Access network nodes and user equipment

Abstract

A method is disclosed that is performed by an access network node in a non-terrestrial network. The method includes receiving at least one non-access stratum (NAS) Protocol Data Unit (PDU) over an available link without triggering the establishment of a connection on a link other than the available link, when either a service link between the access network node and user equipment (UE) or a feeder link between the access network node and a gateway in a terrestrial network is unavailable; storing at least one NAS PDU until another link becomes available; and, when another link becomes available, transferring at least one NAS PDU over the other link.

Description

[Technical Field]

[0001] This disclosure relates to communication systems and components thereof. This disclosure has a non-exclusive but specific relevance to wireless communication systems and devices operating in accordance with 3rd Generation Partnership Project (3GPP®) standards or equivalent standards (including LTE Advanced, Next Generation or 5G networks, Future Generation and beyond) or derivative standards thereof. This disclosure is particularly relevant to, but not limited to, improvements in the use of storage and transfer technologies for the communication of user data in the context of Non-Terrestrial Networks (NTN). [Background technology]

[0002] Previous developments of the 3GPP standard were referred to as Long Term Evolution (LTE) and Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) on Evolved Packet Core (EPC) networks, and are commonly known as "4G." More recently, the terms "5G" and "new radio" (NR) have begun to be used to refer to evolving communication technologies that are expected to support a variety of applications and services. Various details of 5G networks are described in the "NGMN 5G White Paper" V1.0 by the Next Generation Mobile Network (NGMN) Alliance, which is available, for example, at https: / / www.ngmn.org / 5g-white-paper.html. 3GPP intends to support 5G through the so-called 3GPP Next Generation (NextGen) radio access network (RAN) and 3GPP NextGen core network.

[0003] Under the 3GPP standard, a NodeB (or eNB in ​​LTE, and gNB in ​​5G) is a radio access network (RAN) node (or simply an "access node," "access network node," or "base station") through which communication devices (user equipment or "UE") connect to the core network and communicate with other communication devices or remote servers. For simplicity, this application uses the terms access network node, RAN node, or base station to refer to any such access node.

[0004] For simplicity, this application uses the terms mobile device, user device, or UE to refer to any communication device capable of connecting to a core network via one or more base stations. While this application may refer to mobile devices in its description, it will be understood that the technology described can be implemented on any (mobile and / or generally fixed) communication device capable of connecting to a communication network to transmit / receive data, whether such communication device is controlled by human input or software instructions stored in memory. One particular type of UE supported in modern communication systems is the so-called Internet of Things (IoT) device, which is a non-standard hardware device (including everyday physical objects such as sensor devices, gadgets, and appliances) capable of wirelessly connecting to a network to transmit and receive data. The technology for supporting such IoT UEs in cellular communication systems is often referred to as cellular IoT (CIoT) extension or optimization. The CIoT extension includes, for example, the narrowband IoT (NB-IoT) extension, a wireless technology developed to support cellular network IoT devices and services, where the bandwidth is limited to a single narrowband (e.g., transmission is limited to occupying a single 180kHz physical resource block (PRB) / 12 subcarriers of 15kHz each). The CIoT extension also includes features that support so-called "LTE machine" (LTE Cat-M1 or simply LTE-M) technology with a bandwidth-limited UE (BL UE) that operates over a wider narrowband (e.g., limited to 6 PRBs / 1.4MHz) than NB-IoT.

[0005] In current 5G architectures, the gNB structure can be divided into two or more parts. In some RAN implementations, there are two parts, known as the Central Unit (CU or gNB-CU), sometimes referred to as the “control unit,” and the Distributed Unit (DU or gNB-DU), connected by an F1 interface. This makes it possible to use a “split” architecture. Typically, a “split” architecture separates a “higher” CU layer (such as the Packet Data Convergence Protocol (PDCP) layer and the Radio Resource Control (RRC) layer, for example, but not limited to these) and a “lower” DU layer (such as the Radio Link Control (RLC) layer, the Media Access Control (MAC) layer (sometimes referred to as the “medium”), and the Physical (PHY) layer), between a specific CU and one or more DUs connected to and controlled by that CU via an F1 interface. Therefore, for example, upper-layer CU functions for multiple gNBs can be implemented centrally (e.g., by a single processing unit, or in a cloud-based or virtualized system), while lower-layer DU functions are maintained locally and separately for each gNB.

[0006] The core network includes multiple communication entities that provide different functions to support communication.

[0007] For example, in 4G, the core network entities include, among other things, the Mobility Management Entity (MME), the serving gateway (SGW or S-GW), and the packet data network (PDN) gateway (PGW or P-GW). The MME manages the general mobility of the UE and ensures that connectivity with the UE is maintained when the UE is moving within the geographic area covered by the communication system. The MME also handles the UE's control plane signaling and manages various bearers associated with the UE (e.g., Evolved Packet System (EPS) bearers and / or radio bearers) by controlling, for example, the S-GW and P-GW (and / or other network nodes) to which such bearers are served. The S-GW provides connectivity between the UE and the core network (via base stations) to send and receive user plane data via the associated communication bearers (e.g., EPS bearers). Communication bearers typically terminate at the P-GW, but are often complemented by external bearers (e.g., another EPS bearer) between the P-GW and communication endpoints outside the core network (e.g., in the external network). It will be understood that the functions of the S-GW and P-GW can be implemented in a single gateway element.

[0008] In 5G, the core network entity comprises a logical node (or "function") containing a control plane function (CPF) and one or more user plane functions (UPFs). The CPF includes, among other things, one or more Access and Mobility Management Functions (AMFs). The AMF generally corresponds to the MME in 4G and performs many of the functions performed by the MME. Each UPF combines the functions of both the S-GW and P-GW, specifically the user plane functions of the S-GW (SGW-U) and the P-GW (PGW-U). The SMF provides session management functions (which formed part of the MME functions in 4G). The SMF also combines some of the functions provided by the S-GW and P-GW, specifically the control plane functions of the S-GW (SGW-C) and the P-GW (PGW-C). The SMF also assigns an IP address to each UE.

[0009] In 4G, several EPS optimizations were introduced to support CIoT (e.g., NB-IoT) (these are generally applicable to later generations of technology), and these enhancements enabled communication of new user data paths for IoT. In contrast to the original data paths via S-GW and P-GW, these new data paths enable communication of user data via MME (in 4G) (as well as other CN nodes such as S-GW, P-GW, and / or Service Capability Exposure Function (SCEF)), although in later generations this may be via different equivalent nodes (e.g., AMF in 5G). CIoT EPS optimizations using these newer paths are referred to as control plane (CP) mode or "CP mode" CIoT EPS optimizations, while CIoT EPS optimizations using the original data paths are referred to as user plane (UP) mode or "UP mode" CIoT EPS optimizations.

[0010] CP-mode CIoT EPS optimization reduces the total number of control plane messages when handling short data transactions (typically occurring in IoT communications), user data, or SMS messages transmitted via the MME using the service request procedure by encapsulating them in non-access stratum (NAS) messages. For IP data packets, UL data can be forwarded from the base station to the CIoT service via the MME, S-GW, and P-GW. For non-IP data packets, UL data can be forwarded from the base station to the CIoT service via the MME and SCEF.

[0011] On the other hand, UP-mode CIoT EPS optimization transmits user plane data without using a service request procedure to establish an access stratum (AS) context at the serving base station and UE. This UP-mode method is based on UP transport of user data, where data is transferred over the network from the base station to the S-GW and vice versa over the conventional user plane. In UP-mode CIoT, two distinct RRC connection scenarios are possible. In the first scenario, the RRC connection is released with a possible reactivation action indicated, and then a reactivation of the connection may be requested as part of the reactivation procedure. If this reactivation procedure is successful, security is established with the updated key, and the radio bearer is configured as with the original connection. In the second scenario, where there is no prior release of the RRC connection with a reactivation instruction, or the reactivation request is not accepted by the base station, security and the radio bearer must be re-established.

[0012] 3GPP is also working with the satellite communications industry to define integrated satellite and terrestrial network infrastructure in the context of 5G. This is referred to as a non-terrestrial network (NTN), a term that refers to a network or segment of a network that uses aircraft or spacecraft for the transmission of data and control signaling. Satellites refer to spacecraft in Low Earth Orbit (LEO), Medium Earth Orbit (MEO), Geostationary Earth Orbit (GEO), or Highly Elliptical Orbit (HEO). Aircraft refer to High Altitude Platforms (HAPs) that encompass Unmanned Aircraft Systems (UAS), including tethered UAS, lighter-than-air UAS, and heavier-than-air UAS, all of which typically operate in a quasi-geostationary state at altitudes of 8-50 km.

[0013] 3GPP Technical Report (TR) 38.811 is a study on New Radio for supporting such terrestrial networks. This study includes, among other things, NTN deployment scenarios and related system parameters (such as architecture, altitude, orbit, etc.), as well as a description of the adaptation of the 3GPP channel model for non-terrestrial networks (propagation conditions, mobility, etc.). Non-terrestrial networks are, - To help promote the deployment of 5G services in areas that are not serviced or have insufficient service, in order to upgrade the performance of terrestrial networks. - To enhance service reliability by providing service continuity to user equipment or mobile platforms (e.g., passenger vehicles, aircraft, ships, high-speed trains, buses), - To improve service availability everywhere, especially for critical communications, and for future rail / maritime / air communications, and - It is expected that 5G network scalability will be enabled by providing efficient multicast / broadcast resources for data distribution to the network edge or directly to user devices.

[0014] Non-terrestrial network access typically involves the following elements, among others: -NTN terminal: This may refer to a 3GPP UE or a UE specific to the satellite system if the satellite does not directly serve a 3GPP UE. - A service link refers to a radio link between user equipment and a space / airborne platform (which may also be added to a radio link with a ground-based RAN). - (e.g., satellites) space or aerial platforms, - Features a gateway connecting a satellite or air access network to the core network. The gateway is, in most cases, co-located with a base station (e.g., a gNB), i.e., - A feeder link should be understood as referring to a wireless link between a gateway and a space / airborne platform.

[0015] There are several different architectures that can be used to provide NTN access. One such architecture is a “regenerative” access network architecture (sometimes referred to as “regenerative satellite,” “regenerative payload,” or “regenerative mode”) in which a non-terrestrial platform (e.g., a satellite) performs some onboard processing of the payload being communicated between the UE and the core network. Specifically, in the regenerative architecture, at least some of the base station functions (e.g., at least the functions of the DU of a distributed base station, or possibly all of the base station functions) are provided on the non-terrestrial platform. Other regenerative mode architectures are also possible, such as architectures in which at least some of the core network functions are implemented on the non-terrestrial platform.

[0016] Another possible architecture is a “transparent” access network architecture (sometimes referred to as “transparent satellite,” “transparent mode,” or “transparent payload”), in which base stations are located on the ground and transmit and receive communications destined for and originating from the UE via ground-based gateways and via non-terrestrial platforms that do not have base station functionality. The non-terrestrial platforms transparently relay these communications to and from the UE without onboard processing, effectively acting as a so-called “vent pipe.” In this architecture, both service links and feeder links effectively function as part of the air interface between the base station and the UE.

[0017] A satellite or aerial vehicle typically generates several satellite beams over a given area. These beams typically have an elliptical footprint on the Earth's surface. The beam footprint can move across the Earth along with the movement of the satellite or aerial vehicle in its orbit. Alternatively, the beam footprint may be (temporarily) fixed to the Earth, in which case several beampointing mechanisms (mechanical or electronic maneuvering mechanisms) can be used to compensate for the movement of the satellite or aerial vehicle. There are various options for beam identification purposes. One option is that multiple (nearby / adjacent) satellite beams may have the same associated physical cell ID (PCI), and therefore the PCI may remain unchanged as the UE3 moves between beams in a set of beams sharing the PCI. Alternatively, there may be a one-to-one relationship between the PCI and the satellite beams (at least within the coverage area of ​​a particular satellite containing multiple beams).

[0018] 5G coverage is primarily beam-based, not cell-based. There is no cell-level reference channel from which cell coverage can be measured. Instead, each cell has one or more so-called synchronization signal block (SSB) beams (different from satellite beams or NTN beams). The SSB beams form a matrix of beams that cover the entire cell area. Each SSB beam carries the SSB, including the primary synchronization signal (PSS), secondary synchronization signal (SSS), and physical broadcast channel (PBCH).

[0019] The UE searches for SSB beams and performs measurements (e.g., synchronization signal reference signal received power (SS-RSRP), synchronization signal reference signal received quality (SS-RSRQ), and / or synchronization signal to noise or interference ratio (SS-SINR)). The UE maintains a set of candidate beams that may include beams from multiple cells. Thus, PCI and beam ID (or SSB index) distinguish SSB beams from one another. In essence, an SSB beam is like a minicell that can exist within a larger cell. Once the UE has detected and selected a cell (and / or SSB beam in the case of 5G), the UE may attempt to access that cell and / or SSB beam using an initial RRC connection setup procedure with random access procedures.

[0020] Specifically, a UE may attempt to access its cells and / or beams using a random access procedure, which generally involves four distinct steps. Before attempting initial access, the UE may transmit a preamble to the network (e.g., a base station such as a gNB) via a physical random access channel (PRACH / RACH) to initiate a random access procedure (also referred to as the RACH procedure or simply RACH) to achieve synchronization at the uplink (UL). This step is often referred to as the PRACH transmission or simply the transmission of message 1 (Msg1). In response, the network responds with a random access response (RAR). A RAR includes a timing-alignment (TA) command to indicate the reception of a preamble and adjust the UE's transmission timing based on the timing of the received preamble, an uplink grant field indicating the resources to be used on the uplink for the physical uplink shared channel (PUSCH), a frequency hopping flag to indicate whether the UE transmits on PUSCH with or without frequency, an MCS field that allows the UE to determine the modulation and coding scheme (MCS) for PUSCH transmission, and a transmit power control (TPC) command value to set the power for PUSCH transmission. The RAR transmission step is often referred to as a message 2 (Msg2) transmission. Next, the UE sends message 3 (or "Msg3") to the network via the physical uplink shared channel (PUSCH) based on the information in the RAR. The specific message sent by the UE in this step, and its content, depend on the context in which the random access procedure is being used. However, in the example of an initial wireless RRC connection setup, Msg3 would contain an RRC setup request or similar message carrying a temporary, randomly generated UE identifier.To resolve any collision between different UEs using the same preamble sequence, the network responds with message 4 (message 4 or "Msg4") that carries the randomly generated UE identifier received in Msg3 for contention resolution purposes. If successful, Msg4 also causes the UE to transition to a connected state.

[0021] A similar random access procedure can also be used in other contexts, including for example handover, connection re-establishment, and a request for UL scheduling when no dedicated resource for scheduling requests is configured for the UE.

[0022] (In addition to the four-step random access procedure described above) a so-called two-step random access procedure has also been developed. Two-step random access is primarily intended to support, inter alia, (ultra-)low latency communication, 10 ms control plane latency, fast handover, efficient channel access in unlicensed spectrum, and transmission of small data packets. However, this procedure can also be applied to large cells such as non-terrestrial cells. The main difference is that while the four-step random access procedure requires two round-trip cycles between the UE and the base station, the two-step random access procedure aims to reduce latency and control signaling overhead by using a single round-trip cycle between the UE and the base station. Effectively, this is achieved by combining the UE's PRACH preamble (Msg1) transmission and the scheduled PUSCH transmission (Msg3) into a single message (referred to as "MsgA"). Similarly, the random-access response (RAR / Msg2) and the contention resolution message (Msg4) from the base station to the UE are combined in the two-step random access procedure (and referred to as "MsgB").

[0023] As will be appreciated by those skilled in the art, while a contention-based PRACH procedure is described, a non-contention based (or "contention-free") procedure where a dedicated preamble is allocated to a UE by a base station may also be used.

[0024] In addition to the aforementioned RACH-based initial access procedures, so-called RACH-less access procedures were introduced in the context of handover procedures under development for later releases of the LTE standard, also aiming at providing latency reduction. RACH-less based handover eliminates the need to perform random access when first accessing a target cell, thereby shortening the data connection interruption time in each handover and thus reducing the overall handover execution time.

[0025] Movement of a non-terrestrial platform serving a UE can cause discontinuous coverage for that UE even if the UE remains stationary, for example as a result of service link degradation due to satellite movement. In addition to this type of discontinuous coverage, there may also be intermittent feeder link connectivity (e.g. with a gateway at an associated ground station), for example in areas where it is not feasible to deploy a gateway, or where gateway deployment is not cost-effective.

