Safe Call Transfer Extension This section follows the product behavior described in endnote <71>. The safe call transfer extension tailors the routing behavior while transferring calls using the REFER request. Using this extension, a user agent transferring calls can request that the transferee disable call forwarding and voice mail for the triggered INVITE request. Abstract Data Model This section describes a conceptual model of possible data organization that an implementation maintains to participate in this protocol. The described organization is provided to facilitate the explanation of how the protocol behaves. This document does not mandate that implementations adhere to this model as long as their external behavior is consistent with that described in this document. Timers None. Initialization None. Higher-Layer Triggered Events If the user agent supports the safe call transfer procedure described in this section, it MUST advertise this by placing the ms-safe-transfer option tag in the Supported header of both the INVITE request and the response to the INVITE request. Message Processing Events and Sequencing When the user agent receives a REFER request in the INVITE dialog in which it previously advertised support for safe call transfer, as described in section , the user agent MUST examine the Refer-To header field of the REFER request. If the header field is present in the Ms-Sensitivity headers parameter of the URI in the Refer-To header field, the user agent MUST extract the Ms-Sensitivity header field and its value and add it to the INVITE request that it generates as the result of processing the REFER request. Timer Events None. Other Local Events None. Extensions for ICE SDP Interworking and Multipart MIME Support This section follows the product behavior described in endnote <72>. User agents use multi-part MIME to convey multiple SDP parts and call context data in an INVITE request during session initialization. This document describes a method of using multi-part MIME to enable interoperability with SIP elements for which it cannot be determined in advance whether they support or or both.
Safe Call Transfer Extension This section follows the product behavior described in endnote <71>. The safe call transfer extension tailors the routing behavior while transferring calls using the REFER request. Using this extension, a user agent transferring calls can request that the transferee disable call forwarding and voice mail for the triggered INVITE request. Abstract Data Model This section describes a conceptual model of possible data organization that an implementation maintains to participate in this protocol. The described organization is provided to facilitate the explanation of how the protocol behaves. This document does not mandate that implementations adhere to this model as long as their external behavior is consistent with that described in this document. Timers None. Initialization None. Higher-Layer Triggered Events If the user agent supports the safe call transfer procedure described in this section, it MUST advertise this by placing the ms-safe-transfer option tag in the Supported header of both the INVITE request and the response to the INVITE request. Message Processing Events and Sequencing When the user agent receives a REFER request in the INVITE dialog in which it previously advertised support for safe call transfer, as described in section , the user agent MUST examine the Refer-To header field of the REFER request. If the Ms-Sensitivity header field is present in the headers parameter of the URI in the Refer-To header field, the user agent MUST extract the Ms-Sensitivity header field and its value and add it to the INVITE request that it generates as the result of processing the REFER request. Timer Events None. Other Local Events None. Extensions for ICE SDP Interworking and Multipart MIME Support This section follows the product behavior described in endnote <72>. User agents use multi-part MIME to convey multiple SDP parts and call context data in an INVITE request during session initialization. This document describes a method of using multi-part MIME to enable interoperability with SIP elements for which it cannot be determined in advance whether they support or or both.