![This book contains information obtained from authentic and highly regarded sources. Reprinted material
is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable
efforts have been made to publish reliable data and information, but the author and the publisher cannot
assume responsibility for the validity of all materials or for the consequences of their use.
Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic
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All rights reserved. Authorization to photocopy items for internal or personal use, or the personal or
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No claim to original U.S. Government works
International Standard Book Number 0-8493-1333-3
Library of Congress Card Number 2002041927
Printed in the United States of America 1 2 3 4 5 6 7 8 9 0
Printed on acid-free paper
Library of Congress Cataloging-in-Publication Data
The handbook of optical communication networks / Mohammad Ilyas, Hussein T. Mouftah [editors].
p. cm. -- (Electrical engineering handbook series ; 30)
Includes bibliographical references and index.
ISBN 0-8493-1333-3 (alk. paper)
1. Optical communications. I. Ilyas, Mohammad, 1953 - II. Mouftah, Hussein T. III.
Series.
TK5103.59 .H365 2003
621.382’7—dc21 2002041927
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![2 The handbook of optical communication networks
1.5.4 Traffic grooming in WDM mesh networks
1.5.5 IP over WDM
1.5.6 Call admission control based on physical impairments
1.5.7 Network control and signaling
1.5.8 Optical packet switching
1.5.8.1 Optical burst switching
1.6 Future directions
References
1.1 Introduction
The focus of this chapter is to present technological advances, promising archi-
tectures, and exciting research issues in designing and operating next-generation
optical wavelength-division multiplexing (WDM) networks, which are scalable
and flexible. We discuss important building blocks of optical WDM networks
and overview access, metropolitan, and long-haul networks separately. Special
attention has been paid to the long-haul network because there is a tremendous
need to develop new intelligent algorithms and approaches to efficiently design
and operate these wide-area-optical-mesh networks built on new emerging tech-
nologies. We present several research topics including routing and wavelength
assignment, fault management, multicasting, traffic grooming, optical packet
switching, and various connection-management problems. The Internet is devel-
oping rapidly with the ultimate goal being to provide us with easy and fast
access to any desired information from any corner of the world. Information
exchange (or telecommunications) technology, which has been evolving contin-
uously since the telephone was invented, is still striving to meet the users’
demands for higher bandwidth. This demand is attributed to the growing pop-
ularity of bandwidth-intensive networking applications, such as data browsing
on the World Wide Web (WWW), java applications, video conferencing, inter-
active distance learning, on-line games, etc. Figure 1.1 plots the past and pro-
jected growth of data and voice traffic as reported by most telecom carriers.1 It
shows that, while voice traffic continues to experience a healthy growth of
approximately 7% per year, data traffic has been growing much faster. To sup-
port this exponential growth in the user data traffic, there is a strong need for
high-bandwidth network facilities, whose capabilities are much beyond those
of current high-speed networks such as asynchronous transfer mode (ATM),
SONET/SDH* etc.2
Fiber-optic technology can meet the previously mentioned need because
of its potentially limitless capabilities:3 huge bandwidth (nearly 50 terabits
per second [Tbps] for single-mode fiber), low signal attenuation (as low as
0.2 dB/km), low signal distortion, low power requirement, low material
usage, small space requirement, and low cost. Given that a single-mode
* SONET and SDH are a set of related standards for synchronous data transmission over fiber
optic networks. SONET is short for Synchronous Optical NETwork and SDH is an acronym for
Synchronous Digital Hierarchy.
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![12 The handbook of optical communication networks
each node is equivalent to a circuit-switched telephone network; thus, only
the routing problem needs to be addressed, and wavelength assignment is
not an issue.17
Three basic approaches are used for the routing subproblem: fixed rout-
ing, fixed-alternate routing, and adaptive routing.20 Fixed routing is a straight-
forward approach in which same fixed route is always chosen to route a
connection for a given source-destination pair. One example of such an
approach is fixed shortest-path routing. In fixed-alternate routing, each node
in the network maintains a routing table containing an ordered list of a
number of fixed routes to each destination node. For example, these routes
may include the shortest-path route, the second shortest-path route, the third
shortest-path route, etc. When a connection request arrives, the source node
attempts to establish the connection on each of the routes from the routing
table in sequence, until a route with a valid wavelength assignment is found.
If no available route is found from the list of alternate routes, then the
connection request is blocked. In adaptive routing, the route from a source
node to a destination node is chosen dynamically, depending on the network
state. This approach has lower connection blocking than fixed and
fixed-alternate routing, but it is more computationally intensive.
Once a path has been chosen for a connection, a wavelength must be
assigned to it such that any two lightpaths that are sharing the same physical
link are assigned different wavelengths. Assigning wavelengths to different
lightpaths that minimizes the number of wavelengths used under the wave-
length-continuity constraint reduces to the graph-coloring problem.18,21,22 This
problem has been demonstrated to be NP-complete, and the minimum num-
ber of colors needed to color a graph G (called the chromatic number c[G]
of the graph) is difficult to determine. However, there are efficient sequential
graph-coloring algorithms, which are optimal in the number of colors used.
Other RWA heuristics such as First-Fit, Least-Used, Most-Used, etc. can be
found in Reference 22.
1.5.2 Fault management
In a wavelength-routed WDM network (as well in other networks), the failure
of a network element (e.g., fiber link, crossconnect, etc.) may result in the
failure of several optical channels, thereby leading to large data and revenue
losses. Several approaches are used to ensure fiber-network survivability
against fiber-link failures.23 Survivable network architectures are based either
on reserving backup resources in advance (called “protection”),24 or on dis-
covering spare backup resources in an online manner (called “restoration”).25
In protection, which includes automatic protection switching (APS) and
self-healing rings,26,27 the disrupted service is restored by utilizing the precom-
puted and reserved network resources. In dynamic restoration, the spare
capacity, if any, available within the network is utilized for restoring services
affected by a failure. Generally, dynamic restoration schemes are more efficient
in utilizing network capacity due to the multiplexing of the spare-capacity
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![18 The handbook of optical communication networks
absence of wavelength converters, the light-tree-based multicast session
would exhibit the wavelength-continuity constraint.
1.5.3.2 Multicast routing and wavelength assignment
The multicasting problem in communication networks is often modeled as a
Steiner Minimum Tree (SMT), which is an NP-complete problem.38 The problem
complexity increases when several multicast sessions (which we expect to occur
in the future) have to be established at a minimum aggregate cost. Heuristics
are employed for routing and wavelength assignment of multicast sessions.39,40
A single fiber cut on a multicast tree can disrupt the transmission of infor-
mation to several destination nodes on a light-tree. This loss would be large if
several sessions were occupying the affected fiber link. In order to prevent the
large loss of information, it is imperative to protect the multicast sessions
through a protection scheme such as reserving resources along a backup tree.
Protecting such multicast sessions using schemes (dedicated or shared) dis-
cussed in Section 1.5.2 is an important problem that needs to be studied.
1.5.4 Traffic grooming in WDM mesh networks
Today, each wavelength channel has the transmission rate of over a Gbps
(e.g., OC-48 [2.5 Gbps], OC-192 [10 Gbps], or OC-768 [40 Gbps] in the near
future). However, the capacity required by the traffic streams from client
networks (IP, ATM, etc.) can be significantly lower, and they can vary in the
range from OC-1 (51.84 Mbps) or lower, up to full wavelength capacity. In
Figure 1.13 Transparent OXC architecture for supporting multicasting using optical
splitters.
DEMUX MUX
X
Y
Optical
Switch
Optical
Switch
Add Drop Add Drop
1
2
D
1
2
D
Incoming Fibers Outcoming Fibers
Splitter Bank
Amplifier Bank
Coverter Bank
λb
λa
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![Chapter one: Overview of optical communication networks 23
1.5.8 Optical packet switching
WDM and optical-switching technology can provide the necessary band-
width for the growing traffic demand. As data traffic starts to dominate
the communication networks, the traffic even on the long-haul network
becomes more data oriented (i.e., less predictable). In the long term,
optical packet switching (OPS) could become a viable candidate because
of its high-speed, fine-granularity switching, flexibility, and its ability to
use the resources economically. The technology is still in a very early
stage, and several issues need to be solved, including switch architec-
tures, synchronization, contention-resolution schemes, etc. (see Yao et al.
[2000] for a tutorial).56
An optical packet switch includes packet-synchronization stages, a
switch fabric, and a control unit that extracts and reads the packet header
to route the packet through the switch fabric to the proper output port. One
main property here is to decide whether the network should operate syn-
chronously. A globally synchronized (slotted) network can use aligned time
slots as the holders of fixed-size packets. In such a network, the switch fabric
at a node receives the incoming packets aligned, minimizing the packet
contention; however, this switch architecture is more complex because of
synchronization/packet-alignment stages. The other alternative is to build
an asynchronus (unslotted) network where packets may have variable
lengths. The switch architecture is simpler in this case, though packet-con-
tention probability is higher. For a survey of different switch fabrics, please
refer to Reference 57.
Contention of packets in a switch fabric is a major problem and has
important impact on the performance of the network such as packet delay,
packet-loss ratio, throughput, and average hop distance. Contention occurs
Figure 1.15 Network management system for IP-over-WDM networks.
Network Management System (NMS)
Proprietary NNI Standardized
NNI
UNI
IP Router
ADM
1
2 3
4
5
6
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![24 The handbook of optical communication networks
when two or more packets try to leave the switch from the same output port
at the same time. To resolve such a conflict, one of the packets is routed
through the output port while others are routed elsewhere, depending on
the contention-resolution scheme. In electronic switches, contention can be
resolved by the store-and-forward technique where packets in contention
are stored in a buffer and sent out when the port becomes available. Unfor-
tunately, optical buffers similar to electronic counterparts (i.e., ran-
dom-access memory [RAM]) do not exist; the only way to store an optical
packet is to use optical delay lines (fixed length fibers). These “sequential
access” buffers are less flexible than an electronic “random access” buffer
because a packet entering a delay line will emerge from the other end of the
line after a fixed amount of time. Several switch architectures that use optical
buffers were proposed in Reference 56.
Another method for contention resolution is deflection routing, which
is also called hot potato routing. In case of contention, one packet is routed
along the desired link while others are forwarded on some other links,
which may lead to longer paths. Deflection routing can be used along with
optical buffers.
The unique advantage of WDM networks (i.e., several wavelength chan-
nels on the same link) can be used to create a third method for contention
resolution, namely wavelength conversion. This is an attractive solution
because it can achieve the same propagation delay and hop distance as the
optimal case. All three or any two solutions can be combined to provide
better performance.
Today, OPS still seems like a dream because of several technical obstacles.
Our current vision for network planning is to implement a dynamically
reconfigurable optical transport layer using fast OXCs, providing enough
bandwidth to evolving data applications. If and when optical packet switch-
ing becomes available, we may choose to incorporate it into our existing
optical circuit-switching architecture.58 Packet switching is not limited only
to wide-area networks; a tutorial on implementing OPS in metropolitan-area
networks can be found in Reference 59.
