Patent Publication Number: US-2023133792-A1

Title: Handling of collision between pdu session establishment and modification procedure

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 119 from U.S. Provisional Application No. 63/274,983, entitled “Handling of Collision between PDU session establishment and modification procedure”, filed on Nov. 3, 2021, the subject matter of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The disclosed embodiments relate generally to wireless communication, and, more particularly, to method for handling PDU session establishment procedure and PDU session modification procedure collision. 
     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 3 rd  generation 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. 
     In 5G/NR, 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., 3GPP radio access network (RAN), or via a non-3GPP RAN). Both the network and the UE can initiate different PDU session procedures, e.g., PDU session establishment procedure, PDU session modification procedure, and PDU session release procedure, for managing PDU sessions. 
     PDU session establishment procedure can be used to establish a new PDU session, handover an existing PDU session, or establish a second leg for an existing MA PDU session. If there is an existing PDU session, it is possible that the network initiates a PDU session modification procedure to modify it while the UE initiates a PDU session establishment procedure to handover/establish a second leg of the PDU session. The UE/network handling on this collision is not defined. 
     A solution is sought. 
     SUMMARY 
     A method for handling a collision of a UE-requested PDU session establishment procedure and a network-requested PDU session modification procedure is proposed. The collision is detected if the UE receives a PDU SESSION MODIFICATION COMMAND message after sending a PDU SESSION ESTABLISHMENT REQUEST message to the network, and the PDU session ID (PSI) in the PDU SESSION MODIFICATION COMMAND message is the same as the PDU session ID in the PDU SESSION ESTABLISHMENT REQUEST message. When a PDU SESSION ESTABLISHMENT REQUEST message indicates that the UE-requested PDU session establishment request procedure is to handover an existing PDU session between 5G 3GPP access and 5G non-3GPP access, UE and NW proceed with the UE-requested PDU session establishment procedure and abort the NW-requested PDU session modification procedure. When a PDU SESSION ESTABLISHMENT REQUEST message indicates that the UE-requested PDU session establishment request procedure is to establish user plane resources for an MA PDU session, UE and NW proceed with both the UE-requested PDU session establishment procedure and the NW-requested PDU session modification procedure. 
     Other embodiments and advantages are described in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention. 
         FIG.  1    illustrates an exemplary 5G network supporting protocol data unit (PDU) session management and a method for PDU session procedure collision handling in accordance with one novel aspect. 
         FIG.  2    illustrates simplified block diagrams of a user equipment (UE) and a network entity in accordance with embodiments of the current invention. 
         FIG.  3    illustrates one embodiment of PDU session establishment handling for handover when UE also receives a PDU session modification command from the network in accordance with one novel aspect. 
         FIG.  4    illustrates another embodiment of PDU session establishment handling for an established MA PDU session when UE also receives a PDU session modification command from the network in accordance with one novel aspect. 
         FIG.  5    illustrates one embodiment of network behavior when the network receives a PDU session establishment request during a network-requested PDU session modification procedure. 
         FIG.  6    is a flow chart of a method of handling PDU session procedure collision from UE perspective for handover in accordance with one novel aspect of the present invention. 
         FIG.  7    is a flow chart of a method of handling PDU session procedure collision from UE perspective for MA PDU in accordance with one novel aspect of the present invention. 
         FIG.  8    is a flow chart of a method of handling PDU session procedure collision from NW perspective in accordance with one novel aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
       FIG.  1    illustrates an exemplary 5G network  100  supporting protocol data unit (PDU) session management and a method for PDU session procedure collision handling in accordance with one novel aspect. 5G new radio (NR) network  100  includes a user equipment (UE)  101 , a 3GPP access  102  (e.g., a 3GPP radio access network (RAN)), a non-3GPP access  103  (e.g., a non-3GPP RAN), 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 5G core (5GC) data network  120 . The AMF  110  communicates with the base stations in the 3GPP access  102 , the SMF  111 , and the UPF  113  for access and mobility management of wireless access devices in the 5G network  100 . The SMF  111  is primarily responsible for interacting with the decoupled data plane, creating, updating, and removing PDU sessions and managing session context with the UPF  113 . The N3IWF  112  interfaces to 5G core network control plane functions, responsible for routing messages outside 5G RAN. 
