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• Table of Contents

• Index

Mesh-Based Survivable Networks: Options and Strategies for Optical, MPLS, SONET, and ATM Networking

By Wayne D. Grover

Publisher: Prentice Hall PTR Pub Date: August 26, 2003

ISBN: 0-13-494576-X Pages: 880

"Always on" information networks must automatically reroute around virtually any problem-but conventional, redundant ring architectures are too inefficient and inflexible. The solution: mesh-based networks that will be just as survivable-and far more flexible and

cost-effective. Drawing heavily on the latest research, Wayne D. Grover introduces radical new concepts essential for deploying mesh-based networks. Grover offers "how-to" guidance on everything from logical design to operational strategy and evolution planning-including unprecedented insight into migration from ring topologies and the important new concept of p-cycles.

Mesh survivability: realities and common misunderstandings Basic span- and path-restoration concepts and techniques

Logical design: modularity, non-linear cost structures, express-route optimization, and dual-failure considerations Operational aspects of real-time restoration and self-organizing pre-planning against failures

The "transport-stabilized Internet": self-organizing reactions to failure and unforeseen demand patterns Leveraging controlled oversubscription of capacity upon restoration in IP networks

"Forcers": a new way to analyze the capacity structure of mesh-restorable networks New techniques for evolving facility-route structures in mesh-restorable networks

p-Cycles: combining the simplicity and switching speed of ring networks with the efficiency of mesh networks

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Novel Working Capacity Envelope concept for simplified dynamic demand provisioning Dual-failure restorability and the availability of mesh networks

This is the definitive guide to mesh-based networking for every system engineer, network planner, product manager, researcher and graduate student in optical networking.

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[ Team LiB ]

• Table of Contents

• Index

Mesh-Based Survivable Networks: Options and Strategies for Optical, MPLS, SONET, and ATM Networking

By Wayne D. Grover

Publisher: Prentice Hall PTR Pub Date: August 26, 2003

ISBN: 0-13-494576-X Pages: 880

Copyright

About the Book's Web Site www.ee.ualberta.ca/~grover/

Foreword Preface

Acknowledgements Introduction and Outline Historical Backdrop

The Case for Mesh-based Survivable Networks

Outline

Part 1. Preparations

Chapter 1. Orientation to Transport Networks and Technology

Section 1.0.1. Aggregation of Service Layer Traffic into Transport Demands Section 1.0.2. Concept of Logical versus Physical Networks: Virtual Topology Section 1.0.3. Multiplexing and Switching

Section 1.0.4. Concept of Transparency Section 1.0.5. Layering and Partitioning

Section 1.1. Plesiochronous Digital Hierarchy (PDH) Section 1.2. SONET / SDH

Section 1.3. Broadband ISDN and Asynchronous Transfer Mode (ATM) Section 1.4. Concept of Label-Switching: The Basis of ATM and MPLS Section 1.5. Network Planning Aspects of Transport Networks

Section 1.6. Short and Long-Term Transport Network Planning Contexts Chapter 2. Internet Protocol and Optical Networking

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Section 2.1. Increasing Network Efficiency Section 2.2. DWDM and Optical Networking Section 2.3. Optical Cross-Connects (OXC)

Section 2.4. Data-Centric Payloads and Formats for the Transport Network Section 2.5. Enhancing SONET for Data Transport

Section 2.6. Optical Service Channels and Digital Wrapper Section 2.7. IP-Centric Control of Optical Networks Section 2.8. Basic Internet Protocols

Section 2.9. Extensions for IP-Centric Control of Optical Networks Section 2.10. Network Planning Issues

Chapter 3. Failure Impacts, Survivability Principles, and Measures of Survivability Section 3.1. Transport Network Failures and Their Impacts

Section 3.2. Survivability Principles from the Ground Up Section 3.3. Physical Layer Survivability Measures Section 3.4. Survivability at the Transmission System Layer Section 3.5. Logical Layer Survivability Schemes

Section 3.6. Service Layer Survivability Schemes

Section 3.7. Comparative Advantages of Different Layers for Survivability Section 3.8. Measures of Outage and Survivability Performance Section 3.9. Measures of Network Survivability

Section 3.10. Restorability Section 3.11. Reliability Section 3.12. Availability Section 3.13. Network Reliability

Section 3.14. Expected Loss of Traffic and of Connectivity Chapter 4. Graph Theory, Routing, and Optimization

Section 4.1. Graph Theory Related to Transport Networking Section 4.2. Computational Complexity

Section 4.3. Shortest Path Algorithms

Section 4.4. Bhandari's Modified Dijkstra Algorithms Section 4.5. k-Shortest Path Algorithms

Section 4.6. Maximum Flow: Concept and Algorithm Section 4.7. Shortest Disjoint Path Pair

Section 4.8. Finding Biconnected Components of a Graph Section 4.9. The Cut-Tree

Section 4.10. Finding All Cycles of a Graph

Section 4.11. Optimization Methods for Network Design Section 4.12. Linear and Integer Programming Section 4.13. Duality

Section 4.14. Unimodularity and Special Structures Section 4.15. Network Flow Problems

Section 4.16. Techniques for Formulating LP/ILP Problems Section 4.17. Lagrangean Techniques

Section 4.18. Other Combinatorial Optimization Methods: Meta-Heuristics Part 2. Studies

Chapter 5. Span-Restorable and Span-Protected Mesh Networks Section 5.1. Updating the View of Span Restoration

Section 5.2. Operational Concepts for Span Restoration

Section 5.3. Spare Capacity Design of Span-Restorable Mesh Networks Section 5.4. Jointly Optimized Working and Spare Capacity Assignment

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Section 5.5. The Forcer Concept

Section 5.6. Modular Span-Restorable Mesh Capacity Design Section 5.7. A Generic Policy for Generating Eligible Route Sets Section 5.8. Chain Optimized Mesh Design for Low Connectivity Graphs Section 5.9. Span-Restorable Capacity Design with Multiple Service Classes Section 5.10. Incremental Capacity Planning for Span-Restorable Networks Section 5.11. Bicriteria Design Methods for Span-Restorable Mesh Networks Chapter 6. Path Restoration and Shared Backup Path Protection

Section 6.1. Understanding Path Protection, Path Restoration and Path Segments Section 6.2. A Framework for Path Restoration Routing and Capacity Design Section 6.3. The Path Restoration Rerouting Problem

Section 6.4. Concepts of Stub Release and Stub Reuse in Path Restoration Section 6.5. Lower Bounds on Redundancy

Section 6.6. Master Formulation for Path Restoration Capacity Design Section 6.7. Simplest Model for Path Restoration Capacity Design Section 6.8. Comparative Study of Span and Path-Restorable Designs Section 6.9. Shared BackupPath Protection (SBPP)

Section 6.10. Lagrangean Relaxation for Path-Oriented Capacity Design Problems Section 6.11. Heuristics for Path-Restorable Network Design

