METHOD FOR PLACING INCOMING CALLS IN A QUEUE AND FORWARDING FROM THE QUEUE TO DESTINATION CONNECTIONS

Abstract: A method for arranging incoming calls to a subscriber number in a queue and for routing the calls from the queue to destination extensions (107), which are located under at least two separate PBXs (106), in which method, an intelligent telephone network (102, 103) is used to detect a call made to the subscriber number, the call is routed to an audio response unit (104) connected to the intelligent telephone network, the call is placed in a queue in the audio response unit (104), the state of the destination connections (107) is monitored, and the call is routed from the queue, when an idle destination extension (107) is detected.

Description: METHOD FOR PLACING INCOMING CALLS IN A QUEUE AND FORWARDING FROM THE QUEUE TO DESTINATION CONNECTIONS The present invention relates to a method, according to the preamble of Claim 1 , for arranging incoming calls to a subscriber number in a queue and for routing the calls from the queue to destination extensions, which are located under two different private branch exchanges (PBX). Methods of this kind of are used in connection with telephone services implemented in distributed exchange environments, to control queuing and billing for queued calls, when calling a service number. In particular, the method is used in connection with telephone services subject to a surcharge. The queuing facility is required, when the provider of the telephone service has no idle service lines at the moment the call is made. A distributed exchange environment refers to a system, which comprises at least two PBXs, which are connected so that common PBX functions can be provided for the extensions of the connected PBXs. Such common PBX functions can be, for example, queuing that operates in the areas of several PBXs. Thus, a distributed exchange environment refers to an exchange network, in which several PBXs are connected to operate at least partly together, in a manner similar to a single PBX. According to the state of the art, queuing is implemented in the PBX of the service producer. For example, queuing can be free initially with a charge imposed later. Free queuing is based on sending a delayed answer message from the service producer's PBX connection to the switching centre of the telephone network. Queued calls are thus connected to the service producer's PBX, which delays answering the calls. This technique has allowed queuing without a surcharge for not longer than the period permitted by the time supervision of the public telephone network. Typically, the time supervision of the public telephone network permits a delay of 2 - 3 minutes between the connection of the call and the sending of an answer message. If queuing longer than the time supervision period has been desired, the PBX of the service producer has had to send an answer message before the time supervision is tripped. If an answer message has been sent, a charge has bee applied to the queuing. If, on the other hand, an answer message has not been sent, the switch of the telephone network has cut off the queued call when the time supervision has tripped. In this case, the queuing has been completely free and the caller has not even been billed for the local call charge. A drawback in the state of the art is that the time supervision of the public telephone network limits the maximum time for surcharge-free queuing, while a charge for the queuing time cannot be freely set. Another drawback in the state of the art is that each call in a queue created in the service producer's PBX also takes up transfer capacity by one call connection between the telephone network and the PBX. Methods are also known, in which the functioning of an intelligent telephone network is exploited when implementing queuing. Application publication WO 98/35482 discloses a method for dividing calls to a service number between call centres. In the method, an incoming call to the service number is received for routing in a DAP (Data Access Point, corresponding to an SCP). The DAP then begins to implement a routing plan for the call and for this purpose sends a query to the call-centre router. The call-centre router also initiates a routing plan routine, on the basis of which it selects a destination call centre for the call. Next, the call centre checks whether the destination call centre number is idle or busy. If the destination call- centre number is busy, the call-centre router sends a queuing query to the parking manager. The parking manager selects and reserves a suitable parking platform for the call and sends its address to the call-centre router. The call-centre router forwards the address of the parking platform to the DAP, which converts it to a physical routing number of the telephone network. The DAP then issues a command to the switchboard to route the call to the selected parking platform, which holds the call for the duration of queuing. The call-centre router monitors when the call centre defined for the call becomes free and, when this happens, requests the parking platform to release the call. The call is then routed forward to the number of the call centre originally defined for the call. Patent publication US 5,444,774 discloses a method, in which calls are routed to destination extensions and, if necessary, to a queue in a Network Voice Response Unit (NVRU). In the method, an incoming call to the service number is brought under the control of an ACP (Action Point, corresponds to an SCP), when the ACP uses a signalling network link to contact a database, which maintains the control logic of the service number and information on the state of the destination numbers. If, during call processing, all potential destination extensions are seen to be busy, the ACP is instructed by the database to route the call to the Network Voice Response Unit (NVRU). The call is now routed to the NVRU, which collects information from the caller, according to sent definitions. When the destination number becomes available, the NVRU is notified of the idle destination number through the ACP. The call is then disconnected from the NVRU and the