Chapter 7

Chapter 7Chapter 7

Computer Networks, the Computer Networks, the Internet, and the World Wide Internet, and the World Wide

WebWeb

Mozilla.lnk

ObjectivesObjectives

In this chapter, you will learn aboutIn this chapter, you will learn about

Basic networking conceptsBasic networking concepts

Communication protocolsCommunication protocols

Network services and benefitsNetwork services and benefits

A brief history of the Internet and the World A brief history of the Internet and the World Wide WebWide Web

IntroductionIntroduction

Computer networkComputer network

Computers connected togetherComputers connected together

Purpose: Exchanging resources and Purpose: Exchanging resources and informationinformation

Just about any kind of information can be sentJust about any kind of information can be sent

• Examples: Television and radio signals, voice, Examples: Television and radio signals, voice, graphics, handwriting, photographs, moviesgraphics, handwriting, photographs, movies

Basic Networking ConceptsBasic Networking Concepts

Computer networkComputer network

Set of independent computer systems Set of independent computer systems connected by telecommunication linksconnected by telecommunication links

Purpose: Sharing information and resourcesPurpose: Sharing information and resources

Nodes, hosts, or end systemsNodes, hosts, or end systems

Individual computers on a networkIndividual computers on a network

Communication LinksCommunication Links

Switched, dial-up telephone lineSwitched, dial-up telephone line A circuit is temporarily established between A circuit is temporarily established between

the caller and calleethe caller and callee• Circuit lasts for the duration of the call.Circuit lasts for the duration of the call.

Analog mediumAnalog medium

Requires modem at both ends to transmit Requires modem at both ends to transmit information produced by a computerinformation produced by a computer• Computer produces digital informationComputer produces digital information

Figure 7.1 Two Forms of Information Representation

Figure 7.2Figure 7.2

Modulation of a Carrier to Encode Binary InformationModulation of a Carrier to Encode Binary Information

Communication Links Communication Links (continued)(continued)

Dial-up phone linksDial-up phone links Initial transmission rates of 300 bpsInitial transmission rates of 300 bps Later in 1980s increased to 1,200-9,600 bpsLater in 1980s increased to 1,200-9,600 bps Transmission rate now: 56,000 bps (56 Kbps)Transmission rate now: 56,000 bps (56 Kbps)

• Too slow for web pages, MP3, streaming videoToo slow for web pages, MP3, streaming video Still used to access networks in remote areas.Still used to access networks in remote areas.

BroadbandBroadband Transmission rate: Exceeding 256,000 bps Transmission rate: Exceeding 256,000 bps

(256 Kbps)(256 Kbps) Is “always on”, so do not have to wait for Is “always on”, so do not have to wait for

connectionconnection


Options for broadband communicationsOptions for broadband communications Broadband refers to transmission rates over Broadband refers to transmission rates over

256K bps.256K bps. Home useHome use

• Digital subscriber line (DSL)Digital subscriber line (DSL)• Cable modemCable modem

Commercial and office environmentCommercial and office environment• EthernetEthernet• Fast EthernetFast Ethernet• Gigabit EthernetGigabit Ethernet

Communication Links (continued)Communication Links (continued)

Digital subscriber line (DSL)Digital subscriber line (DSL) DSL is a “permanently on” connectionDSL is a “permanently on” connection Transmits digital signals at different Transmits digital signals at different

frequencies, so no interference with voice.frequencies, so no interference with voice. Line is often asymmetric with download & Line is often asymmetric with download &

upload bandwidths.upload bandwidths. Cable modemCable modem

Uses links that deliver TV signals to homes.Uses links that deliver TV signals to homes. Speeds roughly comparable to DSL.Speeds roughly comparable to DSL. Signal is “always on”.Signal is “always on”.

