Page 136 - DCAP207_NETWORKS_DCAP406_COMPUTER_NETWORKS

Unit 8: Data Link Protocols

Spread Spectrum: It is popular in WLAN and provides operation in a number of radio bands Notes
including 900 MHz, 2.4 GHz and 5 GHz. The wireless nodes are restricted to 1 watt of power for
transmissions, which appear as noise to all except intended receivers because the nature of
spread spectrum.
Low-Power Narrowband: It enables to transmit narrowband signals at low-power levels and is
considered an alternative to spread spectrum technique that operates at high data rate. This
approach operates at 10 Mbps in the 5 GHz band with 50 mw of peak transmission power with
a reduced transmission range of 30 meters (100 feet) in a home or office environment.
HiperLAN: It stands for Higher Performance Radio LAN. It is a wireless technology standard
developed by the European Telecommunications Standards Institute. It provides a data rate of
about 24 Mbps using five channels each of them with a channel width of 23.5 MHz in 5 GHz band.
Such throughput is capable of supporting multimedia applications.
Infrared LANs: It is considered an alternative approach to radio based WLANs. Infrared
networking works on electromagnetic radiation with wavelengths of 820 to 890 nanometers
equivalent to a frequency of about 350,000 GHz. The advantages of IR are that it does not require
licenses and safety issues. Additionally, it provides huge potential capacity and good control of
interference. The drawback of this technology is that it does not penetrate walls; so infrared
WLANs are confined in a room only. They can also not perform well in outdoor areas in
sunlight. The Infrared Data Association which is a consortium of manufacturers of IRDA devices
is intending to provide low-cost IR communications characterized by directional point-to-point
communications of up to one meter, 115-Kbps and 4-Mbps connectivity and walk up ad hoc
connectivity for LAN access, printer access and portable computer to portable computer
communications. Laptops are provided with IRDA ports.

Task List the various devices used in wireless networking along with their functionality.

8.9 Bluetooth

Bluetooth is a proprietary open wireless technology standard for exchanging data over short
distances (using short wavelength radio transmissions in the ISM band from 2400-2480 MHz)
from fixed and mobile devices, creating personal area networks (PANs) with high levels of
security. Created by telecoms vendor Ericsson in 1994, it was originally conceived as a wireless
alternative to RS-232 data cables. It can connect several devices, overcoming problems of
synchronization.

Bluetooth is managed by the Bluetooth Special Interest Group, which has more than 14,000
member companies in the areas of telecommunication, computing, networking, and consumer
electronics. The SIG oversees the development of the specification, manages the qualification
program, and protects the trademarks. To be marketed as a Bluetooth device, it must be qualified
to standards defined by the SIG. A network of patents are required to implement the technology
and are only licensed to those qualifying devices; thus the protocol, whilst open, may be regarded
as proprietary.

Bluetooth Implementation

Bluetooth uses a radio technology called frequency-hopping spread spectrum, which chops up the
data being sent and transmits chunks of it on up to 79 bands (1 MHz each; centered from 2402 to
2480 MHz) in the range 2,400-2,483.5 MHz (allowing for guard bands). This range is in the globally
unlicensed Industrial, Scientific and Medical (ISM) 2.4 GHz short-range radio frequency band.

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