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5.5 Channel Survey
The Channel Survey page provides a visual display of how busy the current radio channel is over a given period of
time. Channel utilization is logged by the radio over three separate time intervals:
•
1 second intervals, which covers the previous 60 seconds
•
1 minute intervals, which covers the last 60 minutes
•
1 hour intervals, which covers the last 60 hours
At any given time, an access point and its associated clients occupy a radio channel. This radio channel, or
frequency, may contain interference from other radio transmitters. When installing or diagnosing the WI-MOD-xxx-
E-5W modem, the potential capacity of a given radio channel will be reduced by the existence of these other
interfering RF signals.
Channel utilization allows us to see how much RF activity is on a given channel as a percentage of the total
utilization. When reviewing the utilization graph, you need to look at the average percentage level (rather than peak
bursts ), and also look at the average percentage over a longer time period. It is normal for the graph to show
bursts of 60
–80% utilization, because the WI-MOD-xxx-E-5W uses the majority of the channel when transmitting
due to the lower bandwidth. If most of the graph is filled to 60
–80%, it indicates there is excessive traffic. A
channel that is very busy will have high channel utilization. Conversely, a channel that is quiet will have low channel
utilization.
The Channel Survey and Custom Survey can be valuable tools when performing site surveys because they allow
you to determine how much of the frequency is being used. They are also valuable diagnostics tools for identifying
possible sources of interference.
Channel Utilization on a Live System
Channel utilization can be used on a live system, and is the simplest method for determining how busy the channel
is and how much spare capacity the channel has for additional data transfers. Performing a standard channel
survey scan on a live system will show all transmit and receive packet from the system. It may also show transmit
and receive packets for other systems if they happen to be on the same frequency.
To identify possible interference on the current channel, you can use the Custom Survey page and select
“All RX
Frames.” If possible, temporarily disable all data transfer on the system. If the channel utilization remains high, it will
confirm the presence of outside interference.
Diagnosing Low Throughput
If normal communications between modems is poor, as determined by data throughput measurements are lower
than estimated it could be attributed to interference (see
“5.3 Throughput Testing” on page 71). The channel
utilization graphs can be used to confirm how much other radio traffic or interference is present. If the channel
utilization is high, this could be the contributing factor in poor throughput performance. If the channel utilization was
low (indicating little interference), poor throughput performance could be attributed to a low RSSI, which can be
checked on the Connectivity page (see
“5.2 Connectivity” on page 70).
Channel Utilization Graphs
The Channel Survey page displays a graph showing the percentage of time that a channel is being used for any of
the following activities:
•
The connected modem is transmitting.
•
The connected modem is receiving valid data from other WEIDMULLER WI-MOD-xxx-E-5W modems in the
system.
•
The connected modem is receiving valid data from other WI-MOD-xxx-E-5W modems that are not in the
system but are on the same frequency, or from modems in the same system that are not communicating
directly but through repeaters.
