Abstract: A high bit-rate coupler is connected between a PCM channel bidirectional multiplex and a packet switching unit. Each channel carries packet words, such as octets, grouped in frames separated by flags 01111110. The coupler processes the first level related to the bits of the frame level of a packet exchange procedure. For each received frame, the coupler extracts the filling zeros from the received words between the flags, controls a frame checking sequence included at the end of each frame, counts the realigned words without filling zeros to be transmitted to the switching unit, and detects the flags and the start and end of the frame. At the transmitting end, the coupler inserts filling zeros in each transmitted frame when it detects six contiguous bits "1" in the words delivered from the switching unit, derives the frame checking sequence, transmits the dealigned words with the filling words, and produces flags.