Abstract:
A method and system is disclosed for facilitating voice mailbox operations for a mobile phone capable of operating in both a CDMA and a GSM environment. The system has at least first and second switching points and a global switching point in communication with a control point. Upon a first switching point detecting a busy/no answer condition for a request to terminate a call to a called station (the call originating from a calling station), the first switching point forwards the terminating call to a temporary, unique forward-to number belonging to the global switching point which then sends at least one message to the control point, the at least one message identifying the unique forward-to number designating a voice mailbox. The control point then identifies the second switching point from the unique forward-to number and sends a first call treatment message instructing the second switching point to apply voicemail treatment at a voice mailbox linked thereto.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to telecommunication networks and, more particularly, to a method and system for directing a CDMA service subscriber&#39;s call to voice mail while roaming in a GSM service area.  
       BACKGROUND OF THE INVENTION  
       [0002]     In traditional call processing for cellular CDMA networks, incoming calls from a mobile handset or landline telephone are routed through the network to the home network of the called subscriber. Calls to the particular subscriber subject to call forwarding are typically rerouted by the subscriber&#39;s home mobile switching center (subscriber home MSC) to an alternate, forward-to telephone number (e.g., Voicemail).  
         [0003]     Different types of call forwarding are commonly available. In a call forwarding—busy (CFB) feature, calls are forwarded to the forward-to number only if the called subscriber&#39;s handset is busy. In a call forwarding—no answer (CFNA) feature, calls are forwarded to the forward-to number only if the called subscriber&#39;s handset is not busy but nonetheless does not answer. With CFB and CFNA features, the Subscriber Home MSC forwards the call to the forward-to number typically only after an unsuccessful attempt to terminate the call to the called subscriber&#39; handset.  
         [0004]     CDMA MSCs utilize routing methods such as steering digits or Message Retrieval Service (MRS) indices for providing voice mail delivery. Common to all voice mail delivery methods, the home MSC receives the status of the current call (i.e., busy, no reply, no answer), polls the home location register (HLR) for call treatment and routes the call to the subscriber&#39;s voice mail box.  
         [0005]     The above described prior art method of voice mail routing suffers from numerous deficiencies when a subscriber is roaming in a global system for mobile communications (GSM) environment making it undesirable from various standpoints. Since the GSM serving MSCs are not configured to send the call back to the subscriber&#39;s home CDMA MSC the home MSC cannot apply treatment as discussed above. Furthermore, if a GSM serving MSC was able to forward the call back to the home MSC further complications would follow. Namely, since there would be no way to associate the incoming call from the GSM MSC with the original call, it would appear to the home MSC as a new incoming call. As such, the home MSC could potentially forward it back to the GSM MSC creating a loop condition or, possibly, not treat the call at all.  
         [0006]     One solution has been to use a dedicated, “global” voice mail platform for all global phone subscribers and call routing can be provided to the global platform through a dedicated voice mail access number or voice mail open trees number. This solution commonly relies on the charge number parameter, in the ISUP Initial Address Message (IAM), to provide proper voice mail box identification. However, using the charge number to provide proper voice mail box identification has several drawbacks making it an undesirable solution for providing voicemail access. For example, when a cellular subscriber is roaming internationally this charge number parameter is not available, requiring the caller to re-enter the mobile directory number (MDN) to deposit or retrieve voicemail messages, thus creating an unnecessary burden on the caller.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention provides significant improvements in voice mailbox operations for a CDMA service subscriber roaming in a GSM service area and overcomes the disadvantages described above by leveraging the current redirect request (RedReq) methodology utilized for roaming CDMA subscribers to enable the home MSC to route undeliverable calls (e.g., calls with a call status of busy, no answer or not reachable) to the subscribers voice mail platform.  
         [0008]     A method and system is disclosed for facilitating voice mailbox operations for a mobile phone capable of operating in both a CDMA and a GSM environment. The system has at least first and second switching points and a global switching point in communication with a control point. In accordance with the present invention, upon a first switching point detecting a busy/no answer condition for a request to terminate a call to a called station (the call originating from a calling station), the first switching point forwards the terminating call to a temporary unique forward-to number belonging to the global switching point which then sends at least one message to said control point, the at least one message identifying the unique forward-to number designating a voice mailbox. The control point then identifies the second switching point from the unique forward-to number and sends a first call treatment message instructing the second switching point to apply voicemail treatment at a voice mailbox linked thereto.  
