MXPA98002621A - System and method for implementing extension telephones to give service of short messages within a radiotelecommunication network - Google Patents

Abstract

The present invention relates to a system and method for offering service to extension telephones, from point to point, with short message service, within a telecommunications radio system. The system includes a gate mobile switching center (G-MSC), a home location register (HLR), a plurality of mobile switching centers (MSC) and a plurality of intelligent terminals. Smart terminals are assigned to a single common pilot directory number (PDN) in addition to their individual directory numbers. When the G-MSC receives a call addressed to the PDN, the G-MSC sends a routing request message to the HLR. The HLR sends a short message service (SMS) data transmission to each of the plurality of smart terminals assigned to the PDN by notifying the mobile subscribers associated with an incoming call from an extension telephone. Mobile subscribers who wish to accept the call use their smart terminals to send a replying SMS message back to the HLR. Upon receiving a response by accepting the call from one or more notified smart terminals, the HLR selectively reports the temporary location directory number (TLDN) of a smart terminal responding to the G-MSC then routes the incoming call to the responding smart terminal.

Description

SYSTEM AND METHOD FOR IMPLEMENTING EXTENSION TELEPHONES TO SERVICE SHORT MESSAGES WITHIN A RADIOTELECOMMUNICATION NETWORK BACKGROUND OF THE INVENTION TECHNICAL FIELD OF THE INVENTION The present invention relates to mobile communication systems that have mobile subscriber extension telephone service and, more particularly, to a system and method for implementing extension telephones for short message service within a radio telecommunications network.

Description of the Related Art Integrated services networks use digital signal processing to support sound and data communication channels for the transmission of information between users of the network. Cellular radio-telecommunications networks and, more specifically, mobile telecommunications systems are becoming the providers of integrated services, such as the transmission of voice and data messages. A major problem with the expansion of these integrated networks for mobile systems is that the interactive real-time transmission of data messages between subscribers of the cellular telecommunication system has not been supported, described or devised. Cellular radiocommunication services in the United States are summarized and specified by a plurality of industry standards adopted by groups that constitute the manufacturers and operators of cellular systems. These standards include EIA-627, EIA-553, IS-136 and the signaling standard between systems 13-41 which are incorporated herein by reference. The EIA-TIA requirements established in the IS-41 standard maintain that, a call within a cellular radio system is initially routed to a specific mobile switching center (MSC), according to the location data they identify the mobile station called (MS). For example, a mobile subscriber is assigned a unique telephone number that is recognized by the Public Switched Telephone Network (PSTN) and the Public Land Mobile Network (PLMN). Calls to a specific mobile subscriber are routed to a gate mobile switching center (G-MSC) which consults the home location recorder (HLR) of the subscriber to obtain information regarding the location of the subscriber's mobile station, and other status information, stored in a subscriber profile. A mobile station of the subscriber transmits a unique mobile identification number (MIN) that is detected and identified by the MSCs after an initial registration procedure, each time the mobile station is activated within the service area of a receiving exchange. The actual paging of the called MS can take place at the MSC where the MSC is located before the call is routed. If the location data stored in the IILR is correct and the mobile station is currently in an active on state, the MS responds to the page and the call is completed. The requirements of the EI? / TIA established in the IS-627 standard are responsible for extension telephones for mobile stations within the cellular system. In this implementation, mobile stations subscribing to the extension telephone service are assigned two directory numbers: an individual directory number for normal calls (ie, telephone call without extension) and a pilot directory number (PDN) for extension telephone calls. The PDN is associated with two or more individual mobile stations, each of which has a different MIN. To provide extension telephone service, the HLR keeps the location information data separate for each of the plurality of mobile stations assigned to the same PDN. An incoming call from a PDN causes the cellular network to point to each of the associated mobile stations, establish a voice channel connection with each active MS and selectively route the call to a single responding MS. An example of an extension telephone service is described in US Patent Application Serial No. 08/411, 546, co-owned and co-pending, filed on March 28, 1995, entitled "Method and system for implementing extension telephones within a cellular radiotelecommunications network", which is incorporated herein by reference. The cellular radio network and mobile stations are now implemented with digital technology, thereby enabling the integration of data transmission services with the voice communication service of analog cellular networks. The data transmission services include the short message service (SMS) signaling technology that allows short text messages on a digital control channel to be sent to a mobile subscriber station to be displayed on the station's display screen. mobile. The SMS signaling uses techniques of storing and sending messages by storing SMS messages in a message exchange until the mobile station is assigned to a digital control channel. However, certain applications for businesses and subscriber needs indicate a growing interest in real-time interactive data transmission for a more economical use of network resources and more efficient communication among users. For example, calls to extension telephones in current cellular networks require the system to open or freeze a plurality of voice channels when subscribers with an extension telephone transmit the signals. The voice channels are not released until a mobile station is selected to receive the incoming call. In addition, the current short message service signaling scheme is unsuitable for transmitting extension telephone subscriber signals because its basic storage and retransmission architecture precludes signaling in real time. Although there are no known teachings of the prior art for a solution to the deficiency and drawbacks noted above such as those described herein, U.S. Patent No. 5,351,235 to Lahtmen describes the subject matter that bears some relation to the subject which is described in the present. Patent 235 of Lahtmen describes a protection method with relays or retransmission of short data messages between users in an integrated services network. As described in Lahtmen Patent 235, the method shows a short message service scheme that uses a message switching service to allow a source caller to send a message to a short message service exchange for storage and subsequent transmission to a destination device or terminal of the call. However, Lahtinen's 235 patent is limited to short message transmissions using the "storage and retransmission" principle and does not propose a procedure whereby an originating caller can cause a short message to be immediately sent to a subscriber. terminal and in the same way to support the automatic retransmission of the real-time response of the terminal subscriber. As noted above, in existing mobile telecommunication systems, the integration of data transmission services with voice transmission services to facilitate the correspondence of messages between users requires that the originating caller send a message to a central short message service for storage. The message is subsequently retrieved and sent to the proposed recipient. The use of short message transmission in real time, directly, within the cellular network, would be a different advantage in the fast and efficient communication that companies require between subscribers and the valuable resources of the network would be freed more quickly. Specifically, it would be advantageous to have a system and method for implementing a short message service in real time in groups of cellular extension telephones for a plurality of mobile stations located within the single or multiple MSC. The system and method will use a transmission of short message data in real time to inform the mobile station extensions of an incoming call for a pilot directory number (PDN). The system and method of the present invention provides this solution.

