Patent Description:
In legacy, i.e., existing, systems, the procedure for mobile terminated-short message service (MT-SMS) delivery is triggered by the short message service center (SMSC) by requesting Routing Information for SMS to the home subscriber server/home location register (HSS/HLR) as defined in Third Generation Partnership Project (3GPP) Technical Specification (TS) <NUM>, for example.

When a user equipment (UE) is not registered over any access network (<NUM>/<NUM>/<NUM>), the HSS/HLR responds with an Absent Subscriber error and informs the SMSC that the SMSC will be notified when the UE becomes available again.

The HSS/HLR then sets the UE Reachability for SMS flags for the UE (e.g. MNRF, URRP-MME). When HSS/HLR receives an Update Location for a UE which has its UE Reachability flag set, the HSS/HLR then alerts the SMSC that the SMSC can re-attempt the MT-SMS delivery again.

The procedure for MT-SMS delivery over <NUM>rd Generation Partnership Project (3GPP) <NUM>th Generation (<NUM>) (also known as New Radio (NR)) Non-access Stratum (NAS) is based on the same principles as for legacy systems. The SMSC requests Routing Information for SMS to the HSS/unified data management (UDM) as defined in 3GPP TS <NUM> for example.

However, the procedure for MT-SMS delivery re-attempt in 3GPP TS <NUM> is only covering the case of re-attempt when the MT-SMS delivery via the registered access and management function/short message service function (AMF/SMSF) failed. Arrangements to support MT-SMS delivery re-attempt when the UE is not registered in the <NUM>th Generation Core (5GC) network for SMS service in the first place (e.g., there is no SMSF registered in UDM when the SMSC requests routing information to the UDM) are not defined by 3GPP.

A UE may not be considered to be registered in 5GC for SMS service when the UE is not registered in the 5GC at all (i.e., not registered in AMF) or when the UE is registered in 5GC via an AMF but for some reason the AMF did not select an SMSF for the UE (e.g., the UE did not indicate support for SMS or the AMF area is restricted for the UE or due to error situation when contacting the SMSF).

In either of the above cases, the SMSC may be required to store the message for a while until the SMSC is alerted by the HLR/HSS/UDM that the UE is reachable for SMS service again.

A straightforward solution may be to apply the same principles as for the legacy system by having the HSS/UDM subscribe to UE reachability status notification. However, for the case of 5GC, this is not valid as reachability is managed and reported by the AMF, while the SMS Transport service is managed by the SMSF instead.

That may mean that if the HSS/UDM alerts the SMSC upon detecting an event for UE reachability in an AMF (e.g., when the AMF registers in UDM), but while an SMSF is not yet registered in the UDM for the UE, an endless loop of unsuccessful MT-SMS delivery re-attempts may result. <FIG> shows this case in the context of UDICOM as defined in TS <NUM> for example, where the HSS and the UDM are separated and interwork making use of Nudm services.

The flow diagram of <FIG> includes an access and management function (AMF) <NUM>, a short message service function (SMSF) <NUM>, unified data management (UDM) <NUM>, home subscriber server/home location register (HSS/HLR) <NUM> and a short message service center (SMSC) <NUM>. As shown in <FIG>, the UE is not registered over any access (<NUM>/<NUM>/<NUM>) (as in step <NUM>). The HSS/HLR <NUM> receives a request for routing information from the SMSC <NUM> (as in step <NUM>) and therefore the HSS/HLR <NUM> attempts to retrieve the registered SMSF <NUM> address (if any) from the UDM <NUM> (as in step <NUM>); however, since the UE is not registered, the UDM <NUM> does not find any SMSF <NUM> registered in the UDM <NUM> and responds accordingly (as in step <NUM>). In step <NUM>, the HSS/HLR <NUM> responds with an Absent Subscriber error and informs the SMSC <NUM> that the HSS/HLR <NUM> will be notified when the UE becomes available again in step <NUM>.

