CWNA Guide to Wireless LANs, Second Edition7-1

Chapter 7

Conducting a Site Survey

At a Glance

Instructor’s Manual Table of Contents
  • Overview
  • Objectives
  • Teaching Tips
  • Quick Quizzes
  • Class Discussion Topics
  • Additional Projects
  • Additional Resources
  • Key Terms

Lecture Notes

Overview

In this chapter, the students will explore the necessary steps for locating wireless equipment. First, students learn what this process involves and what tools are used. Next, they will look at how to gather the necessary data and survey the location. Finally, the students will learn about the types of reports that are generated from this process.

Chapter Objectives

  • Explain what a site survey is
  • Describe the tools that are used in a site survey
  • Describe how to perform a site survey

Teaching Tips

What is a Site Survey?

  1. Explain that, unlike setting up a WLAN at home, when installing a WLAN for an organization, areas of dead space may not be tolerated. Mention that you may need to ensure blanket coverage within a building, meeting per-user bandwidth requirements, and minimize "bleeding" of wireless signals outside of the building.
  1. Using the list on pages 226 and 227 of the text as a guide, discuss the factors that may influence meeting wireless coverage goals.
  1. Define the term site survey. Stress that is it essential to perform a site survey prior to implementing a WLAN.
  1. Using the list on page 227 of the text as a guide, discuss some of the design goals to consider when panning/performing a site survey.

Teaching

Tip / Make sure the students understand that a wireless LAN should never be deployed without first conducting a site survey.
  1. Explain that a site survey provides a realistic understanding of the infrastructure required for the proposed wireless link, and that it assists in predicting network capability and throughput as well as indicating the exact location of APs and power levels required.

Teaching

Tip / Conducting a site survey is both an art and a science. Some of the steps in a site survey involve taking detailed measurements, but other aspects can involve experience along with trial and error to achieve optimal results.
  1. Explain that, in additions to just before a WLAN is installed, there are other times that site surveys should be performed. Using the list on page 228 of the text as a guide, discuss these times.

Site Survey Tools

  1. Provide a brief introduction to site survey tools.

Wireless Tools

  1. Explain that the access point (AP) itself is the most basic site survey tool. Mention that it may be necessary to position the AP at one location, and then monitor its signal from various other locations.

Teaching

Tip / Make sure the students understand that it is important that the actual type of access point that will be deployed is used when conducting the site survey.
  1. Explain that access points used as wireless tools in site surveys should first have the ability to adjust the output power. Illustrate with Figure 7-1.

Teaching

Tip / Most consumer-grade access points do not include the capability to adjust the power levels.
  1. Explain why APs used as tools in site surveys should have external antenna connectors. Illustrate with Figure 7-2.

Teaching

Tip / Antennas were covered in detail in Chapter 3.
  1. Describe when and why a DC-to-AC converter should be used to power the AP.
  1. Explain why a notebook computer with a wireless NIC is also an essential site survey tool. Explain why a notebook is preferable to a wireless-enabled PDA. Mention that the notebook should have been previously configured and tested.

Teaching

Tip / Although once very popular, PDA sales have substantially diminished as enhanced capabilities have been added to cellular telephones. Some industry experts predict that PDAs will eventually be replaced by these “smart phones.”

Measurement Tools

  1. Provide a brief overview of the measurement tools that can be used once the AP has been positioned.

Teaching

Tip / Although each of the three types of measurement tools discussed in this section can be found as separate hardware devices, the trend today is for these tools to be software-based and run on a notebook computer. This makes it much easier to conduct a site survey with a single notebook computer instead of using and carrying several hardware devices.

Site Survey Analyzers

  1. Explain that site survey analyzers are specifically designed for the purpose of a site survey. Mention that many APs contain site survey analysis software built in. Discuss the concept of the RSSI value. Explain that this software can convert RSSI values of dBm.

Teaching

Tip / Because the conversions can be different between vendors’ products, different analysis tools may report different values for signal power.
  1. Using the list on pages 231 and 232 of the text as a guide, discuss the settings that may be configured on in a full-featured site survey analyzer package. Describe the difference between unicast and multicast transmission. Illustrate these settings with Figure 7-3.
  1. Describe the output generated by a site survey analyzer package. Illustrate with Figure 7-4.
  1. Discuss the setup options and output for a basic site survey analyzer package, illustrating with Figures 7-5 and 7-6.

Teaching

Tip / Some of the most popular full-featured site survey analyzer software packages include Rollabout, AirMagnet Site Surveyor, WirelessValley, and Ekahau.

Spectrum Analyzers

  1. Explain that a spectrum analyzer scans the desired radio frequency and displays a graphical portrait of the results. Mention that these tools typically display the signal-to-noise ratio in dB as a graph.
  1. Discuss the purpose of single-frequency analyzers.
  1. Illustrate the output from spectrum analyzers with Figures 7-7 and 7-8.
  1. Explain how the output of a spectrum analyzer is useful when attempting to determine the best position and orientation for APs.