1.5.8.1 Optical burst switching
As a midway solution between circuit switching and packet switching, opti-
cal burst switching (OBS) was proposed.60 This approach is motivated by
two problems: routing the IP traffic, which has a bursty characteristic, on a
relatively-static circuit-switched network leads to poor usage of network
resources; and OPS technology is not mature for the near future. In OBS, a
control packet is sent first to reserve an appropriate amount of bandwidth
and to preconfigure the switches along the path. The burst of data, which
can consist of several packets forming a (possibly short) session, immediately
follows the control packet, without waiting for an acknowledgment. OBS
has a lower control overhead compared to OPS and it may lead to better
resource usage compared to circuit switching because reserved resources are
released after the completion of the burst. Several issues need to be addressed
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- 5. © 2002 by CRC Press LLC © 2002 by CRC Press LLC © 2002 by CRC Press LLC © 2003 by CRC Press LLC
- 6. The Electrical Engineering Handbook Series Series Editor Richard C. Dorf University of California, Davis Titles Included in the Series The Handbook of Ad Hoc Wireless Networks, Mohammad Ilyas The Avionics Handbook, Cary R. Spitzer The Biomedical Engineering Handbook, Second Edition, Joseph D. Bronzino The Circuits and Filters Handbook, Second Edition, Wai-Kai Chen The Communications Handbook, Second Edition, Jerry Gibson The Computer Engineering Handbook, Vojin G. Oklobdzija The Control Handbook, William S. Levine The Digital Signal Processing Handbook, Vijay K. Madisetti and Douglas Williams The Electrical Engineering Handbook, Second Edition, Richard C. Dorf The Electric Power Engineering Handbook, Leo L. Grigsby The Electronics Handbook, Jerry C. Whitaker The Engineering Handbook, Richard C. Dorf The Handbook of Formulas and Tables for Signal Processing, Alexander D. Poularikas The Handbook of Nanoscience, Engineering, and Technology, William A. Goddard, III, Donald W. Brenner, Sergey E. Lyshevski, and Gerald J. Iafrate The Handbook of Optical Communication Networks, Mohammad Ilyas and Hussein T. Mouftah The Industrial Electronics Handbook, J. David Irwin The Measurement, Instrumentation, and Sensors Handbook, John G. Webster The Mechanical Systems Design Handbook, Osita D.I. Nwokah and Yidirim Hurmuzlu The Mechatronics Handbook, Robert H. Bishop The Mobile Communications Handbook, Second Edition, Jerry D. Gibson The Ocean Engineering Handbook, Ferial El-Hawary The RF and Microwave Handbook, Mike Golio The Technology Management Handbook, Richard C. Dorf The Transforms and Applications Handbook, Second Edition, Alexander D. Poularikas The VLSI Handbook, Wai-Kai Chen Forthcoming Titles The CRC Handbook of Engineering Tables, Richard C. Dorf The Engineering Handbook, Second Edition, Richard C. Dorf © 2003 by CRC Press LLC
- 7. © 2003 by CRC Press LLC
- 8. This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microÞlming, and recording, or by any information storage or retrieval system, without prior permission in writing from the publisher. All rights reserved. Authorization to photocopy items for internal or personal use, or the personal or internal use of speciÞc clients, may be granted by CRC Press LLC, provided that $1.50 per page photocopied is paid directly to Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923 USA. The fee code for users of the Transactional Reporting Service is ISBN 0-8493-1333-3/03/ $0.00+$1.50. The fee is subject to change without notice. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. The consent of CRC Press LLC does not extend to copying for general distribution, for promotion, for creating new works, or for resale. SpeciÞc permission must be obtained in writing from CRC Press LLC for such copying. Direct all inquiries to CRC Press LLC, 2000 N.W. Corporate Blvd., Boca Raton, Florida 33431. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identiÞcation and explanation, without intent to infringe. Visit the CRC Press Web site at www.crcpress.com © 2003 by CRC Press LLC No claim to original U.S. Government works International Standard Book Number 0-8493-1333-3 Library of Congress Card Number 2002041927 Printed in the United States of America 1 2 3 4 5 6 7 8 9 0 Printed on acid-free paper Library of Congress Cataloging-in-Publication Data The handbook of optical communication networks / Mohammad Ilyas, Hussein T. Mouftah [editors]. p. cm. -- (Electrical engineering handbook series ; 30) Includes bibliographical references and index. ISBN 0-8493-1333-3 (alk. paper) 1. Optical communications. I. Ilyas, Mohammad, 1953 - II. Mouftah, Hussein T. III. Series. TK5103.59 .H365 2003 621.382’7—dc21 2002041927 1333_Frame_00.fm Page iv Wednesday, March 5, 2003 12:28 PM © 2003 by CRC Press LLC
- 9. Preface During the last 3 decades, the field of telecommunications has witnessed tremendous growth. Proliferation of the Internet has started a true revolution that is expected to continue through the foreseeable future. Three factors have played major roles in the unprecedented growth of this field: • Users’ incessant demand for high-speed communication facilities for heavy-duty applications such as rich-content video • Availability of high-speed transmission media such as optical fibers • Availability of high-speed hardware such as high-resolution video cameras and high-speed processors These factors are leading towards an integrated high-speed (and high-bandwidth) communication environment where all communication needs will be supported by a single communication network. The latest trends indicate that bandwidth needs double every 100 days. The volume of data traffic has surpassed the volume of voice traffic. Such a monumental demand for bandwidth can only be met by using optical fiber as transmission media. Other bottlenecks such as bringing fiber to the desktop, or to the home, still exist. However, eventually these obstacles will be overcome. Emerging optical communication networks represent a step in that direction. The Handbook of Optical Communication Networks is a source of compre- hensive reference material for such networks. The material presented here is intended for professionals in the communications industry who are designers and/or planners for emerging telecommunication networks, researchers (faculty members and graduate students), and those who would like to learn about this field. The handbook is organized in the following seven parts: • Introduction and optical networks architectures • Protocols for optical network architectures • Resource management in optical networks • Routing and wavelength assignment in WDM networks • Connection management in optical networks • Survivability in optical networks • Enabling technologies for optical networks 1333_Frame_00.fm Page v Wednesday, March 5, 2003 12:28 PM © 2003 by CRC Press LLC
- 10. Each part consists of 2 to 5 chapters dealing with the topic, and the handbook contains a total of 21 chapters. Although this is not precisely a textbook, it can certainly be used as one for graduate and research-oriented courses that deal with optical communication networks. Any comments from readers will be highly appreciated. Many people have contributed to this handbook in their unique ways. The first and the foremost group that deserves immense gratitude are the highly talented and skilled researchers who have contributed the 21 chapters to this handbook. All have been extremely cooperative and professional. It has also been a pleasure to work with Nora Konopka, Helena Redshaw, and Amy Rodriguez of CRC Press, and we are extremely grateful for their sup- port and professionalism. Our families have extended their unconditional love and strong support throughout this project, and they all deserve very special thanks. Mohammad Ilyas Boca Raton, Florida Hussein T. Mouftah Ottawa, Ontario, Canada 1333_Frame_00.fm Page vi Wednesday, March 5, 2003 12:28 PM © 2003 by CRC Press LLC
- 11. About the Editors Dr. Mohammad Ilyas earned his B.Sc. degree in electrical engineering from the University of Engineering and Technology, Lahore, Pakistan, in 1976. From March 1977 to September 1978, he worked for the Water and Power Development Authority, Pakistan. In 1978, Dr. Ilyas was awarded a scholar- ship for his graduate studies, and he completed his M.S. degree in electrical and electronic engineering in June 1980 at Shiraz University, Shiraz, Iran. In September 1980, he joined the doctoral program at Queen’s University in Kingston, Ontario, Canada. He earned his Ph.D. degree in 1983. His doctoral research was about switching and flow control techniques in computer com- munication networks. Since September 1983, Dr. Ilyas has been with the College of Engineering at Florida Atlantic University, Boca Raton, where he is currently Associate Dean for Graduate Studies and Research. From 1994 to 2000, he was Chair of the department. During the 1993–94 academic year, he was on his sabbatical leave with the Department of Computer Engineer- ing, King Saud University, Riyadh, Saudi Arabia. Dr. Ilyas has conducted successful research in various areas including traffic management and congestion control in broadband/high-speed com- munication networks, traffic characterization, wireless communication net- works, performance modeling, and simulation. He has published one book and over 130 research articles. He has supervised 10 Ph.D. dissertations and 32 M.S. theses to completion and has been a consultant to several national and international organizations. Dr. Ilyas is a senior member of IEEE and an active participant in several IEEE technical committees and activities. Hussein Mouftah joined the School of Information Technology and Engi- neering (SITE) of the University of Ottawa in September 2002 as a Canada research chair (Tier 1) professor in optical networks. He was previously full professor and department associate head of the Department of Electrical and Computer Engineering at Queen’s University (1979–2002). He has three years of industrial experience, mainly at Bell Northern Research of Ottawa (now Nortel Networks) (1977–1979). He also spent three sabbatical years at Nortel Networks (1986–1987, 1993–1994, and 2000–2001), conducting research in the areas of broadband packet switching networks, mobile wireless networks, and quality of service over the optical Internet. He served as editor-in-chief 1333_Frame_00.fm Page vii Wednesday, March 5, 2003 12:28 PM © 2003 by CRC Press LLC
- 12. of the IEEE Communications Magazine (1995–1997) IEEE Communications Soci- ety director of magazines (1998–1999), and chair of the Awards Committee (2002–2003). Dr. Mouftah is the author or co-author of 4 books, 17 book chapters, and more than 650 technical papers and 8 patents in this area. He is the recipient of the Association of Professional Engineers of Ontario (PEO) 1989 Engineering Medal for Research and Development, and the Ontario Distinguished Researcher Award of the Ontario Innovation Trust. He is the joint holder of the Best Paper Award for a paper presented at SPECTS’2002, and the Outstanding Paper Award for papers presented at the IEEE HPSR’2002 and the IEEE ISMVL’1985. He is also a joint holder of an honor- able mention for the Frederick W. Ellersick Price Paper Award for best paper in the IEEE Communications Magazine in 1993. He is the recipient of the IEEE Canada (Region 7) Outstanding Service Award (1995). Dr. Mouftah is a Fellow of the IEEE (1990). 1333_Frame_00.fm Page viii Wednesday, March 5, 2003 12:28 PM © 2003 by CRC Press LLC
- 13. Contributors Mohammed A. Alhaider Electrical Engineering Department King Saud University Riyadh, Saudi Arabia Mohamed A. Ali Department of Electrical Engineering City College of the City University of New York New York, New York Toshit Antani Department of Electrical and Computer Engineering University of California, Davis Davis, California Chadi Assi Department of Electrical Engineering City College of the City University of New York New York, New York David Benjamin Nortel Networks St. Laurent Quebec, Canada Imrich Chlamtac Department of Electrical Engineering University of Texas at Dallas Dallas, Texas Shirshanka Das Department of Computer Science University of California, Los Angeles Los Angeles, California W.R. Franta GATX Capital San Francisco, California Aysegül Gençata Department of Computer Engineering Istanbul Technical University Istanbul, Turkey Mario Gerla Department of Computer Science University of California, Los Angeles Los Angeles, California Peter Green Nortel Networks Ottawa, Ontario, Canada 1333_Frame_00.fm Page ix Wednesday, March 5, 2003 12:28 PM © 2003 by CRC Press LLC
- 14. Mounir Hamdi Department of Computer Science Hong Kong University of Science and Technology Kowloon, Hong Kong Pin-Han Ho Department of Electrical and Computer Engineering University of Waterloo Waterloo, Ontario, Canada Mohammad Ilyas Department of Computer Science and Engineering Florida Atlantic University Boca Raton, Florida Tariq Iqbal City of Riviera Beach West Palm Beach, Florida Jason P. Jue Department of Computer Science University of Texas at Dallas Dallas, Texas Hussein T. Mouftah School of Information Technology and Engineering University of Ottawa Ottawa, Ontario, Canada Biswanath Mukherjee Department of Computer Science University of California, Davis Davis, California C. Siva Ram Murthy Department of Coputer Science and Engineering India Institute of Technology Madras, India Kanna Potharlanka Department of Electrical and Computer Engineering University of California, Davis Davis, California M. Yasin Akhtar Raja Physics and Optical Science Department University of North Carolina, Charlotte Charlotte, North Carolina Byrav Ramamurthy Department of Computer Science and Engineering University of Nebraska, Lincoln Lincoln, Nebraska Matthew N.O. Sadiku Department of Electrical Engineering Prairie View A&M University Prairie View, Texas Laxman Sahasrabuddhe Department of Computer Science University of California, Davis Davis, California Chava Vijaya Saradhi Department of Computer Science and Engineering Indian Institute of Technology Madras, India Abdallah Shami Department of Electrical Engineering Lakehead University Thunder Bay, Ontario, Canada 1333_Frame_00.fm Page x Wednesday, March 5, 2003 12:28 PM © 2003 by CRC Press LLC
- 15. Narendra Singhal Department of Computer Science University of California, Davis Davis, California Emmanuel A. Varvarigos Department of Computer Engineering and Informatics University of Patras Patras, Greece Theodora Varvarigou Department of Electrical and Computer Engineering National Technical University of Athens Athens, Greece Evangelos Verentziotis Department of Electrical and Computer Engineering National Technical University of Athens Athens, Greece Hooman Yousefizadeh Department of Electrical Engineering Florida Atlantic University Boca Raton, Florida Xiaohong Yuan Computer Science Department North Carolina Agricultural and Technical State University Greensboro, North Carolina Ding Zhemin Department of Computer Science Hong Kong University of Science and Technology Kowloon, Hong Kong Jun Zheng School of Information Technology and Engineering University of Ottawa Ottawa, Ontario, Canada Bin Zhou Department of Electrical and Computer Engineering Queen’s University Kingston, Ontario, Canada Ali Zilouchian Department of Electrical Engineering Florida Atlantic University Boca Raton, Florida 1333_Frame_00.fm Page xi Wednesday, March 5, 2003 12:28 PM © 2003 by CRC Press LLC
- 16. Contents Chapter 1 Overview of optical communication networks: Current and future trends Aysegül Gençata, Narendra Singhal, and Biswanath Mukherjee Chapter 2 Evolution of optical networks architecture M. Yasin Akhtar Raja Chapter 3 Design aspects of optical communication networks Kanna Potharlanka, Toshit Antani, Byrav Ramamurthy, Laxman Sahasrabuddhe, and Biswanath Mukherjee Chapter 4 Evolution to an optical broadband services network David Benjamin and Peter Green Chapter 5 Multiprotocol label switching Matthew N.O. Sadiku Chapter 6 Dynamic synchronous transfer mode Matthew N.O. Sadiku Chapter 7 A survey on fair bandwidth allocation for multicast over the Internet Hooman Yousefizadeh, Ali Zilouchian, and Mohammad Ilyas Chapter 8 Emerging optical network management Imrich Chlamtac, W.R. Franta, and Jason P. Jue Chapter 9 Optical network resource management and allocation Ding Zhemin and Mounir Hamdi Chapter 10 Real-time provisioning of optical communication networks Chadi Assi, Abdallah Shami, and Mohamed A. Ali 1333_FrameBookTOC.fm Page xiii Wednesday, March 5, 2003 12:26 PM © 2003 by CRC Press LLC
