In this post, I’ll share how I integrated OpenAI’s real-time API with our SIP Server to create an intelligent voice agent capable of live transcription and AI-generated voice replies — all over a VoIP network.
This project demonstrates how traditional SIP-based telephony can be enhanced using powerful AI services like GPT-4o, without needing to replace existing infrastructure.
What We Built
Using VoIP SIP SDK, I developed a multilingual AI voice agent for VoIP systems. It captures real-time SIP audio in PCM format, streams it to OpenAI’s speech-to-speech WebSocket API, and receives back AI-generated audio replies in real time.
The system performs the following tasks:
- Captures live SIP call audio in raw PCM format
- Streams the audio to OpenAI’s real-time speech-to-speech API via WebSocket
- Receives the AI-generated audio response from OpenAI
- Sends the synthesized audio back to the caller via RTP
Tech Stack
- Language: C#, VBNet
- VoIP SDK: VoIP SIP Server SDK
- AI Services: OpenAI GPT-4o (realtime Speech-to-Speech APIs)
- Audio Handling: Named Pipes, PCM audio streaming
How the Integration Works
Incoming SIP Call
A SIP call is received on the server and accepted using SIP SDK.Audio Captured in Real Time
The SDK provides access to the raw PCM audio stream from the RTP packets.Streaming to OpenAI WebSocket
A client connects to OpenAI’s real-time speech-to-speech API and streams the PCM audio over WebSocket.AI-Generated Audio Response
OpenAI processes the audio, understands the intent, and returns an AI-generated audio reply.Audio Playback to Caller
The received audio is injected directly into the SIP call as RTP media, allowing real-time AI voice interaction.
Real-World Use Cases
- Smart IVR Systems that answer customer queries
- AI-based call routing by understanding caller intent
- Language translation over SIP calls
- VoIP chatbots that feel human
Related Resources
- Develop a Multilingual Conversational Agent
- VoIP SIP SDK for Software Developers
- What is VoIP SIP SDK? A Complete Guide
- Types of VoIP SIP SDK
What’s Next
We’re actively expanding this system to support:
- Multilingual translation across real-time SIP calls
- Emotion detection to adapt responses based on caller sentiment
- Integration with WebRTC gateways to enable AI voice interaction for website visitors
- Open-source plugins and developer tools for easier integration and customization
If you're working on a similar VoIP+AI project, or want to integrate OpenAI with your SIP platform, feel free to connect or ask questions below. I’d love to collaborate or share more details.
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