Interworking SIP REFER Messages

The device supports interworking of SIP REFER messages. SIP UAs may support different versions of the REFER standard while others may not even support REFER.

This feature supports the following:

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Attended, unattended, and semi-attended call transfers

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Sending INVITE, REFER-notifications, BYE, PRACK and Session Timer on behalf of peer PBXs

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Advanced routing rules for the new, initiated INVITE

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Forwarding early media after REFER while attempting to avoid transcoding (by sending session update)

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Interoperate with environments were different SIP UAs lack basic SIP functionality such as re-INVITE, UPDATE, PRACK, Delayed Offer, re-INVITE without SDP

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Session updates after connect to avoid transcoding

The handling of REFER can be configured for all calls, using the global parameter [SBCReferBehavior]. To configure different REFER handling options for different UAs (i.e., IP Groups), use the IP Profiles table parameter, 'Remote REFER Mode'.

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Local handling of REFER: This option is used for UAs that do not support REFER. Upon receipt of a REFER request, instead of forwarding it to the IP Group, the device handles it locally. It generates a new INVITE to the alternative destination according to the rules in the IP-to-IP Routing table (where the 'Call Trigger' field is set to REFER). It is also possible to specify the IP Group that sent the REFER request, as matching criteria for the re-routing rule in this table ('ReRoute IP Group ID' field).

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Transparent handling: The device forwards the REFER with the Refer-To header unchanged.

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Re-routing through SBC: The device changes the Refer-To header so that the re-routed INVITE is sent through the SBC application.

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IP Group Name: The device sets the host part in the REFER message to the name configured for the IP Group in the IP Groups table.