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Embedded SIP stack

 is a performance and memory optimized SIP UA stack designed and developed ground-up for embedded VoIP applications including handsets and IoT devices. In fact, it's the most compact VoIP stack beating the competition by a hefty margin. In addition to being OS portable, sk400vop also integrates easily with our proprietary cooperative kernel. In this configuration, the stack acts like a complete application exporting a very compact API to generate and respond to signaling events. Using callback interface for signaling, media and networking, the stack introduces a new dimension in software portability.


  • SIP, SDP, RTP, RTCP (IAX, SRTP, SRTCP optional)
  • UDP, TCP and TLS support
  • IPv6 support
  • MD5 authentication support (AKAv1 and AKAv2 for 3GPP optional)
  • Supports virtually unlimited number of user accounts translating to unlimited number of virtual phone lines (limited only by available memory)
  • Small run-time memory footprint (less than 200 KB including code and data) suitable for IoT devices
  • Capable of running with or without OS/RTOS (using our cooperative kernel)
  • Easily portable across OS/RTOS using OS mapping layer (reference ports available)
  • Compact API with signaling, media and network callbacks
  • Proven and tested on multiple hardware platforms against various SIP UA implementations and telephone systems
  • Video support
  • Auto-answer support for paging/PA applications
  • EUROCAE ED137B compliant