collected information is sent to the ACP. The ACP routes the call forward to the idle number, and sends the information collected by the NVRU along with the call. Patent publication US 5,600,710 also discloses a method, in which calls to a specific subscriber number initiate a queuing routine in the SCP. In the method of the publication, the SCP analyses the state of the destination number of the incoming call, and, if the number is idle, routes the call to the destination number. If, on the other hand, the destination number is busy, the SCP routes the call to the voice response unit and monitors when the destination number becomes idle. When the destination number becomes idle, the SCP reviews all the calls queuing for the destination number and routes the call with the highest priority from the voice response unit to the destination number. All of the methods described above cause certain problems in practical applications. The most important common problem in the methods is that incoming calls to numbers using the queuing service put a considerable load on the server controlling the calls, i.e. on the SCP. The increased load requires an increase in the performance of the SCP, if the SCP is to cope with routing all the calls it controls. This is because the SCP typically must control a large number of calls requiring intelligent control functions. To increase the call-control capacity, an arrangement is generally used, which distributes the SCP's functions among several servers. However, the control methods of the queuing services described above also have their own problems, even in the case of a distributed SCP, as the performance of the system is then limited by the large exchange of information between the servers that the methods described above require. Particularly if the geographical distance between the servers is great, the exchange of information between the servers, required for call-control, can significantly delay call- routing. Furthermore, it is extremely expensive to use known methods to increase the capacity of the SCP. The method disclosed in application publication WO 98/35482 has the further problem that it cannot be used to implement real-time queuing control. This is because the destination call centre for the call is defined before queuing begins, allowing calls to remain unnecessarily in a queue, even if a parallel call centre becomes available during queuing. The method is also restricted to queuing control taking place on the call-centre level, and thus cannot control queuing at the destination-connection level. Similar restrictions also apply to the methods disclosed in patent publications US 5,444,774 and US 5,600,710. The invention is intended to create a method, which will permit queuing that saves SCP capacity, but nevertheless offers highly advanced service possibilities, even in a distributed exchange environment. The invention is based on the fact that incoming calls to the service number are always routed by the SCP directly to a response unit. Thus, the SCP makes no analysis of possible idle/free destination extensions, instead, the call is held in the response unit during the destination-connection analysis. The queuing function and the assessment of the need for queuing are processed outside the SCP, the network address of a destination extension that has become idle being sent to the SCP from an external server. Thus, an incoming call to the service number is generally routed to the Service Switching Point (SSP) of the intelligent telephone network and the intelligent network service according to the selected service number is initiated in the SCP (Service Control Point). Under the SCP's control, the call is immediately routed to a response unit connected to the service and linked to the network call-centre server, which response unit can receive and terminate calls. The response unit is preferably an IVR device (Interactive Voice Response Unit), so that calls connected to the response unit can be served using voice messages. The network call-centre server communicates with the exchange servers of the PBXs in the PBX network, so that the network call-centre server receives essential information on the state of all extensions connected to the service number. Next, the network call-centre server can issue instructions to the intelligent telephone network (SCP, SSP) to route the call to the extension selected according to the service logic. If all the lines of the service number are busy, the call is left queuing connected to the response unit. Calls connected to the response unit can be freed from the service-number surcharge, or charged a separately-set queuing charge, which can be, for example, lower than the actual service charge. When one of the service number's service lines becomes idle, the network call-centre server instructs the response unit to release the call and the SCP to route the call to the correct number of the correct PBX. More specifically, the method according to the invention is characterized by what is stated in the characterizing section of Claim 1. Considerable advantages are gained with the aid of the invention. The invention can be used to connect several PBXs and/or call centres into a single totality in terms of queuing, and also to provide a queuing function independent of the telephone network's time supervision, without unreasonably increasing the load on the SCP. The solution according to the invention has the additional advantage over solutions implemented in PBXs that the telephone link between the service producer's PBX network and the telephone network is not loaded unnecessarily during call queuing. Thus, the invention allows centralized queuing to be implemented in PBX networks, outside the actual PBX network, and within the limitations of quite normal intelligent network capacity. The saving in SCP capacity is based on the fact that, when using the present method, the SCP does not have to consider the need to queue incoming calls to the service number, or make destination number analyses. The SCP only issues simple instructions to route the call, to the correct response unit, and carry out some other routine operations. Such