The HSS/HLR <NUM> then sets the UE Reachability for SMS flags for the UE (e.g. MNRF, URRP-MME), as in steps <NUM> and <NUM> of <FIG>. Later, in step <NUM>, the UE may register in the access network (<NUM>/<NUM>/<NUM>) in the AMF <NUM> and the AMF <NUM> registers in the UDM <NUM>, as well. In step <NUM>, since e.g., the UE and AMF <NUM> are registered, the UDM <NUM> clears/resets the flag (but the SMSF is still not registered). When the HSS/HLR <NUM> receives an Update Location for a UE which has its UE Reachability flag set, as in step <NUM>, the HSS/HLR <NUM> then alerts the SMSC <NUM> that the SMSC <NUM> can re-attempt the MT-SMS delivery again, as in step <NUM>. Thus, in step <NUM>, the SMSC <NUM> again sends a request for routing information to HSS/HLR <NUM> and the HSS/HLR <NUM> re-attempts to retrieve the registered SMSF <NUM> address (if any) from the UDM <NUM> in step <NUM>; however, since the SMSF <NUM> is still not registered, the UDM <NUM> does not find any SMSF <NUM> registered in the UDM <NUM> and responds accordingly in step <NUM>. The process is repeated over and over in an endless loop as shown in step <NUM>.

The prior art further includes the following document:
"<NPL>.

Further detailed embodiments are defined in the dependent claims.

Some embodiments of the present disclosure propose a definition and/or use of a NEW flag and/or event to detect UE reachability for SMS (e.g., SMSF registration in UDM) to cover the cases where e.g., there is an MT-SMS pending due to the UE not being registered in the 5GC for SMS service.

The NEW flag/event proposed by some embodiments of the present disclosure may provide support for the MT-SMS delivery reattempt when the UE is NOT registered for SMS service in the 5GC (e.g., when the SMSF is NOT registered in the UDM). As described above, the existing UE Reachability flags/events do not provide proper support for this case.

Before describing in detail exemplary embodiments, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to short message service (SMS) delivery. Accordingly, components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

The UE herein can be any type of wireless device capable of communicating with a network node or another UE over radio signals. In some embodiments, the UE may be an autonomous machine configured to communicate via IMS. The UE herein can by any type of communication device capable of communicating with another UE, an application server, a network node, a server, an IMS NF or other IMS network node, via a wired connection and/or a wireless connection. The UE may also be a radio communication device, target device, device to device (D2D) UE, machine type UE or UE capable of machine to machine communication (M2M), low-cost and/or low-complexity UE, a sensor equipped with UE, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, Customer Premises Equipment (CPE), an Internet of Things (IoT) device, or a Narrowband IoT (NB-IOT) device etc..

In some embodiments, the term "node" is used herein and can be any kind of network node, such as, a subscriber database node, a core network node, such as a <NUM> and/or NR network node, an IMS node, a Network Function (NF) node, such as, for example, a P-CSCF node, an S-CSCF node, an I-CSCF node, an AMF node, an SMF node, an NRF node, a UDM node, an HSS node, an HLR node, a SMSC node, a SMSF node, etc..

A node may include physical components, such as processors, allocated processing elements, or other computing hardware, computer memory, communication interfaces, and other supporting computing hardware. The node may use dedicated physical components, or the node may be allocated use of the physical components of another device, such as a computing device or resources of a datacenter, in which case the node is said to be virtualized. A node may be associated with multiple physical components that may be located either in one location, or may be distributed across multiple locations.

It should be understood that the flags and events discussed in the present disclosure may have any name and should not be limited to the specific names used herein, which are exemplary and/descriptive, such as, "SMSF registration notification" flag or "UE ready for SMS" event, since the flag or event may, for example, be given another name in a specification, even though the use/function is as disclosed in the present disclosure.

Any two or more embodiments described in this disclosure may be combined in any way with each other.

Note also that some embodiments of the present disclosure may be supported by standard documents disclosed in Third Generation Partnership Project (3GPP) technical specifications. That is, some embodiments of the description can be supported by the above documents. In addition, all the terms disclosed in the present document may be described by the above standard documents.

Note that although terminology from one particular wireless system, such as, for example, <NUM>rd Generation Partnership Project (3GPP), Long Term Evolution (LTE), <NUM>th Generation (<NUM>) (also known as New Radio (NR)), may be used in this disclosure, this should not be seen as limiting the scope of the disclosure to only the aforementioned system.

Note further, that functions described herein as being performed by a UE <NUM> or a UDM node <NUM> or an HSS node <NUM> or any network node may be distributed over a plurality of UEs <NUM> or a plurality of UDM nodes <NUM> or a plurality of HSS nodes <NUM> or a plurality of network nodes. In other words, it is contemplated that the functions of the UE <NUM>, UDM node <NUM>, HSS node <NUM> or network node described herein are not limited to performance by a single physical device and, in fact, can be distributed among several physical devices.

