ATA Database

Planning Your DIY 2G GSM Network

Before going out and purchasing expensive hardware and configuring your GSM network blindly, it is important to plan your network beforehand, recognizing the requirements and responsibilities. This guide will walk you through the entire planning process of building a small-scale GSM network.

Prerequisites:

To operate a 2G GSM network, there are some basic prerequisites that should be met before setup can begin. These requirements include:

A Full Duplex SDR - The first, and most important requirement is the radio itself. For cellular networks, you will need a radio capable of both transmitting and receiving signals at the same time. Unlike a typical RTL-SDR or a HackRF device, full duplex SDRs have the ability to tune into two independent frequencies at the same time, allowing for simultaneous Transmit and Receive operations. This is vital for operating your GSM network.

A Computer With Linux - Cellular base station software almost exclusively runs on Linux. For the best compatibility, it is recommended to use Ubuntu 22.04 due to its repositories. Any Debian-based distro should be adequate, but Ubuntu includes significantly more repositories by default, simplifying the installation of specialty software.

Open Spectrum - Before transmitting, you must confirm that there is enough open spectrum in your area to safely broadcast your network, without causing interference with other operators.

Phones (Obviously) - A GSM network wouldn't be very useful without a phone, now would it?

SIM Cards - GSM requires SIM cards for authentication. You can either use existing GSM SIM cards from real operators, or you could flash your own SIMs using a smart card reader and blank USIMs, which can be purchased from online stores such as eBay or Amazon.

BTS Software - Lastly, running a GSM network requires specific base station software, such as OpenBTS, YateBTS, or Osmocom. This is what will actually interface with your SDR, allowing a GSM network to operate. More info below

Things to Consider:

Now that the basic requirements are down, here are some additional points to consider before setting up your network:

Legality - Operating your own GSM network is technically illegal under FCC guidelines (and other similar agencies worldwide) due to its use of protected cellular spectrum. However, measures can be taken to ensure that your network remains private and undetected, allowing you to safely use your old devices within your own home. Operate at your own risk, and be a considerate operator.

Tips for safe broadcasting:

• Do not broadcast over existing frequencies! Check your ARFCN (frequency) and ensure that it does not lie within occupied spectrum in your area.

• Keep power levels low! Take precautions to ensure that your network can only be detected by you. Adjust your gain and power limits to ensure that no signals can be detected outside of your property.

• Do not use existing PLMNs! When configuring your network, choose a PLMN (network code) that is not in use by any real operators. This avoids the dangerous situation where other people's phones can accidentally connect to your network, potentially interfering with service or emergency calls. One safe PLMN is 00101: the "test PLMN."

Choosing Software:

There are multiple software solutions for running your own GSM network, each with their pros and cons. Below is an overview of the three popular options: OpenBTS, YateBTS, and Osmocom.

OpenBTS:

• Pro: - Easy setup

• Pro: - Lots of community coverage and documentation

• Con: - Difficult to configure

• Con: - Often finicky and difficult to use

• Con: - Outdated and no longer actively maintained

YateBTS:

• Pro: - Easy setup and configuration

• Pro: - Actively Maintained

• Con: - Limited configuration options

Osmocom GSM:

• Pro: - Highly configurable and flexible

• Pro: - Lots of technical documentation

• Pro: - Actively maintained

• Pro: - Wide hardware support

• Con: - More difficult to initially set up

Due to its superior features, reliability, and support, Osmocom is our most recommended option, and it will be the primary focus of our DIY cellular guides.