Patent Abstract:
In order to prevent a mobile terminated (MT) call to a user equipment (UE) from being lost by addressing a Location Area/Tracking Area (LA/TA) mismatch problem that could occur during a circuit switched (CS) Fallback, the method comprises the steps of: receiving a paging message from a mobility management entity, MME, where the paging message identifies suitable location areas, the paging message is sent because a first mobile switching center, MSC 1 , received a MT call request for the UE; determining that there are no 2G/3G cells belonging to the suitable location areas based on a current location of the UE; identifying a target 2G/3G cell in a location area associated with the current location of the UE but not part of the 2G/3G cells belonging to the suitable location areas; and enabling a signaling connection to be established between the UE and the first MSC 1  via a second mobile switching center, MSC 2 , where the second MSC 2  interfaces with a base station controller, BSC 2 , or a radio network controller, RNC 2 , that manages the target 2G/3G cell, where the signaling connection allows the MT call to be established with the UE.

Full Description:
This application claims the benefit of U.S. Provisional Application No. 61/025,224, filed Jan. 31, 2008, the disclosure of which is fully incorporated herein by reference. 
     CLAIM BENEFIT OF PRIOR FILED U.S. APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/025,224 entitled “CS Fallback for MT Calls: Solutions to the LA/TA Mismatch Problem” which was filed on Jan. 31, 2008, the contents of which are hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention is related to a node and method for preventing a mobile terminated (MT) call to a user equipment (UE) from being lost. More specifically, the present invention is related to a node (e.g., enhanced eNodeB) and method (e.g., implemented by enhanced eNodeB) for preventing a MT call from being lost due to a Location Area/Tracking Area (LA/TA) mismatch problem that could occur during a circuit switched (CS) Fallback when the UE transitions from a SAE/LTE network to a GSM or UMTS network as a result of being notified of that MT call. 
     BACKGROUND 
     The following terms and abbreviations are herewith defined, at least some of which are referred to within the following description of the prior art and the present invention. It should be noted that the reference to the “present invention” or “invention” used herein relates to exemplary embodiments and not necessarily to every embodiment encompassed by the appended claims. 
     ACK Acknowledge 
     BSC Base Station Controller 
     BSSAP Base Station Subsystem Application Part 
     eNodeB E-UTRAN NodeB 
     EPS Evolved Packet System 
     E-UTRAN Evolved-UTRAN 
     GERAN GSM/EDGE Radio Access Network 
     G-MSC Gateway MSC 
     GSM Global System for Mobile Communication 
     HSS Home Subscriber Server 
     HLR Home Location Register 
     IAM Initial Address Message 
     IMSI International Mobile Subscriber Identity 
     ID-HO Inter-Domain Handover 
     LTE Long Term Evolution 
     MAP Mobile Application Part 
     MSC Mobile Switching Center 
     MME Mobility Management Entity 
     PS Packet Switched 
     RNC Radio Network Controller 
     SABM Set Asynchronous Balanced Mode 
     SAE System Architecture Evolution 
     SGSN Serving GPRS Support Node 
     SRI Send Routing Information 
     TA Tracking Area 
     UE User Equipment 
     UMTS Universal Mobile Telecommunications System 
     UTRAN UMTS Terrestrial Radio Access Network 
     VLR Visitor Location Register 
     WCDMA Wideband Code-Division Multiple Access 
