This document provides information on the most frequently asked
questions (FAQ) about a Wireless Site Survey.
What is a site survey?
A. A radio frequency (RF) site survey is the first step in the deployment
of a Wireless network and the most important step to ensure desired operation.
A site survey is a task-by-task process by which the surveyor studies the
facility to understand the RF behavior, discovers RF coverage areas, checks for
RF interference and determines the appropriate placement of Wireless devices.
What is the need for Wireless Site Survey?
A. In a Wireless network, many issues can arise which can prevent the
radio frequency (RF) signal from reaching all parts of the facility. Examples
of RF issues include mulitpath distortion, hidden node problems, and near/far
issues. In order to address these, you need to find the regions where these
issues occur. A site survey helps you to do this. A site survey helps define
the contours of RF coverage in a particular facility. It helps us to discover
regions where mulitpath distortion can occur, areas where RF interference is
high and find solutions to eliminate such issues. A site survey that determines
the RF coverage area in a facility also helps to choose the number of Wireless
devices that a firm needs to meet its business requirements.
What are the design constraints that a proper site survey needs to
A. The four main design requirements that need to be taken care of while a
site survey is performed are:
What are the results of a Wireless site survey?
A. A proper site survey provides detailed information that addresses
coverage, interference sources, equipment placement, power considerations and
wiring requirements. The site survey documentation serves as a guide for
network design and for the installation and verification of the Wireless
What basic equipment is required for the completion of a site
A. Some of the basic equipment and utilities that are required for the
completion of a site survey include:
Wireless access point
Wireless client card
Laptop or PDAs
Variety of antennas (this depends on the requirement of the
Site survey utility software
What are the steps to perform a site survey?
A. A professional installer is needed for optimal results. These are the
steps that are performed:
Obtain a facility diagram in order to identify the potential radio
frequency (RF) obstacles.
Visually inspect the facility to look for potential barriers or the
propagation of RF signals and identify metal racks.
Identify user areas that are highly used and the ones that are not
Determine preliminary access point (AP) locations. These locations
include the power and wired network access, cell coverage and overlap, channel
selection, and mounting locations and antenna.
Perform the actual surveying in order to verify the AP location.
Make sure to use the same AP model for the survey that is used in production.
While the survey is performed, relocate APs as needed and
Document the findings. Record the locations and log of signal
readings as well as data rates at outer boundaries.
What are National Electronics Manufacturers Association (NEMA)
A. Sometimes access points (APs) are located in areas where they are
subject to extreme moisture, temperatures, dust and particles. These APs might
need to be mounted inside a sealed enclosure. The NEMA has a rating system for
these enclosures, which are generally called NEMA enclosures.
What is the function of the Aironet Client Utility (ACU) Site Survey
A. The ACU Site Survey tool can assist you in conducting a site survey.
The tool operates at the radio frequency (RF) level and is used to determine
the best placement and coverage (overlap) for the infrastructure devices of
your network. The current status of the network is read from the client adapter
and displayed four times per second so you can accurately gauge network
performance. The feedback that you receive can help you to eliminate areas of
low RF signal levels that can result in a loss of connection between the client
adapter and its associated access point (or other infrastructure
What are the two modes in which the Aironet Client Utility (ACU) Site
Survey tool can be used?
A. The ACU Site Survey tool can operate in two modes.
In passive mode, the tool does not initiate any RF traffic to
understand RF behavior. Instead, it listens to the traffic that the client
adapter hears and displays the results. Refer to
Passive Mode for more information on how to use the ACU Site Survey tool
in passive mode.
In active mode, the client adapter actively sends and receives
low-level RF packets to or from its associated access point and provides
information on the success rate. It also enables you to set parameters that
govern how the site survey is performed (such as the data rate). Refer to
Active Mode for more information about how to use the ACU Site Survey
tool in active mode.
What is the use of the Link Status Meter (LSM) utility on the Aironet
Client Utility (ACU)?
