WO2020186422A1

WO2020186422A1 - Method and apparatus for fast return to 5gs after eps fallback

Info

Publication number: WO2020186422A1
Application number: PCT/CN2019/078482
Authority: WO
Inventors: Zhendong Li
Original assignee: Zte Corporation
Priority date: 2019-03-18
Filing date: 2019-03-18
Publication date: 2020-09-24
Also published as: CN113597785A

Abstract

A method and apparatus for fast returning to 5G after an EPS fallback process is disclosed. In one embodiment, a method for performing a fast return to 5G by a first wireless communication node of a first wireless communication system, including: receiving a first message from a first core network of the first wireless communication system; and returning a wireless communication device to a second wireless communication system according to the first message, wherein the first message comprises an Evolved Packet System (EPS) fallback indication.

Description

METHOD AND APPARATUS FOR FAST RETURN TO 5GS AFTER EPS FALLBACK

TECHNICAL FIELD

This disclosure relates generally to wireless communications and, more particularly, to a method and apparatus for fast return to a 5G system (5GS) upon a completion of Evolved Packet System (EPS) fallback.

BACKGROUND

With a continuous increasing of global smartphone users, mobile data usage and traffic will continue to grow. During an early development stage of 5G system deployments, EPS fallback (i.e., from 5G to 4G) is recommended to support of voice services in a 5G system (5GS) to seamlessly transfer a voice service to an existing 4G system (i.e., Long-Term Evolution) which is coupled to the 5G system. The control plane embraces all signaling between network elements while the user plane carries the IP flows used for voice and e.g. for Internet access. EPS fallback enables phones to use the 5GC with New Radio prior to all needed voice features are in place in the phone and in New Generation-Radio Access Network (NG-RAN) and before the NG-RAN is dimensioned and tuned for voice. During call establishment the phone is moved from NG-RAN (i.e., 5G) to LTE (i.e., 4G) and the call is finally established on 4G. IP multimedia subsystem (IMS) network is an IP-based network architecture proposed by the 3rd Generation Partnership Project (3GPP) , providing an open and flexible environment that is independent of access and supporting multimedia applications (e.g., voice) . The IMS network can work over 5G to provide voice services, i.e., voice over New radio (VoNR) , and work over 4G to provide voice service, i.e., voice over LTE (VoLTE) . The 5GS and EPS provide IP connectivity and resources to the IMS network for multimedia applications.

SUMMARY OF THE INVENTION

The exemplary embodiments disclosed herein are directed to solving the issues related to one or more problems presented in the prior art, as well as providing additional features that will become readily apparent by reference to the following detailed description when taken in conjunction with the accompany drawings. In accordance with various embodiments, exemplary systems, methods, and computer program products are disclosed herein. It is understood, however, that these embodiments are presented by way of example and not limitation, and it will be apparent to those of ordinary skill in the art who read the present disclosure that various modifications to the disclosed embodiments can be made while remaining within the scope of the invention.

Inter-system handover or redirection of voice services from a 5GS to an EPS, known as EPS fallback (3GPP TS 23.501 and 23.502) , is enabled by common gateways and interworking between network function entities in the two systems. When an inter-system handover or redirection is triggered in NG-RAN, the all Packet Data Unit (PDU) sessions are transferred from 5GS to EPS if it can be moved to EPS. The common gateway ensures IP address preservation. However, after the voice service is complete in EPS, a UE cannot fast return to the 5GS. Therefore, there exists a need to develop a method and apparatus for fast return to 5GS after EPS fallback.

In one embodiment, method for performing a fast return to 5G by a first wireless communication node of a first wireless communication system, includes: receiving a first message from a first core network of the first wireless communication system; and returning a wireless communication device to a second wireless communication system according to the first message, wherein the first message comprises an Evolved Packet System (EPS) fallback indication.

In a further embodiment, a method for performing a fast return to 5G by a first core network of a first wireless communication system, includes: transmitting a first message to a first wireless communication node of the first wireless communication system, wherein the first message comprises an Evolved Packet System (EPS) fallback indication, wherein the EPS fallback indication in the first message is used by the first wireless communication node to return a wireless communication device to a second wireless communication system.

Yet in another embodiment, a computing device comprising at least one processor and a memory coupled to the processor, the at least one processor configured to carry out the method.

Yet, in another embodiment, a non-transitory computer-readable medium having stored thereon computer-executable instructions for carrying out the method.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that various features are not necessarily drawn to scale. In fact, the dimensions and geometries of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1A illustrates an exemplary wireless communication network, in accordance with some embodiments of the present disclosure.

FIG. 1B illustrates a block diagram of an exemplary wireless communication system, in accordance with some embodiments of the present disclosure.

FIG. 2 illustrates a method for performing a fast returning of a UE to a 5GS, in accordance with some embodiments of the present disclosure.

FIG. 3 illustrates a method for performing a fast returning of a UE to a 5GS, in accordance with some embodiments of the present disclosure.

FIG. 4 illustrates a method for performing a fast returning of a UE to a 5GS, in accordance with some embodiments of the present disclosure.

FIG. 5 illustrates a method for performing a fast returning of a UE to a 5GS, in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Various exemplary embodiments of the invention are described below with reference to the accompanying figures to enable a person of ordinary skill in the art to make and use the invention. As would be apparent to those of ordinary skill in the art, after reading the present disclosure, various changes or modifications to the examples described herein can be made without departing from the scope of the invention. Thus, the present invention is not limited to the exemplary embodiments and applications described or illustrated herein. Additionally, the specific order or hierarchy of steps in the methods disclosed herein are merely exemplary approaches. Based upon design preferences, the specific order or hierarchy of steps of the disclosed methods or processes can be re-arranged while remaining within the scope of the present invention. Thus, those of ordinary skill in the art will understand that the methods and techniques disclosed herein present various steps or acts in a sample order, and the invention is not limited to the specific order or hierarchy presented unless expressly stated otherwise.

Embodiments of the present invention are described in detail with reference to the accompanying drawings. The same or similar components may be designated by the same or similar reference numerals although they are illustrated in different drawings. Detailed descriptions of constructions or processes well-known in the art may be omitted to avoid obscuring the subject matter of the present invention. Further, the terms are defined in consideration of their functionality in embodiment of the present invention, and may vary according to the intention of a user or an operator, usage, etc. Therefore, the definition should be made on the basis of the overall content of the present specification.

Figure 1A illustrates an exemplary wireless communication network 100, in accordance with some embodiments of the present disclosure. A wireless communication system, comprises at least one network-side wireless communication node, at least one terminal-side communication device, and a core network. In some embodiments, the at least one network-side wireless communication node each can be one of the following: a node B, an E-utran Node B (also known as Evolved Node B, eNodeB or eNB) , a gNodeB (also known as gNB) in new radio (NR) technology, a pico station, a femto station, or the like. The at least one terminal-side wireless communication device each can be one of the following: a long range communication system like a mobile phone, a smart phone, a personal digital assistant (PDA) , tablet, laptop computer, or a short range communication system such as, for example a wearable device, a vehicle with a vehicular communication system and the like. A network-side wireless communication node is represented by a base station (BS) 102 hereinafter in all embodiments, and is generally referred to as “wireless communication node” . A terminal-side communication device is represented by a user equipment (UE) 104 hereinafter in all embodiments, and is generally referred to as “wireless communication devices” . Such communication nodes and devices may be capable of wireless and/or wired communications, in accordance with various embodiments of the invention. The core network in the wireless communication system further comprises a plurality of network function (NF) entities. It is noted that all the embodiments are merely preferred examples, and are not intended to limit the present disclosure. Accordingly, it is understood that the system may include any desired combination of UEs and BSs, while remaining within the scope of the present disclosure.

