Network Topology

1. Network Topology
Computers in a network have to be connected in some logical manner. The layout pattern of the
interconnections between computers in a network is called network topology. You can think of
topology as the virtual shape or structure of the network. Network topology is also referred to as
'network architecture.'
Devices on the network are referred to as 'nodes.' The most common nodes are computers and
peripheral devices. Network topology is illustrated by showing these nodes and their connections
using cables. There are a number of different types of network topologies, including point-to-
point, bus, star, ring, mesh, tree and hybrid. Let's review these main types.
Point-to-Point
Point-to-point topology is the simplest of all the network topologies. The network consists of a
direct link between two computers. This is faster and more reliable than other types of
connections since there is a direct connection. The disadvantage is that it can only be used for
small areas where computers are in close proximity.
Bus
Bus topology uses one main cable to which all nodes are directly connected. The main cable acts
as a backbone for the network. One of the computers in the network typically acts as the
computer server. The first advantage of bus topology is that it is easy to connect a computer or
peripheral device. The second advantage is that the cable requirements are relatively small,
resulting in lower cost.
One of the disadvantages is that if the main cable breaks, the entire network goes down. This
type of network is also difficult to troubleshoot. For these reasons, this type of topology is not
used for large networks, such as those covering an entire building.
Star
In star topology, each computer is connected to a central hub using a point-to-point connection.
The central hub can be a computer server that manages the network, or it can be a much simpler
device that only makes the connections between computers over the network possible.

2. Transmission mode refers to the mechanism of transferring of data between two devices
connected over a network. It is also called Communication Mode. These modes direct the
direction of flow of information. There are three types of transmission modes. They are:
1. Simplex Mode
2. Half duplex Mode
3. Full duplex Mode
4. Simplex Mode
n this type of transmission mode, data can be sent only in one direction i.e. communication is
unidirectional. We cannot send a message back to the sender. Unidirectional communication is
done in Simplex Systems where we just need to send a command/signal, and do not expect any
response back.
Examples of simplex Mode are loudspeakers, television broadcasting, television and remote,
keyboard and monitor etc.
Half duplex
Half-duplex datatransmissionmeansthatdatacan be transmittedinbothdirectionsona signal carrier,
but notat the same time.
Full duplex
In full duplex system we can send data in both the directions as it is bidirectional at the same
time in other words, data can be sent in both directions simultaneously.
Example of Full Duplex is a Telephone Network in which there is communication between two
persons by a telephone line, using which both can talk and listen at the same time.

3. Data communication is a process of transferring data electronically from one place to another.
Data can be transferred by using different medium. The basic components of data
communications are as follows:
1. Message
2. Sender
3. Receiver
4. Medium/ communication channel
5. Encoder and decoder
6. protocol
. Data:
Communicationof datameansamessageordatawillbe transmittedfromone deviceandwill be received
in the destinationortargetdevice.Thus the firstcomponentina data communicationssystemisdataor
message todeliverandreceive.Dataormessage canbe of variousformssuchastext,audio,video,image
or combinations of these forms etc.
2. Sender:
The device thatsendsthe datatothe destinationortargetisthe Sender.Itcanbe acomputer,cell phone,
video camera and so on.
3. Receiver:
The device that receives the data that was sent by the Sender is the Receiver. A receiver can again be a
computer, cell phone, video camera and so on.
4. Transmission medium:
The transmissionmediumisthe physical pathfor the data to travel to itsdestinationafterbeingsentby
the Sender. Receiver receives the data at one end of this path and the sender sentfrom another endof
the path. Transmission medium could be like twisted-pair cable, coaxial cable, fiber-optic cable etc.
5. Protocol:
A protocol isnothingbuta set of rulesthat appliesonthe full datacommunicationprocedure.Thisislike
an agreementbetweenthe twodevicestosuccessfullycommunicate witheachother.Forexample,how
the data will be sent, how the data will be traveling, how to ensure that full data has received,how to

4. handle errors in transmission etc. Both devices follow the same set of rules or protocol so that they
understand each other.
Osi iso reference model
There are n numbersof userswho use computernetworkand are locatedover the world.So to ensure,
national and worldwide data communication, systems must be developed which are compatible to
communicate witheachotherISOhasdevelopedastandard.ISOstandsfor International organizationof
Standardization. This is called a model for Open System Interconnection (OSI) and is commonly known
as OSI model.
Extranet Internet Intranet
Definition
Extranet is for individuals or group
of personnel who want to send
private information
A global network
which is available to
anyone who wants
to access
information
An intranet is unique to
an organization or
group of people who
work together at a
place
Privacy Extremely Private Public Private intermediately
Dependency Dependent on internet and intranet Independent
Independent yet
dependent on internet
Firewall Yes No Can have
1. Personal Area Network (PAN)
The smallest and most basic type of network, a PAN is made up of a wireless modem, a
computer or two, phones, printers, tablets, etc., and revolves around one person in one building.
These types of networks are typically found in small offices or residences, and are managed by
one person or organization from a single device.
2. Local Area Network (LAN)
We’re confident that you’ve heard of these types of networks before – LANs are the most
frequently discussed networks, one of the most common, one of the most original and one of the
simplest types of networks. LANs connect groups of computers and low-voltage devices together
across short distances (within a building or between a group of two or three buildings in close

5. proximity to each other) to share information and resources. Enterprises typically manage and
maintain LANs.
6. Wide Area Network (WAN)
Slightly more complex than a LAN, a WAN connects computers together across longer physical
distances. This allows computers and low-voltage devices to be remotely connected to each other
over one large network to communicate even when they’re miles apart.
E mail
Electronicmail (email or e-mail) isa method of exchangingmessages("mail")betweenpeople using
electronicdevices.Inventedby RayTomlinson,email firstenteredlimiteduse inthe 1960s and by the
mid-1970s had takenthe formnow recognizedasemail.Email operatesacross computernetworks,
whichtodayis primarilythe Internet.Some earlyemail systemsrequiredthe authorandthe recipientto
bothbe online atthe same time,incommonwith instantmessaging.Today'semailsystemsare based
on a store-and-forwardmodel.
ftp
File Transfer Protocol, is an Internet utility software used to uploaded and download files. It
gives access to directories or folders on remote computers and allows software, data and text
files to be transfer between different kinds of computers. FTP works on the basis of same
principle as that of Client/ Server. FTP “Client” is a program running on your computer that
enables you to communicate with remote computers.
telnet is a protocol used on the Internet or local area network to provide a bidirectional
interactive text-oriented communication facility using a virtual terminal connection. User data is
interspersed in-band with Telnet control information in an 8-bit byte oriented data connection
over the Transmission Control Protocol (TCP).
Telnet was developed in 1969 beginning with RFC 15, extended in RFC 855, and standardized
as Internet Engineering Task Force (IETF) Internet Standard STD 8, one of the first Internet
standards. The name stands for "teletype network".[1

6. Usenet(/ˈjuːznɛt/) isaworldwide distributeddiscussionsystemavailableoncomputers.Itwas
developedfromthe general-purposeUnix-to-Unix Copy(UUCP) dial-upnetworkarchitecture. Tom
Truscott and JimEllis conceivedthe ideain1979, andit wasestablishedin1980.[1]
Users readand post
messages(called articles orposts,andcollectivelytermed news) toone ormore categories,knownas
newsgroups.