a network node , which is designed for switching of time - division multiplex signals ; contains a number of line cards , a switch fabric interconnecting the line cards , and a control system . the switching fabric is a cell based switch with one or more switch modules adapted to switch cells of a predefined cell format on the basis of addresses contained in cell headers of the cells . the line cards have segmentation and reassembly devices for segmenting input time - division multiplex signals into cells of the preformed cell format and adding address information to each cell and for reassembling cells received from said switch fabric into output time - division multiplex signals . the control system is connected to a switched port of the switch fabric and exchanges with the line cards control and / or operation , administration and maintenance messages over the switch fabric using cells of the preformed cell format .