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Chapter 1 5. Networks. Chapter Goals. Describe the core issues related to computer networks List various types of networks and their characteristics Explain various topologies of local-area networks Explain why network technologies are best implemented as open systems

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slide1

Chapter 15

Networks

chapter goals
Chapter Goals
  • Describe the core issues related to computer

networks

  • List various types of networks and their

characteristics

  • Explain various topologies of local-area networks
  • Explain why network technologies are best

implemented as open systems

  • Compare and contrast various technologies

for home Internet connections

chapter goals3
Chapter Goals
  • Explain packet switching
  • Describe the basic roles of various network

protocols

  • Explain the role of a firewall
  • Compare and contrast network hostnames and IP

addresses

  • Explain the domain name system
15 1 networking
15.1 Networking
  • Computer network : A collection of computing devices

that are connected in various ways in order to

communicate and share resources

  • Usually, the connections between computers in a network

are made using physical wires or cables. However,

some connections are wireless, using radio

waves or infrared signals.

  • The generic term node or host refers to any device

on a network.

  • Data transfer rate : The speed with which data is moved

from one place on a network to another. Sometimes the

data transfer rate is referred to as the bandwidth of a

network.

15 1 networking5
15.1 Networking
  • Another key issue in computer networks is the protocols

that are used.

Protocol : A set of rules that defines how data is

formatted and processed on a network.

  • Computer networks have opened up an entire frontier in

the world of computing called the client/server model

Fig. 15.1 Client/Server interaction

15 1 networking6
15.1 Networking
  • Client/server model: A distributed approach in which

a client makes requests of a server and

the server responds.

  • File server : A computer that stores and manages files for

multiple users on a network.

  • Web server : A computer dedicated to responding to

requests (from the browser client) for web pages

  • Using networks and the client/server model, parallel

processing can be accomplished by the client requesting

that multiple machines perform a specific part of a

problem. The client gather the responses from each

to form a complete solution to the problem.

15 1 networking7
15.1 Networking

Types of Networks

  • Computer networks can be classified in various ways.

Local-area network (LAN) : A network that connects

a relatively small number of machines in a relatively

close geographical area.

  • Various configurations, called topologies, have been

used to administer LANs.

    • Ring topology
    • Star topology See Fig. 15.2
    • Bus topology
  • A bus technology called Ethernethas become

the industry standard for local-area networks

15 1 networking8
15.1 Networking

Types of Networks

Fig. 15.2 Various network topologies

15 1 networking9
15.1 Networking

Types of Networks

  • Wide-area network (WAN) : A network that connects

two or more local-area networks over a potentially large

geographic distance.

  • Often one particular node on a LAN is set up to serve as a

gatewayto handle all communication going between that

LAN and other networks.

  • Communication between networks is called

internetworking : The Internet is essentially the ultimate

wide-area network, spanning the entire globe.

  • Metropolitan-area network(MAN): The communication

infrastructures that have been developed in and around

large cities

15 1 networking10
15.1 Networking

Types of Networks

Fig. 15.1 Local-area networks connected across a distance

to create a wide-area network

15 1 networking11
15.1 Networking

Internet Connections

  • These smaller networks are often owned and managed by

a person or organization. The Internet is really defined by

how connections can be made between these networks.

  • Internet backbone : A set of high-speed networks that

carry Internet traffic; These networks are provided by

companies such as AT&T, GTE, and IBM

  • Internet service provider (ISP) : A company that

provides other companies or individuals with access to

the Internet. ISPs connect directly to the Internet backbone

or they connect to a larger ISP with a connection to the

backbone; America OnLine (AOL) and Prodigy.

15 1 networking12
15.1 Networking

Internet Connections

  • There are various technologies available that you can use

to connect a home computer to the Internet.

