Centrex

For companies that do not want to invest in their own communications infrastructure and get bogged down with management complexities, Centrex can provide a viable alternative to obtaining telephone services and advanced calling features. This service is intended as an alternative to buying a PBX—in fact, Centrex can be considered a remote PBX. Not only does Centrex free up a company’s scarce capital for other purchases, it puts responsibility for maintenance and management on the telephone company. Today’s Centrex services boast 100 percent feature parity with the most advanced digital PBXs currently available—including support for wireless communications and LANs.

The switches that implement Centrex services use computer-controlled time-division switching and have distributed architectures consisting of a host module and multiple microprocessor-controlled switching modules. These switches can directly interface with T-carrier systems to provide 24 digitized voice channels over twisted-pair wire at 1.544 Mbps. These capabilities enable Centrex offerings to include interfaces to the Digital Access and Cross-Connect System (DACS), thereby providing gateways to a variety of services over the public telephone network.

Centrex services offer a wealth of call processing and management features. Many Centrex offices routinely offer automatic route selection, local area networking, facilities management and control, message center services, and voice mail capabilities. In addition to basic rate Integrated Services Digital Network (ISDN), Centrex exchanges are in the process of being upgraded to provide primary rate ISDN service.

Centrex offers a variety of options to help communications managers monitor usage and control costs. Among these cost-management features is Station Message Detail Recording to Premises (SMDR-P), which transmits call records directly to the customer premises from the central office. SMDR-P arrangements provide virtually immediate access to call record data.

Centrex also provides on-line management features. With an on-premises terminal and an interactive software program, users can control the numbers, features, services, and billing codes assigned to each line within their systems. Not only can users review the status of their current Centrex configurations; they can also plan ahead to meet future communications demands by determining what changes need to be made and controlling the date of implementation. All such changes are input to a central management system on the carrier’s network; individual Centrex exchanges poll the system daily for any customer changes and automatically update the telephone company’s internal records.

Wireless communications is supported by some Centrex systems. The service enables employees in a building to send and receive telephone calls on low-power wireless telephones while moving around their offices. The system is based on a network of small, low-power transmission cells distributed strategically around the building and linked to a local exchange carrier by a central controller. This controller coordinates the handoff of calls from one cell to the next as the user moves about the workplace.

Despite the many advantages of subscribing to Centrex services, it does have its share of liabilities. In addition to being dependent on the local phone company for service and support, the contracts usually run from 5 to 10 years—the longer the commitment, the better the pricing. However, this can lock you, as a network manager, out of any new technologies that may come along and prevent your company from taking advantage of efficiencies and economies they may offer.