Patent Description:
Long-Term Evolution (LTE) is an umbrella term for so-called fourth-generation (<NUM>) radio access technologies developed within the Third-Generation Partnership Project (3GPP) and initially standardized in Release <NUM> (Rel-<NUM>) and Release <NUM> (Rel-<NUM>), also known as Evolved UTRAN (E-UTRAN). LTE is targeted at various licensed frequency bands and is accompanied by improvements to non-radio aspects commonly referred to as System Architecture Evolution (SAE), which includes Evolved Packet Core (EPC) network. LTE continues to evolve through subsequent releases.

<FIG> shows an exemplary view of an LTE Evolved Packet System (EPS) architecture. E-UTRAN <NUM> includes one or more evolved Node B's (eNB), such as eNBs <NUM>, <NUM>, and <NUM>, and one or more user equipment (UEs), such as UE <NUM>. In 3GPP terminology, "user equipment" or "UE" refers to any wireless device (e.g., smartphone or computing device) capable of communicating with 3GPP-standard-compliant network equipment, including E-UTRAN as well as UTRAN and/or GERAN, as the third-generation ("<NUM>") and second-generation ("<NUM>") 3GPP RANs are commonly known.

As specified by 3GPP, E-UTRAN <NUM> is responsible for all radio-related functions in the network, including radio bearer control, radio admission control, radio mobility control, scheduling, and dynamic allocation of resources to UEs in uplink and downlink, as well as security of the communications with the UE. These functions reside in the eNBs, such as eNBs <NUM>, <NUM>, and <NUM>. Each of the eNBs can serve a geographic coverage area including one more cells, including cells <NUM>, <NUM>, and <NUM> served by eNBs <NUM>, <NUM>, and <NUM>, respectively.

The eNBs in the E-UTRAN communicate with each other via the X2 interface, as shown in <FIG>. The eNBs also are responsible for the E-UTRAN interface to the EPC <NUM>, specifically the S1 interface to the Mobility Management Entity (MME) and the Serving Gateway (SGW), shown collectively as MME/S-GWs <NUM> and <NUM> in <FIG>. In general, the MME/S-GW handles both the overall control of the UE and data flow between the UE and the rest of the EPC. More specifically, the MME processes the signaling (e.g., control plane) protocols between the UE and the EPC, which are known as the Non-Access Stratum (NAS) protocols. The S-GW handles all Internet Protocol (IP) data packets (e.g., data or user plane) between the UE and the EPC and serves as the local mobility anchor for the data bearers when the UE moves between eNBs, such as eNBs <NUM>, <NUM>, and <NUM>.

EPC <NUM> can also include a Home Subscriber Server (HSS) <NUM>, which manages user- and subscriber-related information. HSS <NUM> can also provide support functions in mobility management, call and session setup, user authentication and access authorization. The functions of HSS <NUM> can be related to the functions of legacy Home Location Register (HLR) and Authentication Centre (AuC) functions or operations. HSS <NUM> can also communicate with MMEs <NUM> and <NUM> via respective S6a interfaces.

In some embodiments, HSS <NUM> can communicate with a user data repository (UDR) - labelled EPC-UDR <NUM> in <FIG> - via a Ud interface. EPC-UDR <NUM> can store user credentials after they have been encrypted by AuC algorithms. These algorithms are not standardized (i.e., vendor-specific), such that encrypted credentials stored in EPC-UDR <NUM> are inaccessible by any other vendor than the vendor of HSS <NUM>.

<FIG> shows exemplary control plane (CP) protocol layers of the radio interface between a UE (<NUM>), an eNB (<NUM>), and an MME (<NUM>) in the EPS. The exemplary protocol layers includes Physical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP), and Radio Resource Control (RRC) layers between the UE and an eNB. The PHY layer is concerned with how and what characteristics are used to transfer data over transport channels on the LTE radio interface. The MAC layer provides data transfer services on logical channels, maps logical channels to PHY transport channels, and reallocates PHY resources to support these services. The RLC layer provides error detection and/or correction, concatenation, segmentation, and reassembly, reordering of data transferred to or from the upper layers. The PDCP layer provides ciphering/deciphering and integrity protection for both CP and user plane (UP), as well as other UP functions such as header compression. The exemplary protocol layers also includes non-access stratum (NAS) signaling between the UE and an MME in the EPC.

The RRC layer controls communications between UE and eNB at the radio interface, as well as the mobility of a UE between cells in the E-UTRAN. After a UE is powered ON it will be in the RRC_IDLE state until an RRC connection is established with the network, at which time the UE will transition to RRC_CONNECTED state (e.g., where data transfer can occur). The UE returns to RRC_IDLE after the connection with the network is released. In RRC_IDLE state, the UE does not belong to any cell, no RRC context has been established for the UE (e.g., in E-UTRAN), and the UE is out of UL synchronization with the network. Even so, a UE in RRC IDLE state is known in the EPC and has an assigned IP address.

