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Pearson Education
Sonet and T1: Architectures for Digital Transport Networks / Edition 2

Sonet and T1: Architectures for Digital Transport Networks / Edition 2

by Uyless D. Black, Sharleen Waters


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  • The definitive SONET guide, fully updated for the latest technologies and standards
  • In-depth coverage of SONET operations, administration, and management
  • New coverage: IP-over-SONET optical Internets, WDM integration, MPLS, and much more
  • All new chapter on SDH and SONET/SDH interworking

The professional's guide to SONET—completely updated for the latest innovations!

SONET is the transport technology at the heart of virtually every high-speed optical network. SONET and T1: Architecture for Digital Transport Networks, Second Edition gives communications engineers and other professionals an in-depth understanding of every facet of SONET technology-including breakthrough IP-over-SONET optical Internets, new techniques for integrating SONET with WDM fiber, and other key innovations.

The authors begin with an overview of SONET's goals and architecture, then present the most detailed coverage of SONET operations, administration, and management available in any book. SONET and T1: Architecture for Digital Transport Networks, Second Edition offers detailed information on the "hows" and "whys" of deploying and managing any SONET system, from architecture through maintenance, using real-life applications drawn from diverse carrier and business environments. This second edition's new coverage includes:

  • New deployment examples for metropolitan and long-haul networks
  • New passive optical applications
  • New SONET network management solutions
  • New coverage of SDH, the European SONET standard, and SONET/SDH interworking
  • New techniques for expandincapacity with WDM
  • IP-over-SONET: advantages, risks, and issues
  • SONET and MPLS

From day-to-day administration to long-term planning, SONET and T1: Architecture for Digital Transport Networks, Second Edition is your richest, most up-to-date SONET resource.

Product Details

ISBN-13: 9780130654168
Publisher: Pearson Education
Publication date: 12/26/2001
Series: Prentice Hall Series in Advanced Communications Technologies
Edition description: 2ND
Pages: 384
Product dimensions: 7.00(w) x 9.56(h) x 1.24(d)

About the Author

Uyless Black is a widely respected telecommunications consultant and lecturer with extensive operations and implementation experience in both public and private networks. His clients include Nortel, British Telecom, and major carriers throughout the U.S. His recent books include Voice Over IP, Second Edition; IP Routing Protocols; and MPLS and Label Switching Networks.

Sharleen Waters has served for fifteen years as GTE Senior Technical Instructor in Broadband Technologies, training clients such as AT&T, Nortel, Siemens, Alcatel, NEC, and Fujitsu in installing, testing, and maintaining SONET equipment.

Read an Excerpt

1: Introduction

This chapter introduces the Synchronous Optical Network (SONET) and T1 technology. A brief history of SONET is provided, as well as the reasons that SONET came into existence. We also provide a brief history of the T1 system and make a general comparison of T1 and SONET. As a prelude to later chapters, a general description is provided of the major features of SONET.

What Are SONET and T1?

Digital carrier systems, such as the well-known T1 technology, have served the telecommunications industry well for over 40 years, and they shall continue to do so for quite some time. T1 was first installed in 1962 to provide a high-speed (1.544 Mbit/s) digital carrier system for voice traffic. It was modified later to support data and video applications. In terms of communications technology, 1962 is a very long time ago. Since this date, extraordinary progress has been made in the fields of computers and communications. Many of the technical underpinnings of SONET exploit this new technology.

We have cited T1 in a previous paragraph to help explain the nature of SONET. T1 and associated systems (such as T3 and similar technology in other parts of the world) are first-generation digital transport systems. SONET is a second-generation digital transport system. Like T1, its purpose is to transport, multiplex, and switch digital signals representing voice, video, and data traffic to and from users' applications. However, T1 and SONET differ significantly in how they accomplish these functions. Many facets of the T1 architecture are based on technology that is over four decades old. In contrast to T1, the SONET architecture is based on the technology of today. With this brief comparison in mind, let us take a look at how SONET came into existence and then examine some of the major features of SONET.

The Development of SONET

Some people view SONET as a new technology, and it is only in the last decade that SONET has been deployed extensively. However, SONET did not just appear suddenly on the scene. Extensive research has been underway for well over a decade on many of the features that are found in SONET. One notable achievement began in 1984. It focused on the efforts of several standards groups and vendors to develop optical transmission standards for what is known as the mid-span meet (also known as transverse compatibility). The goal was to publish a specification that would allow different vendors' equipment to interoperate with each other at the fiber level.

In addition, due to the breakup of the Bell System in 1984, there were no standards developed beyond T3 technology. Prior to the divestiture, all equipment was built by AT&T's manufacturing arm, Western Electric (WECO), which ensured that there would be no compatibility problems in any network components.

