`
`
`
`Delivering Voice over
`IP Networks
`
`Second Edition
`
`DANIEL MINOLI
`
`EMMA MINOLI
`
`Wiley Publishing, Inc.
`
`Page 1 of 14
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`Samsung Exhibit 1031
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`Page 1 of 14
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`Samsung Exhibit 1031
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`

`Publisher: Robert lpsen
`Editor: Margaret Eldridge
`Assistant Editor: Adaohi Obi
`
`Managing Editor: Angela Smith
`New Media Editor: Brian Snapp
`Text Design 8:. Composition: North Market Street Graphics
`
`Designations used hy companies to distinguish their products are often claimed as trade-
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`appear in initial. capital or ALL CAPITAL LETI‘ERS. Readers, however, should contact the appro—
`priate companies for more complete information regarding trademarks and registration.
`
`This text is printed on acid~free paper.
`
`Copyright © 2002 by Dan Minoli, Emmanuelle Minna. All rights reserved.
`
`Published by Wiley Publishing, lnc., Indianapolis, lndiana
`
`Published simultaneously in Canada.
`
`No part of this publication may be reproduced, stored in a retrieval system or transmitted in
`any Form or by any means, eiectronic, mechanical, photocopying, recording, scanning or
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`the subject matter covered. it is sold with the understanding that the pubiisher is not
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`the services of a competent professional person should be sought.
`
`Library ofCangres-s Cataloging~in-Publication Dara:
`
`Minoli, Daniel
`Delivering voice over 1'? networks I Dan Minoli, Emma Minoii.— 2nd ed.
`p. cm.
`ISBN 0—471—38606—5
`1. Internet telephony. 2. TCPIIP (Computer network protocol]. 3. Digital! telephone
`systems. 4. Computer networks. 5. Data transmission syterns. I. Minoli, Emma. 11. Title.
`
`TKS] 05.3865 .M57 2002
`621.385—chi
`
`Wiley also publishes its books in a variety of electronic Formats. Some content that appears in
`print may not be available in electronic versions. For more information about \Nilegr products,
`visit our web site at nwutwileyeorn.
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`2002071358
`
`Printed in the United States of America.
`
`[098765432]
`
`Page 2 of 14
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`

`contents
`
`xiii
`PREFACE
`ACKNOWLEDGMENT
`ABOUT THE AUTHORS
`
`XV
`xvii
`
`Introduction and Motivation
`Chapter 1:
`1.1
`INTRODUCTION
`1
`1.2 DRIVERS FOR VOICE OVER IP
`THE NEGATIVE DRIVERS
`
`6
`12
`
`1
`
`_ 1.3 APPROACHES FOR IP-BASED VOICE SYSTEMS
`VOICE SERVERS APPROACH
`15
`IP VOICE AND VIDEO PHONES
`1.4 THE FUTURE
`18
`REFERENCES
`18
`
`18
`
`14
`
`Chapter 2: An Overview of IP, IPOATM, MPLS,
`and RTP
`21
`
`2.1
`2.2
`
`21
`INTRODUCTION
`24
`IN'I‘ERNETPROTOCOI.
`THE ROLE OF THE IP
`IP ROU'I‘ING
`26
`29
`IP DRI‘AORAMS
`SUPPORT OF VOICE AND VIDEO 1N ROUTERS
`
`24
`
`32
`
`33
`IP VERSION 6 [IPV6)
`36
`23 IP OVER ATM (IPOATM)
`39
`2.4
`BASIC SYNOPSIS OF MPLS
`MPLS FORWARDINOXLAEEL—SWITCHING MECHANISM
`MPLS LABEL-DISTRIBUl‘lON MECHANISM
`43
`
`41'
`
`REAL—TIME TRANSPORT PROTOCOL (RTP)
`2.5
`2.6 RTP CONTROL PROTOCOL [RTCP)
`50
`2.7
`STREAM CONTROL TRANSMISSION PRO'I‘OCOL [S CTP)
`
`45
`
`52
`
`Page 3 of 14
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`