     In Access Stratum (AS) layer, an RAN provides radio access for the UE  101  via a radio access technology (RAT). In Non-Access Stratum (NAS) layer, the AMF  110  and the SMF  111  communicate with RAN and 5GC for access and mobility management and PDU session management of wireless access devices in the 5G network  100 . The 3GPP access  102  may include base stations (gNBs or eNBs) providing radio access for the UE  101  via various 3GPP RATs including 5G, 4G, and 3G/2G. The non-3GPP access  103  may include access points (APs) providing radio access for the UE  101  via non-3GPP RAT including WiFi. The UE  101  can obtain access to data network  120  through 3GPP access  102 , AMF  110 , SMF  111 , and UPF  113 . The UE  101  can obtain access to data network  120  through non-3GPP access  103 , N3IWF  112 , AMF  110 , SMF  111 , and UPF  113 . The UE  101  may be equipped with a single radio frequency (RF) module or transceiver or multiple RF modules or transceivers for services via different RATs/CNs. In some examples, UE  101  may be a smart phone, a wearable device, an Internet of Things (IoT) device, a tablet, etc. 
     5GS networks are packet-switched (PS) Internet Protocol (IP) networks. When a UE joins an evolved packet system (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 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, and can be established over a 3GPP RAN, and/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. In 5G, a multi-access (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. 
     Both the network and the UE can initiate different PDU session procedures, e.g., PDU session establishment procedure, PDU session modification procedure, and PDU session release procedure, for managing PDU sessions. When collision of UE-requested PDU session establishment procedure and network-requested PDU session modification procedure occurs, the UE/network handling on such collision is not defined. Further, PDU session establishment procedure may be used for different purposes including initial request, existing PDU session (handover), initial emergency request, existing emergency PDU session (handover), MA PDU request, . . . etc. The corresponding handlings of the detected collision under different scenarios should be distinguished. 
     In accordance with one novel aspect, UE and network behaviors are proposed to handle a collision of the UE-requested PDU session establishment procedure and the network-requested PDU session modification procedure (as depicted by  130 ). The collision is detected if the UE  101  receives a PDU SESSION MODIFICATION COMMAND message after sending a PDU SESSION ESTABLISHMENT REQUEST message to the network, and the PDU session ID in the PDU SESSION MODIFICATION COMMAND message is the same as the PDU session ID in the PDU SESSION ESTABLISHMENT REQUEST message. In a first example, if the UE-requested PDU session establishment procedure is for handover an existing PDU session between 5G 3GPP and 5G non-3GPP access, then as depicted by  140 , UE  101  proceeds with the UE-requested PDU session establishment procedure, and aborts the NW-requested PDU session modification procedure. In a second example, if the UE-requested PDU session establishment procedure is for establishing user-plane resource over a second access type for an existing MA PDU session already established over a first access type, then as depicted by  150 , UE  101  proceeds with both the UE-requested PDU session establishment procedure and the NW-requested PDU session modification procedure. In a third example, if the UE-requested PDU session establishment procedure is for handover an existing PDU session between 5G 3GPP and 5G non-3GPP access, then as depicted by  160 , the network proceeds with the UE-requested PDU session establishment procedure, and aborts the NW-requested PDU session modification procedure. 
       FIG.  2    illustrates simplified block diagrams of wireless devices, e.g., a UE  201  and a network entity  211  in accordance with embodiments of the current invention. Network entity  211  may be a base station and/or an AMF/SMF. Network entity  211  has an antenna  215 , which transmits and receives radio signals. A radio frequency RF transceiver module  214 , coupled with the antenna, receives RF signals from antenna  215 , converts them to baseband signals and sends them to processor  213 . RF transceiver  214  also converts received baseband signals from processor  213 , converts them to RF signals, and sends out to antenna  215 . Processor  213  processes the received baseband signals and invokes different functional modules to perform features in base station  211 . Memory  212  stores program instructions and data  220  to control the operations of base station  211 . In the example of  FIG.  2   , network entity  211  also includes protocol stack  280  and a set of control function modules and circuits  290 . Protocol stacks  280  includes 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. In one example, control function modules and circuits  290  includes PDU session handling circuit  291  that handles PDU establishment, modification, and release procedures, and configuration and control circuit  292  that provides different parameters to configure and control UE of related functionalities including mobility management and PDU session management. 
