cs412 introduction to computer networking & telecommunication

Chi-Cheng Lin, Winona State University

CS412 Introduction to Computer Networking &

Telecommunication

Introduction

2

Topics Introduction Metric Units Network Hardware Network Software Reference Models Example Networks Standards and Standards

Organizations

3

Introduction First two decades of computing

Highly centralized computer systems Now

A large number of SEPARATE but INTERCONNECTED computers

=> Computer networks

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What is Computer Network? An INTERCONNECTED collection of

AUTONOMOUS computersInterconnected: Able to EXCHANGE

INFORMATION via transmission mediaMedia: copper wire, fiber optics,

microwaves, communication satellitesAutonomous: no master/slave relation

NOT autonomous: One computer can control another one e.g., a large computer with remote printers

and terminals

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What is Telecommunication? What is data communication?

Exchange of data between two devices via some form of transmission media

Data are represented by bits – 0s and 1s

What is telecommunication?Exchange of information over

distance using electronic equipment

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What is Telecommunication? Components of data communication

Sender, receiver, medium, message, andProtocol: set of rules governing data

communication Key elements of a protocol

SyntaxStructure/format

SemanticsMeaning

TimingWhen and how fast

7McGraw-Hill ©The McGraw-Hill Companies, Inc., 2004

Figure 1.1 Five components of data communication

8

Why Studying CS412? The instructor looks nice … (Don’t bet

on it!) It is part of our daily life now The job market is good … (?) You want to understand concepts and

technologies of networking and telecomTheory and practice

It is one of the most drastically changing field in CS and you like challenges

It makes you knowledgeable in this field It is FUN!!

9

Distributed System vs. Computer Network Distributed system

TRANSPARENCYA collection of independent computers

appear as a single coherent systemSingle model/paradigm to usersMiddleware on top of OSExample?

Computer networkNo such coherence, model, middlewareMachines visible to users

Users log onto remote machines

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Distributed System vs. Computer Network

A distributed system is a SOFTWARE system built on top of a network

Distinction between network and distributed systemSoftware (especially OS) rather than

hardware However, considerable overlap

between the two subjects

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Uses of Computer Networks Business applications

Resource sharingCommunication mediumE-commerce

Client-server modelClient requests, server performs & then

replies E.g., one or more file servers, many

clients

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Business Applications of Networks

A network with two clients and one server.

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Client-Server Model

1

2

3

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Uses of Computer Networks Home applications

Access to remote informationOn-line publishing, digital library, WWW

Person-to-person communicationEmail, instant messaging, peer-to-peer

communication, videoconferencing, Internet phone, E-learning

Interactive entertainment Video on demand (VOD), games

E-commerceHome shopping, electronic banking and

investment, on-line auction

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Home Network Applications (2) In peer-to-peer system there are

no fixed clients and servers.

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Mobile Users Notebook, PDA, cellular phone M-commerce Wireless networking and mobile

computing

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Metric Units The principal metric prefixes.

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Network Hardware By transmission technology

Broadcast links smaller, geographically localized networks

Point-to-point linkslarger networks

By scalePANLANMANWAN

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Classification by Scale

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Broadcast Network

A single communication channel shared by all machines on the network

Packets (short messages) sent by any machine are “received” by all the othersAddress field of packet: whom it is intended

Message transmissionUnicast: one sends, one receivesBroadcasting: one sends, all receiveMulticasting: one sends, a group receives

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Point-to-Point Networks Many connections between pairs of

machines Intermediate machines (called

routers) might have to be visited by a packet from source to destination – more than one path is possible

Routing algorithms are importantRouting: process of finding a path

from a source to the destination(s) in the network

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Local Area Network (LAN) Private-owned Networks Within a single building/campus Size: up to a few kilometers Characteristics

SizeRestricted by size worst-case transmission time bounded

and known in advance network management simplified

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LAN Characteristics

Transmission technologyMachines attached to a single cableSpeed/capacity (High): 10 - 100 Mbps,