After the breakup, there was little incentive for the other carriers (such as MCI and Sprint) to purchase AT&T-based equipment. Indeed, there was no incentive to purchase AT&T equipment, since AT&T, MCI, and Sprint had begun competing with each other for long distance services. This situation led to the rapid growth of alternate equipment vendors (such as Nortel Networks), who were developing advanced digital switching technologies.

The 1984 divestiture paved the way for alternate long distance carriers through the equal access ruling. The alternate carriers were given equal access to the local exchange carrier (LEC) infrastructure and connections to AT&T for end-to-end long distance service. The LEC could connect to MCI, Sprint, and others through their switching facilities at an interface in the LEC or long distance carrier offices called the point of presence (POP).

During this time, higher capacity schemes beyond T3 became proprietary, creating serious compatibility problems for network operators who purchased equipment from different manufacturers. In addition, the early 1980s witnessed the proliferation of incompatible and competing optical fiber specifications.

Precursors to SONET

We interrupt the discussion on divestiture to explain some of the technology that was being developed during the early 1980s. A landmark project that contributed to SONET was Metrobus, an optical communications system developed at AT&T's Bell Labs in the early 1980s. Its name was derived from its purpose: It was situated in a metropolitan area to serve as a high-speed optical transport network.

Metrobus demonstrated the feasibility of several new techniques that found their way into SONET. (They are explained in this chapter and subsequent chapters.) Among the more notable features were (a) single-step multiplexing, (b) synchronous timing, (c) extensive overhead for network management, (d) accessing low level signals directly, (e) point-to-multipoint multiplexing, and (f) the employment of multi-megabit media for achieving high bandwidth network transmission capacity (of approximately 150 Mbit/s).

This latter decision along with the ensuing research and testing was important, because a 150 Mbit/s signal rate can accommodate voice, video, and data signals, as well as compressed high definition television (HDTV). Moreover, these techniques permitted the use of relatively inexpensive graded-index multimode fibers instead of the more expensive single mode fibers, although single mode fiber is now the preferred media for SONET.

The various standards groups began the work on SONET after MCI send a request to them to establish standards for the mid-span meet. The SONET specifications were developed in the early 1980s, and Bellcore submitted its proposals to the American National Standards Institute (ANSI) T1X1 Committee in early 1985,1 based on a 50.688 Mbit/s transfer rate. The initial SONET work did not arouse much interest until the Metrobus activity became recognized.

Later, using the innovative features of Metrobus, the SONET designers made modifications to the original SONET proposal, principally in the size of the frame and the manner in which T1 signals were mapped into the SONET frame.

From 1984 to 1986, various alternatives were considered by the ANSI T1 Committee, who settled on what became known as the synchronous transport signal number one (STS-1) rate as a base standard. Finally, in 1987, the ANSI T1X1 committee published a draft document on SONET.

Participation by ITU-T
During this time, the international standards body now known as the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) had rejected the STS-1 rate as a base rate in favor of a base rate of 155.520 Mbit/s. For a while, it appeared that the North American and European approaches might not converge, but the SONET frame syntax and structure were altered one more time to a rate of 51.84 Mbit/s which permitted this rate to be multiplexed (concatenated) by an integer of three to the European preference of 155.52 Mbit/s. This work has resulted in almost complete compatibility between the North American and ITU-T approaches. The ITU-T Recommendations are now considered the "official" standards and are collectively called the Synchronous Digital Hierarchy (SDH).

Once the major aspects of the standards were in place, vendors and manufacturers began to develop SONET and SDH equipment and software. These efforts came to fruition in the early 1990s and, as of this writing, SONET and SDH have been deployed throughout the United States and other parts of the world.

Key ITU-T Documents
Listed below are some of the most commonly cited SDH standards available from the ITU-T.2
  • ITU-T G.707: Network Node Interface for the Synchronous Digital Hierarchy (SDH)
  • ITU-T G.781: Structure of Recommendations on Equipment for the Synchronous Digital Hierarchy (SDH)
  • ITU-T G.782: Types and Characteristics of Synchronous Digital Hierarchy (SDH) Equipment
  • ITU-T G.783: Characteristics of Synchronous Digital Hierarchy (SDH) Equipment Functional Blocks
  • ITU-T G.803: Architecture of Transport Networks Based on the Synchronous Digital Hierarchy (SDH)

