How Enables Internet Connectivity
By
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Muhd Azzulfa Jaini – 03B3221
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Mohd Hailmizan Jafar – 03B3219
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Steven Lim -
Contents
What are the various ways of connecting to the Internet?
How does it communicate with other devices?
Introduction
Let's say that you are sitting at your computer, surfing the Web, and
you get a call from a friend who says, "I just read a great article! Type
in this URL and check it out. It's at
http://computer.howstuffworks.com/web-server.htm." So you type that URL
into your browser and press return. And magically, no matter where in the world
that URL lives, the page pops up on your screen.
At the most basic level possible, the following diagram shows the steps that brought that page to your screen:
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Your browser formed a connection
to a Web server, requested a page and received it.
- Behind the Scenes
If you want to get into a bit more detail on the process
of getting a Web page onto your computer screen, here are the basic steps that
occurred behind the scenes:
If you've never explored this process before, that's a lot of new
vocabulary. To understand this whole process in detail, you need to learn about
IP addresses, ports, protocols... The following sections will lead you through
a complete explanation.
- The Internet
So what is "the Internet"? The Internet is a
gigantic collection of millions of computers, all linked together on a computer
network. The network allows all of the computers to communicate with one
another. A home computer may be linked to the Internet using a phone-line modem,
DSL or cable modem that talks to an Internet service provider (ISP). A
computer in a business or university will usually have a network interface card
(NIC) that directly connects it to a local area network (LAN)
inside the business. The business can then connect its LAN to an ISP using a
high-speed phone line like a T1 line. A T1 line can handle approximately
1.5 million bits per second, while a normal phone line using a modem can
typically handle 30,000 to 50,000 bits per second.
ISPs then connect to larger ISPs, and the largest ISPs maintain fiber-optic "backbones" for an entire nation or region. Backbones around the world are connected through fiber-optic lines, undersea cables or satellite links (see An Atlas of Cyberspaces for some interesting backbone maps). In this way, every computer on the Internet is connected to every other computer on the Internet.
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- Putting It All Together
Now you know a tremendous amount about the Internet.
You know that when you type a URL into a browser, the following steps occur:
To start off
the discussion, here is a table to show the major differences between the main
types of wireless connectivity and traditional networking.
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Bluetooth is an industrial specification for wireless
personal area networks (PANs) first developed by Ericsson, later formalized by
the Bluetooth Special Interest Group (SIG). The SIG was formally announced on May
20, 1999. It was established by Sony Ericsson, IBM, Intel, Toshiba and Nokia,
and later joined by many other companies as Associate or Adopter members.
The system is named after a Danish
king Harald Blåtand (Harold Bluetooth in English), King of
Bluetooth provides a way to
connect and exchange information between devices like personal digital
assistants (PDAs), mobile phones, laptops, PCs, printers and digital cameras
via a secure, low-cost, globally available short range radio frequency.
Bluetooth lets these devices
talk to each other when they come in range, even if they're not in the same
room, as long as they are within 10 metres (32 feet of each other).
A typical
Bluetooth mobile phone headset
The latest version currently available
to consumers is 2.0, but few manufacturers have started shipping any products
yet. Apple Computer, Inc. offered the first products supporting version 2.0 to
end customers in January 2005. The core chips have been available to OEMs (from
November 2004), so there will be an influx of 2.0 devices in mid-2005. The
previous version, on which all earlier commercial devices are based, is called
1.2.
Bluetooth is a wireless radio
standard primarily designed for low power consumption, with a short range (up
to 10 metres) and with a low-cost transceiver microchip in each device.
It can be used to wirelessly
connect peripherals like printers or keyboards to computers, or to have PDAs
communicate with other nearby PDAs or computers.
Cell phones with integrated
Bluetooth technology have also been sold in large numbers, and are able to
connect to computers, PDAs and, specifically, to handsfree devices.
The standard also includes
support for more powerful, longer-range devices suitable for constructing wireless
LANs.
A Bluetooth device playing the
role of "master" can communicate with up to 7 devices playing the
role of "slave". At any given instant in time, data can be transfered
between the master and one slave; but the master switches rapidly from slave to
slave in a round-robin fashon. (Simultaneous transmission from the master to
multiple slaves is possible, but not used much in practice). These groups of up
to 8 devices (1 master and 7 slaves) are called piconets.
The Bluetooth specification also
allows connecting two or more piconets together to form a scatternet, with some
devices acting as bridges by simultaneously playing the master role in one
piconet and the slave role in another piconet. These devices have yet to come,
though are supposed to appear within the next two years.
Any device may perform an
"inquiry" to find other devices to which to connect, and any device
can be configured to respond to such inquiries.
Pairs of devices may establish a
trusted relationship by learning (by user input) a shared secret known as a
"passkey". A device that wants to communicate only with a trusted
device can cryptographically authenticate the identity of the other device.
Trusted devices may also encrypt the data that they exchange over the air so
that no one can listen in.
