Chuyển đổi lý thuyết P1

Broadband Integrated Services Digital NetworkA broad overview on the Broadband Integrated Services Digital Network (B-ISDN) is here given. The key issues of the communication environment are first outlined (Section 1.1). Then the main steps leading to the evolution to the B-ISDN are described (Section 1.2), by also discussing issues related to the transfer mode and to the congestion control of the B-ISDN (Section 1.3).
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Chuyển đổi lý thuyết P1 Switching Theory: Architecture and Performance in Broadband ATM Networks Achille Pattavina Copyright © 1998 John Wiley & Sons Ltd ISBNs: 0-471-96338-0 (Hardback); 0-470-84191-5 (Electronic)Chapter 1 Broadband Integrated Services Digital NetworkA broad overview on the Broadband Integrated Services Digital Network (B-ISDN) is heregiven. The key issues of the communication environment are first outlined (Section 1.1). Thenthe main steps leading to the evolution to the B-ISDN are described (Section 1.2), by also dis-cussing issues related to the transfer mode and to the congestion control of the B-ISDN(Section 1.3). The main features of the B-ISDN in terms of transmission systems that are basedon the SDH standard (Section 1.4) and of communication protocols that are based on theATM standard (Section 1.5) are also presented.1.1. Current Networking ScenarioThe key features of the current communication environment are now briefly discussed,namely the characterization of the communication services to be provided as well as the fea-tures and properties of the underlying communication network that is supposed to support theprevious services.1.1.1. Communication servicesThe key parameters of a telecommunication service cannot be easily identified, owing to thevery different nature of the various services that can be envisioned. The reason is the rapidlychanging technological environment taking place in the eighties. In fact, a person living in thesixties, who faced the only provision of the basic telephone service and the first low-speed dataservices, could rather easily classify the basic parameters of these two services. The tremendouspush in the potential provision of telecommunication services enabled by the current network-ing capability makes such classification harder year after year. In fact, not only are new servicesbeing thought and network-engineered in a span of a few years, but also the tremendous2 Broadband Integrated Services Digital Networkprogress in VLSI technology makes it very difficult to foresee the new network capabilities thatthe end-users will be able to exploit even in the very near future. A feature that can be always defined for a communication service provided within a set ofn end-users irrespective of the supporting network is the service direction. A service is unidirec-tional if only one of the n end-users is the source of information, the others being the sink; atypical example of unidirectional service is broadcast television. A service is multidirectional if atleast one of the n end-users is both a source and a sink of information. For decades a multidi-rectional telecommunication service involved only two end-users, thus configuring abidirectional communication service. Only in the seventies and eighties did the interest in pro-viding communication service within a set of more than two users grow; consider, e.g., theelectronic-mail service, videoconferencing, etc. Apparently, multidirectional communicationservices, much more than unidirectional services, raise the most complete set of issues relatedto the engineering of a telecommunication network. It is widely agreed that telecommunications services can be divided into three broadclasses, that is sound, data and image services. These three classes have been developed and grad-ually enriched during the years as more powerful telecommunication and computing deviceswere made available. Sound services, such as the basic telephone service (today referred to asplain old telephone service - POTS), have been provided first with basically unchanged servicecharacteristics for decades. Data services have started to be provided in the sixties with theearly development of computers, with tremendous service upgrades in the seventies and eight-ies in terms of amounts of information transported per second and features of the data service.For about three decades the image services, such as broadcast television, have been providedonly as unidirectional. Only in the last decade have the multidirectional services, such as videoon demand, videotelephony, been made affordable to the potential users. Communication services could be initially classified based on their information capacity,which corresponds to the typical rate (bit/s) at which the information is required to be carriedby the network from the source to the destination(s). This parameter depends on technicalissues such as the recommendations from the international standard bodies, the features of thecommunication network, the required network perfor ...