CWNA Chapter 15 – Radio Frequency Site Survey Fundamentals

My Notes from chapter 15 of the CWNA study guide

WLAN site survey interview

  • Customer briefing
    • If a wireless network is being planned for your company or for a prospective client, it is highly recommended that you sit management down, give them an overview of 802.11 wireless networking, and talk with them about how and why site surveys are conducted
    • Do not need to explain the inner workings of orthogonal frequency division multiplexing or the Distributed Coordination Function; however, a conversation about the advantages of Wi-Fi, as well as the limitations of a WLAN, is a good idea.
    • Chances are that a wireless network is already being considered because the company’s end users have requested wireless access to the company network using their own personal devices such as smartphones and tablets
    • Just as important is a discussion about the bandwidth and throughput capabilities of 802.11a/b/g/n/ac technology.
    • It should also be explained that the medium is a half-duplex shared medium and not full-duplex.
    • Another appropriate discussion is why a site survey is needed.
    • A very brief explanation on how RF signals propagate and attenuate will provide management with a better understanding of why an RF site survey is needed to ensure the proper coverage and enhance performance.
    • If management is properly briefed on the basics of Wi-Fi as well as the importance of a site survey, the forthcoming technical questions will be answered in a more suitable fashion
  • Business requirements
    • What is the purpose of the WLAN?
    • If you have a complete understanding of the intended use of a wireless network, the result will be a better-designed WLAN
    • VoWiFi network has very different requirements than a heavily used data network
    • Here are some of the business requirement questions that should be asked:
      • 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?
        • Different types of users have different capacity and performance needs.
        • Users may also need to be separated for organizational purposes.
        • This is also an important consideration for security roles.
      • What types of devices will be connecting to the WLAN?
        • Will employees be allowed to connect their personal devices to the network?
        • Does the company have a bring your own device (BYOD) strategy and is a mobile device management (MDM) solution needed?
        • The capabilities of the devices may also force decisions in security, frequency, technology, and data rates.
  • Capacity and coverage requirements
    • After the purpose of the WLAN has been clearly defined, the next step is to begin asking all the necessary questions for planning the site survey and designing the wireless network.
    • You will need to sit down with a copy of the building’s floor plan and ask the customer where they want RF coverage
    • Do they really need coverage everywhere? Do laptop data users need access in a storage area? Do they need connectivity in the outdoor courtyard? Do handheld bar code scanners used in a warehouse area need access in the front office?
    • If you can determine that certain areas of the facility do not require coverage, you will save the customer money and yourself time when conducting the physical survey
    • 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
    • When the survey is performed, this will be confirmed or adjusted accordingly.
    • You must not just consider coverage; you must also plan for capacity
    • The following are among the many factors that need to be considered when 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.
        • 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
        • 35 to 50 active Wi-Fi devices per radio on a dual-frequency 802.11n access point is realistic with average application use, such as web browsing.
      • User and Device Density
        • Three important questions need to be asked with regard to users.
        • How many users currently need wireless access and how many Wi-Fi devices will they be using?
        • How many users and devices may need wireless access in the future?
        • These first two questions will help you to begin adequately planning for a good ratio of devices per access point while allowing for future growth
        • The third question of great significance is, 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
      • Peak On/Off Use
        • Be sure to ask what the peak times are—that is, when access to the WLAN is heaviest
        • 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
        • Does not refer just to previously installed 802.11 networks
        • Rather, it refers to interfering devices such as microwaves, cordless headsets, cordless phones, wireless machinery, and so on
        • 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
        • There are two types of mobility
        • First is related to being portable and the other is true mobility
        • Portable think moving laptop from desk to meeting room and back, you don’t need access whilst in transit.
        • True mobility means that a user remains connected 100 percent of the time while traveling through the facility
        • Most users now carry some sort of personal mobile device, such as a smartphone; therefore, true mobility is almost always an understood requirement
        • Determining which type of connectivity is necessary can be key for not only troubleshooting an existing network but also for designing a new one.
