Enterprise Wireless LAN Design
Designing an enterprise class WLAN is not a trivial task. If designed incorrectly the WLAN will have coverage gaps and capacity issues. Outlined below are steps that should be followed when designing an enterprise class WLAN.
One of the biggest mistakes made by IT professionals is to focus on WLAN signal coverage instead of WLAN capacity. Many WLAN projects start with a wireless site survey without any information about why the WLAN is being deployed.
The first step in any WLAN design should be to sit down with the future users/owners of the WLAN and determine where WLAN coverage is needed and what applications will be used. Focusing on WLAN capacity requirements of applications first will usually result in a WLAN design with proper coverage too.
Also, this is a good time to start discussing the security requirements of the organization and any special compliance requirements or integration issues related to wireless LAN security that may need special attention.
Physical Site Survey
Request electronic copy of building drawings and conduct a physical site survey to verify that the information in the drawings is correct. Note any changes not reflected in the drawings, such as new additions or construction material that would significantly attenuate or reflect wireless signals.
Another goal of a physical site survey is to determine the locations where access points should not be installed such as bathrooms, lobby areas, or elevator shafts.
During the physical site survey start thinking about cable paths in relationship to telecom closets and possible mounting locations for access points. Note any special requirements that would impact deployment phase such as high ceilings, outdoor coverage requirements, or historical building regulations.
If allowed, take digital photos of facilities to help with predictive RF WLAN design step and deployment phase.
Predictive RF Design
Using information from requirements gathering step and physical site survey use WLAN predictive RF design tools to determine the number of access points that will be needed and potential placement locations.
Focus on meeting the capacity requirements of the design and disregard any budgetary limitations. In addition to capacity design verify the placement of access points will also meet WLAN coverage requirements. Compare these access point placement locations to information gathered during physical site survey and adjust placement as needed to avoid placing access points in areas where they can not be mounted.
Regarding coverage, design proper overlapping coverage to allow for seamless roaming and redundancy.
Wireless Site Survey
The goal of a wireless site survey is to validate the predictive RF design and to avoid having to survey the entire facility. Focus on areas that are different from floor-to-floor or very radio frequency (RF) unfriendly.
Verify the predictive design by taking test measurements at various locations. When possible, use the same access point and client hardware that will be deployed. Measure RSSI (received signal strength indication) and noise levels. The wireless site survey should also include information about neighboring access points and any other 802.11 or not 802.11 device that may cause interference issues once the WLAN is deployed. Also, any special antennas needed for access points or clients should be noted here and if possible test measurements taken with special antennas.
Identify and record access point placement locations and cable paths back to telecom closet on building drawings. Also note network switch port capacity and power availability per telecom closet.
Wireless Network Design
With information from the requirements gathering, physical site survey, predictive RF design, and wireless site survey designing the wireless LAN should be very pretty easy.
Decide on configuration related items such as SSIDs to be used, VLAN assignment per SSID, channel plans, transmit power, and naming schemes for devices. Regarding channel assignment and transmit power, do not assume that WLAN equipment will correctly â€œauto configureâ€ these settings. In almost all cases, it is best to define exact channel scheme and transmit power and later validate that the â€œauto configureâ€ capability of WLAN equipment is able to do same dynamically due to network conditions.
A very important WLAN design consideration is the security architecture of the network and any special client software requirements. It is very important to communicate the details of security solution to the network owners/operators and have them provide any potential issues with existing client software (personal firewalls, virus scanners, etc). Also, outline how the WLAN and security architecture will integrate with the existing wired network.
Lastly, document all steps of the WLAN design process and communicate roles and responsibilities to all parties. As with any network or device operating in the ISM band, make sure all parties understand that an 802.11 based WLAN is a shared and best effort network. The design is only as good as the 802.11 protocol and FCC regulations related to the ISM band. Set the correct expectations regarding performance, security, and management requirements.
Following the five WLAN design steps above should result in proper coverage, capacity, and security controls that are typically desired in enterprise class WLANs.