Session management back-off timer reset

Abstract

This disclosure provides systems, methods and apparatuses for Session Management (SM) congestion control. The UE starts a back-off timer based on downlink (DL) non-access stratum (NAS) message (150) from a core network (CN 110) informing the UE that there is congestion in a data network or network slice. The DL NAS message can include a back-off timer value indicating for the UE to deactivate the back-off timer. While the back-off timer is running or deactivated, the UE refrains (154) from sending further SM messages regarding the congested data network or slice. The disclosed techniques enable a UE (102) to reset a deactivated back-off timer based on satisfying a reset condition (such as a reset timer expiration or receipt of a subsequent DL NAS message). The UE can send a further UL NAS request (194) after resetting the deactivated back-off timer.

Description

SESSION MANAGEMENT BACK-OFF TIMER RESETCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This International Application claims the benefit of priority of United States Provisional Patent Application No. 63 / 616,609 filed on December 30, 2024, the contents of which are incorporated by reference in their entirety herein.TECHNICAL FIELD

[0002] This disclosure relates generally to wireless communication and some aspects relate to session management (SM) congestion control with a deactivated back-off timer.BACKGROUND

[0003] This background description is provided for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

[0004] A wireless communication system provides resources for a user equipment (UE) to access one or more services. The wireless communication system typically includes one or more radio access networks (RANs) communicatively coupled to a core network (CN). The UE communicates via a radio connection between the UE and the RAN using access stratum (AS) protocol layers that are based on the radio access technology (RAT) of the RAN. After establishing a radio connection to the RAN, the UE can register with the core network and request services using a non-access stratum (NAS) protocol layer. The core network manages UE access to the services, network slices, and packet data networks using NAS protocols. Many of the AS and NAS protocols are defined by the 3rd Generation Partnership Project (3 GPP) technical specifications.

[0005] A core network of a wireless communication system can implement session management (SM) to provide connectivity between a UE and various services. 3GPP supports an SM congestion control mechanism to mitigate NAS signaling congestion. The congestion control mechanism is designed to prevent a UE from sending SM related messages for a datanetwork (or network slice) when the data network is congested. When NAS signaling congestion occurs, the network instructs the UE to start a back-off timer (which may be referred to as a session management timer). While the back-off timer is active, the UE disables NAS signaling to a core network. The 3 GPP technical specifications define several types of back-off timers and congestion control messages depending on the type of core network, congestion, and UE capability. Some SM congestion controls can mitigate congestion for a specific Data Network Name (DNN). For the Evolved Packet System (EPS) or the Universal Mobile Telecommunications System (UMTS), the 3GPP describes an Access Point Name (APN) based SM congestion control mechanism including the usage of an SM level back-off timer (the UE manages NAS timer T3396 for this purpose) which is bound to an APN or no APN. A SM back-off timer prohibits the UE from sending SM signaling to the APN while the timer for that APN is running in the UE. Further details are specified in 3GPP technical specification (TS) 23.401 clause 4.3.7.4.2.2 and 3GPP TS 24.301 clause 6.3.5. For the 5th generation system (5GS), the 3 GPP describes a DNN based congestion control, which is similar to the APN based SM congestion control plus an accounting for the usage of DNN in the 5GS. Additionally, for the 5GS, the 3GPP supports a network slice based SM congestion control mechanism based on Single Network Slice Selection Assistance Information (S-NSSAI). For DNN based congestion control, a back-off timer (referred to as T3396) is associated with a DNN regardless of the presence of an S-NSSAI (as specified in 3GPP TS 23.501 sub-clause 5.19.7.3 and 3GPP TS 24.501 sub-clause 6.2.7). The back-off timers T3396 are started and stopped on a per DNN, and PLMN basis. For S-NSSAI based congestion control mechanism, the back-off timer (T3584 or T3585) is associated with the S- NSSAI and optionally the DNN (as specified in 3GPP TS 23.501 sub-clause 5.19.7.4 and 3GPP TS 24.501 sub-clause 6.2.8). The back-off timer referred to as T3584 is associated with an S-NSSAI and a DNN. The back-off timer referred to as T3585 is associated with the S- NSSAI regardless of the presence of a DNN.

[0006] Collectively, the T3396, T3584, and T3585 (or other timers) may be referred to as back-off timers and they function similarly to prevent NAS signaling during times of congestion. The back-off timers are started by protocol data unit (PDU) session management messages (such as PDU session establishment reject message, PDU session modification reject message, and PDU session release command). For example, the PDU sessionmanagement message includes a cause code (such as cause #26, #67, or #69) to indicate congestion related to a DNN and / or an S-NSSAI. The core network can optionally indicate a timer value for the back-off timer in the PDU session management message. The UE starts the back-off timer as a countdown timer initialized with the indicated timer value. While the back-off timer is running, the UE refrains from communicating NAS signaling for the DNN or network slice. When the back-off timer expires, the UE can reattempt NAS signaling if it is still required. 3GPP TS 24.008 provides additional information regarding timer values that can be provided for a back-off timer. For example, the timer value can be coded as a 1 -octet value consisting of 3-bit value, where each combination of bit values represents a time unit (such as a number in multiples of: 10 minutes, 1 hour, 10 hours, 2 seconds, 30 seconds, 1 minute, 320 hours), and 5 -bit value of actual time value that represents an integer value from 0 to 31, which is multiplied by the time unit above.

[0007] As an alternative to the timer values representing a time duration, the core network can send a timer value (referred to as “deactivated”) that does not have a specific duration. The core network might indicate the timer value of “deactivated” for a back-off timer when the core network experiences a congestion of unknown duration or extent. The “deactivated” timer value informs the UE to deactivate the back-off timer for an indefinite (or infinite) time period. While the back-off timer is deactivated, the UE does not reattempt SM NAS signaling for that DNN and / or S-NSSAI, until the back-off timer is reset. Typically, the back-off timer is reset following a manual user action, such as a power cycle, universal subscriber identity module (USIM) removal and reinsert, change of USIM, or turning on and off the airplane mode.BRIEF SUMMARY

[0008] The systems, methods, and apparatuses of this disclosure each have several innovative aspects, no single one of which is solely responsible for the desirable attributes disclosed herein.

[0009] One innovative aspect of the subject matter described in this disclosure can be implemented as a method for wireless communication by a user equipment (UE). The method includes the UE receiving a downlink (DL) non-access stratum (NAS) message for congestion control of a first data network or network slice. The DL NAS message indicates a timer valuefor a back-off timer is deactivated. The method includes the UE deactivating the back-off timer for the first data network or network slice based on the DL NAS message. The method includes the UE refraining from communicating session management (SM) requests for the first data network or network slice while the back-off timer is deactivated. The method includes the UE resetting the back-off timer based on a reset condition being satisfied.

[0010] Another innovative aspect of the subject matter described in this disclosure can be implemented as a method for wireless communication by a core network. The method includes the core network transmitting a DL NAS message to a UE based on congestion control of a first data network or network slice, where the DL NAS message indicates a timer value for a back-off timer is deactivated. The method includes the core network causing the UE to reset the back-off timer based on a reset condition being satisfied.

[0011] Another innovative aspect of the subject matter described in this disclosure can be implemented as an apparatus that includes a communication unit and a processing system configured to control the communication unit to implement any one of the above-referenced methods.

[0012] Details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Like reference numbers and designations in the various drawings indicate like elements. Note that the relative dimensions of the figures may not be drawn to scale. To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

[0014] FIG. 1A illustrates an example wireless communication system implementing a deactivated back-off timer for session management congestion control.

[0015] FIG. IB illustrates an example wireless communication system supporting various networks and network slices.

[0016] FIG. 2A illustrates an example control plane protocol stack in which the example wireless communication system of FIG. 1A is a 5th generation system (5GS).

[0017] FIG. 2B illustrates an example control plane protocol stack in which the example wireless communication system of FIG. 1A is a 4th generation system evolved packet system (EPS).

[0018] FIG. 3 shows a message flow diagram and related operations for resetting a deactivated back-off timer based on a reset condition being satisfied.

