oSIP is an implementation of SIP.
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 H.323.
The library is available as 32-bit and 64-bit:
Even older version