This document provides information on the most frequently asked
questions about wireless local-area network (WLAN) radios.
What are the different modes of an Access Point (AP)
A. An AP can be performed by one of these modes of operation:
Root Mode— This is the actual AP mode. It can associate wireless
clients and bridge the traffic to the wired network when
Bridge Mode— AP acts as a bridge and can be used to connect wired
networks at a distance.
Repeater Mode— When the Ethernet port is disabled, the AP becomes a
repeater and associates to a nearby root AP.
Work Group Mode— A Workgroup Bridge (WGB) can provide a wireless
infrastructure connection for Ethernet-enabled devices. Devices that do not
have a wireless client adapter in order to connect to the wireless network can
be connected to the WGB through the Ethernet port. The WGB associates to the
root AP through the wireless interface.
Where can I download the latest firmware, drivers, and software for my
A. Cisco Aironet equipment operates best when all components are loaded
with the most current version of the software. Software, driver, and firmware
updates are available at the
Cisco Downloads - Wireless Software Page
registered customers only)
Due to United States export compliance regulations, you must be
registered on Cisco.com to download wireless software. Registration is free.
Refer to the Cisco.com
Registration for information on how to register for a Cisco.com account
and download wireless software.
What Cisco Aironet products are Wi-Fi
A. Refer to
Wi-Fi Certified Products
for current certification
How does roaming work? Who roams when there is not enough signal
strength, the client or the AP?
A. Roaming is an algorithm implemented and controlled by the client
adapter and it is not defined by IEEE standards. The roaming functionality is
based on signal quality, not just the proximity to the AP. Each vendor has
their own logic to implement roaming. For Cisco clients, roaming is caused by
one of these events:
For more information about roaming, refer to
to configure roaming for Wireless LAN Clients and how the roaming capabilities
can be improved.
What is fast roaming?
A. Fast roaming is a feature where the client's credentials are not sent
to the Authentication server every time the client authenticates. Once a client
authenticates to an AAA server, credentials are cached in the AP. The next time
a client roams, the AP authenticates and supplies the credentials by itself to
the client without sending it back to the AAA server. This saves time and
enables faster roams of clients. For more information on fast roaming, refer to
Fast Secure Roaming section of
WDS, Fast Secure Roaming, and Radio Management.
Can the radios be damaged if they are operated without the antennas
A. Some radio equipment manufacturers specifically warn against this
because it damages the transmitter. Most pieces of amateur or commercial radio
equipment carry this warning because they operate at a much higher transmitter
power. The reflected wave standing wave ratio (SWR) caused by the lack of a
proper antenna or load can damage the final amplifier stage known as the power
For Cisco Aironet equipment, the transmitter power output is 100 mW for
the 350 series and 30 mW for the 340 series, so damage is unlikely but
possible. If you absolutely have a requirement to run the devices without
antennas, it is recommended that you turn the transmitter power down to 1-5 mW
or use a 50-52 ohm "dummy load," just to be safe.
Warning: Never connect the antenna port of one device directly into the
antenna port of another device since this could damage the devices.
What are all the authentication mechanisms currently supported by Cisco
Access Points (APs)?
A. This is a list of authentication mechanisms currently supported:
WPA- Personal and WPA2-Personal
WPA-Enterprise and WPA2-Enterprise
Note: For more information on WPA, refer to
Do I need a license to operate WLANs?
A. WLAN equipment operates in a 2.4 GHz and 5 GHz frequency spectrum which
are license free. In the United States, spread spectrum devices fall under
Federal Communications Commission (FCC) Part 15 of the rules that govern
unlicensed devices. However, other countries might require a license if you
operate devices that are partially or completely outdoors, such as
point-to-point bridges. In addition, some countries might require the system
importer to obtain a telecommunications license to sell the product.
Can I use my wireless device on an aircraft?
A. Under current Federal Aviation Administration (FAA) rules, the use of
wireless devices on an aircraft is permitted if the aircraft is parked at the
gate and the door is open, and if usage is allowed in the airport. The device
must not interfere with flight operation equipment such as navigation radar,
communications, or emergency services.
The use of wireless devices on an aircraft with the door closed,
whether it is sitting at the gate, taxiing, or in flight, is prohibited by the
FAA and other Civil Aviation Agencies worldwide. Wireless devices used on the
aircraft (when the door is open at the gate) must meet the requirements of the
local country agency or have been granted a waiver by the agency or airport
Wireless devices that are stored on the aircraft for use at the gate
must meet certification requirements for the country that the local carrier is
flagged for, and must be able to operate in the frequency band of the host
country, unless a waiver is granted to the system user. It is the
responsibility of the system installer to obtain all licenses and frequency or
What is channel interference?
A. When radios on multiple access points share the same channel or nearby
channel, then the frequency band overlaps with other devices. The information
transmitted is lost if there is any channel interference. Refer to
Problems Affecting Radio Frequency Communication for more information on
how to overcome problems with channel interference.
What is World Mode?
A. Generally a wireless client can operate only in its Local Regulatory
domain as channel and power settings carry for each domain. When World Mode is
used, a client can automatically adjust channel and power settings according to
the domain it migrates to. For example, if a user travels from the United
States to Japan a client card that implements World Mode can automatically
adjust its channel and power settings as per the Japan domain. The access point
(AP) should also support World Mode for this to work. The Cisco client card and
AP support World Mode.
Are the WLAN cards safe to use from a health perspective since they use
A. The WLAN devices are safe when used under normal operating conditions
as stated in the user manuals. The power levels are below the power level of a
typical microwave oven. The radio modules were tested by independent test labs
in accordance with various recognized standards. The levels measured when the
PCMCIA antenna was 1 cm away from the user were recorded at 10-12% of the
maximum level allowed.