`

`65
`
`Y9
`
`72
`
`?4
`
`3.3
`
`3.5
`
`Issues in Packet Voice Communication
`Chapter 3:
`3.1
`INTRODUCTION
`63
`SCOPE
`64
`SUMMARY OF RESULTS
`3.2 TRAPPIC MODELS
`66
`INTRODUCTION
`66
`SPEECH EVENIS
`66
`SPEAKER MODELS
`67
`CALL ORIGINA‘I‘ION MODEL
`PEIGORMANCE CRITERIA
`74
`RESULTS OF SUBJECTWE STUDIES
`SMOO’I‘HNESS CRITERLA
`76
`3.4 LINKMODEL
`7'8
`79
`INTRODUCTION
`MODEL DESCRIPTION
`RESULTS
`84
`PROPERTIES OF THE DELAY DISTRIBUTION
`FINITE-BUFEER CASE
`86
`EFFECT OP SPEECH MODELS
`OPTIMAL PACKET LENGTH
`TRANSIENT BEHAVIOR
`92
`3.6 CONCLUSION
`95
`REFERENCES
`96
`
`® (3011:3an
`
`54
`2.8 ATM QOS MECHANISMS
`QUALITY OF SERVICE PARAME‘I‘BRS
`QOS CLASSES
`57
`REFERENCES
`59
`NOTES
`61
`
`_
`
`_
`
`56
`
`
`
`63
`
`84
`
`88
`90
`
`Chapter 4: Voice Technologies for Packet~Based
`Voice Applications
`101
`101
`4.1
`INTRODUCTION
`GENERAL OVERVIEW OF SPEECH TECHNOLOGY
`WAVEPOIUvI CODING
`102
`
`101
`
`4.2
`
`VOCODINO (ANALYSIS/SYNTHESIS] INTI-1E FREQUENCY DOMAIN
`(3.727: ADPCM FOR PACKET NETWORK APPLICATIONS
`111
`INTRODUCTION
`1 11
`ADPCM ENCODER PRINCIPLES
`ADPCM DECODER PRINCIPLES
`
`114
`12]
`
`107
`
`Page 4 of 14
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`

`

`r
`
`:5
`
`. -.
`
`.:- :..- : ..-w1-.-..~ : —_7.-.-.m:.T:—:r:'r::v.-..rr.=v: .-.
`
`.
`
`Contents
`
`EXAMPLE OF APPLICATION
`4.3
`REFERENCES
`123
`NOTES
`123
`
`123
`
`Chapter 5: Technology and Standards for Low—Bit—Rate
`Vocoding Methods
`125
`5.1
`INTRODUCTION
`125
`OVERVIEW
`127’
`VOCODER ATTRIBUTES
`
`128
`
`134
`135
`
`136
`
`139
`140
`
`130
`
`145
`
`5.2
`
`5.3
`
`5.4
`
`5.5
`
`LINEAR PREDICTION ANALYSIS-BY—SYNTHESIS [LPAS) CODING
`INTRODUCTION TO G729 AND G.723.1
`133
`DIPPEREN'I‘IKTIONS
`133
`STANDARDIZATION PROCESS
`STANDARDIMPION INTERVAL
`(1723.1
`136
`136
`INTRODUCTION
`ENCODER/DECODER
`(3.728
`138
`LD—CELP ENCODER
`LD-CELP DECODER
`(3.729
`140
`141
`ENCODER
`143
`DECODER
`145
`5.6 EXAMPLE OF APPLICATIONS
`H.263 VIDEO CODING FOR LOW—Brr—RATE COMMUNICATION
`H.324 MULTIMEDIA COMMUNICATION
`146
`H.323 MULTIMEDLA COMMUNICKI‘IONS STANDARD POR LANS AND ENTERPRISE
`NETWORKS
`148
`REFERENCES
`150
`NOTES
`151
`
`Chapter 6: Voice over IP and the Internet
`6.1
`INTRODUCTION
`153
`157
`6.2
`IP/INTERNET BACKGROUND
`ENTERNET PROTOCOL SUITE
`THE INTERNET
`157
`
`157
`
`153
`
`6.3 VOICE TRANSMISSION AND APPROACHES IN ATM, FRAME REIAY, AND [P
`ATM 162
`FRAME RELAY
`IP
`164
`
`164
`
`162
`
`_ Page 5 of 14
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`

