Campbell Scientific RF500M Radio Modem - Manual (Page 26)

Section 4. Operation of the Radiotelemetry Network
4-6
If the RF remote is storing more data in its buffer than can be sent in the
defined time window of the polling event, the RF Remote requests more time
to send the remaining data. After all RF remotes have had a chance to respond
during their defined time windows within the polling event, the RF remote that
requested additional time to send more data takes control of the RF medium
and takes any additional time necessary to transmit data.
The SendData instruction in the datalogger drives data collection. LoggerNet
merely waits to receive, validate and accept these records. The datalogger
assumes that all records sent to LoggerNet are received and processed. There
is not an acknowledgement for One Way Data packets between the datalogger
and LoggerNet.
Since data could theoretically be lost during transmission when using the One
Way Data method of collection, LoggerNet can be setup to automatically
collect any missing records. A “hole” in the data occurs when data is missing
from the LoggerNet data cache. LoggerNet detects a hole in the data when it
receives a record with a record number larger than the next expected record
number. For example, if the last record number collected by LoggerNet were
100, LoggerNet would expect the next record number to be 101. However, if
the next record collected by LoggerNet were 105, LoggerNet would detect a
hole in the collected data for the missing records 101 through 104. To
automatically collect missing records and maintain a complete historical data
collection in LoggerNet, check the box to “Enable Automatic Hole Collection”
on the datalogger tab of the Setup screen in LoggerNet.
Each time the SendData instruction is called, it looks for a new record in a
specified table and sends that record to LoggerNet. The datalogger remembers
the last record sent and will not send the same record again but will wait until a
new record is written to the table before creating a new data packet for
LoggerNet. One exception is when the datalogger is first powered. If records
already exist in the table, the SendData instruction will send the newest record
in the specified table even if it had previously been sent to LoggerNet.
However, LoggerNet will recognize the duplicate record and it will be
discarded.
If more records or data exist than can fit in the RF remote buffer, the buffer
will act as a ring memory and older records will be overwritten with the newest
records sent by the datalogger. Any missing records must be collected using
Hole Collection where LoggerNet contacts the datalogger directly and
specifies the records to collect.