# Introduction to Computers/Networks

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Introduction to Computers → Networks
This page is part of the Introduction to Computers project. :
A network is a group of computers (or a group of smaller networks) that are connected to each other by various means, so that they may communicate with each other. The internet is the largest network in the world.

## Resource Sharing

Networks are able to share one resource, such as a printer, for numerous computers. This allows many individual computers to access a single network resource. This saves money and space for the organization. w:Computer_printer

### Data

Once networks were setup, people found that the next best thing was the ability to easily share documents. The type of server that stores files is called a file server. Data can be in the form of text, images, numbers or characters. w:Data

### Programs

Server or Network based programs are programs that are loaded onto an online server or network as opposed to directly onto the individual computers. This program can therefor be accessed by any computer possessing the correct amount of bandwidth and system specifications. In short it uses the server as an application server.

### Work better

Many organizations use networks for many purposes such as making schedule for colleagues, pick up days for meetings (when everybody will be able to attend) and provide useful online connections for network-linked employees.
Employees can communicate on a network with other employees through email.
w:Computer_networking

## Types
### mainframe

Mainframe computers are typically large, metal boxed computers with large processing abilities. The terminals are called "dumb terminals" because they only send and receive data, leaving the processing to the mainframe. w:Mainframe_computer

### Client server

The client/server refers to the way two computer programs interact with each other. The client makes a request from the server, who then fulfills the request. Although this idea can be used on one computer it is an efficient way for a network of computers in different locations to interconnect.

#### LAN

LAN stands for Local Area Network. The first LANs were created in the late 1970s. LANs are small networks constricted to a small area like a house, office, or city. LANs are used to share resources like storage,internet,etc... w:Local_area_network
A 'node' on a LAN is a connected computer or device like a printer.

#### WAN

WAN stands for Wide Area Network. WANs are very large networks that interconnect smaller LAN networks, for a large geographic area like a country(i.e., any network whose communications links cross metropolitan, regional, or national boundaries.) w:Wide_area_network
WANs are usually for private companies, however, some built by internet service providers connect LANs to the internet.
* WAN can use a combination of satellites, microwave, and link and variety of computers from mainframes to terminals.
A 'node' on a WAN is a LAN.

#### MAN

When the LANs that you want to connect are not far apart, just blocks away, then you can make a MAN (Metropolitan Area Network). The main difference between a WAN and a MANs is the speed of the connection. Because the LANs are so close in a MAN, high speed fiber optic cables are affordable. w:Metropolitan_area_network

#### PAN

Personal Area Network: a network on you. Usually, uses short range wireless technology is used to connect devises like a cell phone and a PDA. w:Personal area network

#### HAN

Home Area Network: uses cable, wired, or wireless connections to connect a homes' digital devices. For example, fax machines, computers, DVD's etc. See w:Home network.
Usually home networks work on P2P because one of them can't be spared to just be a server. Files are shared from each computer held in shared folders.

#### BGAN

Broadband Global Area Network supports mobile communications across an arbitrary number of wireless LANs and satellite coverage areas. Example: Mobiles,internet etc..... w:Broadband Global Area Network

### P2P

P2P (peer-to-peer) is a type of network where "each workstation has equivalent capabilities and responsibilities".
* Link to document on P2P networks.

#### MP3's

MP3 is a format that allows audio (usually music) files to be compressed so they are small enough to be sent over the internet or stored as digital files. It is popular because the compression method takes out the sounds that less audible to humans thus retained as much sounds that can be heard by human ear in a relative small storage.
They are shared frequently on P2P networks on the internet. A portion of your hard drive becomes a server, so each P2P member is both a server and a client, both serving and receiving mp3 files. Napster is an example of a "pure" P2P network. Through this type of decentralized system, you are able to communicate from node to node, with out the use of a server.

### Internet

The Internet is a worldwide, publicly accessible series of interconnected computer networks that transmit data by packet switching using the standard Internet Protocol. It is a "network of networks" that consists of millions of smaller networks, which together carry various information and services, such as electronic mail, online chat, file transfer, and the interlinked web pages and other resources of the World Wide Web (WWW). So the Internet is a collection of interconnected computer networks, linked by copper wires, fiber-optic cables, wireless connections, etc. In contrast, the Web is a collection of interconnected documents and other resources, linked by hyperlinks and URLs. The World Wide Web is one of the services accessible via the Internet, along with various others including e-mail, file sharing, online gaming and others.
w:Internet

#### Intranet

Intranet is a private computer network used by companies for employees. It is only accessible within a limited area, thus increasing the security of the network. It is not public and can't be accessed via WWW.
It can be described "a private version of the Internet," w:Intranet

#### Extranet

Extranets are basically intranets between a company and its as well as suppliers and customers who must login.
Extranets may be used for simple transactions such as purchasing and have become very popular.

