The present invention relates to a communications method and apparatus, and in particular to a method and apparatus which enables efficient use to be made of the time for which channels of a communications system are occupied.

In a conventional telephone system, a user wishing to communicate with another user of the system telephones that other users number and communicates the desired voice message. Initially all of the messages transmitted over conventional telephone systems were in the form of voice messages. Currently, however, large volumes of data are transmitted through telephone systems in the form of data messages. In order to enable the transmission of large volumes of data over telephone systems, the band width of such systems has been increased. Various system standards have been proposed or introduced, for example the standard referred to as "integrated systems digital network", or ISDN. An ISDN system enables either digital data signals or analogue voice signals to be transmitted.

A single ISDN channel is capable of transferring either digital data, or analogue voice. There are currently two ISDN systems available, that is ISDN 2 and ISDN 30, providing two and thirty channels respectively. Each channel is capable of carrying either an analogue voice signal or a digital data signal. Thus, an ISDN 2 installation can be regarded as two separate telephone lines, and may be configured with separate numbers. The system provider will charge for use of each channel separately.

It is well known in, for example, computer networks for communications resources linking terminals of the network to operate on a multiplex basis. For example, when data has to be sent from one terminal to another, the sending terminal reviews the availability of a common communications channel linking the terminals and transmits data packets making up the appropriate data message during periods for which the communications channel is not occupied by signals transmitted from other terminals. The use of the communications resource is thus distributed on the basis of the demand for use in an efficient manner. The approach is, however, dependent upon continuous access to the communications channel which is clearly only appropriate in a situation in which the network "owner" is in control of the distribution of network resources. In contrast, in the case of a telephone system which seeks to provide services on the basis of payment for intermittent usage of system resources rather than payment for continuous access to the system resources, it is not possible for the system operator to control their customer's activities with sufficient precision to optimise the efficiency with which the system operates. Furthermore, it may not be in the commercial interests of the system operator to expend effort in enabling users to multiplex signals on the system unless the system operator can make separate charges for all of the multiplexed signals. This would be difficult to achieve given that the user's control over access to the system is based on opening and closing communication channels rather than monitoring the precise nature of the signals passing along a channel at anv one time.

In ISDN systems as currently operated, it is often the case that a single user is provided with both a conventional telephone for sending analogue voice messages and a personal computer (PC) for sending data, both voice and data being transmitted and received via a single ISDN channel. Thus the channel carries either voice or data, but not both.

It is an object of the present invention to enable users of a communications system to improve the efficiency with which they utilise access to that system.

According to the present invention, there is provided a method for communicating voice and data messages through a single communications channel, wherein each voice message to be transmitted is converted into a series of audio packets of data, each data message to be transmitted is delivered to a multiplexer connected to the channel in the form of a series of data packets, the audio and data packets are multiplexed with priority being given to the audio packets and the multiplexed packets are transmitted, the transmitted packets are received and demultiplexed, the audio packets are converted to analogue signals for audio reproduction, and the data packets are delivered to a data receiver.

The invention also provides an apparatus for communicating voice and data messages through a single communications channel, comprising means for converting a voice message to be transmitted into a series of audio packets of data, means for generating a series of data packets representing a data message to he transmitted, means for multiplexing the audio and data packets with priority being given to the audio packets, means for transmitting the multiplexed packets, means

for receiving and demultiplexing the transmitted packets, means for converting the audio packets to analogue signals for audio reproduction, and means for receiving a data packet.

Data messages to be transmitted may be stored with data identifying the intended destination of the message. If traffic on the channel is then monitored to detect when the channel is connected to the intended destination, the stored data message may be multiplexed with data packets on the channel when it is detected that the channel is connected to the intended destination. As a result messages may be sent with no transmission costs.

The terminals of a network arranged such that any terminal may be connected to any one of a series of communications channels can be arranged such that data messages to be transmitted are stored in a common store connected to the network. Each data message is stored with data identifying the intended destination of that message. Thus when traffic on the channels is monitored, a stored data message may be read out from the store and multiplexed with data packets on any channel which is connected to the intended destination of that message.

The invention also provides a terminal for an apparatus of the above type, the terminal comprising a first module for transmitting data packets and audio packets via a communications channel and receiving data packets and audio packets from the channel, a digital input/output device for generating data packets for transmission via the first module and receiving data packets from the first

module, a second module connected to the first module and arranged to transmit audio packets to the first module and receive audio packets from the first module, and an analogue input/output device for transmitting analogue audio signals to the second module and receiving analogue audio signals from the second module, wherein the second module converts analogue audio signals from the analogue input/output device to digital audio packets which are delivered to the first module and converts digital audio packets from the first module to analogue audio signals which are delivered to the analogue input/output device, the first module delivers audio packets received from the channel to the second module and delivers data packets received from the channel to the digital input/output device, and the first module multiplexes the audio packets received from the second module and the data packets received from the digital input/output device, the first module allocating transmission priority* to the audio packets such that the data packets are transmitted during intervals between successive audio packets.

