Method performed by access network node, method performed by user equipment, method performed by core network node, access network node, user equipment and core network node

Abstract

A method by an access network node in a non-terrestrial network is disclosed. The method comprises receiving at least one NAS PDU via an available link without triggering establishment of a connection for another link different from the available link in the event that a service link between the access network node and a user equipment (UE) or a feed link between the access network node and a gateway in the terrestrial network is unavailable, the NAS being an abbreviation of an access layer, the feed link being a non-access layer or a non-access layer or a non-access layer or a non-access layer or a non-access layer or a non-access layer or a non-access layer or a non-access layer or a non-access layer or a non-access layer. The PDU is an abbreviation of a protocol data unit; storing at least one NAS PDU until another link becomes available; and forwarding the at least one NAS PDU via the other link when the other link becomes available.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to communication systems and parts thereof. The present disclosure has particular but non-exclusive relevance to wireless communications systems and devices thereof operating in accordance with the Third Generation Partnership Project (3GPP) standards or equivalents or derivatives thereof, including LTE-Advanced, next generation or 5G networks, future generations and beyond. The present disclosure has particular but non-exclusive relevance to improvements relating to the use of store-and-forward techniques for communication of user data in the context of non-terrestrial networks (NTNs). BACKGROUND

[0002] Earlier developments of the 3GPP standards are known as the Long Term Evolution (LTE) of the Evolved Packet Core (EPC) network and Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), also commonly known as “4G”. More recently, the terms “5G” and “New Radio” (NR) have come into use to refer to evolving communications technologies intended to support a wide range of applications and services. Various details of 5G networks are described in, for example, the Next Generation Mobile Networks (NGMN) Alliance’s “NGMN 5G White Paper” V1.0, which document is available from https: / / www.ngmn.org / 5g-white-paper.html. 3GPP intends to support 5G through so-called 3GPP NextGen (Next Generation) Radio Access Networks (RANs) and 3GPP NextGen Core Networks.

[0003] Under the 3GPP standards, a NodeB (or eNB in LTE and gNB in 5G) is a Radio Access Network (RAN) node (or simply “access node”, “access network node” or “base station”) via which communication devices (User Equipment or “UE”) connect to a core network and communicate with other communication devices or remote servers. For simplicity, the present application will use the terms access network node, RAN node or base station to refer to any such access node.

[0004] For simplicity, the present application will use 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. Although the present application can refer to mobile devices in the specification, it will be understood that the described techniques can be implemented on any communication device (mobile and / or generally stationary) that can connect to a communication network for transmitting / receiving data, whether such communication device is controlled by human input or by software instructions stored in memory. One particular type of UE supported in modern communication systems is the so-called Internet of Things (loT) device, which is a non-standard hardware device (including everyday physical objects such as sensor devices, gadgets, appliances, and the like) capable of wirelessly connecting to a network to transmit and receive data. Techniques for supporting such loT UEs in a cellular communication system are generally referred to as Cellular loT (CIoT) enhancements or optimizations. CIoT enhancements include, for example, Narrow Band loT (NB-loT) enhancements, which is a radio technology developed to support cellular network loT devices and services in which the bandwidth is limited to a single narrow band (e.g., where transmissions are limited to occupy a single 180 KHz physical resource block (PRB) / 12 subcarriers each 15 KHz). CIoT enhancements also include features supporting so-called “LTE-Machine” (LTE Cat-M1 or LTE-M for short) technology involving Bandwidth Limited UEs (BLUE), which are faster than NB-loT but operate on a wider narrow band (e.g., limited to 6 PRBs / 1.4 MHz).

[0005] In current 5G architectures, the gNB structure can be split into two or more parts. In some RAN implementations, there are two parts, referred to as a central unit (CU or gNB-CU) (sometimes called a “control unit”) and a distributed unit (DU or gNB-DU), connected over an Fl interface. This enables the use of a “split” architecture in which typically “higher” CU layers (e.g., but not necessarily or exclusively, packet data convergence protocol (PDCP) layers and radio resource control (RRC) layers) and “lower” DU layers (e.g., but not necessarily or exclusively, radio link control (RLC) layers, media (sometimes called “Medium”) access control (MAC) layers, and physical (PHY) layers) are separated between a particular CU and one or more DUs connected to and controlled by that CU via the Fl interface. Thus, for example, the higher layer CU functionality of multiple gNBs can be implemented (e.g., by a single processing unit, or in a cloud-based or virtualized system) centrally, while the lower layer DU functionality is locally retained separately for each gNB.

[0006] The core network includes a plurality of communication entities for providing different functionality for supporting communications.

[0007] For example, in 4G, core network entities include a mobility management entity (MME), a serving gateway (S-GW or S-GW), a packet data network (PDN) gateway (P-GW or P-GW), and so on. The MME manages general mobility aspects of UEs and ensures connectivity when a UE is moving within a geographical area covered by the communication system. The MME also handles control-plane signaling between UEs and the core network, and manages various bearers associated with a UE (e.g., such as an evolved packet system (EPS) bearer and / or a radio bearer, etc.) by controlling the S-GW and P-GW (and / or possibly other network nodes), via which such bearers are provided. The S-GW (via a base station) provides a connection between a UE and the core network for transmitting and receiving user-plane data on an associated communication bearer (e.g., an EPS bearer). The communication bearer typically terminates at the P-GW, although the communication bearer is often supplemented by an external bearer (e.g., another EPS bearer and / or the like) between the P-GW and a communication endpoint outside the core network (e.g., in an external network). It will be appreciated that the functionality of the S-GW and P-GW can be implemented in a single gateway element.

[0008] In 5G, core network entities include logical nodes (or "functions") including control plane functions (CPFs) and one or more user plane functions (UPFs). The CPFs include one or more access and mobility management functions (AMFs) and others. The AMF generally corresponds to the MME in 4G and performs many of the functions performed by the MME. The UPFs combine the functionality of both the S-GW and P-GW— specifically, the user plane functionality of the S-GW (SGW-U) and the user plane functionality of the P-GW (PGW-U). The SMF provides session management functionality (which formed part of the MME functionality in 4G). The SMF also combines some functionality provided by the S-GW and P-GW— specifically, the control plane functionality of the S-GW (SGW-C) and the control plane functionality of the P-GW (PGW-C). The SMF also allocates IP addresses to UEs.

[0009] In 4G, a number of EPS optimizations were introduced for supporting CIoT (e.g., NB-IoT), which are generally applicable to later generations of technology, these enhancements allow for new user data paths for communication for IoT. These new data paths allow for communication of user data via the MME (and other CN nodes such as S-GW, P-GW, and / or Service Capability Exposure Function (SCEF), etc.) in (4G), compared to the original data path via the S-GW and P-GW, although in later generations this can 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 path are referred to as User Plane (UP) mode or "UP mode" CIoT EPS optimizations.

[0010] CP mode CIoT EPS optimizations reduce the total number of control plane messages when handling short data transactions (as typically occur in IoT communications) using the service request procedure passed via the MME, user data, or SMS messages by encapsulating them in Non-Access Stratum (NAS) messages. In the case of IP packets, UL data can be transferred from the base station to the CIoT service via the MME, S-GW, and P-GW. In the case of non-IP packets, UL data can be transferred from the base station to the CIoT service via the MME and the SCEF.

[0011] On the other hand, UP mode CIoT EPS optimizations pass user plane data without establishing an Access Stratum (AS) context in the serving base station and the UE using the service request procedure. This UP mode approach is based on UP transfer of user data, where data is transferred from the base station to the S-GW over the regular user plane by the network and vice versa. For UP mode CIoT, two different RRC connection scenarios are possible. In a first scenario, the RRC connection is released with an indication of possible recovery operation and then the recovery of this connection can be requested as part of a recovery procedure. If this recovery procedure is successful, security is established with updated keys and radio bearers are set up as in the original connection. In a second scenario, security and radio bearers have to be re-established without a previous release of the RRC connection with a recovery indication or if the base station does not accept the recovery request.

[0012] 3GPP is also working with the satellite communication industry to specify integrated satellite and terrestrial network infrastructure in the context of 5G. This is referred to as non-terrestrial networks (NTN), a term referring to networks or network segments that use space- or air-borne vehicles for transmission of data and control signaling. Satellites refer to air-borne vehicles in low earth orbit (LEO), medium earth orbit (MEO), geostationary earth orbit (GEO) or high elliptical orbit (HEO). Space-borne vehicles refer to high-altitude platforms (HAP) containing unmanned aircraft systems (UAS), including lighter-than-air and heavier-than-air tethered UAS, all operating quasi-stationary at altitudes typically between 8 and 50 km.

[0013] 3GPP Technical Report (TR) 38.811 is a study on New Radio to support such non-terrestrial networks. The study includes a description of NTN deployment scenarios and related system parameters (such as architecture, altitude, orbit, etc.) as well as adaptation of 3GPP channel models (propagation conditions, mobility, etc.) and others. Non-terrestrial networks are expected to:

[0014] - help facilitate rollout of 5G services in areas with no or insufficient service to upgrade performance of terrestrial networks;

[0015] - enhance service reliability by providing service continuity for user equipment or for mobile platforms (e.g., passenger vehicles - airplanes, ships, high-speed trains, buses);

[0016] - increase service availability everywhere; in particular for critical communications, future railway / maritime / aeronautical communications; and

[0017] - make 5G network scalability possible by providing efficient multicast / broadcast resources for data delivery to the network edge or even directly to user equipment.

[0018] Non-terrestrial network access is typically characterized by the following elements (among others):

[0019] - NTN terminal: this can refer to a 3GPP UE or to a satellite system specific UE in case the satellite does not directly serve the 3GPP UE;

[0020] - service link, referring to the radio link between the user equipment and the space- or air-borne platform (which can be in addition to a radio link with a ground-based RAN);

[0021] - space- or air-borne platform (e.g., satellite or similar);

[0022] - a gateway, which connects the satellite or aerial access network to the core network. It will be appreciated that the gateway will most likely be co-located with a base station (e.g. gNB);

[0023] - a feeder link, which refers to the radio link between the gateway and the spaceborne / airborne platform.

[0024] There are a number of 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 on-board processing on the payload that is being communicated between the UE and the core network. Specifically, in a regenerative architecture, at least some base station functionality (e.g. the functionality of at least the DUs of a distributed base station, or possibly all base station functionality) is provided on the non-terrestrial platform. Other regenerative mode architectures are also possible, e.g. an architecture in which at least some core network functionality is implemented on the non-terrestrial platform.

[0025] Another possible architecture is a “transparent” access network architecture (sometimes referred to as “transparent satellite”, “transparent mode” or “transparent payload”), in which the base station is located on the ground and transmits and receives communications to and from the UE via a gateway located on the ground and via a non-terrestrial platform that does not have base station functionality. The non-terrestrial platform transparently relays these communications to and from the UE without on-board processing of the communications, effectively acting as a so-called “bent pipe”. In this architecture, both the service link and the feeder link effectively act as part of the air interface between the base station and the UE.

[0026] A satellite or aerial vehicle typically generates several satellite beams over a given area. The beams have a coverage area on the Earth’s surface that is typically elliptical. The beam coverage area can move over the Earth as the satellite or aerial vehicle moves in its orbit. Alternatively, the beam coverage area can be Earth fixed (albeit temporarily), in which case some beam pointing mechanism (mechanical or electronic steering features) can be used to compensate for the satellite or aerial vehicle movement. There are different options for beam identification purposes. In one option, multiple (nearby / adjacent) satellite beams can have the same associated physical cell ID (PCI), and thus the PCI can remain unchanged when a UE 3 moves from one beam to another beam in a set of beams sharing the PCI. Alternatively, there can be a one-to-one relationship between a PCI and a satellite beam (at least within the coverage area of a particular satellite comprising multiple beams).

[0027] Coverage in 5G is primarily beam-based rather than 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 (which are different from satellite or NTN beams). The SSB beams form a matrix of beams that cover the entire cell area. Each SSB beam carries an SSB that includes a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a physical broadcast channel (PBCH).

[0028] A UE searches for and makes measurements (e.g., of 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”)) on SSB beams. The UE maintains a set of candidate beams, which can contain beams from multiple cells. Thus, the PCI and beam ID (or SSB index) distinguish SSB beams from one another. In effect, therefore, SSB beams are like small cells within a larger cell. Once a UE has detected and selected a cell (and / or SSB beam in the case of 5G), the UE can attempt to access the cell and / or SSB beam using an initial RRC connection setup procedure that includes a random access procedure.

[0029] In particular, a UE can attempt to access the cell and / or beam using a random access procedure that typically involves four different steps. Before attempting initial access, the UE can transmit a preamble on a physical random access channel (PRACH / RACH) to the network (e.g., a base station such as a gNB) for initiating a random access procedure (also referred to as a RACH procedure or simply RACH) to obtain synchronization in the uplink (UL). This step is often referred to as a PRACH transmission or simply a transmission of message 1 (Msgl). In response, the network responds with a random access response (RAR). The RAR indicates reception of the preamble and includes a timing alignment (TA) command for adjusting the transmission timing of the UE based on the timing of the received preamble, an uplink grant field indicating resources to be used in the uplink for a physical uplink shared channel (PUSCH), a frequency hopping flag to indicate whether the UE is to transmit on the PUSCH with or without frequency, a modulation and coding scheme (MCS) field from which the UE can determine the MCS for the PUSCH transmission, and a transmission power control (TPC) command value for setting the power of the PUSCH transmission. The RAR transmission step is often referred to as a transmission of message 2 (Msg2). The UE then sends a third message (message 3 or “Msg3”) to the network on a physical uplink shared channel (PUSCH) based on the information in the RAR. The specific message and content of the message that the UE sends in this step depends on the context in which the random access procedure is being used. However, in the example of initial radio RRC connection setup, Msg3 typically includes an RRC setup request or similar message carrying a temporarily randomly generated UE identifier. The network responds with a fourth message (message 4 or “Msg4”) carrying the randomly generated UE identifier received in Msg3 for contention purposes to resolve any conflicts between different UEs using the same preamble sequence. When successful, Msg4 also transitions the UE to a connected state.

[0030] Similar random access procedures can also be used in other contexts including, for example, handover, connection reestablishment, requesting UL scheduling without dedicated resources configured for scheduling request for the UE, etc.

[0031] A so-called two-step random access procedure has also been developed (in addition to the four-step random access procedure described above). Two-step random access is primarily intended to support (ultra-) low latency communications, 10 ms control plane latency, fast handover, efficient channel access in unlicensed spectrum, and transmission of small data packets, among other things. However, two-step random access can also be applicable to large cells such as non-terrestrial cells. The main difference is that the four-step random access procedure requires two round-trip periods between the UE and the base station, but the two-step random access procedure aims to reduce latency and control signaling overhead by using a single round-trip period between the UE and the base station. In practice, this is achieved by combining the UE’s PRACH preamble (Msgl) transmission and the scheduled PUSCH transmission (Msg3) into a single message, referred to as “MsgA”. Similarly, the random access response (RAR / Msg2) from the base station to the UE is combined with the contention resolution message (Msg4) in the two-step random access procedure (and is referred to as “MsgB”).

[0032] 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 can also be used in which the base station assigns a dedicated preamble to the UE.

[0033] In addition to the RACH-based initial access procedures described above, a so-called RACH-less access procedure has also been introduced in the context of handover procedures during development of later releases of the LTE standard, also to provide reduced latency. RACH-less based handover provides a reduction in the data connectivity interruption time at each handover, since RACH-less based handover eliminates the need to perform random access when first accessing the target cell, and thus reduces the overall handover execution time.

[0034] As a non-terrestrial platform that is serving a UE moves, intermittent coverage for that UE can occur as a result of the serving link being lost, e.g. due to the satellite moving, even if the UE remains stationary. In addition to this type of intermittent coverage, there can 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 in areas where it is not cost-effective to deploy a gateway.

[0035] Furthermore, at different times, different NTN platforms (and therefore, where applicable, on-board base stations) can provide feed links and service links separately. Specifically, for a UE at a given location, one or more satellites may be orbiting and providing communication services to that UE at different times. Thus, in practice, the UE will see different base stations during different time windows. Similarly, one or more satellites may be orbiting the ground location of a gateway, via which one or more feed link connections are being provided, meaning that gateway feed connectivity may be via different satellites (and potentially, in the case of a regenerative mode architecture, base stations).

[0036] For regenerative architectures, Figure 1 Here is an example of such a scenario, Figure 1 Examples of satellites providing service links and feeder links in an NTN system, and the resulting changes to base stations. For example... Figure 1 As seen, two NTN platforms (satellites in this example) each providing their respective base stations are shown as circling and providing service links to the UE and feeder links to the gateway (GW) for accessing 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, and the first satellite / base station (base station #1) provides the service link, while the second satellite / base station (base station #2) provides the feeder link. Therefore, data communicated to base station #2 via the service link and data communicated to base station #1 via the feeder link at time T1 cannot be transmitted to the core network and the UE respectively until time T2.

[0037] Therefore, it can be seen that at a given time, the UE may not have a complete (end-to-end) connection all the way to the core network because the feeder link and the associated serving link connection may not be available simultaneously. In such scenarios, to avoid data loss, communication on the serving link needs to be stored on a non-terrestrial platform for forwarding to the core network on the feeder link, or vice versa. Such techniques are called "store-and-forward" techniques. These techniques are particularly suitable for latency-tolerant communication (i.e., non-real-time communication), such as communication typically used in CIoT-based communications.

[0038] By using only examples, in Figure 2 The image illustrates a possible store-and-forward technique. Figure 2 This is a simplified sequence diagram illustrating a general process for establishing a connection in an NTN system, involving the storage and forwarding of user and control data. The illustrated process is within the context of a CIoT CP mode process.

