Private branch exchange
A private branch exchange (PBX) is a privately owned switch. It is typically located on a business customer’s premises and connected to the telephone network by T-1 or ISDN PRI access lines (although other arrangements are possible). Mmodern PBXs are digital switches that bear a striking resemblance to their peers in the public switched telephone network (PSTN). PBXs, however, typically employ software that allows them to offer business customers a variety of useful business features. These include four or five digit dialing, conference calling, and automatically completing a call to a busy telephone once it becomes idle. Two of the primary vendors are Avaya and Nortel Networks.
Communication Manager is the Avaya offering. Communication Manager is software that integrates telephony call processing, call control, and messaging designed to support both circuit-based and IP-based telephony. It can run on many different hardware platforms from Avaya. The S8700 Media Server is their high end system. The S8700 can support up to 300,000 busy-hour call completions, 36,000 stations, and 8000 trunks. Avaya also has other, smaller PBXs.
Nortel Networks offers the Meridian SL-100 PBX, capable of serving up to 30,000 and 8,000 trunks stations. However, the system can be upgraded to support as many as 80,000 stations and 10,000 trunks. It offers the ability to maintain both time division multiplexing (TDM) and Internet Protocol (IP) environments and supports a full suite of applications for voice messaging, call centers, and multimedia.
There are several factors companies should consider when choosing between Centrex service or a PBX:
- their ability to install, operate, and maintain their own switching infrastructure
- their ability to monitor and maintain a controlled environment to ensure effective switch operation.
- the capital expenditure required to purchase one, or the operational expenditure required to lease one
- the space required to house it and its power requirements
- the distribution of their staff (e.g., all one location, or multiple locations)
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