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Developer(s)The Kamailio SIP Server Project
Initial releaseSeptember 2002; 21 years ago (2002-09)
Stable release
5.8.2[1] Edit this on Wikidata / 12 June 2024; 31 days ago (12 June 2024)
Written inC
Operating systemLinux, BSD, Solaris
TypeSIP proxy

Kamailio, formerly OpenSER (and sharing some common history with SIP Express Router (SER)), is an SIP server licensed under the GPL-2.0-or-later license. It can be configured to act as a SIP registrar, proxy or redirect server, and features presence support, RADIUS / syslog accounting and authorization, XML-RPC and JSON-RPC-based remote control, SQL and NoSQL backends, IMS / VoLTE extensions and others.

Kamailio is a Hawaiian word. Kama'ilio means talk, to converse. "It was chosen for its special flavour."[2]


Kamailio is written in pure C with architecture-specific optimizations;[3] it can be configured for many scenarios including small-office use, enterprise PBX replacements and carrier services—it is SIP signaling server—a proxy—aiming to be used for large real-time communication services. Features include:[4]

  • SIP telephony system
  • SIP load balancer
  • SIP security firewall
  • Least cost routing engine
  • IMS/VoLTE platform
  • Instant messaging and presence services
  • SIP IPv4-IPv6 gateway
  • MSRP relay
  • SIP-WebRTC gateway


Kamailio is used by large Internet Service Providers to provide public telephony service. The largest public announced deployment with several million of users is in operation at the German ISP 1&1.[5] Another large deployment is in operation at the provider sipgate.



OpenSIPS, a fork of SER which has diverged—deciding to "go their own way" from the SER and OpenSER[6] codebases—is a free software implementation of SIP for voice over IP (VoIP) that can be used to handle voice, text and video communication. OpenSIPS is intended for installations serving thousands of calls and is IETF RFC 3261 compliant.[7] The software was recognized by Google in 2017 with their Open Source Peer Bonus award.[8]


Kamailio's roots go back to 2001, when the first line of SIP Express Router (SER) was written; at the time, the working group published results at iptel.org—in September 2002 the code itself was published under the GPL.[6] The first fork of SER came in 2005—OpenSER[6]—which would later merge back into the code that would become Kamailio.[9] The codebases of SER and OpenSER (by then known as Kamailio) converged in December 2012, and it was decided to continue to use Kamailio as the main name of the project, which remains open source.[10]

During the first years of development, serweb—a web-based user provisioning—was available.[citation needed]


SIP-Router Family History

  • First third-party contribution (ENUM module)[6]
  • Code is GPL'd and first published[6]
  • Adoption by the general public begins; additional free and open source code is contributed by independent third parties[6]
  • Part of the FOKUS team moves, with the SER copyrights, to the newly created company iptel.org[citation needed]
  • Two of the five SER core developers and one main contributor start a new free and open source software project named OpenSER.[citation needed]
  • The company IPtel.org is bought by TEKELEC, and is responsible for the TEKELEC session router and CSCF.[6]
May 12
  • SER 2.0 RC-1 (Ottendorf) is made available
  • OpenSER is renamed Kamailio to avoid conflict with similar trademarks[6]
November 4
  • Kamailio developers sketch and announce a plan to team up with the SER developers to create the future sip-router project[6]
  • FOKUS and the Kamailio community organize the first iteration of the annual 'Kamailio World' conference in Berlin, Germany.[11]


  1. ^ "Release 5.8.2". 12 June 2024. Retrieved 22 June 2024.
  2. ^ "OpenSER Renamed To Kamailio". Kamailio. 28 July 2008. Archived from the original on 10 July 2017. Retrieved 28 April 2018.
  3. ^ "Kamailio SIP Server". 6 March 2010. Archived from the original on 4 May 2016. Retrieved 2 May 2016. Kamailio can be used on systems with limited resources as well as on carrier grade servers, up to millions of users. It is written in pure C for Unix/Linux-like systems with architecture specific optimizations to offer high performances. Kamailio Project aims to be a collaborative environment of its users to develop secure and extensible SIP server to provide modern Unified Communication and VoIP services.
  4. ^ "Features". The Kamailio SIP Server Project. 6 March 2010. Archived from the original on 25 April 2023. Retrieved 28 April 2018.
  5. ^ "Kamailio used by directory". The Kamailio SIP Server Project. 21 March 2015. Retrieved 7 November 2018.
  6. ^ a b c d e f g h i "History". The SIP-Router Project. Archived from the original on 29 April 2018. Retrieved 29 April 2018.
  7. ^ Goncalves, Flavio E. (20 January 2010), Building Telephony Systems with OpenSIPS 1.6, Packt Publishing, ISBN 9781849510752
  8. ^ "Announcing more Open Source Peer Bonus winners". opensource.googleblog.com. 2017-10-03. Archived from the original on 2018-01-22. Retrieved 2018-01-23.
  9. ^ Mierla, Daniel-Constantin; Modroiu, Elena-Ramona (2011). "Kamailio History". Kamailio SIP Server v3.2.0. asipto. Archived from the original on 16 May 2018. Retrieved 28 April 2018.
  10. ^ "We've completed the merger – and it's Kamailio!" (blog). Kamailio. 29 December 2012. Archived from the original on 10 July 2018. Retrieved 28 April 2018.
  11. ^ "Kamailio World".

External links[edit]