Gonzalo Camarillo
 |
| SIP Demystified |
This book was possible thanks to my management in Ericsson Finland,
namely Christian Engblom, Jussi Haapakangas, Rolf Svanbäck, Roger
Förström, and Stefan Von Schantz. Their encouragement was essential in
the first stages of the book. They together with Carl Gunnar Perntz and
Olle Viktorsson, from Ericsson Sweden, let me go to Columbia University
in New York to work together with Professor Schulzrinne when I was finishing
writing SIP Demystified.
Professor Schulzrinne's advice and guidance has been very important
to me since I began working on SIP-related issues, when SIP was still a
brief Internet draft within the MMUSIC working group.
Miguel Angel GarcÃa and Jonathan Rosenberg provided guidance and
detailed comments. Their reviews of the manuscript contributed to
improve the final product.
Last but not least, Marjorie Spencer, my editor at McGraw-Hill, did a
terrific work on the manuscript. She deserves recognition for her impact
on the final manuscript. She provided new ideas and different points of
view that helped make the technical explanations contained in this book
clearer to readers with all types of backgrounds.
FOREWORD
Unbeknownst to those outside the field of telecommunications, a quiet
revolution is taking place. This revolution is aimed at overthrowing the
decades-old technologies, now long past their prime, which are the cornerstone
of today’s wired and wireless telecommunications networks. This
revolution will free people from the high cost and low value-add of many
telecommunications services, and bring them into the low cost and high
value-added services that are the norm on the Internet. The revolution is
not being fought with swords or guns, but rather, with technologies—
Internet technologies—which are being used to completely redefine the
architecture of telecommunications networks. At the lead of this quiet revolution
is the Session Initiation Protocol (SIP), an Internet standard
developed by the Internet Engineering Task Force (IETF).
Ever heard of SIP? Probably not—and that’s the problem. Up until now,
knowledge of SIP and its related technologies has been the domain of the
technology elite. However, the changes in the telecommunications industry
that SIP is causing are important for many people—from technology
managers to businessmen to enterprise network administrators. These
people don’t need to know the details of the technology, but they need to
appreciate its importance and understand how it might impact their
work. That is where this book fits in. SIP Demystified is not a book
for software developers or protocol engineers. It’s a book for a much
broader audience that helps provide context for SIP and an appreciation
for its purpose, basic operation, and relationship to other protocols and technologies.
Gonzalo Camarillo does an excellent job walking the fine line between
technical completeness and technology overviews. Gonzalo has been an
important contributor to the SIP revolution. He is the author of several
of the key documents being developed within the standards bodies. He is
an active contributor on the mailing lists, and a good teacher for those
who have basic questions. It is this combination of technical depth and
teaching skills that have resulted in a fine book, which I wholeheartedly
recommend to anyone who asks the question, "what is SIP, and why is it important?"
As one of the co-authors of SIP, I have dedicated several years of my
life to its development. I have seen it grow from an academic technology
to a force that is changing the way telecommunications will work in the
years to come. It is truly impressive that throughout its growth, the fundamental
goals and principles on which the technology was built have not
changed. This has happened because of the cadre of people who have come
to believe in the vision SIP presents, and who have worked to promote it
within their organizations. Gonzalo has captured that vision in a book,
and so I encourage you, reader, to turn the page and learn more about
what the future of telecommunications will look like.
DR. JONATHAN ROSENBERG
CO-AUTHOR, SESSION INITIATION PROTOCOL
CHIEF SCIENTIST, DYNAMICSOFT INC.
PREFACE
The Session Initiation Protocol (SIP) has gained a lot of attention over the
last few years. Lately, the decision to use SIP as the signalling protocol to
provide IP multimedia services in the third generation of mobile systems
has dramatically increased the number of people interested in knowing
about SIP. SIP is the protocol that will merge together the cellular and
the Internet worlds. It will provide ubiquitous access to all the services
that have made the Internet so successful . Users will be able to combine
traditional Internet services such as e-mail and the Web with newer services
such as multimedia and instant messaging.
Although the services that SIP can provide are relatively well known,
there is a lack of knowledge about the protocol itself. SIP is seen by many
people as a protocol that can resolve every problem one could imagine,
when in reality, SIP has a limited well-defined scope. During all the years
that I have been working on SIP standardization, I have heard this and
many other misconceptions several times. That was the main reason that
pushed me to write this book. This book intends to clarify the philosophy behind SIP.
In order to have a good understanding of a protocol such as SIP, it is
necessary to be able to answer three simple questions: what, how, and
why. This book deals with all three of them, but sets a special focus on the
last one: why. The reason for doing so is from my own experience of speaking
with several engineers and programmers. I was surprised to meet people
that have a great knowledge about what SIP does and how it does it,
but who did not understand the philosophy behind the protocol. They did
not know why SIP was designed like it was. They understood the protocol
details but were missing the overall picture. The trees did not let them
see the forest. The why part is also very useful for business managers
who do not need to know the protocol details in depth, but need to understand
why to use a particular technology in their products. It would be
sad if SIP was used just because it is fashionable and not for all its good features.
