66 Global Call API for HMP on Windows Programming Guide — August 2006
Call State Models
The gc_HoldCall( ) function places an active call in the On-hold (GCST_ONHOLD) state. The
gc_RetrieveCall() function retrieves the call from the GCST_ONHOLD state and returns it to the
Connected (GCST_CONNECTED) state.
Figure 18 illustrates the transition between call states when a call is put on hold and then retrieved.
Figure 18. Call State Transitions for Hold and Retrieve
Calls in the On-hold state must be returned to the Connected state before they can be dropped.
Calls are dropped following the Basic Call scenario. See Section 3.4, “Basic Call Control in
Asynchronous Mode” for more information.
3.5.4 Call Transfer
This section describes the different types of call transfer. Topics include:
•Call Transfer Overview
•Supervised Transfers
•Unsupervised Transfers

3.5.4.1 Call Transfer Overview

There are two types of call transfers:
Supervised transfers
the person transferring the call stays on the line, announces the call, and consults with the party
to whom the call is being transferred before the transfer is completed
Unsupervised transfers
the call is sent without any consultation or announcement by the person transferring the call.
Unsupervised transfers are also known as one-step transfers or blind transfers
Note: The the call transfer implementations described in this section are common to a number of different
technologies. However, not all technologies support these implementations and some technologies
have technology-specific implementations for call transfer. See the appropriate Global Call
Technology Guide for technology-specific information on call transfer.
gc_RetrieveCall()
state(ch1) = Connected
gc_HoldCall()
state(ch1) = Onhold