Tribhuvan University

ITC 201: Fundamentals of Computer

Communication and NetworksInternet It is the network of networks. It is started in 1960s till now. The internet is a group of two or more networks that are:

Interconnected physically

Capable of communicating and sharing data with each other

Able to act together as a single network.

In 1969, the Department of Defense (DOD), built a network called ARPANET (Advanced Research Projects Administration Network).

ARPANET was to enable sharing of data between various government-funded research centers. The centers included businesses and universities that were equipped with the latest computer technology at that time.

The ARPANET started with just four computers on the network. It connected University of California at Los Angeles, University of California at Santa Barbara, Stanford University (California), and the University of Utah in Salt Lake City.

By 1972, there were 40 different sites attached to ARPANET.

Internet AccessThe access can be done by telephone via Public Switched Telephone Network (PSTN).

Dial-up Connection

Connect to a local ISP. Access is either by way of SLIP (Serial Line Internet Protocol) or PPP (Point to Point Protocol)

Direct Connection

It is dedicated phone line, leased line. Four types of digital leased lines:

Integrated Services Digital Network (ISDN) can carry three or more signals at once using a technique called multiplexing. Need ISDN adapter instead of a modem at both ends. T-Carrier Lines Uses multiplexing so carries many signals. Many ISPs use T-1 lines which supports 24 signals. T-3 lines are equivalent to 28 T-1 lines. That is one T-3 line can support up to 672 signals.

Uses/Services of Internet

1. Electronic Mail (E-Mail)

UserName@DomainName

Username@host.subdomain.second-level-domainram@kcmit.edu.np kcmit.edu.np is the domain name.

Some of the popular email programs are Eudora, Pin and Outlook Express.

2. Telnet Telnet is the Internet tool for using one computer to access a second computer. Using Telnet, you can send commands that run programs and open text or data files. The Telnet program is a transparent window between your own computer and a distant host system- a computer that are logging on to. The computer is in a different physical place, but it is as if you are sitting in front of it and operating it. A Telnet connection sends input from keyboard to host and displays text from the host on your screen.

3. File Transfer Protocol (FTP)

Protocol is rules or standards that govern how computers share information. They are a set of conventions or standards followed by the industry. FTP is one of the most popular methods used for file transfers through the Internet. The reason for its popularity is that it has the capability to transfer files between different types of computers

There are varieties of files that are publicly available through anonymous FTP:

Shareware: software that you can use free for a trial period but then pay a fee for.

Freeware: completely free software, for example fonts, clipart and games.

Upgrades & Patches: upgrades to current software and fixes for software problems.

Documents: examples include research papers, articles and Internet documentation.

4. Search Engines

Even though the WWW simplifies accessing information, its vastness mark it a little difficult to find the relevant information quickly. To make searching easier, search engines were developed. Some of the popular search engines on the Web are:

Yahoo www.yahoo.com

Altavista www.altavista.com

5. World Wide Web (WWW)

The WWW is a system that has made it possible to access almost any document on the net. On the WWW, information is displayed in the form of Web Pages. The Web Pages can hold:

Formatted text

Pictures/images

Audio

Video

This makes the information attractive and easy to use. Web pages also contain hyperlinks. Hyperlinks are text or other objects that are linked to other pages that hold related information. Text that is hyperlinked to another document is underlined and pictures that are hyperlinked may be heavily outlined.

6. BrowsersA browser is the software that is used to view Web pages. They are of two types:

Text based browsers

These browsers only show textual information. They are not equipped to show graphics, movies and sounds. However, they make it easy to pick and follow links by selecting the appropriate highlighted text. For example: Lynx.

Graphical browsers

All graphical Web browsers allow the user to just point and click to access information. They have the capability to support hypermedia i.e. sounds, movies, formatted text and graphics. The most popular graphical browsers are: Netscape Navigator and Internet Explorer

7. E-Commerce

E-commerce stands for electronic commerce. With the Internet, the customers can view the available products and/or services on-line; select the product(s) that he wants to buy and place an order for these products. Payment details are also specified on-line. Payment is typically done by specifying a Credit Card number. The customer is charged on this credit card for the purchases made and will pay for them when he receives the credit card bill.

