Patent Publication Number: US-11641567-B2

Title: Enhancement of MT SM delivery for EDRX enabled mobile terminals

Description:
This application is a continuation of U.S. patent application Ser. No. 16/774,619, filed Jan. 28, 2020, now U.S. Pat. No. 11,109,198, which is a continuation of U.S. patent application Ser. No. 15/771,054, filed Apr. 25, 2018, now U.S. Pat. No. 10,595,170, which is a 35 U.S.C. § 371 national phase filing of International Application No. PCT/EP2016/077871, filed Nov. 16, 2016, which claims the benefit of U.S. Provisional No. 62/262,006, filed Dec. 2, 2015, the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The invention relates to mobility management nodes and methods of the mobility management nodes of enabling delivery of a Mobile Terminating, (MT) Short Message (SM) to a mobile terminal. 
     The invention further relates to computer programs for causing the mobility management nodes to perform the methods according to the invention, and corresponding computer program products. 
     BACKGROUND 
     The Short Message Service (SMS) provides a means of sending messages of limited size to and from mobile terminals in 3rd Generation Partnership Project (3GPP) communications systems such as Global System for Mobile Communications (GSM), Universal Mobile Telecommunications System (UMTS) and Evolved Packet System (EPS). The provision of SMS makes use of a Service Centre, which acts as a store and forward centre for short messages. 
     Mobile terminal originated messages are transported from a terminal to the Service Centre, while mobile terminated messages shall be transported from the Service Centre to a terminal. Short messages are typically input to the Service Centre by other mobile users, and are destined for other mobile users, or for subscribers on a fixed network. This is described in detail in Technical Specification 3GPP TS 23.040. 
     Now, for extending battery lifetime of a mobile terminal, a method known as Discontinuous Reception (DRX) is used where the mobile terminal, oftentimes referred as a User Equipment (UE), only occasionally monitors a Physical Downlink Control Channel (PDCCH) to check if there is downlink data available. 
     Recently introduced UE types, such as Machine Type Communications (MTC) devices, require extremely efficient power saving, which has led to the introduction of a mode referred to as extended idle mode DRX (eDRX). That is, the UE and the network may negotiate over Non-Access Stratum (NAS) signaling the use of extended idle mode DRX for reducing its power consumption, while being available for mobile terminating data and/or network originated procedures within a certain delay dependent on the DRX cycle value. An eDRX enabled UE can only be reachable by the network (i.e. be paged by the network) during its paging transmission window (PTW), and during that window, the UE uses normal DRX. 
     In “MT SMS procedures for UEs in extended idle mode DRX”, C4-152115, 3GPP TSG CT4 Meeting #71, Anaheim, USA; 16-20 Nov. 2015, it is described a mobile terminated (MT) short message (SM) delivery from a Short Message Service Centre (SMSC) to a Mobility Management Entity (MME). 
     Reference is made to the timing diagram of enclosed  FIG.  1   .
         1. The SMSC submits a Send-Routing-Info-for-SM-Request (SRR) command to a Home Subscriber Server (HSS) to retrieve the address of the nodes serving the UE.   2. The HSS replies accordingly by submitting a Send-Routing-Info-for-SM-Answer (SRA) message, indicating the address of the serving MME.   3. The SMSC sends an MT-Forward-Short-Message-Request (TFR) to the serving MME. The SMSC indicates in the TFR a Max Retransmission Time (e.g. 5 to 10 minutes), which indicates for how long the SMSC is ready to store the SM if it cannot be delivered at once due to the UE being in extended idle mode DRX.   4. If the UE is reachable within the Max Retransmission Time provided in the TFR, the MME immediately sends an MT-Forward-Short-Message-Request-Answer (TFA) in step 4a indicating Requested Retransmission Time, i.e. the time at which the SM should be resent by the SMSC. The MME also pages the UE in 4b.   At this stage, the SMSC will not send a Report-SM-Delivery-Status-Request (RDR) to the HSS with the indication that the SM delivery was unsuccessful. Consequently, the HSS will not reply with a Report-SM-Delivery-Status-Answer (RDA) message, and will not store the Service Centre address in its Message Waiting Data (MWD).   5. The UE responds to the paging at which point in time a signalling connection is established between the UE and the MME.   At this stage, the MME does not send a Notify-Request (NOR) to the HSS to signal that the UE has become reachable.   6. The SMSC retransmits the SM at the Requested Retransmission Time which was indicated in the TFA (no Max Retransmission Time is included in this second transmission of the TFR).       

     The solution in “MT SMS procedures for UEs in extended idle mode DRX” is described to present the following merits: 
     a. MT SM for UEs in eDRX does not cause any extra HSS signalling. 
     b. No issue with short eDRX period (e.g. up to 20 s) of synchronization of messages received at HSS. 
     c. Single-attempt-delivery SM can be transmitted to the UE if this procedure is used (without the need to use MWD for single-attempt-delivery SM as previously has been specified). 
     The solution in “MT SMS procedures for UEs in extended idle mode DRX” is further described to present the following drawbacks: 
     a. SM retransmission is triggered without knowing for certain whether the UE indeed is reachable (e.g. the UE may have detached, the UE may be in a tunnel, the eDRX period may have been renegotiated, etc.). 
     b. Greater impact on SMSC (extended buffering of MT-SM e.g. for up to 5-10 min). 
     c. The Mobile Station Not Reachable Flag (MNRF) flag is not set in the HSS, so subsequent MT SM to the same UE from a different SMSC will trigger new MT Forward SM Request to MME for UEs which are unreachable. 
     d. Introduces a further method to deliver MT SMS for UEs using extended idle mode DRX. 
     The applicant has identified further drawbacks with this solution as will be discussed with reference to  FIG.  2   . 