[0026] Furthermore, at different times, different NTN platforms (and hence on-board base stations where present) may respectively provide feeder links and service links. Specifically, for a UE at a given location, one or more satellites may be orbiting and providing communication services to the UE at different times. Thus, the UE will effectively see different base stations during different time windows. Similarly, one or more satellites may be orbiting around the ground position of a gateway via which one or more feeder link connections are provided, meaning that gateway feeder connectivity may be via different satellites (and potentially base stations in case of regenerative mode architectures).

[0027] One such scenario is illustrated in Figure 1 for a regenerative architecture, which shows the changes in satellites, and therefore base stations, providing service links and feeder links, respectively, in an NTN system. As seen in Figure 1, two NTN platforms (satellites in this example), each providing its own base station, cycle through providing service links to the UE and feeder links to the gateway (GW) to access the core network (CN) at different times (T1) and (T2). Specifically, at T1, the first satellite / base station (base station #1) provides the feeder link, and the second satellite / base station (base station #2) provides the service link. At T2, the situation is reversed, with the first satellite / base station (base station #1) providing the service link and the second satellite / base station (base station #2) providing the feeder link. Therefore, data communicated to base station #2 via the service link and to base station #1 via the feeder link at time T1 cannot be transmitted to the core network and UE, respectively, until time T2.

[0028] Therefore, since feeder link connections and associated service link connections are not necessarily available simultaneously, it can be seen that, given a given time, the UE may not have a complete (end-to-end) connection to the core network. In such scenarios, to avoid data loss, communications over the service link must be stored on a non-terrestrial platform for forwarding to the core network via the feeder link, and vice versa. Such techniques are known as “storage and forwarding” techniques. These techniques are particularly applicable to delay-tolerant communications (i.e., non-real-time communications), such as those typically used in CIoT-based communications.

[0029] As an example, one possible storage and transfer technique is shown in Figure 2, which is a simplified sequence diagram illustrating a generalized procedure for forming a connection in an NTN system, including the storage and transfer of user and control data. The illustrated procedure is in the context of a CIoT CP mode procedure.

[0030] As shown in Figure 2, the procedure begins in a scenario where UE3 is within the coverage of the first base station 5A-1 on the first NTN platform, but the feeder link is disconnected (in S210). UE3 and the first base station 5A-1 of the first NTN RAN 5-1 cooperate to establish an RRC connection (S212). This procedure typically includes a random access procedure, as seen in S214 (for example, as described above). The random access procedure ends (in S216) when UE3 sends a message to the first base station 5A-1 indicating that the RRC is complete, containing a UL NAS protocol data unit (PDU) containing a control plane service request (CPSR) and / or control plane data as a non-access stratum (NAS) payload. When the feeder link between the first base station 5A-1 and the core network 7 is disconnected, the first base station 5A-1 stores the NAS PDU and / or any data in S216. In S218, the first base station 5A-1 sends a message to the UE3 to release the RRC connection, which includes an instruction that the feeder link is unavailable and an instruction for a scheduled time when the UE3 may expect a response from the core network 7 and therefore can perform the next transmission. The UE3 can then effectively enter idle mode while waiting for a response. Subsequently, once the feeder link is connected, in S220, the first base station 5A-1 may send an initial UE message containing the NAS PDU / data to the core network 7 in S222. In S224, the core network 7 may determine that the second base station 5A-2 of the second NTN RAN 5-2 (whose feeder link is connected to / will be connected to the core network 7) is likely to provide coverage to the UE3 at some point in the future. If the feeder link to this second base station 5A-2 is available, the core network 7 may send the appropriate DL NAS response PDU along with any DL data in S226. The DL NAS PDU / data is stored in the second base station 5A-2 at S228.When UE3 is within the coverage of the second base station 5A-2 in S230, the second base station 5A-2 can page UE3 in S232. Thus, UE3 and the second base station 5A-2 can cooperate to establish a connection in S234, from which DL NAS PDU and data can be delivered.

[0031] Nevertheless, the procedure in Figure 2 does not take into account all the effects / problems associated with discontinuous coverage and intermittent feeder links.

[0032] In this context, as long as the complete base station is built on the NTN platform, the NAS procedure is likely to have a greater impact than the AS procedure. This is because the NAS procedure requires bidirectional connectivity from the UE to the core network. For example, in the case of a conventional registration / attach procedure, the "storage and transfer" method typically requires a one-way storage and transfer cycle for each request message and another storage and transfer cycle in the opposite direction for each corresponding response message.

[0033] While the impact on AS procedures (such as initial access) is likely to be minimal, data transmission typically requires end-to-end connectivity between the UE and the core network / packet data network, as well as the establishment of the UE context.

[0034] Therefore, further improvements are needed to more effectively support the implementation of storage and transfer technologies, particularly in situations of discontinuous coverage / intermittent feeder links (but not limited to) that occur in NTN systems. [Prior art documents] [Non-patent literature]

[0035] [Non-Patent Document 1] 3GPP Technical Report(TR)38.811 [Non-Patent Document 2] NGMN 5G White Paper V1.0 [Overview of the Initiative] [Problems that the invention aims to solve]

[0036] This disclosure aims to provide one or more apparatuses and / or one or more related methods that contribute to satisfying the above-mentioned needs. [Means for solving the problem]

[0037] In one embodiment, a method is provided that is performed by an access network node in a non-terrestrial network, and the method is If either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable, at least one non-access stratum (NAS) Protocol Data Unit (PDU) is received via an available link without triggering the establishment of a connection on a link other than the available link. Remember at least one NAS PDU until another link becomes available. This includes transferring at least one NAS PDU via another link when another link becomes available.

[0038] In one embodiment, a method is provided that is performed by an access network node in a non-terrestrial network, and the method is This includes transmitting information via system information indicating a mode for storing and transferring data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable. Information is provided on a method for preventing at least one UE that does not support a mode for storing and transferring data when either a service link or a feeder link is unavailable from being camped on to a serving cell of an access network node.

[0039] In one embodiment, a method is provided that is performed by an access network node in a non-terrestrial network, and the method is This includes transmitting information to the core network indicating the ability to store and transfer data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable.

[0040] In one embodiment, a method is provided that is performed by an access network node in a non-terrestrial network, and the method is This includes receiving information from the core network indicating the ability to store and transmit data when either the service link between the access network node and the user equipment (UE), or the feeder link between the access network node and the gateway in the terrestrial network, is unavailable.

[0041] In one embodiment, a method is provided that is performed by user equipment (UE), and the method is This includes transmitting at least one non-access stratum (NAS) Protocol Data Unit (PDU) to an access network node in a non-terrestrial network via a service link between the access network node and the UE, without triggering the establishment of a feeder link connection, when the feeder link between the access network node and the gateway in the terrestrial network is unavailable. At least one NAS PDU is stored by the access network node until a feeder link becomes available. At least one NAS PDU will be transferred via the feeder link when the feeder link becomes available.

[0042] In one embodiment, a method is provided that is performed by user equipment (UE), and the method is The system receives information indicating the mode for storing and transferring data when either the service link between the access network node and the UE in the non-terrestrial network, or the feeder link between the access network node and the gateway in the terrestrial network, is unavailable. This includes not camping on to the serving cell of an access network node if the UE does not support a mode for storing and transferring data when either the service link or feeder link is unavailable.

[0043] In one embodiment, a method is provided that is performed by a core network node, and the method is This includes receiving at least one non-access stratum (NAS) Protocol Data Unit (PDU) from an access network node in a non-terrestrial network via a feeder link between the access network node and a core network node, without triggering the establishment of a connection for the service link, when the service link between the access network node and user equipment (UE) is unavailable. At least one NAS PDU is stored by the access network node until a service link becomes available. At least one NAS PDU will be transferred over the service link when the service link becomes available.

[0044] In one embodiment, a method is provided that is performed by a core network node, and the method is This includes receiving information from an access network node in a non-terrestrial network indicating its ability to store and transmit data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in a terrestrial network connected to a core network node, is unavailable.

[0045] In one embodiment, a method is provided that is performed by a core network node, and the method is This includes transmitting information to an access network node indicating its ability to store and transfer data when either a service link between an access network node in a non-terrestrial network and user equipment (UE), or a feeder link between an access network node and a gateway in a terrestrial network coupled to a core network node, is unavailable.

[0046] In one embodiment, an access network node is provided within a non-terrestrial network, and the access network node is A means for receiving at least one non-access stratum (NAS) Protocol Data Unit (PDU) via an available link, without triggering the establishment of a connection on a link other than the available link, when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable. A means of storing at least one NAS PDU until another link becomes available, The system includes means for transferring at least one NAS PDU via another link when another link becomes available.

[0047] In one embodiment, an access network node is provided within a non-terrestrial network, and the access network node is The system includes means for transmitting, via system information, information indicating a mode for storing and transferring data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable. The information ensures that at least one UE that does not support a mode for storing and transferring data when either the service link or feeder link is unavailable is not camped on to the serving cell of an access network node.

[0048] In one embodiment, an access network node is provided within a non-terrestrial network, and the access network node is The system includes means for transmitting information to the core network indicating the ability to store and transfer data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable.

[0049] In one embodiment, an access network node is provided within a non-terrestrial network, and the access network node is The system includes means for receiving information from the core network indicating the ability to store and transfer data when either the service link between the access network node and the user equipment (UE), or the feeder link between the access network node and the gateway in the terrestrial network, is unavailable.

[0050] In one embodiment, user equipment (UE) is provided. In the event that the feeder link between the access network node and the gateway in the terrestrial network is unavailable, the system provides means for transmitting at least one non-access stratum (NAS) Protocol Data Unit (PDU) to an access network node in a non-terrestrial network via a service link between the access network node and the UE, without triggering the establishment of a feeder link connection. At least one NAS PDU is stored by the access network node until a feeder link becomes available. At least one NAS PDU will be transferred via the feeder link when the feeder link becomes available.

[0051] In one embodiment, user equipment (UE) is provided. Means for receiving information indicating a mode for storing and transferring data when either the service link between the access network node and the UE of a non-terrestrial network or the feeder link between the access network node and the gateway in the terrestrial network is unavailable, via system information; The system includes means for not camping on to a serving cell of an access network node if either a service link or a feeder link is unavailable and the UE does not support a mode for storing and transferring data.

[0052] In one embodiment, core network nodes are provided, In the event that the service link between the access network node and the user equipment (UE) is unavailable, the means for receiving at least one non-access stratum (NAS) Protocol Data Unit (PDU) from an access network node in a non-terrestrial network via a feeder link between the access network node and the core network node without triggering the establishment of a connection for the service link, At least one NAS PDU is stored by the access network node until a service link becomes available. At least one NAS PDU will be transferred over the service link when the service link becomes available.

[0053] In one embodiment, core network nodes are provided, The system includes means for receiving information indicating the ability to store and transfer data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in a terrestrial network connected to a core network node, is unavailable from an access network node in a non-terrestrial network.

[0054] In one embodiment, core network nodes are provided, The system includes means for transmitting information to the access network node indicating its ability to store and transfer data when either the service link between the access network node and user equipment (UE) in a non-terrestrial network, or the feeder link between the access network node and a gateway in a terrestrial network connected to the core network node, is unavailable.

[0055] The various functional means described below, which are part of the UE, may be provided by memory and one or more processors that execute instructions stored in memory. Similarly, the various functional means described below, which are part of the access network node, may be provided by memory and one or more processors that execute instructions stored in memory.

[0056] The various examples described below can be implemented by computer program products that include computer-implementable instructions for causing a programmable computer to perform one of the methods described below. These computer-implementable instructions may be provided as signals or on a tangible computer-readable medium. [Effects of the Invention]

[0057] According to this disclosure, methods performed by access network nodes, methods performed by user equipment, methods performed by core network nodes, access network nodes, user equipment, and core network nodes can be provided. [Brief explanation of the drawing]

[0058] Herein, exemplary embodiments of the present disclosure will be described by reference to the accompanying drawings.

[0059] [Figure 1] This figure shows a scenario in which there are changes to the satellites providing service links and feeder links, and therefore to the base stations, in the NTN system. [Figure 2] This is a simplified sequence diagram showing the generalized procedure for establishing a connection in an NTN system. [Figure 3] An illustrative mobile (cellular or wireless) communication system is shown schematicly. [Figure 4] This is a simplified sequence diagram showing an attachment procedure that may be used in the communication system shown in Figure 3. [Figure 5] Figure 3 is a simplified sequence diagram illustrating the procedure for mobile outbound data transport in the context of CP CIoT EPS optimization, which may be used in the communication system shown. [Figure 6] Figure 3 is a simplified sequence diagram illustrating the procedure for mobile terminal data transport in the context of CP CIoT EPS optimization, which may be used in the communication system shown. [Figure 7] Figure 3 schematically shows a non-terrestrial network (NTN) wireless access network that may be used in the communication system. [Figure 8A] This shows possible architectures for NTN RAN. [Figure 8B]This shows possible architectures for NTN RAN. [Figure 8C] This shows possible architectures for NTN RAN. [Figure 9] This is a simplified sequence diagram showing a CIoT-optimized data transmission flow between NTN RAN base stations, which may be used in the communication system shown in Figure 3 when the service link is available but the feeder link is unavailable. [Figure 10] This is a simplified sequence diagram showing a CIoT-optimized data transmission flow between the NTN RAN and the core network, which may be used in the communication system shown in Figure 3 when the feeder link is available but the service link is unavailable. [Figure 11] This is a simplified sequence diagram showing how some of the procedures shown in Figures 9 and 10 can be extended. [Figure 12] This is a simplified sequence diagram showing the S1 setup procedure. [Figure 13] This is a simplified block diagram showing the main components of user equipment that can be used in the communication system shown in Figure 3. [Figure 14] Figure 3 is a simplified block diagram showing the main components of a base station / access network node that can be used in the communication system. [Figure 15] Figure 3 is a simplified block diagram showing the main components of a core network node that may be used in the communication system. [Modes for carrying out the invention]

[0060] <Overview> Next, an exemplary communication system will be described using general terminology, with reference to Figures 3 to 8.

[0061] Figure 3 schematically shows a mobile ("cellular" or "wireless") communication system 1 to which the examples described herein can be applied.

[0062] In communication system 1, user equipment (UE) 3 (3-1, 3-2, 3-3) (e.g., mobile phones and / or other mobile devices) can communicate with each other via corresponding Radio Access Networks (RANs) 5-1, 5-2 operating according to one or more compatible radio access technologies (RATs). In the illustrated example, each RAN 5-1, 5-2 (which may be NTN-based RANs) includes base stations 5A-1, 5A-2 (e.g., LTE / 4G base stations such as eNBs) that operate one or more associated cells 9 (9-1, 9-2), respectively.

[0063] As those skilled in the art will understand, three UE3s and two RAN5-1s and 5-2s are shown in Figure 3 for illustrative purposes, but the system, when implemented, typically includes other RAN5s and UE3s.

[0064] In an exemplary system, UE3 includes one or more so-called “internet-of-things” (“IoT”) devices, such as narrowband IoT (NB-IoT) devices.

[0065] Each RAN5-1, 5-2 directly controls one or more associated cells, or indirectly controls them through one or more other nodes (e.g., home base stations, relays, remote radio heads, distributed units, etc.). It will be understood that RAN5 may be configured to support 4G, 5G, 6G and / or later generations, and / or any other 3GPP or non-3GPP communication protocols.

[0066] UE3 and their serving RAN5 are connected via appropriate air interfaces (e.g., so-called "Uu" interfaces and / or similar). Adjacent base stations 5A in RAN5 may be connected to each other via appropriate inter-base station interfaces (such as the so-called "X2" interface for 4G, the "Xn" interface for 5G, etc.).

[0067] The core network 7 includes multiple communication nodes / logical nodes (or “functions”) to support communication in the communication system 1. In this example, the core network 7 includes one or more control network node entities (e.g., Mobility Management Entity (MME) 11 or mobility management node 11) for control signaling communication, one or more network node entities (e.g., Serving Gateway (S-GW) 13) for routing incoming and outgoing packets, and one or more network node entities for connecting the core network 7 and the external network 20 (e.g., Packet Data Network Gateway (P-GW) 15), along with several other function nodes (not shown). It will be understood that nodes or functions may have different names in different systems. While Core Network 7 is described in the context of 4G entities and interfaces / reference points, it should be understood that Core Network 7 can be any suitable core network (e.g., 5G / 6G and / or later generations of core networks) that has corresponding communication entities (e.g., control functions (CPFs) such as AMF and SMF, and one or more user plane functions (UPFs)).

[0068] RAN5 connects to the core network nodes via appropriate interfaces (or "reference points"), such as the S1-MME reference point between RAN5 base station 5A and MME11, and the S1-U reference point between RAN5 base station 5A and S-GW13. Each UE3 connects to MME11 via a non-access stratum (NAS) connection via an appropriate interface (e.g., the S1 reference point, similar to the N1 reference point in 5G) where applicable. It will be understood that S1 communication is routed transparently through RAN5.

