The information in this document is based on these software and
Cisco Aironet BR340 and BR350 Series Bridges
All VxWorks BR340 and BR350 software versions
These assumptions are also made:
Before you install the bridges on a tower or roof, configure them in
a test lab and keep them fairly close together.
A new bridge out of the box is, by default, a root bridge. The term
"root bridge” in this document does not refer to spanning-tree root, but to
"802.11b root." In the 802.11b network, there can be only one root bridge. If
you have a point-to-point bridge connection, one bridge must be configured as
root and the other must be non-root. A root bridge cannot talk to another root
bridge. IP addresses can be assigned to the bridges either through DHCP or
statically. Make sure that both bridges are set for the same channel
(frequency). If multiple bridge pairs are installed, use non-overlapping
channels between adjacent pairs. In 802.11b, there are three channels that do
not overlap: 1, 6, and 11. You should run a carrier test to find out which
channel is least busy in the target radio frequency (RF)
The middle LED is labelled Status. If the
Status LED flashes, it means that the bridges are not locked on to each other.
When the two bridges detect each other and an RF link is established (that is,
the bridges are associated), the status LED is solid green. When there are more
than two bridges in a point-to-multipoint configuration, even if one non-root
bridge is not associated and one non-root bridge is associated, the status LED
of the root bridge is still solid.
The bottom LED is labelled Ethernet. If the
Ethernet LED flashes red, a link is not established over the wired side of the
bridge. Normally, a straight-through cable is used from the bridge to a hub or
switch, and a crossover cable is used from one bridge to another, or from a
bridge directly to a wired client.
Make a Telnet or console connection into the
Verify that the same service-set identifier (SSID) has been
configured on both of the bridges. The SSID is case sensitive. Check the roles
of each bridge; one should be root and the other non-root. Check the
association table to see if the remote bridge is listed. Ping the IP address of
the bridge on the opposite end to check the connectivity of the link.
If problems persist and the link does not establish, reset the
bridges to their defaults and reconfigure the bridges with basic settings to
see if the link comes up.
If the root and non-root bridges do not associate with each other,
perform RF troubleshooting.
Line of Sight
Make sure that there is visual and radio line of sight between the
root and non-root bridges. Check to ensure that the Fresnel Zone is not
obstructed. It may be necessary to raise the antenna height in order to clear
the Fresnel Zone. If the bridges are more than six miles apart, the curvature
of the earth encroaches on the Fresnel Zone. For additional assistance, refer
Bridge Range Calculation Utility.
Ensure that the appropriate antennas are used and that antenna
placement and alignment are correct.
Omnidirectional antennas (which provide 360 degree
Directional antennas (which provide a limited range of
Antenna Gain is measured in dBi and dBd (0 dBd = 2.14 dBi). If the
gain of the antenna goes up, the width of the coverage area that antenna
provides goes down. Coverage areas or radiation patterns are measured in
degrees. These angles are referred to as beam width and they have horizontal
and vertical measurements. Wider angles mean wider coverage, while smaller
angles (typically with higher gain) mean more coverage. In most installations,
antennas should be installed in a vertical polarization (antenna perpendicular
to the ground).
The range of powers, voltages, and currents encountered in radio
engineering is too broad to be expressed on a linear scale. Consequently, a
logarithmic scale based on the decibels (dB, one tenth of a bel) is used.
Decibels do not specify a magnitude of a power, voltage, or current, but
rather, a ratio between two values of them. The unit dBm is a power level
relative to 1 milliwatt (mW). An important relationship to remember is:
0 dBm = 1 mW Power (dBm) = 10 log (power in mW/1 mW)
For example, if an amplifier has an output of 20 W, its output in
dBm would be 43 dBm:
Power (dBm) = 10 Log (20000/1) = + 43 dBm
If a high-gain omnidirectional antenna is used, make sure that it
is mounted at a correct height. The omnidirectional antenna radiates the signal
in a donut shape around the tip of the antenna. If the antenna is not mounted
correctly, it is possible that the signal could pass over the target receiver
Poor antenna placement (such as duct taped to a metal object) can
cause many problems. Make sure that the antenna support structure is solid. An
example of a poor antenna support structure would be one mounted on a pole that
waves back and forth in the wind. Make sure that the antenna mounting is
weather proof. Cisco Aironet Bridges are not designed to be subjected to
weather unless contained in an enclosure. Be sure that there is no water in or
on the antenna cable, and that the antenna cable is grounded. Antenna cables
are not designed to protect network devices from static electricity or
lightning surges that travel on coaxial transmission lines.
Antenna Alignment Tool and Carrier Test
It is very important to point the antenna in the right direction.
Cisco has a light duty tool, the antenna alignment tool, built into the bridge
operating system that helps align the antenna in the correct direction. A
carrier busy test is also provided to help to avoid RF interference and to find
out which channel is less busy.
Avoid use of long, coaxial antenna cables. The longer the cable,
the higher the signal loss over that cable. RF energy is carried between the
antennas and the radio equipment through coaxial cable. Actual decibel loss
depends on the type of cable chosen, but Cisco low-loss cable encounters
approximately 6 dB for every 100 feet of cable. Loss occurs on both transmitted
and received signals. If the cable diameter is larger, loss is decreased, but
thicker cable is more costly. Make sure that the cable is not crimped in any
way. Finally, as the transmitted frequency (channel) increases, so does signal
If the signal passes through glass, metallic tint on the glass can
degrade the signal.
Rain, fog, and other environmental conditions degrade the
Federal Communications Commission (FCC) Part 15.204 prohibits the
use of amplifiers in systems with which they have not been
Cisco Aironet BR340 and BR350 Series Bridges can run only VxWorks
firmware. In order to recover from an attempt to upgrade to Cisco
IOS® software, refer to
VxWorks Firmware from the Console and follow the procedure.