PROCEDURE FOR ENSURING EMERGENCY COMMUNICATION IN A CASCADED V5 INTERFACE

Abstract: The invention relates to a procedure for ensuring emergency communication in a telecommunication system comprising a telephone exchange (LE) with a number of subscribers defined in it, an access network (AN) connected to the telephone exchange via a first V5 interface (V5) and comprising a first access node (AN1), a second access node (AN2), which is connected to the telephone exchange, and a subscriber terminal (TE), which is connected to the local exchange via the access network and/or a concentrator. The invention is characterised in that the second access node (AN2) is connected to the first access node (AN1) via a second V5 interface, the connection between the subscriber and the telephone exchange (LE) being set up by cascading the two V5 interfaces; and that, in the event of a failure of the first V5 interface used by the subscriber terminal, a call from the subscriber terminal to an emergency number is connected to a process responsible for emergency communication in a failure situation.

Description: PROCEDURE FOR ENSURING EMERGENCY COMMUNICATION IN A CASCADED V5 INTERFACE The present invention relates to a procedure as defined in the preamble of claim 1 for ensuring emergency communication in a cascaded V5 interface especially when the V5 interface between a telephone exchange and an access node is out of order. V5 interface standards ETS 300 324 and ETS 300 347 describe an interface between a local exchange and an access network and the functionality in each network element. The access network is the part of a local area network that contains the subscriber's lines. Thus, subscribers and subscriber's lines can be connected to the exchange either directly (direct sub- scribers) or via various multiplexers and/or concentrators. V5 interfaces enable subscribers belonging to a physically separate access network to be connected to a local exchange using a standard interface. A dynamic concentrator interface (V5.2) as defined in the ETS 300 347 standard series consists of one or more (1 - 16) PCM (Pulse Code Modulation) lines. One PCM line comprises 32 channels, each of which with a transfer rate of 64 kbit/s, i.e. 2048 kbit/s altogether. The V5.2 interface supports ana- logue telephones as used in the public telephone network, digital, such as ISDN (Integrated Services Digital Network) basic and system subscriber lines as well as other analogue or digital terminal equipment based on semi-fixed connections. A static V5.1 multiplexer interface as defined in the ETS 300 347 standard series consists of one 2048 kbit/s PCM line. The V5.1 interface supports the same subscriber types as the V5.2 interface except ISDN system lines. Terminal equipment can be connected to the subscriber ports of the access node. One access node may have one or more V5 interfaces connected to it. Subscriber ports are created in the V5.1 interface by associating an unambiguous address of each subscriber port with a given address in the V5.1 interface. In the local exchange, this address is created as a V5 subscriber. In other words, each subscriber port has an unambiguous address which is coupled with a V5.1 interface address and which uses a certain time slot (analogue subscribers) or certain time slots (ISDN subscribers) for communication with the local exchange. In the V5.2 interface, too, each subscriber port has an unambiguous address, but the signalling to the local exchange is implemented using a dynamically allocated time slot / dynamically allocated time slots. This means that the BCC (Bearer Channel Control) protocol consistent with the V5 standard allocates the time slots to be used separately for each call . V5 standardisation aims at creating an open interface for use between a local exchange and an access network. However, no interface for use between the access node and the subscribers within the access network has been defined. Therefore, problems are encountered in connecting subscribers to the access node e.g. via a static concentrator interface. A further problem is that, especially in an environment with multiple suppliers, the solutions of different suppliers for concentrating subscribers in an access network differ significantly from each other, which means that operators do not necessarily have enough choice options regarding suppliers of equipment. The objective of arrangements for ensuring emergency communication is to make sure that calls to emergency numbers from subscribers connected to an ac- cess node can be set up even when the V5 interface between the access node and the telephone exchange is out of order. The V5.2 standards contain no defini- tions for ensuring emergency communication in case of failure and especially in a situation where two V5 interfaces are cascaded. Therefore, the problem is that, at present, all communication, including emergency communication, by a given subscriber via a specific V5 interface is hindered when the V5 interface fails. The object of the present invention is to eliminate the problems described above. A specific object of the present invention is to disclose a proce- dure that can be used to ensure subscribers' emergency calls even when the V5 interface between the access node and the telephone exchange breaks down. As for the features characteristic of the invention, reference is made to the claims. Procedure for ensuring emergency communication in a telecommunication system comprising a telephone exchange with a number of subscribers defined in it, an access network connected to the telephone exchange via a first V5 interface and comprising a first access node, a second access node, which is connected to the telephone exchange, and a subscriber terminal, which is connected to the local exchange via the access network and/or via a concentrator. According to the invention, the second access node is connected to the first access node via a second V5 interface, the connection between the subscriber and the telephone exchange (LE) being thus set up by cascading the two V5 interfaces. In a preferred case, the first access node is connected to the tele- phone exchange via a V5.2 interface while the second access node is connected to the first access node via a V5.1 interface. Further, according to the invention, when call setup is started and a failure of the first V5 interface is detected, a call from the terminal device to an emergency number is connected to a process responsible for emergency communication in the event of failure of the (V5 interface) used by the terminal device, which process transmits the emergency call further. In a preferred case, the call to an emergency number is a call addressed to a telephone number pre- defined in the telephone exchange as an emergency number. The process responsible for emergency communication in a failure situation connects a dial tone or equivalent to the subscriber terminal and analyses the dialling sent by the subscriber. If the dialling leads to a predetermined emergency number, then the process will make the required connections. Otherwise, a message or equivalent is transmitted to the subscriber. In a preferred embodiment of the invention, via the process responsible for emergency communica- tion, a call to an emergency number is directed locally to an emergency subscriber line created in the first access node. In practice, when a new connection or call is being set up, the condition of the V5 interface used by the terminal device is monitored in the first access node and a predetermined call setup mode wherein a connection is set up locally in the first access node is activated if the monitoring indicates that the V5 interface concerned is out of order and that the call attempted by the subscriber is ad- dressed to an emergency number. In a preferred embodiment of the present invention, in a failure situation of the first V5 interface, call setup is only allowed for calls addressed to emergency numbers. Other call attempts are re- sponded to by giving the subscriber a message, signal tone or the like if normal call setup fails. In the following, the invention will be described by the aid of a few examples of its embodiments by referring to the attached drawing, which pre- sents a telecommunication system preferable for the procedure of the invention. The telecommunication system presented in the drawing comprises two local exchanges LE ( 1 ) , LE(2) and access nodes AN1(1), AN1(2) respectively connected to the local exchanges. In this example, the access nodes are connected to the local exchanges via V5.2 interfaces V5. As shown in the figure, one access node AN1 can be connected to several local exchanges, thus allowing a subscriber to be easily handed over to another local exchange by using operation control com- mands in the local exchange LE. Moreover, the system comprises a number of second access nodes or multiplexers AN2, which are connected to a local exchange LE via access nodes AN1. The multiplexer AN2 is connected to the access node AN1 via a second V5 inter- face, which is a V5.1 interface V5' . Further, in the example in Fig. 1, a subscriber terminal TE is connected to a local exchange via a multiplexer AN2 and the first access node AN1. The access network AN consists of the subscriber terminal equipment TE, the multiplexer AN2, the first access node AN1 and the lines connecting them. As an example, an emergency subscriber line TE1 is connected to access node AN1(2) and, in the event of a failure of the first V5 interface, an emer- gency call made by a subscriber TE can be connected to this emergency line. To accomplish this in practice, the 3-layer of the first access node AN1(2) according to the OSI model (OSI, Open System Interconnection) checks whether the V5.2 interface V5 is in order when call setup is attempted. If the V5.2 interface is out of order, then the messages are transmitted to the process responsible for emergency communication. If it is detected that the subscriber is trying to set up a call to a number that is not an emer- gency number, then call setup is disabled and a message or signal tone is transmitted to the subscriber. If it is detected that the subscriber is trying to set up a call to an emergency number, then, according to an embodiment of the invention, the call is connected locally to the emergency line TE1 created in access node AN1(2). Service can be provided separately via this emergency line when a failure situation is detected that may cause congestion for subscribers connected to access node AN1(2). Another corresponding solution in respect of the basic idea of the invention is that a channel is allocated dynamically for the subscriber in some other V5.2 interface connected to the first access node AN1(2). Let it be further stated that the V5 interfaces presented in the telecommunication system depicted in the drawing are activated independently of each other. The interfaces are preferably activated in accordance with the normal V5 definitions. Furthermore, in the system illustrated by the drawing, it is possible to implement a so-called management network, which is connected to the local exchange LE, to the first access node AN1 and to the second access node AN2. However, the structure and function of the management network will not be described here in detail, but reference is made to the V5 standards. The invention is not restricted to the exam- pies of its embodiments described above, but many variations are possible within the scope of the inventive idea defined by the claims.