[0069] The core network 7 (for example, of P-GW15) is connected to an external network 20 (for example, an IP network such as the Internet) via another reference point (for example, "SGi") for the communication of user data.

[0070] The MME11 manages the general mobility of the UE3 and ensures that connectivity with the UE3 is maintained when the UE3 is moving within the geographic area covered by the communication system 1 (and / or when the UE3 is handed over between base stations 5A of the communication system 1). The MME11 also handles control plane signaling for the UE3 and manages various bearers associated with the UE3 (e.g., Evolved Packet System (EPS) bearers and / or radio bearers, etc.) by controlling, for example, the S-GW13 and P-GW15 (and / or other network nodes to which such bearers are served).

[0071] S-GW13 provides connectivity (via base station 5A) between UE3 and core network 7 to send and receive user plane data via associated communication bearers (e.g., EPS bearers). Communication bearers typically terminate at P-GW15, but are often complemented by external bearers (e.g., another EPS bearer) between P-GW15 and communication endpoints outside core network 7 (e.g., within external network 20). Although presented as separate entities, it will be understood that the functions of S-GW13 and P-GW15 may be implemented in a single gateway element.

[0072] Furthermore, RAN5 is configured to transmit control information and user data via multiple downlink (DL) physical channels, and UE3 is configured to receive them and transmit multiple physical signals. DL physical channels correspond to resource elements (REs) that carry information transmitted from higher layers, and DL physical signals correspond to REs used in the physical layer that do not carry information transmitted from higher layers.

[0073] Physical channels may include, for example, a physical downlink shared channel (PDSCH), a physical broadcast channel (PBCH), and a physical downlink control channel (PDCCH). The PDSCH carries data that shares its capacity on a time and frequency basis. The PDSCH can carry various types of data, such as user data, UE-specific upper-layer control messages mapped from higher channels, system information blocks (SIBs), and paging. The PDCCH carries downlink control information (DCI) to support multiple functions, including scheduling downlink transmission on the PDSCH and uplink data transmission on the physical uplink shared channel (PUSCH). The PBCH provides the Master Information Block (MIB) to the UE3. It also supports time and frequency synchronization in conjunction with the PDCCH, which assists in cell acquisition, selection, and re-selection.

[0074] DL physical signals may include, for example, a reference signal (RS) and a synchronization signal (SS). The reference signal (sometimes referred to as a pilot signal) is a signal with a predetermined special waveform known to both the UE3 and RAN5 base stations 5A. The reference signal may include, for example, a cell-specific reference signal, a UE-specific reference signal (UE-RS), a downlink demodulation signal (DMRS), and a channel state information reference signal (CSI-RS).

[0075] Similarly, UE3 is configured to transmit control information and user data via multiple uplink (UL) physical channels corresponding to REs that carry information transmitted from higher layers, and to transmit UL physical signals used in the physical layer that do not carry information transmitted from higher layers, and base station 5A of RAN5 is configured to receive that control information and user data and UL physical signals. Physical channels may include, for example, PUSCH, physical uplink control channel (PUCCH), and / or physical random-access channel (PRACH). UL physical signals may include, for example, demodulation reference signal (DMRS) for UL control / data signals, and / or sounding reference signal (SRS) used for UL channel measurement.

[0076] <Attachment Procedure and Initial Access> UE3, base station 5A of RAN5, and core network entity 7 of communication system 1 are configured to perform an attachment procedure to connect UE3 to the network for communication of user data.

[0077] Here, with reference to Figure 4, a simplified sequence diagram showing an attachment procedure that may be used in communication system 1, one possible procedure that can be performed will be described as a mere example.

[0078] As shown in Figure 4, after initial synchronization to the network (for example, based on the reception of PSS and SSS), UE3 receives an MIB at S410 and one or more SIBs (in this example, at least system information block type 1 (SIB1)) at S412. MIBs typically provide information that identifies, for example, the system bandwidth, antenna configuration, and system frame number. The reception of MIBs and other system information enables UE3 to further (downlink) synchronize with base station 5A of RAN5.

[0079] When UE3 needs to connect to the network, it can perform a random access channel (RACH) procedure to access the network. Specifically, UE3 can attempt to access cell 9 (and / or beam) using an initial RRC connection setup procedure that includes a random access procedure. Before attempting initial access, UE3 selects a random access resource (e.g., including a preamble) to use to initiate the RACH procedure. In S414, UE3 sends the selected preamble (e.g., in "Msg1") to base station 5A of RAN5 via physical random access channel (PRACH) to initiate the process of obtaining synchronization on the uplink (UL). In response, base station 5A of RAN5 responds in S416 with a random access response (RAR) (or "Msg2"). The RAR includes a timing-alignment (TA) command to indicate the reception of a preamble and adjust the transmission timing of UE3 based on the timing of the received preamble (for example), an uplink grant field indicating the resources to be used on the uplink for the physical uplink shared channel (PUSCH), a frequency hopping flag to indicate whether UE3 will transmit on PUSCH with or without frequency, an MCS field to allow UE3 to determine the modulation and coding scheme (MCS) for PUSCH transmission, and a transmit power control (TPC) command value to set the power for PUSCH transmission. At this point, an initial signaling radio bearer (SRB) "SRB0" is established to communicate a specific type of RRC message on the common control channel (CCCH). Then, in S418, UE3 sends a third message ("Msg3") to the network via the physical uplink shared channel (PUSCH) based on the information in the RAR (for example, using SRB0).The specific messages sent by UE3 in this step, and the content of those messages, depend on the context in which the random access procedure is being used. However, in the example of an initial wireless RRC connection setup, Msg3 typically contains an RRC connection request or similar message carrying a temporary, randomly generated UE identifier. The network responds at S420 with a fourth message ("Msg4") carrying the randomly generated UE identifier received in Msg3 (for example, for the purpose of resolving any conflicts between different UE3s using the same preamble sequence). If successful, Msg4 also causes UE3 to transition to a connection state in which another SRB "SRB1" is established to communicate specific RRC and NAS messages over a dedicated control channel (DCCH).

[0080] Next, UE3 attempts to achieve a packet data network (PDN) connection by sending a message to base station 5A of RAN5 in S422 indicating that RRC is complete. This message, as a NAS payload, includes an attach request to initiate the attach procedure and a PDN connection request. Then, base station 5A of RAN5 sends its first message, an initial UE message containing the attach request and PDN connection request, to core network 7 in S424. This message is sent to the core network node that provides mobility management functionality (MME11 in this example, but AMF in the case of 5G). This message is sent via the S1-MME interface / reference point and, in this 4G example, includes information such as the tracking area identify (TAI) and E-UTRAN cell global identifier (ECGI) (similar but differently named message / information elements may be used for 5G and other generations).

[0081] In S426, the mobility management node 11 coordinates with another core network node (for example, the home subscriber server HSS and / or authentication centre (AuC)) to obtain security information such as authentication information, for example, KASME (cryptographic key, integrity key, and intermediate key derived in HSS and UE3 from serving network identity (SN id)), AUTN (so-called authentication token generated in AuC), XRES (so-called "expected response" generated in AuC), and / or RAND (random number for use in key generation and authentication).

[0082] In S428, the mobility management node 11 sends an authentication request (including RAND and AUTN) to the UE3, and in S430, the UE3 responds with an authentication response that includes authentication response parameters calculated based on RAND and AUTN, and a key (K) stored in the UE3 (for example, in the subscriber identity module).

[0083] Next, the mobility management node 11 initiates NAS signaling security between itself and the UE3 by sending a NAS security mode command message in S432 that notifies the UE3 of the respective algorithms to be used for integrity protection and (de)encryption. In S434, the UE3 derives the appropriate security information and then (in S436) responds by sending a response message to the mobility management node 11 that the NAS signaling security initialization is complete.

[0084] In S438, the mobility management node 11 coordinates with one or more other core network nodes (e.g., HSS) to obtain location update-related information, such as the PDN enrollment context (including, for example, the EPS enrollment Quality of Service (QoS) profile and subscription access point name aggregate maximum bit rate (APN-AMBR)).

[0085] At S440, the mobility management node 11 initiates the establishment of a communication GPRS tunnelling protocol (GTP) tunnel by coordinating with one or more other core network nodes (e.g., S-GW13 and / or P-GW15 or a combination thereof) to send an appropriate session creation request (e.g., to S-GW13) and receiving an appropriate response once the tunnel is established. For example, after S-GW13 sends a corresponding default bearer request to P-GW15 to create a new entry in its EPS bearer context table, a default bearer response is sent from P-GW15 to S-GW13, containing P-GW15's user plane address, P-GW15's tunnel endpoint identifier (TEID) for the user plane and control plane, EPS bearer identification information, and QoS information. P-GW15 also sends downlink data to S-GW13, which is buffered until the connection is complete. An acknowledgment message indicating that a GTP for control (GTP-C) tunnel has been established is typically sent from S-GW13 to mobility management node 11.

[0086] In S442, the mobility management node 11 sends an initial context setup request (including, for example, an S1 interface context setup request, a NAS attachment acceptance request, and a default bearer activation request).

[0087] A UE capability exchange may follow, in which base station 5A (in S444) sends a UE capability query to UE3 (typically using RRC signaling) to request information about the UE's capabilities. In S446, UE3 responds with the requested UE capability information, and in S448, base station 5A provides instructions for this UE capability information to mobility management node 11.

[0088] Next, access stratum (AS) security is established. Specifically, in S450, base station 5A sends an RRC security mode command to UE3 containing the AS integrity protection and encryption algorithm and the "START" parameter. UE3 uses the received information to calculate an appropriate security key and, in S452, sends a message to base station 5A indicating that the RRC security mode is complete. During this stage, an additional signaling radio bearer (SRB2) is established. SRB2 is used for RRC messages and NAS messages containing logged measurement information, all using DCCH logical channels. SRB2 has a lower priority than SRB1 and is configured by base station 5A after security activation.

[0089] The RRC reconfiguration continues, and in S454, base station 5A sends the RRC reconfiguration to UE3 to activate the default radio bearer. UE3 configures itself based on the information in the RRC reconfiguration and sends an RRC reconfiguration complete message in S456. Next, in S458, base station 5A sends a message to mobility management node 11 indicating that the initial context setup is complete. Mobility management node 11 then coordinates with one or more other core network nodes (e.g., S-GW13) to properly correct the bearer and establish a data radio bearer (DRB) for UE communication.

[0090] Although a four-step contention-based RACH procedure is described, it will be understood that UE3 of communication system 1 and base station 5A of RAN5 can also perform a non-contention-based (or "contention-free") procedure in which a dedicated preamble is assigned to UE3 by base station 5A of RAN5. Furthermore, UE3 of communication system 1 and base station 5A of RAN5 can also perform a two-step RACH procedure (for example, as described in the introduction).

[0091] UE 3 can trigger the start of a RACH procedure by itself (e.g., when UE 3 needs to connect to the network), but it will be appreciated that the start of a RACH procedure may also be triggered by the network. For example, the RACH procedure may be initiated by a message transmitted via downlink control information (DCI) having an appropriate DCI format (e.g., 1_0) on a physical downlink control channel (PDCCH), and such a message is generally known as a PDCCH order. The RACH procedure may be initiated by the base station 5A of RAN 5 when handover is required (e.g., using a handover command message).

[0092] <CP CIoT EPS optimization> The UE 3 of the communication system 1, the base station 5A of the RAN 5, and the core network entity 7 are mutually configured to implement a plurality of procedures in the context of CP CIoT EPS optimization. These procedures include, for example, mobile originated (MO) and mobile terminated (MT) data transport. In these general procedures, which do not have problems associated with discontinuous coverage / intermittent feeder links, there is no need to have an available UE context at the base station 5A. UL / DL data transmitted / received by UE 3 is encapsulated into a NAS PDU when transported via a wider network. Over the air interface, the NAS data PDU is transmitted during and after RRC connection establishment via RRC messages (e.g., piggybacked on an RRC connection complete message or in a UL / DL information transfer message). In these procedures, no DRB is established and no AS security is set up. On the S1-AP (NG-AP for 5GS) interface, the NAS data PDU is transmitted via an S1-AP (NG-AP for 5GS) message.

[0093] <Mobile outgoing data transport> As described above, UE3, RAN5 base station 5A, and the core network entity of communication system 1 are configured to perform MO data transport in the context of CP CIoT EPS optimization.

[0094] Referring to Figure 5, a simplified sequence diagram illustrating the procedure for MO data transport in the context of CP CIoT EPS optimization with P-GW connectivity that may be used in communication system 1, one such procedure is described here as just one example. In this procedure, CP CIoT EPS optimization is described in the context of the 4G entity shown in Figure 3. Nevertheless, it will be understood that the corresponding 5G entity (or corresponding device of a future generation) for CP CIoT 5GS optimization can follow a similar procedure. It will be understood that this description is intended only as an overview, and therefore not all parameters of the message flow are enumerated or described.

[0095] As seen in S500, at the start of the procedure, UE3 is in idle mode / state (in this example, EPS connection management (ECM) or "ECM-IDLE" mode / state, where UE3 does not have a signaling connection to MME11).

[0096] In S501, UE3 establishes an RRC connection or sends an RRC Early Data Request message, including an integrity-protected NAS PDU (e.g., in an RRC connection setup complete message or an RRC Early Data Request message). The NAS PDU carries the EPS Bearer ID (EBI) and encrypted UL data. UE3 may also indicate, for example, in the NAS release support information field of the NAS PDU, whether further UL or DL ​​data transmissions are expected, or whether only a single DL data transmission (e.g., an acknowledgment or response to the UL data) following this UL data transmission is expected.

[0097] In S501b, base station 5A may, in cooperation with MME11 (for example in the case of NB-IoT), retrieve the EPS-negotiated QoS profile from MME11 (if it has not been retrieved previously).

[0098] In S502, the NAS PDU provided to base station 5A in S501 is relayed to MME11 (along with the EBI) using the S1-AP initial UE message (corresponding to the NG-AP message in 5GS). If the RRC early data request message was used in S501, base station 5A may include the "EDT session" instruction in the S1-AP initial UE message.

[0099] In the S503, the MME11 checks the integrity of the incoming NAS PDU and decrypts the data it contains.

[0100] Nevertheless, MME11 may reject the request by discarding the NAS data PDU and sending a denial-of-service message to UE3 with an appropriate cause. Rejection may occur, for example, if there is a service gap timer running in the UE's MME mobility management (MM) context and MME11 is not waiting for an MT paging response from UE3. MME11 may also provide UE3 with a mobility management backoff timer set to the remaining value of the service gap timer, and then trigger the S1 release procedure.

[0101] In S504, MME11 may send a bearer correction request message to S-GW13 for each PDN connection (including, for example, the MME address, MME TEID DL, delayed downlink packet notification request, RAT type, LTE-M RAT type reporting flag to PGW, MO exception data counter, and / or similar). The bearer correction request message may be sent, for example, if a connection has not been established via the user plane interface / reference point (S11-U interface) between MME11 and S-GW13. Here, S-GW13 can transmit downlink data toward UE3. Furthermore, regardless of whether S11-U has already been established, a bearer correction request message may be sent with appropriate information in other scenarios, for example, when P-GW15 requests UE location and / or user-limited subscriber group information and that information changes, when serving network information changes compared to the last reported bearer correction request message, when MME11 sends a bearer correction request message and includes the serving network IE in this message, and / or when the UE time zone changes compared to the last reported UE time zone.

[0102] In S505, if a bearer correction request message is sent, S-GW13 may send a bearer correction request message to P-GW15 that includes information corresponding to the content of the bearer correction request message and / or the reason for its transmission.

[0103] In S506, if a bearer correction request message was sent in S505, P-GW15 may send a bearer correction response to S-GW13.

[0104] In S507, if a bearer correction request message was sent in S504, S-GW13 may return an appropriate bearer correction response (S-GW address and TEID for uplink traffic) to MME11 as a response to the bearer correction request message. The S-GW address and S-GW TEID for the S11-U user plane are used by MME11 to forward UL data to S-GW13, as seen in S508.

[0105] If no DL data is expected in S501 based on the NAS release support information provided by UE3, this indicates that all application layer data exchange has been completed with UL data transfer. If MME11 is not aware of any pending MT traffic and the S1-U bearer has not been established, the procedure can be skipped to S511.

[0106] Otherwise, the DL data may arrive at P-GW15, which may transmit the DL data to MME11 via S-GW13 in S509. If no data is received, S510-S512 may be skipped, and base station 5A may trigger S514 after not detecting any activity in S513. While the RRC connection is active, UE3 may still transmit UL data, and may receive DL data in NAS PDUs carried in S1-AP UL or DL ​​messages, respectively (not shown). Whenever a user plane bearer is not established, UE3 may provide NAS release assistance information along with the UL data. In this case, to assist with location services, base station 5A may, if necessary, indicate the UE's coverage level to MME11.

