WO2000010345A2

WO2000010345A2 - Method and system for implementing signalling between a telephone exchange (dx) and a private automatic branch exchange (pabx)

Info

Publication number: WO2000010345A2
Application number: PCT/FI1999/000677
Authority: WO
Inventors: Petri Sved
Original assignee: Nokia Networks Oy
Priority date: 1998-08-17
Filing date: 1999-08-16
Publication date: 2000-02-24
Also published as: WO2000010345A3; AU5293399A; FI981768A; FI981768A0

Abstract

The invention concerns a method for implementing the signalling between a telephone exchange (DX) and a private automatic branch exchange (PABX) in a telecommunication system comprising a telephone exchange (DX) and a private automatic branch exchange (PABX) connected to the telephone exchange. In method of the invention, retransmission of a message sent by the telephone exchange (DX) to the private automatic branch exchange (PABX) is prevented when, based on the message, the private automatic branch exchange (PABX) has returned to the telephone exchange (DX) a response message indicating an error condition or incompatibility. Moreover, the invention concerns a system for implementing the signalling between a telephone exchange and a private automatic branch exchange in a telecommunication system comprising a telephone exchange (DX) and a private automatic branch exchange (PABX) connected to the telephone exchange. The system of the invention comprises means for preventing the retransmission of a message to be sent from the telephone exchange (DX) to the private automatic branch exchange (PABX) when, based on the message, the private automatic branch exchange (PABX) has returned to the telephone exchange (DX) a response message indicating an error condition or incompatibility.

Description

METHOD AND SYSTEM FOR IMPLEMENTING SIGNALLING BETWEEN TELEPHONE EXCHANGE (DX) AND A PRIVATE AUTOMATIC BRANCH EXCHANGE (PABX)

The present invention relates to telecommunication systems. The invention concerns a method and system for implementing the signalling between a tele- phone exchange and a private automatic branch exchange .

In the signalling between a telephone exchange and a private automatic branch exchange, the telephone exchange may sometimes send the branch ex- change a message that the latter cannot identify. The branch exchange may not be able to handle the message in the state in which it was received. In this case, the branch exchange usually sends the telephone exchange a message informing the latter about an error situation. When corresponding situations recur, the telephone exchange and the branch exchange again exchange messages which do not result in any further action, or the call connection is disconnected in consequence of unknown conditions. The object of the present invention is to eliminate the drawbacks described above. A specific object of the present invention is to disclose a new type of method and system which can be used to eliminate unnecessary messages from the signalling between a telephone exchange and a branch exchange as well as failures of calls.

The invention concerns a method for implementing the signalling between a telephone exchange and a private automatic branch exchange in a telecom- munication system. The telecommunication system comprises a telephone exchange, a private automatic branch exchange connected to the telephone exchange and a telecommunication terminal connected to the branch exchange. According to the invention, a message sent by the telephone exchange to the branch exchange is not sent again when, based on the message, the branch exchange has returned to the telephone exchange a response message indicating an error condition or incompatibility. In other words, repeated transmission of the message is prevented in the telephone exchange. In a preferred embodiment of the invention, the response message returned by the branch exchange to the telephone exchange contains a parameter which has not been identified or which is not supported. In an embodiment, the response message sent by the branch exchange to the telephone exchange contains informa- tion regarding the state of the branch exchange at the time when the message was received.

In a preferred embodiment of the invention, the information contained in the response message sent by the branch exchange to the telephone exchange is stored in conjunction with the telephone exchange. In an embodiment, when the transmission of a message to be sent from the telephone exchange to the branch exchange has been disabled, the setting disabling its transmission can be removed. After this, sending such messages to the branch exchange is again allowed. This function is usable e.g. in a situation where the functions of a branch exchange have been developed further as a consequence of a software update but the telephone exchange is not accurately informed about the modified functions.

