WO2023044616A1

WO2023044616A1 - Intermediate session management function failure and restoration

Info

Publication number: WO2023044616A1
Application number: PCT/CN2021/119695
Authority: WO
Inventors: Zhijun Li; Jinguo Zhu; Yang Yu
Original assignee: Zte Corporation
Priority date: 2021-09-22
Filing date: 2021-09-22
Publication date: 2023-03-30
Also published as: CN117882433A

Abstract

A wireless communication method for use in an intermediate session management function (SMF) is disclosed. The method comprises transmitting, to an anchor SMF, restoration information associated with restoring an intermediate SMF of a protocol data unit (PDU) session.

Description

Intermediate Session Management Function Failure and Restoration

This document is directed generally to wireless communications.

After accessing to a fifth generation, 5G, network, a user equipment (UE) may request establishing a protocol data unit (PDU) session to get internet protocol (IP) connectivity service. For the PDU session, a session management function (SMF) selected to control the PDU session and is also called anchor SMF and a user plane function (UPF) controlled by the anchor SMF to allocate the UE IP address is also called PDU Session Anchor (PSA) or PSA UPF.

Generally, the anchor SMF and the PSA UPF have their own serving area and cannot serve the whole public land mobile network (PLMN) . In order to support the PDU session service when the UE is out of the service area supported by the anchor SMF and the PSA UPF, an intermediate SMF (I-SMF) and an intermediate UPF (I-UPF) are inserted to serve the location area at which the UE locates.

In a PDU session involving an I-SMF, the I-SMF is in the middle path between an access mobility management function (AMF) and an anchor SMF and connects the AMF and the anchor SMF. The intermediate SMF maintains session management (SM) Context of the PDU session, wherein the SM Context includes, e.g., AMF information, N3 tunnel information, etc. The anchor SMF maintains the PDU Session Context, including, e.g., UE internet protocol (IP) address, PDU session policy information, N6 tunnel information, etc. The I-SMF allocates an SM Context identifier (ID) which is used to locate the SM Context in the I-SMF. If the I-SMF fails, neither the AMF nor the anchor SMF can use the SM Context ID to locate the SM Context in the I-SMF. Under such a condition, the AMF signaling cannot go to the anchor SMF even via another I-SMF, and vice versa.

Network function (NF) Set concept is designed in the 5G system to support stateless deployment of an NF and is commonly used in NF failure and restoration cases. Every NF within the same NF Set shares resources (e.g. UE IP address resources) and session contexts (e.g. UE PDU session contexts) . If one NF is detected in failure by another NF, the NF detecting the failure can select another NF within the same NF Set to continue a related service procedure.

However, the NF Set may not always be available, especially in an early period of 5G network deployment. Furthermore, the NF Set concept is not widely supported in the PLMN.

If there is no NF Set deployed, since the SM context information stored in the failed I-SMF cannot be retrieved from elsewhere, the AMF and the anchor SMF cannot continue the service procedure by using another I-SMF.

This document relates to methods, systems, and devices for I-SMF restoration, and in particular to methods, systems, and devices for allowing the AMF and/or the anchor SMF to select an alternative I-SMF when detecting a failure of the I-SMF.

The present disclosure relates to a wireless communication method for use in an intermediate session management function, SMF. The method comprises:

transmitting, to an anchor SMF, restoration information associated with restoring an intermediate SMF of a protocol data unit, PDU, session.

Various embodiments may preferably implement the following features:

Preferably, the restoration information comprises at least one of information associated with an access and mobility management function, AMF, of the PDU session, information associated with a radio access network node of the PDU session or information associated with an intermediate user plane function, UPF.

Preferably, the information associated with the AMF comprises at least one of an AMF Instance identifier, an application program interface uniform resource identifier of an AMF service, or a callback uniform resource identifier of receiving a session management context status notification.

Preferably, the information associated with the radio access network node comprises radio access network N3 tunnel information.

Preferably, information associated with the intermediate UPF comprises at least one of a UPF Instance identifier, UPF N3 tunnel information, UPF N9 tunnel information or an N4 Session identifier.

Preferably, the wireless communication method further comprises:

transmitting, to the anchor SMF, an intermediate SMF restoration indication associated with the PDU session, and

receiving, from the anchor SMF, the restoration information.

Preferably, the wireless communication method further comprises receiving, from an access and mobility management function, an intermediate SMF restoration indication associated with the PDU session.

Preferably, the wireless communication method further comprises performing an intermediate SMF restoration procedure based on the restoration information.

Preferably, performing the intermediate SMF restoration procedure based on the restoration information comprises:

selecting an intermediate UPF indicated by the restoration information for serving the PDU session.

Preferably, the intermediate SMF is selected to serve the PDU session after an intermediate SMF serving the PDU session fails.

Preferably, the intermediate SMF is selected to serve the PDU session during the PDU session establishment

The present disclosure relates to a wireless communication method for use in an anchor session management function, SMF. The method comprises:

receiving, from a first intermediate SMF, restoration information associated with restoring an intermediate SMF of a protocol date unit, PDU, session.

Various embodiments may preferably implement the following features:

Preferably, the wireless communication method further comprises:

receiving, from a second intermediate SMF, an intermediate SMF restoration indication associated with the PDU session, and

transmitting, to a second intermediate SMF, the restoration information.

Preferably, the wireless communication method further comprises:

transmitting, to an access and mobility management function indicated by the restoration information, an intermediate SMF restoration indication of triggering an intermediate SMF restoration procedure.

Preferably, the wireless communication method further comprises:

transmitting, to an access and mobility management function indicated by the restoration information, a PDU session release request comprising a reactivation indication.

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

receiving, from an anchor session management function, SMF, an intermediate SMF restoration indication associated with a protocol data unit, PDU, session, and

triggering a restoration procedure associated with restoring an intermediate SMF of the PDU session.

Various embodiments may preferably implement the following features:

Preferably, triggering restoration procedure of associated with restoring the intermediate SMF of the PDU session comprises:

selecting an intermediate SMF for the PDU session, and

transmitting, to the selected SMF, a session management context create message associated with the PDU session,

Preferably, the session management context create message comprises at least one of a PDU Session identifier, an anchor SMF Instance identifier or the intermediate SMF restoration indication.

The present disclosure relates to a wireless device comprising an intermediate session management function, SMF, the wireless device comprising:

a communication unit, configured to transmit, to an anchor SMF, restoration information associated with restoring an intermediate SMF of a protocol data unit, PDU, session.

Various embodiments may preferably implement the following feature:

Preferably, the wireless device further comprises a processor configured to perform any of aforementioned wireless communication methods.

