Title: 802.11 WLAN data throughput and security overheads
Goals and Objectives – The following Learning outcomes will be addressed in this assignment:
LO1 – Be able to describe, explain critically and analyse wireless data communication technology along with associated security issues.
LO2 – Be able to analyse and model wireless behaviour using appropriate mathematics.
LO3 – Critically analyse enterprise requirements for wireless systems.
LO4 – Critically analyse 802.11 protocol information.
LO5 – Make critical decisions about designing secure wireless networks.
Instructions – Your work must be presented in the form of a short technical paper and be no longer than 7 sides plus a facing page that includes the abstract, but excluding the appendix and references. This should be printed on A4 paper and use a font size no smaller than 10.
Introduction – You are to perform a study on data throughput in 802.11 WLAN systems. This will be carried out with wireless security protocols in place and removed. The study will be partially theoretical and partially practical requiring you to build a theoretical model describing data throughput and verify this model through practical experimentation.
802.11 standards are often characterised by channel bit rates, for example 802.11b is usually described as supporting a bit rate of 11Mbps. WLAN users will notice that actual data throughput, as perceived by the clients on a WLAN only approaches half of this value and is sometimes even less. Implementing secure communications on the wireless link will reduce apparent throughput further. Users will sometimes put this lower actual bit rate down to underperforming systems, but this is usually not the case. The lower through put rate is primarily due to the MAC and physical layer overheads in the 802.11 architecture and is therefore intentional. Security protocols place additional overhead on communications and further reduce apparent throughput rates. Communication between a wireless client and an access point is governed by a strict set of protocols that introduces fixed delays in the communication channel. Indeed the delays do not change significantly despite faster underlying channel bit rates.
Assessment Brief – You are to examine one of 802.11b, 802.11g or 802.11a standards. You can choose which one you prefer to work with, however you must state clearly in your report which standard you are focussing on. Additionally, you must apply one method of secure wireless communications from WEP, WPA1/2 Personal to understand the overhead incurred.
1. Theoretical model –
You will need to do some background research to examine how other authors have developed throughput models. The following two papers are a good start:
A. XIAO Yang, IEEE 802.11n: Enhancements for higher throughput in wireless LANs. IEEE Wireless Communications , Dec 2005, pg 82-91.
B. XIA0 Yang, ROSDAHL Jon, Throughput and Delay Limits of IEEE 802.11. IEEE Communications Letters Vol 6 No 8 Aug 2002.
Here you need to develop a model to allow you to calculate actual data throughput against underlying data rate. You need to plot this data for a number of packet sizes. Additionally you need to provide the data in tabular form as part of an excel spreadsheet within the Appendix.
2. Practical work (or Simulation)
You need to perform a number of experiments to measure actual throughput rates for a system using physical experiments or a network simulator of your choice (OMNET++ or OPNET or any other suitable simulator). You are required to measure data throughput using an access point supporting the 802.11 mode (a, b or g) you chose to investigate. For practical experiments, throughput can be measured using JPERF and IPERF traffic generation software or the more sophisticated ZTI traffic generator. Wireless traffic (i.e. traffic through the air between the AP and WNIC) needs to be monitored using Omnipeek or AirPCap on a probe WNIC. For a simulation environments, select appropriate configurations and parameters to obtains the throughput results.
Throughput measurements should be taken for the maximum speed available for your chosen standard. You will need to analyse the data collected carefully and compare your observations with the theoretical predictions you have developed.
Additionally, you need to measure throughput with your chosen security mechanism implemented on the wireless link. You should end up with a set of results, one with security on and one with security off, so you can make clear comparisons of your observations.
Before carrying out any throughput measurements you should assess the channel busyness using a Channelizer Pro spectrum analyser. Chose the quietest channel available for your work. You need to comment in your results and discussion section the impact of interference and other Wi-Fi transmissions on the same channel.
