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Method for Switching DFT DLC Without Stopping 3270 Emulation Session

IP.com Disclosure Number: IPCOM000100362D
Original Publication Date: 1990-Apr-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 62K

Publishing Venue

IBM

Related People

DuBois, LL: AUTHOR [+3]

Abstract

A method is described for switching the Data Link Control (DLC) code used for 3270 communications to a host from the Distributed Function Terminal (DFT) Non-SNA protocol to the DFT SNA protocol after the 3270 emulation session has been started. This method avoids the delay of stopping and restarting the session and makes the switch transparent to the user, for situations in which the control unit type (SNA or non-SNA) cannot be determined at the time the session is started. Examples of such situations are those in which the control unit is not responding, and in which the coax has not been connected.

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Method for Switching DFT DLC Without Stopping 3270 Emulation Session

       A method is described for switching the Data Link Control
(DLC) code used for 3270 communications to a host from the
Distributed Function Terminal (DFT) Non-SNA protocol to the DFT SNA
protocol after the 3270 emulation session has been started. This
method avoids the delay of stopping and restarting the session and
makes the switch transparent to the user, for situations in which the
control unit type (SNA or non-SNA) cannot be determined at the time
the session is started.  Examples of such situations are those in
which the control unit is not responding, and in which the coax has
not been connected.

      In IBM OS/2* Extended Edition, when the first 3270 emulation
session using the DFT protocol is started, the initialization code
attempts to determine whether the control unit to which the device is
connected is using SNA or Non-SNA DFT protocol.  If the control unit
responds, the protocol can be determined and the appropriate dynamic
link library (DLL) for either the SNA DFT DLC or the Non-SNA DFT DLC
code is loaded.  The DFT DLC code sends messages to other threads
which create the thread and the window used for the session, and
return the message queue handle used by the DFT DLC to send messages
to the session.

      If the DFT protocol cannot be determined when the session
starts, the Non-SNA DFT DLC code is loaded by default, and it sends a
message to create the window for t...