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A common approach is for the exchange to send 'metering pulses' very low frequency voltage changes which cannot be heard, every time a certain unit of money must be charged to the customer. An alternative is to send high frequency audio tones.
These approaches can also be applied to the outgoing lines hotels use for calls from their guests. This enables special equipment at the hotel to record these pulses and so generate a bills for customers whenever they are needed. Both payphones and hotel systems can record all the dialed numbers, which raises some privacy and security problems.
Centrex Services
While the PABX represents moving some intelligence out of the network and into the customer equipment, Centrex is the opposite: the carrier's network provides the functionality of a PABX without the user needing to purchase and manage one. Many aspects of Centrex functionality exceed what a PABX is capable of - such as Centrex's countrywide integration of an organization¿s telephone system.
Centrex customers are typically larger organizations with many offices within a carrier's area. Each customer site is served by analogue lines and/or BR-ISDN lines (for instance for video-conferencing or computer data links at 64 or 128 kb/s) - from a Centrex capable exchange. The carrier has such exchanges in all areas where the customer requires services, and these exchanges communicate via the CCS7 network and operate in a highly unified and sophisticated manner.
Centrex services have their roots in the 1970s, but the current use of the term refers to the technology developed by Northern Telecom (Nortel) in the 1980s with its DMS exchanges. Centrex services are also available from other exchange manufacturers.
Nortel supports three kinds of connection to customers: an analogue line with a standard telephone, an analogue line with a special 'business set' telephone, and BR-ISDN. BR-ISDN, with its separate D channel for signaling, supports sophisticated communication between the user and the exchange. In contrast, an ordinary analogue phone cannot communicate with the exchange whilst a call is in progress, and all Centrex features must be activated by tone-dial sequences, such as '*74', which may be able to be programmed into function keys. The 'business set' customer terminal supports communication to and from the exchange while a call is in progress, using inaudible frequencies carried by the standard twisted pair cable. Such 'business sets' may incorporate liquid crystal displays.
One Centrex service is Automatic Call Distribution (ACD) - the distribution of incoming calls to call-centers in various locations depending on a variety of factors.
Computer Telephony Integration (CTI)
Computer Telephony Integration involves real-time communication, usually in both directions, between one or more computer systems, especially the computers of operators handling calls, and a telephony system: either a PABX or a Centrex service.
On a smaller scale, CTI can involve a computer interfacing to a single telephone line, for instance to make calls, which are then switched to an ordinary telephone. This approach of a single computer and a single analogue phone line is the basis of Microsoft's original TAPI 1.0 API (Application Programming Interface) in 1993. This single line approach is sometimes referred to as 'first party CTI'.
Most interest in CTI focuses on 'third party CTI': connecting a computer to a PABX or Centrex service. PABXs (and Centrex exchanges) are, of course, computer systems in themselves, but not ones on which users can generally run specialized software.
CTI Applications
Most of the interest in CTI relates to call centers - such as those in banks and other large organizations which handle incoming calls from customers. The most common aims are to:
- Identify the customer or their specific needs in some way
- Route the call to the best available operator
- Display on that operator's computer screen all the relevant information to help them respond to the caller and to complete transactions on their behalf
One method of identifying the caller is by the PABX or Centrex exchange providing the caller's number. However this is not available in many instances, due to privacy concerns and technical restrictions. For instance only ISDN PABXs can receive the caller's number from the carrier's exchange, and not all customers call from services which are able to allow the display of their number. When the number is displayed it is not necessarily of much use If the call is made from a PABX, then the number may simply be that of one of dozens of outgoing lines. Customers may call from locations other than their home or regular location.
Another method of automatically identifying the caller is for the caller to hear a recorded voice message asking them to enter their account number, by pressing their tone-dialing buttons, or some other information which relates to the nature of their call. This can provide good information about the caller, but involves them in more complex, lonely and error prone actions than what they would probably prefer: to talk to a human being about who they are and what they want.
Labor is the biggest cost of running a call center, and if CTI can improve productivity even marginally, then it may be a good investment. But long-term productivity is unlikely to be boosted if callers have to negotiate time delays, voice messages and complex procedures every time the call, and if operators are pushed too hard and in an inhuman fashion, for instance by a predictive dialing system which connects them to a fresh called party the moment the operator finishes the previous call.
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