PROCEDURE FOR CASCADING V5 INTERFACES

Abstract: Procedure for connecting a subscriber to a telephone exchange in a data communication 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. According to the invention, 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 thus set up by cascading two V5 interfaces.

Description: PROCEDURE FOR CASCADING ' V5 INTERFACES The present invention relates to a procedure as defined in the preamble of claim 1 for cascading V5 interfaces . 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 subscribers) 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 analogue 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 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 me- ans 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 ac- cess 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 re- garding suppliers of equipment. The object of the present invention is to eliminate the problems described above. A specific object of the present invention is to disclose a new type of procedure in a data communi- cation system using known and supported standard solutions for cascading V5 interfaces as defined in the above-mentioned standards and for connecting subscribers to an access node. A further object of the invention is to eliminate supplier-specific solutions bet- ween subscriber and access node. As for the features characteristic of the invention, reference is made to the claims. The procedure of the invention for connecting a subscriber to a telephone network can be implemented e.g. in a data communication system comprising a telephone exchange and a number of subscribers defined in it. Further, the data communication system comprises an access network connected to the telephone exchange via a first V5 interface and comprising a first access node and a second access node. The V5 interface is preferably either a V5.1 or a V5.2 interface consistent with the above-mentioned standards. The second access node is preferably a switching stage through which a number of interconnecting feeders or subscriber lines carrying a relatively light traffic can be connected to a few lines carrying larger amounts of traffic. Using a subscriber terminal connected to the local exchange via the access network and/or directly via the second access node, connections are set up to other subscriber terminals or network elements. 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 or subscriber terminal and the telephone exchange being thus set up by cascading two V5 interfaces. In a preferred case, the first V5 interface is a standard V5.2 interface and the second V5 interface is a standard V5.1 interface. As compared with prior art, the invention has the advantage that it makes it possible to create access networks using network components manufactured by any manufacturer. In particular, a V5 interface can be used both between the second access node and the first access node and between the first access node and the local exchange. A further advantage of the invention is that, since according to the V5 definitions the first access node can be connected to two or more local exchanges e.g. via a V5.2 interface, the invention significantly facilitates the hand-over of subscribers from one local exchange to another local exchange. Moreover, the invention allows the second access node to be easily connected to the local exchange using a V5 interface either via a first access node supporting the V5 interface or directly via a V5.1 interface. The protocols common to the first and second V5 interfaces are controlled in the first access node either by a common Control and PSTN protocol object or by separate Control and PSTN protocol objects of each interface. In a preferred case, the protocols to be used in the first V5 interface, such as BCC, Link Control and Protection protocol, are determined in the first access node. In an embodiment of the present invention, in conjunction with the creation of the second V5 interface, interface parameters are defined for it, said parameters comprising an interface identifier, interface type, identifier of the physical connection to be used, i.e. the number or equivalent of the PCM line, and the voice time slots to be used in the interface. In addition, the Control protocol of the V5 definitions is assigned to time slot 16. The first and second V5 inter- faces are preferably activated independently in accordance with the V5 definitions. In a preferred embodiment of the present invention, the PSTN signalling between the first and second V5 interfaces is signalled without L3-layer proc- essing consistent with the V5 definitions. This provides the advantage that the first access node will have no need to know anything about national PSTN settings (PSTN mapping) , so the implementation becomes considerably simpler. In the following, the invention will be described in detail by the aid of a few examples of its embodiments by referring to the attached drawing, in which Fig. 1 presents a data communication system preferable for the procedure of the invention; Fig. 2a-2c are diagrams illustrating the parameter conversions carried out in an access node; and Fig. 3 represents the access node signalling in different layers. The data communication system presented in Fig. 1 comprises two local exchanges LE(1), LE(2) and access nodes AN1(1), ANl (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 ANl can be connected to several local exchanges, thus allowing a subscriber to be handed over to another local exchange by operation control commands in the local exchange. Moreover, the system comprises a number of second access nodes or multiplexers AN2, which are connected to a local exchange LE via access nodes ANl. The multiplexer AN2 is connected to the access node ANl via a second V5 interface, which is a V5.1 interface V5' . Further, in the example in Fig. 1, the subscriber terminal TE is connected to a local exchange via a multiplexer AN2 and a first access node ANl. The access network AN consists of the subscriber terminal equipment TE, the multiplexer AN2, the first access node ANl and the lines connecting them. The V5 interfaces presented in the data commu- nication system depicted in Fig. 1 are activated independently of each other. The interfaces are preferably activated in accordance with the normal V5 definitions. Let it be further stated that, in the system illustrated by Fig. 1, it is possible to implement a so-called management network, which is connected to the local exchange LE and to the first and second access nodes ANl and 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. Referring to Fig. 2a-2c, the data to be defined for the V5 interfaces in connection with their creation will now be discussed in more detail. For the first V5 interface V5, an interface identifier v5_interface_id, an identifier pcm_information for the interconnecting feeder used by the interface and the c- channels comprised in the interface must be defined. For the second V5 interface, in addition to the parameters mentioned above, it is necessary to define the fa- channels which are permanently assigned to the subscribers who use the interface. When the access network is activated, all the V5 interfaces will be activated. Each V5 interface is started independently, and the activation of one V5 interface has no effect on the activation of the other interfaces. Therefore, the activation of the interfaces need not necessarily be synchronised with each other. Thus, the V5.1 interfaces V5' can be treated in the same way as the subscriber modules are treated in the first access node ANl. The main idea in the activation of a cascaded V5 interface according to the invention is that both V5 interfaces in the cascaded V5 interfa- ce, see Fig. 1, are initialised independently and that all subscribers are initialised in blocked state. In the activation of a V5.1 interface V5' connected to the access node, three main operations can be distinguished: activation of the data links, PSTN res- tart and blocking/unblocking of subscribers. The V5.1 interface can carry out all the above-mentioned operations independently. It can activate its own data links even if none of the V5.2 interfaces between the first access node ANl and the local exchange has been activa- ted. Likewise, the PSTN restart can be performed in the second V5.1 interface V5' without the V5.2 interfaces. When the V5.1 interface V5' blocks/unblocks the subscribers before any ' one of the V5.2 interfaces has been started, all subscribers can be unblocked via the interface in question. When one of the V5.2 interfaces finally reaches this stage of the starting procedure, it will unblock all subscribers that have been unblocked in the V5.1 interface. On the other hand, if one of the V5.1 interfaces is started after the activation of the V5.2 interfaces, then all subscribers configured in this V5.1 interface will be in the blocked state in the V5.2 interface until the V5.1 interface finishes its starting procedure and unblocks the subscribers . If the local exchange LE wants to block a subscriber, it will send a blocking command and the subscriber will be blocked via the V5.2 interface V5. However, it may be possible to keep this given subscriber in the active state in the V5.1 interface V5 ' even if the local exchange LE should block the subscriber. In this case, the local exchange LE must take care of unblocking the subscriber in the V5.2 interface V5. If the second access node AN2 blocks a subscriber by sending a blocking command, then the subscriber will be blocked in both the V5.2 and in the V5.1 interface. In this case, the second access node AN2 must take care of unblocking the subscriber in the V5.1 interface V5 ' , which again starts the unblocking procedure in the V5.2 interface V5. Referring to Fig. 3, let it be further stated that some of the V5 protocols must be determined in the first access node ANl because they are only used in the first V5 interface V5. These protocols, consistent with the V5 definitions, are the BCC (Bearer Channel Protocol) protocol, the Link protocol and the Protection protocol. In addition, the PSTN signalling can be car- ried out transparently (i.e. without 3 r layer processing) in the first access node ANl. When a PSTN message is received from the second V5 interface V5 ' , it will be transmitted transparently to the first V5 interface V5 and vice versa by using LAPV5 signalling. Thus, no national settings of PSTN signalling need to be known in the access node. 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 by the claims.

