CWNA guide to wireless LANs 2nd ch07

Site Survey Tools: Measurement Tools• Site Survey Analyzers: Specifically designed for conducting WLAN site surveys – Software often built into AP – Receive Signal Strength Indicator RS

CWNA Guide to Wireless LANs, Second Edition

Chapter Seven

Conducting a Site Survey

• Explain what a site survey is

• Describe the tools that are used in a site survey

• Describe how to perform a site survey

What is a Site Survey?

• When installing a WLAN for an organization, areas

of dead space might not be tolerated

– Ensure blanket coverage, meet per-user bandwidth requirements, minimize “bleeding” of signal

• Factors affecting wireless coverage goals:

– Devices emitting RF signals

– Building structure (walls, construction materials)

– Open or closed office doors

– Stationary versus mobile machinery/equipment

– Movement of mobile walls (e.g., cubicles)

What is a Site Survey? (continued)

• Factors affecting wireless coverage goals

– Effectiveness of a WLAN often linked to

thoroughness of the site survey

What is a Site Survey? (continued)

• Design goals for a site survey:

– Achieve best possible performance from WLAN

– Certify that installation will operate as promised

– Determine best location for APs

– Develop networks optimized for variety of

What is a Site Survey? (continued)

• Design goals for a site survey (continued):

– Map nearby wireless networks to determine existing radio interference

– Reduce radio interference as much as possible

– Make wireless network secure

• Survey provides realistic understanding of

infrastructure required for proposed wireless link

– Assists in predicting network capability and

throughput

– Helps determine exact location of APs and power

levels required

What is a Site Survey? (continued)

• When to perform a site survey:

– Before installing a new wireless network

– Before changing an existing wireless network

– When there are significant changes in personnel

– When there are changes in network needs

– After making physical changes to a building

Site Survey Tools: Wireless Tools

• Most basic tool is AP itself:

– Position AP in various locations, monitor signal as you move

– APs should have ability to adjust output power

– APs should have external antenna connectors

• Test effectiveness of different antenna types in different situations

– May need DC-to-AC converter for testing

• Notebook computer with wireless NIC also

essential for testing

– Previously configured and tested

Site Survey Tools: Wireless Tools

(continued)

Figure 7-1: Adjusting AP power levels

Site Survey Tools: Wireless Tools

(continued)

Figure 7-2: External antenna connectors

Site Survey Tools: Measurement Tools

• Site Survey Analyzers: Specifically designed for

conducting WLAN site surveys

– Software often built into AP

– Receive Signal Strength Indicator (RSSI) value

– Full-featured site survey analyzer software settings:

• Destination MAC Address

• Continuous Link Test

• Number of Packets

• Packet Size

• Data Retries

Site Survey Tools: Measurement Tools

(continued)

• Site Survey Analyzers (continued):

– Full-featured site survey analyzer software settings (continued):

• Data Rate

• Delay Between Packets

• Packet Tx Type

– Unicast or multicast

• Percent Success Threshold

– Basic survey analyzer software contains far fewer

features

Site Survey Tools: Measurement Tools

(continued)

Site Survey Tools: Measurement Tools

(continued)

Figure 7-4: Full-featured site survey analyzer software results

Site Survey Tools: Measurement Tools

(continued)

Figure 7-6: Basic site survey analyzer software results

Site Survey Tools: Measurement Tools

(continued)

• Spectrum Analyzers: Scan radio frequency

spectrum and provides graphical display of results

– Typically measure signal-to-noise ratio

– Single-frequency analyzers measure signal-to-noise ratio at specified frequency

– Helpful in identifying interference problems

• Thus, helps properly position/orient AP

Site Survey Tools: Measurement Tools

(continued)

Figure 7-7: Single-frequency analyzer

Site Survey Tools: Measurement Tools

(continued)

Figure 7-8: Spectrum analyzer

Site Survey Tools: Measurement Tools

(continued)

• Network Analyzers: Can be used to pick up

packets being transmitted by other WLANs in area

– Provide additional information on transmissions

– Packet sniffers or protocol analyzers

– Not used in placement of AP

Site Survey Tools: Documentation

Tools

• Create a “hard copy” of site survey results

– Make available for future reference

– No industry-standard form for site survey

Site Survey Tools: Documentation

– Access point configuration

• Use plain paper and building layout blueprints as tools

• Advisable to create database to store site survey information and generate reports

