Computer network

AIM: TO STUDY THE BASICS OF COMPUTER NETWORK

What is computer network:

• A computer network, often simply referred to as a network, is a collection of

hardware components and computers interconnected by communication channels

that allow sharing of resources and information.

• Where at least one process in one device is able to send/receive data to/from at

least one process residing in a remote device, then the two devices are said to be

in a network.

Why networking:

• Information access.

• Sharing of Resources.

• Facilitate Communication.

• Interactive entertainment.

• High reliability.

• Saving money.

What a network includes:

• Transmission Hardware (NIC, MODEM, other transmitter)

• Intermediate hardware devices(Hub, Repeaters, Amplifiers, Switch, Router)

• Protocol software

What a network does:

• Provides communication that is

1. Reliable

2. Fair

3. Efficient

• Automatically detects and corrects

1. Data corruption and data loss

2. Duplication

3. Out of order delivery

• Automatically finds optimal path from source to destination

Link:

Link is defined as the physical transmission medium that connects networked

devices/systems

Different types of links:

• Point-to-Point or Direct Access Link

1. Such links provide a direct path between two devices,thus forming a network

that does not have intermediate devices.

2. Can not be used to connect large networks.

• Multiple Access Link

1. When multiple devices are connected to one another via a single link, such

thateach of the devices is connected by the link to all other devices at the

same time,the link is said to be a multiple-access link.

2. The main channel that connects all thedevices is also called as a ‘bus’ or an

'ether'

AIM: TO STUDY THE TYPES OF NETWORKS

Types of network are:

• MAN(Metropolitan Area Network)

• LAN (Local Area Network)

• WAN(Wide Area Network)

LAN

Features

• A group of computers that share a common connection and are usually in a small

area or even in the same building form a LAN.

• They are usually connected by lan cables and have high speed connections.

• Security & Administration: A LAN administrator is one who supervises the

operation of a LAN. He takes care of tasks like adding or deleting users, creating

passwords providing authorizations and other resources like printers and backing up

data.

• Range of LAN-90mts best but we can go upto 150 also.

ADVANTAGES:

• Reliability & Stability: LANS tend to be very reliable failures on a LAN are mostly

due to wrong or improper installation and monitoring. Software that comes along

with a LAN provides a number of useful programs like error-detection, prevention

of transmission loss and excellent security features.

• 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.

DISADVANTAGES:

• Special security measures are needed to stop users from using programs and data

that they should not have access to.

• Networks are difficult to set up and need to be maintained by skilled technicians.

• If the file server develops a serious fault, all the users are affected, rather than

just one user in the case of a stand-alone machine.

• Limited no. of users.: Most LAN supports number of users usually around five or

ten. More users can be supported by connecting different LANs together, which

gives better results than making one; by network of the nature of MAN.

MAN

Features:

• This is a larger network that connects computer users in a particular geographic

area or region.

• The MAN network usually exist to provide connectivity to local ISPs, cable tv, or

large corporations.

• Range of Man: can connect cities 10 kms - 50kms

• It is far larger than a LAN and smaller than a WAN.

• The network size falls intermediate between LANs and WANs. A MAN typically

covers an area of between 5 and 50 km diameter. Many MANs cover an area the

size of a city, although in some cases MANs may be as small as a group of buildings.

ADVANTAGES

• It provides a good back bone for a large network and provides greater access to

Wans.

• A MAN would probably be the next fastest as the data is only travelling around the

city.

DISADVANTAGES:

• more cable required for a man connection from one place to another. • The large the network becomes difficult to mange.

• It is difficult to make the system secure from hackers and industrial espionage.

WAN

FEATURES:

• This is the largest network and can interconnect networks throughout the world

and is not restricted to a geographical location.

• Most WANs exist to connect LANs that are not in the same geographical area.

• This technology is high speed and very expensive to setup.

• Covers a Large geographical area.

ADVANTAGES:

• Covers a large geographical area so long distance businesses can connect on the one

network • Shares software and resources with connecting workstations

• Messages can be sent very quickly to anyone else on the network. These messages

can have pictures, sounds, or data included with them (called attachments).

• Everyone on the network can use the same data. This avoids problems where some

users may have older information than others.

• large network cover.

DISADVANTAGES:

• Are expensive and generally slow • Need a good firewall to restrict outsiders from entering and disrupting the

network

• Information may not meet local needs or interests

• Vulnerable to hackers or other outside threats

AIM: TO STUDY THE TYPES OF NETWORK TOPOLOGY.

