Cisco Cisco Aironet 340 Ethernet Bridges Guia De Resolução De Problemas
(for example, channel 1) or a channel that overlaps the channel. Radio interfaces are half duplex. Therefore,
radio interfaces are just like collision messages on Ethernet. Here are some reasons for the occurrence of CRC
errors:
radio interfaces are just like collision messages on Ethernet. Here are some reasons for the occurrence of CRC
errors:
Packet collisions that occur due to a dense population of client adapters
•
Overlapping access point coverage on a channel
•
High multipath conditions due to bounced signals
•
Presence of other 2.4−GHz signals from devices like microwave ovens and wireless handset phones
•
Wireless is a more open medium than wired networks, and is subject to environmental effects. The radio
waves bounce off surrounding objects, which can create a weaker or broken signal. This happens with cell
phones, FM radios, and other wireless devices. The more 802.11 radios and clients are in a cell area, higher is
the contention level and the potential for retries and CRC errors. The same applies to wired segments.
waves bounce off surrounding objects, which can create a weaker or broken signal. This happens with cell
phones, FM radios, and other wireless devices. The more 802.11 radios and clients are in a cell area, higher is
the contention level and the potential for retries and CRC errors. The same applies to wired segments.
CRC and PLCP (Physical Layer Control Protocol) errors are normal when traffic flows through the AP. You
do not need to consider these errors to be an issue unless the number of errors is very large. Here are some
parameters you must check if there is a large number of CRC errors:
do not need to consider these errors to be an issue unless the number of errors is very large. Here are some
parameters you must check if there is a large number of CRC errors:
Line of Sight (LOS)Check the LOS between the transmitter and the receiver, and ensure that the
LOS is clear.
LOS is clear.
1.
Radio InterferenceUse a channel that has lower radio interference.
2.
Antennas and CablesEnsure that the antennas and cables are appropriate for the distance of the
radio link.
radio link.
3.
Cisco recommends a site survey in order to minimize these errors. Refer to Performing a Site Survey for more
information on Site Survey.
information on Site Survey.
Use the Carrier Test Option in Bridges to Check for RFI
Cisco wireless bridges can also analyze different channels to detect RFI. The carrier busy test helps to view
the activity in the RF spectrum. The carrier busy test is available on bridges, and enables you to view the radio
spectrum. Figure 1 shows the carrier busy test on the BR500. The numbers 12, 17, 22, and so on represent the
11 frequencies that the bridge uses. For example, 12 represents the frequency 2412 MHz. The asterisk (*)
indicate the activity on each frequency. Whenever possible, choose the frequency with the least activity to
reduce chances of interference. Refer to Performing a Carrier Busy Test for more information on how to
perform Carrier Test.
the activity in the RF spectrum. The carrier busy test is available on bridges, and enables you to view the radio
spectrum. Figure 1 shows the carrier busy test on the BR500. The numbers 12, 17, 22, and so on represent the
11 frequencies that the bridge uses. For example, 12 represents the frequency 2412 MHz. The asterisk (*)
indicate the activity on each frequency. Whenever possible, choose the frequency with the least activity to
reduce chances of interference. Refer to Performing a Carrier Busy Test for more information on how to
perform Carrier Test.
Figure 1 Carrier Busy Test on the BR500