It meets many of their needs, including:

Advertising and marketing

Research and development

Customer support

Supplying information

Taking orders

On-line surveys

Recruitment

Selling

The commercial users of the Internet are from various industries like computer-related industries, oil companies, pharmaceutical companies, healthcare-related industries, financial services, banks and many more.

Many types of businesses have started appearing on the net. Some of them are:

Book sellers

Travel agencies

Courier companies

On-line shopping

E-magazines(electronic magazines)

It is a place where they can reach their customers, promote their products, and provide information to others. It provides a great many advantages.

8. Video Conferencing (real-time)

World Wide video conferencing is an emerging service on the Internet, which allows a group of users located around the globe to talk and interact with each other as if they were sitting and discussing in a single room. The parties interacting can see each other talking on their computer screen and can hear each others voice through a special audio device fixed in their computers

9. CHAT (real-time)The chat feature allows you to exchange typed messages with another person on the Internet. You can chat with one person at a time or with a group of people. You can also connect a camera and a microphone to your computer so that other people can see and hear you on their computer while you are chatting with them.

Business Use of InternetInternet is used to fulfill the following business needs:E-commerce

E- business

EDI (electronic data interchange)

E- supply

Online marketing

Online banking Electronic funds transfer

Online auctions

Intranet:

An "intranet" is the generic term for a collection of private computer networks within an organization. An "extranet" is a computer network that allows controlled access from the outside for specific business or educational purposes. Intranets and extranets are communication tools designed to enable easy information sharing within workgroups.

Advantages:

a rapid server system update

savings in terms of time and money

better communication between a companys various members and services

personalized solutions in accordance to your needs

no application on the client side, with the exception of the Internet browser

The main benefits of an intranet are:

better internal communications- corporate information can be stored centrally and accessed at any time

sharing of resources and best practice- a virtual community can be created to facilitate information sharing and collaborative working

improved customer service- better access to accurate and consistent information by your staff leads to enhanced levels of customer service

reduction in paperwork- forms can be accessed and completed on the desktop, and then forwarded as appropriate for approval, without ever having to be printed out, and with the benefit of an audit trail

Extranet:

A common extension to intranets, called extranets, opens this firewall to provide controlled access to outsiders.

Many schools and non-profit groups have deployed them, but an intranet is still seen primarily as a corporate productivity tool. A simple intranet consists of an internal email system and perhaps a message board service. More sophisticated intranets include Web sites and databases containing company news, forms, and personnel information. Besides email and groupwareapplications, an intranet generally incorporates internal Web sites, documents, and/or databases.

Most extranets use the Internet as the entry point for outsiders, a firewallconfiguration to limit access, and a secureprotocolfor authenticating users.

Advantages:Benefits of an extranet

moreintegrated supply chainsthrough the use of online ordering, order tracking and inventory management

reduced costsby making manuals and technical documentation available online to trading partners and customers

more effectivecollaborationbetween business partners - perhaps members of a project team - by enabling them to work online on common documentation

improved business relationshipswith key trading partners because of the close collaborative working that extranets support

improved customer serviceby giving customers direct access to information and enabling them to resolve their own queries

asingle user interfacebetween you and your business partners

improving thesecurityof communications between you and your business partners, since exchanges can take place under a controlled and secure environment

shared newsof product development exclusively with partner companies

flexible workingfor your own staff, as an extranet allows remote and mobile staff to access core business information 24 hours a day, irrespective of location

Disadvantages

Extranets can be expensive to implement and maintain within an organization (e.g., hardware, software, employee training costs), if hosted internally rather than by anapplication service provider.

Security of extranets can be a concern when hosting valuable or proprietary information.

Firewall:A system designed to prevent unauthorizedaccessto or from a privatenetwork. Firewalls can be implemented in bothhardware andsoftware, or a combination of both. Firewalls are frequently used to prevent unauthorizedInternetusers from accessing private networks connected to the Internet, especiallyintranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specifiedsecuritycriteria.