Section 6.12. Phase 1 Heuristics?Design Construction

Section 6.13. Putting Modularity Considerations in the Iterative Heuristic Section 6.14. Phase 2 Forcer-Oriented Design Improvement Heuristic Section 6.15. A Tabu Search Heuristic for Design Tightening

Section 6.16. Simulated Allocation Type of Algorithm for Design Tightening

Chapter 7. Oversubscription-Based Design of Shared Backup Path Protection for MPLS or ATM Section 7.1. Concept of Oversubscription

Section 7.2. Overview of MPLS Shared Backup Path Protection and ATM Backup VP Concepts Section 7.3. The Oversubscription Design Framework

Section 7.4. Defining the Oversubscription Factor Xj,i

Section 7.5. KST Algorithm for Backup Path Capacity Allocation Section 7.6. Oversubscription Effects with KST-Alg

Section 7.7. Minimum Spare Capacity with Limits on Oversubscription Section 7.8. Minimum Peak Oversubscription with Given Spare Capacity Section 7.9. OS-3: Minimum Total Capacity with Limited Oversubscription Section 7.10. Related Bounds on Spare Capacity

Section 7.11. Illustrative Results and Discussion

Section 7.12. Determining the Maximum Tolerable Oversubscription Section 7.13. Extension and Application to Multiple Classes of Service

Chapter 8. Dual Failures, Nodal Bypass and Common Duct Effects on Design and Availability Section 8.1. Are Dual Failures a Real Concern?

Section 8.2. Dual Failure Restorability Analysis of Span-Restorable Networks Section 8.3. Determining the Network Average Dual Failure Restorability, R2 Section 8.4. Relationship Between Dual Failure Restorability and Availability Section 8.5. Dual Failure Availability Analysis for SBPP Networks

Section 8.6. Optimizing Spare Capacity Design for Dual Failures Section 8.7. Dual Failure Considerations Arising From Express Routes Section 8.8. Optimal Capacity Design with Bypasses

Section 8.9. Effects of Dual Failures Arising from Shared Risk Link Groups Section 8.10. Capacity Design for a Known Set of SRLGs

Section 8.11. Effects of SRLGs on Spare Capacity

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Chapter 9. Mesh Network Topology Design and Evolution

Section 9.1. Different Contexts and Benefits of Topology Planning Section 9.2. Topology Design for Working Flow Only

Section 9.3. Interacting Effects in Mesh-Survivable Topology

Section 9.4. Experimental Studies of Mesh Capacity versus Graph Connectivity Section 9.5. How Economy of Scale Changes the Optimal Topology

Section 9.6. The Single-Span Addition Problem

Section 9.7. The Complete Mesh Topology, Routing, and Spare Capacity Problem Section 9.8. Sample Results: Studies with MTRS

Section 9.9. A Three-Part Heuristic for MTRS

Section 9.10. Studies with the Three-Part Heuristic for MTRS Section 9.11. Ezema's Edge-Limiting Criteria

Section 9.12. Successive Inclusion Heuristic

Section 9.13. Graph Sifting and Graph Repair for Topology Search Section 9.14. A Tabu Search Extension of the Graph Sifter Architecture Section 9.15. Range Sweeping Topology Search

Section 9.16. Overall Strategy and Applications for Topology Planning Chapter 10. p-Cycles

Section 10.1. The Concept of p-Cycles

Section 10.2. Cycle Covers and "Protection Cycles" per Ellinas et al.

Section 10.3. Optimal Capacity Design of Networks with p-Cycles Section 10.4. Application of p-Cycles to DWDM Networks Section 10.5. Schupke et al. ? Case Study for DWDM p-Cycles Section 10.6. Results with Jointly Optimized (VWP) p-Cycles Section 10.7. Heuristic and Algorithmic Approaches to p-Cycle Design

Section 10.8. Concept of a Straddling Subnetwork and Domain Perimeter p-Cycles Section 10.9. Extra Straddling Relationships with Non-Simple p-Cycles

Section 10.10. Hamiltonian p-Cycles and Homogeneous Networks Section 10.11. An ADM-like Nodal Device for p-Cycles

Section 10.12. Self-Organized p-Cycle Formation

Section 10.13. Virtual p-Cycles in the MPLS Layer for Link and Node Protection Section 10.14. Node-Encircling p-Cycles for Protection Against Node Loss Chapter 11. Ring-Mesh Hybrids and Ring-to-Mesh Evolution

Section 11.1. Integrated ADM Functions on DCS/OXC: an Enabler of Hybrids Section 11.2. Hybrids Based on the Ring-Access Mesh-Core Principle Section 11.3. Mesh-Chain Hybrid Networks

Section 11.4. Studies of Ring-Mesh and Mesh-Chain Hybrid Network Designs Section 11.5. Optimal Design of Ring-Mesh Hybrids

Section 11.6. Forcer Clipping Ring-Mesh Hybrids Section 11.7. Ring to Mesh Evolution via "Ring Mining"

Section 11.8. Ring Mining to p-Cycles as the Target Architecture Bibliography

Index

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Copyright

Library of Congress Cataloging-in-Publication Data

Wireless communications: signal processing perspectives / [edited by]

H. Vincent Poor, Gregory W. Wornell.

p. cm.--(Prentice Hall signal processing series) Includes bibliographical references and index.

ISBN 0-13-620345-0

1. Wireless communication systems. 2. Signal processing. I. Poor, H. Vincent.

II. Wornell, Gregory W. III. Series.

TK5103.2.W5718 1998 98-9676 621.382--dc21 CIP

Editorial/production supervision Mary Sudul

Cover design director Jerry Votta

Cover design Talar Boorujy and Nina Scuderi

Manufacturing manager Alexis Heydt-Long

Manufacturing buyer Maura Zaldivar

Publisher Bernard Goodwin

Editorial assistant Michelle Vincenti

Marketing manager Dan DePasquale

Upper Saddle River, New Jersey 07458

Prentice Hall books are widely used by corporations and government agencies for training, marketing, and resale.

The publisher offers discounts on this book when ordered in bulk quantities. For more information, contact Corporate Sales Department, Phone: 800-382-3419; FAX: 201- 236-7141; E-mail: corpsales@prenhall.com

Or write: Prentice Hall PTR, Corporate Sales Dept., One Lake Street, Upper Saddle River, NJ 07458.

Other company and product names mentioned herein are the trademarks or registered trademarks of their respective owners.

Printed in the United States of America 1st Printing Pearson Education LTD.

Pearson Education Australia PTY, Limited Pearson Education Singapore, Pte. Ltd.

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Pearson Education North Asia Ltd.

Pearson Education Canada, Ltd.

Pearson Educación de Mexico, S.A. de C.V.

Pearson Education—Japan

Pearson Education Malaysia, Pte. Ltd.

Dedication

To my wife, Jutta—to my son, Edward (Teddy) and to... TRLabs—still the noble experiment

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About the Book's Web Site www.ee.ualberta.ca/~grover/

A number of appendices and supplements are web-based, so that they may be kept current and easily updated or extended as desired.

This includes:

Glossary

AMPL models to implement design formulations.

