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SIP trunks are the foundation of your RevRing phone system. They connect your AI agents to the public telephone network, enabling both inbound and outbound calling.

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Understanding SIP Trunks

A SIP (Session Initiation Protocol) trunk is a virtual phone line that connects your RevRing agents to the phone network through a telephony provider like Twilio or Telnyx. Each trunk can handle multiple phone numbers and concurrent calls.

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Key Concepts

  • Proxy Address: The SIP server endpoint provided by your telephony provider
  • Authentication: Optional username and password credentials for SIP registration
  • Phone Numbers: The phone numbers routed through this trunk (must be in E.164 format)
  • Cloud vs. On-Premise: RevRing supports cloud-based SIP trunks from providers like Twilio and Telnyx

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RevRing SIP Domain

When configuring your telephony provider to send inbound calls to RevRing, use the following SIP URI: 
sip:sip.revring.ai
SIP Domain: sip.revring.ai This URI must be configured as the Origination destination in your telephony provider’s trunk settings.

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Twilio Elastic SIP Trunking

Twilio Elastic SIP Trunking is recommended for most users due to its reliability, global coverage, and pay-as-you-go pricing.

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Prerequisites

  • Active Twilio account
  • At least one phone number purchased from Twilio
  • Elastic SIP Trunking enabled in your Twilio Console

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Step 1: Configure Twilio

  1. Log into the Twilio Console
  2. Navigate to Elastic SIP Trunking → Trunks
  3. Click Create new SIP Trunk or select an existing trunk
  4. Note your SIP Domain (e.g., yourtrunk.pstn.twilio.com)

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Step 2: Create Credential List

  1. In the Twilio Console, go to Elastic SIP Trunking → Credential Lists
  2. Click Create new Credential List
  3. Give it a name (e.g., RevRing Credentials)
  4. Add a credential with a Username and Password of your choice
  5. Save the Credential List

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Step 3: Assign Phone Numbers in Twilio

  1. In your trunk settings, go to the Numbers tab
  2. Click Add Existing Number
  3. Select the phone numbers you want to use with RevRing
  4. Click Add
Phone numbers must be assigned to the trunk in Twilio before they can be used in RevRing.

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Step 4: Configure Origination (Inbound)

For inbound calls to reach RevRing:
  1. In your trunk settings, go to Origination
  2. Add an Origination SIP URI: 
    sip:sip.revring.ai
  3. Set Priority to 1 and Weight to 1

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Step 5: Configure Termination (Outbound)

  1. In your trunk settings, go to Termination
  2. Note your Termination SIP URI (e.g., yourtrunk.pstn.twilio.com) - you’ll use this as the Proxy in RevRing
  3. Under Authentication → Credential Lists, select the Credential List you created in Step 2
  4. Optionally enable PSTN Transfer if you want your agents to use the Transfer To Number tool to transfer calls to external phone numbers

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Step 6: Add Trunk to RevRing

  1. Navigate to SIP Trunks
  2. Click Add SIP Trunk
  3. Fill in the configuration:
    • Name: Twilio Elastic (or any descriptive name)
    • Proxy: Your Twilio Termination SIP URI from Step 5 (e.g., yourtrunk.pstn.twilio.com) - enter just the domain without the sip: prefix
    • Username: Enter the username from your Credential List (created in Step 2)
    • Password: Enter the password from your Credential List (created in Step 2)
    • Phone Numbers: Enter your phone numbers in E.164 format, comma-separated 
      +12025551234, +14155552671, +13105558899
  4. Click Add Trunk
You can paste a list of phone numbers separated by commas, spaces, or newlines - RevRing will automatically parse them.
Important: Phone numbers must be assigned in both places:
  • In your Twilio Console (assigned to the trunk)
  • In RevRing (entered in the Phone Numbers field above)
For inbound calls to a specific agent, you must also assign the phone number to that agent in the RevRing dashboard under Agent → Phone Numbers. For outbound calls, agents can use any phone number from their assigned SIP trunk.
Processing PHI? If you’re handling protected health information, you must:
  1. Enable Secure Trunking (TLS/SRTP) in your Twilio trunk settings
  2. Contact RevRing support to enable TLS and SRTP on your SIP connection

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Telnyx SIP Trunking

Telnyx offers competitive pricing and global coverage with a developer-friendly API.

