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Global Call IP Technology Guide — November 2007 81
Dialogic Corporation
IP Call Scenarios
3.3.3.3 Successful Transfer with Early Termination of REFER Subscription
Figure 27 illustrates a valid scenario for which Global Call does not support the party B role. In this
scenario, party B terminates the REFER subscription with the first NOTIFY, before party A can be
notified of the transferred call status. The Call Control Library at Party A disconnects the primary
call with party B after the terminating NOTIFY and the application then must tear down the call
using gc_DropCall( ) and gc_ReleaseCallEx( ).
Figure 27. Successful SIP Unattended Call Transfer, Party B Terminates REFER Subscription
prior to Notification of Transferred Call Status
3.3.3.4 Successful Transfer with Primary Call Cleared Prior to Transfer
Completion
The SIP protocol supports unattended transfer scenarios where the primary call is cleared or
dropped before the transfer completes. In some other technologies and protocols, these scenarios
are referred to as “unattended blind transfers” as opposed to “attended blind transfers” where the
primary call is maintained until completion. Note that scenarios similar to these are not supported
by the H.450.2 protocol.
Figure 28 illustrates a scenario in which party A drops the primary call with party B as soon as it
receives notification that party B has accepted the transfer request. In this scenario, party A does
not receive any notification that the transfer has completed.
Pre condition: Primary call between A and B is connected (not shown).
A
(Transferring,
Transferor)
App
A
(Transferring,
Transferor)
IP CCLib
B
(Transferred,
Transferee)
non-Global Call
C
(Transferred To,
Transfer Target)
App
C
(Transferred To,
Transfer Target)
IP CCLib
KEY:
CRNp - primary call
CRNt - transferred call
GCEV_
ANSWERED(CRNt)
gc_AnswerCall
(CRNt)
ACK
200 OK
GCEV_OFFERED(CRNt)
IPEC_IncomingTransfer
(optional)
GCEV_PROCEEDING
(CRNt) (optional)
INVITE
gc_CallAck(CRNt)
(optional)
3rd party UA might terminate the
NOTIFY session with the first NOTIFY
GCEV_INVOKE_
XFER(CRNp)
gc_InvokeXfer
(CRNp)
GCEV_
INVOKE_XFER_
ACCEPTED(CRNp)
gc_DropCall(CRNp)
GCEV_
DROPCALL(CRNp)
gc_ReleaseCallEx
(CRNp)
GCEV_
RELEASECALL
(CRNp)
GCEV_
DISCONNECTED
(CRNp)
202 Accepted
NOTIFY(1xx or 2xx)
Subscription-State = terminated
200 OK
REFER
BYE
200 OK
Post condition: Transferred call between B and C is connected.
Primary call between A and B dropped and released
100 Trying (optional)
180 Ringing (optional)