    • A phone modem converts computer data into an

analog audio signal for transfer over a telephone line,

and then a modem at the destination converts it back

again into data

    • A digital subscriber line (DSL) uses regular copper phone lines to transfer digital data to and from the phone company’s central office
    • A cable modemusesthe same line that your cable TV signals come in on to transfer the data back and forth
15 1 networking13
15.1 Networking

Internet Connections

  • Broadband :A connection in which transfer speeds are

faster than 128K bits per second

    • DSL connections and cable modems are broadband

connections

    • The speed for downloads (getting data from the

Internet to your home computer) may not be the same

as uploads (sending data from your home computer

to the Internet) : DSL and cable modem suppliers use

technology that devotes more speed to download

15 1 networking14
15.1 Networking

Packet Switching

  • To improve the efficiency of transferring information

over a shared communication line, messages are divided

into fixed-sized, numbered packets

  • Network devices called routers are used to direct packets

between networks

Fig. 15.4Messages sent by packet switching

15 2 open systems protocols
15.2 Open Systems & Protocols

Open Systems

  • Proprietary system : A system that uses technologies

kept private by a particular commercial vendor

One system couldn’t communicate with another, leading to the need for

  • Interoperability : The ability of software and hardware

on multiple machines and from multiple

commercial vendors to communicate

Leading to

  • Open systems : Systems based on a common model of

network architecture and a suite of protocols used

in its implementation

15 2 open systems protocols16
15.2 Open Systems & Protocols

Open Systems

  • TheInternational Organization for Standardization (ISO)

established the Open Systems Interconnection (OSI)

Reference Model

  • Each layer deals with a particular aspect of network

communication

Fig. 15.5 The layers of the OSI Reference Model

15 2 open systems protocols17
15.2 Open Systems & Protocols

Network Protocols

  • Network protocols are layered such that each one relies

on the protocols that underlie it.

  • Sometimes referred to as a protocol stack : layers of

protocols that build and rely on each other

Fig. 15.6 Layering of key network protocols

15 2 open systems protocols18
15.2 Open Systems & Protocols

TCP/IP

  • TCP stands for Transmission Control Protocol
    • TCP software breaks messages into packets, hands

them off to the IP software for delivery, and then

orders and reassembles the packets at their destination

  • IP stands for Internet Protocol
    • IP software deals with the routing of packets through

the maze of interconnected networks to their final

destination.

  • TCP/IP : A suite of protocols and programs that support

low-level network communication.

15 2 open systems protocols19
15.2 Open Systems & Protocols

TCP/IP

  • UDP stands for User Datagram Protocol
    • It is an alternative to TCP
    • The main difference is that TCP is highly reliable,

at the cost of decreased performance,

while UDP is less reliable, but generally faster.

  • An IP program called ping (Packet InterNet Groper) can

be used to test the reachability of network destinations.

  • TCP/IP program called traceroute shows the route that

a packet takes to arrive at a particular destination.

15 2 open systems protocols20
15.2 Open Systems & Protocols

High-Level Protocols

  • Other protocols build on the foundation established

by the TCP/IP protocol suite

    • Simple Mail Transfer Protocol (SMTP): e-mail
    • File Transfer Protocol (FTP) : file transfer
    • Telnet : remote login
    • Hyper Text Transfer Protocol (http) : WWW service
  • Several high-level protocols have been assigned a

particular port number.

Port : A numeric designation corresponding to

a particular high-level protocol.

Server and routers use the port number to help control

and process network traffic.

15 2 open systems protocols21
15.2 Open Systems & Protocols

High-Level Protocols

Fig. 15.7Some protocols and the ports they use

15 2 open systems protocols22
15.2 Open Systems & Protocols

MIME Types

  • MIME stands for Multipurpose Internet Mail

Extension

  • MIME Type: A standard for defining the format of files

that are included as email attachments or

an websites

  • Based on a document’s MIME type, an application

program can decide how to deal with the data it is given

15 2 open systems protocols23
15.2 Open Systems & Protocols

Firewalls

  • Firewall : A machine and its software that serve as

a special gateway to a network, protecting it from

inappropriate access

    • Filters the network traffic that comes in, checking the

validity of the messages as much as possible and

perhaps denying some messages altogether

    • Enforces an organization’s access control policy
  • Thesystem administrators of an organization set up a

firewall for their LAN that permits “acceptable” types of

communication and denies other types. For example,

denying a telnet connection to any computer inside the

LAN by denying all traffic that comes in on port 23.

15 2 open systems protocols24
15.2 Open Systems & Protocols

Firewalls

Fig. 15.8 A firewall protecting a LAN

15 3 network addresses
15.3 Network Addresses
  • Hostname : A unique identification that specifies

a particular computer on the Internet.

