Inbound Call Redirection Methods

Inbound calls can be redirected to an external phone number (PSTN) through your account’s Outbound Trunks. Advanced routing is achieved by responding to an incoming call with either a 30x Redirect SIP response or an in-dialog REFER request.


Before You Begin

  • At least one Outbound Trunk is required, with Authentication method set to Credentials & IP-Based, and DIDWW SIP/RTP IP addresses allowed.

  • An Inbound SIP Trunk is required, with Max 30x Redirects or Max Transfers set to a value greater than 0 (configured in Advanced Signaling Settings).

  • Authentication is required on the Inbound SIP Trunk, using the same Auth User and Auth Password configured on the chosen Outbound Trunk.

  • The SIP destination URI is required in the format sip:NEW_PSTN_NUMBER@<outbound_endpoint> and included in the Contact header for 30x responses or the Refer-To header for REFER requests.

Note

  • The full list of outbound endpoints is available at Signaling Endpoints.

  • NEW_PSTN_NUMBER is the E.164 phone number, and <outbound_endpoint> is a DIDWW outbound endpoint (e.g., out.didww.com).


30x Redirect Method

This method redirects an inbound call to a new destination without answering it.

  1. Your system replies to the DIDWW INVITE with a SIP 302 Moved Temporarily (or another 3xx response), including the new destination in the Contact header.

  2. DIDWW then starts a new outbound call to that SIP URI using your Outbound Trunk, authenticated with the credentials set on your Inbound Trunk.

Examples

302 SIP Response

Example of a valid 302 Moved Temporarily response:

SIP/2.0 302 Moved Temporarily
Via: SIP/2.0/UDP 192.0.2.5:5060;branch=z9hG4bK-393929
From: <sip:CALLER_NUMBER@46.19.209.14>;tag=123456
To: <sip:DID_NUMBER@example.com>;tag=abcdef
Call-ID: 01-01-35531111-68BE960300095714-69CF836B
CSeq: 1 INVITE
Contact: <sip:NEW_PSTN_NUMBER@out.didww.com>
Content-Length: 0

For more details, see RFC 3261 Section 21.3 .

Call Flow Diagram
        %%{init: { "theme": "base", "themeVariables": { "actorBkg": "#e6f7ff", "actorBorder": "#1890ff", "noteBkgColor": "#fff7e6", "noteBorderColor": "#fa8c16" }}}%%
sequenceDiagram
  participant caller as Caller
  participant voice_in as DIDWW Inbound Trunk
  participant pbx as Your System
  participant voice_out as DIDWW Outbound Trunk

  caller->>voice_in: INVITE
  voice_in->>pbx: INVITE to your system<br/>sip:DID_NUMBER@example.com
  pbx-->>voice_in: 302 Redirect<br/>Contact: sip:NEW_PSTN_NUMBER@out.didww.com

  Note over voice_in: Redirect processing<br/>checks MAX_30x_REDIRECTS value
  voice_in->>voice_out: INVITE to your Outbound Trunk<br/>sip:NEW_PSTN_NUMBER@out.didww.com
  voice_out-->>voice_in: 401 Unauthorized + Auth Challenge

  Note over voice_in: Applies AUTH_USER and AUTH_PASSWORD from your Inbound Trunk

  voice_in->>voice_out: INVITE with Auth Header<br/>sip:NEW_PSTN_NUMBER@out.didww.com
  voice_out-->>voice_in: 200 OK
  Note over voice_in, voice_out: Call is established via Outbound Trunk
Use Cases

This method is ideal when a routing decision can be made immediately, without answering the call first.

  • Forward calls after hours to a service or mobile phone

  • Instantly route VIP callers to a direct line

  • Redirect desk calls to a mobile phone with follow-me rules


REFER Transfer Method

This method transfers an inbound call to a new destination after it has been answered.

  1. Your system first answers the inbound call, creating an active SIP dialog.

  2. When a transfer is needed, your system sends an in-dialog SIP REFER request with the new destination in the Refer-To header.

  3. DIDWW validates the request against the MAX_TRANSFERS setting and replies with 200 OK.

  4. Your system then sends a BYE to close the original call leg. DIDWW initiates a new outbound call via your Outbound Trunk, authenticated with the credentials from your Inbound Trunk.

Examples

SIP REFER Request

Example of a valid in-dialog REFER request:

REFER sip:CALLER_NUMBER@46.19.209.14 SIP/2.0
Via: SIP/2.0/UDP 192.0.2.5:5060;branch=z9hG4bK-443322
Max-Forwards: 70
From: <sip:DID_NUMBER@example.com>;tag=abcdef
To: <sip:CALLER_NUMBER@46.19.209.14>;tag=123456
Call-ID: 01-01-35531111-68BE960300095714-69CF836C
CSeq: 2 REFER
Refer-To: <sip:NEW_PSTN_NUMBER@out.didww.com>
Referred-By: <sip:DID_NUMBER@example.com>
Contact: <sip:DID_NUMBER@192.0.2.5:5060>
Content-Length: 0

For more details, see RFC 3515 .

Call Flow Diagram
Porting Request Flow
Use Cases

This method is useful when the call must first be answered before deciding where to route it:

  • Transfer calls after IVR menu selection (e.g., “Press 1 for Sales”)

  • Redirect from an AI voicebot to a live agent after intent detection

  • Forward calls from an agent’s softphone to an external specialist on the PSTN