What is SIP?

SIP (Session Initiation Protocol) is a signalling protocol used to establish, manage, and terminate communication sessions over IP networks. It is widely used for real-time communication, including voice and video calls.

Key Concepts in SIP

1. Call Origination:

   Refers to receiving inbound calls. It involves setting up and managing phone numbers, enabling calls from traditional PSTN or IP-based networks to reach your system.

   Example: If your SIP provider has assigned the number +14155552671 to your SIP trunk, inbound calls to this number will be routed to your configured Vapi system.

2. Call Termination:

   Refers to outbound calls routed from your system to the recipient’s network. This requires configurations for routing and managing call quality.

   Example: A user in your system places a call to +442071838750. The call is routed from Vapi through your SIP provider to the intended recipient.

Setup Requirements

From the Vapi Side

1. Create a SIP URI: Use the Vapi API to generate a SIP URI. Example:

   curl --location '<https://api.vapi.ai/phone-number>' \\
   --header 'Authorization: Bearer your-vapi-private-api-key' \\
   --header 'Content-Type: application/json' \\
   --data-raw '{
       "provider": "vapi",
       "sipUri": "<sip:[email protected]>",
       "assistantId": "your-assistant-id"
   }'
   
   

   Replace placeholders with your details:

   • username: Your SIP username.Example: Replace username with johnsmith, resulting in sip:[email protected].
   • assistantId: Identifier for routing calls.Example: Use an assistant ID like abc123.

   Upon completion, a SIP URI like sip:[email protected] will be generated. Inbound calls to this URI will trigger actions in Vapi.

2. Configure Webhooks (Optional): If you want call requests sent to a webhook instead of a specific assistant, update the SIP URI with your webhook:

   curl --location --request PATCH '<https://api.vapi.ai/phone-number/id>' \\
   --header 'Content-Type: application/json' \\
   --header 'Authorization: Bearer your-vapi-private-api-key' \\
   --data '{
       "assistantId": null,
       "serverUrl": "https://your_server_url"
   }'
   
   

   • serverUrl: Your webhook endpoint.Example: https://myserver.com/call-handler.

   When an inbound call is received, the webhook https://myserver.com/call-handler will be triggered.

3. Set Up Outbound Call Credentials: Define the connection between Vapi and your SIP provider using a credential:

   curl -X POST <https://api.vapi.ai/credential> \\
   -H "Content-Type: application/json" \\
   -H "Authorization: Bearer your-private-key" \\
   -d '{
       "provider": "byo-sip-trunk",
       "name": "SIP Provider Name",
       "gateways": [{"ip": "provider-gateway"}]
   }'
   
   

   Replace placeholders with:

   • provider-gateway: The SIP provider’s gateway.Example: fts.telcom.net or sip.telynx.com.

4. Link Phone Numbers to SIP Trunk: Associate phone numbers with the SIP trunk for inbound or outbound calls:

   curl -X POST <https://api.vapi.ai/phone-number> \\
   -H "Content-Type: application/json" \\
   -H "Authorization: Bearer your-private-key" \\
   -d '{
       "provider": "byo-phone-number",
       "name": "SIP Number",
       "number": "your-sip-phone-number",
       "credentialId": "your-credential-id-which-you-got-from-previous-step"‬
   ‭    "numberE164CheckEnabled": false‬
   }'
   
   

   Replace placeholders with:

   • your-phone-number: The assigned phone number.Example: +14155552671.
   • your-credential-id-which-you-got-from-previous-step: The ID from the credentials setup.Example: abc-123-def-456.

From the SIP Provider Side

1. Inbound Configuration:

   • {{TBD}}

2. Outbound Configuration:

   • Whitelist IPs from Vapi.

     • IPs: 44.229.228.186 and 44.238.177.138.

   • Assign a Tech Prefix for routing calls, if required.

     Example: Prefix 1234 for Vapi calls.

3. Number Assignment:

   • Map phone numbers to the SIP trunk.Example: Assign +441632960961 to your SIP trunk.

4. SIP Domain and Invite Setup:

   • Configure the SIP domain (e.g., fts.telcom.net) and modify SIP invites to match Vapi’s URI format.