PROCEDURE AND SYSTEM FOR ENSURING EMERGENCY COMMUNICATION

Abstract: The present invention relates to data communication networks. In particular, the present invention relates to a procedure and a system for ensuring emergency communication in a data communication network in which the terminal devices (4a, 4b, 4c) are connected to a telephone exchange (1) via an access node (3) consistent with the V5 standard. In the procedure of the invention, emergency communication by a subscriber in the event of a failure of the V5 interface used by the subscriber is ensured by using an emergency V5 interface (6) created in the access node and a range of addresses created for this purpose in the telephone exchange.

Description: PROCEDURE AND SYSTEM FOR ENSURING EMERGENCY COMMUNICA¬ TION The present invention relates to data commu¬ nication networks. In particular, the present inven- tion relates to a procedure as defined in the preamble of claim 1 and to a system as defined in the preamble of claim 7 for ensuring emergency communication in an access network or access node connected to a data com¬ munication network and having a number of subscriber lines connected to it for the connection of subscriber terminal equipment to the data communication network. There are at least two commonly known methods for connecting subscribers to a local exchange in a data communication network. In the first method, the subscriber is connected via a subscriber line directly to the local exchange or to an access module connected to it. In the second method, the subscriber is con¬ nected to an access network, whose access node is con¬ nected to the exchange. Open interfaces (V5.1 and V5.2) between an access network and a local exchange are defined in the ETSI (European Telecommunications and Standards Insti¬ tute) standards of the ETS 300 324 and ETS 300 347 se¬ ries. V5 interfaces enable subscribers belonging to a physically separate access network to be connected to a telephone exchange using a standard interface. In this application, V5 interface refers in particular to a dynamic concentrator interface (V5.2) consistent with the standards ETS 300 347-1 and 347-2, which con- sists of one or more (1 - 16) PCM (Pulse Cone Modula¬ tion) cables. One PCM cable comprises 32 channels, each of which with a transfer rate of 64 kbit/s, i.e. 2048 kbit/s in all. The V5.2 interface supports ana¬ logue telephones as used in the public telephone net- work, digital, such as ISDN (Integrated Services Digi¬ tal Network) basic and system subscriptions as well as other analogue or digital terminal equipment based on semi-fixed connections. The terminal equipment can be connected to the access ports of the access node. One or more V5 interfaces can be connected to he access node. The ac¬ cess ports are created in the V5 interface by linking an unambiguous address of each port with a given ad¬ dress of the V5 interface. In the local exchange, this address is created as a V5 subscriber. In other words, each access port has an address which is linked with a V5 address and uses a given time slot or given time slots for signalling to the local exchange. The objective in ensuring emergency communi¬ cation is to make sure that calls to emergency numbers of subscribers connected to an access node can be set up even when the V5 interface between the access node and the telephone exchange is out of order. The V5.x standards contain no definition of systems for ensur¬ ing emergency communication in case of failure. In this situation, the problem is that, at present, all communication, including emergency communication, via a specific V5 interface of a given subscriber is hin¬ dered when the V5 interface fails. One possibility for ensuring emergency commu- nication in case of failure of a V5 interface assigned to a subscriber is to create in the telephone exchange to which the V5 interface is connected a separate emergency address for each subscriber for communica¬ tion during the failure situation. However, the prob- lem with this system is the high capacity required in the exchange, because in this case the exchange must have a double subscriber address range as compared with the number of subscribers. In addition, such an arrangement would significantly increase the size of the interface database of the access node. The object of the present invention is to present a new type of a procedure and system for en- suring emergency communication in the event of a fail¬ ure of the V5 interface between an access node and a local exchange. A further object of the present inven¬ tion is to present a system which does not require an oversized capacity in the exchange connected to the access node. As for the features characteristic of the in¬ vention, reference is made to the claims. In the procedure of the present invention for ensuring emergency communication in a data communica¬ tion network comprising a number of telephone ex¬ changes interconnected via trunk cables, the data com¬ munication network comprises an access node which is connected to at least one of the exchanges. Connected to the access node, preferably via subscriber cables, are a number of terminal devices used by subscribers to set up connections over the data communication net¬ work. Further, in the procedure of the invention, sig¬ nalling according to the V5 standard, which is defined in the standards mentioned above, is used in the con¬ nection between the access node and the telephone ex¬ change, which is a V5 interface consistent with the standard. In the procedure of the invention for ensur- ing emergency communication, in the access node is created a separate V5 interface with no subscribers connected to it and comprising a number of V5 sub¬ scriber addresses created in the access node. These subscriber addresses are not assigned permanently to any