Communication Links (continued)Communication Links (continued)

Commercial and office environmentCommercial and office environment Ethernet – mid 1970’sEthernet – mid 1970’s

• Most common with 10MbpsMost common with 10Mbps• Often available in dorms and new homesOften available in dorms and new homes

Fast Ethernet developed in Fast Ethernet developed in • 100 Mbps – 1990’s100 Mbps – 1990’s• Coaxial cable, fiber-optic cable, or regular Coaxial cable, fiber-optic cable, or regular

twisted-pair copper wire.twisted-pair copper wire. Gigabit Ethernet projectGigabit Ethernet project

• In 1998, achieved 1000 MbpsIn 1998, achieved 1000 Mbps• In 2003 achieved 10 billion bpsIn 2003 achieved 10 billion bps

Transmit entire contents of 1,700 books, each 300 Transmit entire contents of 1,700 books, each 300 pages long in a single secondpages long in a single second


Transmission Time of an Image at Different Transmission SpeedsTransmission Time of an Image at Different Transmission Speeds

Gigabit Networks ApplicationsGigabit Networks Applications

Transmitting real-time video images Transmitting real-time video images without flicker or delaywithout flicker or delay

Exchanging 3D medical imagesExchanging 3D medical images Transmitting weather satellite dataTransmitting weather satellite data Supporting researchers working on Supporting researchers working on

Human Genome project.Human Genome project.


Wireless data communicationWireless data communication

Uses radio, microwave, and infrared signalsUses radio, microwave, and infrared signals

Enables “mobile computing”Enables “mobile computing”

Types of wireless data communicationTypes of wireless data communication

• Wireless local access networkWireless local access network

• Wireless wide-area access networkWireless wide-area access network

Wireless data communicationWireless data communication Wireless local access networkWireless local access network

Transmits few hundred feetTransmits few hundred feet Connected to standard wired networkConnected to standard wired network Found in home, coffee shops, officesFound in home, coffee shops, offices Wi-Fi (Wireless Fidility) connects wireless computer Wi-Fi (Wireless Fidility) connects wireless computer

to internet within 150-300 ft of access point (called to internet within 150-300 ft of access point (called hot spots).hot spots).

Wireless wide-area access networkWireless wide-area access network Computer transmits message to remote base Computer transmits message to remote base

station, which may be miles awaystation, which may be miles away Base station typically a large antenna on top of a

tower. Some are only line-of-sight, so not more than 10-50

miles apart.

Local Area NetworksLocal Area Networks

Local area network (LAN)Local area network (LAN) Connects hardware devices that are in close Connects hardware devices that are in close

proximityproximity

The owner of the devices is also the owner of The owner of the devices is also the owner of the means of communicationsthe means of communications

Common wired LAN topologiesCommon wired LAN topologies

• BusBus

• RingRing

• StarStar


Some Common Some Common LAN TopologiesLAN Topologies

Common LAN TopologiesCommon LAN Topologies BusesBuses

If two or more nodes use the link at the same If two or more nodes use the link at the same time, messages collide and are unreadabletime, messages collide and are unreadable

Nodes must take turns using net.Nodes must take turns using net. RingsRings

Messages circulate in either clockwise or Messages circulate in either clockwise or counterclockwise direction until at destinationcounterclockwise direction until at destination

StarStar Central node routes information directly to any Central node routes information directly to any

other node.other node.

Local Area NetworksLocal Area Networks (continued)(continued)

EthernetEthernet Most widely used LAN technologyMost widely used LAN technology Uses the bus topologyUses the bus topology Node places message including destination Node places message including destination

address on bus.address on bus. This message is received by all other nodesThis message is received by all other nodes All nodes check address to see if message is All nodes check address to see if message is

for them. for them. • Nodes who are not addressed discard messageNodes who are not addressed discard message

Local Area NetworksLocal Area Networks (continued)(continued)

Two ways to construct an Ethernet LANTwo ways to construct an Ethernet LAN Shared cableShared cable Hubs: The most widely used technologyHubs: The most widely used technology

Shared cable featuresShared cable features Wire is strung through the building.Wire is strung through the building. Users connect into cable at nearest point.Users connect into cable at nearest point. RepeaterRepeater amplifies and forwards signal amplifies and forwards signal

• If two Ethernets are connected using a repeater, they If two Ethernets are connected using a repeater, they function as a single network.function as a single network.

BridgeBridge (or (or switchswitch) joining two networks has ) joining two networks has knowledge about nodes on eachknowledge about nodes on each

• It forwards messages to other network only if needed. It forwards messages to other network only if needed.