[0039] likeFigure 2 The procedure begins in a scenario in which the UE 3 is in coverage of a first base station 5A-1 on a first NTN platform but the feeder link is disconnected (at S210). The UE 3 and the first base station 5A-1 of the first NTN RAN 5-1 coordinate with each other to establish an RRC connection (at S212). The procedure will typically involve, for example, a random access procedure, as seen at S214 (e.g., as described above). The random access procedure ends with the UE 3 sending a message to the first base station 5A-1 indicating that the RRC has completed (at S216), the message including a UL NAS protocol data unit (PDU) as a non-access stratum (NAS) payload, the UL NAS protocol data unit (PDU) including a control plane service request (CPSR) and / or control plane data. The first base station 5A-1 stores the NAS PDU and / or any data at S216 when the feeder link between the first base station 5A-1 and the core network 7 is disconnected. The first base station 5A-1 sends a message to the UE 3 at S218 to release the RRC connection, the message including an indication that no feeder link is available and an indication of a scheduled time at which the UE 3 can expect a response from the core network 7 and thus the UE 3 can make the next transmission. The UE 3 can then enter an idle mode - effectively while waiting for a response. When the feeder link is subsequently connected at S220, the first base station 5A-1 can send an initial UE message including the NAS PDU / data to the core network 7 at S222. The core network 7 can determine at S224 that a second base station 5A-2 of a second NTN RAN 5-2 (via which the feeder link connects / is to connect to the core network 7) will likely provide coverage to the UE 3 at a future time. When the feeder link to the second base station 5A-2 is available, the core network 7 can send an appropriate DL NAS response PDU and any DL data at S226. The DL NAS PDU / data is stored at the second base station 5A-2 at S228. When the UE 3 is in coverage of the second base station 5A-2 at S230, the second base station 5A-2 can page the UE 3 at S232. Thus, the UE 3 and the second base station 5A-2 can coordinate with each other to establish a connection at S234, via which the DL NAS PDU and data can be delivered.

[0040] However, Figure 2 The procedure in the above does not take into account all the implications of / associated with intermittent coverage and intermittent feeder links.

[0041] In this context, as long as the full base station is on-boarded on the NTN platform, it is possible that the impact on NAS procedures is greater than the impact on AS procedures. This is because NAS procedures require connectivity in both directions from the UE all the way to the core network. For example, for a regular registration / attach procedure, a "store-and-forward" scheme would typically require a respective store-and-forward period in one direction for each request message and another store-and-forward period in the opposite direction for each corresponding response message.

[0042] While it is possible that the impact on AS procedures (as for initial access) is less, however, data transmission typically requests end-to-end connectivity between the UE and the core network / packet data network and UE context establishment.

[0043] Therefore, further improvements are needed to better support efficient implementation of store-and-forward techniques, in particular in the context of intermittent coverage / intermittent feeder link that arises in NTN systems (but not limited to).

[0044] List of citations

[0045] Non-patent literature

[0046] Non-patent literature 1 : 3GPP Technical Report (TR) 38.811

[0047] Non-patent literature 2: "NGMN 5G White Paper" V1.0 SUMMARY

[0048] Technical problem

[0049] The present disclosure aims at providing one or more devices and / or one or more associated methods that help meet the above-mentioned needs.

[0050] Solution to the problem

[0051] In an aspect, there is provided a method by an access network node in a non-terrestrial network, the method comprising:

[0052] receiving, via an available link, at least one NAS PDU without triggering establishment of a connection for another link different from the available link, NAS being an acronym for Non-Access Stratum, PDU being an acronym for Protocol Data Unit, in case a serving link between the access network node and a user equipment, UE, or a feeder link between the access network node and a gateway in a terrestrial network is not available;

[0053] storing the at least one NAS PDU until the other link becomes available; and

[0054] forwarding the at least one NAS PDU via the other link when the other link becomes available.

[0055] In an aspect, a method by an access network node in a non-terrestrial network is provided, the method comprising:

[0056] transmitting, via system information, information indicating a mode of store-and-forward data in case a serving link between the access network node and a user equipment, UE, or a feeder link between the access network node and a gateway in a terrestrial network is unavailable, and

[0057] wherein the information causes at least one UE not supporting the mode of store-and-forward data in case the serving link or the feeder link is unavailable not to camp on a serving cell of the access network node.

[0058] In an aspect, a method by an access network node in a non-terrestrial network is provided, the method comprising:

[0059] transmitting, to a core network, information indicating a capability of store-and-forward data in case a serving link between the access network node and a user equipment, UE, or a feeder link between the access network node and a gateway in a terrestrial network is unavailable.

[0060] In an aspect, a method by an access network node in a non-terrestrial network is provided, the method comprising:

[0061] receiving, from a core network, information indicating a capability of store-and-forward data in case a serving link between the access network node and a user equipment, UE, or a feeder link between the access network node and a gateway in a terrestrial network is unavailable.

[0062] In an aspect, a method by a user equipment, UE, is provided, the method comprising:

[0063] transmitting, to an access network node in a non-terrestrial network, at least one NAS PDU via a serving link between the access network node and the UE without triggering establishing a connection for a feeder link between the access network node and a gateway in a terrestrial network in case the feeder link is unavailable, NAS being an abbreviation of non-access stratum and PDU being an abbreviation of protocol data unit, and wherein

[0064] the at least one NAS PDU is stored by the access network node until the feeder link becomes available, and

[0065] forwarding the at least one NAS PDU via the feeder link when the feeder link becomes available.

[0066] In an aspect, a method by a user equipment, UE, is provided, the method comprising:

[0067] in case the service link between the access network node in the non-terrestrial network and the UE or the feeder link between the access network node and a gateway in a terrestrial network is not available, receiving information indicating a mode of store-and-forward data via system information; and

[0068] in case the UE does not support the mode of store-and-forward data in case the service link or the feeder link is not available, not camping on a serving cell of the access network node.

[0069] In an aspect, a method by a core network node is provided, the method comprising:

[0070] in case the service link between the access network node in the non-terrestrial network and the UE is not available, receiving at least one NAS PDU from the access network node via a feeder link between the access network node and the core network node without triggering establishment of a connection for the service link, NAS being an abbreviation of non-access stratum, PDU being an abbreviation of protocol data unit, and wherein

[0071] the at least one NAS PDU is stored by the access network node until the service link becomes available, and

[0072] when the service link becomes available, forwarding the at least one NAS PDU via the service link.

[0073] In an aspect, a method by a core network node is provided, the method comprising:

[0074] in case the service link between the access network node in the non-terrestrial network and the UE or the feeder link between the access network node and a gateway in a terrestrial network coupled with the core network node is not available, receiving information from the access network node indicating a capability of store-and-forward data.

[0075] In an aspect, a method by a core network node is provided, the method comprising:

[0076] in case the service link between the access network node in the non-terrestrial network and the UE or the feeder link between the access network node and a gateway in a terrestrial network coupled with the core network node is not available, transmitting information to the access network node indicating a capability of store-and-forward data.

[0077] In an aspect, an access network node in a non-terrestrial network is provided, the access network node comprising:

[0078] a means for receiving at least one NAS PDU via an available link in case the service link between the access network node and a user equipment, UE, or the feeder link between the access network node and a gateway in a terrestrial network is unavailable, without triggering the establishment of a connection for another link different from the available link, NAS being an acronym for Non-Access Stratum, PDU being an acronym for Protocol Data Unit;

[0079] a means for storing the at least one NAS PDU until the other link becomes available; and

[0080] a means for forwarding the at least one NAS PDU via the other link when the other link becomes available.

[0081] In an aspect, there is provided an access network node in a non-terrestrial network, the access network node comprising:

[0082] a means for transmitting, via system information, information for indicating a mode of store-and-forward data in case the service link between the access network node and a user equipment, UE, or the feeder link between the access network node and a gateway in a terrestrial network is unavailable, and

[0083] wherein the information is such that at least one UE not supporting the mode of store-and-forward data does not camp on a serving cell of the access network node in case the service link or the feeder link is unavailable.

[0084] In an aspect, there is provided an access network node in a non-terrestrial network, the access network node comprising:

[0085] a means for transmitting, to a core network, information for indicating a capability of store-and-forward data in case the service link between the access network node and a user equipment, UE, or the feeder link between the access network node and a gateway in a terrestrial network is unavailable.

[0086] In an aspect, there is provided an access network node in a non-terrestrial network, the access network node comprising:

[0087] a means for receiving, from a core network, information for indicating a capability of store-and-forward data in case the service link between the access network node and a user equipment, UE, or the feeder link between the access network node and a gateway in a terrestrial network is unavailable.

[0088] In an aspect, there is provided a user equipment, UE, comprising:

[0089] A means for transmitting at least one NAS PDU, NAS being an abbreviation for Non-Access Stratum, PDU being an abbreviation for Protocol Data Unit, to an access network node via a service link between the access network node and the UE without triggering establishment of a connection for the feeder link in case the feeder link between the access network node and a gateway in a terrestrial network is not available, and

[0090] The at least one NAS PDU is stored by the access network node until the feeder link becomes available, and

[0091] The at least one NAS PDU is forwarded via the feeder link when the feeder link becomes available.

[0092] In an aspect, a user equipment, UE, is provided, comprising:

[0093] A means for receiving information indicating a mode of store-and-forward data via system information in case a service link between an access network node in a non-terrestrial network and the UE or a feeder link between the access network node and a gateway in a terrestrial network is not available; and

[0094] A means for not camping on a serving cell of the access network node in case the UE does not support the mode of store-and-forward data in case the service link or the feeder link is not available.

[0095] In an aspect, a core network node is provided, comprising:

[0096] A means for receiving at least one NAS PDU, NAS being an abbreviation for Non-Access Stratum, PDU being an abbreviation for Protocol Data Unit, from an access network node via a feeder link between the access network node and the core network node without triggering establishment of a connection for a service link between the access network node and a user equipment, UE, in case the service link is not available, and

[0097] The at least one NAS PDU is stored by the access network node until the service link becomes available, and

[0098] The at least one NAS PDU is forwarded via the service link when the service link becomes available.

[0099] In an aspect, a core network node is provided, comprising:

[0100] a means for receiving, from the access network node, information indicating a capability to store and forward data in case of unavailability of a service link between the access network node and a user equipment, UE, in a non-terrestrial network or a feeder link between the access network node and a gateway in a terrestrial network coupled with the core network node.

[0101] In an aspect, a core network node is provided, comprising:

[0102] a means for transmitting, to the access network node, information indicating a capability to store and forward data in case of unavailability of a service link between the access network node and a user equipment, UE, in a non-terrestrial network or a feeder link between the access network node and a gateway in a terrestrial network coupled with the core network node.

[0103] The various functional means described below as part of a UE can be provided by a memory and one or more processors executing instructions stored in the memory. Similarly, the various functional means described below as part of an access network node can be provided by a memory and one or more processors executing instructions stored in the memory.

[0104] The various examples described below can be implemented by means of a computer program product comprising computer implementable instructions for causing a programmable computer to execute any of the methods described below. The computer implementable instructions can be provided as signals, or provided on a tangible computer readable medium.

[0105] Advantageous effects of the invention

[0106] According to the present disclosure, a method by an access network node, a method by a user equipment, a method by a core network node, an access network node, a user equipment and a core network node can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0107] Example embodiments of the present disclosure will now be described, by way of example only, with reference to the attached drawings in which:

[0108] Figure 1 The following scenarios are exemplified in which there is a change of satellite and thus base station providing a service link and a feeder link respectively in an NTN system;

[0109] Figure 2 is a simplified sequence diagram exemplifying a general procedure for forming a connection in an NTN system;

[0110] Figure 3 An exemplary mobile (cellular or wireless) communication system is schematically exemplified;

[0111] Figure 4 is exemplifying a procedure that can be used in an NTN system;Figure 3 A simplified sequence diagram of the attachment process used in communication systems;

[0112] Figure 5 This is an example that can be found in Figure 3 A simplified sequence diagram of the process used in the communication system for data transmission initiated by a mobile station in the context of CP CIoT EPS optimization;

[0113] Figure 6 This is an example that can be found in Figure 3 A simplified sequence diagram of the data transmission process used in the communication system for mobile station termination in the context of CP CIoT EPS optimization;

[0114] Figure 7 Schematic example can be Figure 3 The non-terrestrial network (NTN) radio access network used in communication systems;

[0115] Figure 8A Examples of possible architectures for NTN RAN;

[0116] Figure 8B Examples of possible architectures for NTN RAN;

[0117] Figure 8C Examples of possible architectures for NTN RAN;

[0118] Figure 9 This example illustrates what can happen when the serving link is available but the power supply link is unavailable. Figure 3 A simplified sequence diagram of the CIoT-optimized data transmission process between NTN RAN base stations used in the communication system;

[0119] Figure 10 This illustrates what can happen when the power supply link is available but the service link is unavailable. Figure 3 A simplified sequence diagram of the CIoT-optimized data transmission process between the NTN RAN and the core network used in the communication system;

[0120] Figure 11 This example demonstrates how it can be enhanced. Figure 9 and Figure 10 A simplified sequence diagram of a portion of the process shown;

[0121] Figure 12 This is a simplified sequence diagram illustrating the S1 setup process;

[0122] Figure 13 This is an example that can be found in Figure 3 A simplified block diagram of the main components of user equipment used in a communication system;

[0123] Figure 14 is a simplified block schematic diagram of the main components of a base station / access network node that can be used in the communication system of Figure 3

[0124] Figure 15 is a simplified block schematic diagram of the main components of a core network node that can be used in the communication system of Figure 3 DETAILED DESCRIPTION

[0125] SUMMARY

[0126] An example communication system will now be generally described, by way of example only, with reference to the following drawings: Figure 3 to Figure 8.

[0127] Figure 3 A mobile (“cellular” or “wireless”) communication system 1 to which the examples described herein are applicable is schematically illustrated.

[0128] In the communication system 1, user equipment (UE) 3 (3-1, 3-2, 3-3) (e.g. mobile telephones and / or other mobile devices) can communicate with one another via corresponding radio access networks (RANs) 5-1, 5-2 operating in accordance with one or more compatible radio access technologies (RATs). In the illustrated example, each RAN 5-1, 5-2 (which can be an NTN-based RAN) comprises a base station 5A-1, 5A-2 (e.g. an LTE / 4G base station such as an eNB or the like) operating one or more associated cells 9 (9-1, 9-2) respectively.

[0129] As those skilled in the art will appreciate, although three UEs 3 and two RANs 5-1, 5-2 are shown in Figure 3 for illustrative purposes, the system will typically comprise other RANs 5 and UEs 3 when implemented.

[0130] In the example system, the UEs 3 include one or more so-called “Internet of Things” (“loT”) devices such as Narrowband loT (NB-loT) devices or the like.

[0131] Each RAN 5-1, 5-2 controls one or more associated cells directly, or indirectly via one or more other nodes such as a home base station, a relay, a remote radio head, a distributed unit and / or the like. It will be appreciated that the RANs 5 can be configured to support 4G, 5G, 6G and / or beyond, and / or any other 3GPP or non-3GPP communication protocol.

[0132] ​​The UEs 3 and their serving RAN 5 are connected via appropriate air interfaces (e.g. the so-called “Uu” interface and / or the like). Base stations 5A of the neighbouring RAN 5 can be connected to each other via appropriate base station to base station interfaces such as the so-called “X2” interface for 4G, the “Xn” interface for 5G and / or the like.

[0133] The core network 7 comprises a plurality of communication nodes / logical nodes (or “functions”) for supporting communications in the communications system 1. In this example, the core network 7 comprises one or more network node entities for controlling communications for control signalling (e.g. a mobility management entity (MME) 11 or mobility management node 11), one or more network node entities for routing incoming and outgoing packets (e.g. a serving gateway (S-GW) 13), one or more network node entities for connecting the core network 7 and external networks 20 (e.g. a packet data network gateway (P-GW) 15), and a plurality of other functional nodes (not shown). It will be appreciated that nodes or functions can have different names in different systems. It will be appreciated that while the core network 7 is described in the context of 4G entities and interfaces / reference points, the core network 7 can be any suitable core network (e.g. 5G / 6G and / or later generation core networks) with corresponding communication entities (e.g. control functions (CPFs) such as AMFs, SMFs, etc. - and one or more user plane functions (UPFs)).

[0134] The RAN 5 is connected to the core network nodes via appropriate interfaces (or “reference points”) such as the S1-MME reference point between the base stations 5A of the RAN 5 and the MME 11 and the S1-U reference point between the base stations 5A of the RAN 5 and the S-GW 13, etc. The UEs 3 are each connected to the MME 11 via a non-access stratum (NAS) connection over an appropriate interface (e.g. the S1 reference point (similar to the N1 reference point in 5G)) when applicable. It will be appreciated that S1 communications are routed transparently via the RAN 5.

[0135] The core network 7 (e.g. the P-GW 15) is connected to external networks 20 (e.g. IP networks such as the Internet and / or the like) via another reference point (e.g. “SGi”) for communications of user data.

[0136] The MME 11 manages general mobility aspects of the UE 3 and ensures connectivity with the UE 3 as it moves around (and / or as the UE 3 is handed over between base stations 5A of the communications system 1) within the geographical area covered by the communications system 1. The MME 11 also handles control plane signaling for the UE 3 and manages various bearers (e.g. such as evolved packet system (EPS) bearers and / or radio bearers etc.) associated with the UE 3, e.g. by controlling the S-GW 13 and P-GW 15 (and / or possibly other network nodes), via which such bearers are provided.

[0137] The S-GW 13 (via the base station 5A) provides a connection between the UE 3 and the core network 7 for transmitting and receiving user plane data on an associated communications bearer (e.g. an EPS bearer). The communications bearer is typically terminated at the P-GW 15, although the communications bearer is often also supplemented by an external bearer (e.g. another EPS bearer and / or the like) between the P-GW 15 and a communications endpoint external to the core network 7 (e.g. in an external network 20). It will be appreciated that, although shown as separate entities, the functionality of the S-GW 13 and P-GW 15 can be implemented in a single gateway element.

