\Over here you can see the logon statistics of a specific Intelligent Active GPRS Modem.These are the modem types that connect to Plug and Play Scada over GPRS and where the connection is maintained.\
This include modems that can give us the SIM card number while connected over TCP/IP: \
TruTeq modems, some KoCoS modems and Siemens TC65 modems. It excludes modems which can't do that, for example Landis & Gyr modems, Maestro modems and Enfora modems.Active GPRS Modems that are not intelligent would be set up to connect to a unique port. The Server port is only created when the meter is read.\
In contrast, intelligent GPRS Modems are connected all the time. Each modem type connects to the same port, since Plug and Play Scada can interrogate each connection so as to know their SIM card number.The benefits of using an intelligent Active GPRS modem as opposed to an unintelligent Active GPRS modem are:\
Faster performance: When a meter is read, it can establish a 'connection' to read it very quickly, since the modem is probably already connected.\
More Reliable performance: Plug and Play Scada will attempt to read an out of date meter as soon as the modem connects, meaning that even if the modem only has GPRS connectivity for 5 minutes per day, Plug and Play Scada will use that time to read the meter, instead of waiting for the normal scheduled time to make the read attempt.Each connection is kept alive with a watchdog packet in less than a minute, meaning that the connection remains bi-directional even when it is from behind a fire-wall, and that the modem and the server will both know when the GPRS connection fails.\
The watchdog are in some cases uni-directional for 10 to 20 minutes before it does a bi-directional watchdog. This is to cut down on the traffic to save money, since a bi-directional watchdog costs twice what a uni-directional watchdog costs. That also means that it will sometimes take up to between 10 to 20 minutes before the server notices a connection from the modem has dropped, since the network inbetween does not necessarily register a broken connection.\
The cost of the continuous watchdog is generally less than R7 per month in South African conditions at the time of writing (June 2010).If GPRS is working perfectly, there should be only 1 reconnect during a day. A reconnect could mean that the modem rebooted, and reconnected, which could cost 1c (if the modem logs in to GPRS again), however this is not necessarily the case: it could also have merely lost and re-established the TCP/IP connection, in which case it did not log in to the GPRS network again, but re-used its old session.\
If the Server process restarts (this is typically scheduled to happen once per day in the early hours of the morning), there will also be a reconnection logged. In this case it would typically not cost 1c extra, since the modem would only have lost connection for less than 5 minutes, which should not be enough reason for it to restart its GPRS connection.\
If the modem has a hardware watchdog configured, that cycles its power, that could also be to blame for a reconnect. In this case, it will cost an additional 1c, since the modem was off, and when it comes on again, it has to log in to GPRS from scratch.\
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