     As in  FIG.  1   , the SMSC submits a TFR to the currently serving MME (MME 1 ) to indicate that an SM is to be submitted to the UE. The TFR includes a Max Retransmission Time indicating how long the SMSC is ready to store the SM if it cannot be delivered at once due to the UE being in eDRX. 
     MME 1  correspondingly replies with a TFA indicating Requested Retransmission Time at which the SM should be retransmitted by the SMSC, and will subsequently page the UE at a next paging occasion occurring just shortly before beginning of a next Paging Transmission Window, i.e. just before the indicated Requested Retransmission Time, such that the SM can be timely delivered from the SMSC via MME  1  to the UE when the UE wakes of from its eDRX cycle at the Requested Retransmission Time. 
     Now, a first problem arises if the UE wakes up from its eDRX cycle, thus exiting eDRX mode, for instance due to a UE service request for sending data, and correspondingly initiates NAS signalling towards its currently serving mobility management node, e.g. an MME or a Serving GPRS (General Packet Radio Service) Support Node (SGSN), before having been paged by the serving mobility management node, in this particular example MME 1 . 
     NAS signalling is used to convey non-radio signalling between the UE and the MME for a Long Term Evolution/Evolved Universal Terrestrial Access Network (LTE/E-UTRAN) access. For instance, a NAS request may be a Routing Area Update (RAU) request which updates the location of the UE within the network. A UE initiates a RAU when it detects that it enters a new Routing Area, and thus it will contact the core network, either the current serving SGSN or a new SGSN. 
     Hence, the first problem can be exemplified as occurring in case of an intra SGSN RAU request, i.e. when the UE enters a new Routing Area, but is to remain at the serving SGSN, exemplified in  FIG.  2    by SGSN 1 . When the SMSC attempts to submit the SM to the UE at the TFA specified Requested Retransmission Time, there is a risk that the UE again has entered eDRX mode, and the scheduled MT-SMS delivery will consequently fail. When UE is camping in UTRAN, the eDRX cycle will restart at each Routing Area Update procedure. 
     When the UE is camping in E-UTRAN and GSM, the paging occasion scheme can be maintained, if the serving MME or SGSN would maintain the eDRX cycle regardless of whether the UE requests to change the eDRX cycle at the TAU/RAU. In this scenario, the issue is less troublesome, but the MT-SMS is nevertheless unnecessarily delayed until the next scheduled paging time, extra signalling is required towards the UE, and UE power consumption increases, which indeed should be avoided. 
     Further, a second problem arises if the UE initiates a NAS request towards another mobility management node, thereby effecting an idle mode mobility procedure between two management nodes referred to as an inter MME TAU request, the other node being exemplified by MME 2  in  FIG.  2   , before the UE has responded to the paging message from the network. That is, the paging message has not been sent by the first mobility management node since the paging window has not yet occurred. 
     This would e.g. occur if the UE initiates the MME TAU request after MME 1  has reported the Requested Retransmission Time to the SMSC indicating a next paging occasion based on the eDRX cycle, but before the actual paging occasion occurs. 
     In this case, the SMSC would deliver the MT-SMS to the wrong MME, i.e. MME 1 , at the TFA specified Requested Retransmission Time. 
     SUMMARY 
     An object of the invention is to solve, or at least mitigate, at least one of these problems in the art and thus to provide improved methods of facilitating delivery of Short Messages to a mobile terminal enabled for eDRX mode. 
     This object is attained in a first aspect of the invention by a method of a mobility management node of enabling delivery of a Mobile Terminating, (MT) Short Message (SM) to a mobile terminal, which currently is in eDRX mode. The method comprises receiving an indication from a Short Message Service Gateway Mobile Switching Centre (SMS-GMSC) that the SM is to be delivered, receiving a notification that the mobile terminal has exited the eDRX mode before a paging occasion has occurred, and submitting, in response to the notification, a message indicating to the SMS-GMSC that the mobile terminal is available for delivery of the SM. 
     This object is attained in a second aspect of the invention by a mobility management node configured to enable delivery of an MT SM, to a mobile terminal which currently is in extended eDRX mode, and which mobility management node comprises a processing unit and a memory, said memory containing instructions executable by said processing unit, whereby said mobility management node is operative to receive an indication from an SMS-GMSC that the SM is to be delivered, receive a notification that the mobile terminal has exited the eDRX mode before a paging occasion has occurred, submit, in response to the notification, a message indicating to the SMS-GMSC that the mobile terminal sis available for delivery of the SM. 
     This object is attained in a third aspect of the invention by a method of a mobility management node of enabling delivery of an MT SM to a mobile terminal which currently is in eDRX mode, comprising receiving a notification that the mobile terminal has exited the eDRX mode before a paging occasion has occurred, submitting a context request to another mobility management node by which the mobile terminal was served before the notification was received, receiving from said another mobility management node a context response comprising an indication that the SM is to be delivered; and receiving, from the SMS-GMSC, the SM for delivery to the mobile terminal. 
     This object is attained in a fourth aspect of the invention by a mobility management node configured to enable delivery of an MT SM to a mobile terminal which currently is in eDRX mode, and which mobility management node comprises a processing unit and a memory, said memory containing instructions executable by said processing unit, whereby said mobility management node is operative to receive a notification that the mobile terminal has exited the eDRX mode before a paging occasion has occurred, submit a context request to another mobility management node by which the mobile terminal was served before the notification was received, receive, from said another mobility management node, a context response comprising an indication that the SM is to be delivered, and receive, from the SMS-GMSC, the SM for delivery to the mobile terminal. 
     In an embodiment, the message is submitted directly to the SMS-GMSC. In another embodiment, the message is submitted to the SMS-GMSC via a Home Subscription Server (HSS). 
     In an embodiment, the message submitted to the SMS-GMSC via the HSS further comprises an instruction to the HSS to provide the destination address of the mobility management to the SMS-GMSC. 
     In still another embodiment, the notification is a Non-Access Stratum (NAS) request received from the mobile terminal. 
