Abstract:
A Mobile Switching Center (MSC) receives a short message intended for a mobile station. The MSC determines whether the mobile station is registered at the MSC. If not registered, the MSC sends a query message to associated Mobility Management Entities (MMEs). One of the MMEs sends a message to the MSC indicating that the MME is serving the mobile station.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to communication systems, and more particularly to Short Message Service (SMS). 
       BACKGROUND OF THE INVENTION 
       [0002]    Short Message Service (SMS) has become a very popular feature in communication systems. Because SMS messages are not time-dependent, an acknowledgement message typically is not sent to the sender of an SMS message. 
         [0003]    Currently, when a Mobile Switching Center (MSC) receives an SMS message intended for a mobile station that is not indicated to be located at the MSC, the MSC sends a failure notification to the SMS server. The MSC server does not attempt to deliver the SMS in such a scenario. Instead, the Home Location Register (HLR) waits for the mobile station to register with the HLR so that the SMS delivery may be reattempted. In the meantime, the sender is still waiting for the SMS delivery to complete. 
         [0004]    Therefore, a need exists for a method and system for reliably sending SMS messages to a mobile station when an MSC does not know where the mobile station is located. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    An exemplary embodiment of the present invention provides a method for delivering an SMS message. The MSC sends an alert message or page message to all subtending MMEs. 
         [0006]    An IWMSC sends an SMS message to the MSC. The SMS message is a request to send an SMS message to a mobile station. In accordance with an exemplary embodiment, the SGs association on the MSC between an MME and the MSC is not currently set. 
         [0007]    If the mobile station is not registered with the MSC, the MSC queries subtending MMEs, preferably by sending an alert message to all subtending MMEs. The alert messages help the MSC to determine whether the intended mobile station has registered with any of the MMEs. 
         [0008]    The MME to which the mobile station is registered an acknowledgement message to the MSC to indicate that the mobile station is registered with the associated MME. 
         [0009]    The MSC preferably stores the SMS message and forwards to the mobile station via the acking MME after receiving the alert acknowledgement message from the MME. 
         [0010]    In accordance with an exemplary embodiment, the mobile station sends a TAU (Tracking Area Update) message with combined TA/LA (Tracking Area/Location Area) updating to an eNodeB, which passes the TAU message to the responding MME. 
         [0011]    In response to the TAU message, the MME sends a Location Update message to the MSC. In response to the Location Update message, the MSC re-registers mobile the station so that the SGs association between the MME and the MSC can be re-established. 
         [0012]    The IWMSC sends an SMS message intended for the mobile station to the MSC. The MSC checks the SGs association for the mobile station. Since the MSC re-registered the mobile station and re-established an SGs association, the MSC acknowledges the receipt of the SMS message and processes the delivery of the SMS message to the mobile station. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0013]      FIG. 1  depicts a portion of a communication system in accordance with an exemplary embodiment of the present invention. 
           [0014]      FIG. 2  depicts a flow diagram of a method for delivering an SMS message in accordance with an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    An exemplary embodiment of the present invention can be better understood with reference to  FIGS. 1 and 2 .  FIG. 1  depicts a portion  100  of a communication system in accordance with an exemplary embodiment of the present invention. Portion  100  includes mobile station  101 , eNodeB  103 , MME  105 , MME  115 , MME  125 , MSC  107 , and SMS-IWMSC (SMS Interworking MSC)  109 . 
         [0016]    Mobile station  101  is a device supporting voice and data communication using a wireless air interface. In an exemplary embodiment, mobile station  101  is a Circuit Switch Fall Back (CSFB) mobile station camping on LTE technology. 
         [0017]    eNodeB  103  is an LTE base station that communicates, over the air, with mobile station  101 . 
         [0018]    MME  105 , MME  115 , and MME  125  are Mobility Management Entities that each manage session states, authentication, paging, mobility with SGSN nodes, roaming, and other bearer management functions. 