SUMMARY OF THE INVENTION In cell-based radiotelec networks that implement extension telephone services, a system and method for notifying subscribers of an extension telephone of an incoming call is provided using the transmission of short message data in real time .

In one aspect, the present invention is a method for providing extension telephone services using short message data transmissions within a mobile telecommunication system. The mobile telecommunication system includes a mobile gate switchboard (G-MSC), a home location recorder (HLR) and a plurality of smart terminals. Smart terminals have individual directory numbers to receive normal calls and are assigned to a single common pilot directory number (PDN) to receive extension telephone calls. The system may also include a plurality of visited mobile switching centers (V-MSC) each of which includes an MSC and a visitor location recorder (VLR). Each smart terminal is an integrated service unit that has the capabilities of a mobile station and a bidirectional device to send data messages in a single terminal unit. In another aspect of the method of the present invention, an incoming call is received in the G-MSC which, in turn, sends a location request message to the HLR. The I1LR determines whether the call is for a common PDN and causes a short data message to be transmitted to each of the plurality of intelligent terminals identified as associated with the PDN. Upon receiving a return data message from at least one of the plurality of intelligent terminals, the HLR selects a responding terminal and sends a temporary location directory number (TLDN), associated with the terminal, to the G-MSC. to route the call to the selected subscriber terminal.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood and its numerous objects and advantages will be more apparent to those skilled in the art with reference to the following drawings, together with the accompanying specification in which: Figure 1 (prior art) is a simplified block diagram of a normal cellular radio communication system that supports extension telephone groups; Figure 2 is a simplified block diagram of a cellular radio communication system that supports extension telephone sets with short message service, in accordance with the teachings of the present invention; Figure 3 is a flow chart detailing the procedures for notifying a mobile station, within a cellular telecommunication radio system, of an incoming call from an extension telephone and routing the call to a responding mobile station, in accordance with the teachings of the present invention; and Figure 4 is a flow diagram illustrating the implementation of an extension telephone service for short messages, in accordance with the teachings of the present invention.

