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interface between the DTE and the data port; NOT between the two DTEs.
Before a data call can be established, the data port must know if the DTE is ready to send or
accept data. Therefore the normal on-line operations must be performed (V.24: CT 108 and
CT 107 procedure; X.21: C and I procedure).
In the dialling phase the destination number is received by the DCE either from the keypad
(not for the LAM) or from the connected DTE (either from the terminal keyboard or from the
software program). The DCE transfers the number to the DLC-controller using a protocol-
message in the D-channel. The DLC-controller initiates a call set-up request to the PPU and
further to the CPU using the normal Internal Message Protocol (IMP).
For more information on the D-channel protocol: see Facility Implementation Manual;
Networking and Routing.
If the call is allowed (number analysis, traffic classes, CV allowances and facility class marks)
the ISPBX sends ringing current to the destination data port. The called data port receives a
string from the CPU with the calling party identification. If required this string can be passed
to the DTE.
If the called party answers the call, a transparent 64 kbps connection between the calling data
port and the destination data port is established. If the two ports are located in the same unit
only one switching network is involved. If the ports are located in different units, the 64 kbps
connection is established between two or more switching networks connected together by a
64 kbps timeslot in 2 Mbps inter-unit links. For full duplex communication a reversed path
from the called to the calling data port is also established. The calling data port receives a
message to inform the port that the call has been answered.
After the transparent connection is established, the ISPBX is not involved in the data call any
more until one of the data ports sends a message that the data call has finished. The ISPBX will
then break down the connection.
The set-up of the complete data port can be defined by of programming the interface
parameters. These include transmission speed and mode, separate signals of the interface
control, method of data rate adaption, method used for dialling and the character format.
Programming can be performed locally (using the keypad of the SOPHO-SET or SOPHO-
LAM or by using the keyboard of the DTE) or remotely (by downloading the data compatibility
value). The exact options available depend on the SOPHO-SET, SOPHO-LAM or LAM.
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DTE initiates activity.
If the DCE is idle (i.e. not busy with a data connection), the DTE is able to communicate
with the microprocessor of the DCE for dialling or data port programming. For local
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