METHOD FOR ADDING 3GPP PDN LEG TO AN MA PDU SESSION WITH NON-3GPP LEG

A method of handling multi-access (MA) Protocol data unit (PDU) session establishment procedure for adding a 3GPP PDN leg to an MA PDU session already established with a non-3GPP leg is proposed. In one novel aspect, for a 5GS MA PDU session already established on non-3GPP access, upon receipt of an ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message for establishing a PDN connection as a user-plane resource for the MA PDU session over 3GPP access, the UE sends an ACTIVATE DEFAULT EPS BEARER CONTEXT REJECT message if any value of at least one of the critical parameters, including the PDN type, ESM cause, PDN address, S-NSSAI, SSC mode (set to SSC mode 1), and APN IEs in the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message does not match/sync/compatible to the corresponding stored value of the MA PDU session with a non-3GPP leg.

TECHNICAL FIELD

The disclosed embodiments relate generally to wireless communication, and, more particularly, to method of Multi-Access (MA) PDU session establishment handling for adding a PDN leg to an MA PDU session established with a non-3GPP leg.

BACKGROUND

The wireless communications network has grown exponentially over the years. A Long-Term Evolution (LTE) system offers high peak data rates, low latency, improved system capacity, and low operating cost resulting from simplified network architecture. LTE systems, also known as the 4G system, also provide seamless integration to older wireless network, such as GSM, CDMA and Universal Mobile Telecommunication System (UMTS). In LTE systems, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNodeBs or eNBs) communicating with a plurality of mobile stations, referred to as user equipments (UEs). The 3rdgeneration partner project (3GPP) network normally includes a hybrid of 2G/3G/4G systems. The Next Generation Mobile Network (NGMN) board has decided to focus the future NGMN activities on defining the end-to-end requirements for 5G new radio (NR) systems (5GS).

In 5G, a Protocol Data Unit (PDU) session defines the association between the UE and the data network that provides a PDU connectivity service. The PDU session establishment is a parallel procedure of PDN connection (bearer) procedure in 4G/LTE. Each PDU session is identified by a PDU session ID (PSI), and may include multiple QoS flows and QoS rules. Each PDU session can be established via a 5G Access Network (e.g., a 3GPP radio access network (RAN), or a non-3GPP RAN). The network/UE can initiate different PDU session procedures, e.g., PDU session establishment, PDU session modification, and PDU session release.

Operators are seeking ways to balance data traffic between mobile cellular networks and non-3GPP access in a way that is transparent to users and reduces mobile network congestion. In 5GS, UEs that can be simultaneously connected to both 3GPP access and non-3GPP access (using 3GPP NAS signalling), thus the 5GS is able to take advantage of these multiple accesses to improve the user experience, optimize the traffic distribution across various accesses. Accordingly, 3GPP introduced Multi-Access (MA) PDU session in 5GS. A MA PDU session uses one 3GPP access network or one non-3GPP access network at a time, or simultaneously one 3GPP access network and one non-3GPP access network.

In addition, ATSSS (Access Traffic Steering, Switching, Splitting) is an optional feature that can be supported by the UE and the 5GC network to route data traffic across 3GPP access and non-3GPP access networks for the established MA PDU session. An ATSSS-capable UE establishes an MA PDU session supporting multi-access connectivity over 3GPP access and non-3GPP access networks. At any given time, the MA PDU session can have user-plane resources established on both 3GPP access (also referred as 3GPP 5GS leg) and non-3GPP access (also referred as non-3GPP leg), or on one access only (either 3GPP access or non-3GPP 5GS access).

In certain networks, LTE has more coverage than NR, and sometimes UE are not able to establish 3GPP 5GS leg for an MA PDU session when NR coverage is unavailable. Therefore, it is beneficial that a 4G EPS PDN connection can be established as the user-plane resource for a corresponding MA PDU session over 3GPP access (also referred as 3GPP PDN leg). However, it becomes a challenge for a UE to determine whether the parameters of the adding 3GPP PDN leg are compatible with the stored parameters of an existing MA PDU session that already has a non-3GPP leg, and how the UE handles when the UE determines the parameters are not compatible.

A solution is sought.