     Referring to  FIG. 1  (PRIOR ART), there is a diagram of an exemplary mobile telecommunications network  100  illustrating a reference architecture associated with CS Fallback which is related to the present discussion. The exemplary mobile telecommunications network  100  includes a SAE/LTE network  100   a  and a GSM network  100   b  (or UMTS network) which are described in detail in 3GPP TS 23.002 v.8.2.0 dated December 2007 and 3GPP TS 23.401 v.8.0.0 dated December 2007 (the contents of these documents are incorporated by reference herein). As such, those skilled in the art are familiar with the architecture and functionality of this exemplary mobile packet telecommunications network  100 . Thus, for clarity only components such as the UE, MME, SGSN and MSC server and interfaces such as the SGs which are relevant to the present discussion are discussed in detail herein while the other well known components or entities like the E-UTRAN, UTRAN, GERAN and the interfaces S1-MME, LTE-Uu, Um, Gb, Uu, S3, IuPS, A, and IuCS are not discussed within this document. The SGs is based on the Gs interface procedures and is the reference point located between the MME and the MSC server. The SGs reference point is used for mobility management and paging procedures between the EPS and CS domains which are discussed in detail below with respect to  FIGS. 2-5  (PRIOR ART). Referring to  FIG. 2 , there is a diagram used to illustrate one example of how the SAE/LTE network  100   a  and the GSM network  100   b  may provide overlapping coverage in one location. In this example, UE 1  is attached to the SAE/LTE network  100   a  in LTE cell e 3  which belongs to Tracking Area  1 , TA 1 , and is controlled by eNodeB 1   a  which is connected to MME 1 . The GSM network  100   b  also provides GSM coverage for the UE 1  in the same location (as shown by the dashed lines  200   a  and  200   b ). In this case, the GSM coverage is provided by GSM cell c 3  which belongs to Location Area  1 , LA 1 , and is controlled by the BSC 1   a  which is connected to MSC 1 /VLR 1  and SGSN 1 . In this particular example, there is almost a one-to-one relationship between the GSM network&#39;s LAs and the SAE/LTE network&#39;s TAs (e.g. LA 1  and TA 1  provide coverage in the same area). Alternatively, the SAE/LTE network  100   a  and a UMTS network may also provide overlapping coverage in one geographical location. In this alternative case, the GSM network&#39;s BSCs would be replaced by a UMTS network&#39;s RNCs. Referring to  FIG. 3  (PRIOR ART), there is a signal flow diagram that shows an example of how UE 1  would perform a SAE/LTE Attach to become attached for the PS domain and a CS Attach to become attached for the CS domain based on the situation shown in  FIG. 2 . The steps are as follows: 
     1. UE 1  is located in LTE cell e 3  and performs a SAE attach (see  FIG. 2 ). 
     2. UE 1  sends an attach message with a CS Fallback indicator to MME-1. 
     3. MME-1 initiates the SAE attach per 3GPP TS 23.401 which involves UE 1 , eNodeB 1   a , MME 1  and HSS. 
     4. MME 1  decides that the UE 1  is to be CS attached in MSC 1 /VLR 1 . 
     5. MME 1  sends a location update message to MSC 1 /VLR 1 . 
     6. MSC 1 /VLR 1  and HSS perform a normal location update. 
     7. MSC 1 /VLR 1  sends a location update accept message to MME 1 . 
     8. MME 1  sends an attach accept message to UE 1 . 
     Referring to  FIG. 4  (PRIOR ART), there is a signal flow diagram that shows an example of how the CS Fallback can be performed for a MT call in the case where there is no LA/TA mismatch problem. The steps are as follows: 
     1. UE 1  is SAE/LTE attached and CS attached in MSC 1 /VLR 1  as shown in  FIG. 3 . 
     2. UE 1  is still located in LTE cell e 3 . 
     3. G-MSC receives an IAM (MT call request). 
     4. G-MSC initiates a normal SRI procedure with MSC 1 /VLR 1 . 
     5. G-MSC sends the IAM to MSC 1 /VLR 1 . 
     6. MSC 1 /VLR 1  sends a page message (with suitable LAs) to MME 1 . 
     7. MME 1  sends the page message (with suitable LAs) to eNodeB 1   a  which then interfaces with UE 1 . 
     8. eNodeB 1   a  finds out that the best GSM cell belonging to the suitable LAs (associated with the page message) based on the current location of UE 1  is c 3 . For instance, the eNodeB 1   a  could make this determination based on measurement reports received from UE 1  i.e. indicating how well UE 1  “hears” the GSM cells. Another option could be to configure the eNodeB 1   a  such that it knows an E-UTRAN/LTE cell is totally covered by a specific GSM/WCDMA cell.
 