Referring again to the drawing figures, in which like elements are referred to by like reference numerals, there is shown in <FIG> a schematic diagram of an example communication system <NUM>, according to another embodiment, constructed in accordance with the principles of the present disclosure. The communication system <NUM> in <FIG> is a non-limiting example and other embodiments of the present disclosure may be implemented by one or more other systems and/or networks. Referring to <FIG>, the system <NUM> includes a UE <NUM>, in addition to various support elements for supporting short message service (SMS) delivery to the UE <NUM>, such as, a radio access network (RAN) <NUM> (e.g., <NUM> also known as NR RAN), which may provide radio access to the UE <NUM>. The system <NUM> includes an Access and Mobility Management Function (AMF) node <NUM>, which may provide a function for access and mobility management for the UE <NUM>. The system <NUM> includes the UDM node <NUM>, which stores and manages subscriber information. The system <NUM> includes the HSS node <NUM>, which may provide a database of user subscriber information. It should be noted that, for simplicity, a single node is shown for the various entities in the system <NUM> depicted in <FIG> (e.g., a single UE <NUM>, a single RAN <NUM>, a single AMF node <NUM>, a single UDM node <NUM>, a single HSS node <NUM> and a single SMSC node <NUM>, etc.); however, it should be understood that the system <NUM> may include numerous entities/nodes of those shown in <FIG>, as well as, additional entities/nodes not shown in <FIG>. In addition, the system <NUM> may include many more connections than those shown in <FIG>.

The UDM node <NUM> includes a notifier <NUM>, which may be configured to set a short message service, SMS, function, SMSF, registration notification flag to detect an SMSF registration event associated with a user equipment, UE <NUM>.

The HSS node <NUM> includes a subscriber <NUM>, which may be configured to send a request to subscribe to a notification at a unified data management, UDM, node <NUM> about a short message service, SMS, function, SMSF, registration event associated with a user equipment, UE <NUM>.

Example implementations, in accordance with an embodiment, of the UE <NUM>, UDM node <NUM>, HSS node <NUM> and a network node <NUM> (e.g., SMSC node, AMF node, etc.) discussed in the preceding paragraphs will now be described with reference to <FIG>.

The network node <NUM> (e.g., AMF node, SMSC node, etc.) includes a communication interface <NUM>, processing circuitry <NUM>, and memory <NUM>. The communication interface <NUM> may be configured to communicate with the UE <NUM> and/or other elements in the system <NUM> to facilitate delivery of an SMS message to the UE <NUM> according to one or more of the techniques in the present disclosure. In some embodiments, the communication interface <NUM> may be formed as or may include, for example, one or more radio frequency (RF) transmitters, one or more RF receivers, and/or one or more RF transceivers, and/or may be considered a radio interface. In some embodiments, the communication interface <NUM> may also include a wired interface.

The processing circuitry <NUM> may include one or more processors <NUM> and memory, such as, the memory <NUM>. In particular, in addition to a traditional processor and memory, the processing circuitry <NUM> may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions.

Thus, the network node <NUM> may further include software stored internally in, for example, memory <NUM>, or stored in external memory (e.g., database) accessible by the network node <NUM> via an external connection. The software may be executable by the processing circuitry <NUM>. The processing circuitry <NUM> may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by the network node <NUM>. The memory <NUM> is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software may include instructions stored in memory <NUM> that, when executed by the processor <NUM>, causes the processing circuitry <NUM> and/or configures the network node <NUM> to perform the processes described herein with respect to the network node <NUM> (e.g., AMF node, SMSC node, etc.).

The UE <NUM> includes a communication interface <NUM>, processing circuitry <NUM>, and memory <NUM>. The communication interface <NUM> may be configured to communicate with the RAN <NUM> and/or AMF node <NUM> and/or other elements in the system <NUM> to be delivered an SMS message according to the techniques in the present disclosure. In some embodiments, the communication interface <NUM> may be formed as or may include, for example, one or more radio frequency (RF) transmitters, one or more RF receivers, and/or one or more RF transceivers, and/or may be considered a radio interface. In some embodiments, the communication interface <NUM> may also include a wired interface.