DATPrep programs: These are programs that can be used as is or adapted to new problems for the creation of network specific DAT files that required for execution of the AMPL models.

A library of test-case network and demand files.

A library of programs for basic functions such as routing or cycle enumeration.

Frequently Asked Questions and discussion on survivable networking issues.

Errata for the book.

Technical Reports produced by the authors research group (as available).

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[ Team LiB ]

Foreword

Let me first speak to the topic of mesh-based survivable networks—its history and importance, and then add my comments on the significance of this first comprehensive book on the topic.

One milepost in our society's evolution towards higher expectations of telecommunications network reliability is illustrated by a press release in the early 1990s (paraphrased):

"In response to several consecutive major telephone network outages and at the request of key Members of Congress, on Sept 19, 1991 the FCC issued a Notice of Proposed Rulemaking requesting that all facilities-based common carriers report any major outages that affects over 50 thousand customers for more than ½ hour [eventually reduced to 30 thousand customers]."

In the years prior, networks in the United States mostly consisted of voice (telephone) calls carried over circuit switches. Outages of the underlying transport network were handled at the circuit-switched layer. Most of these remedial actions consisted of forced alternate routing through manual switch overrides by network operators in central Network Operations Centers (NOCs). Over time the capacity of transport networks increased, data overlay networks from other competitive carriers were created, and large end-users instituted private voice and packet networks. The links of such switched overlay (or "service") networks were transported as circuit-based services by carriers and thus the private line business emerged.

The result was that a large carrier transported links of its own switched voice and data overlay networks, as well as the links of other service-layer networks. It became limiting to react to transport network failures only in the service network. From the perspective a customer with its own service-layer network who leases its links from the carrier, there is no knowledge of the physical layer over which it routes its links and thus it is difficult to plan or react to network failures. Conversely, from the perspective of the carrier, it is unreasonable to require that the overlay network handle transport layer failures: the switches of these networks are usually unknown and outside the span of control of the carrier. Furthermore, as transport network bandwidth increased, it became clear that the restoration of services affected by transport failures would be more expensive to do in the service (overlay) networks than at the transport layer itself. At the transport layer multiplex bundling and better economies of scale could be achieved. It thus became clear that automatic restoration should be offered at the transport layer itself.

For the first digital transmission systems (T1-T3) restoration or "protection" was provided on a 1-to-N ratio (1:N) where one standby system would be switched in to protect against failure in any one of the N other systems. However, the protection channel usually was

"in-line"—it resided in the same conduit or cable as the working channels and thus provided little protection against cable cuts. But the impact was minimal because, in the early days, T1 cables did not carry many circuits and businesses had not developed a reliance on high network availability. So the failure had minimal impact or, as importantly at least, it garnered little interest from the press.

As fiber optic transmission and eventually Wavelength Division Multiplexing emerged, the bandwidth of a single fiber soared. With so much capacity and relatively failure-prone laser and electro-optic devices, 1:1 protection was required for the transmitter and receiver line cards. The same "in-line" protection methods were expensive compared to copper or coax -based T1-T3 systems, yet ultimately ineffective from a restoration standpoint. Thus, the deployment of 1:1 protection with diverse geographic routing of the protection path evolved. This solution was tolerable for a while, but as demand for bandwidth and transmission rates grew further, the economics of many overlapping point-to-point transmission systems, each with its own dedicated diverse fiber path, became unattractive.

In the 1990s, Bellcore developed the SONET standard and standardized the concept of self-healing rings, quickly followed by its international twin standard, SDH. Transmission engineers rejoiced. This appeared to be the final answer: one could replace all these cumbersome and expensive point-to-point transmission systems with a few multi-node, self-healing SONET rings. In contrast, AT&T decided to address the growing restoration problem for its long distance network with one of the first automatic centrally-controlled mesh-restoration schemes, called FASTAR, based on DS3 Digital Cross-connect Systems (DCSs). Its restoration speed would not match the eventual SONET rings, but by prioritizing restoration of private line services (especially 1-800 services) it was more than adequate. Moreover, it proved to be very economic in its use of extra transport capacity needed for restoration, often termed the

"restoration overbuild" (—what Grover calls the "spare" capacity).

Many other carriers jumped on the SONET ring bandwagon. This started off an industry debate that rages to this day. Which is better,

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ring or mesh-based restoration? Rings seemed to win the battle through the mid 1990s, until increasing bandwidth again crossed a threshold. Many network researchers found multiple, overlapping SONET rings to be economically unattractive compared to DCS mesh restoration in certain types of networks. However, compared to the early forms of centrally-controlled mesh restoration (where DCSs have no distributed routing intelligence or inter-nodal signaling), rings had the advantage that once the ring was installed, restoration is automatic. In contrast, the centrally-controlled mesh-restoration schemes required a sophisticated central system with a separate signaling network provided between the NOC and the DCSs. This operational difference provided the motivation for the idea of intelligent DCSs, that is, network elements capable of distributed routing, detecting failures of their links, and passing topology, path set-up, and routing messages among themselves via inter-nodal signaling. This was not a unique idea, in that it emulated distributed data networks, but the techniques for distributed restoration would be fundamentally different in some important ways.

In a visionary role and long before this debate peaked, Wayne Grover was the first to observe that the ideas of self-routing in data networks could be extended and applied to circuit switched transport networks in his seminal paper, The Selfhealing Network: A Fast Distributed Restoration Technique for Networks Using Digital Cross-Connect Machines that appeared in Globecom in 1987. However, it was not until the technological advent of the intelligent DCS (now enhanced with Gigabit rate Optical interfaces) in the late 1990s that this debate shifted. AT&T again led the mesh-restoration charge with its decision to implement the Intelligent Optical Switch (IOS) for its long distance transport network at the turn of the new century. This decision resulted from the new, automatic restoration capabilities of intelligent cross-connects with compact and integrated Gigabit-rate optical interfaces, years of network optimization studies at AT&T Labs of rings versus mesh network design, and the final determination that mesh wins economically in long distance networks of sufficiently large demand for bandwidth, size, and geographically diverse path connectivity.

As of this writing, SONET rings still dominate in metropolitan networks, where there is less geographic diversity and less required bandwidth than in intercity networks, but we find that intelligent cross-connects are encroaching further into metro networks as well. Also, as optical cross-connect and WDM switching technologies mature, mesh-based restoration for pure optically-switched networks are under increased interest because of the reduced costs of optical-electrical conversion and economies of scale for integration of WDM and electronics. This option is especially attractive to transport the very-high rate links of IP service-layer networks.

This brings us to the important contribution that this book now makes to the field. During this evolution, many different alternatives for mesh networking have evolved. It is important to understand them and to master the tools needed to evaluate how they work, how to design the network to meet the reliability objective, where they are best deployed, and how to compare alternative architectures and protection methods. This book is much more that just a survey of these topics, but rather forms a series of in-depth tutorials based on the author's own internationally-recognized research. In particular, Grover introduces a large amount of previously unpublished material and, for those published topics, he provides insights, depth, and explanatory discussions beyond that of the original publications.

