WO1996015613A1

WO1996015613A1 - Purpose-built centrex enhancing telephone system

Info

Publication number: WO1996015613A1
Application number: PCT/AU1995/000746
Authority: WO
Inventors: Ray Smith
Original assignee: Telstra Corporation Limited
Priority date: 1994-11-11
Filing date: 1995-11-10
Publication date: 1996-05-23
Also published as: AUPM940594A0

Abstract

The present invention is a purpose-built CENTREX Enhancing Telephone System (PCETS) designed to address the real and user perceived deficiencies in the day to day use, and operation, of CENTREX services. The present invention seeks to address the problems of the prior art by providing a new telephone product which is adapted to provide user flexibility and core 'keysystem' user interface and functionality without the prior art style of equipment which duplicates CENTREX services. These features serve to enable the PCETS to use CENTREX services for performance of PCETS many functions and facilities. The PCETS is thus purpose-built to provide user flexibility, 'core key system' user interface and functionality and without duplication of CENTREX facilities.

Description

PURPOSE-BUILT CENTREX ENHANCING TELEPHONE SYSTEM FIELD

The present invention is directed at providing a new type of telephone system. The new system is to be called a Purpose-built CENTREX Enhancing Telephone System (PCETS). PRIOR ART

1. CENTREX services have been offered by some telecommunication service providers as an alternative to key systems or PABX's. The CENTREX service is nonetheless considered to suffer from a number of problems and has not always found great acceptance to telephone users as a result. Some of the CENTREX user problems include: a) Lack of Information About Other Extensions

CPE which relies on the CENTREX services to provide information about individual extensions is not portable between CENTREX services. No easy connection to other extensions because the user needs to remember extension numbers which can be up to 5 digits.

No easy method to answer call at other extensions.

Because of the lack of information to the user, the process of answering calls unanswered at other extensions requires the user to identify, aurally, the ringing extension, remember the pick up code and remember the 5 digit extension number. That being done, the user needs to dial up to 8 digits (3 for pick up and up to 5 for the extension number). b) Difficult to Use

CENTREX feature/facility access codes are considered complicated and not intuitive because they comprise relatively long digit strings (e.g. 5 digits). c) Too Many Codes to Remember

There are many diffe^rent access codes used with CENTREX, dependent on the feature package the customer subscribes to. Some features have as many as 3 access codes associated with them. d) Access Codes Vary from CO. Switch to CO. Switch

While there are CENTREX services offered on different CO. switches, they often use different access codes and operation protocols to invoke similar features. Thus, swapping from one CENTREX service to another requires learning new feature access codes and operation protocols. This is particularly a problem for organisations spread geographically and/or in different parts of that organisation that use different CENTREX services. Prior art products currently available are also considered to suffer from a number of problems.

A) Telephones With Customer Programmable Keys a) Relatively Complex and Tedious Programming of Feature Access Keys Customers are often intimidated by the programming of feature access keys. Also, programming by installation staff is considered time consuming and costly. b) Rationalisation of Key Usage

There is no rationalisation of key usage, through the use of some "intelligence". Where features require different codes for activation and deactivation, separate keys are needed for each access codes.

B) Smart Telephones

Smart telephones have keys which have been pre-programmed with feature access codes for use with certain CENTREX services. The programming of the keys is fixed, cannot be "overwritten" and requires the user to purchase another piece of hardware if they wish a change. The smart telephones do not provide information as to the status of other extensions.

Figure 1 illustrates a telephone exchange with CENTREX services and with standard or smart telephones.

C) CENTREX Attendant (Operator) Consoles These consoles generally have a number of CENTREX lines (e.g. 4 or 5) directly connected to the console, for use by an operator to answer calls into the system. With reference to Figure 2, the status of each user extension is displayed at the attendant console only. The monitoring lines only passively sense the status of the user extensions. These consoles are specifically designed to emulate, and provide the functionality of, the Operators Console on a PABX. They are not designed to be the general telephone instrument used by every member of an organisation. They are relatively expensive when compared to "standard" telephones and key system terminals.

They require special line sensing equipment to provide the information on user extension status. This information cannot be made available to other user extensions.

They generally have much larger foot prints than telephones, and often require extensive and complicated installation and cabling. D) Key Telephone Systems

Key systems are designed to provide the user with a wide range of features to improve communications inside, and outside, the organisation.

