The GNU oSIP library

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Table of Contents

Introduction to the GNU oSIP library

oSIP is an LGPL implementation of SIP. It's stable, portable, flexible and compliant! -may be more-! It is used mostly with eXosip2 stack (GPL) which provides simpler API for User-Agent implementation.

SIP stands for the Session Initiation Protocol and is described by the rfc3261 (wich deprecates rfc2543). This library aims to provide multimedia and telecom software developers an easy and powerful interface to initiate and control SIP based sessions in their applications. SIP is a open standard replacement from IETF for H323.

antisip services

antisip is my own company. It was started in january 2005 to provide services around SIP and freesoftware. We offer support, training, bug fixes, help and software. Please, come and visit us!

Related software

osip/eXosip has been tested at several SIPit and compliance with most vendors has been verified.

oSIP capabilities

The GNU oSIP library is written in C and get no dependencies except the standard C library. oSIP is thread safe and will generally be used in a multi-threaded application. Nevertheless, this is optional.

oSIP is little in size and code and thus could be use to implement IP soft-phone as well as embedded SIP software. oSIP is not limited to endpoint agents, and can also be used to implement "SIP proxy".

oSIP does not intend to provide a high layer API for controlling "SIP Session" at this step. Instead, it currently provides an API for the SIP message parser, SDP message parser, and library to handle "SIP transactions" as defined by the SIP document.

Downloading area

oSIP CVS is located on savannah:

oSIP can be found on or one of the mirrors.

If the above links does not work, new versions of osip can be found there


The documentation is produced with DOXYGEN. It contains various "How-to" in the module page which you will find usefull if you are using osip for the first time. There is also some general notes on the main page that describes history and available features of the GNU oSIP stack.

Old documentation is still available in ps and pdf format:

The above documentation is not regularly updated, you may get a newer API documentation at

The new one can be rebuilt with the DoxyGen tools.

SIP related links

Latest SIP RFC:

Reliability of Provisional Responses in the Session Initiation Protocol (SIP:

Session Initiation Protocol (SIP): Locating SIP Servers

An Offer/Answer Model with the Session Description Protocol (SDP)

Session Initiation Protocol (SIP)-Specific Event Notification

SIP forum:

IETF's SIP page:

SIP Working group Supplemental Home Page:

SIP rfc (deprecated):

Mailing Lists

On 21th Of May 2012, official mailing list has been moved to The old mailing list has been down for almost one year and I wasn't able maintain it alive.

New Mailing list archive:

Old Mailing list archive:

You can subscribe to the mailing list with by sending a mail to <> with the subject set to "subscribe". Messages can be posted directly to the mailing list to <>.


Aymeric MOIZARD <>

Antisip (me again)

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Copyright © 2012 Aymeric MOIZARD.

Verbatim copying and distribution of this entire article is permitted in any medium, provided this notice is preserved.

Updated: $Date: 2012/05/21 07:48:36 $ $Author: aymeric $