![]() Service Set Identifier (SSID) Method: This is more commonly used for post-deployment scenarios and used to survey multiple APs.Basic Service Set Identifier (BSSID) Method : This method locks a client into an AP’s radio MAC address and does not allow the client to roam.There are two main methods used in active surveys: When a client is associated, it performs all the tasks that a typical 802.11 client performs, which includes rate-shift data rates as the RF condition changes and performs retransmissions.Īctive surveys are commonly used for new WLAN deployments because they provide the most details upon which to base a design. Active SurveyĪctive surveys are performed with the survey client associated to the APs used throughout the survey. PHY rates can only be measured by actual data that is sent to and from an AP. A passive survey only reports signal propagation for beacons measured by particular clients. PHY rates are generally based on RF signal and noise levels. The most significant loss of information with passive surveys is uplink information, Physical (PHY) rate boundaries, and retransmission. These can be accomplished with a passive survey: Such surveys can be helpful when you look for rogue devices or want a good gauge of downlink RF coverage from the infrastructure devices. The survey client never associates to the access point (AP). Passive surveys are performed with a listen-only mode. There are three types of surveys: Passive, Active, and Predictive. Refer to Cisco Technical Tips Conventions for information on document conventions. If your network is live, ensure that you understand the potential impact of any command. All of the devices used in this document started with a cleared (default) configuration. The information in this document was created from the devices in a specific lab environment. This document is not restricted to specific software and hardware versions. Prerequisites RequirementsĬisco recommends knowledge of these topics: The purpose of this document is to provide guidelines for proper planning, preparation, and identification of the key items to check through the analysis of a survey report. It has been discovered that many site surveys are not performed properly or the site survey is omitted altogether. Many issues can arise in a wireless network due to poor planning and coverage. The first step in a wireless LAN (WLAN) deployment is to ensure that desired operation begins with a site survey to assess the Radio Frequency (RF) behavior in a specific environment. Learn more about Signal-to-Noise Ratio.This document describes site survey guidelines for WLAN deployment. Generally, a signal with an SNR value of 20 dB or more is recommended for data networks where as an SNR value of 25 dB or more is recommended for networks that use voice applications. ![]() For instance, a received signal of -65 dBm can be considered good at a location that has a noise floor of -90 dBm (SNR 25 dB) but not so much at a location with a noise floor of -80 dBm (SNR 15 dB). This will degrade wireless throughput and latency as the retransmitted signals will take up airtime in the wireless environment.Ĭisco Meraki Access Points reference the Signal to Noise Ratio as the indication for the quality of the wireless connection. This provides a more accurate depiction of the health of the wireless signals as it takes the RF environment and ambient noise levels into account. The further a received signal is from the noise floor, the better the signal quality. Signals close to the noise floor can be subject to data corruption, which will result in retransmissions between the transmitter and receiver. ![]() For best performance in a wireless environment, it is key that wireless devices are able to distinguish received signals as legitimate information they should be listening to and ignore any background signals on the spectrum. There is a concept known as the Signal to Noise Ratio or SNR, that ensures the best wireless functionality. The SNR is the difference between the received wireless signal and the noise floor. The noise floor is simply erroneous background transmissions that are emitted from either other devices that are too far away for the signal to be intelligible, or by devices that are inadvertently creating interference on the same frequency.įor example, if a client device's radio receives a signal at -75 dBm, and the noise floor is -90 dBm, then the effective SNR is 15 dB. This would then reflect as a signal strength of 15 dB for this wireless connection. ![]()
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