When used on a CENTREX service, key systems duplicate most features offered by that CENTREX service. As a result key systems suffer a number of disadvantages when used with CENTREX: a) Cost To gain maximum benefit from CENTREX, key systems are best equipped in square configuration - one line per extension - resulting in a bigger system needing to be used when compared to a non-CENTREX application.

Also, key systems are equipped with hardware and software for the control and management of internal communications, some of which becomes redundant when used on CENTREX services, which results in additional costs that otherwise would not be incurred. b) Customer Confusion

The duplication of features can easily lead to customer confusion. They need to remember two sets of access codes and/or operational procedures - one for the CENTREX service, the other for the key system.

Customers may also be confused as to when it is most appropriate to use the CENTREX service features or the same key system features. They could even attempt to use key system feature access codes on the CENTREX service, or vice versa. c) Customer Programmable Keys

Key systems also suffer from the same problems as telephones with Customer Programmable Keys - see section A) above. E) Proprietary Signalling Telephones

These telephones use a proprietary signalling protocol for a particular CENTREX service to provide system information, and in some cases the ability to download feature access codes from the exchange. In one form, this type of technology uses transmission techniques which require specialist operations support and exchange line selection. The exchange lines, CPE and exchange based linecards require specialist maintenance procedures for fault diagnosis. This leads to expensive overheads. There is no single standard for this type of signalling, so the use of the

CPE with different CO. switches is considered virtually impossible. SUMMARY OF INVENTION

The present invention is a Purpose-built CENTREX Enhancing Telephone System (PCETS) designed to address the real and user perceived deficiencies in the day to day use, and operation, of CENTREX services.

The present invention seeks to address the problems of the prior art by providing a new telephone product which is adapted to provide user flexibility and core "keysystem" user interface and functionality without the prior art style of equipment which duplicates CENTREX services. The present invention, in one form, is predicated on the provision of a

PCETS, which comprises a relatively localized intelligence and control in each PCETS station together with a local bus interconnecting each PCETS station.

The present invention is predicated, in another form, on the provision of a PCETS which comprises in addition to the combination of localized intelligence and local bus connecting each PCETS, a direct connection between each PCETS and the exchange supporting the CENTREX service.

These features serve to enable the PCETS to use CENTREX services for performance of PCETS many functions and facilities. The PCETS is thus purpose built to provide user flexibility, "core key system" user interface and functionality and without duplication of CENTREX facilities.

The localized intelligence provides user definable operation and control of the operation of the PCETS station and localised generation of CENTREX access codes. The local bus enables exchange of information between PCETS stations. The direct connection between PCETS station and CENTREX service enables operation of each PCETS station in a manner that is independent of other PCETS stations, if required. In combination, these features work in order to provide the complimenting of the CENTREX services (supported by the Exchange) with purpose-built features in the PCETS.

The synergy of the features of local bus and local intelligence serves to provide pre-programmed function keys that enable user keys to be user programmable and/or have their function determined by system status and/or operation history. These may be called "Smart" keys.

The synergy of local bus and local intelligence also allows each of the PCETS stations to determine and/or display the status of the other PCETS stations in the system. The synergy of local bus and local intelligence further enables PCETS stations to support DSS keys.

The features of local bus and local intelligence in synergy further obviates the need for information transfer from the CO. switch to CPE. Voice and data can nonetheless be exchanged. This provides portability of PCETS between different CENTREX services. This also provides lower CO. switch administration.

These features (singularly or in combination) allow the system to emulate (give it the "look and feel" of) a key system.

The feature of direct access together with the features of local bus and local intelligence in synergy obviate the need for duplication of CENTREX services, provided by hardware/software e.g. Central Equipment.

Further, the features of direct access and local intelligence in synergy provide predetermined or defined functionality of PCETS in certain system conditions e.g. power fail. Unlike key systems and PABX's that are designed to share limited lines between a large number of users, and control internal, and external, communications via a Central Equipment, or "distributed intelligence", the present invention, in one form, requires at least one CENTREX line per station and relies on the CENTREX services to provide communications control. The additional intelligence of the present invention provides supervisory functions and information exchange between PCETS stations to control the codes transmitted by the "Smart Keys". TERMINOLOGY Access Codes: Signals sent to telephone exchange (or similar equipment) to Activate/Deactivate CENTREX Features. Hot Key: A type of key that will automatically establish a call to the telephone exchange.