      • Backward Compatibility for Legacy Devices
        • It should be understood in advance that if there is any requirement for backward compatibility with legacy clients, the 802.11 protection mechanisms will always adversely affect throughput
        • Enterprise deployments will almost always require some level of backward compatibility to provide access for older 802.11a/b/g radios found in handhelds, VoWiFi phones, or older laptops
  • Existing wireless network
    • Quite often the reason you are conducting a WLAN site survey is that you have been called in as a consultant to fi x an existing deployment
    • Sadly, many untrained integrators or customers just install the access points wherever they can mount them and leave the default power and channel settings on every AP.
    • Usually, site surveys must be conducted either because of performance problems or diffi culty roaming
    • Performance problems are often caused by RF interference, low SNR, adjacent cell interference, or cochannel cooperation
    • Roaming problems may also be interference related or caused by a lack of adequate coverage and/or by a lack of proper duplicate cell coverage for roaming
    • Here are some of the questions that should be asked prior to the reparative site survey:
      • What are the current problems with the existing WLAN?
        • Ask the customer to clarify the problems.
        • Are they throughput related?
        • Are there frequent disconnects?
        • Is there any difficulty roaming?
        • In what part of the building do the problems occur most often?
        • Is the problem happening with one WLAN device or multiple devices?
        •  How often do the problems occur, and have any steps been taken to duplicate the troubles?
      • Are there any known sources of RF interference?
        • More than likely the customer will have no idea, but it does not hurt to ask.
        • Are there any microwave ovens? Do people use cordless phones or headsets? Does anyone use Bluetooth for keyboards or mice?
        • After asking these interference questions, you should always perform a spectrum analysis
      • Are there any known coverage dead zones?
        • This is related to the roaming questions, and areas probably exist where proper coverage is not being provided
      • Does prior site survey data exist?
        • Chances are that an original site survey was not even conducted. However, if old site survey documentation exists, it may be helpful when troubleshooting existing problems
        • Unless quantifiable data was collected that shows dBm strengths, the survey report should be viewed with extreme caution
      • What equipment is currently installed?
        • Ask what type of equipment is being used, such as 802.11a (5 GHz) or 802.11b/g (2.4 GHz), and which vendor has been used
        • Is the customer looking to upgrade to an 802.11n or 802.11ac network?
        • check the configurations of the devices, including service set identifiers (SSIDs), WEP or WPA keys, channels, power levels, and firmware versions.
    • Depending on the level of troubleshooting that is required on the existing wireless network, a second site survey consisting of coverage and spectrum analysis will often be necessary.
    • Adjustments to the existing WLAN equipment typically are adequate. However, the worst-case scenario would involve a complete redesign of the WLAN
    • If wireless usage requirements have changed, a redesign might be the best course of action.
  • Infrastructure connectivity
    • Asking for a copy of the wired network topology map is highly recommended.
    • For security reasons, the customer may not want to disclose the wired topology, and you may need to sign a nondisclosure agreement
    • Understanding the existing topology will also be of help when planning WLAN segmentation and security proposals and recommendations
    • With or without a topology map, the following topics are important to ensure the desired infrastructure connectivity:
      • Roaming
        • Is roaming required?
        • Any devices that run connection-oriented applications will need seamless roaming
        • Seamless roaming is mandatory if handheld devices and/or VoWiFi phones are deployed
        • With the advent of smartphones and tablets, most end users expect mobility. Providing for secure seamless roaming is pretty much an afterthought.
        • It should also be understood that there might be certain areas where the WLAN was designed so that roaming is a very low priority, such as areas with a high density of users
        • This is a WLAN design with high density as the priority, as opposed to mobility and roaming
        • whether users will need to roam across layer 3 boundaries.
        • A Mobile IP solution or a proprietary layer 3 roaming solution will be needed if client stations need to roam across subnets
        • With regard to the existing network, it is imperative that you determine whether the wired network infrastructure will support all the new wireless features.
      • Wiring Closets
        • Where are the wiring closets located?
        • Will the locations that are being considered for AP installation be within a 100-meter (328-foot) cable drop from the wiring closets?
      • Antenna Structure
        • If an outdoor network or point-to-point bridging application is requested, some additional structure might have to be built to mount the antennas
        • Asking for building diagrams of the roof to locate structural beams and existing roof penetrations is a good idea.
        • Depending on the weight of the installation, you may also need to consult a structural engineer.
      • Switches
        • Will the access points be connected by category 5 (CAT5) cabling to unmanaged switches or managed switches?
