Example Scenario Details:

• The scenario is very simple. You just need to send an SMS when a digital signal coming from an external circuit changes from “0” a “1”.

• The SMS alarm must be sent to 5 telephone numbers for safety (67777771, 67777772 , 67777773, 67777774 y 67777775). The text should be “ALARM DETECTED”.

• One the alarm has gone off, the digital signal can change continuously, therefore you should limit SMS alarm sending to no more than 1 per hour.

Proposed solution with  MTX-65i + MTXTunnel:


MTX-65i + MTXTunnel configuration file for the proposed solution above:

You have to enter this into the modem’s configuration file to be able to run the application as described in the scenario.

MTX_model: MTX65i MTX65i is the MTX model that has been chosen
MTX_mode: none A GPRS-Serial tunnel is not needed
MTX_urc: off We don’t need the URC information messages
ALARM_gpioEnabled: on We enable the SMS alarm service when there is a change in digital input
ALARM_gpioValue: 1 The alarm will go off when the digital input changes from “0” -> “1”
ALARM_gpioMessage1: ALARMA DETECTADA The alarm text that is sent via SMS
ALARM_gpioPause: 3600 We don’t want the modem to send more than one alarm per hour. 
ALARM_smsNumber1: 677777771 Telephone number 1 where the SMS is sent 
ALARM_smsNumber2: 677777772 Telephone number 2 where the SMS is sent
ALARM_smsNumber3: 677777773 Telephone number 3 where the SMS is sent
ALARM_smsNumber4: 677777774 Telephone number 4 where the SMS is sent
ALARM_smsNumber5: 677777775 Telephone number 5 where the SMS is sent


The following example shows you how to configure the MTXTunnel for a transparent GPRS-Serial tunnel (RS232 ó RS485) that is permanently GPRS connected. The particularity of this example is that SIM cards with dynamic IP addresses are used. Therefore every time the MTXTunnel detects a change in the IP address, it will send it to a server that we have in our offices. This way we will be able to know the IP address of every modem at any given time. This will allow us to connect to them and establish GPRS-Serial gateways whenever we want. The example scenario is described in more detail below:

Example scenario details:

• There are 100 devices (black boxes) with a RS232 port (115200,8,N,1 and HW flow control) which need to be monitored from a Central Control Centre via GPRS. To do this 100 MTXTunnels are used and act as a transparent GPRS-Serial tunnel.

• You must be able to access the RS232 devices at any given time, therefore the modem connected to the device’s serial port must remain GPRS connected continuously waiting for a connection.  The modems only accept incoming connections from the central office’s IP: and from an ADSL back-up IP from central offices which is:

• In order to save a bit, SIM cards with dynamic IP addresses are used. As there is a large number of modems DynDNS is disregarded, so it must be MTXTunnel themselves who have to send the IPs provided by the GSM provider from a control centre to a private DNS server at any given time. Each time an MTXTunnel changes its IP address, the new IP has to be sent to the control centre (with IP and TCP port 20000) to report the change. This way the PC Control Centre always knows each modem’s current IP.

MTX-65i + MTXTunnel configuration file for the proposed solution above:

You have to enter this into the modem’s configuration file to be able to run the application as described in the scenario:

The parameters to highlight in the example above are the headers that start with “DNS_”. These parameters are responsible for making sure that every time the MTXTunnel changes the IP address, it is sent to a server. To do this we ensure the parameter “DNS_enabled” is “on”. The frame with the IP address will be sent through a TCP/IP socket to an IP (DNS_server) and a TCP port (DNS_port), hence the parameter “DNS_mode” is “socket”. You could use a webserver to do this with “http” but that would be a different example.