Campbell Scientific RF401-series and RF430-series Spread Spectrum Data Radios/Modems - Manual (Page 55)

Appendix B. Advanced Setup Menu
B.2 Error Handling and Retries
In the RF module received packets are analyzed for data corruption with an
embedded CRC. The radio rejects a received packet (doesn’t send it out a port)
if the packet’s header address fails to match the radio address, if an RF module
receive error is detected, or if the RF packet’s CRC test fails.
B.2.1 Number of Retries
This setting specifies the maximum number of times an RF401 will re-send a
packet failing to get an ACK response. The default setting is zero which
inactivates retries. The allowable range is 0 to 255. Entering a number greater
than zero activates retries. A receiving radio responds to the sending radio
with an ACK packet for every RF packet that it receives, addressed to it, that
has a valid CRC.
B.2.2 Number of Time Slots for Random Retry
This setting is active when the Number of Retries is greater than zero. It
specifies the number of 38 ms time slots to create among which to randomly
re-send a packet which has failed to get an ACK packet response. The
allowable range is 0 to 255.
If packets are failing because of periodic noise or signals, specifying more time
slots for random retries will improve the chances for successful retry packet
delivery. Increasing the number of time slots, however, results in longer
average retry delays which will lower data throughput.
B.2.3 Number of Bytes Transmitted before Delay
This feature prevents radios which have lots of data to transfer from tying up a
network until it is finished. The range of settings is 1 to 65535. The default
value is 400 (bytes). This setting forces an RF401 to pause long enough, after
sending the specified number of bytes, for another radio to send some data.
B.2.4 Sync Timer Setting
This setting determines how often sent packets will include hop
synchronization information in the headers. The default setting is 0 which
specifies that every packet will contain hop sync information. A value greater
than zero specifies the interval at which a packet will contain hop sync
information. The allowable range is 0 to 255 in units of 100 ms. All radios in
the network should have the same Sync Timer Setting.
For example, if you input a value of 50, then packets with hop sync info will be
sent out every 5 seconds improving (shortening) the response time of a
transmit/response sequence. Even though this shortens the time required to
send x amount of data, the throughput is still affected by the CS I/O or RS-232
port baud rate setting.
B.2.5 Number of Retry Failures
This reading is available in Setup Menu/Advanced Setup/Radio
Parameters/Radio Diagnostics. It indicates the number of times that the RF401
has re-transmitted the specified Number of Retries but failed to get an ACK
packet from the receiving radio. For example, if the Number of Retries is set
B-3