[0019] FIG. 4 shows a detailed message flow diagram and related operations implementing a reset timer in association with a deactivated back-off timer.

[0020] FIG. 5 shows a detailed message flow diagram and related operations in which a downlink (DL) non-access stratum (NAS) message causes a user equipment (UE) to reset or stop a deactivated back-off timer.

[0021] FIG. 6 shows example operations of a UE implementing a reset timer, such as described with reference to FIG. 4.

[0022] FIG. 7 shows example operations of a UE resetting a back-off timer based on a DL NAS message, such as described with reference to FIG. 5.

[0023] FIG. 8 shows example operations of a core network based on the reset timer described with reference to FIG. 4 and FIG. 6.

[0024] FIG. 9 shows example operations of a core network based on the DL NAS message described with reference to FIG. 5 and FIG. 7.

[0025] FIG. 10 shows example operations of a core network managing a first example reset mechanism based on UE capability and / or subscription.

[0026] FIG. 11 shows example operations of a core network managing a second example reset mechanism based on UE capability and / or subscription.

[0027] FIG. 12 is a block diagram of an example wireless communication system showing hardware features and communication interfaces.DETAILED DESCRIPTION

[0028] The following description is directed to certain implementations for the purpose of describing innovative aspects of this disclosure. However, a person having ordinary skill inthe art will readily recognize that the teachings herein can be applied in a multitude of different ways. Some of the examples in this disclosure are based on wireless communication according to the 3rd Generation Partnership Project (3GPP) wireless standards, such as the 4th generation (4G) Long Term Evolution (LTE) and 5th generation (5G) New Radio (NR) standards. However, the described implementations can be implemented in any device, system, or network that is capable of transmitting and receiving radio frequency signals according to any of the wireless communication standards, including any of the Institute of Electrical and Electronics Engineers (IEEE) 802.11 or 802.16 wireless standards, or other known signals that are used to communicate within a wireless, cellular, or internet of things (loT) network, such as a system utilizing 4G, 5G, WiFi, or future radio technology.

[0029] As stated above, session management (SM) congestion control enables a core network to mitigate non-access stratum (NAS) signaling congestion for a data network or a network slice. A data network can be identified by a Data Network Name (DNN) or Access Point Name (APN). A network slice can be identified based on Single Network Slice Selection Assistance Information (S-NSSAI). The core network can cause a user equipment (UE) to refrain from sending NAS signaling for a DNN / APN or S-NSSAI. To do so, the core network sends a downlink (DL) NAS message to the UE including congestion control information for a DNN / APN or S-NSSAI. The DL NAS message can indicate a timer value for a back-off timer. If the core network communicates a timer value for a back-off timer, either due to a congestion or due to other reason than a congestion, the UE apply the received timer value to one of various SM back-off timers (such as the T3396, T3584 or T3585 backoff timers). In some cases, the core network can indicate the timer value “deactivated” for a back-off timer to cause the UE to deactivate the back-off timer for a DNN / APN and / or S- NSSAI. While the back-off timer is deactivated, the UE does not send another request for that DNN / APN and / or S-NSSAI, until the back-off timer is reset. When a UE deactivates a back-off timer, some documents refer to the deactivated back-off timer as being running (or started) because the UE is prevented from transmitting UL NAS messages for a DNN / APN or S-NSSAI when the back-off timer is running. Alternatively, or additionally, the back-off timer is referred to as being deactivated which has the same effect as a running back-off timer except that a deactivated back-off timer runs indefinitely without an expiration timer. Conversely, when a UE resets a deactivated back-off timer, the UE stops the back-off timer,which has the effect of allowing the UE to proceed with subsequent UL NAS messages that would otherwise be prevented during a running back-off timer.

[0030] Current techniques for resetting the back-off timer require manual interaction by a user, including power cycling, removing and replacing a Universal Subscriber Identity Module (USIM) card, or cycling an airplane mode. Some types of UE may be unable to trigger such events due to lack of user interaction. For example, some UEs (e.g., Machine Type Communication (MTC) type devices or Internet of Things (loT) devices) are designed to run autonomously and may not have a removeable USIM nor the ability to cycle through an airplane mode or a power mode. Absent the techniques of this disclosure, a UE running a deactivated back-off timer might be unable to send another SM request to the same DNN / APN and / or S-NSSAI until a manual intervention to reset the deactivated back-off timer (e.g., by removing and reinserting a power source such as a battery or capacitor).

[0031] This disclosure provides systems, methods, and apparatuses for a UE to reset a deactivated back-off timer based on satisfying a reset condition. In some aspects, the reset condition is based on a reset timer. In other aspects, the reset condition is based on a DL NAS message from the core network. This application provides several ways to reset a deactivated back-off timer, including some which might not involve user interaction with the UE. The examples of this disclosure are based on a 5G Session Management (5GSM) protocol for a 5G system. However, the techniques can also be used in a 4G system or earlier, including Evolved Packet System (EPS) and EPS Session Management (ESM)

[0032] In some aspects, a UE starts a reset timer at about the same time that the UE deactivates the back-off timer. When the reset timer expires, the UE can reset (or stop) the deactivated back-off timer. The reset timer can have a reset timer value (representing a duration) that is different from the timer value (e.g., “deactivated”) of the back-off timer. In some implementations, the reset timer value is a default, predefined, preconfigured, or manufacturer-specified value. In some implementations, the core network configures the reset timer value.

[0033] In some aspects, the core network causes the UE to reset a deactivated back-off timer using a DL NAS message (referred to as a subsequent DL NAS message) after the congestion is resolved. In some implementations, the subsequent DL NAS message is related to an existing PDU session or packet data network (PDN) connection such that the subsequent DLNAS message does not explicitly indicate the back-off timer needs to be reset because the UE can infer that the congestion is mitigated based on the UE receiving the subsequent DL NAS message. In some implementations, the subsequent DL NAS message can indicate a DNN / APN and / or S-NSSAI and the UE can reset any running back-off timers (including the deactivated back-off timer) for that DNN / APN or S-NSSAI. In some implementations, the subsequent DL NAS message includes additional information or an explicit indication to cause the UE to reset a particular back-off timer that was previously deactivated.

[0034] Particular implementations of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages. A wireless communication system can mitigate congestion using the SM congestion control mechanisms to control the starting and resetting of a back-off timer. For some types of UEs, the disclosed techniques provide a mechanism for resetting a deactivated back-off timer that might not otherwise be available or convenient, such as for MTC or loT devices that cannot be readily manually reset. The disclosed reset timer enables the UE to reset a deactivated back-off timer that might otherwise indefinitely or permanently lock out some types of UEs (e.g., lacking removable USIM, inaccessible power switch).

[0035] In this disclosure, several example scenarios are discussed with reference to various figures. Generally speaking, similar events in the figures are labeled with the same or similar reference numbers, with differences discussed where appropriate. With the exception of the differences shown in the figures and discussed below, any of the alternative implementations discussed with respect to a particular event (e g., for messaging and processing) may apply to events labeled with similar reference numbers in other figures.

[0036] FIG. 1A illustrates an example wireless communication system 100 implementing a deactivated back-off timer for session management congestion control. While FIG. 1A describes an example architecture of a wireless communication system, other architectures are possible. The example wireless communication system 100 includes a UE 102, a base station (BS 106), and a core network (CN 110). The CN 110 can be an evolved packet core (EPC 111) or a fifth generation (5G) core (5GC 112), for example. Alternatively, the CN 110 might be a sixth generation (6G) core. The BS 106 operates a radio access network (RAN) and is connected to the CN 110. The BS 106 and the CN 110 belong to a Public Land Mobile Network (PLMN). The BS 106 can be a terrestrial base station, and the PLMN maybe referred to as a terrestrial network (TN). Alternatively, the PLMN can be a non -terrestrial network (NTN) and the BS 106 might employ NTN technology. For example, the BS 106 can be communicatively coupled, or integrated, with an airborne or spaceborne vehicle.