The present disclosure relates to a wireless device comprising an anchor session management function, SMF. The wireless device comprises:

a communication unit, configured to receive, from an intermediate SMF, restoration information associated with restoring an intermediate SMF of a protocol data unit, PDU, session.

Various embodiments may preferably implement the following feature:

The present disclosure relates to a wireless device comprising an access and mobility management function. The wireless device comprises:

a communication unit, configured to receive, from an anchor session management function, SMF, an intermediate SMF restoration indication associated with a protocol data unit, PDU, session, and

a processor, configured to trigger a restoration procedure associated with restoring an intermediate SMF of the PDU session.

Various embodiments may preferably implement the following features:

Preferably, the processor is further configured to perform any of aforementioned wireless communication 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 one of foregoing 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 accompany 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 schematic diagram of a 5G Home-Routed roaming architecture according to an embodiment of the present disclosure.

FIG. 2 shows a schematic diagram of a 5G non-roaming architecture according to an embodiment of the present disclosure.

FIG. 3 shows a schematic diagram of a PDU session establishment procedure according to an embodiment of the present disclosure.

FIG. 4 shows a schematic diagram of a PDU session establishment procedure according to an embodiment of the present disclosure.

FIGS. 5A and 5B show a schematic diagram of an intermediate SMF restoration procedure according to an embodiment of the present disclosure.

FIG. 6 shows a schematic diagram of an intermediate SMF restoration procedure according to an embodiment of the present disclosure.

FIG. 7 shows a schematic diagram of a PDU Session Release with Re-Activation procedure according to an embodiment of the present disclosure.

FIG. 8 shows an example of a schematic diagram of a wireless terminal according to an embodiment of the present disclosure.

FIG. 9 shows an example of a schematic diagram of a wireless network node according to an embodiment of the present disclosure.

FIG. 10 shows a flowchart of a method according to an embodiment of the present disclosure.

FIG. 11 shows a flowchart of a method according to an embodiment of the present disclosure.

FIG. 12 shows a flowchart of a method according to an embodiment of the present disclosure.

In the present disclosure, the term “information” is equal to or has the same meaning as “info” .

FIG. 1 shows a 5G Home-Routed roaming architecture according to an embodiment of the present disclosure. In FIG. 1, the anchor SMF and PSA UPF cannot directly serve a visited PLMN (VPLMN) on which the UE camps. FIG. 2 shows a 5G non-roaming architecture according to an embodiment of the present disclosure. In FIG. 2, the anchor SMF and the PSA UPF cannot directly serve the area in which the UE locates (i.e. UE location area) . In FIGS. 1 and 2, there are the following network functions and network entities:

1) UE (User Equipment)

2) RAN (Radio Access Network (node) ) :

In the 5G network, the RAN may be a new radio (NR) base station.

3) AMF (Access and Mobility Management function) :

The AMF includes the following functionalities: Registration management, Connection management, Reachability management and Mobility Management. The AMF also performs the access authentication and access authorization. The AMF is the NAS security termination and relay the SM NAS between UE and SMF, etc.

4) SMF (Session Management Function)

The SMF includes the following functionalities: session establishment, modification and release, UE IP address allocation &management (including optional authorization functions) , selection and control of UP function, downlink data notification, etc. The SMF controls the UPF via N4 association.

5) UPF (User plane function)

The UPF includes the following functionalities: serving as an anchor point for intra-/inter-radio access technology (RAT) mobility, packet routing &forwarding, traffic usage reporting, QoS handling for the user plane, downlink packet buffering and downlink data notification triggering, etc. The UPF may be deployed as an intermediated UPF (I-UPF) or a PSA. The PSA/UPF is the UPF terminating the N6 interface towards the data network. The I-UPF provides traffic forwarding between the RAN and PSA/UPF. The I-UPF may support "ULCL" (Uplink classifier: offloading uplink traffic based on target IP address) or “BP” (Branching point: offloading uplink traffic based on source IP address) to offload some traffics to local PSA/UPF.

6) PCF (Policy Control Function)

The PCF provides QoS policy rules to control plane functions to enforce the rules. The PCF (s) transform (s) the AF requests into policies that apply to PDU Sessions. The PCF provides the AF influenced Traffic Steering Enforcement Control in PCC rules to SMF so the SMF can establish the data path to offload the traffic to local data network.

7) AF (Application Function)

The AF interacts with the 3GPP Core Network in order to provide services, e.g., to support application influence on traffic routing. Based on operator deployment, the AFs considered to be trusted by the operator can be allowed to interact directly with relevant Network Functions. The AFs not allowed by the operator to access directly the Network Functions shall use the external exposure framework via a network exposure function (NEF) to interact with relevant Network Functions.

In the PDU Session Establishment procedure, if the selected anchor SMF and PSA UPF cannot serve the area where the UE camps on, an I-SMF and an I-UPF need to be inserted (see FIG. 2) . The visited SMF (V-SMF) shown in FIG. 1 (i.e. Home-Routed roaming scenario) plays a similar role of the I-SMF shown in FIG. 2 (i.e. non-roaming scenario) . Thus, the I-SMF may be equal to V-SMF in the present disclosure. Similarly, the I-UPF may be equal to the visited UPF (V-UPF) shown in FIG. 1 of the present disclosure.

FIG. 3 shows a schematic diagram of a PDU session establishment procedure according to an embodiment of the present disclosure. The PDU session establishment procedure in FIG. 3 involves an I-SMF insertion. Specifically, after the UE registered to a 5G network, the UE may request a PDU session establishment procedure comprising the following steps:

Step 301: The UE transmits a PDU Session Establishment Request to the AMF.

The PDU Session Establishment Request is included in a non-access stratum (NAS) message and encapsulated in a N1 SM container. The NAS message may comprise Single Network Slice Selection Assistance information (S-NSSAI) , UE Requested data network name (DNN) , PDU Session ID, Request type, and N1 SM container (comprising the PDU Session Establishment Request) . The NAS message sent by the UE is encapsulated by the RAN in a N2 message towards the AMF.

Step 302: The AMF selects a proper SMF (i.e. anchor SMF) , to serve the PDU session, based on the requested DNN, the S-NSSAI and current UE location information. If the anchor SMF cannot serve the current location of the UE, the AMF determines to also select an I-SMF for the PDU session.

Step 303: The AMF transmits a Nsmf_PDUSession_CreateSMContext Request to the I-SMF, wherein the Nsmf_PDUSession_CreateSMContext Request comprises a Subscription Permanent Identifier (SUPI) , selected DNN, UE requested DNN, S-NSSAI (s) , PDU Session ID, AMF ID, Request Type, N1 SM container (PDU Session Establishment Request) , User location information, Access Type, RAT Type, Permanent Equipment Identifier (PEI) , General Public Subscription Identifier (GPSI) , AMF callback URI for receiving SM context status notification, etc. The SUPI uniquely identifies the UE subscription. The AMF ID carries a Globally Unique AMF ID (GUAMI) uniquely identifying the AMF serving the UE. The AMF callback URI for receiving SM context notification is used by the SMF (e.g. I-SMF, anchor SMF) to send notification of SM context status to the AMF.

