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

`

`Publisher: Robert Ipsen
`Editor: Margaret Eldridge
`Assistant Editor: Adaobi Obi
`Managing Editor: Angela Smith
`New Media Editor: Brian Snapp
`Text Design & Composition: North Market Street Graphics
`
`Designations used by companiesto distinguish their products are often claimed as trade-
`marks, In all instances where John Wiley & Sons, Inc., is aware of a claim, the product names
`appearin initial capital or ALL CAPITAL LETTERS. Readers, however, should contact the appro-
`priate companies for more complete information regarding trademarks andregistration.
`
`This text is printed on acid-free paper.
`
`Copyright © 2002 by Dan Minoli, Emmanuelle Minoli, All rights reserved.
`
`Published by Wiley Publishing, Inc., Indianapolis, Indiana
`
`Published simultaneously in Canada.
`
`Nopart of this publication may be reproduced, stored in a retrieval system or transmitted in
`any form or by any means, electronic, mechanical, photocopying, recording, scanning or
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`E-mail: permcoordinator@wiley.com.
`
`This publication is designed to provide accurate and authoritative information in regard to
`the subject matter covered.It is sold with the understanding that the publisheris not
`engaged in professional services. If professional advice or other expert assistance is required,
`the services of a competent professional person should be sought.
`
`Library ofCongress Cataloging-in-Publication Data:
`
`Minoli, Daniel
`Delivering voice over IP networks / Dan Minoli, Emma Minoli— 2nd ed.
`p.cm.
`ISBN 0-471-38606-5
`1. Internet telephony. 2. TCP/IP (Computer network protocol). 3. Digital telephone
`systems. 4. Computer networks, 5, Data transmission sytems. I. Minoli, Emma. IL. Title.
`
`TK5105.8865 .M57 2002
`621.385—de21
`
`2002071368
`Wiley also publishes its books in a variety of electronic formats. Some content that appears in
`print may notbeavailable in electronic versions. For more information about Wiley products,
`visit our web site at www.wiley.com.
`
`Printed in the United States of America.
`
`100987654321]
`
`Page 2 of 14
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`Contents
`
`xiii
`PREFACE
`XV
`ACKNOWLEDGMENT
`ABOUT THE AUTHORS—xvii
`
`Introduction and Motivation
`Chapter 1:
`1.1
`INrTRopuUCTION
`1
`6
`1.2 DRIVERS FOR VOICE OVERIP
`12
`THE NEGATIVE DRIVERS
`_ 1.3. APPROACHES FOR IP-BASED VOICE SYSTEMS
`VOICE SERVERS APPROACH
`=15
`IP VOICE AND VIDEO PHONES=18
`1.4 THe FurureE
`18
`REFERENCES
`18
`
`14
`
`1
`
`Chapter 2: An Overview of IP, IPOATM, MPLS,
`and RTP
`21
`
`2.1
`2.2
`
`24
`
`21
`INTRODUCTION
`24
`INTERNET PROTOCOL
`THE ROLE OFTHEIP
`IP ROUTING
`26
`IP DATAGRAMS=.29
`SUPPORT OF VOICE AND VIDEO IN ROUTERS
`32
`IP VERSION 6 (IPV6)
`33
`IP over ATM (IPOATM)
`36
`2.3
`2.4 Basic Synopsis OF MPLS
`—=.39
`MPLS FoRWARDING/LABEL-SWITCHING MECHANISM
`MPLS LaBEL-DISTRIBUTION MECHANISM
`43
`2.5 REAL-TIME TRANSPORT PROTOCOL (RTP)
`45
`2.6 RIP Controi Prorocot (RTCP)
`50
`2.7
`STREAM CONTROL ‘TRANSMISSION PRoTocoL (SCTP)
`
`41
`
`52
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`