DSS Key: Direct Station Selection key. A type of key that allows the user to make a call to another Station within the system by pressing just that one key. All Stations in a system have the same number of DSS Keys. DSS Appearance: Each Station within a system is assigned a DSS

Appearance, which is a unique number chosen from the set of numbers associated with the DSS Keys. (Refer to section 1.7, System Administration) eg: If Station 1 is assigned to DSS Key 1 , its DSS Appearance would be 1. Extension Number: A number (1 or more digits) that the telephone exchange uses to identify a Station for calls within a CENTREX Group. Line Ring Tone: An audible tone produced by a Station that emulates the sound of a normal telephone ringing. Remote Ring Tone: An audible tone produced by the Station that is similar to, but distinguishable from Line Ring Tone.

SDL: Specification & Description Language. Refer to CCITT

Recommendation Z.100 Preferred embodiments of the present invention will now be described, by section. 1. Overall System Layout/Operation;

2. The Local Bus;

3. Localised Intelligence; and 4. Alternatives.

In the drawings:

Figures 1 , 2 and 3 illustrate non-PCETS systems;

Figure 4 illustrates one embodiment of PCETS, in schematic form; Figure 5 illustrates a comparison of one embodiment of PCETS with some prior art CENTREX systems;

Figures 6 and 7 illustrate alternative PCETS embodiments;

Figure 8 shows a brief overview of PCETS Installation/Configuration;

Figures 9, 10 and 11 outline PCETS local bus operation; Figure 12 shows a legend to be used in conjunction with CCITT recommendation Z.100;

Figure 13 outlines "startup" and operation from the "line power" state;

Figures 14 and 15 outline operation from the "idle" state;

Figure 16 outlines operation when PCETS receives a ringing signal from an exchange;

Figures 17 and 18 outline operation of PCETS in actioning a call; and

Figure 19 outlines other events which may occur in the use of PCETS. 1_ OVERALL SYSTEM LAYOUT/OPERATION

The PCETS system utilises at least 2 features and preferably 3 main features (Local Bus, Localised Intelligence and Direct Exchange Connection) to provide the following features/capabilities.

1A, Intelligent use of CENTREX Features.

Through the intelligent use of CENTREX features a PCETS system can provide Key System like functionality. Each Station, which could be a terminal station or a PCETS station, can independently Activate/Deactivate CENTREX type features by sending the appropriate Access Codes to the telepho ^e exchange. PCETS Stations present the user with keys labelled with PCETS reatures. The Station decides which CENTREX feature to use whenever one of these keys is pressed. Examples of CENTREX features: forwarding calls, holding calls, switching between 2 calls, conference calls for 3 parties, auto call back (refer to the PCETS Station Operation Overview SDLs, Figures 14 to 18). 1.1.1. Simplified access to CENTREX Features

The state machine architecture allows the station to determine what

CENTREX feature to activate/deactivate when a user invokes a PCETS feature by pressing one key. It also allows a station to provide DSS keys, which can change their behaviour depending on the status of the other stations (see examples 3 and 4 below).

The state machine architecture allows for a key to be re-used for accessing similar CENTREX features depending on the current status of the system or recent history of the station. When the user of a Station presses a key to invoke a PCETS feature, the

Station looks up the Access Code (in its Access Code memory) of the appropriate CENTREX type feature to Activate/Deactivate, and sends the Access Code to the telephone exchange. These Access Codes are stored in the Station's Non-volatile memory ( ie: EEPROM). The memory is in addition to any Speed Dial memory provisions in the PCETS station.

A Station can choose the type of CENTREX feature to be Activated/Deactivated based on the history of the activating Station or the status of another Station within the system. The Station does this by accessing its Non¬ volatile memory for the Access Code for the feature appropriate to the history of the activating Station and/or the status of another Station. The history and status are stored implicitly because of the use of a State Machine Architecture. (Refer to paragraph 1.2.4, Use of Information Exchanged below).

Example 1 : A user makes an outgoing call and receives a Busy Tone.

The user can then press the Call Back key to request the Auto Call Back CENTREX feature. The Station has remembered that a call is in progress, and sends the Access

Code for Auto Call Back to the telephone exchange. (Refer to the PCETS Station Operation Overview SDLs, Figure 18).