Thus, the UE <NUM> may further include software stored internally in, for example, memory <NUM>, or stored in external memory (e.g., database) accessible by the UE <NUM> via an external connection. The software may be executable by the processing circuitry <NUM>. The processing circuitry <NUM> may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by the UE <NUM>. The memory <NUM> is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software may include instructions stored in memory <NUM> that, when executed by the processor <NUM> causes the processing circuitry <NUM> and/or configures the UE <NUM> to perform the processes described herein with respect to the UE <NUM>.

The UDM node <NUM> includes a communication interface <NUM>, processing circuitry <NUM>, and memory <NUM>. The communication interface <NUM> may be configured to communicate with the AMF node <NUM> and/or HSS <NUM> and/or other elements in the system <NUM> to facilitate delivery of an SMS message to the UE <NUM> according to one or more of the techniques in the present disclosure. In some embodiments, the communication interface <NUM> may be formed as or may include, for example, one or more radio frequency (RF) transmitters, one or more RF receivers, and/or one or more RF transceivers, and/or may be considered a radio interface. In some embodiments, the communication interface <NUM> may also include a wired interface.

Thus, the UDM node <NUM> may further include software stored internally in, for example, memory <NUM>, or stored in external memory (e.g., database) accessible by the UDM node <NUM> via an external connection. The software may be executable by the processing circuitry <NUM>. The processing circuitry <NUM> may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by the UDM node <NUM>. The memory <NUM> is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software may include instructions stored in memory <NUM> that, when executed by the processor <NUM> and/or notifier <NUM>, causes the processing circuitry <NUM> and/or configures the UDM node <NUM> to perform the processes described herein with respect to the UDM node <NUM> (e.g., processes described with reference to <FIG> and/or any of the other flowcharts).

The HSS node <NUM> includes a communication interface <NUM>, processing circuitry <NUM>, and memory <NUM>. The communication interface <NUM> may be configured to communicate with the UDM node <NUM> and/or the SMSC node <NUM> and/or other elements in the system <NUM> to facilitate delivery of an SMS message to the UE <NUM> according to one or more of the techniques in the present disclosure. In some embodiments, the communication interface <NUM> may be formed as or may include, for example, one or more radio frequency (RF) transmitters, one or more RF receivers, and/or one or more RF transceivers, and/or may be considered a radio interface. In some embodiments, the communication interface <NUM> may also include a wired interface.

Thus, the HSS node <NUM> may further include software stored internally in, for example, memory <NUM>, or stored in external memory (e.g., database) accessible by the HSS node <NUM> via an external connection. The software may be executable by the processing circuitry <NUM>. The processing circuitry <NUM> may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by the HSS node <NUM>. The memory <NUM> is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software may include instructions stored in memory <NUM> that, when executed by the processor <NUM> and/or subscriber <NUM>, causes the processing circuitry <NUM> and/or configures the HSS node <NUM> to perform the processes described herein with respect to the HSS node <NUM> (e.g., processes described with reference to <FIG> and/or any of the other flowcharts).

In <FIG>, the connection between the devices UE <NUM>, UDM node <NUM>, HSS node <NUM> and network node <NUM> is shown without explicit reference to any intermediary devices or connections. However, it should be understood that intermediary devices and/or connections may exist between these devices, although not explicitly shown.

Although <FIG> shows notifier <NUM> and subscriber <NUM>, as being within a respective processor, it is contemplated that these elements may be implemented such that a portion of the elements is stored in a corresponding memory within the processing circuitry. In other words, the elements may be implemented in hardware or in a combination of hardware and software within the processing circuitry.

<FIG> is a flowchart of an exemplary process in a UDM node <NUM> for facilitating delivery of an SMS message to the UE <NUM> according to one or more of the techniques in the present disclosure. One or more Blocks and/or functions and/or methods performed by the UDM node <NUM> may be performed by one or more elements of UDM node <NUM> such as by notifier <NUM> in processing circuitry <NUM>, memory <NUM>, processor <NUM>, communication interface <NUM>, etc. according to the example process/method. The example process includes setting (Block S100), such as via notifier <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, a short message service, SMS, function, SMSF, registration notification flag to detect an SMSF registration event associated with a user equipment, UE <NUM>.

In some embodiments, the method further includes as a result of an SMSF registering at the UDM node <NUM> for the UE <NUM> and the SMSF registration notification flag being set for the UE <NUM>, clearing the SMSF registration notification flag and sending a notification, the notification indicating that SMSF is registered at the UDM node <NUM> for the UE <NUM>. In some embodiments, the method further includes receiving notifier <NUM> in processing circuitry <NUM>, memory <NUM>, processor <NUM>, communication interface <NUM>, a request to subscribe to a notification about the SMSF registration event associated with the UE <NUM>; and the setting the SMSF registration notification flag is a result of the request to subscribe to the notification.

