We're trying to setup an environment where a SIP attendant (or controlled) transfer, not blind, is allowed.
In detail, any incoming call comes through a voice gateway and goes to a SIP IVR. When IVR must transfer the call to an agent, it makes a second call to the destination agent (through a SIP INVITE) connected to an SCCP phone on UCCM 6.1 and, if the agent answers the call, it completes the transfer sending a SIP REFER to the original caller with the header replace (containing the call-id of the agent call).
This scenario works fine as described (when the call comes through the voice gateway) but it doesn't work if the original call comes from another UCCM phone.
In this case, when the REFER is issued, we always get a 403 Forbidden error message. Attached you'll find the SIP trace collected from IVR with the list of all messages.
Could someone tell me if the SIP REFER/REPLACES method is supported by UCCM and, if allowed, where I can configure this?
Make sure that here is the restriction for the SIP call transfer using Refer method
- Transfer of a call is not initiated on a gateway. A gateway can be a recipient or final-recipient; but not an originator. For example, transfer can be initiated from a voice-portal, which is a device that is external to the gateway.
- Although SIP IOS gateways currently support SIP URLs and TEL URLs, the Refer-To header and the Also header must be in SIP URL format to be valid. The TEL URL format cannot be used because it does not provide a host portion, and without one, the triggered Invite request cannot be routed.
- Cisco SIP customer premise equipment (CPE) such as 79xx and Analog Telephone Adaptors (ATA) do not currently support TEL URLs.
- The Refer-To and Contact headers are required in the Refer request. The absence of either header results in a 4xx class response to the Refer request. Also, the Refer request must contain exactly one Refer-To header. Multiple Refer-To headers result in a 4xx class response.
- The Referred-By header is required in a Refer request. The absence of this header results in a 4xx class response to the Refer request. Also, the Refer request must contain exactly one Referred-By header. Multiple Referred-By headers result in a 4xx class response.
- Only three overloaded headers in the Refer-to header are accepted: Accept-Contact, Proxy-Authorization, and Replaces. All other headers present in the Refer-To are ignored.
- If early transfer is attempted, and the call between the originator and final-recipient involves QoS or RSVP, the triggered Invite from the recipient with the Replaces header is not processed and the transfer fails. The session between the originator and the final-recipient remains unchanged.
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