         [0009]     The method and system removes all call routing to the global voicemail platform rendering this platform obsolete for all CDMA service subscribers roaming in a GSM service area since the subscriber&#39;s existing voicemail platform off of their home MSC will remain in use. Since cellular subscribers may each have a different home MSC, this arrangement also cuts down on routing costs when the subscriber is roaming domestically because undeliverable calls need not be routed to a single dedicated voicemail platform as discussed above but rather can be forwarded directly to the subscribers home voicemail platform. Additionally, by using a unique forward-to number to identify a voicemail box as opposed to the charge number the need for re-entry of the called party&#39;s MDN when the called party is roaming in a GSM environment is eliminated.  
         [0010]     These and further aspects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a block diagram of a prior art telecommunication system;  
         [0012]      FIG. 2  is a block diagram of a telecommunication system in accordance with an illustrative embodiment of the present invention;  
         [0013]      FIG. 3  is a call flow diagram in accordance with the prior art telecommunication system of  FIG. 1 ; and  
         [0014]      FIGS. 4-5  are call flow diagrams in accordance with an illustrative embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0015]     The present invention described herein includes a method and system for facilitating voice mailbox operations for a mobile phone that is capable of operating in both a CDMA and GSM environment.  
         [0016]     Referring to  FIG. 1 , a block diagram for a telecommunications system  10  is shown which depicts a prior art arrangement for facilitating voice mailbox operations for a CDMA service subscriber roaming in a GSM service area. Dashed lines indicate connections that carry primarily signaling traffic and solid lines indicate connections that carry primarily bearer traffic, such as voice, data, or other media.  
         [0017]     Telecommunications system  10  includes mobile switching centers (MSCs)  12 ,  14  and  16  connected to a public switched telephone network (PSTN)  18 . MSCs  12  and  14  are connected to base transceiver stations (BTSs), such as BTS  20  and  22 , respectively. As understood by one skilled in the art, MSC  16  may also connect to one or more BTSs. BTSs  20  and  22  communicate over an air interface with one or more wireless devices, such as mobile handsets  24  and  26 , to provide wireless telecommunications within a wireless coverage area. The communication between BTS  20 ,  22  and respective mobile handsets  24 ,  26  may occur in a digital format, such as CDMA, TDMA, GSM, or 802.11x, or it may occur in an analog format, such as AMPS. In some salient arrangements, MSC  12  may be connected to BTS  20  via a base station controller and/or other networks or systems.  
         [0018]     Mobile handsets  24 ,  26  are each associated with a home MSC and have a mobile directory number (MDN) that corresponds to a directory number allocated to the mobile handset&#39;s home MSC. Such mobile handsets are typically able to operate in the wireless coverage areas served by their home MSCs, and they are also typically able to “roam,” i.e., to operate in wireless coverage areas served by MSCs other than their home MSCs. In the examples described herein, mobile handset  26  has MSC  12  as its home MSC and is roaming in a GSM serving area serviced by MSC  14  (serving MSC). Mobile handset  24  may, although not necessary to the spirit of the present invention, also have MSC  12  as its home MSC.  
         [0019]     MSCs  12 ,  14  preferably use the advanced intelligent network (AIN) approach of having much of the signaling and call processing logic provisioned in a central service control point (SCP)  28 , such as a Syniverse™ Uniroam platform, rather than in the switch itself. SCP  28  is a centralized signaling point providing signaling interoperability for international roaming. Specifically, SCP  28  is an ANSI-41 call processor that provides translation of international roaming protocols and interoperability among the various revisions of the TIA/EIA ANSI-41 signaling family. SCP  28  enables wireless operators to use one signaling point instead of directly routing to hundreds of switches and networks around the world and enables network elements in one country to route messages to other countries without the need for indirect routing in the home or serving network.  