[0107] In S510, if DL data is received in S509, MME11 encrypts the DL data and protects its integrity.

[0108] In S511, if S510 occurs, the DL data is encapsulated in the NAS PDU and sent to base station 5A in a DL NAS transport message, for example, an S1-AP downlink NAS transport message.

[0109] If the configuration in MME11 indicates that base station 5A supports acknowledgment of downlink NAS data PDUs, and acknowledgment of downlink NAS data PDUs is enabled in the subscription information of UE3, then MME11 can indicate in the S1-AP downlink NAS message that acknowledgment has been requested from base station 5A.

[0110] On the other hand, if S510 is not performed, or if the NAS service acceptance message is not sent, the MME3 can complete the establishment of the UE-related logical S1 connection by sending a connection establishment instruction message to the base station 5A (in S511).

[0111] UE radio capability may be provided from MME11 to base station 5A in a DL NAS transport message or connection establishment instruction message, and base station 5A may store the received UE radio capability information.

[0112] If NAS release support information is received along with UL data and it indicates that DL data was expected, the next DL packet following the transmission of the NAS release support information will be the last packet of application layer data exchange. In this case, unless MME11 is aware of additional pending MT traffic and an S1-U bearer has not been established, MME11 will send an S1 UE context release command in S512, immediately after the S1-AP message containing the DL data encapsulated in the NAS PDU, as an instruction that base station 5A should release the RRC connection immediately after successfully transmitting data to UE3. Alternatively, if an "EDT session" instruction is received in S502, MME11 may include a "termination instruction" in the S1-AP message containing the DL data encapsulated in the NAS PDU indicating that there is no further data. If MME11 includes a "termination instruction" indicating that there is no further data, and base station 5A does not proceed with establishing an RRC connection, base station 5A skips S512a and starts S512b.

[0113] If NAS release assistance information is received indicating that there is no expected downlink data, all application layer data exchange is completed via UL data transfer. In this case, unless MME11 recognizes additional pending MT traffic and an S1-U bearer is established, -MME may send the S1-AP UE context release command immediately after the S1-AP DL NAS transport (indicating acceptance of NAS services), in which case S512b and S514 may be skipped, or it may send the S1-AP UE context release command immediately after the S1-AP connection establishment instruction, in which case S512b to S514 may all be skipped. Alternatively, if MME11 receives an "EDT session" instruction from base station 5A in S502, MME11 may include a "termination instruction" without further data in the S1-AP DL NAS transport (indicating acceptance of NAS services) or the S1-AP connection establishment instruction. If base station 5A does not proceed with RRC connection establishment, base station 5A may skip S512a and start S512b.

[0114] In S512a, base station 5A sends an RRC DL data message to UE3 containing DL data encapsulated in the NAS PDU. In S511, if the S1 UE context release command follows the S1-AP message containing the NAS data PDU, base station 5A can complete the DL data transmission of the NAS PDU to UE3 without needing to monitor NAS PDU activity (in S514), and S515 can be completed immediately after any acknowledgment is sent to MME11 (as seen in S513).

[0115] If, in S512b, a "termination instruction" without further data is received from MME11 in the S1-AP message, base station 5A may send an RRC early data completion message along with any NAS payload received in S511 (either NAS data PDU or NAS service acceptance). In this case, S514 may be skipped.

[0116] In S513, base station 5A may send a NAS distribution instruction to MME11 (if requested).

[0117] In S514, NAS PDU activity is monitored at base station 5A.

[0118] If there is no NAS PDU activity for a period of time, base station 5A detects the inactivity and initiates the S1 release procedure at S515.

[0119] <Mobile Terminal Data Transport> As described above, UE3 of communication system 1, base station 5A of RAN5, and core network entity 7 are configured to perform MT data transport in the context of CP CIoT EPS optimization.

[0120] One such procedure will be described as an example, with reference to Figure 6, a simplified sequence diagram showing the procedure for MT data transport in the context of CP CIoT EPS optimization with P-GW connectivity that may be used in communication system 1. In this procedure, CP CIoT EPS optimization is described in the context of the 4G entity shown in Figure 3. Nevertheless, it will be understood that the corresponding 5G entity (or corresponding device of a future generation) for CP CIoT 5GS optimization can follow a similar procedure. It will be understood that this description is intended only as an overview, and therefore not all parameters of the message flow are enumerated or described.

[0121] As seen in the S600, at the start of the procedure, UE3 is in idle mode / state (in this example, EPS connection management (ECM) or "ECM-IDLE" mode / state, where UE3 does not have a signaling connection to MME11).

[0122] In S601, S-GW13 receives DL data packets / control signaling for UE3 from P-GW15. If the S-GW context data indicates that there is no DL user plane TEID destined for MME11, the S-GW buffers the DL data packets and identifies which MME11 is servicing that UE3.

[0123] In S602a, if S-GW13 is buffering data (for example, as described in S601 above), S-GW13 sends a downlink data notification message (including, for example, allocation and retention priority (ARP) and EPS bearer ID) to MME11 which has control plane connectivity to a given UE3. In S602b, MME11 responds to S-GW13 with a downlink data notification acknowledgment message.

[0124] In S603, assuming that UE3 is registered with MME11 and is considered reachable (and possibly subject to other criteria), MME11 may send one or more paging messages.

[0125] In S604, base station 5A of RAN5, upon receiving one or more paging messages from MME11, pages UE3.

[0126] In S605, since UE3 is in the ECM-IDLE state, upon receiving a paging instruction, UE3 and base station 5A coordinate to establish an RRC connection (as described, for example, with reference to Figure 4). During connection establishment, UE3 may send a control plane service request NAS message using the RRC connection request. Base station 5A may send this to MME11 in the S1-AP initial UE message, as seen in S606.

[0127] When control plane CIoT EPS optimization is applied, the control plane service request NAS message does not trigger the establishment of a data radio bearer by MME11, and MME11 can immediately transmit the received downlink data to base station 5A using the NAS PDU. MME11 monitors the paging procedure using a timer. If MME11 does not receive a response to the paging request message from UE3, it can repeat paging according to any applicable paging strategy.

[0128] In S605b, base station 5A may, in cooperation with MME11 (for example in the case of NB-IoT), retrieve the EPS-negotiated QoS profile from MME11 (if it has not been retrieved previously).

[0129] In S607, MME11 can send a bearer correction request message to S-GW13 for each PDN connection (including, for example, the MME address, MME TEID DL, delayed downlink packet notification request, RAT type, and an LTE-M RAT type reporting flag to the PGW). The bearer correction request message may be sent, for example, if a connection has not been established via the user plane interface / reference point (S11-U interface) between MME11 and S-GW13. Here, S-GW13 can transmit downlink data toward UE3. Furthermore, regardless of whether S11-U has already been established, a bearer correction request message may be sent with appropriate information in other scenarios, for example, when P-GW15 requests UE location and / or user-limited subscriber group information and that information changes, when serving network information changes compared to the last reported bearer correction request message, when MME11 sends a bearer correction request message and includes the serving network IE in this message, and / or when the UE time zone changes compared to the last reported UE time zone.

[0130] In S608, if a bearer correction request message is sent, S-GW13 may send a bearer correction request message to P-GW15 that includes information corresponding to the content of the bearer correction request message and / or the reason why it was sent.

[0131] In S609, if a bearer correction request message was sent in S608, P-GW15 may send an appropriate bearer correction response to S-GW13.

[0132] In S610, if a bearer correction request message is sent in S607, S-GW13 may return an appropriate bearer correction response (S-GW address and TEID for uplink traffic) to MME11 as a response to the bearer correction request message. The S-GW address and S-GW TEID for the S11-U user plane are used by MME11 to forward any UL data to S-GW13.

[0133] In S611, buffered downlink data (if S11-U is not established) may be sent to MME11 by S-GW13.

[0134] In S612, MME11 encrypts and protects the integrity of downlink data.

[0135] In S613, MME11 may transmit encrypted and integrity-protected downlink data to base station 5A using the NAS PDU carried by the downlink S1-AP message. If the configuration in MME11 indicates that base station 5A supports acknowledgment of downlink NAS data PDUs, and acknowledgment of downlink NAS data PDUs is enabled in the UE3 subscription information, MME11 may indicate in the S1-AP downlink NAS message that acknowledgment has been requested from base station 5A.

[0136] In S614, the NAS PDU containing the data is delivered to UE3 via a downlink RRC message. This is considered by UE3 as an implicit acknowledgment of the service request message sent in S605.

[0137] In S615, base station 5A sends a NAS distribution instruction to MME11 (if requested).

[0138] In S616, while the RRC connection is still established, additional UL (and DL) data can be transferred using the NAS PDU. This figure illustrates UL data transfer using a UL RRC message that encapsulates the NAS PDU along with the UL data. Whenever UE3 has not established a user plane bearer, UE3 may provide release assistance information along with the uplink data in the NAS PDU.

[0139] In S617, the NAS PDU containing the data is sent to MME11 via a UL S1-AP message.

[0140] In S618, the data is checked for integrity and then decrypted.

[0141] In S619a and S619b, MME11 transmits UL data to P-GW15 via S-GW13 and performs any actions related to the presence of release support information as follows: -If the release support information indicates that there is no downlink data following the uplink data, MME11 will immediately release the connection and skip to S621, unless MME11 is aware of any pending MT traffic and there is no S1-U bearer. - If the release support information indicates that downlink data will follow uplink transmission, and unless MME11 is aware of additional pending MT traffic and there is no S1-U bearer, MME11 will send an S1 UE context release command to base station 5A immediately after the S1-AP message containing downlink data encapsulated in the NAS PDU.

[0142] In S620, NAS PDU activity is monitored at base station 5A.

[0143] If there is no NAS PDU activity for a period of time, base station 5A detects the inactivity and initiates the S1 release procedure at S621.

[0144] <NTN RAN> In the exemplary communication system 1, each RAN 5 may be implemented as a non-terrestrial network (NTN) RAN.

[0145] Figure 7 schematically shows one such NTN RAN5 that may be used in the communication system shown in Figure 3.

[0146] As shown in Figure 7, NTN RAN5 includes a base station 5A operating one or more associated cells 9, a gateway 5B, and a non-terrestrial (space or air) platform 5C (including, for example, one or more satellites and / or aircraft), which are sometimes referred to simply as "satellites." Communications over NTN RAN5 are routed through the core network 7 and the external network 20 (for example, through the N6 interface / reference point).

[0147] NTN RAN5 controls multiple directional satellite beams that can provide associated NTN cells 9. Specifically, each satellite beam has an associated footprint on the Earth's surface that forms an NTN cell or part of an NTN cell. Each NTN cell has an associated Physical Cell Identity (PCI). The satellite beam footprint may move as the non-terrestrial (space or air) platform 5C moves along its orbit (e.g., as indicated by arrow A in Figure 7). Alternatively, the satellite beam footprint may be fixed to the Earth, in which case appropriate satellite beam directing mechanisms (mechanical or electronic steering) may be used to compensate for the movement of the non-terrestrial (space or air) platform 5C. In NTN, satellite beams and satellites are not considered to be visible from the perspective of the UE. However, this does not preclude the distinction of network types (e.g., NTN and terrestrial systems) at the public land mobile network (PLMN) level.

[0148] NTN RAN5 base station 5A is configured to provide ephemeris data from a non-terrestrial (space or air) platform 5C to UE3 to assist UE3 in performing measurements and cell selection / reselection and to support initial access. This ephemeris data may include orbital information, such as information at the orbital plane level or satellite level, and / or information (e.g., pointers or indices) that allows UE3 (e.g., in a subscriber identification module "SIM") to retrieve more detailed ephemeris data. At least a portion of this ephemeris information may be provided, for example, in system information, and / or using UE-specific (dedicated) signaling, such as RRC signaling.

[0149] Specifically, base station 5A may provide satellite support information about the satellite as part of a dedicated system information block (SIB) broadcast to UE3 in the corresponding cell 9 of NTN RAN5 (in the case of 5G NTN, this may be, for example, SIB19, but in future generations, it may be provided in a different SIB or in a different way). The satellite support information may include information that identifies at least one relevant NTN configuration (for example, as part of NTN-Config IE). The NTN configuration includes parameters (for example, ephemeris data, common timing alignment parameters, scheduling (e.g., k_offset), validity period of uplink synchronization information, and epoch time (reference time for which the support information is valid)) to help UE3 access the network using NTN access.

[0150] <NTN RANアーキテクチャ> Figures 8A, 8B, and 8C show possible architectures for NTN RAN5 that can be used, respectively.

[0151] The architecture in Figure 8A can be referred to as a “transparent satellite” based RAN architecture. In this architecture, base station 5A is a ground-based base station that sends and receives communications destined for and originating from UE3s via a ground-based gateway 5B and via a non-terrestrial (space or air) platform 5C that does not have base station functionality. The non-terrestrial (space or air) platform 5C relays these communications between UE3s in each cell operated by base station 5A and, if necessary, between UE3s and gateway 5B. The non-terrestrial (space or air) platform 5C relays these communications transparently without onboard processing and effectively functions as a so-called “vent pipe.” In this implementation, the feeder link between gateway 5B and the non-terrestrial (space or air) platform 5C effectively functions as part of the respective Uu interface (or reference point) between base station 5A and each UE3. Similarly, the respective service links between the non-terrestrial (space or air) platform 5C and each UE3 effectively function as another part of the respective Uu interface (or reference point) between base station 5A and each UE3. The base station's communication link with the core network 7 (for signaling via, for example, N1, N2, N3 interfaces / reference points, etc.) is provided only on the ground.

[0152] The architecture in Figure 8B is sometimes referred to as a “regenerative satellite” based RAN architecture (i.e., the satellite performs onboard processing of the payload being communicated between UE3 and core network 7). In this architecture, base station 5A is located on the ground, as is central unit (CU) 5A. CU And distributed unit (DU) 5A mounted on non-ground (space or air) platform 5C DU It is a distributed base station 5A having the following: CU5 A located on the ground. CU DU5 A performs some of the functions (typically higher layers) of base station 5A and is not located on the ground. DUexecutes other (typically lower-layer) functions of base station 5A. CU 5A located on the ground CU , via gateway 5B and between gateway 5B and DU 5A DU , via the F1 interface implemented via a satellite radio interface between non-terrestrial (space or airborne) platform 5C where DU 5A is provided, communicates with DU 5A not located on the ground DU .

[0153] Non-terrestrial (space or airborne) platform 5C transmits communications addressed to UE 3 in each cell 9 operated by base station 5A and communications from UE 3, and transmits and receives communications to and from gateway 5B as necessary. However, in this implementation, lower-layer processing of communications respectively addressed to UE 3 and communications originated from UE 3 is performed by DU 5A DU on non-terrestrial (space or airborne) platform 5C, and upper-layer processing of communications respectively addressed to UE 3 and communications originated from UE 3 is performed by CU 5A located on the ground CU .

[0154] Accordingly, in this implementation, the feeder link between gateway 5B and non-terrestrial (space or airborne) platform 5C effectively functions as an F1 interface (or reference point) between CU 5A of base station 5A CU and DU 5A DU . On the other hand, each service link between non-terrestrial (space or airborne) platform 5C and each UE 3 effectively functions as a respective Uu interface (or reference point) between base station 5A and each UE 3. The communication link of the base station with core network 7 (for signaling via, for example, N1, N2, N3 interfaces / reference points, etc.) is provided only on the ground.

[0155] The architecture in Figure 8C is sometimes referred to as a "regenerative satellite" based RAN architecture (i.e., the satellite performs onboard processing of payloads being communicated between UE3 and the core network 7). In this architecture, the base station 5A is mounted on a non-terrestrial (space or air) platform 5C. The base station 5A mounted on the non-terrestrial (space or air) platform 5C transmits and receives communications destined for and originating from UE3 within each cell 9 operated by the base station 5A to and from the core network 7 via the gateway 5B as needed. However, in this implementation, the processing of communications destined for and originating from UE3 is performed by the base station 5A on the non-terrestrial platform 5C.

[0156] Therefore, in this implementation, the feeder link between Gateway 5B and the non-terrestrial (space or air) platform 5C effectively functions as part of the N1 / N2 / N3 interface (or reference point) between Base Station 5A and Core Network 7. Thus, the base station's communication link with Core Network 7 (e.g., for signaling via N1, N2, N3 interface / reference point, etc.) is provided partly via the feeder link and partly on the ground. On the other hand, each service link between the non-terrestrial (space or air) platform 5C and each UE3 effectively functions as the respective Uu interface (or reference point) between Base Station 5A and each UE3.