Figure 7.5An Ethernet LAN ImplementedUsing Shared Cables

Hubs for LANsHubs for LANs

In this construction of a LAN, a box called In this construction of a LAN, a box called a hub is used in place of shared cablea hub is used in place of shared cable

Hubs are boxes with a number of ports. Hubs are boxes with a number of ports. Hubs are placed in a Hubs are placed in a wiring closet.wiring closet. Each node in Ethernet LAN is connected to a Each node in Ethernet LAN is connected to a

portport Hubs connects these ports using a shared Hubs connects these ports using a shared

cable inside hubcable inside hub


An Ethernet LAN Implemented Using a HubAn Ethernet LAN Implemented Using a Hub

Wide Area NetworksWide Area Networks

Wide area networks (WANs)Wide area networks (WANs)

Connect devices that are across town, across Connect devices that are across town, across the country, or across the oceanthe country, or across the ocean

Users must purchase telecommunications Users must purchase telecommunications services from an external providerservices from an external provider

Dedicated point-to-point linesDedicated point-to-point lines

Most use a store-and-forward, packet-Most use a store-and-forward, packet-switched technology to deliver messagesswitched technology to deliver messages


Typical Structure of a Wide Area NetworkTypical Structure of a Wide Area Network

Overall Structure of the InternetOverall Structure of the Internet

All real-world networks, including the Internet, All real-world networks, including the Internet, are a mix of LANs and WANsare a mix of LANs and WANs Example: A company or a collegeExample: A company or a college

• One or more LANs connecting its local computersOne or more LANs connecting its local computers• Individual LANs interconnected into a wide-area Individual LANs interconnected into a wide-area

company networkcompany network Routers are used to connect networks of both

similar and dissimilar types. • A router can connect an LAN to a WAN.• A bridge can only connect two networks of identical

type.

Figure 7.8(a)Figure 7.8(a)

Structure of a Typical Company NetworkStructure of a Typical Company Network

Overall Structure of the Internet Overall Structure of the Internet (continued)(continued)

Internet Service Provider (ISP)Internet Service Provider (ISP) Normally a businessNormally a business Provides a pathway from a specific network to other Provides a pathway from a specific network to other

networks, or from an individual’s computer to other networks, or from an individual’s computer to other networksnetworks

This access occurs through a WAN owned by the ISPThis access occurs through a WAN owned by the ISP ISPs are hierarchicalISPs are hierarchical

Interconnect to each other in multiple layers to Interconnect to each other in multiple layers to provide greater geographical coverageprovide greater geographical coverage

A regional or national ISP may connect to an A regional or national ISP may connect to an international IPS called a tier-1 network or Internet international IPS called a tier-1 network or Internet backbone.backbone.

T1 & T3 LinesT1 & T3 Lines A dedicated phone connection supporting A dedicated phone connection supporting data

rates of 1.544 Mbits per second.rates of 1.544 Mbits per second. Consists of 24 individual Consists of 24 individual channels, each of which , each of which

supports 64Kbits per second. supports 64Kbits per second. Each 64Kbit/second channel can be configured to Each 64Kbit/second channel can be configured to

carry voice or data traffic. carry voice or data traffic. T-1 lines are a popular T-1 lines are a popular leased line option for option for

businesses connecting to the businesses connecting to the Internet and for and for Internet Service Providers (ISPs) connecting to connecting to the Internet backbone..

The Internet backbone itself consists of faster The Internet backbone itself consists of faster T-3 connections. connections.

Reference: WebopediaReference: Webopedia

Figure 7.8(b)Figure 7.8(b)

Structure of a Network Using an ISPStructure of a Network Using an ISP

Figure 7.8(c)Hierarchy of Internet Service Providers

Overall Structure of the Internet Overall Structure of the Internet (continued)(continued)

InternetInternet A huge interconnected “network of networks”A huge interconnected “network of networks”

Includes nodes, LANs, WANs, bridges, routers, Includes nodes, LANs, WANs, bridges, routers, and multiple levels of ISPsand multiple levels of ISPs

Early 2005Early 2005

• 317 million nodes (hosts)317 million nodes (hosts)

• Hundreds of thousands of separate networks Hundreds of thousands of separate networks located in over 225 countrieslocated in over 225 countries

Communication ProtocolsCommunication Protocols A protocolA protocol

A mutually agreed upon set of rules, conventions, and A mutually agreed upon set of rules, conventions, and agreements for the efficient and orderly exchange of agreements for the efficient and orderly exchange of informationinformation

Internet is operated by the Internet Society, a Internet is operated by the Internet Society, a nonprofit society consisting of over 100 nonprofit society consisting of over 100 worldwide organizations, foundations, worldwide organizations, foundations, businesses, etc.businesses, etc.

