NAITA එකේ 2013 IT කරන ඔබව සාදරයෙන් පිලිගන්නවා.... මම මේ වැඩේ කරන්න හිතුවේ අපේ අයට මග හැරෙන, අමාරු සහ ඉක්මනට අමතක වෙන විෂය කරුණු නැවත ආවර්ජනය කරගන්න ඕන නිසා.... කාගේත් යහපත උදෙසා මෙහි රහස්ය භාවය සුරැකීමටත්, මුර පදය වෙනත් අයට ලබා නොදීමටත් මතක තියාගන්න....
මේ තියෙන්නේ අපිට දීපු නෝට් එක...
What is a Network?
A
network consists of two or more computers that are linked in order to share
resources (such as printers and CDs), exchange files, or allow electronic
communications. The computers on a network may be linked through cables,
telephone lines, radio waves, satellites, or infrared light beams.
Two very
common types of networks include:
·
Local
Area Network (LAN)
·
Wide
Area Network (WAN)
·
Metropolitan
Area Network (MAN)
Local
Area Network
A Local
Area Network (LAN) is a network that is confined to a relatively small area. It
is generally limited to a geographic area such as a writing lab, school, or
building
Wide
Area Network
Wide Area
Networks (WANs) connect networks in larger geographic areas, such as Florida,
the United States, or the world. Dedicated transoceanic cabling or satellite
uplinks may be used to connect this type of global network.
Metropolitan
Area Network
A Metropolitan Area Network covers larger geographic areas, such
as cities or school districts. By interconnection smaller networks within a
large geographic area, information is easily disseminated throughout the
network. Local libraties and government agencies often use a MAN to connect to
citiaens and private industries.
What is
a Topology?
The physical topology of a network refers to the configuration of
cables, computers, and other peripherals. Physical topology should not be
confused with logical topology which is the method used to pass information
between workstations. Logical topology was discussed in the Protocol chapter.
Main Types of Physical Topologies
The following sections discuss the physical topologies used in
networks and other related topics.
·
Linear Bus
·
Star
·
Tree etc..
Linear
Bus
A linear
bus topology consists of a main run of cable with a terminator at each end . All
nodes (file server, workstations, and peripherals) are connected to the linear
cable.
Advantages
of a Linear Bus Topology
·
Easy
to connect a computer or peripheral to a linear bus.
·
Requires
less cable length than a star topology.
Disadvantages
of a Linear Bus Topology
·
Entire
network shuts down if there is a break in the main cable.
·
Terminators
are required at both ends of the backbone cable.
·
Difficult
to identify the problem if the entire network shuts down.
·
Not
meant to be used as a stand-alone solution in a large building.
Star
A star
topology is designed with each node (file server, workstations, and
peripherals) connected directly to a central network hub, switch, or
concentrator
Advantages
of a Star Topology
·
Easy
to install and wire.
·
No
disruptions to the network when connecting or removing devices.
·
Easy
to detect faults and to remove parts.
Disadvantages
of a Star Topology
·
Requires
more cable length than a linear topology.
·
If
the hub, switch, or concentrator fails, nodes attached are disabled.
·
More
expensive than linear bus topologies because of the cost of the hubs, etc.
Tree
A tree topology combines characteristics of linear bus
and star topologies. It consists of groups of star-configured workstations
connected to a linear bus backbone cable. Tree topologies allow for the
expansion of an existing network, and enable schools to configure a network to
meet their needs.
Advantages
of a Tree Topology
·
Point-to-point
wiring for individual segments.
·
Supported
by several hardware and software venders.
Disadvantages
of a Tree Topology
·
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.
What is
a Network Operating System?
Unlike operating systems, such as Windows, that are designed for
single users to control one computer, network operating systems (NOS)
coordinate the activities of multiple computers across a network. The network
operating system acts as a director to keep the network running smoothly.
The two major types of network operating systems are:
·
Peer-to-Peer
·
Client/Server
Peer-to-Peer
Peer-to-peer network operating systems allow users to share resources
and files located on their computers and to access shared resources found on
other computers. However, they do not have a file server or a centralized
management source. Peer-to-peer networks are designed primarily for small to
medium local area networks. Nearly all modern desktop operating systems, such
as Macintosh OSX, Linux, and Windows, can function as peer-to-peer network operating
systems.
