Types of networks

LAN (Local area networks)
This network covers a small area such as a school, office or a building. It's usually set up to share files, internet and printers and to play multiplayer games. Local area networks are easy to build and maintain. The simplest LAN is two computers connected by an Ethernet cable (commonly referred to as “LAN Cable”). Multiple computers can be connected to the LAN using a network hub. Multiplayer games can be played by building a temporary LAN which is commonly called a LAN party.
WLAN (Wireless local area network)
As the name suggests, this network provides the same kind of connectivity as LAN without the cables. It uses radio signals to communicate. Your device must be Wi-Fi enabled to connect to a WLAN.
WAN (Wide area network)
Unlike LAN or WLAN, WAN spans a large area such as a city or a country. This is made possible by connecting smaller networks like LAN to each other. The best example of WAN is the internet, which is the world’s biggest WAN. Besides the internet, large businesses and governments use WAN to relay information to their clients and colleagues.
MAN (Metropolitan area networks)
These networks span a large area like a city or a large campus. MANs usually interconnect a number of LANs and provide building blocks for WAN.
SAN (Storage area network)
SAN is a type of local area network (LAN) designed to handle large data transfers.
PAN (Personal area network)
This is your very own personal network. Personal area networks typically involve a mobile computer, a cell phone and/or a handheld computing device such as a PDA or an iPad. You can use the network to transfer files between your devices, sync your calendar etc. Personal area networks can be constructed with cables or wirelessly.
CAN (Controller area network)
This is a network of microchips which can communicate with each other without a host computer. It was designed specifically for automotive applications but is now also used in other areas such as industrial automation and medical equipment.
Desk area network (DAN) is architecture for a multimedia workstation that is based around an ATM (Asynchronous Transfer Mode) interconnect. ATM is a name given to very high speed networking protocols. This architecture allows multimedia devices to be connected to the network instead of the workstation.


DLNA (Digital Living Network Alliance)

When people started networking home entertainment devices, it was difficult and confusing to add a new device and get it to communicate with their computers and other network devices. There was a need for standards and guidelines for home networking media devices. So, several manufacturers got together to create a standard so that all of their products were compatible in a home network and thus the Digital Living Network Alliance (DLNA) was born in 2003.
          When a device is DLNA certified it can connect to other DLNA certified devices irrespective of the manufacturer of the product. DLNA certified devices can: find and play movies; send, display and/or upload photos; find, send, play and/or download music; and send and print photos. DLNA uses Universal Plug and Play (UPnP) for media management, discovery and control so they require little or no setup and can be immediately connected to your existing DLNA network.
CEC (Consumer Electronic Control)
One of the biggest challenges of technological revolution is creating intelligent devices that can communicate with each other. The CEC technology brings us one step closer to the dream. CE (consumer electronic) devices can automatically configure themselves and correct errors without user intervention. Using the HDMI framework, CEC takes user experience to a whole new level. For example, you can connect your camcorder to your CEC-enabled HDTV and the TV will automatically detect the device and display it on the screen. You can now control your camcorder with your CEC-enabled HDTV. Same goes for DVD players and set-top boxes; you don't need to switch remotes when you use different devices. Unlike DLNA, interportability is an issue here. You can control devices only if they have the same manufacturer.
The simplest and most common way for two handheld devices to communicate with each other is via Bluetooth. Bluetooth networking transmits data via low-power radio waves. It communicates on a frequency between 2.402 GHz and 2.480 GHz. This frequency band has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM). Bluetooth devices send out weak signals of about 1 mill watt to avoid interference with other devices such as computers and cell phones. This low power, however, limits its range to 10 meters, but its signal can pass through walls so direct line of sight is not required.
Another great advantage of Bluetooth is that it can connect up to eight devices simultaneously without interference. It uses a technique called “spread-spectrum frequency hopping”which, put in simple words, means it keeps changing its frequency in the designated range and thus interference, if any, lasts for a fraction of a second and goes unnoticed.
