Heretofore, telephone subscribers can obtain direct information about the charges of their call through pulse- signals. Depending on the type of connection, each time a defined number of seconds has lapsed, a pulse is sent from the exchange to the subscriber and represented there, for instance by a counter. Each pulse then represents a fixed amount, which is charged to the subscriber's account.

-Now that telephone connections are more and more often charged per second, this known technique is not accurate enough anymore, while there is still a need to receive information about call charges directly and accurately. This is true not only of private subscribers but especially of hotels, conference centers, etc., where it is desirable for the telephone charges to be charged directly to the client.

Towards realizing the above-described objective, already three different solutions exist at present, but each suffers from an inherent drawback.

According to a first solution, it is necessary to utilize an ISDN connection. ISDN affords the possibility of making use of a charge report service, which arranges for call charge information to be sent to a subscriber during and/or after a call and to be shown on the alphanumeric display of the subscriber's ISDN apparatus. A drawback of this service is that it is not available to subscribers on the normal analog telephone system because in most cases subscribers do not have apparatuses with alphanumeric displays.

-According to a second solution, which has been developed in particular for hotels and conference centers, a printer is provided at the subscriber's site, which printer

is connected to the local exchange via a separate communication line. After each call, a call report specifying the charges of the call is transmitted. The drawback of this solution is, of course, the necessity of a separate connection, exclusively for the charge information.

According to a third solution, finally, the subscriber is automatically telephoned after each call and information on the charges of the call is given by means of a voice machine. A drawback of this solution is that the spoken report entails the risk that it will be understood incorrectly, while obtaining the charge information after each call requires extra time.

The object of the present invention is to provide a solution that has none of the drawbacks of the known solutions and which can be readily provided to subscribers having modern equipment at their disposal.

To that end, according to the invention, there is provided a method for transferring information regarding the charges of a telephone call, wherein after the telephone connection in question has been broken, an electronic mail message with charge information is sent to a personal computer of the calling subscriber.

Accordingly, the invention has the advantage that the subscriber only needs to have a personal computer and an electronic mail address on a computer network. The most obvious option is this connection is sending an e-mail via the Internet, but other solutions are also possible.

In a time where not only hotels and conference centers but also many telephone subscribers that do not yet have an ISDN connection, do have a personal computer, the solution according to the invention is easy to implement, can be provided inexpensively, and is fast. In principle, a separate communication line is not required and errors are precluded because the message is displayed in writing and may optionally be printed.

As desired, the call charges can be sent directly after a call, but they may also be collected in the exchange for a fixed period of time, for instance an hour or a day, and then be sent. Further, the subscriber can also decide that he wants to know the charges for every call or, for instance, just for trunk and/or international calls. It is also possible to send a message from the exchange only when the charges of a call exceed a minimum amount.

The invention further provides a telephone exchange comprising means for establishing a connection between two subscribers and means for determining the duration of the connection, characterized in that the means for determining the duration are coupled to an apparatus for composing an electronic mail message and that an interface is provided for coupling that apparatus to an external computer network.

The invention will be further explained hereinafter, on the basis of an exemplary embodiment, with reference to the drawing. In the drawing, the figure shows a functional block diagram of a telephone exchange which is suitable for implementing the invention.

In the diagrammatically represented telephone exchange, which may be of an existing type, in a block 1 a calling procedure is carried out for connecting a calling- subscriber A with a called subscriber B. Here, in a conventional manner, based on information about the telephone number of subscriber A and the telephone number of subscriber B selected by A, a connection between A and B is established.

During the connection, as part of the calling procedure, when the connection has been established, information on the time of the call is recorded (in connection with telephone charges that vary in amount depending on the time of day), and when the connection is broken, information on the length of the call is recorded. Finally, based on this information, the cost price of the connection for subscriber A is registered.

-During or directly after the call, the information generated by the calling procedure is transmitted to a block

2, where a charging procedure is carried out. In this procedure, all such information is collected as is neededto periodically send the subscriber a bill, and this information is further processed via an interface outside the exchange.

This procedure, too, is standard in conventional exchanges.

According to the invention, in the charging process, for selected subscribers-those who wish to receive the charge information in accordance with the invention- directly after a connection has been broken, the charge information is supplied to an e-mail module, represented by block 3, which carries out an e-mail procedure.

In the e-mail procedure, the charge information is sent to the electronic"mailbox"of the subscriber at an Internet provider, with the use of the Simple Mail Transfer Protocol (SMTP), known per se. This protocol, which is described, for instance, by Jonathan B. Postel in"Simple Mail Transfer Protocol", RFC 821, USC/Information Science Institute, August 1982, comprises three steps, wherein successively a transaction is started by identification of the sender, a command is sent that identifies the recipient, and a data command is sent, whereby all factual data of the sent message are transferred. An"end of message"indicator confirms the transfer. For the purpose of the e-mail procedure, block 3 further includes a memory storing all mailbox addresses of the subscribers for whom the offered service is active. Whether the subscriber is active can be determined either in the calling procedure or in the charging procedure. As soon as call information is received from the charging procedure, the e-mail procedure initiates an SMTP mail transfer. The mailbox of the recipient is then retrieved from the above memory, on the basis of the telephone number of the calling subscriber. The data to be sent is so organized as to provide the subscriber with information on the charges in a neatly arranged form.

The mail data consists of ASCII characters. If the internal representation of the call data is different, a _ conversion must be provided for in a manner known per se.

The e-mail procedure 3 is coupled via an Internet interface 4 with the Internet gateway. This interface provides inter alia for the transport for SMTP. One of the protocols that can be used for this purpose is the Point-to- Point Protocol (PPP), which is described, for instance, by W. Simpson in"The Point-to-Point Protocol", RFC 1661, Network Working Group, July 1994.

The exchange further comprises an interface 5 for the operator of the exchange. Via this interface, the list of active subscribers for the above-described charge information service can be entered and updated. Both via the interface 5 and by the subscriber operating the telephone apparatus, the charge information service can, for individual subscribers, be activated, deactivated or be consulted.

According to the invention, it is also possible to place the e-mail procedure and the Internet interface outside of the exchange by arranging for the delivery of the data required therefor via a suitable interface in the exchange.

Instead of sending an e-mail, it is also possible to make the charge information available on a website, for instance the website of the manager of the telephone network, while the subscriber can have access to the charge information relevant to him on the website through a personal code.