Wireless Communications

Wireless Communications

Wireless communications in the United States extend back to the early 1950s when the Rural Electrification Administration (REA) sought ways to provide telephone service to remote farms and ranches. Early efforts bore little fruit and, as late as 1985, the REA was still trying to get a system into operation. However, by the mid-1990s, a rush of new products resulted following the successful deployment of global analog cellular mobile telephone service. The most common form of wireless telephones came with the application, the CT-10 cordless telephone and later the CT-2 digital phone. Wireless internal telecommunications became fairly commonplace when AT&T, Ericsson, Nortel, NEC, and Rolm introduced wireless adjunct systems for installed PBX systems. These adjunct systems linked to a PBX via separate station line cards based on the standard 2500 nonelectronic desk telephone (see Figure 19.1). These add-on systems supported an RF controller that used the ISM (Industrial-Scientific-Medical) 900-MHz frequencies. Remote RF controllers were positioned around the user's premises to receive transmissions from roving users with mobile handsets.

Today, AT&T (Lucent), Ericsson, NEC, Nortel, and Rolm (Siemens) have introduced an entirely new generation of wireless PBX products that allows the end user to establish a totally integrated wireless voice and data network. For example, Lucent has introduced its Definity Wireless Business Systems as well as the TransTalk 9000 system. This latter system can be either a dual-zone or single-zone system and can support up to 500,000 square feet. A similar two-zone system can be used to support a multilevel building or a combination of several closely coupled buildings (i.e., warehouse, manufacturing, etc.). The Definity Wireless DECT (digital enhanced cordless telecommunications) system, which operates in the 1880- to 1900-MHz range, has similar capabilities and is marketed outside the United States. The Nortel Companion system is a similar wireless system that works off the Meridan I (Option 11 C) system. The Companion system supports all of the same station features as found on a standard electronic desk telephone.

These new wireless PBX systems can be integrated directly to the corporate LAN or WAN and function as centralized communications servers. For example, the Ericsson MD 110 system, when configured with an IP gateway unit, serves to interface the MD 110 PBX to an IP network, allowing voice traffic to share bandwidth with data over the IP network (see Figure 19.2).