User interface¶The user interface could be implemented in
The synchronous X.20/X.21 interfaces were offered at a lower cost (20-30 DM per month less) than the asynchronous X.20bis/X.21bis variants, due to the simpler DCE design for synchronous networks.
Furthermore, the DCE for asynchronous interfaces had to include a keypad to allow the user to manually dial the destination subscriber. Only the synchronous X.21 interface specifies a method how the DTE could dial directly.
- Siemens DFG-300 with X.21bis
- Siemens DFG-9600UE-1 with X.21bis
- Siemens DFG-9600UE-2 with X.21