The OSI model and TCP/IP

©Brooks/Cole, 2003

Chapter 6

ComputerNetworks

©Brooks/Cole, 2003

Understand the rationale for the existence of networks.Understand the rationale for the existence of networks.

Distinguish between the three types of networks: LANs, Distinguish between the three types of networks: LANs, MANs, and WANs.MANs, and WANs.

After reading this chapter, the reader should After reading this chapter, the reader should be able to:be able to:

OOBJECTIVESBJECTIVES

List different connecting devices and the OSI layers in List different connecting devices and the OSI layers in which each device operates.which each device operates.

Understand client-server models.Understand client-server models.

Understand the OSI model and TCP/IP.Understand the OSI model and TCP/IP.

©Brooks/Cole, 2003

NETWORKS, NETWORKS, LARGE AND SMALLLARGE AND SMALL

6.16.1

©Brooks/Cole, 2003

Computer networksComputer networks

A A computer networkcomputer network is a combination is a combination of systems connected through of systems connected through transmission media.transmission media. Local area network (Local area network (LANLAN)) Metropolitan (Metropolitan ( 都市的都市的 ) area network ) area network

((MANMAN)) Wide area network (Wide area network (WANWAN))

©Brooks/Cole, 2003

Model and protocolModel and protocol

A A modelmodel is the specification set by a is the specification set by a standards organization as a standards organization as a guideline guideline for designing networks.for designing networks.

A A protocolprotocol is a set of is a set of rulesrules that that controls the interaction of different controls the interaction of different devices in a network or an devices in a network or an internetwork.internetwork.

©Brooks/Cole, 2003

OSI MODELOSI MODEL

6.26.2

©Brooks/Cole, 2003

The Open Systems Interconnection The Open Systems Interconnection (OSI) model(OSI) model

is a theoretical model that shows is a theoretical model that shows how any two different systems can how any two different systems can

communicatecommunicate with each other. with each other.

Note:Note:

©Brooks/Cole, 2003

Figure 6-1

The OSI model

Figure 6-2

Flow of data in the OSI model

Header

Header

Header

Trailer

©Brooks/Cole, 2003

Seven layers of OSI Seven layers of OSI modelmodel

Physical layerPhysical layer Data-link layerData-link layer Network layerNetwork layer Transport layerTransport layer Session layerSession layer Presentation layerPresentation layer Application layerApplication layer

©Brooks/Cole, 2003

Physical layerPhysical layer

The physical layer is responsible for The physical layer is responsible for transmitting a transmitting a bit streambit stream over a over a physical medium.physical medium.

It encodes and decodes bits into It encodes and decodes bits into groups of bitsgroups of bits..

It then transforms a stream of bits into It then transforms a stream of bits into a a signalsignal..

©Brooks/Cole, 2003

Data-link layerData-link layer

The data-link layer organizes bits into The data-link layer organizes bits into logical unitslogical units called called framesframes..

The data-link layer is responsible only The data-link layer is responsible only for for node-to-node deliverynode-to-node delivery of the frame. of the frame.

The data-link layer is often The data-link layer is often responsible for responsible for error handling error handling between two adjacent stationsbetween two adjacent stations..

©Brooks/Cole, 2003

Network layerNetwork layer

The network layer is responsible for The network layer is responsible for delivery of adelivery of a packet packet between the between the original source and final destination.original source and final destination.

Using Using logical addresses (IP logical addresses (IP addresses)addresses) instead of physical instead of physical addresses.addresses.

Example of IP addressExample of IP address 140.122.76.121 (4 Bytes)140.122.76.121 (4 Bytes)

©Brooks/Cole, 2003

Transport layerTransport layer

The transport layer is responsible for The transport layer is responsible for source-to-destination delivery of the source-to-destination delivery of the entire entire messagemessage..

The transport layer is responsible for The transport layer is responsible for breaking the breaking the entire messageentire message into into several several packetspackets and delivery them to the network and delivery them to the network layer.layer.

The transport layer is responsible for The transport layer is responsible for ensuring that the whole message is ensuring that the whole message is transmitted.transmitted.

If packets arrive If packets arrive out of orderout of order, they must be , they must be reorganized.reorganized.

©Brooks/Cole, 2003

Session layerSession layer

The session layer is designed to control the The session layer is designed to control the dialogdialog between users.between users.

The The synchronization (synchronization ( 同步的同步的 ) points) points divides a long message into smaller ones divides a long message into smaller ones and ensure that each section is received and ensure that each section is received and acknowledged by the receiver.and acknowledged by the receiver.