[0138] The RAN 5 is also configured for transmission of control information and user data via a plurality of downlink (DL) physical channels and for transmission of a plurality of physical signals, and the UE 3 is configured for reception of control information and user data via a plurality of downlink (DL) physical channels and for transmission of a plurality of physical signals. The DL physical channels correspond to resource elements (REs) that carry information originating from higher layers, and the DL physical signals are used in the physical layer and correspond to REs that do not carry information originating from higher layers.

[0139] The physical channels can 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 is shared on a time and frequency basis. The PDSCH can carry various items of data including, for example, user data, UE-specific higher layer control messages mapped down from higher channels, system information blocks (SIBs), and paging. The PDCCH carries downlink control information (DCI) to support multiple functions including, for example, scheduling of downlink transmissions on the PDSCH and also scheduling of uplink data transmissions on the physical uplink shared channel (PUSCH). The PBCH provides a master information block (MIB) to the UE 3. The PBCH also supports synchronization of time and frequency in conjunction with the PDCCH, which facilitates cell acquisition, selection, and reselection.

[0140] DL physical signals can include, for example, reference signals (RS) and synchronization signals (SS). A reference signal (sometimes called pilot signal) is a signal with a predefined special waveform known to both the UE 3 and the base station 5A of the RAN 5. Reference signals can include, for example, cell-specific reference signals, UE-specific reference signals (UE-RS), downlink demodulation signals (DMRS) and channel state information reference signals (CSI-RS).

[0141] Similarly, the UE 3 is configured for transmission of control information and user data via a plurality of uplink (UL) physical channels corresponding to REs carrying information originating from higher layers and UL physical signals using and corresponding to REs not carrying information originating from higher layers, and the base station 5A of the RAN 5 is configured for reception of control information and user data via a plurality of uplink (UL) physical channels corresponding to REs carrying information originating from higher layers and UL physical signals using and corresponding to REs not carrying information originating from higher layers, these UL physical signals being used in the physical layer and corresponding to REs not carrying information originating from higher layers. Physical channels can include, for example, PUSCH, physical uplink control channel (PUCCH) and / or physical random access channel (PRACH). UL physical signals can include, for example, demodulation reference signals (DMRS) for UL control / data signals and / or sounding reference signals (SRS) for UL channel measurement.

[0142] <Attach procedure and initial access>

[0143] The UE 3 in the communication system 1, the base station 5A of the RAN 5 and the core network entity 7 are mutually configured for an attach procedure for connecting the UE 3 to the network for communication of user data.

[0144] Reference will now be made by way of example only to Figure 4 a possible such procedure that can be performed, Figure 4 is a simplified sequence diagram illustrating an attach procedure that can be used in the communication system 1.

[0145] As Figure 4 seen in the

[0146] When the UE 3 needs to connect to the network, the UE 3 can then proceed with a random access channel (RACH) procedure for the UE 3 to access the network. Specifically, the UE 3 can attempt access to the cell 9 (and / or beam) using an initial RRC connection setup procedure that includes a random access procedure. Before attempting initial access, the UE 3 selects a random access resource (including, for example, a preamble) to use to initiate the RACH procedure. The UE 3 transmits the selected preamble (e.g., in a “Msgl”) on a physical random access channel (PRACH) to the base station 5A of the RAN 5 at S414 for initiating a process to obtain synchronization in the uplink (UL). In response, the base station 5A of the RAN 5 responds with a random access response (RAR) (or “Msg2”) at S416. The RAR indicates reception of the preamble and can include, for example: a timing alignment (TA) command to adjust the transmission timing of the UE 3 based on the timing of the received preamble; an uplink grant field indicating resources to use in the uplink for a physical uplink shared channel (PUSCH); a frequency hopping flag to indicate whether the UE 3 is to transmit on the PUSCH with or without frequency; a modulation and coding scheme (MCS) field from which the UE 3 can determine an MCS to use for the PUSCH transmission; and a transmission power control (TPC) command value to set the power of the PUSCH transmission. At this point, an initial signaling radio bearer (SRB) (“SRB0”) is established for communicating certain types of RRC messages on a common control channel (CCCH). The UE 3 then transmits a third message (“Msg3”) on a physical uplink shared channel (PUSCH) to the network based on the information in the RAR (e.g., using the SRB0) at S418. The specific message and content of the message that the UE 3 transmits in this step depends on the context in which the random access procedure is being used. However, in the example of initial radio RRC connection setup, the Msg3 typically includes an RRC connection request or similar message carrying a temporarily randomly generated UE identifier. The network responds with a fourth message (“Msg4”) at S420 that carries the randomly generated UE identifier received in the Msg3 (e.g., for contention purposes to resolve any collisions between different UEs 3 using the same preamble sequence). When successful, the Msg4 also causes the UE 3 to move to a connected state in which another SRB (“SRB1”) is established for communicating certain RRC and NAS messages on a dedicated control channel (DCCH).

[0147] The UE 3 then attempts to achieve packet data network (PDN) connectivity by sending a message to the base station 5A of the RAN 5 at S422 indicating that the RRC has completed. This message includes an attach request to initiate the attach procedure and a PDN connectivity request as NAS payload. The base station 5A of the RAN 5 then sends a first message of the base station 5A of the RAN 5 to the core network 7 at S424 - the initial UE message containing the attach request and the PDN connectivity request. This message is sent to a core network node for providing mobility management functionality (in this example the MME 11, but for 5G it could be an AMF). The message is sent via the S1 -MME interface / reference point and in this 4G example includes information such as tracking area identity (TAI) and E-UTRAN cell global identifier (ECGI) (similar but differently named messages / information elements can be used for 5G and other generations).

[0148] The mobility management node 11 coordinates with another core network node (e.g. in this example the home subscriber server HSS and / or the authentication centre (AuC)) at S426 to obtain authentication information, e.g. security information, such as: KASME (an intermediate key derived in the HSS and in the UE 3 from a cipher key, an integrity key and a serving network identity (SN id)); AUTN (a so-called authentication token generated at the AuC); XRES (a so-called “expected response” generated at the AuC); and / or RAND (a random number for use in key generation and authentication).

[0149] The mobility management node 11 sends an authentication request (including RAND and AUTN) to the UE 3 at S428 and the UE 3 responds with an authentication response at S430 including an authentication response parameter computed based on the RAND and the AUTN and a key (K) stored at the UE 3 (e.g. in a subscriber identity module).

[0150] The mobility management node 11 then initiates NAS signalling security between the mobility management node 11 and the UE 3 at S432 by sending a NAS security mode command message informing the UE 3 of respective algorithms to be used for integrity protection and (de)ciphering. The UE 3 responds after deriving the appropriate security information at S434 by sending a response message informing the mobility management node 11 of the NAS signalling security initialization completion (at S436).

[0151] The mobility management node 11 coordinates at S438 with one or more other core network nodes (e.g., HSS) to obtain location update related information, such as PDN subscription context (including, for example, Quality of Service (QoS) profiles of the EPS subscription and subscribed Access Point Name - Aggregate Maximum Bit Rate (APN-AMBR)).

[0152] The mobility management node 11 coordinates at S440 with one or more other core network nodes (e.g., S-GW 13 and / or P-GW 15 or a combination thereof) to initiate establishment of a communication GPRS Tunneling Protocol (GTP) tunnel by sending an appropriate create session request (e.g., to S-GW 13) and receiving an appropriate response once the tunnel is established. For example, after the S-GW 13 has sent a corresponding default bearer request to the P-GW 15 to create a new entry in the P-GW 15's EPS bearer context table, a default bearer response is sent from the P-GW 15 to the S-GW 13 containing the P-GW 15 user plane address, P-GW 15 tunnel endpoint identifiers (TEIDs) for the user plane and control plane, EPS bearer identity and QoS information. The P-GW 15 also sends downlink data to be buffered in the S-GW 13 until the connection is completed. An acknowledgement message is typically sent from the S-GW 13 to the mobility management node 11 indicating that the GTP for control (GTP-C) tunnel has been established.

[0153] The mobility management node 11 sends at S442 an initial context setup request (e.g., containing an S1 interface context setup request, a NAS attach accept and an activate default bearer request).

[0154] A UE capability exchange can then take place in which the base station 5A sends (at S444) a UE capability enquiry to the UE 3 (typically using RRC signaling) to request information related to the UE's capabilities. The UE 3 responds at S446 with the requested UE capability information, and the base station 5A provides an indication of this UE capability information to the mobility management node 11 at S448.

[0155] Access Stratum (AS) security is then established. In particular, the base station 5A sends an RRC security mode command to the UE 3 at S450 with AS integrity protection and ciphering algorithms and a "START" parameter. The UE 3 uses the received information to compute the appropriate security keys and sends a message to the base station 5A at S452 to indicate RRC security mode complete. During this phase, a further Signalling Radio Bearer (SRB2) is established. SRB2 is used for RRC messages including logged measurement information and for NAS messages, all using the DCCH logical channel. SRB2 has a lower priority than SRB1 and is configured by the base station 5A after security activation.

[0156] An RRC reconfiguration is then conducted in which the base station 5A sends an RRC reconfiguration to the UE 3 at S454 to activate default radio bearers. The UE 3 configures itself based on the information in the RRC reconfiguration and sends an RRC reconfiguration complete message at S456. The base station 5A then sends a message to the mobility management node 11 at S458 to indicate initial context setup complete. The mobility management node 11 then coordinates with one or more other core network nodes (e.g. the S-GW 13) to appropriately modify bearers and establish data radio bearers (DRBs) for the UE's communications.

[0157] While a four-step contention-based RACH procedure is described, it will be appreciated that the UE 3 and the base station 5A of the RAN 5 in the communications system 1 can also conduct a non-contention (or "contention-free") based procedure in which the base station 5A of the RAN 5 assigns a dedicated preamble to the UE 3. Furthermore, the UE 3 and the base station 5A of the RAN 5 in the communications system 1 can conduct a two-step RACH procedure (e.g. as described in the introduction).

[0158] It will be appreciated that while the UE 3 can itself trigger initiation of the RACH procedure (e.g. when the UE 3 needs to connect to the network), initiation of the RACH procedure can be conducted by the network. For example, the RACH procedure can be initiated by a message sent in the Physical Downlink Control Channel (PDCCH) via Downlink Control Information (DCI) with an appropriate DCI format (e.g. 1_0) - such a message is often referred to as a PDCCH order. The RACH procedure can also be initiated by the base station 5A of the RAN 5 when a handover is required (e.g. using a handover command message).

[0159] <CP CIoT EPS Optimisation>

[0160] The UE 3 in the communication system 1, the base station 5A of the RAN 5 and the core network entities 7 are mutually configured for implementing a number of procedures in the context of CP CIoT EPS optimization. These procedures include, for example, mobile originated (MO) and mobile terminated (MT) data transmission.

[0161] In these general procedures, in which there are no problems associated with intermittent coverage / intermittent power link, there is no need to have a UE context available at the base station 5A. UL / DL data being transmitted / received by the UE 3 is encapsulated in NAS PDUs as it is transmitted through the wider network. On the air interface, NAS data PDUs are transmitted via RRC messages (e.g. piggybacked on the RRC connection complete message, or in UL / DL information transfer messages) during and after RRC connection setup. In these procedures, no DRB is established, and no AS security is setup. On the S1-AP (NG-AP for 5GS) interface, NAS data PDUs are transmitted via S1-AP (NG-AP for 5GS) messages.

[0162] <Mobile originated data transmission>

[0163] As mentioned above, the UE 3 in the communication system 1, the base station 5A of the RAN 5 and the core network entities are mutually configured for MO data transmission in the context of CP CIoT EPS optimization.

[0164] Reference will now be made by way of example only to Figure 5 One such procedure is described, Figure 5 is a simplified sequence diagram illustrating a procedure for MO data transmission in the context of CP CIoT EPS optimization with P-GW connectivity that can be used in the communication system 1. In this procedure, CP CIoT EPS optimization is in the context of Figure 3 described in the context of 4G entities. However, it will be appreciated that similar procedures can be followed by corresponding 5G entities for CP CIoT 5GS optimization (or by corresponding apparatus of future generations). It will be appreciated that the description here is only intended as an overview, so not all parameters of the message flows are listed or described.

[0165] As seen at S500, at the start of the procedure, the UE 3 is in idle mode / state (in this example, EPS connection management (ECM) or "ECM-IDLE" mode / state, in which the UE 3 has no signalling connection to the MME 11).

[0166] At S501, the UE 3 establishes an RRC connection, or sends an RRC early data request message, and includes 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 an EPS Bearer ID (EBI) and encrypted UL data. The UE 3 can also indicate, e.g., in a NAS release assistance information field of the NAS PDU, whether no further UL or DL data transmission is expected, or whether only a single DL data transmission (e.g., an acknowledgement or response to the UL data) is expected after the UL data transmission.

[0167] At S501b, the base station 5A can coordinate with the MME 11 (e.g., for the NB-IoT case) to retrieve the EPS negotiated QoS profile from the MME 11 (if not previously retrieved).

[0168] At S502, the NAS PDU provided to the base station 5A at S501 is relayed (with the EBI) to the MME 11 using an S1-AP initial UE message (corresponding to an NG-AP message in 5GS). If an RRC early data request message was used at S501, the base station 5A can include an “EDT session” indication in the S1-AP initial UE message.

[0169] At S503, the MME 11 checks the integrity of the incoming NAS PDU and decrypts the data contained by the NAS PDU.

[0170] However, the MME 11 can reject the request by discarding the NAS data PDU and sending a service reject message to the UE 3 with an appropriate cause. The rejection can occur, for example, if there is a service gap timer running in the MME mobility management (MM) context for the UE and the MME 11 is not waiting for an MT paging response from the UE 3. The MME 11 can also provide a mobility management back-off timer to the UE 3 set to the remaining value of the service gap timer, followed by triggering an S1 release procedure.

[0171] At S504, the MME 11 can send a modify bearer request message (e.g., including MME address, MME TEID DL, delay downlink packet notification request, RAT type, LTE-M RAT type flag to report to P-GW, MO exception data counter, and / or the like) for each PDN connection to the S-GW 13. For example, the modify bearer request message can be sent if no connection is established over the user plane interface / reference point (S11-U interface) between the MME 11 and the S-GW 13. The S-GW 13 is now able to transmit downlink data to the UE 3. In addition, the modify bearer request message with appropriate information can be sent in other scenarios, e.g., if the UE's location and / or user closed subscriber group information is requested by the P-GW 15 and has changed; the serving network information has changed compared to the last reported modify bearer request message; then the MME 11 shall send a modify bearer request message and also include the serving network IE in this message; and / or the UE time zone has changed compared to the last reported UE time zone, regardless of whether the S11-U has been established.

[0172] At S505, if the modify bearer request message is sent, the S-GW 13 can send a modify bearer request message to the P-GW 15 including information depending on the content of the modify bearer request message and / or the reason the modify bearer request message was sent.

[0173] At S506, if the modify bearer request message is sent at S505, the P-GW 15 can send a modify bearer response to the S-GW 13.

[0174] At S507, if the modify bearer request message is sent at S504, the S-GW 13 can return an appropriate modify bearer response (S-GW address and TEID for uplink traffic) to the MME 11 as a response to the modify bearer request message. As seen at S508, the S-GW address and S-GW TEID for the S11-U user plane are used by the MME 11 to forward UL data to the S-GW 13.

[0175] If no DL data is expected based on the NAS release assistance information provided by the UE 3 at S501, this indicates that all application layer data exchange has been completed together with the UL data transfer, and if the MME 11 is not aware of MT traffic pending and the S1-U bearer is not established, the procedure can jump to S511.

[0176] Otherwise, DL data can arrive at the P-GW 15 and at S509 the P-GW 15 can send the DL data to the MME 11 via the S-GW 13. If no data is received, S510 to S512 can be skipped and after the base station 5A detects no activity at S513, the base station 5A can trigger S514. During the time the RRC connection is active, the UE 3 can send UL data in NAS PDUs (not shown in the figure) carried in S1-AP UL or DL messages, respectively, and can receive DL data in these NAS PDUs. At any time the UE 3 has no user plane bearers established, the UE 3 can provide NAS release assistance information with UL data. In this case, to assist the location service, the base station 5A can indicate the coverage level of the UE to the MME 11 if needed.

[0177] At S510, if DL data is received at S509, the MME 11 cipher and integrity protects the DL data.

[0178] At S511, if S510 occurs, the DL data is encapsulated in a NAS PDU and sent to the base station 5A in a DL NAS transport message (e.g., in a S1-AP downlink NAS transport message).

[0179] If the configuration in the MME 11 indicates that the base station 5A supports acknowledgement of downlink NAS data PDUs and if acknowledgement of downlink NAS data PDUs is enabled in the subscription information for the UE 3, the MME 11 can indicate in the S1-AP downlink NAS message that acknowledgement is requested from the base station 5A.

[0180] On the other hand, if S510 does not occur, or a NAS service accept message will not be sent, the MME 3 can send (at S511) a connection establishment indication message to the base station 5A to complete the establishment of the logical S1 connection associated with the UE.

[0181] The UE radio capabilities can be provided from the MME 11 to the base station 5A in the DL NAS transport message or the connection establishment indication message and the base station 5A can store the received UE radio capability information.