`

`Contents
`
`.-._«.«. ---_-.= \Tzwow‘
`
`[TU—T H3 23 GROUP OF STANDARDS
`STREAMING AUDIO
`166
`
`165
`
`6.4
`
`5.5
`
`QoS PROBLEMS AND SOLUTIONS
`167
`PROTOCOLS FOR QOS SUPPORT FOR AUDIO AND VIDEO APPLJCA'I‘IONS
`RSVP APPLICATIONS
`169
`IP MUITICAST
`17']
`
`169
`
`INTERNET TELEPHONY SERVERS (ITSS)
`6.6
`THE VOICE OVER IP/INTERNET MARKB'I‘
`6 .7
`6.8 VOIP REGUIATORY ISSUES
`177
`6.9
`CONCLUSION
`180
`REFERENCES
`181
`NOTES
`181
`
`172
`177
`
`
`
`183
`
`187
`
`189
`
`196
`
`209
`
`215
`
`Chapter 7: Signaling Approaches
`7.1
`INTRODUCTION
`183
`7.2
`SIGNALING IN CIRCUITLSWITCHED NETWORKS
`7.3
`H.323 STANDARDS
`189
`FUNCTIONAL ELEMENTS
`H.323 BASICS
`190
`EXAMPLE OF SIGNALING
`MGCP
`202
`SIP
`207
`SIP PROTOCOL COMPONENTS
`SIP-T
`210
`OTHER IETF SIGNALING EFFORTS
`PINT AND SPIRITS
`215
`ENUM 218
`TRIP
`219
`MEGACO
`219
`221
`SIOTRAN PROTOCOLS
`PERFORMANCE CONSIDERA’HONS FOR CCSS7 OVER IP
`223
`
`7.4
`7.5
`
`7.6
`
`7.7
`7.8
`
`7.9
`
`Page 6 of 14
`
`223
`
`SECURITY REQUIREMENTS 1:011 CCSS? OVER IP
`SCTP USE IN CCSS7
`223
`TRANSPORTINO MTP OVER IP
`TRANSPORTINO SCCP OVER 1?
`SCTP
`230
`230
`INTRODUCTION
`230
`MOTIVA'I‘ION
`ARCHITEC'I‘URAL VIEW OF SCTI’
`FUNCTIONAL VIEW OF SCTP
`KEY 'I‘ERMS
`236
`SERIAL. NUMBER ARI'I‘HMB‘I‘IC
`
`226
`229
`
`230
`
`231
`
`236
`
`Page 6 of 14
`
`