There are several types of firewall techniques:

Packet filter

Application gateway

Circuit-level gateway

Proxy serverWhat is computer Networks?

A computer network is a system for communication among two or more computers. These networks may be fixed (cabled, permanent) or temporary (as via modems).

Computer networking is the scientific and engineering discipline concerned with communication between computer systems. Such networks involves at least two computers, which can be separated by a few centimeters (e.g. via Bluetooth) or thousands of kilometers (e.g. via the Internet)Advantage of Networks

Files can be stored on a central computer (the file server) allowing data to be shared throughout an organization.

Files can be backed up more easily when they are all on a central fileserver rather than when they are scattered across a number of independent workstations.

Networks also allow security to be established, ensuring that the network users may only have access to certain files and applications. Software and resources can be centrally managed.

Network versions of software often allow for their speedy installation on workstations from the file server.

Expensive devices such as laser printers or scanners can be shared.

Users can access their files from any workstation.

Communication channels:

It is the communication path between two devices. It is composed of one or more transmission media. Transmission media are one of the two types:

(1) Physical (Guided media) (2) Wireless (Unguided Media)Physical transmission media use wire, cables and other tangible materials to send communication signals.

Wireless transmission media send communications signals through the air or space using radio, microwave and infrared signals.

Physical Transmission media:

It includes:

Twisted pair

Co-axial cable

Optical fiber cable

Co-axial cable:

A: outer plastic sheathB: copper screenC: inner dielectric insulatorD: copper core

Coaxial cable is an electrical cable consisting of a round conducting wire, surrounded by an insulating spacer, surrounded by a cylindrical conducting sheath, usually surrounded by a final insulating layer.

It is used as a high-frequency transmission line to carry a high-frequency signal.

Coaxial cables may be rigid or flexible. Rigid types have a solid sheath, while flexible types have a braided sheath, both usually of thin copper wire

Thin coaxial: 10base2 is an example of thin coaxial cable which is capable of transmitting signal up to 185m.Thick: Example: 10base5 is an example of thick coaxial cable which is cable of transmitting signal up to 500m.Twisted Pair:

Twisted pair cabling is a common forms of wiring in which two conductors are wound around each other for the purposes of canceling out electromagnetic interference which can cause crosstalk.The greater the number of twists, the more crosstalk is reduced. It can transmit data several kilometers without amplifier. It has high error rate beyond 100m

They are classified into two categories:

1. UTP ( unshielded twisted pair)

2. STP (shielded twisted pair)

UTP: UTP cables are not shielded. This lack of shielding results in a high degree of flexibility as well as rugged durability. UTP cables are found in many Ethernet networks and telephone systems.STP: Twisted pair cables are often shielded to prevent electromagnetic interference. Because the shielding is made of metal, it also serves as a ground

STP cabling includes metal shielding over each individual pair of copper wires. This type of shielding prevents cable from external EMI (electromagnetic interferences).Optical Fiber: It is based on the principle of total internal reflection of light. It is at the one end of optical fibre to accept electrical signal and convert it into light pulses. The presence of pulse indicates a 1 bit and absence of pulse indicates 0 bits. It contains the following components:

Core: It is the innermost part of fibre made up of glass.

Cladding: Glass cladding covers core. Its refractive index is less than core.

Jacket:It is an outermost PVC( polyvinoyl chloride) covering of cladding

Wireless transmission Media: Following are different types of wireless transmission media:

1. Microwaves

2. Satellite

3. Infrared

4. Bluetooth

Microwaves: Microwaves are radio waves that provie high speed signal transmission. Microwaves transmission involves sending signals from one microvwave staion to another. It contains antenna, tranceiver and other equipment necessary for microwave communicatons.Microwaves sometimes called fixed points wireless.

Satellite: In popular usage, the term satellite normally refers to an artificial satellite, which would be a man-made object that orbits the Earth (or another body)

Satellite links uses microwaves frequencies. Satellite contains amplifier that amplify frequencies coming from earth stations.

A major drawback of the satellite communication is high cost of installing satellite in its orbit. Three satellite spaced at equal interval on120 angular degree can give coverage of entire globe.