Step 304: The I-SMF transmits an Nsmf_PDUSession_CreateSMContext Response to the AMF, wherein the Nsmf_PDUSession_CreateSMContext Response comprises a Cause and a SM Context ID. The SM Context ID identifies the SM context created in the I-SMF for the UE.

Step 305: The I-SMF selects an I-UPF to serve the PDU session based on the UE location.

Step 306: The I-SMF initiates an N4 Session Establishment procedure with the selected I-UPF.

Step 307: I-SMF transmits an Nsmf_PDUSession_Create Request to the anchor SMF, wherein the Nsmf_PDUSession_Create Request comprises the DNN, the S-NSSAI, the PDU Session ID, I-SMF Instance ID, the I-SMF SM Context ID and intermediate-core-network (ICN) tunnel info. The ICN tunnel info carries the I-UPF downlink (DL) Fully Qualified Tunnel Endpoint Identifier (F-TEID) which is used to identify GTP-U (GPRS tunneling protocol user plane) tunnel information of the I-UPF to receive downlink traffic.

Step 308: The anchor SMF sends an Nudm_SDM_Get Request to the UDM, to retrieve Session Management Subscription data. The UDM sends back the requested data in response message.

Step 309: The anchor SMF selects an UPF acting as the PSA.

Step 310: The anchor SMF initiates an N4 Session Establishment procedure with the selected UPF.

Step 311: The anchor SMF transmits an Nsm_PDUSession_Create Response to the I-SMF, wherein the Nsm_PDUSession_Create Response comprises quality of service (QoS) rules, QoS flow level, QoS parameters, QoS flow IDs (QFIs) , QoS profiles, Session maximum bit rate (MBR) and H-UPF tunnel info. The H-UPF tunnel info carries the H-UPF GTP-U tunnel info of PSA UPF for receiving UL traffics.

Step 312: The I-SMF initiates an N4 Session Modification procedure with the I-UPF, to update the GTP-U tunnel info of the PSA UPF, i.e. UPF UL F-TEID.

Step 313: The I-SMF transmits an Namf_Communication_N1N2MessageTransfer Request to the AMF, wherein the Namf_Communication_N1N2MessageTransfer Request comprises the PDU Session ID, N2 SM information (PDU Session ID, QFI (s) , QoS Profile (s) , N3 CN Tunnel Info) , N1 SM container (PDU Session Establishment Accept) .

The N2 SM information carries information that the AMF shall forward to the RAN, including the N3 CN Tunnel Info carrying I-UPF UL F-TEID, the QFIs and QoS profiles used by the RAN to setup QoS flows. In an embodiment, the N1 SM container contains the PDU Session Establishment Accept that the AMF shall provide to the UE.

Step 314: The AMF transmits an N2 PDU Session Request to RAN, wherein the N2 PDU Session Request comprises N2 SM information, NAS message (PDU Session ID, N1 SM container (PDU Session Establishment Accept) ) . The AMF sends the NAS message containing PDU Session ID and PDU Session Establishment Accept targeted to the UE and the N2 SM information received from the SMF within the N2 PDU Session Request to the RAN.

Step 315: The RAN may issue AN specific signaling exchange with the UE that is related with the information received from SMF. For example, in case of a 3GPP RAN, an RRC Connection Reconfiguration may take place with the UE establishing the necessary RAN resources related to the QoS Rules for the PDU Session request. RAN forwards the NAS message (PDU Session ID, N1 SM container (PDU Session Establishment Accept) ) to the UE. The RAN also allocates AN N3 tunnel information for the PDU Session.

Step 316: The RAN transmits a PDU Session Response to the AMF, wherein the N2 PDU Session Response comprises the PDU Session ID, Cause, N2 SM information (PDU Session ID, AN Tunnel Info, List of accepted/rejected QFI (s) ) .

The AN Tunnel Info corresponds to the Access Network address of the N3 tunnel corresponding to the PDU Session.

Step 317: The AMF transmits an Nsmf_PDUSession_UpdateSMContext to the I-SMF, wherein the Nsmf_PDUSession_UpdateSMContext Request comprises N2 SM information.

The AMF forwards the N2 SM information received from the RAN to the I-SMF. If the list of rejected QFI (s) is included in N2 SM information, the SMF shall release the rejected QFI (s) associated QoS profiles.

Step 318: The I-SMF initiates an N4 Session Modification procedure with the I-UPF. The I-SMF provides RAN Tunnel Info to the I-UPF as well as the corresponding forwarding rules.

Step 319: The I-SMF sends an Nsmf_PDUSession_UpdateSMContext Response to the AMF.

FIG. 4 shows a schematic diagram of a PDU session Establishment procedure according to an embodiment of the present disclosure. In FIG. 4, the PDU session Establishment procedure involves an I-SMF insertion and the I-SMF stores the I-SMF restoration container info to the anchor SMF. Specifically, the PDU session Establishment procedure comprise the following steps:

Step 401: The UE initiates a PDU Session Establishment procedure (e.g. FIG. 3) . Because the anchor SMF cannot serve the current UE location, an I-SMF is inserted. The I-SMF selects an I-UPF to serve the PDU session.

Step 402: The I-SMF sends a PDU Session Update Request (i.e. Nsmf_PDUSession_Update) to the anchor SMF. Within this message, the I-SMF includes the I-SMF Restoration Container Info (i.e. ivres-container-info shown in FIG. 4) .

In an embodiment, the I-SMF Restoration Container Info includes at least one of the AMF info, the RAN info, the I-UPF info.

In an embodiment, the AMF info comprises at least one of an AMF Instance ID, an application program interface uniform resource identifier (API URI) of AMF service, a callback URI for SM Context Status Notification.

In an embodiment, the AMF Instance ID uniquely identifies an AMF, and can be used by other NF to retrieve AMF profile from the network repository function (NRF) .

In an embodiment, the API URI of the AMF service indicates (or is) the API URI of the services provided by the AMF. For example, the API URI of the AMF service can indicate the API URI of Namf_Communication service, which can be used by an SMF to send N1/N2 message (s) to the AMF.

In an embodiment, the callback URI for SM Context Status Notification is a callback URI belonging to the AMF to receive any SM Context Status Notification from the SMF (e.g. I-SMF) , e.g. to notify the SM Context is transferred to another I-SMF, or to notify the SM Context is released, etc.