Furthermore, in RRC IDLE state, the UE's radio is active on a discontinuous reception (DRX) schedule configured by upper layers. During DRX active periods (also referred to as "On durations"), an RRC_IDLE UE receives system information (SI) broadcast by a serving cell, performs measurements of neighbor cells to support cell reselection, and monitors a paging channel for pages from the EPC via an eNB serving the cell in which the UE is camping.

A UE must perform a random-access (RA) procedure to move from RRC_IDLE to RRC_CONNECTED state. In RRC_CONNECTED state, the cell serving the UE is known and an RRC context is established for the UE in the serving eNB, such that the UE and eNB can communicate. For example, a Cell Radio Network Temporary Identifier (C-RNTI) - a UE identity used for signaling between UE and network - is configured for a UE in RRC_CONNECTED state.

The fifth generation ("<NUM>") of cellular systems, also referred to as New Radio (NR), is being standardized within 3GPP. NR is developed to support a variety of different use cases. These include enhanced mobile broadband (eMBB), machine type communications (MTC), ultra-reliable low latency communications (URLLC), and several other use cases.

<NUM>/NR technology shares many similarities with fourth-generation LTE. For example, the <NUM> system (5GS) architecture is based on a Next Generation RAN (NG-RAN) and a <NUM> Core (5GC), much like the LTE EPS is based on E-UTRAN and EPC. Additionally, the NR RRC layer includes RRC_IDLE and RRC_CONNECTED states, but adds another state called RRC_INACTIVE. In addition to providing coverage via "cells," as in LTE, NR networks also provide coverage via "beams. " In general, a DL "beam" is a coverage area of a network-transmitted reference signal (RS) that may be measured or monitored by a UE.

Historically, UEs provided voice services over a circuit-switched (CS) telephone network. In packet-switched networks, data packets are routed based on protocols specified by the Internet Engineering Task Force (IETF), such as Internet Protocol (IP), User Datagram Protocol (UDP), etc. IP Multimedia Subsystem (IMS) is an architectural framework used to deliver multimedia services to UEs based on these Internet-centric protocols. IMS was originally specified in 3GPP Rel-<NUM> as a technology for evolving mobile networks beyond GSM, e.g., for delivering Internet services over GPRS. IMS has expanded in subsequent releases to support other access networks and a wide range of services and applications.

Document <NPL>, is a 3GPP contribution comprising a summary of an offline discussion about IMS voice EPS fallback, already mentioning that "IMS voice EPS fallback from <NUM>" is already included in S1AP( e.g. indicating during S1AP based HO) and should also introduced in X2AP, (e.g. indicating during X2AP HO).

Even so, voice remains an important IMS application. When an IMS voice call is received in an NG-RAN node, it may trigger an IMS fallback to the EPS (e.g., via inter-system handover) if the NG-RAN node does not support IMS voice. In 3GPP Rel-<NUM>, it was agreed that the "IMS voice EPS fallback from <NUM>" is supported on the S <NUM>-AP interface in the EPS.

In case of inter-system UE handover from 5GS to EPS, it is beneficial for a target eNB in the E-UTRAN to know the reason for the handover. For example, when an IMS voice call is terminated, the target eNB can take actions to facilitate improved end-to-end user experience, such as handing the UE back to 5GS when appropriate. However, there are some scenarios when this may not be possible due to loss of the knowledge within EPS about the original inter-system handover of the UE from 5GS to EPS. This can cause various problems, issues, and/or difficulties.

Embodiments of the present disclosure provide specific improvements to communication between UEs and network nodes in a wireless network, such as by facilitating solutions to overcome exemplary problems summarized above and described in more detail below.

Some embodiments of the present disclosure include methods (e.g., procedures) for a first network node (e.g., base station, eNB, ng-eNB, etc. or component thereof) of a wireless network.

These exemplary methods can include sending, to a second network node of the wireless network, a request to retrieve context information associated with a UE that has been or is being handed over from the second network node to the first network node. These exemplary methods can also include receiving the context information associated with the UE from the second network node. The context information includes an indication of whether the UE has an active IMS voice call that was subject to a first inter-system handover from a 5GS to the wireless network.

In some embodiments, these exemplary methods can also include, based on the received context information, establishing a connection with the UE to carry the active IMS voice call. In some embodiments, the received context information also indicates a radio access bearer (RAB) used for the active IMS voice call.

In some embodiments, these exemplary methods can also include storing the received context information, including the indication, and performing one or more actions towards the UE based on the stored indication. In some of these embodiments, performing one or more actions can include the following: when the indication indicates that the UE has an active IMS voice call that was subject to the first inter-system handover from the 5GS, determining whether the 5GS is available; and based on determining that the 5GS is available, performing a second inter-system handover of the UE from the wireless network to the 5GS.

