Kestrel Signal Processing

OpenBTS

OpenBTS is a GSM network-side protocol "stack" with a SIP network interface and integrated radio resource management functions. OpenBTS 2.x (the current release series) supports 2G GSM speech calling and SMS without the need for any supporting BSC, MSC or VLR, presenting each GSM handset to backing network as a SIP endpoint. In its simplest form, OpenBTS allows GSM handsets to be used as extensions in a SIP-capable VoIP PBX. OpenBTS can also be the foundation for a full-scale cellular system based on a VoIP or IMS core network instead of a conventional GSM hierarchy. Compared to conventional GSM systems, OpenBTS offers these advantages:

• The minimum viable network can be as small as a single cell, operated without integration into an existing GSM network.
• OpenBTS is an all-software system, including a software-defined radio, provided with full source code and portable to any POSIX environment.
• The OpenBTS VoIP-based backhaul is robust against packet loss, allowing it to traverse low-quality IP links reliably.
• When possible, OpenBTS confines all transcoding operations to the handsets, improving voice quality and reducing backhaul bandwidth.
• OpenBTS is highly configurable and offers "hooks" to allow customers to implement custom features through SIP or HTTP interfaces.

OpenBTS distribution has been publicly demonstrated at several recent technology conferences and has been successfully operated under experimental licenses in the US and by users around the world.

OpenBTS Products

The public distribution of the OpenBTS system is available under AGPLv3. See OpenBTS.org for more information on the public open source project.

Range Networks, a company founded by the original authors of this software, offers complete basestations based on custom radio hardware and a commercial release of OpenBTS. This commerical version of OpenBTS provides the following advantages:

• Official documentation and commercial support from the original authors of the software.
• Features not yet released in public distributions.
• real-time database-driven configuration management
• SMS cell broadcasting
• multi-ARFCN operation (up to 5 ARFCNs)
• real-time radio channel and call status reporting to external databases
• RAND-SRES authentication, through an external HTTP or SIP server
• "whitelisting" to restrict specific handsets to specific cell sites
• SMS support for non-Latin alphabets and binary payloads
• "star codes", interfaced through SIP
• handover of active calls (in April 2011)
• USSD, interfaced through HTTP or SIP (in April 2011)
• GPRS (in Summer 2011)
• Non-GPL end-user licensing, releasing operators from the requirements of GPLv3 and AGPLv3 for the GSM protocol stack and radiomodem.
• Improved hardware, designed specifically for use in GSM applications with the OpenBTS radiomodem.

Potential applications for OpenBTS products include:

• rural/village telephony and text messaging
• cellular coverage in remote areas (e.g. ships, oil rigs)
• law enforcement and security operations
• rapidly deployable emergency communications
• network emulation and handset testing
• wireless local loop service
• femtocells

OpenBTS on the Web

Here are some links to news and other information regarding OpenBTS:

• OpenBTS.org: The official web site for the public open source project.
• OpenBTS at eComm 2009: Video and slides from the first conference demonstation of OpenBTS, from March 2009.
• David Burgess on OpenBTS: An interview with Lee Dryburgh prior to the 2009 Emerging Communications Conference.
• The OpenBTS Chronicles: The official project blog.
• David Burgess on VoIP Users Conference: An interview through the VoIP Users Conference.
• OpenBTS and Asterisk: Some comments from John Todd, open-source community director of Asterisk, on OpenBTS.