Gathering business requirements

Purpose of the WLAN

  • The first question that should be posed is, What is the purpose of the WLAN?
  • What applications will be used over the WLAN?
    • This question could have both capacity and quality of service (QoS) implications
  • Who will be using the WLAN?
    • Groups of users might be segmented into separate SSIDs and VLANs
  • What types of devices will be connecting to the WLAN?
    • Does the company have a bring your own device (BYOD) strategy and is a mobile device management (MDM) solution needed?

Capacity and Coverage Requirements

  • Ask all the necessary questions for planning the site survey and designing the wireless network
  • Create preliminary the capacity and coverage needs of the customer is recommended
  • Check with the customer and go over the building’s floor plan and ask the customer where they want RF coverage.
  • Depending on the layout and the materials used inside the building, some preplanning might need to be done as to what type of antennas to use in certain areas of the facility.
  • A high-density area may require semidirectional patch antennas for sectorized coverage as opposed to using omnidirectional antennas. When the survey is performed, this will be confirmed or adjusted accordingly.
  • In order for the wireless end user to experience acceptable performance, a ratio of average number of users per access point must be established.
  • Planning for capacity
    • Data Applications
      • The applications that are used will have a direct impact on the number of  Wi-Fi devices that should be communicating on average through an access point.
      • So the next question is, what is a good average number of connected devices per access point? It depends entirely on the purpose of the WLAN and the applications being used.
      • In an 802.11a/b/g/n network, 35–50 data WLAN devices per radio is an
        often-quoted figure for typical WLAN applications such as web browsing and email.
    • User and Device Density
      • How many users currently need wireless access?
      • How many Wi-Fi devices will they be using?
      • How many users and devices may need wireless access in the future?
      • Where are the users?
      • Sit down with network management and indicate on the floor plan of the building any areas of high user density.
      • Plan to conduct the physical survey when the users are present and not
        during off-hours. A high concentration of human bodies can attenuate the RF signal because of absorption.
      • When deploying over 5 GHz, WLAN vendor, Cisco, recommends a maximum of 27 simultaneous bidirectional voice calls when connected at 24 Mbps or higher.
        Because of medium contention, that number drops to a recommended maximum of 20 calls when connected at 12 Mbps
    • Peak On/Off Use
      • Ask what the peak times are—that is, when access to the WLAN is heaviest.
      • A conference room might be used only once a day or once a month. Certain applications might be heavily accessed through the WLAN at specified times. Another peak period could be when one shift leaves and another arrives.
    • Existing Transmitters
      • Are there interfering devices such as microwaves, cordless headsets, cordless phones, wireless machinery
      • If a large open area will house the help desk after the wireless is installed, you may be thinking of capacity. However, if you don’t know that the employees are using 2.4 GHz cordless headsets or Bluetooth
        keyboards and mice, you may be designing a network destined for failure.
    • Portability vs. Mobility
      • Having true mobility means that a user remains connected 100 percent of the time while traveling through the facility. This would be indicative of VoWiFi or warehouse scanning applications.
    • Backward Compatibility for Legacy Devices
      • It should be understood in advance that if there is any requirement for
        backward compatibility with legacy clients
      • 802.11 protection mechanisms will always adversely affect throughput
      • The impact of protection mechanisms is not as severe on an 802.11n network, but it can be significant on a legacy 802.11b/g network
    • Carefully planning coverage and capacity needs prior to the site survey will help you determine some of the design scenarios you might need, including AP power settings, types of antennas, and cell sizes.
    • The physical site survey will still have to be conducted to validate and further determine coverage and capacity requirements.