Infrared:It is the type of electromagnetic wave of large wavelength and small frequencies than visible light. Its frequencies are low. IR data transmission is also employed in short range communicational among computer peripherals.

It is used in optic fibre communication, wireless LAN, computer and printers & in many other electronic devices.

Bluetooth: Bluetooth is a radio standard and communications protocol primarily designed for low power consumption, with a short range (power class dependent: 1 meter, 10 meters, 100 meters) based around low-cost transceiver microchips in each device.

Bluetooth lets these devices communicate with each other when they are in range. The devices use a radio communications system, so they do not have to be in line of sight of each other, and can even be in other rooms, so long as the received power is high enough

Types of computer Networks: Computer networks may be classified into two types:

1. On the basis of architecture:

a. Peer to peer

b. Client server

c. Hybrid

2. on the basis of geographical location:

a. LAN (Local Area Networks)

b. WAN (Wide area networks)

c. MAN (Metropolitan area networks)

Peer to Peer (P2P): A peer-to-peer (or P2P) computer network is a network that relies primarily on the computing power and bandwidth of the participants in the network rather than concentrating it in a relatively low number of servers.

Such networks are useful for many purposes. Sharing content files containing audio, video, data or anything in digital format is very common, and real time data, such as telephony traffic, is also passed using P2P technology.

A pure peer-to-peer network does not have the notion of clients or servers, but only equal peer nodes that simultaneously function as both "clients" and "servers" to the other nodes on the network

Peers act as equals, merging the roles of clients and server

There is no central server managing the network

There is no central router

Advantages:

Easy to install and configure

Individual users control their own shares resources

Inexpensive to operate

No additional hardware and software beyond a suitable operating system is needed

No dedicated administrated are required.

Disadvantages:

Network security applies only to a single resource at a time

Each machine must be backed up individually to protect all shared data.

There is no centralized organizational scheme to locate or control access to data

Client-Server

Client-server is a network architecture which separates the client (often a graphical user interface) from the server. Each instance of the client software can send requests to a server or application server. There are many different types of servers; some examples include: a file server, terminal server, or mail server.

The term server is most commonly applied to a complete computer system today, but it is also used occasionally to refer only to the hardware or software portions of such a system.

Server software generally, but not always, runs on powerful computers dedicated for exclusive use to running the business application. Client software on the other hand generally runs on common PCs or workstations.

Properties of a server:

Passive (Slave)

Waiting for requests

On requests serves them and send a reply

Properties of a client:

Active (Master)

Sending requests

Waits until reply arrives

Advantages:

Simplified user accounts, security, and access controls to simplify network administration

Single password for network login delivers access to all

More powerful equipment means more efficient access to network resources.

Disadvantages:

At worst, server failures leads to whole network failure

Dedicated hardware and special software (Network Operating Ssystem: NOS) add to the cost.

Increases expenses, it may need system administrator to handle.

Hybrid networks:

They are the combination of the cleint-server & peer-to-peer networks.

On the basis of geographical locatoin:

LAN(Local Area Networks): A Local Area Network (LAN) is a computer network covering a small local area, like a home, office, or small group of buildings such as a home, office, or college. Current LANs are most likely to be based on switched Ethernet or Wi-Fi technology running at 10, 100 or 1,000 Mbit/sThe defining characteristics of LANs in contrast to WANs (wide area networks) are:

a) much higher data rates,

b) smaller geographic range - at most a few kilometers and

c) they do not involve leased telecommunication lines. "LAN" usually does not refer to data running over local analog telephone lines, as on a private branch exchange (PBX).

d) Inexpensive medium of data transmission

Advantages:

1. Highly reliable:failure of one computer in the networks does not effect the functioning for other computers.

2. Addition of new computer to networks is easy.

3. high rate of data transmission is possible.