`

`
`
`239
`SC'l‘P PACKET FORMAT
`SCTP ASSOCIATION STATE DIAGRAM
`ASSOCIATION INITIALIZATION
`260
`USER DATA TRANSFER
`262
`TERMINATION OF AN ASSOCIA‘I'ION
`REFERENCES
`276
`NOTES
`27?
`
`258
`
`273
`
`Chapter 8: Quality Of Service
`8.1
`INTRODUCTION
`279
`8.2
`BACKGROUND
`281
`
`279
`
`284
`8.3 QOS APPROACHES
`284
`PER-FLOW QOS
`288
`CLASS-BASED Q03
`289
`MPLS-BASED QOS
`TRAFFIC MANAGEMEme UEUE MANAGEMENT
`8.4 QOS DETAILS
`294
`IETF INTSERVAIJPROACH
`IETF DIFFSERVAPPROACH
`
`294
`305
`
`29]
`
`ADDITIONAL DETAILS ON QUEUE MANAGEMENT
`CONCLUSION
`326
`CASE STUDY
`327
`
`8.5
`
`320
`
`REAL-TIME SERVICE REQUIREMENTS
`TECHNICAL CHALLENGES
`330
`CISCO SOLUTIONS FOR SUPPORTING IP-BASED REAL-TIME SERVICES
`REFERENCES
`340
`NOTES
`342
`
`32?
`
`330
`
`Chapter 9: Voice over MPLS and Voice over I?
`over MPLS
`343
`
`343
`
`INTRODUCTION AND BACKGROUND
`9.1
`9.2 MO'ITVATIONS
`344
`349
`9.3
`BASIC MPLS FEATURES
`MPLS FORWAROINC/LABEL—SWTTCHING MECHANISM
`MPLS LABEL-DIS'I‘IUBU‘I‘ION MECHANISM
`356
`OTHER FEATURES
`358
`COMPARISON
`359
`
`353
`
`9.4 QDS CAPABILZTIES
`INTRODUCTION
`DETAILS
`368
`
`363
`365
`
`Page 7 of 14
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`

`

`370
`9.5 VOICE APPLICATIONS
`371
`IP HEADER COMPRESSION
`372
`VOIPOMPLS PROPOSAL
`MPLS FORUM SPECIFICA'I'ION
`REFERENCES
`375
`NOTES
`376
`
`374
`
`
`
`377
`
`385
`
`390
`
`Chapter 10: Telephone Number Mapping (ENUM)
`10.]
`INTRODUCTION
`377
`10.2
`BACKGROUND
`379
`10.3
`INTRODUCTION TO ENUM 383
`ENUM: AN EVOLVING ARCHITECTURE
`DEFINING ENUM APRIJCA'I‘IONS
`387
`THE ENUM ROAD TO SUCCESS
`389
`SUMMARY OF CAPABILITIES AND ISSUES
`CAPABILITIES
`390
`ADVOCACY
`397
`10.5 NUMBER POR’I‘ABIIJTY
`TYPES OE NP
`400
`SPNP SCHEMES
`401
`
`10.4
`
`398
`
`405
`
`DATABASE QUERIES IN THE N 1‘ ENVIRONMENT
`CALL ROUTING IN THE NP ENVIRONMENT
`408
`N? IMPLEMENTA'I‘IONS FOR GEOGRAPHIC E.164 NUMBERS
`NP~ENABLED NUMBER CONSERVATION METHODS
`41]
`CONCLUSION
`414
`13.164 NUMBERS AND DNS
`INTRODUCTION
`417
`13.164 NUMBERS AND DNS
`
`417
`
`417
`
`10.6
`
`41}
`
`FE'I‘CHING UNIFORM RESOURCE IDEN'I‘IEIERS (URIS) GIVEN AN E164 NUMBER
`[ANA CONSIDERATIONS
`420
`SECURITY CONSIDERATIONS
`420
`10.? APPENDIX TO THE RFC 2916 SCENARIO
`REFERENCES
`422
`NOTES
`424
`
`421
`
`418
`
`Chapter 11: Carrier Applications
`1 1.1
`INTRODUCTION AND OPPORTUNITIES
`427
`11.2 WHERE THE ACTION SHOULD BE
`432
`11.3
`CARRIER VOlCE NETWORKS
`439
`
`427
`
`Page 8 of 14
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`

`

`Contents ®
`
`_.=......-o....,z::.-. ,
`
`.-.__ ;.\_-.‘2:::;-...:.-.
`
`.- ; .- “r
`
`446
`1 1.4 DEPLOYMENT AND ISSUES
`450
`WIRELESS NETWORKS
`CABLE TELEPI’iONY NETWORKS
`ENTERPRISE APPLICATIONS
`465
`INTERNATIONAL OPPORTUNITIES
`
`11.5
`11.6
`
`458
`
`466
`
`EQUIPMENT/VENDOR TRENDS
`11.7
`REFERENCES
`473
`NOTES
`474
`
`469
`
`INDEX
`
`477
`
`Page 9 of 14
`
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`