In order to understand why SIP is a good signaling protocol, it is
necessary to know the paradigm behind it and compare it with another
paradigm to see its advantages. That is why Chapter 1, “Signaling in
last few years. Lately, the decision to use SIP as the signalling protocol to
provide IP multimedia services in the third generation of mobile systems
has dramatically increased the number of people interested in knowing
about SIP. SIP is the protocol that will merge together the cellular and
the Internet worlds. It will provide ubiquitous access to all the services
that have made the Internet so successful . Users will be able to combine
traditional Internet services such as e-mail and the Web with newer services
such as multimedia and instant messaging.
Although the services that SIP can provide are relatively well known,
there is a lack of knowledge about the protocol itself. SIP is seen by many
people as a protocol that can resolve every problem one could imagine,
when in reality, SIP has a limited well-defined scope. During all the years
that I have been working on SIP standardization, I have heard this and
many other misconceptions several times. That was the main reason that
pushed me to write this book. This book intends to clarify the philosophy behind SIP.
In order to have a good understanding of a protocol such as SIP, it is
necessary to be able to answer three simple questions: what, how, and
why. This book deals with all three of them, but sets a special focus on the
last one: why. The reason for doing so is from my own experience of speaking
with several engineers and programmers. I was surprised to meet people
that have a great knowledge about what SIP does and how it does it,
but who did not understand the philosophy behind the protocol. They did
not know why SIP was designed like it was. They understood the protocol
details but were missing the overall picture. The trees did not let them
see the forest. The why part is also very useful for business managers
who do not need to know the protocol details in depth, but need to understand
why to use a particular technology in their products. It would be
sad if SIP was used just because it is fashionable and not for all its good features.
In order to understand why SIP is a good signaling protocol, it is
necessary to know the paradigm behind it and compare it with another
paradigm to see its advantages. That is why Chapter 1, “Signaling in
the Circuit Switched Network,” provides an introduction to traditional
telephone signaling. This brief introduction helps the reader understand
why a paradigm shift was needed, and the advantages and disadvantages
of the Internet paradigm.
An introduction to packet switching and to IP has been added at the
beginning of Chapter 2, “Signalling in the Packet-Switched Network.”
This introduction is intended for those professionals who have experience
in the telecom world and are trying to jump into the new datacom technologies.
They will find advantages and disadvantages of packet switching
networks and why IP, and not other network layer protocols, is used
to implement packet based services in modern networks.
The remainder of Chapter 2 and Chapter 3, “The Internet Multimedia
Conferencing Architecture and How Protocols Mature,” set SIP in its context.
They describe how SIP interacts with other protocols (the Internet
multimedia conferencing architecture), and how SIP standardization is
carried out within the Internet Engineering Task Force (IETF). This gives
the reader an idea of the different maturity levels of the different SIP
extensions and what they mean. Knowing the Internet multimedia conferencing
architecture is useful in order to understand the scope of SIP
and of the rest of the protocols that belong to the architecture. All these
protocols interact among them to provide multimedia services to the users.
Chapter 4, “The Session Initiation Protocol,” through Chapter 6,
“Extending SIP: The SIP Toolkit,” deal more with what and how, without
forgetting about why. However, these two concepts are kept separate as
much as possible. It is important to distinguish between the functionality
provided by SIP, and the protocol details of how this functionality is
achieved. Understanding first what the protocol does, it is easier to study
how it is implemented. Chapter 4 deals with what SIP does wheras Chapter
5, “SIP: Protocol Operation,” explains the protocol syntax. This distinction
is also present in Chapter 6, where several SIP extensions are
explained. Every extension is clearly divided into two sections: the first
one explains what the extension does, and the second deals with its implementation.
Finally, Chapter 7, “Building Applications with the SIP Tookit,” provides
examples of architectures that have chosen SIP as a signaling
protocol, such as 3G or PacketCable.
After reading this book you will have a good understanding of the three
aspects of SIP: what, how, and why. You will be able to understand its role
in different architectures and its interactions with other protocols. Furthermore,
you will be able to decide if SIP is the proper tool to use in order
to resolve your problem and if so, what other tools you will also need to
build the architecture that suits your application better. It is good to
always keep in mind that rather than being in an isolated protocol, SIP
is part of the Internet multimedia conferencing architectures—a set of
protocols that combined can be used to provide multimedia services.
Screenshot
Purchase Now !