Two or more computers connected together through communication media form a

computer network. The arrangement of computers in a network is called Network

Topology. It is a physical layout of connected computer.

Types of topologies are:-

• STAR TOPOLOGY

• BUS TOPOLOGY

• RING TOPOLOGY

• TREE TOPOLOGY

• MESH TOPOLOGY

STAR TOPOLOGY:

This topology consists of a central node to which all other nodes are connected by a single

path.

ADVANTAGES:

• EASE OF SERVICE: The star topology has a number of concentration points. These

provide easy access for service or reconfiguration of the network. • ONE DEVICE PER CONNECTION: Connection points in any network are inherently

prone to failure. In the star topology, failure of a single connection typically

involves disconnecting one node from an otherwise fully functional node.

• CENTRALIZED CONTROL: The fact that the centralized node is connected

directly to every other node in he network means that faults are easily detected

and isolated. It is a simple matter to disconnect failing nodes from the system.

• SIMPLE ACCESS PROTOCOLS: Any given connection in a star topology involves only

the central node, In this situation, connection for who has control of the medium

for the transmission purposes is easily solved. Thus in a star network, access

protocols are very simple.

DISADVANTAGES:

• LONG CABLE LENGTH: Because each node is directly connected to the centre, the

star topology necessitates a large number quantity of cable.

• DIFFICULT TO EXPAND: The addition of a new node to star network involves a

connection all the way to the central node.

• CENTRAL NODE DEPENDENCY: If the central node faiuls, the entire network is

rendered inoperable.

BUS TOPOLOGY:

In the bus topology, the computers are connected through a common communication media.

A special type of central wire is used as communication media. This central wire is called

Bus. The computer are attached through the bus the ends of the bus are closed with the

terminator .The terminators are used to absorb signals.

ADVANTAGES:

• SHORT CABLE LENGTH AND SIMPLE WIRING LAYOUT: Because there is a single

common data path connecting nodes, the linear topology allows a very short cable

length to be used.

• INEXPENSIVE.

• EASY TO EXTEND: Additional nodes can be added to the network at any point.

DISADVANTAGES:

• Fault diagnosis is difficult.

• Performance decreases.

• Weak signals.

RING TOPOLOGY:

In ring topology each computer is connected to the next computer and the last computer is

connected to the first computer. Data is accepted from one of the neighboring nodes and

is transmitted onwards to another. Thus data travels only in one direction only, from node

to node around the ring.

ADVANTAGES:

• Short cable length.

• It provides an orderly network in which every device has access to the token and

can transmit.

• Suitable for optical fibres.

DISADVANTAGES:

• Node failure causes network failure.

• Difficult to diagnose faults.

• Change mode with adding or removing a device effect the entire network.

TREE TOPOLOGY:

Tree topologies integrate multiple star topologies together onto a bus. In its simplest

form, only hub devices connect directly to the tree bus, and each hub functions as the

"root" of a tree of devices. This bus/star hybrid approach supports future expandability

of the network much better than a bus (limited in the number of devices due to the

broadcast traffic it generates) or a star (limited by the number of hub connection points)

alone.

ADVANTAGES:

• Point-to-point wiring for individual segments.

• Supported by several hardware and software venders

DISADVANTAGES:

• Overall length of each segment is limited by the type of cabling used.

• If the backbone line breaks, the entire segment goes down.

• More difficult to configure and wire than other topologies.

MESH TOPOLOGY:

A mesh network or mesh topology uses separate cable to connect each device to every

other device on the network, providing a straight communication path .

ADVANTAGES:

• Enhance for error tolerance provided by redundant links.

• Easy to troubleshoot.

DISADVANTAGES:

• Difficult to install and maintain.

• Expensive.

• Large cable length.

AIM: TO STUDY THE TYPES OF TRANSMISSION MEDIA.

The means through which data is transformed from one place to another is called

transmission or communication media. There are two categories of transmission media used

in computer communications:

• BOUNDED/GUIDED MEDIA

• UNBOUNDED/UNGUIDED MEDIA

GUIDED MEDIA

• Bounded media are the physical links through which signals are confined to narrow

path. These are also called guided media.

• Bounded media are made up to a external conductor (Usually Copper) bounded by jacket material.

• Bounded media are great for LABS because they offer high speed, good security

and low cast. However, some time they cannot be used due distance communication.

