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: 200.200.200.200 and from an ADSL back-up IP from central offices which is: 200.200.200.201

• 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 200.201.202.203 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.

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This example is the same as the previous “Advanced Example 1″ but instead of using a private DNS server (in our office), we are going to use the service provided by DynDNS.  For those who do no know, DynDNS can associate a myDomain.dyndns.org type of domain to an IP address. This means that when using SIM cards with a dynamic IP address and not a fixed IP, we can always connect to MTXTunnel with DynDNS using miDominio.dyndns.org instead of using an IP address like this xxx.xxx.xxx.xxx that always changes. But let’s look at this scenario in a little bit more detail:

Example scenario details:

• We have a number of devices with an RS232 port that need monitoring from a Central Control Centre via GPRS.

• 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: 200.200.200.200, rejecting any connections from other IPs.

• In order to save a bit, SIM cards with dynamic IP addresses are used. As there are not a large amount of devices to be controlled, you do not need to configure a private DNS server (DNS_enabled: off). Just simply use the service provided by DynDNS.

Proposed solution with MTX-65i + MTXTunnel:

 

MTXTunnel-65i 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:

To use this example, first of all you must open an account at DynDns.org and create some DNS. In the example, mtxtunnel.dyndns.org is the  DNS created.

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In the example shown today we are going to control 2 RS232 devices via GPRS from a remote central control centre with a single MTXtunnel-65i and a single SIM card. Typically these applications use two modems with two SIM cards, connecting a GPRS modem to each serial device. The MTXTunnel-65i, which has two serial ports, allows you to establish TWO transparent GPRS-RS232 gateways at the same time, saving costs. Let’s look at the scenario in a bit more detail.

Example scenario examples:

• The aim is to control 2 RS232  serial devices that are close together. As the MTX65i modem has 2 serial ports, each serial port will be connected to one of the devices that we want to control. This saves the system by using a single modem and a single SIM card.

• You need have simultaneous access to the two serial devices from a Control PC. To do this the modem, which is configured as a server, must listen into two TCP ports.  You can access the serial device connected to the modem’s COM1 with the TCP port 20010 and TCP port 20011 for the serial device connected to the modem’s COM2.

• The tunnel must remain permanently connected. A SIM card with a fixed IP address will be used (although you could use a SIM card without a fixed IP address no problem).

•Access is only permitted to the two IPs from the Control Centre (200.201.202.203 y 200.201.202.204)

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:

In this example, the modem’s serial ports COM1 and COM2 are configured as well as the basic GPRS connectivity parameters. The firewall is activated so that MTXTunnel can only be accessed by 2 authorized IPs and finally the most notable thing from the example is that Telnet is enabled in the TCP 2001 port and TELNET_bypass is “on”. This means that all of the incoming traffic is redirected through the TCP 20011 port to the COM2 port. This way you get 2 independent GPRS-Serial gateways and can control two RS232 serial devices with a single modem and a single SIM card.

If instead of controlling 2 devices with an RS232 port, you would need to use 2 RS485 ports then everything would be identical but instead of using the MTX-65i + MTXTunnel, use the MTX-IND + MTXTunnel.

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