Types of networks
LAN (Local area networks)
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)
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)
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)
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)
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)
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.
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
DLNA (Digital Living Network Alliance)
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
CEC (Consumer Electronic Control)
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.
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
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
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.
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
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
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.
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.
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.
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
Wi-Fi uses 802.11 networking standards, which come in several variants:
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.
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.
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.
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
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.
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.
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
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
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.
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.
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
GSM and CDMA
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.
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.
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.
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
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.
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
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