PROCEDURE FOR THE TRANSMISSION OF PROTOCOLS IN A CASCADED V5 INTERFACE

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 the second access node. 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 set up by cascading the two V5 interfaces, and the Control and PSTN protocols of the first and second V5 interfaces (V5, V5') are transmitted using Control and PSTN protocol objects disposed in the first access node.

Description: PROCEDURE FOR THE TRANSMISSION OF PROTOCOLS IN A CASCADED V5 INTERFACE The present invention relates to a procedure as defined in the preamble of claim 1 for the transmission of protocols in a cascaded V5 interface. 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 net- work 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 ac- cess 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 associa- ting 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 Cont- rol) 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 so- lutions 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. A special problem associated with the cascading of interfaces is how the protocols to be transmitted in the interfaces can be transmitted transparently via the access node. A further problem is how to transmit the protocols with minimum changes relative to the implementations described by the standard. The object of the present invention is to eliminate the drawbacks described above A specific object of the present invention is to disclose a procedure for the transmission of protocols in a cascaded V5 interface. A further object of the inventi- on is to disclose a simple control arrangement for flexibly and quickly directing in the access node the messages transmitted via V5 interfaces so as to cause no delay in call setup. 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. The V5 interface is preferably either a V5.1 or a V5.2 interface consistent with the above-mentioned standards. The data communication system also comprises a second access node or a multiplexer, which is connected to the telephone exchange. The multiplexer 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. Further, the Control and PSTN protocols of the first and second V5 interfaces (V5, V5') are transmitted using Control and PSTN protocol objects disposed in the first access node. The V5 interface between the access network and the telephone exchange is preferably a V5.2 interface and the interface between the multiplexer and the access node is a V5.1 interface . As compared with prior art, the invention has the advantage that it allows cascading of V5 interfaces without any major changes in the functions defined by the V5 standard in the V5 interface, access node and local exchange . Moreover, the invention allows simple and straightforward transmission of certain protocols. In a preferred embodiment of the present invention, the Control and PSTN protocols of the first V5 interface and the Control and PSTN protocols of the second V5 interface are transmitted using the same Control protocol object and PSTN protocol object. The Control and PSTN protocols of the second V5 interface (V5 # ) are preferably transmitted using the Control protocol object and PSTN protocol object of the first V5 interface. This solution has the advantage that the implementation of data transmission is simple as messages can always be routed to the same program or protocol object regardless of the type of the V5 interface. Moreover, the portions of the implementation that are common to both interface types only need to be implemented once in this solution. In another embodiment of the present invention, the Control and PSTN protocols of the first V5 interface are transmitted using a first Control protocol object and a first PSTN protocol object and the Control and PSTN protocols of the second V5 interface are transmitted using a second Control protocol object and a second PSTN protocol object. In this case, for each protocol, information as to which protocol object is responsible for which protocol of which V5 interface is preferably stored in the first access node. Further, in conjunction with each protocol message to be transmitted, a check is carried out in the first access node to determine the protocol object for which the message is intended, and the messages are directed based on this check. In the following, the invention will be descri- bed 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; and Fig. 2a-2c are represent protocol signalling in the first access node. 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 using operation control commands. 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 first 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 second access node AN2 and a first access node ANl. The access network AN consists of the subscriber terminal equipment TE, the second access node AN2 , the first access node ANl and the lines connecting them. The V5 interfaces presented in the data communi- cation 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 manage- ment network, which is connected to the local exchange LE, to the first access node ANl 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. Referring to Fig. 2a-2c, we shall now discuss various alternatives for the handling of protocols consistent with the V5 standards in a cascaded V5 interface, i.e. in a situation as illustrated by Fig. 1, where a subscriber is connected to a local exchange LE via two V5 interfaces V5, V5' connected in series. In Figures 2a-2c, a broken line is used to indi- cate the signalling to be transmitted, and a solid line to indicate a subscriber database interface. The figures present the parts of the first access node that are essential to call setup. Stored in the interface database DB is the essential information regarding the V5 interfa- ces . In addition, call setup is implemented using a program block 5; 5a, 5b responsible for signalling and a program block 6 responsible for call setup. In practice, there are two alternatives for handling the Control protocol and the PSTN protocol. The protocols can be controlled by a protocol object common to both interfaces, in which case the access node ANl contains a protocol object for the Control and PSTN protocols of the first and second V5 interfaces V5 , V5 ' . In this case, the first access node