telephony | Raspberry Pi

Raspberry Pi GSM gateway

If you travel a lot, you’ll be used to absurd roaming charges when you use your mobile phone. But sometimes your phone’s an absolute necessity – those of us at the Foundation can’t really go overseas for work or for holiday without paying those charges, because we need to be in touch with the office and with a lot of other people around the world who need to talk about things Pi. (And we like to be able to phone our mothers.)

Holger Leusch, Benjamin Reichel and Karina Hochstein have found themselves with a similar problem. Worse still, Holger travels to Cambodia a lot, and his German phone provider doesn’t even have a roaming agreement with any of the Cambodian telcos, so he’s not able to use his phone there at all. He found VoIP unusable in Cambodia, with patchy calls, lousy bandwidth, delays and dropouts. Like us, he needed to be in constant touch with his office.

Enter (you knew this was coming, didn’t you?) the Pi.

Many of those in Holger’s position would look into buying a SIP-based GSM gateway. GSM gateways are expensive things: Holger’s research found that a single GSM port (and you’ll need two, one at each end) was priced between €200 and €400. “For this to pay off, I would have to make a whole lot of phonecalls.” So he, Benjamin and Karina built their own, using a Pi running RasPBX; a Huawei dongle for 3G; a Chan dongle which works as an Asterisk channel driver; and a USB modeswitch. The whole kit came to €75.

Holger says:

Now when a caller in Europe calls my german GSM number, first my domestic Snom phone rings, then after 5 seconds, my Cambodian mobile phone gets called. As a sideffect, my Cambodian friends from now on can call and SMS my German phone back at local rates of a few cents…

The connection quality over the 10.000 km spanning 64 kbps Asterisk SIP trunk between both gateways actually is so amazing that none of the callers even noticed that I was out of the country at the time!

Please be aware that in some countries, telecoms law around GSM gateways is a bit fuzzy. In the UK, Ofcom says:

Ofcom has recently clarified that it is entirely legal under UK law for end-users (whether businesses or ordinary consumers) to buy, install and use GSM gateways for their own use. However it is currently illegal under UK law for anyone to use GSM gateway equipment to provide a communications service by way of business to another person or organisation, irrespective of where the gateway equipment is located, or how many or few end-users are connected to each gateway. This prohibition on ‘commercial’ use applies equally to the mobile network operators (MNOs) as to other organisations, since the MNOs’ licences do not currently extend to the installation and use of GSM gateways.

Basically, you can build a gateway yourself in the UK – but woe betide you if you try to sell or lease one. The mobile network operators sometimes take this even further (for reasons which you might, when you consider all the lovely money that results from those roaming charges, think to be a bit…venal): for example, if Vodaphone suspects you’re using one of its sim cards in a GSM gateway it says it will disable the card. So be sure to research what the local rules are carefully before you implement something similar yourself.

You can read more about Holger, Benjamin and Karina’s setup at Carrier Connect Shout Out.

Banana Phone

The Monday Morning Three-Minute-Hate is a time to remember all those things that make life worse, Once you’ve got through poverty, war and injustice, and the way the alarm clock makes you feel, you’re likely to start to dwell on other stuff.

Like those silent robotic telemarketing calls.

I had an email this morning that made the Three-Minute-Hate last a mere two and a half minutes. Alex Ruiz has used a Raspberry Pi to make a really neat tool to stop automated calls, while still providing support to allow through any legitimate automated calls, like those from the emergency services or (eek) charities (I promise that the Raspberry Pi Foundation will never, ever place a marketing call to you, automated or otherwise). Alex says:

I recently submitted a solution for a government initiative here in the USA to stop those pesky automated telemarketing phone calls. You can see the details here:

http://robocall.challenge.gov/

My solution was prototyped using a RPi and an off-the-shelf Analogue Telephone Adapter and it works great. Being an independent coder, the advantages the RPi presented as a development platform both in cost and flexibility made it an obvious choice for writing experimental phone software. Because of the low cost, I was able to successfully fund the development and beta distribution of units on my own. This helps enormously, as I can now claim that my solution is not theoretical and is working in a real business environment.

I was able to fully meet the criteria of the FTC’s challenge entirely.

And all of this was only possible with the RPi.

Again, I cant thank you guys enough for this wonderful piece of hardware and the personal attachment I’ve grown for it. This device showed me my own potential as a developer and for that, I am very grateful.

Here’s video of the Banana Phone in action. I love the big grins plastered all over Alex and his friend when their demo goes off without a hitch.

Thanks Alex – and good luck in the competition!

Elastix – VoIP for your Raspberry Pi

Here’s a nice bit of new functionality for your Raspberry Pi: the good folks at Elastix, the open-source unified communications outfit, have developed a new version of Elastix 32 bits, called μElastix, and ported it to the Raspberry Pi. I know a lot of you were clamouring for Voice over Internet Protocol (VoIP) on your Pis (for people confused by the jargon, VoIP is a way of making cheap phone calls over the internet); we’re very pleased that Elastix have thought the Raspberry Pi significant enough that it’s been worth making a new version for the platform.

Of course, it turns out that VoIP isn’t all Elastix can do: here’s a handy diagram explaining what you’ll get. (Asterisk, the bit in the middle, is the call-report interface Elastix is based on):

Elastix is released under the GPLv2. Click on the image to go to a download page, and to learn more. Let us know how you get on!