9. eNodeB 1   a  triggers an Inter-Domain Handover procedure towards the GSM cell c 3  to initiate the CS Fallback procedure.
 
10. eNodeB 1   a  sends a relocation request message (with target cell=c 3 ) to MME 1 .
 
11. MME 1  sends the forward relocation request message (with target cell=c 3 ) to SGSN 1 .
 
12. SGSN 1  sends a PS handover request message (with target cell=c 3 ) to BSC 1   a.  
 
13. BSC 1   a  allocates PS domain resources and CS domain resources in target cell c 3 .
 
14. BSC 1   a  sends a PS handover request acknowledge message (“ID HO command message”) to SGSN 1 .
 
15. SGSN 1  sends a forward relocation response message to MME 1 .
 
16. MME 1  sends a relocation command to eNodeB 1   a.  
 
17. eNodeB 1   a  sends a handover from eUTRAN command to UE 1 .
 
18. UE 1  initiates GERAN A/Gb Access Procedures with BSC 1   a  using the allocated PS domain resources.
 
19. UE 1  sends a SABM (paging response message) to BSC 1   a  using the allocated CS domain resources.
 
20. BSC 1   a  forwards the paging response message to MSC 1 /VLR 1 . Note: steps  10 - 20  are a normal ID HO.
 
21. MSC 1 /VLR 1  initiates the MT call setup with UE 1 .
 
       FIG. 5  (PRIOR ART) is a diagram used to help describe the LA/TA mismatch problem related to CS Fallback for Mobile Terminated calls. In this case, the GSM LAs and the SAE/LTE TAs are not fully coordinated (i.e. there is no 1-to-1 relationship between the cells). Two different locations for different points in time are shown for UE 1 . The “UE 1 -attach” indicates the location at the time when the UE 1  performed the SAE/LTE Attach in LTE cell e 3  and became also CS Attached to MSC 1 /VLR 1  based on the sequence and principles shown in  FIG. 3 . The “UE 1 -later” shows the location of the UE 1  later when it has moved (while in LTE Idle mode) to the LTE cell e 1 . As LTE cells e 3 , e 2  and e 1  belong to the same TA 1 , after and during moving to LTE cell e 1 , UE 1  does not perform any mobility related signaling towards the SAE/LTE network  100   a  and the UE 1  therefore remains CS Attached in MSC 1 /VLR 1  (i.e. it does not become CS attached in MSC 2 /VLR 2 ). The LA/TA mismatch becomes a problem in this particular case. If there is a MT call arriving at MSC 1 /VLR 1  (as shown in step  5  of  FIG. 4 ) for UE 1  at the “UE-later” location, then there is no GSM cell in the current location of UE 1  that is connected to MSC 1 /VLR 1 . Instead, GSM Cell c 31  is connected to MSC 2 /VLR 2 . This means that the CS Fallback procedure in  FIG. 4  is not sufficient in this case. In particular, if the CS Fallback procedure where to be performed as shown in  FIG. 4 , then UE 1  would experience ID HO to GSM Cell c 31  and the paging response message would be sent to BSC 2  and MSC 2 /VLR 2 . But since MSC 1 /VLR 1  holds the MT call request, there is no way for the MT call to succeed in this situation because MSC 2 /VLR 2  will receive the paging response message and has no way of knowing how to relay the paging response message to MSC 1 /VLR 1  (i.e. there is a mismatch between the MSC receiving the MT call request and the MSC receiving the paging response message). Thus, there has been a need to address this problem and other problems which are associated with the existing CS Fallback procedures. This particular need and other needs have been addressed by the present invention. 
     SUMMARY 
     In one aspect, the present invention provides a node (e.g. enhanced eNodeB) that addresses the LA/TA mismatch problem which could occur during a CS Fallback for a Mobile Terminated call. In one embodiment, the node (enhanced eNodeB) includes a processor and a memory that stores processor-executable instructions where the processor interfaces with the memory and executes the processor-executable instructions to: (a) receive a paging message from a mobility management entity, MME, where the paging message identifies suitable location areas, the paging message is sent because a first mobile switching center, MSC 1 , received a MT call request for the UE; (b) determine that there are no 2G/3G cells belonging to the indicated suitable location areas based on the current location of the UE; (c) identify a target 2G/3G cell in a location area associated with the current location of the UE but not part of the 2G/3G cells belonging to the indicated suitable location areas (i.e. a cell controlled by MSC 2 /BSC 2  is identified); and (d) enable a signaling connection to be established between the UE and the first MSC 1  via a second mobile switching center, MSC 2 , where the second MSC 2  interfaces with a base station controller, BSC 2 , or a radio network controller, RNC 2 , that manages the target 2G/3G cell, where the signaling connection allows the MT call to be established with the UE. In this way, the node effectively prevents the MT call to the UE from being lost. 
     In another aspect, the present invention provides a method that addresses the LA/TA mismatch problem which could occur during a CS Fallback for a Mobile Terminated call. In one embodiment, the method includes the steps of: (a) receiving a paging message from a mobility management entity, MME, where the paging message identifies suitable location areas, the paging message is sent because a first mobile switching center, MSC 1 , received a MT call request for the UE; (b) determining that there are no 2G/3G cells belonging to the indicated suitable location areas based on a current location of the UE; (c) identifying a target 2G/3G cell in a location area associated with the current location of the UE but not part of the 2G/3G cells belonging to the indicated suitable location areas (i.e. a cell controlled by MSC 2 /BSC 2  is identified); and (d) enabling a signaling connection to be established between the UE and the first MSC 1  via a second mobile switching center, MSC 2 , where the second MSC 2  interfaces with a base station controller, BSC 2 , or a radio network controller, RNC 2 , that manages the target 2G/3G cell, where the signaling connection allows the MT call to be established with the UE. In this way, the method effectively prevents the MT call to the UE from being lost. 