SUMMARY

A method of handling multi-access (MA) Protocol data unit (PDU) session establishment procedure for adding a 3GPP PDN leg to an MA PDU session already established with a non-3GPP leg is proposed. In one novel aspect, for a 5GS MA PDU session already established on/over non-3GPP access, upon receipt of an ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message for the purpose of establishing a PDN connection as a user-plane resource for the MA PDU session (over 3GPP access), the UE performs a local release of the MA PDU session if any value of at least one of the critical MA PDU session parameters, including the PDN type, ESM cause, PDN address, S-NSSAI, and APN IEs in the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message does not match to the corresponding stored value of the MA PDU session already established over non-3GPP access, and including the stored SELECTED SSC MODE of the MA PDU session already established over non-3GPP access is not set to SSC mode 1. The UE also performs a registration procedure for mobility and periodic registration update with a REGISTRATION REQUEST message including a PDU session status IE sent over non-3GPP access and performs a tracking area updating procedure with a TRACKING AREA UPDATE REQUEST message including EPS bearer context IE sent over EPS (i.e., 4G 3GPP access).

DETAILED DESCRIPTION

FIG.1illustrates an exemplary 5G network100supporting adding non-3GPP leg to a Multi-Access Protocol Data Unit (MA PDU) session with 3GPP PDN leg in accordance with one novel aspect. 5G network100comprises a user equipment UE101, a 3GPP radio (e.g., NR) access network RAN102, a non-3GPP radio access network RAN103, an Access and Mobility Management Function (AMF)110, a Session Management Function (SMF)111, a Non-3GPP Interworking Function (N3IWF)112, a User-plane Function (UPF)113, and a data network120. The AMF communicates with the base station, SMF and UPF for access and mobility management of wireless access devices in mobile communication network100. The SMF is primarily responsible for interacting with the decoupled data plane, creating, updating, and removing Protocol Data Unit (PDU) sessions and managing session context with the UPF. The N3IWF functionality interfaces to 5G core network control plane functions, responsible for routing messages outside 5G RAN.

In Access Stratum (AS) layer, RAN provides radio access for UE101via a radio access technology (RAT). In Non-Access Stratum (NAS) layer, AMF and SMF communicate with RAN and 5GC for access and mobility management and PDU session management of wireless access devices in 5G network100. 3GPP Radio access network RAN102may include base stations (gNBs or eNB) providing radio access for UE101via various 3GPP RATs including 5G, 4G, and 3G/2G. Non-3GPP radio access network RAN103may include access points (APs) providing radio access for UE101via non-3GPP including WiFi. UE101can obtain access to data network120through 3GPP access102, AMF110, SMF111, and UPF113. UE101can obtain access to data network120through non-3GPP access103, N3IWF112, AMF110, SMF111, and UPF113. UE101may be equipped with a single radio frequency (RF) module or transceiver or multiple RF modules or transceivers for services via different RATs/CNs. UE101may be a smart phone, a wearable device, an Internet of Things (IoT) device, a tablet, etc.

EPS networks are packet-switched (PS) Internet Protocol (IP) networks. This means that the networks deliver all data traffic in IP packets, and provide users with Always-On IP Connectivity. When UE joins an EPS network, a Packet Data Network (PDN) address (i.e., the one that can be used on the PDN) is assigned to the UE for its connection to the PDN. In 4G, EPS has defined a Default EPS Bearer to provide the IP Connectivity that is Always-On. In 5G, a Protocol Data Unit (PDU) session establishment procedure is a parallel procedure of a PDN connection procedure in 4G. A PDU session defines the association between the UE and the data network that provides a PDU connectivity service. Each PDU session is identified by a PDU session ID (PSI), and may include multiple QoS flows and QoS rules.

Each PDU session can be established over a 3GPP RAN, or over a non-3GPP RAN for radio access. 5G Session management (5GSM) for PDU sessions over both 3GPP access and non-3GPP access are managed by AMF and SMF via NAS signaling. Operators are seeking ways to balance data traffic between mobile networks and non-3GPP access in a way that is transparent to users and reduces mobile network congestion. In 5GS, UEs that can be simultaneously connected to both 3GPP access and non-3GPP access (using 3GPP NAS signalling), thus the 5GS is able to take advantage of these multiple accesses to improve the user experience, optimize the traffic distribution across various accesses. Accordingly, 3GPP introduced Multi-Access (MA) PDU session in 5GS. A MA PDU session uses one 3GPP access network or one non-3GPP access network at a time, or simultaneously one 3GPP access network and one non-3GPP access network.

