Developer SDK · version 3.10
PCBest SIP SDK
Build a SIP softphone, IVR or server application in minutes.
A pure host media processing (HMP) VoIP engine with our own SIP stack. Write softphones, IVRs, auto dialers and call center software without telephony boards, and let the SDK deal with SIP messages, call states and threads.
Own SIP stack
Written and owned by PC Best Networks, so we can add any SIP feature or fix anything in the core for your project.
AI-ready
Since v3.10 the SDK connects calls to the OpenAI Realtime API, so an AI agent can handle your calls.
Softphone or server
One SDK for desktop softphones and for high-volume server applications such as IVR and auto dialers.
Media access
Reach RTP and audio streams directly to plug in TTS and ASR engines, detect tones, record and play WAV files.
Proven interop
Works with Asterisk, OpenSER, Cisco CallManager, AudioCodes, 3CX, Radvision and major SIP phones.
Your language
C++ headers and libs, a .NET assembly, an ActiveX control and a standard DLL interface.
Features
Everything in PCBest SIP SDK
Telephony
- Multiple concurrent calls
- Hold, transfer, DND, auto answer, redial, redirect (302)
- Conference, music on hold, MWI (RFC 3842)
- DTMF: RFC 2833, SIP INFO, in-band, or auto
- Answering machine detection (VAD) and tone detection
- Record calls to WAV during a live call
Audio
- G.711 u-law/a-law, G.726, GSM, iLBC, Speex; G.729 optional
- Acoustic echo cancellation and jitter buffer
- Change sound devices during a live call
- Play a WAV file instead of the microphone
- Direct RTP and DirectX audio stream access
Network
- SIP over UDP and TCP
- Outbound proxy, STUN, DNS SRV
- Digest authentication
- REGISTER, INVITE, REFER, SUBSCRIBE, NOTIFY, MESSAGE, UPDATE and more
- RFC 3261, 3264, 3550, 2833, 3515, 3891, 3892 and others
Development
- Samples for Visual Studio 2022 (C++, C#, VB.NET)
- .NET samples on .NET Framework 4.8
- Works with Delphi, C++ Builder, VB6 and any ActiveX host
- Softphone and proxy samples included
- 3 months of free upgrades
The same PCBest SIP stack powers PCBest Phone on Windows, Linux, Android and iOS through a portable C API (gtsp_*). Ask us if you need it on a platform other than Windows.
Downloads
Get PCBest SIP SDK
- SIP SDK v3.10, 64-bitReleased January 12, 2025
- SIP SDK v3.10, 32-bitReleased January 12, 2025
- API reference (PDF)All classes, methods and events (opens in a new tab)
- Why PCBest SIP SDK (PDF)Overview for decision makers (opens in a new tab)
- Robust SIP ActiveX Phone v1.221Legacy ActiveX phone control (OCX)
- ActiveX phone samplesC#, VB.NET, VB6, HTML, C++ Builder, Delphi
Need a license? See the price list or get a trial license.
What customers say
“We had a modem based IVR system for managing street lights and we converted that system to VoIP with PCBest Networks SIP SDK. It took only a couple of days to get it done.”
“Using this SDK we were able to create a commercial grade softphone in a matter of weeks and at a fraction of the cost of any competitive SIP SDKs.”
“We developed an IVR application for pharmacies by using PCBest Networks SIP SDK. It is becoming one of our best selling products.”
Ready to build with PC Best?
Ask for a quote, a trial license, or a quick technical answer. Our technical team is happy to help with your VoIP project.