fwt1 internet technology

8/4/2019 FWT1 Internet Technology

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Internet Technology

Subject InchargePratidnya S. Hegde Patil

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Subject Topics Basics of Internet & Web Technology HTML HTML Forms with JavaScript JavaScript CSS Java Applets & ActiveX Controls ASP CGI with Perl Cookies Ecommerce Security

HTML & WebDesign Tips &Techniques,Kris Jamsa,Konrad King,Andy Anderson

Web Applications, Craig Knuckles, David Yuen


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The Inter-network is a big network

of networks.

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Internet The Internet is a massive network of networks, a

networking infrastructure.

No one owns the Internet. Every person whomakes a connection owns a slice of the Internet.There is no central administration of Internet.

It connects millions of computers togetherglobally, forming a network in which any

computer can communicate with any othercomputer as long as they are both connected tothe Internet. Information that travels over theInternet does so via a variety of languagesknown as protocols.


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Need for Internet

Proprietary computers forming islands ofnetworks.

Need of people grew with time so that a usernetwork A to communicate to user on network B.

There should be a way of communicationbetween (compatibility). Eg : Network of IBMcomputer were unknown entity to a network ofHP computers.

All networks connected through some backbone

network.

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What is an Internet ?

A community of people

Who use and develop the networks

A collection of resources

That can be reached from those networks.

A setup to facilitate collaboration

Among members of the research and

educational communities, world wide. The connected networks use the TCP/IP

protocol.


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Client/Server Architecture

Numerous applications run in a client/server environment,this means that client computers (computers formingpart of the network) contact a server, generally a verypowerful computer in terms of input/output, which providesservices to the client computers. These services areprogrammes which provide data such as the time, files, aconnection, etc.

The services are used by programs client programs whichrun on client computers. Designed to run on a clientcomputer, capable of processing data received from a

server (in the case of the FTP client we are dealing withfiles whereas for the email client we deal with email).

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Advantages of Client/Server Model Centralised resources: given that the server is the centre of the

network, it can manage resources that are common to all users,for example: a central database would be used to avoid problemscaused by redundant and inconsistent data.

Improved security: as the number of entry points giving accessto data is not so important.

Server level administration: as clients do not play a major rolein this model, they require less administration.

Scalable network: thanks to this architecture it is possible toremove or add clients without affecting the operation of thenetwork and without the need for major modification.

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Disadvantages of Client/Server

Model

Increased cost: due to the technical complexityof the server.

A weak link: the server is the only weak link inthe client/server network, given that the entirenetwork is built around it! Fortunately, the serveris highly fault tolerant (primarily thanks to theRAID system).

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Client/Server system operation

The client sends arequest to the serverusing its IP address andthe port, which isreserved for a particularservice running on theserver.

The server receives therequest and respondsusing the client IPaddress and port.

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2 Tier Architecture

2-tier architecture is usedto describe client/serversystems where the clientrequests resources and theserver responds directly tothe request, using its ownresources.

The server does not call onanother application inorder to provide part of the

service.

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3 Tier Architecture In 3-tier architecture, there is

an intermediary level,meaning the architecture isgenerally split up between:

A client, i.e. the computer,which requests the resources,equipped with a user interface(usually a web browser) forpresentation purposes

The application server (also

called middleware), whosetask it is to provide therequested resources, but bycalling on another server

The data server, whichprovides the applicationserver with the data itrequires

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Comparing 2 & 3 Tier Architectures

2-tier architecture is a client-server architecture where theserver is versatile, i.e. it is capable of directly responding toall of the client's resource requests.

In 3-tier architecture however, the server-level applicationsare remote from one another, i.e. each server is specializedwith a certain task (for example: web server/databaseserver).

3-tier architecture provides: A greater degree of flexibility

Increased security, as security can be defined for each service, and at

each level Increased performance, as tasks are shared between servers

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Multi Tier Architecture

In 3-tier architecture, eachserver (tier 2 and 3) performsa specialized task (a service).

A server can therefore useservices from other servers inorder to provide its ownservice.

As a result, 3-tier architectureis potentially an n-tieredarchitecture

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TCP/IP Protocol

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The five-layer networking model for theinternet


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TCP/IP TCP/IP is the communication protocol for the internet.

TCP/IP defines the rule computers must follow tocommunicate with each other over the internet.

TCP/IP standard there are several protocols for handlingdata communication: TCP (Transmission Control Protocol) communication between

applications UDP (User Datagram Protocol) simple communication between

applications IP (Internet Protocol) communication between computers ICMP (Internet Control Message Protocol) for errors and

statistics DHCP (Dynamic Host Configuration Protocol) for dynamic

addressing

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TCP TCP is for communication between applications.