         [0020]     As described above, the AIN approach allows a wireless user to make and receive phone calls while roaming in areas outside the user&#39;s home network. Referring to  FIG. 1 , MSC  12  exchanges messages with SCP  28  in accordance with the specification TIA/EIA ANSI-41 signaling protocol which is incorporated herein by reference. Other signaling protocols could also be used. MSC  12  also exchanges messages with home location register (HLR)  30 , which signaling may conform to IS-41 specifications. A recent revision of the IS-41 specifications, ANSI/TIA/EIA-41-D-97, published in December 1997, is incorporated herein by reference.  
         [0021]     SCP  28  has access to data records stored in data platform  32 . Data platform  32  stores the pooled temporary assigned local directory numbers (PTLDNs) and home MDN information and enables mapping necessary for call delivery, validation and billing. Data platform  32  can be external to SCP  28 , or it may be wholly or partially internal to SCP  28  and may include volatile and/or non-volatile data storage.  
         [0022]     During call processing, when call delivery is attempted to a subscriber roaming in a GSM environment, MSCs  12  and  14  signal/communicate with SCP  28 . Referring to  FIG. 3 , one example of messaging between switching points according the prior art arrangement of  FIG. 1  is shown. The roaming subscriber handset  26  goes through a registration process at steps  308  whereby SCP  28  selects the dedicated voicemail routing number to act as a forward-to number in the event a call forwarding—busy (CFB) or call forwarding—no answer (CFNA) indicator is activated. An UPDATE LOCATION AREA containing the handset&#39;s IMSI is sent from serving MSC  14  to the SCP  28  (step  300 ). The UPDATE LOCATION AREA can be translated through a REGNOT. At step  302  the UPDATE LOCATION AREA is transferred to a REGNOT and the REGNOT is forwarded by SCP  28  to HLR  30 . Upon reception of a REGNOT, HLR  30  sends a registration return result (regnot) to SCP  28  at step  304 . SCP  28  has to translate the regnot into an update location return result to the serving switch  14 . After the update location return result is forwarded to the serving switch  14  at step  306 , SCP  28  will change the calling feature indicators for CFB and CFNA to authorized and activated with the dedicated voicemail routing number and INSERT SUBSCRIBER DATA and locreq messages.  
         [0023]     At some time after registration a call comes into the subscriber&#39;s home MSC  12  (step  310 ) in response to which MSC  12  sends a location request (LOCREQ) to the subscriber&#39;s HLR  30  at step  312 . HLR  30  then sends a route request (ROUTREQ) to SCP  28  at step  314 . SCP  28  sends a PROVIDE ROAMING NUMBER to the serving switch  14  (step  316 ) and then the serving switch  14  sends a TLDN in a provide roaming number return result message to SCP  28  (step  318 ). The SCP  28  then sends a routreq response message at step  320 , including the TLDN, to HLR  30  instructing MSC  12  on how to process the call. Signaling between MSC  12  and SCP  28  may also be routed through one or more signal transfer points (not shown).  
         [0024]     MSC  12  then attempts to connect the call through serving MSC  14  (step  324 ). If a busy or no answer condition is encountered at the handset, the serving MSC  14  will forward the call to global MSC  16  (step  326 ) for treatment by global voicemail platform  34 . Referring to  FIG. 1 , global voicemail platform  34  is a dedicated voicemail platform for all global phone subscribers. This can result in increased routing, requiring the serving MSC  14  to route the call between several intermediate MSCs.  
         [0025]      FIG. 2  is a block diagram for a telecommunications system  50  which depicts an improved exemplary arrangement for facilitating voice mailbox operations for a CDMA service subscriber roaming in a GSM service area in accordance with the present invention.  FIG. 4  illustrates the flow of messaging traffic for system  50 . Referring now to  FIG. 2 , unlike the prior art arrangement discussed above which included a dedicated voicemail platform  34  for all global phone subscribers, here, the serving MSC  14  can re-direct calls to home MSC  12  for voicemail treatment by the home voicemail platform  36 , rendering global voicemail platform  34  of  FIG. 1  obsolete. Additionally, whereas communication between MSC  16  and SCP  28  in the prior art arrangement was unnecessary to call-forwarding operations, here, such communication advantageously allows SCP  28  to populate the call forwarding treatment upon an incoming call. As described in greater detail below, upon encountering a busy/no answer condition at the serving MSC  14 , the serving MSC  14  forwards the PTLDN via an IAM message to MSC  16  which will re-direct the call to home MSC  12  to initiate voicemail treatment.  
