Pragmatic Introduction of Digital Switching and Transmission in Existing Networks

Introduction of digital Switching and transmission in existing networks depends on a multiplicity of factors, which are either network or system dependent. Digital network planning alternatives are discussed with reference to the introduction techniques (stand alone or integrated switching and transmission) and to the interconnection strategies with the analog network. A pragmatic approach with distributed tandem exchanges is proposed, and various network scenarios are presented with reference to different starting points including toll, local tandem, rural area and local terminal levels. A possible transition scenario for a progressive implementation of Integrated Service Digital Networks (ISDN) is also indicated. Finally, the main features and advantages of the pragmatic approach are presented.     

Dynamic operation and maintenance systems for switching networks

Some important concepts and techniques related to dynamic operation and maintenance (O&M) systems for switching networks are demonstrated. Five types of node that comprise the dynamic network O&M system being developed by the authors are discussed. They are local exchanges, a centralized operation system, a database system, a diagnostics expert system, and maintenance workstations. The nodes are implemented on an efficient distributed system and use a standardized interface. This O&M system, which is geared toward improved maintenance, focuses on the switching network as a whole, rather than on individual exchanges. In the case of alarms and fault messages, O&M takes corrective action automatically     

An architecture for IP over WDM using time-division switching

This paper proposes an architecture for routing Internet protocol (IP) packets directly on optical networks. The use of label switching is assumed in the IP routers, while a new routing architecture is introduced to transport IP packets across an optical backbone network. The architecture is based on a two-tier multiplexing approach with wavelength division multiplexing (WDM) addressing the number of regional exchanges and time-division switching communicating among the hubs. Such an architecture not only has the advantages of simple network management and high efficiency with low latency; it also is scalable by addition of regional exchanges, hubs, and fibers     

Public telecoms networks. Is the UK on the right line?

The introduction of digital telephone exchanges, among other factors, is causing telephone operators worldwide to set their standards for the new systems. The UK is following a slightly different path from most other countries. The main differences cover equipment specification and approval, and the installation, operation and maintenance of new equipment. British Telecom has opted for a strategy based largely on the hierarchical technique-a separate digital overlay network of 53 main switching networks interlinked by CCITT Number 7 signalling. The author discusses how this differs from the digital-island technique used in other countries. The UK regulatory situation, standards and administration practices are also discussed     

Considerations on analog and digital electronic switching networks and their applications

It is expected that electronics will play a major role in the next decades in the implementation of switching networks for telephone exchanges, as it has already happened both in transmission and exchange control [1]. Making use of many results of the referenced literature, some considerations are presented in order to compare electronic analog and digital switching networks for telephone exchanges. Some of the highlighted aspects show the more significant tradeoffs to be considered when choosing an electronic switching network. Electromechanical switching is not considered here, but some reference is made when necessary. After some preliminary analysis of the telephony signals and their impact on the design and the characteristics of the switching networks, typical problems of practical relevance are then considered. Furthermore, a general comparison between the various techniques is discussed from an economical point of view, with reference to local and transit application areas.     

An Experimental Local PCM-Switching System

This paper discusses a local PCM switching network. The characteristics of this network are demonstrated with a model of three local exchanges. All subscribers are connected with the exchange via concentrators. An exchange is controlled by a central processor with a stored program. This processor interacts with the peripheral switching units, represented by the central switching network and two types of control circuits, located within the exchange. These control circuits control either the concentrators or they communicate with counterparts, situated in other local exchanges. All control functions that are not executed by programs of the central processor are realized by microprograms in a wired read-only storage (ROS) in these peripheral control circuits.     

Advanced architecture for a one-chip 16×16 digital switch

A one-chip 16×16 digital switch (SWEL) is presented which is designed for use in a wide variety of applications, ranging from digital mobile radio and satellite applications, to PCM switching systems (integrated services digital network). It provides a compact, low-power solution to perform in channel-controlled switching of 64-kb/s or 2-Mb/s channels. Both architecture and design issues are discussed in detail; a 1.2 μm double metal CMOS technology was employed in the design. The multiplexed architecture allows for easy implementation of new application-specific requirements, making this circuit the cornerstone for new telecommunication switching products     

Dr. Hiroshi Inose's pioneering contributions to digital switching systems and his outstanding leadership in informatics