[0037] In general, a RAN can include any number of base stations, and each of the base stations can cover one, two, three, or any other suitable number of cells. The BS 106 operates a cell (not shown) providing coverage for the UE 102. If the base BS 106 is a next generation Node B (gNB), the cell is an NR cell. If the BS 106 is a next generation evolved (ng-eNB) or evolved Node B (eNB), the cell is an evolved universal terrestrial radio access (E-UTRA) cell. The UE 102 can support at least a 5G NR (or simply, “NR”) or E-UTRA air interface to communicate with the BS 106. Each of the base station 1204 can connect to the CN 110 via an interface (e.g., SI or NG interface 107). The BS 106 and other base stations (not shown) in a RAN also can be interconnected via an interface (e.g., X2 or Xn interface) for interconnecting RAN nodes. The UE 102 can have a radio connection to the BS 106 via a user interface (e.g., Uu interface 105). The Uu interface 105 also can be referred to as an access stratus (AS). The non-access stratum (NAS) includes communications between the UE 102 and the CN 110, where the communications traverse both the Uu interface 105 and the Sl / NG interface 107.

[0038] Among other components, the EPC 111 may include a Serving Gateway (SGW) 115, a Mobility Management Entity (MME) 113, and a Packet Data Network Gateway (PGW) 117. The SGW 115 in general is configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., and the MME 113 is configured to manage authentication, registration, paging, and other related functions. The PGW 117 provides connectivity from the UE to one or more external packet data networks, e.g., an Internet network and / or an Internet Protocol (IP) Multimedia Subsystem (IMS) network. The EPC 111 may include other MME, SGW and / or PGW not shown in FIG. 1A. The 5GC 112 includes a User Plane Function (UPF) 118 and an Access and Mobility Management Function (AMF) 114, and / or Session Management Function (SMF) 116. The UPF 118 is configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., the AMF 114 is configured to manage authentication, registration, paging, and other related functions, and the SMF 116 is configured to manage PDU sessions. The 5GC 112 may include other AMF, SMF and / or UPF not shown in FIG. 1A.

[0039] Generally speaking, a base station operating a RAN communicates with a UE using a certain radio access technology (RAT) and multiple layers of a protocol stack. For example, the physical layer (PHY) of a RAT provides transport channels to the Medium Access Control (MAC) sublayer, which in turn provides logical channels to the Radio Link Control (RLC) sublayer, and the RLC sublayer in turn provides data transfer services to the Packet Data Convergence Protocol (PDCP) sublayer. The Radio Resource Control (RRC) sublayer is disposed above the PDCP sublayer. The RRC sublayer specifies the RRC IDLE state, in which a UE does not have an active radio connection with a base station and does not store a UE access stratum (AS) context; the RRC_CONNECTED state, in which the UE has an active radio connection with the base station; and the RRC INACTIVE to allow a UE to more quickly transition back to the RRC CONNECTED state due to Radio Access Network (RAN)-level base station coordination and RAN-paging procedures. Depending on different implementations or scenarios, the base station can configure Small Data Transmission (SDT) for the UE operating in the RRC INACTIVE to transmit one or more small packets.

[0040] After the UE 102 registers with CN 110, a CN node of the CN 110 manages UE parameters while the UE 102 is registered to the CN 110. In case of the EPS, the CN node is MME 113; and in case of the a 5th generation system (5GS), the CN node is AMF 114. In addition to the AMF 114, the SMF 116 can serve as a CN node to implement part of a NAS layer. For brevity, this disclosure refers to operations of the CN node (or just core network) to represent operations that might be performed by the MME 113, the AMF 114, or the SMF 116. The CN node uses a Tracking Area Update (TAU) procedure as described in 3GPP TS 24.301 for the Evolved Packet System (EPS), or Registration procedure and UE Configuration Update (UCU) procedure as described in 3GPP TS 24.501 for 5G System (5GS). If the UE is in idle mode, the CN node pages the UE for a transition to connected mode. While the UE is in connected mode, the CN node updates the UE parameter during the TAU procedure (EPS) or the registration procedure (5GS) by including updated parameters in a NAS accept message. In case of the EPS, NAS accept message is a TAU Accept message, and in case of the 5GS the NAS accept message is a Registration Accept message. The CN node also triggers the UE to initiate the TAU procedure by sending GUTI reallocation command message with non-broadcast TAI (EPS), or provides updated parameters using UCU procedure while the UE is in connected mode (5GS).

[0041] 5GS networks are packet-switched Internet Protocol (IP) networks. The 5GS supports network slicing to manage distributed resources from multiple network elements. Each 5GS network slice dynamically includes isolated resources from various subnets (such as a 5G new radio (NR) radio access network (RAN) subnet, 5G core network subnet, transport subnet, and so on) to create a logical end-to-end network with specific network capabilities. The 3GPP technical specification (TS) 22.261 recites network slicing requirements. Each network slice serves a particular service type with an agreed upon Service-level Agreement (SLA). Single network slice selection assistance information (S- NSSAI) identifies a network slice.

[0042] The CN 110 (e.g., CN Node) can implement a session management (SM) protocol to coordinate access between a UE and a packet data network (PDN, not shown). For example, in the 5GS, the UPF 118 connects the CN 110 to a PDN. The AMF 114 and the SMF 116 implement NAS layer to manage protocol data unit (PDU) sessions between the UE 102 and the PDN or a network slice that includes a connection to the PDN. In an EPS, the PGW 117 provides connectivity to a PDN and the MME 113 implements the NAS layer at the EPC 111. FIG. 2A and FIG. 2B provide additional detail regarding the NAS layer implementations in a 5GC 112 and EPC 111, respectively.

[0043] Congestion control mechanisms are designed to mitigate NAS signaling congestion associated with SM messages. When the network determines that one or more entity related to a specific DNN (APN), e.g., SMF or PGW, is congested or overloaded, the CN node might reject any SM request message for the congested DNN or APN from the UE with a DL NAS message 150 that includes a cause code (such as cause value #26 representing “insufficient resources”). In some implementations, the DL NAS message 150 is a PDU session establishment reject message, a PDU session modification reject message, or a PDU session release command (collectively referred to as “PDU session management message”) or any NAS message that includes a cause code or back-off timer value indicating the NAS signaling congestion. The DL NAS message 150 causes the UE to start a back-off timer (which may be referred to as a session management timer) to prevent the UE from communicating NAS signaling while the back-off timer is active. The DL NAS message 150 can indicate a DNN / APN and / or an S-NSSAI information element to prompt the UE to start a back-off timer for a particular data network or network slice.

[0044] The CN node can store an APN / DNN congestion back-off time on a per UE and congested APN / DNN basis. In the UE 102, a backoff timer (such as NAS timer T3396) for APN based congestion control are started and stopped on a per APN basis. The UE shall not send another SM request message for an existing session or to establish a new session associated with the congested APN / DNN, while the timer T3396 is running. There are some exceptions, including emergency, high priority access or PS data off status report.

[0045] For S-NSSAI based congestion control, similar principles apply, i.e., the network provides a timer value for back-off and the UE is prohibited to send an SM request while the back-off timer is running. The difference from DNN / APN based congestion control is that S- NSSAI based congestion control associates an S-NSSAI and optionally a DNN with the backoff mechanism. When S-NSSAI based congestion control applies, the network provides a back-off timer value for a back-off timer which is associated with an S-NSSAI, or a back-off timer value associated with an S-NSSAI and a DNN. When the network determines that one or more entity related to a specific S-NSSAI is congested or overloaded, the network node might reject any SM request message associated with the congested S-NSSAI from the UE with the SM cause value #69 "insufficient resources for specific slice". In the UE, 5GSM timers T3585 for the S-NSSAI based congestion control are started and stopped on a per S- NSSAI and PLMN or SNPN basis. When the network determines that one or more entity related to a specific S-NSSAI and DNN combination is congested or overloaded, the network node might reject any SM request message associated with the congested S-NSSAI and DNN from the UE with the SM cause value #67 "insufficient resources for specific slice and DNN". In the UE, 5GSM timers T3584 for the S-NSSAI based congestion control are started and stopped on a per S-NSSAI, DNN, and PLMN or SNPN basis.

