NETWORK TOPOLOGIES
Topologies
refer to the techniques / ways of inter connecting computers or networks. Means how the computers and networks are
connected to each other. These can be
connected in the following ways –
Ring Topology
i)
Communication is one way in this topology. The speed is slow.
ii)
Only one node
communicates at a time.
iii)
Short cable length required as compared to star top.
iv)
If one node becomes unserviceable, the whole ring NW is
crashed.
Bus / Serial Topology
i)
All nodes are connected to a straight wire (thinnet of
coaxial cable). Speed is slow.
ii)
Only one node can communicate at a time.
iii)
Communication is both directional but at a time data
can pass only in one direction. At the
other end of the bus the signal is discarded.
iv)
If one node is unserviceable, network past of that node
becomes unserviceable.
Star / Radial Topology
i)
Nodes are attached to a HUB / SWITCH
ii)
Network is faster.
iii)
It is most widely used topology
iv)
If one node becomes unserviceable, the other nodes in
the network are not affected all other nodes carry on receiving
information. Only that node is out of
network.
Mesh Topology
Tree Topology
Point to Point
Graph
NETWORKING TECHNIQUES
Peer to Peer –
Each node in the network is having its own resources / processing capabilities. It may share information among others. Nodes may not have to depend upon others for
carrying out their work. Each node its
own master i.e. has no boss. They are
independent and work the way they like.
Client Server
(C/S) – In this technique there is one dedicated boss that is known as
server. Whole the network works under the server and it has full
control on all the nodes. Boss is known as Master / Server. The other nodes which are controlled by
Server are known as Slaves / Clients. Clients send request to the server and the
server receives their requests and reply.
NETWORKING DEVICES
i)
Hub- device used to connect no of computers
ii)
Active hub- pass the signals from one comp to
another with amplification
iii)
Passive hub- pass the signals from one comp to
another without amplification.
iv)
Switch-device used to segment networks into
different subnetworks called subnets or LAN segments.
v)
Repeater- device used to amplify and restore signals
for long distance transmission.
vi)
Bridges- device which establishes an intelligent
connection between two local networks with the same standard but with different
types of cables. Data not destined for a device on the other network is
prevented from passing over the bridge.
vii)
Router- device that is used to separate different
segments in a network to improve performance and reliability. A router works
like a bridge but can handle different protocols.
viii)
Gateways- device which connects dissimilar networks.It
is actually a node on a network which serves as entrance to another network.
ix)
RJ45 Connector (Registered Jack – 45) is an 8 wire
connector , which is commonly used to connect computers on a LAN especially
Ethernets.
x)
NIC – Network Interface Card –it is an interpreter that
helps establish communication between server and workstation.It is also called
TAP(Terminal Access Point)
xi)
MAC address- it refers to the physical address assigned
by NIC manufacturer.
xii)
Modem- converts analog to digital signals and vice
versa and allows to connect and communicate with other computers via telephone
lines.
xiii)
Ethernets- it is a LAN architecture which uses either
bus or star topology and supports data transfer rates upto 10 Mbps.
MODE OF COMMUNICATIONS (FULL
DUPLEX VS HALF DUPLEX)
Full-Duplex services
support the transfer of data in both directions.
Half-Duplex services
support the transfer of data in a single direction.
NEED / BENEFITS OF A NETWORK
-To share resources in network
-Decrease costs of transfer
-Increase speed in transferring
-Improves communication
Transmission Media / Channels of Communication
Transmission
media is used to establish connectivity between computers or networks.
Two Types of transmission media
Guided Media - in this type connecting cables are the
communication channels between the different works stations.
Name
|
Twisted Pair Cable
|
Coaxial Cable
|
Optical Fibre Cable
|
|
Identity
|
Ordinary Electrical Wire
|
Cable TV wire
|
A high speed wire having thin
glass pipe in it.
|
|
Connectors
|
RJ 45
|
BNC
|
SC / ST
|
|
Speed
|
100 – 1000 mbps
|
10 mbps
|
1000 mbps - gigabits
|
|
Distance
|
100 meters
|
500 meters
|
100 km
|
|
Cost
|
Cheapest
|
Cheaper
|
Costly
|
|
Types
|
STP & UPT
|
Thinnet /
Thicknet
|
Singlenode / Multinode ,
|
Unguided Media - in
this there is no direct connection between the source / destination
workstations and some waves are used to transmit the signal.
Microwave-
These are similar to radio and TV signals and used for long distance
communication.
