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Legacy SIP trunks (deprecated). This page covers legacy SIP trunks: the sip-trunk telephony provider and the /sip-trunks API. Existing legacy trunks keep working. For new setups, use SIP trunks. To move an existing trunk, see Migrate to SIP trunks.
This guide walks you through creating both an inbound and outbound SIP trunk on Plivo’s Zentrunk platform. By the end, your Plivo account will be fully configured to send and receive calls through Bolna’s Voice AI system.

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Prerequisites

Make sure you have the following ready before starting:

Plivo account

A Plivo account is required to create trunks. Sign up for Plivo if you don’t have one. A trial account works for initial testing.

Phone number

You need at least one voice-enabled phone number from Plivo. Purchase a number from the Plivo Console. This will be your DID number for making and receiving calls.

Bolna account

An active Bolna account with SIP trunking access enabled. If you don’t have access yet, contact enterprise@bolna.ai.

Bolna API key

Your Bolna API key, which you can find in the Bolna Dashboard. You will need this later when registering the trunk on Bolna.
Bolna’s SIP Server IP Address: Throughout this guide, you will need to use Bolna’s SIP media server IP: 13.200.45.61. Keep this handy as you will enter it in multiple configuration steps.

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Part 1: Create an inbound trunk (receive calls)

An inbound trunk handles calls coming in to your Plivo phone number. When someone dials your number, Plivo will forward the call to Bolna’s SIP server, where your AI agent picks up and handles the conversation.
1

Navigate to Inbound Trunks

Log in to the Plivo Console and navigate to Zentrunk > Inbound Trunks in the left sidebar. You can also go directly to console.plivo.com/zentrunk/inbound-trunks.
2

Create a New Inbound Trunk

Click Create New Inbound Trunk. Enter a descriptive name that helps you identify this trunk later. For example:
This name is just for your reference within the Plivo Console.
3

Add Bolna's SIP URI as the Primary URI

This is the most important step. You are telling Plivo where to send incoming calls. Click Add New URI and fill in the following:
Do NOT add transport=tcp or transport=tls to the URI. Bolna’s SIP server uses UDP, which is the default SIP transport. Adding a TCP or TLS parameter will cause all calls to fail silently.
4

Create the Trunk

Review your configuration and click Create Trunk. Your inbound trunk is now created. Note down the trunk name for the next step.
5

Connect Your Phone Number to the Inbound Trunk

Now you need to link your Plivo phone number to this trunk so that incoming calls are forwarded to Bolna:
  1. Navigate to Phone Numbers > Your Numbers
  2. Click on the phone number you want to use for inbound calls
  3. In the Number Configuration section, set Application Type to Zentrunk
  4. In the Trunk dropdown, select the inbound trunk you just created (e.g., Bolna-Inbound)
  5. Click Update Number to save
You can connect multiple phone numbers to the same inbound trunk. All of them will route incoming calls to Bolna’s SIP server, where they can be handled by different AI agents.
Your inbound trunk is now configured. Calls to your Plivo number will be forwarded to Bolna. You will configure which AI agent answers these calls in the Register Trunk on Bolna step.

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Part 2: Create an outbound trunk (make calls)

An outbound trunk allows Bolna to place calls out to regular phone numbers through your Plivo account. Your AI agents will use this trunk to initiate conversations with recipients.
1

Navigate to Outbound Trunks

In the Plivo Console, go to Zentrunk > Outbound Trunks.
2

Create a New Outbound Trunk

Click Create New Outbound Trunk and enter a descriptive name:
3

Create a Credentials List for Authentication

Plivo uses username/password authentication for outbound trunks. Bolna will send these credentials with every outbound call so Plivo can verify the request is legitimate.In the Trunk Authentication section:
  1. Click Add New Credentials List
  2. Enter a username, for example: bolna_trunk
  3. Enter a strong password and write it down immediately
Save your username and password securely. You will need both when registering the trunk on Bolna in a later step. Plivo will not show the password again after you create it.
4

Disable Secure Trunking (SRTP)

In the trunk settings, find Secure Trunking and set it to Disabled.
This is critical. Bolna does not support SRTP (Secure RTP). If Secure Trunking is left enabled, the media negotiation between Plivo and Bolna will fail, and you will experience no audio on calls (the call appears to connect but neither side can hear anything).
5

Create the Trunk and Copy the Domain

Click Create Trunk. After creation, Plivo will display a Termination SIP Domain that looks like this:
Copy this domain and save it. This is the gateway address that Bolna will use to route outbound calls through your Plivo account.
The Termination SIP Domain is unique to your outbound trunk. It is the address where Bolna sends SIP INVITE messages when placing outbound calls on your behalf.
Your outbound trunk is now configured on Plivo.

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Part 3: Whitelist Bolna’s IP address

For Plivo to accept SIP traffic from Bolna, you need to whitelist Bolna’s IP address. Navigate to your outbound trunk’s IP Whitelisting or Access Control settings and add:
This ensures that when Bolna sends SIP requests to Plivo, they are recognized and accepted.

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Configuration summary

Here is a quick reference of everything you configured in this guide:

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Plivo-specific notes

Plivo Zentrunk supports G.711 ulaw (u-law) and G.711 alaw (A-law) codecs by default. These are fully compatible with Bolna, so no additional codec configuration is needed on the Plivo side.
When you register this trunk on Bolna with IP-based authentication, you will need Plivo’s IP ranges. Add all of them, not only the India ones: during an outage Plivo routes calls through another region, so your calls can arrive from any of these addresses (Plivo’s published list):
You will add these as ip_identifiers when registering the trunk on Bolna.
If you are using Indian phone numbers (+91), you must complete the DLT (Distributed Ledger Technology) registration process before your numbers will work for outbound calling. See Plivo’s guide on Indian numbers and Bolna’s regulated phone numbers guide.
Trial Plivo accounts have limited functionality. You may only be able to call verified numbers (numbers you have manually added to your Plivo account). Upgrade your Plivo account for full outbound calling capability.

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Next steps

Your Plivo trunks are now configured. Continue with these guides:

Register trunk on Bolna

Register your Plivo trunk with Bolna and add your phone numbers via API

Receive inbound calls

Map your phone numbers to AI agents so they answer incoming calls