DETAILED DESCRIPTION OF THE MODES The present invention implements extension telephones with short message service within a mobile telephone system, whereby, a data message is sent to a plurality of mobile terminals of intelligent terminals that inform the mobile subscribers of an incoming call for a single pilot directory number (PDN). The alerted subscribers, optionally, send a control message to the polling station to indicate the acceptance of the call before the call is routed to one of the responding terminals. The figures of the drawings illustrate the present invention using the communication protocols and extension telephones of the specification Intersyste 13-41 and 13-627 which are incorporated herein by reference. Nevertheless, it is possible to use other suitable communication protocols and extension telephone systems without departing from the scope of the present invention. Referring to Figure 1, a simplified block diagram of a conventional cellular radio communications system providing extension telephone service is illustrated. In general, an incoming call 100 coming from a public switched telephone network. { PSTN) 102 addressed to a PDN is routed to a gate mobile switching center (G-MSC) 110. The G-MSC 110 consults a home location recorder (HLR) 112 to obtain information identifying the serving MSCs in the present location of the mobile stations associated with the PDN. For purposes of illustration, and not by way of limitation, Figure 1 shows the MSCa 120, MSCb 130 and MSCc 140 together with the base stations 121, 131 and 141. The mobile stations 122, 124, and 126 are located in the area of coverage of the MSCa. The mobile stations 132 and 134 are in the MSCb coverage area, while the mobile stations 142 and 144 are in the coverage area of the MSCc. The HLR keeps the location data of each of the mobile stations independent within the group of mobile stations assigned to the same PDN. Upon receiving the call 100 addressed to this PDN, the G-MSC 110 requests the MSCs 120, 130, and 140 to page each mobile station 122, 124, 126, 132, 134, 142 and 144 according to each of the MINs. of the mobile station. The MSCs 120, 130, 140 then page the relevant mobile stations by the base stations 121, 131 and 141, in an almost simultaneous mode regardless of their proximity or separation from each other. It will be understood and appreciated by those skilled in the art that G-MSC 110, HLR 112 and MSCs 120, 130, 140 may be logically separated from one another or may be physically within the same entity. In the same way, since each of the mobile stations that are paginated is identified by a separate MIN, all the mobile stations associated with the PDN can be located in different MSCs and be paged independently of the MSCs through stations Separate bases, as shown herein, or in an alternative mode, the MSC group may be located within the same MSC and be paged concurrently therein. The IS-41C includes a description of an extension telephone process known as "Flexible Alert". In Flexible Alert, each serving MSC that receives a page response from a paged mobile station returns the temporary location directory number (TLDN) of the responding mobile station to the originating MSC. The originating MSC then completes the establishment of the call for each received TLDN. When one of the mobile stations responds, the originating MSC releases the calls for the other TLDNs. In the co-owned and co-pending US Patent Application Serial No. 08 / 411,546, filed March 28, 1995, entitled "Method and System for Implementing Extension Telephones Within a Cellular Radio Telecommunications Network" describes an improved method for providing service of extension telephones. After the execution of the paging attempts, the MSCs 120, 130 and 140 report any of the mobile stations that do not respond, for example, the mobile stations 122, 132, 134 and 144 to the HLR 112, which immediately stops the process Call set-up for stations that do not respond. Next, the MSCs 120 and 140 that received a stable page response in a connection to the radio voice channel within the responding mobile stations 1224, 126 and 142 and alert their respective subscribers of an incoming PDN call. Each responding mobile subscriber responding to the alert is temporarily placed in busy. The M? C 120 and 140 then report to the HLR 112 any mobile station that does not respond and that returns a busy signal. The HLR immediately interrupts the call set-up process for these mobile stations that do not respond or are busy. During the period of time that the respondent subscribers are on hold, their associated MSCs report their routing number to the HLR 112. After a predetermined period of time, the HLR 112 selects one of the reported routing numbers to route the call according to a predetermined criterion which may be, for example, the first to answer. Once the routing number has been selected, the IILR 112 releases all unresponsive mobile subscribers from the occupation. The HLR 112 then returns the routing number to the G-MSC 110 so that the call can be routed to the MSC of the selected number. Now in relation to Figure 2, se4 shows a simplified block diagram of a cellular radio telecommunication system that supports extension telephone sets with short message service according to the teachings of the present invention. As shown in Fig. 2, the system of the invention includes G-MSC 210, HLR 212, virtual intelligent terminal (vIT) 214, MSCs 220, 230, and 240, base stations 221, 231, and 241 and a plurality of smart terminals of associated mobile stations (IT) 222, 224, 226, 232, 242, and 244. The IT used in the system and method of the present invention are integrated digital terminals that include standard technology of mobile stations and remote paging technology of digital presentation in the same unit. Each IT is assigned a unique mobile identification number (MIN). In the same way, the HLR of the present invention includes digital technology to support the transmission of digital data from the virtual IT 214 to the IT located at remote locations. In the present invention, when the G-MSC 210 queries the HLR 212 after receiving the incoming call 200 from, for example, the PSTN 202, the IILR sends the PDN to the vIT 214. The section vIT 214 of the HLR has access to subscriber information in relation to the probable location of the ITs associated with the incoming PDN call 200. The vIT 214 then requests the related MSCs 220, 230, 240 location information from the IT. After acquiring the location of the IT 222, 224,. 