[0157] Therefore, base station 5A controls one or more associated cells via a non-terrestrial (space or air) platform 5C. It will be understood that base station 5A may be configured to support 4G, 5G, 6G and / or later generations, and / or any other 3GPP or non-3GPP communication protocols.

[0158] For purposes of explanation, the NTN RAN5 when implemented in the communication system 1 will be described with reference to the regeneration architecture illustrated in FIG. 8C. However, it will be appreciated that NTN RAN5 may potentially use a different one of the architectures, and the entities of communication system 1 may be adapted accordingly.

[0159] <Extended Store and Forward Technology Based on CP CIoT EPS Optimization> Advantageously, in the case of MO / MT data transmission without a complete end-to-end UE-CN / PDN connection (e.g., as a result of discontinuous coverage / intermediate feeder link connections in the context of NTN-deployed RAN5), the UE 3, the base station 5A of NTN RAN5, and the communication entities of core network 7 in communication system 1 are configured with each other to implement one or more extended CP CIoT optimization-based features (i.e., data encapsulated in an (initial) NAS message can be transmitted to base station 5A via RRC messages without a UE context) to support improved store and forward technology.

[0160] Specifically, effective "store and forward" data transmission is enabled by one or more extensions to the MT / MO data transmission procedure in a "store and forward" mode cell 9 (e.g., as described with reference to FIG. 5 and FIG. 6).

[0161] These extensions are described in more detail below with reference to control plane CIoT EPS optimization, but may be suitably adapted based on CIoT 5GS optimization (or similar).

[0162] In summary, possible extensions include: (introduction of an allowed UE list and / or associated information / context retained at base station 5A, extended cell access control in "store and forward" mode cells based on a new information element in system information, Paging enhancements, including the introduction of a new paging trigger in MME11 (or AMF in the case of 5GS) and redefined processing of paging information / messages in base station 5A. Extensions to the RRC connection setup procedure to confirm / instruct that the RRC connection setup procedure is for data / signaling transmission under the "Storage and Transfer" framework. The introduction of the ability to include multiple (DL / UL) "NAS PDU" transmissions within a single S1-AP (or NG-AP in the case of 5GS) transport message. The introduction of the ability to include the downlink NAS PDU transfer status for each of the multiple downlink NAS PDUs on the S1-AP (or NG-AP in the case of 5GS) after reconnection to the MME (or AMF in the case of 5GS), Enhancements to the S1 setup procedure, including the introduction of new indicators in the S1 setup procedure to support interoperability between base station 5A and core network 7, and / or This includes extensions to the interaction between the access stratum (AS) and non-access stratum (NAS) in UE3.

[0163] It will be understood that any of these extensions can potentially be implemented individually, without necessarily introducing all or any of the other extensions, and may provide benefits with respect to “storage and transfer” data transmission.

[0164] The use of the CP CIoT-based data “storage and transfer” extensions described herein will be seen as having the advantage of enabling small amounts of data to be transmitted without UE context, and having the potential to support base station mobility relatively easily with minimal impact on existing procedures.

[0165] <Data Storage and Transfer - Overview> Next, referring to Figures 9 and 10, we will describe, simply as an example, a possible CP CIoT-optimized storage and transfer data transmission flow.

[0166] In Figures 9 and 10, it will be understood that EDT can potentially be used in conjunction with CP CIoT-based methods (in the same way as described with reference to Figures 5 and 6) for only one data packet in one direction for transmission. Nevertheless, for simplicity, EDT is not included in the message flow.

[0167] <Service Link available / Feeder Link unavailable> Figure 9 is a simplified sequence diagram showing a CP CIoT-optimized data transmission flow between NTN RAN5 base station 5A and communication system 1, which may be used when the service link is available but the feeder link is unavailable.

[0168] In Figure 9, the procedure generally follows the relevant parts of the procedure shown in Figure 5 (for MO) and Figure 6 (for MT) between base station 5A and UE3, and the general explanation relating to the corresponding steps of these procedures also applies here.

[0169] In Figure 9, base station 5A stores / maintains a separate UE-specific buffer / data area 930 for each UE3 that base station 5A serves (which, in some cases, has the associated UE capability, is in the permitted list, and / or meets any other criteria). Each UE-specific buffer / data area 930 contains a set of data type-specific (sub)buffer / data areas 932, 934, and 936. In this example, the data type-specific (sub)buffer / data areas 932, 934, and 936 include an uplink data buffer 932 for storing uplink data, a paging storage area 934 for storing paging information, and a downlink data buffer 936 for storing downlink data. Nevertheless, it will be understood that the UE-specific buffer / data area 930 may be configured to store different sets of information depending on the requirements. Furthermore, the UE-specific buffer / data area 930 may additionally / alternatively be configured to store other data / information types, such as UE context information. For clarity, the UE-specific buffer 930 is described as being "logically" divided into different (sub)buffers, but it should be understood that in implemented systems, such division into (sub)buffers may still store the same type of information, though this may not be immediately apparent.

[0170] In Figure 9, we assume that at the start of the procedure, the downlink data buffer 936 of UE3 is not empty, as shown in S920, because (for example, base station 5A has received downlink data destined for UE3, encapsulated in one or more NAS PDUs provided from core network 7 via the feeder link (through MME 11).

[0171] When the service link becomes available, in the case of MO, UE3 initiates an RRC connection to base station 5A. This typically involves a random access procedure similar to that described with reference to Figure 4 (e.g., with respect to steps S414-S420), for example, UE3 sending a random access preamble (S901), receiving a random access response (S902), sending a connection request (S903), and receiving the relevant connection setup message (S904). Next, in S905, UE3 sends a message to base station 5A indicating that the RRC connection setup is complete. UE3 transmits UL data to base station 5A using a NAS data PDU. The UL NAS data PDU may be included, for example, in the connection setup completion message sent in S905 and / or in one or more UL information transfer messages (as seen in S907). In the example in Figure 9, base station 5A buffers each received UL NAS data PDU in its UL data buffer 932 without triggering any procedure toward the core network 7 (for example, without triggering the S1-AP procedure in this 4G / EPS example). Base station 5A may also transfer any stored downlink data from the downlink data buffer 936 (assuming in this example some downlink data has been previously stored). The downlink data is stored as one or more DL NAS data PDUs and transferred using one or more DL information transfer messages (as seen in S906).

[0172] If there is no more data to transmit or receive by base station 5A, base station 5A may initiate the release of the RRC connection, as seen in S908. This may be triggered, for example, when the UL / DL buffer is empty, there has been no NAS PDU activity for some time, and base station 5A detects the inactivity and initiates the release procedure (similar to S515 in Figure 5, but in this case, it may not be necessary to perform the S1 release).

[0173] This procedure is the same when the service link is available in MT mode. However, in the case of MT data transfer, in addition to one or more downlink NAS data PDUs previously received from MME11 being buffered in the downlink data buffer 936 of base station 5A, base station 5A also stores corresponding paging information in the paging storage area 934. Base station 5A uses this paging information to page UE3 in S900, for example, when base station 5A predicts that UE3 is within coverage but UE3 is not connected.

[0174] In response to the paging at S900, UE3 initiates an RRC connection to base station 5A. This typically involves a random access procedure similar to that described with reference to Figure 4 (for example, with respect to steps S414-S420), for example, UE3 sending a random access preamble (S901), receiving a random access response (S902), sending a connection request (S903), and receiving the relevant connection setup message (S904). Next, at S905, UE3 sends a message to base station 5A indicating that the RRC connection setup is complete. In this MT case (assuming UE3 has no UL data to transmit), after the RRC connection is established, base station 5A transfers the buffered downlink NAS data PDU to UE3 using one or more DL information transfer messages (as seen in S906). UE3 can, of course, also transmit any uplink NAS data PDU to base station 5A using the connection setup completion message sent in S905 and / or one or more UL information transfer messages sent in S907.

[0175] If there is no more data to transmit or receive by base station 5A, base station 5A may initiate the release of the RRC connection, as seen in S908. This may be triggered, for example, when the UL / DL buffer is empty, there has been no NAS PDU activity for some time, and base station 5A detects inactivity (similar to S514 in Figure 5).

[0176] <Feeder link available / Service link unavailable> Figure 10 is a simplified sequence diagram showing a CIoT-optimized data transmission flow between NTN RAN5 and core network 7 that can be used in communication system 1 when the feeder link is available but the service link is unavailable.

[0177] In Figure 10, the procedure generally follows the relevant parts of the procedure shown in Figures 5 (for MO) and 6 (for MT) between NTN RAN5 and core network entities such as MME11, S-GW13, and P-GW15, and the general explanation relating to the corresponding steps of that procedure also applies here. It will be recognized that the procedures in Figures 9 and 10 are not mutually exclusive and may be used in relation to each other in communication system 1 depending on the service link / feeder link status.

[0178] In Figure 10, base station 5A stores / maintains a UE-specific buffer / data area 930 for each UE3 that base station 5A serves (which, in some cases, has the associated UE capability, is in the permitted list, and / or meets any other criteria), as described with reference to Figure 9. Specifically, each UE-specific buffer / data area 930 includes an uplink data buffer 932 for storing uplink data, a paging storage area 934 for storing paging information, and a downlink data buffer 936 for storing downlink data. Nevertheless, it will be understood that the UE-specific buffer / data area 930 may be configured to store different sets of information depending on the requirements. Furthermore, the UE-specific buffer / data area 930 may be configured to store other data / information types, such as UE context information, additionally / alternatively. For clarity, the UE-specific buffer 930 is described as being "logically" divided into different (sub)buffers, but it should be understood that in implemented systems, such division into (sub)buffers may still store the same type of information, though this may not be immediately apparent.

[0179] In Figure 10, at the start of the procedure, UE3 is in idle mode / state (in this example, EPS connection management (ECM) or "ECM-IDLE" mode / state, where UE3 does not have a signaling connection to MME11), as seen in S1000.

[0180] When the feeder link becomes available, in the case of MO, the procedure generally follows steps S1004 to S1012 (similar to, but not identical to, steps S502 to S515 as described with reference to Figure 5).

[0181] Assuming that the UL data for UE3 is present in the UL data buffer 932 of base station 5A, base station 5A sends the S1-AP initial UE message to MME11 in S1004 (corresponding, for example, step S502 in Figure 5), and the UE-related logical S1 connection establishment is initiated as part of the procedure. As shown in the figure, the UL NAS data PDU from the UL data buffer 932 may be included in the initial UE message.

[0182] In S1005, MME11 checks the integrity of the incoming NAS PDU and decrypts the data it contains. In S1006, MME11 may, if necessary, coordinate with S-GW13 (and indirectly with P-GW15) to perform a bearer correction procedure (for example, with MME11, S-GW13, and P-GW15, following a general bearer correction procedure described with reference to steps S504-S507 in Figure 5).

[0183] Therefore, the UL data can be transferred to S-GW13 in S1020 (as described, for example, with reference to step S508 in Figure 5).

[0184] If there is incoming data on the downlink from S-GW13, it may be advantageous for MME11 to simultaneously transmit the data to base station 5A (as shown in S1008) so that it is stored in the downlink data buffer 936 (following any necessary encryption and integrity protection of the DL data, as shown in S1007, if applicable). Any downlink data transmitted in S1008 may be encapsulated in a NAS PDU (as described, for example, with reference to step S511 in Figure 5) and transmitted to base station 5A in one or more DL NAS transport messages, for example in one or more S1-AP downlink NAS transport messages. MME11 may also transmit appropriate paging information to base station 5A for potential subsequent use in paging UE3 later (i.e., when UE3 is in coverage or is expected to be in coverage) so that it is stored in the paging buffer 932 (as shown in S1003a). This paging information may be transmitted simultaneously with (but before or after) the transmission of the downlink data.

[0185] Any further uplink data in the UL data buffer may, advantageously, be transmitted to the MME11 by the base station 5A in one or more UL NAS transport messages, for example, in one or more S1-AP uplink NAS transport messages (as shown in S1009), for forwarding to the S-GW13. This UL communication may occur in parallel with (but before or after) the communication of any DL data described above.

[0186] If there is no more data to be transmitted or received by base station 5A, base station 5A may initiate the S1 release procedure by sending an S1-AP UE context release request, for example, as seen in S1010. This may be triggered, for example, when the UL / DL buffer is empty, there has been no NAS PDU activity for some time, and base station 5A detects inactivity (similar to S514 in Figure 5). The S1 release procedure may proceed, for example, when MME11 sends an S1-AP UE context release command to base station 5A in S1011, and base station 5A responds with an S1-AP UE context release complete message indicating that the S1 release is complete.

[0187] Once the feeder link becomes available, the procedure for MTs is generally similar to, but not identical to, the procedure described with reference to Figure 6.

[0188] In S1001, S-GW13, having received a DL data packet from UE3 from P-GW15 (for example, as described in step S601 of the procedure in Figure 6), can send a downlink data notification message to MME11, which has control plane connectivity to a given UE3 (for example, as described in step S602a of the procedure in Figure 6). Although not shown, MME11 may respond to S-GW13 with a downlink data notification acknowledgment message (for example, as described in step S602b of the procedure in Figure 6).

[0189] In S1002, MME11 determines which base station 5A's coverage UE3 is (next). Then, in S1003, MME11 transmits the associated paging information to base station 5A. It will be understood that this paging does not normally trigger paging via the radio (Uu) interface. Instead, it triggers base station 5A to begin establishing the UE-related logical connection by sending an initial UE message via S1-AP (as seen in S1004). Base station 5A also stores the paging information received from MME11 in the paging buffer 932 for potential subsequent use to later page UE3 for downlink data transfer via the air interface / service link when available.

[0190] If UL data exists in the UL data buffer 932 of base station 5A for UE3, base station 5A may include the relevant UL NAS data PDU in the initial UE message transmitted in S1004.

[0191] In S1005, MME11 checks the integrity of any incoming UL NAS data PDU and decodes the data it contains. In S1006, MME11 may, if necessary, coordinate with S-GW13 (and indirectly with P-GW15) to perform a bearer correction procedure (for example, with MME11, S-GW13, and P-GW15, following the general bearer correction procedure described with reference to steps S607-S610 in Figure 6). Thus, in S1020, any UL data can be transferred to S-GW13.

[0192] Any incoming downlink data from S-GW13 is transmitted to base station 5A by MME11 (as shown in S1008) and may be stored in downlink data buffer 936 (following any necessary encryption and integrity protection of the DL data, as shown in S1007, if applicable). Any downlink data transmitted in S1008 may be encapsulated in a NAS PDU (as described with reference to step S613 in Figure 6, for example) and transmitted to base station 5A in one or more DL NAS transport messages, for example in one or more S1-AP downlink NAS transport messages.

[0193] Any further uplink data in the UL data buffer may, advantageously, be transmitted to the MME11 by the base station 5A in one or more UL NAS transport messages, for example, in one or more S1-AP uplink NAS transport messages (as shown in S1009), for forwarding to the S-GW13. This UL communication may occur in parallel with (but before or after) the communication of any DL data described above.

[0194] If there is no more data to be transmitted or received by base station 5A, base station 5A may initiate the S1 release procedure by sending an S1-AP UE context release request, for example, as seen in S1010. This may be triggered, for example, when the UL / DL buffer is empty, there has been no NAS PDU activity for some time, and base station 5A detects inactivity (similar to S620 in Figure 6). The S1 release procedure may proceed, for example, when MME11 sends an S1-AP UE context release command to base station 5A in S1011, and base station 5A responds with an S1-AP UE context release complete message indicating that the S1 release is complete.

[0195] <List of permitted UEs and related information / context> As described above, the list of allowed UEs and / or related information / context for each UE3 can also be maintained at base station 5A (for example, during a procedure similar to the one described with reference to Figure 9 and / or Figure 10).

[0196] This is in contrast to existing communication systems where the UE context is not available (or not considered necessary) at base station 5A, even when the corresponding UE3 is in RRC idle mode, the UE3 can establish an RRC connection, and at the same time, can transmit at least one NAS data PDU to base station 5A.

[0197] However, in the “storage and transfer” scenario, since the RRC connection and the UE-related logical S1 connection do not exist simultaneously, base station 5A cannot obtain the necessary UE information from MME11 (for example, for access permission purposes, to determine the appropriate RRC configuration, to perform data rate control, and / or similar purposes) once UE3 is RRC connected.

[0198] Therefore, in one favorable example, base station 5A is configured to store / maintain a list of authorized UE3s and, for each authorized UE, information indicating one or more of the following: UE identity (e.g., serving temporary mobile subscriber identity (S-TMSI)), one or more UE-level QoS parameters (e.g., maximum data rate and / or number of NAS PDUs), priority, basic capability, and / or paging information.