     In still an embodiment, the notification is a context request received from a serving mobility management node of the mobile terminal, and the method further comprises submitting, to the serving mobility management node, a context response comprising an indication that the SM is to be delivered, and receiving, from the serving mobility management node, a context acknowledgement comprising a destination address of the serving mobility management node for SM delivery, wherein said submitted message further comprises the destination address of the serving mobility management node. 
     In another embodiment, the notification is a context request received from a serving mobility management node of the mobile terminal, said message being submitted to the SMS-GSMC via the serving mobility management node in a context response and further comprising a destination address of the SMS-GSMC. 
     In still an embodiment, the receiving of an indication from a SMS-GMSC that the SM is to be delivered comprises receiving an indication of maximum retransmission time specifying how long the SMS-GMSC will store the SM if it cannot be delivered at once and capability indication indicating if the SMS-GMSC support receiving subsequent notification of mobile terminal availability for delivering the SM, the method further comprising submitting an indication to the SMS-GMSC comprising a requested retransmission time indicating at which point in time the SM should be retransmitted by the SMS-GMSC and capability confirmation that the mobility management node supports the subsequent notification of mobile terminal availability for delivering the SM. 
     In a further embodiment, the message submitted further indicates a time period specifying the time up until the mobile terminal again enters the eDRX mode. 
     Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the element, apparatus, component, means, step, etc.” are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is now described, by way of example, with reference to the accompanying drawings, in which: 
         FIG.  1    shows a prior art timing diagram illustrating an MT SM delivery from an SMSC to an MME; 
         FIG.  2    shows a timing diagram illustrating problems related to the MT SM delivery procedure of  FIG.  1   ; 
         FIG.  3    illustrates an embodiment of a method of the invention; 
         FIG.  4    illustrates another embodiment of a method of the invention; 
         FIG.  5    illustrates yet another embodiment of a method of the invention; 
         FIG.  6    illustrates still another embodiment of a method of the invention; 
         FIG.  7    illustrates yet a further embodiment of a method of the invention; 
         FIG.  8    illustrates still a further embodiment of a method of the invention; 
         FIG.  9    illustrates another embodiment of a method of the invention; 
         FIG.  10    illustrates yet another embodiment of a method of the invention; 
         FIG.  11    illustrates embodiments of a mobility management node of the invention; and 
         FIG.  12    illustrates further embodiment of a mobility management node of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the description. 
       FIG.  1    shows a timing diagram illustrating an MT SM delivery from an SMSC to an MME disclosed in “MT SMS procedures for UEs in extended idle mode DRX”, as previously discussed. 
       FIG.  2    shows a timing diagram illustrating problems related to the MT SM delivery procedure of  FIG.  1   , as previously has been discussed. The SMSC will in the following be referred to as a Short Message Service Gateway Mobile Switching Centre (SMS-GMSC). 
     In short, a first problem arises if the UE  10  wakes up from an eDRX cycle, i.e. it exits an eDRX mode in which it has been residing, before a next paging occasion takes place. The SMS-GMSC  40  has been scheduled for SM delivery at the next paging occasion, and will thus miss the opportunity to deliver the SM to the UE  10  exiting the eDRX mode via MME 1 /SGSN 1   20 ; once the next paging occasion occurs, there is a risk that the UE  10  again has entered eDRX mode, resulting in another SM delivery failure, and the procedure must be repeated. 
     Further, a second problem arises if the UE  10  exits an eDRX mode in which it has been residing before a next paging occasion takes place, in this scenario by performing e.g. an inter MME TAU. In such a scenario, when the SMS-GMSC  40  is scheduled for SM delivery at the next paging occasion, the SMS-GMSC  40  will deliver the SM to MME 1 /SGSN 1   20 , which no longer is the serving MME, instead of delivering the SM to MME 2 /SGSN 2   30 . 
     In the following, MME 1 /SGSN 1  and MME 2 /SGSN 2  will be referred to MME 1  and MME 2 , respectively. However, it should be noted that they embody mobility management nodes of both UTRAN and E-UTRAN. 
       FIG.  3    illustrates an embodiment of a method of the invention performed at MME 1   20  of enabling delivery of an MT SM from the SMS-GMSC  40  to the UE  10 . 
     In a first step S 101 , MME 1   20  receives an indication from the SMS-GMSC  40  that an SM is to be delivered to the UE  10 , which currently is in eDRX mode. Now, if the UE  10  exits the eDRX mode, for instance as a consequence of a NAS request for intra MME TAU, intra SGSN RAU, or a general Service Request, etc., before a paging occasion has occurred, MME 1   20  will receive a notification accordingly in a second step S 102 . 
     In a third step S 103 , MME 1   20  submits to the SMS-GMSC  40 , in response to the indication received in step S 102 , a message indicating that the UE  10  is available for immediate delivery of the SM. As a result, the SMS-GMSC will advantageously not miss out on the opportunity to deliver the SM to the UE  10 , which is currently not in eDRX mode, in step S 104  via MME 1   20 . 
     In an alternative embodiment, the message is not submitted directly to the SMS-GMSC  40 , but via an HSS (not shown in  FIG.  3   ). In such embodiment, the message submitted to the SMS-GMSC  40  via the HSS further comprises an instruction to the HSS to provide the destination address of MME 1   20  (which is known to the HSS) to the SMS-GMSC  40 , in order for the SMS-GSMC  40  to be able to deliver the SM to the UE  10  via MME 1   20 . 
       FIG.  4    illustrates an embodiment of a method of the invention of enabling delivery of an MT SM from the SMS-GMSC  40  to the UE  10 . 