routine operations can be, for example, defining a charge and a code for the call. Thus, the SCP only carries out tasks taking up hardly any processor capacity and not requiring the call to be kept under the control of the SCP for a longer time. After all, in known methods, the call must be kept under the active control of the SCP for the time required for various analyses and database queries. In the present method, routing the call to the final destination connection also only requires the SCP to carry out rapid operations, as, when the present method is applied in a preferred manner, decision-making for the destination number has already taken place in an external server at the moment call- control returns to the SCP. Thus, the present method can be used to locate the processing capacity required by the queuing service outside the SCP, where possible momentary congestion in the queuing service cannot endanger the entire intelligent telephone network's smooth operation. Because the method does not significantly take up valuable SCP capacity, advantageous additional features can easily be added to queuing. Indeed, the method according to the invention has preferable embodiments offering several additional benefits. For example, the invention can be used to define a desired charge for queuing, independently of the final charge for the service call. The invention can also be applied so that information is collected from the caller, during queuing time, before the call is connected to the PBX of the service producer. In a highly preferable embodiment, this takes place in such a way that when a queued call is connected to a customer attendant in the telephone service, the information collected during queuing is immediately at the customer attendant's disposal, for example, on a computer monitor. Thus, the queuing time can also be exploited. In the following, the invention is examined with the aid of examples and with reference to the accompanying drawings. Figure 1 shows the operation of one method according to the invention in one possible system environment. Figure 2 shows the operation of a second method according to the invention in a second possible system environment. In Figure 1, arrows are used to show the operations carried out when using the first method, graphic symbols being used to show the members participating in these operations. The system environment of the figure comprises a telephone subscriber connection 101 calling the service number, the SSP centre 102 connected to this, a SCP 103 controlling the SSP 102, a network IVR unit 104 connected to the telephone network, and the service producer's call centres 105, of which there may be a great many, depending on the embodiment. The system can include 3 - 10 call centres 105, for instance. In turn, a call centre 105 comprises a PBX 106 and service extensions 107 connected to it. The call centre also includes an exchange server 108, containing the software for controlling the PBX 106, according to the operating logic programmed into the service centre. In addition, the system environment includes a network call-centre server 109, with a telecommunications link to the Network IVR unit 104, the SCP 103, and the exchange servers 108 of the call centres 105 connected to a common queuing function. The task of the exchange server 108 is to communicate with the Network IVR unit 104, the SCP 103, and with each call centre 105 connected to the common queuing function, and to co-ordinate their operation to achieve the desired queuing function. In the whole telephone system, there is naturally a large number of subscriber connections similar to the subscriber connection 101, and these can simultaneously call the service number in question, but, for reasons of clarity, the figure shows only a single subscriber connection 101 calling the service number. The number of service extensions 107 under the PBX 106 can also vary greatly from that in the figure. The PBX 106 can be, for example, of the PBX (Private Branch Exchange) type. When a call arrives in the service number's queue, and later when the call is routed from the queue to the service extension, the following operations according to Figure 1 take place: 1) The customer calls from the subscriber connection 101 to the service number, which is subject to a surcharge, and the call is routed to the SSP 102 of the telephone network. 2) The SSP 102 requests the SCP 103 for instructions for routing the call. The SCP 103 initiates the service relating to the service number and provides the SSP 102 with instructions for routing the call. The SCP 103 instructs the SSP 102 to set the desired queuing charge for the call, for example a charge equal to a local call, and to route the call to the network IVR unit 104. The SCP 103 gives the call a code and places it as the content of a certain signalling message unit field of the telephone network signalling relating to the call. For example, the code can be transmitted using the calling-party field or the REDI (Redirecting Number, the subscriber number that last transferred the call) field. The code is intended to identify the call, so that the individuation data can be transmitted to the system's other operating devices. The code may be, for example, a random number or a sequential number. The SCP 103 also instructs the SSP 102 to wait for what happens later to the call. 3) The SSP 102 routes the call to the network IVR unit 104 and sets a queuing charge of the desired size for the call, for example, a charge equal to the local call charge. 4) The PBXs 106 in the system know the states of the extensions under their control. Each PBX 106 and the PBX-server 108 communicates over a telecommunications link to determine if the extensions belonging to the response series connected to the service number are busy or idle. The PBX-server 108 also controls the operation of the PBX 106. 5) Each PBX-server 108 of the system communicates, through a telecommunications link, the information on the state of the extensions of its call centre 105 to the network call centre server 109, which is thus informed of the state of each extension in the response series. This communication continues without a break. 