In some of these embodiments, performing one or more actions can also include, when the indication indicates that the UE has an active IMS voice call that was subject to the first inter-system handover from the 5GS, detecting one of the following conditions: end of the active IMS voice call, or a reduced QoS for the active IMS voice call. In such embodiments, determining whether the 5GS is available is responsive to detecting one of the conditions.

In some embodiments, the wireless network is an EPS, the first and second network nodes are eNBs, and the indication indicates an IMS voice fallback from 5GS to EPS. In some of these embodiments, the request comprises a RETRIEVE UE CONTEXT REQUEST message and the context information is received in a UE Context Information information element (IE) of a RETRIEVE UE CONTEXT RESPONSE message.

Other embodiments include methods (e.g., procedures) for a second network node (e.g., base station, eNB, ng-eNB, etc., or component thereof) of a wireless network.

These exemplary methods can include receiving, from a first network node of the wireless network, a request to retrieve context information associated with a UE that has been or is being handed over from the second network node to the first network node. These exemplary methods can also include sending the context information associated with the UE to the first network node. The context information includes an indication of whether the UE has an active IMS voice call that was subject to a first inter-system handover from a 5GS to the wireless network.

In some embodiments, these exemplary methods can also include performing the first inter-system handover of the UE from a network node of the 5GS and setting the indication included in the context information according to whether the UE has an active IMS voice call during the first inter-system handover.

In some embodiments, the received context information also indicates a RAB used for the active IMS voice call. In some embodiments, the wireless network is an EPS, the first and second network nodes are eNBs, and the indication indicates an IMS voice fallback from 5GS to EPS. In some of these embodiments, the request comprises a RETRIEVE UE CONTEXT REQUEST message and the context information is received in a UE Context Information IE of a RETRIEVE UE CONTEXT RESPONSE message.

Other embodiments include network nodes (e.g., base stations, eNBs, ng-eNBs, etc., or components thereof) configured to perform operations corresponding to any of the exemplary methods described herein. Other embodiments include non-transitory, computer-readable media storing program instructions that, when executed by processing circuitry, configure such network nodes to perform operations corresponding to any of the exemplary methods described herein.

These and other embodiments of the present invention facilitate consistent handling of UEs after inter-system handover from 5GS to EPS after radio link failure (RLF) and subsequent connection reestablishment. This can lead to improved UE inter-system mobility, more consistent delivery of network services to UEs, and improved end-user experience.

These and other objects, features, and advantages of embodiments of the present disclosure will become apparent upon reading the following Detailed Description in view of the Drawings briefly described below.

Any feature of any of the embodiments disclosed herein can be applied to any other embodiment, wherever appropriate. Likewise, any advantage of any of the embodiments can apply to any other embodiments, and vice versa. Other objects, features, and advantages of the disclosed embodiments will become apparent from the following description.

Furthermore, the following terms are used throughout the description given below:.

Note that the description herein focuses on a 3GPP cellular communications system and, as such, 3GPP terminology or terminology similar to 3GPP terminology is oftentimes used. Furthermore, although the term "cell" is used herein, it should be understood that (particularly with respect to <NUM> NR) beams may be used instead of cells and, as such, concepts described herein apply equally to both cells and beams.

As briefly mentioned above, it is beneficial for a target eNB in the E-UTRAN to know the reason for an inter-system handover of a UE from 5GS to EPS, e.g., due to termination of an IMS voice call in 5GS, such that the target eNB can take actions to improve end-user experience. However, there are some scenarios when this may not be possible due to loss of the knowledge within EPS about the original inter-system handover of the UE from 5GS to EPS. These issues are discussed in more detail after the following introduction to 5GS network architecture.

<FIG> illustrates a high-level view of an exemplary 5GS architecture, consisting of a Next Generation RAN (NG-RAN <NUM>) and a <NUM> Core (5GC <NUM>). NG-RAN <NUM> can include a set of gNodeB's (gNBs) connected to the 5GC via one or more NG interfaces, whereas the gNBs can be connected to each other via one or more Xn interfaces, such as Xn interface <NUM> between gNBs <NUM> and <NUM> in <FIG>. Each of the gNBs can support frequency division duplexing (FDD), time division duplexing (TDD), or a combination thereof on the NR interface to UEs.

