Many digital phones are advertised as Internet-ready, coming
with a browser or a connectivity kit. Advertising for Wireless
Internet modems or Internet-ready phones can be very deceiving,
however. If the ad mentions a data rate of 19.2 Kbps, then
it’s CDPD. The phone may be CDMA or TDMA but the data
connection is through either an internal or external CDPD
modem connected to an analog channel. If a TDMA or CDMA
phone has a data connectivity kit, such as a cable to connect
the phone and a laptop, and it does not mention the data rate,
or if the phone has an internal browser, the modem is integrated
into the phone and probably uses the rate of the traffic
channel, 8 Kbps for TDMA and 9.6 or 14.4 Kbps for CDMA.
GSM phones have long used data capabilities built into the
phones so that they connect to a laptop by cable or include
built-in modems to send data in the traffic channel at 9.6
Kbps. In all of these cases except CDPD, the connection is still
circuit-switched for 2G networks.
A second type of modem is essentially a phone without
voice capabilities on a PCMCIA card. There are modems of
this type for every technology. They have an antenna integrated
into them or are connected by a short cable to an antenna.
Again, if the data rate is specified as 19.2 Kbps, it’s CDPD. If
the rate is not specified, it’s probably using a traffic channel.
Some PCMCIA modems offer a data rate of 56 Kbps and mention
wireless in the same sentence. These actually combine two
modems in one: a 56K landline modem and a wireless traffic
channel modem.
With the launch of 2.5G and 3G networks, modems will
become available having much higher data rates. They will fall
into the same two categories: internal to a phone with a cable
connection to a laptop or as a PCMCIA card. GPRS technology
is just being launched in Europe but as with all new technologies,
GPRS modems are still scarce. The United States will see next
generation modems for CDMA and TDMA phones by 2002. The
CDMA phones will use 1xRTT technology, and the TDMA
phones will use GPRS. The CDMA standard 1xEV, with data
rates up to 2.4 Mbps, will not be available until later. Products for
W-CDMA will become available later in 2002 or 2003. 65
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CDPD MODEMS
Early cellular manufacturers and operators recognized the
need for data communications, and the first modems were very
similar to standard modems used in homes and offices.
However, cellular uses a valuable, shared commodity—spectrum.
(Fixed telephone lines or wires may be shared, but they
can always be increased in number if necessary.) CDPD was
created as a digital packet data service over an analog cellular
telephone: It uses the same analog channels as voice, but with
different modulation applied to the air interface. Traffic channels
not being used for voice calls may be used for CDPD calls.
CDPD was the first digital data application to use packet data
for cellular, and it is still very much in use today by carriers
such as AT&T Wireless Services.
CDPD is fully compatible with analog cellular and is colocated
with AMPS systems. Therefore, the analog infrastructure,
such as frequency spectrum, cell sites, towers, and antennas,
can be shared. The CDPD network elements overlay parallel to
the analog infrastructure (see Figure 2-3). Analog voice or analog
data using an AMPS modem or digital data using a CDPD
modem shares the same frequency spectrum. External modems
are most common for CDPD communications, typically existing
as PCMCIA cards for laptop computers, as accessories for PDA
devices, or as external modems for connection to an analog
phone. Some manufacturers actually include CDPD modems
into their cellular telephone. This makes a 2G digital phone
“Internet ready” because all TDMA and CDMA phones also
include AMPS analog compatibility, and CDPD is carried on
AMPS channels.
Two key design criteria were used to develop the CDPD
protocol. From its inception, it was designed to use TCP/IP, the
Internet protocol, making it transparent to Internet data. It was
also designed to overlay an AMPS network, taking advantage of
existing infrastructure. These design goals make CDPD very
attractive to any carrier that manages an AMPS network. This
becomes even more important when a carrier lacks true 2.5G
or 3G capabilities and finds itself at a competitive disadvantage.
CDPD can make any TDMA or CDMA phone “Internet
ready” with 19.2 Kbps data rates by using TCP/IP in a packetdata
network instead of on a circuit-switched connection.
As of the end of the February 2000, CDPD was available in
184 markets in the United States covering 56 percent of the
United States population and 60 international markets.* As
2.5G and 3G cellular networks launch, CDPD will begin to
fade, but as long as there are 2G or analog phones, CDPD will
retain its usefulness. And although it may compete with SMS
for short text messages, it still has one advantage—CDPD
works across networks with different physical layers. A CDPD
modem in a laptop using CDMA can still send an email to a
phone across the country, which is using TDMA.
need for data communications, and the first modems were very
similar to standard modems used in homes and offices.
However, cellular uses a valuable, shared commodity—spectrum.
