In order to support both signalling processing on a per channel basis and multiple adaptation protocols, an interface (10) is modularised principally by function. Incident channels (60-62, Cho—Chn) are applied to a routing device (16) that consults a connection map (64) to determine an appropriate path, via an interface (90), for signal processing of each channel, as shown in FIG. 2. Modularised processing platforms (70-74) each contain a number of signal processors (80-86), with each processing platform providing an additional level of indirection with respect to channel handling. In this latter respect, one of the signal processors (86) on each platform is assigned to distribute channel processing to appropriately configured other ones of the signal processors and such that signal processing functions may be distributed between the other ones (80-84) of the signal processors. The present invention is particularly useful in relation to a narrowband-broadband interface to support differing adaptation protocols that require different signal processing functions and also to vary signal processing capabilities on a per call basis.