Gbps Mbps/Gbps: Megabit/Gigabit per second 1 megabit=1,000,000 (not 220=1,048,576) bits

Delay (low): microseconds, nanosecondsErrors: very few

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LAN Characteristics

Topology – the way in which a network is laid outExamples: Bus, Ring

Bus Ring


Figure 1.7 Categories of topology


Figure 1.8 Fully connected mesh topology (for five devices)


Figure 1.9 Star topology


Figure 1.10 Bus topology


Figure 1.11 Ring topology

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LAN - Topology Bus (linear cable)

Only one machine can transmit at a timeArbitration mechanism needed to resolve

conflicts when two or more computers want to transmit simultaneouslyCentralized or Distributed

Example: IEEE 802.3 (Ethernet):Bus-based broadcast network with

decentralized control operating at 10 Mbps to 10Gbps.

If two or more packets collide, each computer just waits a random time and tries again later.

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LAN - Topology Ring

Bits propagate around the ringArbitration mechanism is needed, tooExample: IEEE 802.5 (IBM Token

Ring)Ring-based LAN operating at 4 and 16

MbpsArbitration is based on “token”

Only token holder can transmit

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LAN - Channel Allocation Needed as all computers share one

communication pathway Static channel allocation

Divide up time into discrete intervalsRun a round robin algorithmAllow each machine to broadcast only

when its time slot comes upProblem: Wasting channel capacity

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LAN - Channel Allocation Dynamic channel allocation

CentralizedA central entity determines who goes

nextDecentralize

No central entityEach machine decides for itself to

transmit or notAlgorithms needed to resolve potential

chaos

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Metropolitan Area Network (MAN)

Covers city Examples

Cable TV networkIEEE 802.16 high-speed wireless

Internet access


Figure 1.14 MAN

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Metropolitan Area Networks A metropolitan area network based

on cable TV.

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Wide Area Network (WAN) Country or continent Components

Host (end system) Machine running user (application)

programsCommunication subnet (subnet)

Connecting hostsCarrying messages from host to host


Figure 1.15 WAN

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WAN - Subnet Components Transmission lines

Move bits between machines Switching elements

Specialized computers that connect two or more transmission lines

Determine out going line for incoming data

ROUTER

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WAN - Hosts and Subnet

: Host

: Router

H1

H2

R1 R2

R3 R4

R5 R6

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WAN - Architecture Contains numerous cables or

telephone lines Each cable connects a pair of routers Two routers must communicate

indirectly if they are not connected by a cable

There might be more than one route between two hosts and it might change from time to timeE.g., Route from H1 to H2

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WAN - Architecture An intermediate router in a WAN

Receives a packet in its entiretyQueues the packet until required

output line is freeForwards the packet

Subnet using the principle above is calledStore-and-forward or packet-switched

subnet

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Wide Area Networks A stream of packets from sender to

receiver.

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Topology – LANs vs WANs Local networks

Bus, Ring, StarTree

WANs typically irregular

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WAN - Broadcast Systems Satellite system

Each router has an antennaSometimes routers are connected to

a substantial point-to-point subnet, with some of them having a satellite antenna

Inherently broadcast

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Wireless Network System interconnection

Example: Bluetooth Wireless LANs

Easy to install IEEE Standard 802.11

Wireless WANsIEEE Standard 802.16

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Wireless NetworksBluetooth configuration Wireless

LAN

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Wireless Network Combinations of wired and

wireless networking (e.g., flying LAN)

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Home Network Categories Computers

Desktop PC, PDA, shared peripherals Entertainment

TV, DVD, VCR, camera, stereo, MP3 Telecomm

Telephone, cell phone, intercom, fax Appliances

Microwave, fridge, clock, furnace, aircon Telemetry

Utility meter, burglar alarm, babycam

50

Internetwork What is internetwork?

