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2.
DATA COMMUNICATION WITHIN THE ISPBX
The ISPBX acts as a data network `infrastructure' for the interconnection of end user
terminals, peripherals and host computers. Transparent analogue or digital connections are
established between digital peripherals in much the same way as a voice connection is
established between two telephone sets. The end user terminals may use any protocol for
information transfer, provided the path has the capacity for the transmission.
Since the connection between two ports is established for the duration of the data call, this
network acts as a Circuit Switched Data Network (CSDN).
A data connection is established, in general terms, as follows:
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The calling party dials the DNR of the required destination. Dialling can be either from the
DTE keyboard, from the SOPHO-SET, SOPHO-LAM or LAM, automatically under
control of a software program or from a telephone set if a modem is used.
-
The ISPBX uses the dialled information to determine the destination, using number
analysis. A facility such as `hot line' may also be used to determine the destination.
-
The ISPBX checks if the connection is allowed. This involves checking traffic class of the
caller, the IBSC of the caller and the BSPT of the destination and the compatibility value
connection allowance.
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The called party is rung.
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The called party answers. Answering can be either from the DTE keyboard, from the
SOPHO-SET, SOPHO-LAM or LAM, automatically under control of a software program
or from a telephone set if a modem is used.
-
If the two DTEs are compatible then data transfer can take place.
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After data transfer (or even during data transfer), either party may break the connection.
This can be either from the DTE keyboard, from the SOPHO-SET, SOPHO-LAM or LAM,
automatically under control of a software program or from a telephone set if a modem is
used.
If the two DTEs are not located in the same unit, then the data is transferred between the two
involved units over one or more inter-unit links.
The ISPBX supports V.24 and X.21 interfaces for connecting DTEs. The interface is used to
transfer information from the DTE to the CPU for establishing the path to the destination port
and to transfer the user-information through the network after the connection is established.
Glossary
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DTE means Data Terminal Equipment, which can be a data terminal, printer, Personal
Computer, or any similar piece of equipment.
6
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