THE CONCEPT OF the Integrated Services Digital Network (ISDN) and various aspects of its implementation concerning transmission, switching, subscriber interface and signaling are first briefly reviewed. Approaches to the specification of ISDN performance, currently under consideration of the International Telegraph and Telephone Consultative Committee (CCITT) for standardization, are described. A new parameter, percentage Error-Free Blocks (EFB's), is suggested as an additional measure to be specified at different block lengths. The need for more realistic consideration of the impact of burst errors is highlighted and a procedure is outlined using a specific channel model. Also discussed is the effect of delay when satellite channels are revolved. It is suggested that a joint EFB-delay constraint specification might be useful for network routing internal to ISDN.

Performance objectives for ISDN's

A digital private automatic branch exchange provides a plurality of ports which may comprise line trunks or operator circuits, the ports being grouped with each group being controlled by an individual microprocessor circuit which performs all real time control over the ports. Voice communication between ports is effected by time division multiplex in connection with a digital switch system forming part of a common control which is controlled by a central processing unit responsive to the microprocessors in each port group for assigning time slots to each interconnection channel. Isolation between the central processing unit and the rest of the system is provided by a peripheral bus to which the common control units and port groups are connected, which peripheral bus is connected to the CPU bus by way of an interface circuit, permitting the system to operate with various types of central processing units without redesign of the peripheral units. A conference circuit is also provided for making available a range of conference sizes by combining the available lines to the conference circuit into groups of a predetermined size which may be expanded by combining groups to form conferences of larger or intermediate size.

Digital private branch exchanges

This paper describes the architecture of the ROLM CBX II, a highly modular successor to the ROLM CBX. The paper outlines the physical and logical construction of the system and its capabilities, concentrating on data communications. The development goals for the system are presented, and the system characteristics are related to the goals. Architectural features which provide the basis for future enhancements are described.

The CBX II Switching Architecture

This paper describes a voice/data circuit-switching system known as the ROLM CBX II. The paper first discusses what the ROLM CBX II family does, describing the most important functions and relating them to popular voice and data applications. The second section describes how the CBX II works, delineating the architecture and giving some details of the system implementation. The final section offers an assessment of what the CBX II and similar products might become in the future.

An advanced voice/data telephone switching system

Defining a call control interface for browser-based integrations using representational state transfer

It is the purpose of this paper to discuss the capabilities and organization of all digital PBX's currently being manufactured in the United States. A digital PBX is one which encodes incoming signals into representations where the presence, or absense, of pulses, or levels, defines the signal; such a system switches signals by routing, multiplexing, or storing these pulses or levels. Pulse amplitude and pulse width modulation systems are thus excluded from this discussion.

J. Kasson

Papers

Survey of Digital PBX Design