- 17. Chapter 11 Routing and wavelength assignment with multi-granularity traffic in optical networks Pin-Han Ho and Hussein T. Mouftah Chapter 12 Adaptive routing and wavelength assignment in all-optical networks: the role of wavelength conversion and virtual circuit deflection Emmanuel A. Varvarigos, Theodora Varvarigou, and Evangelos Verentziotis Chapter 13 Connection management in wavelength-routed all-optical networks Xiaohong Yuan Chapter 14 A novel distributed protocol for path selection in dynamic wavelength-routed WDM networks Pin-Han Ho and Hussein T. Mouftah Chapter 15 Distributed lightpath control for wavelength-routed WDM networks Jun Zheng and Hussein T. Mouftah Chapter 16 Recent advances in dynamic lightpath restoration in WDM mesh networks Chava Vijaya Saradhi and C. Siva Ram Murthy Chapter 17 Restoration in optical WDM mesh networks Shirshanka Das and Mario Gerla Chapter 18 Shared alternate-path protection with multiple criteria in all-optical wavelength-routed WDM networks Bin Zhou and Hussein T. Mouftah Chapter 19 Optical transport networks: A physical layer perspective M. Yasin Akhtar Raja and Mohammad Ilyas Chapter 20 Fiber optic sensors Tariq Iqbal Chapter 21 Wavelength converters Mohammed A. Alhaider 1333_FrameBookTOC.fm Page xiv Wednesday, March 5, 2003 12:26 PM © 2003 by CRC Press LLC
- 18. © 2003 by CRC Press LLC chapter one Overview of optical communication networks: Current and future trends* Aysegül Gençata Istanbul Technical University Narendra Singhal University of California, Davis Biswanath Mukherjee University of California, Davis Contents 1.1 Introduction 1.2 Enabling WDM technologies 1.3 Access networks 1.3.1 Point-to-point topologies 1.3.2 Passive optical networks 1.3.3 Optical wireless technology (free space optics) 1.4 Metropolitan networks 1.5 Long-haul networks 1.5.1 Routing and wavelength assignment 1.5.2 Fault management 1.5.2.1 Protection 1.5.2.2 Restoration 1.5.3 Multicasting 1.5.3.1 Multicast-capable OXC architectures 1.5.3.2 Multicast routing and wavelength assignment * This work has been supported in part by the U.S. National Science Foundation Grant No. ANI-98-05285. Aysegül Gençata was a visiting scholar at U.C. Davis when this work was performed. 1333_FrameBook.book Page 1 Tuesday, February 25, 2003 11:33 AM
- 19. 2 The handbook of optical communication networks 1.5.4 Traffic grooming in WDM mesh networks 1.5.5 IP over WDM 1.5.6 Call admission control based on physical impairments 1.5.7 Network control and signaling 1.5.8 Optical packet switching 1.5.8.1 Optical burst switching 1.6 Future directions References 1.1 Introduction The focus of this chapter is to present technological advances, promising archi- tectures, and exciting research issues in designing and operating next-generation optical wavelength-division multiplexing (WDM) networks, which are scalable and flexible. We discuss important building blocks of optical WDM networks and overview access, metropolitan, and long-haul networks separately. Special attention has been paid to the long-haul network because there is a tremendous need to develop new intelligent algorithms and approaches to efficiently design and operate these wide-area-optical-mesh networks built on new emerging tech- nologies. We present several research topics including routing and wavelength assignment, fault management, multicasting, traffic grooming, optical packet switching, and various connection-management problems. The Internet is devel- oping rapidly with the ultimate goal being to provide us with easy and fast access to any desired information from any corner of the world. Information exchange (or telecommunications) technology, which has been evolving contin- uously since the telephone was invented, is still striving to meet the users’ demands for higher bandwidth. This demand is attributed to the growing pop- ularity of bandwidth-intensive networking applications, such as data browsing on the World Wide Web (WWW), java applications, video conferencing, inter- active distance learning, on-line games, etc. Figure 1.1 plots the past and pro- jected growth of data and voice traffic as reported by most telecom carriers.1 It shows that, while voice traffic continues to experience a healthy growth of approximately 7% per year, data traffic has been growing much faster. To sup- port this exponential growth in the user data traffic, there is a strong need for high-bandwidth network facilities, whose capabilities are much beyond those of current high-speed networks such as asynchronous transfer mode (ATM), SONET/SDH* etc.2 Fiber-optic technology can meet the previously mentioned need because of its potentially limitless capabilities:3 huge bandwidth (nearly 50 terabits per second [Tbps] for single-mode fiber), low signal attenuation (as low as 0.2 dB/km), low signal distortion, low power requirement, low material usage, small space requirement, and low cost. Given that a single-mode * SONET and SDH are a set of related standards for synchronous data transmission over fiber optic networks. SONET is short for Synchronous Optical NETwork and SDH is an acronym for Synchronous Digital Hierarchy. 1333_FrameBook.book Page 2 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 20. Chapter one: Overview of optical communication networks 3 fiber’s potential bandwidth is nearly three orders of magnitude higher than electronic data rates of a few tens of gigabits per second (Gbps), we need to tap into this huge optic-electronic bandwidth mismatch. Because the maxi- mum rate at which an end user — which can be a workstation or a gateway that interfaces with lower-speed sub-networks — can access the network is limited by electronic speed, concurrency among multiple user transmissions should be introduced to exploit the fiber’s huge bandwidth. WDM is a favorite multiplexing technology in optical communication networks because it supports a cost-effective method to provide concur- rency among multiple transmissions in the wavelength domain. Several communication channels, each carried by a different wavelength, are mul- tiplexed into a single fiber strand at one end and demultiplexed at the other end, thereby enabling multiple simultaneous transmissions. Each communication channel (wavelength) can operate at any electronic pro- cessing speed (e.g., OC-192 or OC-768).* For example, a fiber strand that supports 160 communication channels (i.e., 160 wavelengths, each operat- ing at 40 Gbps) would yield an aggregate capacity of 6.4 Tbps. Today’s telecom network can be considered to consist of three sub-net- works: access (spanning about 1 to 10 km), metropolitan (covering about 10 to 100 km), and long haul (extending to 100s or 1000s of km) (see Figure 1.2); and fiber is being extensively deployed in all three sub-networks. Typ- ically, the network topology for access can be a star, a bus, or a ring; for metro a ring; and for long haul a mesh. Each of these sub-networks has a different set of functions to perform; hence, each has a different set of chal- lenges, technological requirements, and research problems. For example, for the long-haul network, carriers are more concerned with capacity, protection, Figure 1.1 Past and projected future growth of data and voice traffic. * OC-n stands for an “optical channel” with data rate of n x 51.84 Mbps approximately. Relative Load 50 40 30 20 10 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 Data Voice 1333_FrameBook.book Page 3 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 21. 4 The handbook of optical communication networks and restoration, while for the metro or access network, carriers are more concerned with service provisioning/monitoring, flexibility, etc. The focus of this chapter is to present technological advances, promising architectures, and exciting research issues in designing and operating next-generation optical WDM networks that are scalable and flexible. The next section provides a brief discussion on the important building blocks of optical WDM networks. This is followed by an overview of access, metro- politan, and long-haul networks separately. Special attention has been paid to the long-haul network because there is a tremendous need to develop new intelligent algorithms and approaches to efficiently design and operate these wide-area-optical-mesh networks built on new emerging technologies. We present several research topics including routing and wavelength assign- ment (RWA), fault management, multicasting, traffic grooming, optical packet switching, and various connection-management problems. 1.2 Enabling WDM technologies An important factor to consider in the design of a WDM network is the number of wavelengths to use. The maximum number of wavelengths is limited by optical device technology and is affected primarily by the total available bandwidth or spectral range of the components (including the fiber) and the spacing between channels. Conventional fibers have a low attenuation region between 1335 and 1625 nm with a “water-peak window” at 1385 nm. New “all-wave” fibers do not have this water peak and hence can use a larger spectrum (see Figure 1.3). Channel spacing itself is affected by several factors such as the channel bit rates, optical power budget, non- linearities in the fiber, and the resolution of transmitters and receivers. In dense wavelength-division multiplexing (DWDM), a large number of wave- lengths (>160) is packed densely into the fiber with small channel spacing. An alternative WDM technology with a smaller number of wavelengths (< Figure 1.2 Telecom network overview. Long Haul - 100s–1000s km - Mesh Metro (Interoffice) - 10s of km - Rings Access - A Few km - Hubbed Rings, PONs Users 1333_FrameBook.book Page 4 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 22. Chapter one: Overview of optical communication networks 5 10), larger channel width, larger channel spacing, and much lower cost is termed as coarse WDM (CDWM). Although new approaches and technologies are constantly under devel- opment, this section highlights some of the emerging and novel technologies that can revolutionize the design and effectiveness of WDM networks. Opti- cal components employed in building a typical point-to-point optical WDM transmission system are depicted in Figure 1.4. Several optical signals sent by transmitters (lasers) are coupled together using a (wavelength) multiplexer into a fiber. Signals are amplified, when necessary, using amplifiers such as erbium-doped fiber amplifiers (EDFAs) to compensate for signal attenuation. At intermediate nodes, these signals can be dropped and new signals can be added using optical add drop multiplexers (OADMs). At the receiving end, a (wavelength) de-multiplexer is used to segregate the individual wave- lengths arriving on the fiber, which are then fed into the receivers (filters). Figure 1.3 Low-attenuation region of all-wave fiber vs. conventional fiber. Figure 1.4 A typical point-to-point optical fiber communication link. AllWave Eliminates the 1385 nm Water Peak Transmitter (Laser) Receiver (Filter) 1333_FrameBook.book Page 5 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 23. 6 The handbook of optical communication networks The EDFAs with gain spectrum of 30 to 40 nm each (typically in the 1530 to 1560 nm range; see Figure 1.4) can be interconnected to broaden their gain bandwidth. This “amplifier circuit” is referred to as an ultrawide-band EDFA, which can fully exploit the expanded low-attenuation region of the new “all-wave fiber” (see Figure 1.4). OADMs — also referred to as wavelength add-drop multiplexers (WADMs) — are employed to take in (add) and take out (drop) individual wavelengths from an optical fiber completely in the optical domain (i.e., without any conversion of the optical signal into electronic domain). OADMs, which can add and drop a specific predefined channel (or a group of channels), are said to be fixed-tuned (or static) and the technology for manufacturing them is mature. Reconfigurable OADMs (ROADMs), with add-drop wavelengths that can be controlled by an external stimulus (e.g., by software) are said to be tunable (or dynamic). ROADMs are more pow- erful because they can adapt to the fluctuating traffic demand but the tech- nology for building ROADMs is still in nascent stage. When the network topology is a mesh, where nodes are interconnected by fibers to form an arbitrary graph, an additional fiber interconnection device is needed to route the signals from an input port to the desired output port. These devices are called optical crossconnects (OXCs). They can either be transparent (to bit rates and signal formats) in which signals are switched all-optically or be opaque in which incoming signals are converted from optical to electronic domain and switched electronically. A possible architec- ture for a transparent OXC is presented in Figure 1.5, where all signals on a particular wavelength (e.g., l1) arriving on M input fibers are switched separately by a wavelength-specific MxM switch. As more and more wave- lengths are packed into a fiber, the size of the OXCs is expected to increase. Among several technologies (e.g., bubble, liquid crystal, thermo-optic, holo- graphic, electro-optic, LiNbO3, etc.) used for building all-optical OXCs, MEMS (micro-electro-mechanical-systems) based OXCs are becoming pop- ular because of their compact design, low power consumption, and promise Figure 1.5 An optical crossconnect (OXC) of size NM x NM (N is the number of wavelengths; M is the number of incoming/outgoing fibers). 1333_FrameBook.book Page 6 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 24. Chapter one: Overview of optical communication networks 7 for high port count.4 For details on emerging MEMS-based OXC architec- tures, please refer to Reference 5. 1.3 Access networks The access network connects the subscribers (home or business) to the service providers; in other words, it serves as the “last mile” (as well as the “first mile”) of the information flow. To meet the growing traffic demand, service providers expend most of their effort on increasing the bandwidth on their backbone network. But little has changed in the access network. It is now the general opinion that the last mile has become a bottleneck in today’s network infrastructure.6 Optical technology is a promising candidate for solving the bandwidth problem in access networks because it can provide at least 10 to 100 times more bandwidth over a larger coverage area. The next wave in access network deployment will bring the fiber to the building (FTTB) or to the home (FTTH), enabling Gbps speeds at costs comparable to other technologies such as digital subscriber line (DSL) and hybrid fiber coax (HFC).6 Three optical technologies are promising candidates for the next-gener- ation access networks: point-to-point topologies, passive optical networks, and free-space optics. 1.3.1 Point-to-point topologies Point-to-point dedicated fiber links can connect each subscriber to the tele- com central office (CO), as illustrated in Figure 1.6a. This architecture is simple but expensive due to the extensive fiber deployment. An alternative approach is to use an active star topology, where a curb switch is placed close to the subscribers to multiplex/de-multiplex signals between the sub- scribers and the CO. This alternative in Figure 1.6b is more cost effective in terms of deployed fiber. A disadvantage of this approach is that the curb switch is an active component that requires electrical power as well as backup power at the curb-unit location. 1.3.2 Passive optical networks Passive optical networks (PONs) replace the curb switch with a passive optical component such as an optical splitter (Figure 1.6c). This is one of the several possible topologies suitable for PONs including tree-and-branch, ring, and bus. PON minimizes the amount of fiber deployed, total number of optical transceivers in the system, and electrical power consumption. Currently, two PON technologies are being investigated: ATM PONs (APON) and Ethernet PONs (EPON). APON uses ATM as its layer-2 proto- col; thus, it can provide quality-of-service features. EPON carries all data encapsulated in Ethernet frames, and can provide a relatively inexpensive solution compared to APON. EPON is gaining popularity and is being 1333_FrameBook.book Page 7 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 25. 8 The handbook of optical communication networks standardized as a solution for access networks in the IEEE 802.3ah group. In Kramer and Pesavento (2000), design issues are discussed and a new protocol (IPACT) for EPON is proposed.7 1.3.3 Optical wireless technology (free space optics) Low-power infrared lasers can be used to transmit high-speed data via point-to-point (up to 10 Gbps) or meshed (up to 622 Mbps) topologies.8 An optical data connection can be established through the air via lasers sitting on rooftops aimed at a receiver. Under ideal atmospheric conditions, this tech- nology can provide a transmission range of up to 4 km.8 Several challenges need to be addressed for optical wireless technology, including weather con- ditions, movement of buildings, flying objects, and safety considerations. 