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Prerequisites

  • Active Telnyx account
  • At least one phone number purchased from Telnyx
  • SIP trunk created in Telnyx Portal

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Step 1: Configure Telnyx

  1. Log into the Telnyx Portal
  2. Navigate to Voice → SIP Trunks
  3. Click Create SIP Trunk or select an existing trunk
  4. Note your SIP Trunk URI (e.g., sip.telnyx.com)

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Step 2: Configure Outbound Settings

  1. In your trunk settings, go to Outbound
  2. Set Tech Prefix: Leave empty or as configured
  3. Enable ANI Override if you need to set custom caller ID

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Step 3: Configure Inbound Settings

  1. In your trunk settings, go to Inbound
  2. Add a Connection pointing to RevRing’s SIP URI: sip:sip.revring.ai
  3. Set Routing to forward calls to the connection
Optionally enable PSTN Transfer in your trunk settings if you want your agents to use the Transfer To Number tool to transfer calls to external phone numbers.

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Step 4: Assign Phone Numbers

  1. Navigate to Phone Numbers in Telnyx Portal
  2. Select the numbers you want to use
  3. Set Connection to your SIP trunk
  4. Save changes

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Step 5: Add Trunk to RevRing

  1. Navigate to SIP Trunks
  2. Click Add SIP Trunk
  3. Fill in the configuration:
    • Name: Telnyx (or any descriptive name)
    • Proxy: sip.telnyx.com (or your custom domain) - enter just the domain without the sip: prefix
    • Username: Your Telnyx SIP username (if authentication is enabled)
    • Password: Your Telnyx SIP password (if authentication is enabled)
    • Phone Numbers: Enter your phone numbers in E.164 format
  4. Click Add Trunk
Important: Phone numbers must be assigned in both places:
  • In your Telnyx Portal (assigned to the trunk)
  • In RevRing (entered in the Phone Numbers field above)
For inbound calls to a specific agent, you must also assign the phone number to that agent in the RevRing dashboard under Agent → Phone Numbers. For outbound calls, agents can use any phone number from their assigned SIP trunk.
Processing PHI? If you’re handling protected health information, you must:
  1. Enable Secure Trunking (TLS/SRTP) in your Telnyx trunk settings
  2. Contact RevRing support to enable TLS and SRTP on your SIP connection

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Managing SIP Trunks

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Editing Phone Numbers

To add or remove phone numbers from an existing trunk:
  1. Navigate to SIP Trunks
  2. Click the menu (three dots) on the trunk row
  3. Select Edit Numbers
  4. Add or remove phone numbers as needed
  5. Click Save Numbers
Phone numbers must exist and be properly configured in your telephony provider before adding them to RevRing.
Remember: To enable inbound calls for a specific agent, assign the phone number to that agent under Agent → Phone Numbers in the RevRing dashboard.

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Deleting a Trunk

To delete a SIP trunk:
  1. Navigate to SIP Trunks
  2. Click the menu (three dots) on the trunk row
  3. Select Delete
  4. Confirm the deletion
You cannot delete a SIP trunk that is assigned to active agents. Remove the trunk from all agents first.

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Phone Number Format

All phone numbers in RevRing must use E.164 format:
  • Start with +
  • Include country code
  • Include area code and number
  • No spaces, dashes, or parentheses

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Valid Examples

+12025551234  (US number)
+442071234567 (UK number)
+61298765432  (Australia number)

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Invalid Examples

(202) 555-1234  (contains parentheses and dashes)
2025551234      (missing + and country code)
+1-202-555-1234 (contains dashes)

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Troubleshooting

  • Verify the proxy address is correct and matches your provider’s configuration (should be their Termination SIP URI without the sip: prefix)
  • Ensure phone numbers are assigned to the trunk in both your provider and RevRing
  • Check that your provider’s Origination settings include RevRing’s SIP URI: sip:sip.revring.ai
  • Confirm there are no firewall rules blocking SIP traffic
  • Verify the phone number is assigned to an agent in the Phone Numbers tab
  • Check that the agent status is set to Active
  • Ensure your provider is routing calls to RevRing’s origination endpoint
  • Review call logs in your provider’s dashboard for routing errors
  • Confirm your trunk has sufficient balance/credit with your provider
  • Verify the from number is assigned to your trunk
  • Check that the to number is in valid E.164 format
  • Review your provider’s outbound calling restrictions and country permissions
  • If your trunk requires authentication, ensure username and password are correct
  • Verify your provider’s authentication settings are configured correctly
  • Check your provider’s authentication logs for specific error messages

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Best Practices

  • Use descriptive names for your trunks (e.g., “Twilio US Production”, “Telnyx Canada”)
  • Keep phone numbers updated in both your provider and RevRing when making changes
  • Monitor trunk capacity to ensure you have enough concurrent call capacity for your needs
  • Set up redundancy by configuring multiple trunks or providers for failover
  • Review call logs regularly to identify and resolve any routing issues

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Next Steps

Inbound Calls

Configure agents to handle inbound calls

Outbound Calls

Set up outbound calling through your agents