6) On receiving a call and the related code from the SSP 102, the network IVR unit 104 answers the call and sends an answer message. On reception of the answer message, the SSP 102 initiates charging of the call, according to the desired charge. The network IVR unit 104 places calls that arrive at the service in a queue and gives callers a queuing announcement or plays queuing music. The announcement may be, for example, a voice message, 'You are in a queue. Please hold the line.' In a preferred embodiment, the network IVR unit 104 can also implement intelligent, call-controlling queuing. The caller is then asked for more detailed information during queuing, such as where she or he wants her or his call to be routed. Such questions are, for example, 'For the sales department, please press 1 , for faults notification, please press 2.' The network IVR unit 104 collects the caller's choices and sends them in a specific form to the network server 109, along with the code identifying the call. 7) On the basis of the information it receives, the network server 109 decides how and to which extension to route the queued call. For decision-making, the network server 109 contains routing rules for queued calls and other necessary routines. The routing of the call can be influenced by, for example, the calling-party number of the caller, the time, the day of the week, the choices given by the caller to the network IVR unit 104 during queuing, and/or the loading history of the destination extensions that have been defined in the routing rules by the provider of the queuing operation. Once the call's actual destination extension has been determined, the network server 109 informs the network IVR unit 104 that an idle response location is available for the call. 8) Next, the network IVR unit 104 disconnects the call by sending a clear back message to the SSP 102, in which case control of the call returns to the SSP 102. 9) On receiving the clear back message, the SSP 102 asks the SCP 103 what should next be done with the call. 10) The service logic in the SCP 103 detects the called-party-terminates state and retrieves the routing number defined for the call, from the network server 109. The code given to the call is once again used to identify it. 11) The SCP 103 instructs the SSP 102 to route the call to a specific call number 107 in a specific PBX 106. The SCP 103 also instructs the SSP 102 to set the desired service charge for the call, if the service charge differs from the queuing charge. 12) The SSP 102 routes the call to the correct response location, through PBX 106. After response, the call acts as a normal intelligent network call. The call is then charged for according to the service charge. The stages of the above method are not necessarily carried out in the order described, instead, the order may partly vary. As it is also preferable to perform some of the operations continuously, the order as such cannot be defined. In addition, some of the operations described above can be performed, and preferably are performed, simultaneously with some other operation or operations. It should also be noted that, each PBX may have extensions forming part of several different response series. A single individual extension can also form part of several different response series. Network call-centre server 109 may be simultaneously connected to several network servers in different call centres 105. This is so that for the subscriber number visible to a single customer, queuing may be carried out in the network, with response to the call in question being possible in any suitable call centre 105 connected to the control of the network call centre server 109. Thus, it is possible to control a PBX network with the aid of a network call-centre server 109. Call centres 105, which are controlled by different organizations, can be connected to a network call-centre server 109. Thus, it is possible to use a single network call-centre server 109 to control several different PBX networks. The method shown in Figure 1 can be varied in several different ways. Figure 2 shows one variation, utilizing the notification to the call centre 105 of the code given to the call. The method of Figure 2 is used in a system similar to that in Figure 1, in which service-extension-specific computers 1 10 or terminal devices, intended to be used by customer-service attendants, are added in connection with the PBX-server 108, to the call centres 105 which use the code. The method of Figure 2 includes stages 1 - 1 1 of the method of Figure 1, essentially in the same form, as well as the following procedural stages: 12) The network call-centre server 109 notifies the PBX-server 108 of the call code it has received from the network IVR unit 104, and of the choices entered by the customer. 13) The SSP 102 routes the call through the PBX 106 to the correct response location. In connection with the call, the code relating to the call is also transmitted to the PBX, for example, coded in the calling party and REDI field. 14) The PBX 106 forwards the call code and call destination number to the PBX-server 108. The telephone of the customer attendant working at the selected destination extension 107 rings. 15) The PBX-server 108 detects that the codes received from the network call-centre server 109 and the PBX 106 are the same, and logically connects the events and information relating to the codes to each other. The PBX-server 108 opens the correct application in the computer 1 10 of the customer attendant working at the destination extension 107. The opening of the application can also be initiated by a choice given by the user to the network IVR unit 104, and transmitted to the PBX- server 108 through the network call-centre server 109. The information collected from customers in the call queue, during queuing can be, for example, their customer number or, in connection with banking services, their account number. Customers can also be asked which exact service they wish on each occasion. This can take place, for instance, by using a menu function, which asks customers to press a specific number key to select the service they wish. The