1.4 Metropolitan networks Metropolitan-area (or metro) networks serve geographic regions spanning several hundred kilometers, typically covering large metropolitan areas. They interconnect access networks to long-haul backbone service providers. Currently, SONET/SDH-based rings form the physical-layer infrastructure in metro networks. SONET rings utilize a single channel (at 1310 nm wave- length) with a TDM (time-division multiplexing) technique. With TDM, a high-bandwidth channel (e.g., OC-192) can be divided into several low-bandwidth sub-channels (e.g., OC-1, OC-3, etc.), and each sub-channel Figure 1.6 Different technologies for fiber-to-the-home (FTTH). (a) Point-to-Point Network (b) Curb-Switched Network (c) Passive Optical Network 1333_FrameBook.book Page 8 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 26. Chapter one: Overview of optical communication networks 9 can carry a different low-rate traffic stream. A TDM sub-channel is carried physically in a time slot traveling through the ring. A data stream can be added to a time slot at the source node and travel to the destination where it is extracted by SONET add/drop multiplexers (ADMs). With the emergence of WDM technology, a logical step is to upgrade the one-channel SONET ring to a multiple-channel WDM/SONET ring. In a WDM/SONET ring network, each wavelength can operate similar to a SONET TDM channel. However, bandwidth upgrade comes with a price: in a simple-minded solution, a SONET ADM is needed for each wavelength at each node, increasing the total number of ADMs in a network W times, where W is the number of wavelengths. Fortunately, it may be possible to have some nodes on some wavelengths where no add/drop operation is needed on any time slot (see Figure 1.7 for an example). The total number of ADMs can be reduced by carefully packing the low-bandwidth connec- tions into wavelengths. Packing low-speed traffic streams into high-speed traffic streams to minimize the resource usage is called traffic grooming, and it is a research subject that has received a lot of attention.9–14 To realize an architecture with grooming, a new optical component should be used at each node: a wavelength ADM (WADM) that can selec- tively bypass some of the wavelengths and extract the others from a fiber (see Section 1.2). In Chiu and Modiano (2000), a unidirectional WDM ring network is considered where the number of SONET ADMs is minimized.9 In Gerstel et al. (2000), the authors address the problem of designing WADM rings for cost-effective traffic grooming.10 They propose and analyze a col- lection of WADM ring networks considering that the network cost includes the number of wavelengths, transceiver cost, and the maximum number of hops. Another work on cost-effective design of WDM/SONET rings11 min- imizes the number of wavelengths and the total number of ADMs for a given static traffic; this work is applicable to both unidirectional and bidirectional Figure 1.7 Reducing the number of ADMs by traffic grooming. The ADM at node 2 on the outer wavelength channel is not needed if the connections (1,3) and (2,3) in (a) are interchanged. 1 1 1 2 2 4 4 4 3 3 3 Requests: (1,2), (1,3), (1,4), (2,3), (2,4), (3,5) (a) – (b) = Interchanging the connections (1,3) and (2,3) (a) (b) 1333_FrameBook.book Page 9 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 27. 10 The handbook of optical communication networks rings. In Berry and Modiano (2000), the dynamic traffic case is considered, where the traffic is given as a set of matrices.12 The authors formulate the problem as a bipartite graph-matching problem and they develop algorithms to minimize the number of wavelengths that must be processed at each node. A formal definition of the problem is given through integer linear program (ILP) formulations in Wang et al. (2001), and a simulated-annealing-based heuristic is proposed to solve the problem.13 Dutta and Rouskas (2002) present a framework for computing bounds for traffic grooming in ring networks, which can be used to evaluate the performance of heuristic algo- rithms.14 For a survey of traffic grooming in ring topologies, please refer to Modiano (2001).15 The WDM/SONET ring architecture may be the next step to provide a higher-bandwidth solution in the metro network, but the TDM-based infra- structure poses challenges toward a more flexible, data-driven metro net- work. New questions arise as the data traffic grows to be the main component of the overall demand, and consequently brings more “burstiness” and unpredictability. The choice of the future would be a metropolitan optical network architecture that is scalable, flexible, capable of providing just-in-time connection provisioning, and exploiting the full advantages of a WDM system. WDM mesh topologies are the logical candidates to achieve these goals.8 1.5 Long-haul networks The long-haul network (spanning hundreds to thousands of km) typically has OXCs at its nodes interconnected by a mesh of fibers (see Figure 1.2). Traffic from the end users (which could be an aggregate activity from a collection of terminals) is collected by the access networks and fed into the long-haul networks through metro networks. This high-bandwidth traffic is carried on a long-haul WDM network from one end to the other by the wavelength channels available on fibers. In this section, we present signifi- cant research issues concerning provisioning and maintenance of wave- length-channel-based connections. 1.5.1 Routing and wavelength assignment In a wavelength-routed WDM network, end users communicate with one another via end-to-end (possibly all-optical) WDM channels, which are referred to as lightpaths.16 These lightpaths are used for supporting a connection in a wavelength-routed WDM network, and may span multiple fiber links. Figure 1.8 shows several nodes in a network communicating among them- selves through lightpaths (e.g., a lightpath connection from CO to NJ spans across the physical links CO–TX, TX–GA, GA–PA, and PA–NJ). In the absence of wavelength converters, a lightpath must occupy the same wavelength on the fiber links through which it traverses; this property is known as the wavelength-continuity constraint. Given a set of connections, the problem of 1333_FrameBook.book Page 10 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 28. Chapter one: Overview of optical communication networks 11 setting up lightpaths by routing and assigning a wavelength to each connec- tion is called the routing and wavelength assignment (RWA) problem.17,18 Note that fiber links in a mesh network (e.g., the one in Figure 1.8) are bidirectional, while the lightpaths may be unidirectional or bidirectional. Typically, connection requests may be of three types: static, incremental, and dynamic. With static traffic, the entire set of connections is known in advance, and the problem is then to set up lightpaths for these connections in a global fashion while minimizing network resources such as the number of wavelengths in the network. Alternatively, one may attempt to set up as many of these connections as possible for a given fixed number of wave- lengths per fiber link (typically, all fibers are assumed to have the same number of wavelengths). The RWA problem for static traffic is known as the static lightpath establishment (SLE) problem.18 In the incremental-traffic case, connection requests arrive sequentially, a lightpath is established for each connection, and the lightpath remains in the network indefinitely. For the case of dynamic traffic, a lightpath is set up for each connection request as it arrives, and the lightpath is released after some finite amount of time. The dynamic lightpath establishment (DLE) problem18 involves setting up the light- paths and assigning wavelengths to them while minimizing the connection blocking probability or maximizing the number of connections that can be established in the network over a period of time. In a wavelength-routed WDM network, the wavelength-continuity con- straint can be eliminated if we can use wavelength converters to convert the data arriving on one wavelength on a fiber link into another wavelength at an intermediate node before forwarding it on the next fiber link. Such a technique is feasible and is referred to as wavelength conversion.19 Wave- length-routed networks with this capability are referred to as wavelength-con- vertible networks. A wavelength converter that can convert from any wave- length to any other wavelength is said to have full-range capacity. If there is one wavelength converter for each fiber link in every node of the network, the network is said to have full wavelength-conversion capability. A wave- length-convertible network with full wavelength-conversion capability at Figure 1.8 Lightpath connections in a WDM mesh network. (Solid circles mark the end points of a lightpath.) 1333_FrameBook.book Page 11 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 29. 12 The handbook of optical communication networks each node is equivalent to a circuit-switched telephone network; thus, only the routing problem needs to be addressed, and wavelength assignment is not an issue.17 Three basic approaches are used for the routing subproblem: fixed rout- ing, fixed-alternate routing, and adaptive routing.20 Fixed routing is a straight- forward approach in which same fixed route is always chosen to route a connection for a given source-destination pair. One example of such an approach is fixed shortest-path routing. In fixed-alternate routing, each node in the network maintains a routing table containing an ordered list of a number of fixed routes to each destination node. For example, these routes may include the shortest-path route, the second shortest-path route, the third shortest-path route, etc. When a connection request arrives, the source node attempts to establish the connection on each of the routes from the routing table in sequence, until a route with a valid wavelength assignment is found. If no available route is found from the list of alternate routes, then the connection request is blocked. In adaptive routing, the route from a source node to a destination node is chosen dynamically, depending on the network state. This approach has lower connection blocking than fixed and fixed-alternate routing, but it is more computationally intensive. Once a path has been chosen for a connection, a wavelength must be assigned to it such that any two lightpaths that are sharing the same physical link are assigned different wavelengths. Assigning wavelengths to different lightpaths that minimizes the number of wavelengths used under the wave- length-continuity constraint reduces to the graph-coloring problem.18,21,22 This problem has been demonstrated to be NP-complete, and the minimum num- ber of colors needed to color a graph G (called the chromatic number c[G] of the graph) is difficult to determine. However, there are efficient sequential graph-coloring algorithms, which are optimal in the number of colors used. Other RWA heuristics such as First-Fit, Least-Used, Most-Used, etc. can be found in Reference 22. 1.5.2 Fault management In a wavelength-routed WDM network (as well in other networks), the failure of a network element (e.g., fiber link, crossconnect, etc.) may result in the failure of several optical channels, thereby leading to large data and revenue losses. Several approaches are used to ensure fiber-network survivability against fiber-link failures.23 Survivable network architectures are based either on reserving backup resources in advance (called “protection”),24 or on dis- covering spare backup resources in an online manner (called “restoration”).25 In protection, which includes automatic protection switching (APS) and self-healing rings,26,27 the disrupted service is restored by utilizing the precom- puted and reserved network resources. In dynamic restoration, the spare capacity, if any, available within the network is utilized for restoring services affected by a failure. Generally, dynamic restoration schemes are more efficient in utilizing network capacity due to the multiplexing of the spare-capacity 1333_FrameBook.book Page 12 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 30. Chapter one: Overview of optical communication networks 13 requirements, and they provide resilience against different kinds of failures, while protection schemes have a faster restoration time and guarantee recov- ery from disrupted services. Although protection schemes are suitable for the optical layer (with wavelength routing), dynamic restoration schemes are suit- able for Layer 3 (IP packet switching). Below, we examine these two fault-man- agement schemes for mesh networks (see Figure 1.9). 1.5.2.1 Protection Existing connections in a network can be protected from fiber failures either on a link-by-link basis (which we call link protection) or on an end-to-end basis (which we call path protection). In link protection, during connection setup, backup paths and wave- lengths are reserved around each link on the primary path. In the event of a link failure, all the connections traversing the failed link will be rerouted around that link and the source and destination nodes of the connections traversing the failed link would be oblivious to the link failure. In path protection, during connection setup, the source and destination nodes of each connection statically reserve a primary path and a backup path (which are link and/or node disjoint) on an end-to-end basis. When a link fails, the source node and the destination node of each connection that traverses the failed link are informed about the failure (possibly via messages from the nodes adjacent to the failed link) and backup resources are utilized. Although path protection leads to efficient utilization of backup resources, link protection provides faster protection-switching time. The link- and path-protection schemes can either be dedicated or shared. In dedicated-link protection, at the time of connection setup, for each link of the primary path, a backup path and wavelengths are reserved around that link and they are dedicated to that connection. In shared-link protection, the backup wavelengths reserved on the links of the backup path are shared with other backup paths. As a result, backup channels are multiplexed among different failure scenarios (which are not Figure 1.9 Fault-management schemes. Fault-Management Schemes Protection Restoration Link Sub-path Link Path Path Shared Dedicated Shared Dedicated 1333_FrameBook.book Page 13 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 31. 14 The handbook of optical communication networks expected to occur simultaneously). Therefore, shared-link protection is more capacity efficient when compared with dedicated-link protection. In dedicated-path protection, at the time of connection setup for each pri- mary path, a link-disjoint backup path and wavelength are reserved, and dedicated to that connection. The primary and the backup paths can carry identical traffic from the source to the destination simultaneously (referred to as 1+1 protection) or the backup path, although reserved for use in the event of a failure of the primary path, can carry lower-priority preemptive traffic (referred to as 1:1 protection). In shared-path protection, the backup wavelengths reserved on the links of the backup path may be shared with other backup paths. In general, a scheme where M primary paths share N backup paths is known as M:N protection. 