For example, there are single chapters alone that will prove invaluable to network operators and their equipment suppliers, such as how to design and operate span-restorable and path-restorable networks, how to design ring-mesh hybrid networks, how to analyze the availability of mesh networks under multiple failures, and how to evolve ring networks into a mesh-restorable network. Besides providing invaluable background in these "classic" areas, the book provides a wealth of new options and alternatives that have exploded recently upon this field, all developed by Grover and his team of graduate researchers at TRLabs–University of Alberta. A few of the original research areas treated in-depth in this volume include p-cycles, forcer-analysis, distributed pre-planning, and self-organization of transport networks. Grover covers restoration in packet-based networks as well, including topics such as the controlled oversubscription design of MPLS networks, which is of particular research interest to me in recent work on the convergence of transport and packet networks. Other new topics include the "meta-mesh" technique for very sparse networks, and the "working capacity envelope concept."

My own work over the years has demonstrated that efficiency in restoration and design of transport and packet networks saves hundreds of millions of dollars in capital expense in carrier networks—and the concomitant increase in intelligence of network elements results in equally significant operational savings. Based on this, I highly recommend this book to network operators and their equipment suppliers.

As for graduate students and neophytes to transport networks, I find the first four preparatory chapters alone to constitute a reference book on graphs/networks, transport network architectures, and network routing and optimization algorithms, plus the "Studies" chapters contain many further ideas for research projects.

In conclusion, the quality and originality of work from Grover and his group is known world-wide on the topic of mesh-based network survivability—a topic for which he was signified as an IEEE Fellow in 2001. Therefore, I think I can speak for those of us who have contributed to the field, both in theory and practice, and state that no one is better qualified than Grover to write the first comprehensive book on this topic. I whole-heartedly commend this timely and valuable volume to you.

Dr. Robert D. Doverspike

Director, Transport Network Evolution Research AT&T Labs - Research

Middletown, NJ June 6, 2003

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Preface

"Internet hindered by severed cable."

"Internet chaos continues today..."

"Cable break disrupts Internet in several countries."

"Calling and major businesses down from cable cut."

These are headlines arising in just one month from fiber optic cable disruptions. Despite the enormous advantages of fiber optics and wave-division multiplexing, the truth is that the information economy—fueled by fiber-optic capacity—is based on a surprisingly vulnerable physical medium. Every effort can be made to protect the relatively few thumb-sized cables on which our information society is built, but the cable-cuts and other disruptions just don't stop. From deep-sea shark bites to the fabled "backhoe fade," serious transmission outages are common and of increasing impact. Some form of fast rerouting at the network level has become essential to achieve the "always on" information networks that we depend upon.

One way to survive optical network damage is to duplicate every transmission path. In the form of rings and diverse-routed protection switching schemes, this is actually the most widespread solution in use today. Our view has long been that this is an inefficient expedient—the "get a bigger hammer" approach to solving a problem. Admittedly, rings filled the void when survivability issues reached crisis proportions in the 1990s. But now network operators want options that are just as survivable but more flexible, more

growth-tolerant, able to accommodate service differentiation, and far more efficient in the use of capacity. This is where "shared-mesh" or

"mesh-restorable" networks take the stage.

The author's love affair with the mesh-survivability approach began in 1987—with the naive certainty back then that sheer elegance and efficiency would suffice to see it adopted in SONET by 1990! The actual journey has been much longer and complicated than that. The Internet and Optical Networking had to happen first. And all the ideas had much more development to undergo before they would be really ready for use. Today, we understand the important values of mesh-based survivability go beyond just efficiency (and of course you can rarely make money off of elegance alone). Flexibility, automated provisioning, differentiated service capabilities, and the advent of Internet-style signaling and control are all important in making this a truly viable option. But its full exploitation still requires new concepts and ideas about network operation—letting the network self-organize its own logical configuration, for example, and letting it do its own preplanning and self-audit of its current survivability potential. New planning and design models are also required. These are the central topics of this book—designed to stimulate and facilitate the further evolution toward highly efficient, flexible and autonomous

mesh-based survivable networks.

The book is written with two main communities in mind. One is my colleagues in industry; the system engineers, research scientists, technology planners, network planners, product line managers and corporate technology strategists in the telcos, in the vendor companies, and in corporate research labs. The are the key people who are continually assessing the economics of new architectural options and guiding technology and standards developments. Today these assessments of network strategy and technology selection put as much emphasis on operational expense reduction as on capital cost—capacity efficiency and flexibility are both important in future networks. Network operators are in an intensely competitive environment with prices dropping and volumes rising and success is dependent on all forms of corporate productivity enhancement. Mesh networking can provide fundamental productivity enhancements through greater network efficiencies and flexibility. The book aids the operating companies in finding these new efficiencies by giving many new options and ideas accompanied with the "how to" information to assess and compare the benefits on their own networks.

Examples of the new directions and capabilities the book provides are in topology evolution, ring-to-mesh conversion by "ring-mining,"

multiple Quality-of-Protection design, tailoring restoration-induced packet congestion effects in a controlled manner, simplifying dynamic demand provisioning, and so on. An important plus is that the book also contains the first complete treatment of the intriguing and promising new concept called "p-cycles"—offering solutions with ring-speed and mesh-efficiency.[1]

[1] There was thought about a separate book on p-cycles alone, but it seemed more important to get the information out without further delay. That, in part, has been the cause of a bigger book than initially planned.

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Providers of the networking equipment, the vendors, are—as the saying goes—"fascinated by anything that interests their boss." That means their network operating customers. Vendors must not just keep in step with the problems, opportunities, and thinking of their customers, but also aspire to bring their own unique equipment design strategies to the market and to provide leadership in development of advantageous new networking concepts. The vendor community will therefore be especially interested in the techniques for

split-second mesh restoration and self-organizing traffic-adaptation as features for their intelligent optical cross-connects and Gigabit routers, for instance—as well ideas for new transport equipment such as the straddling span interface unit that converts an existing add/drop multiplexer into a p-cycle node. All of the other topics covered are of interest to vendors too because they enhance their ability to assist customers with network planning studies as part of the customer engagement and sales process.

Developers of network modeling, simulation and planning software will also be interested in many ideas in the book. By incorporating capabilities to design all types of architecture alternatives or, for example, to simulate dynamic provisioning operations in a protected working capacity envelope, or to model the incremental evolution of a survivable capacity design in the face of uncertain demand, or to support ring-mining evolutionary strategies—these suppliers enable their customers to pursue a host of interesting new "what if" planning studies.

The second main community for whom the book is intended is that of graduate-level teaching and research and new transport

networking engineers who want a self-contained volume to get bootstrapped into the world of transport networking planning or to pursue thesis-oriented research work. A principle throughout has been to draw directly on my experience since 1992 at the University of Alberta of teaching graduate students about survivable transport networking. This allowed me to apply the test: "What needs to be included so that my graduate students would be empowered both to do advanced investigations in the area, but also to be knowledgeable in general about transport networking?" On one hand, I want these students to be able to defend a Ph.D. dissertation, but on the other hand also to have enough general awareness of the technology and the field to engage in discussion with working engineers in the field. This is really the reason the book has two parts.

