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Designing and maintaining networks has always been complicated, but wireless networks are more complicated than wired networks. With a wired network, throughput doesn't change when you move a desk or steel file cabinet a few feet, but either of these changes can affect a signal path and cause a difference in wireless performance.
To ensure adequate signal coverage and performance, enterprises should conduct wireless surveys. Three types of wireless site surveys are required for a comprehensive evaluation, with each survey performing a different function, as seen below:
- Predictive surveys are performed before moving into a new space.
- Passive surveys collect information about all the signals in the environment after the site is built.
- Active surveys focus on a specific signal or set of signals while the network is in full operation.
Performing a predictive site survey
A predictive survey should be performed before any equipment or furniture is moved into a new space. It relies on a software package designed to predict how wireless signals propagate through a space. The input is a detailed set of blueprints and information on the type of wireless equipment proposed, such as which Wi-Fi standard will be used in the area.
The goal of a predictive site survey is to determine where to place access points (APs) for the best performance throughout the area. Virtual APs are placed on the blueprint, and the software determines signal strength based on information about how signals propagate through walls and around cabinets and desks. The types of applications that will be used in the area should also be a factor -- e.g., heavy video use requires high throughput, while VoIP calls don't require high throughput, but do require tight limits on latency.
Virtual APs can be placed automatically or manually. With automatic location positioning, the software chooses where to place APs, using the same model everywhere. Manual placement enables network managers to select locations and specify the proposed AP model for each location -- e.g., a more powerful model in some locations and a less powerful model in others.
Skipping the predictive survey will result in guessing about the number of APs needed and where to place them. Despite general rules that dictate the number of APs needed for each increment of floor space, they don't account for application performance requirements. For example, constant disruption may occur after users move in and attempt to use the network while APs are moved, added or removed.
Performing a passive site survey
Passive surveys should be performed periodically after the site is built, equipment is installed and the network is in active use. The goal of a passive survey is to report on all signals at each location, including the installed network and signals from neighboring sites or other devices that generate noise at wireless frequencies. These surveys report information on APs and their characteristics, signal strength, signal-to-noise ratios, and interference and may reveal a marginal performance change before users notice it.
Performing an active site survey
Active surveys focus on a specific signal or set of specific signals and produce an extensive list of measurements for each AP that generates a studied signal. These measurements include signal strength, throughput, round-trip time, packet loss and retransmission rate throughout the area where the signal is used. Active site surveys also measure upstream and downstream data rates and may result in moving an AP or adding or removing an unneeded AP. Active surveys should be performed when investigating performance problems.
Who performs wireless site surveys?
Each of these wireless site survey types can be conducted by firms with specialized expertise or with in-house staff. They can be performed using either software that runs on a laptop or equipment designed specifically for wireless surveys.
Wireless network technology has made and continues to make steady progress and now supports applications that previously required a wired network. Despite this progress, a wireless network requires constant maintenance to ensure excellent performance.