Referring to Figure 1A, the wireless communication network 100 includes a first BS 102-1, and a second BS 102-2, and a UE 104. The first BS 102-1, and the second BS 102-2 each is connected to a respective core network (CN) 108, i.e., the first BS 102-1 is connected to a first CN 108-1 through a first interface 107-1 and a second interface 107-2 and the second BS 102-2 is connected to a second CN 108-2 through a third interface 107-3 and a fourth interface 107-4. In some embodiments, the first CN 108-1 is a 5G Core Network (5GC) and the second CN 108-2 is an Evolved Packet System (EPS) . In some embodiments, the first CN 108-1 and the second CN 108-2 are connected through a fifth interface 156. The interfaces 107-1, 107-2, 107-3, 107-4 and 156 are specifically discussed in detail below.

In some embodiments, the first CN 108-1 further comprises at least one of the following network function (NF) entities: Access and Mobility Management Function (AMF) 122, User Plane Function (UPF) 126, and System Management Function (SMF) 124. In some embodiments, the first CN 108-1 further comprises Policy Control Function (PCF) and Unified Data Management (UDM) . In some embodiments, the AMF 122 supports at least one of the following: termination of Non-Access Stratum (NAS) signaling, NAS ciphering and integrity protection, registration management, connection management, mobility management, access authentication and authorization, and security context management. In some embodiments, the UPF 126 supports at least one of the following: packet routing and forwarding, packet inspection, Quality of Service (QoS) handling, acts as external Protocol Data Unit (PDU) session point of interconnect to Data Network (DN) , and is an anchor point for intra-and inter-Radio Access Technology (RAT) mobility. In some embodiments, the SMF 124 supports at least one of the following: session management (session establishment, modification, and release) , UE IP address allocation and management, Dynamic Host Configuration Protocol (DHCP) functions, termination of NAS signaling related to session management, Downlink (DL) data notification, and traffic steering configuration for UPF for proper traffic routing. In some embodiments, the PCF supports at least one of the following: unified policy framework, providing policy rules to Control Plane (CP) functions, and access subscription information for policy decisions in User Data Repository (UDR) . In some embodiments, the UDM supports at least one of the following: generation of Authentication and Key Agreement (AKA) credentials, user identification handling, access authorization and subscription management. In some embodiments, the first CN 108-1 has a CP and User Plane (UP) split. In some embodiments, the UPF supports UP data processing and the AMF, SMF, PCF, and UDM act as CP functions.

In some embodiments, the second CN 108-2 further comprises at least one of the following NF entities: Mobility Management Entity (MME) 130, Serving Gateway (SGW) 128, Packet Data Network (PDN) Gateway control plane (PGW-C) 132, and PGW-User plane (PGW-U) 134. In some embodiments, the second CN 108-2 further comprises Policy and Charging Rules Function (PCRF) , and Home Subscriber Server (HSS) . In some embodiments, the MME 130 of the second CN 108-2 supports at least one of the following: paging and tagging procedure by idle mode UE, bearer activation/deactivation process, choosing a SGW 128 for a UE at the initial attach and during intra-LTE handover, authenticating the user, and ciphering/integrity protection. In some embodiments, the SGW 128 supports one of the following: routing and forwarding user data packets, acting as the mobility anchor for the UP during inter-eNB handovers and as the anchor for mobility between LTE and other 3GPP technologies. In some embodiments, the PGW 132/134 of the second CN 108-2 supports at least one of the following: connectivity from the UE to external packet data networks, policy enforcement, packet filtering, charging support, lawful interception and packet screening, and activing as an anchor for mobility between 3GPP and non-3GPP technologies. In some embodiments, the PCRF of the second CN 108-2 supports at least one of the following: real-time determination of policy rules, aggregates information to and from the network, and creation of rules and automatically making policy decisions for each subscriber active on the network. In some embodiments, the HSS of the second CN 108-2 supports at least one of the following: storage of user-related and subscription-related information, mobility management, call and session establishment support, user authentication and access authorization.

In the illustrated embodiment, the first CN 108-1 and the second CN 108-2 share two combo-nodes, i.e., a first combo-node140-1 and a second combo-node 140-2. In some embodiments, each of the two combo-nodes comprises two NF entities for both of the first CN 108-1 and the second CN 108-2. For example, the first combo-node 140-1 comprises the UPF 126 of the first CN 108-1 and the PGW-U 134 of the second CN 108-2; and the second combo-node 140-2 comprises the SMF 124 of the first CN 108-1 and the PGW-C 132 of the second CN 108-2.

In some embodiments, the UE 104 is connected to the AMF 122 of the first CN 108-1 through a logical N1 interface 164 and is connected to the MME of the second CN 108-2 through an EPC interface 166. In some embodiments, the first BS 102-1 is connected to the AMF 122 of the first CN 108-1 through the first interface 107-1 (i.e., N2 interface) and is connected to UPF 126 of the first CN 108-1 through the second interface 107-2, i.e., N3 interface. In some embodiments, the second BS 102-2 is connected to the SGW 128 of the second CN 108-1 through the fourth interface 107-4, i.e., S1-U interface, and is connected to the MME 130 of the second CN 108-1 through the third interface 107-3, i.e., S1-C interface. In some embodiments, the AMF 122 of the first CN 108-1 is connected to the MME 130 of the second CN 108-2 through the fifth interface 156 (i.e., N26 interface) . In some embodiments, the SGW 128 of the second CN 108-2 is connected to the MME 130 of the second CN 108-2 through a S11 interface 162. In some embodiments, the SGW 128 of the second CN 108-2 is coupled to the first combo- node 140-1 (i.e., the UPF 126 of the first CN 108-1 and the PGW-U of the second CN 108-2) through a S5-U interface 160. In some embodiments, the SGW 128 of the second CN 108-2 is connected to the second combo-node 140-2 (i.e., the SMF 124 of the first CN 108-1 and the PGW-C 132 of the second CN 108-2) through a S5-C interface 158. In some embodiments, the AMF 122 of the first CN 108-1 is coupled to second combo-node 140-2 (i.e., the SMF 124 of the first CN 108-1 and the PGW-C 132 of the second CN 108-2) through a N11 interface 152. In some embodiments, the first combo-node 140-1 is connected to the second combo-node 140-2 through the fifth interface 154, i.e., N4 interface.

Figure 1B illustrates a block diagram of an exemplary wireless communication system 150, in accordance with some embodiments of the present disclosure. The system 150 may include components and elements configured to support known or conventional operating features that need not be described in detail herein. In some embodiments, the system 150 can be used to transmit and receive data symbols in a wireless communication environment such as the wireless communication network 100 of Figure 1A, as described above.

