om technologies are addressed at a high level only, to maintain the focus on network management OSS. Therefore, the book will be useful to those without an engineering or telecom background who just want to learn about network management OSS. At the same time, the book will be useful to engineers who are familiar with some areas of telecommunications but not with network manage- ment OSS. In preparing the book, we have kept in mind the author's experience of not many years ago when, with no knowledge of telecommunications, he joined a network management OSS vendor. At that time, the author keenly felt the need for a book on network management OSS which could clearly introduce network management OSS and explain how it worked. He also observed that in order to get these basic ques- tions answered, he was required to read hundreds of pages on telecom technologies such as asynchronous transfer mode (ATM), synchronous optical network (SONET), code division multiple access (CDMA), etc. In fact, as a telecom and network management OSS beginner, it was difficult to find any suitable book that focused on network management OSS. As far as possible, we spare the reader details of specific network technologies. Of course, some introduction to specific network technologies is necessary, because it is hard to talk about any type of management without some knowledge of what is being managed. We give an especially long introduction to ATM technology as it is such a dominant transmission technology. We cover many excellent OSS products in this book but acknowledge that others have been left out. We do not claim that this book is comprehensive in describing the best OSS products on the market, although the ones that we do describe are among the best. Many OSS vendors were extremely helpful when approached for assistance. We received more offers to examine particular products in detail than we had time to accept. Many more vendors assisted with and influenced this book than the number of products that are explicitly described. We s