     Additional aspects of the invention will be set forth, in part, in the detailed description, figures and any claims which follow, and in part will be derived from the detailed description, or can be learned by practice of the invention. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention may be obtained by reference to the following detailed description when taken in conjunction with the accompanying drawings: 
         FIG. 1  (PRIOR ART) is a diagram of a mobile telecommunications network (including a SAE/LTE network and a GSM network) which has a reference architecture associated with CS Fallback in accordance with the standards 3GPP TS 23.002 and 3GPP TS 23.401; 
         FIG. 2  (PRIOR ART) is a diagram used to illustrate one example of how the SAE/LTE network and the GSM network shown in  FIG. 1  may provide overlapping coverage in one location; 
         FIG. 3  (PRIOR ART) is a signal flow diagram that shows an example of how a UE would perform a SAE/LTE Attach to become attached for the PS domain and a CS Attach to become attached for the CS domain based on the situation that is shown in  FIG. 2 ; 
         FIG. 4  (PRIOR ART) is a signal flow diagram that shows an example of how the CS Fallback can be performed for a Mobile Terminated call in the case where there is no LA/TA mismatch problem; 
         FIG. 5  (PRIOR ART) is a diagram which is used to describe the LA/TA mismatch problem related to CS Fallback for Mobile Terminated calls which is solved by the present invention; 
         FIG. 6  is a signal flow diagram which is used to describe how an enhanced node (enhanced eNodeB) and a method solve the LA/TA mismatch problem related to CS Fallback for MT calls in accordance with a first embodiment of the present invention; 
         FIG. 7  is a signal flow diagram which is used to describe how an enhanced node (enhanced eNodeB) and a method solve the LA/TA mismatch problem related to CS Fallback for MT calls in accordance with a second embodiment of the present invention; and 
         FIG. 8  is a signal flow diagram which is used to describe how an enhanced node (enhanced eNodeB) and a method solve the LA/TA mismatch problem related to CS Fallback for MT calls in accordance with a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The enhanced node (eNodeB 1 ) and method of the present invention solve the aforementioned LA/TA mismatch problem that could occur during a CS Fallback for a MT call. The enhanced node implements a method that prevents a MT call to a UE 1  from being lost by receiving a paging message from a MME 1  after a first MSC 1  receives a MT call request (TAM) for UE 1 . The paging message identifies the suitable LAs associated with the first MSC 1  which is where UE 1  is CS attached but has since re-located to a coverage area managed by a second MSC 2  (e.g. UE 1  is in location “UE 1 -later”). Upon receiving the paging message, the enhanced node determines that there are no 2G/3G cells which belong to the paging message&#39;s suitable LAs based on the current location of UE 1 . Then, the enhanced node identifies a target 2G/3G cell in a LA that is associated with the current location of UE 1  but the target 2G/3G cell is not part of the 2G/3G cells belonging to the paging message&#39;s suitable location areas. Thereafter, the enhanced node enables a signaling connection to be established between UE 1  and the first MSC 1  via the second MSC 2  where the signaling connection allows the MT call to be established with UE 1 . Three exemplary embodiments on how this solution can be implemented are discussed in detail below with respect to  FIGS. 6-8 . 
     Referring to  FIG. 6 , there is a signal flow diagram which is used to describe how the enhanced node (enhanced eNodeB 1 ) solves the LA/TA mismatch problem related to CS Fallback for MT calls in accordance with a first embodiment of the present invention. The steps are as follows: 
     1. UE 1  is SAE/LTE attached and CS attached in MSC 1 /VLR 1  as shown in  FIG. 3 . 
     2. UE 1  has moved from LTE cell e 3  to LTE cell e 1  (see  FIG. 5 ). 
     3. G-MSC receives an JAM (MT call request). 
     4. G-MSC initiates a normal SRI procedure with MSC 1 /VLR 1 . 
     5. G-MSC sends the JAM to MSC 1 /VLR 1 . 
     6. MSC 1 /VLR 1  sends a page message (with suitable LAs) to MME 1 . 
     7. MME 1  sends the page message (with suitable LAs) to the enhanced eNodeB 1   a  which then interfaces with UE 1 . 
     8. Enhanced eNodeB 1   a  finds out that there are no 2G/3G cells belonging to the suitable LAs (associated with the page message) based on the current location of UE 1 . The enhanced eNodeB 1   a  determines that the best GSM cell, based on the current location of UE 1 , is c 31 . The best 2G/3G cell is referred to herein as the target cell c 31 . For instance, the enhanced eNodeB 1   a  could make this determination based on measurement reports received from UE 1  i.e. indicating how well UE 1  “hears” the GSM cells. Another option could be to configure the enhanced eNodeB 1   a  such that it knows an E-UTRAN/LTE cell is totally covered by a specific GSM/WCDMA cell.
 
