The direct data connection (DDV) is a form of fixed connection. It differs from the standard fixed connection (SFV) in that it is more reliable and is monitored by the network operator so that the operator can switch to a substitute connection in the event of a fault.
In the case of the direct data connection, two main connections with a digital connection point, which can be used for their own needs for the transmission of any form of communication, are connected to each other via permanently switched lines. These connections used to be called HfD, which stands for Hauptanschluss für Direktruf, now they are called DDV.monopoly transmission paths. Transmission generally follows the synchronous method.