NG-RAN <NUM> is layered into a Radio Network Layer (RNL) and a Transport Network Layer (TNL). The NG-RAN architecture, i.e., the NG-RAN logical nodes and interfaces between them, is defined as part of the RNL. For each NG-RAN interface (NG, Xn, F1) the related TNL protocol and the functionality are specified. The TNL provides services for user plane transport and signaling transport. In some exemplary configurations, each gNB is connected to all 5GC nodes within an "AMF Region," which is defined in 3GPP TS <NUM>. If security protection for control plane (CP) and user plane (UP) data on TNL of NG-RAN interfaces is supported, NDS/IP (3GPP TS <NUM>) shall be applied.

The NG RAN logical nodes shown in <FIG> include a central (or centralized) unit (CU or gNB-CU) and one or more distributed (or decentralized) units (DU or gNB-DU). For example, gNB <NUM> in <FIG> includes gNB-CU <NUM> and gNB-DUs <NUM> and <NUM>. CUs (e.g., gNB-CU <NUM>) are logical nodes that host higher-layer protocols and perform various gNB functions such controlling the operation of DUs. Each DU is a logical node that hosts lower-layer protocols and can include, depending on the functional split, various subsets of the gNB functions. As such, each of the CUs and DUs can include various circuitry needed to perform their respective functions, including processing circuitry, transceiver circuitry (e.g., for communication), and power supply circuitry. Moreover, the terms "central unit" and "centralized unit" are used interchangeably herein, as are the terms "distributed unit" and "decentralized unit.

A gNB-CU connects to its associated gNB-DUs over respective F1 logical interfaces, such as interfaces <NUM> and <NUM> shown in <FIG>. The gNB-CU and connected gNB-DUs are only visible to other gNBs and the 5GC as a gNB, e.g., the F1 interface is not visible beyond gNB-CU. In the gNB split CU-DU architecture illustrated by <FIG>, DC can be achieved by allowing a UE to connect to multiple DUs served by the same CU or by allowing a UE to connect to multiple DUs served by different CUs.

<FIG> shows another high-level view of an exemplary <NUM> network architecture, including NG-RAN <NUM> and 5GC <NUM>. As shown in the figure, NG-RAN <NUM> can include gNBs (e.g., 410a,b) and ng-eNBs (e.g., 420a,b) that are interconnected via respective Xn interfaces. The gNBs and ng-eNBs are also connected via the NG interfaces to 5GC <NUM>, more specifically to the access and mobility management functions (AMFs, e.g., 430a,b) via respective NG-C interfaces and to the user plane functions (UPFs, e.g., 440a,b) via respective NG-U interfaces. Moreover, the AMFs can communicate with one or more policy control functions (PCFs, e.g., 450a,b) and network exposure functions (NEFs, e.g., 460a,b).

Each of the gNBs support the NR radio interface including FDD, TDD, or a combination thereof. Each of ng-eNBs support the LTE radio interface but unlike conventional LTE eNBs (e.g., in <FIG>), they connect to the 5GC via the NG interface. Each gNB or ng-eNB can serve a geographic coverage area including one more cells, such as cells 411a-b and 421a-b shown in <FIG>. Depending on the cell in which it is located, a UE <NUM> can communicate with the gNB or ng-eNB serving that cell via the NR or LTE radio interface, respectively. Although <FIG> shows gNBs and ng-eNBs as separate entities, it is possible that a single NG-RAN node can have gNB and ng-eNB functionalities.

In some embodiments, gNBs and ng-eNBs can also use various directional beams to provide coverage in the respective cells. In general, a DL "beam" is a coverage area of a network-transmitted reference signal (RS) that may be measured or monitored by a UE. In NR, for example, such RS can include any of the following, alone or in combination: synchronization signal/PBCH block (SSB), CSI-RS, tertiary reference signals (or any other sync signal), positioning RS (PRS), DMRS, phase-tracking reference signals (PTRS), etc. In general, SSB is available to all UEs regardless of RRC state, while other RS (e.g., CSI-RS, DM-RS, PTRS) are associated with specific UEs that have a network connection, i.e., in RRC_CONNECTED state.

When an IMS voice call is received in an NG-RAN node, it may trigger an IMS fallback to the EPS (e.g., via inter-system handover) if the NG-RAN node does not support IMS voice. It is beneficial for the handover target eNB in the E-UTRAN to know the reason for the inter-system handover (e.g., "IMS voice EPS fallback from <NUM>") so that it can take actions to facilitate improved end-to-end user experience, such as handing the UE back to 5GS when appropriate.

However, the target eNB (also referred to as "old eNB") for the original inter-system handover may not be able to handover the UE back to 5GS. If the UE experiences a radio link failure (RLF) or similar condition when operating in a cell served by the target eNB, the UE needs to re-establish its connection with a new cell, which may be served by a different eNB in the E-UTRAN (also referred to as "new eNB"). In such case, the new eNB retrieves the UE's context from the old eNB and uses this information to reestablish the UE's E-UTRAN radio access bearers (E-RABs).