        • CAT5e or higher grade cabling is usually needed to maximize 802.3af PoE.
        • An unmanaged switch will only support a single VLAN.
        • Are there enough switch ports?
        • What is the power budget of the switch?
        • Who will be responsible for configuring the VLANs?
      • PoE
        • How will the access points be powered?
        • Very often the customer will not yet have a PoE solution in place, and further investment will be needed.
        • the customer already does have a PoE solution installed, it must be determined whether the PoE solution is compliant with 802.3af or 802.3at (PoE Plus).
        • it is important to make sure that it is compatible with the system you are proposing to install.
        • If PoE injectors need to be installed, you will need to make sure there are sufficient power outlets.
      • Segmentation
        • How will the WLAN and/or users of the WLAN be segmented from the wired network?
        • Will the entire wireless network be on a separate IP subnet tied to unique
        • Will firewalls or VPNs be used for segmentation? VLANs?
        • Or will the wireless network be a natural extension to the wired
        • network and follow the same wiring, VLAN numbering, and design schemes as the wired infrastructure?
      • Naming Convention
        • Does the customer already have a naming convention for cabling and network infrastructure equipment, and will one need to be created for the WLAN?
      • User Management
        • Considerations regarding RBAC, bandwidth throttling, and load balancing should be discussed
        • Do they have an existing RADIUS server or does one need to be installed?
        • What type of LDAP user database is being used?
        • Where will usernames and passwords be stored?
        • Will usernames and passwords be used for authentication, or will they be using client certificates?
        • Will guest user access be provided?
      • Device Management
        • Will employees be allowed to access the WLAN with their own personal devices?
        • How will personal and company-issued mobile devices be managed?
        • Do they want to provide different levels of access based upon device type
      • Infrastructure Management
        • How will the WLAN remote access points be managed?
        • Is a central management solution a requirement?
        • Will devices be managed using SSH2, SNMP, or HTTP/HTTPS?
        • Do they have standard credentials that they would like to use to access these management interfaces?
  • Security expectations
    • All data privacy and encryption needs should be discussed
    • All AAA requirements must be documented
    • It should be determined whether the customer plans to implement a wireless intrusion detection or prevention system (WIDS or WIPS) for protection against rogue APs and the many other types of wireless attacks.
    • A comprehensive interview regarding security expectations will provide the necessary information to make competent security recommendations after the site survey has been conducted and prior to deployment
    • Industry-specific regulations such as the Health Insurance Portability and Accountability Act (HIPAA), Gramm-Leach-Bliley, and Payment Card Industry (PCI) may have to be taken into account when making security recommendations
    • All of these answers should also assist in determining whether the necessary hardware and software exists to perform these functions
  • Guest access
    • Most companies offer some sort of wireless guest access to the Internet.
    • Guest users access the WLAN via the same access points.
    • However, they usually connect via a guest SSID that redirects the guest users to a captive portal.
    • The guest captive portal serves two purposes:
      • The login screen forces guest users to accept the corporate legal disclaimer.
      • After logging in, the guest users are provided with a gateway to the Internet.
    • It should be noted that all users who connect with the guest SSID should be allowed to go only to the Internet gateway and should be properly segmented from all other network
    • Resources in a separate guest VLAN
    • Firewall restrictions and bandwidth throttling are also common when deploying guest WLANs

Documentation and reports

  • Forms and customer documentation
    • Before the site survey interview, you must obtain some critical documentation from the customer:
      • Blueprints
        • You need a floor plan layout in order to discuss coverage and capacity needs with network administration personnel
        • Some software survey tools allow you to import floor plans, and the software will record the survey results on the floor plan for you
        • These are highly recommended and make the final report much easier to compile
        • What to do if no blueprints:
          • The original architect of the building will probably still have a copy of the blueprints.
          • Many public and private buildings’ floor plans might also be located at a public government resource such as city hall or the fi re department.
          • Businesses are usually required to post a fi re escape plan
      • Topographic Map
        • If an outdoor site survey is planned, a topographic map, also called a contour map, will be needed
        • Contour maps display terrain information, such as elevations, forest cover, and the locations of streams and other bodies of water
        • topographic map will be a necessity when performing bridging calculations, such as Fresnel zone clearance.
