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Connect AI voice agent platforms to the telephone network using Plivo’s SIP trunking (Zentrunk). Enable your AI agents to make and receive phone calls through Plivo’s global voice infrastructure.

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Prerequisites

Before connecting your AI platform to Plivo SIP trunking, you’ll need:

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What is SIP Trunking?

SIP trunking provides a direct connection between your infrastructure and Plivo’s voice network. For AI voice agents, this means:
  • Inbound calls: Route calls from Plivo phone numbers to your AI platform via SIP
  • Outbound calls: Your AI agents can place calls through Plivo to any phone number worldwide
  • Global reach: Access phone numbers and terminate calls globally. See coverage
For complete SIP trunking documentation including technical specifications, APIs, and advanced configuration, see SIP Trunking.

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Inbound vs Outbound Trunks

Only inbound trunks can be attached to phone numbers. To receive calls on a Plivo number, you must create an inbound trunk. Outbound trunks are for placing calls only and won’t appear in phone number configuration.

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How It Works

  1. For inbound calls: Calls to your Plivo phone number are routed via SIP to your AI agent platform
  2. For outbound calls: Your AI agent initiates calls through Plivo’s SIP trunk to reach phone numbers

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Supported Platforms

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Quick Start

LiveKit

Build custom real-time voice applications with LiveKit and Plivo

ElevenLabs

Connect Plivo with ElevenLabs for natural-sounding AI voice agents

Retell AI

Connect Retell AI voice agents to the phone network with Plivo

Vapi

Deploy voice AI assistants quickly using Vapi and Plivo

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Transferring to a Human Agent

When your AI agent needs to hand off a live call to a human, whether for escalations, complex queries, or compliance, use SIP REFER. Your endpoint sends a REFER request mid-call with the transfer target’s number in the Refer-To header. Plivo bridges the caller to the human agent and disconnects your AI endpoint. The caller never re-dials and experiences a seamless handoff. How it works:
  1. Your AI agent is on a live call with a customer (inbound or outbound)
  2. Agent decides to transfer and sends REFER with the target number
  3. Plivo responds 202 Accepted and starts calling the transfer target
  4. Transfer target answers: Plivo bridges the caller and sends your agent a BYE
  5. Caller and human agent continue the conversation
Key details:
  • The Refer-To URI must use your SIP trunk domain (ending in .zt.plivo.com)
  • Your endpoint must handle NOTIFY messages from Plivo to track transfer progress
  • Do not send BYE before receiving NOTIFY 200 OK, as this would drop the caller
  • If the transfer fails, the caller stays on your AI agent’s line, so you can retry or continue

Outbound call transfer

Your AI agent placed the call and wants to hand off.

Inbound call transfer

A caller dialled your Plivo number and your AI agent wants to hand off.

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Regional Considerations

If you’re handling calls to or from India, ensure your AI platform has servers deployed in India to comply with regulatory requirements. See the individual integration guides for platform-specific instructions.