1.5.2.2 Restoration Dynamic restoration schemes can be used to restore the failed link, or the failed paths, or sub-paths (see Figure 1.10). In link restoration, the end nodes of the failed link dynamically dis- cover a route around the link, for each connection (or “live” wavelength) that traverses the link. In the event of a failure, the end nodes of the failed link participate in a distributed algorithm to dynamically discover a new route around the link, for each active wavelength that traverses the link. When a new route is discovered around the failed link for a wavelength channel, the end nodes of the failed link reconfigure their OXCs to reroute that channel onto the new route. If no new route and associated wavelength can be discovered for a broken connection, that connection is dropped. In path restoration, when a link fails, the source and the destination node of each connection that traverses the failed link are informed about the failure (possibly via messages from the nodes adjacent to the failed link). The source and the destination nodes of each connection independently discover a backup route on an end-to-end basis (such a backup path could be on a different wavelength channel). When a new route and wavelength channel is discovered for a connection, network elements such as OXCs are recon- figured appropriately, and the connection switches to the new path. If no new route (and associated wavelength) can be discovered for a broken con- nection, that connection is blocked. In sub-path restoration, when a link fails, the upstream node of the failed link detects the failure and discovers a backup route from itself to the cor- responding destination node for each disrupted connection.28 Upon success- ful discovery of resources for the new backup route, intermediate OXCs are reconfigured appropriately and the connection switches to the new path. A connection is dropped in the absence of sufficient resource availability. Link restoration is the fastest and path restoration is the slowest among the above three schemes. Sub-path restoration time lies in between those of link restoration and path restoration. For a comprehensive review of the 1333_FrameBook.book Page 14 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 32. Chapter one: Overview of optical communication networks 15 literature on the design of survivable optical networks, please consult the literature.29–33 1.5.3. Multicasting Multicasting is the ability of a communication network to accept a single message from an application and deliver copies of the message to multiple recipients at different locations.34 One of the challenges is to minimize the amount of network resources that are employed by multicasting. To illustrate this point, let us assume that a video server wants to transmit a movie to 1000 recipients (Figure 1.11a). If the server were to employ 1000 separate point-to-point connections (e.g., TCP* connections), then 1000 copies of the movie would have to be sent over a single link, thus making poor use of the available bandwidth. A scalable and efficient implementation of multicasting permits a much better use of the available bandwidth by transmitting at Figure 1.10 Mechanisms for restoring connections after fiber failure. * TCP stands for “Transmission Control Protocol,” which is widely used in today’s Internet. Figure 1.11 An example that illustrates the amount of network resources employed by (left) unicasting a movie to 1000 different users as opposed to the amount of network resources employed by (right) multicasting the movie. (R = standard router, MR = multicast router) Path Restoration Subpath Restoration Link Restoration Source R Source MR 1000 Point-to-Point Connections Single Multicast Connection M u l t i c a s t D e s t i n a t i o n s M u l t i c a s t D e s t i n a t i o n s 1333_FrameBook.book Page 15 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 33. 16 The handbook of optical communication networks most one copy of the movie on each link in the network as illustrated in Figure 1.11b. Today, many multicast applications exist, such as news feeds, file distri- bution, interactive games, video conferencing, interactive distance learning, etc. Many more applications are expected to emerge to exploit the enormous bandwidth promised by the rapidly growing WDM technology,35 but the implementation of these applications is not necessarily efficient because today’s long-haul networks were designed to mainly support point-to-point (unicast) communication. In the future, as multicast applications become more popular and bandwidth intensive, there emerges a pressing need to provide multicast support in the underlying communication network. In an optical WDM network, a lightpath provides an end-to-end con- nection from a source node to a destination node. A light-tree is a point-to-multipoint generalization of a lightpath and provides “single-hop”* communication between a “source” node and a set of destination nodes, which makes it suitable for multicast applications.36 A light-tree enables a transmitter at a node to have many more logical neighbors, thereby leading to a denser virtual interconnection diagram and a lower hop distance. A multicast-capable WDM long-haul network can not only support efficient routing for multicast traffic, but it may also enhance routing for unicast traffic by allowing more densely connected virtual topologies (refer to Section 1.5.5). To realize multicast-capable WDM long-haul networks, we need to develop multicast-capable switch architectures and design efficient RWA algorithms, as outlined below. 1.5.3.1 Multicast-capable OXC architectures Two approaches are used to design switches capable of supporting multicast- ing. One approach is to use electronic crossconnects, which perform switching in the electronic domain and the other is to use “all-optical” switches for switching in the optical domain. Although switching in the latter is “transpar- ent” to bit rate and bit-encoding schemes, switching in the former requires knowledge of bit rate and bit-encoding strategies, and hence is “opaque.”37 Opaque switches. Figure 1.12 depicts an opaque approach, in which the incoming optical bit streams are converted to electronic data; the data is switched using an electronic crossconnect, and then the electronic bit streams are converted back to the optical domain. Observe that the signal in a channel arriving on the input fiber link D is replicated into three copies in the electronic domain. One copy is dropped locally at the node and the remaining two are switched to different channels on outgoing fiber links 1 and 2. (Along with the light-trees, the switch can also be used to establish lightpaths from a source to a destination as presented in the figure by a unicast connection from input fiber link 2 to output fiber link D.) This “opaque” switch architecture is currently very popular due to * A hop is an all-optical segment of a path and may span several physical links. 1333_FrameBook.book Page 16 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 34. Chapter one: Overview of optical communication networks 17 the existence of mature technology to design high-bandwidth, multi-chan- nel, non-blocking, electronic cross-connect fabrics at a low cost. Several companies are already shipping optical OXCs based on optical-elec- tronic-optical (O-E-O) conversion, which can be used for building a mul- ticast-capable OXC with O-E-O conversion. Wavelength converters are not needed in a network where nodes are equipped with optical switches based on the opaque approach because, once an incoming bit stream in the optical domain is converted to electronic domain, it can be switched and converted back to the optical domain on any wavelength. In other words, full-range wavelength conversion19 is an inher- ent property of such switches and the wavelength-continuity constraint need not be obeyed. Transparent switches. Figure 1.13 illustrates a multicast-capable all-optical switch that crossconnects optical channels directly in the optical domain. Again, several companies are working toward building all-optical switches using various technologies, a popular one employing tiny mirrors based on micro-electro-mechanical-system (MEMS) technology. For multi- casting in all-optical switches, “optical splitters” are needed to replicate an incoming bit stream to two or more copies as illustrated in Figure 1.13. A signal arriving on wavelength lb from input fiber link D is sent to the optical splitter X for splitting into three identical copies. One of the three replicas is dropped locally at the node while the other two are switched to output fiber links 1 and 2. Observe that the signal arriving on wavelength la from input fiber link 2 bypasses the node. In this architecture, amplifiers are required because the output signal power weakens when the input signal is split (e.g., a 3-dB attenuation in power occurs for a two-way, equal-power splitting of an optical signal). Wavelength converters are useful in such switches to reduce the probability of blocking of multicast sessions. In the Figure 1.12 Opaque OXC architecture for supporting multicasting using electronic crossconnect. MUX DEMUX 1 2 D 1 2 D O–E CONVERTER E–O CONVERTER (D+1)W X (D+1)W CROSS–CONNECT Local Add Local Drop Outgoing Fibers 1333_FrameBook.book Page 17 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 35. 18 The handbook of optical communication networks absence of wavelength converters, the light-tree-based multicast session would exhibit the wavelength-continuity constraint. 1.5.3.2 Multicast routing and wavelength assignment The multicasting problem in communication networks is often modeled as a Steiner Minimum Tree (SMT), which is an NP-complete problem.38 The problem complexity increases when several multicast sessions (which we expect to occur in the future) have to be established at a minimum aggregate cost. Heuristics are employed for routing and wavelength assignment of multicast sessions.39,40 A single fiber cut on a multicast tree can disrupt the transmission of infor- mation to several destination nodes on a light-tree. This loss would be large if several sessions were occupying the affected fiber link. In order to prevent the large loss of information, it is imperative to protect the multicast sessions through a protection scheme such as reserving resources along a backup tree. Protecting such multicast sessions using schemes (dedicated or shared) dis- cussed in Section 1.5.2 is an important problem that needs to be studied. 1.5.4 Traffic grooming in WDM mesh networks Today, each wavelength channel has the transmission rate of over a Gbps (e.g., OC-48 [2.5 Gbps], OC-192 [10 Gbps], or OC-768 [40 Gbps] in the near future). However, the capacity required by the traffic streams from client networks (IP, ATM, etc.) can be significantly lower, and they can vary in the range from OC-1 (51.84 Mbps) or lower, up to full wavelength capacity. In Figure 1.13 Transparent OXC architecture for supporting multicasting using optical splitters. DEMUX MUX X Y Optical Switch Optical Switch Add Drop Add Drop 1 2 D 1 2 D Incoming Fibers Outcoming Fibers Splitter Bank Amplifier Bank Coverter Bank λb λa 1333_FrameBook.book Page 18 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 36. Chapter one: Overview of optical communication networks 19 order to achieve the most efficient utilization of network resources, to reduce operating costs, and to maximize revenue from existing capacity, the low-speed traffic streams need to be efficiently “groomed” onto high-capac- ity optical channels (lightpaths). The traffic-grooming problem has been well studied for WDM/SONET ring networks with the objective of minimizing the total network cost mea- sured in terms of the number of SONET ADMs (see Section 1.4). As today’s optical long-haul backbone networks are evolving from interconnected-rings topology to mesh topology, traffic grooming in WDM mesh networks has become a very important problem for both industry and academe.41,42 In order to support traffic grooming, each node in a WDM mesh network is equipped with an OXC that should be able to switch traffic at wavelength granularity as well as finer granularity. Figure 1.14 shows a simplified archi- tecture of an OXC with grooming capability. In Figure 1.14, the grooming fabric (G-fabric) performs multiplexing, de-multiplexing, and switching of low-speed traffic streams. A transceiver array (T and R) is used to connect the G-Fabric to the W-Fabric (see Figure 1.14). The size of the transceiver array determines how many wavelength channels can be switched in and out of the G-fabric from the W-fabric. Hence, it determines the grooming capacity of an OXC. A lightpath is called a groomable lightpath if it is switched to the G-Fabric at its end nodes. In a static grooming problem, all connection requests (of different band- width granularities) are known a priori. In a dynamic grooming problem, connection requests arrive randomly, hold for a finite duration, and require provisioning in real time and tearing down when they are over. The groom- ing of traffic can be either single-hop or multi-hop. While in the former, con- nections are allowed to traverse only a single lightpath hop, in multi-hop Figure 1.14 Node architecture for traffic grooming. OXC Fabric NNI UNI-N UNI-C TX RX MPLS/IP Router Other ports OXC Edge Device: Router OXC control Fiber link : Multiplexer : Demultiplexer : Wavelength 0 : Wavelength 1 : Wavelength 2 : Transmitter array : Receiver array : Control component : Control message : Edge Device (ED) (Router) can provide flexible software-based bandwidth provisioning capability. TX RX 1333_FrameBook.book Page 19 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 37. 20 The handbook of optical communication networks grooming a connection can be switched by the G-fabric at any intermediate node (i.e., it can traverse multiple lightpath hops). When some low-speed connections require protection, they have to be prudently protected and groomed along with the other existing connections in order to maximize the network throughput. Again, these connections need not be just single-source, single-destination connections but they may be single-source, multiple-destination streams requiring multicasting of infor- mation to a group of nodes. Grooming of low-speed multicast connections, grooming along with protection, etc., are interesting and challenging areas that need more research. 1.5.5 IP over WDM Rapid growth in data traffic and the predominance of Internet Protocol (IP) in data communication have led researchers to investigate the IP-over-WDM inte- gration. In such architecture, network nodes employ OXCs and IP routers. Today’s IP-over-ATM-over-SONET-over-optical approach reduces efficiency as well as the effective bandwidth provided by WDM technology. The trend is to converge the IP layer and the WDM layer by eliminating one or two layers of the protocol stack43 and to offer a multi-protocol support (multi-protocol label switching or MPLS, see Section 1.5.7) for simplified network architecture. An optical channel (i.e., a lightpath) can connect any two IP routers in an IP-over-WDM network. The set of lightpaths forms a virtual interconnec- tion pattern called the virtual (logical) topology.44 A lightpath is established by tuning the transmitter at the source node and the receiver at the destina- tion node to an appropriate wavelength, and by configuring the OXCs along the path. The traffic between two nodes can be carried by the lightpath established between these nodes. Nodes that are not connected directly in the virtual topology can still communicate with one another using the multi-hop approach, namely, by using electronic packet switching at the intermediate nodes in the virtual topology. IP/MPLS routers, ATM switches, etc. can provide electronic packet switching. Interaction between the optical layer and the electronic layer (IP in this case) is a major issue including several functions, such as bandwidth provisioning, fault management, per- formance monitoring, etc. (see Section 1.5.2). Bandwidth provisioning at the optical layer is related to the RWA prob- lem. The latter is a hard (non-polynomial) problem, which includes minimiz- ing the usage of network resources considering constraints on wavelength conversion, nodal-switching capabilities, and physical-layer connectivity (fiber layout).3 The problem gets more complex when one considers the dyna- mism of the IP traffic. When traffic intensities between nodes change over time, the network may need to be re-optimized by online methods. This is a joint optimization problem involving IP routing, virtual-topology reconfigu- ration and therefore optical-layer routing and wavelength assignment.45,47,49,51 To solve these problems, we need automated mechanisms that can interact with today’s IP protocols (IPv4, IPv6, RSVP, etc.). 1333_FrameBook.book Page 20 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 38. Chapter one: Overview of optical communication networks 21 In such network architecture, the failure of a fiber link can lead to the failure of all of the lightpaths that traverse it. Considering that each lightpath operates at a rate of tens of Gbps, such a failure could cause a large amount of data and, consequently, revenue loss. Hence, network survivability is a crucial issue (see Section 1.5.2). 