Great — I’ll walk you through a PSTN-bridging architecture that lets your Python server and LiveKit handle live voice calls, while WhatsApp remains for signaling or notifications if you want it. I’ll also list concrete steps, recommended providers, and sample Python-focused guidance so you can implement the bot that transcribes, generates responses, and speaks back.
First, a quick acknowledgement of your goal:
• You want to accept voice calls from phone numbers (PSTN), bridge them into LiveKit so your bot can transcribe and respond, and you’re building this server-side in Python. Correct?
High-level architecture (PSTN → LiveKit):
• Telephony provider (e.g., Twilio, Vonage, or Plivo) receives the inbound PSTN call.
• Provider bridges the call to a media endpoint that can connect to WebRTC/SIP. Two common bridging approaches:
◦ Provider connects to a SIP gateway that your LiveKit deployment can accept (if you have SIP-to-WebRTC bridging).
◦ Provider uses a WebRTC bridge (some providers support WebRTC natively) or a connector that forwards audio to a LiveKit room.
• A LiveKit room will host the caller’s audio and your bot as a participant.
• Your bot (server-side Python) joins that LiveKit room as a participant, captures the caller’s audio (subscribe to the audio track), performs speech-to-text, runs your dialogue/response generation, and injects TTS audio back into the room.
• Optionally record the session, log transcripts, and send WhatsApp messages (via WhatsApp Business API) for notifications or follow-up.
Recommended providers / capabilities to look for:
• Twilio:
◦ Twilio Programmable Voice can connect PSTN to SIP or TwiML that forwards to a WebRTC client or a SIP endpoint.
◦ Strong Python SDK and good docs for bridging.
• Vonage (Nexmo):
◦ Voice API supports SIP and WebRTC bridging; good for integrating with custom WebRTC servers.
• Plivo:
◦ SIP trunking and call control APIs; also has Python SDKs.
Choose one that supports either SIP bridging to your infrastructure or WebRTC output you can route into LiveKit.
Two feasible integration strategies 1) SIP-to-WebRTC via a media gateway (common)
• Provider -> SIP -> Media gateway (e.g., Asterisk, FreeSWITCH, or hosted SIP gateway) -> WebRTC client/LiveKit.
• Your gateway creates a WebRTC client that joins a LiveKit room and publishes the PSTN caller’s audio.
• Pros: More control, mature tech; works with providers that only speak SIP.
• Cons: More infra (gateway) to manage.
2) Direct provider WebRTC or media relay into LiveKit
• Provider offers WebRTC or a media-relay API you can connect to your LiveKit room or a proxy that pipes audio into LiveKit.
• Pros: Simpler infra if provider supports WebRTC.
• Cons: Not all providers offer direct WebRTC-to-your-app options.
Concrete implementation steps (server-side Python, assuming LiveKit + Twilio example)
1. Provision services
◦ Create LiveKit server (self-hosted or managed) and note the API key/secret and URL.
◦ Sign up with your chosen telephony provider (e.g., Twilio) and configure a phone number that accepts inbound calls.
1. Choose a bridging method
◦ If using Twilio: configure a TwiML webhook for incoming calls that either:
▪︎ Connects to a SIP endpoint you control (SIP URI), which your gateway will turn into a WebRTC client that joins LiveKit, or
▪︎ Uses Twilio’s WebRTC capabilities and you create a connector that forwards that media into LiveKit (this is more advanced).
◦ If you have a SIP gateway (Asterisk/FreeSWITCH), configure it to accept the provider’s SIP and then create a WebRTC client that forwards to LiveKit.
1. Server-side bot workflow (Python)
◦ Create LiveKit tokens server-side in Python for the bot participant and for any web client that might join.
◦ Join the LiveKit room as the bot:
▪︎ Use a WebRTC client that can be driven from server-side. Options:
▪︎ Use a headless WebRTC client/bridge (like Pion in Go, Janus plugin, or a node-based headless browser). There is no official pure-Python headless WebRTC publisher widely adopted; the common pattern is to run a small helper service (Node/Go) or use a media gateway that can join WebRTC and expose audio to your Python process.
▪︎ Alternatively, have the SIP gateway publish the call’s audio as a participant in LiveKit, and have the Python bot subscribe to that participant’s audio track via LiveKit SDK or via a separate service that pulls the audio for processing.
◦ For transcription: stream audio to your chosen STT service (Google Speech, AWS Transcribe, OpenAI Whisper, etc.).
◦ For response generation: pass transcript to your bot logic (LLM or rule-based).
◦ For TTS: generate audio using TTS service (AWS Polly, Google TTS, or open-source TTS). Ensure the audio format and sample rate match what LiveKit expects.
◦ Publish TTS audio into the LiveKit room as the bot’s outgoing audio track so the caller hears the reply.
1. Media formats & timing
◦ Use consistent audio formats (e.g., 16kHz mono, PCM or OPUS).
◦ For low latency, stream audio chunks for transcription (rather than waiting for full recordings).
◦ Handle conversation state (when to listen vs speak), and consider barge-in behavior (interrupting TTS when user speaks).
1. Example Python responsibilities
◦ Generate LiveKit tokens (server-side):
▪︎ Use your LiveKit API key/secret to mint a token for the bot.
◦ Receive call events from provider (webhooks) to create / map a LiveKit room for each incoming call.
◦ Orchestrate gateway actions (instruct the SIP gateway to bridge call into a named LiveKit room).
◦ Call transcription and TTS requests (to chosen cloud provider) and stream audio to/from LiveKit.
Practical notes and constraints
• There is no direct WhatsApp voice call path—WhatsApp can’t be used for PSTN voice bridging. PSTN bridging reaches phone numbers, not WhatsApp calls.
• You will likely need a small media gateway or helper service that can bridge SIP/WebRTC audio into LiveKit, because pure Python lacks a mature headless WebRTC publisher. I can outline options for a small Node or Go helper if you want.
• Latency, audio codec compatibility (OPUS), and proper echo cancellation matter; test with sample calls incrementally.
If you’d like, I can now: 1) Provide a step-by-step example using Twilio + Asterisk + LiveKit, with code snippets for:
• Twilio webhook (Python Flask) that creates/associates a LiveKit room.
• How to mint LiveKit tokens in Python.
• How to configure Asterisk to forward call audio into LiveKit (high level).
• How your Python bot can stream audio to STT and publish TTS back into LiveKit.
OR 2) Provide an alternative example using Vonage or Plivo instead of Twilio. OR 3) Sketch a minimal deployment that avoids running full Asterisk by using a small Node/Go bridge service to join LiveKit and relay provider audio.
Which example would you like? Also tell me:
• Which telephony provider do you prefer (Twilio, Vonage, Plivo, other)?
• Which STT and TTS services would you like to use (Google, AWS, OpenAI/Whisper, others)?
• Do you already have a LiveKit server set up, or should I include LiveKit provisioning steps and token examples?