Teaching

Tip / Some of the most popular spectrum analyzers include those from Cognio, Bantam, and Rohde & Schwarz.

Network Analyzers

  1. Explain that network analyzers can be used to pick up any packets that are being transmitted by other WLANs in the area and can provide additional information on transmissions. Stress that they are not directly used in determining the best position of an AP.

Teaching

Tip / AirMagnet, LinkFerret, Yellowjacket, OptiView, and AiroPeek are a few of the most popular wireless network analyzers.

Documentation Tools

  1. Explain that the purpose of documentation tools is to create a hard copy of site survey results so that they will be available for future reference. Mention that there is no industry-standard form for site survey documentation.
  1. Using the list on page 236 of the text as a guide, discuss the information that should be included in a site survey report.
  1. Explain that plain paper and a blueprint of the building layout are two basic yet important documentation tools. Mention that it is advisable to create a database to store the site survey information.

Teaching

Tip / Another important documentation tool is a digital camera. You can use a digital camera to document the placement of access points and antenna positions.

Quick Quiz 1

  1. The process of planning a wireless LAN to meet the design goals is known as a(n) ______.

Answer: site survey

  1. True of False: The only time when a site survey should be performed is prior to the installation of the wireless network.

Answer: False

  1. True or False: An access point used in a site survey should have external antenna connectors.
    Answer: True
  1. Unlike spectrum analyzers and network analyzers, a(n) ______analyzer is a measurement tool that is specifically designed for conducting a wireless LAN site survey.

Answer: site survey

  1. A(n) ______analyzer scans the radio frequency spectrum and provides a graphical display of the results.

Answer: spectrum

  1. True or False: It is advisable to store site survey information in a word processing document rather than a database.

Answer: False

Performing a Site Survey

  1. Provide a brief introduction to the three steps involved in performing a site survey.

Gathering Data

  1. Explain that much of the work in a site survey is actually performed prior to setting up an access point and testing its radio frequency pattern. Introduce the four key steps in gathering data for a site survey.

Obtaining Business Requirements

  1. Explain that the first data gathering step is to determine why the organization is implementing or extending a WLAN. Stress that without understanding the reasons why the network is needed it will be almost impossible to properly design and implement the network.
  1. Mention that the primary data gathering method during this step is interviewing members of the organization.
  1. Discuss the common business needs that necessitate the implementation of a WLAN. Explain that if the WLAN is being implemented to accommodate mobile users, you must determine the type of mobility that you are dealing with.
  1. Describe the importance of determining the per-user bandwidth requirements for the network. Mention that you may need to differentiate between different types of users, who may have differing bandwidth requirements.

Defining Security Requirements

  1. Explain why considering security is a crucial planning step. Mention that encryption and authentication methods must be considered, and that existing security policies and procedures must be taken into account.

Teaching

Tip / Wireless security will be covered in detail in Chapters 8 and 9.

Gathering Site-Specific Documentation

  1. Discuss the three ways that site-specific documentation is generally accumulated. Explain the importance and uses of items such as blueprints and visual inspection of the site.
  1. Discuss the tools and equipment that may be required for that during the "behind-the-scenes" site inspection, such as a ladder and flashlight.

Documenting Existing Network Characteristics

  1. Explain that the new WLAN will "dovetail" into any existing network infrastructure. Mention that you must determine the degree to which the wireless LAN will interact with other wired networks.
  1. Explain that some legacy systems may not support a WLAN without additional equipment. Mention that roaming from one access point located on one IP subnet to an access point located on another IP subnet in an Ethernet network causes loss of IP connectivity, unless special considerations are made.

Performing the Survey

  1. Provide a brief overview of the steps involved in performing the actual site survey. Mention that an outdoor survey is similar to an indoor survey with a few variations.

Collecting RF Information

  1. Explain that the first step is to document (probably with a camera) the room layout and the objects in the room.
  1. Explain that the second step is to position the AP in what seems to be the most logical position and orientation. Discuss the locations that may be used depending on the type of antenna used. Illustrate with Figure 7-10. Stress that the positioning of the AP should be documented at all times.
  1. Explain that the surveyor should take a notebook computer with site survey analyzer software running and walk slowly away from the AP in one direction. Mention the data that they should monitor on the notebook while they do this.
  1. Introduce the four pieces of information that can be produced from the data collected in the previous steps.
  1. Define the term coverage pattern. Explain that determining the coverage pattern involves observing signal loss and noting it on the map or blueprint that is being used. Illustrate with Figure 7-11.

