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.     

Layer 1 ISDN Recommendations

In the framework of the I-series of Recommendations, layer 1 specifications for ISDN user-network interfaces are given in Recommendation I.430 for the basic access(2B + D)at 144 kbits/s, and in Recommendation I.431 for the primary access at 1544 and 2048 kbits/s. The former Recommendation contains a completely new set of procedural, functional, and electrical characteristics whose definition was started during the last CCITT Study Period and is expected to be completed by the end of the present CCITT Study Period. Moreover, the latter Recommendation is largely based on functional and electrical characteristics of existing Recommendation G.703, which gives specifications for the physical/electrical characteristics of the hierarchical digital interface.     

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.     

Layers 2 and 3 ISDN Recommendations

The main feature of an ISDN user-network interface is the support of a wide range of service capabilities, including voice and nonvoice applications in the same network by offering end-to-end digital connectivity to a user. To handle the wide range of applications, a number of new features were developed and incorporated in the ISDN user-network interface layers 2 and 3 Recommendations. This paper reviews the current status of the ISDN user-network interface layers 2 and 3 Recommendations, with a special emphasis on new features developed and incorporated in these Recommendations.     

ATM: A contribution to the debate on broadband ISDN

The definition of broadband ISDN recently became a major topic of research and predevelopments. Fast packet technologies are widely recognized as the basis for BISDN. Even if international consensus has appeared far more quickly than could have been expected a few years ago, a lot of issues remain open. This paper is a contribution to discussions on some important topics relating to the definition of asynchronous transfer mode.     

An overview of emerging CCITT Recommendations for the synchronousdigital hierarchy: multiplexers, line systems, management, and networkaspects

The scope of CCITT (International Consultive Committee for Telephone and Telegraphy) Recommendations on which significant progress has been made is reviewed. These consist of Recommendations G.781, 782, and 783, dealing with synchronous multiplexers; Recommendation G.784, dealing with synchronous digital hierarchy (SDH) management; Recommendation G.958, concerning digital line systems based on the SDH for use on optical fiber cables; Recommendation G.957, dealing with optical interfaces; and Recommendations G.sna1 and 2, concerning network aspects of SDH     

一种基于ISDN的多媒体通信系统

介绍了一种基于ISDN的多媒体通信系统。在该系统中，ISDN用户一网络接口的S接口是通过数字话机来实现的。数字话机提供2B D的接入能力．具备呼叫控制的功能．既可以传输简单的语音，也可以同时传输语音、图像和数据等多媒体信息。     

CCITT standards on digital speech processing

An overview is given of CCITT activities on speech-processing standards for evolving digital communications networks. Such standards apply to worldwide interconnected digital networks and provide for adequate voice and nonvoice quality as assessed by the leading laboratories and experts in the world telecommunications community. Current status of standards is briefly discussed, and perspectives and given on results to be achieved by the end of CCITT study period (1984-8)     

A custom VLSI architecture for the CCITT wideband coding standard

A custom VLSI architecture for implementing the CCITT G.722 64-kb/s (7-kHz) wideband audio coding standard is presented. By tailoring the architecture to the algorithm, an architecture was designed that is capable of processing a full duplex channel in less than 625 cycles. That is 71-73% less cycles than are required by the reported general-purpose DSP implementations. In a 1.5-μ technology with a 100-ns cycle time, it is estimated that the architecture would consume 95000 mL² of silicon and support two full duplex channels on a single chip. The authors wrote a behavioral simulation of the architecture and its implicit microcode. This simulates the architecture's behavior at the bit level. The simulation passes the CCITT G.722 test vectors, demonstrating that the implementation conforms to the standard     

A Proactive ISDN Implementation Strategy

The ISDN promises to deliver a Wide variety of new services by providing end-to-end digital connectivity over public facilities. However, most administrations have decided upon implementation strategies which are based on pure speculation rather than a response to pent-up demand. This approach is expensive and could lead to disillusionment with the entire concept. This paper presents an ISDN implementation strategy which is based on sound economics and avoids speculation. With this approach, a rapid evolution to a ubiquitous ISDN is foreseen.     

ISDN: a snapshot

A snapshot of the present status of ISDN (integrated services digital network) is presented in terms of standardization efforts, field trials and demonstrations, implementations and services, and equipment and devices. A review of opinions and controversies as well as future trends is also given. The authors emphasize the importance of the worldwide standardization effort and discuss the organizations that are responsible for establishing such standards. It is pointed out that, with the limitation and inflexibility of the narrowband ISDN and the broadband ISDN, issues for higher-rate services have become prominent. For broadband services, the problem is not merely increasing the speed of the operation. It affects the compatibility of switching technology, the workability of the local loop arrangement, the availability of rate adaption, and the efficiency of bandwidth utilization. Although some basic principles of narrowband ISDN can be carried to broadband ISDN, the technology is quite different. For example, the interconnection and transmission problems of video, HDTV, (high-definition television), and high-speed data are different from those of voice. Thus, the standard 64-kb/s B channel itself, the fundamental rate of ISDN transmission, appears inadequate for wideband services. At present, the solution is to establish the multiples of 64 kb/s for accommodation of broadband or higher rates     

Research on Advanced Switching Techniques for the Evolution to ISDN and Broadband ISDN

Switching techniques for packetized data and for video communications are a key element in the evolution of the central office from IDN, to ISDN, and to broadband ISDN. An evolutionary scenario, based both on a short-term and on a longterm reference architecture for the switching system, is proposed, and two advanced switching techniques for labeled switching and for diffusive video switching, respectively, are analyzed which match the above scenario well. Plans and preliminary results are also reported on experimental research through laboratory demonstrators of the two switching techniques.     

A promising application for broadband ISDN: Hypermedia teleconference

The optimum BISDN teleconference service for business, called hypermedia teleconference, is designed based on research into typical business activities and ATM, the most promising BISDN architecture. Service characteristics are determined by analysing the daily work practices of a large set of businessmen. It is shown that communication tasks occupy 44 per cent of the working day. The analysis further shows that some 60 per cent of all communication tasks could be performed through an advanced digital teleconference service. Hypermedia teleconference is designed to satisfy the needs of business through personal communication terminals and ATM public networks. The terminals effectively allocate the BISDN's high-speed transmission capability between a number of subchannels that realize distributed multipoint connection links and multimedia paths. The terminals use a new variable-bit-rate ATM codec created to realize high quality video. Users can easily create full featured teleconferences without a centralized connection facility. Terminals allow the synergistic combination of video, voice, telewriting, telepointing and document transmission services.     

Theoretical analysis of the ADPCM CCITT algorithm

The unfavorable effects of narrowband inputs on the decoder adjustment when the LMS algorithm is used are analyzed. An explanation is given for the behavior of the CCITT algorithm. Suboptimality of prediction is granted to achieve adjustment, resulting in a satisfactory tradeoff between reduction rate and adjustment. The link between adjustment and uniform stability is enhanced     

Transfer efficiency of the CCITT error-protection method

In this letter, the transfer efficiency of the CCITT V.41 error-protection method is determined, pointing out that it is better at a high error rate and long transmisson block than had previously been estimated.     

ISDN: a customer perspective

Early projected benefits of the integrated services digital network (ISDN) are evaluated from a customer premises equipment (CPE) perspective. It is argued that economic conditions continue to affect ISDN investment in the USA. Worldwide customer acceptance of ISDN is contrasted with earlier projections and shown to be running at about 25% of earlier projections. IBM's current ISDN product set is discussed briefly. Even though the rollout of services has not yet achieved expectations, IBM believes the potential for ISDN use by customers is significant