For example

matisse.csc.villanova.edu

condor.develocorp.com

  • Network software translates a hostname into its corresponding IP address (4 bytes)

For example

205.39.145.18

Fig. 15.9An IP address is stored in four bytes

15 3 network addresses26

Network address

Host number

01011011 11100110 01011010 00001101

IP address

(binary)

( Dotted decimal )

155.230.90.13

condor.knu.ac.kr

Hostname

Computer name

Domain name

15.3 Network Addresses
  • Relation betweenHostname IP address

ICANN

(Internet Corporation for

Assigned Names and Numbers)

local system

administrator

15 3 network addresses27
15.3 Network Addresses

Domain Name System

  • A hostname consists of the computer name followed by

the domain name (ex. csc.villanova.edu).

    • A domain name is separated into two or more sections

that specify the organization, and possibly a subset of

an organization, of which the computer is a part

    • Two organizations can have a computer named the

same thing because the domain name makes it clear

which one is being referred to

    • The very last section of the domain is called its top-

level domain (TLD) name.

15 3 network addresses28
15.3 Network Addresses

Domain Name System

Fig. 15.10 Top-level domains,

including some relatively new ones

15 3 network addresses29
15.3 Network Addresses

Domain Name System

  • Organizations based in countries other than the United

States use a top-level domain that corresponds to their

two-letter country codes

Fig. 15.11Some of the top-level

domain names based on country codes

15 3 network addresses30
15.3 Network Addresses

Domain Name System

  • The domain name system (DNS) is chiefly used to

translate hostnames into numeric IP addresses

    • DNS is an example of a distributed database
    • If that server can resolve the hostname, it does so
    • If not, that server asks another domain name server
  • Domain name server: A computer that attempts to

translate a hostname into an IP address.

slide31

Chapter 16

The World Wide Web

chapter goals32
Chapter Goals
  • Compare and contrast the Internet and the World Wide Web
  • Describe general Web processing
  • Write basic HTML documents
  • Describe several specific HTML tags and their purposes
  • Describe the processing of Java applets and Java server

pages

  • Compare and contrast HTML and XML
  • Define basic XML documents and their corresponding

DTDs

  • Explain how XML documents are viewed
16 1 spinning the web
16.1 Spinning the Web
  • Many people use the words Internet and Web

interchangeably,but they are fundamentally different.

  • The Web : An infrastructure of distributed information

combined with software that uses networks as

a vehicle to exchange that information

  • Web page : A document that contains or references

various kinds of data, such as text, images,

graphics, and programs

  • Links : A connection between one web page and another

that can be used “move around” as desired

  • Website : A collection of related web pages
16 1 spinning the web34
16.1 Spinning the Web
  • The Internet makes the communication possible, but the

Web makes that communication easy, more productive,

and more enjoyable

  • Browser: A software tool that issues the request for the

web page we want and displays it when it arrives.

Netscape Navigator or Microsoft’s Internet Explorer

Fig. 16.2 A browser retrieving a Web page

16 1 spinning the web35
16.1 Spinning the Web
  • Web server:The computer that is set up to respond to

web requests.

  • Web address : The core part of a Uniform Resource

Locator, or URL, which uniquely identifies the page

you want out of all of the pages stored anywhere

in the world;

http://www.villanova.edu/academics.html

protocol

hostname

file name

16 1 spinning the web36
16.1 Spinning the Web

Search Engines

  • Search Engine : A website that helps you find other

websites

For example, Yahoo and Google are search engines

You enter keywords and the search engine produces

a list if links to potentially useful sites

  • There are two types of searches
    • Keyword searches
    • Concept-based searches attempt to figure out the context of your search.
16 1 spinning the web37
16.1 Spinning the Web

Instant Messaging

  • Instant messaging (IM) : An application that allows

people to send and receive messages in real time.

    • Both sender and receiver must have an IM running.
    • Most IM applications use a proprietary protocol

that dictates the precise format and structure of the

messages that are sent across the network to the

receiver.

    • Instant messages are not secure.
16 1 spinning the web38
16.1 Spinning the Web

Cookies

  • Cookie:A small text file that a web server stores on your

local computer’s hard disk.

    • A cookie contains information about your visit to the

site.

