Unit 2: Web Foundations

Text book: Web Technology Theory & Practice

by M.Srinivasan

Internet:

• Internet is a network of networks.

• The Internet is a global system of interconnected computer networks that use the standard Internet Protocol Suite (TCP/IP) to serve billions of users worldwide.

A peek into the history of the Web:

Internet Applications:

1. Communication Services

2. Information retrieval Services

3. Web Services

1. Communication Services: E-mail : Used for sending messages Usenet : a network that provides users with discussion

groups. E-Chatting : like talking, except that one type words rather

than speak them. Telnet : Protocol that connects the user to a remote machine

which may be located anywhere on the internet. Internet Telephony : use of internet for voice communication

(protocol used is VOIP-Voice Over Internet Protocol). Video Conferencing : allows a group of users located

around the globe to talk and interact with each others.

Internet Applications: (Contd.)

2. Information retrieval Services: File Transfer Protocol : allows users to transfer files,

from one computer to another. Gopher : Its an information retrieval tool. Veronica : tool for searching the items on gopher menus

throughout the Internet.

3. Web Services: E-Govt : facilitates the operation of government services. E-Commerce : buying or selling of products or services

over the internet. E-News : electronic form of news found on many websites

meant for news. E-Recruitment : its an online recruitment task involving

finding, attracting, assessing interviewing and hiring new personnel.

E-Education : training people through online classes.

NETWORK

A Network is a series of computers connected together physically or virtually.

TYPES OF NETWORKS

Mainly 3 types:

1. Local area networks: generally called LANs, are privately-owned networks within a single building or campus of up to a few kilometers in size.

2. Metropolitan Area Network or MAN: covers a city. The best-known example of a MAN is the cable television network available in many cities.

3. Wide Area Network, or WAN: spans a large geographical area, often a country or continent.

TCP/IP vs. OSI

• Both are network architectures, the OSI contains 7 layers and the TCP/IP contains 4 layers. Each layer has a set of predefined tasks to do.

OSI TCP/IP

Application Layer Application Layer

Presentation Layer

Session Layer

Transport LayerInternet Layer

Network LayerNetwork Layer

Data link Layer Host to Network Layer

Physical Layer

IPv6

• IPv6 supports 128 bit IP address against its previous version (IPV4) which supports 32 bit IP address.

• With IPv6, we have the following advantages: Additional address space Dynamic auto configuration Simpler header format Enhanced security Interoperability with IPv4

HIGHER LEVEL PROTOCOLSSome of the higher level protocols are:

1. FTP

2. Telnet

3. E-mail related protocols SMTP IMAP MIME

4. HTTP

HIGHER LEVEL PROTOCOLS (Contd.)1. FTP It uses port no 21 to respond to client request. The address starts

with: ftp:// It is used to transfer files on the internet. It works on a client server model. The client authenticates with a

FTP server which usually stores the files. Both text and binary files are possible to be handled.

It can work both directions – meaning it can be used for upload as well as download, provided access is allowed.

The following diagram summarizes the communication between them:

HIGHER LEVEL PROTOCOLS (Contd.)

2. TelnetTelnet (stands for Terminal network) connects the user to a remote machine which may be located anywhere on the internet and allows user to type and execute commands on the remote machine.

HIGHER LEVEL PROTOCOLS (Contd.)

E-mail related Protocols:

1.SMTP

It stands for Simple Mail Transfer Protocol. It is a text-based protocol. It works across TCP/IP from ports 25 or 587. The mail server uses SMTP to send and receive messages.

The client uses SMTP to send mails using a browser or software like Microsoft Outlook. For receiving, typically the client uses the POP (Post Office Protocol) or IMAP protocol over the web.

HIGHER LEVEL PROTOCOLS (Contd.)

E-mail related Protocols: (Contd.)

2. IMAP

IMAP stands for Internet Message Access Protocol. It is meant for accessing E-Mails through the internet. It was designed to work even on low bandwidth speeds, by downloading only the header – the user has the option to download in full only those messages that are required. The advantages is that unimportant messages like span or anonymous messages need not be downloaded.

Advanced versions of IMAP (like IMAP4) has facilities to search through the body of mail messages for keywords which will further help in filtering messages.

3. MIME

REFER CHAPTER 1 NOTES

HIGHER LEVEL PROTOCOLS (Contd.)

4. HTTP

Uses Port no-80 to respond to client request.

HTTP has the following features: It is a text-based protocol. It is connectionless. It works by making a connection, sending a request then server responds and the connection is closed. There is a limit of one request per connection. It is a stateless protocol. It does not retain any information about the session between the connection. It is simple and can handle any number of requests efficiently. It is flexible. Allows transmission of different types of data. It is platform-neutral. This means, the request could come from any device which can make a web connection (like mobiles, tablets, iphones, iPods, etc)

HIGHER LEVEL PROTOCOLS (Contd.)

HTTP (Contd.)

Below diagram shows a simplified web communication scenario between client and server using HTTP (refer - Phases of HTTP - chapter 1 for description):

HTTP (Contd.)

Short description of methods used in HTTP communication (Details regarding working of GET and POST – refer CGI for Perl):

IMPORTANT COMPONENTS OF THE WEB

1. Firewalls

2. Routers

3. Browsers

4. Browser Caches

1. Firewalls:

IMPORTANT COMPONENTS OF THE WEB (Contd.)

2. Routers:

They enroute messages to the destination system using the shortest possible route. Their function include route calculation, routing table management, and execution of routing protocols.

They also does the following tasks:

3. Browser: Refer chapter 1.

4. Browser caches:

Caches are meant to increase web speed by reusing information already retrieved. The browser cache has files stored in the temporary internet files folder.

WEB SEARCH ENGINES

APPLICATION SERVER:

An application server (or App server) is a superset of web server. It deploys and manages the web applications on the server.

Following are some of the popular application servers:

JBoss (open source category)

GlassFish (from Oracle)

WebLogic (from Oracle)

WebSphere (from IBM)

SAP Netweaver (for running SAP)