Über die Autorin bzw. den Autor

Dr. Henry Sinnreich (Richardson, TX) is Chief Technology Officer at Pulver.com, a leading media company for VoIP and Internet communication services. Dr. Sinnreich has held engineering and executive positions at MCI where he was an MCI fellow and has been involved in Internet and multimedia services for more than 12 years, including the development of the flagship MCI Advantage service based on SIP. Henry Sinnreich is also a contributor to IETF standards for Internet communications in such areas as SIP telephony devices and using RTP extensions for voice quality monitoring. He was awarded the title Pioneer for VoIP in 2000 at the VON Europe conference. Henry Sinnreich has been a cofounder and board member of the International SIP Forum based in Stockholm. He is a frequent speaker and is known as the leading evangelist, worldwide, for SIP based VoIP, presence, IM, multimedia, and integration of applications with communications. Dr. Sinnreich is also a guest lecturer at the Engineering School of the Southern Methodist University in Dallas, TX.

Alan B. Johnston (St. Louis, MO) is a Consulting Member of Technical Staff at Avaya, Inc. He has coauthored the core Internet SIP standard RFC 3261 and four other SIP related RFCs. He is the co-chair of the IETF Centralized Conferencing Working Group and is on the board of directors of the International SIP Forum. His current areas of interest include peer-to-peer SIP and security. Dr. Johnston is a frequent speaker and lecturer on SIP and contributor to various publications, and is an adjunct professor at Washington University in St. Louis, MO.

Von der hinteren Coverseite

"This book is like a good tour guide.It doesn't just describe the major attractions; you share in the history, spirit, language, and culture of the place."
―Henning Schulzrinne, Professor, Columbia University

Since its birth in 1996, Session Initiation Protocol (SIP) has grown up. As a richer, much more robust technology, SIP today is fully capable of supporting the communication systems that power our twenty-first century work and life.

This second edition handbook has been revamped to cover the newest standards, services, and products. You'll find the latest on SIP usage beyond VoIP, including Presence, instant messaging (IM), mobility, and emergency services, as well as peer-to-peer SIP applications, quality-of-service, and security issues―everything you need to build and deploy today's SIP services.

This book will help you

• Work with SIP in Presence and event-based communications
• Handle SIP-based application-level mobility issues
• Develop applications to facilitate communications access for users with disabilities
• Set up Internet-based emergency services
• Explore how peer-to-peer SIP systems may change VoIP
• Understand the critical importance of Internet transparency
• Identify relevant standards and specifications
• Handle potential quality-of-service and security problems

Aus dem Klappentext

"This book is like a good tour guide.It doesn't just describe the major attractions; you share in the history, spirit, language, and culture of the place."
—Henning Schulzrinne, Professor, Columbia University

Since its birth in 1996, Session Initiation Protocol (SIP) has grown up. As a richer, much more robust technology, SIP today is fully capable of supporting the communication systems that power our twenty-first century work and life.

This second edition handbook has been revamped to cover the newest standards, services, and products. You'll find the latest on SIP usage beyond VoIP, including Presence, instant messaging (IM), mobility, and emergency services, as well as peer-to-peer SIP applications, quality-of-service, and security issues—everything you need to build and deploy today's SIP services.

This book will help you

• Work with SIP in Presence and event-based communications
• Handle SIP-based application-level mobility issues
• Develop applications to facilitate communications access for users with disabilities
• Set up Internet-based emergency services
• Explore how peer-to-peer SIP systems may change VoIP
• Understand the critical importance of Internet transparency
• Identify relevant standards and specifications
• Handle potential quality-of-service and security problems

Auszug. © Genehmigter Nachdruck. Alle Rechte vorbehalten.

Internet Communications Using SIP

John Wiley & Sons

Chapter One

The telecommunications, television, and information technology (IT) network industries are all transformed by the Internet. The transformation is driven by the need for growth based on new services, more complete global coverage, and consolidation. In this chapter, we will explore some of the problems and solutions for end users and every type of business because of the profound disruptions caused by the Internet.

Problem: Too Many Public Networks

Before the emergence of the Internet, users and service providers were generally accustomed to thinking in terms of four distinct network types: Networks for IT (data), networks for voice, mobile networks, and networks for television. Each of these dedicated network types could, in turn, be divided into many incompatible regional and even country-specific flavors with different protocol variants.

Thus, we find many types of telephony numbering plans, signaling, and audio encodings; several TV standards; and various types and flavors of what the telecom industry calls data networks-all of them incompatible and impossible to integrate into one single global network.