Most network implementationsMost network implementations today today do do notnot use a separate session layer, their services use a separate session layer, their services are usually included in theare usually included in the application application layer. layer.

©Brooks/Cole, 2003

Presentation layerPresentation layer

The presentation layer is concerned with The presentation layer is concerned with the syntax and semantics of the the syntax and semantics of the information information exchangedexchanged between two systems. between two systems.

It deals with the fact that different systems It deals with the fact that different systems use use different coding methodsdifferent coding methods.. Compress (Compress ( 壓縮壓縮 ) and decompress () and decompress ( 解壓縮解壓縮 ) )

datadata Encrypt (Encrypt (加密加密 ) and decrypt () and decrypt ( 解密解密 ) data) data

Most implementations doMost implementations do not not use a use a presentation layer presentation layer today,today, their services are their services are usually included in other layer.usually included in other layer.

©Brooks/Cole, 2003

Application layerApplication layer

The application layer enables theThe application layer enables the useruser to access the network.to access the network.

It defines It defines common applicationscommon applications that that can be implemented to make the job can be implemented to make the job of the user of the user simplersimpler..

Will be discussed later…Will be discussed later…

©Brooks/Cole, 2003

CATEGORIES CATEGORIES OFOF

NETWORKSNETWORKS

6.36.3

©Brooks/Cole, 2003

Figure 6-3

Categories of networks

©Brooks/Cole, 2003

Figure 6-4

LANs

©Brooks/Cole, 2003

Local area networkLocal area network

Bus topologyBus topology When a station sends a frame to another When a station sends a frame to another

computer,computer, all all computer receiver the frame computer receiver the frame and check its destination address.and check its destination address.

Star topologyStar topology Hub (all, like a bus) v.s. switch (one)Hub (all, like a bus) v.s. switch (one)

Ring topologyRing topology When a computer needs to send a frame to When a computer needs to send a frame to

another computer, it sends it to its another computer, it sends it to its neighborneighbor..

©Brooks/Cole, 2003

Figure 6-5

MAN

Figure 6-6

WAN

©Brooks/Cole, 2003

Wide area networkWide area network

WAN is the connection of individual WAN is the connection of individual computers or LANs over a computers or LANs over a large arealarge area..

A person using a telephone line to A person using a telephone line to connect to an ISP is using a WAN.connect to an ISP is using a WAN.

ISP: internet service providerISP: internet service provider

©Brooks/Cole, 2003

CONNECTINGCONNECTINGDEVICESDEVICES

6.46.4

©Brooks/Cole, 2003

Figure 6-7

Connecting devices

©Brooks/Cole, 2003

Figure 6-8

Repeater

A repeater is an electronic device and operate A repeater is an electronic device and operate only in the only in the physical layerphysical layer of the of the OSI OSI model.model.

A repeater can A repeater can regenerateregenerate the signal and the signal and sendsend it to the rest of the network.it to the rest of the network.

©Brooks/Cole, 2003

Repeaters operate at the first layer Repeaters operate at the first layer (physical layer) of the(physical layer) of the

OSI model.OSI model.

Note:Note:

©Brooks/Cole, 2003

Figure 6-9

Bridge

©Brooks/Cole, 2003

BridgesBridges

In bus topology, a bridge is a traffic In bus topology, a bridge is a traffic controller.controller. It can divide a long bus into smaller It can divide a long bus into smaller

segments so that each segments so that each segmentsegment is is independentindependent trafficwise. trafficwise.

The bridge uses a The bridge uses a table table to decide if the to decide if the frame needs to be forwarded to another frame needs to be forwarded to another segment.segment.

With a bridge, With a bridge, two or more pairstwo or more pairs of stations of stations can can communicate at the same timecommunicate at the same time..

©Brooks/Cole, 2003

Bridges operate at the first two Bridges operate at the first two layerslayers

(physical layer and data-link layer) (physical layer and data-link layer) of the OSI model.of the OSI model.

Note:Note:

©Brooks/Cole, 2003

Figure 6-10

Switch—one kind of dynamic bridge

©Brooks/Cole, 2003

Figure 6-11

Routers in an internet

©Brooks/Cole, 2003

Routers operate at the first three Routers operate at the first three layerslayers

(physical, data-link, and network (physical, data-link, and network layer)layer)

of the OSI model. of the OSI model.

Note:Note:

©Brooks/Cole, 2003

RoutersRouters

Whereas aWhereas a bridge bridge filters a frame based filters a frame based on the on the physical physical address of the frame, a address of the frame, a routerrouter routes a packet based on the routes a packet based on the logicallogical address of the packet. address of the packet.