TCP/IP TCP/IP The Internet protocol hierarchyThe Internet protocol hierarchy Governs the operation of the InternetGoverns the operation of the Internet Named after 2 of the most successful protocolsNamed after 2 of the most successful protocols Consists of five layers (see next slide)Consists of five layers (see next slide)


The Five-Layer TCP/IP Internet Protocol HierarchyThe Five-Layer TCP/IP Internet Protocol Hierarchy

Physical LayerPhysical Layer

Protocols govern the exchange of binary Protocols govern the exchange of binary digits across a physical communication digits across a physical communication channelchannel

Specify such things asSpecify such things as What signal is used to indicate a bit on the lineWhat signal is used to indicate a bit on the line How long will “bit on the line” signal lastHow long will “bit on the line” signal last Will signal be digital or analogWill signal be digital or analog What voltage levels are used to represent 0 & 1What voltage levels are used to represent 0 & 1

Goal: Create a bit pipe between two Goal: Create a bit pipe between two computerscomputers

Data Link LayerData Link Layer

Protocols carry outProtocols carry out Error detection and correctionError detection and correction FramingFraming

• Which bits in incoming stream belong togetherWhich bits in incoming stream belong together• Identifying start and end of messageIdentifying start and end of message

Creates an error-free message pipe Creates an error-free message pipe Composed of two stagesComposed of two stages

Layer 2a: Medium access controlLayer 2a: Medium access control

Layer 2b: Logical link controlLayer 2b: Logical link control

Data Link Layer (continued)Data Link Layer (continued)

Medium access control protocolsMedium access control protocols

Determine how to arbitrate ownership of a shared Determine how to arbitrate ownership of a shared line when multiple nodes want to send at the line when multiple nodes want to send at the same timesame time

Logical link control protocolsLogical link control protocols

Ensure that a message traveling across a Ensure that a message traveling across a channel from source to destination arrives channel from source to destination arrives correctlycorrectly

Layer 2aMedium access control protocols

Automatic Repeat Request (ARQ) Algorithm

Part of Logical Link Protocols - layer 2b

Assures message travels from A to B correctly

Automatic Repeat Request Automatic Repeat Request (ARQ)(ARQ)

Process of requesting that a data transmission be Process of requesting that a data transmission be resentresent

Main ARQ protocolsMain ARQ protocols Stop and Wait ARQ (A half duplex technique)Stop and Wait ARQ (A half duplex technique)

• Sender sends a message and waits for acknowledgment, Sender sends a message and waits for acknowledgment, then sends the next messagethen sends the next message

• Receiver receives the message and sends an Receiver receives the message and sends an acknowledgement, then waits for the next messageacknowledgement, then waits for the next message

Continuous ARQ (A full duplex technique) Continuous ARQ (A full duplex technique) • Sender continues sending packets without waiting for the Sender continues sending packets without waiting for the

receiver to acknowledgereceiver to acknowledge• Receiver continues receiving messages without Receiver continues receiving messages without

acknowledging them right awayacknowledging them right away

Stop and Wait ARQStop and Wait ARQ

Sends the packet, then waits to hear from receiver. Sends

acknowledgement

Sends negative

acknowledgementResends the packet again

Sends the next packet

Sender Receiver

ContinuousContinuous ARQ ARQSender sends packets continuously without

waiting for receiver to acknowledge

Notice that acknowledgments now

identify the packet being acknowledged.

Receiver sends back a NAK for a specific packet to be resent.

