# Inbound call redirection Inbound call redirection allows a SIP platform that receives a call from a DIDWW inbound SIP trunk to send that call to an external phone number through a DIDWW outbound SIP trunk. The platform can redirect the call before it is answered or transfer it after a SIP dialog has been established. To set up the trunks and SIP platform, see [Configure call transfers](../how-to-guides/configure-call-transfers.html). DIDWW supports the following methods: | Method | Timing | Inbound trunk field | Destination header | | --- | --- | --- | --- | | SIP 30x Redirect | Before the inbound call is answered. | [Max 30x Redirects](../sip-trunk-settings-reference.html#inbound-sip-trunks-settings-signalling) | `Contact` in the SIP 301 or 302 response. | | SIP REFER transfer | After the inbound call is answered and a SIP dialog is established. | [Max Transfers](../sip-trunk-settings-reference.html#inbound-sip-trunks-settings-signalling) | `Refer-To` in the in-dialog `REFER` request. | ## How redirection works The SIP platform receives an incoming call through a DIDWW inbound SIP trunk and selects a new destination. It then returns a SIP 301 or 302 response, or sends an in-dialog SIP `REFER` request. DIDWW validates the message against the corresponding limit on the inbound trunk. Both limits default to `0`, which disables the method. When the request is accepted, DIDWW creates a new call through a DIDWW outbound SIP trunk. The inbound trunk's **Authorization** settings must contain the credentials of that outbound trunk. The destination SIP URI must point to a [DIDWW outbound signaling endpoint](../../../outbound-trunks/outbound-sip-information.html#voice-out-signaling-endpoints). For a Static Endpoint inbound trunk, the inbound and outbound trunks must use compatible IP versions. Warning Ensure that the destination does not route back to the original DID number. Otherwise, the configuration can create a call loop. ## SIP 30x Redirect This method redirects an inbound call to a new destination without answering it. 1. Your system replies to the DIDWW `INVITE` with `301 Moved Permanently` or `302 Moved Temporarily` and places the new destination in the `Contact` header. 2. DIDWW validates the response against **Max 30x Redirects**. 3. DIDWW starts a new outbound call to that SIP URI through your outbound trunk, authenticated with the credentials from your inbound trunk. 302 SIP response example The following example redirects the call to `NEW_PSTN_NUMBER` through the DIDWW outbound SIP service: ``` 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 the SIP response definition, see [**RFC 3261 Section 21.3**](https://datatracker.ietf.org/doc/html/rfc3261.html#section-21.3). SIP redirect call flow ``` %%{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: Checks Max 30x Redirects 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 Authorization header
sip:NEW_PSTN_NUMBER@out.didww.com voice_out-->>voice_in: 200 OK Note over voice_in, voice_out: Call is established through the Outbound Trunk ``` Use cases This method fits when the routing decision can be made without answering the call: - Forwarding calls after hours to a service or mobile phone. - Routing VIP callers directly to a dedicated line. - Redirecting desk calls to a mobile phone through follow-me rules. ## SIP REFER transfer This method transfers an inbound call to a new destination after it has been answered. 1. Your system answers the inbound call, which creates 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 **Max Transfers** and replies with `200 OK` or `202 Accepted`. 4. Your system sends `BYE` to close the original call leg. DIDWW starts a new outbound call through your outbound trunk, authenticated with the credentials from your inbound trunk. SIP REFER request example The following example transfers the call to `NEW_PSTN_NUMBER` through the DIDWW outbound SIP service: ``` 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 the SIP method definition, see [**RFC 3515**](https://datatracker.ietf.org/doc/html/rfc3515.html). SIP REFER call flow [![SIP REFER flow from an inbound call to a DIDWW outbound trunk](../../../../_images/siprefer-diagram.png)](../../../../_images/siprefer-diagram.png) **Fig. 1.** SIP REFER call flow Use cases This method fits when the call must be answered before the routing decision: - Transferring a caller after an IVR menu selection. - Escalating a call from an AI voicebot to a live agent. - Transferring a call from an agent's softphone to an external specialist. ## Related resources - [Configure call transfers](../how-to-guides/configure-call-transfers.html) - Configure the trunks and SIP platform for either method. - [SIP trunk settings reference](../sip-trunk-settings-reference.html) - Review Authorization and Signalling fields, defaults, and limits. - [Outbound SIP information](../../../outbound-trunks/outbound-sip-information.html) - Select signaling endpoints and review outbound SIP requirements. - [SIP connectivity reference](../sip-connectivity-reference.html) - Review DIDWW signaling and media addresses. On this page