In an embodiment, the RAN info comprises the N3 tunnel info (RAN DL F-TEID) .

In an embodiment, the RAN N3 tunnel info may indicate whether the N3 tunnel of RAN node is allocated.

In an embodiment, the I-UPF info comprises at least one of the UPF Instance ID, UP Connection State (ACTIVATED, RELEASED) , N3 tunnel info (I-UPF UL F-TEID) , N9 tunnel info (I-UPF DL F-TEID) , N4 Session ID of the N4 session between the I-SMF and the I-UPF.

In an embodiment, the UPF Instance ID is used to uniquely identify the I-UPF.

In an embodiment, the UP Connection State is used to indicate the N3 connection state with the RAN node. The ACTIVATED state indicates the N3 connection is activated, and the RELEASE state indicates the N3 connection is released.

In an embodiment, the N3 tunnel info indicates the I-UPF UL F-TEID, which used by the RAN to send uplink traffic.

In an embodiment, the N9 tunnel info indicates the I-UPF DL F-TEID, which is used by the PSA UPF to send downlink traffics.

Step 403: The anchor SMF stores the I-SMF Restoration Container Info in its local storage.

Step 404: the anchor SMF sends a PDU Session Update Response (i.e. response message of Nsmf_PDUSession_Update Request message) to the I-SMF.

Once the I-SMF Restoration Container Info is stored in (or transmitted to) the anchor SMF, it can be used by a new I-SMF to select the old I-UPF in an I-SMF restoration procedure (see, e.g., FIGS. 5A and 5B) , be used by the anchor SMF to find the serving AMF and request the serving AMF to trigger the I-SMF restoration procedure (see, e.g., FIG. 6) , or be used by the anchor SMF to find the serving AMF via which to send PDU Session Release Command to the UE (see, e.g., FIG. 7) .

FIGS. 5A and 5B describes a schematic diagram of the AMF initiated an I-SMF restoration procedure according to an embodiment of the present disclosure. Note that the PDU session has been established and the I-SMF Restoration Container Info associated with the PDU session is transmitted and stored in the anchor SMF in this embodiment (see FIG. 4) . In FIGS. 5A and 5B, the AMF performs the I-SMF restoration procedure by the assistance of the I-SMF Restoration Container Info. During the AMF initiated I-SMF restoration procedure, the anchor SMF returns the I-SMF Restoration Container Info to a newly selected I-SMF (i.e. new I-SMF shown in FIGS. 5A and 5B) , to allow the newly selected SMF to select the old I-UPF.

Step 501 (FIG. 5A) : The UE sends a mobile-originating (MO) signaling to the AMF.

For example, the UE sends a Service Request when the UE is in an IDLE state. As an alternative, the UE sends a non-access stratum (NAS) SM signaling (e.g. PDU Session Modification Request) to the AMF targeting the SMF.

Step 502: The AMF detects the old I-SMF is not reachable (i.e. detects a failure of the I-SMF) . That is, the old I-SMF fails.

Step 503: The AMF re-selects a new I-SMF for this PDU session.

Step 504: The AMF sends a (PDU Session) CreateSMContext Request (i.e. Nsmf_PDUSession_CreateSMContext Request) to the new I-SMF, wherein the CreateSMContext Request carries the following information: PDU Session ID, NF Instance ID of the anchor SMF, API URI of the anchor SMF. In addition, an I-SMF Restoration Indication (i.e. ivres-indication) is also included in this message.

If a user plane (UP) connection is required to be activated, e.g. as requested by the UE initiated Service Request, the UP Connection State attribute is included in this message and is set to ACTIVATING.

The NF Instance ID of the anchor SMF and the API URI of the anchor SMF can be used by the new I-SMF to find the anchor SMF and to locate the PDU session context in the anchor SMF.

In an embodiment, the new I-SMF may not retrieve SM Context from the anchor SMF or from the old I-SMF, if detecting the I-SMF Restoration Indication in the CreateSMContext Request.

In an embodiment, in order to assist the new I-SMF to rebuild the SM context, the AMF may provide other related information (e.g. the selected PCF info) in the CreateSMContext Request.

Step 505: The new I-SMF sends a (PDU Session) CreateSMContext Response (i.e. Response to Nsmf_PDUSession_CreateSMContext Request) to the AMF.

Step 506: The new I-SMF may select a new I-UPF to serve the PDU session.

Step 507: The new I-SMF initiates an N4 Session Establishment procedure with the newly selected I-UPF.

Step 508: The new I-SMF sends a (PDU Session) Create Request (i.e. Nsmf_PDUSession_Create Request) to the anchor SMF, wherein the Create Request includes an I-SMF Restoration Indication (i.e. ivres-indication shown in FIG. 5A) . In an embodiment, the Create Request further carries at least one of the following information: PDU Session ID, NF Instance ID of the I-SMF, callback URI of the I-SMF, N9 tunnel info of the I-UPF.

Step 509: The anchor SMF detects the Create Request is used to trigger the I-SMF restoration procedure based on the I-SMF Restoration Indication. Thus, the anchor SMF updates the I-SMF information for this PDU session, prepares and sends the SM context related information (e.g. at least part of I-SMF Restoration Container Info) back to the new I-SMF.

Step 510: If the N9 tunnel info of the I-UPF is provided in the Create Request, the anchor SMF triggers an N4 session modification procedure with the PSA UPF, to update the N9 tunnel info of the I-UPF.

Step 511: The anchor SMF sends a (PDU Session) Create Response (i.e. a Response corresponding to the Nsmf_PDUSession_Create Request) to the new I-SMF. In an embodiment, the I-SMF Restoration Container Info (i.e. ivres-container-info) is also included in this message if the anchor SMF detects the I-SMF Restoration Indication (i.e. ivres-indicaiton) is present in the corresponding request message (see step 508) and the anchor SMF has stored the I-SMF Restoration Container Info (i.e. ivres-container-info) in previous procedures.

In an embodiment, the Create Response further comprises at least one of the following information: SM context information and N9 tunnel info of the PSA UPF.

Step 512: The new I-SMF stores the I-SMF Restoration Container Info (i.e. ivres-container-info) received from the anchor SMF in its storage. The new I-SMF gets information of the old I-UPF from the I-SMF Restoration Container Info. The new I-SMF may use the stored information for the subsequent procedures:

In an embodiment, if the UPF Instance ID is present in the I-SMF Restoration Container Info, the new I-SMF may re-select the old I-UPF identified by the said UPF Instance ID.