Source of Error What causes it How to prevent it

Line Outages

Faulty equipment, Storms, Accidents (circuit fails)

White Noise (hiss)

(Gaussian Noise)Movement of electrons (thermal energy)

Increase signal strength (increase SNR)

Impulse Noise (Spikes)

Sudden increases in electricity (e.g., lightning, power surges)

Shield or move the wires

Cross-talk Multiplexer guard bands are too small or wires too close together

Increase the guard bands, ormove or shield the wires

Echo

Poor connections (causing signal to be reflected back to the source)

Fix the connections, ortune equipment

Attenuation

Gradual decrease in signal over distance (weakening of a signal)

Use repeaters or amplifiers

Intermodulation Noise

Signals from several circuits combine

Move or shield the wires

Jitter

Analog signals change (small changes in amp., freq., and phase)

Tune equipment

Harmonic Distortion

Amplifier changes phase (does not correctly amplify its input signal)

Tune equipment

Sources of Errors and PreventionSources of Errors and Prevention

mo

stly on

analo

gM

ore im

po

rtant

Error DetectionError Detection

Mathematical calculations

?=

Mathematical calculations

Data to be transmitted

Sender calculates an Error Detection Value (EDV) and transmits it along with data

Receiver recalculates EDV and checks it against the received EDV

– If the same No errors in transmission

– If different Error(s) in transmission

EDV

Larger the size, better error detection (but lower efficiency)

Error Detection TechniquesError Detection Techniques

Parity checksParity checks Longitudinal Redundancy Checking (LRC)Longitudinal Redundancy Checking (LRC) Polynomial checkingPolynomial checking

ChecksumChecksum Cyclic Redundancy Check (CRC)Cyclic Redundancy Check (CRC)

Parity CheckingParity Checking

One of the oldest and simplestOne of the oldest and simplest A single bit added to each characterA single bit added to each character

Even parity: number of 1’s remains evenEven parity: number of 1’s remains even Odd parity: number of 1’s remains oddOdd parity: number of 1’s remains odd

Receiving end recalculates parity bitReceiving end recalculates parity bit If one bit has been transmitted in error the received If one bit has been transmitted in error the received

parity bit will differ from the recalculated oneparity bit will differ from the recalculated one Simple, but doesn’t catch all errors Simple, but doesn’t catch all errors

If two (or an even number of) bits have been transmitted If two (or an even number of) bits have been transmitted in error at the same time, the parity check appears to be in error at the same time, the parity check appears to be correctcorrect

Detects about 50% of errorsDetects about 50% of errors

Examples of Using ParityExamples of Using Parity

sender receiver01101010

EVEN parity

parity

number of all transmitted 1’s remains EVEN

To be sent: Letter V in 7-bit ASCII: 0110101

sender receiver01101011

ODD parity

paritynumber of all transmitted 1’s remains ODD

LRC - LRC - Longitudinal Redundancy Longitudinal Redundancy CheckingChecking

Adds an additional character (instead of a bit)Adds an additional character (instead of a bit) Block Check Character (BCC) to each block of dataBlock Check Character (BCC) to each block of data Determined like parity but, but counting longitudinally Determined like parity but, but counting longitudinally

through the message (as well as vertically)through the message (as well as vertically) Calculations are based on the 1st bit, 2nd bit, etc. (of all Calculations are based on the 1st bit, 2nd bit, etc. (of all

characters) in the blockcharacters) in the block• 1st bit of BCC 1st bit of BCC number of 1’s in the 1st bit of characters number of 1’s in the 1st bit of characters• 2nd bit of BCC 2nd bit of BCC number of 1’s in the 2ndt bit of charactersnumber of 1’s in the 2ndt bit of characters

Major improvement over parity checkingMajor improvement over parity checking 98% error detection rate for burst errors ( > 10 bits)98% error detection rate for burst errors ( > 10 bits) Less capable of detecting single bit errorsLess capable of detecting single bit errors

LetterDATA

Using LRC for Error DetectionUsing LRC for Error Detection

Note that the BCC’s parity bit is also determined by parity

BCC 1 1 0 1 1 1 1 1

Parity bit1101

Example: Send the message “DATA” using ODD parity and LRC

ASCII 1 0 0 0 1 0 0 1 0 0 0 0 0 11 0 1 0 1 0 01 0 0 0 0 0 1

Polynomial CheckingPolynomial Checking

Adds 1 or more characters to the end of message Adds 1 or more characters to the end of message (based on a mathematical algorithm)(based on a mathematical algorithm)