[0046] The CN node can include a back-off timer value in a session management reject message to regulate the time interval at which the UE may retry the same procedure for a variety of SM cause values: #26 "insufficient resources", #28 "unknown PDU session type", #39 "reactivation requested", #46 "out of LADN service area", #50 "PDU session type IPv4 only allowed", #51 "PDU session type IPv6 only allowed", #54 "PDU session does not exist", #57 "PDU session type IPv4v6 only allowed", #58 "PDU session type Unstructured only allowed", #61 "PDU session type Ethernet only allowed", #67 "insufficient resources forspecific slice and DNN", #68 "not supported SSC mode" and #69 “insufficient resources for specific slice.”

[0047] For 5GSM cause values other than #26 "insufficient resources", #28 "unknown PDU session type", #39 "reactivation requested", #46 "out of LADN service area", #54 "PDU session does not exist", #67 "insufficient resources for specific slice and DNN", #68 "not supported SSC mode", and #69 "insufficient resources for specific slice", and #86 "UAS services not allowed", the network may also include the re-attempt indicator to indicate whether the UE is allowed to re-attempt the corresponding session management procedure for the same DNN in SI mode after inter-system change. The UE 102 can maintain various backoff timers associated with a DNN or an APN, which are started and stopped on a per DNN and / or S-NSSAI basis based on the cause value or time values included in the DL NAS message 150.

[0048] The CN node can indicate a timer value for one of the back-off timers (e.g., the Backoff timer, T3396, T3584 or T3585) using an information element (IE) in the DL NAS message 150. The coding of timer values can follow a “GPRS timer3" type defined in 3GPP TS 24.008 (section 10.5.7.4a). The purpose of the GPRS Timer 3 IE is to specify GPRS specific timer values, e g., for the timer T3396. The GPRS timer 3 is a type 4 information element with 3 octets length. The GPRS timer 3 information element is coded as shown below (Table 1 and Table 2, from 3GPP TS 24.008, Figure 10.5.147a and table 10.5.163a, respectively):8 7 6 5 4 3 2 1Table 1Table 2

[0049] Based on a DL NAS message 150, the UE 102 starts a back-off timer for a DNN / S- NSSAI. While the back-off timer is running the UE 102 refrains (154) from transmitting SMsignaling to the CN 1 10 for that DNN / S-NSSAI. In some scenarios, the DL NAS message 150 can include a cause or back-off timer value that causes the UE 102 to “deactivate” a backoff timer. A deactivated back-off timer might also be referred to as “running” with a deactivated time value. In some implementations, the DL NAS message 150 includes a backoff timer value that represents “deactivated.” In some implementations, the cause code in the DL NAS message 150 is sufficient to inform the UE 102 to start the back-off timer with a “deactivated” timer value.

[0050] If the UE 102 receives a timer value in the DL NAS message 150 from the CN node, the UE 102 starts one of the back-off timers according to the cause value, e.g., start T3396 for SM cause #26, start T3584 for SM cause #67, start T3585 for SM cause #69, or Back-off timer for other SM causes. If the received timer value is 0, the UE can retry to send SM request without any back-off. If the received value is any binary value, the UE sets the timer with the value and starts the timer and be prohibited to send another request for the same DNN and / or S-NSSAI. If the received timer value indicates that the timer is “deactivated”, the UE shall not send another request for the same DNN and / or S-NSSAI, until the timer is reset due to some events, e.g., power cycle, USIM removal and reinsert, change of USIM, or turning on and off the airplane mode. If the UE receives specific cause code that requires back-off but without timer value, the UE may start a timer with a default value, or a random value within a pre-defined range.

[0051] Typically, the running (or deactivated) back-off timer is stopped when the UE 102 receives a subsequent DL NAS message that indicates the same DNN / S-NSSAI. For example, the subsequent DL NAS message might be a PDU SESSION AUTHENTICATION COMMAND message, a PDU SESSION MODIFICATION COMMAND message, a PDU SESSION MODIFICATION REJECT message or a PDU SESSION RELEASE COMMAND message. In each of these examples, the subsequent DL NAS message assumes that the UE 102 already has an established PDU session. However, that might not always be the case, such as when the DL NAS message 150 is a PDU SESSION ESTABLISHMENT REJECT message and the UE 102 does not have a previously established PDU session.

[0052] In accordance with aspects of this disclosure, the UE 102 can send a UL NAS message 194 (such as a new or repeated request) for a DNN / S-NSSAI after resetting a deactivated back-off timer for that DNN / S-NSSAI. The UE 102 resets the deactivated back-off timer based on a reset condition. This disclosure provides several example reset conditions. In some aspects, the reset condition is based on a reset timer (which is different from the back-off timer). In some aspects, the reset condition is based on a DL NAS message that causes the UE to reset or stop the running deactivated back-off timer.

[0053] FIG. IB illustrates an example wireless communication system supporting various networks and network slices. As described with reference to FIG. 1 A, a CN 110 can operate a PLMN associated with one or more RANs. One PLMN might be referred to as a Home PLMN (HPLMN). In the example illustrated in FIG. IB, the UE 102 can have a subscription for HPLMN 103 that includes one or more base stations (such as BS 106 of FIG. 1A). The mobile network operator (MNO) 101 can also permit roaming on other PLMNs, referred to as Visited PLMN (VPLMN). Thus, the UE 102 might roam to other VPLMNs (for example, VPLMNs 109A to 109N). Additionally, the UE 102 can be configured for operation using one or more network slices provisioned by the MNO 101 on VPLMNs 109A-109N and / or HPLMN 103. During roaming situations, available / authorized slices may be specified by a CN node (such as the AMF 114 of FIG. 1A).

[0054] During operation of UE 102, the RAN to which UE 102 is currently registered may experience congestion, and begin congestion control procedures. Each of the VPLMNs 109A- 109N and / or HPLMN 103 can be associated with the data network 140 or different data networks. Each data network can be identified by a different DNN or APN. In a 5GS, the VPLMNs 109A-109N and / or HPLMN 103 can operate various network slices, each of which are identified by a different S-NSSAI. Using the congestion control mechanisms of this disclosure, a CN 110 can cause the UE 102 to start or deactivate a back-off timer for a particular DNN, APN, or S-NSSAI. Each back-off timer can be reset based on satisfaction of a reset condition. Furthermore, the reset condition (such as a reset timer or DL NAS message) can be specific to a particular back-off timer for a particular DNN, APN, or S-NSSAI.

[0055] FIG. 2A illustrates an example control plane protocol stack in which the example wireless communication system of FIG. 1A is a 5GS. FIG. 2A shows the control plane protocol stack 200A for the UE 102, the BS 106, the AMF 114 and the SMF 116. The 5G access network can include 5GNR (where the BS 106 is referred as a gNB) or EUTRA (where the BS 106 is referred to as an eNB).

[0056] The protocol layers between the UE 102 and the BS 106 include a physical (PHY) sub-layer that provides transport channels. A media access control (MAC) sub-layer provides logical channels for a radio link control (RLC) sub-layer. The RLC sublayer in turn provides data transfer services to the PDCP sublayer. The PDCP sublayer in turn can provide data transfer services to a radio resource control (RRC) sublayer. For a 5GC, the protocol layers between the BS 106 and the core network include a layer 1 (LI) sub-layer, layer 2 (L2) sublayer, an Internet protocol (IP) sub-layer, Stream Control Transmission Protocol (SCTP) sublayer, and Next Generation Application Protocol (NGAP) sub-layer. The AMF 114 and the SMF 116 can implement any variety of protocol layers (shown as Ni l) to manage communication via the Ni l interface between them.

