Abstract:
A Mobile Switching Center (MSC) receives a short message service (SMS) message from a mobile station. The MSC checks a link between it and an MME to see if the link is currently set. If the link is not currently set, the mobile station is re-registered at the MSC, which re-established the link between the MSC and the MME. The mobile station will resend the SMS message to the MSC, which now utilizes the re-established link to deliver the SMS message.

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 3G Mobile Switching Center (MSC) receives an SMS message from a mobile station, if the state of the SGs interface between the 4G Long Term Evolution (LTE) MME and the 3G MSC is Null, the 3G MSC will ignore the SMS request. The 3G MSC will therefore not send a failure notification to the MME. Because the MME was not the original sender of the SMS message, the MME will not have set a timeout timer for the SMS message. 
         [0004]    So in the above scenario, the sending mobile station will not receive a failure notification from the 3G MSC indicating that the SMS message was not delivered. In addition, the MME assumes that the association with the 3G-MSC for the mobile station is still alive and will continue to pass the mobile station originated SMS messages to the 3G-MSC. However, the MSC will continue to ignore the SMS requests. This situation can last up to several hours or longer without notices. 
         [0005]    Therefore, a need exists for a method and system for reliably sending SMS messages from a mobile station when the state of the SGs interface between the 4G LTE MME and the 3G MSC is inoperative. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    An exemplary embodiment of the present invention provides a method for re-registering a mobile station. The mobile station initiates an SMS message by sending an SMS message to an eNodeB. The mobile station may start a timeout timer to assist in resending the message should an acknowledgement message not be received in a timely manner. 
         [0007]    The eNodeB passes the SMS message to an MME, which checks the SGs association with an MSC. If the SGs association between the MME and the MSC is active at the MME, the MME encapsulates the SMS message and sends it to the MSC. 
         [0008]    In the situation where the SGs association on MSC between the MME and the MSC is not currently set, such as when a VLR record associated with the mobile station is deleted due to VLR overload control or other administrative reasons or the SGs association is equal to SGs-NULL, the MSC re-registers the mobile station. The re-registration re-establishes an SGs association at the MSC between the MSC and the MME. 
         [0009]    Upon expiration of the timeout timer, the mobile station resends the SMS message. Alternately, the SMS message can be stored during registration at the MSC and resent by the MSC once registration is complete. In this alternate embodiment, the mobile station would not need to start a timeout timer or resend the SMS message. 
         [0010]    The eNodeB passes the SMS message to the MME, which encapsulates the SMS message and sends it to the MSC. 
         [0011]    The MSC checks the SGs association between it and the MME. Since the MSC re-registered the mobile station and re-established an SGs association between the MSC and the MME, the MSC acknowledges the receipt of the SMS message with an Ack message. The MME passes the acknowledgement to the eNodeB via a downlink Ack message. The eNodeB passes the acknowledgement to the mobile station. The MSC also delivers the SMS message to an SMS-IWMSC. An acknowledgement message can be sent to the mobile station to indicate successful delivery of the SMS message. 
         [0012]    In an alternate embodiment, an SMS message can be successfully delivered when an SGs link in nonoperational by having the mobile station perform a location update. 
         [0013]    A mobile station initiates an SMS by sending an SMS message to an eNodeB. The eNodeB passes the SMS message to an MME. The MME checks the SGs association with an MSC. If the SGs association between the MME and the MSC is active at the MME, the MME encapsulates the SMS message and sends the SMS message to the MSC. 
         [0014]    In this exemplary embodiment, the SGs association on the MSC between the MME and the MSC is not currently set at the MSC. In typical communication systems, the MSC would ignore the SMS request. In accordance with an exemplary embodiment, the MSC sends an error message to the MME that indicates to the MME that the SGs association on the MSC between the MME and the MSC is not currently set. 
         [0015]    Upon receiving the error message at the MME, the MME sets the SGs association at the MME to NULL and also preferably sets an MSC/VLR reliable flag for the mobile station to “FALSE”. 
         [0016]    The mobile station sends a Tracking Area Update message, preferably with combined TA/LA (Tracking Area/Location Area) updating. The eNodeB passes the Tracking Area Update message to the MME. 
         [0017]    In response to the Tracking Area Update message, the MME sends a Location Update message to the MSC. In response to the Location Update message, the MSC re-registers the mobile station so that the SGs association between the MME and the MSC can be re-established. 
         [0018]    SMS messages now sent by the mobile station can be properly delivered because the SGs association between the MME and the MSC at the MSC is properly established. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0019]      FIG. 1  depicts a portion of a communication system in accordance with an exemplary embodiment of the present invention. 
           [0020]      FIG. 2  depicts a flow diagram of a method for delivering an SMS message by re-registering a mobile station in accordance with an exemplary embodiment of the present invention. 
           [0021]      FIG. 3  depicts a flow diagram of a method for delivering an SMS message by having a mobile station perform a location update in accordance with an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    An exemplary embodiment of the present invention can be better understood with reference to  FIGS. 1 through 3 .  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 , MSC  107 , and SMS-IWMSC (SMS Interworking MSC)  109 . 
         [0023]    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. 
         [0024]    eNodeB  103  is an LTE base station that communicates, over the air, with mobile station  101 . 