Thus, in the case of, for example, a large company with a number of networks located at different sites interconnected by ISDN channels provided by a telecommunications utility, when an individual user at one site wishes to transmit a data message to another site, but the data does not have to be delivered immediately, that data message can be stored in a data storage device local to the site from which the data message is to be sent. Whenever a communications channel is subsequently opened between the site of the source of the data and the intended recipient of the data, for example to enable a simple voice exchange of

information, the opening of that channel will be detected and the data message will be transmitted in the form of a series of data packets multiplexed with a series of audio packets. At the destination, the data packets will be demultiplexed from the audio packets and delivered to a storage device, for example a PC. The delivered data message can then be distributed within the destination site as appropriate. Thus, in circumstances where there is regular voice traffic between two sites, data messages can be transmitted between those two sites whenever a voice channel is established, effectively at zero expense, given that the channel opened to enable voice communication has the capacity to carry large volumes of data. Accordingly, the invention enables users to dramatically reduce the cost of data transmission, assuming, of course, that as is generally the case, the data is to be transferred between sites which regularly communicate by voice.

Embodiments of the present invention will now be described, by wa of example, with reference to the accompanying drawings, in which:-

Fig. 1 is a schematic illustration of a terminal in accordance with the invention for connection to an ISDN data channel; and

Fig. 2 is a schematic illustration of a local area network which may be incorporated in a communications system in accordance with the invention.

Referring to Fig. 1, the illustrated terminal is intended to communicate both voice messages and data messages to an identical terminal via an ISDN data channel indicated by line 1. The terminal comprises a conventional PC 2 and a

telephone handset 3, the PC 2 and handset 3 being connected via a multiplexer 4 to the channel 1.

The multiplexer comprises a first ISDN module 5 and a second audio module 6. The ISDN module 5 exchanges packets of data with the audio module 6, those packets of data representing components of voice messages. The ISDN module 5 is arranged to transmit and receive packets of data via the channel 1 and to exchange packets of data with the PC 2. The audio module is linked to the handset 3 by an analogue input/output line 7 and its function is to convert such analogue signals into audio packets of data for transmission to the ISDN module 5 and to perform the reverse process in respect of audio packets of data received from the module 5. A link is provided between the audio module 6 and the PC 2 to enable audio packets of data to be stored for subsequent reproduction. The ISDN module 5 performs the function of multiplexing data packets received from both the PC 2 and the audio module 6 for transmission on the channel 1. In addition it performs the reverse process, that is demultiplexing packets of data received on the channel 1 for distribution either to the PC 2 or to the audio module 6.

When the user of the terminal illustrated in Fig. 1 wishes to make a call to another terminal, a data call is made to that other terminal, that call occupying only a single ISDN channel. Generally the call will be routed through the relevant utilities exchange via line 1. The audio module 6 monitors the line 7 so as to detect any analogue input, for example signals resulting from the user speaking into the handset 3. Any detected audio signals are digitised and compressed into packets of

data, these packets being referred to hereinafter as audio packets. The audio packets are then passed by the module 6 to the module 5 for transmission. The ISDN module 5 monitors both its input from the audio module 6 and its input from the PC 2. Data messages to be transmitted from the PC 2 will be in the form of a series of data packets, and that term is used hereinafter to distinguish signals from the PC from the audio packets from the audio module 6. Audio packets received by the module 5 from the module 6 are prefixed with an identifying header so as to enable the module 5 to distinguish them from the data packets received from the PC 2. The audio packets are given a higher priority than the data packets and thus are transmitted over the ISDN channel 1 without significant delay. The data packets are interleaved with the audio packets. In addition, the audio module 6 monitors its analogue input channel for silent periods and signals the ISDN module 5 accordingly. This allows data packets to be sent in an uninterrupted stream from the PC 2 during periods of silence.

In addition, digitised audio packets can be transferred between the audio module 6 and the PC 2. This allows recording and playback of audio packets to enable the provision of, for example, an answering machine service at the terminal.

When data is received by the ISDN module 5 over line 1, each packet is examined by the module to determine if it is an audio or data packet. Audio packets are directed to the audio module 6, data packets to the host PC 2. On receipt of audio packets the audio module 6 decompresses the receiv ed data, converts it into analogue form, and transmits those analogue signals to the handset

3 for reproduction. Data packets delivered to the PC 2 are handled in an appropriate manner, for example being written to disc or displayed on the users screen.

Data packets to be transmitted to a predetermined destination may be processed and stored in the PC 2 for subsequent transmission. When audio messages are being exchanged with the destination to which the stored data packets are to be transmitted, the PC 2 is programmed to interleave the previously stored data packets with the audio packets resulting from the audio exchange. Thus the stored data packets are transmitted without cost as soon as an audio message exchange is initiated with the intended destination.

It should be noted that it is not just voice calls which may initiate multiplexing, but also data calls. This means that a user with an urgent file (for example E-mail) to send to an intended destination may initiate a data transfer to that destination. The software may then multiplex any previously stored data for the same destination which is stored in the PC with the E-mail file that is being transmitted.

