# 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](../../outbound-trunks/how-to-guides/create-outbound-trunk.html#outbound-trunk-create-trunk) is required, with **Authentication method** set to **Credentials & IP-Based**, and DIDWW [SIP/RTP IP addresses allowed](sip.html#service-did-sip). > - An [Inbound SIP Trunk](../creating-a-new-sip-trunk.html#user-panel-sipin-trunk) is required, with **Max 30x Redirects** or **Max Transfers** set to a value greater than 0 in the [Signalling tab](../creating-a-new-sip-trunk.html#user-panel-sipin-trunk-general-advanced-signaling-settings-timeout). > - Authorization is required on the [Inbound SIP Trunk](../creating-a-new-sip-trunk.html#user-panel-sipin-trunk-authentication), using the same **Auth User** and **Auth Password** configured on the chosen [Outbound Trunk](../../outbound-trunks/how-to-guides/view-outbound-trunk-credentials.html#view-outbound-trunk-credentials). > - The SIP destination URI is required in the format `sip:NEW_PSTN_NUMBER@` 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](../../outbound-trunks/outbound-sip-information.html#voice-out-signaling-endpoints). - `NEW_PSTN_NUMBER` is the E.164 phone number, and `` 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: ;tag=123456 To: ;tag=abcdef Call-ID: 01-01-35531111-68BE960300095714-69CF836B CSeq: 1 INVITE Contact: Content-Length: 0 ``` For more details, see [**RFC 3261 Section 21.3**](https://datatracker.ietf.org/doc/html/rfc3261.html#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
sip:DID_NUMBER@example.com pbx-->>voice_in: 302 Redirect
Contact: sip:NEW_PSTN_NUMBER@out.didww.com Note over voice_in: Redirect processing
checks MAX_30x_REDIRECTS value voice_in->>voice_out: INVITE to your Outbound Trunk
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
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: ;tag=abcdef To: ;tag=123456 Call-ID: 01-01-35531111-68BE960300095714-69CF836C CSeq: 2 REFER Refer-To: Referred-By: Contact: Content-Length: 0 ``` For more details, see [**RFC 3515**](https://datatracker.ietf.org/doc/html/rfc3515.html). Call Flow Diagram [![Porting Request Flow](../../../_images/siprefer-diagram.png)](../../../_images/siprefer-diagram.png) 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 --- ## Additional Resources **Configure Call Transfers** Step-by-step guide on configuring inbound and outbound SIP trunks in DIDWW to enable call transfers using SIP 30x Redirect or SIP REFER signaling. [Configure Call Transfers](call-transfers.html#call-transfers-use-cases) On this page