Computer Network and Types of Network | Communication Media

Computer Network

A computer network is a group of computer systems and other computing hardware devices that are linked together through communication channels to facilitate communication and resource-sharing among a wide range of users. 

Advantages of Network:

• Facilitate communication via email, video conferencing, instant messaging, etc. 
• Enable multiple users to share a single hardware device like a printer or scanner. 
• Enable file sharing across the network.
• Allow for the sharing of software or operating programs on remote systems.
• Make information easier to access and maintain among network users.

Disadvantages of Network:

• Data and information maybe stolen by computer hackers. 
• If any computer in the network get affected by the virus, there is high chance of spreading computer virus. 
• Computers on the network have to depend on the server.

Communication Media/Channel:

Communication media refers to the means of delivering and receiving data or information. In telecommunication, these means are transmission and storage tools or channels for data storage and transmission. 
There are two main types of communication channels: 
A. Guided or Bounded or Wired Communication Media 
B. Unbounded or Unguided or Wireless Communication Media

Guided Media:

• A transmission media where data signals are transmitted along a specific path through cable is known as Guided Transmission Media. 
• It transfer data from one place to another with the help of wire. 
• There are three types of cables used for wired network. 
– Twisted Pair Cable 
– Co-axial cable 
– Fiber optic cable 
Twisted Pair Wire:
• It is used for almost all business telephone wiring. 
• It consists of strands of copper wire twisted in pair. 
• It is inexpensive, easy to work and it can be made relatively unobtrusive by running it inside walls, floors or ceilings. 
• It is relatively slow for data transmission. 
• it is susceptible to interference from other electrical sources. 
• It can be easily tapped for gaining unauthorized acess. 

Co-axial Cable: 
• It is commonly used to carry high-speed data traffic and tv signals.
• It consists of insulated copper wire. 
• It is less susceptible to electrical interferences. 
• It more expensive and less flexible than twisted pair. 
• Data transmission over coaxial cable is divided in to two basic types : 
a. Baseband:
 Transmission is analog and each wire carries only one signal at a time. 
b. Broadband:
 Transmission is digital and each wire carries multiple signal at time.

Fiber Optic Cable: 
• Fiber optic cables are made up of plastic or glass fibers and gives high quality transmission of signal at a very high speed. 
• It transmits light rather than electronic signals. 
• Fiber optic cable transmission are not affected by electromagnetic interference. 
• These can be used to communicate either analog or digital signals. 
• These are most commonly used for point to point one way communication. 
• It can transmit data at much higher rate than twisted pair and coaxial cable. 
• It can carry more data at very high speed and to long distances.
• No significant loss of intensity of light, so repeaters need not be placed so closer together as in coaxial cable. 
• Transmissions are not affected by electrical and magnetic interferences. 
• Smaller in size and lighter in weight than others. 
• Provides security as it is difficult to tap optical signals. 
• Optical fibers are fragile and can't be bend. 
• Joining two optical fiber cables is not simple and easy.

Unguided Media/Wireless Channel:

The way to transfer data without the help of wire is called Unguided media. 
• The type of Communication media in which communication devices sends and receives data signals through air or space is called Unguided media. 
• The data is communicated in the form of wave. 
• Unguided media provides means to transmit data signals but does not guide them along a specific path.
• The data signals are not bounded to a cabling media. 
• Therefore, unguided media is also called Unbounded media. 
• The type of Communication media in which communication devices sends and receives data signals through air or space is called Unguided media. 
• The data is communicated in the form of wave. 
• Unguided media provides means to transmit data signals but does not guide them along a specific path. • The data signals are not bounded to a cabling media. 
• Therefore, unguided media is also called Unbounded media. 

Types of unguided media are as follows:

• In microwave transmission, data is transmitted through air or space, instead of through cables or wires. • Microwaves are high frequency radio waves. 
• Microwave uses line-of-sight transmission through space. 
• Microwave works in LOS (Line of Sight) 
• The line-of-sight means that data signals (or waves) can only travel in straight lines and cannot bend. 
• The data is transmitted and received through a microwave station. • A microwave station is also called relay station or booster. 
• A microwave station contains an antenna, transmitter, receiver, and other equipments that are required for microwave transmission. 
• Microwave antennas are placed on the high towers or buildings. 
• These are placed within 20 to 30 miles of each other. there may be many microwave stations between the sender and receiver. 
• Data is transmitted from one microwave station to another. 
• Each microwave station receives signals from previous microwave station and transmits to next station. 