If one application wants to communicate with another viaTCP, it sends a communication request. This request mustbe sent to an exact address. After a "handshake" betweenthe two applications, TCP will set up a "full-duplex"communication between the two applications.

The "full-duplex" communication will occupy thecommunication line between the two computers until it is

closed by one of the two applications.

UDP is very similar to TCP, but simpler and less reliable.


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IP

Network layer protocol of internet isInternet Protocol (IP).

Its job is to provide a best-effort way totransport datagrams from source todestination, without regard to whether ornot these machines are on the samenetwork, or whether or not there are othernetworks in between them.

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IP Addresses

Every host & router on the Internet has an IPaddress, which encodes its network number andhost number.

All IP addresses are 32 bits long and are used inthe source address & destination address fields ofIP packets.

Those machines connected to multiple networkshave a different IP address on each network.


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Internet Control Message Protocol (ICMP)

The operation of the Internet is monitored closelyby the routers. When something unexpectedoccurs, the event is reported by the ICMP whichis also used to test the Internet.

Each ICMP message type is encapsulated in an IPpacket.

Messages like : DESTINATION UNREACHABLE,

TIME EXCEEDED, PARAMETER PROBLEM,REDIRECT etc.

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Applications of Internet1.Remote Login

TELNETRlogin

2.File Transfer and AccessFTP

TFTPNFS3.Electronic Mail

SMTPMIME

4.Internet ManagementSNMP

5.USENET NEWS


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Terminal Network Emulator (TELNET)

Allows a user at one site to establish a TCP connection to alogin server at another.

It then passes keystrokes from the users keyboard directlyto the remote computer as if they had been typed on akeyboard attached to the remote machine.

It also carries output from the remote machine back to theusers screen. The service is called transparent because itgives the appearance that he users keyboard and displayattach directly to the remote machine.

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TELNET Ex: when a user invokes TELNET, an application program

on the users machine becomes the client. The clientestablishes a TCP connection to the server over which theywill communicate. Once the connection has beenestablished, the client accepts keystrokes from the userskeyboard and sends them to the server, while itconcurrently accepts characters that the server sends backand displays them on the users screen. Then server mustaccept a TCP connection from the client, and then relaydata between the TCP connection and the local operatingsystem.


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Remote Login (Rlogin) Operating system derived from BSD UNIX includes a

remote login service, rlogin, that supports trusted hosts.

It allows system administrators to choose a set of machinesover which login names and file access protections areshared and to establish equivalences among user logins.

Users can control access to their accounts by authorizingremote login based on remote host and remote user name.Thus, it is possible for a user to have login name X on onemachine and Y on another, and still be able to remotelylogin from one of the machines to the other without typing

a password each time.

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File Transfer Protocol (FTP) For managing files across machines without having to establish a remote

session with Telnet. FTP enables you to transfer files back and forth,manage directories. FTP is not designed to enable access to anothermachine to execute programs, but it is the best utility for file transfers.

FTP uses two TCP channels. TCP port 20 is the data channel, and port 21 isthe command channel. FTP is different from most other TCP/IP applicationprograms in that it does use two channels, enabling simultaneous transferof FTP commands and data. It also differs in one other important aspect:FTP conducts all file transfers in the foreground, instead of the background.In other words, FTP does not use spoolers or queues, so you are watchingthe transfer process in real time. By using TCP, FTP eliminates the need toworry about reliability or connection management, because FTP can rely onTCP to perform these functions properly.


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Trivial File Transfer Protocol (TFTP) It differs from FTP in two primary ways: it does not log onto the remote

machine, and it uses the User Datagram Protocol (UDP) connectionlesstransport protocol instead of TCP. By using UDP, TFTP does not monitorthe progress of the file transfer, although it does have to employ morecomplex algorithms to ensure proper data integrity. By avoiding loggingonto the remote, user access and file permission problems are avoided.TFTP uses the TCP port identifier number 69, even though TCP is notinvolved in the protocol.

TFTP has few advantages over FTP. It is not usually used for file transfersbetween machines where FTP could be used instead, although TFTP isuseful when a diskless terminal or workstation is involved. Typically, TFTPis used to load applications and fonts into these machines, as well as forbootstrapping. TFTP is necessary in these cases because the disklessmachines cannot execute FTP until they are fully loaded with an operatingsystem. TFTP's small executable size and memory requirements make itideal for inclusion in a bootstrap, where the system requires only TFTP,UDP, and a network driver, all of which can be provided in a small EPROM.

It runs on top of UDP or any other unreliable packet delivery system,using timeout and retransmission to ensure that data arrives. The sendingside transmits a file in fixed size blocks and awaits an acknowledgementfor each block before sending the next. The receiver acknowledges eachblock upon receipt.