Two types: Checksum and CRCTwo types: Checksum and CRC ChecksumChecksum

Calculated by adding decimal values of each character in the Calculated by adding decimal values of each character in the message, message,

Dividing the total by 255. and Dividing the total by 255. and Saving the remainder (1 byte value) and using it as the Saving the remainder (1 byte value) and using it as the

checksumchecksum 95% effective95% effective

Cyclic Redundancy Check (CRC)Cyclic Redundancy Check (CRC) Computed by calculating the remainder to a division problem: Computed by calculating the remainder to a division problem:

P / G = Q + R / G

Cyclic Redundancy Check Cyclic Redundancy Check (CRC)(CRC)

– Most powerful and most common– Detects 100% of errors (if number of errors <= size of R)

–Otherwise: CRC-16 (99.998%) and CRC-32 (99.9999%)

Message (treated as one long binary number)

A fixed number (determines the length of the R)

Remainder:–added to the message as EDV)

–could be 8 bits, 16 bits, 24 bits, or 32 bits long

Quotient (whole number)

Example:P = 58G = 8Q = 7R = 2

Network LayerNetwork Layer

Delivers a message from the site where it Delivers a message from the site where it was created to its ultimate destinationwas created to its ultimate destination

Critical responsibilitiesCritical responsibilities

Create a universal addressing scheme for all Create a universal addressing scheme for all network nodesnetwork nodes

Deliver messages between any two nodes in Deliver messages between any two nodes in the networkthe network

Network Layer (continued)Network Layer (continued) Provides a true network delivery serviceProvides a true network delivery service

Messages are delivered between any two Messages are delivered between any two nodes in the network, regardless of where nodes in the network, regardless of where they are locatedthey are located

Universal addressing scheme usedUniversal addressing scheme used IP (Internet Protocol) layerIP (Internet Protocol) layer Example:Example:

• One author’s host name is macalester.eduOne author’s host name is macalester.edu• The IP address for host is (in decimal) The IP address for host is (in decimal)

141.140.1.5141.140.1.5• Corresponds to following 32 bit addressCorresponds to following 32 bit address

10001101 10001100 0000000 100000101 10001101 10001100 0000000 100000101 • Clearly, the symbolic name is easier to remember.Clearly, the symbolic name is easier to remember.

Network Layer (cont.)Network Layer (cont.) Domain Name System (DNS)Domain Name System (DNS)

It is the job of the DNS to convert symbolic names to It is the job of the DNS to convert symbolic names to a sequence of 32 binary bitsa sequence of 32 binary bits

DNS is a massive distributed databaseDNS is a massive distributed database If local name server does not recognize host name, it

is forwarded to a remote name servers until one locates its name.

Routing Algorithms There are normally multiple routes a message can

take to its destination. A routing algorithm called “Dijkstra’s shortest path”

algorithm is used, based on time required to send a message along various paths.

For large networks with 107 nodes or more, algorithm may require 1014 or more calculations.

Network Layer (cont)Network Layer (cont) Keeping these routing tables up to date is Keeping these routing tables up to date is

an enormous task.an enormous task. Data changes regularly, so they have to be Data changes regularly, so they have to be

recalculated frequently.recalculated frequently. When a network node or sections of network When a network node or sections of network

fails, must route around the failed nodes.fails, must route around the failed nodes. Network Layer also handles other thingsNetwork Layer also handles other things

Network managementNetwork management BroadcastingBroadcasting Locating mobile nodesLocating mobile nodes

Transport LayerTransport Layer Provides a high-quality, error-free, order- Provides a high-quality, error-free, order-

preserving, end-to-end delivery servicepreserving, end-to-end delivery service

TCP (Transport Control Protocol)TCP (Transport Control Protocol) Primary transport protocol on the InternetPrimary transport protocol on the Internet Requires the source and destination programs to Requires the source and destination programs to

initially establish a connectioninitially establish a connection Uses ARQ algorithm on sending & receiving Uses ARQ algorithm on sending & receiving

messages.messages. Messages sent in packets and have to be Messages sent in packets and have to be

reassembled in order at destinationreassembled in order at destination Standard applications (e.g., POP3 or IMAP for email) Standard applications (e.g., POP3 or IMAP for email)

have fixed port numbers for all computers.have fixed port numbers for all computers.