A. The LSM utility is used to determine the performance of the radio
frequency (RF) link between the client adapter and its associated access point
(AP). The information on the LSM can be used to determine the optimum number
and placement of the APs in the RF network. By using the LSM to assess the RF
link at various locations, you can avoid areas of weak performance and
eliminate the risk of losing the connection between the client adapter and the
What are the guidelines to follow when you perform a site survey using
the Aironet Client Utility (ACU) Site Survey tool?
A. Follow these guidelines when you use the ACU Site Survey tool:
Perform the site survey when the radio frequency (RF) link functions
with all other systems and noise sources are operational.
Execute the site survey entirely from the mobile station.
Conduct the site survey with all variables set to operational values
when active mode is used.
Is there a Site Survey tool available with the Aironet Desktop Utility
(ADU). I use a CB21AG Wireless card and I do not see a Site Survey tool in the
A. The Site Survey tool is available with ADU release 2.0 and later. The
older releases of the ADU do not come with the Site Survey tool. Check your ADU
release. If you use an older version of ADU, upgrade the ADU to the latest
release. The latest release of the client adapter firmware and utilities are
located on the
registered customers only)
I have installed the latest release of the Aironet Desktop Utility (ADU)
from Cisco.com. But I am not able to find the Site Survey tool in the
A. The Site Survey tool is installed only if you check Install
Site Survey Utility during the installation of the client adapter
software. If you did not check this and want to use the Site Survey tool,
uninstall the client adapter software, reinstall it, and make sure to check
Install Site Survey Utility.
Where can I find documents which explain in detail how to use the Site
Survey tool available on the Aironet Client Desktop (ADU) and Aironet Client
A. Refer to the
a Site Survey section of the Cisco Aironet 802.11a/b/g
Wireless LAN Client Adapters (CB21AG and PI21AG) Installation and Configuration
Guide to use the Aironet Desktop Utility (ADU) Site Survey tool.
Refer to the
a Site Survey section of Cisco Aironet 340, 350, and CB20A
Wireless LAN Client Adapters Installation and Configuration Guide for
Windows to use the Aironet Client Utility (ACU) Site Survey tool.
Can I perform a site survey using Cisco Aironet 1131 and 1242 access
points and then use the results to deploy an Airespace Wireless solution?
A. Yes, you can do this as long as a proper site survey is conducted and
the results yield an effective Wireless solution. In this case, you can use any
site survey tool.
Can I use the Aironet Client Utility (ACU) and Aironet Desktop Utility
(ADU) Site Survey tools to perform a complete site
A. The site survey tool that comes with the Aironet Client Utility (ACU)
and the Aironet Desktop Utility (ADU) only assist in a site survey. Do not use
these tools for a complete site survey. The site survey should be done by
professional installers and there are many other tools that they use to perform
the professional site survey. The ACU/ADU site survey tool is not intended to
replace the professional site survey engineers.
Can I use a 802.11b client card to do a site survey for a 802.11g access
A. The 802.11b radio can be used to conduct the site survey with the
802.11g radios. However, use the 802.11g cards to do the site survey in order
to do a more complete site survey specific to the 802.11g radio.
I have to install Cisco Aironet 1242 access point (AP) in our office. Can
I use AP 1232 for site survey?
A. Cisco recommends to use the same AP for site survey and installation.
This is because the range of two APs is different. If you do the site survey
with one type of AP and install a different type, then the range differs. Refer
Aironet 1230AG Series 802.11A/B/G Access Point Data Sheet and
Aironet 1240AG Series 802.11A/B/G Access Point Data Sheet for more
I need to measure the coverage for an Aironet 1210 access point and want
to use the Aironet Desktop Utility (ADU) Site Survey tool on a laptop. However,
I cannot prevent the laptop from roaming to another access point before I can
find the edge of coverage for the target access point. Is there a way to
prevent the laptop from roaming from the target access point so I can find the
extent of coverage? I set the "Preferred AP" in the ADU, but that does not
A. Create a test SSID on the target access point (AP) and the client. This
SSID should not exist on the other APs in the Wireless network. With this SSID
you can measure the extent of coverage. The client does not roam to other APs
since the test SSID does not exist on any other AP except the AP for which you
measure the coverage. Once you are done with this you can disable the test SSID
on the AP and activate the production SSID.
