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.

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Outline

Introduction Classical Approach Dynamic Load Balance Approach Experimental results Conclusion

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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

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Introduction

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Introduction

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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.

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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

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Introduction

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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.

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Dynamic Load Balance Approach

The algorithm acts in three different levels:– AP Channel Autoselection Level.– Station Join Decision Level.– Link Observation Level.

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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).

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Dynamic Load Balance Approach

The Station Join Decision Level

Ni: Number of stations associated to Api

Si: RSSI value of the Probe Request in Api

Mi: Mean RSSI value for the set of stations associated to the APi.

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Dynamic Load Balance Approach

The Station Join Decision Level– The station selects the AP that maximizes the

following weighted function.

Wi=Di*Pwi*Pi

Di denotes the difference between Si and Mi, of all associated stations to APi, including the new WS (Di=Mi-Si)

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Dynamic Load Balance Approach

The Station Join Decision Level

Pi is the weight proportional to the number of the already associated WS to an APi.

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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

Si,Mi and Ni, or monitors the Mi and the Ni through the Beacon frames.

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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)

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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.

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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.