6 ms·

Build Your Own Cellular Network

106 points by cwan 17y ago

jolan 17y ago
Awesome, can't wait to see more details! When I worked at Motorola we had our own private cell network on campus which was fun to play around on.
- devicenull 17y ago
  Their blog has a lot more information then this article: http://openbts.blogspot.com/ http://openbts.blogspot.com/
pmjordan 17y ago
This sounds extremely cool, although I have a feeling the regulators won't be too happy if I start broadcasting in the GSM band(s) with enough intensity to be useful.
- eagleal 17y ago
  Not if you implement this in a third-world country, where regulators can't enforce. (But, in a country like that, you may be forced with guns to shut down :P)
  - stcredzero 17y ago
    Not if you implement this in a third-world country, where regulators can't enforce. Burning Man (Not exactly 3rd world. More like 2(e - Phi))
- chronomex 17y ago
  The downlink (tower -> phone) band used outside the US lies partially inside the ISM band in the US. I'm not exactly sure about the legality of it, but you can use OpenBTS to transmit only in the ISM band and a quadband telephone will transmit the other direction somewhere rather outside it. You might be able to argue that the phone is out of spec to transmit in that band within the US. What I do know for sure is that I've done this in two places and the FCC Mobile Death Squad hasn't come over for a visit.
  - dedward 17y ago
    You generally won't find a death squad - but when something starts misbehaving on a licensed cellular frequency, the cellular providers will be the first ones to show up at your door to find out what's going on - and they'll only do that if something actually causes them a problem.
- biafra 17y ago
  You have to get a license to do that. At the "Hacking at Random" and the last "Chaos Communication Congress" we had "testing" licenses with restrictions about signal strength and height above ground for installing the BTSes.
aw3c2 17y ago
There have been interesting talks on GSM on the Chaos Communication Congresses: http://events.ccc.de/congress/2008/Fahrplan/events/3007.en.html http://events.ccc.de/congress/2008/Fahrplan/events/3007.en.h... -> Recordings on http://events.ccc.de/congress/2008/wiki/Conference_Recordings/index.html http://events.ccc.de/congress/2008/wiki/Conference_Recording... http://events.ccc.de/congress/2009/Fahrplan/events/3535.en.html http://events.ccc.de/congress/2009/Fahrplan/events/3535.en.h... http://events.ccc.de/congress/2009/Fahrplan/events/3654.en.html http://events.ccc.de/congress/2009/Fahrplan/events/3654.en.h...
cosmicray 17y ago
Hmmmm... I thought the link between the GSM handset and the tower (or BTS) was encrypted. Was this recently cracked ? If so, does this unit take advantage of that ?
- sjs 17y ago
  I'm not sure if this unit does take advantage, but GSM encryption was cracked late December 2009. http://www.google.ca/search?q=gsm+cracked http://www.google.ca/search?q=gsm+cracked
Judson 17y ago
The brief writeup says that any gsm phone will recognize an OpenBTS "tower", does this mean that I could improve at&t reception at my house (for use with my iPhone)?
- biafra 17y ago
  If you happen to have your BTS talk to the AT&T infrastructure: Yes
- notauser 17y ago
  Short answer: No. Long answer: No but you wouldn't want it to anyway. Very long answer: You can essentially turn your mobile phone into a cordless phone plugged into your own home phone system (via Asterisk). Caller ID spoofing (or the co-operation of AT&T - no chance) is required to make that invisible to the outside world. This means you pay land-line rates when at home rather than AT&T rates. Useful answer: If you want better signal at home buy a re-radiating antenna like this one (this is not a brand I have used, just a demonstration of the kind of thing you need): http://www.alternativewireless.com/cellular-antennas/wilson-antennas/wilson_cellular_amplifiers/wilson-soho-dualband-cellular-amplifier-repeater.html http://www.alternativewireless.com/cellular-antennas/wilson-...
biafra 17y ago
What's most interesting to me is how the security of GSM will hold when GSM stacks in mobile phones can finally be tinkered with. OpenBTS provides the opportunity to program and test your own baseband software. Think about fuzzing GSM towers. Right now some enthusiasts here in Berlin are developing their own GSM stack for cheap Motorola phones.