Does the procedure for a site survey change if there are voice-based
applications in a Wireless LAN (WLAN) network?
A. With the introduction of voice to a predominantly wireless data
network, the methodology of site surveys needs to be altered. Surveying for
Wireless voice coverage requires more effort and time than for data-only
coverage at the same site. A voice survey requires planning of coverage plus
the planning of capacity. Wireless data is less susceptible to disruption than
Wireless voice when it comes to cell overlap, radio frequency (RF) noise, and
packet delay. Refer to
for Successful VoIP Surveys for more information on how to perform a
site survey for voice based WLAN.
What are the different types of voice site surveys that Cisco
A. There are two types of Wireless LAN (WLAN) Voice over IP (VoIP)
a WIPT Survey for more information on conducting Wireless LAN VoIP site
What are the possible sources of radio frequency (RF) interference that
one has to look for when conducting a site survey?
A. WLAN interference can be generated by microwave ovens, 2.4 GHz cordless
phones, Bluetooth devices, or other electronic equipment that operates in the
2.4 GHz band. Interference also typically comes from other access points (APs)
and client devices that belong in the WLAN but that are far enough away so that
their signal is weakened or has become corrupted. APs that are not part of the
network infrastructure can also cause WLAN interference and are identified as
rogue APs. When a site survey is performed, these devices have to be identified
and have to be eliminated.
I have a Wireless LAN Solution Engine (WLSE). Can I use this to perform
a site survey?
A. You can use the Assisted Site Survey tool and the Automated Resite
Surveys tool to do a site survey using the WLSE. Refer to
the Location Manager Assisted Site Survey Wizard for information on how
to use the Assisted Site Survey tool to perform the site survey.
Auto Re-Site Survey for information on how to use the Automated Re-Site
Do I need to configure Wireless Domain Services (WDS) on the Wireless LAN
Solution Engine (WLSE) to do a site survey?
A. Yes, only members of WDS can be involved in a site survey using the
WLSE. WDS needs to be operational for all of the Radio Management capabilities
of the WLSE. This includes radio coverage and rogue detection to work. Refer to
up the WDS for information on how to setup WDS.
What is channel utilization?
A. Channel utilization is the amount of time that the channel is
unavailable or is being used. A given AP can have no clients attached, minimal
transmit time, and minimum receive time (yet have significant channel
utilization). The channel is shared by every AP on the same channel both ours
and neighboring networks. It can also be elevated by non wi-fi
What is the recommended or minimum Single-to-Noise ratio for different
A. This table lists the minimum Signal-to-Noise ratio values for the voice
and data cells.
For detailed information about SNR, RSSI, and EIRP, refer to
RSSI, EIRP and Free Space Path Loss
I use the Cisco a/b/g wi-fi card (CB21AG) and it uses the latest driver.
I use the Aironet Site Survey Utility. Under the access point (AP) Scan List
tab, I see a couple of APs that do not have a network name (for example, SSID),
but that do have an AP name. What is the AP name information? Why can I see the
AP name but not the SSID? This appears to be on a couple of APs that are secure
and that are 802.11b. Is this information relayed only when Aironet extensions
A. AP Name is the hostname for the AP. It is shown on site survey outputs
only if Aironet Extensions are enabled on the AP. The SSID (Network Name) of an
AP appears in the list of available networks only if a Guest Mode SSID is
enabled or the Broadcast SSID in Beacon option is selected in the AP.
What is meant by Pico Cell Mode functionality and how does it optimize
performance in a WLAN environment?
