The implementation of Wireless LANs (WLAN) has become the cornerstone of many organizations’ mobile computing initiatives. The pervasive WLAN is the primary technology platform for increasing the productivity of your mobile and distributed knowledge workers. An efficient and optimized WLAN implementation improves communication flows, enables rapid access to senior management and enhances collaboration. All of these benefits provide competitive advantages that can positively affect your business.
Although your WLAN architecture may appear sound on paper, testing the actual system across the technology stack and from end-to-end is essential to ensure that your WLAN implementation provides the essential capabilities required to deliver the promised business benefits. Building a WLAN infrastructure from scratch or extending an existing implementation can present issues and risks that need to be addressed through a robust and effective WLAN test strategy.
Despite the existence of the IEEE 802.11 standards-based WLAN market, there is still no guarantee that a WLAN infrastructure constructed from multi-vendor, or even single vendor, hardware and software will provide a seamless and transparent platform for end-to-end business processes.
Some of the issues that need to be addressed are:
Wireless technology continues to outpace the capacity of industry interoperability consortia to provide comprehensive certification programmes;
Operational risks can be mitigated by implementing a homogeneous, single vendor solution but enhanced business benefits may only be realized from a heterogeneous, multi-vendor solution;
There is no single approach to building and operating enterprise scale WLANs and new architectures continue to be developed;
Physical implementation needs to consider the impact of RF interference on the operational mode and the performance of the WLAN;
Latency caused by roaming and re-authentication, especially for real-time applications such as VoIP.
Types of Testing
Functional Testing
Functional testing should be performed at all level of the technology stack, as failure at any level has the potential to disrupt the availability of applications to their users.
Protocol Level Testing
Protocol level testing generally involves comparing network traffic to a specification or standard. Often such specifications or standards include bit-level protocol descriptions. Wireless client adapters and wireless access points need to be tested at this level to ensure compliance with the protocols that the devices are designed to support.
In the wireless medium, protocol level testing involves the expert use of wireless protocol analyzer(s) that allow the tester to see what is happening at Layers 2-7 of the OSI model. Testing at this level is exacting work that requires the ability to understand and interpret the published specification or standard and compare it to the captured network traffic. The following is typical of the output from a protocol analyzer and shows the low level nature of this type of testing:
==== 802.11 packet (encrypted) ====
08 41 02 01 00 40 96 21 DC 83 00 40 96 28 8D DC FF FF FF FF FF FF A0 38 00 01 15 00 EB B1 C7 6A B1 96 B2 16 58 C4 04 5E 2D 6A F3 4B 92 EB FC FC ED 70 98 D0 64 6C 5E BB 1A DD D4 2A 26 2A 8B EF C2 41 67 75 9D FB FE 5D 4E CA A0 45 6D 7C 36 22 22 7D D0 BD 09 16 1D E6 41 D9 94 BE 9B 53 C5 CB
==== CK (basic CKIP key) ====
19 59 8D F5 EF 19 59 8D F5 EF 19 59 8D F5 EF 19
==== PK (permuted key) ====
00 01 15 E6 8B D6 03 23 0B 6A 60 B9 F4 EB 46 99
==== 802.11 packet decrypted ====
08 41 02 01 00 40 96 21 DC 83 00 40 96 28 8D DC FF FF FF FF FF FF A0 38 00 01 15 00 AA AA 03 00 40 96 00 02 2F F1 C0 A6 00 00 00 C0 08 06 00 01 08 00 06 04 00 01 00 40 96 28 8D DC A1 2C EE 03 00 00 00 00 00 00 A1 2C EE 14 21 BD D8 23 21 BD A8 AC 52 E1 01 00 00 00 28 AC 0F 82 46 86 F9 D9
==== Original MSDU ====
DA: FF FF FF FF FF FF
SA: 00 40 96 28 8D DC
Payload: 08 06 00 01 08 00 06 04 00 01 00 40 96 28 8D DC A1 2C EE 03 00 00 00 00 00
00 A1 2C EE 14 21 BD D8 23 21 BD A8 AC 52 E1 01 00 00 00 28 AC 0F 82
Compatibility Testing
The 802.11 wireless world is governed by standards. However the different wireless components do not always interoperate well. Within a single WLAN infrastructure there may be many combinations of client adapters and wireless access points. Even if the model numbers of the components are the same, there may be different software versions deployed within the devices. Compatibility testing is required to prove that the chosen devices do actually work together as expected.
Security Testing
Wireless networks are becoming more popular in the corporate environment. As such, corporate network administrators rightfully insist on making the network as secure as possible. A secure wireless strategy includes encryption, authentication, and key management. Encryption ranges from static WEP to rotating keys generated by the access point. The wireless network can authenticate the wireless user or client using a variety of authentication protocols and backend systems. Key management refers to the mechanism being employed to rotate the keys. Some of the most common systems and
mechanism that are deployed are:
Microsoft Internet Authentication Service (IAS)
Cisco Access Control Server (ACS)
Key Management:
Cisco Centralized Key Management (CCKM)
WPA
WPA2
802.1x Extensible Authentication Protocol (EAP) of all kinds
EAP-TLS (certificate-based authentication)
EAP-GTC (password or token-based authentication)
PEAP
EAP-FAST
LEAP
Although it may seem that these systems and mechanisms should work together and that each one is being used successfully and securely already, there are so many possible permutations that it is entirely possible that many WLAN implementations are effectively uniquely constructed and security testing is required to verify their end-to-end integrity.
Quality of Service Testing
One of the ways that wireless networking has evolved surrounds the use of multimedia applications (voice, video, etc) over the wireless medium. Such applications require guaranteed access to the network in order that the audio/video stream is of an acceptable quality. The mechanism employed to ensure the quality of multimedia communications over the network is called “Quality of Service” (QoS) and is implemented on a wireless network using the Wi-Fi Multimedia (WMM) functionality. WMM is based on a subset of the IEEE 802.11e WLAN QoS draft standard. The implementation of WMM is judged by generating known traffic types on the network and validating correct behavior in terms of priority values in the packets and traffic flow through the network.
End-to-End Testing
A comprehensive WLAN test strategy will include full end-to-end business process testing within the test WLAN environment allowing business risk mitigation before WLAN deployment occurs on site. Due to the many configurations that may need to be tested, this is essentially application regression testing. Regression testing is the form of testing most amenable to test automation. Consideration needs to be given to the feasibility of test automation and the potential cost and quality benefits that may be obtained through test automation.
Performance Testing
A common measure of wireless performance is throughput. Regardless of the 802.11 band (a/b/g), wireless client adapter vendors are concerned with throughput as a performance metric and point of comparison. In the wireless world, range is simulated by adding attenuation to the antenna on the wireless access point.
Wireless throughput is a function of multiple factors, most notably:
Distance between the client adapter and the access point (often simulated in the test environment by introducing attenuation to the wireless signal)
Noise in the environment
Relative orientation of the client and access point antennas
The curve of throughput versus distance (attenuation) varies from adapter to adapter. Even a single adapter’s throughput curve varies with the implemented antenna and its orientation.
Poor throughput will manifest itself to the end user as increasing response times from their applications. To determine the overall degradation in response times under normal operating conditions load testing can be performed to simulate multiple concurrent users.
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