WLAN Service Quality and Performance Check

by S K Tsui
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Introduction

Since the CityU Wireless Local Area Network (WLAN) has rapidly become an essential requirement for the University community, the usability and stability of the WLAN service is therefore very important. In this regard, the Computing Services Centre (CSC) has decided to conduct performance tests periodically to closely monitor the quality of the service. The test results will enable us to make further improvement.

 

Details of the Performance Check

The first series of tests were conducted at the start, middle and end of Semester B of academic year 10/11. Each test involved the measurement of attributes showing throughput, latency and packet loss from 10:00am to 19:00pm, Monday to Friday at selected locations. These locations were either highly populated or designated for m-learning courses.

A. Test equipment and software tool used

  1. Lenovo X200 Notebook computer running 802.11g and 802.11a respectively
  2. iPad
  3. OFTA Broadband Performance Test web site (speedtest1.ofta.gov.hk)

B. Test Locations:

  1. Library (main study area, Law section and Humanities Academy)
  2. 4/F Mall area (purple, blue and yellow zone)
  3. CSC Room H
  4. LT-4 and LT-17
  5. P7907

C. Testing procedures

  1. Find a proper position in the test location and power on or wake up the test equipment
  2. Re-initialize the wireless connection by switching the wireless mode (802.11a to 802.11g or vice versa) or turn off/on the wifi module so that the test equipment can re-associate to the most adjacent Access Point with the strongest signal
  3. Use a web browser to run the OFTA Broadband Performance Test and log the results
  4. Repeat step 1 to 3 at other locations

Results

A. Internet Speed Test

The test aimed to detect the performance of the WLAN by checking the transfer speed via the Internet.

Test Period

5 Jan 11 - 14 Jan 11

28 Feb 11 - 4 Mar 11

11 Apr 11 - 15 Apr 11

No. of tests performed

1249

470

493

Average Download

29.06Mbps

6.45Mbps*

6.87Mbps*

Average Upload

24.24Mbps

6.61Mbps*

7.28Mbps*

Download speed >= 4Mbps

92%

78%

85%

Upload speed >= 4Mbps

89%

74%

82%


* Note: Upload/Download bandwidth control of 10Mbps capped has been applied to each WLAN IP after 1 Feb 2011 (see the Summary Section for the rationale behind)

 

B. Network Latency Test

The test measured the time delay when data was transmitted from the University to the OFTA web site. The latency depends on the propagation path, server loading, etc.

Test Period

5 Jan 11 - 14 Jan 11

28 Feb 11 - 4 Mar 11

11 Apr 11 - 15 Apr 11

Network Latency <= 50ms

96%

96%

94%

 

C. Packet Loss

Packet loss occurs when one or more packets of data being transmitted across a network fail to reach their destination. Under most circumstances, packet re-transmit will take place to recover the data. However, in some cases, especially video streaming and voice over IP, lost data cannot be recovered. If packet loss > 5%, then it may cause significant problems such as lost frames and choppy voice.

Test Period

5 Jan 11 - 14 Jan 11

28 Feb 11 - 4 Mar 11

11 Apr 11 - 15 Apr 11

Packet Loss <= 1%

97%

98%

99%


Summary

The performance of the WLAN depends on a variety of factors such as the total online traffic of an access point, radio interferences, etc. To optimize the performance and to allow fair share of WLAN bandwidth among users, we have applied bandwidth control to mitigate the risk of traffic monopolisation especially due to machines being hacked or infected by viruses, software and hardware bugs on the WLAN controller, application software bugs, turning on features incompatible to our WLAN environment, conducting illegal or unauthorized activities that affect the stability of the WLAN, etc.

The test results show that the WLAN has an average of 6.4Mbps transfer speed, small network latency and little packet loss. The performance is good enough for generic web applications, Internet surfing and supporting m-learning even during peak hours in the most crowded area.