226, 232, 234 and 242, the vIT 214 sends short data messages to the ITs informing the subscribers of an incoming call to the PDN. Although the short data messages of the vIT 214 are transmitted by the MSCs 220, 230, and 240 and the base stations 221, 231 and 241, the SMS communications are essentially transparent to the switching nodes of the MSC. 3i is available, the subscriber chooses if he sends a reply signal back to the vlT 214 indicating that he is ready to accept the call 200. The vIT 214 then passes the terminal identification numbers to the responding ITs back to the HLR 212. If more than one response is received, the HLR 212 selects one of the responding IT using predefined selection criteria and returns the TLDN of the selected IT to the G-MSC 210 to send the call using the normal procedures for establishing the call. As illustrated in Figure 2, the system and method of the present invention provides a cellular extension telephone service using point-to-point data transmission with short message service (SMC-PP) during the identification and selection of the IT. . As used herein, SMS-PP messages are real-time data messages transmitted digitally from the source source to the destination terminal and vice versa, within a cellular network without being sent to a central message service intermediate shorts for storage and retransmission. SMS-PP messages are "real-time" in the sense that they are transmitted through the telecommunications network almost without delay using techniques without storage and retransmission. If a specific destination terminal is, for example, switched off, in a sleep mode, or is not operating in a digital control channel at the moment the data messages are sent to the extension telephone group, the data message addressed to this terminal is lost. In this case, the source of origin is vIT 214 and the destination terminals are IT 222, 224, 226, 232, 234, 242 and 244. This direct transmission of MSC-PP messages does not unnecessarily take up the valuable resources of the system establishing and maintaining open voice channels for each responding MS until the selected MS is identified and duplicative resources are released. In addition, the transmission of short messages directly to the ITs (deriving switching exchanges) can inform the subscriber of an incoming PDN call, even if the IT is connected in another terminal function such as a previously completed voice call. Now, the flow diagram shown in Figure 3 illustrates a procedure by which extension telephones with short message service, within a cellular radio system, can be implemented in accordance with the teachings of this invention. In step 300, the G-MSC receives an incoming call for a subscriber directory number and sends a location request message (LOCREQ) to the HLR. In step 302 the 1ILR receives the LOCREQ message and proceeds to determine whether or not the incoming call is an individual directory number or a PDN with a group of assigned mobile stations. This is carried out in step 303 by determining whether the directory number fits a list of mobile stations associated with the HLR. The list may include a plurality of mobile identification numbers (MIN). If the HLR determines that the directory number is associated with only a single MIN, the system moves to step 304 where the call is sent to the mobile station or the smart terminal having the assigned MIN, in accordance with the procedures for establishing normal calls, and ends with step 350. If the HLR determines, however, that the directory number is associated with multiple MIN, the system recognizes that the call is for a group of PDN extension telephones and proceeds to step 306. In step 306, the vIT of the HLR sends a routing request message (ROUTREQ) for each IT to the MSCs identified in the HLR database as the current location of each of the corresponding ITs is carried out. After the MSCs return a message from the ROUTREQ result back to the vIT in step 308, the system continues to step 310 where the vIT transmits short message service point-to-point data messages (SMS-PP) in real time to each localized IT. If a subscriber using one of the contacted IT is interested in accepting the PDN call, the subscriber sends a SMS-PP return or response signal to the vIT in step 312. After a predetermined period of time, the system moves to step 314 where the vIT returns the results, including the identification of the responding ITs, to the HLR. In step 315, the HLR determines the number of the responding ITs. Without any of the subscribers responding, the system continues with step 312 and initiates normal recovery procedures such as sending a non-response message to the originating caller, and the process ends in step 350. If a subscriber responds, the system continue from step 315 to step 318, where the HLR sends the TLDN of the IT responding to the G-MSC. The process then proceeds to step 319, where the call is sent to the responding IT following the normal procedures for the establishment of the calls, before finishing the process in step 350. If more than one subscriber answers, the system is moves to step 315 to step 320, where the IILR selects a reported routing number according to a predetermined criterion. This criterion may include, for example, the routing of the call to the first responding subscriber, for the subscriber closest to the calling originating party or the responding subscriber having the highest priority assigned to the subscriber's IT in the profile of the subscriber. subscriber PDN. After the selection is finished, the system continues with step 322, where the HLR sends the TLDN of the selected IT to the G-MSC. The process continues with step 324 to send the incoming call to the selected respondent IT before completing the process in step 350.

