A computer network is a group of two or more computers connected together to share information and resources. A computer network permits sharing of resources among devices communicated in the network. ARPANET is the first network developed by Robert Kahn and Vinton Cart in 1969.

Benefits of Network Nowadays, a computer network is very useful for communication all over the world.

• Facilitating communication: By using the network, people can communicate easily at anywhere throughout the world. Example: E-mail, Facebook, Video telephone calls and chat rooms.


• Sharing hardware: In the network, users can access and use hardware components like printers, hard drives, and CD-ROM drives. If a printer is connected to the network, then every user can access the printer.


• Sharing software: By using the network, each user can access applications.


• Sharing files: In the network, any user can access the data or information and can be shared with other users. It can share the storage files and information.

Network Classification The network is mainly classified into 3 types. Connection method A computer network can be classified based on the software and hardware technologies used for communicating computer systems.

• Ethernet is a physical and data link layer of LAN network. It can explain how the data is transmitted to other network devices on the same network.


• Ethernet is using wiring technology to communicate with computers. It includes hubs, switches, bridges and routers.

Wired technology Twisted pair wires Twisted are telephone wires. These are mainly used in telecommunication networks. These wires consist covered copper wires and are used for voice and data transmission.

• Twisted wires are mainly used to reduce cross-talk and electromagnetic induction.


• Transmission speed range is 2-100 million bits per second.

Coaxial cable Coaxial cable is used for television systems. The cable consists of copper or aluminum wire, covered with a flexible material with high dielectric constant.

• Transmission speed range is 200-500 million bits per second.

Optical fiber cable Optical fiber cable is mainly used in a long distance telecommunication system. The cable consists of one or more filaments of glass fiber wrapped in securing layers.

• Fiber-optic cables cannot be affected by electromagnetic radiation.


• Transmission speed is trillions of bits per second. Transmission speed is hundred times faster than coaxial and thousand times faster than twisted pair wire.

Wireless technology

• Terrestrial Microwaves are utilizing earth-based transmitter and receiver with low gigahertz range. Microwave antennas are placed on the top of buildings, towers, and hills. These are stationed in space at 30 miles.


• Communications Satellites have the capability of receiving and relaying voice, data and TV signals. These are stationed in space at 22,000 miles above the equator.


• Cellular and PCS Systems are used in radio communication technologies. It relays the calls from one area to the next area with a low power transmitter.


• Wireless LANs are used to allow communication between multiple devices in a limited area by using spread spectrum technology. Bluetooth is an open wireless protocol used for data transfer over a short distance.

Network classification on the basis of scale Computer network is mainly classified into 3 types.
Local Area Network LAN is a network, in which computers are interconnected within a small geographical area such as home, office buildings, and schools.

• LAN is a single-site network and works based on the Ethernet technology. In this network, each computer is called as a node. LAN can use client & server architecture and peer-to-peer architecture.


• All the terminals are communicated with the main computer, which is known as the server. Data transfer range is 10-100 megabits per second. LAN is owned by single organization or person.


• Wireless LAN works on radio waves and gives the network connection to all users in the surrounding area.


• Wi-Fi stands for Wireless - Fidelity and is used for providing wireless internet access and implements WLANs by using radio waves.

Wide Area Network A WAN is a network, in which computers are connected in a large geographical area such as a city, and country. It is a collection of LANs.

• A WAN is connected to LAN through a network device called as the router. It is connected by using telephone wires, satellite links, and other long-range communication technologies.


• A WAN is not owned by a single organization but exists under collective or distributed ownership. It works on physical, data link layer and network layer.

Metropolitan Area Network A MAN is a network, which connects two or more local area networks such a town, and city. It is larger than LAN and smaller than WAN.

• MAN is mainly used for sharing hardware and software resources among various users.


• This network uses coaxial cables or optical fiber cables and also uses the hub, routers, and switches.


• The other types of networks are
  
  
  • PAN: PAN stands for Personal Area Network. It is a small communication network and establishes communication between various technological devices. PAN is connected within 10 meters and is created by using USB and Bluetooth.
  
  
  • VPN: VPN stands for Virtual Private Network. It is a global internet used for Intra and inter-organization. VPN is a private, but virtual network is used to divide traffic of various user communities under network with strong security features.
  
  
  • Intranet and Extranet: These are the extensions of a computer network. An intranet is a group of networks connected by using Internet protocol and IP tools. A large intranet should have one or more web servers to provide information to the user. An extranet has limited connections to the network and does not include single LAN network.

Hardware components of a Network All networks are invented with basic hardware building blocks to interconnect network nodes.

• Network interface card: It is a part of computer hardware component used to access computers and to connect with a network. It can provide low-level addressing system through the use of MAC address. Sometimes these acts like Ethernet cards.