[0057] Aspects of this disclosure are related to the NAS communications between the UE 102 and the core network (such as a 5GC). Generally speaking, a NAS protocol manages the UE’s mobility, session, and control plane signaling between the UE 102 and the CN 110, transparent to any 5G access network node (e.g., BS 106). In some aspects, the core network implements various discrete control plane functions (shown as the AMF 114 and the SMF 116). Together the AMF 114 and the SMF 116 can implement portions of the NAS layer. The AMF 114 can provide mobility management (MM) aspects of the NAS layer while the SMF 116 can provide SM aspects of the NAS layer. The UE 102 communicates with an SMF 116 via NAS messages that are first sent to the AMF 114. The AMF 114 is responsible for managing the UE’s mobility and connection to the CN 110. Also, any upper layer control signal can be delivered over NAS layer between the AMF 114 and the UE 102, which is also called NAS-MM layer. The SMF 116 is responsible for managing PDU sessions, and a UE 102 can be associated with one or more SMFs 116 at the same time. The NAS protocol between the UE 102 and the SMF 116 is also called NAS-SM layer. The AMF 114 and the UE 102 communicate with each other via a logical interface referred to as the N1 control interface. The N1 control interface is a logical interface that traverses the Uu interface 105 (Nr-Uu when the BS 106 is a gNB) and the Sl / NG interface 107 (sometimes referred to as the NG-C or N2 interface in a 5GC).

[0058] FIG. 2B illustrates an example control plane protocol stack in which the example wireless communication system of FIG. 1A is a 4th generation system evolved packet system (EPS). The control plane protocol stack 200B of the EPS is similar to the control planeprotocol stack 200A described with reference to FIG. 2B. Some nomenclature differences between FIG. 2B and FIG. 2A include: the BS 106 is shown as a EUTRA base station (eNB), the Uu interface 105 is labeled as an LTE-Uu interface, and the Sl / NG interface 107 is referred to as an SI -MME interface. In the EPS, the MME 113 serves as a single endpoint for the NAS protocol in the core network. The MME 113 is responsible for both mobility management and session management aspects, although SM related protocols are considered to be upper to MM related protocols.

[0059] Aspects of this disclosure are related to the NAS protocol and can be applied to either the 5GS (FIG. 2A) or EPS (FIG. 2B). For avoidance of doubt, in this disclosure when referring to UL NAS messages, the UL NAS message is communicated from the UE 102 to any of the NAS endpoints in the core network (such as the SMF 116, the AMF 114, or the MME 113). DL NAS messages are communicated to the UE 102 from the AMF 114, the SMF 116, or the MME 113. The SMF 116 is responsible for handling SM requests and responses and can implement congestion control based on a DNN / S-NSSAI managed by the SMF 116. In some instances, the AMF 114 can also identify a congestion of a DNN / S-NSSAI and can implement congestion control by responding to the UE 102 without relaying an SM request to the SMF 116.

[0060] FIG. 3 shows a message flow diagram 300 and related operations for resetting a deactivated back-off timer based on a reset condition being satisfied. The flow diagram 300 shows NAS signaling between a UE 102 and CN 110. Here, the functions and messages of the CN 110 can include any type of CN Node, such as an AMF, SMF, or MME, or a new entity for a later generation of wireless communication system.

[0061] In FIG. 3, the CN 110 implements a congestion control mechanism 340. For example, the CN 110 might determine that an SM congestion control is needed for a DNN and / or S-NSSAI, e.g., the relevant data network entity is overloaded or about to be overloaded (e.g., the load level, or change in load level, comes over a threshold). The CN 110 determines to apply the SM congestion control mechanism for the DNN and / or S-NSSAI. Whilst under this condition, if the UE 102 sends an UL NAS message 344 (such as an UL SM NAS request) for the DNN and / or S-NSSAI under the congestion control, the CN 110 might reject the SM request 344 by sending a DL NAS message 350, with a SM cause value. For some causevalues, the CN 1 10 might include a timer value for a back-off timer, which might be set to “deactivated.”

[0062] In some implementations, the CN 110 might determine to reject the UL SM NAS request for other reasons than congestion, as specified in 3GPP TS 24.301 or 3GPP TS 24.501. The CN 110 might reject the SM request by sending an DL SM NAS message (DL NAS message 350), with a SM cause value. For some cause values, the CN 110 might include a timer value for a back-off timer, which might be set to “deactivated.”

[0063] In some implementations, if the CN 110 is a 5GC, the AMF of the CN 110 might reject an SM request by sending an DL MM NAS message, with a MM cause value due to the congestion in DNN and / or S-NSSAI. Thus, the DL NAS message 350 might be a DL SM NAS message (from an SMF) or a DL MM NAS message (from the AMF). In some implementations, the DL NAS message 350 is a DL NAS TRANSPORT message. In some implementations, the CN 110 might actively send a DL NAS message 350, e.g., PDU session release command, with cause value and / or a timer value for a back-off timer due to congestion.

[0064] After the UE 102 receives the DL NAS message 350 which is a reject message with a SM cause value or an MM cause value, the UE can start a back-off timer. If the DL NAS message 350 includes a back-off timer value, the UE 102 applies it the corresponding NAS back-off timer. In some implementations, the NAS timer is timer T3396, T3584, or T3585 if the cause value is the 5GSM cause value #26 "insufficient resources", #67 "insufficient resources for specific slice and DNN", or #69 "insufficient resources for specific slice," respectively. In some implementations, the NAS timer is timer T3396, T3584, or T3585 if the cause value is the 5GMM cause value #22 "Congestion", #67 "insufficient resources for specific slice and DNN", cause #69 "insufficient resources for specific slice", respectively. In other implementations, the NAS timer is the back-off timer if the SM cause value is different from #26 "insufficient resources", #28 "unknown PDU session type", #39 "reactivation requested", #46 "out of LADN service area", #50 "PDU session type IPv4 only allowed", #51 "PDU session type IPv6 only allowed", #54 "PDU session does not exist", #57 "PDU session type IPv4v6 only allowed", #58 "PDU session type Unstructured only allowed", #61 "PDU session type Ethernet only allowed", #67 "insufficient resources for specific slice and DNN", #68 "not supported SSC mode", #69 "insufficient resources for specific slice", #86 "UASservices not allowed", and #33 "requested service option not subscribed", when the CN 1 10 is a 5GC. In yet other implementations, the NAS timer is the Back-off timer if the SM cause value is different from #26 "insufficient resources", #28 "unknown PDN type", #50 "PDN type IPv4 only allowed", #51 "PDN type IPv6 only allowed", #54 "PDN connection does not exist", #57 "PDN type IPv4v6 only allowed", #58 "PDN type non IP only allowed", #61 "PDN type Ethernet only allowed", #65 "maximum number of EPS bearers reached", and #66 "requested APN not supported in current RAT and PLMN combination", when the CN 110 is an EPC.

[0065] In block 352, the UE 102 obtains the received timer value and applies it to a backoff timer (i.e., starting the back-off timer with the received timer value). After the UE 102 starts one of the back-off timer, the UE refrains 354 from sending any SM request to same DNN and / or S-NSSAI while the back-off timer is running. If the back-off timer is “deactivated” (i.e., running with deactivated state), the UE 102 does not send any request for the DNN and / or S-NSSAI until the back-off timer is reset. Traditional techniques for resetting the back-off timer might include manual intervention, such as power cycle, USIM removal and reinsert, change of USIM, or turning on and off the airplane mode. However, such techniques might not be convenient or even possible for some types of UEs such devices designed for MTC or loT applications.

[0066] In accordance with this disclosure, the UE 102 can reset 360 the back-off timer when a reset condition is satisfied. Examples of reset conditions include a reset timer expires 370 (as further described with reference to FIG. 4) and receipt of a DL NAS message 380 (as described with reference to FIG. 5). Other types of reset conditions can be implemented in addition to, or in lieu of, the examples described with reference to FIG. 3 through FIG. 11.

[0067] After the back-off timer is reset 360, the UE 102 might resume SM operations 390 for the DNN / S-NSSAI by communicating a further UL NAS message 394 to the CN 110. The CN 110 might respond to the UL NAS message 394 (request) by sending a DL NAS message 396 (response).

[0068] FIG. 4 shows a detailed message flow diagram 400 and related operations implementing a reset timer in association with a deactivated back-off timer. The reset timer enables the 102 to determine when to reset one or more deactivated back-off timers. The resettimer can be referred to by other names and "reset timer” is used as a name to distinguish it from the back-off timer which is to be reset.

