GB2258787A

GB2258787A - Telephone communications systems

Info

Publication number: GB2258787A
Application number: GB9117652A
Authority: GB
Inventors: John Burton
Original assignee: Northern Telecom Ltd
Current assignee: Nortel Networks Ltd
Priority date: 1991-08-15
Filing date: 1991-08-15
Publication date: 1993-02-17
Anticipated expiration: 2011-08-15
Also published as: GB9117652D0; GB2258787B

Abstract

A digital telephone system (PABX) comprises a number of service agents, e.g. telephone sets, fax machines or trunk lines coupled to a call handler via which communications are routed. The call handler incorporates fixed system software to provide a basic switching function. Further system functions are developed by auxilliary software which is stored in the service agents. The service agents communicate with the call handler via dedicated communication channels. Each service agent has a unique address so that any service agent may be coupled to the call handler via any convenient wired connection. In setting up a call, the call handler accepts a call request, broadcasts address data to all service agents and determines which wired connections are occupied by the service agents to be connected. The new status e.g. PREDIAL, ACTIVE, IDLE of the connected service agents is broadcast to all other service agents as the call proceeds. If a special feature, such as a call diversion is in operation, the appropriate service agent intercepts the call setting up procedure and the call handler responds to the diversion message to set up the call to the diverted service agent. <IMAGE>

Description

COMMUNICATIONS SYSTEM This invention relates to communication systems, and in particular to an office communications system in which a number of subscriber terminals are coupled to a central switch or PABX.

A conventional office communications system comprises a number of terminal stations which may be selectively coupled together, to provide a communications channel, via a central switch or PABX. The switch is controlled by a processor or computer and responds to service requests from the various terminal stations according to the programme that was stored in the processor when the system was originally installed. This introduces problems when the system is to be upgraded and/or further system features are to be provided. An upgrading of this nature generally requires changes to the process software. In a conventional system this requires considerable effort and expense as the entire software package then requires regression testing to ensure freedom from errors. Such a procedure is both costly and time consuming.Furthermore, as customer requirements can be widely different, the manufacturer of the system is committed to the provision of software, almost on an individual basis, for each customer requirement. This increases development time and raises manufacturing costs.

The object of the present invention is to minimise or overcome this disadvantage.

According to the invention there is provided a telephonic communications system, including a plurality of stations or service agents, a central switch to which each said service agent is coupled and whereby communications channels may be established between service agents, control means associated with the switch for providing a basic telephone switching function, and means associated with at least one service agent for downloading auxiliary programming instructions into that and other service agents whereby to provide further telephone features.

According to the invention there is further provided a telephonic communications system, including a plurality of telephone sets, a central switch to which each telephone is coupled via voice and signalling digital channels, means associated with the switch for providing a basic telephone switching function whereby to establish voice channel communication between selected telephones, and means associated with at least one said telephone for downloading auxiliary programming instructions into the system whereby to provide further telephone features, wherein said auxiliary instructions are stored in the telephones, wherein signalling between each said telephone and the switch is effected over a data channel, and wherein signals transmitted by any one telephone over a said data channel are broadcast to all telephones of the system whereby each telephone is continuously updated with the current state of the system.

According to the invention there is further provided a telephonic communications system, including a plurality of stations or service agents, a central switch to which each said service agents is coupled via a wired link and whereby communications channels may be established between service agents, and call control means distributed between the central switch and the service agents, wherein each service agent is allocated at least one identifying address whereby operation of the system is logically independent of the physical relationship between the service agents and the wired links to which they are coupled.

According to a further aspect of the invention there is provided a telephonic instrument adapted to communicate with a central switch over digital voice and data channels, the central switch being controlled by configuration software, wherein the instrument includes means for storing additional software, complementary to the configuration software, whereby to determine the manner in which the central switch handles calls.

According to another aspect of the invention there is provided a cabling arrangement for a telephone system in which a plurality of service agents are coupled to a central switch each via any available conductor pair, the cabling arrangement including a multipair main cable coupled to the switch, and one or more smaller cables coupled between the main cable and the conductor pairs to which the service agents are connected and wherein all connections between cables are provided via plug-in connectors.

The system software is divided between the call handler and the peripherals. The call handler is provided with fixed call control software with very few features. Essentially the call handler software provides only call control/routing. All the system features are provided by user software which is separately developed, e.g. via a PC and downloaded into a peripheral from which it is then loaded into another system peripheral. In this way the user can customise the system to suit his particular requirements. It will be appreciated that the user software can be developed to provide the same features on all peripherals, or to provide different peripherals with different levels of service.