     Similarly, UE  201  has memory  202 , a processor  203 , and radio frequency (RF) transceiver module  204 . RF transceiver  204  is coupled with antenna  205 , receives RF signals from antenna  205 , converts them to baseband signals, and sends them to processor  203 . RF transceiver  204  also converts received baseband signals from processor  203 , converts them to RF signals, and sends out to antenna  205 . Processor  203  processes the received baseband signals and invokes different functional modules and circuits to perform features in UE  201 . Memory  202  stores data and program instructions  210  to be executed by the processor to control the operations of UE  201 . 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 UE  201 . 
     UE  201  also includes protocol stacks  260  and a set of control function modules and circuits  270 . Protocol stacks  260  includes NAS layer to communicate with an AMF/SMF/MME entity connecting to the core network, RRC layer for high layer configuration and control, PDCP/RLC layer, MAC layer, and PHY layer. Control function modules and circuits  270  may be implemented and configured by software, firmware, hardware, and/or combination thereof. The control function modules and circuits, when executed by the processors via program instructions contained in the memory, interwork with each other to allow UE  201  to perform embodiments and functional tasks and features in the network. 
     In one example, control function modules and circuits  270  includes a PDU session handling circuit  271  that performs PDU session establishment, modification, and release procedures with the network, and a config and control circuit  272  that handles configuration and control parameters for mobility management and session management. Upon detecting a collision between a UE-requested PDU session establishment procedure and a network-requested PDU session modification procedure, UE and network decide whether to proceed with the UE-requested PDU session establishment procedure and abort the NW-requested PDU session modification procedure, or proceed with both procedures, depending on the request type of the PDU session establishment request. 
       FIG.  3    illustrates one embodiment of PDU session establishment handling when UE also receives a PDU session modification command from the network in accordance with one novel aspect. In step  311 , UE  301  establishes and/or maintains one or more PDU session(s). For example, one of the PDU sessions has PSI==5 is established between UE  301  and the 5GS network over 3GPP access type (or over non-3GPP access type). In step  321 , UE  301  decides to perform a handover of the existing PDU session PSI==5, from 3GPP access to non-3GPP access (or from non-3GPP access to 3GPP access). UE  301  then triggers a UE-requested PDU session establishment procedure in step  322  by sending an UL NAS TRANSPORT message, which contains a PDU SESSION ESTABLISHMENT REQUEST message for the PDU session (PSI==5), and the request type is set to “existing PDU session” or “existing emergency PDU session”. 
     In step  323 , UE  301  receives a DL NAS TRANSPORT message that contains a PDU SESSION MODIFICATION COMMAND message for the same PDU session (PSI==5), after the UE-requested PDU session establishment procedure is triggered, but before the UE-requested PDU session establishment procedure is completed. Accordingly, UE  301  detects a collision between the UE-requested PDU session establishment procedure and the network-requested PDU session modification procedure. The collision is detected when UE  301  receives a PDU SESSION MODIFICATION COMMAND message after sending a PDU SESSION ESTABLISHMENT REQUEST message to the network, and the PDU session ID in the PDU SESSION MODIFICATION COMMAND message is the same as the PDU session ID in the PDU SESSION ESTABLISHMENT REQUEST message (PSI==5). 
     UE  301  then determines the corresponding handling of the detected collision. Under this scenario, UE  301  intended to handover an existing PDU session from one access type to another access type, and the PDU SESSION ESTABLISHMENT REQUEST message was sent with a request type set to “existing PDU session”, or “existing emergency PDU session” in order for the handover of an existing PDU session (e.g., PSI=5) between 3GPP access and non-3GPP access. Accordingly, UE  301  proceeds with the UE-requested PDU session establishment procedure, and aborts the NW-requested PDU session modification procedure. In step  331 , UE aborts the NW-requested PDU session modification procedure, e.g., UE  301  does not send a 5GSM message (e.g., PDU SESSION MODIFICATION COMPLETE or PDU SESSION MODIFICATION COMMAND REJECT) to respond to the network. In step  341 , UE  301  proceeds with the UE-requested PDU session establishment procedure for handover the PDU session (PSI==5), e.g., waiting to receive a PDU SESSION ESTABLISHMENT ACCEPT message from the network. 