          Like any wireless network, security is a concern with Bluetooth. The automatic nature of the connection which makes it easy to use can also be used against you by sending you data without your permission. To avoid this, Bluetooth offers several security modes, and device manufacturers determine which mode to include in a Bluetooth-enabled gadget. When any other device tries to establish a connection to the user's gadget, the user has to decide whether to allow it. If you use the device quite often, you can mark the device as “trusted”and it will be able to exchange data without permission.
 Inspite of all the security measures, there are certain Bluetooth specific problems.
Ø  Bluejacking:Bluejacking is sending text messages or audio/video files to a person without his permission. Although harmless, it can make the user think that his phone is malfunctioning.
Ø  Bluebugging:Bluebuggingis a more serious problem. It allows hackers to use your phone's features, for example by placing calls or sending messages without the user realizing it.
Ø  Car Whisperer:Car Whisperer is a piece of software that allows hackers to send audio to and receive audio from a Bluetooth-enabled car stereo.
One of the many uses of Infrared technology is short range communication. It uses an infrared spectrum of light which is invisible to the naked eye. The device is fitted with infrared light-emitting diodes (LEDs) to emit infrared radiation which is focused by a plastic lens into a narrow beam. The beam is modulated, i.e. switched on and off, to encode the data. The receiver uses a silicon photodiode to convert the infrared radiation to an electric current. It responds only to the rapidly pulsing signal created by the transmitter, and filters out slowly changing infrared radiation from ambient light. It doesn't penetrate walls and so can’t interfere with other devices in adjoining rooms. Before the Bluetooth technology, mobiles exchanged data using infrared but now the most common application of infrared technology is your everyday remote control.
Although the Wi-Fi technology has been around since 1985, it was widely used only after 1997.  Wi-Fi or Wireless Fidelity is actually a play on words with Hi-Fi. It's a trademark of the Wi-Fi Alliance and the brand name for products using the IEEE 802.11 family of standards.
Wi-Fi has made it cheaper and easier to create local area networks in places where cables cannot be run. As the price of chipsets for Wi-Fi continues to drop, manufacturers are building wireless network adapters not only into laptops but also into cell phones and other handheld devices.
Like all wireless technologies, Wi-Fi uses electromagnetic waves to communicate. They are transmitted at frequencies of 2.4 GHz or 5 GHz. This frequency is considerably higher than the frequencies used for cell phones, walkie-talkies and televisions. The higher frequency allows the signal to carry more data and thus make it faster than Bluetooth or Infrared.
 Wi-Fi uses 802.11 networking standards, which come in several variants:
Ø  8O2.11a:Released in September 1999, it transmits at 5 GHz and can move up to 54 megabits of data per second. It also uses a more efficient coding technique called orthogonal frequency-division multiplexing (OFDM) that splits that radio signal into several sub-signals before they reach a receiver. This greatly reduces interference. It has an approximate range of 35 m.
Ø  802.11b:Released with 802.11a, 802.11b is the slowest and the least expensive standard. 802.llb transmits in the 2.4 GHz frequency band of the radio spectrum. It can handle up to 11 megabits of data per second. Its low cost made it popular but its popularity has reduced since newer standards offer better speeds at lower prices.
Ø  802.11g:802.11g was released in June 2003 and transmits at 2.4 GHz like 802.llb, but at a higher speed of 54 megabits of data per second. 802.11g is faster because it uses the same OFDM coding as 802.lla.
Ø  80211n:This is the latest standard and was released in October 2009. It transmits at 2.4 GHz using OFDM technique and offers speeds up to 150 megabits per second.
Wi-Fi has undergone many overhauls because of security concerns. Wired Equivalent Privacy (WEP) encryption was designed to protect against casual snooping but it’s no longer considered secure. Because of WEP’s weakness the Wi-Fi Alliance approved Wi-Fi Protected Access (WPA). Though more secure than WEP, WPA has known vulnerabilities. The more secure WPA2 using Advanced Encryption Standard was introduced in 2004 and is supported by most new Wi-Fi devices.
Radio-frequency identification (RFID) is a technology that uses radio waves to transfer data from an electronic tag, called RFID tag or label, to a receiver within the range of a few meters. These RFID tags are small and can be attached to objects to identify and track them.