Example 2: A user, while not in a call, presses the Call Back key to deactivate a previously activated Auto Call Back CENTREX feature. The Station has remembered that no call is in progress, and sends the Access Code for Auto Call Back Cancel to the telephone exchange. (Refer to the PCETS

Station Operation Overview SDLs, Figures 15 and 18).

Example 3: Station A is Idle (not involved in a call). A user at Station B presses the DSS key associated with Station A. Station B will send the Access Codes for the Internal Call CENTREX feature, along with Station A's Extension Number, to the telephone exchange. (Refer to the PCETS Station

Operation Overview SDLs, Figures 14 and 17).

Example 4: Station A is receiving Ring Signal from the telephone exchange. A user at Station B presses the DSS key associated with Station A. Station B will send the Access Codes for the Individual Call Pick Up feature, along with Station A's extension number, to the telephone exchange. (Refer to the PCETS Station Operation Overview SDLs, Figure 14).

1 -1 -2- Portabilit^y of Features The PCETS System and or Stations may work with a number of different telephone exchanges (or similar equipment) and that may use different Access Codes to Activate/Deactivate the CENTREX Features supported by PCETS. The Access Codes in Non-volatile memory are loaded from the Station's

Read Only Memory when the Station is configured. Each Station stores the Access Codes for a number of different telephone exchanges that implement CENTREX type features, and one of these is selected when a Station is configured. Any of the Access Codes in a Station can also be changed by the user and stored in its Non-volatile memory.

Access codes are changed by the user following a predetermined sequence of key presses. For example, the user can press the PROG key, then the # key, then the key who's code is to be changed, then press keys to enter the new Access code, then press the SPKR key to signal the end of the code. ___ Interstation Communications

To solve the problem of a lack of information about other extensions, each Station is able to communicate with every other Station in the System. The information exchanged is made up of, but not limited to, Station Status, DSS Appearance & Extension Number, Calling Line Identification information. This information is communicated so that all Stations can display the status of all other Station's, the behaviour of the Station in responding to key presses can be modified, and so that the initial configuration and ongoing system administration is simplified. The Local Bus description provides more detail on how this information is exchanged (refer to section 2, The Local Bus).

This exchange of information between the stations makes the system independent of the Centrex Service implementation. This means that the system is more portable as it can easily move from one Centrex service implementation to another. This independence reduces the amount of system administration required to be performed by the Centrex service provider because the Centrex service does not need to know what type of CPE a customer is using or provide the infrastructure to support/maintain the transferring of status information between stations. There is also no need to transfer Station related information between the Centrex service and each Station. 1.2.1. Status Information Exchange Each Station transmits its current status to every other Station in the System using the Local Bus. Each Station repeatedly and/or periodically sends its current status to every other Station. The status values, which may be represented by DTMF digits, that can be sent, but are not limited to, are: Busy ( involved in a call)

Ringing ( receiving Ring Signal from the exchange) Idle (none of the above)

Page Request (A Station is requesting Paging to be started) Page End (A Station is indicating that Paging is completed) The receiving Stations display this status on the BLF(Busy Lamp Field) associated with the sending Station's DSS Appearance. 1.2.2. Configuration Information Exchange

Each Station transmits its DSS appearance and Extension number to every other Station in the System using the Local Bus. The Local Bus may be hardwired or "virtual", such as shown in Figure 7. This is done to simplify initial configuration and ongoing system administration.

When a Station is powered-up or configured, it sends out a request for all Stations in the system to transmit their DSS appearance & Extension number. All Stations receive this request and transmit their data in an order preferably based upon their DSS appearance. All Station's record this information in their Non-volatile memory for use in Activating/Deactivating certain CENTREX features. (Refer to Section 1.1 , Intelligent use of CENTREX Features). 1.2.3. Other Information Exchange Other useful information, such as Calling Line Identification (CLI), can be transmitted by a Station to all other Stations in a System in a manner similar to DSS Appearance & Extension number transmission using the Local Bus. 1 -2.4. Use of Information Exchanged Each station remembers the status and configuration information of other stations within the system. This can become an input to the State Machine to modify the behaviour of the station. (Refer to 1.1.1 Simplified access to CENTREX Features).

