Abstract: A method for providing dynamic allocation of trunk circuits of different classes of traffic having different bandwidths in a Digital Private Network Signalling System (DPNSS) link between two switching nodes is disclosed. The trunk circuits are grouped into trunk groups. Trunk Access Class (TAC) is a code used to differentiate different classes of traffic. In the switching nodes, a table exists which defines to which trunk groups access is allowed or barred by TAC whereby bandwidth (or trunks) in the DPNSS link can be allocated by class of traffic. The grouping of trunks into trunk groups and the table which allows or bars access to trunk groups by TAC may be altered from time to time in the switching nodes at each end of the link by management command, to vary the allocation of bandwidth between classes of traffic in the DPNSS link.

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.