Remote data switching device

from Wikipedia, the free encyclopedia

Remote data switching devices ( DFG ) were transmission devices with which end devices could be connected to the Datex-L network. Devices with a transmission speed of 64 kbit / s are referred to as remote message switching devices (NFGt). NFGts could be interconnected so that the transmission speed reached 256 kbit / s.

From a functional point of view, all devices offered the end device interfaces from the V or X series of ITU-T . The Datex-L network required the X.21 protocol as the access procedure . The reason for using the V recommendations was that when the Datex-L network was introduced , the end devices were often designed for V interfaces and a compatible interface at the DFG was therefore required.

For asynchronous operation (up to 300 bit / s), DFGs worked according to recommendation X.20 . This recommendation makes do with one line each for the send and receive data; there is also a return line (system ground).

In synchronous operation , DFGs either worked according to the X.21 procedure or with V.24 interface lines ; the process is then described in recommendation X.21bis .

DFGs had three tasks:

  • establish a connection to the desired communication partner,
  • To carry out data transfer
  • To enable fault diagnosis with the help of test loops.

Examples of DFGs and terminal adapters

DFG9600UE-01
This device has two DEE interfaces, functionally according to V.24: One for data transmission and one for automatic connection establishment according to V.25 (integrated AWD ). The DFG was responsible for the connection control, making it more complex than the DFG9600UE-02. Since not all terminal equipment allowed automatic dialing, a connection could also be initiated via key dialing or a direct call key .
DFG9600UE-02
The terminal interface corresponds to X.21; This means that the entire connection control and data transmission is a function of the DEE .
NFGt64UE
One of the last DFGs of the Deutsche Bundespost . The speed of 64 kbit / s also allowed the transmission of voice, therefore the name was changed to remote communication device.
TA X.21 / X.21bis type 2 with keypad
With the introduction of the ISDN (motto: Everything via one network), terminal adapters (TA) became necessary as converters for the Datex-L network, these devices were functionally practical DFGs.

  • DFG9600UE-1

  • DFG9600UE-2

  • NFGt64UE

  • TA X.21 type 2

  • Remote data switching devices, backs with interfaces

  • Remote data switch NFGT64UE, rear side with interfaces

  • TA X.21