Claims: CLAIMS 1. Procedure for ensuring emergency communication in a telecommunication system comprising a telephone exchange (LE) with a number of subscribers defined in it, an access network (AN) connected to the telephone exchange via a first V5 interface (V5) and comprising a first access node (AN1) , a second access node (AN2), which is connected to the telephone exchange, and a subscriber terminal (TE) , which is con- nected to the local exchange via the access network and/or a concentrator, cha r a ct e r i s ed in that the second access node (AN2) is connected to the first access node (AN1) via a second V5 interface, the connection between the subscriber and the telephone ex- change (LE) being set up by cascading the two V5 interfaces; and that, in the event of a failure of the first V5 interface used by the subscriber terminal, a call from the subscriber terminal to an emergency number is connected to a process responsible for emer- gency communication in a failure situation. 2. Procedure as defined in claim 1, cha r a ct e r i s e d in that, via the process responsible for emergency communication, a call to an emergency number is directed locally to an emergency subscriber line created beforehand in the first access node (AN1) • 3. Procedure as defined in claim 1 or 2, cha r a ct e r i s e d in that, when a new connection is being set up, the condition of the V5 interface used by the terminal device is monitored in the first access node (AN1) ; and if the monitoring indicates that the V5 interface concerned is out of order, a predetermined call setup mode, wherein the connection is set up lo- cally in the first access node, is activated. 4. Procedure as defined in any one of claims 1 - 3, cha ra c t e r i s ed in that, in a failure situation of the first V5 interface, call setup is only allowed for calls addressed to emergency numbers. 5. Procedure as defined in any one of claims 1 - 4, cha ract e r i s ed in that the subscriber is given a message, signal tone or the like if normal call setup fails. 6. Procedure as defined in any one of claims 1 - 5, cha ra ct e r i s e d in that the call to an emergency number is a call to a telephone number predefined as an emergency number in the telephone exchange (LE) . 7. Procedure as defined in any one of the preceding claims 1 - 6, charact e ri s ed in that the interface between the access network (AN) and the telephone exchange (LE) is a V5.2 interface and the V5 interface between the second access node (AN2) and the first access node (AN1) is a V5.1 interface.

Inventors: JUNTUNEN TIMO, LALLUKKA TOIVO, JUNTUNEN, TIMO, LALLUKKA, TOIVO
Applicants: JUNTUNEN TIMO, LALLUKKA TOIVO, NOKIA TELECOMMUNICATIONS OY, JUNTUNEN, TIMO, LALLUKKA, TOIVO
Application year: 1998
Main classification: H04Q3
IPC codes: H04Q11