A collection of interconnected networks "Internet" and "internet"

internet: internetworkInternet: the worldwide internetwork using

TCP/IP protocol suite Problem: Communication between

networks with different SW/HWSolution: Gateways

Machines connect different, incompatible networks

Connection and translation


Figure 1.16 Internet today

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Network Software Old computer networks:

HW main concernSW afterthoughtNot working now!

Network SW is now highly structuredProtocol Hierarchies Implemented in hardware or firmware

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Protocol Hierarchies What is protocol?

Agreement between communication parties on HOW communication is processed

Layered architectureReduce design complexity- Lower layer offers

service to higher layerHiding implementation detailsLayer n on one machine talks to layer n on

anotherRules and conventions used in layer n’s talk:

Layer n protocol

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Protocol Hierarchies Peers

Entities comprising corresponding layers on different machines

Virtual communication using protocolPeer process abstraction make network design

becomes that of individual layers Physical communication

Sender: Data and control passed to layer below Data transmitted via physical mediaReceiver: Data and control passed to layer

above

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Layers, Protocols, and Interfaces

Virtual Communication

Physical Communication

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Protocol Hierarchies Interface between two adjacent

layers Defines primitive operations and

services a lower layer offers to the upper one

Minimizes amount of information passed between two layers

Simplifies replacement of implementationE.g., telephone lines satellite channels

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Protocol Hierarchies Network architecture

Set of layers and protocolsImplementation and interface

specification not included Protocol stack

A list of protocols used by a certain system, one protocol per layer

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Multilayer Communication - Example

Philosopher-translator-secretary architectureIt is ok if

Dutch is replaced by Finnish

fax is replaced by email

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Information Flow - Example Virtual communication for layer 5

Header: control information

Layer 1protocol00011100011100001110 … 00011100011100001110 …

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Key Design Issues for the Layers

Sender/receiver identification mechanism Transmission direction modes

SimplexData only travel in one direction

Half-duplex Data can travel in either direction, but not

simultaneouslyFull-duplex

Data can travel in both directions simultaneously Number of logical channels and properties

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Error controlError-detectingError-correcting

Sequencing Flow control

Needed for fast sender, slow receiverApproaches

Feedback mechanismTransmission rate agreement

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Message disassembling, transmitting, reassembling

MultiplexingThe process of combining signals from

multiple sources for transmission across a single data link

Multiple connections can share the link Routing

Selecting the best path for sending a packet from one point to another

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Connection-Oriented and Connectionless Services

Two basic types of servicesConnection-orientedConnectionless

Consider reliability …Reliable Connection-oriented

Unreliable Connectionless Note that: Connection Reliability

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Connection-Oriented Service A connection is established first,

then used, and then released when done.

Works like a pipe:Sender pushes data in at one endReceiver takes them out, often in the

same order, at the other end Analogy

Telephone system

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Connectionless Service No need to set up a connection

first Each message carrying full

destination address is routed independently of othersNo guarantees on the order

AnalogyPostal system

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Six Service Types

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Service Primitives Service is formally specified by a

set of primitives (e.g., OS’s system calls) available to users or entities

Five service primitives for implementing a simple connection-oriented service.

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Service Primitives Packets sent in a simple client-

server interaction on a connection-oriented network.

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Relationship of Services to Protocols

ServiceSet of primitives a layer provides to the

layer above itDefine WHAT operations

not HOW implemented Protocol

Set of rules governing format and meaning of message exchanged by peer entities within a layer

Used by entities to implement service definition

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Services to Protocols Relationship

The relationship between a service and a protocol.

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Relationship of Services to Protocols

Analogy: Object-oriented languages Service :: Object

Users do not know the implementation of a service

Protocol :: ImplementationThe protocol of the service is invisible to

usersDo you have to understand http

(hypertext transport protocol) before you can surf the Internet?