The test of needed background has guided the definition of Chapters 1 to 4 which are called the "Preparatory" chapters. These chapters cover a lot of generally useful ground on IP and optical technology, routing algorithms, graph theory, network flow problems and optimization. Their aim is to provide a student or new engineer with tools to use, and an introductory understanding of issues, trends, and concepts that are unique to transport networking. In my experience, students may have done good theoretical research, but at their dissertations a committee member may still stump them with a down-to-earth question like "How often do cables actually get cut?" "Is this just for SONET or does it work for DWDM too?", "How does restorability affect the availability of the network?" or (perennially it seems) "...but I don't see where are you rerouting each phone call or packet." These few examples are meant just to convey my philosophy that as engineers we should know not only the theory, the mathematical methods, and so on, to pursue our "neat ideas" but we also need to know about the technology and the real-world backdrop to the research or planning context. This makes for the best-prepared graduate students and it transfers to the training of new engineers in a company so that they are prepared to participate and contribute right away in all discussions within the network planning group he or she joins. An engineer who can, for example, link the mathematics of availability analysis to a contentious, costly, and nitty-gritty issue such as how deep do cables have to be buried, is exactly the kind of valuable person this book aims to help prepare. Someone who can optimize a survivable capacity envelope for mixed dynamic services, but is also savvy enough to stay out of the fruitless "50 ms debate" is another conceptual example of the

complimentary forms of training and knowledge the book aspires to provide.

The book is ultimately a network planners or technology strategists view of the networking ideas that are treated. It employs

well-grounded theoretical and mathematical methods, but those are not the end in itself. The book is also not filled with theorems and proofs. The emphasis is on the network architectures, strategies and ideas and the benefits they may provide, not primarily on the computational theory of solving the related problems in the fastest possible way. Our philosophy is that if the networking ideas or science look promising, then the efforts on computational enhancement are justified and can follow. Fundamental questions and ideas about networks, and network architecture, (which is the main priority in my group) stand on their own, not to be confused with questions and ideas about algorithms and solution techniques to solve the related problems as fast as possible (others are stronger in that task).

Obviously work in this area involves us in both networking science and computation, but the logical distinction is important—and often seems lost in the academic literature.[2]

The book is also not a compendium or survey of previously published papers. While suitably referenced, its content is unabashedly dominated by the author's own explorations and contains a large amount of previously

unpublished material. Although setting the context in terms of modern transport technologies (WDM, SONET, ATM, IP, MPLS) our basic treatment of the networking ideas and related planning problems is in a generic logical framework. The generic models can be easily adapted for to any specific technologies, capacities, costs, or signaling protocols, etc. The book thus provides a working engineer or a new researcher with a comprehensive, theoretically based, reference book of basic architectural concepts, design methods and network strategy options to be applied on mesh-survivable networks now and in the future.

[2] For instance an algorithm for optimal p-cycle design might be NP-hard, but it would be nonsense to say that p-cycles themselves are complex because of this. One is an algorithm, the other is a network architecture. In the same spirit—we tend to say "so what" if Integer Programming is theoretically NP-hard—in practice we can solve enormously large and useful problems with it in 15 minutes! And if not, then we pursue whatever else we have to do. But networking insight is the end, computation is only the means.

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A few words about the flow of the book. The Introduction gives a much fuller roadmap of the content and novelty in each chapter. Briefly, however, Chapter 1 is an orientation to transport networking. Chapter 2 is devoted to background on IP and DWDM optical networking developments, as the technological backdrop. Part of Chapter 3 is partly just "interesting reading" on the effects of failures and the range of known schemes and techniques to counteract or avoid failures. The rest of Chapter 3 includes a more technical "sorting out" of the

"—ilities": availability, reliability, network reliability, restorability, and other measures. Chapter 4 is then devoted to graph theory, routing algorithms and optimization theory and techniques but only as these topics specifically relate to transport network problems. Chapter 5 starts the second part of the book on more advanced studies and applications with an in-depth treatment of span protection and restoration. It has its counterpart devoted to path restoration in Chapter 6. Chapter 5 considerably "updates" the thinking about span-oriented survivability in optical networks with dynamic traffic.

If the book was a musical score, Chapters 7 through 11 would be the "variations." Each chapter treats a more advanced topic or idea selected by the author because of its perceived usefulness or possible influence on the direction of further research and development.

These are some of the author's "shiny pebbles" (in the earnestly humble sense of Newton[3]

). Chapter 7 recognizes an important difference—and opportunity—in cell or packet-based transport: that of controlled oversubscription of capacity upon restoration. This is a unique advantage for MPLS/IP-based transport survivability. Chapter 8 is devoted to all aspects of dual-failure considerations in mesh restorable networks. An especially interesting finding is that with a "first-failure protection, second-failure restoration" concept, higher than 1+1 availability can be achieved for premium service paths at essentially no extra cost. Chapter 9 treats the challenging, and so far almost unaddressed, problem of optimizing or evolving the basic facility-route (physical layer) topology for a mesh-restorable network. Chapter 10 explains the new (and to us, very exciting) concept of p-cycles, which are rooted in the idea of pre-configuration of mesh spare capacity.

[3] A quote attributed to Newton paints a humbling but touching image—that all of us (researchers) are as yet like children on a beach—calling out to each other about the "shiny pebbles" we have found. He said: "I have been only like a boy, playing on the sea-shore... now and then finding a smoother pebble or a prettier shell, while the great ocean of truth lay all undiscovered before me.''

p-Cycles are, in a sense, so simple, and yet they combine the fast switching of ring networks with the capacity-efficiency of mesh-based networks. We include p-cycles as a mesh-based survivable architecture because they exhibit extremely low mesh-like capacity redundancy and because demands are routed via shortest paths over the entire facilities graph. They are admittedly, however, a rather unique form of protection scheme in their own right in that lies in many regards in-between rings and mesh. Candidly, I venture that many colleagues who went through the decade-long ring-versus-mesh "religious wars" of the 1990s would understand when I say that p-cycles call for that forehead-bumping gesture of sudden realization—this solution (which combines ring and mesh) was unseen for the whole decade-long duration of this debate! As of this writing the author knows several research groups that are shifting direction to work on p-cycles as well as a half-dozen key industry players looking closely at the concept.

Chapter 11 on ring-mesh hybrids and ring to mesh evolution is placed at the end. The logic is that if we assume success of the prior chapters in motivating the mesh-based option then the "problem" this creates is that many current networks are ring-based. Its like "Ok, we believe you—but how do we get there now?" The closing chapter therefore devotes itself to bridging the gulf between existing ring-based networks and future mesh or p-cycle based networks by considering the design of intermediate ring-mesh hybrid networks and "ring-mining" as a strategy to get to a mesh future from a ring starting-point today.