     In a first step S 101 , MME 1   20  receives an indication from the SMS-GMSC  40  that an SM is to be delivered to the UE  10 , which currently is in eDRX mode. Now, if the UE  10  exits the eDRX mode, for instance as a consequence of a NAS request in step S 102   a  for TAU, RAU, or a general Service Request, etc., to an MME 2   30  before a paging occasion has occurred, the other MME 1   20  will receive a notification accordingly. However, in contrast to the embodiment described with reference to  FIG.  3   , the notification is in this scenario not received from the UE  10 , but from MME 2  (now being the serving MME) in the form of a Context Request in step S 102   b.    
     As a consequence, MME 1   20  submits a Context Response in step S 102   c  to be received by MME 2   30  and comprising an indication that the SM is to be delivered. In response thereto, MME 1   20  receives a Context Acknowledgement sent by MME 2  in step S 102   d  and comprising a destination address of the new serving MME, i.e. MME 2   30 , for subsequent SM delivery. 
     In step S 103 , MME 1   20  submits to the SMS-GMSC  40 , in response to the notification received in step S 102   b , a message indicating that the UE  10  is available for immediate delivery of the SM, which message in this embodiment further comprises the destination address of MME 2   30  being the serving MME. 
     As a result, the SMS-GMSC  40  will advantageously deliver the SM to the correct MME in step S 105 , i.e. to MME 2   30 , and further on to the UE  10 , which is currently not in eDRX mode. 
     With reference again to  FIG.  4   , in an alternative embodiment, the notification of the UE  10  having exited eDRX mode is again received in the form of a context request in step S 102   b  from MME 2   30 . However, the message indicating that the SM can be delivered immediately to the UE  10  is submitted in step S 103   a  to the SMS-GSMC  40  via MME 2   30  in the Context Response in step S 102   c , which message in this embodiment further comprises a destination address of the SMS-GSMC  40  for the information of MME 2   30 . 
     It may, similar to the embodiment discussed with reference to  FIG.  4   , be envisaged in an embodiment that the message is not submitted directly to the SMS-GMSC  40 , but via an HSS (not shown in  FIG.  4   ). In such embodiment, the message submitted to the SMS-GMSC  40  via the HSS further comprises an instruction to the HSS to provide the destination address of MME 2   30  to the SMS-GMSC  40 , in order for the SMS-GSMC  40  to be able to deliver the SM to the UE  10  via the correct MME, i.e. MME 2   30 . 
     With reference to  FIGS.  3  and  4   , it can be envisaged in embodiments that step S 101 , where MME 1   20  receives an indication from the SMS-GMSC  40  that an SM is to be delivered to the UE  10 , which currently is in eDRX mode, is expanded to include steps  101   a  and  101   b  of  FIG.  5    to be described in the following. 
       FIG.  5    illustrates an embodiment of the invention performed at MME 1   20  of enabling delivery of an MT SM from the SMS-GMSC  40  to the UE  10  based on the embodiment previously discussed with reference to  FIG.  3   . 
     In a first step S 101   a , MME 1   20  receives an indication from the SMS-GMSC  40  that an SM is to be delivered to the UE  10  in the form of a TFR including a Max Retransmission Time, which indicates how long the SMS-GMSC  40  will store the SM if it cannot be delivered at once, and further a capability indication indicating if the SMS-GMSC  40  support receiving subsequent notification of UE availability for delivering the SM. 
     Thereafter, in step S 101   b , MME 1   20  responds with a TFA indicating Requested Retransmission Time, i.e. the time at which the SM should be retransmitted by the SMS-GMSC  40  since the UE  10  currently is in an eDRX mode. The TFA further indicates whether MME 1  supports subsequent notification of UE availability for delivering the SM when the UE  10  exits eDRX mode. 
     As previously has been described, if the UE  10  exits the eDRX mode, for instance as a consequence of a NAS request for intra MME TAU, intra SGSN RAU, or a general Service Request, etc., before a paging occasion has occurred, MME 1   20  will receive a notification accordingly in step S 102 . 
     In a step S 103 , MME 1   20  submits to the SMS-GMSC  40 , in response to the indication received in step S 102 , a message indicating that the UE  10  is available for immediate delivery of the SM. As a result, the SMS-GMSC will advantageously not miss out on the opportunity to deliver the SM to the UE  10 , which is currently not in eDRX mode, in step S 104  via MME 1   20 . 
     Optionally, for all embodiments of the invention, the message includes a Maximum-UE-Availability-Time, i.e. a time period specifying the time up until the UE  10  again enters the eDRX mode, thereby advantageously indicating a time window during which the UE  10  will be available for SM delivery. 
     As can be seen in  FIG.  5   , the submission in step S 103  either uses an existing message such as an OFR, or a new Diameter message. The SMS-GMSC  40  acknowledges the message in step S 104   a  correspondingly using an existing message such as an OFA, or a new Diameter message. 
     The pending SM is delivered by the SMS-GMSC  40  in the TFR of step S 104 , and MME 1  acknowledges the delivery accordingly with a TFA in step S 106 . 
       FIG.  6    illustrates an embodiment of the invention performed at MME 1   20  of enabling delivery of an MT SM from the SMS-GMSC  40  to the UE  10  based on an embodiment previously discussed with reference to  FIG.  4   . 
     In a first step S 101   a , MME 1   20  receives an indication from the SMS-GMSC  40  that an SM is to be delivered to the UE  10  in the form of a TFR including a Max Retransmission Time, which indicates how long the SMS-GMSC  40  will store the SM if it cannot be delivered at once, and further a capability indication indicating if the SMS-GMSC  40  support receiving subsequent notification of UE availability for delivering the SM. 
     Thereafter, in step S 101   b , MME 1   20  responds with a TFA indicating Requested Retransmission Time, i.e. the time at which the SM should be retransmitted by the SMS-GMSC  40  since the UE  10  currently is in an eDRX mode. The TFA further indicates whether MME 1  supports subsequent notification of UE availability for delivering the SM when the UE  10  exits eDRX mode. 
