> ## Documentation Index
> Fetch the complete documentation index at: https://docs.unpod.ai/llms.txt
> Use this file to discover all available pages before exploring further.
# Telephony Deep Dive: Bridges, Numbers & Providers
> How Unpod routes calls through bridges, SIP providers, and phone numbers - and how to configure it for your use case
**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:
| 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**:
```json theme={null}
{
"name": "support-bridge",
"provider": "livekit",
"agent_handle": "aria-support",
"inbound_enabled": true,
"outbound_enabled": true
}
```
### Creating a Bridge via API
```bash theme={null}
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
```bash theme={null}
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
1. Caller dials your number
2. SIP provider receives the call, looks up the number's bridge assignment
3. Bridge routes call to the configured provider (LiveKit/Vapi)
4. Provider streams audio to the Unpod voice pipeline
5. Voice pipeline runs: STT → LLM (with your agent config) → TTS
6. Audio streams back to caller in real time
7. 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:
```bash theme={null}
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:
```bash theme={null}
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
Full API reference for bridges, numbers, and providers.
Dashboard walkthrough for telephony setup.
Configure and manage voice infrastructure providers.
Trigger outbound AI calls via API.