`

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`Chaprer Two-W
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`transport portion based on Am, PO S, MPLS, and Ethernet. Media plane protocols
`are covered in this chapter; signaling plane protocols are covered in Chapter 7; and
`QoS protocols are covered in Chapter 8.
`This chapter covers the following issues that will play a role in voice over data
`networks:
`
`0 IP and IPv6 {4, S]
`' I? over ATM
`
`- MPLS
`
`0 RTP
`
`II Stream Control Transmission Protocol [SCTP)
`
`2.2
`
`Internet Protocol
`
`This section highlights key IP functionability and capabilities.
`
`The Role of the IP
`
`TCP/IP is the name for a family of communications protocols used to support
`lntemetting in enterprise and interenterprise applications. Protocols include the
`Internet Protocol UP], the Transmission Control Protocol ['I‘CP), the User Data-
`gram Protocol [UDP), and other protocols that support specific tasks, such as
`transferring files between computers, sending mail, or logging into another com—
`puter. TCP/IP protocols are normally deployed in layers, with each layer responsi—
`ble for a different facet of the communications. Each layer has a different
`responsibility.
`
`1. The link layer (sometimes called the nemark interface hime normally
`includes the device driver in the operating system and the corresponding
`network interface card in the computer. Together they handle all the hard-
`ware details of physically interfacing with the cable.
`
`2. The network layer (sometimes called the interns: layer] handles the move-
`ment of packets in the network. Routing of packets, for example, takes
`place here. IP provides the network layer in the TCP/IP protocol suite.
`
`3. The transport layer provides a flow of data between two end system hosts
`for the application layer above. In the Internet protocol suite there are two
`transport protocols, TC-P and UDP. TCP provides a reliable flow of data
`between two hosts. It is concerned with such things as partitioning the data
`passed to it from the application into appropriately sized frames for the net-
`work layer below, acknowledging received packets, and setting timeouts to
`
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`