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Network File System (NFS)

NFS provides on-line shared file accessthat is transparent and integrated; manyTCP/IP sites use NFS to interconnect theircomputers file system.

From the users perspective NFS is almostinvisible. A user can execute an arbitrary

application program and use arbitrary filesfor input or output. The file namesthemselves do not show whether the filesare local or remote.


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Email System

Electronic mail is among the most widelyavailable application services. Like mostTCP/IP services, it uses the client-server

paradigm. The mail system buffers outgoingand incoming messages, allowing the transfer

from client and server to occur in

background.

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Electronic mail (email) Email systems consists of two subsystems :

user agents, which allow people to read and sendemail. They are local programs that provide interfacefor interacting with the email system.

message transfer agents, which move themessages from the source to the destination. They aresystem daemons that run in the background andmove email through the system.

Five basic functions:1. Composition : process of creating messages and answers.2.

Transfer : moving messages from the originator to therecipient.3. Reporting : telling the originator what happened to the

message.4. Displaying : Simple conversions and formatting required for

reading incoming messages.5. Disposition : Concerns what the recipient does with the

message after receiving it.


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Message Transfer

Establish a transport connectionfrom the source machine to thedestination machine and thenjust transfer the message

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Simple Mail Transfer Protocol (SMTP)

Simple ASCII protocol.

Within the Internet, email is delivered by havingthe source machine establish a TCP connection toport 25 of the destination machine. Listening tothis port is an email daemon that speaks SMTP.

This daemon accepts incoming connections and

copies messages into the appropriate mailboxes.If message not delivered, an error reportcontaining the first part of the undeliveredmessage is returned to the sender.


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Post Office Protocol (POP) Simple protocol used for fetching email from a remote

mailbox.

Ex : In many companies, users work at desktop PCs thatare not on the Internet and are not capable of sending orreceiving email from outside the company. Instead thecompany has one or more email servers that can send andreceive email.

Useful to only user having one workstation.

To send or receive messages, one must talk to an emailserver using some kind of delivery protocol.

The goal of POP is to fetch email from the remote mailboxand store it on the users local machine to be read later.

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Interactive Mail Access Protocol (IMAP)

A more sophisticated delivery protocol than POP.

It was designed to help the user who usesmultiple computers, perhaps a workstation in theoffice, a PC at home, and a laptop on the road.

The goal of IMAP is to maintain a central

repository that can be accessed from anymachine. Unlike POP, IMAP does not copy emailto users personal machine because the user canhave many access points.


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Distributed Mail System Protocol (DMSP)

Also known as PCMAIL.

It allows users to download email from theserver to a workstation, PC, or laptop andthen disconnect.

The email can be read and answered while

disconnected. When reconnection occurslater, email is transferred and the systemis resynchronized.

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Message Formats

Format of the email messages


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Multipurpose Internet Mail Extensions (MIME)

In the early days of the ARPANET, email consisted exclusively oftext messages written in English and expressed in ASCII. But forworldwide Internet, this approach is no longer adequate.

MIME uses the basic RFC 822 format (text format) but also addsstructure to the message body and defines encoding rules fornon-ASCII messages.

MIME messages can be sent using the existing mail programs andprotocols only the sending and receiving programs are changed.

Multipurpose Internet Mail Extensions is a standard used toencode data such as images as printable. MIME adds lines to theheader of an e-mail message to define the type of the data andencoding used. MIMEs mixed multipart type permits a singlemessage to contain multiple data types.

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Network Management

In addition to protocols that provide networklevel services and application programs that

use those services, an Internet needssoftware that allow managers to debug

problems, control routing and find computers

that violate protocol standards. Suchactivities are referred as InternetManagement.


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Simple Network Monitoring Protocol (SNMP)

It is a standard protocol used to monitor hosts, routers andthe networks to which they attach.

A router being managed must keep control and statusinformation that the manager can access.

For example, router keeps statistics on the status of itsnetwork interfaces, incoming and outgoing traffic, droppeddatagrams, and error messages generated. Although itallows a manager to access these statistics, SNMP does notspecify exactly which data can be accessed. Instead, aseparate standard specifies the details. Known as

Management Information Base (MIB), the standardspecifies the data items a host or router must keep and theoperations allowed on each.

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USENET NEWS

A newsgroup is a worldwide discussion forum onsome specific topic. People interested in thesubject can subscribe to the newsgroup.

Subscribers can use a special kind ofuser agent,a news reader, to read all the articles to thenewsgroup.

People can also post articles to the newsgroup.Each article posted to a newsgroup isautomatically delivered to all the subscribers,wherever they may be in the world.

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