The invention also concerns a system for implementing the signalling between a telephone exchange and a branch exchange in a telecommunication system comprising a telephone exchange, a private automatic branch exchange connected to the telephone exchange and a telecommunication terminal connected to the branch exchange. The system comprises means for preventing retransmission of a message to be sent from the telephone exchange to the branch exchange when, based on the message, the branch exchange has returned to the telephone exchange a response message indicating an error situation or incompatibility. In a preferred embodiment, the private automatic branch exchange comprises means for sending a parameter that has caused a disorder in the response message of the branch exchange to the telephone ex- change. A parameter sent by the telephone exchange to the branch exchange may go unidentified by the branch exchange. The branch exchange may be in a state in which it does not support the parameter. In an embodiment, the private automatic branch exchange comprises means for sending to the telephone exchange information concerning the state of the branch exchange at the time when the message was received.

The system preferably comprises means for storing the information contained in the response mes- sage sent by the branch exchange to the telephone exchange in conjunction with the telephone exchange. In an embodiment, the system comprises means for removing a setting disabling the transmission of a message to be sent from the telephone exchange to the branch ex- change.

In the following, the invention will be described by the aid of a few examples of its embodiments with reference to the attached drawing, wherein

Fig. la and lb present, by way of example, a signalling arrangement according to the invention;

Fig. 2 presents a signalling example; and

Fig. 3 is an example illustrating an error situation occurring in the signalling.

The method and system of the invention are applicable e.g. in the DX200 switching system manufactured by Nokia. 'Branch exchange' refers to a private exchange used by an enterprise or other community and connected to a public telecommunication network. Calls are connected automatically. The branch exchange is often provided with different functions than an exchange in the public telecommunication network, e.g. direct inward dialling and night service connection. The telephone exchange and the branch exchange are connected to each other e.g. via an ISDN line (ISDN, Integrated Services Data Network) . Possible signalling protocols are e.g. DSS1 (Digital Subscriber Signalling System No. 1) , DSS1+ or PSS1 (Private Subscriber Signalling System No. 1) .

The signalling sent to the branch exchange subscription may contain a message that is not identified or which cannot be handled in the state in which it was received. Correspondingly, the message may contain a parameter which cannot be identified or which is not supported. In this case, a STATUS message with an appropriate CAUSE value (e.g. #101 - Message not compatible with call state, #97 - Message type non- existing or not implemented, #99 - Information element non-existent or not implemented) can be sent from the branch exchange. In addition, the message includes the call state in which the message was received as well as the parameter or message identifier not identified. These data can be used to maintain information regarding things not understood by the subscription in question. Next time, this message or parameter will not be sent to that subscription. When necessary, the original data can be restored, in which case the informa- tion in question may again be sent to the subscription. Thus, the signalling originally functions in the same way against each subscription. This learning procedure reduces unnecessary message exchange (STATUS) and failures of calls. The function of the invention can also be implemented using the ISUP (ISDN User

Part) , which comprises a CONFUSION message, which corresponds to the STATUS message. The CONFUSION message contains the same kind of Cause parameter, but no status data. Fig. la and lb present a telephone exchange

DX and a private automatic branch exchange PABX. Fig. 1 illustrates the action when the private automatic branch exchange PABX 1 for the first time receives a message concerning call transfer. In the NO state, the branch exchange sends a SETUP message to the telephone exchange DX . The telephone exchange DX goes to state Nl and returns a CALL PROCEEDING message to the branch exchange PABX 1. The telephone exchange DX goes to state N3 and examines a file to establish whether the NOTIFY message and the Notification Indicator ("Diverting") parameter are supported for this branch ex- change. The branch exchange is sent the information regarding call transfer because, according to the file, NOTIFY was supported. However, the branch exchange does not support the NOTIFY message in the N3 state, so it sends a STATUS message giving the Cause as #97 (Message type non-existent or not implemented) and status data N3 indicating that NOTIFY is not supported in the state in question. In state N3 , the telephone exchange DX sends an ALERTING message to the branch exchange PABX 1, indicating that the called subscriber is on-hook and the called subscriber's telecommunication terminal is ringing. After this, the system goes e.g. to state N4 and starts corresponding actions .

The information that the branch exchange PABX 1 does not identify the NOTIFY message in state N3 is stored by the telephone exchange DX in a record for branch exchange PABX 1 in an appropriate file. In a situation as illustrated by Fig. lb, where the initial situation is the same as in the case of Fig. la, the telephone exchange DX examines the data for branch exchange PABX 1 in the file to establish whether the NOTIFY message is supported for that branch exchange. Since the file for the branch exchange now contains information, stored on the previous occasion, indicat- ing that the branch exchange PABX 1 did not identify the message, no NOTIFY message will be sent, but in- stead an ALERTING message will be sent directly in state N3.

