AT&T SYSTEM 25 Manual page 185

Third-Party Call Setup Using a Data Terminal
Third-Party Call Setup allows a data terminal (the third party) in Command Mode to set up
a call between an on-premises voice or data terminal (the source) and another voice or data
terminal (the destination), which can be on- or off-premises. Once the call has been set up,
the third party drops off and is not included in the call.
Each third-party data terminal may be administered to have a particular source terminal
"associated" with it. This association allows an abbreviated form of dialing when activating
Third-Party Call Setup.
The third-party data port is configured in one of the following three ways:
Configured to set up calls for any PDC or DDC.
Configured to set up calls for only one predetermined PDC or DDC (the
associated PDC or DDC).
Restricted from using this feature.
The following procedure describes how to use a data terminal to set up a call between two
other stations. Although the procedure instructs the user to select "Voice call, " this item can
also be used to set up a call between two data endpoints.
Pause characters should be inserted at appropriate places in the dialed digit string.
NOTE:
Also, Third-Party Call Setup calls are subject to the administered restrictions assigned to the
source voice or data port. For example, if the source terminal is restricted to on-premises
calls, a call to an off-premises destination terminal will be blocked.
Third-Party Call Setup Using a Data Terminal
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