The system 150 generally includes a first BS 102-1, a second BS 102-2, and a UE 104, collectively referred to as BS 102 and UE 104 below for ease of discussion. The first BS 102-1 and the second BS 102-2 each comprises a BS transceiver module 152, a BS antenna array 154, a BS memory module 156, a BS processor module 158, and a network interface 160. In the illustrated embodiment, each module of the BS 102 are coupled and interconnected with one another as necessary via a data communication bus 180. The UE 104 comprises a UE transceiver module 162, a UE antenna 164, a UE memory module 166, a UE processor module 168, and an I/O interface 169. In the illustrated embodiment, each module of the UE 104 are coupled and interconnected with one another as necessary via a date communication bus 190. The BS 102 communicates with the UE 104 via a communication channel 192, which can be any wireless channel or other medium known in the art suitable for transmission of data as described herein.

As would be understood by persons of ordinary skill in the art, the system 150 may further include any number of modules other than the modules shown in Figure 1B. Those skilled in the art will understand that the various illustrative blocks, modules, circuits, and processing logic described in connection with the embodiments disclosed herein may be implemented in hardware, computer-readable software, firmware, or any practical combination thereof. To clearly illustrate this interchangeability and compatibility of hardware, firmware, and software, various illustrative components, blocks, modules, circuits, and steps are described generally in terms of their functionality. Whether such functionality is implemented as hardware, firmware, or software depends upon the particular application and design constraints imposed on the overall system. Those familiar with the concepts described herein may implement such functionality in a suitable manner for each particular application, but such implementation decisions should not be interpreted as limiting the scope of the present invention.

A wireless transmission from a transmitting antenna of the UE 104 to a receiving antenna of the BS 102 is known as an uplink (UL) transmission, and a wireless transmission from a transmitting antenna of the BS 102 to a receiving antenna of the UE 104 is known as a downlink (DL) transmission. In accordance with some embodiments, the UE transceiver 162 may be referred to herein as an "uplink" transceiver 162 that includes a RF transmitter and receiver circuitry that are each coupled to the UE antenna 164. A duplex switch (not shown) may alternatively couple the uplink transmitter or receiver to the uplink antenna in time duplex fashion. Similarly, in accordance with some embodiments, the BS transceiver 152 may be referred to herein as a "downlink" transceiver 152 that includes RF transmitter and receiver circuitry that are each coupled to the antenna array 154. A downlink duplex switch may alternatively couple the downlink transmitter or receiver to the downlink antenna array 154 in time duplex fashion. The operations of the two

transceivers

152 and 162 are coordinated in time such that the uplink receiver is coupled to the uplink UE antenna 164 for reception of transmissions over the wireless communication channel 192 at the same time that the downlink transmitter is coupled to the downlink antenna array 154. Preferably, there is close synchronization timing with only a minimal guard time between changes in duplex direction. The UE transceiver 162 communicates through the UE antenna 164 with the BS 102 via the wireless communication channel 192. The BS transceiver 152 communications through the BS antenna 154 of a BS (e.g., the first BS 102-1) with the other BS (e.g., the second BS 102-2) via a wireless communication channel 196. The wireless communication channel 196 can be any wireless channel or other medium known in the art suitable for direct communication between BSs.

The UE transceiver 162 and the BS transceiver 152 are configured to communicate via the wireless data communication channel 192, and cooperate with a suitably configured RF antenna arrangement 154/164 that can support a particular wireless communication protocol and modulation scheme. In some exemplary embodiments, the UE transceiver 162 and the BS transceiver 152 are configured to support industry standards such as the Long Term Evolution (LTE) and emerging 5G standards (e.g., NG-RAN) , and the like. It is understood, however, that the invention is not necessarily limited in application to a particular standard and associated protocols. Rather, the UE transceiver 162 and the BS transceiver 152 may be configured to support alternate, or additional, wireless data communication protocols, including future standards or variations thereof.

The

processor modules

158 and 168 may be implemented, or realized, with a general purpose processor, a content addressable memory, a digital signal processor, an application specific integrated circuit, a field programmable gate array, any suitable programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof, designed to perform the functions described herein. In this manner, a processor module may be realized as a microprocessor, a controller, a microcontroller, a state machine, or the like. A processor module may also be implemented as a combination of computing devices, e.g., a combination of a digital signal processor and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a digital signal processor core, or any other such configuration.

Furthermore, the steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in firmware, in a software module executed by

processor modules

158 and 168, respectively, or in any practical combination thereof. The

memory modules

156 and 166 may be realized as RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. In this regard, the

memory modules

156 and 166 may be coupled to the

processor modules

158 and 168, respectively, such that the

processors modules

158 and 168 can read information from, and write information to,

memory modules

156 and 166, respectively. The

memory modules

156 and 166 may also be integrated into their

respective processor modules

158 and 168. In some embodiments, the

memory modules

156 and 166 may each include a cache memory for storing temporary variables or other intermediate information during execution of instructions to be executed by

processor modules

158 and 168, respectively. The

memory modules

156 and 166 may also each include non-volatile memory for storing instructions to be executed by the

processor modules

158 and 168, respectively.

The network interface 160 generally represents the hardware, software, firmware, processing logic, and/or other components of the base station 102 that enable bi-directional communication between BS transceiver 152 and other network components and communication nodes configured to communication with the BS 102. For example, network interface 160 may be configured to support internet or WiMAX traffic. In a typical deployment, without limitation, network interface 160 provides an 802.3 Ethernet interface such that BS transceiver 152 can communicate with a conventional Ethernet based computer network. In this manner, the network interface 160 may include a physical interface for connection to the computer network (e.g., Mobile Switching Center (MSC) ) . The terms “configured for” or “configured to” as used herein with respect to a specified operation or function refers to a device, component, circuit, structure, machine, signal, etc. that is physically constructed, programmed, formatted and/or arranged to perform the specified operation or function. The network interface 160 could allow the BS 102 to communicate with other BSs or a CN over a wired or wireless connection.

Referring again to Figure 1A, as mentioned above, the BS 102 repeatedly broadcasts system information associated with the BS 102 to one or more UEs 104 so as to allow the UEs 104 to access the network within the cells (e.g., 110-1 for the first BS 102-1 and 110-2 for the second BS 102-2) where the BS 102 is located, and in general, to operate properly within the cell. Plural information such as, for example, downlink and uplink cell bandwidths, downlink and uplink configuration, cell information, configuration for random access, etc., can be included in the system information, which will be discussed in further detail below.

Referring again to Figure 1B, in some embodiments, the major system information carried by the first broadcast signal may be transmitted by the BS 102 in a symbol format via the communication channel 192 (e.g., a PBCH) . In accordance with some embodiments, an original form of the major system information may be presented as one or more sequences of digital bits and the one or more sequences of digital bits may be processed through plural steps (e.g., coding, scrambling, modulation, mapping steps, etc. ) , all of which can be processed by the BS processor module 158, to become the first broadcast signal. Similarly, when the UE 104 receives the first broadcast signal (in the symbol format) using the UE transceiver 162, in accordance with some embodiments, the UE processor module 168 may perform plural steps (de-mapping, demodulation, decoding steps, etc. ) to estimate the major system information such as, for example, bit locations, bit numbers, etc., of the bits of the major system information. The UE processor module 168 is also coupled to the I/O interface 169, which provides the UE 104 with the ability to connect to other devices such as computers. The I/O interface 169 is the communication path between these accessories and the UE processor module 168.