subscriber. The separate V5 interface with no sub¬ scribers connected to it is generally created in con¬ junction with the installation and start-up of the ac¬ cess node. The separate V5 interface is an interface that in a normal situation is not used for the switch- ing of voice or data communication of any subscriber. In the telephone exchange to which this separate V5 interface is connected, a few permanent subscriber ad- dresses have been created for this V5 interface, al¬ though in the access node these V5 interface addresses have not been created permanently in the subscriber- line interfaces. Further, according to the invention, in the event of failure of the V5 interface used by a subscriber, a new V5 subscriber address is allocated for the subscriber from the set of V5 subscriber ad¬ dresses of the separate V5 interface. The set of sub¬ scriber addresses of the separate V5 interface con- sists of a number of subscriber addresses that can be used when necessary to handle the communication of any one of the subscribers connected to the access node concerned. A failure situation occurs when a sub¬ scriber's signalling connection to the telephone ex- change fails. Further, subscriber connections are set up using a V5 subscriber address, which is released after the call is disconnected. As compared with prior art, the present in¬ vention has the advantage that, using the procedure of the invention, emergency communication of subscribers connected to an access node can be effectively and re¬ liably guaranteed even in the event of a failure of the V5 interface used by the subscriber. A further ad¬ vantage of the invention is that it makes it unneces- sary to reserve a double number of V5 addresses in the exchange to ensure successful emergency communication of V5 subscribers in a failure situation. In an embodiment, the separate V5 interface is connected to a different telephone exchange than the other V5 interfaces of the access node. This is advantageous because in this case the connection of this interface is very likely to run along a physi¬ cally different route, e.g. in a different cable trench than the other V5 interfaces of the access node. A further advantage of this arrangement is that a failure of the exchange to which the other V5 inter¬ faces are connected is not likely to cause a failure of the separate emergency V5 interface as it is con¬ nected to a different exchange. In a preferred embodiment of the present in¬ vention, a connection setup request given by a sub- scriber is monitored in the telephone exchange and, based on this monitoring, connection setup using a V5 subscriber address of the separate V5 interface is prevented if it is detected that the connection is in¬ tended for communication other than emergency communi- cation. In a further preferred case, the first free V5 subscriber address in the set of V5 subscriber ad¬ dresses of the separate V5 interface is reserved for the subscriber. This arrangement ensures that the emergency interface will not be used for communication other than emergency communication. Thus, in a failure situation, when the emergency interface is in opera¬ tion, its whole capacity can be used for emergency communication. In a preferred case, the connection set up is a call set up between two terminal devices, and the emergency communication consists of an emergency call, alarm message, alarm call or the like. According to the invention, the access node comprises a separate V5 interface having no subscrib¬ ers connected to it and comprising a number of V5 sub- scriber addresses and means for reserving for the sub¬ scriber a new V5 subscriber address from the set of V5 subscriber addresses of the separate V5 interface in a failure situation of the V5 interface used by the sub¬ scriber. The means for reserving a new V5 subscriber address for the subscriber are preferably implemented by using the program segments of the access node. In the system of the invention, the separate V5 interface is preferably connected to a different telephone ex¬ change than the other V5 interfaces of the access node. In a preferred embodiment of the present in¬ vention, the system comprises means for monitoring the subscriber's connection setup request in the telephone exchange and, based on the monitoring, the system pre¬ vents connection setup if it is detected that the con¬ nection is intended for communication other than emer- gency communication. The monitoring can be implemented using components existing in the telephone exchange, of which at least the push-button dialling receivers and the central control unit can be used. In the following, the invention is described by the aid of a few examples of its embodiments by re¬ ferring to the attached drawing, in which Fig. 1 presents a pnor-art signalling ar¬ rangement for a normal call over a V5 interface; Fig. 2 presents an example of the system of the present invention; and Fig. 3 is a flowchart representing call setup according to an embodiment of the present invention. Fig. 1 presents an example of the signalling in the case of a prior-art ISDN call over a V5 inter¬ face. When the subscriber picks up the headphone (step 1) , LAPD signalling (data link layer protocol in ISDN channel D) is started. The access node (AN) 3 acti¬ vates the terminal device (step 2) and sends a message indicating activation of the terminal device to the telephone exchange (LE) 1 (step 3) , using the control protocol. Once activated, the terminal device 4c sends a SETUP message over channel D of the subscriber ca¬ ble. On receiving the SETUP message, the access node identifies (step 5) the corresponding V5 interface and the V5 subscriber address of the subscriber cable (which in fact is a third-layer address, L3 address, consistent with the OSI architecture (Open Systems In¬ terconnection) ) on the basis