Installation guide

Wireless Guide 103
Advanced Features for Wireless Analysis
How Utilization is Calculated
The Dashboard provides network utilization percentage measurements on
both the Gauge and Detail tabs. The Sniffer software calculates network
utilization by storing the airtime (in microseconds) for each observed frame in
a buffer. Every second, the value in this buffer is divided by 1,000,000
microseconds (that is, a second) to obtain a percentage utilization
measurement.
The airtime for each frame is calculated as follows:
1 First, the duration of the frame’s PLCP header is stored. PLCP headers
can be either:
 192 microseconds. This is the Long header format specified in
IEEE 802.11b/g for 1 and 2 Mbps wireless LANs.
 96 microseconds. This is the Short header format specified in
IEEE 802.11b/g for 5.5 and 11 Mbps wireless LANs.
NOTE: The calculations for 802.11a are performed similarly except that
they use the duration of the PLCP header specified for different
802.11a rates.
2
Each frame’s PLCP header includes a field indicating the length of the
data portion of the frame in microseconds. The Sniffer software adds
this value to the duration of the PLCP header observed in the previous
step and stores the sum in a buffer.
3 Each second, the value in the buffer is divided by 1,000,000
microseconds to obtain a percentage utilization measurement.
e Distribution graphs Click (+) to expand and view configurable
graphs of the corresponding statistics.
f Short Term and
Long Term options
Click these options to narrow (Short term)
or widen (Long term) the scale of the
Network, Detail Errors, and Size
Distribution graphs.
Table 10-1. Dashboard Contents
Item in
Figure 10-1
Name Description