       FIG.  4    illustrates another embodiment of PDU session establishment handling for MA PDU session when UE also receives a PDU session modification command from the network in accordance with one novel aspect. In step  411 , UE  401  establishes and/or maintains one or more PDU session(s). For example, one of the PDU sessions has PSI==5, and it is an MA PDU session that is established between UE  401  and the 5GS network over 3GPP access type (or over non-3GPP access type). In step  421 , UE  401  decides to establish user plane resources of the existing MA PDU session PSI==5 over the other non-3GPP access (or over the other 3GPP access). UE  401  then triggers a UE-requested PDU session establishment procedure in step  422  by sending an UL NAS TRANSPORT message, which contains a PDU SESSION ESTABLISHMENT REQUEST message for the PDU session (PSI==5), and the request type is set to “MA PDU request”. 
     In step  423 , UE  401  receives a DL NAS TRANSPORT message that contains a PDU SESSION MODIFICATION COMMAND message for the same PDU session (PSI==5), after the UE-requested PDU session establishment procedure is triggered, but before the UE-requested PDU session establishment procedure is completed. Accordingly, UE  401  detects a collision between the UE-requested PDU session establishment procedure and the network-requested PDU session modification procedure. The collision is detected when UE  401  receives a PDU SESSION MODIFICATION COMMAND message after sending a PDU SESSION ESTABLISHMENT REQUEST message to the network, and the PDU session ID in the PDU SESSION MODIFICATION COMMAND message is the same as the PDU session ID in the PDU SESSION ESTABLISHMENT REQUEST message (PSI==5). 
     UE  401  then determines the corresponding handling of the detected collision. Under this scenario, UE  401  intended to establish user plane resources for an existing PDU session over the other access type, and the PDU SESSION ESTABLISHMENT REQUEST message was sent with a request type set to “MA PDU request”. Accordingly, UE  401  proceeds with the UE-requested PDU session establishment procedure, and also proceeds with the NW-requested PDU session modification procedure. In step  431 , UE proceeds with the NW-requested PDU session modification procedure for the PDU session (PSI==5), e.g., UE  401  sends a PDU SESSION MODIFICATION COMPLETE or PDU SESSION MODIFICATION COMMAND REJECT message to the network. In step  441 , UE  401  proceeds with the UE-requested PDU session establishment procedure for establishing user plane resources for the PDU session (PSI==5), e.g., UE  401  wait to receive a PDU SESSION ESTABLISHMENT ACCEPT message from the network. 
       FIG.  5    illustrates one embodiment of network behavior when the network receives a PDU session establishment request during a network-requested PDU session modification procedure. In step  511 , UE  501  establishes and/or maintains one or more PDU session(s). For example, one of the PDU sessions has PSI==5 is established between UE  501  and the 5GS network over 3GPP access type (or over non-3GPP access type). In step  521 , UE  501  decides to perform a handover of the existing PDU session PSI==5, from 3GPP access to non-3GPP access (or from non-3GPP access to 3GPP access). UE  501  then triggers a UE-requested PDU session establishment procedure in step  522  by sending an UL NAS TRANSPORT message, which contains a PDU SESSION ESTABLISHMENT REQUEST message for the PDU session (PSI==5), and the request type is set to “existing PDU session” or “existing emergency PDU session” for handover purpose. 
     In step  523 , the network sends a DL NAS TRANSPORT message that contains a PDU SESSION MODIFICATION COMMAND message for the same PDU session (PSI==5), the network also starts a timer T3591. Meanwhile, the UE-requested PDU session establishment procedure is triggered, but the UE-requested PDU session establishment procedure is not yet completed. Accordingly, the network detects a collision between the UE-requested PDU session establishment procedure and the network-requested PDU session modification procedure. The collision is detected when the network receives a PDU SESSION ESTABLISHMENT REQUEST message after sending a PDU SESSION MODIFICATION COMMAND message to the UE, and the PDU session ID in the PDU SESSION MODIFICATION COMMAND message is the same as the PDU session ID in the PDU SESSION ESTABLISHMENT REQUEST message (PSI==5). 