1.5.6 Call admission control based on physical impairments Optical networking technology has many desirable features and, in general, offers better transmission-error characteristics compared to other physi- cal-layer technologies, such as copper or radio. Its low error characteristics make it the best candidate to deploy for worldwide data-transmission back- bones. However, even the optical-layer technology is far from being perfect, and at the scale of continent-wide or worldwide networks, physical-layer impairments may cause serious problems that we need to consider. In a large-scale network, an optical signal may propagate through a number of nodes and long fiber spans (1000s of km) connecting the nodes. Throughout its propagation, the signal is subjected to degradation by several impairments: cross-talk from OXCs, amplified spontaneous emission (ASE) from EDFAs, four-wave mixing (FWM) from other signals propagating in the same fibers, laser phase noise at the transmitter, fiber dispersion and nonlinearities, etc.3 As a result, the optical signal’s bit-error rate (BER) may become too high to recover the original signal at the receiver. To exploit optical technology in long-haul mesh networks, and to make the future all-optical networks a reality, we need to develop intelligent approaches that can correct these undesirable effects. To date, most of the studies on call admission and RWAproblems assume an ideal physical layer that does not have any of the impairments cited above. The work in Ramamurthy et al. (1999) considers the physical-layer limita- tions by capturing the most significant impairments (ASE and cross-talk) before setting up a lightpath.46 It estimates the on-line BER on candidate routes and wavelengths, and establishes a call on a lightpath only if the received BER is lower than a certain threshold (e.g., 10–12). Signal regeneration is another method to overcome signal degradation, and it may be performed in three forms: 1R-Regeneration: Re-amplifying. Signal is amplified using optical amplifi- ers, such as EDFA. 2R-Regeneration: Re-amplifying and re-shaping. The optical signal is converted to an electronic signal. It is both re-amplified and re-shaped. Re-shaping eliminates most of the noise and provides clear electrical 0s and 1s. 3R-Regeneration: Re-amplifying, re-shaping, and re-timing. The optical sig- nal is converted to an electronic signal. Added to 2R-regeneration, it is also re-timed (or re-clocked). The time between bits at the receiver is not rigid, as it is at the source; re-timing adjusts the 1s and 0s so that they are equally spaced and match the bit rate of the system. 1333_FrameBook.book Page 21 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 39. 22 The handbook of optical communication networks 1.5.7 Network control and signaling In an optical network, a control plane is needed to coordinate the necessary algorithms that provide the following functions: 1. A signaling protocol for setting up, maintaining, and tearing down the connections 2. A routing process for handling the topology and resource usage, and for calculating the routes 3. A naming and addressing scheme 4. A signaling protocol for providing communication between the en- tities requesting the services and those that provide the services.48 Several initiatives are being developed to define and standardize such a control plane. MPLS is a set of protocols for provisioning and managing core net- works. It provides resource reservation and route set up to create data tunnels between ingress and egress nodes.* A label-switching mechanism ensures that all packets of the same data stream are routed through their predefined tunnel. Originally, MPLS was designed for packet-switching networks to overlay the Internet Protocol and to provide a standard inter- face that can communicate with several protocols (ATM, IP, frame relay, etc.). It has been generalized for optical networking, resulting in general- ized MPLS or GMPLS.50,52 GMPLS supports switching in time, wavelength, and space domains along with packet switching, by extending the signaling and routing protocols used in MPLS: Link management protocol (LMP), open-shortest-path-first/intermediate system to intermediate system (OSPF/ISIS) protocols, resource reservation protocol (RSVP), and con- straint-based routing-label distribution protocol (CR-LDP).53 GMPLS can provide traffic engineering** and fast rerouting mechanisms by the features of resource discovery, state information dissemination, path selection, and path management.54 Another effort, OIF-UNI (Optical Internetworking Forum-User Network Interface), defines the interoperation procedures for requesting and estab- lishing dynamic connectivity between clients (e.g., IP, ATM, SONET devices, etc.) connected to an optical transport network (see Figure 1.15).55 The UNI defines the set of services, signaling protocols used to invoke the services, the mechanisms used to transport signaling messages, and the auto-discov- ery procedures. Connection establishment, connection deletion, status exchange, auto-discovery, and information exchange (user data) are sup- ported across the UNI. * Nodes where traffic enters (ingress node) or leaves (egress node) a network. ** Traffic engineering is the process of controlling traffic flows in a network so as to optimize resource utilization and network throughtput. 1333_FrameBook.book Page 22 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 40. Chapter one: Overview of optical communication networks 23 1.5.8 Optical packet switching WDM and optical-switching technology can provide the necessary band- width for the growing traffic demand. As data traffic starts to dominate the communication networks, the traffic even on the long-haul network becomes more data oriented (i.e., less predictable). In the long term, optical packet switching (OPS) could become a viable candidate because of its high-speed, fine-granularity switching, flexibility, and its ability to use the resources economically. The technology is still in a very early stage, and several issues need to be solved, including switch architec- tures, synchronization, contention-resolution schemes, etc. (see Yao et al. [2000] for a tutorial).56 An optical packet switch includes packet-synchronization stages, a switch fabric, and a control unit that extracts and reads the packet header to route the packet through the switch fabric to the proper output port. One main property here is to decide whether the network should operate syn- chronously. A globally synchronized (slotted) network can use aligned time slots as the holders of fixed-size packets. In such a network, the switch fabric at a node receives the incoming packets aligned, minimizing the packet contention; however, this switch architecture is more complex because of synchronization/packet-alignment stages. The other alternative is to build an asynchronus (unslotted) network where packets may have variable lengths. The switch architecture is simpler in this case, though packet-con- tention probability is higher. For a survey of different switch fabrics, please refer to Reference 57. Contention of packets in a switch fabric is a major problem and has important impact on the performance of the network such as packet delay, packet-loss ratio, throughput, and average hop distance. Contention occurs Figure 1.15 Network management system for IP-over-WDM networks. Network Management System (NMS) Proprietary NNI Standardized NNI UNI IP Router ADM 1 2 3 4 5 6 1333_FrameBook.book Page 23 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 41. 24 The handbook of optical communication networks when two or more packets try to leave the switch from the same output port at the same time. To resolve such a conflict, one of the packets is routed through the output port while others are routed elsewhere, depending on the contention-resolution scheme. In electronic switches, contention can be resolved by the store-and-forward technique where packets in contention are stored in a buffer and sent out when the port becomes available. Unfor- tunately, optical buffers similar to electronic counterparts (i.e., ran- dom-access memory [RAM]) do not exist; the only way to store an optical packet is to use optical delay lines (fixed length fibers). These “sequential access” buffers are less flexible than an electronic “random access” buffer because a packet entering a delay line will emerge from the other end of the line after a fixed amount of time. Several switch architectures that use optical buffers were proposed in Reference 56. Another method for contention resolution is deflection routing, which is also called hot potato routing. In case of contention, one packet is routed along the desired link while others are forwarded on some other links, which may lead to longer paths. Deflection routing can be used along with optical buffers. The unique advantage of WDM networks (i.e., several wavelength chan- nels on the same link) can be used to create a third method for contention resolution, namely wavelength conversion. This is an attractive solution because it can achieve the same propagation delay and hop distance as the optimal case. All three or any two solutions can be combined to provide better performance. Today, OPS still seems like a dream because of several technical obstacles. Our current vision for network planning is to implement a dynamically reconfigurable optical transport layer using fast OXCs, providing enough bandwidth to evolving data applications. If and when optical packet switch- ing becomes available, we may choose to incorporate it into our existing optical circuit-switching architecture.58 Packet switching is not limited only to wide-area networks; a tutorial on implementing OPS in metropolitan-area networks can be found in Reference 59. 1.5.8.1 Optical burst switching As a midway solution between circuit switching and packet switching, opti- cal burst switching (OBS) was proposed.60 This approach is motivated by two problems: routing the IP traffic, which has a bursty characteristic, on a relatively-static circuit-switched network leads to poor usage of network resources; and OPS technology is not mature for the near future. In OBS, a control packet is sent first to reserve an appropriate amount of bandwidth and to preconfigure the switches along the path. The burst of data, which can consist of several packets forming a (possibly short) session, immediately follows the control packet, without waiting for an acknowledgment. OBS has a lower control overhead compared to OPS and it may lead to better resource usage compared to circuit switching because reserved resources are released after the completion of the burst. Several issues need to be addressed 1333_FrameBook.book Page 24 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 42. Chapter one: Overview of optical communication networks 25 before OBS can be deployed, such as optical burst switch architecture, decid- ing on the time gap between the control packet and data burst (offset time), resolving resource conflicts without optical buffering, etc.57,61 1.6 Future directions This chapter has provided an overview of several aspects of optical com- munication networks, specifically on WDM networks, and presented sev- eral challenging research advances involved therein. New technologies providing large bandwidth are being deployed in the long-haul and will migrate down to metro and access networks, moving the bottleneck closer to customers. Optical Ethernet, a technology that extends Ethernet beyond the local area network (LAN) or access and into MANs and the long-haul networks is attracting attention. The transport style of optical Ethernet has the advan- tages of simplicity and ease of integration with long-haul DWDM systems, because a well-aggregated gigabit-Ethernet stream can either be mapped to a wavelength or aggregated further into a 10-gigabit Ethernet channel and then mapped to a wavelength for transport across the long-haul network. As we feed more and more bandwidth to the insatiable customers, they are expected to create new “killer” applications that consume all the band- width — and will still be hungry for more — thereby creating the urgency for even more technological advancements. With every technological progress, new and exciting challenges and research problems are expected to sprout in the ever-expanding horizon. References 1. http://www.rhk.com. 2. W.J. Goralski, SONET, 2nd Edition, McGraw-Hill, New York, May 2000. 3. B. Mukherjee, Optical Commun. Networks, McGraw-Hill, New York, July 1997. 4. D.J. Bishop, C.R. Giles, and G.P. Austin, The Lucent LambdaRouter: MEMS technology of the future here today, IEEE Commun. Mag., vol. 40, no. 3, pp. 75–79, Mar. 2002. 5. P.B. Chu, S. Lee, and S. Park, MEMS: the path to large optical crossconnects, IEEE Commun. Mag., vol. 40, no. 3, pp. 80–87, Mar. 2002. 6. G. Kramer and G. Pesavento, Ethernet passive optical networks (EPON): building a next-generation optical access network, IEEE Commun. Mag., vol. 40, no. 2, pp. 66–73, Feb. 2002. 7. G. Kramer, B. Mukherjee, and G. Pesavento, IPACT: A dynamic protocol for an ethernet PON (EPON), IEEE Commun. Mag., vol. 40, no. 2, pp. 74–80, Feb. 2002. 8. http://www.lightreading.com 9. A.L. Chiu and E.H. Modiano, Traffic grooming algorithms for reducing elec- tronic multiplexing costs in WDM ring networks, IEEE J. Lightwave Technol., vol. 18, no. 1, pp. 2–12, Jan. 2000. 1333_FrameBook.book Page 25 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 43. 26 The handbook of optical communication networks 10. O. Gerstel, R. Ramaswami, and G.H. Sasaki, Cost-effective traffic grooming in WDM rings, IEEE/ACM Trans. Networking, vol. 8, no. 5, pp. 618–630, Oct. 2000. 11. X. Zhang and C. Qiao, An effective and comprehensive approach for traffic grooming and wavelength assignment in SONET/WDM rings, IEEE/ACM Trans. Networking, vol. 8, no. 5, pp. 608–617, Oct. 2000. 12. R. Berry and E.H. Modiano, Reducing electronic multiplexing costs in SO- NET/WDM rings with dynamically changing traffic, IEEE J. Selected Areas in Commun., vol. 18, no. 10, pp. 1961–1971, Oct. 2000. 13. J. Wang, W. Cho, V.R. Vemuri, and B. Mukherjee, Improved approaches for cost-effective traffic grooming in WDM ring networks: ILP formulations and single-hop and multihop connections, IEEE J. Lightwave Technol., vol. 19, no. 11, pp. 1645–1653, Nov. 2001. 14. R. Dutta and G.N. Rouskas, On optimal traffic grooming in WDM rings, IEEE J. Selected Areas in Commun., vol. 20, no. 1, pp. 110–121, Jan. 2002. 15. E.H. Modiano, Traffic grooming in WDM networks, IEEE Commun. Mag., vol. 39, no. 7, pp. 124–129, Jul. 2001. 16. I. Chlamtac, A. Ganz, and G. Karmi, Lightpath communications: an approach to high bandwidth optical WANs, IEEE Trans. Commun., vol. 40, no. 7, pp. 1171–1182, Jul. 1992. 17. R. Ramaswami and K. Sivarajan, Optical Routing and Wavelength Assign- ment in All-optical Networks, IEEE/ACM Trans. Networking, vol. 3, no. 5, pp. 489–500, Oct. 1995. 18. D. Banerjee and B. Mukherjee, A practical approach for routing and wave- length assignment in large wavelength-routed optical networks, IEEE J. Se- lected Areas in Commun., Special Issue on Optical Networks, vol. 14, no. 5, pp. 903–908, June 1996. 19. B. Ramamurthy and B. Mukherjee, Wavelength conversion in optical net- works: progress and challenges, IEEE J. Selected Areas in Commun., vol. 16, no. 7, pp. 1040–1050, Sept. 1998. 20. S. Ramamurthy and B. Mukherjee, Fixed-alternate routing and wavelength conversion in wavelength-routed optical networks, IEEE Globecom, Sydney, vol. 4, pp. 2295–2302, Nov. 1998. 21. D.W. Matula, G. Marble, and J.D. Issacson, Graph coloring algorithms, in R.C. Read, Ed., Graph Theory and Computing, Chapter 10, pp. 109–122, Academic Press, New York and London, 1972. 22. H. Zang, J.P. Jue, and B. Mukherjee, A review of routing and wavelength assignment and approaches for wavelength routed optical WDM networks, Optical Networks Mag., vol. 1, no. 1, pp. 47–58, Jan. 2000. 23. H. Zang and B. Mukherjee, Connection management for survivable wave- length routed WDM mesh networks, Optical Networks Mag., Special Issue on Protection and Survivability in Optical Networks, vol. 2, no. 4, pp. 17–28, Jul. 2001. 24. S. Ramamurthy and B. Mukherjee, Survivable WDM mesh networks, Part I — Protection, Proc., IEEE INFOCOM, New York, pp. 744–751, March 1999. 25. S. Ramamurthy and B. Mukherjee, Survivable WDM mesh networks, Part II — Restoration, Proc., IEEE Int. Conf. on Commun., (ICC ’99) Vancouver, Can- ada, pp. 2023–2030, June 1999. 26. W.D. Grover, The self-healing network: a fast distributed restoration tech- nique for networks using digital cross-connect machines, Proc., IEEE Globecom, pp. 28.2.1–28.2.6, Tokyo, Japan, Nov. 1987. 1333_FrameBook.book Page 26 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 44. Chapter one: Overview of optical communication networks 27 27. T. Wu, Fiber Network Service Survivability, Artech House, Norwood, MA, 1992. 28. J. Wang, L. Sahasrabuddhe, and B. Mukherjee, Path vs. sub-path vs. link restoration for fault management in IP-over-WDM networks: performance comparisons using GMPLS control signaling, IEEE Commun. Mag., vol. 40, no. II, pp. 80–87, Nov. 2002. 29. S. Ramamurthy, Optical design of WDM network architectures, Ph.D. disser- tation, Computer Science Department, University of California, Davis, Sept. 1998. 30. L.H. Sahasrabuddhe, Multicasting and fault tolerance in WDM optical net- works, Ph.D. dissertation, Computer Science Department, University of Cal- ifornia, Davis, Nov. 1999. 31. H. Zang, Design and analysis of WDM network architectures, Ph.D. disser- tation, Computer Science Department, University of California, Davis, Apr. 2000. 