`(i) Contents
`
`_
`
`54
`2.8 ATM QoS MECHANISMS
`QUALITY OF SERVICE PARAMETERS
`QoS CLAsses
`57
`REFERENCES
`59
`Notes
`61
`
`—
`
`56
`
`co
`
`
`
`63
`
`3.2.
`
`Issues in Packet Voice Communication
`Chapter 3:
`3.1
`INTRODUCTION
`63
`Score
`64
`SUMMARY OF RESULTS
`TRAFFIC MODELS
`66
`INTRODUCTION
`66
`SPEECH EVENTS
`66
`SPEAKER MODELS
`67
`CALL ORIGINATION MODEL=72
`3.3.
`PERFORMANCE CRITERIA
`74
`RESULTS OF SUBJECTIVE STUDIES
`SMOOTHNESS CRITERIA
`76
`3.4 Link MopEL
`78
`79
`INTRODUCTION
`MopeL DESCRIPTION
`3.5 Resutts
`84
`PROPERTIES OF THE DELAY DISTRIBUTION
`FINITE-BUFFER CASE
`86
`EFFECT OF SPEECH MopELS=88
`OPTIMAL PACKET LENGTH
`90
`TRANSIENT BEHAVIOR
`92
`3.6 CONCLUSION
`95
`REFERENCES
`96
`
`65
`
`79
`
`74
`
`84
`
`Chapter 4: Voice Technologies for Packet-Based
`Voice Applications
`101
`101
`4.)
`INTRODUCTION
`101
`GENERAL OVERVIEW OF SPEECH TECHNOLOGY
`WAVEFORM CODING=102
`VocopDING (ANALYSIS/SYNTHESIS) IN THE FREQUENCY DOMAIN—107
`4.2. G.727: ADPCM For PACKET NETWORK APPLICATIONS
`111
`INTRODUCTION
`111
`ADPCM ENCODER PRINCIPLES
`ADPCM DECODER PRINCIPLES
`
`114
`121
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`

`ot
`
`Contents
`
`EXAMPLE OF APPLICATION
`4.3
`REFERENCES
`123
`Notes
`123
`
`123
`
`5.2
`
`Chapter 5: Technology and Standards for Low-Bit-Rate
`Vocoding Methods
`125
`5.1
`INTRODUCTION
`125
`OVERVIEW
`127
`128
`VOCODER ATTRIBUTES
`LINEAR PREDICTION ANALYSIS-BY-SYNTHESIS (LPAS) CopING
`INTRODUCTION TO G.729 AND G.723.1
`133
`DIFFERENTIATIONS
`133
`STANDARDIZATION PRocEsS
`STANDARDIZATION INTERVAL
`5.3 G723.1
`136
`136
`INTRODUCTION
`ENCODER/DECODER
`5.4 G728
`138
`LD-CELP ENcopER
`LD-CELP Decoper
`5.5 G729
`140
`14]
`ENCODER
`143
`DECODER
`145
`5.6 EXAMPLE OF APPLICATIONS
`H.263 VIDEO CODING FOR Low-BIT-RATE COMMUNICATION
`H.324 MULTIMEDIA COMMUNICATION
`146
`H.323 MULTIMEDIA COMMUNICATIONS STANDARD FOR LANs AND ENTERPRISE
`Networks
`148
`REFERENCES
`150
`Nores
`15]
`
`134
`135
`
`136
`
`139
`140
`
`130
`
`145
`
`Chapter 6: Voice over IP and the Internet
`6.1
`INTRODUCTION
`153
`
`6.2. IP/INTERNET BACKGROUND=157
`INTERNET PROTOCOL SUITE
`157
`THE INTERNET
`157
`6.3. VoICE TRANSMISSION AND APPROACHES IN ATM, FRAME RELAY, ANDIP=162
`ATM—162
`FRAME RELAY
`164
`IP
`164
`
`153
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`