[0182] If the NAS release assistance information is received together with UL data and the NAS release assistance information indicates that DL data is expected, the next DL packet after sending the NAS release assistance information will be the last packet of the application layer data exchange. For this case, the MME 11 sends the S1 UE context release command immediately after the S1-AP message including DL data encapsulated in NAS PDU at S512, as an indication that the base station 5A should release the RRC connection immediately after successfully sending data to the UE 3, unless the MME 11 knows additional pending MT traffic and unless the S1-U bearer is established. Alternatively, if the "EDT session" indication is received at S502, the MME 11 can include an "end indication" for no further data in the S1-AP message including DL data encapsulated in NAS PDU. If the MME 11 includes the "end indication" indicating no further data and if the base station 5A does not continue with the RRC connection setup, the base station 5A skips S512a and initiates S512b.

[0183] If the NAS release assistance information indicating that no downlink data is expected is received, all application layer data exchange has been completed with the UL data transfer. For this case, the MME 11 can send the S1-AP UE context release command immediately after the S1-AP DL NAS transport (in this case, S512b and S514 can be skipped) or immediately after the S1-AP connection setup indication (in this case, S512b to S514 can be skipped), unless the MME 11 knows additional pending MT traffic and unless the S1-U bearer is established.

[0184] - The MME can send the S1-AP UE context release command immediately after the S1-AP DL NAS transport (in this case, S512b and S514 can be skipped) or immediately after the S1-AP connection setup indication (in this case, S512b to S514 can be skipped), unless the MME 11 knows additional pending MT traffic and unless the S1-U bearer is established.

[0185] - Alternatively, if the MME 11 receives the "EDT session" indication from the base station 5A at S502, the MME 11 can include an "end indication" for no further data in the S1-AP DL NAS transport (indicating NAS service accept) or in the S1-AP connection setup indication. If the base station 5A does not continue with the RRC connection setup, the base station 5A can skip S512a and initiate S512b.

[0186] At S512a, base station 5A sends an RRC DL data message to UE 3, which includes DL data encapsulated in the NAS PDU. If the S1 UE context release command follows the S1-AP message with the NAS data PDU at S511, S515 can be completed immediately after the DL data transmission to the NAS PDU of UE 3 has been completed and any acknowledgment has been sent to MME 11 (as seen at S513), without base station 5A monitoring NAS PDU activity (at S514).

[0187] At S512b, if a "Termination Instruction" with no further data is received in the S1-AP message from MME 11, base station 5A can send the RRC Early Data Completion message along with any NAS payload (NAS data PDU or NAS service acceptance) received at S511. In this case, S514 can also be skipped.

[0188] At S513, base station 5A can send a NAS delivery instruction to MME 11 (if requested).

[0189] At S514, NAS PDU activity is monitored at base station 5A.

[0190] If there is no NAS PDU activity for a period of time, base station 5A detects inactivity and initiates the S1 release process at S515.

[0191] <Data transmission terminated by the mobile station>

[0192] As described above, UE 3, RAN 5 base station 5A and core network entity 7 in communication system 1 are configured to perform MT data transmission in the context of CP CIoT EPS optimization.

[0193] Now we will refer to it through examples only. Figure 6 Describe such a process, Figure 6 This is a simplified sequence diagram illustrating a process for MT data transmission in the context of CP CIoT EPS optimization, which has P-GW connectivity that can be used in communication system 1. In this process, CP CIoT EPS optimization is... Figure 3 The description is given within the context of the illustrated 4G entity. However, it will be understood that similar processes can be followed by corresponding 5G entities (or by corresponding devices of future generations) for CP CIoT 5GS optimization. It will be understood that the description herein is intended only as an overview, and therefore not all parameters for the message flow are listed or described.

[0194] As seen at S600, at the start of the procedure, the UE 3 is in idle mode / state (in this example, EPS Connection Management (ECM) or "ECM-IDLE" mode / state, in which the UE 3 does not have a signaling connection to the MME 11).

[0195] At S601, the S-GW 13 receives a DL data packet / control signaling for the UE 3 from the P-GW 15. If the S-GW context data indicates that there is no DL user plane TEID towards the MME 11, the S-GW buffers the DL data packet and identifies which MME 11 is serving the UE 3.

[0196] At S602a, if the S-GW 13 is buffering data (e.g., as described above for S601), the S-GW 13 sends a downlink data notification message (e.g., including an Allocation and Retention Priority (ARP) and an EPS Bearer ID) to the MME 11 for which the S-GW 13 has control plane connectivity for the given UE 3. The MME 11 responds to the S-GW 13 with a downlink data notification acknowledgement message at S602b.

[0197] At S603, assuming that the UE 3 is registered in the MME 11 and considered reachable (and possibly subject to other criteria), the MME 11 can send one or more paging messages.

[0198] At S604, the base station 5A of the RAN 5, which receives the one or more paging messages from the MME 11, pages the UE 3.

[0199] At S605, when the UE 3 is in the ECM-IDLE state, upon receiving the paging indication, the UE 3 and the base station 5A coordinate with each other to establish an RRC connection (e.g., as described with reference to Figure 4 At S606, the base station 5A can send the control plane service request NAS message to the MME 11 in an S1-AP initial UE message. As seen at S606, the base station 5A can send the control plane service request NAS message to the MME 11 in an S1-AP initial UE message.

[0200] When the control plane CIoT EPS optimization is applicable, the control plane service request NAS message does not trigger a data radio bearer setup with the MME 11, and the MME 11 can use the NAS PDU to send the downlink data received by the MME 11 to the base station 5A immediately. The MME 11 supervises the paging procedure with a timer. If the MME 11 does not receive a response to the paging request message from the UE 3, the MME 11 can repeat the paging according to any applicable paging policy.

[0201] At S605b, the base station 5A can coordinate with the MME 11 (e.g., for NB-IoT case) to retrieve the EPS negotiated QoS profile from the MME 11 (if not previously retrieved).

[0202] At S607, the MME 11 can send a modify bearer request message to the S-GW 13 for each PDN connection (e.g., including MME address, MME TEID DL, delay downlink packet notification request, RAT type, LTE-M RAT type flag reported to P-GW, and / or the like). The modify bearer request message can be sent, for example, if a connection is not established over the user plane interface / reference point (S11-U interface) between the MME 11 and the S-GW 13. The S-GW 13 is now able to transmit downlink data to the UE 3. In addition, the modify bearer request message can be sent with appropriate information in other scenarios, e.g., if the UE's location and / or user closed subscriber group information was requested by the P-GW 15 and has changed; the serving network information has changed compared to the last reported modify bearer request message; then the MME 11 shall send a modify bearer request message and also include the serving network IE in this message; and / or the UE time zone has changed compared to the last reported UE time zone, regardless of whether the S11-U has been established.

[0203] At S608, if a modify bearer request message is sent, the S-GW 13 can send a modify bearer request message to the P-GW 15 including information depending on the content of the modify bearer request message and / or the reason the modify bearer request message was sent.

[0204] At S609, if a modify bearer request message is sent at S608, the P-GW 15 can send an appropriate modify bearer response to the S-GW 13.

[0205] At S610, if a modify bearer request message is sent at S607, the S-GW 13 can return an appropriate modify bearer response (S-GW address and TEID for uplink traffic) to the MME 11 as a response to the modify bearer request message. The S-GW address and S-GW TEID for the S11-U user plane are used by the MME 11 to forward any UL data to the S-GW 13.

[0206] At S611, buffered (if S11-U is not established) downlink data can be sent by the S-GW 13 to the MME 11.

[0207] At S612, the MME 11 encrypts and integrity protects the downlink data.

[0208] At S613, the MME 11 can send the encrypted and integrity protected downlink data to the base station 5A using the NAS PDU carried by the downlink S1-AP message. If the configuration in the MME 11 indicates that the base station 5A supports acknowledgement of downlink NAS data PDUs, and if acknowledgement of downlink NAS data PDUs is enabled in the subscription information for the UE 3, the MME 11 can indicate in the S1-AP downlink NAS message that acknowledgement is requested from the base station 5A.

[0209] At S614, the NAS PDU with data is delivered to the UE 3 via a downlink RRC message. This is considered by the UE 3 as an implicit acknowledgement of the service request message sent at S605.

[0210] At S615, the base station 5A (if requested) sends a NAS delivery indication to the MME 11.

[0211] At S616, further UL (and DL) data can be communicated using NAS PDUs during the time the RRC connection is still established. In this figure, UL data communication is shown using an UL RRC message encapsulating a NAS PDU with UL data. At any time the UE 3 has no user plane bearers established, the UE 3 can provide release assistance information with uplink data in a NAS PDU.

[0212] At S617, the NAS PDU with data is sent in an UL S1-AP message to the MME 11.

[0213] At S618, the integrity of the data is checked and the data is decrypted.

[0214] At S619a and S619b, the MME 11 sends the UL data to the P-GW 15 via the S-GW 13, and performs any actions related to the presence of release assistance information as follows:

[0215] - For the case where the release assistance information indicates that there is no downlink data following the uplink data, then unless the MME 11 is aware of pending MT traffic, and unless there is an S1-U bearer, the MME 11 releases the connection immediately and jumps to S621.

[0216] - For the case where the release assistance information indicates that downlink data will follow the uplink transmission, then the MME 11 sends an S1 UE context release command to the base station 5A immediately after the S1-AP message including the downlink data encapsulated in a NAS PDU, unless the MME 11 is aware of additional pending MT traffic, and unless there is an S1-U bearer.

[0217] At S620, NAS PDU activity is monitored at the base station 5A.

[0218] If there is no NAS PDU activity for a period of time, then the base station 5A detects inactivity and initiates the S1 release procedure at S621.

[0219] <NTN RAN>

[0220] In the exemplary communication system 1, each RAN 5 can be implemented as a non-terrestrial network (NTN) RAN.

[0221] Figure 7 One such NTN RAN 5 is schematically illustrated which can be used in a communication system of the type Figure 3 .

[0222] As seen in Figure 7 , the NTN RAN 5 comprises a base station 5A operating one or more associated cells 9, a gateway 5B and a non-terrestrial (space-based or aerial-based) platform 5C (e.g. comprising one or more satellites and / or aerial vehicles), which for simplicity can be generally referred to as “satellite”. Communication via the NTN RAN 5 is routed through the core network 7 and the external network 20 (e.g. via the N6 interface / reference point).

[0223] The NTN RAN 5 controls a plurality of directional satellite beams via which the associated NTN cells 9 can be provided. In particular, each satellite beam has an associated coverage area on the Earth’s surface which forms an NTN cell or part of an NTN cell. Each NTN cell has an associated physical cell identity (PCI). As the non-terrestrial (space-based or aerial-based) platform 5C is travelling along its orbit, the satellite beam coverage area can be moving (e.g. as exemplified by arrow A in Figure 7 . Alternatively, the satellite beam coverage area can be Earth-fixed, in which case the movement of the non-terrestrial (space-based or aerial-based) platform 5C can be compensated using appropriate satellite beam pointing mechanisms (mechanical or electronic steering). In an NTN, from the perspective of a UE, the satellite beam and the satellite are not considered to be visible. However, this does not preclude distinguishing the type of network (e.g. NTN vs. terrestrial) at the public land mobile network (PLMN) level.

[0224] The base station 5A of the NTN RAN 5 is configured to provide ephemeris data for non-terrestrial (spaceborne or airborne) platforms 5C to the UE 3 to assist the UE 3 in measurements and cell selection / reselection and for supporting initial access. This ephemeris data can include information related to orbital information, such as information related to an orbital plane level or a satellite level, and / or information from which more detailed ephemeris data stored in the UE 3 (e.g., in a subscriber identity module “SIM”) can be obtained (e.g., a pointer or index), etc. At least some of this ephemeris information can be provided, e.g., in system information and / or can be provided using UE-specific (dedicated) signaling, such as RRC signaling, etc.

[0225] In particular, the base station 5A can provide satellite assistance information for a satellite as part of a dedicated system information block (SIB) broadcast to UEs 3 in the corresponding cell 9 of the NTN RAN 5 (for 5G NTN, this can be, e.g., SIB19, but for future generations it can be in another SIB or provided differently). The satellite assistance information can include, e.g., information identifying at least one associated NTN configuration (e.g., as part of an NTN-Config IE or similar). The NTN configuration includes parameters for assisting the UE 3 in accessing the network using NTN access (e.g., ephemeris data, common timing alignment parameters, scheduling (e.g., k_offset), validity duration and epoch time for uplink synchronization information (reference time for which the assistance information is valid)).

[0226] <NTN RAN architecture>

[0227] Figure 8A 、 Figure 8B and Figure 8C Each illustrates a possible architecture of the NTN RAN 5 that can be used, respectively.

[0228] Figure 8AThe architecture can be described 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 UE 3 via a ground-based gateway 5B and a non-ground-based (space-based or air-based) platform 5C, which does not have base station functionality. The non-ground-based (space-based or air-based) platform 5C relays these communications to and from UE 3 in the cells operated by base station 5A, and relays these communications from and to gateway 5B as needed. The non-ground-based (space-based or air-based) platform 5C transparently relays these communications without requiring on-board processing, effectively acting as a so-called "bend." In this implementation, the feed link between gateway 5B and the non-ground-based (space-based or air-based) platform 5C effectively serves as part of the corresponding Uu interface (or reference point) between base station 5A and each UE 3. Similarly, the corresponding service links between the non-terrestrial (air-based or space-based) platform 5C and each UE 3 actually serve as another part of the corresponding Uu interface (or reference point) between the base station 5A and each UE 3. The communication links between the base station and the core network 7 (e.g., signaling via the N1, N2, N3 interfaces / reference points, etc.) are provided only on the ground.

[0229] Figure 8B The architecture can be described as a "regenerative satellite" RAN architecture (i.e., in which satellites perform on-board processing of the payload communicating between UE 3 and core network 7). In this architecture, base station 5A is a distributed type of base station 5A, which has a central unit (CU) 5A located on the ground. CU And the distributed unit (DU) 5A provided on a non-ground (air-based or space-based) platform 5C. DU CU 5A located on the ground CU Perform some (typically higher-level) functionalities of base station 5A, while DU 5A is located off-ground. DU Perform other (typically lower-layer) functionalities of base station 5A. CU 5A located on the ground. CU Connected to DU 5A, which is located off-ground, via gateway 5B and F1 interfaces. DU Communication is achieved via the F1 interface through gateway 5B and a non-terrestrial (space-based or space-based) platform 5C (in which DU 5A is provided). DU The satellite radio interface between them is implemented.

[0230] The non-terrestrial (air- or space-borne) platform 5C transmits communications to and from UEs 3 in cells 9 operated by the base station 5A, and transmits communications to and from UEs 3 in cells 9 operated by the base station 5A as needed from and to the gateway 5B. However, in this implementation, the lower-layer processing of communications to and from UEs 3 is performed by the DU 5A DU in a manner on-board the non-terrestrial (air- or space-borne) platform 5C, and the higher-layer processing of communications to and from UEs 3 is performed by the CU 5A CU located on the ground.

[0231] Thus, in this implementation, the feeder link between the gateway 5B and the non-terrestrial (air- or space-borne) platform 5C effectively acts as an Fl interface (or reference point) between the CU 5A CU and the DU 5A DU of the base station 5A. On the other hand, the respective service links between the non-terrestrial (air- or space-borne) platform 5C and UEs 3 effectively act as respective Uu interfaces (or reference points) between the base station 5A and UEs 3. The base station’s communication link with the core network 7 (e.g., for signaling over N1, N2, N3 interfaces / reference points, etc.) is provided on the ground only.

[0232] Figure 8C The architecture of FIG. 1 can also be referred to as a “regenerative satellite”-based RAN architecture (i.e., in which a satellite regenerates payloads being communicated between UEs 3 and the core network 7 on-board). In this architecture, the base station 5A is provided in a manner on-board the non-terrestrial (air- or space-borne) platform 5C. The base station 5A on-board the non-terrestrial (air- or space-borne) platform 5C transmits communications to and from UEs 3 in cells 9 operated by the base station 5A, and transmits communications to and from UEs 3 in cells 9 operated by the base station 5A as needed from and to the core network 7 via the gateway 5B. However, in this implementation, the processing of communications to and from UEs 3 is performed by the base station 5A in a manner on-board the non-terrestrial platform 5C.

[0233] Thus, in this implementation, the feeder link between the gateway 5B and the non-terrestrial (air- or space-borne) platform 5C effectively acts as part of the N1 / N2 / N3 interfaces (or reference points) between the base station 5A and the core network 7. The base station’s communication link with the core network 7 (e.g., for signaling over N1, N2, N3 interfaces / reference points, etc.) is thereby provided partly via the feeder link and partly on the ground. On the other hand, the respective service links between the non-terrestrial (air- or space-borne) platform 5C and UEs 3 effectively act as respective Uu interfaces (or reference points) between the base station 5A and UEs 3.

[0234] The base station 5A thereby controls one or more associated cells via a non-terrestrial (air- or space-borne) platform 5C. It will be appreciated that the base station 5A can be configured to support 4G, 5G, 6G and / or later generations, and / or any other 3GPP or non-3GPP communication protocols.

[0235] For the purposes of the description, the communication system 1 will be described in terms of Figure 8C The NTN RAN 5 is described in terms of the illustrated regenerative architecture. However, it will be appreciated that the NTN RAN 5 can potentially use a different architecture among the architectures, and the entities of the communication system 1 can be adapted accordingly.

[0236] <Enhanced store-and-forward techniques based on CP CIoT EPS optimization>

[0237] Beneficially, for MO / MT data transmissions without full / end-to-end UE to CN / PDN connectivity (e.g., as a result of intermittent coverage / intermediate feeder link connectivity in the context of the NTN-deployed RAN 5), the UE 3, the base station 5A of the NTN RAN 5 and the communication entities of the core network 7 in the communication system 1 are mutually configured to implement one or more features based on enhanced CP CIoT optimization (i.e., where data encapsulated in (initial) NAS messages can be sent to the base station 5A via RRC messages without UE context) to support improved store-and-forward techniques.