Figure 2 illustrates a method 200 for performing fast return to a 5GS, in accordance with some embodiments of the present disclosure. It is understood that additional operations may be provided before, during, and after the method 200 of Figure 2, and that some operations may be omitted or reordered. The communication system in the illustrated embodiment comprises a first BS 102-1, second BS 102-2, a first CN 108-1, a second CN 108-2, and a UE 104. In the illustrated embodiments, the UE 104 is in one of at least one serving cell covered by the first BS 102-1 and the second BS 102-2, i.e., the UE 104 is in connection with one of the following: the first BS 102-1 and the second BS 102-2. In the illustrated embodiments, the UE 104 is in connection with the first BS 102-1 initially. In the illustrated embodiment, the first BS 102-1 is a NG RAN and the first CN 108-1 is a 5GC, the second BS 102-2 is a 4G RAN (i.e., eNB) and the second CN 108-2 is an EPC. Figure 2 is for illustration purposes and is not intend to be limiting. It should be noted that that any numbers of BS 102 can be used, which is within the scope of this invention.

The method 200 starts with operation 202 in which a first message is transmitted from the first BS 102-1 to the first CN 108-1 according to some embodiments. In some embodiments, when the first BS 102-1 initiates a first handover procedure for EPS fallback, the first message transmitted by the first BS 102-1 is a handover request message. In some embodiments, the first message is received by an AMF of the first CN 108-1. In some embodiments, the first message comprises a first information entity (IE) for an EPS fallback indication and in some embodiments, the first IE is carried in a source-to-target transparent container. In some embodiments, the first IE for the EPS fallback indication has a binary value, e.g., a value of 0 indicate that no EPS fallback is performed and a value of 1 indicates that an EPS fallback is performed. In some embodiments, the EPS fallback indication is used to trigger a return to a 5GS of the UE 104 after an IMS voice session is completed. In some embodiments, the source-to-target container further comprises a second IE, wherein the second IE comprises a 5G Public Land Mobile Network (PLMN) Identifier (ID) . In some embodiments, the 5G PLMN ID in the EPS fallback indication is used to locate a neighboring cell of an NG-RAN within the 5G PLMN.

The method 200 continues with operation 204 in which a second message is transmitted from the first CN 108-1 to the second CN 108-2 according to some embodiments. In some embodiments, the second message is a Forward Relocation message. In some embodiments, the second message is transmitted from the AMF of the first CN 108-1 to a MME of the second CN 108-2. In some embodiments, the second message further comprises the source to target transparent container.

The method 200 continues with operation 206 in which a third message is received by the second BS 102-2 from the second CN 108-2 according to some embodiments. In some embodiments, the third message is a Handover Request message. In some embodiments, the third message comprises the source to target transparent container.

The method 200 continues with operation 208 in which an IMS voice session is established according to some embodiments. In some embodiments, a PGW of the second CN 108-2 transmits a Create Bearer Request message to the MME through a SGW of the second CN 108-2. The MME of the second CN 108-2 further transmits a Bearer Setup Request message to the second BS 102-2. After a dedicated bearer for the IMS voice service is setup, an IMS network (not shown) continues an IMS voice session establishment for the UE 104. After dedicated bearer for the IMS voice session is established, the EPC notifies the IMS network. The NF entity of the IMS network, i.e., Proxy-Call Session Control Function (P-CSCF) , continues sending IMS signaling to establish the IMS voice session.

The method 200 continues with operation 210 in which a fourth message is received by the second BS 102-2 from the second CN 108-2 according to some embodiments. In some embodiments, the fourth message is received from the MME of the second CN 108-2. In some embodiments, the fourth message is a Deactivate Bearer Request message so as to delete the dedicated bearer for the IMS voice session. In some embodiments, a Quality of Service Class Identifier (QCI) of the dedicated bearer is 1.

The method 200 continues with operation 212A in which a fifth message is transmitted by the second BS 102-2 to the second CN 108-2 according to some embodiments. In some embodiments, the fifth message is a Handover Required message so as to initiate a second handover procedure, through which the UE 104 is returned from the second BS 102-2 to a 5GS, according to at least one of the following: the EPS fallback indication and the 5G PLMN ID. In some embodiments, the UE 104 accesses a third BS (not shown) , wherein the third BS is an NG-RAN within the 5GS which is identified by the 5G PLMN ID. In some embodiments, the third BS is the same as the first BS 102-1. In some other embodiments, the third BS 102-3 is different from the first BS 102-1.

Alternatively, the method 200 continues with operation 212B in which a fifth message is transmitted from the second BS 102-2 to the UE 104 according to some embodiments. In some embodiments, the fifth message is a Radio Resource Control (RRC) Release message with redirection information so as to initiate an RRC release procedure, through which BS 102-2 initiates RRC release with redirection, according to at least one of the following: the EPS fallback indication and the 5G PLMN ID. In some embodiments, the fifth message comprises redirection information to return the UE 104 to the 5GS. In some embodiments, the UE 104 access a third BS (not shown) , wherein the third BS is an NG-RAN within the 5GS which is identified by the 5G PLMN ID. In some embodiments, the third BS is the same as the first BS 102-1. In some other embodiments, the third BS 102-3 is different from the first BS 102-1.

The method 200 continues with operation 214 in which the UE access the 5GS according to prior art. In some embodiments, when the fifth message is a Handover Required message, the second BS 102-2 transmits a Handover Command to the UE 104, the UE 104 accesses the third BS on radio resources reserved by the third BS. In some other embodiments, when the fifth message is a Radio Resource Control (RRC) Release message, the UE 104 accesses the third BS according to the redirection information in the fifth message.

Figure 3 illustrates a method 300 for performing a fast returning of a UE 104 to a 5GS, in accordance with some embodiments of the present disclosure. It is understood that additional operations may be provided before, during, and after the method 300 of Figure 3, and that some operations may be omitted or reordered. The communication system in the illustrated embodiment comprises a first BS 102-1, second BS 102-2, a third BS 102-3, a first CN 108-1, a second CN 108-2, and a UE 104. In the illustrated embodiments, the second CN 108-2 comprises a first NF 302-1 and a second NF 302-2, wherein the first NF 302-1 and the second NF 302-2 each is a MME. In the illustrated embodiments, the UE 104 is in one of at least one serving cell covered by one of the following: the first BS 102-1, the second BS 102-2, and the third BS 102-3, i.e., the UE 104 is in connection with one of the following: the first BS 102-1, the second BS 102-2, and the third BS 102-3. In the illustrated embodiment, the first BS 102-1 is a NG-RAN and the first CN 108-1 is a 5GC, the second BS 102-2 and the third BS 102-3 each is a 4G RAN (i.e., eNB) and the second CN 108-2 is an EPS. In some embodiments, the UE 104 can be moved from the second BS 102-2 to the third BS 102-3 during an intra-RAT handover. Figure 3 is for illustration purposes and is not intend to be limiting. It should be noted that that any numbers of BS 102 can be used, which is within the scope of this invention.