<FIG> shows an exemplary procedure used by the new eNB (<NUM>) to retrieve the UE context from the old eNB (<NUM>). In particular, the new eNB sends a RETRIEVE UE CONTEXT REQUEST message to the old eNB, which responds with a RETRIEVE UE CONTEXT RESPONSE message. These messages can be exchanged over an X2 interface between the two eNBs, as further defined in 3GPP TS <NUM> (v16.

With respect to the scenario discussed above, one problem is that the old eNB does not provide the new eNB with any information about the UE's previous inter-system handover from 5GS to 4GS. Accordingly, the new eNB is not aware that it should take actions such as handing the UE back to 5GS when appropriate.

Embodiments of the present disclosure can address these and other issues, problems, and/or difficulties by introducing an indication that the "UE is handed over from <NUM> to <NUM> due to IMS fallback" (or similar name) in the UE context retrieve procedure, e.g., exemplified in <FIG>. A new eNB (e.g., an eNB in which the UE has reestablished its connection after RLF) stores this information and uses it to take actions towards the UE that are preferrable and/or necessary to improve quality-of-service (QoS) and/or end-user experience, such as handing the UE back to 5GS when appropriate.

Embodiments disclosed herein can provide various advantages, benefits, and/or solutions to problems. All embodiments of the present invention provide a consistent handling of UEs after an inter-system handover from 5GS to EPS, even after RLF and subsequent connection reestablishment. This leads to improved UE inter-system mobility and, consequently, more consistent delivery of network services to UEs and improved end-user experience.

In some embodiments, an indication that a UE has been handed over from 5GS to EPS via inter-system handover can be a field in a UE Context Information information element (IE) that is included in the RETRIEVE UE CONTEXT RESPONSE message of the exemplary procedure shown in <FIG>. The following proposed text for 3GPP TS <NUM> defines a UE Context Information IE that includes such a field, called "IMS voice EPS fallback from <NUM>". Note that the proposed text is not intended to be complete and may omit certain aspects that are not essential to explanation and/or understanding of these embodiments.

This message is sent by the old eNB to transfer the UE context to the new eNB. Direction: old eNB -> new eNB.

Note that the name of the indication and its location within the exemplary UE Context Information IE above are merely exemplary, such that the indication can be given a different name and placed at different location within the IE. Additionally, the indication can be included in a different IE in the same RETRIEVE UE CONTEXT RESPONSE message, or in a different message as appropriate.

When the new eNB receives a UE Context Information IE that includes this field, it will store the indication in the UE context together with other information and use it as appropriate. For example, when the UE's IMS voice service that caused the handover is terminated on EPS, the new eNB can send the UE back to 5GS.

The embodiments described above can be further illustrated with reference to <FIG>, which depict exemplary methods (e.g., procedures) for a first network node and a second network node, respectively. Put differently, various features of the operations described below correspond to various embodiments described above. For example, the first network node can correspond to the "new eNB" discussed above and the second network node can correspond to the "old eNB" discussed above.

The exemplary methods shown in <FIG> can be used cooperatively to provide various exemplary benefits and solve various exemplary problems, including those described herein. Although <FIG> show specific blocks in particular orders, the operations of the exemplary methods can be performed in different orders than shown and can be combined and/or divided into blocks having different functionality than shown. Optional blocks or operations are indicated by dashed lines.

More specifically, <FIG> shows a flow diagram of an exemplary method (e.g., procedure) for a first network node of a wireless network, according to various embodiments of the present disclosure. The exemplary method can be performed by a network node (e.g., base station, eNB, ng-eNB, etc. or component thereof) such as described elsewhere herein.

The exemplary method can include the operations of block <NUM>, where the first network node can send, to a second network node of the wireless network, a request to retrieve context information associated with a UE that has been or is being handed over from the second network node to the first network node. The exemplary method can also include the operations of block <NUM>, where the first network node can receive the context information associated with the UE from the second network node. The context information includes an indication of whether the UE has an active IMS voice call that was subject to a first inter-system handover from a 5GS to the wireless network.

In some embodiments, the exemplary method can also include the operations of block <NUM>, where based on the received context information, the first network node can establish a connection with the UE to carry the active IMS voice call. In some embodiments, the received context information also indicates a radio access bearer (RAB) used for the active IMS voice call. For example, the connection established in block <NUM> can include the RAB indicated in the received context information.

In some embodiments, the exemplary method can also include the operations of blocks <NUM>-<NUM>, where the first network node can store the received context information, including the indication, and perform one or more actions towards the UE based on the stored indication. In some of these embodiments, performing one or more actions in block <NUM> can include the operations of sub-blocks <NUM>-<NUM>. In sub-block <NUM>, when the indication indicates that the UE has an active IMS voice call that was subject to the first inter-system handover from the 5GS, the first network node can determine whether the 5GS is available. In sub-block <NUM>, based on determining that the 5GS is available, the first network node can perform a second inter-system handover of the UE from the wireless network to the 5GS.