In some embodiments, the request to subscribe to the notification is received from a home subscriber server (HSS) node <NUM> and the notification is sent to the HSS node <NUM>. In some embodiments, the request to subscribe is received by a Nudm_EE_Subscribe service operation. In some embodiments, the method further includes, as a result of receiving, from a short message service center, SMSC, node <NUM>, a request for routing information for the UE <NUM>, determining that the UE <NUM> is at least one of not registered in a network associated with the UDM node <NUM> and not registered for an SMS service in the network; and the setting the SMSF registration notification flag is a result of the determination.

In some embodiments, the method further includes as a result of the determination that the UE <NUM> is at least one of not registered in the network associated with the UDM node <NUM> and not registered for the SMS service in the network, indicating notifier <NUM> in processing circuitry <NUM>, memory <NUM>, processor <NUM>, communication interface <NUM>, to the SMSC node <NUM> that the UE <NUM> is absent. In some embodiments, sending notifier <NUM> in processing circuitry <NUM>, memory <NUM>, processor <NUM>, communication interface <NUM>, the notification indicating that the SMSF is registered at the UDM node <NUM> for the UE <NUM> further comprises sending an alert to the SMSC node <NUM> to retry an SMS delivery to the UE <NUM>.

In some embodiments, the method includes receiving, such as via notifier <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, from a home subscriber server (HSS) node <NUM>, a request to subscribe to a notification, the notification being when a user equipment (UE) <NUM> registers in a network for short message service (SMS). The process includes as a result of the received request to subscribe, setting, such as via notifier <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, a SMS function (SMSF) registration notification flag to detect SMSF registration events associated with the UE <NUM>.

In some embodiments, the method further includes, as a result of an SMSF registering at the UDM node for the UE, detecting/determining, such as via notifier <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, that the SMSF registration notification flag is set for the UE <NUM> for which the SMSF is registered for. In some embodiments, the method includes, as a result of the detecting/determining, resetting/clearing, such as via notifier <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, the SMSF registration notification flag. In some embodiments, the method includes, as a result of the detecting/determining, notifying, such as via notifier <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, the HSS node <NUM> that the UE <NUM> is registered in the network for SMS. In some embodiments, the network for the UE to be registered in for SMS is a 5th Generation core (5GC) network. In some embodiments, the notification is a UE <NUM> ready for SMS notification. In some embodiments, the request to subscribe is received by a Nudm_EE_Subscribe service operation.

<FIG> is a flowchart of an exemplary process in an HSS node <NUM> for facilitating delivery of an SMS message to the UE <NUM> according to one or more of the techniques in the present disclosure. One or more Blocks and/or functions and/or methods performed by the HSS node <NUM> may be performed by one or more elements of HSS node <NUM> such as subscriber <NUM> in processing circuitry <NUM>, memory <NUM>, processor <NUM>, communication interface <NUM>, etc. according to the example process/method. The example process includes sending (Block S102), such as via subscriber <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, a request to subscribe to a notification at a unified data management, UDM, node <NUM> about a short message service, SMS, function, SMSF, registration event associated with a user equipment, UE <NUM>.

In some embodiments, the method further includes as a result of the subscription, receiving, such as via subscriber <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, from the UDM node <NUM>, a notification, the notification indicating that an SMSF is registered at the UDM node <NUM> for the UE <NUM>; and as a result of receiving the notification, indicating, such as via subscriber <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, to a short message service center, SMSC, node <NUM> that the SMSF is registered at the UDM node <NUM> for the UE <NUM>.

In some embodiments, indicating, such as via subscriber <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, to the SMSC node <NUM> further comprises sending an alert to the SMSC node <NUM> to retry an SMS delivery to the UE <NUM>. In some embodiments, sending, such as via subscriber <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, the request to subscribe to the notification about the SMSF registration event is based at least in part on a determination that an SMSF is not registered at the UDM node <NUM> for the UE <NUM>. In some embodiments, sending, such as via subscriber <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, the request to subscribe to the notification about the SMSF registration event is based further on a determination that the UE <NUM> is not registered at the HSS node <NUM> for SMS.