The method 300 starts with operation 312 in which a first message is transmitted from the first BS 102-1 to the first CN 108-1 according to some embodiments. In some embodiments, when the first BS 102-1 initiates a first handover procedure for EPS fallback, the first message transmitted by the first BS 102-1 is a handover request message. In some embodiments, the first message is received by an AMF of the first CN 108-1. In some embodiments, the first message comprises a first information entity (IE) for an EPS fallback indication and in some embodiments, the first IE is within a source-to-target transparent container. In some embodiments, the first IE for the EPS fallback indication is a binary value, e.g., a value of 0 indicate that no EPS fallback is performed and a value of 1 indicates that an EPS fallback is performed. In some embodiments, the EPS fallback indication is used to trigger a return to a 5GS for the UE 104 after an IMS voice session is completed. In some embodiments, the source-to-target transparent container further comprises a second IE, wherein the second IE comprises a 5G Public Land Mobile Network (PLMN) Identifier (ID) . In some embodiments, the 5G PLMN ID in the EPS fallback indication is used to locate a neighboring cell of an NG-RAN within the 5G PLMN.

The method 300 continues with operation 314 in which a second message is transmitted from the first CN 108-1 to the second CN 108-2 according to some embodiments. In some embodiments, the second message is a Forward Relocation message. In some embodiments, the second message is transmitted from the AMF of the first CN 108-1 to the first NF 302-1 of the second CN 108-2. In some embodiments, the second message further comprises the source to target transparent container.

The method 300 continues with operation 316 in which a third message is received by the second BS 102-2 from the first NF 302-1 of the second CN 108-2 according to some embodiments. In some embodiments, the third message is a Handover Request message. In some embodiments, the third message comprises the source-to-target transparent container.

The method 300 continues with operation 318 in which an IMS voice session is established according to some embodiments. In some embodiments, a PGW (not shown) of the second CN 108-2 transmits a Create Bearer Request message to the first NF 302-1 (i.e., MME) through a SGW (not shown) of the second CN 108-2. The first NF 302-1 of the second CN 108-2 further transmits a Bearer Setup Request message to the second BS 102-2. After a dedicated bearer for the IMS voice service is setup, an IMS network (not shown) continues IMS voice session establishment for the UE 104. After dedicated bearer for the IMS voice session is established, the EPS notifies the IMS network. An NF entity of the IMS network, i.e., Proxy-Call Session Control Function (P-CSCF) , continues sending IMS signaling to establish the IMS voice session.

The method 300 continues with operation 320 in which a fourth message is transmitted from the second BS 102-2 to the first NF 302-1 of the second CN 108-2 according to some embodiments. In some embodiments, the fourth message is a Handover Request message, when the second BS 102-2 initiates a second handover procedure. In some embodiments, the fourth message comprises the source-to-target transparent container.

The method 300 continues with operation 322 in which a fifth message is transmitted from the first NF 302-1 of the second CN 108-2 to the second NF 302-2 of the second CN 108-2 according to some embodiments. In some embodiments, the fifth message is a Forward Relocation Request message. In some embodiments, the fifth message comprises the source-to-target transparent container. In some other embodiments, when the second BS 102-2 and the third BS 102-3 share the same MME, i.e., the first NF 302-1 is the same as the second NF 302-2, the operation 322 is optional.

The method 300 continues with operation 324 in which a sixth message is transmitted from the second NF 302-2 of the second CN 108-2 to the third BS 102-3 according to some embodiments. In some embodiments, the sixth message is a Handover Request message. In some embodiments, the sixth message comprises the source-to-target transparent container.

.The method 300 continues with operation 326 in which a seventh message is received by the third BS 102-3 from the second NF 302-2 of the second CN 108-2 according to some embodiments. In some embodiments, the seventh message is a Deactivate Bearer Request so as to delete the dedicated bearer for the IMS voice session. In some embodiments, a Quality of Service Class Identifier (QCI) of the dedicated bearer is 1.

The method 300 continues with operation 328A in which an eighth message is transmitted by the third BS 102-3 to the second NF 302-2 of the second CN 108-2 according to some embodiments. In some embodiments, the eighth message is Handover required message so as to initiate a third handover procedure, through which the UE 104 is returned from the third BS 102-3 to a 5GS, according to at least one of the following in the source-to-target container: the EPS fallback indication and the 5G PLMN ID. In some embodiments, the UE 104 is handed over to a fourth BS (not shown) , wherein the fourth BS is a NG-RAN within the 5G PLMN. In some embodiments, the fourth BS is the same as the first BS 102-1. In some other embodiments, the fourth BS 102-3 is different from the first BS 102-1.

Alternatively, the method 300 continues with operation 328B in which an eighth message is transmitted from the third BS 102-3 to the UE 104 according to some embodiments. In some embodiments, the eighth message is a Radio Resource Control (RRC) Release message so as to initiate an RRC release procedure, through which BS 102-2 initiates RRC release with redirection, according to at least one of the following: the EPS fallback indication and the 5G PLMN ID. In some embodiments, the eighth message comprises redirection information to return the UE 104 to the 5GS. In some embodiments, the UE 104 accesses a fourth BS (not shown) , wherein the fourth BS is a NG-RAN within the 5G PLMN. In some embodiments, the fourth BS is the same as the first BS 102-1. In some other embodiments, the fourth BS is different from the first BS 102-1.

The method 300 continues with operation 330 in which the UE 104 accesses the 5GS according to prior art. In some embodiments, when the eighth message is a Handover Required message, the second BS 102-2 transmits a Handover Command to the UE 104, the UE 104 accesses the fourth BS on radio resources reserved by the fourth BS for the UE 104. In some other embodiments, when the eighth message is a Radio Resource Control (RRC) Release message, the UE 104 accesses the fourth BS according to the redirection information in the eighth message.

Figure 4 illustrates a method 400 for performing a fast returning of a UE 104 to a 5GS, in accordance with some embodiments of the present disclosure. It is understood that additional operations may be provided before, during, and after the method 400 of Figure 4, and that some operations may be omitted or reordered. The communication system in the illustrated embodiment comprises a first BS 102, second BS 102-2, a third BS 102-3, a first CN 108-1, a second CN 108-2, and a UE 104. In the illustrated embodiments, the second CN 108-2 comprises a first NF 302-1 and a second NF 302-2, wherein the first NF 302-1 and the second NF 302-2 each is a MME. In the illustrated embodiments, the UE 104 is in one of at least one serving cell covered by one of the following: the first BS 102-1, the second BS 102-2, and the third BS 102-3, i.e., the UE 104 is in connection with one of the following: the first BS 102-1, the second BS 102-2, and the third BS 102-3. In the illustrated embodiment, the first BS 102-1 is a NG-RAN and the first CN 108-1 is a 5GC, the second BS 102-2 and the third BS 102-3 each is a 4G RAN (i.e., eNB) and the second CN 108-2 is an EPS. In some embodiments, the UE 104 can be moved from the second BS 102-2 to the third BS 102-3 during an intra-RAT handover. Figure 4 is for illustration purposes and is not intend to be limiting. It should be noted that that any numbers of BS 102 can be used, which is within the scope of this invention.