Role of ANSI and Key Standards Documents

Today, ANSI coordinates and approves the SONET standards. The standards are developed by the T1 committee. T1X1 and T1M1 are the primary T1 Technical Subcommittees responsible for SONET. T1X1 deals with the digital hierarchy (shown in Figure 1–5) and synchronization. T1M1 deals with internetworking operations, administration, maintenance, and provisioning (OAM&P). Listed below are some of the most commonly cited SONET standards available from ANSI.3
  • ANSI T1.105: SONET—Basic Description including Multiplex Structure, Rates and Formats
  • ANSI T1.105.01: SONET—Automatic Protection Switching
  • ANSI T1.105.02: SONET—Payload Mappings
  • ANSI T1.105.03: SONET—Jitter at Network Interfaces
  • ANSI T1.105.03a: SONET—Jitter at Network Interfaces – DS1 Supplement
  • ANSI T1.105.03b: SONET—Jitter at Network Interfaces – DS3 Wander Supplement
  • ANSI T1.105.04: SONET—Data Communication Channel Protocol and Architectures
  • ANSI T1.105.05: SONET—Tandem Connection Maintenance
  • ANSI T1.105.06: SONET—Physical Layer Specifications
  • ANSI T1.105.07: SONET—Sub-STS-1 Interface Rates and For-mats Specification
  • ANSI T1.105.09: SONET—Network Element Timing and Synchronization
  • ANSI T1.119: SONET—OAM&P, Communications
  • ANSI T1.119.01: SONET: OAM&P, Communications, and Protec-tion Switching Fragment

The Network and Services Integration Forum (NSIF)

In order to assist in the SONET standards process, the Network and Services Integration Forum (NSIF) was formed to provide an open industry forum for the discussion and resolution of multiple technology integration and SONET interoperability issues.4 Its goal is to enable the delivery of services across a set of networks from different vendors and different network operators. NSIF coordinates with the appropriate standards groups, such as ANSI and the ITU-T, as required by a specific issue.

NSIF is a nonprofit membership organization comprised of equipment vendors, service providers, and other industry players who cooperatively develop end-to-end multitechnology service delivery capabilities based on industry and international standards....

1 The initial proposal stipulated a transfer rate of 50.688 Mbit/s, a 125 microsecond (µsec) signal, and a frame format of three rows by 265 columns (264 octets ×3 rows ×8 bits per octet ×8000 = 50,688,000). Later chapters explain the concepts of rows and columns.