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Reference Models Two reference models will be

discussedOSI reference modelTCP/IP model

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OSI Reference Model ISO/OSI (Open Systems

Interconnection) Reference Model NOT a network architecture itself

Exact services and protocols are not specified

Just "what should be done" in each layerHowever, standards are produced for all

layers

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OSI Reference Model Seven layers

Layer 7: application layer Layer 6: presentation layer Layer 5: session layerLayer 4: transport layerLayer 3: network layerLayer 2: data link layerLayer 1: physical layer (lowest)

Diagram of OSI reference modelNote: this is one of the most important figures in

the whole book!!

75Physical medium

77

Host A Host B

Subnet

Physical mediumEnd-to-End

Point-to-Point Point-to-Point Point-to-Point

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Physical Layer Transmitting raw bits (0s and 1s) Design issues

Representation of bitsHow is 0/1 represented?

Data rate: number of bits sent per secondHow long does a bit last?

Transmission modeMechanical, electrical, procedural

interfacesUnderlying physical transmission medium

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Data Link Layer Takes a raw transmission facility

and transforms it into a line (link) that appears free of undetected transmission errors to network layer

Basic functionBreaks up input data to data frames Transmits data framesProcesses acknowledgement frames

sent back from receiver

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Data Link Layer Responsibilities (cont’d)

Physical addressingFraming

creating and recognizing frame boundariesError control (adjacent nodes)

Errors: damaged, lost, duplicateFlow control (adjacent nodes)

Traffic regulation between fast sender and slow receiver

Medium access controlShared channel access control in broadcast

networks

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Network Layer Subnet operation control Responsibilities

Logical addressingRouting

Static tablesDetermined at the start of conversationDynamic

Congestion controlQuality of serviceAccountingHeterogeneous network interconnection

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Transport Layer

End-to-end layerTalk to destination machine directly

(virtually)Layers 4 through 7 are end-to-endLayers 1 through 3 are node-to-node

Basic functionSplit data from session layer into smaller

unitsPass units to network layerEnsure units arrive correctly at the other end

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Transport Layer Determine services provided to

session layer (and ultimately to users)Error-free point-to-point channel that

delivers messages in the order in which they were sent

Transport of isolated messages w/o guarantee about order

Broadcasting Normally, a distinct network

connection is created for each transport connection required by session layer

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Transport Layer Responsibilities include

Service-point addressingWhich message belong to which

connection (application): Information in header Needed as multiprogramming in a host

(End-to-end) Flow control Compare to the

(End-to-end) Error control Data Link layer

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Session layer Session establishment between

users on different machines Responsibilities

Dialogue controlDeciding who sends, and when

Token managementControl of same operation not to be

performed at the same time Synchronization

Inserting checkpoints (checkpointing)

Figure 3-11 from Forouzan’s 2/e

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

Session Layer

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Presentation Layer Syntax/semantics of information Responsibilities

EncodingConvert from data representation used in

one host to the standard abstract data structure and back

EncryptionCompression

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Application Layer Provides interface and support for

services to users (human, software, robots)

Application servicesNetwork virtual terminal (telnet)File transferEmailNetwork managementHypertext transfer

Figure 3-14 from Forouzan’s 2/e

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

Summary of Layer Functions

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TCP/IP Reference Model Goals

InternetworkingFault toleranceFlexible architecture

Four layers of TCP/IP Reference Model Host-to-network layerInternet layerTransport layerApplication layer

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Internet Layer Packet-switching, connectionless Packets injected to network

Independent travelOut-of-order arrival

AnalogyMail system

IP (Internet Protocol)Packet routingCongestion control

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Transport Layer Two end-to-end protocols

UDP (User Datagram Protocol)TCP (Transmission Control Protocol)

UDP (User Datagram Protocol)Unreliable, connectionlessWidely used for

client-server type request-reply queriesspeech, video

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Transport Layer TCP

Reliable connection-orientedIncoming byte stream (form

application layer) is fragmented into discrete messages and passed onto internet layer

Message is reassembled at destination

Flow controlAnalogyA B

Pipe

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Applications and Host-to-Network Layers

