[Sip] Question regarding draft-ietf-sip-cc-transfer-05

Hi Robert,

This is a question regarding Call transfer successful scenario.

In the Call transfer draft, section 4, it mentions the connection between transferor and the transferee MUST be maintained in case of un-successful cases. (i.e. No answer, busy, & etc.), such that the transferor has the ability to retreat the call back.

In section 5, it mentions "Note that a successful REFER transaction does not terminate the session between the Transferor and the Transferee. If those parties wish to terminate their session, they must do so with a subsequent BYE request." 

The questions are :

1) neither party (transferor or the transferee) physically hits an "end" key to release the call, then the session will not be released. Is it what we want? It wastes resources.

2) each party (transferor or transferee) can send a re-INVITE request message to get the conversation back. It is different behavior than the PSTN network. (In the existing call transfer, especially PSTN network, the connection between transferor and the transferee is released.)

3) If the transferee sends a re-INVITE request message to the transferor, does it become a 3-way call? 

Here is my penny thought, Can we change the note in section 5 as" the User Agent application for the transferor SHALL automatically send a subsequent BYE request message to release the session between the transferor and the transferee"? For transferee, we might say " the User Agent application for the transferee MAY automatically send a subsequent BYE request message to release the session between the transferor and the transferee."

By the way, I do not have problem for a PSTN user as the transferor because the PSTN network (i.e. switch) will ensure the disconnect, which is mapped to a BYE request message for the IP network. The same behavior is used for MGCP user too. The only problem is in SIP environment (i.e. Transferor, transferee and transfer Target are SIP phones), which requires an extra step to release the session.

Regards,

Mark Chiou

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