      • Network Topology Map
        • Understanding the layout of the customer’s current wired network infrastructure will speed up the site survey process and allow for better planning of the WLAN during the design phase
        • Acquiring a network topology map from the customer is a highly recommended practice that will result in a well-designed and properly integrated WLAN
      • Security Credentials
        • You might need proper security authorization to access facilities when conducting the site survey
        • A meeting with security personnel and/or the facilities manager in advance of the survey will be necessary in order to meet all physical security requirements
        • Regardless of the security requirements, it is always a good idea to have the network administrator alert everyone that you will be in the area.
      • Interview Checklist
        • A detailed checklist containing all the questions to be asked during the site survey interview should be created in advance
      • Installation Checklist
        • Many site survey professionals prefer to record all installation details on the floor plan documents
        • An installation checklist detailing hardware placement and mounting for each individual access point is also an option.
        • Information about AP location, antenna type, antenna orientation, mounting devices, and power sources may be logged
      • Equipment Checklist
        • A checklist of all the hardware and software tools used during the survey might also be a good idea
  • Deliverables
    • After the interview process has been completed and the survey has been conducted, a fi nal report must be delivered to the customer
    • Compiled information contained in the deliverables will include the following:
      • Purpose Statement
        • The final report should begin with a WLAN purpose statement that stipulates the customer requirements and business justification for the WLAN.
      • Spectrum Analysis
        • Be sure to identify potential sources of interference
      • RF Coverage Analysis
        • Define RF cell boundaries
      • Hardware Placement and Configuration
        • Recommend AP placement, antenna orientation, channel reuse pattern, power settings, and any other AP-specific information such as installation techniques and cable routing
      • Capacity and Performance Analysis
        • Include results from application throughput testing, which is sometimes an optional analysis report included with the final survey report
  • Additional reports
    • Along with the survey report, other recommendations will be made to the customer so that appropriate equipment and security are deployed
    • The person conducting the survey might not be doing the installation
    • Regardless of who handles the installation work, other recommendations and reports will be provided along with the site survey report:
      • Vendor Recommendations
        • It is a highly recommended practice to conduct the site survey using equipment from the same vendor who will supply the equipment that will later be deployed on site
        • The mere fact that every vendor’s radios use proprietary RSSI thresholds is reason enough to stick with the same vendor during surveying and installation.
        • It is not unheard of for a survey company to conduct two surveys with equipment from two different vendors and present the customer with two separate options.
        • However, the interview process will usually determine in advance the vendor recommendations that will be made to the customer.
      • Implementation Diagrams
        • The implementation diagram is basically a wireless topology map that illustrates where the access points will be installed and how the wireless network will be integrated into the existing wired infrastructure.
        • AP placement, VLANs, and layer 3 boundaries will all be clearly defined.
      • Bill of Materials
        • Itemizes every hardware and software component necessary for the final installation of the wireless network
        • The model number and quantity of each piece of  equipment will be necessary
      • Project Schedule and Costs
        • Outlines all timelines, equipment costs, and labour costs
        • Particular attention should be paid to the schedule dependencies, such as delivery times and licensing, if applicable.
      • Security Solution Recommendations
        • Comprehensive wireless security recommendations
        • All aspects of authentication, authorization, accounting, encryption, and segmentation should be included in the security recommendations documentation
      • Wireless Policy Recommendations
        • An addendum to the security recommendations might be corporate wireless policy recommendations
      • Training Recommendations
        • One of the most overlooked areas
        • It is highly recommended that wireless administration and security training sessions be scheduled with the customer’s network personnel

Vertical market considerations

  • Outdoor surveys
    • Calculations necessary for outdoor bridging surveys are numerous, including the Fresnel zone, earth bulge, free space path loss, link budget, and fade margin.
    • outdoor site surveys for the purpose of providing general outdoor wireless access for users are becoming more commonplace
    • Outdoor site survey kits using outdoor mesh APs will be needed.
    • Weather conditions, such as lightning, snow and ice, heat, and wind, must also be contemplated
    • Unless the hardware is designed for outdoor use, the outdoor equipment must ultimately be protected from the weather elements by using NEMA-rated enclosure units (NEMA stands for National Electrical Manufacturers Association)
    • Safety is also a big concern for outdoor deployments. Consideration should be given to hiring professional installers.