[0069] In some implementations, the UE 102 sets up a timer value for the reset timer before any back-off timer is started or deactivated. Alternatively, the timer value for the reset time can be determined during or after a DL NAS message that initially causes a back-off timer to be started or deactivated. Before configuring the timer value, the CN 110 determines (shown at block 432) the applicability of the reset timer for the UE 102, such as whether the UE 102 supports a reset timer and whether the UE 102 can utilize a reset timer or not. In some implementations, the CN 110 might check with the subscription to determine whether the UE 102 can use the reset timer or not. In some implementations, the subscription might indicate the applicability in an explicit way, i.e., an explicit indicator on the applicability. In other implementations, the subscription might indicate it in an implicit way, e.g., only the type of the UE or the category of radio access technology. For example, the CN 110 might determine the applicability of the reset timer by the type of the UE, e.g., if the UE is an MTC (Machine Type Communication) UE or an loT devices, or if the Cat is Ml or M2. In FIG. 4, the reset timer is applicable to the UE 102.

[0070] At block 424, the UE 102 might be pre-configured with the reset timer value. In some implementations, the pre-configured value is a binary value that corresponds to a specific time value (e.g., 30 seconds, 10 minutes, or 1 hour). In other implementations, the pre-configured value is a range of time with minimum and maximum value (e.g., 10 to 30 minutes). In yet other implementations, the pre-configured value is a range of time with maximum value which implies that the range starts from 0 to maximum value (e.g., 0 to 30 minutes). In some implementations, the UE can be pre-configured within the memory element (ME), e.g., in a non-volatile memory inside the ME. In other implementations, the UE can be pre-configured via a file in USIM. In yet other implementations, the UC can be pre-configured via over-the- air (OTA) methods, e.g., NAS management object (MO) via Open Mobile Alliance Device Management (OMA DM) technology. In some implementations, the pre-configured value is not associated with any DNN and / or S-NSSAI, i.e. the value can be used as a reset timer for deactivated back-off timer associated with any DNN / S-NSSAI.

[0071] At block 438, the UE may store the reset timer value for later use when initializing the reset timer. In some implementations, the stored reset timer value applies to any DNN(also including APN hereafter) and / or S-NSSAI, if there is no associated DNN and / or S- NSSAI. For example, the UE 102 can apply the same reset timer value for a reset timer associated with any DNN and / or S-NSSAI in the later steps. In other implementations, the UE stores the reset timer value in association with an associated DNN and / or S-NSSAI. Then, the UE can apply the stored reset timer value for a reset timer associated with the DNN and / or S-NSSAI in the later steps.

[0072] As an alternative, the timer value for the reset timer can be provided by the CN 110 via a DL MM NAS message 436A. The DL MM NAS message 436A is sent by an MME 114 if the CN 110 is an EPC 111, or by an AMF 164 if the CN 110 is an 5GC. If the UE receives the timer value for the reset timer via the DL MM NAS message 436A, the UE stores the received timer value to be used for PDN connections or PDU sessions with any DNN and / or S-NSSAI. For example, the UE can apply the same stored value for a reset timer associated with any DNN and / or S-NSSAI in the later steps.

[0073] In some implementations, the DL MM NAS message 436A is an ATTACH ACCEPT message, TRACKING AREA UPDATE ACCEPT message, a DETACH ACCEPT message, a SERVICE ACCEPT message, a GUTI REALLOCATION COMMAND message, an EMM INFORMATION message as specified in 3GPP TS 24.301. In other implementations, the DL MM NAS message is an ATTACH REJECT message, a TRACKING AREA UPDATE REJECT message, or a SERVICE REJECT message as specified in 3GPP TS 24.301. In yet other implementations, the DL MM NAS message is a REGISTRATION ACCEPT message, a REGISTRATION REJECT message, a DEREGISTRATION ACCEPT message, a SERVICE ACCEPT message, a SERVICE REJECT message, or a CONFIGURATION UPDATE COMMAND message as specified in 3GPP TS 24.501.

[0074] As another alternative, the timer value for the reset timer can be provided by the CN 110 via a DL SM NAS message 436B. The DL SM NAS message 436B is sent by an MME 114 if the CN 110 is an EPC 111, or by an SMF 166 if the CN 110 is an 5GC. If the UE receives the timer value for the reset timer via the DL SM NAS message 436B together with a DNN and / or an S-NSSAI value, the UE stores the received timer value to be used for PDN connections or PDU sessions with the received DNN and / or S-NSSAI. For example, the UE apply the stored timer value for a reset timer associated with the DNN and / or S-NSSAI in the later steps.

[0075] In some implementations, the DL SM NAS message 436B is an ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message, an ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST message, a MODIFY EPS BEARER CONTEXT REQUEST message, an ESM INFORMATION REQUEST message, or an ESM STATUS message as specified in 3GPP TS 24.301. In other implementations, the DL SMNAS message is a PDN CONNECTIVITY REJECT message, a BEARER RESOURCE ALLOCATION REJECT message, a BEARER RESOURCE MODIFICATION REJECT message, a PDN DISCONNECT REJECT message, or a DEACTIVATE EPS BEARER CONTEXT REQUEST message as specified in 3GPP TS 24.301. In yet other implementations, the DL SM NAS message is a PDU SESSION ESTABLISHMENT ACCEPT message, a PDU SESSION MODIFICATION COMMAND message, a 5GSM STATUS message, a PDU SESSION ESTABLISHMENT REJECT message, a PDU SESSION MODIFICATION REJECT message, a PDU SESSION RELEASE REJECT message, or a PDU SESSION RELEASE COMMAND message as specified in 3GPP TS 24.501.

[0076] In FIG. 4, the CN 110 implements a congestion control mechanism 340 as described with reference to FIG. 3, with some additional detail and options shown in FIG. 4. The CN node 110 determines 448 that an SM congestion control is needed for a DNN and / or S-NSSAI. The UE 102 might send a UL SM NAS message 442 with an SM request for the DNN and / or S-NSSAI under the congestion control. In response to the UL SM NAS message 442, the CN 110 might reject the SM request by sending a DL NAS message. The DL NAS message might be a either DL SM NAS message 450A or a DL MM NAS message 450B. In a first example, the DL NAS message is a DL SM NAS message 450A, with a SM cause value. For some cause values, the CN 110 might include a timer value for a back-off timer, which might be set to “deactivated.” In some implementations, the CN 110 might determine to reject the UL SM NAS message 442 for other reasons than congestion, as specified in 3GPP TS 24.301 or 3GPP TS 24.501. The CN 110 might reject the SM request by sending a DL SM NAS message 450A, with a SM cause value. For some cause values, the CN 110 might include a timer value for a back-off timer, which might be set to “deactivated.”

[0077] In some implementations, if the CN 1 10 is a 5GC, the AMF of the CN 1 10 might reject the SM request by sending a DL MM NAS message 450B, with a MM cause value due to the congestion in DNN and / or S-NSSAI. In some implementations, the DL MM NASmessage 450B is a DL NAS TRANSPORT message. In some implementations, the CN 1 10 might actively send a DL NAS message, e.g., PDU session release command, with cause value and / or a timer value for a back-off timer due to congestion.

[0078] After the UE 102 receives the DL SM NAS message 450A or the DL MM NAS message 450B, the UE obtains (shown at block 452) the received timer value, if it is included in the message, and applies it to a corresponding NAS timer, as described with reference to FIG. 3. After the UE 102 starts (or deactivates) one of the SM back-off timers, the UE refrains (shown at block 454) itself from sending any SM request to same DNN and / or S-NSSAI while the timer is running or deactivated.

[0079] If the UE 102 applies a “deactivated” value for a back-off timer, and if the UE 102 has a stored reset timer value, either pre-defined 424 or was provided before via NAS message 436A or 436B, where the associated DNN and / or S-NSSAI matches the DNN and / or S-NSSAI or the back-off timer, the UE 102 starts 462 a reset timer with the reset timer value stored from block 438. In some implementations, the reset timer is specific to the DNN and / or S- NSSAI associated with the deactivated back-off timer. If the stored value for a reset timer does not have an associated DNN and / or S-NSSAI, the UE 102 applies the stored value regardless of the associated DNN and / or S-NSSAI of the back-off timer with “deactivated” value.