     As previously has been described, if the UE  10  exits the eDRX mode, for instance as a consequence of a NAS request for intra MME TAU, intra SGSN RAU, or a general Service Request, etc., before a paging occasion has occurred, MME 1   20  will receive a notification accordingly in a second step S 102 . 
     In step S 103   b , MME 1   20  submits to the SMS-GMSC  40 , via the HSS  50 , in response to the indication received in step S 102 , a message indicating that the UE  10  is available for immediate delivery of the SM. The message may be submitted e.g. in the form of an Update Location Request (ULR) or Notify-Request (NOR) and includes an instruction to the HSS  50  to subsequently provide the destination address of MME 1   20  to the SMS-GMSC  40 . 
     The HSS  50  responds accordingly in step S 103   c  with an acknowledgement in the form of e.g. a Update Location Answer (ULA) or Notify-Answer (NOA), and sends in step S 103   d  the message indicating UE availability and address of MME 1   20  in an Alert-Service-Centre-Request (ALR). The SMS-GMSC thus sends an acknowledgement Alert-Service-Centre-Answer (ALA) in step S 103   e  to the HSS  50 . 
     Optionally, the message in S 103   b  and S 103   d  includes a Maximum-UE-Availability-Time, i.e. a time period specifying the time up until the UE  10  again enters the eDRX mode, thereby advantageously indicating a time window during which the UE  10  will be available for SM delivery. 
     The pending SM is delivered by the SMS-GMSC  40  in the TFR of step S 104 , and MME 1  acknowledges the delivery accordingly with a TFA in step S 106 . As a result, the SMS-GMSC  40  will advantageously not miss out on the opportunity to deliver the SM to the UE  10 , which is currently not in eDRX mode, in step S 104  via MME 1   20 . 
       FIG.  7    illustrates an embodiment of the invention of enabling delivery of an MT SM from the SMS-GMSC  40  to the UE  10  based on an embodiment previously discussed with reference to  FIG.  4   . 
     In a first step S 101   a , MME 1   20  receives an indication from the SMS-GMSC  40  that an SM is to be delivered to the UE  10  in the form of a TFR including a Max Retransmission Time, which indicates how long the SMS-GMSC  40  will store the SM if it cannot be delivered at once, and further a capability indication indicating if the SMS-GMSC  40  support receiving subsequent notification of UE availability for delivering the SM. 
     Thereafter, in step S 101   b , MME 1   20  responds with a TFA indicating Requested Retransmission Time, i.e. the time at which the SM should be retransmitted by the SMS-GMSC  40  since the UE  10  currently is in an eDRX mode. The TFA further indicates whether MME 1  supports subsequent notification of UE availability for delivering the SM when the UE  10  exits eDRX mode. 
     If the UE  10  exits the eDRX mode, for instance as a consequence of a NAS request in step S 102   a  for TAU, RAU, or a general Service Request, etc., to MME 2   30  before a paging occasion has occurred, MME 1   20  will receive a notification accordingly from MME 2   30  (now being the serving MME) in the form of a Context Request in step S 102   b.    
     As a consequence, MME 1   20  submits a Context Response in step S 102   c  to MME 2   30  comprising an indication that the SM is to be delivered, which message in this embodiment further comprises a destination address of the SMS-GSMC  40  for the information of MME 2   30 . In response thereto, MME 2   30  transmits a Context Acknowledgement in step S 102   d  to MME 1   20 . 
     In step S 103   a , MME 2   30  submits to the SMS-GMSC  40 , in response to the indication received in step S 102   c , a message indicating that the UE  10  is available for immediate delivery of the SM. As a result, the SMS-GMSC  40  will advantageously deliver the SM to the correct MME in step S 105 , i.e. to MME 2   30 , and further on to the UE  10 , which is currently not in eDRX mode. 
     Optionally, the message includes a Maximum-UE-Availability-Time, i.e. a time period specifying the time up until the UE  10  again enters the eDRX mode, thereby advantageously indicating a time window during which the UE  10  will be available for SM delivery. 
     As can be seen in  FIG.  7   , the submission in step S 103   a  either uses an existing message such as an OFR, or a new Diameter message. The SMS-GMSC  40  acknowledges the message in step S 105   a  correspondingly using an existing message such as an OFA, or a new Diameter message. 
     The pending SM is delivered by the SMS-GMSC  40  in the TFR of step S 105 , and MME 2   30  acknowledges the delivery accordingly with a TFA in step S 106   a.    
       FIG.  8    illustrates an embodiment of the invention of enabling delivery of an MT SM from the SMS-GMSC  40  to the UE  10  related to that previously discussed with reference to  FIG.  7   . 
     However, in this particular embodiment, the message indicating UE availability for SM delivery is sent by MME 2   30  to the SMS-GSMC  40  via the HSS  50 . 
     In a first step S 101   a , MME 1   20  receives an indication from the SMS-GMSC  40  that an SM is to be delivered to the UE  10  in the form of a TFR including a Max Retransmission Time, which indicates how long the SMS-GMSC  40  will store the SM if it cannot be delivered at once, and further a capability indication indicating if the SMS-GMSC  40  support receiving subsequent notification of UE availability for delivering the SM. 
     Thereafter, in step S 101   b , MME 1   20  responds with a TFA indicating Requested Retransmission Time, i.e. the time at which the SM should be retransmitted by the SMS-GMSC  40  since the UE  10  currently is in an eDRX mode. The TFA further indicates whether MME 1  supports subsequent notification of UE availability for delivering the SM when the UE  10  exits eDRX mode. 
     If the UE  10  exits the eDRX mode, for instance as a consequence of a NAS request in step S 102   a  for TAU, RAU, or a general Service Request, etc., to MME 2   30  before a paging occasion has occurred, MME 1   20  will receive a notification accordingly from MME 2   30  (now being the serving MME) in the form of a Context Request in step S 102   b.    