The mobile telephone networks have converged on a smaller number of standards in the second generation (2G) networks and in the emerging third generation (3G) mobile networks. It may turn out, however, that with the proliferation of new radio technologies for the so-called 4th generation (4G), such as Wi-Fi and WiMAX, all modern mobile networks will become just a wireless access mechanism to the Internet, where all public communications, entertainment, and applications will reside anyhow.

Data networks that originated in the telecom industry came in many forms, such as digital private lines, X.25, Integrated Services Digital Network (ISDN), Switched Multimegabit Data Service (SMDS), Frame Relay, and Asynchronous Transfer Mode (ATM) networks. These so-called data networks were mostly inspired by circuit-switched telephony concepts. Their names are meant to suggest that they were not designed primarily to carry voice.

Voice networks are still used for data and fax because of their general availability, though less and less so. However, these networks have come to the end of their evolution, since they are fundamentally optimized for voice only. TV networks were designed and optimized for the distribution of entertainment video streams.

Needless to say, all network types (data, voice, TV, and mobile) have specific end-user devices that cannot be ported to other service providers or network types, and most often cannot be globally deployed.

The impact of the Internet has made the wired and wireless phone companies and the TV cable companies look for new business models that can take advantage of Internet technologies and protocols, among them the Session Initiation Protocol (SIP) for real-time communications, such as Voice over IP (VoIP), instant messaging (IM), video, conferencing/collaboration, and others. Examples of the various categories and their business models are illustrated in Table 1.1. We assume that most readers are familiar with the acronyms used in the table, and we also explain these acronyms and terms in the book. They can also be found in the index.

The proliferation of isolated communication islands as shown in Table 1.1 makes them less useful as their number keeps increasing (think of many more communication islands all over the world). Building communication islands (also called "walled gardens") is in conflict with Metcalfe's law that the value of the network increases by the square of the number of connected endpoints. Last, but not least, in case of an emergency, having many networks that cannot communicate directly is not very helpful.

Closed networks are an impediment for innovation, since innovators must work (technology and legal agreements) with every closed network separately to bring a new service or product to market. By contrast, the Internet extends the reach for new applications and services instantly to the whole world.

Another observation from Table 1.1 is that the strongest financing available is at present for closed networks (walled gardens), the ones that are most limited in reach and usefulness. This raises business issues and regulatory questions (what are the public interest obligations, if any?) that are beyond the scope of this book.

Incompatible Enterprise Communications

Enterprise communication systems are often an even greater mix of incompatible and disjoint systems and devices:

* Proprietary PBX and their phones. Phones from one PBX cannot be used by another.

* Instant messaging is a separate system from the PBX.

* Various IM systems don't talk to each other.

* Voice conferencing and web-based collaboration use yet other systems.

Maintaining various incompatible and nonintegrated proprietary enterprise systems is quite costly and reduces the overall productivity of the workforce.

Network Consolidation: The Internet

The Internet has benefited from a number of different fundamentals compared to legacy networks, such as the tremendous progress of computing technology and the open standard Internet protocols that define it. This progress can be attributed to the expertise of the research, academic, and engineering communities whose dedication to excellence and open collaboration on a global basis have surpassed the usual commercial pressure for time-to-market and competitive secrecy.

The result is an Internet that uses consistent protocols on a global basis, and is equally well suited to carry data, transactions, and real-time communications, such as instant messaging (IM), voice, video, and conferencing/collaboration. Actually, the Internet is the "dumb network," designed for any application, even those not yet invented. This is in stark contrast to the isolated "walled gardens" with central control of all services illustrated in Table 1.1.

Voice over IP

Although the Internet has quickly established itself as the preeminent network for data, commercial transactions, and audio-video distribution, the use of voice over the Internet has been slower to develop. This has less to do with the capability of the Internet to carry voice with equal or higher quality than the telephone network but rather with the complex nature of signaling in voice services, as you will see in Chapter 6, "SIP Overview."

There are various approaches for voice services over the Internet, based on different signaling and control design. Some examples include the following:

* Use signaling concepts from the telephone industry-H.323, MGCP, MEGACO/H.248.

* Use control concepts from the telephone industry-central control and softswitches.

* Use the Internet-centric protocol-Session Initiation Protocol (SIP), the topic of this book.

The movement from such concepts as telephony call models to discovery/ rendezvous and session setup between any processes on any platform anywhere on the Internet is opening up completely new types of communication services.

The use of SIP for establishing voice, video, and data sessions places...