2 Go to the ITU web site at for a complete list of SDH standards, along with information on purchasing the documents.

3 Go to the ANSI web site at for a complete list of SONET standards along with information on purchasing the documents.

Table of Contents

Notes for the Readerxxi
Chapter 1Introduction1
What Are SONET and T1?1
The Development of SONET2
Role of ANSI and Key Standards Documents5
The Network and Services Integration Forum (NSIF))6
SONET and T16
Features of SONET and T18
Synchronous Networks9
SONET Timing10
Payloads and Envelopes12
Optical Fiber--the Bedrock for SONET13
Typical SONET Topology15
Present Transport Systems and SONET18
Clarification of Terms18
Chapter 2Digital Transmission Carrier Systems22
Organization of Telephone Services22
Types of Signaling25
Connecting the User to the Telephone System26
Frequency Division Multiplexing (FDM) Carrier Systems30
Analog-to-Digital Conversion31
Other Analog-to-Digital Techniques42
Newer Digital Voice Schemes49
The New Voice Coders52
Appendix 2ACoding and Coding Violations53
Chapter 3Timing and Synchronization in Digital Networks57
Timing and Synchronization in Digital Networks57
Effect of Timing Errors60
The Clocking Signal60
Types of Timing in Networks61
Timing Variations65
Slip Operations in More Detail67
Frequency Departures and Accuracies70
Methods of Clock Exchange72
Distribution of Timing Information with SONET and DS1 Signals78
Decoupling the Clocks79
Other Uses and Examples of Pointer Operations79
Source Clock Frequency Recovery for Asynchronous Transfer Mode (ATM) Systems86
Synchronization Status Messages and Timing Loops87
Examples of Timing Supply Systems87
Chapter 4The T1 Family93
T1 Line Configurations93
The Digital Network95
Introduction to The D Family Channel Banks97
North American Asynchronous Digital Hierarchy98
Digital Loop Carrier Systems101
T1 Line and Trunks103
D1 Channel Banks104
D2 Channel Banks109
D3 Channel Banks114
D4 Channel Banks115
Vendors' D4 Channel Banks117
Other D4 Features120
D5 Channel Banks126
Subscriber-type Systems129
Final Thoughts on the D Channel Banks132
Fractional T1 (FT1)133
Dividing and Filling the T1 Channel133
Compensating for Clock Differences in a T1 System134
Appendix 4AFrame Formats137
Chapter 5SONET Operations146
Example of SONET Interfaces146
Configuration Possibilities149
SONET Layers151
Beyond OC-192154
Examples of Payload Mappings156
The SONET Envelope in More Detail157
SONET Equipment and Topologies160
Chapter 6Payload Mapping and Management165
A Brief Review165
SONET STS-1 Envelope167
The SONET STS-3c Frame Structure168
AT&T DDM-2000 OC-3 Shelf169
Mapping and Multiplexing Operations175
Rows and columns of the VTs182
Construction of the Entire SPE185
A Final Look At Another Mapping Operation193
Chapter 7Topologies and Configurations195
Typical Topologies195
Protection Switching in More Detail195
The BLSR198
Add-Drop and Cross-Connects on Ring or Point-to-Point Topologies205
Provisioning SONET Machines for Add-Drop and Cross-Connect Operations208
Example of Protection Switching on a Two Fiber Bidirectional Ring215
Cascading the Timing on Multiple Rings217
Chapter 8Operations, Administration, and Maintenance220
Need for Rigorous Testing220
Alarm Surveillance221
Categories of Tests222
OAM and the SONET Layers231
The SONET OAM Headers233
More Information on the D Bytes239
STS-3c Frames and Overhead239
Maintenance Signals and Layers241
Examples of OAM Operations243
ATM and SONET OAM Operations245
SONET and Network Management Protocols247
The Network Management Model247
Chapter 9Manufacturers' and Vendors' Systems254
SONET Releases254
The Major Vendors256
Examples of Nortel Networks' Products257
Example of OPTera Node258
Examples of Fujitsu's Products259
Examples of Alcatel's Products264
Examples of Lucent Technologies' Products266
Examples of NEC's Products268
Chapter 10The Synchronous Digital Hierarchy269
SDH Systems Connecting to the United States269
Comparison Of SONET and SDH270
Key Terms271
Transporting E4, H4, and DS-1 Signals273
The SDH Multiplexing Hierarchy273
SONET (1.544 Mbit/s) Mapping and Multiplexing Structure274
SDH (2.048 Mbit/s) Mapping and Multiplexing Structure275
SONET (DS1C) Mapping And Multiplexing Structure276
SONET (DS-2) Mapping And Multiplexing Structure276
SONET 44.736 Mbit/s, SDH 34.368 Mbit/s, and 139.264 Mbit/s Mapping and Multiplexing Structure277
Three Types of Mapping for the VC-11, VC-12, or VC-2 Signals277
Revised SDH Digital Hierarchy279
SDH Overhead Bytes280
Chapter 11SONET and WDM, Optical Ethernet, ATM, IP, and MPLS286
Introduction to WDM287
Capacity of WDM287
Running SONET over WDM288
Erbium-Doped Fiber (EDF)289
WDM Amplifers290
Wavelength WDMs291
Optical Cross-Connects (OXC) with WDM292
Passive Optical Networks (PONs)293
The "Sweet Spot"294
Optical Ethernets and Ethernet PONs295
ATM and SONET296
IP and SONET298
ATM in the SONET Envelope298
IP and PPP in the SONET Envelope299
ATM vs. IP over SONET300
Evolution of the Optical Broadband Network303
Migration to Label Switching Networks304
Mapping Labels to Wavelengths306
Label Switched Paths (LSPS) and Optical Switched Paths (OSPS)307
Protocol Stack Possibilites309
Summary and Conclusions310
A New Optical Network Model312
In Conclusion313
Appendix ATransmission Media314
Properties of Light and Optical Fiber315
Electromagnetic Spectrum317
Properties of Light: Reflection and Refraction319
Types of Fibers324
Sources and Receivers of Optical Fiber Signals327
Fiber Cable Structure334
Fiber Losses337


This book is part of a series titled Advanced Communications Technologies. This particular book also has a close "companion" in this series, titled ISDN and SS7: Architectures for Digital Signaling Networks.

When we were planning this book, our initial intent was for it to be a SONET book, with little discussion of the T1 technology. However, we decided that the book should also include T1 because many of the SONET operations are centered around T1. In addition, as we surveyed the literature on T1, we were surprised to discover that the existing books on T1 did not cover several important aspects of the subject--omissions that we have corrected in this book.

Also, we have included material on some of the original T1 channel banks. To our knowledge, this material has not appeared in any text, and the information is essential to understanding how T1 is the way it is.

In setting out to write this book, we established two goals. First, we wish to complement the overall series, and avoid undue overlapping of the subject matter of the other books. Second, we wish to explain aspects of the subject matter that have not been provided in other reference books. We found that not much tutorial literature exists on synchronization and timing, on the Building Integrated Timing Supply (BITS), on SONET configuration (crafting) operations, and some other important subjects. This information is provided in this book.

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