1.a.Communication : The process of exchanging views, ideas or information between two or more persons or device is called communication. Example . Telephone, newspaper, email etc.
b. Data communication: Exchanging data in form of text, sound, graphics, video etc between two or more devices in different places is called data communication. Eg. Telephone, email, chat, etc.
c. Telecommunication: Exchanging information and data inform of text, sound, video etc. between two or more devices in a significant distance is known as telecommunication.
d. Components of telecommunication
i. Sender: a person/device which sends the data to the receiver. Sender is the source of information.
ii. Receiver: a person/device who/ which receives information and data from sender.
iii.Data : It is the matter of information which is sent by the sender to the receiver. Data may be text, sound, video, graphics etc.
iv. Medium : It is the path or channel through which data transmit from sender to receiver. They are wired and wireless.
v. Protocol : It the set of rule which governs the data communication over the network devices.
e. Modes of communication:
There are three modes of data communication. They are :
i. Simplex mode : It the one way communication mode where data flow only in a direction. Eg, Newspaper, TV, Radio.
ii. Duplex mode: It is two way communication mode where data flow in both directions. It is further divided into two categories;
a.Half duplex mode: Two way communication alternatively where data flow form sender to receiver first, then receiver to sender later. Eg. Email, walky- talky etc.
b.Full duplex mode : Two way communication simultaneously( side by side at the same time) where data flow in both direction at the same time. Eg. Telephone, chat etc.
2.a Computer network : Computer network is defined as a physical and logical interconnection of two or more computers and devices with the help of cable or wireless media for sharing hardware ,software and information.
i. Advantages:
* Hardware resources can be shared
* Software and application can be shared
* It reduces the cost of computer installation by sharing resources.
* Fast and easy communication
ii. Disadvantages :
· Difficult to maintain data security.
· Hackers may enter into the system easily and cause loss of data.
· It is expensive to maintain and to keep system upto date.
b. Network Terminology :
i. Server : It is the powerful and main computer in network which provides services to the clients by sharing resources. It controls and manages overall network nodes. There are five types of server ;they are
* file server
* print server
* database server
* application server
* message server
ii. Client /workstation/node : Computers and devices attached to the network is called nodes. They request for data and services to the server to be accessed. Client or workstation are only computers attached under server.
ii. NIC (Network Interface card/Ethernet card ): It is an electronic board/card which is installed to all the network computers for data communication. It provides dedicated fulltime connection via cable or wireless media among all the network computers. It is an intelligent device which acts as bridge and amplifies the signals during transmissions over network devices.
iv. NOS ( Network Operating System ) : It is the collection of powerful programs that manages and control over network system and resources. It is installed in server computer. Eg. Window 2000, windows NT, Window ME, Windows ‘7 , windows ‘8, Window Vista, LINUX, UNIX, Novell Netware etc.
v. Protocol : A set of rules and procedures which governs the data transmissions over network devices.
Protocol makes logical connections among all the components and control traffic and data collision.
Few examples of protocols are :
TCP/IP, FTP, SMTP, POP, NETBIOS, NETBIUE, TOKEN RING, EATHENET , ARP, VOIP, APPLE TALK,PPP
vi. Media connecter: It is a device which acts as an interface between NIC and network cables. Different connectors are used for different types of cables. They are
ST/ SC — Fiber optic cable
RJ- 45— Twisted pair cable( STP and UTP)
BNC/T connector — Coaxial cable
vii. Bandwidth : It refers to the data handling capacity of transmission ( communication media). It measures the amount of data transmission per second over a communication channel. bps ( Bits per second is a unit of bandwidth measured in digital device, where as cycle per second( Hz) is unit of bandwidth in analog device.
3.a Communication media/Channel
Definition : It is defined as a path or channel through which data or signal flow in electromagnetic form from one device to another or in a specific direction.
There are two types of communication channels viz;
i. Wired( Bounded) transmission media
ii. Wireless( Unbounded )transmission media
i. Wired./ Guided transmission media: The path or channel where data or signal flow through physical cable connection from one device to another in a specific directions. The types of wired media are as follows
a. Twisted pair cable : It the combination of two insulated copper wires twisted together in pair to form a cable for transmission. It is further divided into two types :
* UTP ( Unshielded Twisted Pair): It is the combination of two unshielded wires twisted around each other to carry the signal through cable. It is very common, popular and less expensive. It has maximum transmission rate ie, 1 Gbps. It is commonly used in Star topology and is available in 7 categories ( Cat 1 to cat 7).
