Support of Existing Data Interfaces by the ISDN

During the past decade, the opportunity has arisen to economically combine data and voice services onto a single system, the integrated services digital network (ISDN). Studies in CCITT have led to the production of a set of Recommendations covering aspects of the ISDN, including the customer terminal interface. Inevitably, there are significant differences between the customer terminal interfaces recommended for dedicated data networks and that proposed for the ISDN. To ensure a smooth transition towards the introduction of ISDN based services, the CCITT have published recommendations describing how existing terminal interface designs may be connected to an ISDN. These recommendations are the subject of this paper.     

Evolution of ISDN towards broadband ISDN

Worldwide activities to evolve integrated services digital network (ISDN) into an optical-fiber-based universal broadband network have resulted in the first baseline documents, such as CCITT Recommendation I.121. The asynchronous transfer mode has been established as a key element of broadband ISDN (BISDN). The adoption of the G.707-709 recommendations on the new digital transmission hierarchy will also strongly influence further BISDN development. The author presents the current state of the BISDN discussion, especially within CCITT, briefly addressing broadband services and then concentrating on the user-network interface, as its definition is of utmost importance with respect to the introduction of a worldwide unique BISDN. Network scenarios and evolution and interworking aspects of the arising broadband realizations are also addressed     

ISDN protocols for connection control

The technical details of the integrated services digital network (ISDN) access protocols for connection control are described. These protocols are the ISDN physical layer, link layer, and layer 3, which are documented in International Telegraph and Telephone Consultative Committee (CCITT) Recommendations I.430, I.441, and I.451, respectively. Other work that supports or enhances these protocols is described. In particular, the ISDN protocol reference model, how it relates to the open systems interconnection reference model, and CCITT Recommendation Q.932 on service feature control on ISDN are discussed. Possible uses of ISDN, possible evolution paths, and some understanding issues related to ISDN are also described     

ISDN protocol architecture

IT IS NOW widely recognized that the Integrated Services Digital Network (ISDN) concept is providing a useful framework for the development of future telecommunications networks and services. An ISDN can be regarded as a generalpurpose digital network capable of supporting (or integrating) a wide range of services (voice and non-voice) using a small set of standard multipurpose user-network interfaces. Relevant CCITT Recommendations (or standards) on ISDN interfaces were expected to be available in 1984, the final year of the current study period. This paper reviews CCITT progress on the architectural studies of protocols associated with ISDN's, in particular, the ISDN Protocol Reference Model being developed by Study Group XVIII. This Model, based on the concepts and principles of the ISO/CCITT Open Systems Interconnection (OSI) Reference Model, aims at providing a unified framework for modeling ISDN multiservice communications and capabilities. The new Model is applied to several possible ISDN communications configurations, enabling a number of technical issues to be easily identified.     

ISDN standardization

The history and achievements of ISDN (integrated services digital network) standardization in the CCITT are reviewed. Two of the most important developments, ISDN basic and supplementary services and broadband ISDN, are focused upon. The underlying concepts in the discussions of ISDN standardization are briefly explained     

CCITT Recommendations on the ISDN: A Review

This paper gives a brief overview of the I-Series of Recommendations on the integrated services digital network (ISDN) developed by the International Telephone and Telegraph Consultative Committee (CCITT). This set of Recommendations is printed in the CCITT "Red Book." The I-Series Recommendations represent the first major step towards worldwide harmonization of the fast-growing digital network capabilities in support of multiservice (voice, data, and image) user applications. Over 25 different Recommendations set up standard guidelines and features for service capability, network architecture, and user-network interfaces in the ISDN.     

An Idea Turns Into Reality--CCITT Activities on the way to ISDN

This paper traces, in broad terms, how the idea of integration of telecommunication services into one network has evolved in the CCITT. A brief overview of existing telecommunication networks is followed by a review of CCITT activities from 1968 to 1980. It had become evident by 1968 that digital technology would not be restricted to transmission only, but would also intrude into switching, signaling, and the terminal field. The CCITT acknowledged this tendency by setting up a Special Study Group entrusted with the study of all questions related to PCM and the coordination of work going on in other Study Groups in the digital field. By 1980 the first ISDN Recommendation (G. 705) was agreed upon, and activities during 1980-1984, when the ISDN took shape, are related in some detail. The structure of the I-Series Recommendations, all relevant to ISDN matters, is described.     

Common channel signaling for international service applications

The message transfer, telephone user, and integrated services digital network (ISDN) user parts of CCITT Signaling System No.7 (SS7) are described. The introduction of SS7 to provide control of international circuits is described. The intent is to provide a perspective on the advantages of using common channel signaling for ISDN     

Grade of service in the ISDN era

The grade of service (GOS) concept is explained, and effect of ISDN (integrated-service digital network) services on GOS parameters is explored. Consideration is given to quality degradation that could be caused by traffic congestion, other than effects on the existing parameters such as call setup delay and call blocking probability, and to the changes that would be induced on the existing parameters. Current studies, including CCITT standardization, are reviewed, and a direction for GOS specification methods in the ISDN era is suggested     

ISDN user-network interface management protocol

The author discusses an ISDN user-network interface management protocol. The protocol enables users to manage network services, operation (such as network reconfiguration and routing change), and maintenance. That the user equipment should be looked at from both user-of-service and manager-of-service perspectives is emphasized in a discussion of the relation of the user equipment to the Telecommunication Management Network (TMN). The current status of the ISDN UNI management protocol architecture studies in CCITT is reviewed, and problems specific to the ISDN environment are identified. The need to strengthen the convergence function to solve ISDN-specific problems is stressed. Examples of ISDN UNI management protocol applications are given     

Signaling System No. 7 ISDN User Part

The integrated services digital network (ISDN) user part of Signaling System No. 7 defines the signaling protocol which supports the establishment, supervision, and release of voice and nonvoice calls over circuit-switched connections between ISDN terminations of digital subscriber access lines. This paper gives an overview of the ISDN user part protocol, as defined in CCITT Recommendations Q.761-Q.766 [1], in terms of the signaling functions and procedures provided to support call and connection control in an ISDN, and in terms of the information elements and signaling messages that are used by the signaling functions in ISDN exchanges to communicate.     