In addition, the UE and the network can support Access Traffic Steering Switching and Splitting (ATSSS) functionalities to distribute traffic over 3GPP access and non-3GPP access for the established MA PDU session. An ATSSS capable UE establishes an MA PDU session supporting multi-access connectivity over 3GPP access and non-3GPP access networks. At any given time, the MA PDU session can have user-plane resources established on both 3GPP access (referred as 3GPP 5GS leg) and non-3GPP access (referred as non-3GPP leg), or on one access only (either 3GPP access or non-3GPP 5GS access). In certain networks, LTE has more coverage than NR, and sometimes UE are not able to establish 3GPP 5GS leg for an MA PDU session when NR coverage is unavailable. Therefore, it is beneficial that a 4G EPS PDN connection can be established as the user-plane resource for a corresponding MA PDU session over 3GPP access (referred as 3GPP PDN leg).

For an MA PDU session establishment, it becomes a challenge on adding a 3GPP PDN leg to an existing MA PDU session that already has a non-3GPP leg. In accordance with one novel aspect, a method of handling MA PDU session establishment procedure with an ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message for adding a 3GPP PDN leg to an MA PDU session with a non-3GPP leg is proposed. UE101is registered to 5GC via 4G EPS/EPC for 3GPP access as well as registered to 5GC via WiFi for non-3GPP access. In step131, UE101maintains an MA PDU session with user-plane resources established over non-3GPP access (non-3GPP leg). In order to establish a PDN connection as a user-plane resource of the already established MA PDU session, in step132, UE101initiates a UE-requested PDN connectivity procedure, by sending a PDN CONNECTIVITY REQUEST message. UE101then receives an ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message of a default EPS bearer context activation procedure as a response to the PDN CONNECTIVITY REQUEST message. The default EPS bearer parameters in the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST need to be fully synced with the stored PDU session parameter of the already established MA PDU session with non-3GPP leg.

In step133, UE101determines and compares the critical parameters of the PDN connection and the parameters of the existing MA PDU session with non-3GPP leg. In step134, UE101detects that at least one of the critical parameters of the PDN connection (e.g., PDN address) are not synced with the parameters of the MA PDU session with non-3GPP leg (e.g., PDU address). Then, it is proposed that, in step135, UE101sends an ACTIVATE DEFAULT EPS BEARER CONTEXT REJECT message to the network. Optionally, UE101may perform a local release of the MA PDU session and the registration procedure for mobility and periodic registration update with a REGISTRATION REQUEST message including the PDU session status IE sent over non-3GPP access.

FIG.2illustrates simplified block diagrams of wireless devices, e.g., a UE201and a network entity211in accordance with embodiments of the current invention. Network entity211may be a base station and/or an AMF/SMF. Network entity211has an antenna215, which transmits and receives radio signals. A radio frequency RF transceiver module214, coupled with the antenna, receives RF signals from antenna215, converts them to baseband signals and sends them to processor213. RF transceiver214also converts received baseband signals from processor213, converts them to RF signals, and sends out to antenna215. Processor213processes the received baseband signals and invokes different functional modules to perform features in base station211. Memory212stores program instructions and data220to control the operations of base station211. In the example ofFIG.2, network entity211also includes protocol stack280and a set of control functional modules and circuitry290.

Similarly, UE201has memory202, a processor203, and radio frequency (RF) transceiver module204. RF transceiver204is coupled with antenna205, receives RF signals from antenna205, converts them to baseband signals, and sends them to processor203. RF transceiver204also converts received baseband signals from processor203, converts them to RF signals, and sends out to antenna205. Processor203processes the received baseband signals and invokes different functional modules and circuits to perform features in UE201. Memory202stores data and program instructions210to be executed by the processor to control the operations of UE201. Suitable processors include, by way of example, a special purpose processor, a digital signal processor (DSP), a plurality of micro-processors, one or more micro-processor associated with a DSP core, a controller, a microcontroller, application specific integrated circuits (ASICs), file programmable gate array (FPGA) circuits, and other type of integrated circuits (ICs), and/or state machines. A processor in associated with software may be used to implement and configure features of UE201.