          This technology has been around since 1970 but it was too expensive to be used on a large scale. These tags were expensive because they were inductively coupled RFID tags which had a complex system of metal coils, antennae and glass. Then came the capacitively coupled tags which could be mass manufactured at a significantly lower cost. They used conductive carbon ink instead of metal coils to transmit data. There has also been a considerable decrease in the size of RFID. There are RFID chips as small as 0.05 x 0.05 millimeters.
Every RFID tag works in the same way:
1.    Data is stored in an RFID microchip
2.    When the tag’s antenna receives electromagnetic energy from an RFID Reader’s antenna, the tag sends back radio waves to the reader.
3.    These waves are decoded by the reader and data transfer is complete.
There are three types of RFID tags:
Ø  Active tags: These RFID tags use internal batteries as a power source. They have a range of around 30 m which can be boosted to 100 m by using additional batteries.
Ø  Semi-passive tags: They too have batteries but are only activated in the presence of a reader.
Ø  Passive tags: Passive RFID tags rely entirely on the reader for power. They use the electromagnetic energy of the radio waves emitted by the reader. They are small in size and cheaper to manufacture. Because of the limited power source, they have a short range of 6.m.
RFID technology was originally meant to replace bar codes. This could potentially save thousands of man hours spent waiting in lines for check out. With RFID tags, you could just walk out of the store and the reader would automatically bill you for the products you've shopped.
It's currently being used to track livestock. This is done by fitting animals with location-tracking RFID chips. Pets are also being implanted with tiny RFID tags containing information about their owners and their medical history. More recently, these RFID tags are implanted in humans. These tags contain all the medical history of the person and prove extremely useful for Alzheimer’s patients. However, all hospitals are not equipped with RFID readers rendering the tag useless.
Though RFID is commonly used, it will take considerable technological advancement for it to become an everyday use technology.
Near Field Communication (NFC) technology is a short-range wireless communication. NFC uses RFID communication protocols and data exchange formats. Using this, you can communicate with another NFC device or an unpowered NFC chip, called a “tag”.
This technology is being used in credit cards. The new credit cards are fitted with NFC chips which can be simply tapped against a NFC payment terminal to make payment. NFC is also used to make “smart posters”with embedded NFC chips. Tap your NFC enabled phone against them to get all the information you need about the poster.
To know what GSM and CDMA mean, we must first know how a cell phone works. The mobile phone was devised by combining Alexander Graham Bell’s telephone and the radio invented by Nikola Tesla.
Primitive mobile communication technology consisted of CB radios and walkie-talkies. A CB radio system consists of central antenna with around 20-30 channels and the phone transmits data on a particular channel to the tower which then retransmits it and can be received by any one logged on to that channel. A walkie-talkie is also used for communication but it has a single channel and no tower to retransmit its signal, hence it has a limited range. Both walkie-talkies and CB radios are half-duplex devices. That is, two people communicating on a CB radio use the same frequency, so only one person can talk at a time. That’s why you always hear soldiers saying “over”after they finish their sentence so that the other person can start talking. Also limited number of conversations can take place simultaneously because of the limited number of channels.
On the other hand, a cell phone is a full-duplex device. That means that you use one frequency for talking and a second, separate frequency for listening. Both people on the call can talk at the same time. The cellular system divides the city into small cells (25 sq km) so thousands of people can use their cell phones simultaneously. A cell phone also has considerable large number of channels to communicate. Each carrier in each city also runs one central office called the Mobile Telephone Switching Office (MTSO). This office handles all of the phone connections to the normal land-based phone system, and controls all of the base stations in the region.
Now that we have a fair idea about the setup of a cellular network, let’s see how a call is placed.
When you turn on the phone, the phone tries to communicate with a specific channel called the control channel. The phone receives a unique identity number called System Identification Code (SID, specific to each network operator) and compares it to the SID programmed into the phone. If they match, it knows that it's using the home network, if it doesn't, it's on roaming. If the phone can’t find any control channels to listen to, it knows it’s out of range and displays a “no service”message.
It also sends a registration request. This way, the MTSO can keep a track of your location in its database. It looks for you in the database when you get a call.
