WO2021093086A1

WO2021093086A1 - Communication method for requesting packet data network connection information

Info

Publication number: WO2021093086A1
Application number: PCT/CN2019/126467
Authority: WO
Inventors: Zhendong Li; Jinguo Zhu
Original assignee: Zte Corporation
Priority date: 2019-12-19
Filing date: 2019-12-19
Publication date: 2021-05-20
Also published as: CN114846843A

Abstract

A wireless communication method for use in an access and mobility management function (AMF) comprises transmitting, to a session management function (SMF) a context request for packet data network, PDN, connection information of a packet data unit (PDU) session, wherein the context request comprises a list of at least one evolved packet system (EPS) bearer identity (EBI), and receiving, from the SMF, PDN connection context corresponding to the PDU session.

Description

Communication Method for Requesting Packet Data Network Connection Information

This document is directed generally to wireless communications.

When a 5G system (5GS) is designed, one of features of the 5G system is supporting interoperability with an evolved packet system (EPS) , i.e. a 4G network. In order to support the interoperability with the EPS, an EPS bearer identity (EBI) is assigned to a quality of service (Qos) flow of each of packet data unit (PDU) sessions in the 5GS. When a user equipment (UE) is moved from the 5GS to the EPS, the PDU session is transferred to the EPS as a packet data network (PDN) connection and the Qos flow with the assigned EBI is transferred to the EPS as a bearer.

This document relates to methods, systems, and devices for requesting PDN connection information, and in particular for requesting PDN connection information for a UE when determining a UE mobility from 5GS to EPS.

The present disclosure relates to a wireless communication method for use in an access and mobility management function, AMF. The wireless communication method comprises:

transmitting, to a session management function, SMF, a context request for packet data network, PDN, connection information of a packet data unit, PDU, session, wherein the context request comprises a list of at least one evolved packet system, EPS, bearer identity, EBI, and

receiving, from the SMF, PDN connection context corresponding to the PDU session.

Various embodiments may preferably implement the following features:

Preferably, the wireless communication method further comprises determining a user equipment, UE, mobility to a target wireless network.

Preferably, the target wireless network is an evolved packet system, EPS.

Preferably, the wireless communication method further comprises determining that the target wireless network does not support an EBI extension.

Preferably, when the target wireless network does not support an EBI extension a range of EBIs supported by the target wireless network node does not comprise 0 to 4 and/or the range of EBIs supported by the target wireless network node is 5 to 15.

Preferably, the wireless communication method further comprises transmitting, to a target wireless network node, a UE context comprising the received PDN connection context.

Preferably, the target wireless network node is a mobility management entity, MME.

Preferably, the wireless communication method further comprises receiving, from a target wireless network node, a context request for a UE context.

Preferably, the wireless communication method further comprises receiving, from a next generation radio access network, NG-RAN, a handover request indicating a handover from the NG-RAN, to an evolved packet system, EPS.

Preferably, all of the EBI of the list are within a range of EBI supported by a target wireless network node.

Preferably, all of the EBI of the list are capable of being transferred to a target wireless network.

Preferably, the PDU session is assigned with at least one EBI.

Preferably, all of the EBI of the list are the EBI assigned for the PDU session.

Preferably, the number of EBIs in the list corresponding to the PDU session is smaller than or equal to a given threshold.

Preferably, the threshold is determined based on the number of EBIs capable of being transferred on an interface between a target wireless network node and the AMF.

Preferably, the EBI in the list corresponding to the PDU session is determined based on a priority of the EBI.

Preferably, the priority of the EBI is determined based on at least one of a data network name, DNN, single network slice selection assistance information, S-NSSAI of the corresponding PDU session, or an allocation and retention priority, ARP, of the EBI.

The present disclosure also relates to a wireless communication method for a session management function, SMF. The wireless communication method comprises:

receiving, from an access and mobility management function, AMF, a context request for packet data network, PDN, connection information of a packet data unit PDU session, wherein the context request comprises a list of at least one evolved packet system, EPS, bearer identity, EBI, and

transmitting, to the AMF, PDN connection context corresponding to the PDU session based on the list.

Various embodiments may preferably implement the following features:

Preferably, the PDN connection context comprises session context corresponding to the EBI in the list.

Preferably, the SMF comprises a PDN gateway control plane function, PGW-C.

