A switching apparatus distributes incoming calls to end point terminals that belong to a service group and that interact with the switching apparatus via messages. This identification provides a way to separate time-sliced elementary stream from non-time-sliced elementary streams by defining two descriptors in PSISI tables. At least one optical signal is transmitted away from the ring along a link that does not incorporate chromatic dispersion compensation. Suitable biopolymers include heparin complexes, and linkage may be provided by a silane having isocyanate functionality. None of the frames of data are assigned to both the display subsystem and the decode subsystem.