Archive for May, 2008

As I said yesterday, today I’m going to present a new product that Matrix is going to distribute soon. It’s a firmware, only 7 Euros, for the MTX65 GPRS modem that we have already talked about (and of course we are going to keep talking about) in this blog. This firmware + the MTX65 GPRS modem are called MTX-Tunnel.

Basically MTX-Tunnel is a GPRS-serial gateway designed for remote maintenance application this means that you can avoid moving by simply connecting an RS232 serial cable to a device. It’s also designed to provide a GPRS connection to those devices that only have an RS232 serial port (e.g. meters, temperature sensors etc.).

There are other solutions, I’ve already told you about some on here like some Digi routers but the MTX-Tunnel has certain advantages in both performance and price that I will tell you about soon.

MTX-tunnel

To be honest I have to say that this device is special to me, as I have quite involved with the firmware that goes inside the MTX65 and altogether they make the MTX-Tunnel.

That said, for those of you who are interested I’ll put more information on here like I usually do. You already know the question/answer routine.

What is the MTX-Tunnel device used for? 

The MTX-Tunnel is basically a GPRS-serial gateway that allows you to connect to an office with any device that has an RS232 serial port without moving via GPRS. You could do the same thing connecting an RS232 serial cable to the device; you can do it remotely via GPRS with MTX-Tunnel.

Is it complicated to set up?

In all, it is very simple. Basically you have to edit a file with notepad to configure certain parameters (IP, port, baud rate etc.). Once configured, simply drag the file inside the modem as if it were a pen drive. The MTX-Tunnel is then configured.

How does it work? Is it the MTX-Tunnel who connects to the central server in the office via GPRS or does it wait for incoming connections? In other words, does it act as a TCP/IP client or server?

It can be configured to work in two ways.

If MTX-Tunnel is configured to work in client mode, when you power it up it automatically connects to a server i.e. to a certain IP and port (specified in the configuration file). Once the connection is established with the server, all the data that comes from the server through the TCP/IP socket via GPRS is sent out through the serial port and vice versa. All of the data that enters through the serial port is sent towards the server through the socket via GPRS.

In server mode the MTX-Tunnel is connected to the GPRS and is stays listening through a certain port waiting to receive an external connection. Upon receiving the connection it behaves the same as in the previous case. When it comes via GPRS it is sent out through the RS232 serial port and vice versa.

Does MTX-Tunnel have to have a SIM card with a fixed IP address in client mode? 

No, not in this mode seeing as the MTX-Tunnel initiates the connection you don’t need to have a fixed IP. The server that is connects to has to have a fixed IP address, if it doesn’t you need to get an office router with DynDNS so that a DNS type yourOffice.yourDomain can tell you your company’s IP address.

And if it’s in server mode does it have to have a fixed IP address? 

It’s recommended but it’s not essential. If you have a SIM card with a fixed IP address it’s very quick to make a connection. If you don’t the IP you should work out the IP address assigned by the operator (Movistar, Vodafone etc.) to MTX-Tunnel when it connects to the GPRS.

And how do you find out the IP address that has been assigned to MTX-Tunnel by the operator? 

There are two ways. You can make a missed call or send an SMS to MTX-Tunnel. If MTX-Tunnel is configured to do this (indicated in the configuration file), the MTX-Tunnel will return an SMS to the phone number that sent the SMS or made the missed call, the SMS will contain the IP address that has been assigned by the operator.

So anyone who accidentally makes a missed call can get the device’s IP? 

No. In the MTX-Tunnel’s configuration file you can set up to ten valid phone numbers which can request actions like sending the IP address. If the telephone isn’t valid the MTX-Tunnel doesn’t do anything.

Does the MTX-Tunnel have to be permanently connected to GPRS? 

It depends. In client mode yes, the connection is permanent. As soon as the device has power it is connected to a specific IP address and port as I said before. If communication is lost for any reason, the MTX-Tunnel keeps trying to reconnect (every 30 seconds) until it is connected.

In server mode you do not need to be permanently connected to GPRS. If we want to be connected to GPRS at any point, all we need to do is make a missed call or send an SMS with the word “on”. Then you will be connected to GPRS and as I said in point 6, if configured to do so it will send an SMS with the IP address assigned by the operator.

And if MTX-Tunnel is in server mode and you don’t want the connection to be permanent, once you remotely activate the GPRS connection with the missed call or SMS, how do you disconnect from the GPRS connection? 

You can define a time out in the configuration file. Let’s suppose that you set it to 3 minutes. If the MTX-Tunnel doesn’t detect GPRS traffic after 3 minutes it will automatically disconnect from the GPRS network.

And if MTX-Tunnel works in server mode can you connect to any IP? I.e. can intruders connect to my devices? 

No. It’s the same with the telephone numbers. You can set up to 10 IPs that you can connect to in the configuration file. Any other attempted connection with an unauthorized IP is aborted.

But I already have a private VPN network i.e. I’m not going to have any unauthorized access to MTX-Tunnel. Do you need to specify authorized IP addresses like you said in the previous section? 

It’s not necessary. If you specify an authorized IP as 0.0.0.0 you can connect to MTX-Tunnel from any IP address. Remember that this option is only recommended for VPN networks in order to avoid any unauthorized access.

Can you configure the MTX-Tunnel’s serial port parameters?

Of course. You can change the baud rate, flow control, data bits and stop bits. As always you can do all this through the configuration file.

Let’s imagine that we have 100 temperature sensors which are all the same, without any intelligence and all using 100 MTX-Tunnels in client mode i.e. all 100 are permanently GPRS connected to a server. If the MTX-Tunnels don’t have a fixed IP address, how do I know which temperature probe corresponds to which temperature that the server receives? 

MTX-Tunnel has a configurable identification parameter that allows you to set which is sent to the server first once the connection is established. With this you always know which device corresponds to which data in cases like I mentioned where devices work in client mode and don’t have a fixed IP address to send identification.

Will I have a problem with any up to date application that I use with a serial cable if I substitute it for an MTX-Tunnel? 

Usually not, but there is one thing that you should keep in mind. That is that GPRS communications are quick but they have a bit of a delay (just as it’s not the same to work with a LAN via the internet). Let me explain. If you have a question-answer application (a typical example of a PC questioning a temperature sensor), you have to take into account the time from when you send the command from via GPRS to when you receive the answer with the sensor’s data. This obviously will take more time than if you used a cable. It’s the only things that you have to keep in mind so that you can modify the timeout.

There’s more information on Matrix: gsmsupport@matrix.es / telephone 915602737

I hope that you found it interesting. See you next time, have a good weekend. ;)

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