Digital Data System: User's View of the Network

Vol. 54, No. 5, M a y - J u n e 1975 Printed in U.S.A. Digital Data System: User's View of the Network By J. J. MAHONEY, JR., J. J. MANSELL, and R. C. MATLACK (Manuscript received July 12, 1974) The utilitarian aspect of the Digital Data System is discussed with emphasis on performance objectives that will be important when data communications is inserted into a system of data processing. Objectives for the dependability and quality of data communications are quantified and evaluated in terms of their impact on data processing. Characteristics of the several types of channels available are described in detail along with operational features of particular importance at the interface between data communication and data processing. I. PERFORMANCE OBJECTIVES 1.1 General Modern industries are motivated to centralize the control of their integrated operations at a powerful computer and to disperse important operational functions to outlying areas. Modern telecommunications provide the data transmission services that are essential to coordinate dispersed functions with centralized control. Viewed in this light, data communication becomes one link in a larger chain of operations. Objectives for the reliability and quality of data transmission are evaluated in terms of their impact on the larger operation. D a t a service should generally be deemed excellent when the capability of a data processing system is not diminished perceptibly by the insertion of data communication. 1.2 Availability The dependability of data service may be expressed in terms of availability, which is simply the complement of average annual down time.