OpenBTS

OpenBTS (Open Base Transceiver Station) is a software-based GSM access point, allowing standard GSM-compatible mobile phones to be used as SIP endpoints in Voice over IP (VoIP) networks. OpenBTS is open-source software developed and maintained by Range Networks. The public release of OpenBTS is notable for being the first free-software implementation of the lower three layers of the industry-standard GSM protocol stack. It is written in C++ and released as free software under the terms of version 3 of the GNU Affero General Public License.

== Open GSM infrastructure == OpenBTS replaces the conventional GSM operator core network infrastructure from layer 3 upwards. Instead of relying on external base station controllers for radio resource management, OpenBTS units perform this function internally. Instead of forwarding call traffic through to an operator's mobile switching center, OpenBTS delivers calls via SIP to a VOIP soft switch (such as FreeSWITCH or yate) or PBX (such as Asterisk). This VOIP switch or PBX software can be installed on the same computer used to run OpenBTS itself, forming a self-contained cellular network in a single computer system. Multiple OpenBTS units can also share a common VOIP switch or PBX to form larger networks