Teaching

Tip / Absorption, reflection, scattering, refraction, and diffraction are covered in Chapter 3.
  1. Define the term data rate boundary. Illustrate with Figure 7-12.
  1. Define the term packet throughput. Explain that if the software measurement tools do not have the ability to test throughput, this can be done manually by performing successive TCP/IP “pings” or FTP operations on large files.
  1. Define the term transmission range. Mention that transmission ranges are affected by distance as well as objects in the path.

Collecting Non-RF Information

  1. Explain that any potential sources of interference must be documented. Using the list on page 243 of the text as a guide, discuss the objects that pose the greatest risk for interference that are often found in an office environment.
  1. Explain why electrical and network connections should be documented at this point, even though they are documented on the building blueprints and other documentation items previously generated.

Outdoor Surveys

  1. Explain the conditions that must be considered when conducting an outdoor survey that were not necessary when performing an indoor survey. Using the list on page 244 of the text as a guide, discuss the additional tools and equipment that may be required to perform an outdoor survey.

Finalizing the Survey Documents

  1. Explain that the final result of the survey is a map of the optimal areas of coverage for the placement of the access point. Mention that, depending on the results, it may be necessary to reposition the AP(s) and perform the whole process over again.

Creating the Site Survey Report

  1. Explain that the site survey report should contain a narrative section and a graphical section.
  1. Discuss the contents that should be included in the narrative section of the report. Stress the importance of outlining all steps involved in the methodology. Mention that some narrative sections include tables of results. Illustrate with Figure 7-13. Also mention that the recommendation section should also address security issues.
  1. Describe the typical content of the graphic section of the report. Illustrate with Figures 7-14 and 7-15.

Quick Quiz 2

  1. True or False: Much of the work in a site survey is performed prior to setting up an access point and testing its radio frequency pattern.

Answer: True

  1. True or False: Blueprints and other similar documents always reveal the current state of the building.

Answer: False

  1. True or False: The first position that you should try for an access point with an omnidirectional antenna is in the corner of the room.

Answer: False

  1. The ______is the area in which the signal can be received from the AP.

Answer: coverage pattern

  1. Packet ______information is summarized as the number of packets sent and received and the data rates for each.

Answer: throughput

  1. True or False: The final result of a site survey is a map of the optimal areas of coverage for the placement of the access point.

Answer: True

  1. The ______section of a site survey report generally includes maps and diagrams of the coverage area.

Answer: graphic

Class Discussion Topics

  1. The city of Philadelphia is currently working on the implementation of a city-wide wireless network, and many other cities are considering similar projects. Have the students discuss the logistics of a site survey of such a massive scale. If they had been contracted to lead such a project, how would they proceed with a site survey that covers an entire metropolitan area?
  1. Can the students think of any other items that should be taken into consideration in a site survey besides what was mentioned in this chapter? What if the site survey is dealing with multiple access points?

Additional Projects

  1. Identify a room in which the students can use to perform a site survey. Have the students set up an access point in the room and use a notebook computer or site surveyor software to record the signal-to-noise ratio in all areas of the room. Based on the data collected, have the students generate the coverage pattern, data rate boundaries, throughput, and total transmission range for the wireless site. This exercise would work best if the selected room is relatively large (such as the main area in a library.
  2. In this chapter, surveying a site with one access point was detailed. However, it will be more common to perform a site survey where there are multiple access points to consider. Have the students alter or expand on the stepsdescribe in the "Performing the Survey" section of this chapter to account for the need for multiple access points. The students should point out the complications that arise from having to consider multiple APs simultaneously.

Additional Resources

  1. 802.11a/b Site Survey: A Testimonial:
  1. Wireless LAN Deployment Considerations:
  1. Commercial WLAN Analyzers:
  1. Open Source WLAN Analyzers:
  1. Tools Simplify 802.11 Deployments:

6.The Ins and Outs of Network Analyzers (Part 1):

7.The Ins and Outs of Network Analyzers (Part 2):

  1. Intel® PRO/Wireless 2011 LAN Access Point Site Survey/System Administrator's Guide (pdf):

ftp://download.intel.com/support/wireless/wlan/pro2011/accesspoint/sitesurvey.pdf

Key Terms

Coverage pattern: The area in which the signal can be received from the access point.

Data rate boundaries: The range of coverage for a specific transmission speed.

DC-to-AC converter: A device that converts direct current (DC) from a battery to alternating current (AC).

Multicast: A transmission that sends a frame from one sender to multiple receivers with a single “transmit” operation.

Packet throughput: The number of packets sent and received.

Site survey: An in-depth examination and analysis of a proposed wireless LAN site in order to meet design goals.

Site survey analyzer: A measurement tool designed for conducting a wireless LAN site survey.

Spectrum analyzer: A device that scans the entire radio frequency spectrum and provides a graphical display of the results.

Transmission range: The farthest distance in which the signal can be received by the wireless device.

Unicast: A transmission that sends a frame from one sender to a single receiver