information collected during queuing can be used to route a service call, once a service line 107 becomes available. The call can be routed, for example, directly to the department or person selected by the customer. An attempt can also be made to route the call to the person or department responsible for serving the customer in question. The queuing system can also be set to operate together with the data system of the service producer, so that the customer information of a customer in the queue and identified during queuing appears on the screen of the computer terminal 1 10 of the customer attendant, when the call is connected to the telephone device 107 of the customer attendant. In the method disclosed above, incoming calls to the service are identified by means of an individuation code defined separately inside the service system. The calling-party information conventionally attached to a call is generally unsuitable for use as an individuation code. The use of only the calling-party number as an individuation code could lead to problems in cases in which more than one call at a time comes from the same PBX and all give the number of the PBX, and not the extension number, as the calling-party data. Certain company PBXs operate in this fashion. The above examples deal with cases in which there is a queue in the service when it is called. However, there is not necessarily always be a queue. In such cases too, the call is first routed to the network IVR unit 104. However, in the methods shown in Figures 1 and 2, the call can be routed directly forward, if there is no queue. In this case, the caller receives no announcement, instead, the call is transferred rapidly out of the control of the network IVR unit 104. Thus the caller is saved from an unnecessary wait. If desired, the system can also operate so that, before the call is transferred away from the network IVR unit 104, certain predetermined information is collected from the caller, or the caller receives some kind of welcome announcement, stating that the call is being transferred, for example, to the nearest customer attendant. Such a welcome announcement can be, for instance, the following, 'Welcome to the telephone service of company X, your call is being transferred to the first available customer attendant.' Queued calls can be placed in the queue, for example, in the order in which they arrive. Thus, the call that has been in the queue longest would be the first in the queue and would be routed to the first extension, suiting the call information, that becomes available. However, queuing priority can also be set differently. For example, the service producer can give priority to calls made from certain calling-party numbers. Thus, calls coming from the PBX of, for example, some large customer company, can be given priority in the queue. If prioritization takes place on the basis of the calling- party number, the calling-party information must not be destroyed, at least entirely, when making the individuation code. In such cases, the individuation code can be placed in some other field than the calling-party number field. Alternatively, the calling- party number, or queuing-priority information can be coded into an individuation code to be placed in the calling-party number field. When a method according to the invention is used in the case of a call, which is first queued connected to the network IVR and is later connected to the actual service number, two separate billing tickets can be made. The first ticket is made for the call connected to the network IVR and the second for the call connected to the PBX controlling the service number. From the caller's point of view, these two calls are. however, a single call, as the call is not terminated from the calling-party end, when the call is transferred, as another call in terms of the telephone network, from the network IVR to the second called-party address, i.e. to the PBX controlling the service number. In this case, two separate tickets are obtained for the queuing part and the actual service- call part of a call made to the service number. Such an embodiment of the invention can thus be used to differentiate, in terms of billing, the queuing and service parts of a service call from each other. These separate billing data can be used, for example, to divide the profit on the call between the telecommunications operator and the service producer. The invention can also be applied in connection with telephone services without a surcharge, or those that are entirely free. In such cases, a service call can correspond to the price of a local call or be free of charge. In principle, it is also possible for the service charge to be less that the queuing charge. The invention can also be applied in such a way that the connection making the call is only billed for the queuing time, when the caller, for instance, enters the information required by the service, the actual service part being free of charge. The examples refer to call centres 105, which comprise a PBX 106 and a separate PBX- server 108 connected to this over a telecommunications link. It will be, however, obvious to one versed in the art that the functions of the PBX-server 108 can be integrated as part of the PBX 106, thus replacing the separate PBX 106 and PBX-server 108 with a single apparatus. Correspondingly, it is also possible to integrate the tasks of, for example, the network IVR unit 104 and the network call-centre server 109 to be performed by the same apparatus. In turn, the operations of the network call-centre server 109 can be set to be performed in the SCP 103. The above discloses such preferred embodiments of the invention, in which queued calls are served by means of a voice response unit. As network terminal devices, such as UMTS mobile phones, containing comprehensive data-transfer properties, become increasingly common, response units, which communicate with the terminal device of a queued subscriber connection over a data link, can also be applied in queuing, in place of a voice response unit. Thus, information can be collected during queuing, through menus appearing on the screen of the caller's network terminal device.