The present disclosure relates to an access and mobility management function, AMF. The AMF comprises a communication unit, configured to:

transmit, to a session management function, SMF, a context request for packet data network, PDN, connection information of a packet data unit, PDU, session, wherein the context request comprises a list of at least one evolved packet system, EPS, bearer identity, EBI, and

receive, from the SMF, PDN connection context corresponding to the PDU session.

Various embodiments may preferably implement the following feature:

Preferably, the AMF further comprises a processor being configured to perform a wireless communication method of any of the foregoing described methods.

The present disclosure relates to a session management function, SMF. The SMF comprises a communication unit, configured to:

receive, from an access and mobility management function, AMF, a context request for packet data network, PDN, connection information of a packet data unit PDU session, wherein the context request comprises a list of at least one evolved packet system, EPS, bearer identity, EBI, and

transmit, to the AMF, PDN connection context corresponding to the PDU session based on the list.

Various embodiments may preferably implement the following feature:

transmitting, to a session management function, SMF, a context request for packet data network, PDN, connection information of each of at least one packet data unit, PDU, session, wherein the context request comprises a list of at least one evolved packet system, EPS, bearer identity, EBI, and

receiving, from the SMF corresponding to each of the at least one PDU session, PDN connection context corresponding to the at least one PDU session.

Various embodiments may preferably implement the following features:

Preferably, the target wireless network is an evolved packet system, EPS.

Preferably, when the target wireless network does not support an EBI extension, a range of EBIs supported by the target wireless network node does not comprise 0 to 4 and/or the range of EBIs supported by the target wireless network node is 5 to 15.

Preferably, each of the at least one PDU session is assigned with at least one EBI.

Preferably, all of the EBI of the list are the EBI assigned for each of the at least one PDU session.

Preferably, the number of EBIs in the list corresponding to each of the at least one PDU session is smaller than or equal to a given threshold.

Preferably, the EBIs in the list corresponding to each of the at least one PDU session is determined based on a priority of each of the EBIs.

Preferably, the priority of each of the EBIs is determined based on at least one of a data network name, DNN, single network slice selection assistance information, S-NSSAI, of the corresponding PDU session or an allocation and retention priority, ARP, of each of the EBIs.

The present disclosure relates to an access and mobility management function, AMF. The AMF comprises a communication unit configured to:

transmit, to a session management function, SMF, a context request for packet data network, PDN, connection information of each of at least one packet data unit, PDU, session, wherein the context request comprises a list of at least one evolved packet system, EPS, bearer identity, EBI, and

receive, from the SMF corresponding to each of the at least one PDU session, PDN connection context corresponding to the at least one PDU session.

Various embodiments may preferably implement the following feature:

Preferably, the AMF further comprises a processor being configured to perform a wireless communication method of any of foregoing described methods.

The present disclosure relates to a computer program product comprising a computer-readable program medium code stored thereupon, the code, when executed by a processor, causing the processor to implement a wireless communication method recited in any of the foregoing described methods.

The exemplary embodiments disclosed herein are directed to providing features that will become readily apparent by reference to the following description when taken in conjunction with the accompanying drawings. In accordance with various embodiments, exemplary systems, methods, devices 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 present disclosure.

Thus, the present disclosure is not limited to the exemplary embodiments and applications described and illustrated herein. Additionally, the specific order and/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 disclosure. 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 present disclosure is not limited to the specific order or hierarchy presented unless expressly stated otherwise.

The above and other aspects and their implementations are described in greater detail in the drawings, the descriptions, and the claims.

FIG. 1 shows a wireless network structure according to an embodiment of the present disclosure.

FIG. 2 shows an example of a schematic diagram of a network device according to an embodiment of the present disclosure.

FIG. 3 shows an example of a schematic diagram of a network node according to an embodiment of the present disclosure.

FIG. 4 shows a handover procedure according to an embodiment of the present disclosure.

FIG. 5 shows a procedure of UE idle mobility according to an embodiment of the present disclosure.

FIG. 6 shows a procedure of UE idle mobility according to an embodiment of the present disclosure.

FIG. 7 shows a handover procedure according to an embodiment of the present disclosure.

FIG. 1 relates to a wireless network structure according to an embodiment of the present disclosure, wherein this wireless network structure supports interworking between the 5GS and the EPS. In FIG. 1, a user equipment (UE) is accessed to the EPS (i.e. a 4G network) via an evolved universal terrestrial radio access network (E-UTRAN) and interacts with a mobility management entity (MME) of the core network via non-access-stratum (NAS) signaling.