9. Enhanced eNodeB 1   a  sends a paging redirect message (identifying the new target cell=c 31 ) to MME 1 .
 
10. MME 1  forwards the paging redirect message (identifying the new target cell=c 31 ) to MSC 1 /VLR 1 .
 
11. MSC 1 /VLR 1  sends a MAP-Prep-Handover request (identifying the new target cell=c 31 ) to MSC 2 /VLR 2 . MSC 2 /VLR 2  is associated with BSC 2   c  (or RNC 2   c ) which manages the target cell c 31 .
 
12. MSC 2 /VLR 2  sends a BSSAP Handover Request to BSC 2   c  (or RNC 2   c ).
 
13. BSC 2   c  (or RNC 2   c ) sends a BSSAP Handover Request Acknowledgment to MSC 2 /VLR 2 .
 
14. MSC 2 /VLR 2  sends a MAP-Prep-Handover response to MSC 1 /VLR 1 . Note: steps  9 - 14  are “almost” a normal Inter-MSC Handover.
 
15. Enhanced eNodeB 1   a  sends a relocation request message (with target cell=c 31 ) to MME 1 . Note: the enhanced eNodeB 1   a  can trigger in parallel both steps  9  and  15  (see discussion below).
 
16. MME 1  forwards the relocation request message (with target cell=c 31 ) to SGSN 2 .
 
17. SGSN 2  sends a PS handover request message to BSC 2   c.  
 
18. BSC 2   c  allocates both PS domain and CS domain resources and sends a PS handover request acknowledge message (“ID HO Command message”) to SGSN 2 .
 
19. SGSN 2  sends a forward relocation response message to MME 1 .
 
20. MME 1  sends a relocation command to enhanced eNodeB 1   a.  
 
21. Enhanced eNodeB 1   a  sends a handover from eUTRAN command to UE 1 .
 
22. UE 1  initiates GERAN A/Gb Access Procedures with BSC 2   c  using allocated PS domain resources.
 
23. UE 1  sends a SABM (paging response message) to BSC 2   c  using allocated CS domain resources. Note: steps  15 - 23  are a normal Inter-Domain Handover.
 
24. BSC 2   c  forwards the paging response message to MSC 2 /VLR 2 .
 
25. MSC 2 /VLR 2  forwards the paging response message to MSC 1 /VLR 1 .
 
26. MT call setup: MSC 1             MSC 2           BSC 2   c           UE 1 .
 
Note 1: This signal flow diagram shows how this embodiment of present invention would function based on the scenario shown in  FIG. 5 . It should be appreciated that this mobile telecommunications network is exemplary and that the present invention should not be construed as needing to be used in any specific type or any specific architecture of a mobile telecommunications network.
 
Note 2: The enhanced eNodeB 1  has a processor  602  that accesses instructions from a memory  604  and processes those instructions to perform the aforementioned steps  7 - 9 ,  15 ,  20  and  21 .

