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Zero Runtime lets you handle both inbound and outbound SIP calls in a single configuration. When you create a phone number, Zero Runtime provisions both the inbound and outbound gateways for that number in one go, so you can receive calls from traditional telephony users into your rooms, and dial out from rooms to external phone numbers or SIP endpoints, using the same setup. This guide walks you through:
  • How inbound and outbound calls flow through Zero Runtime.
  • Configuring a phone number with inbound + outbound gateways.
  • Setting up routing rules.
  • Initiating outbound calls via the API.
videosdk.live is expected here. Zero Runtime runs on VideoSDK’s real-time infrastructure, so its SIP, media, and API endpoints are served from the videosdk.live domain. Use the hostnames and URLs exactly as shown.

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Understanding Inbound Call Flow

Inbound SIP call flow: a caller dials a number; the SIP provider (Twilio, Plivo, Telnyx, or Vonage) forwards the call to your Zero Runtime SIP URI; the inbound gateway receives it; routing rules match by number; and an AI agent is invoked.
The diagram above illustrates the end-to-end flow for handling inbound SIP calls with Zero Runtime:
  1. User Initiates Call: A user dials a phone number using their phone or SIP device.
  2. SIP Provider Receives Call: The call is received by your SIP provider (such as Twilio, Plivo, Telnyx, or Vonage).
  3. Forward to Zero Runtime: The SIP provider is configured to forward the call to your organization’s Zero Runtime SIP URI (e.g., orgId.sip.videosdk.live).
  4. Inbound Gateway: The call reaches the Inbound Gateway in Zero Runtime, which acts as the entry point for all SIP traffic.
  5. Routing Rules: The Inbound Gateway applies your configured Routing Rules to determine how the call should be handled. Routing is decided based on the number.
  6. Zero Runtime Cloud: Based on the routing, the call is either:
    • Connected to a User: The caller is connected into a Zero Runtime room with any other participants.
    • Routed to an AI Agent: An AI agent is invoked into the same room.

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Understanding Outbound Call Flow

Outbound SIP call flow: your app initiates a call via the Zero Runtime API; routing rules pick the outbound gateway; the outbound gateway sends a SIP INVITE through your SIP provider; and the callee receives the call. An AI agent is invoked once the call connects.
The diagram above illustrates the complete flow for making outbound SIP calls with Zero Runtime:
  1. Initiate Outbound Call via API: An outbound call is triggered from Zero Runtime Cloud by making a POST request to /v2/sip/call using the API. This can be done programmatically or via the dashboard.
  2. Routing Rules: The call request is processed by the configured Routing Rules, which determine how and where the call should be routed (e.g., to a user or an AI agent) and which outbound gateway to use.
  3. Outbound Gateway: The call is sent to the Outbound Gateway based on the matched routing rule, which holds the SIP provider configuration (termination address, credentials, etc.).
  4. SIP Provider: The Outbound Gateway sends a SIP INVITE to the configured SIP provider (such as Twilio, Plivo, Telnyx, or Vonage) using the provided authentication credentials.
  5. User Receives Call: The SIP provider places the call to the destination user (phone number or SIP endpoint). The user receives the call and can answer it on their device.
  6. Connect or invoke: The caller is connected to the Zero Runtime room, and an AI Agent is invoked depending on the routing rule.

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Configure Phone Number (Inbound + Outbound)

With Zero Runtime’s unified flow, creating a phone number provisions both the inbound and outbound gateways for that number. You can do this from the dashboard or via the API.

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Configure your provider

For the provider you want to use, you need:
  • The SIP URI to forward inbound calls to Zero Runtime:
    Replace $YOUR_ORG_ID with your actual Zero Runtime organization ID.
    If you want to restrict calls to a specific region, you can use:
    Available regions:
    • in1 → India
    • us2 → US
  • The termination SIP address and authentication credentials (username/password) of your provider, used for outbound calls.

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Create the Phone Number

When creating a phone number in Zero Runtime, provide the following:
  • Phone Number: The number in E.164 format (e.g., +14155552671).
  • Inbound Gateway: Created automatically when you add a number from your SIP provider. It becomes the entry point for incoming SIP calls.
  • Outbound Gateway:
    • Gateway Name: A descriptive name for your gateway.
    • Termination Address: The SIP URI or IP address where outbound calls should be sent.
    • Authentication Credentials: Username and password for your SIP provider.
    • Transport: Protocol to use (e.g., UDP, TCP, TLS).
By default, the SIP server region for outbound calls is automatically selected based on the location nearest to the number being dialed. To pin a specific region, update the outbound gateway using the geoRegion property via the API.Available regions:
  • us002 → US
  • in001 → India

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Setup Routing Rules

Once your phone number is configured, define Routing Rules to determine how calls are routed.
  • Routing Rule Configuration:
    • Gateway: Select the gateway you created.
    • Number: Specify the phone number(s) associated with this rule.
    • Dispatch: Choose how calls should be routed.
  • Room Configuration:
    • Dynamic: A new room is created for each call. You can customize the room ID using a prefix:
      • random: Generates a random room ID for each call.
      • participant number: Uses the caller’s phone number as part of the room ID.
      • SIP number: Uses the SIP number (the number you purchased) as part of the room ID.
    • Static: All calls are routed to a fixed, pre-defined room.

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Configure using Dashboard

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Configure using APIs

You can create a phone number with both inbound and outbound gateways in a single API call. See the Create Phone Numbers + SIP Gateways API for the full request and response schema.

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Initiate an Outbound Call

Once your phone number is configured, you can initiate outbound calls using the Zero Runtime API. This allows you to dial out from a room to any external phone number or SIP endpoint. Parameters:
  • sipCallFrom: The source phone number (E.164 format) to place the call from.
  • sipCallTo: The destination phone number (E.164 format).
  • routingRuleId: ID of the routing rule to use for this call.
  • destinationRoomId: (Optional) The room ID to connect the call to.
The routing rule referenced by routingRuleId must be of type outbound, and the business number provided in sipCallFrom must be associated with that routing rule. The call will be rejected if either condition is not met.
Example Request:
See the Call Trigger API for the full request and response schema.
All configurations and calls can be managed via the Zero Runtime dashboard or automated using the Zero Runtime API. For detailed information on each API endpoint, refer to the Zero Runtime API Documentation.

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API Reference

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Phone Number APIs

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Routing Rule APIs