[0199] Base station 5A stores this UE information for each UE3 in an allowed UE list for later use, even when the corresponding UE3 is in RRC idle mode. The stored information can be used for one or more of the following purposes: to perform access permissions, to prioritize and / or not prioritize UE RRC connection requests, paging, and / or data transmissions, to control the maximum amount of data that can be transmitted to and from base station 5A for a particular UE3 and / or to store in base station 5A for a particular UE3, and / or to calculate paging opportunities.

[0200] Alternatively or additionally, it will be understood that base station 5A may, in accordance with this, maintain a list of unapproved UEs.

[0201] To obtain this information, MME11 may compile a list of UE3s authorized to access / service based on UE3s having historical information, operations, administration, and management (OAM information, registration data, forecasts, and / or downlink data stored in the base station and / or MME buffers). MME11 may then transmit this list of authorized UE3s, along with their identification information (and possibly further information), to base station 5A, regardless of the RRC status of the listed UE3s.

[0202] Alternatively or additionally, some or all of the information may be obtained via a dedicated, UE-triggered “storage and transfer” access request procedure, as follows: 1. UE3 first initiates an RRC connection to the "storage and transfer" mode cell. 2. If UE3 is not in the list of permitted UEs stored in base station 5A, base station 5A may a) release / deny the UE connection request and notify UE3 that UE3 is "waiting for identification / authentication for further data storage and transfer", and / or b) allow the transmission of a limited amount of NAS PDU from that UE3. 3. Once the feeder link becomes available, base station 5A requests core network 7 (e.g., via MME11) to authorize whether UE3 is permitted / authorized to use the storage and transport services. 4. Core network 7 responds with further necessary UE information if UE3 is permitted / authorized. 5. If UE3 is authorized / permitted by the core network 7, base station 5A adds UE3 to the list of permitted UEs (associated with any corresponding information obtained in this procedure).

[0203] Therefore, after this procedure, UE3 can access the "Storage and Transfer" cell for data transmission services while UE3 is within coverage.

[0204] It will also be understood that UE3 may optionally maintain a list of base stations 5A and / or cell 9 that have “storage and transfer” modes (for example, those previously accessed by UE3) and prioritize these cell 9 for future data transmissions.

[0205] <Cell access control> As described above, communication system 1 can implement extended cell access control in "storage and transfer" mode cells based on new information elements provided in the system information within its cell 9. This will be explained in more detail here, merely as an example.

[0206] More specifically, a base station 5A that operates a cell in "memory and transfer" mode may be configured to prohibit legacy UE3s (which cannot use / do not support memory and transfer data transmission), allow UE3s that support memory and transfer data transmission to camp on to and / or access a "memory and transfer" mode cell, and / or prevent non-legacy UE3s that cannot perform memory and transfer transmission from camping on to and / or accessing a "memory and transfer" mode cell.

[0207] To achieve this, a new “storage and transfer mode” (or similar) indicator is introduced in the system information broadcast in “storage and transfer” mode cells (e.g., system information block type 1 (SIB1)) and sets a “legacy bar bit” in the system information to indicate prohibition.

[0208] As a result, any legacy UE3 will be denied access to cell 9. Non-legacy UE3s that support and wish to use the "Remember and Transfer" feature will ignore this legacy bar bit but will check the "Remember and Transfer" indicator to determine whether to camp on to a specific cell 9 and / or initiate access to cell 9.

[0209] In a "memory and transfer" enabled cell 9, where the "memory and transfer mode" indicator is currently set to indicate that the cell is operating in "memory and transfer mode" (e.g., to "true" or "1"), if a feeder link connection becomes temporarily available, base station 5A may be configured to set the "memory and transfer mode" indicator to indicate that cell 9 is not operating in "memory and transfer mode" (e.g., to "false" or "1").

[0210] Nevertheless, it will be understood that, alternatively, the “Memory Transfer Mode” indicator may be maintained to indicate that cell 9 is operating in “Memory Transfer Mode” (for example, it may be maintained as “True” or “1”). In this case, base station 5A can notify UE3 of the time / length of time the feeder link will be available by broadcasting the time (or time window) during which the feeder link will be temporarily available. Base station 5A may indicate the time (time window) during which the feeder link will be available in system information (e.g., SIB1), for example, base station 5A may indicate the time window (T0-T1) before or when the feeder link connection becomes available. It will also be understood that base station 5A may indicate a list of time / time windows (e.g., multiple [T0-T1] indications) to indicate multiple times / time windows during which the feeder link connection will be available.

[0211] <paging> As described above, communication system 1 may implement one or more paging extensions. Next, some possible paging extensions will be described in more detail, only as examples.

[0212] Conventionally, paging is initiated by MME11 (or an equivalent node) when, for example, a data notification is received or data is buffered to MME11 (or an equivalent node). Paging is received at base station 5A, which transmits the paging via the air interface. Paging triggers UE3 to initiate the establishment of an RRC connection and subsequent S1-AP connection. MT data can then be transmitted to UE3.

[0213] Advantageously, in the case of a "storage and transfer" mode cell, base station 5A of communication system 1 (not MME11) initiates paging to UE3 when downlink data for its UE3 is stored in base station 5A.

[0214] To support this, base station 5A is provided with paging-related information by MME11 (as described with reference to, for example, Figures 9 and 10). This paging information may include, for example, identity and discontinued reception (DRX) for paging occasion calculation. This paging information is stored in base station 5A (for example, in paging memory area 934) so ​​that base station 5A can start paging to UE3 at the appropriate time.

[0215] There are several different ways in which paging-related information can be communicated to base station 5A. For example, paging-related information may be provided as part of the UE context stored in base station 5A (for example, as described above in the section titled “Allowed UE List and Associated Information / Context”).

[0216] Alternatively or additionally, paging-related information may be provided as part of a conventional paging message transmitted via the S1-AP interface when, for example, downlink data / data notification is received at MME11 and the feeder link becomes available to base station 5A, which is attempting to transmit downlink data for “storage and transfer” data transmission (as described with reference to, for example, Figure 10). The “paging” message can be transmitted to base station 5A, which may be followed by an “S1-AP” UE initial message (as described with reference to, for example, steps S1003 and S1004 in Figure 10).

[0217] Alternatively or additionally, a “paging message via S1-AP” may be triggered when any downlink data is available to be transmitted to base station 5A for storage and transfer data transmission. This paging message via S1-AP may be transmitted from MME 11 together with or following downlink data transmitted to base station 5A for storage and transfer (as described, for example, with reference to steps S1003a and S1008 in Figure 10).

[0218] <RRC connection setup procedure> As mentioned above, the communication system 1 can implement an extended RRC connection setup procedure in which indication information confirming / indicating that the RRC connection setup procedure (for example, as described with reference to Fig. 9) is for data / signaling transmission according to the "store and forward" framework is transmitted to the base station 5A.

[0219] Specifically, the RRC connection setup complete message transmitted by the UE 3 at the end of RRC connection establishment may include indication information for confirming / indicating that the RRC connection is for data / signaling transmission according to the "store and forward" framework (that is, for store-and-forward data transmission).

[0220] A description in abstract syntax notation one (ASN.1) of how this indication may be introduced into the RRC connection setup complete message is provided below purely for illustrative purposes. (Conventional information element) attachWithoutPDN-Connectivity-r13 ENUMERATED {true} OPTIONAL, up-CIoT-EPS-Optimisation-r13 ENUMERATED{true} OPTIONAL, cp-CIoT-EPS-Optimisation-r13 ENUMERATED {true} OPTIONAL, … (New information element) attachWithoutPDN-ConnectivityNTN-r1x ENUMERATED {true} OPTIONAL, up-CIoT-EPS-OptimisationNTN-r1x ENUMERATED {true} OPTIONAL,

[0221] <Multiple NAS PDUs on S1-AP> As described above, the communication system 1 may implement the capability of including multiple (DL / UL) "NAS PDU" transmissions in a single S1-AP (or NG-AP for 5GS) transport message.

[0222] Specifically, in conventional communication systems, messages that may be used for NAS PDU transport (including initial UE messages, UL NAS transport messages, and DL NAS transport messages) can only include a single NAS data PDU.

[0223] However, in this example where the store-and-forward data transmission technique is employed, there may be a plurality of stored NAS data PDUs stored in the base station 5A for transmission on the uplink via the S1-AP interface, or stored in the MME 11 for transmission on the downlink via the S1-AP interface.

[0224] Therefore, in order to support efficient communication of these NAS data PDUs via the S1-AP interface, in this exemplary enhancement, the base station 5A and the MME 11 are capable of encapsulating two or more NAS data PDUs in each of different S1-AP messages that can be used for NAS PDU transport (e.g., an initial UE message, a UL NAS transport message, and / or a DL NAS transport message) that the base station 5A / MME 11 can transmit.

[0225] <Multiple NAS PDU delivery status reporting> As described above, after reconnecting to MME11 (or AMF in the case of 5GS), communication system 1 can implement the ability to include the respective downlink NAS PDU transfer status for each of the multiple downlink NAS PDUs via S1-AP (or NG-AP in the case of 5GS).

[0226] Specifically, base station 5A is configured to provide delivery instruction messages (for example, in the DL NAS transport messages described above, particularly with reference to Figures 9 and 10) indicating the delivery / non-delivery status of the NAS PDU received via the S1-AP interface. These messages include the following: NAS delivery non-delivery instruction message: This message is sent by base station 5A and is used to report the non-delivery of a previously received NAS PDU within a downlink NAS transport message via the S1 interface. NAS distribution instruction message: This message is sent by base station 5A and is used to report to UE3 the successful delivery of the NAS PDU previously received within the downlink NAS transport message.

[0227] In the previous communication system 1, these messages could only be used to indicate whether a previously received NAS PDU had been delivered. However, in the "storage and transfer" scenario, it is not possible to indicate the delivery status of the downlink NAS PDU via the Uu interface immediately after receiving the NAS PDU from MME11. Furthermore, in the context of storage and transfer data transmission, indicating only the delivery status of a single NAS PDU is inefficient.

[0228] Therefore, in this exemplary extension, base station 5A is configured to send dedicated S1-AP messages (e.g., a "Downlink NAS Forwarding Status Report" message) to report the forwarding (delivery) status of multiple downlink NAS PDUs.

[0229] This message can, for example, include each NAS PDU that was not delivered successfully (one or more NAS PDUs) (implicitly, this will be understood to mean that the NAS PDUs that were not included were successfully transferred to UE3).

[0230] Nevertheless, it will be understood that the NAS PDUs may be indexed by the MME11 when transmitted to base station 5A, and base station 5A may explicitly indicate which PDUs were successfully transferred and / or which PDUs were not successfully transferred. It will be understood that the message may indicate this information in any suitable way, for example by including a list of PDU indices, by a bitmap having each bit representing the corresponding PDU (e.g., "1" indicates a successful transfer, "0" indicates a failed transfer, or vice versa), or in any other way.

[0231] Alternatively or additionally, it will be understood that the S1-AP NAS non-delivery instruction message and the NAS delivery instruction message may be extended to allow instructions to the MME11 regarding the forwarding status of one or more downlink NAS PDUs received from the MME11 when the feeder link was previously available.

[0232] <Example Implementation Form> Next, with reference to Figure 11, a simplified sequence diagram showing how parts of the procedure shown in Figures 9 and 10 can be extended, we will describe, only as examples, some exemplary implementations with the extensions described above.

[0233] Specifically, as in Figure 10, in Figure 11, base station 5A stores / maintains each UE-specific buffer / data area 930, as described with reference to Figure 9, for each UE3 that base station 5A serves (and which, if applicable, has associated UE capabilities, is in the permitted list, and / or meets any other criteria). Specifically, each UE-specific buffer / data area 930 includes an uplink data buffer 932 for storing uplink data, a paging storage area 934 for storing paging information, and a downlink data buffer 936 for storing downlinks. However, Figure 11 shows how the UE-specific buffer / data area 930 may also (optionally) store “offline” UE context information 938.

[0234] Similar to Figure 10, in Figure 11, at the start of the procedure, UE3 is in idle mode / state (in this example, EPS connection management (ECM) or "ECM-IDLE" mode / state, where UE3 does not have a signaling connection to MME11), as seen in S1100.

[0235] In box (A) of Figure 11, it will be understood that the feeder link is available, the service link is unavailable, and the general procedure described in Figure 10 can be followed. However, as described above in the section titled "Multiple NAS PDUs via S1-AP", when an uplink NAS data PDU is transferred to MME11 via the S1-AP interface, if multiple such NAS PDUs exist in the uplink data buffer 932 (as seen in S1102), the multiple NAS data PDUs may be transferred in a single S1-AP message (for example, as a list of UL NAS data PDUs). Similarly, when a downlink NAS data PDU is transferred to base station 5A via the S1-AP interface, if two or more such NAS PDUs require transfer (as seen in S1104), the multiple NAS data PDUs may be transferred in a single S1-AP message (for example, as a list of DL NAS data PDUs).

[0236] When there is no further data to be transmitted or received by base station 5A, the UE context release procedure can be performed via the S1-AP interface (as explained with reference to, for example, S1010-S1012 in Figure 10).

[0237] In box (B) of Figure 11, when the feeder link is unavailable but the service link is available, base station 5A may paging UE3 (for example, based on paging information 934 stored in UE buffer 930, as described above in the section titled “Paging”) in an attempt to initiate an RRC connection to UE3 for receiving downlink NAS data PDUs stored in downlink data buffer 936 (for example, as described with reference to Figure 9). These downlink NAS data PDUs may or may not be successfully transferred.

[0238] In box (C) of FIG. 11, if the feeder link becomes available again and the service link is not available, the base station 5A may, for example, as described above in the section entitled "Multiple NAS PDU Delivery Status Report", report the transfer (delivery) status of a plurality of downlink NAS PDUs (e.g., in a downlink NAS PDU transfer status report).

[0239] <S1 setup procedure> As described above, the communication system 1 can implement an extension to the S1 setup procedure. The purpose of the S1 setup procedure is to exchange application-level data necessary for the base station 5A and the MME 11 to interoperate correctly over the S1 interface. The S1 procedure is the first S1-AP procedure that is triggered after a transport network layer (TNL) association becomes operational. This procedure uses non-UE related signaling.

[0240] More specifically, in this exemplary extension, the base station 5A and the MME 11 are mutually configured to perform an extended S1 setup procedure, for example, for use after the feeder link becomes available but before any UE-related signaling occurs. Specifically, to ensure support for multi-vendor networks (RAN 5 and core network 7), the extended S1 setup procedure allows at least one of the messages used during the S1 setup procedure to include an indication of network capability / support for store-and-forward data transmission.

[0241] This will be described in more detail by way of example only with reference to FIG. 12, which is a simplified sequence diagram illustrating the S1 setup procedure.

[0242] As can be seen in S1200, in one optional approach, the S1 setup request includes an information element for indicating capability / support for store-and-forward data transmission. For example, the information element may indicate support for "store-and-forward mode", "discontinuous feeder link", "intermittent NTN connection", "non-continuous S1 connection for NTN", etc. The information element may, for example, be an enumeration type indicating "true" or "false" for the capability / support. If the feature is supported in MME 11, MME 11 may respond with a normal S1 setup response message (as seen in S1202a). If the feature is not supported in MME 11, MME 11 may respond with an S1 setup failure message (as seen in S1202b).

[0243] As can be seen in S1210, in another optional approach, a normal S1 setup request is transmitted, and MME 11 may respond with an S1 setup response message (as seen in S1212) that includes an information element for indicating capability / support for store-and-forward data transmission. For example, the information element may indicate support for "store-and-forward mode", "discontinuous feeder link", "intermittent NTN connection", "non-continuous S1 connection for NTN", etc. The information element may, for example, be an enumeration type indicating "true" or "false" for the capability / support.

[0244] <UE AS / NAS interaction> As described above, the communication system 1 may implement an extension of interaction between the access stratum (AS) layer and the non-access stratum (NAS) layer of the UE 3.

[0245] For example, in one option, when the UE 3 receives an RRC release message from the base station 5A, the NAS layer of the UE can enter an idle mode / state (e.g., ECM idle). To facilitate this, the RRC release message may include an appropriate cause value (such as nas-Release, s1-Release, ntn-NoS1-Connection, ntn-FeederlinkNotAvailable, etc.). The AS layer of the UE forwards this RRC release cause to the NAS layer of the UE, and in response, the NAS layer of the UE will terminate the procedure locally (and enter ECM idle).