Whereas a Whereas a bridgebridge may connect may connect two two segments of a LANsegments of a LAN, a , a routerrouter can connect can connect two independent networkstwo independent networks..

©Brooks/Cole, 2003

GatewaysGateways

A A gatewaygateway is a connecting device that is a connecting device that acts as a protocol converter.acts as a protocol converter.

A gateway is usually a computerA gateway is usually a computer installed installed with the necessary software.with the necessary software.

Today the term Today the term gatewaygateway is used is used interchangeably with the terminterchangeably with the term router router. The . The distinction between the two terms is distinction between the two terms is disappearing.disappearing.

©Brooks/Cole, 2003

Figure 6-12

Connecting devices and the OSI model

©Brooks/Cole, 2003

ProtocolsProtocols

TCPTCP: Transmission control protocol : Transmission control protocol UDPUDP: User datagram protocol: User datagram protocol IPIP: Internet protocol: Internet protocol FTPFTP: File transfer protocol: File transfer protocol SMTPSMTP: Simple mail transfer protocol: Simple mail transfer protocol POP:POP: Post office protocol Post office protocol HTTPHTTP: Hypertext transfer protocol: Hypertext transfer protocol

Figure 6-13

TCP/IP and OSI model

©Brooks/Cole, 2003

Client-server modelClient-server model

Client:Client: an application program running on an application program running on a local machinea local machine

Server:Server: an application program running an application program running on a remote machineon a remote machine

A client requests a service from a server.A client requests a service from a server. The server program is always running, The server program is always running,

and the client program runs only when and the client program runs only when needed.needed.

©Brooks/Cole, 2003

FTP -- FTP -- Client-server modelClient-server model

FTP was designed to resolve two FTP was designed to resolve two problems:problems: Different coding systems in useDifferent coding systems in use

One machine may use ASCII, and other may use One machine may use ASCII, and other may use UnicodeUnicode

Different file formats in useDifferent file formats in use

©Brooks/Cole, 2003

Figure 6-19

TELNET-- a general client-server modela general client-server model

Local login v.s. remote loginLocal login v.s. remote login TELNET is a general client-server program on TELNET is a general client-server program on

the Internet that allow remote loginthe Internet that allow remote login

©Brooks/Cole, 2003

Figure 6-20

URL

http://www.ice.ntnu.edu.tw/~violet

ftp://140.122.77.121

HTTPHTTP

URL: Uniform resource locatorURL: Uniform resource locator A special kind of addressing using by HTTPA special kind of addressing using by HTTP

http://www.ice.ntnu.edu.tw/~violet

ftp://140.122.77.121/

©Brooks/Cole, 2003

WWWWWW

WWW: World wide webWWW: World wide web Hypertext: home pageHypertext: home page BrowserBrowser Document TypesDocument Types

Static documents Static documents Dynamic documents Dynamic documents Active documentsActive documents

©Brooks/Cole, 2003

Figure 6-22

Categories of Web documents

Static documents Static documents HTML: Hypertext Markup LanguageHTML: Hypertext Markup Language

Dynamic documents Dynamic documents CGI: Common Gateway Interface (Perl)CGI: Common Gateway Interface (Perl)

Active documentsActive documents Java languageJava language

©Brooks/Cole, 2003

Key termsKey terms Active documentActive document Application layerApplication layer BridgeBridge BrowserBrowser Bus topologyBus topology ClientClient Client-server modelClient-server model Computer networkComputer network Connecting devicesConnecting devices Data-link layerData-link layer Dotted-decimal notationDotted-decimal notation Dynamic documentDynamic document

EmailEmail HTMLHTML HTTPHTTP InternetInternet Internet addressInternet address InternetworkInternetwork Internet protocol (IP)Internet protocol (IP) IP addressIP address LANLAN Lical loginLical login MANMAN ModelModel Network layerNetwork layer

©Brooks/Cole, 2003

NodeNode Node-to-node deliveryNode-to-node delivery OSIOSI Physical addressPhysical address Physical layerPhysical layer Presentation layerPresentation layer Protocol Protocol Remote login Remote login RepeaterRepeater Ring topologyRing topology RouterRouter SegmentSegment ServerServer Session layerSession layer SMTPSMTP Source-to-destination deliverySource-to-destination delivery

Star topology Star topology Static documentStatic document SwitchSwitch Synchronization pointSynchronization point TELNETTELNET TopologyTopology TrailerTrailer TCPTCP TCP/IPTCP/IP Transport layerTransport layer URLURL UDPUDP WebWeb WANWAN WWWWWW

The OSI model and TCP/IP

Education

Transcript of The OSI model and TCP/IP