Logical View of a TCP ConnectionLogical View of a TCP Connection

Application LayerApplication Layer

Implements the end-user services provided Implements the end-user services provided by a networkby a network

There are many application protocolsThere are many application protocols HTTPHTTP

SMTPSMTP

POP3POP3

IMAPIMAP

FTPFTP


Some Popular Application Protocols on the InternetSome Popular Application Protocols on the Internet

Application Layer (continued)Application Layer (continued) Uniform Resource Locator (URL)Uniform Resource Locator (URL)

A symbolic string that identifies a Web pageA symbolic string that identifies a Web page

FormForm

protocol://host address/pageprotocol://host address/page

The most common Web page format is The most common Web page format is hypertext informationhypertext information

• Accessed using the HTTP protocolAccessed using the HTTP protocol

• Example: Example: http://www.macalester.edu/about/history.htmlhttp://www.macalester.edu/about/history.html

Network Services and BenefitsNetwork Services and Benefits

Services offered by computer networksServices offered by computer networks Electronic mail (email)Electronic mail (email)

• Send message when you want & read at receiver’s Send message when you want & read at receiver’s convenienceconvenience

• From U.S., arrives anywhere in world in about a From U.S., arrives anywhere in world in about a minute.minute.

Bulletin boardsBulletin boards

Internet Services (cont)Internet Services (cont)

Services offered by c. networks (cont) Services offered by c. networks (cont) News groupsNews groups

Chat roomsChat rooms

Resource sharingResource sharing

• Physical resourcesPhysical resources

• Logical resourcesLogical resources

Network Services and Benefits Network Services and Benefits (continued)(continued)

Services offered by computer networksServices offered by computer networks

Client-server computingClient-server computing

Information sharing (databases)Information sharing (databases)

Information utility Information utility

• reference documents onlinereference documents online

Electronic commerce (e-commerce)Electronic commerce (e-commerce)

A Brief History of the Internet and A Brief History of the Internet and the World Wide Web: The Internetthe World Wide Web: The Internet

August 1962: First proposal for building a August 1962: First proposal for building a computer networkcomputer network Written by J. C. R. Licklider of MITWritten by J. C. R. Licklider of MIT

ARPANETARPANET Built by the Advanced Research Projects Agency Built by the Advanced Research Projects Agency

(ARPA) in Dept of Defense in the late1960s(ARPA) in Dept of Defense in the late1960s Packet switching viewed as more secure than phone Packet switching viewed as more secure than phone

lines.lines. First two nodes were at Stanford Research Institute First two nodes were at Stanford Research Institute

(SRI) and UCLA, in 1969(SRI) and UCLA, in 1969• Univ. of Calif. at Santa Barbara & Univ. Utah added in 1969Univ. of Calif. at Santa Barbara & Univ. Utah added in 1969

Grew quickly during the early 1970sGrew quickly during the early 1970s

The Internet (continued)The Internet (continued) ARPANET (cont)ARPANET (cont)

Electronic Email developed in 1972Electronic Email developed in 1972 Huge success of ARPANET lead to creation of Huge success of ARPANET lead to creation of

other research and commercial networksother research and commercial networks In 1973, Kahn at ARPA and Cerf at Stanford In 1973, Kahn at ARPA and Cerf at Stanford

started work to allow different networks to started work to allow different networks to communicatecommunicate A common address schemeA common address scheme The TCP/IP protocols that provided a common The TCP/IP protocols that provided a common

languagelanguage Additional “Killer Applications” in early 1980’sAdditional “Killer Applications” in early 1980’s

Telnet – Log on remotely to another computerTelnet – Log on remotely to another computer FTP – File Transfer ProtocolFTP – File Transfer Protocol

The Internet (continued)The Internet (continued) Most people with Internet access in early 1980’s Most people with Internet access in early 1980’s

were physicist, engineers, & computer scientistwere physicist, engineers, & computer scientist ARPANET connected only 235 computers in 1982, ARPANET connected only 235 computers in 1982,

one of which was KSU Mathematical Science Dept. one of which was KSU Mathematical Science Dept. NSFNet: A national “network of networks” built NSFNet: A national “network of networks” built

by the National Science Foundation (NSF) in by the National Science Foundation (NSF) in 19841984 Goal was to bring internet services to all academic Goal was to bring internet services to all academic

and professional groups.and professional groups. Included universities, libraries, museums, medical Included universities, libraries, museums, medical

centers, etc.centers, etc.