of the subscriber cable. Moreover, the access node adds a V5 header to the SETUP message and sends it via the Ds channel of the corresponding V5 interface to the telephone exchange 1. The LAPD signalling itself is passed as such over the V5 interface via the signalling channel reserved for the subscriber. Thus, the V5 interface software in the access node 3 does not interfere with the contents of messages in any way. In the telephone exchange 1, the V5 header is removed (step 6) and the SETUP mes¬ sage is transmitted further to an ISDN call setup con¬ trol stage, where it is terminated. Based on the first SETUP message, the local exchange selects the V5 time slot to be used, and this information is given to the access node 3 together with the L3 address (step 7) . The access node 3 identifies the subscriber cable on the basis of the L3 address received and, via its lo¬ cal group switch, connects (step 8) the B channel of the subscriber cable to the V5 interface time slot re¬ served for it. Further, the access node 3 sends (step 9) to the telephone exchange 1 a message confirming completion of the connection. The telephone exchange 1 sends the standard ISDN call control messages relating to call setup to the terminal device via the access node over the Ds channel reserved for the subscriber cable (step 10) . The system of the invention, presented in Fig. 2, comprises a telephone exchange 1, which is part of a data communication network 11. The telephone exchange 1 is linked to the other exchanges in the data communication network via a trunk cable 12. The system represented by Fig. 2 further comprises a num¬ ber of terminal devices 4a, 4b, 4c, which may be ana- logue telephones used in the public telephone network, digital, such as ISDN (Integrated Services Digital Network) basic and system connections or analogue or digital terminal equipment based on semi-fixed connec¬ tions. Via the terminal equipment 4a, 4b, 4c, the us- ers of the data communication network, i.e. the sub¬ scribers, set up voice and/or data connections over the data communication network 11. Fig. 2 further shows a part of the data com¬ munication network, i.e. an access node 3 together with subscriber lines, connected as an example to an¬ other telephone exchange 11. The access node 3 func- tions between the telephone exchange 1 and the sub¬ scriber 4a, 4c and connects subscribers to the ex¬ change 1 of the data communication network. The access node 3 is connected via a V5.2 interface 5 comprising 1 - 16 PCM cables (2 Mbit/s) to the exchange terminal (ET) 10 of the telephone exchange 1. The exchange ter¬ minal contains the functions required by the V5 inter¬ face. The access node also comprises means 7 for allo¬ cating a new V5 subscriber address for the subscriber from the set of subscriber addresses of the separate V5 interface in the event of a failure of a connection via the V5 interface used by the subscriber. Gener¬ ally, the allocation of a new V5 address performed us¬ ing the access node signalling programmes. Furthermore, the exchange is provided with means 8 for monitoring the connection setup request given by a subscriber. These means 8 preferably con¬ sist of call and usage control technology commonly used in telephone exchanges. To guarantee successful emergency communication, the access node is provided with at least one extra V5 interface 6 with no sub¬ scribers connected to it. This is a kind of emergency V5 interface and it is connected to a different ex¬ change la than the other V5 interfaces 5 of the access node 3. Depending on the size of the access node, the V5 interface 6 without subscribers may have a capacity of e.g. 30 subscribers. In the case of a failure of the V5 interface 5 assigned to the subscriber, a new V5 subscriber address, which is associated with the emergency V5 interface connected to exchange la, is reserved for the subscriber. As there are no subscribers assigned to V5 interface 6, it can be used to connect as many calls as its capacity permits, if necessary. Since, accord¬ ing to the invention, call setup from a subscriber line is monitored by the telephone exchange in a situation where V5 interface 5 has failed, use of the emergency interface 6 can be prevented as soon as it is detected that the interface 6 is being used for communication other than emergency communication. Referring to Fig. 3, a preferred procedure according to the present invention, used in conjunc- tion with call setup, is presented as a flow diagram. The call setup process advances in a stepwise manner as follows. First, the subscriber picks up the head¬ phone, block 31, and this is detected by the access node, which passes corresponding information to the telephone exchange. Next, the terminal device 3 is ac¬ tivated, block 32, as was described above by referring to Fig. 1. In block 33, the V5 interface used by the subscriber is identified, and in block 34 the status of the V5 interface used by the subscriber is moni- tored, and, based on this monitoring, normal call setup is carried out if no fault is detected in the V5 interface under observation, and if a fault is de¬ tected, then a check is performed to establish whether the call is an emergency call, block 35. If it is, then the emergency V5 interface is used for call setup and the process is continued according to the present invention by selecting a free V5 subscriber address, block 39, and using this address for the call setup, block 40. If the monitoring function in block 35 indi- cates that the call is not an emergency call, the call attempt is rejected, block 37. In this case, the sub¬ scriber can be given a notice or other signal. The invention is not restricted to the exam¬ ples of its embodiments described above, but many variations are possible within the framework of the inventive idea defined by the claims.