         [0019]    MSC  107  is a Mobile Switching Center. In an exemplary embodiment, MSC  107  comprises a 3G MSC. MSC  107  is the network element that provides voice services and enables mobile terminals to communicate to the Public Switched Telephone Network (PSTN). 
         [0020]    SMS-IWMSC  109  is an MSC that is capable of receiving SMS messages from a mobile network and submitting the SMS messages to an appropriate Short Message Service Center (SMSC). 
         [0021]      FIG. 2  depicts a flow diagram  200  of a method for delivering an SMS message in accordance with an exemplary embodiment of the present invention. In this exemplary embodiment, the MSC sends an alert message to all subtending MMEs. In an alternate exemplary embodiment, the MSC can send a page message and deliver the SMS to the MME that responds to the page message. 
         [0022]    SMS-IWMSC  109  sends ForwardSMS message  217  to MSC  107 . ForwardSMS message  217  is a request to send an SMS message to mobile station  101 . In the exemplary embodiment depicted in  FIG. 2 , mobile station  101  is not registered with MSC  107 . In an exemplary embodiment, the SGs association on MSC  107  between MME  115  and MSC  107  is not currently set. In a first exemplary embodiment, this can occur when a VLR record associated with mobile station  101  is deleted, for example due to VLR overload control or other administrative reasons. In a second exemplary embodiment, this can occur when the SGs association is equal to SGs-NULL. 
         [0023]    In accordance with the exemplary embodiment, MSC  107  queries subtending MMEs, in this exemplary embodiment MME  105 , MME  115 , and MME  125 , by sending SGsAP Alert Request message  213  to MME  115 , SGsAP Alert Request message  203  to MME  105 , and SGsAP Alert Request message  223  to MME  125 . The SGsAP Alert Request messages will help MSC  107  determine whether mobile station  101  has registered with any of the MMEs. In an alternate exemplary embodiment, MSC  107  sends a page message, preferably over an SGs interface, to corresponding MMEs and delivers ForwardSMS message  217  to the MME that responds to the page message. 
         [0024]    In this exemplary embodiment, mobile station  101  is registered with MME  115 . Therefore MME  105  sends SGs Alert Reject message  205  to MSC  107  and MME  125  sends SGs Alert Reject message  225  to MSC  107 . 
         [0025]    MME  115  sends SGsAP Alert Ack message  227  to MSC  107 . SGsAP Alert Ack message  227  indicates to MSC  107  that mobile station  101  is registered with MME  115 . 
         [0026]    In an exemplary embodiment, MSC  107  stores the SMS message and forwards to mobile station  101  via MME  115  after receiving SGsAP Alert Ack message  227  from MME  115 . 
         [0027]    In accordance with an exemplary embodiment, mobile station  101  sends a TAU (Tracking Area Update) message  311 , preferably with combined TA/LA (Tracking Area/Location Area) updating to eNodeB  103 . In an alternate exemplary embodiment, message  311  can be any message that indicates user activity by mobile station  101 . 
         [0028]    eNodeB  103  passes TAU message  311  to MME  115  via TAU message  313 . 
         [0029]    In response to TAU message  313 , MME  115  sends an SGsAP Location Update message  315  to MSC  107 . In response to SGsAP Location Update message  315 , MSC  107  re-registers mobile station  101  so that the SGs association between MME  115  and MSC  107  can be re-established. 
         [0030]    SMS-IWMSC  109  sends ForwardSMS message  317  to MSC  107 . ForwardSMS message  317  is intended for mobile station  101 . MSC  107  checks the SGs association for mobile station  101 . Since MSC  107  re-registered mobile station  101  and re-established an SGs association, MSC  107  acknowledges the receipt of ForwardSMS message  317  and processes the delivery of the SMS message to mobile station  101 . 
         [0031]    While this invention has been described in terms of certain examples thereof, it is not intended that it be limited to the above description, but rather only to the extent set forth in the claims that follow.