`Telecommunications
`Essentials
`The Complete Global Source
`for Communications Fundamentals,
`Data Networking and the Internet,
`and Next-Generation Networks
`
`Lillian Goleniewski
`
`vvAddison-Wesley
`Boston * San Francisco e New York * Toronto * Montreal
`London * Munich e Paris * Madrid
`Capetown * Sydney * Tokyo * Singapore * Mexico City
`
`
`
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`Page 1
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`AT&T Exhibit 1016
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`
`
`
`
`Manyofthe designations used by manufacturersandsellers to distinguish their products are claimedas trade-
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`the designations have been printed withinitial capital letters or in all capitals.
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`Lido Telecommunications Essentials® is the registered trademark of The Lido Organization, Inc.
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`The authorand publisher have taken care in the preparation of this book, but make no expressed or implied war-
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`Library of Congress Cataloging-in-Publication Data
`
`Goleniewski, Lillian.
`Telecommunications essentials : the complete global source for communications
`fundamentals, data networking and the Internet, and next-generation networks/ Lillian Goleniewski.
`p. cm.
`Includes bibliographical references and index.
`ISBN 0-201-76032-0
`1. Telecommunication. I. Title.
`
`TK5101 G598 2002
`621.382—dc21
`
`Copyright © 2002 by Pearson Education,Inc.
`
`2001053752
`
`All rights reserved. No part of this publication maybe reproduced,stored in a retrieval system, or transmitted, in
`any form, or by any means,electronic, mechanical, photocopying, recording, or otherwise, withoutthe prior con-
`sent of the publisher. Printed in the United States of America. Published simultaneously in Canada.
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`Pearson Education, Inc.
`Rights and Contracts Department
`75 Arlington Street, Suite 300
`Boston, MA 02116
`Fax: (617) 848-7047
`
`ISBN 0-201-76032-0
`Text printed on recycled paper
`
`123456789 10—CRS—0504030201
`First printing, December 2001
`
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`| 99
` Establishing Connections: Switching Modes and Networking Modes
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`certain position andare switched to a different position. The position to whichbits
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`are switched is determined by a combination of one or more of three dimensions:
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`space(thatis, the interface or port number), time, and wavelength. Packet switch-
`ing is based onlabels; addressing information in the packet headers,or labels, helps
`to determine how to switch or forward a packet through the network node.
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`
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`Circuit Switching
`Circuit switching has been the basis of voice networks worldwide for many years.
`You can apply three termsto the nature of a circuit-switched call to help remember
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`whatthis is: continuous, exclusive, and temporary. One of the key attributes of a
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`circuit-switched connection is that it is a reserved network resource that is yours
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`and only yours for the full duration of a conversation. But when that conversation
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`is over, the connectionis released. A circuit-switched environmentrequires that an
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`end-to-end circuit be set up before a call can begin. A fixed share of network
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`resources is reserved for the call, and no other call can use those resources until the
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`original connection is closed. A call request signal must travel to the destination
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`and be acknowledged before any transmission can actually begin. As Figure 4.1
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`illustrates, you can trace the path from one endofthe call to the other end; that
`path would notvary for the full duration of the call, and the capacity provisioned
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`on that path would be yours and yours alone.
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`Advantages and Disadvantages of Circuit Switching Circuit switching uses
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`many lines to economize on switching and routing computation. Whena callis set
`up, a line is dedicated to it, so no further routing calculations are needed.
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`Intermediate Switching Offices
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`Trunk that stays in place
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`pe eae Connection set up when call is placed
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`Exchange
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`Figure 4.1Acircuit-switchedcall
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`Chapter 4
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`= Establishing Communications Channels
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`Since they were introduced in the mid-1980s, digital cross-connect systems
`(DCSs) have greatly eased the process of reconfiguring circuit-switched networks
`and responding to conditions such as congestion and failure. DCSs create pre-
`defined circuit capacity, and then voice switches are used to routecalls over circuits
`that are set up by these DCSs. DCSs are analogousto the old patch panels. You may
`have seen a main distribution frame (MDF) on which twisted-pair wiring is termi-
`nated. The MDF is a manualpatch panel, and before DCSs were introduced, when
`it was necessary to reconfigure a network based on outage, congestion, or cus-
`tomer demandas a result ofshifting traffic patterns, technicians had to spend days
`or even weeks, manually making changes at the MDF The DCSis a software patch
`panel, and within the software are databases that define alternate routes—alternate
`connections that can be activated in the event that the network encounters a con-
`dition that requires some form of manipulation. DACSs are one of the elements of
`the PSTN that contribute to its reliability: When network conditions change, in a
`matter of minutes, a DCScan reconfigure the network around those changes. With
`such tools, the PSTN is able to offer five 9s reliability—in other words, 99.999%
`guaranteed uptime. (DCSsare discussed in more detail in Chapter5.)
`Circuit switching offers the benefits oflow latency and minimal delays because the
`routing calculation on the path is made only once, at the beginning of the call, and
`there are no moredelays incurred subsequently in calculating the next hop that should
`be taken. Traditionally, this was sometimes seen as a disadvantage because it meantthat
`the circuits might not be usedasefficiently as possible. Around half of most voice calls
`is silence. Most people breathe and occasionally pause in their speech.So, when voice
`communications are conducted overa circuit that’s being continuously held, and half
`the time nothing is being transmitted,the circuit is not being used very efficiently. But
`rememberthatthis is an issue thatis important when bandwidth is constrained. And as
`mentioned earlier in the book, through the optical revolution, bandwidth is being
`released at an astoundingrate,so theefficientuse ofcircuits because ofbandwidth con-
`straints will not present the samesort ofissue in the future that it once did. Hence, the
`low latencies or delays that circuit switching guarantees are more important than its
`potential drawbacks in bandwidth efficiency.
`Circuit switching has been optimized for real-time voice traffic for which Quality of
`Service (QoS) is needed. Because it involvespath calculation at the front end, you know
`how many switches and cables you're going to go through, so you can use a pricing
`mechanism that’s based on distance and time. The more resources you use, either over
`time or over distance, the greater the cost. Again, developments in fiber economics are
`changing someoftheold rules, and distance is no longer necessarily an added cost ele-
`ment. (QoSis discussed in more detail in Chapter 10, “Next-Generation Networks.”)
`Generations of Circuit Switches Circuit switches have been around for quite
`some time, We've already been through three basic generations, and we're begin-
`ning to see a fourth generation.
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