18.3 Slow Motion Over Plain Old Cellular

In 1969, engineers at Bell Labs developed the cellular telephone technology known as Advanced Mobile Phone System (AMPS). This system uses the 800-MHz frequency band and has been widely deployed in North and South America for mobile voice communications. Although the AMPS cellular network was designed primarily for voice transmission, techniques have been developed to send data over the network. In order for the mobile worker to do a database query or check e-mail over a dial-up circuit-switched connection, it was necessary to dial in; establish the communication channel through the cellular network, server, mainframe, and database; and stay connected while the application is launched and information is retrieved. The process was slow and cumbersome, and oftentimes sending a fax was faster and easier. In that sense, the AMPS, in much the same way as the "plain old telephone system" used to access the Internet with a trusty 28.8-kbps analog modem, was prone to data loss and high and variable propagation delay, impeding reliability and reducing effective throughput.

AMPS wireless data service was similar to a standard cellular phone call, using the same channels and the same frequency as the cellular voice call, but with specialized protocols used by the modems on each end for circuit switched cellular data. The mobile device required a modem, such as SpeedPaq 336 offered by Compaq, which connected to a cellular phone and supported the necessary cellular protocols. To send a data signal using AMPS over-the-air protocols, a temporary dedicated path was established for the duration of the communication session. All signals flow continuously over the same path, and billing for AMPS data service was generally a function of airtime used, typically in 1 minute increments, with charges based on the user's selected rate plan. And, just as with a normal phone call, all applicable long distance charges, roaming charges, and taxes also were billed.

In 1991, U.S. cellular operators initiated an activity to see if they could offer a digital data service for uses like email and telemetry. The analog cellular worked, but the operators did not see the expected return from the subscribers and the technology cost was too high. The data throughput offered over the AMPS networks was very slow, ranging from 2.4 to 14.4 kbps, affected by interference, noise, fading, and overall channel degradation, common RF-related affects, and varied from one location to another. Dropped calls also were common. Security was another issue. There was a limited amount of the content available for the wireless Internet users. Mainly the AMPS wireless networks were used to connect to the custom build corporate gateways that were designed to serve data often in proprietary format. Browsers also were primarily proprietary, and limited standards existed for the Mobile Data communications.