(Fixed telephone lines or wires may be shared, but they
can always be increased in number if necessary.) CDPD was
created as a digital packet data service over an analog cellular
telephone: It uses the same analog channels as voice, but with
different modulation applied to the air interface. Traffic channels
not being used for voice calls may be used for CDPD calls.
CDPD was the first digital data application to use packet data
for cellular, and it is still very much in use today by carriers
such as AT&T Wireless Services.
CDPD is fully compatible with analog cellular and is colocated
with AMPS systems. Therefore, the analog infrastructure,
such as frequency spectrum, cell sites, towers, and antennas,
can be shared. The CDPD network elements overlay parallel to
the analog infrastructure (see Figure 2-3). Analog voice or analog
data using an AMPS modem or digital data using a CDPD
modem shares the same frequency spectrum. External modems
are most common for CDPD communications, typically existing
as PCMCIA cards for laptop computers, as accessories for PDA
devices, or as external modems for connection to an analog
phone. Some manufacturers actually include CDPD modems
into their cellular telephone. This makes a 2G digital phone
“Internet ready” because all TDMA and CDMA phones also
include AMPS analog compatibility, and CDPD is carried on
AMPS channels.
Two key design criteria were used to develop the CDPD
protocol. From its inception, it was designed to use TCP/IP, the
Internet protocol, making it transparent to Internet data. It was
also designed to overlay an AMPS network, taking advantage of
existing infrastructure. These design goals make CDPD very
attractive to any carrier that manages an AMPS network. This
becomes even more important when a carrier lacks true 2.5G
or 3G capabilities and finds itself at a competitive disadvantage.
CDPD can make any TDMA or CDMA phone “Internet
ready” with 19.2 Kbps data rates by using TCP/IP in a packetdata
network instead of on a circuit-switched connection.
As of the end of the February 2000, CDPD was available in
184 markets in the United States covering 56 percent of the
United States population and 60 international markets.* As
2.5G and 3G cellular networks launch, CDPD will begin to
fade, but as long as there are 2G or analog phones, CDPD will
retain its usefulness. And although it may compete with SMS
for short text messages, it still has one advantage—CDPD
works across networks with different physical layers. A CDPD
modem in a laptop using CDMA can still send an email to a
phone across the country, which is using TDMA.
CELLULAR DATA MODEM TECHNOLOGIES
Today’s cellular technology offers several different methods for
data communications—an internal modem with built-in browser,
an internal modem with an external port for connection (typically
RS-232 or infrared (IR) to computer, or internal SMS
messaging.
Modems fall into two categories: CDPD or traffic channel.
CDPD offers true packet data communications at 19.2 Kbps
whereas modems using the traffic channels are limited to the
maximum rate for a traffic channel ( 14.4 Kbps, depending on
the standard). Future 2.5G and 3G networks will differ in two
distinct ways: Traffic channel rates will be higher, from 64
Kbps to 2.4 Mbps, and all data will be either packet-based or
high speed circuit-switched.
data communications—an internal modem with built-in browser,
an internal modem with an external port for connection (typically
RS-232 or infrared (IR) to computer, or internal SMS
messaging.
Modems fall into two categories: CDPD or traffic channel.
CDPD offers true packet data communications at 19.2 Kbps
whereas modems using the traffic channels are limited to the
maximum rate for a traffic channel ( 14.4 Kbps, depending on
the standard). Future 2.5G and 3G networks will differ in two
distinct ways: Traffic channel rates will be higher, from 64
Kbps to 2.4 Mbps, and all data will be either packet-based or
high speed circuit-switched.
CELLULAR AND PCS-BASED TECHNOLOGIES
Cellular and PCS telephones will be the predominant mobile
communications technologies for the foreseeable future. This
does not mean to imply that cellular is superior to other technologies,
only that it is more prevalent. With nearly 1 billion
users worldwide, there is no close second. These mobile technologies
are currently facing a major evolution in many areas,
however, including the technical and business sectors, because
they provide the economical means for realization of not only
mobile computing, but also many other applications ranging
from financial and retail communications to remote control
and signaling.
Recent technology, whether it’s TDMA, CDMA, or GSM
has experienced severe physical layer and user interface constraints.
Wireless data transmission is limited to relatively low
speeds, 19.2 Kbps or less. Cellular display applications for data
are limited to text messaging through SMS or WAP. There is a
wide disparity between browser applications. Some simple
graphics can be accomplished with WAP applications on some
phones, whereas i-Mode in Japan offers extensive graphics
including color displays on PDC phones,* even though the
data rates are similar. As GPRS is launched on GSM networks,
users will finally be able to access data at speeds superior to
traditional dial-up Internet service, approaching 115 Kbps.
With the launch of next-generation cellular systems and 3G
systems, users will have greater choice for data communications.