The protocol operates in the
license-free ISM band at 2.45 GHz. In order to avoid interfering with other
protocols which use the 2.45 GHz band, the Bluetooth protocol divides the band
into 79 channels and changes channels up to 1600 times per second.
Implementations with versions 1.1 and 1.2 reach speeds of 723.1 kbit/s. Version
2.0 implementations feature Bluetooth Enhanced Data Rate (EDR), and thus
reach 2.1 Mbit/s. Technically version 2.0 devices have a
higher power consumption, but the three times faster rate reduces the
transmission times, effectively reducing consumption to half that of 1.x
devices (assuming equal traffic load).
Bluetooth differs from Wi-Fi in
that the latter provides higher throughput and covers greater distances but
requiries more expensive hardware and higher power consumption. They use the
same frequency range, but employ different multiplexing schemes. While
Bluetooth is a cable replacement for a variety of applications, Wi-Fi is a
cable replacement only for local area network access. A glib summary is that
Bluetooth is wireless USB whereas Wi-Fi is wireless Ethernet.
Bluetooth devices and modules
are increasingly being made available which come with an embedded stack and a
standard UART port. The UART protocol can be as simple as the industry standard
AT protocol, which allows the device to be configured to cable replacement
mode. This means it now only takes a matter of hours (instead of weeks) to
enable legacy wireless products that communicate via UART port.
Versions 1.0 and 1.0B had
numerous problems and the various manufacturers had great difficulties in
making their products interoperable. 1.0 and 1.0B also had mandatory Bluetooth Hardware
Device Address (BD_ADDR) transmission in the handshaking process, rendering
anonymity impossible at a protocol level, which was a major set-back for
services planned to be used in Bluetooth environments, such as Consumerium.
In version 1.1 many errata found
in the 1.0B specifications were fixed. There was added support for non-encrypted
channels.
This version is backwards
compatible with 1.1 and the major enhancements include
This version is backwards
compatible with 1.x and the major enhancements include
- Other Wireless Connections
There are already a couple of ways to get around using
wires. One is to carry information between components via beams of light
in the infrared spectrum. Infrared refers to light waves of a lower
frequency than human eyes can receive and interpret. Infrared is used in most
television remote control systems, and with a standard called IrDA (Infrared
Data Association) it's used to connect some computers with peripheral devices.
For most of these computer and entertainment purposes, infrared is used in a
digital mode -- the signal is pulsed on and off very quickly to send data from
one point to another.
Infrared communications are fairly reliable and don't cost very much to build into a device, but there are a couple of drawbacks. First, infrared is a "line of sight" technology. For example, you have to point the remote control at the television or DVD player to make things happen. The second drawback is that infrared is almost always a "one to one" technology. You can send data between your desktop computer and your laptop computer, but not your laptop computer and your PDA at the same time.
These two qualities of infrared
are actually advantageous in some regards. Because infrared transmitters and
receivers have to be lined up with each other, interference between devices is
uncommon. The one-to-one nature of infrared communications is useful in that
you can make sure a message goes only to the intended recipient, even in a room
full of infrared receivers.
The second alternative to wires,
cable synchronizing, is a little more troublesome than infrared. If you
have a Palm Pilot, a Windows CE device or a Pocket PC, you know about
synchronizing data. In synchronizing, you attach the PDA to your computer
(usually with a cable), press a button and make sure that the data on the PDA
and the data on the computer match. It's a technique that makes the PDA a
valuable tool for many people, but synchronizing the PDA with the computer and
making sure you have the correct cable or cradle to connect the two can be a
real hassle.
Most Bluetooth
devices are described as 'Class 2'. These are very low power (typically 1
milliwatt - 1/1000th of a watt) and have a range of about 10 m (33 ft).
Some devices -
for example, some plug in 'dongles' that can be added to to laptop computers -
are Class 1. These have range comparable to that of Wi-Fi, ie, 100 m or
330 ft.
With
Bluetooth, short range is actually a benefit, because it reduces the chance of
interference between your Bluetooth devices and those belonging to other people
nearby.
A limited, but
growing number of devices use Bluetooth at present. Devices that are starting
to have Bluetooth connectivity built in include :
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Digital
cameras and camcorders
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Printers
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Scanners
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Cell
Phones
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PDAs
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Laptops
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Keyboards
and Mice
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Headsets
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In-car
handsfree kits
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GPS
navigation receivers
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Home
appliances (microwaves, washers, driers, refrigerators)
In addition, add
on Bluetooth adapters are available for computers (eg with a USB interface) and
for PDAs (eg SD cards).
- Bluetooth Frequency
Bluetooth communicates on a frequency of 2.45
gigahertz, which has been set aside by international agreement for the use
of industrial, scientific and medical devices (ISM).
A number of devices that you may already use take advantage of this same radio-frequency band. Baby monitors, garage-door openers and the newest generation of cordless phones all make use of frequencies in the ISM band. Making sure that Bluetooth and these other devices don't interfere with one another has been a crucial part of the design process.