#### VPN

Virtual Private Network shares wires with another network, but has encrypted packets of data that only you can see. It is private through technology, thus virtual. w:Virtual_private_network

## hardware
### Topologies
#### Bus

All nodes are connected to a single wire or cable (the bus) which has two endpoints. Each communications device on the network transmits electronic messages to other devices. If some of those messages collide, the sending device will wait and then try to transmit again. The advantage of bus network is that it can be organized as a peer-to-peer network or client/server network.
It is also relatively inexpensive to install.
The disadvantage is that if the bus network fails, the whole system network fails.
The wider the bus the better!

#### Ring

The ring network is a network in which all communications devices and microprocessors are connected in a continuous loop. Electronic messages pass around the ring until they reach the correct destination; there is no central server.
The advantage of a ring network is that messages only flow in one direction.
The disadvantage is that if a single connection is broken, the whole network stops working. The distributed star or tree topology can provide many of the advantages of the bus and the star topologies. It connects workstations to a central point, called a hub. This hub can support several workstations or hubs which, in turn, can support other workstations. Distributed star topologies can be easily adapted to the physical arrangement of the facility site. (Integrated Publishing)

#### Star

A network that links all microcomputer and other communication devices through a central server.
The advantages of this hub is that it prevents impact between messages. The network forms a star shape having the central server in the middle with a single branch outward, the branch will not branch to another device.
Other Advantages Include:
* Good performance.
* Scalable, Easy to set up and to expand.
* Any non-centralised failure will have very little effect on the network, whereas on a ring network it would all fail with one fault.
* Easy to detect faults
* Data Packets are sent quickly as they do not have to travel through any unnecessary nodes.
* It is used for centralised control.

### Components
#### Host

A central computer (mainframe or midsize) that controls a network and the devices on it, called nodes.
The host computer has all the control over who has access to what hardware, software and all other resources on the network.

#### Node

A node is any device that is attached to a network. Some examples of a node are: printer, terminal, microcomputer, and storage device.

#### Hub

A hub facilitates multiple input of the same device. It acts like a power bar to enable the multiple plugs to share 1 source of electricity. For example, there is a ethernet hub where all the ethernet cables are connected to to share a terminal. A USB hub will allow multiple units of USB devices to plug into a single USB port.
A hub is called a half-duplex device because data can not be transfered back and forth simultaneously, it only goes one way at a time.

#### Switch

It connects a single computer to the network and allows it to use all the bandwidth available. Unlike a hub, it sends messages to the computer that is the intended recipient.
Data can be transmitted back and forth at the same time, improving the performance of the network. This is called a full-duplex device.
Can be used in connection with a hub.

#### Bridge

Connects local area networks which are similar using a bridge interface to make a larger network. It also connects the same kind of networks This is crucial because similar networks can be joined together to make bigger ones!

#### Gateway

A gateway allows the communication between dissimilar networks. It can be between a WAN and a LAN or 2 LANs on different operating systems or layouts. A gateway can come as either a hardware, software or possibly both.

#### Router

A router is a device that connects several devices together, and directs messages to communicate them. This is important because high speed routers can handle major data traffic.

#### Backbone

As the name suggests, the backbone includes significant communication equipment such as gateways and routers that serve to connect computer networks within an organization.
The thing that distinguishes the backbone from other paths on the network is it's speed (bandwidth). The backbone is the fastest. This is important because it is the central structure that connects all other elements of the internet.

### bandwidth

Bandwidth refers to the amount of information that can be sent through a given communication channel in a given amount of time. When connecting to the internet you have the option of connecting through:
* narrow bandwidth (100 kbps - kilo bits per second)
* medium bandwidth (1 Mbps)
* broad bandwidth (100 Mbps)

### wires
#### twisted pair

A twisted pair is two copper wires that act as insulators that are "twisted" together. Its purpose is to reduce the interference that comes from electric fields. Twisted pair wire has been the most common channel (or medium) used for telephone systems.

#### coaxial cable

A coaxial cable consists of a center conductor surrounded by an insulator which is in turn surrounded by an outer conducting shield. Coaxial cables are used to carry high frequency (usually radio frequency)signals for long distances. It can be used for cable television.

#### fiber optic

Fiber optics is a glass or plastic fiber designed to guide light along its length. Optical fiber can be used as a medium for telecommunication and networking. It currently supplies the widest commercial bandwith available. w:Fiber_optic

### wireless
#### IR

Infra red light can be used to transfer data wirelessly. This is how remote controls work. Line of sight must be preserved for it to work.

