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WIRELESSLANs 825Table 2Evolution of Wireless Systems1G systems
Established in late 1970s
Based on analog technology
Aimed at providing voice telephony service
Major technologies: AMPS, TACS, ETACS, NMT, JTACS, NTACS, NTT, C-450, RMTS, Radiocom
2G systems
Established in early 1990s
Based on digital and PCS technology
Aimed at providing a better spectral efficiency, a more robust communication, voice privacy,
and authentication capabilities
Major technologies: GSM, TIA/EIA/IS-136 or D-AMPS, JDC, PHS, TIA/EIA/IS-95A, IS-54, PACS,
CT-2, DECT
2.5G systems
Based on 2G Systems
Aimed at providing the 2G systems with a better data rate capability
Major technologies: GPRS, IS-95B, HDR, GSM/EDGE
3G systems
First planned in 1992, embodied by IMT-2000
Based on digital and PCS technologies
Supports hybrid air interfaces
Aimed at supporting multimedia services
Major technologies: UTRA, W-CDMA, UWC-136, IMT-2000, CDMA 2000, UMTS
4G systems
Developed in the labs, targeted for deployment beginning in 2010
Aimed at providing data rates of up to 100 MbpsC-HTML (Compact HTML)
C-HTML (compact HTML) is a simplified version of
HTML. As the Web became more focused on powerful
computers with high-bandwidth connections, it was de-
cided to create a special version of HTML for devices
with limited computing power. It has only the core textual
display language and simple graphics. The advantage of
C-HTML is that it displays perfectly normal on any regular
Internet browser.HDML (Handheld Device Markup Language)
HDML (handheld device markup language) is a more rad-
ical departure from HTML. HDML requires that a site
avoid the use of tables, frames, flashing lights, and other
complicated features. HDML replaces the familiar con-
cept of Web pages with two new test layout metaphors
called card and decks. A card is a single-user interaction,
which would equate to a page in HTML. A single HDML
file is called a deck because it can include many cards.XML (Extensible Markup Language)
XML (extensible markup language) is a code that lets Web
authors define their own tags. This means that it can be
used for any type of device that becomes Internet-enabled.
XML provides more flexibility. Unlike HTML, it is not lim-
ited to the description built in the language.WIRELESS LANs
The emergence and continual growth of wireless LANs
are being driven by the need to lower the costs associatedwith network infrastructures and to support mobile net-
working applications that offer gains in process efficiency,
accuracy, and lower business costs (Wood, n.d.).
The implementation of wireless networks offers many
tangible cost savings when performing installations in
difficult-to-wire areas. If rivers, freeways, or other obsta-
cles separate buildings you want to connect, a wireless
solution may be much more economical than installing
physical cables or leasing communication circuits. The
deployment of wireless networking in these situations
costs thousands of dollars, but it will result in a definite
cost savings in the long run.
A problem inherent to wired networks is downtime due
to cable faults. With wired networks, a user might acci-
dentally break the network connector when trying to dis-
connect a PC from the network to move it to a different
location. Wires and connectors can easily break though
either misuse and/or normal use. An advantage of wire-
less networking, results from the use of less cables. This
reduces the downtime of the network and the costs asso-
ciated with replacing cables.
The installation of cabling is often a time-consuming
activity. For LANs, installers must pull twisted-pair wires
or optical fibers above the ceiling and drop cables through
walls to network outlets that they must affix to the wall.
These tasks can take days or weeks. The deployment of
wireless networks greatly reduces the need for cable in-
stallations, making the network available for use much
sooner.
Unfortunately, wireless LANs suffer from a fatal flaw—
they are slow. The result is that wireless LANs have