Abstract: A digital adaptive echo canceller for use in cancelling echo signals caused by trans-hybrid losses in two-wire to four-wire converters comprises first and second adaptive filters (20,22) each arranged to generate synthetic echo signals. Transfer control logic (23) compares difference signals relative to the difference between the synthetic echo signal generated by the first filter (22), and a real echo signal and the synthetic echo signal generated by the second filter (20) and the real echo signal, and if the synthetic echo signal from the first filter (22) is closer to the real echo signal causes transfer of the coefficients of the first filter (22) to the second filter (20) such that the synthetic signal mixed with transmitted speech signals in a mixer (24) is updated when necessary.

Abstract: Methods for establishing and maintaining synchronization between communicating multiplexers are provided, wherein a first multiplexer having a frame format multiplexes at least data according to the frame format, and wherein the second multiplexer demultiplexes at least said data according to the frame format, and synchronization is established by: providing the frame format with bit positions for a plurality of bits including first predetermined bit positions for a plurality of checksum bits, and second predetermined bit positions for bits other than checksum bits; calculating a checksum for the bit values of bits located at said second predetermined bit positions, and inserting bits representing the said calculated checksum into said first predetermined bit positions; sending bits including bits located at said first and second predetermined bit positions in said frame format from said first multiplexer to said second multiplexer; and establishing synchronization between said first and second multiplexers b