Application layerNo session and presentation layersTELNET, FTP, SMTP, DNS, NNTP, HTTP

Host-to-network layer

Host has to connect to to the network using some protocol so it can send IP packets

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Initial TCP/IP Protocols and Networks

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OSI and TCP/IP Models Correspondence

OSI TCP/IP

7654321

ApplicationPresentation

SessionTransportNetwork

Data LinkPhysical

Application

TransportInternetHost-to-Network

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OSI and TCP/IP Models Similarities

Stack of independent protocolsLayer functionalityTransport layer Application layer

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Differences between OSI and TCP/IP Models

OSIDistinction between services, interfaces, and protocols

(perhaps the biggest contribution) Better Protocol-HiddenModel first, then protocols

Pro: No bias, more generalCon: Designers did not have

much experience with the subject a good idea of which functionality to put in which layer

No thought given to internetworking7 layersCommunication

Connection-Oriented and connectionless in network layerOnly connection-oriented in transport layer

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Differences between OSI and TCP/IP Models

TCP/IP:No clear distinction between services, interfaces,

and protocolsWorse protocol-hiddenProtocol first, then model

Pro: Protocols fit model perfectlyCon: Model does not fit any other protocol stacks (not

general)4 layersCommunication

Connectionless in network layerBoth in transport layer (good for request-response

protocols)

100

Summary of Reference Models

OSIOSI model exceptionally useful for

discussing computer networksOSI protocols not popular

TCP/IPTCP/IP model practically nonexistentTCP/IP protocols widely used

Modified framework is used in the text

101

Summary of Reference Models

Modified framework is used in the text


Figure 2.3 Peer-to-peer processes


Figure 2.4 An exchange using the Internet model


Figure 2.5 Physical layer


The physical layer is responsible for transmitting individual bits from one

node to the next.

Note:Note:


Figure 2.6 Data link layer


The data link layer is responsible for transmitting frames from

one node to the next.

Note:Note:


Figure 2.7 Node-to-node delivery


Example 1Example 1

In Figure 2.8 a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link. At the data link level this frame contains physical addresses in the header. These are the only addresses needed. The rest of the header contains other information needed at this level. The trailer usually contains extra bits needed for error detection


Figure 2.8 Example 1


Figure 2.9 Network layer


The network layer is responsible for the delivery of packets from the

original source to the final destination.

Note:Note:


Figure 2.10 Source-to-destination delivery


Example 2Example 2

In Figure 2.11 we want to send data from a node with network address A and physical address 10, located on one LAN, to a node with a network address P and physical address 95, located on another LAN. Because the two devices are located on different networks, we cannot use physical addresses only; the physical addresses only have local jurisdiction. What we need here are universal addresses that can pass through the LAN boundaries. The network (logical) addresses have this characteristic.


Figure 2.12 Transport layer


The transport layer is responsible for delivery of a message from one process

to another.

Note:Note:


Figure 2.12 Reliable process-to-process delivery of a message


Example 3Example 3

Figure 2.14 shows an example of transport layer communication. Data coming from the upper layers have port addresses j and k (j is the address of the sending process, and k is the address of the receiving process). Since the data size is larger than the network layer can handle, the data are split into two packets, each packet retaining the port addresses (j and k). Then in the network layer, network addresses (A and P) are added to each packet.


Figure 2.15 Application layer


The application layer is responsible for providing services to the user.

Note:Note:


Figure 2.16 Summary of duties

124

Example Networks The Internet Connection-Oriented Networks

X.25, Frame Relay, and ATM Ethernet Wireless LANs: 802:11

125

Standards and Standards Organizations Why standards?

Categoriesde factode jure

OrganizationsITU-T (formerly CCITT)ISOANSIIEEEIETFATM Forum

cs412 introduction to computer networking & telecommunication

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large computer

computer networkswhat

computer networkno

peer system

exchange of data

peer communication

software system

exchange information