`TET
`
`
`
`~=165
`
`ITU-T H.323 Group OF STANDARDS
`STREAMING AUDIO
`166
`6.4 QoS PROBLEMS AND SOLUTIONS~—167
`6.5
`PROTOCOLS FOR QOS SupporT FOR AUDIO AND VIDEO APPLICATIONS
`RSVP APPLICATIONS
`169
`IP Mutricast
`17]
`INTERNET TELEPHONY SERVERS (ITSs)
`6.6
`THE VOICE OVER JP/INTERNET MARKET
`6.7
`6.8 VOIP REGULATORY [ssuES
`177
`6.9
`CONCLUSION
`180
`REFERENCES
`18]
`Notes
`18]
`
`172
`177
`
`183
`
`Chapter 7: Signaling Approaches
`7.1
`INrropuUCTION
`183
`
`7.2. SIGNALING IN CIRCUIT-SWITCHED NETWORKS=187
`7.3. H.323 STANDARDS
`189
`FUNCTIONAL ELEMENTS
`H.323 Basics
`190
`EXAMPLE OF SIGNALING
`7.4 MGCP
`202
`7.5
`SIP
`207
`SIP PROTOCOL COMPONENTS
`SIP-T
`210
`215
`7.6 OTHER IETF SIGNALING EfrorTs
`PINT AND SPIRITS=215
`ENUM 218
`TRIP
`219
`7.7 MEGACO
`219
`221
`7.8
`SIGTRAN PROTOCOLS
`PERFORMANCE CONSIDERATIONS FOR CCSS7 OVER IP
`SECURITY REQUIREMENTS FOR CCSS7 OVER IP
`SCTP Use In CCSS7
`223
`226
`TRANSPORTING MTP OVER IP
`TRANSPORTING SCCP OVER IP=229
`7.9
`SCTP
`230
`230
`INTRODUCTION
`230
`MotIvaTION
`ARCHITECTURAL VIEW OF SCTP—-230
`FUNCTIONAL VIEW OFSCTP=231
`Key TERMS
`236
`SERIAL NUMBER ARITHMETIC
`
`189
`
`196
`
`209
`
`236
`
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`

`

`=239
`SCTP PACKET ForMAT
`SCTPASSOCIATION STATE DIAGRAM—-.258
`ASSOCIATION INITIALIZATION
`260
`UseR DATA TRANSFER
`262
`TERMINATION OF AN ASSOCIATION
`REFERENCES
`276
`Notes
`277
`
`273
`
`
`
`Chapter 8: Quality of Service
`8.1
`INTRODUCTION
`279
`8.2
`BACKGROUND
`281
`284
`8.3. QoS APPROACHES
`PER-FLow QoS=284
`CLass-BASED QOS=.288
`MPLS-BaseD QoS=289
`"TRAFFIC MANAGEMENT/QUEVE MANAGEMENT=291
`8.4 QoS Derans
`294
`IETF INTSERV APPROACH=.294
`IETF DIFFSERV APPROACH==305
`ADDITIONAL DETAILS ON QUEUE MANAGEMENT=320
`CONCLUSION
`326
`8.5 CAsE STUDY
`327
`REAL-TIME SERVICE REQUIREMENTS
`TECHNICAL CHALLENGES
`330
`Cisco SOLUTIONS FOR SUPPORTING IP-BASED REAL-TIME SERVICES
`REFERENCES
`340
`Notes
`342
`
`279
`
`327
`
`330
`
`Chapter 9: Voice over MPLS and Voice overIP
`over MPLS
`343
`
`343
`
`INTRODUCTION AND BACKGROUND
`9.1
`9.2. Motivations
`344
`349
`9.3.
`BASIC MPLS Features
`MPLS FoRWARDING/LABEL-SWITCHING MECHANISM
`MPLS LABEL-DISTRIBUTION MECHANISM
`356
`OTHER FEATURES
`358
`COMPARISON
`359
`9.4 QoS CapaBiLiries
`363
`INTRODUCTION
`365
`DETAILS
`368
`
`353
`
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`

`

`370
`9.5 Vorce APPLICATIONS
`371
`IP HEADER COMPRESSION
`372
`VOIPOMPLS ProrosaAL
`MPLSForuM SPECIFICATION
`REFERENCES
`375
`Notes
`376
`
`374
`
`
`
`377
`
`10.4.
`
`Chapter 10: Telephone Number Mapping (ENUM)
`10.1
`INTRODUCTION
`377
`10.2)
`BACKGROUND
`379
`
`10.3. INTRODUCTION TO ENUM—383
`ENUM: AN EVOLVING ARCHITECTURE
`385
`DEFINING ENUM ApPLicATIONS
`387
`THE ENUM Roap To Success
`389
`SUMMARY OF CAPABILITIES AND IssuES
`390
`CAPABILITIES
`390
`Apvocacy
`397
`10.5 NUMBER PORTABILITY
`Types OF NP
`400
`SPNP SCHEMES
`401
`DATABASE QUERIES IN THE NP ENVIRONMENT=405
`CALL ROUTING IN THE NP ENVIRONMENT
`408
`NP IMPLEMENTATIONS FOR GEOGRAPHIC E,164 NuMBERS
`NP-ENABLED NUMBER CONSERVATION METHODS
`41]
`CONCLUSION
`414
`10.6 E.164 NuMBERS AND DNS
`INTRODUCTION
`417
`417
`E.164 NUMBERS AND DNS
`FETCHING UNIFORM RESOURCE IDENTIFIERS (URIs) GIVEN AN E.164 NUMBER
`IANA CoNnsIDERATIONS
`420
`SECURITY CONSIDERATIONS
`420
`10.7. APPENDIX TO THE RFC 2916 ScENARIO
`REFERENCES
`422
`Notes
`424
`
`398
`
`417
`
`421
`
`41]
`
`418
`
`Chapter 11: Carrier Applications
`11.1
`INTRODUCTION AND OPPORTUNITIES
`427
`11.2. WHERE THE ACTION SHOULD BE
`432
`11.3.
`CARRIER Voice NeTworKS
`439
`
`427
`
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`