The Appendices, and other resources such as chapter supplements, a glossary, student problems, research project ideas, network models, and more are all web-based—so they can be continually updated and expanded in scope and usefulness. Many directly usable tools and resources are provided for work in the area of mesh-survivable networking. This includes AMPL models and programs to permit independent further study of most of the planning strategies presented, plus Powerpoint lectures on a selection of topics, technical reports, and additional references and discussions. The aim has been to create a highly useful and hopefully interesting book that is laden with new options, ideas, insights and methods for industry and academia to enjoy and benefit from.

Wayne D. Grover,

TRLabs and the University of Alberta, Edmonton, Canada.

July 11, 2003

[ Team LiB ]

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[ Team LiB ]

Acknowledgements

This project reflects contributions and support from many people and a few key organizations. First and foremost, I have been especially fortunate in the four years that this book was in preparation to work with TRLabs leading an outstanding group of likable, highly capable, and seemingly inexhaustible graduate students who have shown terrific enthusiasm for this book and the related EE 681 course at the University of Alberta. Just as the commercial says—these are the people that "live, breathe and eat this stuff"—they love it and they're experts at it too. Among those that contributed—not only with repeated proofreading, suggestions, questions and comments, but in most cases also with direct contributions of sample results or other data and/or diagrams for inclusion in the book are:

John Doucette, Ph.D. candidate and TRLabs Research Engineer Matthieu Clouqueur, Ph.D. candidate and TRLabs Research Engineer Anthony Sack, M.Sc. candidate

Gangxiang Shen, Ph.D. candidate Govind Kaigala, M.Sc. candidate Adil Kodian, M.Sc. candidate Dion Leung, Ph.D. candidate

Dominic Schupke, Doctoral candidate, Technische Universitat Munchen

Specific papers and materials related to collaboration with these and other students are noted throughout the book. But I want to make special mention of John, Matthieu and Anthony. In the course of working at the book (off and on) over the last 4 years, I would repeatedly call up John or Matthieu, Anthony too, and begin a conversation with: "I wonder if we could....—". Almost every conversation led to production of some original new test-case results or other experiment, data or drawings to be used in the book. Often it led to whole projects that these students carried out enthusiastically and capably and were then synopsized in the book and/or became the basis for whole separate research papers. Collaborations with John to produce results and other material in Chapters 5 (Span Restoration) and 9 (Topology) were especially fruitful, but John's hand is found in Chapters 6, 8 and 10 as well. Work with Matthieu, especially on multi-QoP and mesh availability is found in Chapter 5 and is central to Chapter 8. And by now Anthony must feel wedded to the p-cycles chapter, having been through it with a fine-tooth comb, and been an intimate collaborator on the Hamiltonian-related aspects of p-cycles. I deeply appreciate his critical-thinking skills, and time spent providing exceptionally thoughtful, detailed markups of most chapters. I can hardly praise enough the skill and tirelessness of these three in supporting and enriching this project.

Another group of students have finished and moved on, but left theses and other materials from investigations we undertook, that I have adapted, summarized, or otherwise blended into the mix. Material I selected was—in my view—useful or valuable work, or good tutorial background, that was previously published only in theses or documented in internal reports or notes. In other cases I have drawn upon, or extended, the unpublished results of past collaborations with visiting researchers or TRLabs Research Staff—bringing culmination to some "good stuff" that was never published. Beyond the normal use of citations for acknowledgement, I want to especially mention:

Dave Morley, former Ph.D. student and now TRLabs Director of Business Development Demetrios Stamatelakis, former M.Sc. student and now TELUS Research Engineer Jim Slevinsky, former M.Sc. student and now with TELUS Technology Strategy Rainer Iraschko, former Ph.D. student and management of ONI and Network Photonics.

Chioma Nebo (nee Ezema), former M.Sc. student now with Shell Petroleum Brad Venables, former M.Sc. student now with Nortel Networks

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Yong Zheng, former M.Sc.student

Mike MacGregor, former Ph.D. student and now U. of A. Assoc. Prof. Computing Science Graeme Brown, BT Labs, Visiting Researcher to TRLabs

Oliver Yang and Donna He, SITE, University of Ottawa

Mandana Asadi, former M. Eng. student and with Rogers Communications Kent Lam, former M.Eng student

Matthias Scheffel, former exchange student Technische Universitat Munchen Nelly Hamon, former ENSEA (France) exchange student

Chee Yoon Lee, former M.Sc. student and with Nortel Networks Ernest Siu, former M.Sc. student now with Yotta Yotta

Dave Allen at MCI

Kent Felske, Jeff Fitchett, Alan Graves and others at Nortel Networks

Organizations?— TRLabs and the University of Alberta! Many thanks for the environment that made the book project possible as well as all of the research that fed into it. TRLabs and its sponsors have fostered the 17 years of research in transport networks that is behind this work. To TRLabs and its leaders, present (Dr. Roger Pederson) and past (Glenn Rainbird and Ray Fortune), I can only say "Thanks for persisting—and believing." The TRLabs story is a terrific example of vision and success in industry-university collaboration (please see www.trlabs.ca). I am just pleased to add this book to the list of TRLabs' accomplishments. The many years of interacting with people at TRLabs sponsor companies—especially Nortel, TELUS, MCI, SaskTel, but others as well—have also been a tremendous benefit. It feels tough when they don't immediately accept our ideas, and they challenge our thinking. But this improves the "product" immensely in the end and fuels the engine of further work. It forces my students and I to refine our understandings of the issues and always work harder to combine academic depth with practical relevance. So, to all those TRLabs companies over the years that patiently heard our presentations, explained what we were missing, and suggested directions for the next steps—Thank you! Also my sincere appreciation goes to Linda Richens at TRLabs who has so capably and efficiently handled many TRLabs administrative and management-support tasks that maximize my time available for research, students, sponsors, and writing.

The University of Alberta in turn fosters TRLabs and my academic position that led to this book. I am especially grateful for the 1999/2000 sabbatical year that allowed me to launch this project and to work in residence with Level(3)—(Thanks there to Lorraine Lotosky, Linos Frantzeskakis, Russ Rushmeier, Robert Feuerstein and others) and to give specialty lectures in the area at the University of Colorado—(Thanks there to Prof. Frank Barnes). Back at home, ECE chair Witold Pedrycz, has been constantly encouraging.

Reminders that he "wants a copy of the book to display in the cabinet" were a clever and gentle device to encourage me to finish —to visualize it in the cabinet. I also want to thank NSERC. Through the Discovery Grant program and added funding and time from the E.W.R Steacie Fellowship, combined with TRLabs, I was able to build a team of 14 students, all working on topics in transport networking.

