A method of dynamically adjusting a transmission capacity of a data transmission connection is proposed. The method comprises different steps at a network end node. An incoming frame-structured time division multiplex signal carrying incoming timeslots is received from a client. Furthermore, a request data set comprising for at least one incoming timeslot a corresponding subset is received. The subset has an identifier for identifying an existing data transmission connection and a status indicator for indicating to the network end node a status requested by the client for the corresponding timeslot. If the status indicator indicates a request for adding the timeslot to the data transmission connection or removing the timeslot from the data transmission connection, the network end node adjusts the transmission capacity of the data transmission connection. If the status indicator indicates valid data in the incoming timeslot, the network end node transmits the data of the incoming timeslot via the existing data transmission connection to a far-end network end node.