Three common types of bounded media are used of the data transmission. These are:

1. Coaxial Cable

2. Twisted Pairs Cable

3. Fiber Optics Cable

COAXIAL CABLES:

Coaxial cable is very common & widely used commutation media. For example TV wire is

usually coaxial. Coaxial cable gets its name because it contains two conductors that are

parallel to each other. The center conductor in the cable is usually copper. The copper can

be either a solid wire or stranded martial. Outside this central Conductor is a non-conductive material. It is usually white, plastic material used to separate the inner

Conductor form the outer Conductor. The other Conductor is a fine mesh made from

Copper. It is used to help shield the cable form EMI. Outside the copper mesh is the final

protective cover.

CHARACTERISTICS:

• Low cost • Easy to install

• Up to 10Mbps capacity

• Medium of attenuation

ADVANTAGES: • Inexpensive

• Easy to wire

• Easy to expand

• Moderate level of EMI immunity

DISADVANTAGES: • Single cable failure can take down an entire network.

TWISTED PAIR CABLE:

The most popular network cabling is Twisted pair. It is light weight, easy to install, inexpensive and support many different types of network. It also supports the speed

of 100 mbps. Twisted pair cabling is made of pairs of solid or stranded copper twisted

along each other. The twists are done to reduce vulnerably to EMI and cross talk. The

number of pairs in the cable depends on the type. There are two types of twisted pairs

cabling:

• Unshielded twisted pair (UTP)

• Shielded twisted pair (STP)

UNSHIELDED TWISTED PAIR (UTP): UTP is more common. It can be either voice grade or data grade depending on the

condition. UTP cable normally has an impedance of 100 ohm. UTP cost less than STP and

easily available due to its many use. There are five levels of data cabling.

TYPE DESCRIPTION

CAT1 Voice-grade transmission only; No data transmission.

CAT2 Data grade transmission up to 4 mbps.

CAT3 Data grade transmission up to 10 mbps.

CAT4 Data grade transmission up to 16 mbps.

CAT5 Data grade transmission up to 1000 mbps.

CHARACTERISTICS: • low cost

• easy to install

• High speed capacity • High attenuation

• Effective to EMI

• 100 meter limit

ADVANTAGES: • Easy installation

• Capable of high speed for LAN

• Low cost

DISADVANTAGES: • Short distance due to attenuation.

SHIELDED TWISTED PAIR (STP):

It is similar to UTP but has a mesh shielding that’s protects it from EMI which allows for

higher transmission rate.

CHARACTERISTICS:

• Medium cost

• Easy to install

• Higher capacity than UTP

• Higher attenuation, but same as UTP

• Medium immunity from EMI

• 100 meter limit

ADVANTAGES: • Shielded

• Faster than UTP and coaxial

DISADVANTAGES: • More expensive than UTP and coaxial

• More difficult installation

• High attenuation rate

Fiber Optics:

Fiber optic cable uses electrical signals to transmit data. It uses light. In fiber optic cable

light only moves in one direction for two way communication to take place a second

connection must be made between the two devices. The fibre cable consists of three pieces:

• The Core i.e the glass or plastic through which light travels.

• The Cladding which is the covering of the core that reflects light back to the core.

• The Protective covering, which protects the fibre cable from hostile environment.

CHARACTERISTICS: • Expensive

• Very hard to install

• Capable of extremely high speed

• Extremely low attenuation

• No EMI interference

ADVANTAGES: • Fast

• Low attenuation

• No EMI interference

DISADVANTAGES: • Very costly

• Hard to install

COMPARISON TABLE OF GUIDED MEDIA:

TYPE SUBTYPE MAX.

SEGMENT

LENGTH

BANDWIDTH

SUPPLIED

INSTALLATION COST INTERFERENCE

TWISTED

PAIR

CABLE

UTP 100 MTS 100 Mbps Easy Cheapest High

STP 100 MTS 500 Mbps Moderate Moderate Moderate

COAXIAL

CABLE

THINNET 185 MTS 10 Mbps Easy Cheap Moderate

THICKNET 500 MTS 100 Mbps Hard Moderate Low

FIBRE

OPTIC

CABLE

MULTINODE 2 KMS 100 Mbps Very Hard Expensive None

SINGLENODE 100KMS 2 Gbps Very Hard Expensive None

UNGUIDED MEDIA:

Unguided media relates to data transmission through the air and is commonly referred to as wireless. The transmission and reception of data is carried out using antenna.