    • All RF power regulations, as defined by the regulatory body of your country, will need to be considered
    • If towers are to be used, you may have to contact several government agencies
    • you must contact the proper RF regulatory authority and aviation authority to find out the details
  • Aesthetics
    • An important aspect of the installation of wireless equipment is the “pretty factor.”
    • Many businesses prefer that all wireless hardware remain completely out of sight.
    • Extremely important in retail environments and in the hospitality industry
    • WLAN vendors continue to design more aesthetic-looking access points and antennas
  • Government
    • The key concern during government wireless site surveys is security.
    • Be sure to check export restrictions before traveling to other countries with certain equipment.
    • Obtaining the proper security credentials will most likely be a requirement before conducting the government survey
    • An identification badge or pass often is required.
    • In some government facilities, an escort is needed in certain sensitive areas
  • Education
    • As with government facilities, obtaining the proper security credentials in an education environment usually is necessary.
    • Properly securing access points in lockable enclosure units is also necessary to prevent theft or tampering
    • user density should be accounted for during capacity and coverage planning.
    • In campus environments, wireless access is required in most buildings, and very often bridging solutions are needed between buildings across the campus
    • Most school buildings use dense wall materials such as cinderblock or brick to attenuate the sound between classrooms. These materials also heavily attenuate RF signals.
  • Healthcare
    • One of the biggest concerns in a healthcare environment is sources of interference from the biomedical equipment that exists on site.
    • A thorough spectrum analysis survey using a spectrum analyser is extremely important.
    • Hospitals are usually large in scale, and a site survey may take many weeks; a predictive site survey can save a lot of time.
    • The applications used in the medical environment should all be considered during the interview and the survey.
    • VoWiFi phone deployments are commonplace in hospitals because of the communication mobility that they provide to nurses
    • Wi-Fi real-time location systems (RTLSs) using active 802.11 RFID tags are commonplace in hospitals for asset management tracking
    • Because of the presence of medical patients, proper security credentials and/or an escort will often be necessary
    • Many applications are connection oriented, and drops in connectivity can be detrimental to the operation of these applications
  • Hotspots
    • Security solutions at hotspots are usually limited to a captive portal solution for user authentication against a customer database.
  • Retail
    • A retail environment often has many potential sources of 2.4 GHz interference.
    • The inventory storage racks and bins and the inventory itself are all potential sources of multipath problems
    • Heavy user density should also be considered, and a retail site survey should be done in the height of the shopping season as opposed to the offseason when the malls are empty.
    • Wireless applications that are used in retail stores include handheld scanners used for data collection and inventory control
    • Coverage is usually a greater concern than capacity because wireless data-collection devices require very little bandwidth, and the number used in a particular area is typically limited.
  • Warehouses
    • 2.4 GHz WLAN will likely be deployed because most handheld devices currently use 2.4 GHz radios.
    • Coverage, not capacity, is usually the main objective when designing a wireless network in a warehouse
    • Warehouses are filled with metal racks and all sorts of inventory that can cause reflections and multipath
    • High ceilings often cause mounting problems as well as coverage issues
    • Indoor chain-link fences that are often used to secure certain areas will scatter and block a 2.4 GHz RF signal
    • Seamless roaming is also mandatory
    • Handheld WLAN barcode scanners are now often being replaced with smart phones that use barcode scanning applications.
  • Manufacturing
    • Often similar to a warehouse environment in terms of multipath interference and coverage design.
    • A manufacturing plant presents many unique site survey challenges, including safety and the presence of employee unions
    • Heavy machinery and robotics may present safety concerns to the surveyor, and special care should be taken so as not to mount access points where they might be damaged by other machines.
    • Proper protection gear may need to be worn, and ruggedized access points or enclosures may have to be installed
    • Many manufacturing plants are union shops with union employees. A meeting with the plant’s union representative may be necessary to make sure that no union policies will be violated by the site surveyor team.
  • Multitenant buildings
    • The biggest issue when conducting a survey in a multitenant building is the presence of other WLAN equipment used by nearby businesses
    • Almost assuredly all of the other tenants’ WLANs will be powered to full strength, and some equipment will be on nonstandard channels such as 2 and 8, which will likely interfere with your WLAN equipment
    • If at all possible, strong consideration should be given to deploying a WLAN using the 5 GHz U-NII bands.
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