In 1977 AT&T and Bell Labs constructed a prototype analog cellular telephone system. The following year the first public trials occurred in Chicago with 2000 users. The analog system called Advanced Mobile Phone System (AMPS) was developed in a cooperative venture between Bells Labs and Motorola. It was the primary analog mobile phone system in North America (and other locales) through the 1980s and into the 2000s. A first-generation cellular technology, AMPS usesd separate frequencies, or "channels", for each conversation, requiring considerable bandwidth for a large number of users. In general terms, AMPS was very similar to the older "0G" 0G system it replaced, but used considerably more computing power to select frequencies, hand off conversations to land lines, and handle billing and call setup. It was also susceptible to static and noise, and provided no protection from 'eavesdropping' using a scanner.