#### RF

Radio frequency is a combination of electrical energy and magnetic energy that carries communication signals. It is short for radio frequency and is measured in Mhz. Internationally, the RF spectrum is assigned by the International Telecommunications Union in Geneva, Switzerland.

#### microwave

Microwaves are electromagnetic waves with wavelengths shorter than one meter and longer than one millimeter, or frequencies between 300 megahertz and 300 gigahertz.
Microwaves can't curve or bend around the earth, so there has to be many microwave stations placed "25-30 miles" away from each other (line-distance), with nothing to block the connection. Each station takes signals from the next and makes the signal stronger and then sends it to the following station. (361)

### Short-range wireless
#### Bluetooth

Bluetooth provides a way to connect and exchange information between devices such as mobile phones, laptops, PCs, printers, digital cameras, and video game consoles over a secure, globally unlicensed short-range radio frequency. w:Bluetooth

#### ZigBee

It is a commerical network wireless protocol. It is low-cost, low-power, long battery life, wireless sensor networks.

#### Wi-Fi

Open source wireless network protocols. We use it in college to connect wireless laptops. WiFi has a lot of advantages. Wireless networks are easy to set up and inexpensive. They're also unobtrusive -- unless you're on the lookout for a place to use your laptop, you may not even notice when you're in a hotspot. A wireless network uses radio waves, just like cell phones, televisions and radios do. In fact, communication across a wireless network is a lot like two-way radio communication. Here's what happens: A computer's wireless adapter translates data into a radio signal and transmits it using an antenna. A wireless router receives the signal and decodes it. It sends the information to the Internet using a physical, wired Ethernet connection.

#### GEO

Short for Geostationary Earth Orbit, a satellite system used in telecommunications. GEO orbit the earth at 22,300 miles above the earth's surface. They are tied to the earth's rotation and are therefore in a fixed position in space in relation to the earth's surface. The satellite goes around once in its orbit for every rotation of the earth. The advantage of a GEO system is that the transmission station on earth needs to point to only one place in space in order to transmit the signal to the GEO satellite. GEO systems are used for transmissions of high-speed data, television signals and other wideband applications.
w:Geostationary_orbit

#### Piro

Short for Middle Earth Orbit, a satellite system used in telecommunications. MEO satellites orbit the earth between 1,000 and 22,300 miles above the earth's surface. MEOs are mainly used in geographical positioning systems,known as GPS and are not stationary in relation to the rotation of the earth Medium Earth orbit satellites (2000 km). w:Medium_Earth_Orbit

#### LEO

Short for Low Earth Orbit, a satellite system used in telecommunications or data communication such as e-mail, paging and videoconferencing.
Low Earth Orbit satellites (400 km) used for communication. More satellites are needed (because fewer are visible around the horizon) but they are cheeper to get up and require less signal strength. w:Communications_satellite#Low-Earth-orbiting_satellites

### NOS

NOS stands for Network Operating System. NOS is software that manages the activity of a network through an operating system w:Network_operating_system
Some examples of popular NOS software are Novell NetWare, Linux, and Microsoft Windows NT/2000.

### packet

A packet is a formatted block of data that is carried by a packet mode computer network. When data is converted into a packet, the network can give out longer messages, more reliably. w:Packet_(information_technology)

### Protocol

A standard that controls the connection or communication between two end points of computing. It can be controlled by hardware or software or a combination of the two. In other words, a protocol defines the behavior of the computer.

### ethernet

A local area network technology which can be used with almost any kind of computer. Describes how data can be sent in packets, within a range, between computers and other net worked devices. Ethernet is a family of frame-based computer networking technologies for local area networks.

### token ring

Token Ring is a local area network (LAN) where all computers are connected in a ring or star which a bit is used in order to prevent the collision of data between two computers that which would like to send messages at the same time. Is it said that the Token Ring protocol is the "second most widely-used protocol on local area networks after Ethernet".
Source: http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci213154,00.html

## Examples
### GPS
#### 24 MEO's
#### 10 feet accurate

When downloading GPS signals via GPS receiver & software you will get two answers - 1) broadcast ephemeris & 2) precise ephemeris. This is due to an effect known as the Doppler effect. Similar to sound waves from a moving vehicle being heard after a car passes line of sight, satellites will pass before the radio signals reach the receiver on Earth. When you open your file with the downloaded signals you will, depending on the software, get two sets of data. One with a corrected set of coordinates that account for the velocity of the satellites, their instant coordinates & the time it takes for their radio signal to reach Earth, known as Precise Ephemeris. The second set will contain the satellites' position at the time they broadcasted it from orbit, known as Broadcast Ephemeris.

### cell phones
#### 1G analog
#### 3G smart

3RD GENERATION

#### 4G smart

4th Generation