In an embodiment, if the new I-SMF determines to re-use the old I-UPF to serve the PDU session, the new I-SMF may further use the UPF info (e.g. UP Connection State, N3 tunnel info, N9 tunnel info) comprised in the I-SMF Restoration Container Info to restore the N3 tunnel and the N9 tunnel. For example, if the stored UP Connection State indicates ACTIVATED, the new I-SMF restores the N3 tunnel, e.g., by using the N3 tunnel info in the stored I-SMF Restoration Container Info. As an alternative or in addition, if N9 tunnel info is stored (i.e. comprised in the I-SMF Restoration Container Info) , the new I-SMF restores the N9 tunnel, e.g., by using the stored N9 tunnel info.

Step 513 (FIG. 5B) : The new I-SMF initiates an N4 Session Release procedure with the new I-UPF.

Step 514: The new I-SMF initiates an N4 Session Modification procedure with the old I-UPF.

In step 514, if the new I-SMF determines to re-use the old I-UPF to serve the PDU session, the new I-SMF may use the UPF info (e.g. UPF Instance ID, N4 Session ID) included in the I-SMF Restoration Container Info to construct the N4 Session Modification Request sent to the old I-UPF.

Step 515: The new I-SMF sends a (PDU Session) Update Request to the anchor SMF, to update the N9 tunnel info of the I-UPF (which is changed back to the old I-UPF) . The anchor SMF updates the N9 tunnel info of the I-UPF and sends a (PDU Session) Update Response to the I-SMF.

In step 515, if the new I-SMF determines to re-use the old I-UPF to serve the PDU session, the new I-SMF may use the UPF info (e.g. N9 tunnel info) included in I-SMF Restoration Container Info to restore the N9 tunnel.

Step 516: the new I-SMF sends an N1N2MessageTransfer Request (i.e. Namf_Communication_N1N2MessageTransfer Request) to the AMF. In an embodiment, the N1N2MessageTransfer Request may carry at least one of the following information: UP Connection State, N2 SM Information.

If the UP Connection State (i.e. upCnxState) is set to ACTIVATING in the CreateSMContext Request (which means that the user plane connection is requested to be activated by the UE as per Service Request) , the new I-SMF establishes N3 tunnel User Plane resources for the PDU session and includes the following information in the response message: the upCnxState attribute set to ACTIVATING, the N3 tunnel information of the I-UPF, N2 SM information carrying PDU Session Resource Setup Request Transfer IE to request the RAN to assign resources to the PDU session.

If the new I-SMF detects the stored UP Connection State as ACTIVATED (which means the user plane connection is previously activated before I-SMF restoration procedure) , the new I-SMF re-establish N3 tunnel User Plane resources for the PDU session and includes the following information in the response message: the upCnxState attribute set to ACTIVATED, the N3 tunnel information of the I-UPF, N2 SM information carrying PDU Session Resource Modify Request Transfer IE to request the RAN to assign resources to the PDU session. In step 516, if the new I-SMF decides to re-use the old I-UPF and restore the original N3 tunnel, the UPF info (e.g. UP Connection State, N3 tunnel info) and the RAN info (e.g. RAN N3 tunnel info) included in I-SMF Restoration Container Info are used to restore the original N3 tunnel (hosted by the old I-UPF) and to construct the PDU Session Resource Modify Request Transfer sent to the RAN. Otherwise, the new I-SMF requests the new I-UPF to establish N3 tunnel and construct the PDU Session Modify Request Transfer sent to the RAN accordingly.

Step 517: The AMF sends an N2 PDU Session Request message to the RAN. The N2 SM information received from the SMF is included in the N2 PDU Session Request message. The RAN allocates RAN resources for the PDU session and returns an N2 PDU Session Request Ack (Acknowledgement) to the AMF.

Steps 518 to 520: The AMF sends a (PDU Session) UpdateSMContext Request to the I-SMF, wherein the PDU Session UpdateSMContext Request carries the RAN N3 tunnel info (RAN DL F-TEID) which triggers the I-SMF to update the RAN N3 tunnel info in the I-UPF.

Step 521: the I-SMF sends a (PDU Session) UpdateSMContext Request (i.e. Nsmf_PDUSession_UpdateSMContext Request) to the anchor SMF, wherein the PDU Session UpdateSMContext Request carries the updated I-SMF Restoration Container Info. The anchor SMF updates the stored I-SMF Restoration Container Info based on the received I-SMF Restoration Container.

Step 522: Subsequent procedures are performed to handle the MO signaling initiated by the UE. Note that, step 522 may be performed before or no later than step 521.

FIG. 6 shows a schematic diagram of an I-SMF restoration procedure according to an embodiment of the present disclosure. In FIG. 6, the anchor SMF receives and/or stores the I-SMF Restoration Container Info from the old I-SMF serving the PDU session. Based on the I-SMF Restoration Container Info, the anchor SMF finds the AMF and triggers the AMF to initiate the I-SMF restoration procedure.

In this embodiment, the anchor SMF is triggered to request the AMF to initiate I-SMF (i.e. I-SMF/V-SMF) restoration procedure after

step

601a, 601b or 601c:

Step 601a: The anchor SMF itself needs to send mobile terminated (MT) signaling towards the AMF or towards the UE.

Step 601b: The anchor SMF receives MT signaling towards the AMF or towards the UE.

Step 601c: The anchor SMF receives a GTP-U Error Report from the PSA UPF.

In an embodiment, the PSA UPF may receive a GTP-U Error Indication from the I-UPF. For example, when the UE is in IDLE state and the downlink traffic arrives at the old I-UPF, the I-UPF cannot trigger the I-SMF to send a Downlink Data Notification to the AMF if the I-SMF is in failure. Under such a condition, the I-UPF may send the GTP-U Error Indication to the PSA UPF and the PSA UPF may trigger the GTP-U Error Report to the anchor SMF.

Step 602: The anchor SMF detects the failure of the I-SMF.

Step 603: The anchor SMF determines to notify the AMF about the I-SMF failure.

In some embodiments, the anchor SMF may use the following method to notify the AMF:

a) If the AMF Instance ID is present in the I-SMF Restoration Container Info, the anchor SMF uses the AMF Instance ID to find the AMF profile from a network repository function (NRF) , and gets the API URI to send notification to the AMF.

b) If the API URI of AMF service is present in the I-SMF Restoration Container Info, the anchor SMF uses the stored API URI to send notification to the AMF.

c) If the callback URI of SM Context Notification is present in the I-SMF Restoration Container Info, the anchor SMF uses the stored callback URI to send an SM Context Notification to the AMF.

Step 604: The anchor SMF sends the notification to the AMF, wherein the notification carries an I-SMF Restoration Indication (i.e. ivres-indication) or an I-SMF Failure Indication (i.e. ivfail-indication) .