1.3. Display of Station/System Status

Each Station displays the status of itself and other stations in its Busy Lamp Field(BLF). LEDs can be used to make up the BLF and these can be directly associated with each stations DSS key. The status of the stations can be displayed on the BLF LEDs by either turning it OFF, ON or flashing it a varying rates.

1.3.1. Incoming Calls on Other Stations Incoming calls on other stations may be displayed on the Busy Lamp

Fields of one or more stations. These other incoming calls can, under user control, cause their station to Ring with Remote Ring Tone. Remote Ring Tone can, under user control, start after a user definable delay. lA_m Power SUDDIV Preferably, the power for the stations is supplied from a Power Supply

Central Unit. Other configurations are also possible, such as providing power to each station individually from the local mains supply. 1-4.1. Normal Operation

The PCU supplies power to all the Stations within a System and generates the SYNC timing signal used by the Local Bus (refer to Section 2,

The Local Bus). Preferably, the PCU only uses one pair of wires for the distribution of power and Local Bus functions, but other configurations are possible, such as separate wires for power and Local Bus.

The PCU puts DC power onto the Local Bus. Each Station draws its power from this DC supply via a dedicated circuit. SYNC signals may be generated and placed onto the Local Bus and/or the PCU by modulating the DC current.

1.4.2. Power Failure Operation In the event of a Power Failure, each Station can act as a simple telephone using its direct connection to the telephone exchange to make and receive calls. In other words, the PCETS stations are effectively configured in power fail mode to operate using only the direct connection to the CENTREX exchange. In this way, all PCETS stations can still access the CENTREX features by virtue of the direct connection to the CENTREX exchange.

The Local Intelligence reacts to the loss of Local Power by changing the behaviour of the station to reduce power consumption. The State Machine architecture allows easy implementation of this feature. (Refer to PCETS Station Operation Overview SDL, Figures 13 and 19).

Direct connection to the telephone exchange allows the power supply to be smart. On loss of Local Power, the station may start drawing power from the telephone exchange and stop supplying power to parts of the station that would draw too much power from the exchange. It may also signal the Local

Intelligence that Local Power has failed.

Preferably, in Local Power fail mode the Local Intelligence provides basic phone operation. For example, LEDs, audible tones, Interstation communications and HandsFree operation may not be provided. The selection of features not provided in power fail can be predetermined or user definable and, for example, if lower power consumption parts are used, more features could be supported, but at a higher station cost. In a further alternative to the SDL diagrams shown, the line power idle state can be removed and the test for power mode as shown in Figure 13 can be distributed to predetermined events in other states. ___, Basic Phone Operation Each Station has a direct connection to a telephone exchange (or similar equipment, eg: PABX) that provides CENTREX type features. 1.5.1. Outgoing Calls Each Station can always make outgoing calls as it has its own direct connection to the telephone exchange. This means that it cannot be blocked from making a call due to congestion within the system (too many stations trying to make calls at the same time). A Station can also make outgoing calls if the Local Power Supply fails (Refer to section 1.4, Power Supply).

The user can make an outgoing call by performing any of the following: Lifting the HandSet

Pressing the SPKR key ( entering HandsFree mode or while in HeadSet mode)

Pressing a Hot key while not on a call (eg: Speed Dial key, some CENTREX Feature key) Pressing a DSS key

The Station Loops the line, connects either the HandsFree or HandSet circuit to the line and allows the user/Station to dial DTMF digits to the exchange, (refer to the PCETS Station Operation Overview SDLs, Figures 12 to 19). 1.5.2. Incoming Calls

The telephone exchange will signal the Receiving Station when there are any incoming calls. If the Receiving Station is not on a call, then the Receiving Station, and optionally all other Stations, produce a visual & audible indication, (refer to the PCETS Station Operation Overview SDLs, Figures 13 and 14). If the Station is not already on a call, the telephone exchange sends a

Ring Signal on the line which the Station will recognise. The Station then starts a Line Ring Tone audible indication and start flashing the visual indicator associated with its DSS Appearance. A user at the Receiving Station can answer the incoming call by: Lifting the HandSet

Pressing the SPKR key ( entering HandsFree mode or while in HeadSet mode)

The Receiving Station informs all other Stations in the system (refer to section 1.2, Interstation Communications) that it is receiving Ring Signal. These other Stations will start flashing the visual indicator associated with the Receiving Station's DSS Appearance. If configured to, these Station's will also start to produce a Remote Ring Tone audible indication. A user at one of these other Stations may answer the call by pressing the DSS Key associated with the Receiving Station.