The method 400 starts with operation 402 in which a first message is transmitted from the first BS 102-1 to the first CN 108-1 according to some embodiments. In some embodiments, when the first BS 102-1 initiates a first handover procedure for EPS fallback, the first message transmitted by the first BS 102-1 is a handover request message. In some embodiments, the first message is received by an AMF of the first CN 108-1. In some embodiments, the first message comprises a first information entity (IE) for an EPS fallback indication and in some embodiments, the first IE is within a source-to-target transparent container. In some embodiments, the first IE for the EPS fallback indication is a binary value, e.g., a value of 0 indicate that no EPS fallback is performed and a value of 1 indicates that an EPS fallback is performed. In some embodiments, the EPS fallback indication is used to trigger a return to a 5GS for the UE 104 after an IMS voice session is completed. In some embodiments, the source-to-target transparent container in the first message further comprises a second IE, wherein the second IE comprises a 5G Public Land Mobile Network (PLMN) Identifier (ID) . In some embodiments, the 5G PLMN ID in the EPS fallback indication is used to locate a neighboring cell of an NG-RAN within the 5G PLMN.

The method 400 continues with operation 404 in which a second message is transmitted from the first CN 108-1 to the second CN 108-2 according to some embodiments. In some embodiments, the second message is a Forward Relocation message. In some embodiments, the second message is transmitted from the AMF of the first CN 108-1 to the first NF 302-1 of the second CN 108-2. In some embodiments, the second message further comprises the source-to-target transparent container.

The method 400 continues with operation 406 in which a third message is received by the second BS 102-2 from the first NF 302-1 of the second CN 108-2 according to some embodiments. In some embodiments, the third message is a Handover Request message. In some embodiments, the third message comprises the source-to-target transparent container.

The method 400 continues with operation 408 in which an IMS voice session is established according to some embodiments. In some embodiments, a PGW (not shown) of the second CN 108-2 transmits a Create Bearer Request message to the first NF 302-1 (i.e., MME) through a SGW (not shown) of the second CN 108-2. The first NF 302-1 of the second CN 108-2 further transmits a Bearer Setup Request message to the second BS 102-2. After a dedicated bearer for the IMS voice service is setup, an IMS network (not shown) continues IMS voice session establishment for the UE 104. After dedicated bearer for the IMS voice session is established, the EPS notifies the IMS network. An NF entity of the IMS network, i.e., Proxy-Call Session Control Function (P-CSCF) , continues sending IMS signaling to establish the IMS voice session.

The method 400 continues with operation 410 in which a fourth message is transmitted from the second BS 102-2 to the third BS 102-3 according to some embodiments. In some embodiments, the fourth message is a Handover Request message, when the second BS 102-2 initiates a second handover procedure. In some embodiments, the fourth message is transmitted through an X2 interface. In some embodiments, the fourth message further comprises the source-to-target transparent container.

The method 400 continues with operation 412 in which a fifth message is received by the third BS 102-3 from the second NF 302-2 of the second CN 108-2 according to some embodiments. In some embodiments, the seventh message is a Deactivate Bearer Request so as to delete the dedicated bearer for the IMS voice session. In some embodiments, a Quality of Service Class Identifier (QCI) of the dedicated bearer is 1.

The method 400 continues with operation 414A in which a sixth message is transmitted by the third BS 102-3 to the second NF 302-2 of the second CN 108-2 according to some embodiments. In some embodiments, the eighth message is Handover required message so as to initiate a third handover procedure, through which BS 102-2 initiates RRC release with redirection, according to at least one of the following in the source-to-target transparent container: the EPS fallback indication and the 5G PLMN ID. In some embodiments, the eighth message comprises redirection information to return the UE 104 to the 5GS. In some embodiments, the UE 104 accesses a fourth BS (not shown) , wherein the fourth BS is a NG-RAN within the 5G PLMN. In some embodiments, the fourth BS is the same as the first BS 102-1. In some other embodiments, the fourth BS is different from the first BS 102-1.

Alternatively, the method 400 continues with operation 414B in which a sixth message is transmitted from the third BS 102-3 to the UE 104 according to some embodiments. In some embodiments, the eighth message is a Radio Resource Control (RRC) Release message so as to initiate an RRC release procedure, through which the UE 104 is returned from the third BS 102-2 to a 5GS, according to at least one of the following: the EPS fallback indication and the 5G PLMN ID. In some embodiments, the eighth message comprises redirection information to return the UE 104 to the 5GS. In some embodiments, the UE 104 locates a fourth BS (not shown) , wherein the fourth BS is a neighboring NG-RAN of the UE 104 with the 5G PLMN ID. In some embodiments, the fourth BS is the same as the first BS 102-1. In some other embodiments, the fourth BS is different from the first BS 102-1.

The method 400 continues with operation 416 in which the UE 104 accesses the 5GS according to prior art. In some embodiments, when the eighth message is a Handover Required message, the second BS 102-2 transmits a Handover Command to the UE 104, the UE 104 accesses the fourth BS on radio resources reserved by the fourth BS for the UE 104. In some other embodiments, when the eighth message is a Radio Resource Control (RRC) Release message, the UE 104 accesses the fourth BS according to the redirection information in the eighth message.

Figure 5 illustrates a method 500 for performing a fast returning of a UE 104 to a 5GS, in accordance with some embodiments of the present disclosure. It is understood that additional operations may be provided before, during, and after the method 500 of Figure 5, and that some operations may be omitted or reordered. The communication system in the illustrated embodiment comprises a first BS 102-1, a second BS 102-2, a first CN 108-1, a second CN 108-2, and a UE 104. In the illustrated embodiments, the second CN 108-2 further comprises a plurality of network function (NF) entities, including a first NF 502-1, a second NF 502-2, and a third NF 502-3. In the illustrated embodiments, the first NF 502-1 is at least one of the following: a PGW-C and a PGW-U; the second NF 502-2 is a SGW; and the third NF 502-3 is a MME. In the illustrated embodiments, the first CN 108-1 comprises a plurality of NF entities, including the first NF 502-1, and a fourth NF 502-4. In some embodiments, the first NF 502-1 is a combo-node supporting network functions of the first CN 108-1 and the second CN 108-2. Specifically, the first NF 502-1 is one of the following: a first combo-node with the SMF of the first CN 108-1 and the PGW-C of the second CN 108-2, and a second combo-node with the UPF of the first CN 108-1 and the PGW-U of the second CN 108-2. In some embodiments, the fourth NF 502-4 is an AMF of the first CN 108-1. In the illustrated embodiments, the UE 104 is in one of at least one serving cell covered by one of the following: the first BS 102-1 and the second BS 102-2, i.e., the UE 104 is in connection with one of the following the first BS 102-1 and the second BS 102-2. In the illustrated embodiment, the first BS 102-1 is a NG-RAN and the first CN 108-1 is a 5GC, the second BS 102-2 is a 4G RAN (i.e., eNB) and the second CN 108-2 is an EPS. Figure 5 is for illustration purposes and is not intend to be limiting. It should be noted that that any numbers of BS 102 can be used, which is within the scope of this invention.