`._
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`..
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`make certain that the other end acknowledges packets that are sent. Because
`this reliable flow of data is provided by the transport layer, the application
`layer can ignore all those details UD P, on the other hand, provides a much
`simpler service to the application layer. It sends packets of data called data-
`grams from one host to the other, but there is no guarantee that the data-
`grams will be delivered to the other end. Any desired reliability must be
`added by the application layer.
`
`4. The application Myer handles the details of the particular application. There
`are many common TCP/IP applications that almost every implementation
`provides:
`
`' Telnet for remote login
`
`- The file transfer protocol [FTP]
`
`‘ The Simple Mail Transfer Protocol [SMTP] for e—m ail
`
`' The Simple Network Management Protocol [SNMP)
`- Others
`
`In this architecture, TCP is responsible for verifying the correct delivery of
`data from the sender to the receiver. ’l‘CP allows a process on one end system to
`reliably send a stream of data to a process on another end system. It is connection—
`oriented: Before transmitting data, participants must establish a connection. Data
`can be lost in the intermediate networks. TCP adds support to detect lost data and
`to trigger retransmissions until the data is correctly and completely received.
`11’ is responsible for relaying packets of data [protocol data units [PDU)] from
`node to node. 1P provides the basis for connectionless best-effort packet delivery
`service. IP'S job is to moveespecifically to routeublocks of data over each of the
`networks that sit between the end systems that want to communicate. 1? provides
`for the carriage of datagrams from a source host to destination hosts, possibly pass-
`ing through one or more gateways [routers] and networks in the process. An IP
`protocol data unit (datagram) is a sequence of fields containing a header and a pay—
`load. The header information identifies the source, destination, length, and charac—
`teristics of the payload contents. The payload is the actual data transported. Both
`end system hosts and routers in an internet are involved in the processing of the 1P
`headers. The hosts must create and transmit them and process them on receipt; the
`routers must examine them for the purpose of making routing decisions and mod—
`ify them [e.g., update some fields in the header) as the 1P packets make their way
`from the source to the destination.
`
`IP protocols are supported over a variety of underlying media, such as ATM,
`frame relay, dedicated lines, ISDN, Ethernet, DSL, and so forth. As IP networks
`have become ubiquitous, the business community has become sophisticated about
`utilizing IP networks as a cost-effective corporate tool, first in data communica-
`tions and now for other real-time applications. Organizations favor networks based
`
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`on IP because of the flexibility and vendor support. IP networks run under the
`most widely used network. operating systems; they are scaleable to a large degree;
`and they enjoy extensive implementation across product lines [e.g., in the routers,
`PC clients, server switches, etc]. As noted, a relatively new IP application now in
`demand is toll'quality, low—bandwidth voice [and fax] transmission over IP net-
`works.
`_
`Intranets use the same WWW/t-ITML/H’ITP and 'l‘CPfIP technology used for
`the Internet. When the Internet caught on in the early to mid-19905, planners
`were not looking at it as a way to run their businesses. But just as the action of
`putting millions of computers around the world on the same protocol suite
`fomented the Internet revolution, so connecting islands of information in a corpo~
`ration via intranets is now sparking a corporate—based information revolution.
`Thousands of corporations now have intranets. Across the business world, employ—
`ees from engineers to office workers are creating their own home pages and sharw
`ing details of their projects with the rest of the company.
`
`iP Routing
`One of the common ways to interconnect LANs and subnetworks at this time is
`through the use of routers. Routers are found at the boundary points between two
`logical or physical subnetworks. Routing is a more sophisticated—and, hence, more
`effective—method of achieving internetworkin g, as compared to bridging. In the—
`ory, a router or, more specifically, a network layer relay, can translate between a
`subnetwork with a physical layer protocol P1, a data link layer protocol BL}, and a
`network layer protocol N] to a subnetwork with a physical layer protocol P2, a
`data link layer protocol DLZ, and a network layer protocol N2. In general, how"
`ever, a router is used for internetworking two networks or subnetworks that use
`the same netw0rk layer but have different data link layer protocols [6H8] (see Fig-
`ure 2.2).
`Routers have become the fundamental and the predominant building technol-
`ogy for data internetworking; however, ATM technology will likely impact the
`overall outlook. Routers permit the physical as well as the logical interconnection
`of two networks. Routers support interconnection of LANs over WANs using tra~
`ditional as well as new services, including frame relay and ATM. Some routers
`operate directly over synchronous optical network (SONET). They also are uti—
`lized to interconnect dissimilar LANs, such as Token Ring to Ethernet. With the
`introduction of Layer 2 switching, ATM, and /or MPLS, however, the role of
`routers in enterprise networks could change slightly. For example, devices enabling
`connectivity between locations based on router technology may, conceivably, no
`longer be obligatory elements—but the concept of routing [forwarding frames at
`the network layer of the protocol model) will Certainly continue to exist. In addi-
`tion, routers work well for traditional data applications, but new broadband video