32. O. Gerstel and R. Ramaswami, Optical layer survivability — a services per- spective, IEEE Commun. Mag., vol. 38, no. 3, pp. 104–113, Mar. 2000. 33. O. Gerstel and R. Ramaswami, Optical layer survivability — an implemen- tation perspective, IEEE J. on Selected Areas in Commun., vol. 18, no. 10, pp. 1885–1899, Oct. 2000. 34. L.H. Sahasrabuddhe and B. Mukherjee, Multicast routing algorithms and protocols: a tutorial, IEEE Network, vol. 14, no. 1, pp. 90–102, Jan./Feb. 2000. 35. R. Malli, X. Zhang, and C. Qiao, Benefit of multicasting in all-optical networks, Proc., SPIE Conf. on All-Optical Networking, vol. 2531, pp. 209–220, Nov. 1998. 36. L.H. Sahasrabuddhe and B. Mukherjee, Light-trees: optical multicasting for improved performance in wavelength-routed networks, IEEE Commun. Mag., vol. 37, no. 2, pp. 67–73, Feb. 1999. 37. N.K. Singhal and B. Mukherjee, Architectures and algorithm for multicasting in WDM optical mesh networks using opaque and transparent optical cross- connects, Technical Digest, OFC, Anaheim, CA, paper TuG8, Mar. 2001. 38. S.L. Hakimi, Steiner’s Problem in Graphs and its Implications, Networks, vol. 1, no. 2, pp. 113–133, 1971. 39. Y. Sun, J. Gu, and D.H.K. Tsang, Multicast routing in all-optical wavelength routed networks, Optical Networks Mag., vol. 2, no. 4, pp. 101–109, Jul./Aug. 2001. 40. B. Chen and J. Wang, Efficient routing and wavelength assignment for mul- ticast in WDM network, IEEE J. on Selected Areas in Commun., vol. 20, no. 1, pp. 97–109, Jan. 2002. 41. K. Zhu and B. Mukherjee, Traffic grooming in an optical WDM mesh network, IEEE J. on Selected Areas in Commun., vol. 20, no. 1, pp. 122–133, Jan. 2002. 42. K. Zhu and B. Mukherjee, On-line approaches for provisioning connections of different bandwidth granularities in WDM mesh networks, Technical Digest, OFC, Anaheim, CA, paper ThW5, pp. 549–551, Mar. 2002. 43. N. Ghani, S. Dixit, and T.-S. Wang, On IP-over-WDM integration, IEEE Com- mun. Mag., vol. 38, no. 3, pp. 72–84, Mar. 2000. 44. B. Mukherjee, D. Banerjee, S. Ramamurthy, and A. Mukherjee, Some princi- ples for designing a wide-area WDM optical network, IEEE/ACM Trans. on Networking, vol. 4, no. 5, pp. 684–696, Oct. 1996. 45. D. Banerjee and B. Mukherjee, Wavelength routed optical networks: linear formulation, resource budgeting tradeoffs, and a reconfiguration study, IEEE/ ACM Trans. on Networking, vol. 8, no. 5, pp. 598–607, Oct. 2000. 1333_FrameBook.book Page 27 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 45. 28 The handbook of optical communication networks 46. B. Ramamurthy, D. Datta, H. Feng, J.P. Heritage, and B. Mukherjee, Impact of transmission impairments on the teletraffic performance of wavelength routed optical networks, IEEE J. Lightwave Technol., vol. 17, no. 10, pp. 1713–1723, Oct. 1999. 47. J.-F.P. Labourdette and A.S. Acampora, Logically rearrangeable multihop lightwave networks, IEEE Trans. on Commun., vol. 39, no. 8, pp. 1223–1230, Aug. 1991. 48. A. McGuire, S. Mirza, and D. Freeland, Application of control plane technol- ogy to dynamic configuration management, IEEE Commun. Mag., vol. 39, no. 9, pp. 94–99, Sept. 2001. 49. A. Gencata and B. Mukherjee, Virtual-topology for WDM mesh networks under dynamic traffic, Proc., IEEE INFOCOM, New York, June 2002. 50. N. Jerram and A. Farrel, MPLS in optical networks, White Paper. 51. A. Gencata, L. Sahasrabuddhe, and B. Mukherjee, Virtual-topology adapta- tion with minimal lightpath change for dynamic traffic in WDM mesh net- works, Proc., Optical Fiber Commun. Conf. — OFC, pp. ThGG119, Anaheim, CA, Mar. 2002. 52. Internet Engineering Task Force, http://www.ietf.org 53. A. Banerjee et al., Generalized multiprotocol label switching: an overview of routing and management enhancements, IEEE Commun. Mag., vol. 39, no. 1, pp. 144–150, Jan. 2001. 54. D. Awduche and Y. Rekhter, Multiprotocol lambda switching: combining MPLS traffic engineering control with optical crossconnects, IEEE Commun. Mag., vol. 39, no. 3, pp. 111–116, Mar. 2001. 55. Implementation Agreement OIF-UNI-01.0, http://www.oiforum.com, Sept. 2001. 56. S. Yao, B. Mukherjee, and S. Dixit, Advances in photonic packet switching: an overview, IEEE Commun. Mag., vol. 38, no. 2, pp. 84–94, Feb. 2000. 57. L. Xu, H.G. Perros, and G. Rouskas, Techniques for optical packet switching and optical burst switching, IEEE Commun. Mag., vol. 39, no. 1, pp. 136–142, Jan. 2001. 58. M.J. O’Mahony et al., The application of optical packet switching in future communication networks, IEEE Commun. Mag., vol. 39, no. 3, pp. 128–135, Mar. 2001. 59. S. Yao, S.J.B. Yoo, B. Mukherjee, and S. Dixit, All-optical packet switching for metropolitan area networks: opportunities and challenges, IEEE Commun. Mag., vol. 39, no. 3, pp. 142–148, Mar. 2001. 60. C. Qiao and M. Yoo, Optical burst switching (OBS) — a new paradigm for an optical internet, J. High Speed Networks, vol. 8, no. 1, pp. 69–84, 1999. 61. S. Verma, H. Chaskar, and R. Ravikanth, Optical burst switching: a viable solution for terabit IP backbone, IEEE Network, vol. 14, no. 6, pp. 48–53, Nov. 2000. 1333_FrameBook.book Page 28 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 46. © 2003 by CRC Press LLC chapter two Evolution of optical networks architecture M. Yasin Akhtar Raja University of North Carolina, Charlotte Contents 2.1 Introduction 2.2 Background 2.3 Optical networks architecture 2.4 Long-haul optical networks 2.5 Regional/metro optical networks 2.6 Optical access networks (OAN) 2.7 All-optical networks — the wave of the future 2.8 Acknowledgment References 2.1. Introduction This chapter, together with Chapter 19, on optical transport networks, reviews the evolution of optical networks from the architectural and signal transport perspectives, respectively. The architectural delineation of optical networks can be considered from various geographical domains, multiplex- ing technologies, switching and routing functions, and transport capacity and technologies. Today, a revolution has occurred from earlier single-wave- length synchronous optical net (SONET)/synchronous digital heirarchy (SDH)-based point-to-point transport to various phases of multi-wavelength optical transmission networking and subsequent bandwidth explosion via advances in dense-wavelength division multiplexing (DWDM). Currently, an interconnection of various point-to-point optical links based on SONET/ SDH rings, trees, and optical mesh topologies constitute the optical networks 1333_FrameBook.book Page 29 Tuesday, February 25, 2003 11:33 AM
- 47. 30 The handbook of optical communication networks infrastructure. However, the evolution of the optical networks toward more flexible, survivable, scalable, and interoperable architectures is ongoing as we write these chapters. Despite all progress in the optical transport from high-speed TDM (OC-192) and DWDM, true all-optical networks have yet to be realized. In limited cases, long-haul and metro-area networks have achieved some wavelength-routing capabilities. Meanwhile, although the optical-packet switching area has progressed with innovative protocols and optical labeling approach, it seems to be a technology of the future. The bottleneck in the optical networks obviously is the absence of all-optical switching and routing. Currently, several tech- nologies are competing in a wide-open space. Namely, reconfigurable opti- cal add/drop multiplexers (OADM), along with the rare-earth doped-fiber optical amplifiers (XDFA), are the enabling technologies of wave- length-routed DWDM optical networks using optical cross-connects (OXC) that are limited in size. In this chapter, the discussion is confined to the geographical architecture only. Meanwhile, optical transport networks, which encompass all geo- graphic domains, are considered in Chapter 19. Various multiplexing tech- nologies are also included. 2.2 Background The evolution of optical networks started from the SONET1–4 with the defi- nition of hierarchical electric time-domain multiplexing (ETDM) as synchro- nous transport signal (STS-n) for high bit rate in optical domain as optical channel of order “n” (OC-n). SONET is an interface (not a network) that aggregates all traffic at the electrical multiplexers using ETDM (i.e., all low-bit-rate streams add up to a high bit-rate using a common synchronized clock). The high bit stream STS-n is then converted (by the optical transmit- ter) to an optical signal OC-n that travels in fiber. At the physical layer synchronous time domain multiplexing (SONET/SDH) defines a frame for- mat (125 ms duration) and TDM hierarchy as OC-n/STM-m with n = 3m, and the bit-rate compatibility first establishes between OC-3 and STM-1 (i.e., OC-1 has no equivalent bit-rate) and STM-m hierarchy involves 4¥ multi- plexing.1,4 A finer granularity exists at the OC-1 and STS-1 levels in North America. An equivalent compatible global standard exists outside of North America that is commonly known as the synchronous digital hierarchy (SDH), and uses synchronous transport module (STM-m) standards. An STM-1 is equivalent to STS-3, and STM-4 is equivalent to STS-12 and so on (see Chapter 19). SONET/SDH-based networks consist of nodes or network elements (NE) that are interconnected with fiber cable over which user and network man- agement information is transmitted. Such point-to-point circuit-entities and NEs are the building blocks of the SONET- based optical networks that exist today in various topologies (e.g., rings, trees, and meshes). SONET NEs receive signals from various sources such as access multiplexers, asynchronous 1333_FrameBook.book Page 30 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 48. Chapter two: Evolution of optical networks architecture 31 transfer mode (ATM), and other LAN/MAN/and WAN gears. SONET NEs and SDH circuit-elements must have a proper interface to convert (or emulate) the incoming data traffic into the SONET/SDH format.4 Overall, SONET-based optical networks (SONET-rings) have dominated the long-haul and metro-space, and use optical-to-electrical-to-optical (OEO) switching and routing functions. Since its first deployment in the 1980s, SONET/SDH has almost replaced copper in the long haul, and every year millions of miles of new fiber have been laid down all over the globe. As the SONET/SDH-based optical links evolved from STS-3 (STM-1)/OC-3 to STS-48 (STM-4)/OC-48 bit-rates and recently to OC-192, with experimental deployment of OC-768.5 Concurrently, a revolution has occurred in the wavelength domain by multi- plexing several wavelengths on a single fiber strand. In parallel to wavelength division multiplexing (WDM) and TDM tech- nologies, researchers are pushing optical time domain multiplexing (OTDM) that can take tens of gigabit streams to several hundreds of gigabits streams.3 Although the nominal wavelength domain multiplexing had been imple- mented for 1310 and 1550 nm in the mid 1980s, an explosive growth occurred in the 1990s when EDFAs6 became available and multiple wavelength signals could be amplified without de-multiplexing. The so-called coarse WDM migrated to dense-WDM (DWDM) and ultra-dense WDM, and new stan- dards are still evolving.7 This added dimension to the OC-n hierarchy has resulted in a truly explosive growth in capacity from single-wavelength 2.5 and 10Gb/s to hundreds of gigabits and even terabits with a potential trend towards petabits.8,9 Although ultra high-bit and ultra broadband became reality in the long-haul space, the switching and routing still remains a major obstacle with only limited deployment of optical switches at a wavelength granularity. In literature,1–10 one finds an array of terminology to describe the various optical networks related to architecture, geographical coverage, multiplex-technology, management, switching- and routing-based technol- ogies and so on. It is virtually impossible to fully cover all the aspects of optical networks in a single chapter or even in a single monograph. In the forthcoming sections, we will confine to an overview of optical networks architectural topologies with respect to geographical coverage only and few multiplexing technologies in Chapter 19. Meanwhile, other aspects such as grooming, and switching and routing will be also briefly reviewed in Chapter 19, whereas functionality, optical-packet switching, optical mul- ticasting, self-healing, virtual private networks, IP-over WDM, management, and other issues of optical networks are left for the future. Another classifi- cation pertains to first-, second-, and third-generation of networks, and inter- ested readers can find more details in Optical Networks by Ramaswami and Sivarajan (1998), and Optical Networks by Black (2002).3,10 From the hybrid and all-optical networks perspective, based on the hardware infrastructure of the optical/photonic layer as defined in the layered model of communi- cation networks,2,3,10 today’s networks fall under the hybrid categories. Gen- erally, the all-optical networks will become a reality when an all-optical switching fabric replaces the optoelectronic (OEO) switching and routing 1333_FrameBook.book Page 31 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 49. 32 The handbook of optical communication networks nodes and photonics reaches the access/metro-edge. In Chapter 19, however, a more focused discussion will be given on the “optical transport networks,” also known as “photonic transport networks,” because their functionality encompasses all the categories from the edge to the core. 2.3 Optical networks architecture Aside from the other enabling component technologies (switches and rout- ers), a point-to-point optical transport link is the basic building block of all type of optical networks.11 Interconnections of several point-to-point optical links constitutes an optical network with certain logical topologies (e.g., rings, trees, or meshes and various combinations thereof). Several books and countless articles, which describe a single-wavelength (SONET-based)1–4 and multi-wavelength (i.e., open WDM12 point-to-point optical links), are avail- able in the literature. For clarity, we illustrate the concept of “open WDM architecture” in the point-to-point optical transport link in Figure 2.1. An open architecture allows the 1310-nm based short-reach SONET interfaces to communicate with the transponders. A single or multiple wavelengths are then assigned, multiplexed, amplified, and transported over a dual fiber for up/down traffic streams. At the open WDM terminals, the transponders convert/groom the incoming SONET/SDH as well as non-SONET signals and assign the available wavelengths from the ITU-grid and then multiplex all channels (wavelengths). Subsequently an EDFA (optical amplifier) boosts the signals before launching into the transport fiber (if the distance limita- tions so stipulate). Typically, for longer fiber spans, several EDFAs amplify the signals almost at every 120 km sections. At the other end, the incoming multi-wavelength signals are pre-amplified prior to de-multiplexing and sending into the transponders. A similar process occurs for the upstream traffic in the other fiber strand. Several point-to-point optical transport links (such as Figure 2.1) con- stitute an optical network infrastructure. Depending upon the stretch of the deployed fiber, multiplexers, and switching and routing hardware, the Figure 2.1 A schematic of a high-capacity open WDM point-to-point link, a building block of optical networks. Long-Haul Link 1310 nm λi λi 1310 nm Transponders WDM EDFAs WDM (1550 nm) Transponders 1333_FrameBook.book Page 32 Tuesday, February 25, 2003 11:33 AM © 2003 by CRC Press LLC
- 50. Another Random Scribd Document with Unrelated Content
- 51. Cut marshmallows into small pieces and dissolve in top of double boiler and add sugar and boiling water and heat thoroughly; add orange extract. Let cool and serve. Medium White Sauce 6 tbs. butter 6 tbs. flour 3 cups scalded milk Melt butter, add flour, and blend. Add scalded milk. Cook on LOW heat, stirring frequently until thick. Cool. Add salt and pepper just before serving. Nut Sauce 1½ cups sugar 1 cup chopped walnut meats ½ cup water 1 tsp. vanilla ⅛ tsp. salt Boil sugar and water to a thick syrup, add nuts, salt, and extract. Serve on ice cream, hot or cold. Orange Sauce 4 whites of eggs 3 oranges 4 tbs. confectioners’ sugar 1 tsp. lemon extract
- 52. 26 Beat whites of eggs until stiff, add sugar and beat again, then add grated rind and strained orange juice and lemon extract. Stir the mixture well. Thin White Sauce 6 tbs. butter 3 tbs. flour 3 cups scalded milk Melt butter, add flour, and blend. Add scalded milk. Cook on LOW heat, stirring frequently until thick. Cool. Add salt and pepper just before stirring. Whipped Cream Sauce ½ cup confectioners’ sugar 1 cup heavy cream 1 tsp. vanilla extract Whip cream until stiff, beat in sugar and vanilla. Chill and serve on any frozen dessert. Chopped candied fruit or nuts may be added to this sauce, or ½ cup maraschino cherries, chopped fine.