The UE is accessed to the 5GS and obtains services via a next generation radio access network (NG-RAN) and interacts with an access and mobility management function (AMF) of the core network via the NAS signaling.

An E-UTRAN base station (eNB) is responsible for air interface resource scheduling and air interface connection management of a network to which the UE is accessed to.

The MME is a core network control plane entity, and is mainly responsible for user authentication, authorization and subscription checking, user mobility management, packet data network (PDN) connection, bearer maintenance, paging triggering in a user IDLE state, and other functions.

A serving gateway (S-GW) is a core network user plane function entity, and is mainly responsible for an interaction with a PDN gateway (P-GW) .

The NG-RAN is responsible for the air interface resource scheduling and air interface connection management of the network to which the UE is accessed to.

The AMF is a common control plane function in the core network. One UE can only access to one AMF at a time. The AMF is responsible for mobility management and selecting an appropriate SMF when the UE initiates a PDU connection establishment, forwarding the NAS signaling between the UE and the SMF, and forwarding access stratum (AS) signaling between the NG-RAN and the SMF.

The SMF+PGW-C is a combo wireless network node of the SMF and P-GW control plane entity (PGW-C) and has both functionality of the SMF in the 5GS and the PGW-C in the EPS.

The UPF+PGW-U is a combo wireless network node of UPF and P-GW user plane entity (PGW-U) and has both functionality of UPF in the 5GS and the PGW-U in the EPS.

The P-GW (not shown in FIG. 1) is a core network user plane function entity and an access point which is used for the UE to access the PDN, being responsible for user Internet Protocol (IP) address allocation, network-triggered bearer establishment, modification and deletion, Quality of Service (QoS) control, charging and other functions. The P-GW is divided into two parts, wherein one part is the PGW-C and another part is the PGW-U. The PGW-C is responsible for signaling control and the PGW-U is responsible for IP data forwarding.

A session management function (SMF) interacts with the UE, and is responsible for processing requests of user packet data unit (PDU) session (PDU session) establishment, modification and deletion, selecting user plane functions (UPF) , establishing a user plane connection between the UE and the UPF, determining session QoS parameters together with a policy control function (PCF) , and the like. Each PDU session of the UE has a corresponding SMF, and different PDU sessions may have different SMFs.

The UPF provides user plane processing functions, including data forwarding and QoS execution. When users move, the UPF also provides user plane anchor points to ensure service continuity.

The HSS+UDM is a combo wireless network node of HSS and UDM. It has both functionality of UDM in 5GS and HSS in EPS. A home subscription server (HSS) stores subscription information of the user in the EPS and Unified data management (UDM) stores subscription data of the user in 5GS.

A policy and charging control function (PCF) is responsible for resource authorization and provide the PCC rule to SMF+PGW-C.

An N26 interface is between the AMF and the MME, and is used to transfer a UE context between EPS and 5GS during mobility (handover and idle mobility) .

In the EPS, there is one default bearer and multiple dedicated bearers for each PDN connection established between the UE and the network. Each bearer has a corresponding EPS bearer identity (EBI) .

The EBI identification is of 4 bits, so the value space of the EBI is from 0 to 15 in theory. When the EPS does not support an EBI extension, the valid EBI value space is from 5 to 15 (i.e. comprises 11 values) in the EPS. The values from 0 to 4 is reserved and is not used. The EBI is unique per UE and shared among all the PDN connections for the UE.

In the 5GS, there is one default QoS flow and multiple dedicated QoS flows for each PDU session established between the UE and the network.

When the UE moves from the 5GS to the EPS, a PDU session established in the 5G system is converted to a PDN connection in the EPS and the QoS flow in the PDU session is converted to a bearer in the EPS. Similarly, when the UE moves from the EPS to the 5GS, the PDN connection established in the EPS is converted to the PDU session established in the 5GS and the bearer in the PDN connection is converted to the QoS flow in the 5GS.

In order to ensure a seamless mobility, when a QoS flow of the PDU session is established for the UE in the 5GS, the SMF/PGW-C requests the AMF to allocate an EBI for the Qos flow (the EBI is unique among all the PDN connections for one UE) to allocate other 4G session parameters and/or bearer information corresponding to the Qos flow and to transmit the session parameters and/or the bearing information to the UE. When a PDN connection and a bearer are established in the 4G system, the PGW-C/SMF also needs to allocate a 5G PDU session and QoS flow information corresponding to the PDN connection and the bearer and transmits the 5G PDU session and the QoS flow information to the UE.