[0246] Alternatively or additionally, in another option, when the UE 3 receives an RRC release message from the base station 5A, the NAS layer of the UE may remain in a connected mode / state (e.g., ECM connected). To facilitate this, the RRC release message may include an appropriate cause value (such as pendingNas-ConnectionRelease, pendingS1-Release, ntn-NoS1-Connection, ntn-FeederlinkNotAvailable, etc.). The AS layer of the UE forwards this RRC release cause to the NAS layer of the UE. In response, the NAS layer of the UE remains in ECM connected (instead of entering ECM idle). Following this, the NAS layer of the UE may terminate the procedure locally (and enter ECM idle) after a timer expires. Alternatively or additionally, the MME 11 may transmit the information required for S1 release to the NAS layer of the UE (via the base station 5A), after which the NAS layer of the UE can transition to ECM idle.

[0247] <User Equipment> Figure 13 is a simplified block diagram showing the main components of the UE 3 for implementation in the system of Figure 3.

[0248] As shown in the figure, UE3 has a transceiver circuit 31 capable of transmitting and receiving signals to and from base station 5A via one or more air interfaces 33 (e.g., having one or more antenna elements). UE3 has a controller 37 that controls the operation of UE3. The controller 37 is associated with memory 39 and coupled to the transceiver circuit 31. Although not necessarily required for the operation of UE3, UE3 may, of course, have all the usual functions of a conventional UE3 (e.g., user interfaces 35 such as a touchscreen / keypad / microphone / speaker to enable direct user control and interaction with the user), which may be provided, as appropriate, by one or any combination of hardware, software, and firmware. The software may be pre-installed in memory 39 and / or downloaded, for example, via communication system 1 or from a removable data storage device (RMD).

[0249] In this example, the controller 37 is configured to control the overall operation of the UE3 by program instructions or software instructions stored in memory 39. As shown in the figure, these software instructions include, among other things, the operating system 41 and the communication control module 43.

[0250] The communication control module 43 is operable to control communication between the UE3 and its serving base station 5A or multiple base stations 5A (and other communication devices connected to the base station 5A, such as further UE3s and / or core network nodes). The communication control module 43 is configured for the overall handling of uplink communication via relevant uplink channels (e.g., via the physical uplink control channel (PUCCH), random access channel (RACH), and / or physical uplink shared channel (PUSCH)), including both dynamic and semi-static signaling (e.g., such as SRS). The communication control module 43 is also configured to handle the overall handling of downlink communication reception via relevant downlink channels (e.g., via the physical downlink control channel (PDCCH) and / or physical downlink shared channel (PDSCH) of DCI), including both dynamic and semi-persistent scheduling (e.g., such as SPS). The communication control module 43 is responsible for, for example, determining where to monitor downlink control information, determining the resources used by the UE3 for UL / DL communication transmission / reception (including interleaved resources and resources subject to frequency hopping), managing frequency hopping on the UE3 side, determining how slots / symbols are configured (for example, for UL, DL, or full-duplex communication), determining which bandwidth portion is configured for the UE3, and determining how uplink transmissions should be encoded.

[0251] It will be understood that the communication control module 43 may include multiple submodules ("layers" or "entities") to support specific functions. For example, the communication control module 43 may include a PHY submodule, a MAC submodule, an RLC submodule, a PDCP submodule, an RRC submodule, and so on.

[0252] The communication control module 43 is configured, in particular, to control the communications of the UE in accordance with any of the methods described herein.

[0253] <Base station> Figure 14 is a simplified block diagram showing the main components of base station 5A for implementation in the system of Figure 3 (for example, in the NTN access network or other such RAN5).

[0254] As shown, base station 5A has a transceiver circuit 51 that sends and receives signals to and from a communication device (such as UE3) via one or more air interfaces 53 (e.g., single or multi-panel antenna arrays / large antennas), and a core network interface 55 that sends and receives signals to and from network nodes in the core network 7. Although not shown, base station 5A may also be coupled to other base stations 5A via an appropriate interface (e.g., the so-called "X2" interface in LTE or the "Xn" interface in NR). Base station 5A has a controller 57 that controls the operation of base station 5A. The controller 57 is associated with memory 59. Software may be pre-installed in memory 59 and / or downloaded, for example, via communication system 1 or from a removable data storage device (RMD). In this example, the controller 57 is configured to control the overall operation of base station 5A by program instructions or software instructions stored in memory 59.

[0255] As shown in the figure, these software instructions include, in particular, an operating system 61 and a communication control module 63.

[0256] The communication control module 63 is operable to control communication between base station 5A, UE3, and other network entities (e.g., core network nodes) communicating with base station 5A. The communication control module 63 is configured to generally control the reception and decoding of uplink communications via associated uplink channels (e.g., via the physical uplink control channel (PUCCH), random-access channel (RACH), and / or physical uplink shared channel (PUSCH)), which include both dynamic and quasi-static signaling (e.g., SRS). The communication control module 63 is also configured to generally control the transmission of downlink communications via associated downlink channels (e.g., via the physical downlink control channel (PDCCH) and / or physical downlink shared channel (PDSCH)), which include both dynamic scheduling and semi-persistent scheduling (e.g., SPS). The communication control module 63 is responsible for, for example, determining where the UE3 should be configured to monitor downlink control information (e.g., the location of the search space, CORESET, and associated PDCCH candidates to be monitored), determining the resources to be scheduled for UE3 transmission / reception of UL / DL communication (including interleaved resources and resources subject to frequency hopping), managing frequency hopping on the base station 5A side, appropriately configuring slots / symbols (e.g., for UL, DL, or full-duplex communication), configuring the bandwidth portion for the UE3, and providing the relevant configuration signaling to the UE3.

[0257] It will be understood that the communication control module 63 may include multiple submodules ("layers" or "entities") to support specific functions. For example, the communication control module 63 may include a PHY submodule, a MAC submodule, an RLC submodule, a PDCP submodule, an RRC submodule, etc., to communicate with the UE3. Furthermore, the communication control module 63 may include S1 application protocol (S1-AP) submodules, stream control transmission protocol (SCTP) submodules, IP submodules, layer 1 (L1) submodules, layer 2 (L2) submodules, etc. (or corresponding submodules for communicating with AMF) for communicating with core network entities such as MME11 (or similar nodes such as AMF).

[0258] The communication control module 63 is configured to control the base station's communications, in particular, according to one of the methods described herein.

[0259] <Core network node / function> Figure 15 is a block diagram showing the main components of a core network node or function such as MME11, S-GW13, or P-GW15 (or a functionally similar node / function for 5G or other cellular technologies such as AMF, CPF, UPF, SMF).

[0260] As shown, the core network function includes a transceiver circuit 71 capable of transmitting and receiving signals to and from other nodes (including UE3, base station 5A, and other core network nodes) via the network interface 72. The controller 73 controls the operation of the core network function according to software stored in memory 74. The software may be pre-installed in memory 74 and / or downloaded, for example, via the communication system 1 or from a removable data storage device (RMD). The software includes, among other things, an operating system 75 and a communication control module 76.

[0261] The communication control module 76 is responsible for handling (generating / transmitting / receiving) signaling between the core network functions and other nodes such as UE3, base station 5A, and other core network nodes.

[0262] It will be understood that the communication control module 76 may include multiple submodules ("layers" or "entities") to support specific functions. For example, if the core network node is implemented as MME11 (or AMF in the case of 5G), the communication control module 76 may include an S1-AP submodule, an SCTP submodule, an IP submodule, an L1 submodule, an L2 submodule, etc. (or the corresponding submodule in the case of AMF) to communicate with the base station 5A.

[0263] The communication control module 76 is configured to control communication of the core network nodes, in particular, according to one of the methods described herein.

[0264] <Examples of variations and alternatives> Detailed examples are given above. As those skilled in the art will understand, several modifications and substitutions can be made to the above examples while still benefiting from the disclosures embodied herein.

[0265] It will be understood that the description of the features of base station 5A (or eNB or gNB), NTN nodes, and UE 3, and the operations performed thereby, may be equally applicable to base station 5A and UE 3 that communicate only via the terrestrial plane (i.e., as part of a terrestrial RAN 5 that does not have the characteristics of NTN RAN 5 such as gateway 5B and a space or aerial platform), as well as to base station 5A that communicates via a non-terrestrial plane.

[0266] Further, the description of the features of base station 5A (or eNB or gNB) and the operations performed by base station 5A is equally applicable to distributed base station 5A as well as non-distributed base stations.

[0267] It will also be understood that while information elements having specific names are described, information elements having different names may be used as long as they serve the same purpose.

[0268] In the above description, UE 3 and base station 5A are described as having a plurality of separate functional components or modules for ease of understanding. These modules may be provided as such, for example, in specific applications where an existing system is modified to implement the present disclosure, but in other applications, for example, systems designed with the features of the present invention in mind from the outset, such modules may be integrated into the overall operating system or code, and thus these modules may not be identified as separate entities.

[0269] The above example described several software modules. As those skilled in the art will understand, these software modules can be provided in compiled or uncompiled form and supplied to the UE3 or base station 5A as signals over a computer network or on a recording medium. Furthermore, some or all of the functions performed by this software may be performed using one or more dedicated hardware circuits. However, the use of software modules is preferred because it facilitates updating the UE3 or base station 5A to update its functions.

[0270] Each controller may include, but is not limited to, one or more hardware-implemented computer processors, microprocessors, central processing units (CPUs), arithmetic logic units (ALUs), input / output (IO) circuits, internal memory / cache (programs and / or data), processing registers, communication buses (e.g., control buses, data buses and / or address buses), direct memory access (DMA) functions, hardware or software-implemented counters, pointers and / or timers, and any other suitable form of processing circuitry. Various other modifications are obvious to those skilled in the art and will not be described in further detail here.

[0271] In this disclosure, user equipment (or "UE," "mobile station," "mobile device," or "wireless device") is an entity connected to a network via a wireless interface.

[0272] Furthermore, as explained below, this disclosure is applicable not only to dedicated communication devices but also to any device having communication capabilities.

[0273] The terms “User Equipment” or “UE” (as used by 3GPP), “Mobile Station,” “Mobile Device,” and “Radio Device” are generally intended to be synonymous with each other and include standalone mobile stations such as terminals, cell phones, smartphones, tablets, cellular IoT devices, IoT devices, and machines. The terms “Mobile Station” and “Mobile Device” will be understood to also include devices that remain stationary for extended periods.

[0274] UE may be items of equipment for production or manufacture and / or items of energy-related machinery, such as equipment or machinery (including boilers, engines, turbines, solar panels, wind turbines, hydroelectric generators, thermal generators, nuclear generators, batteries, nuclear systems and / or related equipment, heavy electrical machinery, pumps including vacuum pumps, compressors, fans, blowers, hydraulic equipment, pneumatic equipment, metalworking machinery, manipulators, robots and / or their application systems, tools, molds or dies, rolls, conveying equipment, elevators, material handling equipment, textile machinery, sewing machinery, printing and / or related machinery, paper conversion machinery, chemical machinery, mining machinery and / or construction machinery and / or related equipment, machinery and / or equipment for agriculture, forestry and / or fisheries, safety and / or environmental protection equipment, tractors, precision bearings, chains, gears, power transmission equipment, lubrication equipment, valves, pipe fittings and / or application systems for any of the aforementioned equipment or machinery, etc.).

[0275] UE may be items of transport equipment, such as (railway cars, automobiles, motorcycles, bicycles, trains, buses, carts, rickshaws, ships and other vessels, aircraft, rockets, satellites, drones, balloons, and other transport equipment).

[0276] UE may be, for example, an item of information and communication equipment (such as electronic computers and related equipment, communication and related equipment, electronic components, etc.).

[0277] UE may include, for example, refrigerators, refrigerator applications, trading and / or service industry equipment items, vending machines, automated service machines, office machines or equipment, and household appliances and electronic devices (such as audio equipment, video equipment, loudspeakers, radios, televisions, microwave ovens, rice cookers, coffee machines, dishwashers, washing machines, dryers, electronic fans or related equipment, vacuum cleaners, etc.).

[0278] UE may be an electrical application system or device, for example, (such as an electrical application system or device, like an X-ray system, particle accelerator, radioisotope device, sound wave device, electromagnetic application device, or power application device).

[0279] UE may include, for example, electronic lamps, lighting fixtures, measuring instruments, analyzers, testers, or detection or sensing devices (e.g., smoke detectors, human alarm sensors, motion sensors, wireless tags, etc.), watches or clocks, laboratory equipment, optical devices, medical devices and / or systems, weapons, bladed tools, or hand tools.

[0280] The UE may be, for example, a wireless-equipped personal digital assistant or related device (such as a wireless card or module designed to be attached to or inserted into another electronic device, such as a personal computer or electrical measuring instrument).

[0281] UE may be part of a device or system that uses various wired and / or wireless communication technologies to provide the following uses, services, and solutions related to the Internet of Things (IoT).

[0282] Internet of Things devices (or "Things") may comprise appropriate electronics, software, sensors, network connectivity, and / or similar that enable them to collect and exchange data with each other and with other communication devices. IoT devices may comprise automated devices that follow software instructions stored in internal memory. IoT devices may operate without requiring human supervision or interaction. IoT devices may also remain stationary and / or inactive for extended periods. IoT devices may be implemented as part of (generally) stationary equipment. IoT devices may also be incorporated into non-stationary equipment (such as vehicles) or attached to animals or people to be monitored / tracked.

[0283] It will be understood that IoT technology can be implemented on any communication device that can connect to a communication network to send / receive data, regardless of whether such communication device is controlled by human input or software instructions stored in memory.

[0284] It should be understood that IoT devices are sometimes referred to as Machine-Type Communication (MTC) devices or Machine-to-Machine (M2M) communication devices. It should be understood that a UE may support one or more IoT or MTC applications. Some examples of MTC applications are listed in Table 1 below. This list is not exhaustive and is intended to illustrate some examples of machine-type communication applications.

[0285] Table 1 TIFF2026529493000002.tif226150TIFF2026529493000003.tif24150

[0286] Furthermore, the UE categories described above are merely examples of applications of the technical ideas and examples described herein. Of course, such technical ideas and examples are not limited to the UEs described above, and various modifications are possible.

[0287] Each feature disclosed herein (this term includes the claims) and / or shown in the drawings may be incorporated into this disclosure independently of (or in combination with) any other disclosed and / or illustrated features, where it is technically feasible to do so. In particular, but not limited to, any feature of a claim dependent on a particular independent claim may be introduced into that independent claim in any combination or individually, provided that doing so does not result in a technical incompatibility or result in something that does not make technical sense.

[0288] Various other variations are obvious to those skilled in the art and will not be described in further detail here.

[0289] While the present disclosure has been described above with reference to embodiments, the disclosure is not limited thereto. Various modifications to the structure and details of the present disclosure are possible, as can be understood by those skilled in the art within the scope of the present disclosure.

[0290] This application claims priority based on UK Patent Application No. 2311347.5, filed on 24 July 2023, and incorporates all of its disclosures by reference herein.

[0291] A program can be stored and provided to a computer device using any type of non-temporary computer-readable medium. Non-temporary computer-readable medium includes any type of tangible storage medium. Examples of non-temporary computer-readable medium include magnetic storage media (such as floppy disks, magnetic tapes, and hard disk drives), magneto-optical storage media (e.g., magneto-optical disks), CD-ROMs (Read Only Memory), CD-Rs, CD-R / Ws, and semiconductor memory (such as mask ROMs, PROMs (Programmable ROMs), EPROMs (Erasable PROMs), flash ROMs, and RAMs (Random Access Memory)). A program may also be provided to a computer device using any type of temporary computer-readable medium. Examples of temporary computer-readable medium include electrical signals, optical signals, and electromagnetic waves. Temporary computer-readable medium can be provided to a computer device via wired communication lines such as electric wires and optical fibers, or via wireless communication lines.

