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8-4 DTE CONNECTIONS
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Terminal Emulators
Many host and personal computer manufacturers endorse terminal emulation software that will send data in
a format that the destination DTE expects. For example, DEC’s VT100 terminal emulation package, and
AT&T’s ATT513 and ATT4410 packages give IBM-compatible PCs the ability to communicate in the
same formats as the terminals for which the packages are named. In addition, some data communications
packages — like TERRANOVA — provide IBM-compatible PC users with terminal emulation, file
transfer, and scripting capabilities. Ask your computer manufacturers to recommend a communications
package for your PC or host.
PC/PBX or PC/ISDN
The PC/PBX and PC/ISDN are both hardware/firmware platforms on which terminal emulation software
runs. Both are housed on circuit boards that can be plugged into an IBM XT/AT compatible personal
computer. When either of these boards are in place, you can use their respective 3270 emulation or
asynchronous communications packages to communicate with a host. Figure 8-1 shows how to configure
the connection between an IBM mainframe and a personal computer on which the PC/PBX or PC/ISDN
platform and 3270 emulation are running.
DCP
DCP
3270C
CLUSTER
CONTROLLER
3270C
FRONT
END
PROCESSOR
COMTEN
PROCESSOR
DMI
IBM
HOST
D
C
P
P
O
R
T
PC/ISDN
DCP
BRI
D
C
P
P
O
R
T
B
R
I
P
O
R
T
D
S
1
P
O
R
T
D
C
P
P
O
R
T
PC/PBX
Figure 8-1. PC/PBX and PC/ISDN 3270 Emulation Connections
Note that the PC/PBX communicates through a DCP port (known as a digital-line port on the System 75
and Generic 1 communications systems, and as a GPP port on the System 85 and Generic 2
communications systems); while the PC/ISDN uses a BRI port (currently available on the Generic 2
communications system only, but soon to be available on the Generic 1) for the PC connection, but a DCP
port (GPP or digital-line port) for the 3270C connection. PC/ISDN sends data over both the BRI B-
channels and the D-channel. The Generic 2 system can circuit switch the B-channel data, but cannot
process the D-channel X.25 data packets.