In some of these embodiments, performing one or more actions in block <NUM> can also include the operations of sub-block <NUM>, where when the indication indicates that the UE has an active IMS voice call that was subject to the first inter-system handover from the 5GS, the first network node can detect one of the following conditions: end of the active IMS voice call, or a reduced QoS for the active IMS voice call. In such embodiments, determining whether the 5GS is available in sub-block <NUM> is responsive to detecting one of the conditions in sub-block <NUM>.

In some embodiments, the wireless network is an EPS and the first and second network nodes are eNBs. In such embodiments, the indication indicates an IMS voice fallback from 5GS to EPS. The exemplary 3GPP specification text above provides an example of these embodiments. In some of these embodiments, the request comprises a RETRIEVE UE CONTEXT REQUEST message and the context information is received in a UE Context Information IE of a RETRIEVE UE CONTEXT RESPONSE message. An example of these embodiments was discussed above.

In addition, <FIG> shows a flow diagram of an exemplary method (e.g., procedure) for a second network node of a wireless network, according to various embodiments of the present disclosure. The exemplary method can be performed by a network node (e.g., base station, eNB, gNB, ng-eNB, etc., or component thereof) such as described elsewhere herein.

The exemplary method can include the operations of block <NUM>, where the second network node can receive, from a first network node of the wireless network, a request to retrieve context information associated with a UE that has been or is being handed over from the second network node to the first network node. The exemplary method can also include the operations of block <NUM>, where the second network node can send the context information associated with the UE to the first network node. The context information includes an indication of whether the UE has an active IMS voice call that was subject to a first inter-system handover from a 5GS to the wireless network.

In some embodiments, the exemplary method can also include the operations of blocks <NUM> and <NUM>, where the second network node can perform the first inter-system handover of the UE from a network node of the 5GS and set the indication included in the context information (e.g., sent in block <NUM>) according to whether the UE has an active IMS voice call during the first inter-system handover.

In some embodiments, the received context information also indicates a RAB used for the active IMS voice call. In some embodiments, the wireless network is an EPS and the first and second network nodes are eNBs. In such embodiments, the indication indicates an IMS voice fallback from 5GS to EPS. The exemplary 3GPP specification text above provides an example of these embodiments. In some of these embodiments, the request comprises a RETRIEVE UE CONTEXT REQUEST message and the context information is received in a UE Context Information IE of a RETRIEVE UE CONTEXT RESPONSE message. An example of these embodiments was discussed above.

Although various embodiments are described above in terms of methods, techniques, and/or procedures, the person of ordinary skill will readily comprehend that such methods, techniques, and/or procedures can be embodied by various combinations of hardware and software in various systems, communication devices, computing devices, control devices, apparatuses, non-transitory computer-readable media, computer program products, etc..

<FIG> shows an example of a communication system <NUM> in accordance with some embodiments. In this example, the communication system <NUM> includes a telecommunication network <NUM> that includes an access network <NUM>, such as a radio access network (RAN), and a core network <NUM>, which includes one or more core network nodes <NUM>. The access network <NUM> includes one or more access network nodes, such as network nodes 810a and 810b (one or more of which may be generally referred to as network nodes <NUM>), or any other similar <NUM>rd Generation Partnership Project (3GPP) access node or non-3GPP access point. The network nodes <NUM> facilitate direct or indirect connection of user equipment (UE), such as by connecting UEs 812a, 812b, 812c, and 812d (one or more of which may be generally referred to as UEs <NUM>) to the core network <NUM> over one or more wireless connections.

The host <NUM> may be under the ownership or control of a service provider other than an operator or provider of the access network <NUM> and/or the telecommunication network <NUM> and may be operated by the service provider or on behalf of the service provider.

In some examples, the UEs <NUM> are configured to transmit and/or receive information without direct human interaction. For instance, a UE may be designed to transmit information to the access network <NUM> on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the access network <NUM>. Additionally, a UE may be configured for operating in single- or multi-RAT or multi-standard mode. For example, a UE may operate with any one or combination of Wi-Fi, NR (New Radio) and LTE, i.e., being configured for multi-radio dual connectivity (MR-DC), such as E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) New Radio - Dual Connectivity (EN-DC).