Fig. 2 presents an initial situation corresponding to Fig. la and lb, where the telephone ex- change DX exchanges messages with another branch exchange PABX 2. In this case, the telephone exchange DX can see from the information for branch exchange PABX 2 that the branch exchange PABX 2 does identify the NOTIFY message, so it is sent to the branch exchange PABX 2.

Fig. 3 presents a situation that is common in the signalling between a branch exchange PABX and a telephone exchange DX in current technology. The initial situation is again as in Fig. la and lb. In state N3 , the telephone exchange DX sends to the private automatic branch exchange PABX a notice of diversion of a call. The branch exchange PABX announces that it does not support the NOTIFY message. However, the telephone exchange DX has already sent an ALERTING message and changed its state. The branch exchange PABX indicates that it is in state N3 , but the telephone exchange DX is already in state N4. According to the specification, the call is disconnected if the states are not the same. Another possibility is the situation presented in Fig. la.

By using the solution of the invention, in the situation illustrated in Fig. 3, sending a NOTIFY message to the branch exchange PABX would be avoided and the branch exchange would not send a STATUS mes- sage which would result in a failure of the call. In this way, unnecessary exchange of messages would also be reduced.

The invention is not restricted to the examples of its embodiments described above, but many variations are possible within the scope of the inventive idea defined in the claims

Claims

1. Method for implementing the signalling between a telephone exchange (DX) and a private automatic branch exchange (PABX) in a telecommunication system comprising a telephone exchange (DX) and a private automatic branch exchange (PABX) connected to the telephone exchange, charac t er i s ed in that retransmission of a message sent by the telephone exchange (DX) to the private automatic branch exchange (PABX) is prevented when, based on the message, the private automatic branch exchange (PABX) has returned to the telephone exchange (DX) a response message indicating an error condition or incompatibility.

2. Method as defined in claim 1, char - ac t e r i s ed in that the response message sent by the private automatic branch exchange (PABX) to the telephone exchange (DX) contains a parameter which has not been identified or which is not supported.

3. Method as defined in claim 1 or 2 , charac t eri s ed in that the response message sent by the private automatic branch exchange (PABX) to the telephone exchange (DX) contains information giving the call status during which the message was received.

4. Method as defined in any one of claims 1 -

3, charact e r i s ed in that information regarding the response message sent by the private automatic branch exchange (PABX) to the telephone exchange is stored in conjunction with the telephone exchange (DX) .

5. Method as defined in any one of claims 1 -

4, charac t e r i s ed in that the setting disabling the retransmission of the message from the telephone exchange (DX) to the private automatic branch exchange (PABX) is removed.

6. System for implementing the signalling between a telephone exchange and a private automatic branch exchange in a telecommunication system comprising a telephone exchange (DX) and a private automatic branch exchange (PABX) connected to the telephone exchange, charac t e ri s ed in that the system comprises means for preventing the retransmission of a message to be sent from the telephone exchange (DX) to the private automatic branch exchange (PABX) when, based on the message, the private automatic branch exchange (PABX) has returned to the telephone exchange (DX) a response message indicating an error condition or incompatibility.

7. System as defined in claim 6, char ac t e ri s ed in that the private automatic branch exchange (PABX) comprises means for sending in its re- sponse message to the telephone exchange (DX) a parameter not identified or not supported.

8. System as defined in claim 6 or 7, charac t e r i s ed in that the private automatic branch exchange (PABX) comprises means for sending to the telephone exchange (DX) information regarding the call status during which the message was received.

9. System as defined in any one of claims 6 - 8, charac t eri s ed in that the system comprises means by which the information contained in the response message sent by the private automatic branch exchange (PABX) to the telephone exchange (DX) is stored in conjunction with the telephone exchange.

10. System as defined in any one of claims 6 - 9, charac t eri s ed in that the system com- prises means for removing a setting disabling the transmission of a message to be sent from the telephone exchange (DX) to the private automatic branch exchange (PABX) .