NOTE The site survey list is only refreshed when the module starts up, and only if the client is not
connected to an existing access point. When the client does connect to an access point, the list will
refresh and only indicate the access point to which the module is connected.
Figure 75 Site Survey
Mac Address
Mac address of the access point.
RSSI
Last radio receive signal strength from the access point (only scanned on startup).
Beacon Interval
Beacon Interval configured on the access point.
SSID
SSID of the access point.
5.3 Throughput Testing
Radio Throughput
There are a number of throughput estimations that may help to determine the amount of data that can be
successfully transmitted through the modems. These throughput estimations are based on perfect radio conditions
in which there is little to no outside radio interference present while data is being passed, and are calculated using
real-life conditions and communication constraints.
The performance of a wireless link is best measured in terms of the maximum throughput that can be achieved.
Two methods are recommended for measuring modem throughput:
•
Modbus TCP Client Polling
—Use an external Modbus client to poll the internal Modbus server on the remote
modem.
•
FTP File Transfer
—Use an FTP server/client arrangement and transfer a file, measuring the time it takes to
send.
•
Iperf Throughput Test
—Uses a MS-DOS-based application that is run on a PC or laptop at each end of
the radio link and measures the data throughput. When used in conjunction with Jperf, it can display the
throughput data graphically.
It is recommended that the throughput tests be performed on point-to-point link with minimal radio interference
(no communications from other wireless network traffic). All of the following procedures measure the raw data
throughput, and from these throughput measurements you can determine if interference is a contributing factor in
the overall performance of the modems.
Modbus TCP Client Polling Test
The following table shows the maximum number of polls per minute (ppm) based on the radio receiver signal
level. The results show two test polls using different data speeds, with and without data compression. For more
information about data compression and how to implement it, see
“Data Compression” on page 35.
The test is designed to simulate a Modbus TCP client polling a Modbus TCP server through the radio modems
using two different data rates (2 Level FSK and 4 Level FSK) and scanning a different number of I/O points. The
setup for the Modbus client was made to simulate the fastest polling rate possible and then determine the number
of messages that were successfully polled in a one minute period. The TCP client scan rate was 5 msec, poll delay
was 5 msec, and the slave response time was 10 seconds.
