M2M Network Topologies

M2M Network Topologies

Machine-To-Machine networks allow you to connect to your remote or hard-to-connect devices by using the mobile phone network and the Internet.

There are actually a few ways to set up your M2M network, depending on how much of the infrastructure you're interested in maintaining.

Most M2M networks use a Virtual Private Network (VPN) to connect your devices to each-other or to your server.

Why? There are three reasons.

Firstly, it makes the data transferred between your various devices extremely secure, despite the fact that it's being transferred across the Internet.

Secondly, because using a VPN allows you to get around the firewall rules built into the mobile network.Most mobile phone SIMS only allow outgoing connections - for instance, to web pages. It's simply not possible for a standard mobile SIM card to accept a connection coming in - so if you are running services (such as an ARDI service, a MODBUS RTU etc) on the other side of the 3G modem, you are simply unable to access it.

Thirdly, it gives you much more control over your network - you can assign particular IP addresses to each of your devices, even though the mobile provider network is giving the device random IP addresses when they connect.

You're best off with dedicated M2M sim cards - they are less expensive and come in some unusually low data ranges. Many providers also allow you to have several cards 'on the shelf' that you don't pay for until you start actually using them.

Using the Telco VPN

This option is by far the easiest, but also the most expensive way to deploy your M2M network.

In this case, the telco takes care of setting up and maintaining your VPN - all you need to do is insert the SIM and you're away.

However, the following costs are involved (note - these prices were valid at the time of writing, but may have changed since)

  • Initial VPN Setup Charge: $150, once off
  • VPN Client Access - to allow a server or PC to access the VPN without a SIM: $150, once off
  • SIM Static IP Address: $5 per month, per sim
  • SIM VPN Access Fee: $5 per month, per sim

The major disadvantage is price.

However, the advantages to the big spend include...

  • No need to maintain VPN services
  • SIM cards can be used on extremely low-cost devices with no built-in VPN support.
  • Adding additional devices is extremely simple

Using your own VPN

This requires the ability to prepare and maintain your own VPN server, which can be done for as little as $10.00 per month using services such as Digital Ocean, or $35.00 per month using Amazon Web Services.

In this case, the device that needs to connect to the internet needs to be smart enough to understand OpenVPN. So either your modem needs to be more elaborate (such as the Vodafone / Netcomm Machinelink 3G and 3G Plus), or the device(s) you're connecting to need to know how to talk OpenVPN (most Linux based devices such as the Raspberry PI can run OpenVPN clients).

Simply start up a Linux (we suggest Ubuntu 14.04 LTS) virtual machine, install OpenVPN, setup the configuration file, and you're away - you have a VPN that you can connect with on laptop, desktop, tablet, mobile and from a wide range of devices and modems that naively support OpenVPN.

Your field device only needs a standard SIM, or a run-of-the-mill M2M sim - you don't need features such as static IP. This means that you can set up an M2M network very cheaply.

The major advantage is price - deploying this way is very inexpensive, only takes a couple of hours to set up, and your virtual server has all the access it needs to your data straight away.

Disadvantages include...

  • Your VPN service may require occasional maintenance, and you'll need to re-deploy security certificates from time to time (usually every 10 years).
  • Your devices will need to be 'smarter' in order to connect.
  • There is some additional work to adding devices, as you'll need to generate and deploy certificates.