New modems will be commercially available to take
advantage of higher bandwidth networks, and packet data will
replace circuit-switched data. Choices will include either SMS
or a wireless modem using packet data at higher speeds. New
high-speed data capabilities will provide the platform for
mobile multimedia services, access to corporate LANs, and
financial transactions from a mobile terminal. The type of service
will determine the best data service to use. Many applications
will find SMS satisfactory even if a modem is available for
high data-rate service. And those that must use analog cellular
will still have CDPD.
Other devices such as PDAs and Pocket PCs as shown in
Figure 2-1 may use cellular networks or proprietary networks.
(Some cellular manufacturers have integrated PDAs into their
phones.)
Some cellular-based products will bear little resemblance to
a cellular phone at all, such as PCMCIA modems that incorporate
a cellular phone without voice capabilities. In addition
to standard products, custom products will be available for
wireless remote data and control applications. Examples are
shown in Figure 2-2.
communications technologies for the foreseeable future. This
does not mean to imply that cellular is superior to other technologies,
only that it is more prevalent. With nearly 1 billion
users worldwide, there is no close second. These mobile technologies
are currently facing a major evolution in many areas,
however, including the technical and business sectors, because
they provide the economical means for realization of not only
mobile computing, but also many other applications ranging
from financial and retail communications to remote control
and signaling.
Recent technology, whether it’s TDMA, CDMA, or GSM
has experienced severe physical layer and user interface constraints.
Wireless data transmission is limited to relatively low
speeds, 19.2 Kbps or less. Cellular display applications for data
are limited to text messaging through SMS or WAP. There is a
wide disparity between browser applications. Some simple
graphics can be accomplished with WAP applications on some
phones, whereas i-Mode in Japan offers extensive graphics
including color displays on PDC phones,* even though the
data rates are similar. As GPRS is launched on GSM networks,
users will finally be able to access data at speeds superior to
traditional dial-up Internet service, approaching 115 Kbps.
With the launch of next-generation cellular systems and 3G
systems, users will have greater choice for data communications.
New modems will be commercially available to take
advantage of higher bandwidth networks, and packet data will
replace circuit-switched data. Choices will include either SMS
or a wireless modem using packet data at higher speeds. New
high-speed data capabilities will provide the platform for
mobile multimedia services, access to corporate LANs, and
financial transactions from a mobile terminal. The type of service
will determine the best data service to use. Many applications
will find SMS satisfactory even if a modem is available for
high data-rate service. And those that must use analog cellular
will still have CDPD.
Other devices such as PDAs and Pocket PCs as shown in
Figure 2-1 may use cellular networks or proprietary networks.
(Some cellular manufacturers have integrated PDAs into their
phones.)
Some cellular-based products will bear little resemblance to
a cellular phone at all, such as PCMCIA modems that incorporate
a cellular phone without voice capabilities. In addition
to standard products, custom products will be available for
wireless remote data and control applications. Examples are
shown in Figure 2-2.
DRIVING TECHNOLOGIES: COMPETING AND COMPLEMENTARY
Numerous technologies fuel Wireless Internet development,
some associated with the terminals and some with the network
infrastructure equipment. Many of these diverse technologies
are related by the wireless access method used,
whether it’s GPRS or CDPD for example. We cover technologies
related to terminal devices and network infrastructure in
this chapter:
• Access technologies
• Application protocols and languages
• IP network design and equipment
Many technologies are used on multiple platforms, so
applications must be device independent to be successful.
Applications cannot be customized for a dozen different protocols
or operating systems. If a Wireless Internet application is
to be truly mobile, it must also function ubiquitously as the
user moves from one location to another. This requires IP
mobility over multiple access methods. Cellular users should
be able to go indoors and on to a WLAN seamlessly. Therefore,
wireless LANs should not compete with cellular or PDA wireless
access, rather they should complement or extend its usefulness.
Some of the leading WLAN technologies also will be
discussed.
some associated with the terminals and some with the network
infrastructure equipment. Many of these diverse technologies
are related by the wireless access method used,
whether it’s GPRS or CDPD for example. We cover technologies
related to terminal devices and network infrastructure in
this chapter:
• Access technologies
• Application protocols and languages
• IP network design and equipment
Many technologies are used on multiple platforms, so
applications must be device independent to be successful.
Applications cannot be customized for a dozen different protocols
or operating systems. If a Wireless Internet application is
to be truly mobile, it must also function ubiquitously as the
user moves from one location to another. This requires IP
mobility over multiple access methods. Cellular users should
be able to go indoors and on to a WLAN seamlessly. Therefore,
wireless LANs should not compete with cellular or PDA wireless
access, rather they should complement or extend its usefulness.
Some of the leading WLAN technologies also will be
discussed.
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