bil 374 internet technologies

Dr. Ahmet Cengizhan DiricanBIL 374 Internet Technologies

1. Fundamentals

1-2Internet Technologies Dr. Ahmet Cengizhan Dirican

Internet History


Internet History

• Origins•ARPAnet - late 1960s and early 1970s

• Network reliability • For ARPA-funded research organizations

• BITnet, CSnet - late 1970s & early 1980s• email and file transfer for other institutions

•NSFnet - 1986 • Originally for non-DOD funded places• Initially connected five supercomputer centers• By 1990, it had replaced ARPAnet for non-military uses• Soon became the network for all (by the early 1990s)

•NSFnet eventually became known as the Internet


What is Internet?

• What the Internet is:• A world-wide network of computer networks• At the lowest level, since 1982, all connections use TCP/IP• TCP/IP (Transmission Control Protocol/Internet Protocol ) hides the differences among devices connected to the Internet .

• TCP/IP can be used directly to allow a program on one computer to communicate with a program on another computer via the Internet.

• In most cases, a higher-level protocol runs on top of TCP/IP. Nevertheless, it’s important to know that TCP/IP provides the low-level interface that allows most computers (and other devices) connected to the Internet to appear exactly the same.


International Internet Backbone (2009)


Global Internet Traffic Map (2010)


Partial Map of The Internet (2005)• Each line is

drawn between two nodes, representing two IP addresses.

• This is a small look at the map of the Internet in 2005.


Internet in Turkey

• Turkey has had public Internet access since 1993.

• The first available connections were dial-up.

• Cable Internet has been available since 1998 and ADSL since 2003.

• Now Turk Telecom ADSL24 is popular (1-16 Mbit/s).

• Internet Acces Dates of Some Intitutions in Turkey.• ODTÜ: 1993

• Ege Üniversitesi: 1994

• Bilkent: 1995

• Boğaziçi Üniversitesi: 1995

• İTÜ: 1996

• Turnet / Ulaknet (Ulakbim): 1996

• TTNet: Şubat 1998


Internet Protocols


Internet Protocols

• Internet Protocol (IP) Addresses

• Every node has a unique numeric address

• Form: 32-bit binary number

• New standard, IPv6, has 128 bits (1998)

• Organizations are assigned groups of IPs for their computers

• Problem: By the mid-1980s, several different protocols had been invented and were being used on the Internet, all with different user interfaces (Telnet, FTP, Usenet, mailto)Users were required to learn all the different interfaces to gain all the advantages of the Internet.Than, a better approach was developed the World Wide Web.


Domain Names (1/2)

• Form: host-name.domain-names

• First domain is the smallest; last is the largest

• Last domain specifies the type of organization

• Fully qualified domain name - the host name and all of the domain names

• DNS servers - convert fully qualified domain names which are given by users, to Ips

• Name servers serve a collection of machines on the Internet and are operated by organizations that are responsible for the part of the Internet to which those machines are connected.


Domain Names Servers


The World-Wide Web


The World-Wide Web

• A possible solution to the proliferation of different protocols being used on the Internet; a new protocol for the internet, as well a system of document access to use it..

• Origins• Tim Berners-Lee at CERN proposed the Web in

1989• Purpose: to allow scientists to have access to

many databases of scientific work through their own computers


The World-Wide Web

• The proposed new system was designed to allow a user anywhere on the Internet

• to search for and

• retrieve documents

• from databases on any number of different document-serving computers connected to the Internet.

• Document form: hypertext

• Pages? Documents? Resources?• We’ll call them documents

• Hypermedia – more than just text – links, images, sound, etc.


The World-Wide Web

• In an abstract sense,

• the Web is a vast collection of documents,

• some of which are connected by links.

• These documents

• are accessed by Web browsers,

• and are provided by Web servers.


The World-Wide Web

• Web or Internet?

• The Internet is a collection of computers / networks and other devices connected by equipment that allows them to communicate with each other.

• The Web is a collection of software and protocols that has been installed on most, if not all, of the computers on the Internet.

• The Web uses one of the protocols, http, that runs on the Internet--there are several others (telnet, mailto, etc.)

• The Web constitutes an important part of the internet, though, the Internet can continue to function and be usefull without the Web.


Web Browsers (Clients) and Web Servers


Client and Server

• Clients and Servers are programs that communicate with each other over any network and the Internet.