In some embodiments, the following messages can be used by the anchor SMF to send the notification to the AMF:

a) Namf_Communication_N1N2MessageTransfer Request carrying I-SMF Restoration Indication (ivres-indication) or I-SMF Failure Indication (ivfail-indication) .

b) Namf_Communication_SMContextStatusNotify Request carrying an SM Resource Failure Indication (ivres-indication) or I-SMF Failure Indication (ivfail-indication) .

c) a newly defined Namf_Communication_IvSmfRestoration Request.

Step 605: In response to receiving the indication from the anchor SMF, the AMF may perform one of the following actions:

A) Initiating an I-SMF restoration procedure if the UE is in IDLE state:

The AMF re-selects a new I-SMF and performs the I-SMF restoration procedure (e.g. steps 502/503 to 522 shown in FIGS. 5A and 5B. For the UE in IDLE state, the N3 tunnel activation is not required in the I-SMF restoration procedure. Therefore, it is no harm to the I-SMF restoration procedure that even if the anchor SMF does not return the stored UP Connection State to the newly selected I-SMF.

B) Initiating an I-SMF restoration procedure even if the UE is in CONNECTED state:

The AMF re-selects a new I-SMF and performs the I-SMF restoration procedure (e.g. steps 502/503 to 522) shown in FIGS. 5A and 5B. For the UE in CONNECTED state, the N3 tunnel activation is required in the I-SMF restoration procedure. The new I-SMF may either request the new I-UPF to establish N3 tunnel or request the old I-UPF to restore the original N3 tunnel if the old I-UPF is re-used for the PDU session. Under such conditions, the anchor SMF may return the stored UPF info (i.e. UP Connection State, and optionally other UPF info (i.e. UPF Instance ID, N3 tunnel info, N9 tunnel N4 session) ) to the newly selected I-SMF (e.g. step 511) . If the new I-SMF cannot get the UP Connection State the N3 tunnel cannot be activated, resulting in failure of the I-SMF restoration procedure.

C) Releasing the N2 connection associated with the UE if the UE is in CONNECTED state:

When the N2 connection is released, the UE is forced to be in IDLE state from CONNECTED state. In this embodiment, the AMF may trigger an I-SMF restoration procedure until/after receiving a UE initiated Service Request (e.g. FIGS. 5A and 5B) . The alternative C may be a simple replacement to the alternative B because alternative C only requires the new I-SMF to store the AMF info and UP Connection State in the anchor SMF while the alternative B requires the I-SMF to store more info (e.g. the UPF info such as UP Connection State, UPF Instance ID, N3 tunnel info, N9 tunnel info, N4 Session ID) from the anchor SMF.

FIG. 7 shows a schematic diagram of a PDU Session Release with Reactivation procedure according to an embodiment of the present disclosure. In FIG. 7, the anchor SMF detects the I-SMF failure and triggers the PDU Session Release with Reactivation procedure.

Specifically, the anchor SMF is triggered to request the AMF to initiate the PDU Session Release with Reactivation procedure after

step

701a, 701b or 701c. The

steps

701a, 701b and 701c are similar to

steps

601a, 601b and 601c, respectively, and are not narrated herein for brevity.

Step 702: The anchor SMF detects the failure of the I-SMF.

Step 703: The anchor SMF determines to release and re-activate the PDU session.

In step 703, the anchor SMF constructs a PDU Session Release message, wherein a Reactivation indication is included in the PDU Session Release message.

Step 704: The anchor SMF sends an N1N2MessageTransfer (i.e. Namf_Communication_N1N2MessageTransfer) carrying the N1 SM Container (PDU Session Release message with Reactivation) to the AMF.

In step 704, the anchor SMF uses the stored AMF info in the Intermediate Restoration Container Info to find the AMF to which the N1N2MessageTransfer Request is sent.

Step 705: The PDU session is re-activated after a PDU Session Release with Reactivation procedure is performed. During the PDU Session Release with Reactivation procedure, the AMF detects the failure of the old I-SMF and selects a new I-SMF to serve the PDU session.

FIG. 8 relates to a schematic diagram of a wireless terminal 80 according to an embodiment of the present disclosure. The wireless terminal 80 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 80 may include a processor 800 such as a microprocessor or Application Specific Integrated Circuit (ASIC) , a storage unit 810 and a communication unit 820. The storage unit 810 may be any data storage device that stores a program code 812, which is accessed and executed by the processor 800. Embodiments of the storage unit 812 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 820 may a transceiver and is used to transmit and receive signals (e.g. messages or packets) according to processing results of the processor 800. In an embodiment, the communication unit 820 transmits and receives the signals via at least one antenna 822 shown in FIG. 8.

In an embodiment, the storage unit 810 and the program code 812 may be omitted and the processor 800 may include a storage unit with stored program code.

The processor 800 may implement any one of the steps in exemplified embodiments on the wireless terminal 80, e.g., by executing the program code 812.

The communication unit 820 may be a transceiver. The communication unit 820 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. 9 relates to a schematic diagram of a wireless network node 90 according to an embodiment of the present disclosure. The wireless network node 90 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) , a radio access network (RAN) node, a next generation RAN (NG-RAN) node, a gNB, an eNB, a gNB central unit (gNB-CU) , a gNB distributed unit (gNB-DU) a data network, a core network or a Radio Network Controller (RNC) , and is not limited herein. In addition, the wireless network node 90 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. The wireless network node 90 may include a processor 900 such as a microprocessor or ASIC, a storage unit 910 and a communication unit 920. The storage unit 910 may be any data storage device that stores a program code 912, which is accessed and executed by the processor 900. Examples of the storage unit 912 include but are not limited to a SIM, ROM, flash memory, RAM, hard-disk, and optical data storage device. The communication unit 920 may be a transceiver and is used to transmit and receive signals (e.g. messages or packets) according to processing results of the processor 900. In an example, the communication unit 920 transmits and receives the signals via at least one antenna 922 shown in FIG. 9.

In an embodiment, the storage unit 910 and the program code 912 may be omitted. The processor 900 may include a storage unit with stored program code.

The processor 900 may implement any steps described in exemplified embodiments on the wireless network node 90, e.g., via executing the program code 912.

The communication unit 920 may be a transceiver. The communication unit 920 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. 10 shows a schematic diagram of a method according to an embodiment of the present disclosure. The method shown in FIG. 10 may be used in an I-SMF (e.g. V-SMF shown in FIG. 1 or I-SMF shown in FIG. 2, a wireless device comprising the I-SMF, a wireless device performing (a part of or all of) functionalities of the I-SMF) and comprises the following step:

Step 1001: Transmit, to an anchor SMF, restoration information associated with restoring an I-SMF of a PDU session.