         [0026]     When handset  26  roams in a GSM environment, upon encountering an incoming call for the subscriber  26 , SCP  28  populates a PTLDN for use when CFNA or CFB indicators are activated/triggered. Referring to  FIG. 2 , any redirected calls are processed by the system as follows: a call is routed to serving MSC  14  for delivery to subscriber handset  26 ; if a busy/no answer condition occurs, serving MSC  14  sends an IAM containing a PTLDN to MSC  16 ; MSC  16  receives the IAM and sends a LOCREQ to SCP  28 , SCP  28  maps the PTLDN in the LOCREQ, to a corresponding MIN/ESN/BID and it sends a REDREQ (with the MIN/ESN/BID) to the subscriber&#39;s home MSC  12 ; interaction between MSC  12  and HLR  30  in regards to a treatment for the REDREQ (containing busy or no answer status) results in steering digits or MRS index being sent back to the MSC  12 ; and the home MSC  12  routes the call to the subscriber&#39;s home voicemail platform  36 .  
         [0027]     Referring to  FIG. 4 , the flow of messaging traffic for the above outlined system is illustrated in greater detail. Several of the below steps have been discussed above with reference to  FIG. 2  and are now repeated with respect to specific messaging between the various system components. Unlike the prior art solution shown in  FIG. 3 , where the Dedicated VM number is assigned upon registration, here, the PTLDN is assigned during an incoming call. Otherwise, registration proceeds as discussed above. During an incoming call after registration, SCP  28  selects a PTLDN to represent a call forwarding (forward-to) number in the event of a CFB or CFNA condition occurs and sets the PTLDN at the serving MSC  14  via an insert subscriber data message.  
         [0028]     After registration, the system proceeds as follows: a call placed on handset  24  (step  410 ) comes into home MSC  12 ; a location request (LOCREQ) is sent from MSC  12  to HLR  30  (step  412 ); HLR  30  sends a ROUTREQ to SCP  28  to obtain a TLDN and to set call forwarding parameters (step  414 ); SCP  28  sends a PROVIDE ROAMING NUMBER to the serving switch  14  (step  416 ); MSC serving switch  14  sends a provide roaming number return result with a TLDN (step  418 ); the SCP  28  accesses data records stored in data platform  32  to secure a PTLDN (steps  420 ); the SCP  28  sends an INSERT SUBSCRIBER DATA message to assign the pooled TLDN for CFB/CFNA (step  422 ); a routreq return results with a TLDN used to deliver the call (step  426 ); HLR  30  sends a locreq to home MSC  12  (step  428 ) and the call is delivered to the serving MSC  14  via the TLDN at step  430 ; upon a busy/no answer condition at serving MSC  14 , serving MSC  14  attempts to call forward by sending an IAM to the global MSC  16  by sending an IAM including the PTLDN to global MSC  16  (step  432 ) which in turn prompts MSC  16  to send a LOCREQ including the PTLDN to SCP  28  (step  434 ); at step  436  SCP  28  sends a REDREQ message to home MSC  12 ; MSC  12  sends a TRANNUMREQ request to HLR  30  (not shown); trannumreq is returned to MSC  12  with voicemail treatment (not shown); and home MSC  12  sends call to voicemail (not shown) and at the same time tears down the call leg to the TLDN established at step  430  (not shown). MSC  12  sends a redreq to the SCP  28  (step  438 ); and the SCP  28  sends a locreq to the Global MSC  16  (step  440 ).  
