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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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Chapter 15

Networks


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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


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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


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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.


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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


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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.


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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


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15.1 Networking

Types of Networks

Fig. 15.2 Various network topologies


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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


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15.1 Networking

Types of Networks

Fig. 15.1 Local-area networks connected across a distance

to create a wide-area network


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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.


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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


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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


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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


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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


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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


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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


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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.


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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.


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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.


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15.2 Open Systems & Protocols

High-Level Protocols

Fig. 15.7Some protocols and the ports they use


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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


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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.


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15.2 Open Systems & Protocols

Firewalls

Fig. 15.8 A firewall protecting a LAN


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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


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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


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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.


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15.3 Network Addresses

Domain Name System

Fig. 15.10 Top-level domains,

including some relatively new ones


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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


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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.


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Chapter 16

The World Wide Web


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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


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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


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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


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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


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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.


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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.


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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 .


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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.


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16.2 HTML

Fig. 16.2A marked-up document


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16.2 HTML

Fig. 16.3The Student Dynamics Web page

as displayed in Netscape Navigator


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16.2 HTML

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


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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


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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.


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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


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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>


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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.


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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.


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16.4 XML

Fig. 16.5 An XLML document containing data about books


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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


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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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