Claims: CLAIMS 1. Procedure for connecting a subscriber to a telephone exchange in a data communication 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 (ANl) , 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, characterised in that the second access node (AN2) is connected to the first access node (ANl) via a second V5 interface, the connection between the subscriber and the telephone exchange (LE) being thus set up by cascading two V5 interfaces . 2. Procedure as defined in claim 1, characterised in that, in conjunction with the creation of the second V5 interface (V5')_ interface para- meters are defined for it, said parameters comprising an interface identifier, interface type, identifier of the physical connection to be used, and the time slots to be used in the interface. 3. Procedure as defined in claim 1 or 2, characteri sed in that the Control protocol of the V5 definitions is assigned to time slot 16. 4. Procedure as defined in any one of the preceding claims 1 - 3, characteri sed in that the first and second V5 interfaces (V5, V5 ' ) are star- ted independently in accordance with the V5 definitions . 5. Procedure as defined in any one of the preceding claims 1 - 4, characteri sed in that the protocols common to the first and second V5 inter- faces (V5, V5 ' ) are controlled in the first access node ANl. 6. Procedure as defined in any one of the preceding claims 1 - 5, characteri sed in that the protocols to be used in the first V5 interface are determined in the first access node (ANl) . 7. Procedure as defined in any one of the preceding claims 1 - 6, characteri s ed in that the PSTN signalling between the first and second V5 interfaces (V5, V5 ' ) is signalled without L3-layer processing consistent with the V5 definitions. 8. Procedure as defined in any one of the preceding claims 1 - 7, characteri 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 (ANl) is a V5.1 interface.

Inventors: HAUKILAHTI JARMO, LIINAMAA OLLI, VEHMER SEPPO, HAUKILAHTI, JARMO, LIINAMAA, OLLI, VEHMER, SEPPO
Applicants: HAUKILAHTI JARMO, LIINAMAA OLLI, NOKIA TELECOMMUNICATIONS OY, VEHMER SEPPO, HAUKILAHTI, JARMO, LIINAMAA, OLLI, VEHMER, SEPPO
Application year: 1998
Main classification: H04Q3
IPC codes: H04Q11