Site Survey Tools: Documentation

Tools (continued)

Performing a Site Survey: Gathering

Data

• Obtaining Business Requirements: Determine

business reasons why WLAN being proposed or extended

– If this step skipped, almost impossible to properly

design and implement the network

– Primary data gathering method is interviewing

– Must determine type of mobility required within

organization

– Must determine per-user bandwidth requirements

• May be different “types” of users with different bandwidth requirements

Performing a Site Survey: Gathering

Data (continued)

• Defining Security Requirements: Consider type

of data encryption and type of authentication that will take place across WLAN

– Consider existing security policies and procedures

• Gathering Site-Specific Documentation:

– Blueprints, facility drawings, and other documents

• Show specific building infrastructure components

– Inspecting the site

• Document changes to blueprints and get visual perspective

Performing a Site Survey: Gathering

Data (continued)

• Gathering Site-Specific Documentation

(continued):

– Behind-the-scenes site inspection

• May require ladder, flashlight, and an escort

• Documenting Existing Network Characteristics:

New or expanded WLAN will “dovetail” into network already in place

– Determine degree to which WLAN will interact with other wired networks

– Legacy systems may require additional equipment to support WLAN

Performing a Site Survey: Performing

the Survey

• Collecting RF Information:

– Note objects in and layout of room

• Use digital camera

– Position AP

• Initial location will depend on antenna type

• Document starting position of AP

– Using notebook computer with site survey analyzer software running, walk slowly away from AP

• Observe data displayed by analyzer program

– Data rate, signal strength, noise floor, and to-noise ratio

signal-Performing a Site Survey: signal-Performing

the Survey (continued)

Performing a Site Survey: Performing

the Survey (continued)

• Collecting RF Information (continued):

– Continue moving until data collected for all areas

– Data collected used to produce:

• Coverage pattern: Area where signal can be received

from the AP

• Data rate boundaries: Range of coverage for a

specific transmission speed

• Throughput: Number of packets sent and received

and data rates for each

• Total transmission range: Farthest distance at which

signal can be received by wireless device

Performing a Site Survey: Performing

the Survey (continued)

Performing a Site Survey: Performing

the Survey (continued)

Performing a Site Survey: Performing

the Survey (continued)

• Collecting Non-RF Information:

– Sources of interference can include:

• Wire mesh security windows, Aquariums, Outer walls, Ceramic or marble floors, Concrete floors or pillars, Security booth bullet-proof glass, Mirrors, and Elevator shafts or filing cabinets

– Electrical and network connections

• Outdoor Surveys: Similar to indoor surveys, but

must consider climatic conditions, trees, different possibilities for antenna positions

Performing a Site Survey: Performing

the Survey (continued)

• Outdoor Surveys (continued):

– Different tools may be required

• GPS

• Range finder

• Tape measure

• Lighting beacons, flares, and spotlights

• Finalizing the Survey Documents: Final result is

map of optimal areas of coverage for placement of access point

– If results unacceptable, must relocate AP and start over

Performing a Site Survey: Creating the

Site Survey Report

• Narrative section:

– State customer requirements

– Outline methodology

• Outline all steps taken during survey

– Clearly state results of measurements

• May have tables of measurements

– Recommendations

• Should always address security

Performing a Site Survey: Creating the

Site Survey Report (continued)

Figure 7-13: Table of measurements

Performing a Site Survey: Creating the

Site Survey Report (continued)

• Graphic section:

– Generally includes maps and diagrams of coverage area

• Data rate coverage map

• Signal-to-noise ratio plot

Performing a Site Survey: Creating the

Site Survey Report (continued)

Performing a Site Survey: Creating the

Site Survey Report (continued)

• A site survey is an in-depth examination and

analysis of a proposed wireless LAN site to meet design goals

• Three categories of tools used

– Wireless tools include the access point and

notebook computers with a wireless NIC

– Measurement tools include site survey analyzers, spectrum analyzers, and network analyzers

– Documentation tools create a “hard copy” of the site survey results for future reference

Summary (continued)

• Three steps in conducting a site survey

– Gather the background data

– Perform the actual survey

– Create the site survey report, containing a narrative and a graphical section