         [0029]     Two of the above discussed steps need to occur at the SCP  28  to enable SCP  28  to instruct the home MSC to redirect the call: the unique forward-to number (the PTLDN) for each incoming call is defined at the SCP  28  (step  420 ) and a LOCREQ for the PTLDN call is received from MSC  16  by the SCP  28  (step  434 ). The SCP also retains the PC_SSN (point code subsystem number) received in the ROUTREQ so that if the call encounters a busy condition the SCP will have the information necessary to route a request to MSC  12  to be redirected. Without a unique PTLDN assigned for the incoming call and associated MIN/ESN/BID, SCP  28  will not be able to request the home MSC  12  to redirect the call because it will not know where to send the REDREQ. Since SCP  28  handles all global calls and is capable of assigning the forward-to number, when it receives a LOCREQ from MSC  16  at step  434  it will have the mapping information (the pre-specified PTLDN for a given MDN) required to send a REDREQ to the home MSC  12  that services the MIN/ESN/BID. Thus, the voicemail PTLDN contained in the LAM sent from serving MSC  14  through the LOCREQ at MSC  16  acts as a trigger telling SCP  28  to send a REDREQ to home MSC  12 . For example, when SCP  28  receives the LOCREQ (containing a PTLDN) in step  434  it maps that PTLDN to the subscriber&#39;s MIN/ESN/BID and launches a REDREQ to the subscriber&#39;s home MSC  12 . Since, the PTLDN range can be completely contained at one of the network switches such as MSC  16 , or any other switch in the network, SCP  28  will not require voice trunking capabilities.  
         [0030]     Unlike the prior-art telecommunications system  10  which routes CFB and CFNA events through PSTN  18  to a dedicated global voicemail platform  34 , when a Busy/No Answer condition occurs in telecommunications system  50 , the serving MSC  14  routes the call to SCP  28  via MSC  16  since the forward-to number (PTLDN) “belongs” to the SCP. This is accomplished by sending an IAM containing the PTLDN to MSC  16 , which in turn sends a LOCREQ to SCP  28 . Since SCP  28  is capable of mapping a subscriber&#39;s MIN/ESN/BID to the TLDN, when SCP  28  receives the IAM it is able to generate a REDREQ to the Subscriber&#39;s MIN/ESN/BID including a reason why access was denied (e.g., busy/no answer). When the Subscriber&#39;s home MSC  12  receives the REDREQ (with access reason denied), it can provide proper treatment (as it customarily would for domestically roaming subscribers) by routing the call to the subscriber&#39;s home voicemail system based on a trannureq from HLR  30 .  
         [0031]     Accordingly, since the call is not physically routed to home MSC  12 , SCP  28  does not need voice trunking or switching capabilities. The call is “routed” back to the Home MSC via signaling messages, the IAM to the MSC  16 , the LOCREQ to SCP  28 , and the REDREQ to the home MSC  12 . Such a process is facilitated by building the translations or triggers at MSC  16  and SCP  28  to send their corresponding messages when they receive a message from the previous party. The call from home MSC  12  to serving MSC  14  (step  420 ) is torn down and is not routed back to the home MSC  12  because it is already there. Thus, to the serving MSC  14  no call is charged because the call appears as no answer and disconnected from the originating home MSC  12 . The SCP is preferably capable of sending a REDREQ to home MSC  12  for the above discussed benefits to be realized.  
         [0032]     An example of an implementation of the above system is as follows. At some time after registration a call comes into the subscriber&#39;s home MSC  12  in response to which MSC  12  sends a LOCREQ to the subscriber&#39;s HLR  30  at step  412 . HLR  30  then sends a ROUTREQ with a set of relevant parameters, i.e., with MIN/ESN/BID, to SCP  28  at step  414 . SCP  28  sends a PROVIDE ROAMING NUMBER to the serving switch  14  (step  416 ). MSC serving switch  14  sends a provide roaming number return result with a TLDN accesses data records stored in data platform  32  to secure a PTLDN (steps  418 ). The SCP  28  sends an INSERT SUBSCRIBER DATA message to assign the pooled TLDN for CFB/CFNA (step  422 ). Next, SCP  28  requests data platform  32  to assign the PLTDN. Then data platform  32  checks the PTLDN table for a currently “in use” entry, most likely from a previous call, associated with the MIN/ESN specified in the ROUTREQ, and if no match is found, data platform looks in the table for a free or expired PTLDN. If a PTLDN is free, data platform  32  assigns it to the MIN/ESN for a configurable interval, or if a PTLDN is expired (no longer in use) data platform  32  deactivates it from the current MIN/ESN and reassigns it to the new MIN/ESN for a configurable interval. Reassignment of PTLDNs is discussed later in greater detail with reference to  FIG. 5 . Continuing with  FIG. 4 , the SCP  28  instructs the data platform  32  to assign a PTLDN. Referring to step  420 , data platform  32  sends a PTLDN back to SCP  28  and SCP  28  sets the calling feature indicators for CFB and CFNA to authorized. With CFB and CFNA set, SCP  28  sends a INSERT SUBSCRIBER DATA to MSC  14  to and SCP  28  responds to each invoke request of data platform  32  with the assigned PTLDN. Finally, at step  426 , SCP  28  sends the routreq with the TLDN (different than the PTLDN) to HLR  30  of the subscriber&#39;s home MSC  12 .  
