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Since the systems are largely software controlled, they are relatively easy to upgrade. As new software is released, associated functions and features are released in the form of programmable functions; the system software can be upgraded as required. Additionally, bugs (program errors) can be fixed, with corrections perhaps even being downloaded over the network. Examples of the hundreds of such programmable functions and features include the following:

Automatic Route Selection (ARS) or Least Cost Routing (LCR)
is optional software which allows the user to program the system to route individual calls over the most appropriate selection of carrier and service offering. Routing factors typically might include the nature of the call; the Class of Service (COS); or level of privilege of the user; the time of day; and the day of the year (weekends and holidays). In this fashion, high-priority users with no calling restrictions (company president) are connected on a priority basis, even if a high-cost carrier and service offering were all that were available at the time. On the other hand, low priority users (clerks) are forced to queue for a low-cost facility. The system remembers their request and rings their telephones to alert them when that facility is available, and automatically connects the previously requested call.
Call Pick-up Groups
let users within the same work group answer calls for one another. This option can be invoked by authorized users by keying a code on the set keypad or by depressing a designated button on an electronic set.
Call Forward
lets a user either predefine or selectively and flexibly define an extension to which a call will be transferred in the event of a busy or no answer condition.
Conference Calling
, which can be set up either by the user or by the console attendant, makes use of a special conference bridge card in the system, which might support 8 or 16 parties to such a call.
Call Detail Recording (CDR) or Station Message Detail Recording (SMDR)
information provides detail on all incoming and outgoing calls (see Figure 4.4) so that the system administrator can develop network usage reports. Information typically includes the originating and terminating station, outgoing and incoming trunk or trunk group, time of connection, time of termination (or elapsed time), access code dialed (for instance, 9 for an outside line or 8 for a private line), telephone number dialed, and account code or authorization code used.


Figure 4.4  Example CDR outgoing call records.

Many contemporary PBXs contain adjunct software that allows the generation of a number of reports including usage costs by station, account code, department, and work group. This feature assists in cost and fraud control, as well as permitting costs to be charged to the customers’ clients. Becuase this software is limited in capability, most users prefer to acquire more substantial TeleManagement software residing on an adjunct computer, that accepts CDR output from a special PBX port, processes the data, and creates user-definable reports. Such software typically includes a number of other modules that share a common database for purposes of cost allocation, equipment inventory management, wire and cable management, and numerous other critical administrative functions. Leading manufacturers of such software include The Angeles Group (CA), IntegraTRAK (WA), and Stonehouse & Company (TX) [4-6].
Automatic Call Distribution (ACD)
software routes incoming calls to the most available and appropriate agent. Incoming call centers make extensive use of such specialized software to enhance customer service. Calls are answered by a frontend voice processor that lets users make menu selections. Calls are then queued by specialized agent group and routed to the next available agent. While such capability is often delivered through a specially equipped and partitioned PBX, the PBX can also be specially configured as a standalone ACD. More intensive applications typically make use of specialized ACDs, which function as highly intelligent switches for the processing of incoming calls. Such specially designed high-speed interfaces to the PBX allow the systems to function on an integrated, networked basis.
Universal Call Distribution (UCD)
is a standard feature of many PBXs. While it serves somewhat the same functions, it lacks the same level of intelligence. Therefore, it is much less capable than is ACD, although it is much less costly.

Switching Matrix

Contemporary PBXs employ Time Division Multiplexing (TDM) in both analog and digital systems. Through this process, multiple conversations are sampled, traveling sequentially over a single bus, or common physical path.


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