• A Server runs continuously, waiting to be contacted by a Client

• Each Server provides certain services

• Services include providing web pages for Web servers

• A Client will send a message to a Server requesting the service provided by that server

• The client will usually provide some information, parameters, with the request


Web Browsers

• Browsers are clients - always initiate, servers react (although sometimes servers require responses)

• Mosaic - NCSA (Univ. of Illinois), in early 1993• First to use a GUI, led to explosion of Web use• Initially for X-Windows, under UNIX, but was ported to

other platforms by late 1993• Most requests are for existing documents, using HyperText

Transfer Protocol (HTTP)• But some requests are for program execution, with

the output being returned as a document


Web Servers

• Provide responses to browser requests, either • existing documents or • dynamically built documents

• Browser-server connection is now maintained through more than one request-response cycle.

• All communications between browsers and servers use Hypertext Transfer Protocol (HTTP)


Web Server Operation

•Web servers run as background processes in the operating system

–Monitor a communications port on the host, accepting HTTP messages when they appear

• All current Web servers came from either

1.The original from CERN

2.The second one, from NCSA


Web Server Operation Details

• Web servers have two main directories:

1.Document root (servable documents)

2.Server root (server system software)

• Document root is accessed indirectly by clients

– Its actual location is set by the server configuration file

–Requests are mapped to the actual location

• Virtual document trees

• Virtual hosts • Proxy servers• Web servers now support other Internet protocols


Web Server Operation : Apache

•Apache (open source, portable, fast, reliable)•Operation is maintained through a configuration file.–Directives (operation control):

ServerName

ServerRoot

ServerAdmin,

DocumentRoot

Alias

Redirect

DirectoryIndex

UserDir


Web Server Operation : IIS

- The Web Server solution of Microsoft.

- The second most popular web server.

- Operation is maintained through a program with a GUI interface.

- Designed and available to work only within the Windows.

- Although this limits the deployment platforms for IIS-based Web

services, it also provides a number of benefits, including

- greater cooperation with the host operating system

- easier management and control through a variety of

standard OS tools and utilities.


Uniform Resource Locators (URLs)


URLs

• Uniform (or universal) resource locators (URLs) are used to identify documents (resources) on the Internet.

• There are many different kinds of resources, identified by different forms of URLs.

• General form:

scheme:object-address

• The scheme is often a communications protocol, such as telnet or ftp

• For the http protocol, the object-address is: fully qualified domain

name/doc path

• //fully-qualified-domain-name/path-to-document

• For the file protocol, only the doc path is needed

• file://path-to-document


URLs

• Host name may include a port number, as in zeppo:80 (80

is the default, so this is silly)

• URLs cannot include spaces or any of a collection of other

special characters (semicolons, colons, ...)

• The doc path may be abbreviated as a partial path

• The rest is furnished by the server configuration

• If the doc path ends with a slash, it means it is a directory

• file: http://www.w3schools.com/html/html_xhtml.asp

• Directory: http://www.hostway.com/web-resources/


Multipurpose Internet Mail Extentions (MIME)


Multipurpose Internet Mail Extensions (MIME)

• Originally developed for email

• Used to specify to the browser the form of a file returned by the server (attached by the server to the beginning of the document)

• Type specifications

• Form:

type/subtype

• Examples: text/plain, text/html, image/gif, image/jpeg


Multipurpose Internet Mail Extensions (MIME)

• Server gets type from the requested file name’s suffix (.html implies text/html)

• Browser gets the type explicitly from the server

• Experimental types

• Subtype begins with x-

• e.g., video/x-msvideo

• Experimental types require the server to send a helper application or plug-in so the browser can deal with the file


HyperText Transfer Protocol (HTTP)


The HyperText Transfer Protocol

• HTTP is an Applicaiton Layer Protocol for disributed, collobrative, hypermedia information systems.

• The protocol used by ALL Web communications

• Request Phase

• Form:

HTTP method domain part of URL HTTP ver.

Header fields

blank line

Message body

• An example of the first line of a request:

GET /degrees.html HTTP/1.1


The HyperText Transfer Protocol: Methods

• GET - Fetch a document

• POST - Execute the document, using the data in body

• HEAD - Fetch just the header of the document

• PUT - Store a new document on the server

• DELETE - Remove a document from the server


HTTP Headers

• Four categories of header fields:

General, request, response, & entity

• Common request fields:

Accept: text/plain

Accept: text/*

If-Modified_since: date

• Common response fields:

Content-length: 488

Content-type: text/html

- Can communicate with HTTP without

a browser

> telnet blanca.uccs.edu http

GET /respond.html HTTP/1.1

Host: blanca.uccs.edu


HTTP Response

• Form:

Status line

Response header fields

blank line

Response body

• Status line format:

HTTP version status code explanation

• Example: HTTP/1.1 200 OK

(Current version is 1.1)

Status code is a three-digit number; first digit specifies the general status

1 => Informational

2 => Success

3 => Redirection

4 => Client error

5 => Server error

The header field, Content-type, is required


Security


Computer and Security• The objective of computer security includes protection of

information and property from theft, corruption, or natural disaster, while allowing the information and property to remain accessible and productive to its intended users.

