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the United States. In Europe, the Global System for Mobile Communica-
tions (GSM) is based on TDMA. In the United States, the IS-54 standard is
based on TDMA, and the IS-95 standard is based on CDMA. There are also
other cordless telephony technologies that are limited to short ranges, like the
British second-generation cordless telephone (CT2), based on FDMA, and
the digital European cordless telephone (DECT), based on TDMA.
10.4.3
Wireless Wide-Area Networks
Because the cellular products previously mentioned are relatively expensive
and slow, some other technologies are being deployed that are based on
packet switching instead of circuit switching. For example, the advanced
radio data information system (ARDIS), which provides a data transmission
rate from 8 to 19.2 Kbps; the RAM mobile data system, which provides a
data rate of 8 Kbps; the cellular digital packet data (CDPD) system, which
provides data services on top of the AMPS analog system with a maximum
data transmission rate of 19.2 Kbps but with an effective rate of 9.6 Kbps;
and the general packet radio service (GPRS), which is being developed by
the GSM consortium to include packet switching with higher expected data
rates than the previous ones. In general, with all these WAN technologies the
transmission rates are not very high.
10.4.4
Wireless Local-Area Networks
Wireless LANs provide higher data rates (more than 1 Mbps) to mobile users
who have less mobility (e.g., inside a building, on a campus). Some products
try to provide wireless Ethernet connections and use different link technolo-
gies like radio frequencies, infrareds, and microwaves. Examples of products
are FreePort, WaveLAN, and Altair, and standards, like the IEEE 802.11
and the HiperLAN, are being developed.
10.4.5
Satellite Networks
Mobile satellite networks allow global coverage for two-way voice commu-
nications but limited data capabilities. Data rates and propagation times
depend on the type of satellites used. Geostationary satellites (GEOS) pro-
vide global coverage with few but expensive stations and with great delays
when establishing communications that require a high power cost. Low earth
orbit satellites (LEOS) are smaller and less expensive, and communications
have low cost but also a low data rate. The cells are much smaller and allow