The Internet (continued)The Internet (continued)

Many countries quickly followed lead of NSFNet Many countries quickly followed lead of NSFNet and connected their professional groups to the and connected their professional groups to the internet.internet.

October 24, 1995: Formal acceptance of the October 24, 1995: Formal acceptance of the term term Internet Internet by the U.S. Govt.

Internet service providers start offering Internet Internet service providers start offering Internet access once provided by the ARPANET and access once provided by the ARPANET and NSFNetNSFNet

Figure 7.20State of Networking in the Late 1980s

The World Wide WebThe World Wide Web Development completed in May 1991Development completed in May 1991

Designed and built by Tim Berners-Lee at CERN Designed and built by Tim Berners-Lee at CERN (European High Energy Physics Lab) in Geneva (European High Energy Physics Lab) in Geneva Switzerland.Switzerland.

Purpose was to allow scientists to more easily Purpose was to allow scientists to more easily exchange information such as research articles, exchange information such as research articles, experimental dataexperimental data

Would be a big improvement of earlier methods Would be a big improvement of earlier methods of email messaging and FTP.of email messaging and FTP.


Hypertext DocumentsHypertext Documents

The World Wide Web (cont)The World Wide Web (cont) ComponentsComponents

HypertextHypertext• A collection of documents interconnected by A collection of documents interconnected by

pointers called linkspointers called links Hypertext links called a URL (Uniform Hypertext links called a URL (Uniform

Resource Locator)Resource Locator)• The worldwide identification of a Web page located The worldwide identification of a Web page located

on a specific host computeron a specific host computer In 1993 CERN announced their web technology In 1993 CERN announced their web technology

would be freely available.would be freely available. Realized impact it could have on research throughout Realized impact it could have on research throughout

world.world.

The World Wide Web (cont)The World Wide Web (cont) A graphic browser (MOSIAC) was also released A graphic browser (MOSIAC) was also released

in late 1993in late 1993 Allowed public to make use of new technologyAllowed public to make use of new technology Forerunner of Netscape Navigator (1994) and Forerunner of Netscape Navigator (1994) and

Microsoft Internet Explorer (1995)Microsoft Internet Explorer (1995) The WWW became the killer app of the 21 The WWW became the killer app of the 21

century century

Summary of Level 3Summary of Level 3

Virtual environmentVirtual environment Created by system softwareCreated by system software Easy to use and easy to understandEasy to use and easy to understand Provides services such asProvides services such as

• Resource managementResource management• SecuritySecurity• Access controlAccess control• Efficient resource useEfficient resource use

Operating systems continue to evolveOperating systems continue to evolve

SummarySummary

Computer network: A set of independent Computer network: A set of independent computer systems connected by computer systems connected by telecommunication linkstelecommunication links

Options for transmitting data on a network: Options for transmitting data on a network: Dial-up telephone lines, DSL, cable modem, Dial-up telephone lines, DSL, cable modem, Ethernet, Fast EthernetEthernet, Fast Ethernet

Types of networks: Local area network (LAN) Types of networks: Local area network (LAN) and wide area network (WAN)and wide area network (WAN)

Summary (continued)Summary (continued)

The Internet is a huge interconnected The Internet is a huge interconnected "network of networks" "network of networks"

TCP/IP is the Internet protocol hierarchy, TCP/IP is the Internet protocol hierarchy, composed of five layers: physical, data link, composed of five layers: physical, data link, network, transport, and applicationnetwork, transport, and application

The World Wide Web is an information The World Wide Web is an information system based on the concept of hypertextsystem based on the concept of hypertext

Chapter 7

Documents

Transcript of Chapter 7