VEGA INSYS Modem GPRS 5.0 - Manual (Page 44)

Connection INSYS GPRS 5.0 serial
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5.2.8 During the connection
5.2.8.1 Keep Alive
The data transfer via GPRS is packet-oriented. If no side of the TCP connection
sends data, there will be no traffic via the transmission link. This also means that
it can not be determined if the remote terminal has disappeared without properly
terminating the connection (e.g. due to a failure of the radio network or a failure
of the remote terminal).
It can also occur that GPRS network providers terminate connections themselves
to be able to offer the resources to other participants, if there is no data transfer
for an extended period of time.
For these cases, TCP offers a suitable accessory by sending Keep Alive messages.
The period between two monitoring packets can be set to 1 minute steps (or be
turned off completely).
If three successive monitoring packets are not responded to, the connection is re-
garded as terminated, and the INSYS GPRS 5.0 serial returns to offline mode. If the
device is configured as a leased line device, the connection will then be re-
established.
Keep Alive will mostly be used for leased lines, because the application on location
is usually not able to assume the connection control and monitoring.
Alternatively, the settings can be entered or modified using the terminal pro-
gram.
TCP Keep Alive Timer is set to 10 minutes
AT**KEEP=10
Save changes AT**SAVE
Changes take effect with a restart of the de-
vice AT**RESET
Note
Keep Alive creates traffic, as each Keep Alive packet is in principle
an empty TCP/IP message which must be confirmed by the remote
terminal. For a Keep Alive, two empty TCP/IP messages with 40 byte
each are sent.
When selection the TCP aggregation timeouts, the rate and the bill-
ing type in your GPRS agreement must be considered as well.
See also Chapter 8.8
5.2.8.2 Forming data packets