Claims: Claims: 1. A method for arranging incoming calls to a subscriber number in a queue and for routing the calls from the queue to destination extensions (107), which are located under at least two separate private branch exchanges ( 106), c h a r a c t e r i z e d by - detecting, with the aid of an intelligent telephone network (102, 103), a call made to the telephone number, routing the call to a response unit (104) connected to the intelligent telephone network, placing the call in a queue in the response unit (104), - monitoring the state of the destination extensions (107), detecting an idle destination extension (107), and routing the call from the queue to the detected idle destination extension (107). 2. A method for arranging incoming calls to a subscriber number, for which a control logic has been set, in a queue and for routing the calls from the queue to destination extensions (107), which are located under at least two separate private branch exchanges (106), c h a r a c t e r i z e d by detecting, by means of an intelligent telephone network (102, 103), calls made to the subscriber number, - routing each detected call to a response unit (104) connected to the intelligent telephone network, for holding the call in the response unit (104) for the duration of a destination extension analysis, determining the potential destination extensions (107) for each call routed to the response unit (104), according to the control logic, and placing the call in the queue, - monitoring the state of the potential destination extensions (107) determined for each call, detecting an idle destination extension ( 107), - selecting from the queue the first call queuing for the detected idle destination extension (107), and routing the selected first call to the idle destination extension (107). 3. A method according to Claim 1 or 2, characterized in that when the call is routed to the response unit (104), the desired queuing charge is set for the call, and when the call is routed forward from the response unit (104) to the destination extension, the desired service charge is set for the call. 4. A method according to one of Claims 1-3, characterized in that, in order to individuate the call, the call is given a code, which can be transmitted to identify the call in the exchange of data between the operating devices participating in implementing the method, and to link together the call's supplementary data. 5. A method according to Claim 4, characterized in that, when the call is connected to the response unit (104) information is collected from the caller, with the aid of the response unit (104), - the information collected is connected to the call on the basis of the code given to the call, and a message or group of messages, containing the collected data and the code, is formed to be sent to another operating device participating in the implementation of the method. 6. A method according to Claim 5, characterized in that information collected from the caller by the response unit (104) is taken into account when determining the order of the calls in the queue and/or a suitable group of destination extensions. 7. A method according to Claim 5 or 6, characterized in that the information collected from the caller is transmitted to a computer (110) or terminal device operating in connection with the destination extension (107) selected for the call. 8. A method according to one of Claims 1-7, characterized in that, when the destination extensions' (107) state is monitored, state data, sent over a telecommunications link by the private branch exchanges (106) controlling the destination extensions (107) and/or the exchange servers (108) combined with the private branch exchanges (106), is received. 9. A method according to one of Claims 1-8, characterized in that, when routing a call from the queue to an idle destination extension (107) the queued call connected to the response unit (104) is disconnected from the response unit (104), the intelligent telephone network (102, 103) takes the disconnected call under control, the intended routing number for the call, according to the service logic, is requested with the aid of the intelligent telephone network, and the call is routed to the routing number defined by the service logic. 10. A method according to one of Claims 1-9, characterized in that a voice response unit is used as the response unit (104).

Inventors: ISOTALO LAURI, KAVONIUS JUHA, LAIHONEN MARKKU, ISOTALO, LAURI, KAVONIUS, JUHA, LAIHONEN, MARKKU
Applicants: HELSINGIN PUHELIN OYJ, ISOTALO LAURI, KAVONIUS JUHA, LAIHONEN MARKKU, HELSINGIN PUHELIN OYJ - HELSINGFORS TELEFON ABP, ISOTALO, LAURI, KAVONIUS, JUHA, LAIHONEN, MARKKU
Application year: 2000
Main classification: H04M3
IPC codes: H04M3, H04Q3