4. Computer can share resources like: printer, CDROM and magnetic disk.

Disadvantages:

1. If the communication line fails the entilre network system breaks down.

2. User authority and users identification is poor.

WAN (Wide Area Network): A wide area network or WAN is a computer network covering a wide geographical area, involving a vast array of computers. WANs are used to connect local area networks (LANs) together, so that users and computers in one location can communicate with users and computers in other locations. Many WANs are built for one particular organization and are private. Others, built by Internet service providers(ISP), provide connections from an organization's LAN to the Internet

Difference between LAN and WAN:

LAN

1. Computers and peripherals are in physical contact to each other.

2. The data transfer speed: 0.1 to 1000 Mbps & it has low error rate.

3. Economic

WAN

1. Computers and peripherals are not in physical contact to each other.

2. Data transfer speed: 1800 to 9600 bps. It has high error rate.

3. Not economic compared to LAN

MAN (Metropolitan Area Networks)MANs are large computer networks usually spanning a campus or a city. They typically use wireless infrastructure or optical fiber connections to link their sites.

For instance a university or college may have a MAN that joins together many of their local area networks (LANs) situated around site of a fraction of a square kilometer.Specifically, this type of MAN is known as a campus area network.

Topology:

A network topology is the pattern of links connecting pairs of nodes of a network. So It is a physical layout of the networks computers, terminals, and links. The different network topologies are:

1. Star

2. Ring

3. Bus

4. Mesh

5. Tree

6. Hybrid

Ring:

Figure: Ring network layout.A ring network is a topology of computer networks where each node is connected to two other nodes, so as to create a ring.

Disadvantage:

if one of the nodes in the network breaks down then the entire network will break down with it as it requires a full circle in order to function

inefficient when compared to Star networks because data must travel through more points before reaching its destination.

Communication delay is the directly proportional to number of node.

Bus:

A bus network is a network architecture in which a set of clients are connected via a shared communications line, called a bus.

Bus networks are the simplest way to connect multiple clients, but often have problems when two clients want to transmit at the same time on the same bus.Advantages

Easy to implement and extend

Well suited for temporary networks (quick setup)

Typically the cheapest topology to implement

Disadvantages

Difficult to administer/troubleshoot

Limited cable length and number of stations

A cable break can disable the entire network

Maintenance costs may be higher in the long run

Low security

Star:

Star networks are one of the most common computer network topologies. In its simplest form, a star network consists of one central switch, or hub computer which acts as a router to transmit messages.

Advantages

Easy to implement and extend, even in large networks

Well suited for temporary networks (quick setup)

The failure of a non-central node will not have major effects on the functionality of the network.

No problems with collisions of Data

Security can be implemented in the hub/switch.

Disadvantages

Failure of the central node can disable the entire network

Limited cable length and number of stations

Maintenance costs may be higher in the long run

Tree:

It is the modification of bus topology. Coaxial cable is iften used to connect computers in a bus topology. T- connectors are used to branch off in a third direction to enable a new computer to be connected to the network.Special hardware has to be used to terminate both ends of coaxial cable such that a signal travelling to the end of the bus would come back as repeat data transmission.

Mesh:

All computers are connected to each other so it is sometimes called completely connected networks. The number of links on networks are determined by: n (n-1)/2.

Advantages:

Reliable: any line breakdown will affect only communication between the connected computers

Each node of the network need not have individual routing capacity.

Communication is very fast between any two nodes.

Hybrid:

Mixture of more than two of star, ring, bus, mesh, tree etc topology is known as hybrid topology.

MODEM (MOdulator-DEModulator):

Modem is an electronic device used to convert digital signal into analog and vice versa. Modulator convert analog signal into digital signal where as demodulator converts analog signal into digital.

The digital signal is not suitable for long distance communication through bounded media because signal suffer from strong attenuation, delay distortion and noises so modem is used to convert digital signal into analog signal.

There are three kind of modem: 1) Internal 2) External 3) PC card are available.

Difference between Analog and Digital Signal:

Analog:

1. Analog signal is continuously varying electromagnetic wave called sine wave.

2. It is suitable for long distance communication through bounded media

3. Demodulator converts Analog into digital signals

Digital:

1. It is a sequence of discrete voltage pulse called square waves.

2. It is not suitable for long distance communication through bounded media.

3. Digital signal is converted into analog through modulator.

Short Notes:

Repeater:

Simply, repeater is an electronic device that receives a weak or low-level signal and retransmits it at a higher level or higher power, so that the signal can cover longer distances without degradation.Analog repeaters frequently can only amplify the signal while digital repeaters can reconstruct a signal to near its original quality.