The system is open in the sense that persons other than the system manufacturer can develop and add functionality.

An embodiment of the invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a general schematic diagram of a communications system according to the invention; Fig. 2 is a schematic diagram of a wiring system for the communications system of Fig. 1; Fig. 3 is a flow chart illustrating the progress of a call; Fig. 4 is a schematic diagram of the core unit or call handler of the system of Fig. 1; Fig. 5 shows a system card for use in the call handler of Fig. 4; Fig. 6 is a block schematic diagram of a telephone instrument for use in the system of Fig. 1; Fig. 7 illustrates the software architecture of the system; Fig. 8 illustrates the logical model of the system; and Fig. 9 illustrates a typical system message format.

Referring to Fig. 1, the system includes a core unit or call handler 11 to which a number of service agents are connected e.g. by two-wire links. Each two-wire link is allocated a TDM time slot. The service agents or peripherals comprise a number of telephone sets 120, and may also include e.g. a facsimile terminal 121 and one or more trunk cards for providing access to the public network. Each service agent is assigned an address or system directory number (SDN). It should be noted that SDN's are allocated to service agents and not the particular two-wire links to which they may be connected Depending on the system requirements, a single SDN may be assigned to a number of service agents and/or more than one SDN may be assigned to a single service agent.

Any item of equipment that is able to send request messages is referred to as a service agent. The most common form of service agent is a telephone set, but the term also includes e.g.

FAX machines and trunks. Every service agent attached to the system has a unique identifying number (SAID) which identifies the particular line or port to which the service agent is connected. Thus, when a service agent is coupled to a different line its SAID will change although its system directory number (described below) will not change.

Communication with the service agents is effected over data channels (D-channels) that are used for signalling and voice channels (B-channels) that carry user signals such as voice or user data. Each D-channel is a hardware channel that carries information between a service agent and the call handler and is not switchable. Each B-channel is a hardware channel that carries voice communication between a service agent and the call handler. It is the B-channels that are switched to establish voice communication between service agents in response to signals carried on the D-channels. Communication on a B-channel is end-to-end between service agents. Both types of channel are digital with the D-channels operating at e.g.

l6kbit/sec and the B-channels at e.g. 64 kbit/sec.

The system intelligence is distributed between the call handler and the peripherals (including the sets and the trunk cards), processing facilities being provided in both. The call handler performs a basic B-channel switching function, the remaining system functions being controlled by the peripherals All signals carried on the D-channel are broadcast to all peripherals so that every peripheral is continuously updated with the current state of the entire system. This allows system functions to be implemented by the peripherals rather than by the call handler.

System peripherals communicate with the system via the same fixed message set, and all peripheral addressing is effected via system directory numbers (SDN's). The call handler has no concept of what is attached to the system nor of its physical location, i.e. each peripheral is identified by its SDN and not by the particular time slot to which it is allocated. This simplifies the installation wiring of the system as the engineer does not have to identify which wiring pair is to be associated with a particular peripheral. The conventional wiring with distribution boxes can thus be replaced with multipair cables to which smaller cables and single pairs are coupled via plug-in connectors. A peripheral is connected to the system via any convenient unused pair.

Figure 2 illustrates a typical system wiring arrangement. The system includes one or more main multipair cables 21 coupled between the call handler and one or more stages of smaller distribution cables 22 whereby individual pairs 23 are coupled to the cable handler. All intercable connections are effected via plug-in connectors. This obviates the need for the conventional distribution frames and significantly reduces the installation costs of the system.

The progress of a typical call is illustrated in the flow chart of Fig. 3. This shows the progress of a simple call between two peripherals, e.g. telephone sets, each of which is associated with an SDN (SDNA and SDNB). Fig. 3 illustrates the way in which the call sequence is enhanced by parameters in the call handler.

The sequence is shown on the left of Fig. 3, the progression from one call state to the next being influenced by parameters in the call handler. These parameters are associated with the parties in the call, the diagram showing the points in the sequence where they have effect. Where a parameter is set to its default value the effect is for the call to proceed along the main sequence. At any time the call is at a particular point in this sequence. This point is represented by the cursor to the right of the diagram.

This cursor progresses downwards as the call proceeds.