[0238] In particular, efficient “store-and-forward” data transmission is made possible by one or more enhancements to the MT / MO data transmission procedure in the “store-and-forward” mode cell 9 (e.g., as described with reference to Figure 5 and Figure 6 These enhancements are described in more detail later with reference to control plane CIoT EPS optimization, but can be adapted as appropriate based on CIoT 5GS optimization (or similar optimization).

[0239] In summary, possible enhancements include:

[0240] In summary, possible enhancements include:

[0241] Introduction of a list of allowed UEs and / or associated information / context maintained at the base station 5A;

[0242] Enhanced cell access control in the “store-and-forward” mode cell based on a new information element in system information;

[0243] Paging enhancements including introduction of a new paging trigger at the MME 11 (or AMF for 5GS) and redefined handling of paging information / messages at the base station 5A;

[0244] Enhancements to the RRC Connection Setup procedure to confirm / indicate that the RRC Connection Setup procedure is used for data / signalling transfer according to the "store and forward" framework;

[0245] Introduction of the capability to include multiple (DL / UL) "NAS PDU" transfers in a single S1-AP (or NG-AP for 5GS) transport message;

[0246] Introduction of the capability to include, by the S1-AP (or NG-AP for 5GS), for each of multiple downlink NAS PDUs, a respective downlink NAS PDU forwarding status after reconnection to the MME (or AMF for 5GS);

[0247] Enhancements to the S1 setup procedure including the introduction of a new indicator in the S1 setup procedure to support interworking between base station 5A and core network 7; and / or

[0248] Enhancements to the interaction between the Access Stratum (AS) and Non-Access Stratum (NAS) layers of the UE 3.

[0249] It will be appreciated that any of these enhancements can potentially be introduced individually, without necessarily introducing all or any other enhancements, to provide the benefits in terms of "store and forward" data transfer.

[0250] It will be appreciated that the use of the CP CIoT based data "store and forward" enhancements described herein beneficially has the potential to allow for the transfer of small amounts of data without the UE context and to support inter-base station mobility relatively easily, with minimal impact on existing procedures.

[0251] <Store and forward data transfer - overview>

[0252] Reference will now be made to Figure 9 and Figure 10 A possible CP CIoT optimised store and forward data transfer procedure is described by way of example only.

[0253] In Figure 9 and Figure 10 It will be appreciated that the EDT can potentially be used with the CP CIoT based approach (in a similar manner to that described with reference to Figure 5 and Figure 6 However, for simplicity, the EDT has not been included in the message flows.

[0254] <Service link available / Feeder link unavailable>

[0255] Figure 9is a simplified sequence diagram illustrating a CP CIoT optimized data transfer procedure between base stations 5A of the NTN RAN 5 that can be used in the communications system 1 when the service link is available but the feeding link is not.

[0256] In Figure 9 , the procedure generally follows the relevant parts of the procedures illustrated in Figure 5 (for MO cases) and Figure 6 (for MT cases), and the general description related to the corresponding steps of these procedures also applies here.

[0257] In Figure 9 , the base station 5A stores / maintains a respective UE specific buffer / data area 930 for each UE 3 that the base station 5A is serving (and possibly has an associated UE capability, is in the allowed list and / or fulfils some other criteria). The UE specific buffer / data area 930 comprises a set of data type specific (sub-) buffers / data areas 932, 934 and 936. In this example, the data type specific (sub-) buffers / data areas 932, 934 and 936 comprise: 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. However, it will be appreciated that the UE specific buffer / data area 930 can be configured to store different sets of information depending on the requirements. Furthermore, the UE specific buffer / data area 930 can be configured to additionally / alternatively store other data / information types, e.g. UE context information, etc. It will also be appreciated that although the UE specific buffer 930 is described as being “logically” divided into different (sub-) buffers for the sake of clarity, in an implemented system, this division into (sub-) buffers can not be immediately apparent, although the same types of information are still stored.

[0258] In Figure 9 , at the start of the procedure, it is assumed that the downlink data buffer 936 for the UE 3 is not empty, as indicated at S920 (e.g. because the base station 5A has received downlink data for the UE 3 encapsulated in one or more NAS PDUs provided from the core network 7 over the feeding link (via the MME 11)).

[0259] When the service link becomes available, for MO cases, the UE 3 initiates an RRC connection to the base station 5A. This typically involves, for example, the procedures described with reference to Figure 4The random access procedure described (e.g. particularly in relation to steps S414 to S420) is analogous to a random access procedure in which the UE 3 transmits a random access preamble (S901), receives a random access response (S902), transmits a connection request (S903), and receives an associated connection setup message (S904). The UE 3 then transmits a message to the base station 5A at S905 indicating that the RRC connection setup has been completed. The UE 3 will use NAS data PDUs to transmit UL data to the base station 5A. The UL NAS data PDUs can be included, for example, in the connection setup complete message transmitted at S905, and / or in one or more UL information transfer messages (as seen at S907). In Figure 9 In the example, the base station 5A buffers each received UL NAS data PDU in the UL data buffer 932 of the base station 5A without triggering a procedure towards the core network 7 (e.g. without triggering an S1-AP procedure in this 4G / EPS example). The base station 5A can also forward any stored downlink data from the downlink data buffer 936 (in this example, it is assumed that some downlink data has been stored previously). The downlink data is stored as one or more DL NAS data PDUs, and is forwarded using one or more DL information transfer messages (as seen at S906).

[0260] When there is no more data to be transmitted or received by the base station 5A, the base station 5A can initiate release of the RRC connection as seen at S908. This can be triggered, for example, if the UL / DL buffers are empty, there is no NAS PDU activity for a period of time, and the base station 5A detects inactivity and initiates a release procedure (in a similar manner to S515 in Figure 5 in the S515, although in this case an S1 release can not be required).

[0261] The procedure is similar when the serving link becomes available for the MT case. However, for MT data transfer, in addition to one or more downlink NAS data PDUs previously received from the MME 11 having been buffered in the downlink data buffer 936 of the base station 5A, the base station 5A also stores corresponding paging information in the paging storage area 934. The base station 5A uses this paging information in order to page the UE 3 at S900, for example at a time when the base station 5A has predicted that the UE 3 will be in coverage but the UE 3 is not connected.

[0262] In response to the paging at S900, the UE 3 initiates an RRC connection to the base station 5A. This typically involves, for example, the steps described with reference to Figure 4The random access procedure described (e.g. particularly with respect to steps S414 to S420) is analogous to a random access procedure in which the UE 3 transmits a random access preamble (S901), receives a random access response (S902), transmits a connection request (S903), and receives an associated connection setup message (S904). The UE 3 then transmits a message to the base station 5A at S905 indicating that the RRC connection setup has been completed. For this MT case (assuming that the UE 3 has no UL data to transmit), after the RRC connection setup, the base station 5A forwards the buffered downlink NAS data PDU(s) to the UE 3 using one or more DL information transfer messages (as seen at S906). Of course, the UE 3 can also transmit any uplink NAS data PDU(s) to the base station 5A using the connection setup complete message transmitted at S905 and / or the one or more UL information transfer messages transmitted at S907.

[0263] When there is no more data to be transmitted or received by the base station 5A, the base station 5A can initiate release of the RRC connection as seen at S908. This can be triggered, for example, if the UL / DL buffers are empty, there is no NAS PDU activity for a period of time, and the base station 5A detects inactivity (in the same way as in S514 of Figure 5

[0264] <Feeding link available / serving link not available>

[0265] Figure 10 is a simplified sequence diagram illustrating a CIoT optimized data transfer procedure between the NTN RAN 5 and the core network 7 that can be used in the communication system 1 when the feeding link is available but the serving link is not.

[0266] In Figure 10 , the procedure generally follows the relevant parts of the procedures illustrated in Figure 5 (for the MO case) and Figure 6 (for the MT case), and the general description of the corresponding steps related to the procedures applies here as well. It will be understood that the procedures of Figure 9 and Figure 10 are not mutually exclusive and can be used in combination with each other in the communication system 1 depending on the serving link / feeding link conditions.

[0267] In Figure 10 , the base station 5A stores / maintains reference Figure 9 ​The respective UE-specific buffer / data area 930 is described. In particular, the UE-specific buffer / data area 930 comprises: 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. However, it will be appreciated that the UE-specific buffer / data area 930 can be configured to store different sets of information depending on requirements. Furthermore, the UE-specific buffer / data area 930 can be configured to additionally / alternatively store other data / information types, such as UE context information, etc. It will also be appreciated that, although the UE-specific buffer 930 is described as being "logically" divided into different (sub-)buffers for clarity, in an implemented system, such division into (sub-)buffers can not be immediately apparent, although the same types of information are still stored.

[0268] In Figure 10 At the start of the procedure, as seen at S1000, the UE 3 is in idle mode / state (in this example, the EPS Connection Management (ECM) or "ECM-IDLE" mode / state, in which the UE 3 does not have a signalling connection to the MME 11).

[0269] When the feeding link becomes available, for the MO case, the procedure generally follows from S1004 to S1012 (which is similar but not identical to the procedure described with reference to Figure 5 from step S502 to step S515).

[0270] Assuming that there is UL data for the UE 3 in the UL data buffer 932 of the base station 5A, the base station 5A sends an S1-AP Initial UE Message to the MME 11 at S1004 (e.g. corresponding to step S502 of Figure 5 ), and initiates the logical S1 connection setup for the UE association as part of the procedure. As shown, the UL NAS data PDU from the UL data buffer 932 can be included in the Initial UE Message.

[0271] At S1005, the MME 11 checks the integrity of the incoming NAS PDU and decrypts the data contained by the NAS PDU. At S1006, the MME 11 can coordinate with the S-GW 13 (and indirectly with the P-GW 15) to perform a modify bearer procedure (e.g. following the general modify bearer procedure described with reference to steps S504 to S507 of Figure 5 ), if required, with the MME 11, S-GW 13 and P-GW 15.

[0272] Thus, the UL data can be forwarded at S1020 to the S-GW 13 (e.g. as described with reference to step S508 of Figure 5 .

[0273] If there is incoming data from the S-GW 13 in the downlink at the same time (as indicated at S1021), the MME 11 can also beneficially send the data to the base station 5A (as indicated at S1008) for storage in the downlink data buffer 936 (possibly after any necessary ciphering and integrity protection of the DL data as indicated at S1007). Any downlink data sent at S1008 can be encapsulated in NAS PDUs and sent to the base station 5A in one or more DL NAS transport messages (e.g. in one or more S1-AP downlink NAS transport messages) (e.g. as described with reference to step S511 of Figure 5 . The MME 11 can also send appropriate paging information to the base station 5A (as indicated at S1003a) for storage in the paging buffer 932 for potential later use in paging the UE 3 (i.e. when the UE 3 is in or expected to be in coverage). This paging information can be sent at the same time as the downlink data (but can be sent before or after).

[0274] Any further uplink data in the UL data buffer can beneficially be sent by the base station 5A to the MME 11 (as indicated at S1009) in one or more UL NAS transport messages (e.g. in one or more S1-AP uplink NAS transport messages) for forwarding to the S-GW 13. This UL communication can occur in parallel with the communication of any DL data described above (but can occur before or after).

[0275] When there is no more data to be transmitted or received by the base station 5A, the base station 5A can initiate an S1 release procedure, e.g. by sending an S1-AP UE context release request as seen at S1010. This can be triggered, for example, if the UL / DL buffers are empty, there is no NAS PDU activity for a period of time, and the base station 5A detects inactivity (in a similar manner to S514 of Figure 5 . The S1 release procedure can proceed, for example, with the MME 11 sending an S1-AP UE context release command to the base station 5A at S1011, and the base station 5A responding with an S1-AP UE context release complete message to indicate that the S1 release is complete.

[0276] When the feeder link becomes available, for the MT case, the procedure generally follows that described with reference to Figure 6The described procedure is similar but not identical to the procedure.

[0277] At S1001, the S-GW 13 that has received DL data packets for the UE 3 from the P-GW 15 (e.g. as described for step S601 of the procedure of Figure 6 ) can send a downlink data notification message to the MME 11 for which the S-GW 13 has control plane connectivity for the given UE 3 (e.g. as described for step S602a of the procedure of Figure 6 ). Although not shown, the MME 11 can respond to the S-GW 13 with a downlink data notification acknowledgement message (e.g. as described for step S602b of the procedure of Figure 6 ).

[0278] At S1002, the MME 11 determines in which base station 5A the UE 3 will (next) be in coverage. Then, at S1003, the MME 11 sends the associated paging information to the base station 5A. It will be understood that this paging does not trigger a paging over the air (Uu) interface in the normal way. Instead, this triggers the base station 5A to initiate the establishment of the UE-associated logical connection by sending an initial UE message via the S1-AP (as seen at S1004). The base station 5A also stores the paging information received from the MME 11 in the paging buffer 932 for potential later use to page the UE 3 for downlink data forwarding over the air interface / service link when available.

[0279] If there is UL data for the UE 3 in the UL data buffer 932 of the base station 5A, the base station 5A can include the associated UL NAS data PDU in the initial UE message sent at S1004.

[0280] At S1005, the MME 11 checks the integrity of any incoming UL NAS data PDU and decrypts the data contained by the UL NAS data PDU. At S1006, the MME 11 can coordinate with the S-GW 13 (and indirectly with the P-GW 15) to perform a modify bearer procedure (e.g. following the general modify bearer procedure described for steps S607 to S610 of the procedure of Figure 6 ) with the MME 11, S-GW 13 and P-GW 15 if required. Thus, any UL data can be forwarded to the S-GW 13 at S1020.

[0281] Any incoming data from the S-GW 13 in the downlink can be sent by the MME 11 to the base station 5A (as indicated at S1008) for storage in the downlink data buffer 936 (possibly after any necessary ciphering and integrity protection of the DL data as indicated at S1007). Any downlink data sent at S1008 can be encapsulated in NAS PDUs and sent to the base station 5A in one or more DL NAS transport messages (e.g. in one or more S1-AP downlink NAS transport messages), for example as described with reference to steps S613 in Figure 6

[0282] Any further uplink data in the UL data buffer can beneficially be sent by the base station 5A to the MME 11 (as indicated at S1009) in one or more UL NAS transport messages (e.g. in one or more S1-AP uplink NAS transport messages) for forwarding to the S-GW 13. This UL communication can occur in parallel with (but can occur before or after) the communication of any DL data described above.

[0283] When there is no more data to be transmitted or received by the base station 5A, the base station 5A can initiate an S1 release procedure, for example by sending an S1-AP UE context release request as seen at S1010. This can be triggered, for example, if the UL / DL buffers are empty, there is no NAS PDU activity for a period of time, and the base station 5A detects inactivity (in a similar manner to S620 in Figure 6 The S1 release procedure can proceed, for example, with the MME 11 sending an S1-AP UE context release command to the base station 5A at S1011, and the base station 5A responding with an S1-AP UE context release complete message to indicate that the S1 release is complete.

[0284] <Allowed UE list and associated information / context>

[0285] As described above, the allowed UE list and / or associated information / context for each UE 3 can also be maintained at the base station 5A (for example, during a similar procedure to that described with reference to Figure 9 and / or Figure 10

[0286] This contrasts with existing communication systems in which the UE context is not available (or considered unnecessary) at the base station 5A when the corresponding UE 3 is in RRC idle mode, and the UE 3 is able to establish an RRC connection and simultaneously transmit at least one NAS data PDU to the base station 5A.

[0287] ​​However, for a "store-and-forward" scenario, the RRC connection and the logical S1 connection associated with the UE will not exist at the same time, and thus the base station 5A cannot obtain the necessary UE information from the MME 11 when the UE 3 becomes RRC connected (e.g. for the purpose of access admission, determining a suitable RRC configuration, performing data rate control and / or the like).

[0288] Thus, in one beneficial example, the base station 5A is configured to store / maintain a list of allowed UEs 3, and for each allowed UE, to store / maintain information indicating one or more of: a UE identity (e.g. a Serving Temporary Mobile Subscriber Identity (S-TMSI)); one or more UE level QoS parameters (e.g. a maximum data rate and / or a number of NAS PDUs); a priority; a basic capability; and / or paging information.

[0289] The base station 5A will store this UE information for each UE 3 in the list of allowed UEs for later use, even if the corresponding UE 3 is in RRC idle mode. The stored information can be used, for example, for one or more of: making access admission; prioritizing and / or deprioritizing RRC connection requests, paging and / or data transmissions for the UE; controlling the maximum amount of data that can be transmitted to / from the base station 5A and / or stored at the base station 5A for a certain UE 3; and / or calculating paging occasions.

[0290] It will be appreciated that the base station 5A can alternatively or additionally maintain a list of not allowed UEs accordingly.

[0291] To obtain this information, the MME 11 can compile a list of access / service allowed UEs 3 based on: historical information; Operation, Monitoring and Administration (OAM) information; registration data; predictions; and / or UEs 3 storing downlink data in base station and / or MME buffers. The MME 11 can then send this list of allowed UEs 3, together with the identification information of the UEs 3 (and possibly further information), to the base station 5A, regardless of the RRC state of the listed UEs 3.

[0292] Alternatively or additionally, some or all of this information can be obtained via a dedicated, UE triggered "store-and-forward" access request procedure as follows:

[0293] 1. The UE 3 initially initiates an RRC connection to a "store-and- forward" mode cell;

[0294] 2. If the UE 3 is not in the stored list of access allowed UEs at the base station 5A, then the base station 5A can: a) release / reject the UE connection request and inform the UE 3 that the base station 5A is "waiting for identification / authentication for more data store and forward"; and / or b) allow a limited amount of NAS PDU transmission from the UE 3;

[0295] 3. When the feeder link becomes available, the base station 5A requests the core network 7 to authorize whether the UE 3 is allowed / authorized to use the store and forward service (e.g. via the MME 11);

[0296] 4. If the UE 3 is allowed / authorized, the core network 7 responds with further necessary UE information; and

[0297] 5. If the UE 3 is authorized / allowed by the core network 7, the base station 5A adds the UE 3 (associated with any corresponding information obtained in the procedure) to the list of access allowed UEs.