     As a consequence, MME 1   20  submits a Context Response in step S 102   c  to MME 2   30  comprising an indication that the SM is to be delivered, which message in this embodiment further comprises a destination address of the SMS-GSMC  40  for the information of MME 2   30 . In response thereto, MME 2   30  transmits a Context Acknowledgement in step S 102   d  to MME 1   20 . 
     In step S 103   f , MME 2   30  submits to the SMS-GMSC  40 , via the HSS  50 , in response to the indication received in step S 102   c , a message indicating that the UE  10  is available for immediate delivery of the SM. The message may be submitted e.g. in the form of an ULR or NOR and includes an instruction to the HSS  50  to subsequently provide the destination address of MME 2   30  to the SMS-GMSC  40 . 
     The HSS  50  responds accordingly in step S 103   g  with an acknowledgement in the form of e.g. a ULA or NOA, and sends in step S 103   h  the message indicating UE availability and address of MME 2   30  in an ALR. The SMS-GMSC  40  thus sends an acknowledgement (ALA) in step S 103   i  to the HSS  50 . 
     Optionally, the message in steps S 103   f  and S 103   h  includes a Maximum-UE-Availability-Time, i.e. a time period specifying the time up until the UE  10  again enters the eDRX mode, thereby advantageously indicating a time window during which the UE  10  will be available for SM delivery. 
     The SMS-GMSC  40  will advantageously deliver the SM to the correct MME in step S 105 , i.e. to MME 2   30 , and further on to the UE  10 , which is currently not in eDRX mode, and MME 2   30  acknowledges the delivery accordingly with a TFA in step S 106   a.    
       FIG.  9    illustrates an embodiment of the invention of enabling delivery of an MT SM from the SMS-GMSC  40  to the UE  10  based on an embodiment previously discussed with reference to  FIG.  4   . 
     In a first step S 101   a , MME 1   20  receives an indication from the SMS-GMSC  40  that an SM is to be delivered to the UE  10 . Preferably the indication is in the form of a TFR including a Max Retransmission Time, which indicates how long the SMS-GMSC  40  will store the SM if it cannot be delivered at once. The indication may further include a capability indication indicating if the SMS-GMSC  40  support receiving subsequent notification of UE availability for delivering the SM. 
     Thereafter, in step S 101   b , MME 1   20  responds to the SMS-GMSC  40 , preferably with a TFA indicating Requested Retransmission Time, i.e. the time at which the SM should be retransmitted by the SMS-GMSC  40  since the UE  10  currently is in an eDRX mode. The TFA may further indicate whether MME 1  supports subsequent notification of UE availability for delivering the SM when the UE  10  exits eDRX mode. 
     If the UE  10  exits the eDRX mode, for instance as a consequence of a NAS request in step S 102   a  for TAU, RAU, or a general Service Request, etc., to an MME 2   30  before a paging occasion has occurred, the other MME 1   20  will receive a notification accordingly from MME 2   30  (now being the serving MME) in the form of a Context Request in step S 102   b.    
     As a consequence, MME 1   20  submits a Context Response in step S 102   c  to MME 2   30  comprising an indication that the SM is to be received by MME 2   30 . In response thereto, MME 2   30  transmits a Context Acknowledgement in step S 102   d  to MME 1   20  comprising a destination address of MME 2   30 . 
     In step S 103 , MME 1   20  submits to the SMS-GMSC  40  a message indicating that the UE  10  is available for immediate delivery of the SM, and the destination address of MME 2   30 . As a result, the SMS-GMSC  40  will advantageously deliver the SM to the correct MME in step S 104 , i.e. to MME 2   30 , and further on to the UE  10 , which is currently not in eDRX mode. 
     Optionally, the message includes a Maximum-UE-Availability-Time, i.e. a time period specifying the time up until the UE  10  again enters the eDRX mode, thereby advantageously indicating a time window during which the UE  10  will be available for SM delivery. 
     As can be seen in  FIG.  9   , the submission in step S 103  either uses an existing message such as an OFR, or a new Diameter message. The SMS-GMSC  40  acknowledges the message in step S 104   a  correspondingly using an existing message such as an OFA, or a new Diameter message. 
     The pending SM is delivered by the SMS-GMSC  40  in the TFR of step S 105 , and MME 2   30  acknowledges the delivery accordingly with a TFA in step S 106   a.    
       FIG.  10    illustrates an embodiment of the invention of enabling delivery of an MT SM from the SMS-GMSC  40  to the UE  10  related to that previously discussed with reference to  FIG.  9   . 
     However, in this particular embodiment, the message indicating UE availability for SM delivery is sent by MME 1   20  to the SMS-GSMC  40  via the HSS  50 . 
     In a first step S 101   a , MME 1   20  receives an indication from the SMS-GMSC  40  that an SM is to be delivered to the UE  10  in the form of a TFR including a Max Retransmission Time, which indicates how long the SMS-GMSC  40  will store the SM if it cannot be delivered at once, and further a capability indication indicating if the SMS-GMSC  40  support receiving subsequent notification of UE availability for delivering the SM. 
     Thereafter, in step S 101   b , MME 1   20  responds with a TFA indicating Requested Retransmission Time, i.e. the time at which the SM should be retransmitted by the SMS-GMSC  40  since the UE  10  currently is in an eDRX mode. The TFA further indicates whether MME 1  supports subsequent notification of UE availability for delivering the SM when the UE  10  exits eDRX mode. 
     If the UE  10  exits the eDRX mode, for instance as a consequence of a NAS request in step S 102   a  for TAU, RAU, or a general Service Request, etc., to MME 2   30  before a paging occasion has occurred, MME 1   20  will receive a notification accordingly from MME 2   30  (now being the serving MME) in the form of a Context Request in step S 102   b.    
     As a consequence, MME 1   20  submits a Context Response in step S 102   c  to MME 2   30  comprising an indication that the SM is to be delivered. In response thereto, MME 2   30  transmits a Context Acknowledgement in step S 102   d  to MME 1   20  comprising a destination address of MME 2   30 . 
