAN • Not requiring the hardware support. • Avoiding overloading situation. • Having the best fault-tolerant capability. • Numerical analysis and simulation experiments results • The failure-free and fault-tolerant overheads of the proposed approach are small.

  28. References [1] Hector Velayos, Victor Aleo, Gunnar Karlsson, Load Balancing in Overlapping Wireless LAN Cells, ICC 2004 - IEEE International Conference on Communications (2004) 3833-3836. [2] Colubris Networks Inc., Data Sheet for Colubris Networks Management System (CNMS), 2004. [3] D. Chen, C. Kintala, S. Garg, K. S. Trivedi, Dependability Enhancement for IEEE 802.11 Wireless LAN with Redundancy Techniques, Proceedings of the International Conference on Dependable Systems and Networks (2003) 521-528. [4] Gandhi R., Tolerance to Access-Point Failures in Dependable Wireless Local-Area Networks, The Ninth IEEE International Workshop on Object-Oriented Real-Time Dependable Systems (2003) 136-143. [5] Proxim Corp., User's Guide for ORiNOCO AP-2500, June 2003. [6] Carlos Oliveira, Jaime Bae Kim, Tatsuya Suda, Long-Range Dependence in IEEE 802.11b Wireless LAN Traffic: An Empirical Study, Computer Communications, 2003. CCW 2003. Proceedings. 2003 IEEE 18th Annual Workshop on (2003) 17-23. [7] F. K. Al-Bin-Ali, P. Boddupalli, N. Davies, An Inter-Access Point Handoff Mechanism for Wireless Network Management: The Sabino System, In Proceedings of The 2003 International Conference on Wireless Networks (2003) 225-230.

  29. References [8] Huan-Yun Wei, Ching-Chuang Chiang, Ying-Dar Lin, Co-DRR: An Integrated Uplink and Downlink Scheduler for Bandwidth Management over Wireless LANs, IEEE Symposium on Computers and Communications (2003) 1415-1420. [9] A. Malloy, U. Varshney, A. P. Snow, Supporting Mobile Commerce Applications Using Dependable Wireless Networks, Mobile Networks and Applications (2002) 225-234. [10] Anand Balachandran, Geoffrey M. Voelker, Paramvir Bahl, P. Venkat Rangan, Characterizing User Behavior and Network Performance in a Public Wireless LAN, In Proceedings of the ACM Sigmetrics Conference on Measurement and Modeling of Computer Systems (2002) 195-205. [11] Anand Balachandran, Paramvir Bahl, Geoffrey M. Voelker, Hot-Spot Congestion Relief in Public-Area Wireless Networks, Mobile Computing Systems and Applications, 2002. Proceedings Fourth IEEE Workshop on (2002) 70-80. [12] Gast, Matthew S., 802.11 Wireless Networks: The Definitive Guide, O'Reilly & Associates, April 2002. [13] Cisco Systems Inc., Data Sheet for Cisco Aironet 350 Series Access Points, June 2001. [14] I. Papanikos, M. Logothetis, A Study on Dynamic Load Balance for IEEE 802.11b Wireless LAN, In Proceedings of the 8th International Conference on Advances in Communication & Control, COMCON 8, Rethymna,Crete/Greece (2001).

  30. References [15] D. Tipper, S. Ramaswamy, T. Dahlberg, PCS Network Survivability, In Proceedings of IEEE Wireless Communications and Networking Conference (1999) 1028-1032. [16] Shiann-Tsong Sheu, Chih-Chiang Wu, Dynamic Load Balance Algorithm (DLBA) for IEEE 802.11 Wireless LAN, Tamkang Journal of Science and Engineering (1999) 45-52. [17] IEEE Std 802.11b-1999, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: Higher-Speed Physical Layer Extension in the 2.4 GHz Band, IEEE, September 1999. [18] J. Case, M. Fedor, M. Schoffstall, J. Davin, A Simple Network Management Protocol (SNMP), Technical Report IETF RFC 1157, May 1990. [19] D. Gross, C. M. Harris, Fundamentals of Queuing Theory, John Wiley & Sons, 1985. [20] NS-2 Network Simulator, Available: http://www.isi.edu/nsnam/

More Related