The increasing diversity of hardware devices and software procedures developed for remote processing has yielded a multiplicity of new facilities and telecommunication network structures. The corresponding architectures for front-end systems range from specialized device control to sophisticated multi-purpose multi-terminal support. Simultaneously, the very complexity of new data transmission and processing techniques has created a need for flexible and powerful yet transparent communications processors. The functions of a front-end system will be analyzed in order to derive the concepts which will be used to establish a classification.