ew the log for the access point experiencing performance problems A high re-try count under good SNR conditions will indicate re-tries due to competing traffic Consider additional access points on non-overlapping channels, or running dual mode networks (e.g. 802.11a and g) to increase capacity authentication process to see if a breakdown of this process is preventing user authentication and access. If the authentication server is denying a user access, the analyser results will help to determine whether the problem lies with the user's access rights or security configuration, or with the authentication server itself. Besides a wide range of commercial tools, a number of free or open source analysis tools are also available, the most popular being NetStumbler (see the Section "Wireless LAN Resources by Standard, p. 367"). This "free for non-commercial use" tool will identify SSID, channel, encryption settings and SNR of all detected access points, and can be used to verify network configuration and to detect any rogue stations within range. In small-scale implementations it can also be used to perform a simple site survey, checking for holes in RF coverage and detecting other 802.11a/g/b networks that may cause interference. Wireless LAN Troubleshooting Table 9-6: WLAN Analysers - Analysis Tools and Typical Usage WLAN analysis tools Typical usage Site surveying Locating non-802.11 interference sources Investigating intermittent connection problems caused by interference Monitoring of all 802.11a/b/g channels Determining a noise floor and identifying high noise or low SNR problems Verify access point channel usage and power level Mitigating channel overlap problems Performing pre-installation modelling and identifying problem areas with insufficient coverage Analysing site survey results in the light of specific technical requirements, e.g. for VoWLAN applications Security assessment Ensuring access points have policy compliant security con- figurations Visibility of encrypted network traffic (WEP, WPA, WPA2) Detec