The idea of time slot interchange (TSI), the fundamental concept of implementing time switches in digital switching systems, was first conceived by Dr. Hiroshi Inose, then at the University of Tokyo, Japan, in 1957 while he was a visiting consultant at Bell Telephone Laboratories. The TSI collects each subscriber?s pulse code modulation (PCM)- coded voice information to be stored into a small time interval (time slot), and then aligns multiple time slots on a common transmission bus to constitute a repetitive frame. The TSI enables any time slot to be interchanged with another time slot within a frame once the time slots in the frame are buffered in memories. Thus, TSI gives the time switch functionality equivalent to Ninput by N-output space switch functionality. He built a prototype digital time-division multiplexing (TDM) electronic switching system called CAMPUS, which is based on the TSI principle, using a magnetostrictive delay line as a memory device. TSI received little attention until the end of the 1960s because memory devices were very costly. However, with the rapid advancement of semiconductor technologies in the 1970s, the TSI scheme became more widespread. TSI was first commercially deployed in 1976 as the time switch of AT&T?s no. 4 ESS, the world?s first stored-program control time-division switching system. Since then, TSI has been used in almost all digital central office switching systems and digital private branch exchanges (PBXs). Dr. Inose?s contributions were not limited to research on such things as switching systems, PCM integrated communications, computer communications, and road traffic control systems; he was also actively involved in a number of Japanese governmental and international activities in the area of communications and information processing technologies. His final work was the establishment of the National Institute of Informatics (NII) in 2000, Japan?s sole comprehensive academic institute in the field of informati     

ISDN Activities in Italy

Digitalization of the Italian telecommunications network is underway, as in many other countries, and a significant diffusion of digital transmission has already been achieved. Digital switching has already been introduced at both transit and local levels, with some 450 exchanges presently in operation. Both packet- and circuit-switched data networks are in operation. CCITT No. 7 is presently being introduced. In this network scenario, the already planned Italian developments towards the ISDN will include the provision in 1986 of 64 kbit/s digital connectivity and, two years later, the activation of a pilot ISDN service, whose main characteristics are described in the paper. An overview on further developments in ISDN research areas is also given.     

SPCE交换网络的优化实现及其元器件选用

介绍了程控交换机(SPCE)中的空分交换网络和时分交换网络,说明了网络实现中所使用的元器件和数字逻辑电路,并提出了一种典型的时分交换网络的优化实现方案,然后通过比较CMOS器件和BiCMOS器件,总结了利用BiCMOS新工艺器件构成SPCE交换网络部件的优势,最后设计了几个用于SPCE中的CMOS/BiCMOS接口/驱动器。     

Optimal Digital Switching Introduction Into the Local Network

This paper describes a local network evolution model for digital switching introduction and the associated algorithm used to determine a feasible optimal network evolution policy. Such a policy is defined by the type, location, and time of placement of digital switches and remote concentrators as well as the homing pattern, i.e., the assignment of concentrators to digital switches. In addition, the evolution policy is characterized by the mode in which the digital switch or remote concentrator is used. Two modes are considered here: 1) overlay where analog equipment is retained at a switching center, growth as well as potentially removed analog lines being served by digital eqmpment; and 2) replacement where analog switches are replaced by digital equipment. The basic cash flows considered in the economic analysis correspond to switching, trunking, and interface costs. Optimality is understood here in terms of minimizing an economic criterion such as the present worth of annual Charges (PWAC) or net present value (NPV). Results obtained using the optimization algorithm in conjunction with a real local telephone exchange network are also presented.     

Subscriber Line Testing for Digital Switching Offices

This paper presents an overview of subscriber line testing as provided in Northern Telecom's Digital World^®family of host and remote digital switching systems. Capabilities provided in Digital World satisfy the major telco needs related to subscriber line testing. The various products incorporate interfaces to external test systems as well as internal line test facilities. A new subscriber line measurement technique is identified. It offers further advantages in speed and accuracy and has many potential applications in the analog and digital switching environments.     

