Ozeki VoIP SIP .NET SDK allows to develop a DTMF navigated IVR system written in VB.NET. In this sample program an IVR tree is built up from .xml file and SIP communication is supported by Ozeki SIP SDK. The extended codec support (G.729 and further codecs) assures excellent sound quality. The SDK makes it possible to build IP based telephone solutions like softphones, webphones, VoIP client software, etc. This IVR system registers a softphone to a PBX with a SIP account that is defined in an application configuration file. This file is a standard tool that can be used for configuration purposes. The IVR tree navigation is made by receiving DTMF signals. This means that the call needs to be subscribed for the DtmfReceived event and a specified event handler needs to be written. The IVR tree information is read up using text to speech conversion. Ozeki VoIP SIP .NET SDK is a versatile tool that can be used to build: Softphone, SIP client applications, VoIP client applications like Dialers, Call assistant, Call center clients, Call center servers, PBX systems, IVR systems, Webphone solutions, Conferencing systems, Voice recording systems, VoIP tunneling systems, Security monitoring systems, Mobile communication systems. Tools: SIP protocol implementation, RTP implementation, RTCP implementation, Audio device support (mic, speaker), Audio encoding / decoding (audio codecs), Tools for voice quality improvement (AEC, AVG, NR, Jitter buffer), Support of video devices (camera and playback), Video encoding / decoding (video codecs), Implemented network communication protocols: UDP, TCP, Implemented firewall passthrough (STUN, TURN), Implemented file formats (mp3, wav, avi). Capacity: multiple phone lines and calls are available. Ozeki VoIP SIP SDK offers high rate compatibility with numerous PBX systems like Cisco Unified CM, Asterisk, 3CX, etc., and it also works with almost all VoIP service providers like Skype Connect, Callcentric, SureVoIP, etc. Royalty free licensing.