In some embodiments, the method further includes receiving, such as via subscriber <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, from a short message service center, SMSC, node <NUM>, a request for routing information for the UE <NUM>; and as a result of receiving the request from the SMSC node <NUM>, as least one of: querying, such as via subscriber <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, whether an SMSF registration notification flag is set at the UDM node <NUM>; determining, such as via subscriber <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, whether to retrieve an SMSF address from the UDM node <NUM> for the UE <NUM> based at least in part on whether the SMSF registration notification flat is set; determining, such as via subscriber <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, that an SMSF address in not registered at the UDM node <NUM> for the UE <NUM> and that a target node address for SMS is not registered at the HSS node <NUM> for the UE <NUM>; and as a result of the determination that the SMSF address and the target node address is not registered for the UE <NUM> in the UDM <NUM> and HSS nodes <NUM> respectively, indicating to the SMSC node that the UE <NUM> is absent.

In some embodiments, the request to subscribe is sent by a Nudm_EE_Subscribe service operation.

In some embodiments, the method includes subscribing, such as via subscriber <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, to a notification at a unified data management (UDM) node <NUM>, the notification being when a user equipment (UE) <NUM> registers in a network for short message service (SMS).

In some embodiments, the method further includes, as a result of the subscription, receiving, such as via subscriber <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, from the UDM node <NUM>, a notification that the UE <NUM> is registered in the network for SMS. In some embodiments, the method further includes, as a result of receiving the notification, sending, such as via subscriber <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, an alert to a short message service center (SMSC) node <NUM> that the UE <NUM> is ready for an SMS. In some embodiments, the network for the UE to be registered in for SMS is a 5th Generation core (5GC) network. In some embodiments, the notification is a UE ready for SMS notification. In some embodiments, the subscribing further includes subscribing, such as via subscriber <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, using a Nudm_EE_Subscribe service operation. In some embodiments, the subscribing to the notification at the UDM node is responsive to receiving, such as via subscriber <NUM>, processing circuitry <NUM>, memory <NUM>, processor <NUM> and/or communication interface <NUM>, a response message from the UDM node <NUM> that an SMSF is not registered at the UDM node <NUM> for the UE <NUM>.

Having generally described arrangements for short message service (SMS) delivery, a more detailed description of some of the embodiments are provided as follows with reference to <FIG>, and which may be implemented by UE <NUM>, UDM node <NUM>, HSS node <NUM> and/or network node <NUM> (e.g., AMF node <NUM>, SMSC node <NUM>, etc.).

Some embodiments of the present disclosure provide a definition and/or use of a NEW flag/event to detect UE <NUM> reachability for SMS (e.g., SMSF registration in UDM node <NUM>) to cover the cases where there is an MT-SMS pending due to the UE <NUM> not being registered in the 5GC for SMS service.

One example of the use of the new flag/event is illustrated in <FIG>, as described in the steps below (note that as in <FIG>, <FIG> shows that the UE <NUM> (not shown here) is not connected to 5GC, i.e., no AMF/SMSF <NUM>/<NUM> registered in UDM node16):.

It should be understood that although the example embodiments discussed herein may use one or another type of message or one or another network node arrangement or context, the techniques disclosed herein may be used with other types of messages or other types of network architecture arrangements or other contexts, to support SMS delivery according to the techniques provided in this disclosure.

Some embodiments of the present disclosure provide for a definition and/or use of a NEW flag/event to detect UE reachability for SMS (e.g., SMSF registration in UDM) to cover the cases where, for example, there is an MT-SMS pending due to the UE not being registered in the 5GC for SMS service.

Some embodiments may include one or more of the following:.

Claim 1:
A method of enabling short message delivery re-attempt for a user equipment (UE), the method comprising:
as a result of receiving, from a short message service center, SMSC, node, a request for routing information for the UE, determining that the UE is at least one of not registered in a network and not registered for an SMS service in the network;
as a result of the determination that the UE (<NUM>) is at least one of not registered in the network and not registered for the SMS service in the network via an SMS function, SMSF, setting an indication for indicating that a Mobile Terminating, MT-SMS is pending and indicating to the SMSC node (<NUM>) that the UE (<NUM>) is absent;
as a result of receiving a registration for SMS service for the UE for which the MT-SMS is pending sending an alert to the SMSC node to retry delivery of the MT-SMS to the UE based on the indication.