As can be seen from the above, the valid EBI value space is 5 to 15 (11 values) in the EPS when the EPS does not support the EBI extension. Under such a condition, only the PDU session with the EBI value from 5 to 15 can be converted to the PDN connection. Furthermore, only at most 8 out of 11 EBI values (5 to 15) can be transferred in the N26 interface between the AMF and the MME. Therefore, the procedure of converting the PDU session to the PDN connection may operate abnormally when the EPS does not support the EBI extension.

FIG. 2 relates to a schematic diagram of a wireless terminal 20 according to an embodiment of the present disclosure. The wireless terminal 20 may be a user equipment (UE) , a mobile phone, a laptop, a tablet computer, an electronic book or a portable computer system and is not limited herein. The wireless terminal 20 may include a processor 200 such as a microprocessor or Application Specific Integrated Circuit (ASIC) , a storage unit 210 and a communication unit 220. The storage unit 210 may be any data storage device that stores a program code 212, which is accessed and executed by the processor 200. Embodiments of the storage unit 212 include but are not limited to a subscriber identity module (SIM) , read-only memory (ROM) , flash memory, random-access memory (RAM) , hard-disk, and optical data storage device. The communication unit 220 may a transceiver and is used to transmit and receive signals (e.g. messages or packets) according to processing results of the processor 200. In an embodiment, the communication unit 220 transmits and receives the signals via at least one antenna 222 shown in FIG. 2.

In an embodiment, the storage unit 210 and the program code 212 may be omitted and the processor 200 may include a storage unit with stored program code.

The processor 200 may implement any one of the steps in exemplified embodiments on the wireless terminal 20, e.g., by executing the program code 212.

The communication unit 220 may be a transceiver. The communication unit 220 may as an alternative or in addition be combining a transmitting unit and a receiving unit configured to transmit and to receive, respectively, signals to and from a wireless network node (e.g. a base station) .

FIG. 3 relates to a schematic diagram of a wireless network node 30 according to an embodiment of the present disclosure. The wireless network node 30 may be a satellite, a base station (BS) , a network entity, a Mobility Management Entity (MME) , Serving Gateway (S-GW) , Packet Data Network (PDN) Gateway (P-GW) , an NG-RAN or a Radio Network Controller (RNC) . In addition, the wireless network node 30 may comprise (perform) at least one network function such as an access and mobility management function (AMF) , a session management function (SMF) , a user place function (UPF) , a policy control function (PCF) , an application function (AF) , etc. Furthermore, the wireless network node 30 may be a combo wireless network node, such as the combo wireless network node HSS+UDM, SMF+PGW-C or UPF+PGW-U shown in FIG. 1. The wireless network node 30 may include a processor 300 such as a microprocessor or ASIC, a storage unit 310 and a communication unit 320. The storage unit 310 may be any data storage device that stores a program code 312, which is accessed and executed by the processor 300. Examples of the storage unit 312 include but are not limited to a SIM, ROM, flash memory, RAM, hard-disk, and optical data storage device. The communication unit 320 may be a transceiver and is used to transmit and receive signals (e.g. messages or packets) according to processing results of the processor 300. In an example, the communication unit 320 transmits and receives the signals via at least one antenna 322 shown in FIG. 3.

In an embodiment, the storage unit 310 and the program code 312 may be omitted. The processor 300 may include a storage unit with stored program code.

The processor 300 may implement any steps described in exemplified embodiments on the wireless network node 30, e.g., via executing the program code 312.

The communication unit 320 may be a transceiver. The communication unit 320 may as an alternative or in addition be combining a transmitting unit and a receiving unit configured to transmit and to receive, respectively, signals to and from a wireless terminal (e.g. a user equipment) or another wireless network node.

FIG. 4 shows a handover procedure of handing over a UE from 5GS to EPS according to an embodiment of the present disclosure. The handover procedure shown in FIG. 4 may be utilized in the wireless network structure shown in FIG. 1 and comprises the following steps:

Step 400: The UE establishes PDU session (s) in the 5GS. In an embodiment, the UE may also establish dedicated QoS flow (s) for the PDU session (s) in the 5GS. In addition the 4G session parameters/bearer information corresponding to each of the PDU session (s) is assigned and sent to the UE.

Step 401: An NG-RAN determines that the UE needs to be handed over to the 4G network and sends a handover request to an AMF.