If the Station is on a call, the user may answer the incoming call by activating the CENTREX Call Wait feature by pressing a single key. The Station then sends the appropriate Access Codes to the telephone exchange.

1.5.2.1 _■ Ring Tone Volume and Tone Adjustment Each station allows the user to adjust the volume and tone of the ring signal.

1.5.3. HandsFree Operation The station allows the user to operate in a HandsFree manner. It does this by providing a loud speaker and a microphone to replace the HandSet. 1.5,3,1 , Volume Ad^justment HandsFree speaker volume can be adjusted by the user during a call. 1.5.4. HeadSet Operation The station allows the HandSet to be replaced by a HeadSet, and for the

Speaker key to be used to make or finalise calls, rather than the Hook Switch. 1 -5.5. Handsfree/HandSet Mic Muting The station allows the user to disconnect both the HandSet and HandsFree microphones so that no voice signal is transmitted to the other party. 1.5.6. Speed Dial Memories

The station provides a number of memories that the user can load with telephone numbers or CENTREX access codes. 1 .5.7- Last Number Radial The station provides a memory of the last number dialled, and a single key for the user to request that this number be dialled again. 1.6. System Administration Refer to Figure 8.

1.6.1. Initial Configuration This is simplified in the present PCETS as compared to prior art because, with the Local Bus, Configuration Information only needs to be entered for each station once. For example, the installer only needs to select the DSS Appearance and enter the Extension number for each station in a System once. Each station then sends this information to all other stations in the system. After all stations have been configured, all stations will know information or broadcasts about every other station, (refer to Section 2.2, How Information is Exchanged, and Section 1.1.2, Configuration Information Exchange). 1.6.2. Ongoing Administration

This is simplified because all the stations in a system may update each other when any configuration information on a station changes. _ _ Optional Display

1.7.1. Display of Dialled Digits All digits that are dialled by the user or from Speed Dial memories can be displayed so that the user can validate that the correct number has been dialled.

1.7.2. Display of Messages

An Optional Display can be used to inform the user of actions performed in response to key presses. It can also be used to display messages/information while configuring the station to the configuration process.

__ THE LOCAL BUS

The Local Bus is provided so that stations can exchange information (see

Section 1.2, Interstation Communications). This facility allows the stations to exchange status information and configuration information. This information may then be used to display the status of all the stations within a system, and to intelligently use the CENTREX features of the connected exchange to provide Key System functionality.

___ How Information is Exchanged

The Stations communicate with each other via a common Local Bus. All Stations in the system are connected to this Bus and all Stations preferably receive everything that is transmitted onto the Bus. (refer to Section 1.2, Interstation Communications).

The PCU generates a Synchronising signal (SYNC) at a regular interval. This SYNC signals indicates the start of a Frame. A Frame consists of a number of equal sized Time Slots.

The Local Bus has 2 operating modes, namely Status Update mode and Exclusive Usage mode.

Status Update mode (refer to Local Bus Operation SDLs, Figure 9) is the default mode of operation for the Local Bus. In this mode, all Stations wait for the SYNC signal (which indicates the start of a Frame), and then when it is their turn (their Time Slot) they Broadcast their status. They preferably calculate which is their Time Slot from their assigned DSS appearance. Time Slots are may be determined by either timing or by receiving another station's status.

Exclusive Usage mode (refer to Local Bus Operation SDLs, Figures 10 and 11 ) is used for transferring larger amounts of signalling information than can be sent in one Time Slot. An example of its use is in the transfer between

Stations of DSS Appearance and Extension Number information at configuration. This facility is used to simplify system installation and administration (refer to 1.7, System Administration). To enter Exclusive Usage mode, the Sending Station sends an Exclusive

