Planning WLAN Step 3 - Performing Site Survey

For a comprehensive plan, you must perform a site survey for each physical location where you intend to install a wireless LAN. The site survey includes careful consideration of the geographic coverage area, per−site security requirements, and profiling wireless LAN users and devices.

Considering the Geographic Coverage Area

Wireless LAN signals are susceptible to interference from other competing devices that use the same frequency bandwidth. For example, 802.11b operates in 2.4−GHz ISM band and is vulnerable to interference from microwave ovens, cordless phones, and Bluetooth−based devices.

In addition to the interference−related problems that wireless LANs suffer, steel objects and thick walls easily obstruct wireless LAN signals.

The interference and obstruction in the wireless LAN data path reduce the performance of a wireless LAN. Performance degradation also occurs when the distance between a wireless LAN device and an access point (AP) increases.

Such problems can be answered by carefully locating the best spots for AP placement, locating dead spots (areas where wireless LAN signals cannot reach), and ensuring that the least number of competing devices operate in the region where you are planning to roll out a wireless LAN.

  • Locating the Best Spots for Wireless Access Points

The best spots for installing wireless LAN access points are the areas that allow the least obstructed signal transmission and are the closest to the wireless LAN users.

To locate the best spots, the signal strength should be monitored using a signal monitoring software. Most wireless LAN equipment comes with signal monitoring software that can show you the relative signals at various distances from a given AP.

You should plan on examining signals from each AP that you intend to install at a given site. Plan to install APs at distances such that the APs barely overlap the coverage area. Installing APs this way ensures that a mobile user roaming between two APs always receives a wireless LAN signal.

  • Locating Dead Spots

Dead spots in a wireless LAN are physical regions where wireless LAN signals cannot reach due to the nature of physical construction (for example, steel locker or a bunker−like construction) or excessive interference.

All such dead spots must be identified, and a decision should be made whether it is worth providing wireless services to these areas.

If wireless services are necessary for those areas, either additional APs should be installed or a wireless LAN technology should be selected that is less vulnerable than originally planned.

If the availability of wireless LANs is not necessary in the dead spots, you should consider using wired LAN extensions for LAN connectivity at the dead spots.

  • Per−Site Security Requirements

If a wireless LAN is quite large, consists of one or more floors, or is located in an area that requires high security, a blanket security policy might not be the best approach.

Different regions on a wireless LAN may be planned to use different security primitives, where some will require high security and others lower security.

For example, regions on the outer periphery of a site may require longer encryption keys, whereas inner regions may require shorter encryption keys.

Profiling Wireless LAN Users and Devices

If all LAN devices and users are to be connected using wireless LAN equipment, for instance in the case of a standalone wireless LAN, then this step may be skipped.

In all other cases a thorough and careful examination of all computers and devices that will operate in the wireless LAN must be performed to ensure better planning for the equipment that wireless LAN users might need.

You should profile users and devices based on the following criteria:

  • Nature of use.

Users of wireless LANs who travel with their computers and have mobile computing requirements are better candidates for wireless LANs, whereas users who only work at their desks are not the best candidates for wireless LANs.

  • Computing device type.

Users with mobile computing devices (for example, laptops, notebooks, and handheld personal digital assistants [PDAs]) are true users of wireless LANs, whereas users with desktop computers and workstations may not need wireless LAN capability.

However, in circumstances where wireless LANs are being deployed to replace wired LANs, this qualification may not apply and all computers may be planned to use wireless LAN.

  • Operating system (OS).

Generally speaking, all computing devices are installed with an operating system (OS). All such devices should be carefully accounted for, as all OSs might not support the wireless LAN technology that you are planning to use.

If a scenario is noticed where an OS does not support the intended wireless LAN technology, you should contact the OS vendor or plan to install a different operating system on such devices.

For example, if you encounter a computer system with Windows 95 installed and you are using 802.11b wireless LAN technology, it is most likely that the drivers for the 802.11b might not be available for Windows 95 and you should plan on upgrading the operating system or use wired LANs to connect this computer to the LAN.

  • Bandwidth requirements of the computers.

If computers that need to be in wireless LANs require high network throughput (for example, a file server), you might try using a wireless LAN technology that allows such throughput.

For example, 802.11b supports speeds up to 11 Mbps, but if you have higher speed requirements, you might want to think about using 802.11a−standard LAN equipment that provides operating speeds of up to 54 Mbps.