• Satellite communication system consists of a satellite and several earth stations. 
• The communication satellite is a space station. 
• Each earth station consists of large dish antenna. It can send and receive data signals. 
• A satellite receives microwave signals (or messages) from earth station. 
• It amplifies the signals and sends them to another earth station. Data transmission speed of satellite is fast. 
• There are generally three types of satellite : 
a, GEO (GeoStatonary Orbit), 
b. MEO (Medium Earth Orbit), 
c. LEO (Lower Earth Orbit) 
• Advantage: 
The main advantage of satellite communication system is that a large amount of data can be communicated from one country to another. 
• Disadvantage: 
The disadvantage of satellite communication is that bad weather can affect the quality of satellite transmission.

Global Positioning System:

 The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. 
• GPS was originally intended for military applications.
• In the 1980s, the government made the system available for civilian use. 
• GPS works in any weather conditions, anywhere in the world, 24 hours a day. 
• There are no subscription fees or setup charges to use GPS. 

How GPS Works?

How GPS Works?

 GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use trilateration to calculate the user’s exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. Now, with distance measurements from a few more satellites, the receiver can determine the user’s position and display it on the unit’s electronic map. A GPS receiver must be locked on to the signal of at least 3 satellites to calculate a 2-D position (latitude and longitude) and track movement. With four or more satellites in view, the receiver can determine the user’s 3-D position (latitude, longitude and altitude). Once the user’s position has been determined, the GPS unit can calculate other information, such as speed, bearing, track, trip distance, distance to destination, sunrise and sunset time and more. Radiowave. A very low frequency electromagnetic wave (from roughly 30 kilohertz to 100 gigahertz). Radio waves are used for the transmission of radio and television signals; the microwaves used in radar and microwave ovens are also radio waves. Many celestial objects, such as pulsars, emit radio waves.

Types of Network:

A. Local Area Network (LAN) 
B. MAN (Metropolitan Area Network) 
C. WAN (Wide Area Network)

• A local area network (LAN) is a group of computers and associated devices that share a common communications line or wireless link to a server. 
• Typically, a LAN encompasses computers and peripherals connected to a server within a small geographic area such as an office building or home.
• Computers and other mobile devices can share resources such as a printer or network storage. 
• A local-area network (LAN) is a computer network that spans a relatively small area (about 2000 ft) • Most often, a LAN is confined to a single room, building or group of buildings, however, one LAN can be connected to other LANs over any distance via telephone lines and radio waves. 
• LANs are capable of transmitting data at very fast rates, much faster than data can be transmitted over a telephone line; but the distances are limited and there is also a limit on the number of computers that can be attached to a single LAN. 

• Types of LAN are : 
– WLAN : 
A wireless local area network (WLAN) is a wireless computer network that links two or more devices using a wireless distribution method (often spread-spectrum or OFDM radio) within a limited area such as a home, school, computer laboratory, or office building. 
– Bluetooth Network: 
Bluetooth personal area network (PAN) is a technology that allows you to create an Ethernet network with wireless links between laptops, mobile phones, and handheld devices. 
– PBX: 
PBX stands for Private Branch Exchange, which is a private telephone network used within a company. Users of the PBX phone system share a number of outside lines for making external phone calls.

• A metropolitan area network (MAN) is a network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network (LAN) but smaller than the area covered by a wide area network (WAN). 
• The term is applied to the interconnection of networks in a city into a single larger network (which may then also offer efficient connection to a wide area network). 
• It is also used to mean the interconnection of several local area networks by bridging them with backbone lines. 
• The latter usage is also sometimes referred to as a campus network.

• A computer network that spans a relatively large geographical area.
• Typically, a WAN consists of two or more local-area networks (LANs). 
• Computers connected to a wide-area network are often connected through public networks, such as the telephone system. 
• They can also be connected through leased lines or satellites. 
• The largest WAN in existence is the Internet. 

• Types of WAN :
 – Value Added Network A value-added network (VAN) is a hosted service offering that acts as an intermediary between business partners sharing standards based or proprietary data via shared business processes. 
– VPN (Virtual Pvt Network) VPN is a network that is constructed by using public wires ? usually the Internet to connect to a private network, such as a company’s internal network. There are a number of systems that enable you to create networks using the Internet as the medium for transporting data.


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