         [0025]    MME  105  manages session states, authentication, paging, mobility with SGSN nodes, roaming, and other bearer management functions. 
         [0026]    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). 
         [0027]    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). 
         [0028]      FIG. 2  depicts a flow diagram  200  of a method for re-registering a mobile station  101  in accordance with an exemplary embodiment of the present invention. 
         [0029]    Mobile station  101  initiates an SMS message by sending Uplink NAS Transport SMS message  201  to eNodeB  103 . In accordance with an exemplary embodiment, mobile station  101  starts a timeout timer. 
         [0030]    eNodeB  103  passes Uplink NAS Transport SMS message  201  to MME  105  via Uplink NAS Transport SMS message  203 . 
         [0031]    MME  105  checks the SGs association with MSC  107 . In an exemplary embodiment, the SGs association between MME  105  and MSC  107  is active. MME  105  encapsulates Uplink NAS Transport SMS message  203  in SGsAP Uplink Unidata (SMS)  205  and sends to MSC  107 . 
         [0032]    In this exemplary embodiment, the SGs association on MSC  107  between MME  105  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. 
         [0033]    Rather than ignoring the SMS request, as would happen in current communication systems, in accordance with an exemplary embodiment MSC  107  re-registers mobile station  101 . The re-registration re-establishes an SGs association between MSC  107  and MME  105 . 
         [0034]    Upon expiration of the timeout timer, mobile station  101  resends Uplink NAS Transport SMS message  201  as Uplink NAS Transport SMS message  211 . Alternately, Uplink NAS Transport SMS message  201  can be stored during registration at MSC  107  and resent by MSC  107  once registration is complete. In this alternate embodiment, mobile station  101  would not need to start a timeout timer or resend Uplink NAS Transport SMS message  201 , which saves bandwidth on the network. 
         [0035]    eNodeB  103  passes Uplink NAS Transport SMS message  211  to MME  105  via Uplink NAS Transport SMS message  213 . 
         [0036]    MME  105  encapsulates Uplink NAS Transport SMS message  213  in SGsAP Uplink Unidata (SMS) message  215  and sends to MSC  107 . 
         [0037]    MSC  107  checks the SGs association. Since MSC  107  re-registered mobile station  101  and re-established an SGs association, MSC  107  acknowledges the receipt of SGsAP Uplink Unidata (SMS) message  215  with a SGsAP Downlink Unidata (Ack) message  216 . MME  105  passes the acknowledgement to eNodeB  103  via Downlink Unidata (Ack) message  218 . eNodeB  103  passes the acknowledgement to MS  101  via SGsAP Downlink Unidata (Ack) message  220 . MSC  107  also delivers SGsAP Uplink Unidata (SMS) message  215  to SMS-IWMSC  109  as ForwardSMS message  217 . 
         [0038]    SMS-IWMSC  109  sends Delivery Report message  221  to MSC  107 . 
         [0039]    MSC  107  sends SGsAP Downlink Unidata (Delivery Report) message  223  to MME  105 . 
         [0040]    MME  105  sends Downlink NAS Transport (Delivery Report) message  225  to eNodeB  103 . 
         [0041]    eNodeB  103  sends Downlink NAS Transport (Delivery Report) message  227  to mobile station  101 . 
         [0042]      FIG. 3  depicts a flow diagram  300  of a method for delivering an SMS message by having mobile station  101  perform a location update in accordance with an exemplary embodiment of the present invention. 
         [0043]    Mobile station  101  initiates an SMS by sending Uplink NAS Transport SMS message  301  to eNodeB  103 . 
         [0044]    eNodeB  103  passes Uplink NAS Transport SMS message  201  to MME  105  via Uplink NAS Transport SMS message  303 . 
         [0045]    MME  105  checks the SGs association with MSC  107 . In an exemplary embodiment, the SGs association between MME  105  and MSC  107  is active. MME  105  encapsulates Uplink NAS Transport SMS message  303  in SGsAP Uplink Unidata (SMS)  305  and sends to MSC  107 . 
         [0046]    In this exemplary embodiment, the SGs association on MSC  107  between MME  105  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. 
         [0047]    In typical communication systems, MSC  107  would ignore the SMS request. In accordance with an exemplary embodiment, MSC  107  sends an error message, SGsAP Status (Unknown IMSI) message  307 , to MME  105 . Message  307  indicates to MME  105  that the SGs association on MSC  107  between MME  105  and MSC  107  is not currently set. 
         [0048]    Upon receiving SGsAP Status (Unknown IMSI) message  307  at MME  105 , MME  105  sets the SGs association at MME  105  to NULL. MME  105  also preferably sets an MSC/VLR reliable flag for mobile station  101  to “FALSE”. 
         [0049]    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. 
         [0050]    eNodeB  103  passes TAU message  311  to MME  105  via TAU message  313 . 
         [0051]    In response to TAU message  313 , MME  105  sends a 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  105  and MSC  107  can be re-established. 
         [0052]    In accordance with an exemplary embodiment, when an SMS message is now sent by mobile station  101 , the SGs association between MME  105  and MSC  107  is properly established so that the SMS message can be properly delivered. 
         [0053]    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.