`a amenaae
`
`Contents ()
`
`446
`11.4 DEPLOYMENT AND Issues
`450
`WIRELESS Networks
`CABLE TELEPHONY NETWORKS
`ENTERPRISE APPLICATIONS
`465
`11.5
`INTERNATIONAL OPPORTUNITIES
`11.6
`EQUIPMENT/VENDOR TRENDS
`11.7
`REFERENCES
`473
`Notes
`474
`
`458
`
`466
`469
`
`INDEX
`
`477
`
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`

`transport portion based on ATM, POS, 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:
`
`IP and IPv6 [4, 5]
`e IP over ATM
`
`e MPLS
`
`e RTP
`
`e 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 namefor a family of communications protocols used to support
`internetting in enterprise and interenterprise applications. Protocols include the
`Internet Protocol (IP), the Transmission Control Protocol (TCP), 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. Eachlayer has a different
`responsibility.
`
`1. The link layer (sometimes called the network interface layer) normally
`includes the device driver in the operating system and the corresponding
`networkinterface card in the computer. Together they handle all the hard-
`ware details of physically interfacing with thecable.
`2. The network layer (sometimescalled the internet layer) handles the move-
`mentof packets in the network. Routing of packets, for example, takes
`place here. IP provides the networklayer in the TCP/IP protocolsuite.
`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, TCP and UDP. TCPprovidesa reliable flow of data
`between twohosts. It is concerned with such things aspartitioning the data
`passed to it from the application into appropriately sized framesfor the net-
`worklayer below, acknowledging received packets, and setting time-outs to
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`