In the embodiment of FIG. 10, a PDU session is established with insertion of the I-SMF. In order to enable the restoration of the I-SMF of the PDU session, the I-SMF transmits restoration information (i.e. I-SMF Restoration Container Info or ivres-container info) associated with restoring the I-SMF of the PDU session to the anchor SMF (of the PDU session) . Note that the I-SMF may transmit the container information to the anchor SMF if the container information changes or is updated, so as to keep the container information up to date. The transmission of the restoration information enables the anchor SMF to trigger a procedure associated with restoring the I-SMF of the PDU session if the anchor SMF detects a failure of the I-SMF.

In an embodiment, the restoration information comprises at least one of information associated with an AMF of the PDU session (i.e. AMF info) , information associated with a RAN node of the PDU session (i.e. RAN info) or information associated with an I-UPF (i.e. I-UPF info) .

In an embodiment, the AMF info comprises at least one of an AMF Instance ID, an API URI of AMF service, a callback URI for (receiving) SM Context Status Notification.

In an embodiment, the AMF Instance ID uniquely identifies an AMF, and can be used by other NF to retrieve AMF profile from the NRF.

In an embodiment, the API URI of AMF service indicates the API URI of the services provided by the AMF. For example, the API URI of AMF service may indicate the API URI of Namf_Communication service, which can be used by an SMF to send N1/N2 message (s) to the AMF.

In an embodiment, the callback URI for the SM Context Status Notification is a callback URI belonging to the AMF and is used to receive any SM Context Status Notification from the SMF (e.g. I-SMF) , wherein the SM Context Status Notification may notify, e.g., that the SM Context is transferred to another I-SMF, that the SM Context is released, etc.

In an embodiment, the RAN info comprises the N3 tunnel info (RAN DL F-TEID) .

In an embodiment, the UPF Instance ID is used to uniquely identify the I-UPF.

In an embodiment, the I-SMF may transmit an intermediate SMF restoration indication associated with the PDU session to the anchor SMF and receive the restoration information from the anchor SMF. For example, the I-SMF may be a newly selected I-SMF for the PDU session (e.g. The new I-SMF shown in FIGS. 5A and 5B) . The I-SMF may transmits a Create request comprising the intermediate SMF restoration indication to the anchor SMF and receives a Create response comprising the restoration information from the anchor SMF (see, e.g., steps 508 and 511 shown in FIG. 5A) . In this embodiment, the I-SMF may perform the step 1001 after the restoration information changes (e.g. step 521) . In addition, the I-SMF may further receive the intermediate SMF restoration indication from the AMF of the PDU session (e.g. step 504) in this embodiment.

In an embodiment, the I-SMF may perform an intermediate SMF restoration procedure based on the (received) restoration information. For instance, the I-SMF may select an I-UPF indicated by the restoration information (e.g. old I-UPF shown in FIGS. 5A and 5B) for serving the PDU session. As an alternative or in addition, the I-SMF may use/reuse tunnel information in the restoration information (e.g. N3 tunnel info and/or N9 tunnel info) to restore corresponding tunnel (s) (e.g. N3 tunnel and/or N9 tunnel) .

In an embodiment, the I-SMF is selected to serve the PDU session after an I-SMF serving the PDU session fails (e.g. after the failure of the intermediate SMF serving the PDU session is detected) . That is, the I-SMF may be the new I-SMF shown in FIGS. 5A, 5B, 6 or 7.

In an embodiment, the I-SMF may be selected to serve the PDU session during the PDU session establishment. In other words, the I-SMF may be the I-SMF shown in FIG. 4 or the old I-SMF shown in FIGS. 5A, 5B, 6 or 7.

FIG. 11 shows a schematic diagram of a method according to an embodiment of the present disclosure. The method shown in FIG. 11 may be used in an anchor SMF (e.g. a wireless device comprising the anchor SMF, a wireless device performing (a part of or all of) functionalities of the I-SMF) and comprises the following step:

Step 1101: Receive, from a first I-SMF, restoration information associated with restoring an intermediate SMF of a PDU session.

In FIG. 11, the anchor SMF (of the PDU session) may receive restoration information from a first I-SMF (serving the PDU session) , wherein the restoration information is associated with (e.g. used for) the I-SMF of the PDU session. The anchor SMF may receive the restoration information during or after the establishment of the PDU session.

In an embodiment, In an embodiment, the restoration information comprises at least one of information associated with an AMF of the PDU session (i.e. AMF info) , information associated with a RAN node of the PDU session (i.e. RAN info) or information associated with an I-UPF (i.e. I-UPF info) .

In an embodiment, the RAN info comprises the N3 tunnel info (RAN DL F-TEID) .

In an embodiment, the UPF Instance ID is used to uniquely identify the I-UPF.

In an embodiment, the anchor SMF receives an intermediate SMF restoration indication associated with the PDU session from a second I-SMF (e.g. new I-SMF shown in FIGS. 5A and 5B) . The anchor SMF transmits the received (or stored) restoration information to the second I-SMF.

In an embodiment, the anchor SMF may trigger a restoration procedure associated with restoring the I-SMF of the PDU session based on the restoration information. Specifically, the anchor SMF may find (e.g. determine) an AMF indicated by the restoration information and transmit an indication to the AMF to trigger the restoration procedure associated with restoring the I-SMF of the PDU session. For example, the anchor SMF may transmit an intermediate SMF restoration indication of triggering an intermediate SMF restoration procedure to the AMF indicated by the restoration information (see, e.g., FIG. 6) . As an alternative, the anchor SMF may transmit a PDU session release request comprising a reactivation indication to the AMF indicated by the restoration information. That is, the triggered procedure may be PDU Session Release with Reactivation procedure (see, e.g., FIG. 7) .

Note that the anchor SMF may trigger the restoration procedure if detecting/determining at least one of:

- failure of the I-SMF serving the PDU session;

- I-SMF serving the PDU session fails;

- I-SMF serving the PDU session cannot be reached or is not reachable;

- I-SMF serving the PDU session cannot (successfully) handle requests.

FIG. 12 shows a schematic diagram of a method according to an embodiment of the present disclosure. The method shown in FIG. 12 may be used in an AMF (e.g. a wireless device comprising the AMF or a wireless device performing (a part of or all of) functionalities of the AMF) and comprises the following steps:

Step 1201: Receive, from an anchor SMF, an intermediate SMF restoration indication associated with a PDU session.

Step 1202: Trigger a restoration procedure associated with restoring an intermediate SMF of the PDU session.

In FIG. 12, the AMF receives an intermediate SMF restoration indication associated with a PDU session and triggers a restoration procedure associated with restoring an intermediate SMF of the PDU session (e.g. based on or in response to the intermediate SMF restoration indication) .

