Search Mailing List Archives

Limit search to: Subject & Body Subject Author
Sort by: Reverse Sort
Limit to: All This Week Last Week This Month Last Month
Select Date Range     through    

[liberationtech] Open-source GSM network update

Katrin Verclas katrin at
Mon Jun 20 12:13:31 PDT 2011

Hi all - 

Following on the discussions on mesh networks, let me update you all on a little experiment we did on a rooftop in NYC (in a non-descript building - we all seem to have a knack for those).  See below for the short overview. We'll be writing mre on this, as well as setting up a network simulator in our Open Mobile Lab in NYC to test certain aspects further.  But, alas - we might just have a GSM network in a box at some point : )  Thank you to Nathan from the Guardian project who wrote this brief summary

Last week, the SaferMobile team (, together with the GuardianProject), as part of a semi-private hackday with members of the UC Berkeley TIER Group, set up an USRP (software radio) open hardware box running the OpenBTS GSM base station sotware. With this, we could run our own very VERY low power GSM network (10m range?) on the 900mhz frequency.

We  connected the network via USB to a netbook running Freeswitch, an open-source PBX/phone switch, much simple and more functional alternative to Asterisk. That netbook was then connected to a Buffalo router running the TorRouter firmware as built/flashed by Daniel Bryg of Access Now. 

At that point, Freeswitch was connecting out to the Internet over Tor, to reach our VoIP service provider. We then dialed a number on the sub-$30 USD GSM phone connected to our special private GSM network, and that call was routed out via Freeswitch over Tor. The receiving phone (running on a large US MNO), received a call, and it came through loud and clear.

We were also testing a number of configurations, potential threats, exploits and applications of these tools, including running this entire setup over a BGAN satellite network, which also worked relatively well, though with a 5 second lag.

In the end, by adding Tor into this mix, we provided a means for the connection between our PBX and the VoIP provider to be protected, anonymized and circumvention-enabled, such that we can better protect deployments of PBXs in regions where crackdown on non-state approved telecommunications systems may be happening.

Exciting times!

All the best,


Katrin Verclas
katrin at

skype/twitter: katrinskaya
(347) 281-7191

A global network of people using mobile technology for social impact

More information about the liberationtech mailing list