While in a call state the peripherals are in control and the call handler is awaiting a request. A message request from a peripheral causes the call handler to take control and determine the next call state, this next state being determined by the type of request, the existing state and the parameters associated with the SDN parties. These parameters are shown to the right of the call sequence.

It should be noted that the system has a sequence of fixed call states that are common to all calls. The call is initiated e.g. by the user lifting his handset. In response to this the telephone set software sends, on behalf of SDNA, an activate message over the D-channel to the call handler. Assuming that SDNA is not busy, the call handler marks SDNA as being bound to that telephone set and puts the call into a call state of PREDIAL with SDNA as the originating party. This new state of SDNA is broadcast and, at the same time, dial tone is returned to the originating party who can then dial the required number e.g. as a DTMF signal over the B-channel. Now that SDNA is bound to the originating telephone, other messages requesting access to SDNA are rejected. An SDN can be bound to only one peripheral at a time.

The call handler translates the dialled digits into the address (SDNB) of the called telephone and determines whether or not SDNB is busy. Assuming SDNB is not busy, the call handler associates SDNA with SDNB and broadcasts an ALERT message to all peripherals. At the same time that the ALERT message is broadcast, the call handler returns e.g. ring tone to the initiating terminal over the B-channel. Note that the call handler does not know where SDNB is located: it is up to each peripheral to recognise its own SDN in the broadcast signal. The SDN addressing mechanism is thus independent of the system hardware, i.e. it is logical rather than physicaL On recognising its own SDN (SDNB) the called peripheral alerts the user e.g. by operation of a tone ringer. The response of a peripheral to the ALERT message will of course depend on the nature of that peripheral.For example, a telephone set may activate a line ringer, a FAX machine may enable a paper feed, and a trunk card may access the public network.

When the called party answers the call, e.g. by lifting his handset, that telephone set sends an ACTIVATE message for SDNB to the call handler. In response the call handler binds SNDB to the terminal and switches through the B-channel between the terminals so that the parties can talk to each other.

To terminate the call, either party hangs up and his terminal sends a RELEASE message for SDNA (as this terminal is bound to SDNA the call handler accepts a release request only from this terminal). The call handler responds to the request by broadcasting an IDLE message for SDNA and SDNB and disconnects the B-channel between the terminals.

A particular variation of the above sequence is the MOVE message which is used to re-route a dialled number. Suppose there is an unconnected call between SDNA and SD NB. Any service agent can transmit a MOVE message to the call handler to modify the terminating party of the call. The message may have the form MOVE (SDNA, SDNB, SDNC) The call handler will process the call to the new SDN.

Assuming that the next state in the fixed call sequence is ALERTING the call handler will broadcast the messages ALERTING (SDNA, SDNC) IDLE SDNB The call sequence between SDNA and SDNC then continues as described above.

The general structure of the call handler is illustrated in Fig. 4.

The call handler includes a power supply (PSU), a system card incorporating a processor and a switch, one or more digital line cards and, optionally, one or more trunk cards which provide access to a remote system, e.g. the public telephone network.

An analogue line card may also be provided for peripheral equipment such as a facsimile machine. Each digital line card services a number, e.g. 64 of telephone instruments. The cards may be mounted in the backplane of the call handler and are coupled to the system card (CPU/SWITCH) e.g. via a DS30 bus.

Operation of the call handler is controlled by the system card which is shown in greater detail in Fig. 5. The system card provides all the switching for the system and processes service requests from the intelligent peripherals. In addition the system card maintains the state of all calls in progress and broadcasts state changes to all peripherals. The card incorporates a processor which, together with an associated memory, processes service requests received over the D-channels and controls switching of the B-channels via an IVD bus coupled to an array of switches. Configuration software for operating the processor is loaded into an input serial port during start up and configuration.

The construction of a typical telephone set is illustrated in Fig.

6. Operation of the telephone is controlled by a processor 61 and an associated memory 62. The processor 61 may be programmed via an input serial port to provide system features additional to the basic switching function of the call handler. Software which is input via the serial port is loaded into the other telephone sets of the system.

Power for operation of the terminal is derived from the two wire line via a DC to DC converter. Advantageously a back-up battery (not shown) is provided to prevent erasure of the memory e.g. when the terminal is temporarily disconnected from the line.

As all signalling on the line is digital, an A - D/D - A interface circuit 64 is provided between the line and the speech or analogue circuitry 65 of the terminal.

