This guide will help you set up SIP trunking between Twilio and Callers. Follow these steps to establish the connection and configure your phone numbers.
Please follow steps below if you are looking to connect a Twilio Flex account.

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Prerequisites

Before you begin, ensure you have:
  • A Twilio account with SIP Trunking enabled
  • Access to the Twilio Console
  • Your Callers account credentials

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Step 1: Configure SIP in Callers

  1. Log in to your Callers dashboard
  2. Navigate to Settings > SIP Configuration
  3. Add a new SIP trunk with the following details:
    • Name: Twilio SIP
    • SIP URL: Choose the appropriate regional endpoint based on your location:
      • US/Canada: us1.sip.twilio.com
      • Europe: ie1.sip.twilio.com
      • Asia-Pacific: sg1.sip.twilio.com
    • Authentication: Username and password from your Twilio SIP trunk credentials
    • Save the configuration

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Step 2: Create a SIP Trunk in Twilio

  1. Go to the Twilio Console
  2. Navigate to Voice > SIP Trunking > Trunks
  3. Click “Create new SIP Trunk”
  4. Configure the following settings:
    • Friendly Name: Callers SIP
    • Termination:
      • Enable Termination: Yes
      • Termination URI: Your Callers SIP endpoint
      • IP Access Control: Create a new list for Callers’ IP addresses
    • Origination:
      • Enable Origination: Yes
      • Configure allowed destinations

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Step 3: Configure IP Access Control

  1. In the Twilio Console, go to SIP Trunking > IP Access Control Lists
  2. Create a new IP Access Control List
  3. Add Callers’ IP addresses to the allowed list
  4. Associate this IP Access Control List with your SIP trunk

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Step 4: Purchase and Configure Twilio Numbers

  1. Buy phone numbers from Twilio’s inventory
  2. For each number:
    • Go to the number’s configuration
    • Set the voice configuration to “SIP Trunk”
    • Select the SIP trunk you created
    • Configure the regional routing if needed

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Step 5: Configure Numbers in Callers

  1. In Callers, go to Phone Numbers
  2. Add your Twilio numbers
  3. Set the connection type to “SIP”
  4. Associate them with the Twilio SIP trunk you created

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Important Notes

  • Regional Configuration: Twilio processes and stores call data in the region where the SIP trunk is configured. Choose the region closest to your infrastructure for optimal performance.
  • NAT Configuration: If deploying behind NAT:
    • For UDP: Send periodic SIP OPTIONS to keep NAT bindings open
    • For TCP/TLS: Use either SIP OPTIONS or CR-LF keep-alives
  • Firewall Settings: Allow ALL of Twilio’s IP ranges for both signaling and media traffic
  • SIP Headers: Ensure your infrastructure sends a value of 70 for the Max-Forwards header
  • Phone Numbers: Always use E.164 format for phone numbers sent via SIP

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Testing

  1. Make test calls in both directions to verify the connection
  2. Monitor call quality and latency
  3. Check Twilio’s Voice Insights for detailed call analytics

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Troubleshooting

If you encounter issues:
  1. Verify IP access control lists are correctly configured
  2. Check SIP credentials and authentication
  3. Ensure firewall rules allow Twilio’s IP ranges
  4. Review Twilio’s Voice Insights for detailed diagnostics
For additional help, consult Twilio’s SIP Trunking documentation or contact Callers support.