         [0033]     With call forwarding setup, when MSC  12  receives the TLDN (different than PTLDN) at step  428  it attempts to the complete the call to the serving MSC  14  through the PSTN and waits for either answer supervision or for an incoming IS 41  message such as a REDREQ. Thus, the home MSC  12  is still in the process of call delivery. If a busy or no answer condition is encountered the serving MSC  14  call forwards the call and sends an IAM to global MSC  16  at step  432 . MSC  16  is a conventional mobile switching center and any MSC, including the subscriber&#39;s home MSC  12 , can act in place of MSC  16 . MSC  16  then sends a location request (LOCREQ message) with the PTLDN to SCP  28 . As discussed above the LOCREQ received by SCP  28  for the transfer attempt acts as a trigger for SCP  28  to send a REDREQ to home MSC  12  (CDMA environment). Specifically, SCP  28  uses the PTLDN in the invoke to look-up the MIN/ESN that was assigned the PTLDN and sends a REDREQ message to the subscriber&#39;s home MSC  12  including the identified MIN/ESN and a redirection reason parameter set to busy. When MSC  12  receives the REDREQ it will essentially treat is as exactly as it would if the request came from a domestically roaming subscriber roaming in a CDMA environment because that is normally how calls are handled by a MSC when it receives a REDREQ while the call delivery attempt is still in progress. SCP  28  knows to send the REDREQ to MSC  12  when it receives the LOCREQ from the serving MSC  14  to transfer the call. Thus, as long as SCP  28  has a means to know when to send the REDREQ to the home MSC  12  while the call delivery attempt (from the home MSC&#39;s  12  perspective) is still in progress, the call will transfer using the home MSC  12  translations and subscriber profile. From the home MSC&#39;s  12  perspective, this will essentially look transparent and no different than if handset  26  was roaming locally in a CDMA environment. Additionally, the billing ID in the REDREQ will be the billing ID from the last ROUTREQ successfully processed by SCP  28 . This is applicable for a two or more incoming calls scenario and for CFB treatment for the last call received.  
         [0034]     While  FIG. 2  shows only MSCs  12 ,  14  and  16  in communication with SCP  28 , in general SCP  28  may communicate with a plurality of network MSCs. SCP  28  essentially appears as another roaming MSC&#39; to the other MSCs. Also, PSTN  18  may be connected to other switching points that do not signal to SCP  28 , i.e., MSC  16  discussed with respect to the prior art arrangement of  FIG. 1 . Instead, such switching points may exchange messages with a different control point, or they may not use the intelligent network approach for call processing at all.  
         [0035]      FIG. 5  illustrates the steps for reassigning expired PTLDNs. Discussion of steps  500 - 508  has been eliminated as these steps proceed essentially the same as steps  400 - 408  discussed above. Turning to step  512 , a LOCREQ containing a called number is sent from home MSC  12  to HLR  30 . Next, at step  514 , a ROUTREQ with a new MIN/ESN is sent from HLR  30  to SCP  28 . In this instance SCP  28  checks the data platform  32  and finds that all PTLDNs are in use but that one or more entries have expired. The expired PTLDN can then be assigned to the new MIN/ESN and call processing continues as in  FIG. 4  discussed above.  
         [0036]     One skilled in the art will appreciate that the present invention is not limited to use with CDMA and GSM systems. Rather, it is understood that the present invention is applicable to any combination of wireless telecommunications systems where a Redirection Request or corresponding functionality is not sent from a serving MSC to a home MSC to instruct the home MSC to redirect the call. Thus, for example, the above described method and system is applicable to a situation involving any ANSI  41  standard switch and any ITU based switch.