Primitive Digital Data Over Packet-Switching Networks
In
the early 1990s, the cellular carriers concerned with the decreasing
revenue per subscriber saw a considerable opportunity in the provision
of the mobile data services. The operators saw the increasing demand
for Internet services and growing trends
for mobile devices supported by virtual and mobile corporate working
environments. In 1992, all of the leading cellular carriers formed a
group to develop a digital service that was in line with the Internet
protocols to provide data. It was to become CDPD (Cellular Digital
Packet Data) and it was designed to address critical mobile data issues
such as roaming, billing, security, and authentication.
CDPD was intelligently designed to use spare radio
channels in the AMPS spectrum to carry data in packet form (IP
packets). When the end user created a request to send or receive data,
the data was segmented into small sequence-numbers packets by the
modem, and sent separately on different paths toward the nearest modem,
where the receiver assembled the packets according to the sequenced
order. User charges were typically based on the number of packets
transmitted and received, but some carriers offered flat rates with
unlimited data. The maximum data rate of the CDPD data transmission
capped at 19.2 kbps.
The goal of the CDPD service providers was to offer
nationwide, seamless, wireless data service, combining the services
provided by multiple carriers through appropriate intercarrier and
partnership agreements. Among the carriers participating are Ameritech
Cellular, AT&T Wireless Services, Bell Atlantic, NYNEX, Mobilem,
and GTE Mobilnet (PCSI). In addition, some major equipment
manufacturers have participated in the CDMA initiative, including
Hughes Network Systems, Motorola, Inc., and Sierra Wireless, Inc. Ten
years after its conception, CDPD was found in over 209 markets,
including 123 metropolitan areas, 43 rural areas, and 43 international
markets, with coverage extending to nearly 39 million people in the
United States, almost 55 percent of the population. GoAmerica, OmniSky
and Tellus were all wireless service resellers using the same CDPD
hardware and network configurations from the leading carriers. The
differences were in the included software, the customized Web subsets
that each offered and, of course, the price of the plans.
The primary advantage of the CDPD wireless Internet was
the full Web-browsing capability, and not just Web-clipping services.
Not only did CDPD offer raw data rates of 19,200 bps, but also it
provided full-duplex communications, allowing a radio modem to talk and
listen at the same time. This allowed CDPD to handle real-time
interactive applications that competing packet networks like RAM and
ARDIS could not support due to their half-duplex nature. An ARDIS or
RAM radio modem must switch between transmit and receive, taking up
valuable time.
Another packet switching network, ARDIS, started out in
the 1980s when Motorola built a custom solution for IBM's nationally
distributed technical field-service crew. In the early 1990s, when
packet-switching technology caught the eye of fast-growing cellular
companies, IBM tried to reposition ARDIS as a public wireless data
network, but never attained the mainstream appeal it was looking for.
In 1998, it sold its entire majority position to American Mobile
Satellite Corporation (AMSC), which soon was renamed Motient. With a
19.2-kbps access architecture that has a presence in 430 of the top 500
U.S. wireless markets, Motient had inherited substantial network
assets. The slow acceptance of wireless data overall was a mixed
blessing for the company, which had the most success in the corporate
world, especially in the financial verticals.
Motient played its cards right when it teamed up with a
Canadian company, Research in Motion (RIM). Together they created
something of a wireless phenomenon with
Blackberry devices, which put the power of the "always-on" e-mail into
a form factor as small as a wireless pager. RIM worked well because it
was a small device with long battery life and great usable design for
its purpose as a mobile e-mail device. But end-user needs evolved, the
expectations were changed by the introduction of high-level color
Pocket PC devices with larger, easier to read and browse Internet
screens, multimedia capabilities, easy synchronization with desktops,
and even faster wireless capabilities. Motient was not able to realize
revenues to cover the costs and was forced to file Chapter 11. Many blame it on the introduction of the new 2.5G and 3G networks.
Although the early packet-switching CDPD and Motient
networks were a definite upgrade from the AMPS technology, wireless
Internet services that it offered were still very primitive. The radio
environment that CDPD and Motient relied on was just as delicate as the
AMPS, and if the user was out of range of the base station, the radio
connection could suddenly be lost. Applications and wireless Internet
developers were forced to design an application that could handle
intermittent connections, which increased the system development and
maintenance cost. Performance was another important issue. With the
channel rate of 19.2 kbps, the actual throughput to the end wireless
Internet user was averaging 10 kbps. Moreover, CDPD and Motient
networks were still too expensive to be widely accepted by the end
users in the consumer and enterprise market.
Yet, these early packet-switching networks whet
the appetite for the wireless Internet in the consumer and enterprise
markets. Carriers definitely caught on the interest that the wireless
data services instigated; however, they realized that in order to
maximize the return on investment, wireless Internet had to become
faster and cheaper.
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