At Prentice-Hall, Bernard Goodwin feels like my "book-writing father" now! Bernard and I went on an odyssey where he taught me how to get a book written and—believe it or not—I made him into an advocate for mesh-based networking! Bernard explains this book to others in the publishing field as well as I could now. But I'd do a lot of things differently next time—having learned a lot, thanks to Bernard. I also salute him for his leadership on some tough decisions. I had started out on an even bigger (but unrealistic) initial plan—Bernard saw that first and got me to realize it. Then the economy was terrible while the book was written, and telecom was down the most. Add to that, that this is a big book and it is two years overdue—so I really appreciate Prentice-Hall's (read Bernard's) faith in the project, and patience and persistence in getting what this mesh-networking stuff is, and where it fits in. As of writing these notes, my main journey with Mary Sudul is not over yet—the production process. Lots of wrestling with PDF! Thanks Mary, for all the editorial markups, advice, cover design, and FrameMaker tips so far!

That leaves the home-front. Thanks Jutta, especially for your shared experience with scientific writing, and with helping me realize I had to stop working on it at some point. Thanks also to both Jutta and Teddy for all the nights I was over at the office with the lights on late, or at the computer at home. Teddy—this is what I was doing all that time. I hope you like it!

Wayne D. Grover,

TRLabs/University of Alberta,

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July 12, 2003

[ Team LiB ]

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[ Team LiB ]

Introduction and Outline

Network survivability is a fascinating topic, both as an area of technical study and because it is not removed from our everyday lives—a failure can affect our plans, in some cases even our lives, fairly directly. The growth of the Internet, the increasing number of "mission critical" business functions that rely on communication networks, and the emergence of general societal dependencies on

communications, all make survivability a now-essential, but only fairly recently considered, aspect of network design. With up to 100 terabits per second of data flowing through a single fiber with DWDM, failure can have catastrophic and far-reaching consequences. And such events, cable-cuts in particular, are surprisingly frequent. In the first eight months of 2002 alone, the FCC logged 116 network outages in the United States with wide-ranging effects and often peculiar causes. On February 13 in Yadkinville, NC, town workers severed a Sprint cable while repairing a water line, cutting 52 trunk groups and 13 DS-3 links for over 5 hours. A week later a fire in a Maryland power transformer melted a Verizon fiber cable affecting 5000 customers for over 9 hours. On March 14, a contractor accidentally cut functional fiber during removal of retired cable, cutting 911 service to a part of San Diego for over 4 hours. Despite considerable efforts at physical protection of cables, FCC statistics are that metro networks annually experience 13 cuts for every 1000 miles of fiber, and long haul networks experience 3 cuts for 1000 miles fiber. The numbers may sound small, but even the lower rate for long-haul implies a cable cut every four days on average in a network with 30,000 route-miles of fiber. And such failures are having increasing societal impact. Consider the following estimate of the direct revenue impact alone:

"Through 2004, large U.S. enterprises will have lost more than $500 million in potential revenue due to network failures that affect critical business functions." [Gartner Group, 2002]

We are now almost as dependent on the availability of communications networks as on other basic infrastructure like roads, water, and power. The phrase "mission critical business functions" has even been coined to refer to applications that must be running and available over communication networks 24 hours a day, seven days a week, for the related businesses to survive. Put together, these factors mean that survivability must be a foremost consideration in the basic design of any network, not an afterthought.

Despite considerable efforts to physically protect network elements—fiber optic cables in particular, the real world is surprisingly creative in finding ways to cut them. Who would have guessed failure of the TAT-8 undersea fiber system from deep-sea shark bites? Who would have foreseen the loss of air-traffic control at JFK airport at the end of a causality chain beginning with street works that cut a cable?

Who would have foreseen youths building a fire under a bridge abutment—below the cable trays? On the other hand, imagine the quiet excitement of the engineer who watched his network react spontaneously, literally in the "blink of an eye," completely hiding from 129,000 users the fact that an ice-storm had finally pulled down the most burdened aerial cable section. Perhaps especially for engineers, it is fascinating to learn about the often elegant concepts that, by-and-large are unseen by the public, but underlie the basic infrastructures of our lives. This book is about one of the most important of those infrastructures—optical transport networks—and a range of techniques to make them withstand such failures by design, and as efficiently as possible.

[ Team LiB ]

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[ Team LiB ]

Historical Backdrop

Telecommunication equipment makers, carriers, and users have historically been concerned with reliability, but not with such an intense focus as in recent times. Previously, attention was paid to ensuring certain levels of availability[1]

in network elements, through redundant design at the equipment level. Operators would estimate service availability over such network elements configured in series

"hypothetical reference path" configurations. The situation could be described as one where the transmission equipment was redundantly designed, but not the network as a whole. If a failure arose that overcame these measures, a service outage would occur until repair was completed, or until a manual effort at partial rerouting was completed. A carrier would measure performance by the overall annual fraction of time a hypothetical reference path would be in the "up" state, but there was no expectation of split-second recovery times against a major failure such as a cable cut.

[1] A technical concept to which we will return.

Today the goal, and increasingly the reality, is one of virtually instantaneous recovery against the most significant and frequent types of failure. What changed to cause this escalation in our expectations? Fiber optic technology, deregulation and competition, and

unprecedented growth in the use of communication service, especially Internet-based services and applications, are perhaps the three main factors. Optical networks based on wave-division multiplexing over fiber optics offer huge point-to-point capacities—over a terabit per second in total over each fiber. The advantages of optical fiber as a transmission medium include low loss, light weight,

electromagnetic immunity, high bandwidth, low cost, and so on. But a humbling reality is that no matter how advanced the fiber and system technology becomes, this is a cable-based technology—it goes in the ground or on poles, or it lies on the ocean bottom. In all cases it is surprisingly vulnerable. With thousands of route-kilometers of fiber deployed in national or regional networks, cable cuts and other line-related disruptions are an operational certainty. Consistent with the FCC data given for the U.S.A., Hermes, a pan-European

"carrier's carrier" has independently estimated an average of one cable cut every four days on their network. At the same time, the high capacity and economy of scale of fiber optics at higher transmission rates drives operators toward relatively sparse backbone topologies, making each cable section even more important to the network as a whole.

Deregulation in the 1980s also lead to pell-mell competition between incumbents and new entrants in the 1990s. This may have contributed to some of the headline-making failures of the era but it also made survivability a selling point, especially in competition for large corporate users and backbone Internet providers. The costs of redundancy for survivability can be very high, however, compared to a corresponding network designed only to serve the working demands under nominal conditions. Without careful choices of architecture and design methods it is easy to find the costs of a survivable network approaching twice the cost of a non-survivable network. This is a considerable motivation to look at new ways of designing and operating a survivable transport infrastructure.

Mesh survivability schemes can be viewed in one sense as the extension and automation of the essentially manual restoration methods used in the 1970s and early 1980s. In that era, 1:N or 1+1 automatic protection switching (APS) would often be designed into the transmission systems, but there would be no automated means for restoration from a complete facility cut. A great deal of the backbone transport network of the time was based on microwave radio that inherently has high structural availability. Individual equipment items could experience failures and radio paths could suffer from fading, but the APS systems would take care of that. When the need for restoration did arise, it was generally handled on a best-efforts basis, manually, by rearrangements at the DSX-3 patch panels. The DSX-3 panel was a manual patch board, similar to the old operator boards in concept, at which DS-3 level rearrangements of signals on and off of the transmission systems could be made. The process of rearranging connections between equipment with manual patch cords was called "cross-connection" and gives its name to the automated optical or SONET layer cross-connect systems of the current era.