Step 402: The AMF requests 4G PDN context information corresponding to the PDU session (s) of the UE from a SMF (e.g. SMF+PGW-C) per PDU session.

Step 403: The AMF selects a target MME and transmits a forward relocation request to the target MME.

Step 404: The MME transmits a create session request to an S-GW.

Step 405: The MME transmits a handover request to an eNB for radio resources reservation.

Step 406: After receiving a response (e.g acknowledge (Ack) ) from the eNB, the MME transmits a forward relocation response to the AMF.

Step 407: The AMF may invoke an update session management (SM) service operation (e.g. Nsmf_PDUSession_UpdateSMContext service operation) for data forwarding handling.

Step 408: The AMF transmits a handover command to the NG-RAN and the NG-RAN node transmits the handover command to the UE.

Step 409: The UE is accessed to the 4G system and transmits a handover complete message to the eNB.

Step 410: The eNB transmits a handover notify message to the MME.

Steps 411 to 415: A modify bearer request is initiated by the MME to the S-GW and then sent by the S-GW to a P-GW and finally a user plane is established for every PDN connection.

Step 416: The UE performs a tracking area update (TAU) procedure over the 4G system.

FIG. 5 shows a procedure of UE idle mobility from 5GS to EPS (i.e. the 4G system) according to an embodiment of the present disclosure. The procedure of UE idle mobility shown in FIG. 5 may be utilized in the wireless network structure shown in FIG. 1 and comprises the following steps:

Step 500: The UE establishes PDU session (s) in the 5GS. In an embodiment, the UE also establishes dedicated QoS flow (s) for the PDU session (s) in the 5GS. In addition, 4G session parameters/bearer information corresponding to the PDU session (s) is assigned and sent to the UE. In this embodiment, the UE is in idle status in the 5GS.

Step 501: The UE determines a 4G cell and prepares to access the 4G system.

Step 502: The UE sends a TAU request to MME via an eNB.

Step 503: The MME sends a context request to an AMF of the UE for a UE context.

Step 504: For each PDU session established by the UE in the 5GS, the AMF requests the SMF+PGW-C to provide corresponding 4G PDN context information.

Step 505: The AMF responses the MME with the UE context.

Step 506: The MME sends a create session request to an S-GW.

Step 507: The S-GW sends a modify bearer request to the SMF+PGW-C.

Step 508: The SMF+PGW-C sends the modify bearer response to the S-GW.

Step 509: The S-GW sends a create session response to the MME.

Step 510: The MME sends an update location to a UDM/HSS.

Step 511: The UDM/HSS invokes a deregistration request notification (e.g. Nudm_UECM_DeregistrationNotification) to notify the AMF with a reason as 5GS to EPS mobility.

Step 512: The UDM/HSS sends the update location acknowledge (Ack) to the MME.

Step 513: The MME sends a TAU accept to the UE.

As discussed in the previous paragraphs, the valid EBI value space is from 5 to 15 (11 values) in the EPS when the EPS does not support the EBI extension. Thus, only the PDU session with the EBI value from 5 to 15 can be converted to the PDN connection in the handover procedure shown in FIG. 4 or the idle mobility procedure shown in FIG. 5. Furthermore, only at most 8 out of 11 EBI values (from 5 to 15) can be transferred in the N26 interface between the AMF and the MME. Therefore, the handover procedure shown in FIG. 4 or the idle mobility procedure shown in FIG. 5 may fail or operate abnormally.

In order to solve the above issues, when the AMF transmits a context request for PDN connection information of each of PDU session (s) established by the UE with the 5GS to a SMF corresponding to the PDU session, the AMF includes a list of at least one EBI (hereinafter referred to as EBI list) to the SMF for indicating the EBI capable of being transferred to a target wireless network (e.g. the EPS) . After receiving the EBI list, the SMF transmits PDN connection context corresponding to the PDU session to the AMF based on the EBI list. In an embodiment, the PDN connection context transmitted from the SMF to the AMF may (only) comprise session context corresponding to the EBI in the EBI list. As a result, the handover procedure or the UE idle mobility procedure would operate normally and avoid failure.

Note that, the UE may establish multiple PDU sessions in the 5GS. Thus, the AMF transmits the context request with the EBI list to each of SMFs corresponding the multiple PDU sessions. As a result, the AMF may receive the PDN connection context from each of the SMFs corresponding to the multiple PDU sessions and transmits a UE context comprising the received PDN connection contexts to a target wireless network node (e.g. MME) .