[0292] For example, some or all of the embodiments disclosed above may also be described as follows, but are not limited to the following: (Note 1) A method performed by an access network node in a non-terrestrial network, the method is: If either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable, at least one non-access stratum (NAS) Protocol Data Unit (PDU) is received via an available link without triggering the establishment of a connection on a link other than the available link. Remember at least one NAS PDU until another link becomes available. A method that includes transferring at least one NAS PDU via another link when another link becomes available. (Note 2) Receiving data is performed using control plane CIoT optimization features or Early Data Transmission (EDT). The method described in Appendix 1. (Note 3) The transfer is performed using control plane CIoT optimization features or Early Data Transmission (EDT). The method described in Appendix 1. (Note 4) If either the service link or the feeder link is unavailable, further includes maintaining UE information for at least one UE permitted by the core network connected to the gateway. The method described in any one of the appendices 1 to 3. (Note 5) UE information is, UE Identity, At least one Quality of Service (QoS) parameter, priority information, Ability information, or Paging information, including at least one of the following: The method described in Appendix 4. (Note 6) UE information is, History information, Operations and Management (OAM) data, Registration data, Prediction, or Determined based on at least one of the following: an access network node or at least one UE having downlink data within a buffer in the core network. The method described in Appendix 4 or 5. (Note 7) This further includes receiving UE information from the core network regardless of the UE's Radio Resource Control (RRC) status. The method described in any one of the appendices 4 to 6. (Note 8) Receiving a message from the UE to establish a connection to the access network node, This involves transmitting a request to the core network to authorize whether or not the UE can be allowed, If the core network authorizes the UE to be allowed, this further includes receiving UE information from the core network, The method described in any one of the appendices 4 to 6. (Note 9) The paging information used to transfer at least one NAS PDU to the UE via the service link is received via the feeder link, This further includes, when a service link becomes available, paging the UE using paging information, The method described in any one of the appendices 1 to 8. (Note 10) Paging information is, Paging messages from the core network, or UE information from the core network, which is included in at least one of the following: The method described in Appendix 9. (Note 11) At least one NAS PDU is included in the signaling message, The method described in any one of the appendices 1 to 10. (Note 12) The further includes transmitting a message to the core network via the feeder link to notify the status of the transfer of at least one NAS PDU received from a core network node while the feeder link was previously available, The method described in any one of the appendices 1 to 11. (Note 13) The message contains information indicating at least one NAS PDU that was not delivered. The method described in Appendix 12. (Note 14) A method performed by an access network node in a non-terrestrial network, the method is: This includes transmitting information via system information indicating a mode for storing and transferring data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable. Information is provided on a method for preventing at least one UE that does not support a mode for storing and transferring data when either a service link or a feeder link is unavailable from being camped on to a serving cell of an access network node. (Note 15) The information is updated based on whether or not a feeder link is available. The method described in Appendix 14. (Note 16) The information includes time information indicating the time window during which the feeder link will be temporarily available for activation, If either the service link or the feeder link is unavailable to camp on to the serving cell of the access network node during the time window, then, including at least one UE that does not support a mode for storing and transferring data, The method described in Appendix 14. (Note 17) This further includes receiving support information from the UE indicating that the UE supports a mode for storing and transferring data when either the service link or the feeder link is unavailable, The method described in any one of the appendices 14 to 16. (Note 18) Support information is included in the Radio Resource Control (RRC) connection setup completion message. The method described in Appendix 17. (Note 19) A method performed by an access network node in a non-terrestrial network, the method is: A method comprising transmitting information to the core network indicating the ability to store and transfer data when either a service link between an access network node and user equipment (UE), or a feeder link between an access network node and a gateway in the terrestrial network, is unavailable. (Note 20) A method performed by an access network node in a non-terrestrial network, the method is: A method comprising receiving information from the core network indicating the ability to store and transmit data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable. (Note 21) This further includes transmitting information to the UE indicating the reason for the release of Radio Resource Control when the service link becomes unavailable. RRC release is to UE, Entering an idle state for the Evolved Packet System (EPS) Connection Management (ECM), or To make it perform at least one of the following actions: remain in an ECM connected state. The method described in any one of the appendices 1 to 20. (Note 22) A method performed by user equipment (UE), the method is: This includes transmitting at least one non-access stratum (NAS) Protocol Data Unit (PDU) to an access network node in a non-terrestrial network via a service link between the access network node and the UE, without triggering the establishment of a feeder link connection, when the feeder link between the access network node and the gateway in the terrestrial network is unavailable. At least one NAS PDU is stored by the access network node until a feeder link becomes available. A method by which at least one NAS PDU is transferred over the feeder link when the feeder link becomes available. (Note 23) A method performed by user equipment (UE), the method is: The system receives information indicating the mode for storing and transferring data when either the service link between the access network node and the UE in the non-terrestrial network, or the feeder link between the access network node and the gateway in the terrestrial network, is unavailable. A method including not camping on to a serving cell of an access network node if the UE does not support a mode for storing and transferring data when either a service link or a feeder link is unavailable. (Note 24) A method performed by the core network nodes, the method is This includes receiving at least one non-access stratum (NAS) Protocol Data Unit (PDU) from an access network node in a non-terrestrial network via a feeder link between the access network node and a core network node, without triggering the establishment of a connection for the service link, when the service link between the access network node and user equipment (UE) is unavailable. At least one NAS PDU is stored by the access network node until a service link becomes available. A method by which at least one NAS PDU is transferred over the service link when the service link becomes available. (Note 25) A method performed by the core network nodes, the method is A method comprising receiving information indicating the ability to store and transmit data from an access network node in a non-terrestrial network when either a service link between the access network node and user equipment (UE), or a feeder link between the access network node and a gateway in a terrestrial network coupled to a core network node, is unavailable. (Note 26) A method performed by the core network nodes, the method is A method comprising transmitting information to an access network node indicating its ability to store and transfer data when either a service link between an access network node in a non-terrestrial network and user equipment (UE), or a feeder link between an access network node and a gateway in a terrestrial network coupled to a core network node, is unavailable. (Note 27) An access network node in a non-terrestrial network, and the access network node is A means for receiving at least one non-access stratum (NAS) Protocol Data Unit (PDU) via an available link, without triggering the establishment of a connection on a link other than the available link, when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable. A means of storing at least one NAS PDU until another link becomes available, An access network node comprising means for transferring at least one NAS PDU via another link when another link becomes available. (Note 28) An access network node in a non-terrestrial network, and the access network node is, The system includes means for transmitting, via system information, information indicating a mode for storing and transferring data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable. Information is provided that the access network node does not camp on at least one UE that does not support a mode for storing and transferring data when either the service link or feeder link is unavailable to the serving cell of the access network node. (Note 29) An access network node in a non-terrestrial network, and the access network node is An access network node comprising means for transmitting information to the core network indicating its ability to store and transfer data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable. (Note 30) An access network node in a non-terrestrial network, and the access network node is An access network node having means for receiving information from the core network indicating its ability to store and transfer data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable. (Note 31) User equipment (UE), In the event that the feeder link between the access network node and the gateway in the terrestrial network is unavailable, the system provides means for transmitting at least one non-access stratum (NAS) Protocol Data Unit (PDU) to an access network node in a non-terrestrial network via a service link between the access network node and the UE, without triggering the establishment of a feeder link connection. At least one NAS PDU is stored by the access network node until a feeder link becomes available. At least one NAS PDU is transferred over the feeder link when the feeder link becomes available, UE. (Note 32) User equipment (UE), Means for receiving information indicating a mode for storing and transferring data when either the service link between the access network node and the UE of a non-terrestrial network or the feeder link between the access network node and the gateway in the terrestrial network is unavailable, via system information; A UE comprising means of not camping on to a serving cell of an access network node if the UE does not support a mode for storing and transferring data when either a service link or a feeder link is unavailable. (Note 33) It is a core network node, In the event that the service link between the access network node and the user equipment (UE) is unavailable, the means for receiving at least one non-access stratum (NAS) Protocol Data Unit (PDU) from an access network node in a non-terrestrial network via a feeder link between the access network node and the core network node without triggering the establishment of a connection for the service link, At least one NAS PDU is stored by the access network node until a service link becomes available. At least one NAS PDU is a core network node that is forwarded over the service link when the service link becomes available. (Note 34) It is a core network node, A core network node having means for receiving information indicating its ability to store and transfer data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in a terrestrial network connected to the core network node, is unavailable from an access network node in a non-terrestrial network. (Note 35) It is a core network node, A core network node that, when either a service link between an access network node in a non-terrestrial network and user equipment (UE), or a feeder link between an access network node and a gateway in a terrestrial network connected to a core network node is unavailable, has means for transmitting information to an access network node indicating its ability to store and transfer data. [Explanation of Symbols]

[0293] 1. Communication System 3 UE 5 Radio Access Network (RAN) nodes, NTN RAN 5A base station 5B Gateway 5C Platform 7 Core Network 9 cells 11 Mobility Management Entities (MMEs) 13 Serving Gateways (S-GWs) 15 Packet Data Network Gateways (P-GWs) 20 External Network 31, 51, 71 Transceiver Circuits 33, 53 Air Interface 35 User Interface 55 Core Network Interfaces 37, 57, 73 Controllers 39, 59, 74 memory 72 Network Interfaces 41, 61, 75 Operating Systems 43, 63, 76 Communication control modules

Claims

1. A method performed by an access network node in a non-terrestrial network, wherein the method is If either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable, at least one non-access stratum (NAS) Protocol Data Unit (PDU) is received via an available link without triggering the establishment of a connection on a link other than the available link. The NAS PDU is stored until the aforementioned other link becomes available. A method comprising transferring the at least one NAS PDU via the other link when the other link becomes available.

2. The aforementioned receiving is performed using control plane CIot optimization features or Early Data Transmission (EDT). The method according to claim 1.

3. The aforementioned transfer is performed using control plane CIot optimization features or Early Data Transmission (EDT). The method according to claim 1.

4. If either the service link or the feeder link is unavailable, the gateway further includes maintaining UE information for at least one UE permitted by the core network connected to the gateway. The method according to any one of claims 1 to 3.

5. The aforementioned UE information is, UE Identity, At least one Quality of Service (QoS) parameter, priority information, Ability information, or Paging information, including at least one of the following: The method according to claim 4.

6. The aforementioned UE information is, History information, Operations and Management (OAM) data, Registration data, Prediction, or Determined based on at least one of the access network node or at least one UE having downlink data in the buffer of the core network, The method according to claim 4 or 5.

7. Regardless of the Radio Resource Control (RRC) status of the aforementioned UE, the further includes receiving the aforementioned UE information from the core network. The method according to any one of claims 4 to 6.

8. Receiving a message from the UE to establish a connection to the access network node, Transmitting a request to the core network to authorize whether or not the UE can be permitted, If the core network authorizes the UE to permit the UE, the recipient further includes receiving the UE information from the core network. The method according to any one of claims 4 to 6.

9. Receiving paging information used to transfer at least one NAS PDU to the UE via the service link via the feeder link, The further includes, when the service link becomes available, paging the UE using the paging information, The method according to any one of claims 1 to 8.

10. The aforementioned paging information is, Paging messages from the core network, or UE information from the core network, which is included in at least one of the following: The method according to claim 9.

11. The aforementioned at least one NAS PDU includes in the signaling message: The method according to any one of claims 1 to 10.

12. The further includes transmitting a message to the core network via the feeder link to notify the status of the transfer of the at least one NAS PDU, which was received from the core network node while the feeder link was previously available, The method according to any one of claims 1 to 11.

13. The aforementioned message includes information indicating at least one NAS PDU that was not delivered. The method according to claim 12.

14. A method performed by an access network node in a non-terrestrial network, wherein the method is This includes transmitting information via system information indicating a mode for storing and transferring data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable. The information relates to a method for preventing at least one UE that does not support the mode of storing and transferring data when either the service link or the feeder link is unavailable from being camped on to the serving cell of the access network node.

15. The aforementioned information is updated based on whether the feeder link is available or not. The method according to claim 14.

16. The information includes time information indicating a time window in which the feeder link becomes temporarily available for activation, If either the service link or the feeder link is unavailable to camp on to the serving cell of the access network node during the time window, then the at least one UE that does not support a mode for storing and transferring the data includes, The method according to claim 14.

17. If either the service link or the feeder link is unavailable, the further includes receiving support information from the UE indicating that the UE supports the mode for storing and transferring the data, The method according to any one of claims 14 to 16.

18. The aforementioned support information is included in the Radio Resource Control (RRC) connection setup completion message. The method according to claim 17.

19. A method performed by an access network node in a non-terrestrial network, wherein the method is A method comprising transmitting information to the core network indicating the ability to store and transfer data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable.

20. A method performed by an access network node in a non-terrestrial network, wherein the method is A method comprising receiving information from the core network indicating the ability to store and transfer data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable.

21. If the aforementioned service link becomes unavailable, the system further includes transmitting information indicating the reason for the release of the Radio Resource Control to the UE. The aforementioned RRC release to the UE, Entering an idle state for the Evolved Packet System (EPS) Connection Management (ECM), or To cause at least one of the following to occur: remain in an ECM connected state. The method according to any one of claims 1 to 20.

22. A method performed by user equipment (UE), wherein the method is This includes transmitting at least one non-access stratum (NAS) Protocol Data Unit (PDU) to the access network node in a non-terrestrial network via a service link between the access network node and the UE, without triggering the establishment of a connection on the feeder link, when the feeder link between the access network node and the gateway in the terrestrial network is unavailable. The at least one NAS PDU is stored by the access network node until the feeder link becomes available. A method wherein the at least one NAS PDU is transferred over the feeder link when the feeder link becomes available.

23. A method performed by user equipment (UE), wherein the method is The system receives information indicating a mode for storing and transferring data when either the service link between the access network node of the non-terrestrial network and the UE, or the feeder link between the access network node and the gateway in the terrestrial network, is unavailable. A method comprising: not camping on to the serving cell of the access network node if either the service link or the feeder link is unavailable and the UE does not support the mode of storing and transferring the data.

24. A method performed by a core network node, the method is This includes receiving at least one non-access stratum (NAS) Protocol Data Unit (PDU) from the access network node in a non-terrestrial network via a feeder link between the access network node and the core network node, without triggering the establishment of a connection for the service link, when the service link between the access network node and user equipment (UE) is unavailable. The at least one NAS PDU is stored by the access network node until the service link becomes available. A method wherein the at least one NAS PDU is transferred over the service link when the service link becomes available.

25. A method performed by a core network node, the method is A method comprising receiving information from an access network node in a non-terrestrial network indicating its ability to store and transfer data when either a service link between the access network node and user equipment (UE), or a feeder link between the access network node and a gateway in a terrestrial network coupled to the core network node, is unavailable.

26. A method performed by a core network node, the method is A method comprising transmitting information to an access network node indicating its ability to store and transfer data when either a service link between an access network node of a non-terrestrial network and user equipment (UE), or a feeder link between the access network node and a gateway in a terrestrial network coupled to the core network node, is unavailable.

27. An access network node in a non-terrestrial network, wherein the access network node is If either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable, means for receiving at least one non-access stratum (NAS) Protocol Data Unit (PDU) via an available link without triggering the establishment of a connection on a link other than the available link, means for storing the at least one NAS PDU until the aforementioned other link becomes available, An access network node comprising means for transferring the at least one NAS PDU via the other link when the other link becomes available.

28. An access network node in a non-terrestrial network, wherein the access network node is The system includes means for transmitting, via system information, information indicating a mode for storing and transferring data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable. The information provided indicates that the access network node does not camp on at least one UE that does not support the mode of storing and transferring data when either the service link or the feeder link is unavailable to the serving cell of the access network node.

29. An access network node in a non-terrestrial network, wherein the access network node is An access network node comprising means for transmitting information to the core network indicating the ability to store and transfer data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable.

30. An access network node in a non-terrestrial network, wherein the access network node is An access network node having means for receiving information from the core network indicating its ability to store and transfer data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in the terrestrial network, is unavailable.

31. User mode (UE), When the feeder link between the access network node and the gateway in the terrestrial network is unavailable, the system provides means for transmitting at least one non-access stratum (NAS) Protocol Data Unit (PDU) to the access network node in the non-terrestrial network via a service link between the access network node and the UE, without triggering the establishment of a connection for the feeder link. The at least one NAS PDU is stored by the access network node until the feeder link becomes available. The at least one NAS PDU is transferred via the feeder link when the feeder link becomes available.

32. User mode (UE), Means for receiving information indicating a mode for storing and transferring data when either the service link between the access network node of a non-terrestrial network and the UE, or the feeder link between the access network node and a gateway in a terrestrial network, via system information, A UE comprising means of not camping on to the serving cell of the access network node if either the service link or the feeder link is unavailable and the UE does not support the mode of storing and transferring the data.

33. It is a core network node, When the service link between the access network node and user equipment (UE) is unavailable, the means for receiving at least one non-access stratum (NAS) Protocol Data Unit (PDU) from the access network node in a non-terrestrial network via a feeder link between the access network node and the core network node without triggering the establishment of a connection for the service link, The at least one NAS PDU is stored by the access network node until the service link becomes available. The at least one NAS PDU is a core network node that is forwarded over the service link when the service link becomes available.

34. It is a core network node, A core network node having means for receiving information indicating its ability to store and transfer data when either the service link between the access network node and user equipment (UE), or the feeder link between the access network node and a gateway in a terrestrial network connected to the core network node, is unavailable from an access network node in a non-terrestrial network.

35. It is a core network node, A core network node that, when either a service link between an access network node in a non-terrestrial network and user equipment (UE), or a feeder link between the access network node and a gateway in a terrestrial network connected to the core network node is unavailable, has means for transmitting information to the access network node indicating its ability to store and transfer data.

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