Site Survey

When conducting a wireless site survey, consider the following steps:

To understand the wireless requirements

In order to identify appropriate locations for deployment of access points (APs), we need to thoroughly understand specific requirements for the network and any possible impacts to the signal coverage. By knowing the target throughput and data rates, we are able to correctly interpret the results of site survey. And also, some devices of users may have lower transmitting power, so we must take this into consideration.

To obtain detailed diagram

Locate a set of building blueprints of the site; prepare a drawing that depicts the actual location of walls, windows, furniture and interior spaces. The detailed diagram helps us to identify any potential obstacles or impediments in the area to be served.

Visual inspection of site

By walking through the site before performing any testing to verify the accuracy of the detailed diagram, we are able to identify any potential attenuation barriers that may obstruct and degrade the propagation of RF signals.

Assessment of existing network infrastructure

Verifying the capacity of the existing wired networks that can interface the access points and check on how much of the existing networks can be made available for supporting the wireless network.

To identify the coverage areas

Indicating all areas where signal coverage is needed by marking on the detailed diagram, and also, identifying the areas where wireless coverage is not required is also important for site survey as we can avoid wasting time on surveying. In addition to time saving, we can also reduce the number of access points and lower the costs of equipment.

To determine locations for preliminary access point

To determine the preliminary access point locations, we need to consider the wireless network equipments products we are using, and analyze the locations of access points that will provide adequate coverage throughout the areas. And plan for some overlap of propagation among adjacent access points, also assign the channel for access points to be far enough from each others to avoid inter-access point interferences. The mounting locations also need to be considered as it could be vertical posts or metal supports above ceiling tiles. Identify appropriate locations for installing the access point and data cable. Various types of antennas will be taken into consideration when the positions of access points are determined.

Verification of access point locations

When the site survey testing is ready to begin, we can utilize good wireless network surveying software to assess the signals on the site. This kind of software can help us to pick up the signals, trace and evaluate various parameters such as:

• Strength of signal
• Signals at channel
• Presence of access points
• Signal-to-noise ratio
• Potential interference
• Best location to place access points

Next, when an access point is installed at each preliminary location, we will have to walk by varying distances away from the access point in order to obtain the readings from the site survey tool. This procedure is just to ping the access point or obtain the beacon signal strength, therefore connecting the access point to the distribution system is not necessarily need.

Documenting

Once all the locations of access points that capable of providing adequate signal coverage is confirmed, we will document our findings on the detailed diagrams by marking the location of each access point as this information is needed by the installer later.

Dual-band radios and dual-radio access points

IEEE 802.11b/a/g/n dual-band access points with two radios can support both 2.4 GHz and 5 GHz RF bands at the same time, on different radios. They offer a backward compatibility, a larger number of channels, and increased throughput. Wireless network devices with a dual-band radio can scan both the 2.4 and 5 GHz bands and choose the best access point on either band. Dual-band access points are suitable to a wide range of network topologies.

Dual-band access points are not only providing increased bandwidth, but it is also fairly using dual-band radios to segregate data types onto the different RF bands. The 5 GHz radio can serve wireless traffic from time-sensitive voice/data clients while the 2.4 GHz radio supports data traffic from laptops. This helps to reduce data and voice traffic contention by creating two separate RF networks.

Since both 802.11a and 802.11n are able to use a different RF band, it is not affected by interference from the possible pervasive 802.11b or 802.11g wireless networks, and is better insulated from overhead activity, such as probes or responses from clients generated by internal and external 802.11b or 802.11g wireless networks.

Wireless Network Architectures

In planning the wireless network, we will have to determine which wireless network architecture to adopt in the network environment. There are two architectures available, namely standalone and centrally coordinated wireless network.

Standalone architecture (Ad hoc mode)

By using ad hoc mode, all devices in the wireless network are directly communicating with each other in peer to peer communication mode. No access point (routers/switches) is required for communication between devices.

For setting up ad hoc mode, we need to manually configure the wireless adaptors of all devices to be at ad hoc mode instead of infrastructure mode, and all adaptors must use the same channel name and same SSID for making the connection active.

Ad hoc mode is most suitable for small group of devices and all of these devices must be physically present in close proximity with each other. The performance of network suffers while the number of devices grows. Disconnections of random device may occur frequently and also, ad hoc mode can be a tough job for network administrator to manage the network. Ad hoc mode has another limitation is that, ad hoc mode networks cannot bridge to wired local area network and also cannot access internet if without the installation of special gateways.

However, Ad hoc mode works fine in small environment. Because ad hoc mode does not need any extra access point (routers/switches), therefore it reduces the cost. Ad hoc can be very useful as a backup option for time being if network based on centrally coordinated wireless network (infrastructure mode) and access points are malfunctioning.

An ad hoc mode uses the integrated functionality of each adaptor to enable wireless services and security authentication. The characteristics of an Ad hoc wireless network are listed as below:

• All access points in the network operate independently and has own configuration file.
• Access point is responsible for the encryption and decryption.
• The network configuration is static and does not respond to changing network conditions.

Centrally Coordinated Architecture (Infrastructure mode)

The other architecture in wireless network is centrally coordinated (infrastructure mode). All devices are connected to wireless network with the help of Access Point (AP). Wireless APs are usually routers or switches which are connected to internet by broadband modem.

Infrastructure mode deployments are more suitable for larger organizations or facility. This kind of deployment helps to simplify network management, and allows the facility to address operational concerns. And resiliency is also assured while more users can get connected to the network subsequently.

The infrastructure mode provides improved security, ease of management, and much more scalability and stability. However, the infrastructure mode incurs extra cost in deploying access points such as routers or switches.

An infrastructure mode wireless network has the characteristics as below:

• The wireless centralized controller coordinates the activity of access point.
• The controller is able to monitor and control the wireless network by automatically reconfiguring the access point parameters in order to maintain the health of the network.
• The wireless network can be easily expanded or reduced by adding or removing access points and the network can be reconfigured by the controller based on the changes in RF footprint.
• Tasks such as user authentication, fault tolerance, control of configuration, policy enforcement and expansion of network are done by the wireless network controller.
• Redundant access points can be deployed in separate locations to maintain control in the event of an access point or switch failure.