Referring now to Fig. 7, the system software architecture is depicted in highly schematic form. The software is split into functions on either side of an interface which separates the interface between the call handler and the system service agents. The call processing function to the left of the interface executes on the central switch while the functions to the right of the interface execute on service agents. The key to the architecture is the separation of the functions via a clean unchanging (evergreen) interface. This interface is common across the entire range of service agents. This is further exemplified in Fig. 8 which illustrates the logical model of the system.

The interface of Fig. 7 constitutes functional messages to service agents addressed by SDN's that are carried on the D-channel. These are of two types; datagram and call processing. Datagrams have source and destination SDN addresses. They are reflected by the call processing function to all service agents. They thus provide a hardware-independent method of communication between service agents. Call processing messages from service agents to the call handler are requests for service. Messages in the other direction are responses. As illustrated in Fig. 9, each message consists of header portion comprising a request (from a service agent) or a command (from the call handler) followed by a number of addresses to which the message relates. The call handler maintains the state of all calls as calls between SDN's.It is aware of the current state of all SDN's, but has no conception of the variety of service agent types nor of which SDN's are resident on which service agent.

The functions to the right of the interface are products which can be developed and packaged independently for installation by the customer to suit his particular business needs. The call handler software sees messages which influence its handling of calls. These parameters like all parameters in the system are managed by the configuration package provided on installation of the system. The service agents use appropriate sequences of messages to implement functions.

Various call handling operations can be developed on a personal computer (PC), seen by the call handler as a peripheral, and attached to any telephone instrument via its serial data port. To achieve this flexibility the call processing function provides points in the call sequence where an outside PC-based function can re-route a call in real time.

Claims

CLAIMS:

1. A telephonic communications system, including a plurality of stations or service agents, a central switch to which each said service agent is coupled and whereby communications channels may be established between service agents, control means associated with the switch for providing a basic telephone switching function, and means associated with at least one service agent for downloading auxiliary programming instructions into that and other service agents whereby to provide further telephone features.

2. A system as claimed in claim 1, wherein signalling communication between the service agents and the central switch is effected via a fixed message set whereby to provide a fixed interface between the central means and the auxiliary programming instructions.

3. A system as claimed in claim 1 or 2, wherein the control means processes calls via a sequence of call states, progression along the sequence being determined by requests from service agents.

4. A system as claimed in claim 1, 2 or 3, wherein each service agent is identified by an address, said address being independent of the particular connection between that service agent and the central switch.

5. A system as claimed in claim 4, wherein said signalling communications are broadcast to all service agents, and wherein each service agent responds only to those communications incorporating its address.

6. A system as claimed in any one of claims 1 to 5, wherein voice communication between service agents is effected over digital channels.

7. A system as claimed in any one of claims 1 to 6, wherein each said service agent is coupled to the switch via a pair of conductors.

8. A system as claimed in claim 7, wherein at least some service agents are line powered via DC/DC converter means.

9. A telephonic communications system substantially as described herein with reference to and as shown in the accompanying drawings.

10. A telephonic communications system, including a plurality of telephone sets, a central switch to which each telephone is coupled via voice and signalling digital channels, means associated with the switch for providing a basic telephone switching function whereby to establish voice channel communications between selected telephones, and means associated with at least one said telephone for downloading auxiliary programming instructions into the system whereby to provide further telephone features, wherein said auxiliary instructions are stored in the telephone, wherein signalling between each said telephone and the switch is effected over a data channel, and wherein signals transmitted by any one telephone over a said data channel are broadcast to all telephones of the system whereby each telephone is continuously updated with the current state of the system.

11. A telephonic communications system, including a plurality of stations or service agents, a central switch to which each said service agent is coupled via a wired link and whereby communications channels may be established between service agents, and call control means distributed between the central switch and the service agents, wherein each service agent is allocated at least one identifying address whereby operation of the system is logically independent of the physical relationship between the service agents and the wired links to which they are coupled.

12. A telephone instrument adapted to communicate with a central switch over digital voice and data channels, the central switch being controlled by configuration software, wherein the instrument includes means for storing additional software, complementary to the configuration software, whereby to determine the manner in which the central switch handles calls.

13. A telephone instrument substantially as described herein with reference to and as shown in Fig. 6 of the accompanying drawings.

14. A cabling arrangement for a telephone system in which a plurality of service agents are coupled to a central switch each via any available conductor pair, the cabling arrangement including a multipair main cable coupled to the switch, and one or more smaller cables coupled between the main cable and the conductor pairs to which the service agents are connected, and wherein all connections between cables are provided via plug-in connectors.