Claims: CLAIMS 1. Procedure for ensuring emergency communi¬ cation in a data communication network comprising a number of telephone exchanges interconnected via trunk cables and an access node which is connected to at least one of the exchanges and to which are connected a number of terminal devices used by subscribers to set up connections via the data communication network, in which procedure signalling according to the V5 standard is used in the connection between the access node and the telephone exchange, which connection is an access node V5 interface consistent with the V5 standard, c h a r a c t e r i z e d in that in the event of a failure of the V5 interface used by the subscriber, a new V5 subscriber address is allocated for the subscriber from a set of V5 sub¬ scriber addresses created beforehand in the access node for a separate V5 interface with no subscribers connected to it; this new V5 subscriber address is used for connection setup; and the V5 subscriber address is released after disconnection of the connection. 2. Procedure as defined in claim 1, c h a r - a c t e r i z e d in that the separate V5 interface without subscribers is connected to a different tele¬ phone exchange than the other V5 interfaces of the ac¬ cess node. 3. Procedure as defined in claim 1 or 2, c h a r a c t e r i z e d in that a connection setup re¬ quest given by a subscriber is monitored in the tele¬ phone exchange and, based on this monitoring, connec¬ tion setup using a V5 subscriber address of the sepa¬ rate V5 interface is prevented if it is detected that the connection is intended for communication other than emergency communication. 4. Procedure as defined in any one of claims 1 - 3, c h a r a c t e r i z e d in that the first free V5 subscriber address in the set of V5 subscriber ad¬ dresses of the separate V5 interface is allocated to the subscriber. 5. Procedure as defined in any one of claims 1 - 4, c h a r a c t e r i z e d in that the connection set up is a call set up between two terminal devices; and that the emergency communication is an emergency call. 6. Procedure as defined in any one of claims 1 - 4, c h a r a c t e r i z e d in that the emergency communication is an automatic alarm message, an alarm call or the like. 7. System for ensuring emergency communica¬ tion in a data communication network comprising a num¬ ber of telephone exchanges (1, la) interconnected via trunk cables (2) and an access node (3) which is con¬ nected to at least one of the exchanges and to which are connected a number of terminal devices (4a, 4b, 4c) used by subscribers to set up connections via the data communication network, in which system the con¬ nection between the access node and the telephone ex¬ change is implemented using signalling according to the V5 standard, said connection being an access node V5 interface (5) consistent with the V5 standard, c h a r a c t e r i z e d in that the access node (3) comprises a separate V5 interface (6) with no subscrib- ers connected to it, which comprises a set of V5 sub¬ scriber addresses; and means (7) for allocating a new V5 subscriber address for the subscriber from the set of V5 sub¬ scriber addresses of the separate V5 interface if a connection from the subscriber to the telephone ex¬ change (1) fails to be set up. 8. System as defined in claim 7, c h a r a c ¬ t e r i z e d in that the separate V5 interface (6) is connected to a different telephone exchange (la) than the other V5 interfaces (5) of the access node. 9. System as defined in claim 7 or 8, c h a r a c t e r i z e d in that the system comprises means (8) permitting a connection setup request given by a subscriber to be monitored in the telephone ex¬ change, and that, based on this monitoring, connection setup using a V5 subscriber address of the separate V5 interface is prevented in the system if it is detected that the connection relates to communication other than emergency communication.

Inventors: YRJAENAE MARTTI, YRJAENAE, MARTTI
Applicants: NOKIA TELECOMMUNICATIONS OY, YRJAENAE MARTTI, YRJAENAE, MARTTI
Application year: 1997
Main classification: H04M11
IPC codes: H04L1, H04Q11