Information Technology Reference
In-Depth Information
WDN is a cluster of technologies primarily related to, developed for, and marketed
by vendors in the telephony and handheld market. This market covers a lot of ground
from basic digital cellular phones to relatively sophisticated PDAs and tablet PCs
that may rival notebook computers in capabilities. WDN includes protocols such as
the Cellular Digital Packet Data (CDPD), an older 19.2 Kbps wireless technology
that is still in use in some police departments for network communication with pa-
trol cars; General Packet Radio Service (GPRS) and Code Division Multiple Access
2000 (CDMA2000) which are multi-user, combined voice and data 2.5 generation
technologies that exceed 100 Kbps; and Wireless Application Protocol (WAP) which
provides wireless support of the TCP/IP protocol suite and now provides native sup-
port of HTTP and HTML. If you're using a cellular phone with text messaging and
Web support, you're likely using some form of WAP.
PANs began as “workspace networks.” Bluetooth, for example, is a desktop
mobility PAN that was designed to support cable-free communication between com-
puters and peripherals. Blackberry ( http://www.blackberry.com ) is like Bluetooth
on steroids. It integrates telephony, web browsing, email, and messaging services
with PDA productivity applications. As such it blurs the distinction between PAN
and WLAN.
WLAN is what most of us think of as Wireless technology. It includes the now-
ubiquitous 802.11 family of protocols, as well as a few others. Table I provides a
quick overview of some of the 802.11 protocol space. Note that all but the first are
derivative from the original 802.11 protocol introduced in 1997.
We note in passing that both the 802 and 802.11 landscape is somewhat more clut-
tered than our table suggests. For example, 802 also allows for infrared support at the
physical layer. In addition, proprietary standards for 802.11 have been proposed. In
T ABLE I
T HE 802.11 P ROTOCOL F AMILY
Standard
802.11
802.11a
802.11b
802.11g
802.11n
Year
1997
1999
1999
2003
2006
Frequency
2.4 GHz
5 GHz
2.4 GHz
2.4 GHz
?
Band
ISM
UNII
ISM
ISM
?
Bandwidth
2 Mbps
54 Mbps
11 Mbps
54 Mbps
300+ Mbps
Encoding
DSSS/ FHSS
OFDM
DSSS
OFDM
?
techniques
“Year” denotes approximate year of introduction as a standard (e.g., 802.11a and 802.11b were introduced
at the same time, though 802.11a came to market later). The two bands used for “WiFi” are Industrial,
Scientific and Medical (ISM) and Unlicensed National Information Infrastructure (UNII). Bandwidth is
advertised maximum. Encoding, aka “spectrum spreading” techniques appear at the physical or link layer
and include frequency-hopping spread-spectrum (HPSS), direct-sequence spread-spectrum (DSSS), and
orthogonal frequency division multiplexing (OFDM). (Source: [2] .)
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