It is the human process of inspecting the network state at the time of the failure, and developing a rerouting or "patch plan," that is the origin for the concept of mesh-restorable networks. The differences are that now we will carefully design-in specific amounts of spare capacity, with various theories for doing so, and embed real-time mechanisms to implement or even develop the "patch plan" itself, in a fraction of second. But the basic concepts are the same as when humans, knowing their network well, would work up an ad-hoc scheme of patching around the fault. The spare capacity would come from a variety of sources—some of it true spare channels, some of it from the spare spans of APS systems, and some of it from bumping low-priority traffic and/or the use of satellite transponders on a pre-contracted basis for restoration.

[ Team LiB ]

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[ Team LiB ]

The Case for Mesh-based Survivable Networks

Through the 1990s the industry vigorously debated ring versus mesh-based principles for survivable transport. Rings greatly predominated in practice, however, because the urgency for a "fix" to the survivability problems (which reached crisis proportions about 1994) was so great, and, in terms of development costs and time, ring systems were relatively easy extensions of existing point-to-point transmission systems with APS. (One of the first commercial ring-protected transport system, a precursor to the BLSR, was actually just existing FD-565 transmission systems each with 1+1 APS, simply connected in a ring with some re-wiring of the protection span inputs at each pair of back-to-back terminals.) Rings offer the advantages of being closed transport subsystems, with unquestionably fast protection

switching, and "pay as you grow" cost characteristics. At least initially people thought mesh-restoration was too complicated. One ring looks very simple, and this captivated the industry. But with time it was found that multi-ring networks are actually more complex (and in many ways more brittle) than a single integrated mesh network. With the growing dominance of data over voice, and a merging of viewpoints from people with data-centric backgrounds with those having more traditional telco ("Bell-heads") backgrounds, the pendulum has swung back toward an interest in mesh restoration. The primary reasons are that mesh offers greater flexibility, efficiency, and inherent support for multiple service classes. The greater capacity efficiency comes from the more direct routing of working paths, the need for less spare capacity for restoration, and the avoidance of "stranded capacity" effects in rings (where one or more ring spans may exhaust while other spans of the ring have valuable but unusable remaining working capacity). Mesh-based networks also offer the prospect of fully self-organizing operation in response to time-varying patterns of demand. "Point and click" or fully automated path provisioning is more difficult through a collection of transport rings than through a single integrated mesh network.

Achieving capacity efficiency from the sharing of spare capacity is a central aspect of the design methods in this book. Over 100%

redundancy is required with either APS or ring systems. In contrast, mesh restorable networks are based on generalized rerouting as needed for restoration using any or all diverse routes of the network. Figure I-1 conveys the idea of generality and flexibility of the rerouting patterns, and hence the sharing of spare capacity, that is implicit in mesh restoration. Spare capacity on one span typically contributes to the restorability of many other spans. Such networks are called "mesh-restorable" not to imply that the network is a full mesh, but to reflect the ability of the routing mechanism to exploit an irregular mesh-like topology. Anywhere network cost correlates to total installed capacity, or where maximum demand-serving ability is required out of a given transmission capacity base, the low redundancy of a mesh-restorable network is a factor in its favor.

Figure I-1. Mesh restoration involves network-wide sharing of spare capacity.

Capacity efficiency is not the only consideration in a choice of network architecture, but in a competitive environment the combination of

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efficiency, ease of growth, and service-provisioning flexibility that a mesh network can offer can provide carriers with a productivity edge over their competitors. The notion that "bandwidth is free" is simply not accurate at the scale of investment faced by transport network planners where incremental capital expenditures of $US 300 to 400 million for transport equipment are typical. If a 40% increase in capacity efficiency leads to even just 15 to 20% cost savings on a budget like that, then "going mesh" would be a well-qualified project for corporate productivity and profit enhancement.

Efficiency in capacity is also inherently linked to flexibility to cope with forecasting uncertainty, and provisioning productivity in terms of handling high growth rates and/or high rates of customer "churn." Mesh-based networks are more "future-proof" because for the same investment in capacity, one can serve more working demand, and in more diverse patterns than a corresponding set of rings. Sustained rapid growth or churn also creates an environment where there is a premium for capacity efficiency purely because the speed of deploying new capacity or making changes in routing and protection arrangements is the rate-limiting step to earnings growth. Any time new transmission capacity can barely be provisioned fast enough to keep up with demand, then a more efficient architecture will also serve more demand (and hence earn more revenue) given a currently installed base of transmission systems.

[ Team LiB ]

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[ Team LiB ]

Outline

Chapters are grouped as being either preparatory or specialized in nature, giving the book two main parts. The aim is to provide a new planner, or a graduate student, with a combination of in-depth technical exposures to advanced concepts (Part II), while also being informed by an overall awareness of the technology and general issues and setting of the field (Part I). The Part I chapters not only facilitate access, absorption, and use of material in the later chapters but also provide a backgrounder on the technology directions and network planning issues that influence the ongoing direction and use that a reader can make of the specialized Part II topics.

Part I "Preparations"

Chapter 1: Orientation to Transport Networks

Here we introduce the key concepts of transport networking which is different in important ways from telephone circuit switching and packet data routing networks that many readers will already know. The concept of "transport networking" has evolved as an extension of transmission system engineering more than anything else. Key ideas here are of service layer networks being clients of the transport layer, and awareness of multiplexing, switching, grooming, aggregation, and carrier transmission system technology basics. This includes an overview of SONET and still widely employed "plesiochronous" digital signals as well as looking at the basic concept of label switching that underlies ATM and MPLS. In closing Chapter 1 we look introduce some aspects of network planning that are specific to transport networks such as modularity of capacity, physical route structures, demand modeling, and shared-risk entity concepts.

Chapter 2: IP and Optical Networking

The dominance of Internet Protocol (IP) packets as the main source of traffic, and the emergence of Dense Wavelength Division Multiplexing (DWDM) technology to carry huge increases in total demand, are two of the greatest technical "discontinuities" affecting network operators, planners and equipment vendors. The material of this chapter is devoted to these important developments—essential for a new student or engineer to join in, in informed participation, on topics related to modern transport network planning. This includes a review of data-centric payloads, gigabit Ethernet, extensions to SONET for enhanced data transport, optical service channel and "digital wrapper" concepts that provide signaling overheads for provisioning and restoration or protection applications. The chapter also familiarizes readers with the concept of adapting and using classical IP protocols for topology discovery and link-state dissemination for control of the optical transport network. This completes the technology backdrop in which the more general design theories and methods of the Part II chapters are set.

Chapter 3: Failure Impacts, Survivability Principles, and Measures of Survivability

This chapter starts with background on the causes and frequency of transport network failures and their impact on various service types.

This includes a discussion on the role and real need for the so-called "50 ms" restoration times. Basic techniques for avoiding or