• The term computer system security means the collective processes and mechanisms by which sensitive and valuable information and services are protected from publication, tampering or collapse by unauthorized activities or untrustworthy individuals and unplanned events respectively.

• Internet and the Web are fertile grounds for security problems.

• Client – Server communication

• The larger/complexer the system, the bigger the problems


Web Security (1/2)• One aspect of Web security is the matter of getting one’s

data from the browser to the server and having the server deliver data back to the browser without anyone or any device intercepting or corrupting those data along the way.

• Example: Transmitting the credit card number• Privacy—it must not be possible for the credit card number to be

stolen on its way to the company’s server.

• Integrity—it must not be possible for the credit card number to be modified on its way to the company’s server.

• Authentication—it must be possible for both the purchaser and the seller to be certain of each other’s identity.

• Nonrepudiation—it must be possible to prove legally that the message was actually sent and received.

• Solution: Encryption


Web Security (2/2)• Other problem: the intentional and malicious destruction of

data on computers attached to the Internet.

• DoS Attacks

• Viruses : the ILOVEYOU virus, and the CodeRed

• Worms: the Blaster worm

• Solution: Antivirus softwares, Firewalls, Using captcha (Completely Automated Public Turing test to tell Computers and Humans Apart), Conscious Users


The Web Programmer’s Toolbox

• Document languages and programming languages that are the building blocks of the web and web programming.

XHTMLPlug-insFiltersXMLJavascriptJava, Perl, Ruby, PHP


Client-side or Server-side• Web programs and scripts are divided into two

categories—client side and server side

• —according to where they are interpreted or executed.

• XHTML and XML are client-side languages;

• PHP and ASP are server-side languages;

• JavaScript is most often a client-side language, although it can be used for both.


HTML• HTML is a language for describing web pages.

• stands for Hyper Text Markup Language

• is not a programming language, it is a markup language

• A markup language is a set of markup tags

• HTML uses markup tags to describe web pages

• HTML markup tags are usually called HTML tags

• HTML tags are keywords surrounded by angle brackets like <html>

• HTML tags normally come in pairs like <b> and </b>


Why XHTML• Many pages on the internet contain "bad" HTML

• XML is a markup language where documents must be marked up correctly and "well-formed".

• Today's market consists of different browser technologies. Some browsers run on computers, and some browsers run on mobile phones or other small devices. Smaller devices often lack the resources or power to interpret a "bad" markup language.

• Therefore - by combining the strengths of HTML and XML, XHTML was developed. XHTML is HTML redesigned as XML.


XHTML

• XHTML stands for EXtensible HyperText Markup Language

• XHTML is almost identical to HTML 4.01

• XHTML is a stricter and cleaner version of HTML 4.01

• XHTML is HTML defined as an XML application

• XHTML is supported by all major browsers.


Creating XHTML documents

• XHTML editors - make document creation easier

• Shortcuts to typing tag names, spell-checker,

• WYSIWYG (Wizzy-Wig)) XHTML editors

• What You See is What You Get

• Need not know XHTML to create XHTML documents


Plugins and Filters for XHTML

• Plugins

• Integrated into tools like word processors, effectively

converting them to WYSIWYG XHTML editors

• Filters

• Convert documents in other formats to XHTML


Plugins and Filters: Advantages and Disadvantages

• Advantages of both filters and plug-ins:

• Existing documents produced with other tools can be

converted to XHTML documents

• Use a tool you already know to produce XHTML

• Disadvantages of both filters and plug-ins:

• XHTML output of both is not perfect - must be fine tuned

• XHTML may be non-standard

• You have two versions of the document, which are difficult

to synchronize


CSS• Cascadin Style Sheets

• Provides the means to control and change presentation of HTML documents.

• Not technically HTML, but can be embedded in HTML documents.

• More capable than HTML in enrching the document view.

• Style sheets allow you to impose a standard style on a whole document, or even a whole collection of documents.