In an embodiment, the AMF transmits the context request with the EBI list to the SMF after determining a UE mobility to a target wireless network (e.g. the EPS) . In an embodiment, the AMF transmits the EBI list to the SMF after determining the target wireless network does not support the EBI extension. For example, the AMF may acknowledge that the range of EBI supported by the target does not comprise 0 to 4 when determining the target wireless network does not support the EBI extension. In another example, the AMF may acknowledge that the range of EBIs supported by the target wireless network node is 5 to 15 when determining the target wireless network does not support the EBI extension. In an embodiment, the AMF transmits a UE context comprising the received PDN connection context to the target wireless network node (e.g. MME) during the procedure of the UE mobility (e.g. the handover procedure or the UE idle mobility procedure) .

In an embodiment, the AMF may receive a context request for a UE context from a target wireless network node (e.g. MME) of a target wireless network (e.g. EPS) during a UE idle mobility procedure before transmitting the context request with the EBI list. For example, the AMF may determine a UE mobility to the target wireless network of the UE idle mobility procedure after receiving the context request for the UE context.

In an embodiment, the AMF may receive, from the NG-RAN, a handover request indicating a handover from the NG-RAN to the EPS before transmitting the context request with the EBI list. For example, the AMF may determine a UE mobility to the target wireless network (i.e. EPS) of the handover procedure after receiving the handover request.

In an embodiment, the AMF determines the EBI list before transmitting the context request with the EBI list to the SMF. The criteria of determining the EBI list may comprise at least one of:

(1) All of the EBI in the EBI list are in the range of EBI supported by the target wireless network (i.e. 5 to 15) .

(2) All of the EBI of the list are EBI (s) assigned for the PDU session (s) established by the UE in the 5GS.

(3) All of the EBI in the EBI list are capable of being transferred to the target network.

In an embodiment, the AMF transmits the context request only for each of the PDU session (s) assigned with at least one EBI. In this embodiment, the at least one EBI assigned to each of the PDU session (s) is in the EBI list.

In an embodiment, the number of EBI (s) in the list corresponding to each of the PDU session (s) is smaller than or equal to a given threshold, wherein the threshold is preferably determined based on an interface between the AMF and the target wireless network node (e.g. MME) . For example, the threshold may be 8 which is the maximum number of EBIs capable of being transmitted on the interface N26 between the AMF and the MME.

In an embodiment, the EBI (s) assigned for the established PDU session (s) and within the valid EBI range of the target MME (i.e. from 5 to 15) may exceed 8 which is the maximum number of EBIs allowed to be transmitted on the N26 interface between the AMF and the MME. In this embodiment, the AMF may select (e.g. determines) the EBI (s) in the EBI list (s) from the EBI (s) assigned for the established PDU session (s) based on priority of each of EBI (s) assigned for the established PDU session (s) . In an embodiment, the AMF determines the priority of each of the EBI (s) based on at least one of a data network name (DNN) of the corresponding PDU session, single network slice selection assistance information (S-NSSAI) of the corresponding PDU session or an allocation and retention priority, ARP, of each of the EBI (s) .

FIG. 6 shows a procedure of UE idle mobility from 5GS to EPS (i.e. the 4G system) according to an embodiment of the present disclosure. The procedure of UE idle mobility shown in FIG. 6 may be utilized in the wireless network structure shown in FIG. 1 and comprises the following steps:

Step 600: The UE establishes PDU session (s) in 5GS. In an embodiment, the US also establishes dedicated QoS flow (s) for the PDU session (s) in the 5GS. The 4G session parameters/bearer information corresponding to each of the PDU session (s) is/are assigned and sent to the UE. In this embodiment, the UE is in idle status in 5GS.

Step 601: The UE sends a TAU request to a target MME via an eNB.

Step 602: The target MME sends a context request to an AMF for a UE context.

Step 603: The AMF determines that the target MME does not support the EBI extension. The AMF selects (e.g. determines) the EBIs which can be transferred to the target MME. In an embodiment, the AMF may select the EBI (s) assigned for the established PDU session (s) in 5GS and/or within the range supported by the target MME (i.e. range from 5 to 15) . In an embodiment, when the number of EBI (s) assigned for the established PDU session (s) and being within the range supported by the target MME is greater than a threshold (e.g. 8) , the AMF selects the EBI (s) from EBI (s) assigned for the established PDU session (s) and within the range supported by the target MME based on a priority of each of EBIs assigned for the established PDU session (s) and within the range supported by the target MME. For each of established PDU session (s) assigned with the EBI in the EBI list, the AMF invokes the Nsmf_PDUSession_ContextRequest service operation (e.g. transmits a session context request) to request a corresponding SMF+PGW-C provide 4G PDN context information. Note that FIG. 6 shows only one SMF+PGW-C for illustrations. In this service operation, the AMF include an EBI list (e.g. in the session context request) to the SMF+PGW-C, wherein the EBI list may comprise the selected (determined) EBI (s) .