The MTSO then selects a frequency pair on which you’ll communicate and using the control channel tells your phone to use these frequencies. Once your phone and the tower switch on those frequencies, the call is connected.
If you're travelling you’re bound to change cells. As you move closer to the edge of a cell, your signal strength decreases, meanwhile the tower in the other cell (the one you’re moving closer to) notices that your phone signal strength is increasing. These two towers co-ordinate with the MTSO and it records that you’ve switched cells.
There are three technologies that are used by network operators to carry out this communication. Although the names look scary, you can break it down to simple parts. The first word tells you what the access method is. The second word, division, lets you know that it splits calls based on that access method. The last part says multiple accesses which mean that more than one user can utilize each cell.
Ø  Frequency division multiple accesses (FDMA):FMDA puts each call on a different frequency. It separates the spectrum into distinct voice channels by splitting it into uniform chunks of bandwidth. It’s used for analog transmission but is not considered an efficient method for digital transmission.
Ø  Time division multiple access (TDMA):In TMDA, a narrow band (channel) that is 30 kHz wide and 6.7 milliseconds long is split time-wise into three time slots. Each conversation gets the radio for one-third of the time. This is possible because voice data that has been converted to digital information is compressed so that it takes up significantly less transmission space. Therefore, TDMA has three times the capacity of an analog system using the same number of channels. This technology is used for GSM. GSM systems use encryption to make phone calls more secure.
Ø  Code division multiple access (CDMA):In CDMA, the data is digitized and spread out over the entire available bandwidth. Multiple calls are overlaid on each other on the channel, with each assigned a unique sequence code. In simple words, data is sent in small pieces over a number of the discrete frequencies available for use at any time in the specified range. At the receiver, that same unique code is used to recover the signal.
          What does this mean for you? In terms of connectivity and speeds, there's not much difference between them. However, in CDMA, there's no SIM (subscriber identification module) card and so changing your network provider can be a little difficult. In a GSM phone, you can switch networks by simply changing your SIM card. To overcome this drawback, CDMA network providers try to provide better rates and plans.
GPS or Global Positioning System is a satellite navigation system that provides location to any user with a GPS receiver free of cost. The GPS project was developed in 1973 to overcome the limitations of previous navigation systems. GPS is a network of 27 Earth-orbiting sat elites maintained by the Unites States of America. They orbit at 19,300 km within a time period of 12 hours. The orbits are arranged in a specific way so that at least four satellites are in the line of sight of the receiver.
For the GPS receiver to receive a signal it should have a clear view of the sky. To understand how GPS calculates your exact location, we must first understand Trilateration. Imagine you know your distance from point A, then you know that you can lie anywhere on a circle centered at A and the radius being your distance from the point. Now suppose you know your distance from another point B; you can infer that you'll lie on one of the two intersection points of the two circles. If you know your distance from a third point, you can pinpoint your location as the intersection point of the three circles. This is called 2-D Trilateration. If you extend this logic to 3-D, you'll need your distance from four points. Since you already know your distance from the center of the earth, you need to know your distance from three other points. This information is provided by the GPS satellites.
          Every satellite continually transmits messages that include the time at which it was transmitted, its orbital information, its general health and rough orbits of other satellites. When this signal is received by your GPS receiver, there's a very tiny time lag because of the time taken by the signal to reach the GPS receiver. This lag is used to calculate the distance of the satellite (speed of light x time lag). Since the speed of light is very high, the time lag is very low and to measure this lag accurately the clocks on the satellite as well as the GPS receiver should be synchronised down to the nanosecond. Such high level of accuracy is possible using atomic clocks which are very expensive. Instead of having atomic clocks on the satellite and the receiver, only the satellite has the atomic clock and the receiver contains a simple quartz clock. The receiver calculates its own accuracy by receiving signals for four satellites and corrects itself. Every GPS has stored data of where every satellite should be at what time and using that it can calculate the location. Speed is simply calculated by the change in location divided by time.
Once your location is calculated by the GPS device, it can help you in navigation, traffic updates, weather forecast etc. Any average smartphone has a GPS device and can provide you basic navigation information. There are more sophisticated GPS devices for cars which offer a wider range of features.