In the example, the hub <NUM> communicates with the access network <NUM> to facilitate indirect communication between one or more UEs (e.g., UE 812c and/or 812d) and network nodes (e.g., network node 810b). In some examples, the hub <NUM> may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, the hub <NUM> may be a broadband router enabling access to the core network <NUM> for the UEs. As another example, the hub <NUM> may be a controller that sends commands or instructions to one or more actuators in the UEs. Commands or instructions may be received from the UEs, network nodes <NUM>, or by executable code, script, process, or other instructions in the hub <NUM>. As another example, the hub <NUM> may be a data collector that acts as temporary storage for UE data and, in some embodiments, may perform analysis or other processing of the data. As another example, the hub <NUM> may be a content source. For example, for a UE that is a VR headset, display, loudspeaker or other media delivery device, the hub <NUM> may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which the hub <NUM> then provides to the UE either directly, after performing local processing, and/or after adding additional local content. In still another example, the hub <NUM> acts as a proxy server or orchestrator for the UEs, in particular in if one or more of the UEs are low energy IoT devices.

The hub <NUM> may have a constant/persistent or intermittent connection to the network node 810b. The hub <NUM> may also allow for a different communication scheme and/or schedule between the hub <NUM> and UEs (e.g., UE 812c and/or 812d), and between the hub <NUM> and the core network <NUM>. In other examples, the hub <NUM> is connected to the core network <NUM> and/or one or more UEs via a wired connection. Moreover, the hub <NUM> may be configured to connect to an M2M service provider over the access network <NUM> and/or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with the network nodes <NUM> while still connected via the hub <NUM> via a wired or wireless connection. In some embodiments, the hub <NUM> may be a dedicated hub - that is, a hub whose primary function is to route communications to/from the UEs from/to the network node 810b. In other embodiments, the hub <NUM> may be a nondedicated hub - that is, a device which is capable of operating to route communications between the UEs and network node 810b, but which is additionally capable of operating as a communication start and/or end point for certain data channels.

<FIG> shows a UE <NUM> in accordance with some embodiments. As used herein, a UE refers to a device capable, configured, arranged and/or operable to communicate wirelessly with network nodes and/or other UEs. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, voice over IP (VoIP) phone, wireless local loop phone, desktop computer, personal digital assistant (PDA), wireless cameras, gaming console or device, music storage device, playback appliance, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), smart device, wireless customer-premise equipment (CPE), vehicle-mounted or vehicle embedded/integrated wireless device, etc. Other examples include any UE identified by the 3rd Generation Partnership Project (3GPP), including a narrow band internet of things (NB-IoT) UE, a machine type communication (MTC) UE, and/or an enhanced MTC (eMTC) UE.

The output may be periodic (e.g., once every <NUM> minutes if it reports the sensed temperature), random (e.g., to even out the load from reporting from several sensors), in response to a triggering event (e.g., when moisture is detected, an alert is sent), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient).

A UE, when in the form of an Internet of Things (IoT) device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application and healthcare. Non-limiting examples of such an IoT device are a device which is or which is embedded in: a connected refrigerator or freezer, a TV, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door/window sensor, a flood/moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, a fitness tracker, a head-mounted display for Augmented Reality (AR) or Virtual Reality (VR), a wearable for tactile augmentation or sensory enhancement, a water sprinkler, an animal- or item-tracking device, a sensor for monitoring a plant or animal, an industrial robot, an Unmanned Aerial Vehicle (UAV), and any kind of medical device, like a heart rate monitor or a remote controlled surgical robot. A UE in the form of an IoT device comprises circuitry and/or software in dependence of the intended application of the IoT device in addition to other components as described in relation to the UE <NUM> shown in <FIG>.

As yet another specific example, in an IoT scenario, a UE may represent a machine or other device that performs monitoring and/or measurements and transmits the results of such monitoring and/or measurements to another UE and/or a network node.

In practice, any number of UEs may be used together with respect to a single use case. For example, a first UE might be or be integrated in a drone and provide the drone's speed information (obtained through a speed sensor) to a second UE that is a remote controller operating the drone. When the user makes changes from the remote controller, the first UE may adjust the throttle on the drone (e.g., by controlling an actuator) to increase or decrease the drone's speed. The first and/or the second UE can also include more than one of the functionalities described above. For example, a UE might comprise the sensor and the actuator, and handle communication of data for both the speed sensor and the actuators.

<FIG> shows a network node <NUM> in accordance with some embodiments. As used herein, network node refers to equipment capable, configured, arranged and/or operable to communicate directly or indirectly with a UE and/or with other network nodes or equipment, in a telecommunication network.

Other examples of network nodes include multiple transmission point (multi-TRP) <NUM> access nodes, multi-standard radio (MSR) equipment such as MSRBSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs), base transceiver stations (BTSs), transmission points, transmission nodes, multi-cell/multicast coordination entities (MCEs), Operation and Maintenance (O&M) nodes, Operations Support System (OSS) nodes, Self-Organizing Network (SON) nodes, positioning nodes (e.g., Evolved Serving Mobile Location Centers (E-SMLCs)), and/or Minimization of Drive Tests (MDTs).

