A computer network connects computers together to share resources like internet access or printers. The main goals are sharing resources across locations, high reliability through file replication, saving money by sharing devices, and providing security. There are several types of networks including personal area networks (PANs) for individuals, local area networks (LANs) within buildings, metropolitan area networks (MANs) within cities, and wide area networks (WANs) for long distance transmission across large areas. Network software manages different protocols and services efficiently, separating the control and data planes. Software-defined networking (SDN) uses a smart controller to direct traffic through routers and switches in the infrastructure layer, with network intelligence residing in a separate control layer.

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Sagor Saha
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Computer Networks:
A computer network is a set of computers connected together for the purposeof
sharing resources. Themostcommon resourceshared today is connection to the
Internet. Other shared resources can include a printer or a file server. The
Internetitself can be considered a computer network
Distributed systems:
Distribution systemis a collection of autonomous computer linked by a computer
network and all this equipped with distributed systemsoftware.
Goals of computer network:
1. Resources sharing: Itis the main object of the computer networking, the
goal is to provideall the program, data and hardwareavailable to everyone
the network withoutregard to the physicallocation of resourceand the
users.
2. Highly reliability: Highly reliability can be achieved by replicating the files on
two or more machine so if one of the them is unavailable due to failure of
hardwareor softwarethe other copies could be available.
3. Saving money: Network of devices and computer saves a lot of money
Example- one printer can be shared with multiple computers so no need to
buy separate printer for each computer.
4. Security: Security is the main characteristics of Computer network where
you can take necessary steps for protecting your data fromunauthorized
access.
Network classification:
Mainly four types of computer network

2.  PAN(PersonalArea Network)
 LAN(LocalArea Network)
 MAN(Metropolitan Area Network)
 WAN(WideArea Network)
PAN:
A personalarea network is a computer network organized around an
individual person. Personalarea network can be constructed with cabal or be
wireless.
Personalarea networks includes mobile devices, tablet, and laptop.
Thomas Zimmerman was the firstresearch scientist to bring the idea of the
PersonalArea Network.
LAN:
A network that connects a relatively small no of machine in a relatively close
geographicalarea such as school, laboratory, homeand office building.
Itis a network which consists of less than 5000 interconnected devices across
severalbuildings.
Local Area Network provides higher security.
MAN:
Network in a city is called a Metropolitan Area Network.
The most widely used protocols in MAN are RS-232, FrameRelay, ATM, ISDN,
OC-3, ADSL, etc.
Itoffers fastcommunication using high-speed carriers, like fiber optic cables.
WAN:
Network that provides long distance transmission of data, voice, image and
video information over large geographicalare is called wide area network.
A Wide Area Network is widely used in the field of Business, government, and
education.

3. Network software:
network softwareis one of the highly structured components. network
softwareis defined in such a way so that it can handle different protocols and
services in an efficient manner.
SDN:
The main purposeof SDNis to separate the controlplane and data plane.
vendors using the SDNtech the brocade ,Cisco, HP and VMware.
SDNis having smart controller that means all network traffic and series of
routers and switches that forward packets of traffic.
SDNArchitecture:
Infrastructurelayer: it consists of network devices. this layer will be the
physicallayer.
Control layer: network intelligence resides in the control layer. control plan has
the controlplan has the control logic for managing the network .