     In step S 103   b , MME 1   20  submits to the SMS-GMSC  40 , via the HSS  50 , a message indicating that the UE  10  is available for immediate delivery of the SM. The message may be submitted e.g. in the form of an ULR or NOR and includes an instruction to the HSS  50  to subsequently provide the destination address of MME 2   30  to the SMS-GMSC  40 . 
     The HSS  50  responds accordingly in step S 103   c  with an acknowledgement in the form of e.g. a ULA or NOA, and sends in step S 103   d  the message indicating UE availability and address of MME 2   30  in an ALR. The SMS-GMSC  40  thus sends an acknowledgement (ALA) in step S 103   e  to the HSS  50 . 
     Optionally, the message in S 103   b  and S 103   d  includes a Maximum-UE-Availability-Time, i.e. a time period specifying the time up until the UE  10  again enters the eDRX mode, thereby advantageously indicating a time window during which the UE  10  will be available for SM delivery. 
     The SMS-GMSC  40  will advantageously deliver the SM to the correct MME in step S 105 , i.e. to MME 2   30 , and further on to the UE  10 , which is currently not in eDRX mode, and MME 2   30  acknowledges the delivery accordingly with a TFA in step S 106   a.    
     With reference to Figure ii, the steps of the methods performed by the mobility management nodes  20 ,  30  according to embodiments of the invention are in practice performed by a processing unit  21 ,  31  embodied in the form of one or more microprocessors arranged to execute a computer program  22 ,  32  downloaded to a suitable storage medium  23 ,  33  associated with the microprocessor, such as a Random Access Memory (RAM), a Flash memory or a hard disk drive. The processing unit  21 ,  31  is arranged to cause the computing device  20 ,  30  to carry out the method according to embodiments of the present invention when the appropriate computer program  22 ,  32  comprising computer-executable instructions is downloaded to the storage medium  23 ,  33  and executed by the processing unit  21 ,  31 . The storage medium  23 ,  33  may also be a computer program product comprising the computer program  22 ,  32 . Alternatively, the computer program  22 ,  32  may be transferred to the storage medium  23 ,  33  by means of a suitable computer program product, such as a Digital Versatile Disc (DVD) or a memory stick. As a further alternative, the computer program  22 ,  32  may be downloaded to the storage medium  23 ,  33  over a network. The processing unit  21 ,  31  may alternatively be embodied in the form of a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a complex programmable logic device (CPLD), etc. 
       FIG.  12    illustrates a first mobility management node  20  according to an embodiment of the invention configured to enable delivery of an MT SM to a mobile terminal. The mobility management node  20  comprises receiving means  24  adapted to receive an indication from an SMS-GMSC that the SM is to be delivered, receiving means  25  adapted to receive a notification that the mobile terminal has exited an eDRX mode before a paging occasion has occurred, and submitting means  26  adapted to submit, in response to the notification, a message indicating to the SMS-GMSC that the mobile terminal is available for delivery of the SM. 
     The means  24 - 26  may comprise a communications interface for receiving and providing information, and further a local storage for storing data, and may (in analogy with the description given in connection to  FIG.  11   ) be implemented by a processor embodied in the form of one or more microprocessors arranged to execute a computer program downloaded to a suitable storage medium associated with the microprocessor, such as a RAM, a Flash memory or a hard disk drive. 
       FIG.  12    illustrates a second mobility management node  30  according to an embodiment of the invention configured to enable delivery of an MT SM to a mobile terminal. The mobility management node  30  comprises receiving means  34  adapted to receive a notification that the mobile terminal has exited an eDRX mode before a paging occasion has occurred submitting means  35  adapted to submit a context request to another mobility management node by which the mobile terminal was served before the notification was received, receiving means  36  adapted to receive, from said another mobility management node, a context response comprising an indication that the SM is to be delivered and a destination address of an SMS-GMSC delivering the SM, and submitting means  37  adapted to submit, in response to the context response, a message indicating to the SMS-GMSC that the mobile terminal is available for delivery of the SM. 
     The means  34 - 37  may comprise a communications interface for receiving and providing information, and further a local storage for storing data, and may (in analogy with the description given in connection to  FIG.  11   ) be implemented by a processor embodied in the form of one or more microprocessors arranged to execute a computer program downloaded to a suitable storage medium associated with the microprocessor, such as a RAM, a Flash memory or a hard disk drive. 
     Some embodiments described above may be summarised in the following manner: 
     A first embodiment is directed to a method of a mobility management node of enabling delivery of a Mobile Terminating (MT) Short Message (SM), to a mobile terminal, which currently is in extended idle mode discontinuous reception (eDRX) mode. 
     The method comprising:
         receiving an indication from a Short Message Service Gateway Mobile Switching Centre (SMS-GMSC) that the SM is to be delivered;   receiving a notification that the mobile terminal has exited the eDRX mode before a paging occasion has occurred; and   submitting, in response to the notification, a message indicating to the SMS-GMSC that the mobile terminal is available for delivery of the SM.       

     Said message may be submitted directly to the SMS-GMSC. 
     Said message may be submitted to the SMS-GMSC via a Home Subscription Server (HSS). 
     The message submitted to the SMS-GMSC via the HSS may further comprise an instruction to the HSS to provide the destination address of the mobility management to the SMS-GMSC. 
     The notification may be a Non-Access Stratum (NAS) request received from the mobile terminal. 
     The may further comprise: receiving, from the SMS-GMSC, the SM for delivery to the mobile terminal. 
     The notification may be a context request received from a serving mobility management node of the mobile terminal, the method may further comprise: submitting, to the serving mobility management node, a context response comprising an indication that the SM is to be delivered; and receiving, from the serving mobility management node, a context acknowledgement comprising a destination address of the serving mobility management node for SM delivery, wherein said submitted message further comprises the destination address of the serving mobility management node. 