Step 604: After receiving the Nsmf_PDUSession_ContextRequest service operation (e.g. the session context request) , the SMF+PGW-C sends the 4G PDN SM context which (only) contains (e.g. comprises) session context corresponding to the EBI (s) in the received EBI list.

Step 605: The AMF responses the MME with the UE context.

Step 606: The MME sends a create session request to an S-GW.

Step 607: Perform steps 507 to 512 shown in FIG. 5.

Step 608, The MME sends the TAU accept to the UE.

FIG. 7 shows a handover procedure of handing over a UE from the 5GS to the EPS according to an embodiment of the present disclosure. The handover procedure shown in FIG. 7 may be utilized in the wireless network structure shown in FIG. 1 and comprises the following steps:

Step 700: The UE establishes PDU session (s) in the 5GS. In an embodiment, the UE may also establish dedicated QoS flow (s) for the PDU session (s) in the 5GS. The 4G session parameters/bearer information corresponding to the PDU session (s) is/are assigned and sent to the UE.

Step 701: The NG-RAN determines that the UE needs to be handed over to the EPS and sends a handover request to the AMF.

Step 702: The AMF determines that the target MME of the handover procedure does not support the EBI extension. Under such a condition, the AMF determines the EBI (s) which can be transferred to the target MME. In an embodiment, the AMF may select the EBI (s) which is/are assigned for the established PDU session (s) in the 5GS and/or within the range supported by the target MME (i.e. value from 5 to 15) . In an embodiment, when the number of EBI (s) assigned for the established PDU session (s) and within the range supported by the target MME is greater than a given threshold (e.g. 8) , the AMF selects the EBI (s) from EBI (s) assigned for the established PDU session (s) and within the range supported by the target MME based on a priority of each of the EBI (s) assigned for the PDU session (s) and within the range supported by the target MME. For each of established PDU session (s) assigned with the EBI in the EBI list, the AMF invokes the Nsmf_PDUSession_ContextRequest service operation (e.g. transmits a session context request) to a corresponding SMF+PGW-C, to request the SMF+PGW-C provide related PDN context information. Note that FIG. 7 shows only one SMF+PGW-C for illustrations. In this service operation, the AMF includes the EBI list (e.g. in the session context request) to the SMF+PGW-C, wherein the EBI list may comprise the selected (determined) EBI (s) .

Step 703: After receiving the Nsmf_PDUSession_ContextRequest service operation (e.g. the session context request) , each SMF+PGW-C sends the PDN SM context which (only) comprises session context corresponding to the EBI (s) in the received EBI list to the AMF.

Step 704: The AMF sends relocation request to target MME.

Step 705: The MME transmits a create session request to an S-GW.

Step 706: The MME transmits a handover request to an eNB for radio resources reservation.

Step 707: After receiving a response from the eNB, the MME transmits a forward relocation response to the AMF.

Step 708: Performing steps 407 to 416 shown in FIG. 4.

While various embodiments of the present disclosure 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 present disclosure. Such persons would understand, however, that the present disclosure 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 skilled person would further appreciate that any of the various illustrative logical blocks, units, 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) , firmware, various forms of program or design code incorporating instructions (which can be referred to herein, for convenience, as "software" or a "software unit” ) , or any combination of these techniques.

To clearly illustrate this interchangeability of hardware, firmware and software, various illustrative components, blocks, units, 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 techniques, 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 do not cause a departure from the scope of the present disclosure. In accordance with various embodiments, a processor, device, component, circuit, structure, machine, unit, etc. can be configured to perform one or more of the functions described herein. The term “configured to” or “configured for” as used herein with respect to a specified operation or function refers to a processor, device, component, circuit, structure, machine, unit, etc. that is physically constructed, programmed and/or arranged to perform the specified operation or function.

Furthermore, a skilled person would understand that various illustrative logical blocks, units, 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, units, 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 "unit" 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 units are described as discrete units; however, as would be apparent to one of ordinary skill in the art, two or more units may be combined to form a single unit that performs the associated functions according embodiments of the present disclosure.