*STP( Shielded Twisted pair) : It consist of two twisted pair copper cables are separately wrapped in a metal sheath to provide better noise protection from external disturbance. It is expensive and difficult to install. It covers maximum 90 mt.
b. Co-axial cable : It is made up of copper wire in center and surrounded with insulator. The center wire carries the data signal. It provides better noise rejection. It is used in bus topology as well as TV signals. Its maximum speed is 10 Mbps.
c. Fiber optic cable: It is the collection of thin transparent fiber glass in a bundle ( cladding) through which data travels in pulse of light. It is made up of pure silicon dioxide. It transmits the data 2 billion bps. In a half inch bundle, 50,000 thin glass fiber can be bundled together. It is used for broad band media for longer distance. It is secure because it is immune to electromagnetic interference. It is used for networking
ii. Wireless./ Unguided transmission media:
The path or channel where data and signal flow without physical cable connection is called wireless communication channel. Data and signal flow in electromagnetic form through air, laser beam or vacuum. The types of wireless media are as follows:
a. Radio wave: it is a wireless transmission media through which data and signal flow in radio frequency(RF). It is used to send radio signal in far and distance by modulating radio wave into following different frequency. They are :
* FM(Frequency Modulation)
*PM( Phase Modulation)
* AM( Amplitude Modulation)
b. Micro wave Transmission: It is wireless transmission media where signal are sent via electromagnetic pulse between two visible tower(antenna) covering maximum 40km distance. It provides a good bandwidth and useful for MAN. Obstacle like tall building, mountain etc disturb the communication , so it is also called line of sight transmission.
c. Infrared transmission : It is a type wireless transmission media where signals are sent via pulses of infrared light. It is used for LAN.
d. Satellite transmission: It is a broad band wireless transmission media which is used to transmit radio and TV signal, internet and telephone data over longer distance. It is faster and cheaper to transmit data all over the world .Generally, it is placed 36,000 Km above the earth’s surface.
4.a Network categories ( Types of Network )
On the basis of distance and size computer network is divided into three categories . They are as follows:
i. LAN (Local Area Network): Interconnection of Network computer and devices inside a room or building via wired or wireless media is called LAN.
Features:
*It is owned by single person/organization.
* It uses cable or infrared or short radio frequency for data transmission.
* It is installed inside building or a room covering maximum5 km. distance and distance between one node to another is 1 m to 1 km..
ii. MAN( Metropolitan Area Network ): It is a network of computer that spans over a city or town in a same geographical region. It is used to link between offices in different location of the same city. Eg. Network of Himalayan bank, cellular phone etc.
Features :
· It is owned by single or multiple organization.
· It uses microwave or fiber optic cable for communication.
iii. WAN( Wide Area network): It is a network of computers that spans over a large geographical area covering different countries, cities or provenances. It covers all LAN and MAN together and make a huge network.
Features :
· It uses Public transmission media like telephone and satellite
· It is owned by multiple organization
5. a Network models ( architecture):
The design pattern of LAN networks are as follows.
i. Centralized computing network :
It is a network of computers where there is a central computer called host for data processing and storing ,and other computers connected to it called terminal. It is used by large business organization for huge data processing. It is also called host- based networks.
ii. Client server networks : The network model where there are one or more servers and others are workstation is client server network. Server shares the resources, and control the workstations. It is considered to be the best network model because it maintains data security and manages central control over all the clients. The server always must be on and it is good to connect server wit UPS for regular power supply.
iii. Peer to peer network : A group of computers that acts as both server and workstation is called peer to peer network model. All computers in networks aer equal for providing and using resources. It is useful in very small organization but it does not maintain data security. It is inexpensive network model.
6.a. Netwok Topology :
Physical arrangement of network computers and devices and cables in a LAN is called network topology. It is the arrangement pattern of LAN computers for communication. There are 3 types of topology; they are as follows:
I. Bus topology : A pattern of network where all the computers and devices are connected to a single cable ( trunk) is called bus topology. The devices are connected to both sides of a trunk via nodes. Information flow through the entire length of cable unless they are taped by any nodes. It uses Ethernet protocol.
Advantages:
· Less expensive because it requires less cable
· Easy to install and add new node
Disadvantages:
*The length of the cable limit the nodes to be added.
*Traffic will be slower if more nodes are added.
*If there is wrong in cable whole system will go down.
ii. Star topology : It is a network pattern where all network computers and deices are arranged in star pattern connected through central device called hub.
Each node and server are connected to each other to the hub for communication. It uses Ethernet protocol.
Advantages :
· It is easy to install and reconfigure
· More nodes can be added or removed as required
· It is suitable for smaller as well as bigger size of network.
Disadvantages:
· It requires more cable and hub ,so it is expensive.
· If there is wrong in hub, whole network will go down.
iii. Ring topology : A pattern of network where all computers and devices are arranged in a circular loop connecting all the nodes via single cable. It connects all workstation and server through a short (fiber optic)cable. It is suitable smaller network. It uses token ring protocol.
Advantages:
i. It is cheaper and suitable for small organization.
Disadvantages:
i. It is difficult to reconfigure.
ii. If one system fail , whole network will come to the end.
7. Network communication device.
i. Bridge : It the the device which communicates between two or more similar network patterns and protocol. It receives and sends the data packet where the address is matched.
ii. Router : It is a network communication device which exchanges data between two or more different network shaving same protocols.
iii. Gateway: It is a device which convert and communicate the data over two or more completely dissimilar networks pattern and protocol. It is mostly used in intranet and internet.
iv. Hub : It is a device used in star topology as a central control for data communication. It connects all network components to its node . It is also called multi port repeater.
v. Repeater: It is a network component which receives the weak signal, amplify them and forward to the destination device. It makes the communication faster in longer distance.
vi. MODEM: It is a device which communicates with other computers connecting through telephone line. It receives the analog signal via telephone line and convert into digital pulse called demodulation similarly, while sending the data, it converts the digital signal into analog signals called modulation. There are two types of modem viz; internal modem and external modem .