UE201also comprises a set of functional modules and control circuitry to carry out functional tasks of UE201. Protocol stacks260comprise Non-Access-Stratum (NAS) layer to communicate with an AMF/SMF/MME entity connecting to the core network, Radio Resource Control (RRC) layer for high layer configuration and control, Packet Data Convergence Protocol/Radio Link Control (PDCP/RLC) layer, Media Access Control (MAC) layer, and Physical (PHY) layer. System modules and circuitry270may be implemented and configured by software, firmware, hardware, and/or combination thereof. The function modules and circuits, when executed by the processors via program instructions contained in the memory, interwork with each other to allow UE201to perform embodiments and functional tasks and features in the network.

In one embodiment, system modules and circuits270comprise PDU session handling circuit221that performs PDU session establishment and modification procedures with the network, a registration handling circuit222that performs registration with the network via 3GPP or non-3GPP access, and a configuration and control circuit223that handles configuration and control parameters for mobility management and session management. In one example, UE201initiates adding a 3GPP PDN leg to an existing MA PDU session that already has a non-3GPP PDN leg. UE201receives an ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message for adding a PDN connection as a user-plane resource for the MA PDU session. UE201sends an ACTIVATE DEFAULT EPS BEARER CONTEXT REJECT message if any of the critical parameters of the PDN connection is different from the corresponding stored parameters of the MA PDU session. UE201may also perform a local release of the MA PDU session and a registration procedure for mobility and periodic registration update with a REGISTRATION REQUEST message including a PDU session status IE that is sent over non-3GPP access.

FIG.3illustrates the different procedures for registration to 5GS over 3GPP and non-3GPP accesses, establishing an MA PDU session with a non-3GPP leg, and adding a 3GPP PDN leg to the MA PDU session. An MA PDU session in 5GS can be established after a UE is registered to the network over both 3GPP access type and non-3GPP access type. The UE can establish a MA PDU session by initiating a PDU session establishment procedure with the network over either 3GPP or non-3GPP access type and activating the MA PDU session. The activation of the MA PDU connectivity service refers to the establishment of user-plane resources on both 3GPP access and non-3GPP access. UE can also establish a MA PDU session by initiating a PDN connectivity procedure, where the PDN connection can be established as the user-plane resource for the MA PDU session.

In the embodiment ofFIG.3, UE301first performs registration procedure (310). UE301is registered to 4G via 4G EPS/EPC (LTE) for 3GPP access, and is registered to 5GC via WiFi for non-3GPP access. Note that UE301may not be registered to 5GC via NR for 3GPP access. Next, UE301performs PDU session establishment procedure for the purpose of establishing an MA PDU session (320). UE301establishes user-plane resources of the MA PDU session over non-3GPP access. Afterward, UE301considers that the MA PDU session is established based on parameters in a PDU SESSION ESTABLISHMENT ACCEPT message from the network. UE301stores corresponding MA PDU session parameters including: PDU session type, PDU address, SSC mode, 5GSM cause, S-NSSAI, and DNN.

Next, in step330, UE301initiates a UE-requested PDN connectivity procedure in order to establish a PDN connection as a user-plane resource of the already established MA PDU session. UE301sends a PDN CONNECTIVITY REQUEST message, and receives an ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message of a default EPS bearer context activation procedure as a response to the PDN CONNECTIVITY REQUEST message. The UE considers that the PDN connection is established as a user-plane resource of the MA PDU session. Otherwise, upon receipt of a PDN CONNECTIVITY REJECT message, the UE considers that the PDN connection is not established as a user-plane resource of the MA PDU session.

UE301needs to determine that if any of the critical parameters of the PDN connection and of the existing MA PDU session are matched/compatible/synced. The critical PDN parameters include at least one of PDN/PDU type, PDN/PDU address, SSC mode, ESM/5GSM cause, S-NSSAI, and APN/DNN. If any mismatch/un-compatible/in-synced is detected, then UE301should send ACTIVATE DEFAULT EPS BEARER CONTEXT REJECT message to the network. Optionally, UE301may perform a local release of the MA PDU session and the registration procedure for mobility and periodic registration update with a REGISTRATION REQUEST message including the PDU session status IE sent over non-3GPP access.