In an embodiment, the AMF triggers the restoration procedure by:

selecting an I-SMF (e.g. new I-SMF) for (serving) the PDU session, and

transmitting, to the selected SMF, SM Context Create message associated with the PDU session (e.g. steps 503 and 504) .

Note that, the context create message comprises at least one of a PDU Session identifier, an anchor SMF Instance identifier or the intermediate SMF restoration indication.

In an embodiment, if the UE associated with the PDU session is in IDLE state, the AMF triggers an I-SMF restoration procedure (e.g. steps 502/503 to 522) as the restoration procedure. In this embodiment, the UPF info transmitted from the anchor AMF to the new I-SMF (e.g. at step 511) may not comprise a UP Connection State.

In an embodiment, if the UE associated with the PDU session is in CONNECTED state the AMF triggers an I-SMF restoration procedure (e.g. steps 502/503 to 522) as the restoration procedure. In the I-SMF restoration procedure, the newly selected I-SMF may receive UPF info from the anchor SMF, wherein the UPF info comprises a UP Connection State. The UPF info in this embodiment may further comprise at least one of a UPF Instance ID, an N3 tunnel info, an N9 tunnel N4 session.

In an embodiment, the triggered restoration procedure comprises releasing an N2 connection associated with the UE of the PDU session. For example, the N2 connection associated with the UE is the connection which is between the AMF and a RAN node serving the UE and is established for the UE. In this embodiment, the new I-SMF receives the UPF info comprising (only) a UP Connection State from the anchor SMF. In this embodiment, the UPF info may not comprise other info.

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 one 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 one 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 one 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 intermediate session management function, SMF, the method comprising:

transmitting, to an anchor SMF, restoration information associated with restoring an intermediate SMF of a protocol data unit, PDU, session.
The wireless communication method of claim 1, wherein the restoration information comprises at least one of information associated with an access and mobility management function, AMF, of the PDU session, information associated with a radio access network node of the PDU session or information associated with an intermediate user plane function, UPF.
The wireless communication method of claim 2, wherein the information associated with the AMF comprises at least one of an AMF Instance identifier, an application program interface uniform resource identifier of an AMF service, or a callback uniform resource identifier of receiving a session management context status notification.
The wireless communication method of claim 2 or 3, wherein the information associated with the radio access network node comprises radio access network N3 tunnel information.
The wireless communication method of any of claims 2 to 4, wherein information associated with the intermediate UPF comprises at least one of a UPF Instance identifier, UPF N3 tunnel information, UPF N9 tunnel information or an N4 Session identifier.
The wireless communication method of any of claims 1 to 5, further comprising:

transmitting, to the anchor SMF, an intermediate SMF restoration indication associated with the PDU session, and

receiving, from the anchor SMF, the restoration information.
The wireless communication method of claim 6, further comprising:

receiving, from an access and mobility management function, an intermediate SMF restoration indication associated with the PDU session.
The wireless communication method of claim 6 or 7, further comprising:

performing an intermediate SMF restoration procedure based on the restoration information.
The wireless communication method of claim 8, wherein performing the intermediate SMF restoration procedure based on the restoration information comprises:

selecting an intermediate UPF indicated by the restoration information for serving the PDU session.
The wireless communication method of any of claims 1 to 9, wherein the intermediate SMF is selected to serve the PDU session after an intermediate SMF serving the PDU session fails.
The wireless communication method of any of claims 1 to 5, wherein the intermediate SMF is selected to serve the PDU session during the PDU session establishment.
A wireless communication method for use in an anchor session management function, SMF, the method comprising:

receiving, from a first intermediate SMF, restoration information associated with restoring an intermediate SMF of a protocol date unit, PDU, session.
The wireless communication method of claim 12, wherein the intermediate restoration information comprises at least one of information associated with an access and mobility management function, AMF, of the PDU session, information associated with a radio access network node of the PDU session or information associated with an intermediate user plane function, UPF.
The wireless communication method of claim 13, wherein the information associated with the AMF comprises at least one of an AMF Instance identifier, an application program interface uniform resource identifier of an AMF service, or a callback uniform resource identifier of a session management context status notification.
The wireless communication method of claim 13 or 14, wherein the information associated with the radio access network node comprises radio access network N3 tunnel information.
The wireless communication method of any of claims 13 to 15, wherein information associated with the intermediate UPF comprises at least one of a UPF Instance identifier, UPF N3 tunnel information, UPF N9 tunnel information or an N4 Session identifier.
The wireless communication method of any of claims 12 to 16, further comprising:

receiving, from a second intermediate SMF, an intermediate SMF restoration indication associated with the PDU session, and

transmitting, to a second intermediate SMF, the restoration information.
The wireless communication method of any of claims 12 to 16, further comprising:

transmitting, to an access and mobility management function indicated by the restoration information, an intermediate SMF restoration indication of triggering an intermediate SMF restoration procedure.
The wireless communication method of any of claims 12 to 16, further comprising:

transmitting, to an access and mobility management function indicated by the restoration information, a PDU session release request comprising a reactivation indication.
A wireless communication method for use in an access and mobility management function, the method comprising:

receiving, from an anchor session management function, SMF, an intermediate SMF restoration indication associated with a protocol data unit, PDU, session, and

triggering a restoration procedure associated with restoring an intermediate SMF of the PDU session.
The wireless communication method of claim 20, wherein triggering restoration procedure of associated with restoring the intermediate SMF of the PDU session comprises:

selecting an intermediate SMF for the PDU session, and

transmitting, to the selected SMF, a session management context create message associated with the PDU session,
The wireless communication method of claim 21, wherein the session management context create message comprises at least one of a PDU Session identifier, an anchor SMF Instance identifier or the intermediate SMF restoration indication.
A wireless device comprising an intermediate session management function, SMF, the wireless device comprising:

a communication unit, configured to transmit, to an anchor SMF, restoration information associated with restoring an intermediate SMF of a protocol data unit, PDU, session.
The wireless device of claim 23, further comprising a processor configured to perform a wireless communication method of any one of claims 2 to 11.
A wireless device comprising an anchor session management function, SMF, the wireless device comprising:

a communication unit, configured to receive, from an intermediate SMF, restoration information associated with restoring an intermediate SMF of a protocol data unit, PDU, session.
The wireless device of claim 25, further comprising a processor configured to perform a wireless communication method of any one of claims 13 to 19.
A wireless device comprising an access and mobility management function, the wireless device comprising:

a communication unit, configured to receive, from an anchor session management function, SMF, an intermediate SMF restoration indication associated with a protocol data unit, PDU, session, and

a processor, configured to trigger a restoration procedure associated with restoring an intermediate SMF of the PDU session.
The wireless device of claim 27, wherein the processor is further configured to perform a wireless communication method of claim 21 or 22.
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 one of claims 1 to 22.