`and multimedia applications need different forwarding treatment, higher through-
`put, and tighter QoS control.
`
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`Voice over IP and the Internet
`
`
`
`
`
`6.2
`
`lP/internet Background
`
`Network communications can be categorized into two basic types, as implied in
`Chapter 2: circuit-switched (sometimes called connection—oriented) and packet— or
`fastbaclaemwirched [these can be connectionless or connection—oriented]. Circuit-
`switched networks operate by forming a dedicated connection [circuit] between
`two points. In packet—switched networks, data to be transferred across a network is
`segmented into small blocks called packets [also called datagrams or protocol data
`units [PDUs]] that are multiplexed onto highucapacity intermachine connections.
`A packet, which usually contains a few hundred bytes 01C data, carries identification
`that enables the network hardware to know how to send it forward to the specified
`destination. In frame relay, the basic transfer unit is the data link layer frame; in cell
`relay, this basic unit is the data link layer celL Services such as Jframe relay and
`ATM use circuit—switching principles; namely, they use a call setup mechanism
`similar to that of a circuiteswitched [ISDN] call. I]J has become the de facto stan—
`dard connectionless packet network layer protocol for both local area networks
`[LANS) and wide area networks [WANS). in a connectionless environment there is
`no call setup. Each packet finds its way across the network independently of the
`previous one.
`
`Internet Protocol Suite
`
`Chapter 2 provided a basic review of the TCP/IP and UDPXIP suite of networking
`protocols. TCP/IP is a family of over 100 data cormnunications protocols used in
`the Internet and in intranets. In addition to the communication functions sup—
`ported by TC? [end~to-end reliability over a cormection—oriented session) and IP
`(subnetwork—level routing and forwarding in a connectionless manner], the other
`protocols in the suite support specific application—oriented tasks, for example,
`transferring files between computers, sending mail, or logging into a remote host.
`TCP/IP protocols support layered communication, with each layer responsible for
`a different facet of the communications [as seen in Table 6.2). Some of the VOIP
`applications utilize TCP, while others utilize RTCP and UDP.
`
`The Internet
`
`The same IP technology now used extensively in corporate internets is also used in
`(and, in fact, originated from] the Internet. The Internet is a global collection of
`interconnected business, government, and education computer networks—in effect,
`a network of networks. Recently there has been a near—total commercialization of the
`Internet, allowing it to be used for pure 'business applications [the original roots of
`the Internet were in the research and education arenas). A person at a computer ter~
`minal or personal computer equipped with the proper software communicates
`across the Internet by having the driver place the data in an IP packet and addreming
`
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`Table 6.2 Functionality of the TCPIIP Suite Layers
`
`Network interface
`layer
`
`Network layer
`[Internet layer)
`
`Transport layer
`
`Application layer
`
`This layer is responsible for accepting and transmitting
`1P datagrams. This layer may consist of a device driver
`(eg, when the network is a local network to which the
`machine attach es directly] or of a complex subsystem
`that uses its own data link protocol.
`This layer handles communication from one machine to
`the other. It accepts a request to send data from the
`transport layer, along with the identification of the
`destination. It encapsulates the transport layer data
`unit in an IP datagram and uses the datagram routing
`algorithm to determine whether to send the datagram
`directly onto a router. The internet layer also handles
`the incoming datagrm'ns and uses the routing algo-
`rithm to determine whether the datagram is to be
`processed locally or he fonvardecl.
`In this layer the software segments the stream of data
`being transmitted into small data units and passes each
`packet, along with a destination address, to the next
`layer for transmission. The software adds information
`to the packets, including codes that identify which
`application program sent it, as well as a checksum.
`This layer also regulates the flow of information and
`provides reliable transport, ensuring that data arrives in
`sequence and with no errors.
`At this level, users invoke application programs to
`access available services across the TCP/IP internet.
`
`The application program chooses the kind of transport
`neededI which can be either messages or stream of
`
`bytes, and passes it to the transport level.
`
`the packet to a particular destination on the Internet. Communications software in
`routers in the intervening networks between the source and destination networks
`reads the addresses on packets moving through the Internet and forwards the pack—
`ets toward their destinations. TCP guarantees end—to-end integrity.
`From a thousand or so networks in the mid~198[}s, the Internet has grown to
`an estimated 100 million connected network hosts with about 300 million people
`having access to it [as of 2001). The majority of these Internet users currently live
`in the United States or Europe, but the Internet is expected to have ubiquitous
`global reach over the next few years.
`In 1973, ARPA initiated a research program to investigate techniques and tech-
`nologies for interlinking packet networks of various kinds. The objective was to
`develop communication protocols that would allow networked computers to com—
`municate transparently across multiple packet networks. The project became very
`successful and there was increasing demand to use the network, so the government
`separated military traffic from civilian research traffic, bridging the two by using
`
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