La commutation de paquets dans le RNIS: de (l’experimentation à I’intégration dans les systèmes*

Integrated service digital networks concepts are currently well established and a number of administrations or network operators are expecting to offer some isdn services soon on a commercial basis: most of these services currently under consideration are based on 64 kbit/s circuit switched bearer capabilities which are inherent to the integrated digital networks from which the isdns are emerging. However network evolution strategies are still under elaboration for the integration of packet switching capabilities. This paper focusses on the steps that, in the view of the French PTT Administration, are necessary to allow a smooth integration of packet switching features in the isdn while preserving a valuable coexistence with existing and well established public switched packet data networks, such as the Transpac network in France. Whilst the commercial opening of the circuit switched based isdn services is planned by 1988, following the Renan pilot, the PTT research center is carrying out the evaluation of the packet feature integration strategy in the isdn, with the Cérame experiment presented here after. Finally the Alcatel developments in relation to the support of isdn packet switched services are presented together with indications on systems impacts.     

Evolution of the Italian Telecommunication Network towards SDH

The digitalization of both transmission and switching facilities as the basis for both a high standard quality of service and the introduction of advanced network features (like intelligent network and integrated services digital network, or ISDN) is described. The development of synchronous digital hierarchy (SDH) systems is discussed, with particular attention given to the add-drop multiplexer and to management issues. The impact of the new SDH transmission equipment on the present plesiochronous network is assessed. The currently envisaged strategy for introducing SDH systems into the Italian transmission network is examined. Deploying SDH systems within large metropolitan areas, both at loop plant and urban junction levels, is discussed     

Performance enhancement of multistage interconnection networks withunit step buffering

Multistage interconnection networks (MINs) have been widely used for parallel computer systems, and also recognized as an efficient switching fabric for digital communication. In this paper, we propose a new switching mechanism for MINs called unit step buffering (USB) which significantly improves the network performance. Here each cell is allowed to move only one buffer entry position using short network cycle. The proposed USB scheme is compared to the traditional scheme by analytical modeling and computer simulation. They reveal that throughput and delay are improved about 60%-80% for practical size MINs with reasonable traffic in the asynchronous transfer mode (ATM) switching environment. Improvement on parallel computer systems with larger size packets is more significant at about 100%. More importantly, the scheme does not require any additional hardware or operational overhead     

Testing of three-stage switching networks for coupling faults

A coupling fault diagnosis procedure is proposed for digital switching networks constructed of uniform time-division switches. The procedure is executed in two phases. Each phase consists of eight test steps; the number of tests for detecting the most likely coupling faults inside a single switch is independent of the network size. The concept of primitive and convolutional test vectors is introduced in order to analyze test stimuli applied to successive switches during the test. The approach can be easily adapted for use in many modern digital exchanges     

网络简化与多业务交换

PSTN（公用交换电话网）将逐渐向分组化和宽带化的方向演变,在演变过程中,PSTN的网络简化与采用多业务交换平台,将起重要的作用。文中对这两方面作一简要介绍,说明网络简化的目标和应考虑的实际问题,包括远端交换模块和转接局、网关局的合理配置,以及大容量交换系统的选用。并以E-Cube多媒体交换系统为例,说明窄带STM（同步传送模式）和宽带ATM（异步传送模式）的综合交换,窄带业务与IP的结合,以及ATM与IP的结──MPLS（多协议标记交换）。这种多业务交换平台用在ATM／IP骨干网的边缘级,将有利于PSTN与各种新型网络互通。     

Integration of Public and Private Networks

As the designs of private automatic branch exchanges (PABX's) evolve towards "electronic offices" and incorporate aspects of the integrated services digital network (ISDN), public exchanges are themselves taking on functions that were often only found in private networks. It is therefore pertinent to question the status of the PABX as a node of the ISDN rather than as a mere customer terminal. With the present designs of PABX's, public exchanges, and the signaling systems employed, it is not possible to provide PABX extensions with all the facilities on the public network which are available to directly connected main-exchange subscribers, although facilities available over private networks continue to proliferate. This paper considers aspects of signaling via both public and private networks to ensure that there need be no restriction on the facilities offered.     

Les progrès de la commutation électronique dans le monde

Following the review of the systems developed in industrialized countries (Part. I), the current trends of electronic switching are analysed. Structure basic principles are brought out: stored program control, standardization of languages, digital techniques and integrated networks, information interchange (signalling and data transmission), distribution network, data switching, message switching. The objectives are made accessible by the improvements in microelectronics (integrated circuits and microprocessors). The development of the various concepts and means leads to converging architectures and methods for the networks as well as for the systems (functional modularity, compatibilities, distributed control), to the standardization of new services, to the centralization of maintenance and to the dynamic management of the network.