RADIO WAVES:

Radio transmission works with or without line of sight. If line of sight is possible then

transmission can take place between sending antenna and receiving antenna. The placement

of antenna has to take into account the curvature of the Earth with antenna being built

taller accordingly. This will also allow for greater transmission distances. If line of sight

cannot be implemented then signals can be broadcast to the upper layers or the

atmosphere or space and then transmitted back to Earth.

ADVANTAGES:

• Radio wave transmission offers mobility.

• It provides cheaper than digging trenches for laying cables and maintaining

repeaters and cables if cables get broken by a variety of causes.

• It offers freedom from land acquisition rights that are required for laying,

repairing the cables.

DISADVANTAGES:

• It is an insecure communication.

• Radio wave propagation is susceptible to weather effects like rains, thunder storms

etc.

MICRO WAVES:

In microwave communication, parabolic antennas are mounted on towers to send a beam to

other antennas tens of kilometers away. The higher the tower, the greater the range.

With a 100-meter high tower, distances of 100 km between tower are feasible. It is a line

of sight transmission.

ADVANTAGES:

• No cables needed

• Multiple channels available.

• Have the ability to communicate over oceans.

• Wide bandwidth

DISADVANTAGES:

• Line-of-sight will be disrupted if any obstacle, such as new buildings, are in the way

• Signal absorption by the atmosphere. Microwaves suffer from attenuation due to

atmospheric conditions.

• Towers are expensive to build.

SATELLITE:

In satellite communication the earth station consists of a satellite dish that functions as

an antennae and communication equipment to transmit and receive data from satellites

passing overhead.

ADVANTAGES:

• High bandwidth

• Coverage over a large geographical area

• Can be cheaper over long distances

DISADVANTAGES:

• Huge initial cost

• Noise and interference

• Propagation delay

AIM: TO STUDY TCP/IP PROTOCOLS.

TCP/IP is based on a four-layer reference model. All protocols that belong to the TCP/IP

protocol suite are located in the top three layers of this model. As shown in the above

illustration, each layer of the TCP/IP model corresponds to one or more layers of the

seven-layer Open Systems Interconnection (OSI) reference model proposed by the

International Standards Organization (ISO).

LAYER DESCRIPTION PROTOCOLS

APPLICATION Defines TCP/IP application protocols and how host

programs interface with transport layer services to

use the network.

HTTP, Telnet,

FTP, TFTP,

SNMP, DNS,

SMTP,

TRANSPORT Provides communication session management between

host computers. Defines the level of service and

status of the connection used when transporting data.

TCP, UDP,

RTP

INTERNET Packages data into IP datagram’s, which contain

source and destination address information that is

used to forward the datagrams between hosts and

across networks. Performs routing of IP datagrams.

IP, ICMP,

ARP, RARP

NETWORK INTERFACE Specifies details of how data is physically sent

through the network, including how bits are

electrically signaled by hardware devices that

interface directly with a network medium, such as

coaxial cable, optical fiber, or twisted-pair copper

wire.

Ethernet,

Token Ring,

FDDI, X.25,

Frame Relay,

RS-232, v.35

AIM: TO STUDY INNER WORKING OF AN E-MAIL.

Introduction

E-mail (electronic mail) is the exchange of computer-stored messages by telecommunication. E-mail messages are usually encoded in ASCII text. However, you can

also send non-text files, such as graphic images and sound files, as attachments sent in

binary streams. E-mail is one of the protocols included with the Transport Control

Protocol/Internet Protocol (TCP/IP) suite of protocols. A popular protocol for sending e-

mail is Simple Mail Transfer Protocol and a popular protocol for receiving it is POP3. Both

Netscape and Microsoft include an e-mail utility with their Web browsers.

HOW EMAIL WORKS:

EMAIL CLIENTS:

Many people use well-known stand-alone clients like Microsoft

Outlook, Outlook Express, Eudora or Pegasus. People who subscribe to free e-mail services

like

Hotmail or Yahoo uses an e-mail client that appears in a Web Page. No matter which type

Of client you are using, it generally does four things: • It shows you a list of all of the messages in your mailbox by displaying the message

headers. The header shows you who sent the mail, the subject of the mail and may

also show the time and date of the message and the message size.

• It lets you select a message header and read the body of the e-mail message.

• It lets you create new messages and send them. You type in the e-mail address of

the recipient and the subject for the message, and then type the body of the

message. • Most e-mail clients also let you add attachments to messages you send and save the

attachments from messages you receive.

