The following example will show how to configure MTX-Tunnel to create a transparent Serial GPRS (RS232 or RS485) tunnel that is permanently connected to GPRS. SIM cards with dynamic IP addresses will be used; therefore, each time a change in the IP address is detected, MTX-Tunnel must send the new IP address to the server so that it is known at all times and a connection can be made to establish a Serial GPRS gateway whenever required.
Details of the example scenario:
- There are 100 devices with RS232 ports (115200,8,N,1 and hardware flow control) which need to be monitored from a control center via GPRS. 100 MTX-Tunnels will be used to act as a transparent Serial GPRS tunnel.
- Access to the RS232 devices must be available at all times, so the modem connected to the device’s serial port must remain continuously connected to GPRS, waiting for a connection. Modems will only accept incoming connections from the IP central office (22.214.171.124) and the backup ADSL of the central office (126.96.36.199).
- In order to reduce the cost, SIM cards with dynamic IP addresses will be used. As there are many devices to be controlled, DynDNS cannot be used and the MTX-Tunnels must send their IP address to the private DNS server. Each time the MTX-Tunnel changes its IP address, it must be sent to the control center (IP address 188.8.131.52 and TCP port 20000). In this way, the control center PC will always know the current IP address of each modem.
This configuration is what must be inputted in the configuration file of the modem to be able to carry out the implementation described in the scenario.
The parameters to be looked at from this example are those with the “DNS_” prefix. These are the ones that make sure MTX-Tunnel sends its IP address to the server each time it changes. For this we configure the “DNS_enabled” parameter to “on”. The IP address will be sent via a TCP/IP socket to an IP (DNS_server) and TCP port (DNS_port), meaning the “DNS_mode” parameter contains “socket”. A Web server with “http” could be used, but this would be another example.