Computer network

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Network

A network is a series of points or nodes interconnected by communication paths.

Networks can interconnect with other networks and contain sub networks.



What is a computer network?

• A group of geographically distributed computers which are interconnected using communication lines in such a way that any computer in the group may be accessed or used from any other computer in the group.

• Interconnection of two or more computers and peripherals.



• Computer Networking is basically the process of connecting two or more computers or devices, using hardware and software, so that data can be transferred and shared between them.



Computer Networks:

• Facilitate communications• Permit sharing of files, data, and other

types of information• Share network and computing resources• May be insecure• May interfere with other technologies• May be difficult to set up



What A Network Includes:

• Transmission Hardware

- NIC (Network interface controller), MODEM, Other transmitter

• Intermediate hardware devices

- Hub, Repeaters, Amplifiers, Switch, Router, Firewalls

• Protocol software

- encodes and formats data

- detects and corrects problems



Communication media

• Computer networks can be classified according to the hardware and associated software technology that is used to interconnect the individual devices in the network, such as electrical cable (HomePNA, power line communication), optical fiber, and radio waves (wireless LAN).



Communication media

Wired technologies• Twisted pair wire is the most widely used

medium for telecommunication. Twisted-pair cabling consist of copper wires that are twisted into pairs. Ordinary telephone wires consist of two insulated copper wires twisted into pairs.

• Coaxial cable is widely used for cable television systems, office buildings, and other work-sites for local area networks.



Communication media

• Optical fiber cable consists of one or more filaments of glass fiber wrapped in protective layers that carries data by means of pulses of light. It transmits light which can travel over extended distances. Fiber-optic cables are not affected by electromagnetic radiation.



Communication media

Wireless technologies• Terrestrial microwave – Terrestrial microwaves

use Earth-based transmitter and receiver. The equipment looks similar to satellite dishes. Terrestrial microwaves use low-gigahertz range, which limits all communications to line-of-sight. Path between relay stations spaced approx, 48 km (30 mi) apart. Microwave antennas are usually placed on top of buildings, towers, hills, and mountain peaks.



Terrestrial microwave dish



Communication media

• Communications satellites – The satellites use microwave radio as their telecommunications medium which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically 35,400 km (22,000 mi) (for geosynchronous satellites) above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.



Communications satellite



Communication media

• Cellular and PCS systems – Use several radio communications technologies. The systems are divided to different geographic areas. Each area has a low-power transmitter or radio relay antenna device to relay calls from one area to the next area.



PCS cellular systems



Communication media

• Wireless LANs – Wireless local area network use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANs use spread spectrum technology to enable communication between multiple devices in a limited area. An example of open-standards wireless radio-wave technology is IEEE 802.11.



Communication media

• Infrared communication can transmit signals between devices within small distances of typically no more than 10 meters.

• A global area network (GAN) is a network used for supporting mobile across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is handing off the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial wireless LANs.



Types of Computer Networks

• Networks are classified depending on the geographical area covered by the network:

1. Local Area Network or LAN

2. Metropolitan Area Network or MAN

3. Wide Area Network or WAN

4. Wireless Networks

5. Internetworks



Local Area Network

• is a network that connects computers and devices in a limited geographical area such as home, school, computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network is a node.

• covers a small area



• Computers connected to a network are broadly

categorized as servers or workstations. • Servers are generally not used by humans

directly, but rather run continuously to provide "services" to the other computers (and their human users) on the network. Services provided can include printing and faxing, software hosting, file storage and sharing, messaging, data storage and retrieval, complete access control (security) for the network's resources, and many others.



• Workstations are called such because they

typically do have a human user which interacts with the network through them. Workstations were traditionally considered a desktop, consisting of a computer, keyboard, display, and mouse, or a laptop, with integrated keyboard, display, and touchpad. With the advent of the tablet computer, and the touch screen devices such as iPad and iPhone, our definition of workstation is quickly evolving to include those devices, because of their ability to interact with the network and utilize network services.



Local Area NetworkAdvantages of connecting computers in a LAN:• workstations can share peripheral devices

like printers. This is cheaper than buying a printer for every workstations.

• User can save their work centrally on the network file server. This means that they can retrieve their work from any workstation on the network. They don’t need to go back to the same workstation all the time.



Advantages of connecting computers in a LAN:

• User can communicate with each other and transfer data between workstations very easily.

• One copy of each application package such as word processor, spreadsheet ect. can loaded onto the file and shared by all users. When a new version comes out, it only has to be loaded onto the server instead of onto every workstation.



Disadvantages of connecting computers in a LAN

• Special security measures are needed to stop users from using programs and data that they should not have access to;

• Networks are difficult to set up and need to be maintained by skilled technicians.

• If the file server develops a serious fault, all the users are affected, rather than just one user in the case of a stand-alone machine.



Metropolitan Area Network or MAN

• A metropolitan area network (MAN) is a computer network that usually spans a city or a large campus. A MAN usually interconnects a number of local area networks (LANs) using a high-capacity backbone technology, such as fiber-optical links, and provides up-link services to wide area networks (or WAN) and the Internet.



Wide Area Network or WAN

• A wide area network (WAN) is a computer network that covers a large geographic area such as a city, country, or spans even intercontinental distances, using a communications channel that combines many types of media such as telephone lines, cables, and air waves. A WAN often uses transmission facilities provided by common carriers, such as telephone companies.



Wireless Network• Wireless network refers to any type of

computer network that is not connected by cables of any kind. It is a method by which homes, telecommunications networks and enterprise (business) installations avoid the costly process of introducing cables into a building, or as a connection between various equipment locations. Wireless telecommunications networks are generally implemented and administered using a transmission system called radio waves. This implementation takes place at the physical level (layer) of the network structure.



Internetwork

• An internetwork is the connection of multiple computer networks via a common routing technology using routers. The Internet is an aggregation of many connected internetworks spanning the Earth.



Networks may also be different in their design and layout. There are client/server networks and peer-to-peer

networks.

• A computer network is referred to as client/server if (at least) one of the computers is used to "serve" other computers referred to as "clients".

• In a client/server environment, each computer still holds (or can still hold) its (or some) resources and files. Other computers can also access the resources stored in a computer, as in a peer-to-peer scenario. One of the particularities of a client/server network is that the files and resources are centralized. This means that a computer, the server, can hold them and other computers can access them. Since the server is always On, the client machines can access the files and resources without caring whether a certain computer is On.



Client/Server Networking



• In a peer-to-peer network, each computer holds its files and resources. Other computers can access these resources but a computer that has a particular resource must be turned on for other computers to access the resource it has. For example, if a printer is connected to computer A and computer B wants to printer to that printer, computer A must be turned On.

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Peer-to-Peer Networking


Computer network

Technology

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