Additionally, memory or other storage, as well as communication components, may be employed in embodiments of the present disclosure. It will be appreciated that, for clarity purposes, the above description has described embodiments of the present disclosure 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 present disclosure. 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 wireless communication method for use in an access and mobility management function, AMF, the wireless communication method comprising:

transmitting, to a session management function, SMF, a context request for packet data network, PDN, connection information of a packet data unit, PDU, session, wherein the context request comprises a list of at least one evolved packet system, EPS, bearer identity, EBI, and

receiving, from the SMF, PDN connection context corresponding to the PDU session.
The wireless communication method of claim 1, further comprising:

determining a user equipment, UE, mobility to a target wireless network.
The wireless communication method of claim 2, wherein the target wireless network is an evolved packet system, EPS.
The wireless communication method of claim 2 or 3, further comprising:

determining the target wireless network does not support an EBI extension.
The wireless communication method of claim 4, wherein when the target wireless network does not support an EBI extension a range of EBIs supported by the target wireless network node does not comprise 0 to 4 and/or the range of EBIs supported by the target wireless network node is 5 to 15.
The wireless communication method of any of claims 1 to 5, further comprising:

transmitting, to a target wireless network node, a UE context comprising the received PDN connection context.
The wireless communication method of claim 6, wherein the target wireless network node is a mobility management entity, MME.
The wireless communication method of any of claims 1 to 7, further comprising:

receiving, from a target wireless network node, a context request for a UE context.
The wireless communication method of any of claims 1 to 7, further comprising:

receiving, from a next generation radio access network, NG-RAN, a handover request indicating a handover from the NG-RAN, to an evolved packet system, EPS.
The wireless communication method of any of claims 1 to 9, wherein all of the EBI of the list are within a range of EBI supported by a target wireless network node.
The wireless communication method of any of claims 1 to 10, wherein the PDU session is assigned with at least one EBI.
The wireless communication method of any of claims 1 to 11, wherein all of the EBI of the list are the EBI assigned for the PDU session.
The wireless communication method of any of claims 1 to 12, wherein the number of EBIs in the list corresponding to the PDU session is smaller than or equal to a given threshold.
The wireless communication method of claim 13, wherein the threshold is determined based on the number of EBIs capable of being transferred on an interface between a target wireless network node and the AMF.
The wireless communication method of any of claims 1 to 14, wherein the EBI in the list corresponding to the PDU session is determined based on a priority of the EBI.
The wireless communication method of claim 15, wherein the priority of the EBI is determined based on at least one of a data network name, DNN, single network slice selection assistance information, S-NSSAI of the corresponding PDU session, or an allocation and retention priority, ARP, of the EBI.
A wireless communication method for a session management function, SMF, the wireless communication method comprising:

receiving, from an access and mobility management function, AMF, a context request for packet data network, PDN, connection information of a packet data unit PDU session, wherein the context request comprises a list of at least one evolved packet system, EPS, bearer identity, EBI, and

transmitting, to the AMF, PDN connection context corresponding to the PDU session based on the list.
The wireless communication method of claim 17, wherein the PDN connection context comprises session context corresponding to the EBI in the list.
The wireless communication method of claim 17 or 18, wherein the SMF comprises a PDN gateway control plane function, PGW-C.
An access and mobility management function, AMF, comprising:

a communication unit, configured to:

transmit, to a session management function, SMF, a context request for packet data network, PDN, connection information of a packet data unit, PDU, session, wherein the context request comprises a list of at least one evolved packet system, EPS, bearer identity, EBI, and

receive, from the SMF, PDN connection context corresponding to the PDU session.
The AMF of claim 20, further comprising a processor being configured to perform a wireless communication method of any of claims 2 to 16.
A session management function, SMF, comprising:

a communication unit, configured to:

receive, from an access and mobility management function, AMF, a context request for packet data network, PDN, connection information of a packet data unit PDU session, wherein the context request comprises a list of at least one evolved packet system, EPS, bearer identity, EBI, and

transmit, to the AMF, PDN connection context corresponding to the PDU session based on the list.
The SMF of claim 22, further comprising a processor being configured to perform a wireless communication method of claim 18 or 19.
A computer program product comprising a computer-readable program medium code stored thereupon, the code, when executed by a processor, causing the processor to implement a wireless communication method recited in any of claims 1 to 19.