     The notification may be a context request received from a serving mobility management node of the mobile terminal, said message being submitted to the SMS-GSMC via the serving mobility management node in a context response and further comprising a destination address of the SMS-GSMC. 
     The receiving of an indication from a SMS-GMSC that the SM is to be delivered may comprise:
         receiving an indication of maximum retransmission time specifying how long the SMS-GMSC will store the SM if it cannot be delivered at once and capability indication indicating if the SMS-GMSC support receiving subsequent notification of mobile terminal availability for delivering the SM; and the method further comprising:   submitting an indication to the SMS-GMSC comprising a requested retransmission time indicating at which point in time the SM should be retransmitted by the SMS-GMSC and capability confirmation that the mobility management node supports the subsequent notification of mobile terminal availability for delivering the SM.       

     A second embodiment is directed to a method of a mobility management node of enabling delivery of a Mobile Terminating (MT) Short Message (SM) to a mobile terminal, which currently is in extended idle mode discontinuous reception (eDRX) mode. 
     The method comprising:
         receiving a notification that the mobile terminal has exited the eDRX mode before a paging occasion has occurred;   submitting a context request to another mobility management node by which the mobile terminal was served before the notification was received;   receiving, from said another mobility management node, a context response comprising an indication that the SM is to be delivered; and   receiving, from the SMS-GMSC, the SM for delivery to the mobile terminal.       

     Said message may be submitted directly to the SMS-GMSC. 
     Said message may be submitted to the SMS-GMSC via a Home Subscription Server (HSS), the message submitted to the SMS-GMSC via the HSS further comprises an instruction to the HSS to provide the destination address of the mobility management to the SMS-GMSC. 
     Said message submitted further indicating a time period specifying the time up until the mobile terminal again enters the eDRX mode. 
     Another embodiment is directed to a mobility management node configured to enable delivery of a Mobile Terminating (MT) Short Message (SM) to a mobile terminal, which currently is in extended idle mode discontinuous reception (eDRX) mode, and which mobility management node comprises a processing unit and a memory, said memory containing instructions executable by said processing unit, whereby said mobility management node is operative to:
         receive an indication from a Short Message Service Gateway Mobile Switching Centre (SMS-GMSC) that the SM is to be delivered;   receive a notification that the mobile terminal has exited the eDRX mode before a paging occasion has occurred; and   submit, in response to the notification, a message indicating to the SMS-GMSC that the mobile terminal is available for delivery of the SM.       

     The mobility management node may be operative to submit the message directly to the SMS-GMSC. 
     The mobility management node may be operative to submit the message to the SMS-GMSC via a Home Subscription Server (HSS). 
     The mobility management node may further be operative to include an instruction to the HSS to provide the destination address of the mobility management to the SMS-GMSC in the message submitted to the SMS-GMSC via the HSS. 
     The notification may be a Non-Access Stratum (NAS) request received from the mobile terminal. 
     The notification may be a context request received from a serving mobility management node of the mobile terminal, further being operative to:
         submit, to the serving mobility management node, a context response comprising an indication that the SM is to be delivered; and   receive, from the serving mobility management node, a context acknowledgement comprising a destination address of the serving mobility management node for SM delivery, wherein said submitted message further comprises the destination address of the serving mobility management node.       

     The notification may be a context request received from a serving mobility management node of the mobile terminal, further being operative to submit the message to the SMS-GSMC via the serving mobility management node in a context response and further to include a destination address of the SMS-GSMC. 
     The mobility management node may further be operative to, when receiving an indication from a SMS-GMSC that the SM is to be delivered:
         receive an indication of maximum retransmission time specifying how long the SMS-GMSC will store the SM if it cannot be delivered at once and capability indication indicating if the SMS-GMSC support receiving subsequent notification of mobile terminal availability for delivering the SM; the method further comprising: and   submit an indication to the SMS-GMSC comprising a requested retransmission time indicating at which point in time the SM should be retransmitted by the SMS-GMSC and capability confirmation that the mobility management node supports the subsequent notification of mobile terminal availability for delivering the SM.       

     Another embodiment is directed to a mobility management node configured to enable delivery of a Mobile Terminating (MT) Short Message (SM) to a mobile terminal which currently is in extended idle mode discontinuous reception (eDRX) mode, and which mobility management node comprises a processing unit and a memory, said memory containing instructions executable by said processing unit, whereby said mobility management node is operative to:
         receive a notification that the mobile terminal has exited the eDRX mode before a paging occasion has occurred;   submit a context request to another mobility management node by which the mobile terminal was served before the notification was received;   receive, from said another mobility management node, a context response comprising an indication that the SM is to be delivered; and   receive, from the SMS-GMSC, the SM for delivery to the mobile terminal.       

     The mobility management node may further be operative to submit said message directly to the SMS-GMSC. 
     The mobility management node may further be operative to submit said message to the SMS-GMSC via a Home Subscription Server (HSS) the message submitted to the SMS-GMSC via the HSS further comprising an instruction to the HSS to provide the destination address of the mobility management to the SMS-GMSC. 
     The mobility management node may further be operative to include, in said submitted message, a time period specifying the time up until the mobile terminal again enters the eDRX mode. 
     Another embodiment is directed to a first computer program comprising computer-executable instructions for causing a device to perform steps recited in the first embodiment when the computer-executable instructions are executed on a processing unit included in the device. 
     Another embodiment is directed to a computer program product comprising a computer readable medium, the computer readable medium having the first computer program embodied thereon. 
     Another embodiment is directed to a second computer program comprising computer-executable instructions for causing a device to perform steps recited in the second embodiment summarized above when the computer-executable instructions are executed on a processing unit included in the device. 
     Another embodiment is directed to a computer program product comprising a computer readable medium, the computer readable medium having the second computer program embodied thereon. 
     The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.