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 0014BFE6535E
• ESSID"dtn_demo"
• ModeMaster
• Frequency2.412 GHz (Channel 1)
• Quality37/100 Signal level12/100 Noise
  level0/100
• Encryption keyoff
• Bit Rates54 Mb/s
• Cell 02 - Address 0016B65BE4A4
• ESSID"aalto"
• ModeMaster
• Frequency2.412 GHz (Channel 1)
• Quality38/100 Signal level13/100 Noise
  level0/100
• Encryption keyoff
• Bit Rates54 Mb/s
• Cell 03 - Address 0016B65BCBFB
• ESSID"aalto"
• ModeMaster

13
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
TCP Traffic Without Channel Selection Utility TCP Traffic Without Channel Selection Utility TCP Traffic Without Channel Selection Utility
Time (sec) Data Transferred (Kbytes) Throughput (Mbits/sec)
240 42086.4 1.43
300.5 52428.8 1.43
600.5 104448 1.43
900.5 157696 1.43
3600.5 624640 1.42
7200.5 1139160 0.158
10800.7 1866465 1.42
21600.5 3718705 1.42
17
Data Sheet 1.2
TCP Traffic With Channel Selection Utility TCP Traffic With Channel Selection Utility TCP Traffic With Channel Selection Utility
Time (sec) Data Transferred (Kbytes) Throughput (Mbits/sec)
240.5 18124.8 0.617
300.4 30617.6 0.833
600.4 82227.2 1.12
900.5 142336 1.3
3600.6 615424 1.4
7717 1290824 0.167
10800.8 1939865.6 1.47
21600.4 3845923 1.46
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
UDP Traffic Without Channel Selection Utility UDP Traffic Without Channel Selection Utility UDP Traffic Without Channel Selection Utility UDP Traffic Without Channel Selection Utility UDP Traffic Without Channel Selection Utility UDP Traffic Without Channel Selection Utility
Time (sec) Data Transferred (Kbytes) Throughput (Kbits/sec) Jitter (msec) lost/total lost
240 30 1.05 1.867 1/21401 0.0046
300 37 1.05 0.297 0/26751 0
600 75 1.05 1.117 0/53501 0
900 113 1.05 0.04 0/80251 0
UDP Traffic With Channel Selection Utility UDP Traffic With Channel Selection Utility UDP Traffic With Channel Selection Utility UDP Traffic With Channel Selection Utility UDP Traffic With Channel Selection Utility UDP Traffic With Channel Selection Utility
Time (sec) Data Transferred (Kbytes) Throughput (Kbits/sec) Jitter (msec) lost/total lost
124 6.98 473 0.554 6219/11198 56
240 14.3 623 0.069 8689/21401 41
300 25.7 719 0.261 8403/26751 31
600 63.2 884 0.014 8398/53501 16
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