- 53. FROZEN SALADS Chicken Salad 4 cups cooked chicken 4 cups celery ¼ cup finely-chopped sweet cucumber pickles ⅔ cup cooked salad dressing 1 tbs. lemon juice Salt and pepper to taste 2 tbs. mayonnaise dressing Cut chicken in ½-inch pieces and cut celery in small pieces. Mix together. Add pickles, cooked salad dressing, and lemon juice. Mix by tossing together with two forks. Add mayonnaise. Freeze. Frozen Cheese Salad ¾ lb. roquefort cheese 1½ cups butter 1 tsp. paprika 1½ tsp. salt ⅛ tsp. red pepper 2 tbs. chopped olives or pickles or chives 1 cup cream Shred cheese and beat it thoroughly with the butter, add the seasoning, olives, and cream. Freeze.
- 54. 27 Frozen Cheese Salad ¼ cup scalding milk ½ lb. roquefort cheese 1 cup whipping cream 3 tbs. crushed and drained pineapple 6 chopped stuffed olives Mash the cheese with a fork, add the scalding milk, and work to a smooth paste. Add the crushed pineapple and chopped olives, then fold in the cream whipped until it holds its shape. Freeze. Frozen Cheese and Prune Salad 1½ cups cooked prune pulp 4 tsp. lemon juice 1½ tbs. sugar ⅓ cup finely-chopped pecans ½ cup mild American cheese, freshly grated ½ cup whipping cream Remove the stone from cooked prunes and rub through a sieve, enough to measure 1½ cups. Add the lemon juice, sugar, and pecans. Fold the grated cheese into the cream whipped but not stiff. Freeze. Frozen Fruit Salad 1 cup grated canned pineapple 1 cup white grapes (Seeds removed and chopped fine) 1 cup sliced bananas 1 tsp. salt ½ cup powdered sugar 1 cup orange juice and pulp
- 55. ¼ cup lemon juice 1 cup apples (chopped fine) ½ cup English walnuts (chopped fine) 2 tbs. powdered gelatine Mix the fruit, celery, and nuts. Season with salt and sugar. Add gelatine which has been softened in 2 tbs. cold water and dissolved over boiling water. Freeze. Frozen Fruit Salad 4 beaten egg yolks ¼ cup sugar ¼ cup vinegar or lemon juice ⅛ tsp. salt 2 cups whipping cream Mix the beaten egg yolks with the sugar, add the vinegar or lemon juice and salt, and cook in a double boiler until thick, stirring occasionally. Cool and add the cream which has been whipped until thick. Add the following: 3 cups diced, drained, canned pineapple ½ cup cut maraschino cherries 12 marshmallows cut into pieces 1 cup blanched and chopped almonds or other nut meats Mix and freeze. Frozen Tomato Salad 7 cups tomato juice and pulp 1 tsp. minced onion 3 tbs. sugar
- 56. 28 ½ tsp. paprika 1 tbs. vinegar 1 tsp. salt ¼ tsp. black pepper Press tomatoes through a sieve, add paprika, onion, vinegar, sugar, salt, and pepper. Let stand 1 hour. Freeze. Frozen Vegetable Salad 1 cup cottage cheese 1 tbs. mayonnaise 1 tsp. salt 1 cup canned or diced fresh tomatoes 2 tbs. minced red pepper 2 tbs. minced green pepper 1 cup whipping cream ½ cup cooked and chopped green beans Break up the cottage cheese and stir in the mayonnaise and salt. Run the canned tomatoes through a sieve to remove the more solid parts. Fresh tomatoes are peeled, diced quite finely, and used without draining. Add the chopped green beans and minced peppers to the cottage cheese mixture. Whip the cream and fold in last. Freeze. Miss B. Hammer, Iowa.
- 57. MAIN DISHES Chicken Mousse 2 cups chicken, chopped fine 2 cups heavy cream 1 tsp. salt ⅛ tsp. cayenne pepper 1 cup chicken stock 1 tbs. powdered gelatine ¼ tsp. black pepper ⅛ tsp. nutmeg 1 tbs. cold water Chop chicken to almost a paste and press it through a sieve. Season with salt, pepper, and nutmeg. Heat chicken stock and add gelatine which has been softened in the cold water, mix with chicken. Whip cream and add. Freeze. Chicken Mousse in Patty Shells 3 egg yolks 1 cup hot chicken stock Salt, white pepper, paprika 1 tsp. gelatine 1 tbs. cold water ⅔ cup cooked, chopped chicken ⅓ cup minced cashew nuts 1 cup whipping cream 6 patty shells
- 58. Sliced cherries Beat the egg yolks lightly, add the chicken stock, and cook over hot water until thick, smooth sauce is formed, stirring occasionally. Remove from the stove, and add the gelatine which has been soaked in the cold water for 5 minutes, then add the chicken and the minced cashew nuts or pecans. Cool and fold in the cream which has been whipped until thick but not stiff. Freeze. Mrs. K. S. Scott, Washington. Frozen Chicken Pie 1 tbs. butter 1 tbs. flour 1 cup milk 1 tbs. gelatine 1 tbs. cold water ¼ cup mayonnaise Salt 1 tbs. lemon juice 1½ cups cold diced chicken ½ cup white grapes cut in half ½ cup diced celery ½ cup blanched and chopped almonds ½ cup whipping cream 8 individual pastry shells Melt the butter in a saucepan. Add the flour and smooth to a paste. Add the milk and stir until a thin, smooth white sauce is formed. In the meantime soak the gelatine in the cold water for 5 minutes, then add to the hot sauce and stir until the gelatine is dissolved. Cool and add the mayonnaise, lemon juice, chicken, grapes, celery, and almonds. Whip the cream until thick but not stiff, fold into the mixture, and season to taste with salt. Freeze.
- 59. 29 Mrs. H. P. Gregory, Illinois. Frozen Chicken a la King Make a cream sauce of the following: 1½ tbs. butter 1½ tbs. flour ½ cup chicken stock 2 egg yolks ½ cup cream or undiluted evaporated milk When thick, remove from the heat and add the beaten yolks of the 2 eggs, return to the stove, and cook 1 minute. Meanwhile prepare the following ingredients: 1 cup finely-minced chicken ¼ cup thinly-sliced stuffed olives ¼ cup sliced, canned mushrooms ¼ cup ground nut meats, preferably almonds or cashews ½ cup whipping cream 2 egg whites Add the chicken, olives, mushrooms, and nut meats to the cream sauce, and chill. When cold, fold in the cream, whipped, then the beaten egg whites, and freeze. Mrs. T. Lessmeister, Illinois. Frozen Crab Meat in Tomatoes 2 cups canned tomatoes 2 whole cloves 1 small onion, minced
- 60. ½ tsp. celery seed 1 tbs. sugar 1 tsp. salt ⅛ tsp. white pepper 1 tbs. lemon juice 1 tbs. gelatine 2 tbs. cold water 1 cup crab meat 3 tbs. finely-diced green pepper 1 cup whipping cream Combine the tomatoes, cloves, onion, celery seed, sugar, salt, and white pepper, and simmer for 15 minutes. Strain, add the lemon juice and the gelatine which has been softened in the cold water for 5 minutes. Chill and, when beginning to thicken, fold in the crab meat (flaked and drained of any juice), the minced green pepper, and the whipped cream. Freeze. Mrs. D. L. McKnight, Ohio. Ham Mousse 1 tbs. gelatine ¼ cup cold water ¼ cup boiling water ¼ cup mayonnaise 2 cups finely-chopped cooked ham 10 ripe olives, minced fine 1½ cups whipping cream Salt to taste 1 tsp. prepared horseradish Soak the gelatine in the cold water for 5 minutes. Add the boiling water and stir until the gelatine is dissolved. Cool and add the
- 61. 30 mayonnaise, horseradish, ham, and olives. Fold in the cream whipped until it holds its shape. Season to taste with salt. Freeze. Ethel Schaefer, Texas. Ham and Chicken Mousse 3 egg yolks 1½ cups scalded milk 1 tbs. gelatine ¼ cup cold water ½ cup tomato juice 1 cup chopped cooked ham 1 cup chopped cooked chicken ½ cup finely-grated American cheese Salt and pepper 1 tbs. chopped pimento 1 cup whipping cream Beat the egg yolks, mix with the scalded milk, and cook in a double boiler, stirring often until the mixture thickens slightly. Soak the gelatine in the cold water for 5 minutes and dissolve in the hot tomato juice. Add to the hot custard mixture and stir until thoroughly mixed. Add the ham, chicken, cheese, pimento, salt and pepper to taste, and cool. Fold in the cream whipped until it holds its shape. Freeze. Mrs. A. E. Taylor, West Virginia. Rice and Chicken Luncheon Dish 1 tbs. gelatine 2 tbs. cold water 1 cup hot, well-seasoned chicken stock
- 62. 2 cups cooked and drained rice 1½ cups chopped cooked chicken or fish ¼ cup finely-cut pimentos Salt to taste 1½ cups whipped cream Soak the gelatine in the cold water for 5 minutes. Add the hot chicken stock and stir until the gelatine is dissolved. Cool and add the rice, chicken, pimentos, and season to taste with salt. Fold in the cream which has been whipped until thick but not stiff. Freeze. Mrs. J. A. Dresp, So. Dakota. Tomato Mousse 3 lbs. tomatoes 1 bay leaf 1½ tsp. salt 1 tsp. pepper 3 tsp. sugar 2 cloves ½ tsp. celery salt 1 tbs. vinegar 1 cup water 4 tbs. tomato catsup 1½ cups whipped cream ¾ cup milk Crisp lettuce leaves Wash and dry tomatoes, cut them in quarters, put them into a saucepan with water and seasonings. Stir over the fire until reduced to a pulp, simmer 5 minutes and rub tomatoes through a sieve, then allow to cool. Beat up cream until thick, add milk and 2½ cups of the tomato purée. Freeze.
- 63. 31 Tuna Fish Mousse 1 tbs. gelatine ¼ cup cold water ¾ cup tart mayonnaise 1 cup whipping cream 1½ cups flaked tuna fish ½ cup finely-chopped celery 2 tbs. minced parsley ½ cup chopped fresh cucumber 2 tbs. chopped stuffed olives ½ tsp. salt ½ tsp. paprika Soak the gelatine in cold water for 5 minutes, dissolve over hot water, and add gradually to the mayonnaise. Whip the cream until thick and fold into the mayonnaise mixture. Add the remaining ingredients and freeze. Mrs. F. Barnhill, Ohio.
- 64. Apple Mint Banana Caramel Chocolate No. 1 Chocolate No. 2 Coffee Date Ginger-Orange Golden Glow Grape-Nuts Lemon Marshmallow Nut and Raisin Prune Peach Sour Cream Strawberry (Cooked) Strawberry No. 1 Strawberry No. 2 Six Threes Velvet Vanilla No. 1 Vanilla Variations Vanilla No. 2 Wintermint Butter Brickle INDEX Page ICE CREAMS 3 3 3 3 4 4 4 5 5 5 6 6 6 6 6 4 7 7 7 7 7 8 8 8 8 MOUSSES 9
- 65. Cherry and Orange Chocolate Fruit Coffee Ginger Maple Peach Raspberry Mint Strawberry No. 1 Strawberry No. 2 Toasted Cocoanut Apricot No. 1 Apricot No. 2 Banana Cranberry Economy Favorite Fruit Glenridge Grape Grapefruit Lemon Cream Lemon Milk Lime Orange Cream Orange Fruit Orange Pineapple Pineapple Pineapple Cream Raspberry Alaska Pudding Chocolate Raisin Pudding 9 9 9 9 9 10 10 10 10 10 11 11 SHERBETS 11 11 11 11 12 12 12 12 12 13 13 13 13 13 14 14 14 14 14 PUDDINGS AND BISQUES 15 15
- 66. Frozen Caramel Pudding Frozen Custard Frozen Custard with Marrons Frozen Plum Pudding Marshmallow Pudding Mexican Frozen Pudding Pineapple Pudding Macaroon Date Bisque Macaroon Orange Bisque Pineapple Bisque Pistachio Bisque Angel Banana and Browned Almond Caramel Caramel Coffee Chocolate No. 1 Chocolate No. 2 Coffee No. 1 Coffee No. 2 Fruit Golden Hawaiian Delight Lemon Maple No. 1 Maple No. 2 Maple Nut Peach Pineapple Plain Apricot Frappe Banana Frappe Coffee Frappe Fruit Frappe 15 15 16 16 16 16 17 17 17 17 17 PARFAITS 18 18 18 18 18 19 19 19 19 19 20 20 20 21 20 20 20 21 FRAPPES AND ICES 21 21 21 21
- 67. Grape Juice Frappe No. 1 Grape Juice Frappe No. 2 Orange Frappe No. 1 Orange Frappe No. 2 Pineapple Frappe Raspberry Frappe Spiced Grapefruit Frappe Strawberry Frappe No. 1 Strawberry Frappe No. 2 Creme de Menthe Ice Ginger Ale Ice Grape Juice Ice Lemon Ice Lemon Water Ice Mint Ice Orange Ice No. 1 Orange Ice No. 2 Pear Ice Strawberry Ice Caramel Chocolate Fruit Hot Maple Lemon Cream Marshmallow Medium White Nut Orange Thin White Whipped Cream Chicken Frozen Cheese No. 1 Frozen Cheese No. 2 22 22 22 22 22 22 22 23 23 23 23 23 23 23 24 24 24 24 24 SAUCES 24 24 25 25 25 25 25 25 25 26 26 FROZEN SALADS 26 26 26
- 68. Frozen Cheese and Prune Frozen Fruit No. 1 Frozen Fruit No. 2 Frozen Tomato Frozen Vegetable Chicken Mousse Chicken Mousse in Patty Shells Frozen Chicken Pie Frozen Chicken a la King Frozen Crab Meat in Tomatoes Ham Mousse Ham and Chicken Mousse Rice and Chicken Luncheon Dish Tomato Mousse Tuna Fish Mousse 26 27 27 27 27 MAIN DISHES 28 28 28 28 29 29 29 30 30 30
- 69. Transcriber’s Notes Silently corrected a few typos. Retained publication information from the printed edition: this eBook is public-domain in the country of publication. In the text versions only, text in italics is delimited by _underscores_.
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