Client/Server
Client/server network operating systems allow the network to centralize
functions and applications in one or more dedicated file servers. The file
servers become the heart of the system, providing access to resources and
providing security. UNIX/Linux and the Microsoft family of Windows Servers are
examples of client/server network operating systems.
What is
a Protocol?
A protocol is a set
of rules that governs the communications between computers on a network. In
order for two computers to talk to each other, they must be speaking the same
language. Many different types of network protocols and standards are required
to ensure that your computer (no matter which operating system, network card,
or application you are using) can communicate with another computer located on
the next desk or half-way around the world. The OSI (Open Systems
Interconnection) Reference Model defines seven layers of networking protocols.
The complexity of these layers is beyond the scope of this tutorial; however,
they can be simplified into four layers to help identify some of the protocols
with which you should be familiar
What is
Networking Hardware?
·
Network interface card
·
Cables
·
BNC Connectors used with coaxial
cable
·
RJ45 connectors are used with twisted
pair cable and ethernet cable
·
Hub
·
Switch
·
repeaters
·
Bridges
·
Routers
·
Gateways
(Network
Equipments)
Network
Interface Card (NIC)
A computer is
connected to a network through a hardware device called a network interface
card. A NIC controls the data flow to and from the network. It fits in to one
of the expansion slots of the main circuit board of a computer and contains a
port where the network cable can be attached (RJ45, Coaxial adapter, Optical
connector). The control of the NIC is governed by the network software and the
operating system.
HUB
A common connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports. When a packet arrives at one port, it is copied to the other ports so that
all segments of the LAN can see all packets.
ROUTER
· ·
A router connects two or more networks having
different IP addresses.
·
The function of a router is to manage the paths along
which information is forwarded within a network. They are necessary to
facilitate communication between computers and the Internet.
·
A router is a networking tool/device with the aim of
selecting the appropriate path for to transfer data packages between different
networks. This procedure is identified as routing.
Switch
An ethernet switch is a device that
provides a central connection point for cables from workstations, servers, and
peripherals. In a star topology, twisted-pair wire is run from each workstation
to a central switch/hub. Most switches are active, that is they electrically
amplify the signal as it moves from one device to another.
Modem
When we get the internet connection
we have to use a modem. To get the internet connection we use computers and a
telephone line. Computer transmits digital singnals. Telephone line transmit
analog signals. There for to transmit messages in internet we have to convert
digital signal to analog signal (Modulation) and convert to ananlog signal to
digital signals (Demodulation) to do these wer e use a modem.
(Network
Materials)
Cables
Coaxial
Cable
Coaxial cabling has a single copper conductor at its
center. A plastic layer provides insulation between the center conductor and a
braided metal shield (See fig. 3). The metal shield helps to block any outside
interference from fluorescent lights, motors, and other computers
Fiber
Optic Cable
Fiber optic cabling consists of a center glass core
surrounded by several layers of protective materials. It transmits light rather
than electronic signals eliminating the problem of electrical interference.
This makes it ideal for certain environments that contain a large amount of
electrical interference. It has also made it the standard for connecting
networks between buildings, due to its immunity to the effects of moisture and lighting.
Unshielded
Twisted Pair (UTP) Cable
Twisted pair cabling
comes in two varieties: shielded and unshielded. Unshielded twisted pair (UTP)
is the most popular and is generally the best option for school networks
Network
cabling Tools
Punch Down Tool
Crimping tool &
cutter Plier
Cabling Tester
Mini Wire Stripper
Keystone Jack
RJ-45 Connector
Phase plate
Patch panel
Patch Cord
Wi-Fi
Wi-Fi is a standard for
wireless LANs. The Wi-Fi accesspoint (a trans-receiver) has a normal range of
about 100m. The area covered by one of these access points is refered to as a
”Wi-Fi Hot Spot”. If a computer or device which supports Wi-Fi and is in a Wi-Fi
hot spot can connect to these access points network. Wi-Fi hot spots are
located in public places like airports, restaurants and roads. For example the
Colombo airport has Wi-Fi hotspots through which you can access the Internet if
you have a Wi-Fi enabled laptop, while waiting for the flight.
Bluetooth
Bluetooth is a wireless
standard which describes how devices like computers , cellular phones and PDAs
can be linked within a short range. Bluetooth uses radio signals to transmit
data. For example you can connect a Bluetooth enabled digital diary to a
Bluetooth enabled computer to backup your notes at the end of the day.
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