For the vast majority of people right now, the real e-mail system consists of two

differentservers running on a server machine. One is called the SMTP server, where SMTP

stands for Simple Mail Transfer Protocol. The SMTP server handles outgoing mail. The

other is either a POP3 server or an IMAP server, both of which handle incoming mail. POP

stands for Post Office Protocol, and IMAP stands for Internet Mail Access Protocol. The

SMTP server listens on well-known port number 25, POP3 listens on port 110 and IMAP

Uses port 143.

SMTP Server Whenever you send a piece of e-mail, your e-mail client interacts with the SMTP server to

handle the sending. The SMTP server on your host may have conversations with other

SMTP servers to actually deliver the e-mail. The SMTP server takes the "to" address

([email protected]) and breaks it into two parts:

• The recipient name (suresh)

• The domain name (daybegins.com) If the "to" address had been another user at xserves.com, the SMTP server would simply

hand the message to the POP3 server for xserves.com (using a little program called the

Delivery agent). Since the recipient is at another domain, SMTP needs to communicate

with that domain.

The SMTP server has a conversation with a Domain Name Server, or DNS. It says, "Can

you give me the IP address of the SMTP server for daybegins.com?" The DNS replies

with the one or more IP addresses for the SMTP server(s) that Daybegins operates. The SMTP server at xserves.com connects with the SMTP server at Daybegins using port

25. It has the same simple text conversation that my e-mail client had with the SMTP

server for Xserves, and gives the message to the Daybegins server. The Daybegins server

recognizes that the domain name for suresh is at Daybegins, so it hands the message to

Daybegins's POP3 server, which puts the message in suresh's mailbox.

If, for some reason, the SMTP server at Xserves cannot connect with the SMTP server at

Daybegins, then the message goes into a queue. The SMTP server on most machines uses a

program called send mail to do the actual sending, so this queue is called the send mail queue. Send mail will periodically try to resend the messages in its queue. For example, it

might retry every 15 minutes. After four hours, it will usually send you a piece of mail that

tells you there is some sort of problem. After five days, most send mail configurations give

up and return the mail to you undelivered.

POP3 Server In the simplest implementations of POP3, the server really does maintain a collection of

text files

-- one for each e-mail account. When a message arrives, the POP3 server simply appends it

to the bottom of the recipient's file!

When you check your e-mail, your e-mail client connects to the POP3 server using port

110. The POP3 server requires an account name and a password. Once you have logged in, the POP3 server opens your text file and allows you to access it.

IMAP Server As you can see, the POP3 protocol is very simple. It allows you to have a collection of

messages stored in a text file on the server. Your e-mail client (e.g. Outlook Express) can

connect to your POP3 e-mail server and download the messages from the POP3 text file

onto your PC. That is about all that you can do with POP3.

Many users want to do far more than that with their e-mail, and they want their e-mail to remain on the server. The main reason for keeping your e-mail on the server is to allow

users to connect from a variety of machines. With POP3, once you download your e-mail it

is stuck on the machine to which you downloaded it. If you want to read your e-mail both

on your desktop machine and your laptop (depending on whether you are working in the

office or on the road), POP3 makes life difficult. IMAP (Internet Mail Access Protocol) is

a more advanced protocol that solves these problems. With IMAP, your mail stays on the

e-mail server. You can organize your mail into folders, and all the folders live on the server as well. When you search your e-mail, the search occurs on the server machine, rather

than on your machine. This approach makes it extremely easy for you to access your e-mail

from any machine, and regardless of which machine you use, you have access to all of your

mail in all of your folders. Your e-mail client connects to the IMAP server using port 143.

The e-mail client then issues a set of text commands that allow it to do things like list all

the folders on the server, list all the message headers in a folder, get a specific e-mail

message from the server, delete messages on the server or search through all of the e-

mails on the server. One problem that can arise with IMAP involves this simple question: “If all of my e-mail is

stored on the server, then how can I read my mail if I am not connected to the Internet?”

To solve this problem, most e-mail clients have some way to cache e-mail on the local

machine.

For example, the client will download all the messages and store their complete contents

on the local machine (just like it would if it were talking to a POP3 server). The messages

still exist on the IMAP server, but you now have copies on your machine. This allows you to

read and reply to e-mail even if you have no connection to the Internet. The next time you establish a connection, you download all the new messages you received while disconnected

and send all the mail that you wrote while disconnected.