It consists of transmitter , receiver and
atmosphere.
Parabolic antennas are mounted on
towers to send beam to other antennas. Higher the tower higher the range.
It can communicate over the
oceans.
It is cheaper than digging
trenches for laying cable.
It is insecure medium.
Radio
Wave- It contains transmitter and receiver. The transmitter takes some message , encode it
onto sine wave and transmit it with radio waves. The receiver receives the
radio wave , decode the message from sine wave it receives.
It proves cheaper than digging
trenches for laying cables.
It is insecure medium.
Satellite-
In it the earth station consists of a satellite dish that functions
as antenna and communication equipment to transmit and receive data from
satellite passing overhead.
Area coverage is quite large.
High investment cost.
Overcrowding of bandwidth.
Data Communication Terminologies
Data Channel – is a medium used
to carry information / data from one point to another point.
Baud / Baud Rate – it the measurement unit of data carrying
capacity of a data channel
bps bps is bits per second transmitted on a data
channel
Bps - Bytes per
second transmitted.
Bandwidth – it is amount of
information traveling through a single channel at any point of time.
Data Transmission Switching Techniques / How the information is shared /
Transferred in a NW –
Information
transferred from one node to another node in a network is known as
switching. Switching takes places in the
following ways –
Circuit Switching - ex Telephone line. In this source is connected to destination
from end to end.
Message Switching - ex E-mails. Uses store and forward technology for transfer
of information.
Source sends information that is
received by its nearby switch office.
This switch office sends the information to another switch office and
that further forwards to another switch office until the whole information is
reached at the switch office that is nearer to the destination. Then this switch office forwards information
to the destination.The message is stored on the hard disk , so access speed is
slow.
Packet Switching - This technique also uses store and
forward technique but the data is broken into small fixed size which are known as packets. The packets are
stored in the main memory , so the access speed is high.
PROTOCOL
Protocols
are the set of rules that govern the communication over a network. Some important protocols are –
TCP / IP – Transmission
Control Protocol. This protocol
establishes reliable or unreliable connection
between the source and destination. It
also breaks the data into segments.
IP – Internet
Protocol. This protocol is
responsible for providing Network Address / IP Address of the destination network. IP Address is 32 bit address. IP Address is divided into Network Address and Host Address.
HTTP – Hypertext
Transfer Protocol - It allows different
types of computers / Networks to
establish communication
between them. It has two features –
requests and responses.
DIFFERENCE BETWEEN WIRELESS / MOBILE
Wireless
is without use of wire (land line / physical connection).
Mobile
- The device is in touch with the
data source continuously without physical connection. It may use others media like satellite
or laser etc.
Video Conferencing - It is sounds, video, talking and viewing over
internet communication. We need Internet
connection, PC Camera and its Software, videophone Software (Net Meeting) for
video conferencing.
WWW – World Wide Web is a
protocol that allows to access documents on the internet.
Web Page – A document on
the net is called a web page.
URL – Each web page has an
address that is called URL. Uniform
Resource Locator.
Hypertext – The contents
of a web page is called Hypertext. It
can be audio, video, text, graphic and even link to some other page.
Hyperlink - Link
to some other page in a web page is called Hyperlink.
Telnet – Terminal
Emulation. It is a program that is used to remotely login network server /
devices.
Web Browser- It is a program that is used to navigate
through the web pages and display their contents. Ex Internet Explorer, Netscape Navigator and Mozilla etc
Web Server – A www server
that responds to the requests made by web browsers.
Web Site – A location on a
web server is called a web site. It
contains web pages and has a unique address.
This address is called URL.
HTML – Hypertext Markup
Language – used to develop web pages.
Web Hosting – Hosting of
web server application on a computer.
Network Security
As
we have seen that the NW offers a large number of benefits. These benefits are prone to threats. NW security means to counter such threats to
the NW.
Methods of NW Security
Authentication
– giving passwords etc
Authorization
– only the users login
Biometric
Systems – scan retina / DNA etc
Firewall –
prevents unauthorized access to / from a private network.
Cookies – It is a message
sent by web server to the web browser so that it can keep track of user’s
activities on a specific web site.
Crackers – These are the
malicious programmers who break into secure systems.
Hackers – The persons who
are interested in gaining knowledge about computer system and possibly using this
knowledge for playful pranks.
Cyber law – it is a
generic term which refers to all the legal and regulatory aspects of internet
and world wide web.
_