     The network then determines the corresponding handling of the detected collision. Under this scenario, the network knows that UE  501  intended to handover an existing PDU session from one access type to another access type, and the PDU SESSION ESTABLISHMENT REQUEST message was sent with a request type set to “existing PDU session”, or “existing emergency PDU session” in order for the handover of an existing PDU session (e.g., PSI=5) between 3GPP access and non-3GPP access. Accordingly, the network proceeds with the UE-requested PDU session establishment procedure, and aborts the NW-requested PDU session modification procedure. In step  531 , the network aborts the NW-requested PDU session modification procedure, e.g., stops timer T3591 and does not send a 5GSM message to respond (e.g., PDU SESSION ESTABLISHMENT ACCEPT or PDU SESSION ESTABLISHMENT REJECT) to the UE. In step  541 , the network proceeds with the UE-requested PDU session establishment procedure for handover the PDU session (PSI==5) to the other access type, e.g., sends a PDU SESSION ESTABLISHMENT ACCEPT message to UE  501 . 
       FIG.  6    is a flow chart of a method of handling PDU session procedure collision from UE perspective for handover in accordance with one novel aspect of the present invention. In step  601 , a UE transmits a protocol data unit (PDU) session establishment request message in a 5G system (5GS) to initiate a UE-requested PDU session establishment procedure for a PDU session. In step  602 , the UE receives a PDU session modification command message for a network-requested PDU session modification procedure. UE detects a collision between the establishment procedure and the modification procedure when a PDU session ID (PSI) in the received PDU session modification command message is the same as a PSI in the transmitted PDU session establishment request message. In step  603 , the UE determines that the UE-requested PDU session establishment procedure is to perform a handover for the PDU session between 3GPP and non-3GPP. In step  604 , the UE proceeds with the UE-requested PDU session establishment procedure, and aborts the network-requested PDU session modification procedure upon detecting the collision. 
       FIG.  7    is a flow chart of a method of handling PDU session procedure collision from UE perspective for MA PDU in accordance with one novel aspect of the present invention. In step  701 , a UE transmits a protocol data unit (PDU) session establishment request message in a 5G system (5GS) to initiate a UE-requested PDU session establishment procedure for an already established MA PDU session. In step  702 , the UE receives a PDU session modification command message for a network-requested PDU session modification procedure. UE detects a collision between the establishment procedure and the modification procedure when a PDU session ID (PSI) in the received PDU session modification command message is the same as a PSI in the transmitted PDU session establishment request message. In step  703 , the UE determines that the UE-requested PDU session establishment procedure is to request the establishment of user plane resources for the MA PDU session. In step  704 , the UE proceeds with the UE-requested PDU session establishment procedure, and proceeds with the network-requested PDU session modification procedure upon detecting the collision. 
       FIG.  8    is a flow chart of a method of handling PDU session procedure collision from NW perspective for handover in accordance with one novel aspect of the present invention. In step  801 , a network entity transmits a protocol data unit (PDU) session modification command message to a user equipment (UE) in a 5G system (5GS) to initiate a NW-requested PDU session modification procedure for a PDU session. In step  802 , the network entity receives a PDU session establishment request message for a UE-requested PDU session establishment procedure, wherein the network entity detects a collision between the establishment procedure and the modification procedure when a PDU session ID (PSI) in the received PDU session establishment request message is the PDU session that the network requested to modify. In step  803 , the network entity determines that the UE-requested PDU session establishment procedure is to perform a handover for the PDU session between 3GPP access and non-3GPP access. In step  804 , the network entity proceeds with the UE-requested PDU session establishment procedure, and aborts the network-requested PDU session modification procedure upon detecting the collision. 
     Although the present invention has been described in connection with certain specific embodiments for instructional purposes, the present invention is not limited thereto. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.