User`s guide

Dialogic
®
System Release 6.0 PCI for Windows
®
Release Update, Rev 62 — January 30, 2008 190
Dialogic Corporation
Figure 3. Successful SIP Unattended Call Transfer, Party B Terminates REFER Subscription
prior to Notification of Transferred Call Status
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 4 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)