• Repeaters: A repeater is an electronic device that consists of two ports and two segments to connect to LAN. Repeaters are required for cable in twisted wire Ethernet configuration. Repeaters can operate on the physical layer.


• Hub: It is similar to Repeater, but consists of multiple ports to connect to the network. It works on the physical layer. Hub receives a packet data from one network channel and transmits to the other network channels. It acts as the main connection for various computers and server in a network.


• Switch: It is small hardware component used to forward and filter data link layer data grams based on MAC address. These are mainly used for forwarding decisions of frames. Switches that have the capability of routing additional layers are called as multi-layer switches.


• Bridges: A Bridge is used to establish communication between multiple networks at the data link layer of OSI model. If a bridge is connected to a port and address, it will send traffic for that particular address only.
  
  
  • Local bridge is directly communicated with local area networks.
  
  
  • Remote bridges can be used to implement a wide area network.
  
  
  • Wireless bridges can be used to connect remote stations to Local Area Networks.


• Routers: A router is a hardware device, which can move the packets from one network to other networks using information in protocol headers.

Data Transmission The data communication channels are used to transmit the data electrically. These channels are divided into three types.
Narrow Band: Narrow band is used with the audio spectrum to generate sounds. Narrow band refers to radio communication and telecommunication tools and services.

• Narrow band uses the narrow set of frequency in the communication channel. It is more narrow than broadband and is easy to focus on particular technological solutions. The frequency range of narrow band is 300-340 Hz.

Voice band: A voice frequency or voice band is a part of the audio range. It is used for the voice transmission. In telephony, the range of voice frequency is 300-3400 Hz.

• The range of ultra frequency band of the electromagnetic spectrum is 300-3000 Hz. A single voice- frequency transmission channel can allocate 4kHz bandwidth. 8 kHz frequency is used for the digital PSTN on the basis of the pulse code modulation.


• Telephone wires transmit the data in analog form. A sound is directly converted into electrical signal but results in analog signals. A telephone wire is connected to the modem to convert analog signals into digital signals.

Broadband: The broadband in telecommunication refers to a signaling method that can handle wide range frequencies.

• These frequencies can be divided into channels. A television antenna has the capability of receiving a wide range of frequencies. In data communication, a digital modem will transmit 56 kilobits per second.


• Broadband is used to increase the effective rate of data transmission. Broadband in analog video distribution is used to refer to individual channels that are modulated at fixed frequencies.

Network Topology The network topology is the layout of a network installation. It explains the configuration of the connection between nodes. The main types of topologies are: 1.BUS topology 2.Mesh topology 3.Ring topology 4.Star topology
Bus Topology The Bus topology is a network topology, mainly used in Ethernet networks. It is used to move one cable from the first device in the network to the last device.

Advantages:

• All the nodes are directly connected to each other, so it requires very short length cable.


• The architecture is very simple and can be easily extended to other sides.


• The bus topology requires less number of cables and the cables are less expensive.

Disadvantages:

• It is difficult to find the problem in communication.


• Flat isolation is difficult in data transmission and it becomes slow while increasing nodes in the network.

Ring Topology The ring topology works with large bandwidth in high- performance networks. It is also called as circular topology.

• Ring topology is implemented as Token ring and Fiber distributed data interface by using protocols.


• This data is transmitted in the form of token ring. The nodes are connected in a circular way.

The key advantage of ring topology is it requires short length cable and is suitable for optical fiber.
Disadvantages:

• In ring topology, nodes are connected in a circular way, if any transmission problem occurs, then the entire network will stop functioning.


• In this, fault diagnosis is difficult and every node must connect with two other nodes. If the ring is broken, then that particular node cannot work.


• If any computer fails, then that affects the entire network. The network gets disturbed while adding and removing nodes in the network.

Star Topology In the network topology, the peripheral nodes communicate with a central node directly such as hubs and switch. Star topology gives fault tolerant and will not affect other nodes. In this topology, if the hub or any central node fails, then the entire network will be collapsed.

Advantages:

• All the nodes are directly connected to the central node.


• Installation of this topology is very easy and the faults can be found easily.


• If a node fails, then it will not affect the other systems.

Disadvantage:

• It requires cable length and if the hub fails, the entire network will be disabled.


• It is difficult to expand.

Mesh Topology It is also known as completely interconnected topology. In this technology, every node follows point to point the link to every other node. Star topology contains at least two nodes with two or more paths between them. It has the highest fault tolerance of all the network topologies.

The advantage of mesh topology is: This topology is perfectly suitable for long distance networking. If one path is busy, then it will communicate through another route.
Disadvantage of the mesh topology is its cable length and the installation and maintenance costs are more.