Introduction

Introduction

		First there was ISDN, and then came ''portable" 800 numbers. Soon, cellular providers were talking of tying their networks together so subscribers could roam from one cellular network to another without special roaming numbers. And now, we are talking over the Internet using our computers as telephones.

		But during all of these discussions, nothing (or at least very little) has been mentioned about how all of this is possible. How is it possible that many networks can communicate with one another, and what control mechanism is used to maintain the connections and data communications?

		Behind the scenes is a quiet, highly reliable, fault-tolerant data communications network that links the world's telephone networks together and allows them to share vital signaling and control information. This one network, which controls telecommunications networks around the world, is being prepared to control the broadband networks that will form the framework for tomorrow's "Information Highway."

		This data communications network is so robust, so sophisticated, that few really know much about it. Only recently has anything been written about this network, and what information does exist has been sparse and ambiguous. The very standards that define the network are written to answer the needs of so many different audiences that they remain vague and reliant on reader interpretation.

		This network, often dubbed the world's largest data communications network, is known as Signaling System #7 (SS7). It started as a way to access 800 databases here in the U.S., although its functions provide much more. Soon SS7 was being used to send signaling information from exchange to exchange. Today, the same network is being used to control central office switching equipment from remote locations.

		SS7 is really a control network, as well as a signaling network. This is important to understand, because as the Information Highway rolls out, and as the Advanced Intelligent Network (AIN) is implemented, SS7 will be relied on almost exclusively as a means for telephone companies and other service providers to share database information and switching control without human intervention.

		Already we are seeing SS7 play an important role in Local Number Portability (LNP), a new requirement for all telephone service providers (both wireline and wireless) defined in the Telecommunications Act of 1996. SS7 continues to grow in use and function, as the industry discovers new uses for this powerful technology.

		Without SS7, AIN is not possible. Cellular roaming is not seamless. 800 numbers are not portable. And the many features and services we take for granted today (such as caller ID) would not be feasible.

		When someone asks me how to break into the telecommunications field, I provide one suggestion: Learn SS7. Every telephone company needs it. Every manufacturer develops around it, yet there is a lack of expertise in SS7 in this country. That is what this book is all about.

		As I began studying SS7 protocols and began providing seminars around the country, I came to the conclusion that there is no reference material available that provides a comprehensive view of SS7: nothing to explain the various acronyms and the true applications of this network.

		Hence the reason for this book. If you are looking for more than a reference book a tutorial on SS7, a text book which provides realworld applications, and a futuristic look at the telephone networks read on.

		The intent of this book is to provide a comprehensive introduction to this fascinating network and its protocols, as well as a reference for those already familiar with SS7. Although the various standards are always the best source for specific details, this book provides something the standards do not: explanations as to when and why procedures are used and what they mean to the network, the subscriber, and the service provider.

		Although it is based on ANSI and Bellcore standards, the text is of value to anyone seeking knowledge about SS7 networks. Although the message types and the protocol parameters may be different between countries, the principles and applications are universal.

I hope you find this to be as fascinating as I did while writing this book. Truly, we are at an exciting period for the telecommunications industry, as new services and applications are defined almost monthly. Keeping up with all of the new technologies and advances can be a dizzying experience. Yet the future is today, and this technology is a key player in making it all happen.

		TRAVIS RUSSELL