Usage Request signal (Symbol) instead of its status in its Time Slot to request

Exclusive use of the Local Bus in the next Frame (refer to 'Receive Command,

Request Configuration Information' in Local Bus Operation SDLs, Figure 11 and 'Status Update Time Slots' state in Figure 9). In the first Time Slot of the next Frame, the Station sends a code that describes what the Bus is being used for (eg: DSS Appearance and Extension number). All Stations respond to this code by remembering not to transmit their status in their Time Slot and they prepare to receive the incoming information (refer to Local Bus Operation SDLs, Figure 10). The Sending Station then outputs the information in the rest of the Time Slots of that Frame (refer to Local Bus Operation SDLs, Figure 11 ). To exit Exclusive Usage mode, the Sending Station does not transmit anything in the first Time Slot after the next SYNC signal. All the other Stations see this Time Slot as empty, and return to Status Update mode. ___ Preferred Bus Signals

Any type of signals could be used on the Local Bus. The type would be determined by a PCETS implementation. The following are examples of Bus Signals that could be used.

A SYNC signal is a DTMF digit D and is transmitted approx. every 650 msec.

The Status signals are other DTMF digits, with each Digit representing a different status (eg: DTMF 1 for Busy, DTMF 2 for Idle, DTMF 3 for Ringing). The Configuration Information is represented using a series of DTMF digits, with the first specifying the sender, the next describing the type of information and the rest the actual information. __ LOCALISED INTELLIGENCE

The localised intelligence of the Stations enables the system to work without the need of any central or common equipment. It allows each station to decide what is the appropriate action to take in response to user inputs, exchange signals, other stations status and it own history of events.

It allows for the co-ordination of the exchange of information between all the stations in a cost effective manner. It also allows for the display of station status and other useful information.

For example, refer to the features described in sections 1.1 , 1.2, 1.4, 1.5, 1.6, 1.7 and 2. which are provided by the use of Localised Intelligence. __ ALTERNATIVES __ PABX version This alterative shows a PCETS system connected to a PABX, instead of a

CENTREX exchange. The PCETS system can work in this way by using the appropriate PABX Access Codes to access the required CENTREX type features needed by the PCETS system. (Refer to Figure 6).

___ CENTREX Virtual Local Bus

This alternative shows a different type of PCETS system where the Distribution frame and PCU are effectively replaced by the CENTREX Exchange. The extra direct connection to the exchange would be for information exchange between the stations and possible power distribution to the stations.

In this alternative, the stations could have Localised intelligence, which would minimise any changes required to the CENTREX exchange, or the stations could be dumb (minimal intelligence) and the CENTREX exchange could be modified to provide the required intelligence to implement a PCETS system. (Refer to Figure 7).

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A Purpose-Built CENTREX Enhancing Telephone System (PCETS) comprising: a plurality of PCETS stations, each station having localised intelligence; and a local bus interconnecting each station.

2. A telephone system adapted to interact with a CENTREX service, the system comprising: a plurality of PCETS stations; each station including relatively localised intelligence; each station being connected to the CENTREX service; and a local bus interconnecting each PCETS station.

3. A system as claimed in claim 1 or 2, further comprising a direct connection between each PCETS station and the CENTREX service.

4. A system as claimed in claim 1 or 2, wherein the localised intelligence provides user defineable operation and control of each station, together with generation of CENTREX access codes.

5. A system as claimed in claim 1 or 2, wherein the local bus is adapted to enable exchange of information between each station.

6. A system as claimed in claim 1 or 2, wherein connection between each station and the CENTREX service provides station operation independent of other stations.

7. A system as claimed in claim 1 or 2, wherein each station can activate or deactivate CENTREX type features by sending appropriate access codes to the CENTREX service.

8. A system as claimed in claim 7, wherein the CENTREX service activated or deactivated is based on the history of activation of the station or the status of another station within the system.

9. A system as claimed in claim 1 or 2, wherein each station stores access codes applicable to a number of different types of CENTREX services.

10. A system as claimed in claim 1 or 2, wherein information exchanged between each station includes station status, DSS appearance, extension number and call line identification information.

11. A system as claimed in claim 1 or 2, wherein upon a power failure, each station communicates only directly with the CENTREX service in a manner independent of other stations.

12. A system as claimed in claim 11, wherein the operation of each station is changed to reduce power consumption.

13. A system as claimed in claim 1 or 2, wherein the local bus is provided within the CENTREX service.

14. A system as claimed in claim 1 or 2, wherein intermediate each station and the CENTREX service there is provided customer premises equipment, such as PABX, and each station is connected directly to the customer premises equipment.