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A Transfer Call node can send the caller to a DID, an extension, or a SIP URI on your trunk instead of a phone number. On the node, turn on Allow SIP/DID targets and enter the target, for example 2001 or sip:2001@pbx.example.com. Bland resolves the target over the trunk the call arrived on. For a call that did not arrive over SIP, Bland uses your organization’s outbound trunk. You choose how the transfer is delivered: SIP REFER hand-off. Bland sends the REFER on the existing dialog, so no new connection reaches your SBC and no firewall change is needed. Custom headers travel as header parameters on the Refer-To URI (sip:2001@pbx.example.com?X-Account=42). Your PBX must copy them onto the INVITE it sends to the target. If your PBX cannot do that, use a new INVITE instead. New INVITE. Bland’s SIP infrastructure sends the INVITE to your trunk endpoint over TLS with SRTP, and your custom headers arrive as SIP headers on that INVITE. If your SBC answers with a 401 or 407 challenge, Bland responds with the outbound call credentials saved on the trunk. Warm transfer. Bland places the consult call to your trunk the same way as a new INVITE, briefs whoever answers, then joins the caller. With Attended transfer via SIP REFER + Replaces on, Bland completes the merge by sending your PBX a REFER with Replaces, which requires a call that arrived over SIP.
Bland sends your trunk’s credentials and custom headers only to the trunk’s own host. A full SIP URI that points at a different host is dialed as written, without them.

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Custom headers

To read headers from inbound calls as variables, see SIP headers. Headers on a transfer come from the trunk’s outbound header mapping, set in the Headers section of the trunk’s Configure tab or with the headers object in POST /v1/sip/attach. Each entry maps a call variable to a SIP header name. If the trunk has no outbound header mapping, no custom headers are sent on any transfer method.
  • Header names get an X- prefix. A name that does not start with X- is sent as X-<name>, and a leading x_ becomes X-. User-to-User, Remote-Party-ID, P-Preferred-Identity, and P-Called-Party-ID are sent as written.
  • Up to 15 headers per direction.
  • Numbers inherit the trunk’s headers. Saving the trunk’s header mapping updates every number bound to it.

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Common failures

The INVITE came from an IP your SBC doesn’t trust as a SIP peer. Trust every IP under Connection endpoints as a SIP peer, signaling and media.
A firewall is dropping TLS from Bland. Allow all of Bland’s IPs for your region to reach your SBC’s SIP TLS port.
Your SBC offered or required plain RTP. Enable SRTP on the trunk toward Bland.
Your PBX doesn’t copy Refer-To header parameters onto the new INVITE. Turn Hand off via SIP REFER off so Bland sends the INVITE with the headers.

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Next steps

Set up a trunk

Map call variables to headers on the trunk.

Warm transfer

Brief the person before the caller joins.
Docs for agents: llms.txt