The method 500 starts with operation 512 in which a first message is received by the first CN 108-1 from the first BS 104-1 according to some embodiments. In some embodiments, the first message is received by the fourth NF 502-4 of the first CN 108-1. In some embodiments, the first message is an N2 Protocol Data Unit (PDU) Session Acknowledgement message. In some embodiments, the first message further comprises a first information entity (IE) for an EPS fallback indication. In some embodiments, the EPS fallback indication is used to trigger a return to a 5GS of the UE 104 after an IMS voice session is completed.

The method 500 continues with operation 514 in which a second message is transmitted from the fourth NF 502-4 to the first NF 502-1 of the first CN 108-1 according to some embodiments. In some embodiments, the second message is Nsmf_PDUSession_UpdateSMContext service operation so as to inform the first NF 502-1 of the first CN 108-1 about rejection of the PDU session modification to setup a QoS flow for the IMS voice session with an indication that mobility due to the EPS fallback for the IMS voice session.

The method 500 starts with operation 516 in which a third message is transmitted in the second CN 108-2 from the first NF 502-1 to the second NF 502-2 according to some embodiments. In some embodiments, the operation 516 is performed after the EPS fallback, when a dedicated bearer for an IMS voice session is initiated by the first NF 502-1. In some embodiments, the first message is a Create Bearer Request message. In some embodiments, the third message further comprises the first IE for the EPS fallback indication. In some embodiments, the third message further comprises the second IE with the 5G PLMN ID.

In some other embodiments, the operation 516 is performed after the EPS fallback, when a dedicated bearer for an IMS voice session is deleted by the first NF 402-1. In some embodiments, the third message is a Delete Bearer Request message. In some embodiments, the third message further comprises the first IE for the EPS fallback indication. In some embodiments, the third message further comprises the second IE with the 5G PLMN ID.

The method 500 continues with operation 518 in which a fourth message is transmitted in the second CN 102-2 from the second NF 502-2 to the third NF 502-3 according to some embodiments. In some embodiments, the fourth message is a Delete Bearer Request message, when the third message is a Delete Bearer Request message. In some other embodiments, the fourth message is a Create Bearer Request message, when the third message is a Create Bearer Request message. In some embodiments, the fourth message further comprises the first IE for the EPS fallback indication received from the first NF 502-1. In some embodiments, the fourth message further comprises the second IE with the 5G PLMN ID. In some embodiments, the fourth message further comprises the information of the dedicated bearer for the IMS voice session.

The method 500 continues with operation 520 in which a fifth message is received by the second BS 102-2 from the second CN 108-2 according to some embodiments. In some embodiments, the fifth message is received by the second BS 102-2 from the third NF 502-3 of the second CN 108-2. In some embodiments, the fifth message is a Bearer Setup Request message. In some embodiments, the fifth message comprises the information of the dedicated bearer so as to establish the dedicated bearer for the IMS voice session by the second BS 102-2.

The method 500 continues with operation 522 in which an IMS voice session is established according to some embodiments. In some embodiments, the first NF 502-1 of the second CN 108-2 transmits a Create Bearer Request message to the third NF 502-3 through the second NF 502-2 of the second CN 108-2. The third NF 502-3 of the second CN 108-2 further transmits a Bearer Setup Request message to the second BS 102-2. After a dedicated bearer for the IMS voice service is setup, an IMS in the application layer transmits a signaling to the UE 104 to continue the establishment of the voice session.

Alternatively, after operation 518, the method 500 continues with operation 522 followed by operation 524 in which a sixth message is received by the second BS 102-2 from the second CN 108-2 according to some embodiments. In some embodiments, the sixth message is a Deactivate Bearer Request message so as to delete the dedicated bearer for the IMS voice session. In some embodiments, the sixth message comprises the first IE for the EPS fallback indication. In some embodiments, the sixth message further comprises the second IE with the 5G PLMN ID. In some embodiments, the sixth message is received by the second BS 102-2 from the third NF 402-3 of the second CN 108-2.

The method 500 continues with operation 526A in which a seventh message is transmitted by the second BS 102-2 to the second CN 108-2 according to some embodiments. In some embodiments, the seventh message is a Handover Required message so as to initiate a handover procedure, through which the UE 104 is returned from the second BS 102-2 to a 5GS, according to the EPS fallback indication. In some embodiments, the UE 104 is handed over to a third BS (not shown) , wherein the third BS is a NG-RAN within the 5G PLMN. In some embodiments, the third BS is the same as the first BS 102-1. In some other embodiments, the third BS 102-3 is different from the first BS 102-1. In some other embodiments, when an intra-system handover takes place (i.e., a handover from the second BS 102-2 to a fourth BS) before the IMS voice session is completed, the fourth BS (not shown) , which is an eNB, can obtain the EPS fallback indication from a corresponding NF of the second NF 108-2. In this case, the operation 526A is then transmitted from the fourth BS.

Alternatively, the method 500 continues with operation 526B in which a seventh message is transmitted from the second BS 102-2 to the UE 104 according to some embodiments. In some embodiments, the fifth message is a Radio Resource Control (RRC) Release message so as to initiate an RRC release procedure, through which the UE 104 is returned from the second BS 102-2 to a 5GS, according to at least one of the following: the EPS fallback indication. In some embodiments, the seventh message comprises redirection information. In some embodiments, the redirection information in the seventh message comprises frequency information of at least one cell of at least one NG-RAN of the 5GS, which can be further used by the UE 104 to scan and access the at least one cell according to the frequency information.. In some embodiments, the seventh message comprises redirection information to return the UE 104 to the 5GS. In some embodiments, the UE 104 accesses a third BS (not shown) , wherein the third BS is a NG-RAN within the 5G PLMN. In some embodiments, the third BS is the same as the first BS 102-1. In some other embodiments, the third BS 102-3 is different from the first BS 102-1. In some other embodiments, when an intra-system handover takes place (i.e., a handover from the second BS 102-2 to a fourth BS) before the IMS voice session is completed, the fourth BS (not shown) , which is an eNB, can obtain the EPS fallback indication from a corresponding NF (i.e., MME) of the second NF 108-2. In this case, the operation 526B is then transmitted from the fourth BS.

The method 500 continues with operation 528 in which the UE 104 accesses the 5GS according to some embodiments. In some embodiments, when the seventh message is a Handover Required message, the second BS 102-2 transmits a Handover Command to the UE 104, the UE 104 accesses the fourth BS on radio resources reserved by the fourth BS for the UE 104. In some other embodiments, when the seventh message is a Radio Resource Control (RRC) Release message, the UE 104 accesses the fourth BS according to the redirection information in the seventh message.

While various embodiments of the invention have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation. Likewise, the various diagrams may depict an example architectural or configuration, which are provided to enable persons of ordinary skill in the art to understand exemplary features and functions of the invention. Such persons would understand, however, that the invention is not restricted to the illustrated example architectures or configurations, but can be implemented using a variety of alternative architectures and configurations. Additionally, as would be understood by persons of ordinary skill in the art, one or more features of one embodiment can be combined with one or more features of another embodiment described herein. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments.

It is also understood that any reference to an element herein using a designation such as "first, " "second, " and so forth does not generally limit the quantity or order of those elements. Rather, these designations can be used herein as a convenient means of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements can be employed, or that the first element must precede the second element in some manner.