[0080] At some point, the CN node 110 might determine (shown at block 465) that the congestion is resolved for a DNN and / or S-NSSAI. The CN node 110 stops applying the SM congestion control mechanism.

[0081] When the reset timer expires 470, the UE 102 can reset the running or deactivated back-off timer. For example, at block 470, the reset timer expiring is an example satisfaction of a reset condition that causes the UE 102 to reset the deactivated back-off timer. Resetting the back-off timer can also be referred to as stopping the back-off timer. After resetting the back-off timer at block 470, the UE 102 can re-try the SM request (as in UL SM NAS message 442) or send a new SM request for the same DNN and / or S-NSSAI. In other words, the UE 102 can resume SM operations for the DNN and / or S-NSSAI that were previously prevented by the running or deactivated back-off timer. For example, the UE 102 might send a UL SM NAS message 494 for the same DNN and / or S-NSSAI. In some implementations, the UL SM NAS message 494 is the same message as the UL SM NAS message 442 that was previouslyrejected. In other implementations, the UL SM NAS message 494 is different message from the UL SM NAS message 442, although for the same DNN and / or S-NSSAI. If the CN 110 determines that the congestion control for the DNN and / or S-NSSAI has stopped in the block 465, the CN 110 responds with a DL SM NAS message 496 which is an accept or a command message for UL SM NAS message 494. If the CN 110 determines that the congestion control for the DNN and / or S-NSSAI is still needed, the CN 110 responds with a DL SM NAS message 496 which is a reject message, which might be similar to the DL SM NAS message 450A or DL MM NAS message 450B.

[0082] FIG. 5 shows a detailed message flow diagram 500 and related operations in which a DL NAS message causes a UE to reset or stop a deactivated back-off timer. The congestion control mechanism 340 in FIG. 5 is the same as described with reference to FIG. 4. Although FIG. 4 provided an example where the DL SM NAS message 450A indicated “deactivated” back-off timer value, FIG. 5 might be used with any back-off timer value (including “deactivated” or a time duration). Thus, FIG. 5 shows the DL SM NAS message 550A (similar to the DL SM NAS message 450A) or the DL SM NAS message 550A (similar to DL SM NAS message 450A) can include any back-off timer value. The CN 110 can send either of the 550A or the DL MM NAS message 550B to the UE 102 to indicate congestion control and cause the UE 102 to start a back-off timer using an indicated back-off timer value. In some implementations, the back-off timer value is “deactivated” as described in FIG. 4.

[0083] FIG. 5 also differs from FIG. 4 in that the reset condition is based on a DL NAS message (either of the DL SM NAS message 586A or DL MM NAS message 586B). FIG. 5 does not show a reset timer. In some implementations, the concepts of the reset timer in FIG. 4 can be combined with the features of FIG. 4. For brevity, the description of FIG. 5 focuses on the DL NAS message to update or reset the back-off timer. When the CN 110 determines 465 that the congestion is resolved (or improved) for a DNN and / or S-NSSAI, the CN node 110 can determine 584 whether to stop (or update) the deactivated back-off timers of the UE 102. The CN 110 might check with the subscription on whether the UE can be notified to update stop the deactivated back-off timers or not as detailed in FIG. 11. In some implementations, the subscription might indicate the applicability in an explicit way, i.e., an explicit indicator on the applicability. In other implementations, the subscription might indicate it in an implicit way, e.g., only the type of the UE or the category of radio accesstechnology. For example, the CN 1 10 might determine the applicability of the reset timer by the type of the UE, e.g., if the UE is an MTC (Machine Type Communication) UE or an loT devices, or if the Cat is Ml or M2.

[0084] In other implementations, the CN 110 determines whether or not the CN 110 notifies the UE 102 to stop the deactivated back-off timers based on the UE configuration stored in the CN node 110. For example, the CN 110 might store the back-off timer value that has been provided before for the UE 102, and the CN 110 might determine to notify the UE 102 if the CN 110 has previously provided a “deactivated” value as a back-off timer value (such as via the DL SM NAS message 550A or DL MM NAS message 550B).

[0085] The CN 1 10 might send DL SM NAS message 586A or DL MM NAS message 586B to the UE 102 to notify the UE 102 to stop or update a back-off timer. If there is one or more existing PDU sessions or PDN connections associated with the DNN and / or S-NSSAI already, the CN 110 sends a DL SM NAS message 586A related to the existing PDN connections or PDU sessions. In some implementations, the DL SM NAS message 586A is a PDU SESSION MODIFICATION COMMAND message as specified in 3GPP TS 24.501, or an ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST message or a MODIFY EPS BEARER CONTEXT REQUEST message as specified in 3GPP TS 24.301. DL SM NAS message associated with the existing PDN connections or PDU sessions might not need additional information to notify the UE 102 to stop the timer, since the PDU sessions or PDN connections are already associated with the DNN and / or S-NSSAI which is related to the running backoff timer with “deactivated” value.

[0086] In other implementations, the DL SM NAS message 586A is an ESM STATUS message as specified in 3GPP TS 24.301, or a 5GSM STATUS as specified in 3GPP TS 24.501. The DL SM NAS message which is not associated with a specific PDU session or PDN connection might include additional information. In some implementations, the additional information is a PDU session ID or EBI (EPS Bearer ID), which corresponds to the existing PDU session or PDN connection that is associated to the DNN and / or S-NSSAI that congestion control applied previously. In other implementations, the additional information is a DNN and / or an S-NSSAI that that congestion control applied previously. In yet other implementations, additional indicator might be included together with other additionalinformation. The indicator means that the SM congestion control related to other additional information (e.g., PDU session ID or DNN+S-NSSAI) has been terminated.

[0087] In yet other implementations, the DL SM NAS message 586A is a new type of DL NAS message to provide updated configuration regarding session management. In some implementations, The DL NAS message might be associated with an existing PDN connection or PDU session, by indicating PDU session ID or EBI. In other implementations, the additional information is a DNN and / or an S-NSSAI that that congestion control applied previously. In yet other implementations, additional indicator might be included together with other additional information. The indicator means that the SM congestion control related to other additional information (e.g., PDU session ID or DNN+S-NSSAI) has been terminated.

[0088] The CN 110 might send a DL MM NAS message 586B to the UE 102 to notify the UE 102 to stop the back-off timer with a value “deactivated” or update the back-off timer. The DL MM NAS message 586B might include additional information on the SM congestion control handling. In some implementation, the DL MM NAS message includes a PDU session ID or EBI (EPS Bearer ID), which corresponds to the existing PDU session or PDN connection that is associated to the DNN and / or S-NSSAI that congestion control applied previously. In some implementations, this information is provided as a bitmap of existing connections. In other implementations, the additional information is a DNN and / or an S- NSSAI that that congestion control applied previously. In yet other implementations, additional indicator might be included together with other additional information. The indicator means that the SM congestion control related to other additional information (e g., PDU session ID or DNN+S-NSSAI) has been terminated. In some implementations, the DL MM NAS message is a TRACKING AREA UPDATE ACCEPT message, a SERVICE ACCEPT message, a GUTI REALLOCATION COMMAND message, or an EMM INFORMATION message as specified in 3GPP TS 24.301. In other implementations, the DL MM NAS message is a REGISTRATION ACCEPT message, a DEREGISTRATION ACCEPT message, a SERVICE ACCEPT message, a SERVICE REJECT message, or a CONFIGURATION UPDATE COMMAND message as specified in 3GPP TS 24.501.

[0089] After the UE 102 receives a DL SM NAS message 586A or a DL MM NAS message 586B including update information to stop or update 580 a running back-off timer, the UE 102 might stop the corresponding SM back-off timer or update the back-off timer. If thereceived information includes an ID of existing connection, i.e., PDU session ID or EBI, the UE 102 stops the back-off timer associated with the DNN and / or S-NSSAI that is allocated for the existing connection. If the received information includes specific DNN and / or S- NSSAI, the UE 102 stops 580 the back-off timer associated with the DNN and / or S-NSSAI.