A. A Pico Cell is a small area of wireless provisioning provided by an
antenna, which allows for a dense high-bandwidth deployment for installations
such as stock exchanges. Pico Cell wireless configurations require a specific
supplicant to function correctly with Pico Cell environments. Off-the-shelf
laptop supplicants are not supported. If you have many APs in close proximity,
this Pico Cell mode optimizes the controllers for small wireless cells.
Note: Do not attempt to configure Pico Cell functionality within your WLAN
without consulting your sales team. Non-standard installation is not supported.
Cell Functionality for more information.
What is Signal-to-Noise Ratio (SNR)?
A. SNR is an electrical engineering concept defined as the ratio of a
given transmitted signal to the background noise of the transmission media. It
is widely used in the wireless environment and usually referred to as a power
ration between a signal and background noise.
SNR = P(Signal)/P(Noise)
SNRs are usually expressed in terms of the logarithmic decibel scale.
In decibels, the SNR is 20 times the base-10 logarithm of the amplitude ratio,
or 10 times the logarithm of the power ratio.
Should I use the dynamic control features of Radio Resource Management
(RRM) like Dynamic Channel Assignment (DCA) and Transmit Power Control (TPC) or
should I use the static values that are given to me from a site survey? Does a
problem occur if I use VoIP on wireless with the dynamic method
A. Typically, RRM focuses on power levels more than channel selection. It
is very rare for RRM to change the channel of access points (APs) once all of
the APs are deployed. However, it can react to neighboring interference and
rotate all the channels if necessary.
For power, it is good if your phones, such as the 7920, support dynamic
power management (DTPC). DTPC automatically takes care of the power and channel
The initial survey is essential to get enough density for your needs,
but after that let the controller do its job. The only possible exception is
for outdoor, where the tendency is to do manual power due to the nature of
sector antenna coverage. Refer to
for more information.
I plan to deploy Cisco 7920 IP phones in a Cisco Unified Wireless
Network. Are there any best practices or requirement guidelines to deploy this
model of IP phones in order to achieve optimum
A. Here are some of the important requirements to deploy 7920 IP phones in
a Cisco Unified Wireless Network.
The phone must run at least Software Version 3.01.
The controller must run at least 3.2.116 or later.
Dot11-phone compat and CAC limit must be "ON" in the WLAN.
ARP unicast must be disabled under controller settings if 7921 phones
Aggressive load-balancing status must be disabled under controller
DHCP address assignment under the WLAN must be set for NOT
If the controller tags packets, the Cisco switches require the native
VLAN to be VLAN 1.
If WMM is required in the voice VLAN for voice clients other than the
Cisco Wireless IP Phone 7920, the WMM setting must be set to Allowed.
Otherwise, it can be disabled.
WLAN QOS must be set to Platinum.
Mobility must be "ON" if the Cisco Unified Wireless has more than one
The RF domain-name must be "ON" if the Cisco Unified Wireless has
more than one WLC.
Disable rates below 11M; 11M must be basic/mandatory and the others
(higher ones) 'supported.'
If you use EAP-FAST with the WLC, the 802.1x timeout is 2 seconds.
This is not enough time for the 7920 to download and process the PAC. The
timeout can be increased with the command: config advanced eap
Peer-to-Peer blocking must be OFF
under the 'controller' tab, which is off by
There must be at least 2 APs on non-overlapping channels within range
of the phone with an RSSI of >35 and QBSS of <45.
There must be at least one AP on overlapping channels within range of
the phone with an RSSI of >35 and QBSS of <45.
These values appear in the 7920 under the Network >
Site survey in the form: channel, RSSI,
There must be no more than a 15-20% overlap in cell
The AP placement must be such that there are no more than 10 calls
Unified Wireless IP Phone 7921G Deployment Guide to know about the
prerequisites, as well as best practices to deploy7921G phones
in a Cisco Unified Wireless Network.