     In this embodiment, the “paging request redirect” solution can also be described as follows when the enhanced eNodeB 1   a  receives the paging message from the MME 1  it finds out that there are no 2G/3G cells belonging to the “Suitable LAs” based on the current location (LTE cell e 1 ) of UE 1  (steps  7  and  8 ). However, the enhanced eNodeB 1   a  identifies a good 2G/3G cell (2G/3G cell c 31 ) which can be the target cell for the CS Fallback, but that target cell is controlled by another MSC/MSC-Pool (i.e. it is not part of the Suitable LAs indicated by the page message) (step  8 ). At this point, two different sequences can be triggered by the enhanced eNodeB 1   a  in parallel. 
     Sequence  1 : The enhanced eNodeB 1   a  sends a “paging request redirect” message back to the MME 1  which forwards the paging request redirect message to MSC 1 /VLR 1  which sent the page message (steps  6  and  9 - 10 ). The identity of the target cell is included in the paging request redirect message. When MSC 1 /VLR 1  receives the paging request redirect message, it triggers an Inter-MSC Handover towards that target cell and includes the IMSI of the UE 1  and an optional flag indicating “HO for Paging Response” (steps  11 - 14 ). This Inter-MSC Handover results in a signalling connection being established between MSC 1  (which received the MT call request) and BSC 2   c /RNC 2   c  via the MSC 2  (which manages BSC 2   c /RNC 2   c  associated with the target cell and which will receive the paging response message upon the UE 1 s arrival in the target cell) (steps  15 - 26 ). As part of this Inter-MSC Handover procedure, the BSC 2   c /RNC 2   c  which controls the target cell could receive a Handover Request message indicating the optional “HO for Paging Response” and would store the IMSI associated with the signalling connection to MSC 2  (which extends back to MSC 1 ) (step  12 ). This signaling connection will be used for sending the paging response message and the subsequent MT call establishment signalling that will be performed between UE 1  and MSC 1  after UE 1  completes the normal ID HO to the target cell (steps  15 - 26 ). The BSC 2   c /RNC 2   c  may also use the optional “HO for Paging Response” flag to know that no CS resources need to be returned in the signalling back to MSC 2  which triggered the Handover request (step  13 ). The purpose of this sequence is to create the signalling connection between the BSC 2   c /RNC 2   c  controlling the target cell and the MSC 1  holding the MT Call request (i.e. with MSC 2  providing a signaling relay function in this example). 
     Sequence  2  (performed in parallel with sequence  1  above): The enhanced eNodeB 1   a  triggers a normal Inter-Domain HO towards the target cell (IMSI is also included in this signalling by the MME 1 ) (step  15 ). This results in an ID HO COMMAND message being sent to the UE 1  (step  21 ). Once UE 1  accesses the target cell and sends the paging response message using the allocated CS domain resources, BSC 2   c /RNC 2   c  knows that this paging response message needs to be forwarded on the signalling connection (which goes all the way back to MSC 1 ) created during the above described Inter-MSC Handover procedure (e.g. based on the same IMSI received during both sequences) (steps  9 - 25 ). This means that the paging response message is returned to MSC 1  which holds the MT call and at that point normal MT call establishment signalling may continue between UE 1  and MSC 1  (where MSC 2  only serves to relay these messages) (steps  25 - 26 ). 
     Referring to  FIG. 7 , there is a signal flow diagram which is used to describe how the enhanced node (enhanced eNodeB 1 ) solves the LA/TA mismatch problem related to CS Fallback for MT calls in accordance with a second embodiment of the present invention. The steps are as follows: 
     1. UE 1  is SAE/LTE attached and CS attached in MSC 1 /VLR 1  as shown in  FIG. 3 . 
     2. UE 1  has moved from LTE cell e 3  to LTE cell e 1  (see  FIG. 5 ). 
     3. G-MSC receives an IAM (MT call request). 
     4. G-MSC initiates a normal SRI procedure with MSC 1 /VLR 1 . 
     5. G-MSC sends the IAM to MSC 1 /VLR 1 . 
     6. MSC 1 /VLR 1  sends a page message (with suitable LAs) to MME 1 . 
     7. MME 1  sends the page message (with suitable LAs) to the enhanced eNodeB 1   a  which then interfaces with UE 1 . 
     8. Enhanced eNodeB 1   a  finds out that there are no 2G/3G cells belonging to the suitable LAs (associated with the page message) based on the current location of UE 1 . The enhanced eNodeB 1   a  determines that the best GSM cell based on the current location of UE 1  is c 31 . The best 2G/3G cell is referred to herein as the target cell c 31 . For instance, the enhanced eNodeB 1   a  could make this determination based on measurement reports received from UE 1  i.e. indicating how well UE 1  “hears” the GSM cells. Another option could be to configure the enhanced eNodeB 1   a  such that it knows an E-UTRAN/LTE cell is totally covered by a specific GSM/WCDMA cell.
 
9. Enhanced eNodeB 1   a  sends a relocation request message (identifying target cell=c 31 , suitable LAs, NRI) to MME 1 .
 
10. MME 1  sends the forward relocation request message (identifying target cell=c 31 , suitable LAs, NRI) to SGSN 2 .
 
11. SGSN 2  sends a PS handover request message (identifying target cell=c 31 , suitable LAs, NRI) to BSC 2   c.  
 
12. BSC 2   c  allocates both PS domain and CS domain resources and sends a PS handover request acknowledge message (“ID HO Command message”) to SGSN 2 .
 
13. SGSN 2  sends a forward relocation response message to MME 1 .
 
14. MME 1  sends a relocation command to enhanced eNodeB 1   a.  
 
15. Enhanced eNodeB 1   a  sends a handover from eUTRAN command to UE 1 .
 
16. UE 1  initiates GERAN A/Gb Access Procedures with BSC 2   c  using the allocated PS domain resources.
 
17. UE 1  sends a SABM (paging response message) to BSC 2   c  using the allocated CS domain resources.
 
18. BSC 2   c  sends a paging response message (identifying suitable LAs, NRI) to MSC 2 /VLR 2 . Note: these suitable LAs and NM are the same as the ones in the relocation request message at step  9 .
 
19. MSC 2 /VLR 2  forwards the paging response message (identifying suitable LAs, NRI) to MSC 1 /VLR 1 . A detailed discussion is provided below about this particular step and the establishment of the signaling connection between MSC 2 /VLR 2  and MSC 1 /VLR 1 .
 