XML

• XML (Extensible Markup Language)• Derived from Standard Generalized Markup Language (SGML)

• Open technology for electronic data exchange and storage

• Create other markup languages to describe data in structured manner

• XML documents• Contain only data, not formatting instructions

• Highly portable

• XML parser

• Support Document Object Model or Simple API XML

• Document Type Definition (DTD, schema)

• XML document can reference another that defines proper structure

• XML-based markup languages• XML vocabularies


JavaScript

• A client-side HTML-embedded scripting

language

• Only related to Java through syntax

• Dynamically typed and not object-oriented

• Provides a way to access elements of HTML

documents and dynamically change them


VBScript

– Subset of Microsoft Visual Basic– Specific to Internet Explorer– JavaScript has replaced VBScript as standard– Most commonly used alongside ASP

• Active Server Pages• VBScript is case-insensitive

• Not necessary to declare a data type• Limited use in modern web programming.


CGI (1/2)• The Common Gateway Interface (CGI) is a protocol

describing a standard way of providing server-side active web content.

• Standard interface through which users interact with applications on Web servers

• Provides way for clients to interact with applications on Web server

• CGI script

• Can be written in many different languages, including Perl

• Data from forms will be encoded in a request sent do the server

• This data can be used by a CGI program.


CGI (2/2)

Data path of a typical CGI-based application.


Perl

• Provides server-side computation for HTML documents,

through CGI (Communication Gateway Interface)

• Perl is good for CGI programming because:

• Direct access to operating systems functions

• Powerful character string pattern-matching operations

• Access to database systems

• Perl is highly platform independent, and has been ported to

all common platforms

• Perl is not just for CGI


ASP• ASP is a server-side scripting technology developed by

Microsoft.

• With ASP you can create dynamic web pages by putting script code inside your HTML pages.

• The code is executed by the web server before the page is returned to the browser.

• Both VBScript and JavaScript can be used.

• ASP is a standard component in Windows 95,98, 2000, and XP but not Vista, 7 and 8. Nevertheless, it can be activated on all computers running Windows.

• ASP code is contained between the tags <% and %>


PHP

• Originally called “Personal Home Page Tools”

• A server-side scripting language and alternative to CGI

• Similar to Perl and C

• Great for form processing and database access through the Web

• Open-source:Anyone may view, modify and redistribute source code and supported freely by community

• PHP supports many databases, such as MySQL, Informix, Oracle, Sybase, Solid, PostgreSQL, Generic ODBC, etc.

• PHP code is contained between the tags <?php and ?>


Java (Applets, Servlets, JSP, JFS)

• General purpose object-oriented programming language

• Based on C++, but simpler and safer

• Web solutions:

• Client side: applets

• Serve side: servlets, JSP


Java: Servlets• A servlet is a compiled Java class, an object of which is

executed on the server system when requested by the XHTML document being displayed by the browser.

• A servlet produces an XHTML document as a response,

• some parts of which are static and are generated by simple output statements,

• while other parts are created dynamically when the servlet is called.

• A servlet is a Java class designed to be run in the context of a special servlet container


Java: Servlet Sample


Java: JSP• JSP is a server-side technology much like ASP, developed

by Sun.

• JSP takes an opposite approach to that of servlets:• Instead of embedding XHTML in Java code that provides

dynamic documents, code of some form is embedded in XHTML documents to provide the dynamic parts ofa document.

• With JSP you can create dynamic web pages by putting Java code inside your HTML pages. The code is executed by the web server before the page is returned to the browser.

• Since JSP uses Java, the technology is not restricted to any server-specific platform.

• A Java Server Page is first converted to a servlet which is then operates as previously described


ASP.NET (1/2)• NET is a collection of technologies

• Run time environment, Library, Programming languages

• Independent from a specific programming language

• Promotes software reuse

• Include tools for porting, adapting existing software components

• Web services


ASP.NET (2/2)• ASP.NET documents extend the System.Web.UI.Page class

• Server-side technology that dynamically builds documents in response to client requests

• Can be used on a server to create Web applications

• Supports over 25 programming languages

• Object-oriented programming


Ajax• AJAX = Asynchronous JavaScript and XML.

• Ajax is not an API or a programming language

• Ajax aims to provide more responsive web applications

• In normal request/response HTTP cycles, the browser locks waiting for the response and an entire page must be displayed

• With Ajax, asynchronous requests may be made and responses are used to update part of a page

• User can continue to interact with a page while the request is in progress

• Less data needs to be transmitted

• Page update is quicker because only a part of a page is modified


Flash• Adobe Flash was created in 1996 as a way to display rich

media on a webpage. In the mid-90s, most websites were a collection of static pages that displayed only text and images.

• People were able to create moving animations and clickable interactive graphics that went beyond the capabilities of standard HTML and CSS.

• Quickly create rich interactive graphics using a timeline-based software tool.

• These documents are served by Web server to browsers, which use the flash player plug-in to display the documents.

• It’s a a cross-browser compatible tool that works the same on Internet Explore, Firefox, Mozilla, Opera and Chrome.

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