Just with Paypal
Just with Paypal
Product details
Price
|
|
|---|---|
File Size
| 5,359 KB |
Pages
|
284 p |
File Type
|
PDF format |
Print Version
| 0-07-137340-3 |
Copyright
| 2002 by The McGraw-Hill Companies, Inc |
Table of Contents
Preface xiii
Foreword xvii
Chapter 1 Signalling in the Circuit-Switched Network
The Origins of Circuit-Switching 3
Characteristics of Circuit-Switching 6
Strengths of Circuit-Switching 6
Weaknesses of Circuit-Switching 7
Introduction to Signalling 8
FDM and In-band Signalling 11
Analog Transmission 12
Digital Transmission 13
Time Division Multiplexing 15
Digital Signalling Systems 16
Access Signalling 18
Trunk Signalling 19
SS7 23
The Paradigm Behind SS7 25
Conclusions 28
Chapter 2 Packet Switching, IP, and the IETF
Packet Switching 30
Strengths of Packet Switching 35
Weaknesses of Packet Switching 36
X.25 36
IP and the Internet Paradigm 37
IP Connectivity 37
Intelligence Pushed to the End Systems 38
End-to-End Protocols 41
General Design Issues 42
History of the Internet Protocol Development Process 45
Origins of the Request For Comments (RFCs) 45
Coordination Bodies 46
The IETF 48
The IESG 49
The Technical Work 49
IETF Specifications: RFCs and I-Ds 50
Chapter 3 The Internet Multimedia Conferencing Architecture
The Internet Layered Architecture 56
Transport Layer Protocols 57
Real-Time Services in the Internet 59
Multicast 62
Routing Towards Many Receivers 62
Advantages of Multicast 64
Multicast Routing Protocols 65
IGMP 68
The Mbone 70
Transport of Real-Time Data: RTP 70
Jitter and Sequencing of Datagrams 71
Real-Time Transport Control Protocol 73
QoS Provisioning: Integrated Services and Differentiated Services 74
Integrated Services 74
Differentiated Services (DiffServ) 79
Session Announcement Protocol (SAP) 81
Session Descriptions 82
Session Description Protocol (SDP) 82
SDP Syntax 83
SDP Next Generation (SDPng) 86
Real-Time Streaming Protocol (RTSP) 87
Usage Example of the Internet Multimedia Conferencing Toolkit 87
Chapter 4 The Session Initiation Protocol: SIP
SIP History 90
Session Invitation Protocol: SIPv1 91
Simple Conference Invitation Protocol: SCIP 92
Session Initiation Protocol: SIPv2 92
Functionality Provided by SIP 94
Session Establishment, Modification, and Termination 94
User Mobility 96
SIP Entities 98
User Agents 98
Redirect Servers 102
Proxy Servers 103
Registrars 105
Location Servers 105
Good Features of SIP 106
SIP Is Part of the IETF Toolkit 106
Separation Between Establishing and Describing a Session 108
Intelligence in the End System: End-to-End Protocol 109
Interoperability 109
Scalability 110
SIP as a Platform for Service Creation 110
Chapter 5 SIP: Protocol Operation
Client/Server Transactions 116
SIP Responses 116
SIP Requests 117
Types of Proxy Servers 126
Call Stateful Proxy 127
Stateful Proxy 127
Stateless Proxy 129
Distribution of Proxies 129
Format of SIP Messages 130
SIP Request Format 132
SIP Response Format 132
SIP Headers 134
SIP Bodies 142
Transport Layer 144
INVITE Transactions 144
CANCEL Transactions 148
Other Transactions 150
Detailed Example 151
SIP Call Through a Proxy 151
Chapter 6 Extending SIP: The SIP Toolkit
Extension Negotiation 160
How It’s Done 161
Design Principles for SIP Extensions 162
Do Not Break the Toolkit Approach 163
Peer-to-Peer Relationship 163
Independence from Session Type 164
Do Not Change Method Semantics 164
Extensions to SIP 165
The SIP Toolkit 165
Reliable Delivery of Provisional Responses 165
Mid-session Transactions That Do Not Change the State
of the Session 169
Multiple Message Bodies 170
Instant Messages 171
Automatic Configuration of UAs 172
Preconditions to Be Fulfilled Before Alerting 174
Caller Preferences 176
Asynchronous Notification of Events 179
Third-party Call Control 181
Session Transfer 184
Sending Commands 186
SIP Security 187
Chapter 7 Building Applications with the SIP Toolkit
Third-generation Mobile Systems 192
Network Domains 193
Call Flow Examples 195
Instant Messages and Presence 199
SIMPLE Working Group 199
Presence Architecture 200
Instant Messaging 201
PacketCable 202
Architecture 203
Call Flow Example 203
PSTN to SIP Interworking 204
Low-Capacity Gateways 207
High-Capacity Gateways 209
SIP Extensions for PSTN Interworking 210
The PINT Service Protocol 213
SIP for Conferencing 214
Multicast Conferences 215
End User Mixing Model 215
Multipoint Control Unit (MCU) 216
Decentralized Multipoint Conference 217
Control of Networked Appliances 219
Appendix Finding Futher Information on SIP 221
IETF Web site 221
Henning Schulzrinne’s SIP Web page 223
Dean Willis’ Web Pages 225
The SIP forum 226
RFC example 227
RFC 229
Acronyms 239
References 245
Index 251
●▬▬▬▬▬❂❂❂▬▬▬▬▬●
●▬▬❂❂▬▬●
●▬❂▬●
●❂●
═════● ●═════