FIG.4illustrates a sequence flow between a UE and a 5GS network for establishing an MA PDU over both EPS 3GPP access and 5GS non-3GPP access, and abnormal error handling in one novel aspect. In step411, UE401performs registration (attach) with the 4G EPS network. In step412, UE401performs registration with the 5GS network over non-3GPP access. In step421, UE401sends a PDU SESSION ESTABLISHMENT REQUEST message to 5GS over non-3GPP access, indicating a PDU session ID (e.g., PDU session ID==5) and a Request type==MA PDU for establishing user-plane resources for the MA PDU session on/over non-3GPP access. In step422, UE401receives a PDU SESSION ESTABLISHMENT ACCEPT message over non-3GPP access from 5GS for the MA PDU session. The accept message includes ATSSS container IE, and includes a set of MA PDU session parameters, e.g., PDU session type, PDU address, selected SSC mode, 5GSM cause, S-NSSAI, and DNN IEs. In step423, UE401considers that the MA PDU session is established, having the user-plane resources established on/over non-3GPP access.

Once the MA PDU session is established with a non-3GPP leg, UE401then wants to add a 3GPP PDN leg to the existing MA PDU session (PDU session ID==5). In step431, UE401initiates a UE-requested PDN connectivity procedure to establish a PDN connection as a user-plane resource of the MA PDU session. UE401sends a PDN CONNECTIVITY REQUEST message to 4G EPS. In the PDN CONNECTIVITY REQUEST message or, when applicable, in the ESM INFORMATION RESPONSE message, of the UE requested PDN connectivity procedure, the UE sets the request type to “handover”, sets the PDN Type IE to “IPv4”, “IPv6”, “IPv4v6”, “Ethernet” or “non-IP”. In the protocol configuration options (PCO) or extended PCO IE of the PDN CONNECTIVITY REQUEST message, the UE includes the ATSSS request PCO parameter. In step432, UE401receives an ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message of a default EPS bearer context activation procedure from the EPS network, as a response to the PDN CONNECTIVITY REQUEST message. The ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message contains the extended PCO IE with the ATSSS response having the length of two octets PCO parameter.

If at least one of the critical parameters does not match/sync/compatible the corresponding stored parameter, then the MA PDU session may not function properly and the UE has no way to know how to choose (trust) between the parameters of the PDN leg and the parameters of the non-3GPP leg (sometimes the parameters in the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message (PDN leg) are correct, but sometimes the parameters stored in the MA PDU session (non-3GPP leg) are correct; however the UE has no way to know which parameters are correct). For example, the same MA PDU session cannot have different PDU addresses. Thus, in step441, UE401sends an ACTIVATE DEFAULT EPS BEARER CONTEXT REJECT message to the network. In addition, UE401may locally release the MA PDU session (step442) and perform a registration procedure for mobility and periodic registration update by sending a REGISTRATION REQUEST message including PDU session status IE to the network over non-3GPP access. Specifically, the status IE is sent to 5GS over non-3GPP access to indicate to the network that the user-plane resources of the MA PDU session on non-3GPP access are released at the UE side.

FIG.5is a flow chart of a method of adding a PDN leg to a multi-access (MA) Protocol data unit (PDU) session having a non-3GPP leg and corresponding error handling in accordance with one novel aspect. In step501, a UE maintains a multi-access protocol data unit (MA PDU) session and user-plane resources over non-3GPP access for the MA PDU session, wherein the MA PDU session has a stored first set of parameters stored in the UE. In step502, the UE transmits a PDN CONNECTIVITY REQUEST message to establish a PDN connection as a user-plane resource for the same MA PDU session. In step503, the UE receives an ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message of a default EPS bearer context activation procedure, wherein the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message contains a second set of parameters. In step504, the UE determines a condition is not fulfilled when at least one parameter in the second set of parameters does not match/sync/compatible to a corresponding parameter in the first set of parameters. In step505, in response to not fulfilling the condition, the UE transmits an ACTIVATE DEFAULT EPS BEARER CONTEXT REJECT message to the network. The UE MAY locally release the MA PDU session and perform registration update for non-3GPP access.