Telephony Deep Dive: Bridges, Numbers & Providers

May 27, 2026 · 7 min read

Telephony is the layer that connects your AI agent to the real phone network. Unpod abstracts away the complexity of SIP, PSTN, and WebRTC — but understanding how the pieces fit together helps you configure it correctly and debug issues faster.

The Three Components

Unpod telephony has three core concepts:

Phone Number → Bridge → Provider → Agent

Component	What It Is	Example
Phone Number	A real PSTN/VoIP number	+1 415 555 0100
Bridge	Routing config linking number + provider + agent	`support-bridge`
Provider	Voice infrastructure that handles media	LiveKit, Vapi

Providers: The Voice Infrastructure

Providers handle the actual audio — WebRTC media servers, transcription, and TTS streaming.

LiveKit

LiveKit is an open-source, WebRTC-based media server. Unpod’s real-time voice pipeline runs on LiveKit.

Sub-300ms end-to-end latency
Can be self-hosted (cost control at scale)
Supports SIP trunking for PSTN connectivity
Best for: developers who want full control, self-hosted deployments

Vapi

Vapi is a hosted voice AI infrastructure platform.

Fully managed — no infrastructure to run
Built-in SIP trunking and number management
Simplified setup for faster time to production
Best for: teams that want managed infra without ops overhead

Bridges: The Routing Layer

A Bridge is a named configuration that connects:

One provider (LiveKit or Vapi)
One or more agents
One or more phone numbers

Think of it as a switchboard. When a call arrives at a number, the bridge decides which agent handles it.

Creating a Bridge via Dashboard

Go to Dev Platform → Telephony → Bridges → Create Bridge:

{
  "name": "support-bridge",
  "provider": "livekit",
  "agent_handle": "aria-support",
  "inbound_enabled": true,
  "outbound_enabled": true
}

Creating a Bridge via API

curl -X POST https://api.unpod.ai/api/v1/bridges/ \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "support-bridge",
    "slug": "support-bridge",
    "provider_id": 1,
    "agent_handle": "aria-support"
  }'

Phone Numbers

Unpod provisions real phone numbers through your connected SIP provider. Numbers are then assigned to bridges.

Number Types

Type	Description	Use Case
Local DID	Local area code number	Customer support, sales
Toll-Free	800/888/877 numbers	Enterprise support lines
International	Non-US numbers	Global operations

Provisioning a Number

curl -X POST https://api.unpod.ai/api/v1/numbers/ \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "country": "US",
    "area_code": "415",
    "bridge_slug": "support-bridge"
  }'

The number is immediately active and routed to your bridge once assigned.

Call Flow: What Happens on an Inbound Call

Caller dials your number
SIP provider receives the call, looks up the number’s bridge assignment
Bridge routes call to the configured provider (LiveKit/Vapi)
Provider streams audio to the Unpod voice pipeline
Voice pipeline runs: STT → LLM (with your agent config) → TTS
Audio streams back to caller in real time
Call ends, transcript and metadata written to Call Logs

Total setup latency target: under 300ms from first word to agent response start.

Outbound Calls

For outbound (agent-initiated) calls, create a Task via API:

curl -X POST https://api.unpod.ai/api/v1/tasks/ \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "agent_handle": "aria-support",
    "phone_number": "+14155550100",
    "bridge_slug": "support-bridge",
    "space_token": "sp_abc123"
  }'

Unpod dials the number, connects it through the bridge, and the agent begins the conversation.

Multi-Agent Routing

One bridge can route to different agents based on custom logic. Use the API to update bridge routing dynamically:

curl -X PATCH https://api.unpod.ai/api/v1/bridges/support-bridge/ \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "agent_handle": "billing-agent"
  }'

Combine this with your own IVR or pre-call webhook to build intelligent call routing before the AI agent picks up.

Debugging Common Issues

Symptom	Likely Cause	Fix
Call connects but agent doesn’t respond	Provider not reachable or misconfigured	Check LiveKit URL and API key in env
Number provisioning fails	No SIP provider connected to bridge	Connect a provider first
High latency on first word	TTS model cold start	Use a faster TTS model (OpenAI TTS > ElevenLabs for latency)
Call drops after 30s	WebRTC ICE timeout	Check firewall rules for UDP 10000-60000

What’s Next

Telephony API Reference

Full API reference for bridges, numbers, and providers.

Dev Platform: Telephony

Dashboard walkthrough for telephony setup.

Providers Overview

Configure and manage voice infrastructure providers.

Create a Task (Outbound Call)

Trigger outbound AI calls via API.

Documentation Index

​The Three Components

​Providers: The Voice Infrastructure

​LiveKit

​Vapi

​Bridges: The Routing Layer

​Creating a Bridge via Dashboard

​Creating a Bridge via API

​Phone Numbers

​Number Types

​Provisioning a Number

​Call Flow: What Happens on an Inbound Call

​Outbound Calls

​Multi-Agent Routing

​Debugging Common Issues

​What’s Next