20. MT call setup: MSC 1             MSC 2           BSC 2   c           UE 1 .
 
Note 1: This signal flow diagram shows how this embodiment of present invention would function based on the scenario shown in  FIG. 5 . It should be appreciated that this mobile telecommunications network is exemplary and that the present invention should not be construed as needing to be used in any specific type or any specific architecture of a mobile telecommunications network.
 
Note 2: The enhanced eNodeB 1  has a processor  702  that accesses instructions from a memory  704  and processes those instructions to perform the aforementioned steps  7 - 9  and  15 .

     In this embodiment, the “paging response redirect” solution can also be described as follows when the enhanced eNodeB 1   a  receives the paging message from the MME 1  it finds out that there are no 2G/3G cells belonging to the “Suitable LAs” based on the current location (LTE cell e 1 ) of UE 1  (steps  7  and  8 ). The enhanced eNodeB 1   a  then triggers the ID HO towards the best target 2G/3G cell available (step  9 ). The UE 1  is then commanded to perform ID HO to that target cell and upon arrival in the target cell it sends the paging response message to BSC 2   c /RNC 2   c  which controls that target cell (steps  15  and  17 ). However, when the BSC 2 /MSC 2  receives the paging response message there is no signalling connection available from BSC 2   c /RNC 2   c  towards MSC 1  (which received the MT call request) (step  18 ). Thus, the signalling connection needs to be established from the BSC 2   c /RNC 2   c  towards the MSC/MSC-Pool holding the MT call (in this example MSC 1 ) (step  19  and  20 ). 
     The identifiers used for establishing this signalling connection from BSC 2   c /MSC 2   c  to MSC 1  are for example (i) target cell (only steps  9 - 11 ), (ii) the “Suitable LAs” that will uniquely identify the correct MSC or the correct MSC-Pool which covers the target cell in which the UE 1  is currently located, and (iii) NRI which will identify the correct MSC-Pool member (in the above example MSC 1 ) in the case MSC-pool is deployed (steps  9 - 11  and  18 - 19 ). MSC 2  would then establish a signaling link to some MSC-X within the indicated suitable LAs (step  19 ). MSC-X would then look at the NRI it receives from MSC 2  and if it determines it was not MSC 1  then MSC-X would then establish another signaling link to MSC 1  (and eventually a signaling path can be established between MSC 1  and MSC 2  and by-pass MSC-X altogether). In the current example shown in  FIG. 7 , the simple case is assumed whereby MSC-X=MSC 1 . As such, if BSC 2   c /RNC 2   c  indicates both the “Suitable LAs” and the NRI when the signalling connection is established towards MSC 2 , then this will allow for establishing the required signalling connection towards the correct MSC/MSC-Pool (in this example MSC 1 ) using these identifiers (steps  18 - 20 ). Once established, BSC 2   c /RNC 2   c  uses this signalling connection to send the received paging response message to MSC 1  (via MSC 2 ) and then for the subsequent MT call establishment signalling between UE 1  and MSC 1  (steps  18 - 20 ). At some point during the MT call establishment with UE 1 , the MSC 1  and MSC 2  can signal the establishment of a user plane connection appropriate for terminating the MT call with UE 1  (step  20 ). 
     Referring to  FIG. 8 , there is a signal flow diagram which is used to describe how the enhanced node (enhanced eNodeB 1 ) solves the LA/TA mismatch problem related to CS Fallback for MT calls in accordance with a third embodiment of the present invention. The steps are as follows: 
     1. UE 1  is SAE/LTE attached and CS attached in MSC 1 /VLR 1  as shown in  FIG. 3 . 
     2. UE 1  has moved from LTE cell e 3  to LTE cell e 1  (see  FIG. 5 ). 
     3. G-MSC receives an IAM (MT call request). 
     4. G-MSC initiates a normal SRI procedure with MSC 1 /VLR 1 . 
     5. G-MSC sends the IAM to MSC 1 /VLR 1 . 
     6. MSC 1 /VLR 1  sends a page message (with suitable LAs) to MME 1 . 
     7. MME 1  sends the page message (with suitable LAs) to the enhanced eNodeB 1   a  which then interfaces with UE 1 . 
     8. Enhanced eNodeB 1   a  finds out that there are no 2G/3G cells belonging to the suitable LAs (associated with the page message) based on the current location of UE 1 . The enhanced eNodeB 1   a  determines that the best GSM cell based on the current location of UE 1  is c 31 . The best 2G/3G cell is referred to herein as the target cell c 31 . For instance, the enhanced eNodeB 1   a  could make this determination based on measurement reports received from UE 1  i.e. indicating how well UE 1  “hears” the GSM cells. Another option could be to configure the enhanced eNodeB 1   a  such that it knows an E-UTRAN/LTE cell is totally covered by a specific GSM/WCDMA cell.
 