Additionally, a person having ordinary skill in the art would understand that information and signals can be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits and symbols, for example, which may be referenced in the above description can be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

A person of ordinary skill in the art would further appreciate that any of the various illustrative logical blocks, modules, processors, means, circuits, methods and functions described in connection with the aspects disclosed herein can be implemented by electronic hardware (e.g., a digital implementation, an analog implementation, or a combination of the two, which can be designed using source coding or some other technique) , various forms of program or design code incorporating instructions (which can be referred to herein, for convenience, as "software" or a "software module) , or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware, firmware or software, or a combination of these technique, depends upon the particular application and design constraints imposed on the overall system. Skilled artisans can implement the described functionality in various ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

Furthermore, a person of ordinary skill in the art would understand that various illustrative logical blocks, modules, devices, components and circuits described herein can be implemented within or performed by an integrated circuit (IC) that can include a general purpose processor, a digital signal processor (DSP) , an application specific integrated circuit (ASIC) , a field programmable gate array (FPGA) or other programmable logic device, or any combination thereof. The logical blocks, modules, and circuits can further include antennas and/or transceivers to communicate with various components within the network or within the device. A general purpose processor can be a microprocessor, but in the alternative, the processor can be any conventional processor, controller, or state machine. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other suitable configuration to perform the functions described herein.

If implemented in software, the functions can be stored as one or more instructions or code on a computer-readable medium. Thus, the steps of a method or algorithm disclosed herein can be implemented as software stored on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that can be enabled to transfer a computer program or code from one place to another. A storage media can be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer.

In this document, the term "module" as used herein, refers to software, firmware, hardware, and any combination of these elements for performing the associated functions described herein. Additionally, for purpose of discussion, the various modules are described as discrete modules; however, as would be apparent to one of ordinary skill in the art, two or more modules may be combined to form a single module that performs the associated functions according embodiments of the invention.

Additionally, memory or other storage, as well as communication components, may be employed in embodiments of the invention. It will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units, processing logic elements or domains may be used without detracting from the invention. For example, functionality illustrated to be performed by separate processing logic elements, or controllers, may be performed by the same processing logic element, or controller. Hence, references to specific functional units are only references to a suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organization.

Various modifications to the implementations described in this disclosure will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other implementations without departing from the scope of this disclosure. Thus, the disclosure is not intended to be limited to the implementations shown herein, but is to be accorded the widest scope consistent with the novel features and principles disclosed herein, as recited in the claims below.

Claims

A method for performing a fast return to 5G by a first wireless communication node of a first wireless communication system, comprising:

receiving a first message from a first core network of the first wireless communication system; and

returning a wireless communication device to a second wireless communication system according to the first message, wherein the first message comprises an Evolved Packet System (EPS) fallback indication.
The method of claim 1, wherein the first message comprises a 5G Public Land Mobile Network Identifier (PLMN ID) of the second wireless communication system.
The method of claim 1, wherein the EPS fallback indication in the first message is received by the first wireless communication node of the first wireless communication system from a first network function (NF) entity of the first core network of the first wireless communication system, wherein the first NF entity is a first Mobility Management Entity (MME) .
The method of claim 3, wherein the EPS fallback indication in the first message is further received in a second message by the first NF entity from a second NF entity .
The method of claim 4, wherein the second NF entity is one of the following: an Access and Mobility Management Function (AMF) of a second core network of the second wireless communication system, a second MME of the first core network of the first wireless communication system, and a second wireless communication node of the first wireless communication system.
The method of claim 4, wherein the first message is a Handover Request message, and wherein the second message is a Forward Relocation Request message, wherein the first and the second message each comprises a source-to-target transparent container, wherein the source-to-target transparent container comprises the EPS fallback indication.
The method of claim 4, wherein the EPS fallback indication in the second message is received by the second NF entity from a second wireless communication node of the second wireless communication system.
The method of claim 3, wherein the EPS fallback indication in the first message is further received in a second message by the first NF entity from a second NF entity of the first core network of the first wireless communication system.
The method of claim 8, wherein the first message is one of the following: a Bearer Setup Request message and a Deactivate Bearer Request message, wherein the second message is one of the following: a Create Bearer Request message and a Delete Bearer Request message.
The method of claim 8, wherein the second NF entity is a Service Gateway (SGW) .
The method of claim 8, wherein the EPS fallback indication in the second message is further received in a third message by the second NF entity from a third NF entity.
The method of claim 11, wherein the third NF entity is a combo-node with a Packet Data Network Gateway (PGW) of the first core network of the first wireless communication system and a Session Management Function (SMF) of the second core network of the second wireless communication system.
The method of claim 11, wherein the third message is one of the following: a Create Bearer Request message and a Delete Bearer Request message.
A method for performing a fast return to 5G by a first core network of a first wireless communication system, comprising:

transmitting a first message to a first wireless communication node of the first wireless communication system,

wherein the first message comprises an Evolved Packet System (EPS) fallback indication, wherein the EPS fallback indication in the first message is used by the first wireless communication node to return a wireless communication device to a second wireless communication system.
The method of claim 14, wherein first message further comprises a 5G Public Land Mobile Network Identifier (PLMN ID) of the second wireless communication system.
The method of claim 14, wherein the EPS fallback indication in the first message is transmitted by a first network function (NF) entity of the first core network of the first wireless communication system to the first wireless communication node, wherein the first NF entity is a first Mobility Management Entity (MME) .
The method of claim 16, wherein the EPS fallback indication in the first message is received by the first NF entity in a second message from a second NF entity.
The method of claim 17, wherein the second NF entity is one of the following: an Access and Mobility Management Function (AMF) of a second core network of the second wireless communication system, a second MME of the first core network of the first wireless communication system, and a second wireless communication node of the first wireless communication system.
The method of claim 17, wherein the first message is a Handover Request message, and wherein the second message is a Forward Relocation Request message, wherein the first and the second message each comprises a source-to-target transparent container, wherein the source-to-target transparent container comprises the EPS fallback indication.
The method of claim 17, wherein the EPS fallback indication in the second message is received by the second NF entity from a second wireless communication node of the second wireless communication system..
The method of claim 16, wherein the EPS fallback indication in the first message is further received in a second message by the first NF entity from a second NF entity of the first core network of the first wireless communication system.
The method of claim 21, wherein the first message is one of the following: a Bearer Setup Request message and a Deactivate Bearer Request message, wherein the second message is one of the following: a Create Bearer Request message and a Delete Bearer Request message.
The method of claim 21, wherein the second NF entity is a Service Gateway (SGW) .
The method of claim 21, wherein EPS fall back indication in the second message is further received in a third message by the second NF from a third NF entity.
The method of claim 24, wherein the third NF entity is a combo-node with a Packet Data Network Gateway (PGW) of the first core network of the first wireless communication system and a Session Management Function (SMF) of the second core network of the second wireless communication system.
The method of claim 24, wherein the third message is one of the following: a Create Bearer Request message and a Delete Bearer Request message.

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A computing device comprising at least one processor and a memory coupled to the processor, the at least one processor configured to carry out the method of any one claims 1 through 26.
A non-transitory computer-readable medium having stored thereon computer-executable instructions for carrying out the method of any one claims 1 through 26.