Sofia-SIP library runtime Sofia-SIP is an open-source SIP User-Agent library, compliant with the IETF RFC3261 specification. It can be used as a building block for SIP client software for uses such as VoIP, IM, and many other real-time and person-to-person communication services. The library is implemented in ANSI C, and provides an extensive set of features for implementing SIP/SIMPLE User-Agents. Highlights include full UDP/TCP/TLS support, IPv4/6 support, SIMPLE presence and messaging support, SIP offer/answer engine and numerous mechanisms for NAT/FW traversal. This package provides the main library runtime files.