[0298] After this procedure, the UE 3 is thus able to access the "store and forward" cell for data transmission service when the UE 3 is in coverage.

[0299] It will be appreciated that the UE 3 can also optionally maintain a list of base stations 5A and / or cells 9 (e.g. which the UE 3 has previously accessed) with "store and forward" mode, and prioritize these cells 9 for future data transmission.

[0300] <CELL ACCESS CONTROL>

[0301] As mentioned above, the communication system 1 can implement enhanced cell access control in "store and forward" mode cells based on a new information element provided in the system information in that cell 9. This will now be described in more detail by way of example only.

[0302] In more detail, a base station 5A operating a cell in "store and forward" mode can be configured to: bar (cannot use / support store and forward data transmission) legacy UEs 3; allow UEs 3 supporting store and forward data transmission to camp on and / or access the "store and forward" mode cell; and / or not allow (non-legacy) UEs 3 which cannot store and forward transmissions to camp on and / or access the "store and forward" mode cell.

[0303] To implement this, a new "store-forward mode" (or similar) indicator is introduced into the system information (e.g. System Information Block Type 1 (SIB1) or similar) broadcast in the "store and forward" mode cell, and a "legacy barring bit" is set in the system information to indicate barring.

[0304] As a result, any legacy UE 3 will be barred from accessing the cell 9. Non-legacy UEs 3 that support and wish to use the "store and forward" feature will ignore the legacy barring bit, but will check the "store-and-forward" indicator to determine whether to camp on and / or initiate access to the particular cell 9.

[0305] In the event that the feeder link connection becomes temporarily available in a cell 9 that has "store and forward" capability (in which the "store-and-forward mode" indicator is currently set to indicate that the cell is operating in "store-and-forward mode" (e.g. set to "true" or "1")), the base station 5A can be configured to set the "store-and-forward mode" indicator to indicate that the cell 9 is not operating in "store-and-forward mode" (e.g. set to "false" or "1").

[0306] However, it will be appreciated that, alternatively, the "store-and-forward mode" indicator can be maintained to indicate that the cell 9 is operating in "store-and-forward mode" (e.g. left as "true" or "1"). In this case, the base station 5A can broadcast the time (or time window) for which the feeder link will be temporarily available to inform the UEs 3 when / how long the feeder link will be available. The base station 5A can indicate the time (time window) for which the feeder link will be available in system information (e.g. SIB1), for example the base station 5A can indicate the time window (T0 to T1) before or when the feeder link connection becomes available. It will be appreciated that the base station 5A can also indicate a list of times / time windows (e.g. multiple [T0-T1] indications) to indicate multiple times / time windows for which the feeder link connection will be available.

[0307] <page>

[0308] As mentioned above, the communication system 1 can implement one or more paging enhancements. A number of possible paging enhancements will now be described in more detail by way of example only.

[0309] Conventionally, a page is initiated by the MME 11 (or equivalent node), for example upon receiving a data notification or data being buffered in the MME 11 (or equivalent node). The page is received at the base station 5A and the base station 5A transmits the page over the air interface. The page triggers the UE 3 to initiate establishment of an RRC connection and subsequently an S1-AP connection. The MT data can then be transferred to the UE 3.

[0310] Beneficially, for "store and forward" mode cells, the base station 5A of the communication system 1 (rather than the MME 11) initiates a page to the UE 3 when there is stored downlink data for that UE 3 at the base station 5A.

[0311] To support this, the MME 11 provides paging related information to the base station 5A (e.g. as described with reference to Figure 9 and Figure 10 ). This paging information can include, for example, identity and discontinuous reception (DRX) for paging occasion calculation. This paging information is stored at the base station 5A (e.g. in the paging storage area 934) so that the base station 5A can initiate a page to the UE 3 at the appropriate time.

[0312] There are a number of different ways in which the paging related information can be informed to the base station 5A. For example, the paging related information can be provided as part of the UE context stored at the base station 5A (e.g. as described above in the section entitled "Allowed UE list and associated information / context").

[0313] Alternatively or additionally, the paging related information can be provided as part of a regular paging message sent over the S1-AP interface when, for example, downlink data / data notification is received at the MME 11 and the feeder link has become available to the base station 5A for "store and forward" data transmission (e.g. as described with reference to Figure 10 ). The "paging" message can be sent to the base station 5A and this can be followed by an "S1-AP" UE initial message (e.g. as described with reference to Figure 10 steps S1003 and S1004 in

[0314] Alternatively or additionally, a "paging message over S1-AP" can be triggered when any downlink data is available to be sent to the base station 5A for store and forward data transmission. This paging message over S1-AP can be sent from the MME 11 together with or after the downlink data to be transmitted to the base station 5A for store and forward (e.g. as described with reference to steps S1003a and S1008 in Figure 10 ).

[0315] <RRC connection setup procedure>

[0316] As described above, the communication system 1 can implement an enhanced RRC connection setup procedure in which an indication is sent to the base station 5A to confirm / indicate that the RRC connection setup procedure (e.g. as described with reference to Figure 9 ) is for data / signalling transmission according to the "store and forward" framework.

[0317] In particular, the indication can be included in the RRC Connection Setup Complete message sent by the UE 3 at the end of the RRC connection setup to confirm / indicate that the RRC connection is for data / signalling transmission according to the "store-and-forward" framework (i.e. for store-and-forward data transmission).

[0318] For illustration purposes only, an Abstract Syntax Notation One (ASN.1) description is provided below on how this indication can be introduced in the RRC Connection Setup Complete message:

[0319] (Regular information elements)

[0320] attachWithoutPDN-Connectivity-r13 with enumerated values {TRUE}

[0321] Optional,

[0322] up-CIoT-EPS-Optimisation-r13 with enumerated values {TRUE}

[0323] Optional,

[0324] cp-CIoT-EPS-Optimisation-r13 with enumerated values {TRUE}

[0325] Optional,

[0326] ...

[0327] (New information element)

[0328] attachWithoutPDN-ConnectivityNTN-r1x with enumerated values {TRUE}

[0329] Optional,

[0330] up-CIoT-EPS-OptimisationNTN-r1x with enumerated values {TRUE}

[0331] Optional,

[0332] <Multiple NAS PDU over S1-AP>

[0333] As mentioned above, the communication system 1 can implement the capability of including multiple (DL / UL) "NAS PDU" transmissions in a single S1-AP (or NG-AP for 5GS) transport message.

[0334] In particular, in the previous communication system, the messages that can be used for NAS PDU transmission (including the initial UE message, the UL NAS transport message and the DL NAS transport message) can include only a single NAS data PDU.

[0335] However, in this example using store-and-forward data transfer techniques, it is possible that multiple accumulated NAS data PDUs are stored at the base station 5A for transmission in the uplink over the S1 -AP interface, or at the MME 11 for transmission in the downlink over the S1 -AP interface.

[0336] Accordingly, to support efficient communication of these NAS data PDUs over the S1 -AP interface, in this example enhancement the base station 5A and the MME 11 are able to encapsulate more than one NAS data PDU in each of the different S1 -AP messages (e.g. Initial UE Message, UL NAS Transport Message and / or DL NAS Transport Message) that the base station 5A / MME 11 is able to send that can be used for NAS PDU transmission.

[0337] <Multiple NAS PDU Delivery Status Reporting>

[0338] As described above, after reconnection to the MME 11 (or AMF for 5GS), the communications system 1 can implement the ability to include, over the S1 -AP (or NG-AP for 5GS), for each of multiple downlink NAS PDUs, a respective downlink NAS PDU forwarding status.

[0339] In particular, the base station 5A is configured to provide delivery indication messages (e.g. in the DL NAS Transport Message as previously described and in particular with reference to Figure 9 and Figure 10 These messages include:

[0340] NAS Non-Delivery Indication Message:

[0341] This message is sent by the base station 5A and is used to report non-delivery of a NAS PDU previously received over the S1 interface within a downlink NAS Transport Message.

[0342] NAS Delivery Indication Message:

[0343] This message is sent by the base station 5A and is used to report successful delivery of a NAS PDU previously received within a downlink NAS Transport Message to the UE 3.

[0344] In early communication system 1, these messages can only be used to indicate whether a previously received NAS PDU has been delivered or not. However, in a "store-and-forward" scenario, it is not possible to indicate the delivery status of a downlink NAS PDU over the Uu interface immediately after its reception from the MME 1 1. Furthermore, in the context of store-and-forward data transmission, it is inefficient to indicate only the delivery status of a single NAS PDU.

[0345] Accordingly, in this example enhancement, the base station 5A is configured to be able to transmit a dedicated S1 -AP message (e.g. a "Downlink NAS Forwarding Status Report" message or similar) for reporting the forwarding (delivery) status of multiple downlink NAS PDUs.

[0346] This message can comprise, for example, each NAS PDU (of one or more NAS PDUs) that was not successfully delivered (it will be understood that, implicitly, this means that the NAS PDUs not included were successfully forwarded to the UE 3).

[0347] However, it will be understood that, when the NAS PDUs are transmitted to the base station 5A, the NAS PDUs can be indexed by the MME 1 1, and the base station 5A can explicitly indicate which PDUs were successfully forwarded and / or which PDUs were not successfully forwarded. Here, it will be understood that the message indicates this information in any suitable way, for example: by including a list of the indices of the PDUs that were successfully and / or unsuccessfully forwarded; by means of a bitmap having bits representing each of the corresponding PDUs (e.g. "1 " indicates successful forwarding, and "0" indicates unsuccessful forwarding, or vice versa); or in some other way.

[0348] It will be understood that, alternatively or additionally, the S1 -AP NAS Non-Delivery Indication message and the NAS Delivery Indication message can be enhanced to allow the indication to the MME 1 1 of the forwarding status of one or more downlink NAS PDUs received from the MME 1 1 when the feeder link was previously available.

[0349] <Example Implementation>

[0350] Reference will now be made to Figure 11 An example implementation involving some of the above enhancements is described by way of example only, Figure 11 is a simplified sequence diagram illustrating Figure 9 and Figure 10 how parts of the procedures shown in

[0351] In particular, as Figure 10 is described in Figure 11In the middle, base station 5A stores / maintains references for each UE that it is serving (and may have associated UE capabilities, is on the allowed list, and / or meets some other criteria). Figure 9 The corresponding UE-specific buffer / data area 930 is described. 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. However, Figure 11 Example of how a UE-specific buffer / data area 930 can (optionally) also store “offline” UE context information 938.

[0352] like Figure 10 In that way, Figure 11 As seen in S1100, at the start of the process, UE 3 is in idle mode / state (in this example, EPS Connection Management (ECM) or “ECM-IDLE” mode / state, in which UE 3 does not have a signaling connection to MME 11).

[0353] Will understand, in Figure 11 In box (A), the power supply link is available, the service link is unavailable, and it can follow... Figure 10 The general process described above. However, as described in the section titled "Multiple NAS PDUs via S1-AP", when an uplink NAS data PDU is forwarded to MME 11 via the S1-AP interface, if there is more than one such NAS PDU in the uplink data buffer 932, multiple NAS data PDUs can be forwarded in a single S1-AP message (e.g., as a list of UL NAS data PDUs) (as seen at S1102). Similarly, when a downlink NAS data PDU is forwarded to base station 5A via the S1-AP interface, if more than one such NAS PDU needs to be forwarded, multiple NAS data PDUs can be forwarded in a single S1-AP message (e.g., as a list of DL NAS data PDUs) (as seen at S1104).

[0354] When there is no more data to be transmitted or received by base station 5A, the UE context release procedure can be performed through the S1-AP interface (e.g., as referenced). Figure 10 (As described in S1010 to S1012).

[0355] exist Figure 11In block (B) of FIG. 1, when the feeder link is unavailable but the service link is available, the base station 5A can page the UE 3 (e.g., based on the paging information 934 stored in the UE buffer 930, as described above in the section entitled "Paging") to attempt to cause the UE 3 to initiate an RRC connection for receiving downlink NAS data PDUs (e.g., as described above with reference to FIG. 2) stored in the downlink data buffer 936. These downlink NAS data PDUs can be successfully forwarded, or can not be successfully forwarded. Figure 9

[0356] In block (C) of FIG. 1, when the feeder link becomes available again and the service link is unavailable, the base station 5A can report the forwarding (delivery) status of the plurality of downlink NAS PDUs (e.g., in a downlink NAS PDU forwarding status report), for example, as described above in the section entitled "Multiple NAS PDU Delivery Status Report." Figure 11

[0357] <S1 Setup Procedure>

[0358] As described above, the communication system 1 can implement an enhancement to the S1 Setup procedure. The purpose of the S1 Setup procedure is to exchange application level data required for the base station 5A and the MME 11 to correctly interoperate on the S1 interface. The S1 procedure is the first S1-AP procedure triggered after the Transport Network Layer (TNL) association has become operational. This procedure uses non-UE-associated signaling.

[0359] In more detail, in this exemplary enhancement, the base station 5A and the MME 11 are configured for each other for an enhanced S1 Setup procedure, for example, for use after the feeder link becomes available but before any UE-associated signaling occurs. In particular, to ensure support for multi-vendor networks (RAN 5 and core network 7), the enhanced S1 Setup procedure allows for inclusion of an indication of network capability / support for store-and-forward data transfer in at least one of the messages used during the S1 Setup procedure.

[0360] This will now be described in more detail by way of example only with reference to Figure 12 This will now be described in more detail by way of example only with reference to Figure 12 is a simplified sequence diagram illustrating the S1 Setup procedure.

[0361] ​​As seen at S1200, in one option, the S1 setup request includes an information element to indicate capability / support for store-and-forward data transmission. For example, the information element can indicate support for "store-and-forward mode", "intermittent feeder link", "intermittent NTN connection", "non-continuous S1 connection for NTN", and / or the like. The information element can be an enumerated type indicating, e.g., "true" or "false" for capability / support. If the feature is supported at the MME 11, the MME 11 can respond with a normal S1 setup response message (as seen at S1202a). If the feature is not supported at the MME 11, the MME 11 can respond with a S1 setup failure message (as seen at S1202b).

[0362] As seen at S1210, in another option, a normal S1 setup request is sent, and the MME 11 can respond with a S1 setup response message (as seen at S1212) that includes an information element to indicate capability / support for store-and-forward data transmission. For example, the information element can indicate support for "store-and-forward mode", "intermittent feeder link", "intermittent NTN connection", "non-continuous S1 connection for NTN", and / or the like. The information element can be an enumerated type indicating, e.g., "true" or "false" for capability / support.

[0363] <UE AS / NAS interaction>

[0364] As noted above, the communication system 1 can implement enhancements to the interaction between the access stratum (AS) and non-access stratum (NAS) layers of the UE 3.

[0365] 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 idle mode / state (e.g., ECM-idle). To facilitate this, the RRC release message can include an appropriate cause value (e.g., nas-Release, s1-Release, ntn-NoS1-Connection, ntn-FeederlinkNotAvailable, and / or the like). 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 locally terminates the procedure (and enters ECM-idle).

[0366] Alternatively or additionally, in another option, when the UE 3 receives the RRC release message from the base station 5A, the UE's NAS layer can remain in connected mode / state (e.g. ECM-Connected). To facilitate this, the RRC release message can include an appropriate cause value (e.g. pendingNas-ConnectionRelease, pendingS1-Release, ntn-NoS1-Connection, ntn-FeederlinkNotAvailable and / or similar). The UE's AS layer forwards this RRC release cause to the UE's NAS layer. In response, the UE's NAS layer remains in ECM-Connected (rather than going into ECM-IDLE). Thereafter, the UE's NAS layer can locally terminate the procedure (and go into ECM-IDLE) upon expiry of a timer. Alternatively or additionally, the MME 11 can send the necessary information for S1 release (via the base station 5A) to the UE's NAS layer and the UE's NAS layer can then go into ECM-IDLE.

[0367] <user equipment>

[0368] Figure 13 is a simplified block schematic diagram of the main components of a UE 3 exemplifying a UE for implementation in a system for Figure 3

[0369] As shown, the UE 3 has transceiver circuitry 31 which is operable to transmit signals to and to receive signals from the base station 5A via one or more air interfaces 33 (e.g. comprising one or more antenna elements). The UE 3 has a controller 37 to control the operation of the UE 3. The controller 37 is associated with a memory 39 and is coupled to the transceiver circuitry 31. Although not necessarily required for the operation of the UE 3, the UE 3 can of course have all the usual functionality of a conventional UE 3 (e.g. a user interface 35 such as a touchscreen / keypad / microphone / speaker and / or similar for allowing direct control by and interaction with a user) and this can be provided by any one or any combination of hardware, software and firmware as appropriate. For example, software can be pre-installed in the memory 39 and / or can be downloaded via the communications system 1 or from a removable data storage device (RMD).

[0370] The controller 37 is configured to control the overall operation of the UE 3 in this example by program or software instructions stored within the memory 39. As shown, these software instructions include an operating system 41 and a communications control module 43 amongst others.

[0371] ​The communication control module 43 is operable to control communications between the UE 3 and its serving base station 5A or base station 5A (and other communication devices connected to the base station 5A, such as other UEs 3 and / or core network nodes, etc.). The communication control module 43 is configured for overall handling of uplink communications (including both dynamic and semi-static signaling (e.g., SRS)) via associated uplink channels (e.g., via a physical uplink control channel (PUCCH), random access channel (RACH), and / or physical uplink shared channel (PUSCH)). The communication control module 43 is also configured for overall handling of reception of downlink communications (including both dynamic and semi-persistent scheduling (e.g., SPS)) via associated downlink channels (e.g., via a physical downlink control channel (PDCCH) and / or DCI of a physical downlink shared channel (PDSCH)). The communication control module 43 is responsible for, for example: determining where to monitor for downlink control information; determining resources (including interleaved resources and resources subject to frequency hopping) to be used by the UE 3 for transmission / reception of UL / DL communications; managing frequency hopping on the UE 3 side; determining how to configure time slots / symbols (e.g., for UL, DL, or full-duplex communications or the like); determining which bandwidth parts are configured for the UE 3; determining how uplink transmissions should be encoded; and the like.

