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Functions INSYS GPRS 5.1 serial
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Note
A connection can be established independent from the callback set-
tings via SMS command (provided that the sender number is stored
at
AT**CLIP<index>=<n> ).
6.3 Defined Termination of GPRS Connections for Incoming
CSD Calls ("CSDPRIO")
For different applications, it is necessary to access them with CSD data connections, alt-
hough the normal operation runs with TCP connections.
The reasons may be as follows:

To perform time-critical applications (e.g. software updates from controllers).

To enable service technicians to access the application or the INSYS GPRS 5.1 seri-
al, which are not integrated in the communication system based on TCP connec-
tions.

To still have remote access to the application in case the GPRS network fails.

To still have remote access to the application in case the TCP infrastructure of the
control center fails.

The basic requirement for the utilization of CSDPRIO is the support of the selective
call acceptance (
AT**CLIP=1
). Two modes are available: In the first mode
(
AT**CSDPRIO=1
), only authorized calls may trigger this function and terminate
the connection. In the second mode (
AT**CSDPRIO=2
), any caller may terminate
the connection.

If during the CSD call the following applies:
o
A TCP connection is established: It will be terminated (NO CARRIER); some
topics must be observed due to the nature of this:

In some cases (depending on the provider), the TCP RST which the
INSYS GPRS 5.1 serial creates in this case to terminate, the connec-
tion will be sent to the remote terminal only after the CSD connec-
tion is ended.

If data is transmitted via GPRS during the CSD call (e.g. via a TCP
connection), it may occur that the caller receives the BUSY signal. In
this case, the dial-in should be repeated. The rule of thumb would
be that the CSD call will be forwarded after a minimum of approxi-
mately 30 seconds after the last data byte was transmitted via
GPRS.
o
A GPRS dial-in (TCP Listen mode, waiting for incoming TCP connection): In
this case, the TCP Listen mode is terminated for the duration of the CSD call
(+PPP-IP RELEASE), and restarted afterwards (+PPP-IP SETUP).