Hubs can operate as repeaters by relaying messages to all connected computers. A repeater cannot do the intelligent routing performed by bridges and routers.

Bridge:

It is a store and forward device used to connect different or similar networks (LAN) together. It receives frames from one LAN and transfer to other LAN without any modification and encapsulation.

Bridge are classifies into two categories 1) Local 2) Remote.

Router:

A router is a computer networking device that forwards data packets across an internetwork toward their destinations, through a process known as routing.

Gateway:

It is used to link dissimilar LANs. It also performs all functions of bridge and router. When we connect Ethernet (LAN) to token ring (LAN), Gateway converts Ethernet protocol onto token ring protocol. Gateway is works like as server for other server.

Hub:

Hub or concentrator is a device for connecting multiple twisted pair or fibre optic Ethernet devices together, making them act as a single segment.

There are different types of hubs:

Active hubs

Passive hubs

Hybrid hubs

Protocol:

Protocol is a convention or standard that controls or enables the connection, communication, and data transfer between two computing endpoints.

Protocols may be implemented by hardware, software, or a combination of the two. At the lowest level, a protocol defines the behavior of a hardware connection.

TCP /IP

Application layer: It provides applications the ability to access the services of the other layers and defines the protocols that applications use to exchange data. There are many Application layer protocols and new protocols are always being developed. The most widely-known Application layer protocols are those used for the exchange of user information:

The Hypertext Transfer Protocol(HTTP) is used to transfer files that make up the Web pages of the World Wide Web. The File Transfer Protocol(FTP) is used for interactive file transfer. The Simple Mail Transfer Protocol(SMTP) is used for the transfer of mail messages and attachments. Telnet,a terminal emulation protocol, is used for logging on remotely to network hosts.

Additionally, the following Application layer protocols help facilitate the use and management of TCP/IP networks:

The Domain Name System (DNS) is used to resolve a host name to an IP address. The Routing Information Protocol (RIP) is a routing protocol that routers use to exchange routing information. The Simple Network Management Protocol (SNMP) is used between a network management console and network devices (routers, bridges, intelligent hubs) to collect and exchange network management information.

Transport Layer

TheTransport layer(also known as the Host-to-Host Transport layer) is responsible for providing the Application layer with session and datagram communication services. The core protocols of the Transport layer areTransmission Control Protocol(TCP) and theUser Datagram Protocol(UDP). Either of these two protocols are used by the application layer process, the choice depends on the application's transmission reliability requirements. The mechanisms used by the Transport layer to determine whether data has been correctly delivered are:

Acknowledgement responses Sequencing Flow control

The Transport layer facilitates two types of communication:

Connection-oriented (TCP) A connection must be established at the Transport layer of both systems before the application can transmit any data and Connectionless (UDP) All systems do not need to establish a connection with the recipient prior to data exchange. TCP is a more reliable form of data exchange than UDP.

Internet Layer

This layer is responsiblefor addressing, packaging, and routing functions. It allows communication across networks of the same and different types and carries out translations to deal with dissimilar data addressing schemes. The core protocols of the Internet layer are IP, ARP, ICMP, and IGMP. TheInternet Protocol(IP) is a routable protocol responsible for IP addressing, routing, and the fragmentation and reassembly of packets. TheAddress Resolution Protocol(ARP) is responsible for the resolution of the Internet layer address to the Network Interface layer address such as a hardware address.

TheInternet Control Message Protocol(ICMP) is responsible for providing diagnostic functions and reporting errors due to the unsuccessful delivery of IP packets. TheInternet Group Management Protocol(IGMP) is responsible for the management of IP multicast groups.

