Digital subscriber line circuit for connecting an ISDN subscriber to the trunk side of a digital exchange

A digital subscriber line circuit for connecting an ISDN subscriber to the trunk side of a digital exchange, comprising:

• an SLD interface operating according to the SLD system, and
• a transfer arrangement for exchanging, during a transfer time window having a lower boundary and upper boundary, data signals between incoming and outgoing time slots of a SL line of the SLD interface and time slots assigned thereto of outgoing or incoming trunks of the digital exchange,
• characterized in that the subscriber line circuit comprises
• a slip detection means for detecting a slip of a time slot of the incoming or outgoing trunk out of the transfer time window with respect to a slip detection reference, said slip detection reference being one of said boundaries of the transfer time window,
• said slip detection means comprising means producing an output signal when the slip detection reference coincides with the time slot of the trunks, and a slip detection reference switch circuit for switching, in response to said output signal, the slip detection reference to the other one of the said boundaries, and
• a slip correction means controlled by the slip detection means, for controlling the transfer arrangement in response to detection of a slip, to skip data in one data transfer direction and to repeat data in the other data transfer direction.