`AnOverviewofIP,IPOATM,MPLS,andRTP(@)-
`
`makecertain 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. UDP, 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 applicationlayer.
`4. The application layer handles the details of the particular application. There
`are many common TCP/IPapplications that almost every implementation
`provides:
`° Telnet for remote login
`° Thefile transfer protocol (FTP)
`¢ The Simple Mail Transfer Protocol (SMTP) for e-mail
`® 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.TCP 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 mustestablish 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.
`IP is responsible for relaying packets of data [protocol data units (PDU)] from
`node to node. IP provides the basis for connectionless best-effort packet delivery
`service. IP’s job is to move—specifically to route—blocks of data over each of the
`networks thatsit between the end systems that want to communicate. IP 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 offields 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 IP
`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 somefields in the header) as the IP packets make their way
`from the source to the destination.
`IP protocols are supported overa variety of underlying media, such as ATM,
`framerelay, 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 nowforotherreal-time applications. Organizations favor networks based
`
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`
`
` AATRERTTART
`
`on IP because of theflexibility and vendor support. IP networks run under the
`most widely used networkoperating systems; they are scaleable to a large degree;
`and they enjoy extensive implementation across productlines (e.g., in the routers,
`PCclients, server switches, etc.). As noted, a relatively new IP application now in
`demandis toll-quality, low-bandwidth voice (and fax) transmission over IP net-
`works,
`Intranets use the same WWW/HTML/HTTPand TCP/IP technology used for
`the Internet. Whenthe Internet caught onin the early to mid-1990s, planners
`were not lookingat it as a way to run their businesses. But just as the action of
`putting millions of computers around the world on the sameprotocolsuite
`fomented the Internet revolution, so connectingislands of information in a corpo-
`ration via intranets is now sparking a corporate-based information revolution.
`Thousands of corporations now haveintranets. Across the business world, employ-
`ees from engineers to office workers are creating their own homepages and shar-
`ing details of their projects with the rest of the company.
`
`IP Routing
`Oneof the common waysto interconnect LANs and subnetworksat this timeis
`through the use ofrouters. Routers are found at the boundary points between two
`logical or physical subnetworks. Routing is a more sophisticated—and, hence, more
`effective—methodof achieving intemetworking, 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 DL1, and a
`network layer protocol N1 to a subnetwork with a physical layer protocol P2, a
`data link layer protocol DL2, and a network layer protocol N2. In general, how-
`ever, a router is used for internetworking two networks or subnetworks that use
`the same networklayer but have different data link layer protocols [6-8] (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 WANsusingtra-
`ditional as well as new services, including frame relay and ATM. Somerouters
`operate directly over synchronousoptical network (SONET). Theyalso 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, therole of
`routers in enterprise networks could changeslightly. For example, devices enabling
`connectivity between locations based on router technology may, conceivably, no
`longer be obligatory elements—but the conceptof routing (forwarding frames at
`the network layer of the protocol model) will certainly continue to éxist. 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
`‘BGPPNSTIRETERSRTREa aTITETTT
`
`SRE
`
`
`6.2
`
`IP/Internet Background
`
`Network communications can be categorized into twobasic types, as implied in
`Chapter 2:circuit-switched (sometimes called connection-oriented) and packet- or
`fastpacket-switched (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 high-capacity intermachine connections.
`A packet, which usually contains a few hundred bytesof data, carries identification
`that enables the network hardware to know how tosendit forward to the specified
`destination, In framerelay, the basic transfer unit is the data link layer frame; in cell
`relay, this basic unit is the data link layercell. Services such as frame relay and
`ATM usecircuit-switching principles; namely, they use a call setup mechanism
`similar to that of a circuit-switched (ISDN)call, IP has becomethe de facto stan-
`dard connectionless packet network layer protocol for both local area networks
`(LANs) and wide area networks (WANs). In a connectionless environmentthereis
`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 UDP/IP suite of networking
`protocols, TCP/IP is a family of over 100 data communications protocols used in
`the Internet and in intranets. In addition to the communication functions sup-
`ported by TCP (end-to-endreliability over a connection-oriented session) and IP
`(subnetwork-level routing and forwarding in a connectionless manner), the other
`protocols in the suite support specific application-orientedtasks, 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 sameIP technology now used extensively in corporate internetsis 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 addressing
`
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`2g
`
`__ChapterSix
`
`Haai
`i
`i !
`t
`F
`y
`e
`E
`i eT EEAIhr A adIPCSTSOa ai al ele 9p ce at
`
`RTTP AS
`
`Table 6.2 Functionality of the TCP/IP Suite Layers
`
`Network interface
`layer
`
`Network layer
`(Internet layer)
`
`This layer is responsible for accepting and transmitting
`IP datagrams. This layer may consist of a device driver
`(eg., when the network is a local network to which the
`machine attaches directly) or of a complex subsystem
`that uses its owndata link protocol.
`This layer handles communication from one machine to
`the other. It accepts a request to send data fromthe
`transport layer, along with the identification of the
`destination, It encapsulates the transport layer data
`unit in an JP datagram and uses the datagram routing
`algorithm to determine whether to send the datagram
`directly onto a router. The internetlayer also handles
`the incoming datagrams anduses the routing algo-
`rithm to determine whether the datagram is to be
`processed locally or be forwarded.
`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 sentit, as well as a checksum.
`This layer also regulates the flow of information and
`providesreliable 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
`needed, which can be either messages or stream of
`bytes, and passes it to the transportlevel.
`
`Transport layer
`
`Application layer
`
`the packet to a particular destination on the Internet. Communications softwarein
`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-endintegrity.
`From a thousand or so networks in the mid-1980s, the Internet has grown to
`an estimated 100 million connected network hosts with about 300 million people
`having accessto it (as of 2001). The majority of these Internet users currently live
`in the United States or Europe, but the Internetis expected to have ubiquitous
`global reach over the next few years.
`In 1973, ARPAinitiated a research program to investigate techniques and tech-
`nologies for interlinking packet networks ofvarious 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 demandto use the network, so the government
`separated military traffic from civilian research traffic, bridging the two by using
`
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