Network Interface Layer

TheNetwork Interface layer(also called the Network Access layer) is responsible for placing TCP/IP packets on the network medium and receiving TCP/IP packets off the network medium. TCP/IP was designed to be independent of the network access method, frame format, and medium. In this way, TCP/IP can be used to connect differing network types. This layer includes LAN technologies such as Ethernet and Token Ring and WAN technologies such as X.25 and Frame Relay.TCP and UDP:

TCPis areliable, connection-orientedprotocol that provides error checking and flow control through a virtual link that it establishes and finally terminates. TCP is responsible for the establishment of a TCP connection (TCP handshake), the sequencing and acknowledgment of packets sent, and the recovery of packets lost during transmission.

UDPis anunreliable, connectionlessprotocol that provides data transport with lower network traffic overheads than TCP. UDP is used when the amount of data to be transferred is small (such as the data that would fit into a single packet), or when the overhead of establishing a TCP connection is not desired or when the applications or upper layer protocols provide reliable delivery. UDP does not error check or offer any flow control, this is left to the application process.

OSI

The physical layerdefines the way in which data is physically converted into digital signals on the communication media (electric pulses, light modulation, etc.).

The data link layerdefines the interface with the network interface card and the sharing of the transmission media.

The network layermakes it possible to manage addressing and routing of data, i.e. their path via the network

The transport layeris in charge of data transport, its division into packets and management of potential transmission errors.

The session layerdefines the opening and destruction of communication sessions between networked machines.

The presentation layerdefines the format of data handled by the application layer (its representation and potentially its compression and encryption) independently of the system.

The application layerprovides the interface with applications. It is therefore the closest level to the users, managed directly by the software.

The major protocols of the TCP/IP suite are:

Transmission Control Protocol (TCP) User Datagram Protocol (UDP)

Domain Name System (DNS)

Internet Protocol (IP)

Address Resolutions Protocol (ARP)

File Transport Protocol (FTP)

Simple Mail Transport Protocol (SMTP)

Post Office Protocol (POP3)

Interactive Mail Access Protocol (IMAP)

Internet Control Message Protocol (ICMP)

Routing Information Protocol (RIP)

Open Shortest Path First (OSPF)

Hypertext Transfer Protocol (HTTP)The difference between OSI and TCP/IP suit are:

The TCP/IP protocol suite comes prior to the OSI model. ISO first introduce the idea of TCP/IP suite. After some time the idea of OI model comes into existence. So the TCP/IP suite is older than OSI model. The TCP/IP suite is based on protocols whereas the OSI model is layer based model. TCP/IP suite based on protocols. It means that the model is created on the basis of protocol. If any network is needed to set up then first the protocols of that system are selected and on the basis of these protocols the layers are created. So, this model is simply a protocols based model. The OSI model is based on layers. The system is set up on the basis of layers. Protocols are selected on the basis of requirement for the system for which we want to set up the network. Both the models are based on the concept of stack of independent protocols. Another difference is in the communication. The OSI model supports both connectionless and connection oriented communication in the network layer, but only connection oriented communication in the transport layer, where it counts. The TCP/IP suite has only connectionless mode in network layer, but supports both connectionless and connection oriented communication in the transport layer, so user can have choice. The TCP/IP model can't distinguish between service, interface and protocols. OSI model have seven layers whereas the TCP/IP suite have only five layers. The three layers are combined together and works like a single layer in the TCP/IP suite.OSI Model:

Layer #NameMnemonicEncapsulation UnitsDevices or Components

7ApplicationAlldataPC

6PresentationPeopledata

5SessionSeemdata

4TransportTosegments

3NetworkNeedpacketsrouter

2Data LinkDataframesbridge, switch, NIC

1PhysicalProcessingbitsrepeater, hub, transceiver

Comparison between OSI and TCP/IP Model:

OSI #OSI Layer NameTCP/IP #TCP/IP Layer NameEncapsulation UnitsTCP/IP Protocols

7Application4ApplicationdataFTP, HTTP, POP3, IMAP, telnet, SMTP, DNS, TFTP

6Presentationdata

5Sessiondata

4Transport3TransportsegmentsTCP, UDP

3Network2InternetpacketsIP

2Data Link1Network Accessframes

1Physicalbits

13. Internet and World Wide Web

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