Bell Canada ISDN Trial Plans

After years of work by the CCITT and other standards bodies, the ISDN concept has reached the stage where manufacturers are announcing the availability of ISDN network and terminal products. Bell Canada has responded to this development by planning an extensive ISDN trial program, including access-loop verification, switch hardware and software verification, and, finally, customer market trials. This trial program will permit Bell Canada to refine the technology and services to best meet customer needs. The trial program is only the most recent manifestation of the evolution towards ISDN through digital network modernization. An early move towards digital technology within Bell has already paid substantial dividends in terms of new services and revenues. These services, and the emerging ISDN-based service opportunities, are highlighted in this paper.     

A signaling protocol for complex multimedia services

The author introduces a signaling protocol for user applications that invokes multimedia services provided by the EXPANSE research prototype, a broadband ISDN testbed. A generic framework that flexibly accommodates a wide variety of services involving multiple parties with heterogeneous terminals is described. The author describes the generic services supported, introduces the EXPANSE call model, discusses syntax and message flow procedures, and relates EXPANSE signaling to the ISDN signaling control part (ISCP) and long-term broadband ISDN signaling work currently under study by CCITT     

Error performance in evolving digital networks including ISDNs

Some recent developments on error performance design methodology and the status of international standardization activities on network performance objectives are discussed. The effects of errors in various services and common error performance parameters are outlined, and a fundamental strategy for ISDN (integrated-services digital network) performance design methodology is presented. Error performance under real operating conditions and in-service monitoring of error performance are described. The status of CCITT Recommendations G.821 and M.550 is examined, and the areas that must be addressed by future studies are identified     

CCITT Recommendations--Network Aspects of the ISDN

This paper presents an outline of the key network standards issues addressed in CCITT as a necessary part of the development and implementation of ISDN. The results achieved in the 1981-1984 Study Period focused on ISDN network functional requirements, ISDN numbering plan, connection types to link ISDN interfaces across the network, and the relationship of the ISDN protocol model with the seven-layer ISO model. The additional network issues which must be resolved in the current (1985-1988) Study Period are identified and briefly discussed. Of particular interest are internetworking between ISDN and existing networks, numbering plan interworking, routing, and maintenance standards. The market success of ISDN depends upon early resolution of these network standards to meet the field trials scheduled for 1986-1988 and the first implementations expected in 1988-1990.     

A Review of CCITT Standardization to Date

This paper describes the key elements of the International Telephone and Telegraph Consultative Committee's (CCITT's) three Recommendations on ISDN services. Telecommunication services which can be offered to customers are the natural starting point for all standardization work on telecommunication networks. The necessary features of telecommunication networks can only be derived from the services' requirements. The early standardization of services has the added advantage that it allows communication across borders to be made available on identical terms. For the reasons given here, the CCITT has, in all its work on ISDN, given a high priority to a uniform definition of the services and to the specification of services to be offered internationally.     

Omissions and ambiguities in CCITT Recommendation Q.921

The data link layer protocol for the integrated services digital network (ISDN) user/network interface, known as link access protocol-D (LAPD), is a protocol that operates at layer 2 of the open systems interconnection (OSI) architecture. Its purpose is to safely convey information between layer 3 entities using the D-channel. The information types that LAPD is intended to transport include call control signaling, packet mode communications, and management information. Observations are made in this article about what are, in the authors' opinion, the most confusing points of CCITT Recommendation Q.921 with comments related to data link layer address field, broadcast connections, terminal endpoint identifier (TEI) management procedures, layer 2 frames exchange, and connection management entity response to MDL-error indication primitives. This article intends solely to clarify the recommendations so that their concepts and procedures become easier to understand and implement, which can lead to significant saving of time for those who must eventually use LAPD procedures or develop the software for handling them     

B-ISDN architecture and protocol

The authors discuss the architecture and protocol for broadband ISDN (B-ISDN) based on the CCITT standards. The discussion attempts to address the general concept of B-ISDN architecture and protocol and, whenever possible, present alternatives and the rationale for decisions in the selection of the protocol. B-ISDN is presented as a network evolution, and the impact of the asynchronous transfer mode (ATM) on the network is described. The role of virtual channel and virtual path in B-ISDN is discussed. The B-ISDN protocol structure and lower layer functions comprising the physical, ATM, and adaptation layers are presented, and the tentative trends of signaling and traffic control for the B-ISDN are delineated     

Video and image applications on narrowband and broadband isdn

Two major ISDN applications which will undoubtedly affect world-wide telecommunications in the coming decade are discussed. They are: (1) video transmission and (2) image transmission. Brief reviews of videophone chronicle and the current video coding technologies are presented. The application of videophones using p × 64 (CCITT coding algorithm up to 1·5 Mb/s) and the DCT (discrete cosine transform) algorithm for narrowband ISDN are discussed. Broadcast TV quality DS3-45 MB/s video codecs are also briefly discussed as a probable videophone system in the broadband ISDN era. The explosive growth of facsimile services is reviewed, and the progress of image coding technologies and their standards are covered. The prospects of high resolution image transfer systems with ISDN are addressed.