1. A Study on Dynamic Load Balance for IEEE 802.11b Wireless LAN Proc. 8th International Conference on Advances in Communication & Control, COMCON 8, Rethymna, Crete/Greece, June, 2001.

2. 2002/9/30 asing 2 Outline Introduction Classical Approach Dynamic Load Balance Approach Experimental results Conclusion

3. 2002/9/30 asing 3 Introduction Based on the IEEE 802.11 protocol, two different topologies can be configured in order to service different communication needs. – Infrastructure Mode – Ad Hoc Mode

4. 2002/9/30 asing 4 Introduction

5. 2002/9/30 asing 5 Introduction

6. 2002/9/30 asing 6 Introduction Basic network components in the Infrastructure. – Wireless Stations(WS) – Wire stations – Access Points(AP) There is not any function specifying the AP selected by a WS.

7. 2002/9/30 asing 7 Introduction Proposed algorithms are based only on the received signal strength indicator(RSSI). Study the problem of load balancing in 802.11- based infrastructure wireless networks

8. 2002/9/30 asing 8 Introduction

9. 2002/9/30 asing 9 Classical Approach A WS scans the available channels of each AP in the region and listens to the Beacon or Probe Response Frames. The WS stores the RSSI of Beacon or Probe Response Frames and other information. The WS selects that AP with the maximum RSSI.

10. 2002/9/30 asing 10 Dynamic Load Balance Approach The algorithm acts in three different levels: – AP Channel Autoselection Level. – Station Join Decision Level. – Link Observation Level.

11. 2002/9/30 asing 11 Dynamic Load Balance Approach The AP Channel autoselection level – At the start-up phase of each AP, the AP is informed the existence of other AP in the same region, by Inter Access Point Protocol(IAPP).

12. 2002/9/30 asing 12 Dynamic Load Balance Approach The Station Join Decision Level N i : Number of stations associated to Ap i S i : RSSI value of the Probe Request in Ap i M i : Mean RSSI value for the set of stations associated to the AP i.

13. 2002/9/30 asing 13 Dynamic Load Balance Approach The Station Join Decision Level – The station selects the AP that maximizes the following weighted function. W i =D i *P wi *P i D i denotes the difference between S i and M i, of all associated stations to AP i, including the new WS (D i =M i -S i )

14. 2002/9/30 asing 14 Dynamic Load Balance Approach The Station Join Decision Level P i is the weight proportional to the number of the already associated WS to an AP i.

15. 2002/9/30 asing 15 Dynamic Load Balance Approach The Link Observation Level – Each AP updates Mi, Ni, in each Beacon or Probe Response Frame. – The WS probes periodically the AP and updates S i,M i and N i, or monitors the M i and the N i through the Beacon frames.

16. 2002/9/30 asing 16 Protocol Modifications New fields must be added in Beacons and Probe responses frames. – The number of associated stations (Beacon, Probe Response) – Mean RSSI for the associated stations (Beacon, Probe Response) – RSSI of the incoming Probe Request (Probe Response)

17. 2002/9/30 asing 17 Experimental Results Three AP 30 WS Transferred data files of 12MB to and from the Ethernet network. The traffic load conditions were the same for all WS.

18. 2002/9/30 asing 18 Conclusion The resultant distribution of WS to AP is absolutely satisfactory, that is, symmetry in the numbers of associated station to AP exists. In order to face the problem of large traffic variations among the WS and AP, real time measurements for the resource availability and frame error rate have to be added in the decision level of the algorithm.