Now referring to Figure 4, the messages sent and received during the implementation of an incoming call for an extension telephone with short message service are shown, according to the teachings of the present invention. As illustrated herein, the system of the invention includes G-MSC 410, HLR 412, vIT 414, MSCs 420, 430, and 440 and IT 422, 432, and 442. It will be understood and appreciated by those skilled in the art. technique that the network nodes G-MSC 410, HLR 412, and MSC 420, 430 and 440 may be logically separated from each other or may be physically within the same entity. In addition, those skilled in the art will appreciate that actual communication along the signal lines between the nodes may vary depending on the design of the telecommunication system and the demands placed on it at the time of paging and the process of transmission of short messages. An incoming call 400 for a PDN is routed to a polling system having a G-MSC 410 and an HLR 412 with improvements in the virtual intelligent terminal (vIT) 441. The G-MSC 410 determines the home location recorder of the number of called subscriber and sends a location request message (LOCREQ) 450 to HLR 412. If a profile analysis of the subscriber number indicates that the called number is for a PDN extension telephone with SMS-PP service support, the subscriber unit signal processing from vIT 414 of HLR 412 receives the information from the LOCREQ message. MS 420, 430, and 440, associated with the extension telephone group receives a routing request message (LOCREQ) 415 from vIT 414 for identification of any of the ITs in the service area of each MSC. It will be understood and appreciated by those skilled in the art that the location number of the MSCs receiving a LOCREQ message from vIT 414 will depend on the profile contained in the HLR for the called PDN and the reported location of the associated ITs. If an MSC has an IT in its area associated with the PDN, the MSC notifies the HLR that the IT is in this MSC by sending a LOCREQ 456 return result message to vIT 414. The vIT then transmits call request messages from extension to the ITs located along lines 458a, b, n of SMS-PP data signals. The contacted IT may choose to send an extension call response with a return signal to the investigating IT 414, as shown by the signal lines 460b and 460n. The HLR then selects an IT to receive the call (e.g., ITb based on the selection criteria discussed in connection with Figure 3. The HLR 414 then transmits a message of the return LOCREQ result 464 to the G-MSC 410 e includes the TLDN for the ITb The normal procedures for establishing the voice call are then followed as indicated along the signal line 470. In this manner, the present invention allows subscribers of extension telephone groups to use Better system resources within the telecommunications network With real-time point-to-point short message services, incoming call notification for multiple subscriber stations does not require reserving voice channels before determining where they will go The incoming call: Those skilled in the art who have access to this description will understand and appreciate that short message services in real time can be sent from a point of origin to a point of destination at any time during the standard procedure for establishing calls as long as the interrogation HLR and the destination mobile station have improvements of the integrated intelligent terminal. Other alterations and modifications of the invention in the same manner will be apparent to those skilled in the art upon reading the present disclosure, and it is proposed that the scope of the invention described herein be limited only by the broadest interpretation of the annexed claims for which the inventors are legally entitled.

