Implementation of Test Bed for Dynamic Channel Selection In WLANs

1. Implementation of Test Bed for Dynamic Channel Selection In WLANs Communications Laboratory TKK/HUT

2. WLANs – Increasing Popularity • Growing Popularity of WLANs • Inexpensive and Flexible • Growing Trend in ad hoc networking • Easy to configure

3. WLANs – Shortfalls and Issues • Intrinsic unreliable nature of the wireless channel • Unreliable and unpredicable Transmission medium • Speeds less than wired networks • Security

4. WLAN Standards • IEEE 802.11 - 1 Mbit/s and 2 Mbit/s, 2.4 GHz RF and IR standard (1997) • IEEE 802.11a - 54 Mbit/s, 5 GHz standard (1999, shipping products in 2001) • IEEE 802.11b - Enhancements to 802.11 to support 5.5 and 11 Mbit/s (1999) • IEEE 802.11g - 54 Mbit/s, 2.4 GHz standard (backwards compatible with b) (2003) • IEEE 802.11h - Spectrum Managed 802.11a (5 GHz) for European compatibility (2004)

5. Contribution of Thesis • Comparative Study of DFS in 802.11b Vs Static Channels In Ad hoc Networks • Multiple radio interferences on a limited Bandwidth • Multilple networks on a Single Channel • Degradation in Throughput • Inflexibility of Channel allocation • Better quality link possible of unused channel

6. The Solution • Creating a Dynamic Channel Selection (DSC) Mechanism for WLANs in the 2.4GHz band • Providing a testbed to obsreve the Improvements offered by the use of a DSC Application • Analyse the improvement in Throughput

7. Dynamic Frequency Selection in WLANs • Provided by the IEEE 802.11h extention to the IEEE 802.11a standard • No mechanism currently being employed in IEEE 802.11b/g WLANs

8. A Simple DFS Algorithm

9. Channel Deployment Issues in the 2.4GHz band • A total of 11 channels in both IEEE 802.11b and IEEE 802.11g standards • Limited to 3 usable channels due to the interchannel interfernces • Limits the DSC scheme to effectively only switch between 3 channels

10. Channelization scheme for IEEE 802.11b

11. Setting Up Test Enviornment • Pentium III Desktop PCs with Realtek 802.11b/g wireless lan cards • Ubuntu v 5.10 linux • wireless_tools.28 toolkit from IBM • Traffic Generator IPerf • Shell Scripting Knowledge  • Patience to install WLAN drivers on linux • Configuring WLANs

12. Lab enviornment • iwlist wlan0 scan • wlan0 Scan completed : • Cell 01 - Address: 00:14:BF:E6:53:5E • ESSID:"dtn_demo" • Mode:Master • Frequency:2.412 GHz (Channel 1) • Quality=37/100 Signal level=12/100 Noise level=0/100 • Encryption key:off • Bit Rates:54 Mb/s • Cell 02 - Address: 00:16:B6:5B:E4:A4 • ESSID:"aalto" • Mode:Master • Frequency:2.412 GHz (Channel 1) • Quality=38/100 Signal level=13/100 Noise level=0/100 • Encryption key:off • Bit Rates:54 Mb/s • Cell 03 - Address: 00:16:B6:5B:CB:FB • ESSID:"aalto" • Mode:Master • Frequency:2.437 GHz (Channel 6) • Quality=32/100 Signal level=5/100 Noise level=0/100 • Encryption key:off • Bit Rates:54 Mb/s • Cell 04 - Address: 42:DC:B9:77:91:7B • ESSID:"wrt54gs" • Mode:Ad-Hoc • Frequency:2.437 GHz (Channel 6) • Quality=36/100 Signal level=11/100 Noise level=0/100 • Encryption key:off • Bit Rates:11 Mb/s • Cell 05 - Address: 6E:FF:7B:87:23:1B • ESSID:"adhoc_test" • Mode:Ad-Hoc • Frequency:2.412 GHz (Channel 1) • Quality=62/100 Signal level=47/100 Noise level=0/100 • Encryption key:off • Bit Rates:22 Mb/s

13. Node-A Start Channel Quality Monitoring Quality < Threshold No Yes Channel Change Procedure Node-A Send Channel No. to Peer Node Self Channel Change Procedure Delay Probe Channel for Change Request Yes Received No Change Channel& Send ACK Wait for Confirmation Node-B ACK Received No ACK within a Time Frame Send Confirmation Node-A Channel Quality Measurements Start Again/Stop DSC Application • Text based signalling • Client Server • 3-way Acks • Link Quality analysis and selection Algorithm • Application Layer Implementation

14. Sequence Diagram for the DCS tool

15. Test Case – 1 • Comparison of channel performance in a bad channel versus a channel selected by using the Channel Selection Utility for TCP traffic • Intervals of 300, 900, 3600, 7200, 10800, 21600

16. Data sheet – 1.1

17. Data Sheet – 1.2

18. Results • Time consumed in the execution of DCS degrades throughput at smaller intervals due to the silent period • Improvement only seen in times greater than one hour

19. Test Case – 2 • Comparison of channel performance in a bad channel versus a channel selected by using the Channel Selection Utility for UDP traffic with a continuous data transfer. • Intervals of 300, 900, 3600, 7200, 10800, 21600

20. Data Sheet – 2.1

21. Results • No retrials so lots of lost packets. • Requires a buffer mechanism to be effective to cater when the silent period occurs.

22. Test Case – 3 • The purpose of this test case is to compare the throughput of the radio interface when burst of traffic is generated instead of continuous traffic. • 5 Mbytes of traffic every 5 minutes from 0800hrs to 1800hrs • DCS mechanism initated every 20 minutes • Alternatively quality threshold can be used to initate the DCS Mechanism

23. Throughput over the time interval of 0600hrs to 1800hrs, where 5Mbytes of data is transferred every 5 minutes on the worst channel. Average Throughput 1.408 Mbits/sec

24. Throughput over the time interval of 0600hrs to 1800hrs, where 5Mbytes of data is transferred every 5 minutes while the Channel Selection Utility is used 2-3 times per hour. Average Throughput 1.467Mbits/sec

25. Comparison of the throughputs when the worst channel is in use versus when the Channel Selection Utility is used to select the best channel.

26. Conclusions • Very distinct Improvement in throughput • Implementation on application layer is not efficient • Taking advantage of the Draft IEEE 802.11k standard for development of DCS mechanim • Buffer for UDP traffic during silent period • Development of selection algorithms • Compatibilty of WLAN drivers in Linux distribution. www.linux-wlan.org • Simplification of network configuration needed