106 points by cwan 17y ago

jolan 17y ago

Awesome, can't wait to see more details! When I worked at Motorola we had our own private cell network on campus which was fun to play around on.

devicenull 17y ago
Their blog has a lot more information then this article: http://openbts.blogspot.com/ http://openbts.blogspot.com/

pmjordan 17y ago

This sounds extremely cool, although I have a feeling the regulators won't be too happy if I start broadcasting in the GSM band(s) with enough intensity to be useful.

eagleal 17y ago
Not if you implement this in a third-world country, where regulators can't enforce. (But, in a country like that, you may be forced with guns to shut down :P)
- stcredzero 17y ago
  Not if you implement this in a third-world country, where regulators can't enforce. Burning Man (Not exactly 3rd world. More like 2(e - Phi))
chronomex 17y ago
The downlink (tower -> phone) band used outside the US lies partially inside the ISM band in the US. I'm not exactly sure about the legality of it, but you can use OpenBTS to transmit only in the ISM band and a quadband telephone will transmit the other direction somewhere rather outside it. You might be able to argue that the phone is out of spec to transmit in that band within the US. What I do know for sure is that I've done this in two places and the FCC Mobile Death Squad hasn't come over for a visit.
- dedward 17y ago
  You generally won't find a death squad - but when something starts misbehaving on a licensed cellular frequency, the cellular providers will be the first ones to show up at your door to find out what's going on - and they'll only do that if something actually causes them a problem.
biafra 17y ago
You have to get a license to do that. At the "Hacking at Random" and the last "Chaos Communication Congress" we had "testing" licenses with restrictions about signal strength and height above ground for installing the BTSes.

aw3c2 17y ago

There have been interesting talks on GSM on the Chaos Communication Congresses: http://events.ccc.de/congress/2008/Fahrplan/events/3007.en.html http://events.ccc.de/congress/2008/Fahrplan/events/3007.en.h... -> Recordings on http://events.ccc.de/congress/2008/wiki/Conference_Recordings/index.html http://events.ccc.de/congress/2008/wiki/Conference_Recording... http://events.ccc.de/congress/2009/Fahrplan/events/3535.en.html http://events.ccc.de/congress/2009/Fahrplan/events/3535.en.h... http://events.ccc.de/congress/2009/Fahrplan/events/3654.en.html http://events.ccc.de/congress/2009/Fahrplan/events/3654.en.h...

cosmicray 17y ago

Hmmmm... I thought the link between the GSM handset and the tower (or BTS) was encrypted. Was this recently cracked ? If so, does this unit take advantage of that ?

sjs 17y ago
I'm not sure if this unit does take advantage, but GSM encryption was cracked late December 2009. http://www.google.ca/search?q=gsm+cracked http://www.google.ca/search?q=gsm+cracked

Judson 17y ago

The brief writeup says that any gsm phone will recognize an OpenBTS "tower", does this mean that I could improve at&t reception at my house (for use with my iPhone)?

biafra 17y ago
If you happen to have your BTS talk to the AT&T infrastructure: Yes
notauser 17y ago
Short answer: No. Long answer: No but you wouldn't want it to anyway. Very long answer: You can essentially turn your mobile phone into a cordless phone plugged into your own home phone system (via Asterisk). Caller ID spoofing (or the co-operation of AT&T - no chance) is required to make that invisible to the outside world. This means you pay land-line rates when at home rather than AT&T rates. Useful answer: If you want better signal at home buy a re-radiating antenna like this one (this is not a brand I have used, just a demonstration of the kind of thing you need): http://www.alternativewireless.com/cellular-antennas/wilson-antennas/wilson_cellular_amplifiers/wilson-soho-dualband-cellular-amplifier-repeater.html http://www.alternativewireless.com/cellular-antennas/wilson-...

biafra 17y ago

What's most interesting to me is how the security of GSM will hold when GSM stacks in mobile phones can finally be tinkered with. OpenBTS provides the opportunity to program and test your own baseband software. Think about fuzzing GSM towers. Right now some enthusiasts here in Berlin are developing their own GSM stack for cheap Motorola phones.