9. Enhanced eNodeB 1   a  sends a relocation request message (identifying target cell=c 31 , Global MSC-ID) to MME 1 .
 
10. MME 1  forwards the relocation request message (identifying target cell=c 31 , Global MSC-ID) to SGSN 2 .
 
11. SGSN 2  sends a PS handover request message (identifying target cell=c 31 , Global MSC-ID) to BSC 2   c.  
 
12. BSC 2   c  allocates both PS domain and CS domain resources and sends a PS handover request acknowledge message (“ID HO Command message”) to SGSN 2 .
 
13. SGSN 2  sends a forward relocation response message to MME 1 .
 
14. MME 1  sends a relocation command to enhanced eNodeB 1   a.  
 
15. Enhanced eNodeB 1   a  sends a handover from eUTRAN command to UE 1 .
 
16. UE 1  initiates GERAN A/Gb Access Procedures with BSC 2   c  using the allocates PS domain resources.
 
17. UE 1  sends a SABM (paging response message) to BSC 2   c  using the allocated CS domain resources.
 
18. BSC 2   c  sends a paging response message (identifying Global MSC-ID) to MSC 2 /VLR 2 .
 
19. MSC 2 /VLR 2  forwards the paging response message (identifying Global MSC-ID) to MSC 1 /VLR 1 . A detailed discussion is provided below about this particular step and the establishment of the signaling connection between MSC 2 /VLR 2  and MSC 1 /VLR 1 .
 
20. MT call setup: MSC 1             MSC 2           BSC 2   c           UE 1 .
 
Note 1: This signal flow diagram shows how this embodiment of present invention would function based on the scenario shown in  FIG. 5 . It should be appreciated that this mobile telecommunications network is exemplary and that the present invention should not be construed as needing to be used in any specific type or any specific architecture of a mobile telecommunications network.
 
Note 2: The enhanced eNodeB 1  has a processor  802  that accesses instructions from a memory  804  and processes those instructions to perform the aforementioned steps  7 - 9  and  15 .

     In this embodiment, the alternative “paging response redirect” solution can also be described as follows when the enhanced eNodeB 1   a  receives the paging message from the MME 1  it finds out that there are no 2G/3G cells belonging to the “Suitable LAs” based on the current location (LTE cell e 1 ) of UE 1  (steps  7  and  8 ). The enhanced eNodeB 1   a  then triggers the ID HO towards the best target 2G/3G cell available (step  9 ). The UE 1  is then commanded to perform ID HO to that target cell and upon arrival in the target cell it sends the paging response message to BSC 2   c /RNC 2   c  which controls that target cell (steps  15  and  17 ). However, when the BSC 2   c /MSC 2   c  receives the paging response message there is no signalling connection available from BSC 2   c /RNC 2   c  towards MSC 1  (which received the MT call request) (step  18 ). Thus, the signalling connection needs to be established from the BSC 2   c /RNC 2   c  towards the MSC/MSC-Pool holding the MT call (in this example MSC 1 ) (step  19  and  20 ) after completion of the PS handover procedure using the allocated PS domain resources. 
     The identifiers used for establishing this signaling connection from BSC 2   c /MSC 2  to MSC 1  are for example (i) target cell (only steps  9 - 11 ) and (ii) a “Global MSC-ID” which specifically identifies the MSC 1  (in this example) as the MSC that received the MT call request (see steps  9 - 11  and  18 - 19 ). In this case, the BSC 2   c /RNC 2   c  would be passed the “Global MSC-ID” in a forward transparent container (for example) during the ID HO preparation phase (step  11 ). Then, the BSC 2   c /RNC 2   c  could pass this “Global MSC-ID” along with the paging response message it sends to MSC 2  which will then use this information to establish the required signalling connection to MSC 1  (steps  18 - 19 ). Once established, BSC 2   c /RNC 2   c  uses this signalling connection to send the received paging response message to MSC 1  (via MSC 2 ) and then for the subsequent MT call establishment signalling between UE 1  and MSC 1  (steps  18 - 20 ). At some point during the MT call establishment with UE 1 , the MSC 1  and MSC 2  can signal the establishment of a user plane connection appropriate for terminating the MT call with UE 1  (step  20 ). 
     Although three embodiments of the present invention have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it should be understood that the invention is not limited to the disclosed embodiments, but instead is also capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as has been set forth and defined by the following claims.

Technology Classification (CPC): 7