18.5 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.