The FCC limits the maximum system power to 4 watts Effective
Isotropically Radiated Power (EIRP) for non point-to-point systems. However, a
properly tested and certified system is allowed to exceed the 4 watt EIRP for a
point-to-point system. I have two parabolic dishes aimed at an Omni. Can I
exceed the 4 watt EIRP limit if I consider each leg point-to-point?
A. No. The FCC defines the system that uses directional gain antennas as
only part of the complete system. You cannot exceed the 4W EIRP for any of the
legs of this system since the whole system is a point-to-multipoint. This topic
is defined in FCC docket 96-8, which covers the spread spectrum transmitter.
My WLAN system sees radio frequency interference (RFI) or electromagnetic
interference (EMI) from another device. What can I do?
A. Relocate the Cisco Aironet equipment as far away as practical from
potential sources of EMI/RFI or reorient the point-to-point antennas away from
the RFI/EMI emitter.
Use a different frequency range for the phone and WLAN.
It is suggested that you perform a site survey before you install a
WLAN. In site survey you can detect all kinds of interference sources. This
includes non-802.11 sources such as microwave ovens, cordless phones, etc. You
can collect information on key parameters such as Signal strength, Noise, and
Data rates that exist in the actual deployment scenario. Based on this, WLANs
can be planned and deployed accordingly. For more information on site survey,
Site Survey FAQ.
Would the frequency hopping (FH) equipment of another vendor that sits
next to our direct sequence (DS) equipment have any negative effect?
A. Yes. By its very nature, an FH product hops across the entire 2.4
frequency band. Therefore, it causes interference to WLAN 802.11 b/g products
that operate in 2.4 GHz. There is no way to control where an FH unit hops.Try
one or all of these steps:
Change the location of the access point and/or the base of the
Switch to channel 1 on the access point. If that does not work, try
Use a remote antenna on the client card if it is a PCI- or ISA-based
card and you have that option.
Operate the phone with the antenna lowered, if that is an option.
If all else fails, use a 900-MHz phone instead of a 2.4-GHz phone.
My WLAN system sees interference from a cordless phone. What can I do?
A. Most cordless phones operate in 2.4 GHz and are another major source of
interference. See Would the FH equipment of another vendor
that sits next to our direct sequence (DS) equipment have any negative
effect? for more information.
What is the maximum speed of 802.11 a,b,g
A. 802.11b has a maximum speed of 11 Mbps while 802.11g and 802.11a have
Does Cisco currently support 802.11n?
A. Yes. Cisco supports 802.11n. However, 802.11n is supported only in 1250
series APs currently. For more information on 802.11n, refer to
Cisco 802.11n Design and Deployment Guidelines
registered customers only)
What antenna should I use for the Cisco Aironet 1010 access
A. This device has a built in antenna. You do not need to connect an
Aironet Antenna Reference Guide has all the information about the
different types of antennas and accessories that Cisco provides as a part of
the Cisco WLAN solution.
I have an access point about 50 feet away from my client. The signal is
very weak and there is significant interference in the path (paper storage).
What should I do to obtain proper coverage?
A. Install a high gain antenna for greater transmission and reception so
that the signal at a longer distance can be picked up easily.
What type of antennas should I use for
A. There are different types of external antennas which are designed for
external uses only. Choose one of them as per the individual requirement (Yagi,
Dish, and so forth). Refer to
Aironet Antennas and Accessories Reference Guide for more information on
Where should I install my access point?
A. The co-location of an access point depends on the nature of the
physical place where you need Wireless LAN coverage. It also depends on the
type of facility warehousee, office, conference room, home, and so forth). The
materials used in the physical place have an important role. Cisco strongly
recommends to perform a site survey before any access point is placed. Refer to
Site Survey FAQ for details on how to perform a site survey.
Does Cisco provide any management software or a device to manage multiple
access points (APs)?
A. Yes . Cisco provides a management device know as Wireless LAN Solution
Engine (WLSE) to manage multiple APs. You can push configurations and upgrade
firmware simultaneously for multiple APs. The radio environment in which the
APs operate can be monitored and controlled by the WLSE by perodically
collecting RF information from the APs. For more information on WLSE, refer to
Guide for the CiscoWorks WLSE and WLSE Express, 2.13.
What is Dynamic Transmit Power Control (DTPC) and how does it
A. DTPC is a beacon and probe information element that allows the access
point to broadcast its transmit power. Clients can use this information to
automatically configure themselves to that power while associated with that
access point. In this manner, both devices transmit at the same level. The
Cisco Wireless IP Phone 7920 automatically adjusts its transmit power to the
same level as the access point to which it is associated. Refer to
Power Control Algorithm for more information.
What is the difference between 802.3 bridging and 802.11
A. A bridge is a device that connects two or more networks. The bridges
can be separated with the media type they are connected with. If two wired
networks are bridged together, then these are called 802.3 bridging while those
which bridges the wireless network with the wired network are called 802.11
bridges. 802.3 frames differs in format and length that those of 802.11 frames.
In order to communicate between them, there should be a translation of frame
from one format to another. Translation is usually done by the access
If I wish to install antenna at some distance from an access point (AP),
which extension cable do I need between the AP and the antenna?
A. There are two types of cable supplied by Cisco for mounting the antenna
away from the radio unit LMR600 type cable and LMR400 type cables. These are
low loss cables designed for better efficiency. For more information, refer to
Aironet Antennas and Accessories Reference Guide.