The memory <NUM> may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and/or other instructions (referred to collectively as computer program product 1004a) capable of being executed by the processing circuitry <NUM> and utilized by the network node <NUM>.

Applications <NUM> (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment Q400 to implement some of the features, functions, and/or benefits of some of the embodiments disclosed herein.

Hardware <NUM> includes processing circuitry, memory that stores software and/or instructions (referred to collectively as computer program product 1204a) executable by hardware processing circuitry, and/or other hardware devices as described herein, such as a network interface, input/output interface, and so forth. Software may be executed by the processing circuitry to instantiate one or more virtualization layers <NUM> (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1208a and 1208b (one or more of which may be generally referred to as VMs <NUM>), and/or perform any of the functions, features and/or benefits described in relation with some embodiments described herein. The virtualization layer <NUM> may present a virtual operating platform that appears like networking hardware to the VMs <NUM>.

Hardware <NUM> may be implemented in a standalone network node with generic or specific components. Hardware <NUM> may implement some functions via virtualization. Alternatively, hardware <NUM> may be part of a larger cluster of hardware (e.g., such as in a data center or CPE) where many hardware nodes work together and are managed via management and orchestration <NUM>, which, among others, oversees lifecycle management of applications <NUM>. In some embodiments, hardware <NUM> is coupled to one or more radio units that each include one or more transmitters and one or more receivers that may be coupled to one or more antennas. Radio units may communicate directly with other hardware nodes via one or more appropriate network interfaces and may be used in combination with the virtual components to provide a virtual node with radio capabilities, such as a radio access node or a base station. In some embodiments, some signaling can be provided with the use of a control system <NUM> which may alternatively be used for communication between hardware nodes and radio units.

<FIG> shows a communication diagram of a host <NUM> communicating via a network node <NUM> with a UE <NUM> over a partially wireless connection in accordance with some embodiments. Example implementations, in accordance with various embodiments, of the UE (such as a UE 812a of <FIG> and/or UE <NUM> of <FIG>), network node (such as network node 810a of <FIG> and/or network node <NUM> of <FIG>), and host (such as host <NUM> of <FIG> and/or host <NUM> of <FIG>) discussed in the preceding paragraphs will now be described with reference to <FIG>.

One or more of the various embodiments improve the performance of OTT services provided to the UE <NUM> using the OTT connection <NUM>, in which the wireless connection <NUM> forms the last segment. All embodiments of the present invention provide a consistent handling of UEs after an inter-system handover from 5GS to EPS, even after RLF and subsequent connection reestablishment. This leads to improved UE inter-system mobility and, consequently, more consistent delivery of OTT services to UEs via the network as well as improved end-user experience. This increases the value of OTT services to both end-users and service providers.

In some examples, a measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring the OTT connection <NUM> between the host <NUM> and UE <NUM>, in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection may be implemented in software and hardware of the host <NUM> and/or UE <NUM>. In some embodiments, sensors (not shown) may be deployed in or in association with other devices through which the OTT connection <NUM> passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above or supplying values of other physical quantities from which software may compute or estimate the monitored quantities. The reconfiguring of the OTT connection <NUM> may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not directly alter the operation of the network node <NUM>. In certain embodiments, measurements may involve proprietary UE signaling that facilitates measurements of throughput, propagation times, latency and the like, by the host <NUM>. The measurements may be implemented in that software causes messages to be transmitted, in particular empty or 'dummy' messages, using the OTT connection <NUM> while monitoring propagation times, errors, etc..

The foregoing merely illustrates the principles of the disclosure. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements, and procedures that, although not explicitly shown or described herein, embody the principles of the invention as defined by the appended claims. Various embodiments can be used together with one another, as well as interchangeably therewith, as should be understood by those having ordinary skill in the art.

The term unit, as used herein, can have conventional meaning in the field of electronics, electrical devices and/or electronic devices and can include, for example, electrical and/or electronic circuitry, devices, modules, processors, memories, logic solid state and/or discrete devices, computer programs or instructions for carrying out respective tasks, procedures, computations, outputs, and/or displaying functions, and so on, as such as those that are described herein.

Claim 1:
A method for a first network node of a wireless network for connection re-establishment of a user equipment, UE, the method comprising:
sending (<NUM>), to a second network node of the wireless network, a request to retrieve context information associated with the user equipment, UE, the connection of said UE has been or is being reestablished with the first network node following radio link failure, RLF, towards the second network node, wherein the wireless network is an Evolved Packet System, EPS, and the first and second network nodes are evolved NodeBs, eNBs; and
receiving (<NUM>) the context information associated with the UE from the second network node, wherein the context information includes an indication that the UE due to an active IP Multimedia System, IMS, voice fallback was handed over from a <NUM> System, 5GS, to EPS via a first inter-system handover