This document provides an overview of computer networks and networking concepts. It discusses what a computer network is, why networks are used, what components make up a network, and what networks do to reliably transmit data. It also describes different types of networks including LANs, MANs, and WANs; various network topologies such as star, bus, ring, tree, and mesh; and different transmission media used in networks. The key details covered include the purpose and advantages and disadvantages of different network types, topologies, and transmission media.

1. 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)

2. • 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'

3. 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.

4. • 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.

5. • 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.

6. 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

7. 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.

8. • 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:

9. • 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.

10. • 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

11. 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.

12. 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:

13. 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.

14. 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):

15. 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.

16. • 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.

17. 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.

18. 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.

19. ADVANTAGES:
• High bandwidth
• Coverage over a large geographical area
• Can be cheaper over long distances
DISADVANTAGES:
• Huge initial cost
• Noise and interference
• Propagation delay

20. 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

21. 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.

22. 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
(suresh@daybegins.com) 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.

23. 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.