Claims (1)

1. An extension telephone system, of mobile telecommunication, consisting of: a plurality of intelligent terminals, each of which is assigned to an individual directory number, the plurality of intelligent terminals is also assigned to a single pilot directory number common (PDN), each intelligent terminal includes the means to transmit and receive data messages; a home location recorder that maintains an information profile for each of the plurality of intelligent terminals; a mobile switching center having a service area in which at least one of the plurality of intelligent terminals is currently located; a mobile gate switching exchange consisting of: a receiving mechanism for receiving an incoming call addressed to the common PDN; a signaling mechanism to send signals to the HLR; and a switching mechanism for routing the incoming call to the MSC; a mechanism for transmitting data messages to transmit a data message, in real time, from the HLR to each of the plurality of intelligent terminals; means for sending to the HLR a real-time return data message transmitted from at least one of the intelligent terminals; and means for routing, selectively, the incoming call to one of the intelligent terminals that transmitted the return data message to the HLR. The mobile telecommunication extension telephone system of claim 1, wherein the means for selectively routing the incoming call includes the means for routing the call according to a series of predefined criteria. The mobile telecommunication extension telephone system of claim 1, wherein the data message and the return data message are short message service (SMS) messages. The mobile telecommunication extension telephone system of claim 3, wherein the data message identifies the incoming call as a PDN extension telephone call. The mobile telecommunication extension telephone system of claim 1, wherein each of the plurality of smart terminals is a mobile station that has a mechanism for sending and receiving SMS messages. A mobile telecommunication extension telephone system comprising: a plurality of mobile stations having individual directory numbers, each of the mobile stations is also assigned to a single common pilot directory number and which has a transmission mechanism of Real-time data messages to send and receive data messages in real time; a home location recorder associated with the plurality of mobile stations, the HLR includes: an information profile for each of the plurality of mobile stations; and a mechanism for transmitting real-time data messages to send and receive data messages in real time; a mobile switching center having a service area in which at least one of the mobile stations is currently located, the MSC includes: a paging mechanism for paging at least one mobile station; and a switching mechanism for establishing a voice channel between the MSC and at least one mobile station; and a gate mobile switching exchange for receiving an incoming call addressed to the common PDN and routing the incoming call to the MSC, the G-MSC includes: a signaling mechanism for sending signals to the IILR; and a switching mechanism for routing calls to the MSC. The mobile telecommunication extension telephone system having a gate mobile switching center, a home location recorder and a plurality of mobile switching centers, the system comprises: a plurality of smart terminals, each of the plurality of terminals smart is assigned to an individual directory number as well as to a single common pilot directory number; means for transmitting a real-time data message from the HLR to each of the plurality of intelligent terminals; means for receiving in the HLR a real-time data message of return from at least one of the plurality of intelligent terminals; and means for selectively routing an incoming call directed to the PDN for one of the plurality of intelligent terminals that transmitted a return data message to the IILR. A method for servicing extension telephones within a mobile radio communication system, having a mobile gate switching center, a home location recorder, a plurality of mobile switching centers and a plurality of smart terminals, each of the plurality of intelligent terminals is assigned to an individual directory number, as well as a single common pilot directory number (PDN), the method comprises the steps of: receiving a call in the G-MSC directed towards the common PDN; transmitting a real-time data message from the HLR to each of the plurality of intelligent terminals; transmitting a return data message in real time from at least one of the plurality of intelligent terminals to the HLR in response to the transmitted data message; and selectively route the call to one of the smart terminals that responded to the data message. The method for servicing extension telephones within a mobile radio communication system of claim 0, wherein the step of selectively routing the call includes selecting one of the intelligent terminals to receive the call according to a series of criteria predefined The method for providing extension telephone service within a mobile radio communication system of claim 9, wherein the step of transmitting a real-time data message from the HLR includes the transmission of a message service message. short (SMS) from the HLR. The method for servicing an extension telephone within a mobile radio communication system of claim 10, wherein the step of transmitting a return data message in real time from at least one of the plurality of intelligent terminals it includes transmitting an SMS message from at least one of the plurality of intelligent terminals. SUMMARY OF THE INVENTION The present invention relates to a system and method for offering service to extension telephones, from point to point, with short message service, within a telecommunications radio system. The system includes a gate mobile switching center (G-MSC), a home location register (HLR), a plurality of mobile switching centers (MSC) and a plurality of intelligent terminals. Smart terminals are assigned to a single common pilot directory number (PDN) in addition to their individual directory numbers. When the G-MSC receives a call addressed to the PDN, the G-MSC sends a routing request message to the HLR. The HLR sends a short message service (SMS) data transmission to each of the plurality of smart terminals assigned to the PDN by notifying the associated mobile subscribers of an incoming call from an extension telephone. Mobile subscribers who wish to accept the call use their smart terminals to send a replying SMS message back to the HLR. Upon receiving a response by accepting the call from one or more notified smart terminals, the HLR selectively reports the temporary location directory number (TLDN) of a smart terminal responding to the G-MSC. The G-MSC then routes the incoming call to the selected responding smart terminal.