[0372] It will be appreciated that the communication control module 43 can comprise a plurality of sub-modules (“layers” or “entities”) to support particular functionality. For example, the communication control module 43 can comprise a PHY sub-module, a MAC sub-module, a RLC sub-module, a PDCP sub-module, a RRC sub-module, and / or the like.

[0373] The communication control module 43 is particularly configured to control communications of the UE in accordance with any of the methods described herein.

[0374] <base station>

[0375] Figure 14 is a simplified block schematic diagram of the main components of a base station 5A as exemplifying a base station implemented in a system for Figure 3 is a simplified block schematic diagram of the main components of a base station 5A as exemplifying a base station implemented in a system for

[0376] As shown, the base station 5A has transceiver circuitry 51 for transmitting and receiving signals to and from communication devices such as the UE 3 via one or more air interfaces 53 (e.g. single-panel or multi-panel antenna arrays / massive antennas); and a core network interface 55 for transmitting and receiving signals to and from network nodes in the core network 7. Although not shown, the base station 5A can also be coupled to other base stations 5A via appropriate interfaces (e.g. the so-called “X2” interface in LTE or the so-called “Xn” interface in NR). The base station 5A has a controller 57 to control the operation of the base station 5A. The controller 57 is associated with a memory 59. For example, software can be pre-installed in the memory 59 and / or can be downloaded via the communication system 1 or from a removable data storage device (RMD). The controller 57 is configured to control the overall operation of the base station 5A, in this example by program or software instructions stored within the memory 59.

[0377] As shown, these software instructions include an operating system 61 and a communication control module 63 among other things.

[0378] The communication control module 63 is operable to control communications between the base station 5A and the UE 3 and other network entities (e.g. core network nodes) with which the base station 5A communicates. The communication control module 63 is configured for overall control of the reception and decoding of uplink communications (including both dynamic and semi-static signaling (e.g. SRS)) via associated uplink channels (e.g. via the physical uplink control channel (PUCCH), random access channel (RACH) and / or physical uplink shared channel (PUSCH)). The communication control module 63 is also configured for overall control of the transmission of downlink communications (including both dynamic and semi-persistent scheduling (e.g. SPS)) via associated downlink channels (e.g. via the physical downlink control channel (PDCCH) and / or physical downlink shared channel (PDSCH)). The communication control module 63 is responsible for, for example: determining where to configure the UE 3 to monitor for downlink control information (e.g. locations of search spaces, CORESETs and associated PDCCH candidates to monitor); determining resources (including interleaved resources and resources subject to frequency hopping) to be scheduled for UE 3 transmissions / receptions for UL / DL communications; managing frequency hopping at the base station 5A side; appropriately configuring time slots / symbols (e.g. for UL, DL or full-duplex communications or similar); configuring bandwidth parts for the UE 3; providing relevant configuration signaling to the UE 3; and similar.

[0379] It will be appreciated that the communication control module 63 can comprise a plurality of sub-modules (“layers” or “entities”) to support particular functionality. For example, the communication control module 63 can comprise a PHY sub-module, a MAC sub-module, a RLC sub-module, a PDCP sub-module, a RRC sub-module, and so on, for communicating with the UE 3. Furthermore, the communication control module 63 can comprise an S1 Application Protocol (S1-AP) sub-module, a Stream Control Transmission Protocol (SCTP) sub-module, an IP sub-module, a Layer 1 (L1) sub-module, a Layer 2 (L2) sub-module, and so on (or corresponding sub-modules for communicating with an AMF), for communicating with core network entities such as the MME 11 (or similar nodes such as an AMF).

[0380] The communication control module 63 is particularly configured to control communications of the base station in accordance with any of the methods described herein.

[0381] <Core network node / functionality>

[0382] Figure 15 is a block diagram illustrating the main components of a core network node or functionality such as the MME 11, the S-GW 13, or the P-GW 15 (or functionally similar nodes / functionality of 5G or other cellular technologies such as AMF, CPF, UPF, SMF, and so on).

[0383] As shown, the core network functionality comprises transceiver circuitry 71 operable to transmit and to receive signals to and from other nodes including the UE 3, the base station 5A, and other core network nodes via the network interface 72. The operation of the core network functionality is controlled by a controller 73 in accordance with software stored in a memory 74. The software can be pre-installed in the memory 74 and / or can be downloaded via the communications system 1 or from a removable data storage device (RMD), for example. The software includes an operating system 75 and a communication control module 76, among other things.

[0384] The communication control module 76 is responsible for handling (generating / sending / receiving) signalling between the core network functionality and other nodes such as the UE 3, the base station 5A, and other core network nodes.

[0385] It will be appreciated that the communication control module 76 can comprise a plurality of sub-modules (“layers” or “entities”) to support particular functionality. For example, where the core network node is implemented as the MME 11 (or AMF for 5G), the communication control module 76 can comprise an S1-AP sub-module, an SCTP sub-module, an IP sub-module, an L1 sub-module, an L2 sub-module, and so on (or corresponding sub-modules for an AMF), for communicating with the base station 5A.

[0386] The communication control module 76 is in particular configured to control the communication of the core network node in accordance with any of the methods described herein.

[0387] <Modifications and Alternatives>

[0388] The above describes detailed examples. As will be appreciated by the person of skill in the art, many modifications and alternatives can be made to the above examples while still benefiting from the disclosure embodied in these examples.

[0389] It will be understood that the description of features of the base station 5A (or eNB or gNB), the NTN node and the UE 3 and actions performed by the base station 5A (or eNB or gNB), the NTN node and the UE 3 can equally apply to the base station 5A and the UE 3 communicating in the ground plane only (i.e. as part of a ground RAN 5 not having features such as the NTN RAN 5 of the gateway 5B and the space- or sky-based platform), as well as to the base station 5A communicating via a non-ground plane.

[0390] Furthermore, the description of features of the base station 5A (or eNB or gNB) and actions performed by the base station 5A (or eNB or gNB) equally applies to base stations 5A of the distributed type as well as to base stations of the non-distributed type.

[0391] It will also be understood that, although information elements having specific names have been described, information elements having different names but having similar purposes can be used.

[0392] In the above description, the UE 3 and the base station 5A have been described as having a number of discrete functional components or modules in order to facilitate understanding. While these modules can be provided in this way for certain applications, for example where an existing system has been modified to implement the disclosure, in other applications, for example in systems designed from the ground up with the inventive features in mind, these modules can be built into the whole operating system or code, and so these modules can not be identifiable as discrete entities.

[0393] In the above examples, a number of software modules have been described. As will be appreciated by the person of skill in the art, the software modules can be provided in compiled or un-compiled form and can be supplied to the UE 3 or the base station 5A as a signal over a computer network, or on a recording medium. Further, the functionality performed by part or all of the software modules can be performed using one or more dedicated hardware circuits. However, the use of software modules is preferred because of the advantages of upgradability and flexibility that software offers over hard-wired solutions.

[0394] The controllers can include any suitable form of processing circuitry, including but not limited to, for example: one or more hardware-implemented computer processors; microprocessors; central processing units (CPUs); arithmetic logic units (ALUs); input / output (IO) circuitry; internal memory / cache (program and / or data); processing registers; communication buses (e.g., control, data, and / or address buses); direct memory access (DMA) functionality; hardware- or software-implemented counters, pointers, and / or timers; and / or the like. Various other modifications will be apparent to those skilled in the art, and will not be described in further detail herein.

[0395] A user equipment (or "UE," "mobile station," "mobile device," or "wireless device") in the present disclosure is an entity that connects to a network via a wireless interface.

[0396] It should be noted that the present disclosure is not limited to a dedicated communication device, and can be applied to any device with a communication function as explained in the following paragraphs.

[0397] The terms "user equipment" or "UE" (as the term is used by 3GPP), "mobile station," "mobile device," and "wireless device" are generally intended to be synonymous with one another, and include standalone mobile stations such as terminals, cell phones, smartphones, tablets, cellular loT devices, loT devices, and machinery, etc. It will be understood that the terms "mobile station" and "mobile device" also encompass devices that remain stationary for extended periods of time.

[0398] The UE can be, for example, an apparatus for production or manufacturing and / or an energy-related machine (e.g., an apparatus or machine such as: a boiler; an engine; a turbine; a solar panel; a wind turbine; a hydroelectric generator; a thermal power generator; a nuclear power generator; a battery; a nuclear system and / or related apparatus; a heavy electrical machine; a pump including a vacuum pump; a compressor; a fan; a blower; a hydraulic device; a pneumatic device; a metalworking machine; a robot and / or application system thereof; a tool; an injection molding or die-casting mold; a reel; a conveying device; a lifting device; a material handling device; a textile machine; a sewing machine; a printing and / or related machine; a paper processing machine; a chemical machine; a mining and / or construction machine and / or related apparatus; a machine and / or implement for agriculture, forestry, and / or fisheries; a safety and / or environmental protection device; a tractor; a precision bearing; a chain; a gear; a power transmission device; a lubricating device; a valve; a pipe fitting; and / or an application system of any of the foregoing apparatuses or machines; etc.).

[0399] The UE, for example, can be a transportation device (e.g., a transportation device such as a locomotive vehicle, a motor vehicle, a motorcycle, a bicycle, a train, a bus, a cart, a rickshaw, a ship and other watercraft, an airplane, a rocket, a satellite, a drone, a balloon, etc.).

[0400] The UE, for example, can be an information and communication device (e.g., an information and communication device such as an electronic computer and related devices, a communication and related devices, an electronic component, etc.).

[0401] The UE, for example, can be a refrigerator, a product to which a refrigerator is applied, a device of a trade and / or service industry, a vending machine, a service machine, an office machine or device, a consumer electronic and electronic device (e.g., a consumer electronic device such as an audio device, a video device, a speaker, a radio, a television, a microwave oven, an electric rice cooker, a coffee maker, a dishwasher, a washing machine, a dryer, an electric fan or related devices, a vacuum cleaner, etc.).

[0402] The UE, for example, can be an electrical application system or device (e.g., an electrical application system or device such as an x-ray system, a particle accelerator, a radioisotope device, an acoustic device, an electromagnetic application device, an electronic power application device, etc.).

[0403] The UE, for example, can be an electronic lamp, a luminaire, a measuring instrument, an analyzer, a tester, or a surveying or sensing instrument (e.g., a surveying or sensing instrument such as a smoke alarm, a human alarm sensor, a motion sensor, a wireless tag, etc.), a watch or clock, a laboratory instrument, an optical device, a medical device and / or system, a weapon, a piece of tableware, a hand tool, or the like.

[0404] The UE, for example, can be a personal digital assistant or related device of wireless equipment (such as a wireless card or module designed to be attached to or inserted into another electronic device (e.g., a personal computer, an electrical measuring machine), etc.).

[0405] The UE can be a part of a system or a device that provides applications, services and solutions described below with respect to "Internet of Things (IoT)" using various wired and / or wireless communication technologies.

[0406] Internet of Things devices (or "things") can be equipped with appropriate electronics, software, sensors, network connectivity, and / or the like that make it possible for these devices to collect and exchange data with each other and with other communicating devices. IoT devices can include automated equipment that follows software instructions stored in an internal memory. IoT devices can operate without the need for human supervision or interaction. IoT devices can also remain stationary and / or inactive for extended periods of time. IoT devices can be implemented as part of (generally) stationary equipment. IoT devices can also be embedded in non-stationary equipment (e.g., vehicles) or attached to animals or humans to be monitored / tracked.

[0407] It will be appreciated that IoT technology can be implemented on any communication device that can be connected to a communication network for sending / receiving data, regardless of whether such communication device is controlled by human input or by software instructions stored in a memory.

[0408] It will be appreciated that IoT devices are also sometimes referred to as Machine Type Communication (MTC) devices or Machine-to-Machine (M2M) communication devices. It will be appreciated that a UE can 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 indicate some examples of machine type communication applications.

[0409] Table 1

[0410]

[0411] Furthermore, the above-mentioned UE categories are merely examples of application of the technical ideas and examples described herein. Needless to say, these technical ideas and examples are not limited to the above-mentioned UE and various modifications can be made to this UE.

[0412] Features disclosed in this specification (the term "specification" includes the claims) and / or shown in the drawings can be implemented independently of any other disclosed and / or illustrated features (or in combination with any other disclosed and / or illustrated features) and can be implemented and / or combined in any

[0413] Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

[0414] Although the present disclosure has been described with reference to example embodiments, the present disclosure is not limited to the above described. Various changes that can be understood by those skilled in the art can be made to the configurations and details of the present disclosure within the scope of the present disclosure.

[0415] This application is based on and claims the benefit of priority of United Kingdom Patent Application No. 2311347.5, filed on July 24, 2023, the disclosure of which is incorporated herein in its entirety by reference.

[0416] Any type of non-transitory computer readable medium can be used to store a program and provide the program to a computer device. The non-transitory computer readable medium includes any type of tangible storage medium. Examples of the non-transitory computer readable medium include a magnetic storage medium (such as a floppy diskette, a magnetic tape, a hard disk drive, etc.), an opto-magnetic storage medium (e.g., a magneto-optical disk), a CD-ROM (Read Only Memory), a CD-R, a CD-R / W, and a semiconductor memory (such as a mask ROM, a PROM (Programmable ROM), an EPROM (Erasable PROM), a flash ROM, a RAM (Random Access Memory), etc.). Any type of non-transitory computer readable medium can be used to provide a program to a computer device. Examples of the transitory computer readable medium include an electric signal, an optical signal, and an electromagnetic wave. The transitory computer readable medium can provide a program to a computer device via a wired communication line (such as an electric wire and an optical fiber, etc.) or a wireless communication line.

[0417] For example, all or a part of the example embodiments disclosed above can be described as, but not limited to, the following supplementary notes.

[0418] (Supplementary note 1)

[0419] A method by an access network node in a non-terrestrial network, the method comprising:

[0420] receiving at least one NAS PDU via an available link in case a serving link between the access network node and a user equipment, UE, or a feeder link between the access network node and a gateway in a terrestrial network is not available, without triggering establishment of a connection for another link different from the available link, NAS is an abbreviation for non-access stratum, PDU is an abbreviation for protocol data unit;

[0421] storing the at least one NAS PDU until the other link becomes available; and

[0422] forwarding the at least one NAS PDU via the other link when the other link becomes available.

[0423] (Supplementary note 2)

[0424] The method according to supplementary note 1, wherein,

[0425] The receiving is using control plane CIoT optimization features or early data transmission, EDT.

[0426] (Supplementary note 3)

[0427] According to any of Supplementary notes 1 to 3, wherein

[0428] The forwarding is using control plane CIoT optimization features or early data transmission, EDT.

[0429] (Supplementary note 4)

[0430] According to any of Supplementary notes 1 to 3, further comprising:

[0431] maintaining UE information for at least one UE allowed by a core network coupled with the gateway in case the service link or the feeder link is not available.

[0432] (Supplementary note 5)

[0433] According to Supplementary note 4, wherein

[0434] The UE information comprises at least one of:

[0435] a UE identity;

[0436] at least one quality of service parameter, at least one QoS parameter;

[0437] priority information;

[0438] capability information; and

[0439] paging information.

[0440] (Supplementary note 6)

[0441] According to Supplementary note 4 or 5, wherein

[0442] The UE information is determined based on at least one of:

[0443] historical information,

[0444] operation and management data, OAM data,

[0445] registration data,

[0446] prediction, and

[0447] at least one UE having downlink data in a buffer of the access network node or the core network.

[0448] (Supplementary note 7)

[0449] The method of any one of Supplementary Notes 4 to 6, further comprising:

[0450] receiving the UE information from the core network regardless of a radio resource control, RRC, state of the UE.

[0451] (Supplementary Note 8)

[0452] The method of any one of Supplementary Notes 4 to 6, further comprising:

[0453] receiving, from the UE, a message for establishing a connection to the access network node;

[0454] transmitting, to the core network, a request for authorizing whether the UE can be allowed; and

[0455] receiving the UE information from the core network in a case that the core network has authorized that the UE is allowed.

[0456] (Supplementary Note 9)

[0457] The method of any one of Supplementary Notes 1 to 8, further comprising:

[0458] receiving, via the feeder link, paging information for forwarding at least one NAS PDU to the UE via the service link; and

[0459] paging the UE using the paging information in a case that the service link becomes available.

[0460] (Supplementary Note 10)

[0461] The method of Supplementary Note 9, wherein,

[0462] the paging information is comprised in at least one of:

[0463] a paging message from a core network, and

[0464] UE information from the core network.

[0465] (Supplementary Note 11)

[0466] The method of any one of Supplementary Notes 1 to 10, wherein,

[0467] the at least one NAS PDU is comprised in a signaling message.

[0468] (Supplementary Note 12)

[0469] The method of any one of Supplementary Notes 1 to 11, further comprising:

[0470] transmitting, via the feeder link, a message to the core network informing of a status of at least one NAS PDU received from a core network node during a previous availability of the feeder link.

[0471] (Supplementary note 13)

[0472] The method according to supplementary note 12, wherein

[0473] The message comprises information indicating the at least one NAS PDU that was not delivered.

[0474] (Supplementary note 14)

[0475] A method by an access network node in a non-terrestrial network, the method comprising:

[0476] transmitting, via system information, information indicating a mode of store-and-forward data in case the service link between the access network node and a user equipment, UE, or the feeder link between the access network node and a gateway in a terrestrial network is unavailable, and

[0477] wherein the information is such that at least one UE not supporting the mode of store-and-forward data in case the service link or the feeder link is unavailable does not camp on a serving cell of the access network node.

