DTMF Transmission via SIP

This documentation describes how to transmit Dual-Tone Multi-Frequency (DTMF) signaling through the SIP (Session Initiation Protocol) interface using 100ms' REST API. DTMF tones are used for telecommunication signaling over the line in voice-frequency bands to the call control.

Overview

The DTMF API provided by 100ms enables the transmission of DTMF tones directly to SIP participants during a call. This capability is essential for interacting with voice response systems, navigating phone trees or for controlling aspects of a session that require numeric input.

Points on Server-Side DTMF Generation

1. Simplified Client Logic: Offloading DTMF generation to the server reduces complexity on client devices (iOS, Android, Web), which don't need to implement DTMF logic.
2. Data Integrity: Keeping data in digital form until necessary minimizes the risk of data loss due to packet loss, which can occur when converting digital signals to analog prematurely.
3. Selective Transmission: Ensures that DTMF tones are only sent to SIP connections, avoiding unnecessary transmission to non-SIP participants.
4. Vendor Limitations: Not all service providers support server-side DTMF transmission. This could limit flexibility if switching providers or integrating with other systems. However, this is mitigated by 100ms providing a simple client-side implementation for generating DTMF.

REST API Endpoint for DTMF Transmission

Endpoint: https://api.100ms.live/v2/sip/dtmf

Method: POST

Headers:

• Authorization: Bearer <AUTH TOKEN> -> Client Auth Tokens are required to access this API; Management Tokens are not compatible with this API. For instructions on generating the auth tokens, please refer to this documentation.
• Content-Type: application/json

Request Body Example:

{
  "digits": ["0", "1"]  // Array of DTMF digits
}

Request Parameters Description:

• Target Recipients: The DTMF tones will only be sent to all SIP participants present in the call. WebRTC participants will not receive these tones.
• Transmission Order: Requests are queued and processed sequentially; subsequent requests will not be processed until all previous tones have been sent.
• Timing: Tones are transmitted at an interval of 100 milliseconds and last for 100 milliseconds. This timing is consistent across all requests.

Responses

200 OK - Indicates successful request processing. The body will be empty as the focus is on the action performed rather than data returned.

{}

400 Bad Request - When the request is invalid.

{
  "code": 400,
  "message": "no sip participants in the call",
  "details": [""]
}

This documentation provides a clear pathway for integrating DTMF transmission capabilities within your applications, ensuring effective interaction with systems requiring numerical input during SIP calls.