    • Cookies can be used
      • to determine number of unique visitors to the site
      • to customize the site for your future visits
      • to implement shopping carts that can be maintained

from visit to visit

    • Cookies are not dangerous; Web-based technology .
16 2 html
16.2 HTML
  • Web pages are created (or built) using a language called

the HyperText Markup Language, or HTML.

Hypertext (jump from one place to another)

 Hypermedia

  • The term markup language comes from the fact that the

primary elements of the language take the form of tags

that we insert into a document to annotate the information

stored there.

Tags are enclosed in angle brackets (<. . . >)

Words such as HEAD, TITLE, and BODY are called

elements and specify the type of the tag.

16 2 html40
16.2 HTML

Fig. 16.2A marked-up document

16 2 html41
16.2 HTML

Fig. 16.3The Student Dynamics Web page

as displayed in Netscape Navigator

16 2 html42
16.2 HTML

Fig. 16.4The HTML document defining the Student Dynamics Web page

16 2 html43
16.2 HTML

Images and Links

  • An image can be incorporated into a web page using the

IMG element, which takes an attribute that identifies the

image file to display

For Example : <IMG SRC = "myPicture.gif" >

  • A link is specified using the element A, which stands for

anchor. The tag includes an attribute called HREF that

specifies the URL of the destination document.

For Example :

<A HREF = "http://duke.csc.villanova.edu/docs/">

Documentation Central!</A>

attribute name

16 3 interactive web pages
16.3 Interactive Web Pages
  • When HTML was first developed, there was no way to

interact with the information and pictures presented in

a web page. HTML is static.

  • As users have clamored for a more dynamic web,

new technologies were developed to accommodate these

requests: Java Applets (Sun Microsystems),

Active X (Microsoft)

Java Server Pages (JSP)

Java Applets

  • Java applet : A java program designed to be embedded

into on HTML document, transferred

over the Web, and executed in a browser.

16 3 interactive web pages45
16.3 Interactive Web Pages

Java Applets

  • An applet is embedded into an HTML document

using the APPLET tag

<APPLETcode="MyApplet.class" width=250 height=150 >

</APPLET>

  • Java programs are compiled into Bytecode, a low-level

representation of a program that is not the machine code

for any particular type of CPU

  • Java applets are restricted as to what they can do
    • The Java language has a carefully constructed security

model

    • An applet, for instance, cannot access any local files

or change any system settings

16 3 interactive web pages46
16.3 Interactive Web Pages

Java Server Pages

  • A Java Server Page, or JSP, is a web page that has JSP

scriptlets embedded in an HTML document.

  • Scriptlet : A portion of code embedded in an HTML

document designed to dynamically contribute

to the content of the Web page.

  • A JSP scriptlet is encased in special tags beginning with <% and ending with %>

<H3>

<% out.printIn(“hello there”); %>

</H3>

16 3 interactive web pages47
16.3 Interactive Web Pages

Java Server Pages

  • Note that JSPs are executed on the server side where the

web page resides.

  • By the time it arrives at your computer, all active

processing has taken place, producing a static

(though dynamically created) web page.

  • JSPs are particularly good for coordinating the interaction

between a web page and an underlying database.

16 4 xml
16.4 XML
  • HTML has a predefined set of tags and each tag has its

own meaning. HTML specifies how the information in

a web page should be formatted, but doesn’t really

indicate what the information represents. There is nothing

about HTML tags that describes the true content of a

document.

  • The Extensible Markup Language, or XML, allows the

creator of a document to describe its contents by defining

his or her own set of tags.

  • Metalanguage: A language for talking about, or

defining, other languages

XML is a metalanguage.

16 4 xml49
16.4 XML

Fig. 16.5 An XLML document containing data about books

16 4 xml50
16.4 XML
  • Document Type Definition (DTD) : A specification of

the organization of the document

  • The structure of a particular XML document is described

by its corresponding DTD document

Fig. 16.6 The DTD document corresponding to the XML books document

16 4 xml51
16.4 XML
  • XML represents a standard format for organizing data

without tying it to any particular type of output.

  • Extensible Stylesheet Language (XSL) : A language for

defining transformations from XML documents

to other output formats.

Fig. 16.7 An XML document can be transformed into many output formats

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