[0478] (Supplementary note 15)

[0479] The method according to supplementary note 14, wherein

[0480] The information is updated based on whether the feeder link is available or not.

[0481] (Supplementary note 16)

[0482] The method according to supplementary note 14, wherein

[0483] The information comprises time information indicating a time window during which the feeder link will be temporarily available for enabling, and

[0484] The at least one UE not supporting the mode of store-and-forward data in case the service link or the feeder link is unavailable camps on the serving cell of the access network node during the time window.

[0485] (Supplementary note 17)

[0486] The method according to any of supplementary notes 14 to 16, further comprising:

[0487] In case the service link or the feeder link is not available, receiving support information from the UE indicating that the UE supports the mode of store-and-forward data.

[0488] (Supplementary note 18)

[0489] According to any of Supplementary notes 17, wherein

[0490] The support information is comprised in a radio resource control connection setup complete message, RRC connection setup complete message.

[0491] (Supplementary note 19)

[0492] A method by an access network node in a non-terrestrial network, the method comprising:

[0493] In case the service link between the access network node and a user equipment, UE, or the feeder link between the access network node and a gateway in a terrestrial network is not available, transmitting information to a core network indicating capability of store-and-forward data.

[0494] (Supplementary note 20)

[0495] A method by an access network node in a non-terrestrial network, the method comprising:

[0496] In case the service link between the access network node and a user equipment, UE, or the feeder link between the access network node and a gateway in a terrestrial network is not available, receiving information from a core network indicating capability of store-and-forward data.

[0497] (Supplementary note 21)

[0498] The method according to any of Supplementary notes 1-20, further comprising:

[0499] In case the service link becomes not available, transmitting information to the UE indicating a radio resource control release cause, RRC is an abbreviation for radio resource control, and wherein

[0500] The RRC release causes the UE to at least one of:

[0501] Enter ECM-idle state, ECM is an abbreviation for EPS connection management, EPS is an abbreviation for evolved packet system, and

[0502] Stay in ECM-connected state.

[0503] (Supplementary note 22)

[0504] A method by a user equipment, UE, the method comprising:

[0505] transmitting at least one NAS PDU to the access network node via a serving link between the access network node and the UE without triggering establishment of a connection for the feeder link, NAS is an abbreviation of non-access stratum, PDU is an abbreviation of protocol data unit, and wherein

[0506] the at least one NAS PDU is stored by the access network node until the feeder link becomes available, and

[0507] forwarding the at least one NAS PDU via the feeder link when the feeder link becomes available.

[0508] (Supplementary note 23)

[0509] A method by a user equipment, UE, the method comprising:

[0510] receiving information indicating a store-and-forward data mode via system information in case a serving link between an access network node in a non-terrestrial network and the UE or a feeder link between the access network node and a gateway in a terrestrial network is not available; and

[0511] not camping on a serving cell of the access network node in case the UE does not support the store-and-forward data mode in case the serving link or the feeder link is not available.

[0512] (Supplementary note 24)

[0513] A method by a core network node, the method comprising:

[0514] receiving at least one NAS 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 establishment of a connection for a serving link between the access network node and a user equipment, UE, NAS is an abbreviation of non-access stratum, PDU is an abbreviation of protocol data unit, and wherein

[0515] the at least one NAS PDU is stored by the access network node until the serving link becomes available, and

[0516] forwarding the at least one NAS PDU via the serving link when the serving link becomes available.

[0517] (Supplementary note 25)

[0518] A method by a core network node, the method comprising:

[0519] receiving, from the access network node, information indicating a capability to store and forward data in case a service link between the access network node and a user equipment, UE, or a feeder link between the access network node and a gateway in a terrestrial network coupled with the core network node is unavailable.

[0520] (Supplementary note 26)

[0521] A method by a core network node, the method comprising:

[0522] transmitting, to the access network node, information indicating a capability to store and forward data in case a service link between the access network node and a user equipment, UE, or a feeder link between the access network node and a gateway in a terrestrial network coupled with the core network node is unavailable.

[0523] (Supplementary note 27)

[0524] An access network node in a non-terrestrial network, the access network node comprising:

[0525] means for receiving at least one NAS PDU, NAS being an abbreviation for non- access stratum, PDU being an abbreviation for protocol data unit, via an available link without triggering establishment of a connection for another link different from the available link in case a service link between the access network node and a user equipment, UE, or a feeder link between the access network node and a gateway in a terrestrial network is unavailable;

[0526] means for storing the at least one NAS PDU until the other link becomes available; and

[0527] means for forwarding the at least one NAS PDU via the other link when the other link becomes available.

[0528] (Supplementary note 28)

[0529] An access network node in a non-terrestrial network, the access network node comprising:

[0530] means for transmitting, via system information, information indicating a mode to store and forward data in case a service link between the access network node and a user equipment, UE, or a feeder link between the access network node and a gateway in a terrestrial network coupled with the core network node is unavailable, and

[0531] wherein the information causes at least one UE not camping on a serving cell of the access network node in a mode where the store-and-forward data is not supported in case the serving link or the feeder link is not available.

[0532] (Supplementary note 29)

[0533] An access network node in a non-terrestrial network, the access network node comprising:

[0534] means for transmitting, to a core network, information indicating a capability for storing and forwarding data in case a serving link between the access network node and a user equipment, UE, or a feeder link between the access network node and a gateway in a terrestrial network is not available.

[0535] (Supplementary note 30)

[0536] An access network node in a non-terrestrial network, the access network node comprising:

[0537] means for receiving, from a core network, information indicating a capability for storing and forwarding data in case a serving link between the access network node and a user equipment, UE, or a feeder link between the access network node and a gateway in a terrestrial network is not available.

[0538] (Supplementary note 31)

[0539] A user equipment, UE, comprising:

[0540] means for transmitting, to an access network node in a non-terrestrial network, at least one NAS PDU via a serving link between the access network node and the UE without triggering establishing a connection for a feeder link between the access network node and a gateway in a terrestrial network in case the feeder link is not available, NAS being an abbreviation of non-access stratum, PDU being an abbreviation of protocol data unit, and wherein

[0541] the at least one NAS PDU is stored by the access network node until the feeder link becomes available, and

[0542] the at least one NAS PDU is forwarded via the feeder link when the feeder link becomes available.

[0543] (Supplementary note 32)

[0544] A user equipment, UE, comprising:

[0545] a means for receiving information indicating a mode of store-and-forward data via system information in case the service link between an access network node in a non-terrestrial network and the UE or the feeder link between the access network node and a gateway in a terrestrial network is not available; and

[0546] a means for not camping on a serving cell of the access network node in case the UE does not support the mode of store-and-forward data in case the service link or the feeder link is not available.

[0547] (Supplementary note 33)

[0548] A core network node comprising:

[0549] a means for receiving at least one NAS PDU from an access network node in a non-terrestrial network in case a service link between the access network node and a user equipment, UE, is not available via a feeder link between the access network node and the core network node, NAS being an abbreviation of non-access stratum, PDU being an abbreviation of protocol data unit, and wherein

[0550] the at least one NAS PDU is stored by the access network node until the service link becomes available, and

[0551] the at least one NAS PDU is forwarded via the service link when the service link becomes available.

[0552] (Supplementary note 34)

[0553] A core network node comprising:

[0554] a means for receiving information indicating a capability of store-and-forward data from an access network node in a non-terrestrial network in case a service link between the access network node and a user equipment, UE, or a feeder link between the access network node and a gateway in a terrestrial network coupled with the core network node is not available.

[0555] (Supplementary note 35)

[0556] A core network node comprising:

[0557] a means for transmitting information indicating a capability of store-and-forward data to an access network node in a non-terrestrial network in case a service link between the access network node and a user equipment, UE, or a feeder link between the access network node and a gateway in a terrestrial network coupled with the core network node is not available.

[0558] List of reference signs

[0559] 1 communication system

[0560] 3 UE

[0561] 5 radio access network (RAN) node, NTN RAN

[0562] 5A base station

[0563] 5B gateway

[0564] 5C platform

[0565] 7 core network

[0566] 9 cell

[0567] 11 mobility management entity (MME)

[0568] 13 serving gateway (S-GW)

[0569] 15 packet data network gateway (P-GW)

[0570] 20 external network

[0571] 31, 51, 71 transceiver circuitry

[0572] 33, 53 air interface

[0573] 35 user interface

[0574] 55 core network interface

[0575] 37, 57, 73 controller

[0576] 39, 59, 74 memory

[0577] 72 network interface

[0578] 41, 61, 75 operating system

[0579] 43, 63, 76 communication control module

Claims

1. A method performed by an access network node in a non-terrestrial network, the method comprising: When the service link between the access network node and the user equipment (UE) or the power supply link between the access network node and the gateway in the terrestrial network is unavailable, at least one NAS PDU is received via the available link without triggering the establishment of a connection to another link different from the available link. NAS is an abbreviation for Non-Access Stratum, and PDU is an abbreviation for Protocol Data Unit. Store the at least one NAS PDU until the other link becomes available; as well as When the other link becomes available, the at least one NAS PDU is forwarded via the other link.

2. The method according to claim 1, wherein, The reception is performed using control plane CIoT optimization features or early data transmission, i.e., EDT.

3. The method according to claim 1, wherein, The forwarding is performed using control plane CIoT optimization features or early data transmission (EDT).

4. The method according to any one of claims 1 to 3, further comprising: In the event that the service link or the power supply link is unavailable, maintain UE information for at least one UE permitted by the core network coupled to the gateway.

5. The method according to claim 4, wherein, The UE information includes at least one of the following: UE identifier; At least one Quality of Service (QoS) parameter; Priority information; Capability information; and Paging message.

6. The method according to claim 4 or 5, wherein, The UE information is determined based on at least one of the following: Historical information Operational and management data, also known as OAM data, Registration data, Prediction, and At least one UE having downlink data in the buffer of the access network node or the core network.

7. The method according to any one of claims 4 to 6, further comprising: Regardless of the UE's Radio Resource Control (RRC) status, the UE information is received from the core network.

8. The method according to any one of claims 4 to 6, further comprising: The UE receives a message for establishing a connection to the access network node; Transmit a request to the core network to authorize whether the UE can be allowed; as well as If the core network has authorized the UE to be permitted, the UE information can be received from the core network.

9. The method according to any one of claims 1 to 8, further comprising: Receive paging information via the power supply link for forwarding at least one NAS PDU to the UE via the service link; as well as When the service link becomes available, the paging information is used to page the UE.

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

11. The method according to any one of claims 1 to 10, wherein, The at least one NAS PDU is included in the signaling message.

12. The method according to any one of claims 1 to 11, further comprising: The power supply link is used to transmit a message to the core network informing it of the status of at least one NAS PDU received from a core network node during the period when the power supply link was previously available.

13. The method according to claim 12, wherein, The message includes information indicating at least one NAS PDU that has not been delivered.

14. A method performed by an access network node in a non-terrestrial network, the method comprising: In the event that 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, information indicating the mode for storing and forwarding data is transmitted via system information transmission, and The information enables at least one UE that does not support the mode of storing and forwarding data when the service link or the power supply link is unavailable to remain on the serving cell of the access network node.

15. The method according to claim 14, wherein, The information is updated based on whether the power supply link is available.

16. The method of claim 14, wherein, The information includes time information indicating the time window during which the power supply link will be temporarily available for enabling, and At least one UE that does not support the mode of storing and forwarding data when the serving link or the power supply link is unavailable remains on the serving cell of the access network node during the time window.

17. The method according to any one of claims 14 to 16, further comprising: If the service link or the power supply link is unavailable, the UE receives support information from the UE indicating that the UE supports the mode of storing and forwarding data.

18. The method according to claim 17, wherein, The support information is included in the Radio Resource Control Connection Setup Complete Message, i.e., the RRC Connection Setup Complete Message.

19. A method performed by an access network node in a non-terrestrial network, the method comprising: When the service link between the access network node and the user equipment (UE) or the power supply link between the access network node and the gateway in the terrestrial network is unavailable, information indicating the ability to store and forward data is transmitted to the core network.

20. A method performed by an access network node in a non-terrestrial network, the method comprising: When the service link between the access network node and the user equipment (UE) or the power supply link between the access network node and the gateway in the terrestrial network is unavailable, information indicating the ability to store and forward data is received from the core network.

21. The method according to any one of claims 1 to 20, further comprising: In the event that the service link becomes unavailable, information indicating the cause of the radio resource control release is transmitted to the UE, and wherein... RRC release causes the UE to perform at least one of the following, where RRC is an abbreviation for Radio Resource Control: Entering ECM idle state. ECM is an abbreviation for EPS connection management, and EPS is an abbreviation for evolved packet system. Keep the ECM connected.

22. A method performed by a user equipment (UE), the method comprising: When the feed link between an access network node in a non-terrestrial network and a gateway in a terrestrial network is unavailable, at least one NAS PDU is transmitted to the access network node via the service link between the access network node and the UE, without triggering the establishment of a connection for the feed link. NAS is an abbreviation for Non-Access Stratum, PDU is an abbreviation for Protocol Data Unit, and includes... The at least one NAS PDU is stored by the access network node until the power supply link becomes available, and When the power supply link becomes available, the at least one NAS PDU is forwarded via the power supply link.

23. A method performed by a user equipment (UE), the method comprising: When the service link between the access network node in the non-terrestrial network and the UE or the power supply link between the access network node and the gateway in the terrestrial network is unavailable, information indicating the mode of storing and forwarding data is received via system information. as well as If the UE does not support the mode of storing and forwarding data when the service link or the power supply link is unavailable, it will not camp on the serving cell of the access network node.

24. A method performed by a core network node, the method comprising: In the event that the service link between the access network node and the user equipment (UE) in a non-terrestrial network is unavailable, at least one NASPDU is received from the access network node via the feeder link between the access network node and the core network node without triggering the establishment of a connection for the service link. NAS is an abbreviation for Non-Access Stratum, PDU is an abbreviation for Protocol Data Unit, and [the specific details are missing from the original text]. The at least one NAS PDU is stored by the access network node until the service link becomes available, and When the service link becomes available, the at least one NAS PDU is forwarded via the service link.

25. A method performed by a core network node, the method comprising: When the service link between the access network node in the non-terrestrial network and the user equipment (UE) or the power supply link between the access network node and the gateway in the terrestrial network coupled to the core network node is unavailable, information indicating the ability to store and forward data is received from the access network node.

26. A method performed by a core network node, the method comprising: When the service link between the access network node in the non-terrestrial network and the user equipment (UE) or the power supply link between the access network node and the gateway in the terrestrial network coupled to the core network node is unavailable, information indicating the ability to store and forward data is transmitted to the access network node.

27. An access network node in a non-terrestrial network, the access network node comprising: A component for receiving at least one NAS PDU via an available link without triggering the establishment of a connection to another link different from the available link when 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. NAS is an abbreviation for Non-Access Stratum, and PDU is an abbreviation for Protocol Data Unit. Components used to store the at least one NAS PDU until the other link becomes available; as well as A component for forwarding 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, the access network node comprising: A component for transmitting information indicating the mode of storing and forwarding data via system information when 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, and The information enables at least one UE that does not support the mode of storing and forwarding data when the service link or the power supply link is unavailable to remain on the serving cell of the access network node.

29. An access network node in a non-terrestrial network, the access network node comprising: A component for transmitting information indicating the ability to store and forward data to the core network when the service link between the access network node and the user equipment (UE) or the power supply link between the access network node and the gateway in the terrestrial network is unavailable.

30. An access network node in a non-terrestrial network, the access network node comprising: A component for receiving information from the core network indicating the ability to store and forward data when the service link between the access network node and the user equipment (UE) or the power supply link between the access network node and a gateway in the terrestrial network is unavailable.

31. A user equipment, or UE, comprising: Components for transmitting at least one NASPDU to the access network node via the service link between the access network node and the UE when the feed link between the access network node in a non-terrestrial network and the gateway in a terrestrial network is unavailable, without triggering the establishment of a connection for the feed link. NAS is an abbreviation for Non-Access Stratum, PDU is an abbreviation for Protocol Data Unit, and wherein... The at least one NAS PDU is stored by the access network node until the power supply link becomes available, and When the power supply link becomes available, the at least one NAS PDU is forwarded via the power supply link.

32. A user equipment, or UE, comprising: A component for receiving information via system information indicating the mode of storing and forwarding data when the service link between the access network node in a non-terrestrial network and the UE or the power supply link between the access network node and the gateway in a terrestrial network is unavailable. as well as A component for not residing on the serving cell of the access network node when the UE does not support the mode of storing and forwarding data in the event that the serving link or the power supply link is unavailable.

33. A core network node, comprising: A component for receiving at least one NAS PDU from an access network node via a feeder link between the access network node and the core network node in a non-terrestrial network when the service link between the access network node and the user equipment (UE) is unavailable, without triggering the establishment of a connection for the service link. NAS is an abbreviation for Non-Access Stratum, PDU is an abbreviation for Protocol Data Unit, and wherein... The at least one NAS PDU is stored by the access network node until the service link becomes available, and When the service link becomes available, the at least one NAS PDU is forwarded via the service link.

34. A core network node, comprising: A component for receiving information from an access network node indicating its ability to store and forward data when the service link between an access network node and a user equipment (UE) in a non-terrestrial network or the power supply link between the access network node and a gateway in a terrestrial network coupled to the core network node is unavailable.

35. A core network node, comprising: A component for transmitting information indicating the ability to store and forward data to an access network node when the service link between an access network node and a user equipment (UE) in a non-terrestrial network or the power supply link between the access network node and a gateway in a terrestrial network coupled to the core network node is unavailable.

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