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Current status of the network:

  • SIM-cards can be bought from the POC
    • If you bought the simcard before 9pm on day 0 and are experiencing SMS issues, please go to the POC and have it fixed
  • Extensions (phone numbers) can be activated as described below
  • We currently have deactivated GPRS/EDGE, as the Base Transciever Stations are crashing under the load

Please take the current status as-is and do not try to contact us regarding the listed issues, we're working on them!


GSM Network at 27C3

Following the success at the HAR2009 and 26C3 events, there will again be a private GSM cellular telephony network at 27C3. This private GSM network is interconnected with the DECT and wired telephony network of the POC, which is in turn connected to the public telephone network.

We also plan to offer GPRS and EDGE data services this year.

Purpose of the private GSM network

The purpose of this private GSM network is

  • education about cellular telephony technology
  • gain experience in network operation
  • test the OpenBSC software to operate such a network
  • experiment with projects like OsmocomBB, airprobe or Kraken without affecting a real operator.

In order to do this, the test network of course needs to be used, i.e. we need real voice calls, SMS and data use.

User Manual

Voice calls

You should be able to make voice calls to any extension number that is listed in the Eventphone GURU Phonebook, independent of it being a DECT, wired or GSM extension number.

Furthermore, you should be able to dial out and dial in, just like indicated at POC#Dial_Out and POC#Dial_In.


SMS messages can only be sent between participants of the 27C3 GSM network.

There is no provision for exchanging SMS with public telephone networks. You cannot send SMS to regular telephone numbers, and you cannot receive any incoming SMS either. Sorry.

GPRS/EDGE Data services

Please note that this is an even more experimental feature, and the total capacity we can deploy is less than 1MBps for all subscribers together!

You can configure any APN name you like, we will simply ignore that in our OsmoSGSN software. The IPv4 address and DNS server IP addresses are automatically provided by our SGSN to your telephone, so everything should work out of the box.

We do not implement any of the optional header or payload data compression schemes.


We have a GSM helpdesk close to the POC desk. For more information visit the Linux-Call-Router project. (This info taken from the POC page, please update if necessary)


Frequently Asked Questions

How can I participate in the network

  1. Bring a GSM capable mobile phone supporting the 1800 MHz band, without any SIM/Operator lock
  2. Pre-register a telephone extension at the GURU registration too of the POC, similar to registering telephone numbers for DECT phones. Read detailed instructions at POC#GSM
  3. Go to the GSM#Helpdesk to obtain a SIM card (there will be a minimal fee of EUR 2 for the SIM card itself!).
  4. Put the SIM into your mobile phone
  5. Place a phone call to the token phone number that is provided by the GURU tool in order to associate your extension telephone number with the SIM card.

Why do I need to buy your SIM card to participate?

Using our own SIM has several advantages

  1. we can run real GSM authentication + encryption in our network, which in turn means that people can legally use this network with tools like Kraken to crack the keys
  2. the SIM card you have from your real operator is owned by that operator. We are not certain about the legality of using such SIM cards in networks that do not officially exist and have roaming agreements with the operator
  3. you do not have to use the cumbersome manual network selection of your phone, but it will automatically register to the 27C3 GSM network

The nominal charge per SIM card is really only to recover the cost of the SIM card hardware itself. No profits are being made.

Can I return the SIM at the end of 27C3?

No, we will not reimburse you for returned SIM cards. This is just too much work on our side. However, you will be able to use that same SIM on any future network that our team will run, like the 2011 CCC Camp.

What if something doesn't work

Please notice that this is a volunteer-driven project running on (partially) very experimental software. Outages may (and most likely will) happen. The network capacity we can provide with the hardware at hand is also quite limited.

If you encounter a problem that is not only of temporary nature, please contact the GSM#Helpdesk for further assistance.

User Questions

Q: How to obtain the IMEI/IMSI (needed for GSM registration)?

A: No, it is not required this year. Read above how to register your GSM phone. (But anyway dial *#06# on your phone to get the IMEI.)

Q: Do I need to redial the token when I move the Sim to another phone or "phonelike device" ? I have a couple of gsm devices lying around that do NOT have a dialpad or the ability to dial at all. I would love to test them on the CCC network...

A: The token seems to be bound to the sim card. No redial of the Token is needed if the simcard is moved to another device. So put it in a normal phone, dial the token, put it in any GSM enabled device.

Q: I sometime receive multiple "garbage" SMS messages (up to maybe 40) alongside the real message. The message content looks something like "TNìÉΨk£Måì;¥mp5MÄnx£mp5Ymx£QìKÉΨS¥Ñ"ΨKΨ¥5MÄ$AJ?ØΨ¥Q?¥_ΨSΨK7';Ψ¥MΨKÄ'åΨ?YΨKO'?;¥%;@Ω:ìØ3" One case I caused this was sending message using gnokii on a Noikia 9065. If you would like futher details txt me on 9786. Is this a known issue or is there something that I can do to help you diagnose? Thanks for all your great work!

Technical Parameters

The test network operates under an experimental spectrum license by the German regulatory authority (Bundesnetzagentur).


The network operates on Mobile Network Code (MNC) 42 within the Mobile Country Code (MCC) 262 for Germany. You will see the network as D 42 or 262-42 in the list of networks of your mobile phone (manual network selection).

ARFCN / Frequencies

The ARFCNs on which we operate are: 871, 873, 875, 877, 879 and 881.

BTS / TRX configuration

We will be operating 3 BTS, each in a 2 TRX configuration, resulting in a total capacity of 45 time slots that are usable for user traffic (voice/data). Each level (floor) of the conference building will have one BTS installed.

The transmit power of each TRX is 200mW (23dBm)


Usage Terms

The 27C3 GSM network is a test network intended for testing and analysis of GSM protocols and related technologies. The software is operating on beta software. Furthermore, the network capacity is fairly limited.

More specifically, the network

  • is not a production network with any service guarantee
  • is not provisioned with any facility to make emergency calls, e.g. 112
  • is not using any sufficient form of cryptographic authentication or encryption

By using the network, you accept that it is provided without any warranties and that you know you cannot use it to receive inbound calls on your regular cellphone number from the public phone network.

Use of the network is provided for free. You can make and receive calls as well as short messages from/to other participants in this test network. Service limitations might arise from capacity restrictions or system maintenance.

All signalling data (including SMS content!) is logged for further protocol analysis. We do not keep any personal information, as there is no connection for us between a person and his or her real name / postal address and the protocol data. You are free to use any pseudonym / alias of your choice, and you do not need to provide any valid contact data to us. Nonetheless, protocol data will not be disclosed to any third party.

If you register and configure your phone to use this network, You will not be reachable on your regular phone number!.

The network is operated for 27C3 by the OpenBSC project.

Spectrum License

The test network operates under an experimental spectrum license by the German regulatory authority (Bundesnetzagentur). 27c3-bnetza-gsm-license.png

Archived page - Impressum/Datenschutz