The embodiment of the invention represented in Figure 1 may be implemented in a single PC by plugging into the PC a single customised card carrying all the required audio and data processing components including a multiplexer, and providing a connection to the card for a telephone handset incorporating only a speaker and microphone. This enables a conventional P and conventional telephone to be replaced by a PC incorporating the customised

card and handset and associated software. This provides a low-cost replacement for telephone, fax, modem, voice and E-mail facilities.

The embodiment of the invention represented in Fig. 1 assumes that only data generated at the same terminal as that from which a voice message is to be transmitted can be multiplexed on the same ISDN line. In many circumstances, however, users are connected to local area networks and in such circumstances the concept of the present invention can be applied in a yet more efficient manner by enabling data from any PC connected to the network to be carried with voice messages from any other user of the network. Fig. 2 illustrates in highly simplified form a local area network which has been modified accordingly.

Referring to Fig. 2, a network ring 8 is connected to, for example, a private exchange by an ISDN line 9, the private exchange being linked in a normal manner to the outside world through the local utilities communication system. Connected to the ring 8 is a terminal of the type illustrated in Fig. 1, comprising a PC 10, a telephone 11 and a multiplexer 12. Also connected to the ring are a PC 13 which is not provided with its own telephone and a simple telephone 14. In addition, a central data store 15 is connected to the ring 8 and it is this central data store that is used to coordinate the delayed transmission of data messages from the user of the PC 10 and the user of the PC 13.

If the user of the PC 10 wishes to send data immediately, an appropriate call is made via telephone 11 in the manner described with reference to Fig. 1. If, however, the user of the PC 10 has data to be transmitted to a particular remote

network, but that data does not have to be transmitted immediately, the data is loaded into the central data store 15 together with information identifying the intended destination for that data. In a similar manner, the operator of the PC 13 may generate data for transmission to a remote user of the system, that data also being loaded into the central data store with information identifying its intended destination. The data loaded into the store 15 will remain there until such time as either a call is made from one of the telephones 11 and 14 to the intended destination or an alternative transmission condition has been achieved, for example the data has been in the store for a predetermined period of time or a predetermined time of day has been reached, for example 6pm at which time telecommunications tariffs in some areas are reduced.

By way of example, let us assume that a telephone call is made from the telephone 14 to a destination for which data has previously been delivered to the store 15. The store 15 monitors the ring 8 and detects when a call to the intended destination is in process. Quiet periods on the line are detected by the store and the relevant data is downloaded onto the line during such periods. Thus data is delivered to the end user without increasing the charges to be made by the telephone utility at all.

The only drawback to obtaining free transmission of data is the delay that occurs between the generation of the data and the making of the first voice message call to the intended destination. In manv instances where busy offices are

intercommunicating repeatedly during the course of any one day the delay will be of no significance to the efficiency of the operation.

Systems in accordance with the invention may be incorporated in multi- featured Windows communications packages providing E-mail, voice-mail, file transfers and image transfers. The hardware used can interface with ISDN lines, asynchronous modems and any data communication system in which channels have a bandwidth sufficient to carry multiplexed voice and data signals. Although the data stores may be separate components, generally these will be resources provided by one of the PC's connected to the network. A minimum specification for such a PC would be a 386 processor with 4 Mb of RAM and, for example, 5 Mb of hard disc free space. The PC would also be provided with an appropriate hardware device to interface with the communications channel with which it is used, for example, a modem or ISDN interface such as an 8 channel ISDN card. Such a card would enable simultaneous connections to be made to eight other users of the system. Raw data transfers at rates of up to 8 Kbytes per second per channel are practicable.

The user may selectively alter the relative bandwidths of the audio/data transfer to allow very high quality audio with slower data transfers or fast data transfers at the expense of audio quality. Audio compression may be implemented supporting compression rates up to 8:1, thereby increasing the effective bandwidth considerably and further increasing the amount of data that may be sent during a conversation.

Audio data may be routed in several ways, allowing recording/playback of local speech, as well as recording and playback over ISDN. This allows the system to support sophisticated voice mail features, with the ability to tailor messages for each user known to the database.

User dependent voice recognition could be incorporated to allow a user to control the actions of the system by spoken commands, and even to control the routing of data by detecting keywords within a conversation. Voice recognition

combined with text to speech conversion would also allow remote control of the user's PC over a telephone line.

Each system user would be provided with a database of users and addresses, a list of connection types the user supports with connection addresses (numbers) and preferences for each, and both an outgoing and incoming director or mailbox. The outgoing mailbox is used for automated data transmission, anything stored in this directory being sent to the appropriate user when a channel is opened to that user. Similarly, any incoming files from a user will be placed in the incoming mailbox.

The system can be used with a single PC acting as a gateway between networks. Files placed in a common outgoing mailbox can thus be automatically sent to the appropriate destination transparently and free of charge.