ANl needs to know where the messages handled by the protocol object are being transmitted, i.e. whether the messages are intended for a V5.1 or a V5.2 interface. Another alternative is that separate protocol objects are provided for the Control and PSTN protocols of both interfaces. In this case, the ac- cess node ANl must know which object is responsible for which protocol in order that the messages can be transmitted to the right protocol objects. Fig. 2 presents an example of call signalling in conjunction with a call addressed to a subscriber in a case where a protocol object common to both protocols is used. The program block 5 responsible for the signalling in conjunction with a call addressed to a subscriber receives from the local exchange LE a call setup message consistent with the V5 definitions. Program block 5 reads the subscriber data from the interface database DB, forms a V5.2 pointer and sends the call setup message to it. The V5.2 pointer starts the program block for call cont- rol, which reads from the interface database DB that the subscriber has been defined in a cascaded V5 interface V5 ' . After this, the call control program block sends the call setup message for the second V5 interface V5' back to the program block 5b responsible for signalling, which determines from the message that the subscriber is a subscriber defined in a second V5 interface V5'. The program block 5b responsible for signalling in the second V5 interface forms a V5.1' pointer and sends the call se- tup message to it. The V5.1' pointer sends the call setup message to the concentrator AN2 , whereupon the call setup procedure continues normally. In Fig. 2b, a subscriber defined in a cascaded V5 interface V5' initiates a call, in which case the call setup request message comes from a multiplexer AN2 via a second V5 interface V5 ' to the program block 5 responsible for signalling, which recognises from the interface identifier internal to the access network, comprised in the message, that the message comes from a cascaded V5 interface V5'. Based on this information, the program block responsible for signalling forms a V5' pointer and sends the call setup message to it. The pointer reads the subscriber data from the interface database DB and sends the call setup message to the program block 6 responsible for call control. From the subscriber data, program block 6 recognises that the call setup request has to be directed to a certain V5.2 interface V5 and sends the call setup message further to the program block 5 responsible for signalling. Program block 5 also recognises that the call setup message is going to a certain V5.2 interface, and forms a V5.2 pointer for it and sends the call setup message to the pointer. The V5.2 pointer sends the call setup message further to the V5.2 interface. Fig. 2c illustrates a situation where both in- terfaces have their own protocol objects. In a call addressed to a subscriber defined in a second V5 interface V5', the local exchange LE sends a call setup message to the program block responsible for signalling, which reads the subscriber data from the interface database DB . The program block 5 responsible for signalling sends the call setup message to the program block 6 responsible for call control, which reads from the database DB the identifier data of the second V5 interface V5 ' defined for the subscriber. After this, the program block 6 responsible for call control sends the call setup message to the protocol object PSTN' responsible for the PSTN protocol of the second V5 interface V5' . The protocol object starts a call setup process according to the definitions with the concentrator AN2. A call initiated by a subscriber defined in a second V5 interface V5' is signalled observing the principles described above although such a case is not described here. 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 subscri- bers 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 the second access node , c h a r a c t e r i s e d 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 set up by cascading the two V5 interfaces; and that the Control and PSTN protocols of the first and second V5 interfaces (V5, V5') are transmitted using Control and PSTN protocol objects disposed in the first access node. 2. Procedure as defined in claim 1, c h a - rac t eri s ed in that the Control and PSTN protocols of the first V5 interface (V5) and the Control and PSTN protocols of the second V5 interface (V5') are transmitted using the same Control protocol object and a second PSTN protocol object. 3. Procedure as defined in claim 2, cha rac t eri s ed in that the Control and PSTN protocols of the second V5 interface (V5') are transmitted using the Control protocol object and PSTN protocol object of the first V5 interface. 4. Procedure as defined in claim 1, cha racteri sed in that the Control and PSTN protocols of the first V5 interface (V5) are transmitted using a first Control protocol object and a first PSTN protocol object and the Control and PSTN protocols of the second V5 interface (V5') are transmitted using a second Control protocol object and a second PSTN protocol object. 5. Procedure as defined in claim 4, cha racterised in that, for each protocol, information as to which protocol object is responsible for which protocol of which V5 interface (V5, V5 ' ) is stored in the first access node (ANl) . 6. Procedure as defined in claim 4 or 5, characterised in that, in conjunction with each protocol message to be transmitted, a check is carried out in the first access node (ANl) to determine the pro- tocol object for which the message is intended, and the messages are directed based on this check. 7. Procedure as defined in any one of the preceding claims 1 - 8, characterised in that the interface between the access network (AN) and the tele- phone 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: LALLUKKA TOIVO, LEHTO PEKKA, LIINAMAA OLLI, RUKAJAERVI ARTO, SAARELA JAAKKO, LALLUKKA, TOIVO, LEHTO, PEKKA, LIINAMAA, OLLI, RUKAJAERVI, ARTO, SAARELA, JAAKKO
Applicants: LALLUKKA TOIVO, LEHTO PEKKA, LIINAMAA OLLI, NOKIA TELECOMMUNICATIONS OY, RUKAJAERVI ARTO, SAARELA JAAKKO, LALLUKKA, TOIVO, LEHTO, PEKKA, LIINAMAA, OLLI, RUKAJAERVI, ARTO, SAARELA, JAAKKO
Application year: 1998
Main classification: H04Q3
IPC codes: H04Q11