Description of Systems Used for Data Transmission (An ASA Tutorial).

The decomposition of a complex data transmission system into segments and the identification of the terminal configurations employed on each segment appear to offer promise as a powerful tool for permitting and clarifying measurements and comparisons of the performance of like system segments, and for describing the features of systems which are significant to performance measurements. Many problem areas remain, however, for further study. For example, the question of combining the individual performance measures of a multisegment, multi-mode-of-operation system into a meaningful measure of total systems performance appears quite formidable. It is the intent of the Task Group to approach these problems of performance measurement gradually and to resolve them first for the simpler systems before proceeding to complex system configurations. Although the techniques which this Task Group has evolved for system description may appear to be voluminous or even redundant when applied to very simple configurations, they are orderly, and every effort has been made to seek and exploit the "common denominators" of data transmission systems having arbitrary degrees of complexity. We doubt that much further compaction can be realized without, severely curtailing or destroying the generality and (hopefully) universal applicability of these methods. The format which has been described is admittedly incomplete. It is suggestive rather than exhaustive. It is believed that its chief virtue lies in the identification of an orderly succession of levels of abstraction which permits the regular decomposition of highly complex systems into functional subgroupings having a size structure within the span of human attention. The details of description outlined within these subgroupings require further study and elucidation and it will probably always be necessary for the system describer Io employ good judgment and imagination in extending the scope of description in those areas where new advances, unique applications and/or common sense so dictate. [ABSTRACT FROM AUTHOR]