[0090] After the UE 102 stops (block 580) the back-off timer or the back-off timer expires, the UE 102 might resume SM operations 390 as described with reference to FIG. 3 and FIG. 4.

[0091] Next, several example methods that can be implemented in a UE (e.g., the UE 102) or a CN node such as an MME or an AMF are discussed with reference to FIG. 6 through FIG. 1 1. Each of these methods can be implemented using processing hardware such as one or more processors to execute instructions stored on a non-transitory computer-readable medium such as computer memory. Although FIG. 6 through FIG. 11 depict a particular sequence of operations, the sequence may be altered without departing from the scope of the present disclosure. For example, some of the operations depicted may be performed in parallel or in a different sequence that does not materially affect the function of the routine. In other examples, different components of an example device or system that implements the routine may perform functions at substantially the same time or in a specific sequence.

[0092] FIG. 6 shows example operations 600 of a UE implementing a reset timer, such as described with reference to FIG. 4. In block 636, the UE receives a timer value for the reset timer via NAS. Alternatively, or additionally, in block 624, the UE obtains a pre-configured timer value. At block 638, the UE stores a timer value for the reset timer. In some implementations, the stored timer value is associated with a particular DNN and / or S-NSSAI.

[0093] At block 650, the UE receives from the CN a DL NAS message containing a reject cause value and a back-off timer value set to “deactivated.” At block 652, the UE starts the back-off timer with the back-off timer value set to “deactivated.” At block 654, the UE refrains from sending an SM request to associated DNN and / or S-NSSAI.

[0094] At block 661, the UE determines whether it has a stored value of a reset timer associated with congested DNN and / or S-NSSAI or a reset timer that can be applied to any DNN and / or S-NSSAI. If so, then the flow chart proceeds to block 662. Otherwise, the flow chart proceeds to block 697.

[0095] At block 662, the UE starts the reset timer associated with the back-off timer. At block 670, when the reset timer expires, the UE stops the back-off timer. At block 694, the UE might retry the SM request (or a new SM request) to the same DNN / S-NSSAI,

[0096] Returning to block 661, if the UE does not have a stored value for a reset timer associated with the congested DNN and / or S-NSSAI or a reset timer that can be applied to any DNN and / or S-NSSAI, the flow chart proceeds to block 697. AT block 697, the UE might reset the back-off timer based on specific events according to legacy procedures (e.g., power cycle, USIM change).

[0097] FIG. 7 shows example operations 700 of a UE resetting a back-off timer based on a DL NAS message, such as described with reference to FIG. 5. At block 750, the UE receives, from the CN, a DL NAS message containing a reject cause value and a back-off timer value set to "deactivated." At block 752, the UE starts the back-off timer with value "deactivated." At block 754, the UE refrains from sending an SM request to the DNN and / or S-NSSAI associated with the deactivated back-off timer.

[0098] At blocks 786A and 786B, the UE receives a DL NAS message indicating to stop the back-off timer for DNN / S-NSSAI or session. Block 786A shows the DL NAS message as a DL SM NAS message from a SMF, while block 786B shows the DL NAS message as a DL MM NAS message from an AMF. Alternatively, the DL NAS message can be a DL NAS message from an MME. At block 780, the UE stops the back-off timer based on the DL NAS message from blocks 786A or 786B.

[0099] FIG. 8 shows example operations 800 of a core network based on the reset timer described with reference to FIG. 4 and FIG. 6. At block 832, the CN might determine the applicability of the reset timer for the UE. At block 824, the CN might pre-configure a timer value for the reset timer. At block 836, the CN might provide a timer value for the reset timer via NAS.

[0100] At block 848, the CN determines that an SM congestion control is needed for a DNN and / or S-NSSAI. At block 850, the CN rejects an SM request from the UE with cause value and back-off timer value set to “deactivated” based on the congestion.

[0101] Later, at block 865, the CN might determine that the congestion is resolved for a DNN and / or S-NSSAI. Because the reset timer will cause the UE to reset the deactivatedback-off timer, the CN might receive an SM request from the UE at block 894 after the reset timer has expired and the UE has stopped the deactivated back-off timer.

[0102] FIG. 9 shows example operations 900 of a core network based on the DL NAS message described with reference to FIG. 5 and FIG. 7. The events at block blocks 848, 850, and 865 are the same as described with reference to FIG. 8.

[0103] At block 980, the CN might determine the applicability of notifying the UE to stop the backoff timer. Note that the CN might decide to notify the UE to stop the back-off timer for any variety of reason including a change in congestion or a reason unrelated to the congestion.

[0104] At block 986, the CN sends a DL NAS message indicating to stop the back-off timer with value “deactivated” associated with DNN and / or S-NSSAI. Thereafter, the CN might receive, from the UE, an SM request for the DNN and / or S-NSSAI at block 994.

[0105] FIG. 10 shows example operations 1000 of a core network managing a first example reset mechanism based on UE capability and / or subscription. FIG. 10 describes the reset condition (reset timer) and reset mechanism as described with reference to FIG. 4 and FIG. 8, with the additional detail that applicability of the reset timer might be conditional on UE capability or subscription data.

[0106] At block 1032, the CN determines that the UE needs to be configured with the reset timer value. At block 1033, the CN might transmit a first message to a second CN node (such as a Home Subscriber Server (HSS), Authentication Server Function (AUSF), Unified Data Management (UDM), or Policy Control Function (PCF), among other examples) to request subscription data for the UE. At block 1034, the CN might receive a second message from the second CN node that includes the subscription data response for the UE.

[0107] At block 1035, the CN determines whether the UE is allowed to use a reset timer for a back-off timer having the back-off timer value set to “deactivated.” If the UE is not allowed to use the reset timer for the deactivated back-off timer, the flowchart proceeds to block 1098 where no further action is needed. Otherwise, if the UE is allowed to use the reset timer for the deactivated back-off timer, the flow chart proceeds to block 1036, where the CN transmits a DL NAS message to the UE with a reset timer value.

[0108] FIG. 11 shows example operations of a core network managing a second example reset mechanism based on UE capability and / or subscription. FIG. 11 describes the reset condition (DL NAS message) and reset mechanism as described with reference to FIG. 5 and FIG. 9, with the additional detail that applicability of the DL NAS message might be conditional on UE capability or subscription data.

[0109] At block 1165, the CN determines that the congestion is resolved for a DNN and / or S-NSSAI. At block 1180, the CN determines to notify the UE to stop the back-off timer based on the congestion being resolved. In some implementations, the CN can determine to notify the UE to stop the back-off timer for any reason, including reasons unrelated to the congestion being resolved.

[0110] As described with reference to FIG. 10, the CN can communicate with a second CN node to request (block 1033) and receive (block 1034) subscription data about the UE as described with reference to FIG. 10. In FIG. 10, the subscription data indicates whether the UE can use a reset timer. In FIG. 11, the subscription data indicates whether the UE can be notified to stop a running back-off timer. At block 1181, CN determines whether the UE is allowed to be notified to stop the running back-off timer (such as based on the subscription data, the type of the UE, UE capabilities, among other example criteria). If the UE is not allowed to be notified to stop the back-off timer, the flow chart proceeds to block 1098, where no further action is needed. Otherwise, if the UE is allowed to be notified to stop the backoff timer, the flow chart proceeds to block 1186. At block 1186, the CN transmits a DL NAS message to the UE to notify the UE to stop the back-off timer.

[0111] FIG. 12 is a block diagram of an example wireless communication system 1200 showing hardware features and communication interfaces. The depicted hardware configurations may omit certain components well-understood to be frequently implemented in such electronic devices, such as displays, peripherals, power supplies, and the like. The wireless communication system 1200 includes the same elements as described with reference to FIG. 1A, including the UE 102, the BS 106, and the CN 110. The UE 102 can support at least a 5G NR (or simply, “NR”) or E-UTRA air interface to communicate with the BS 106. The BS 106 connects to the CN 110 via an interface (e.g., SI or NG interface). The BS 106 can connect to other base stations (such as the BS 1204) via an interface (e.g., X2 or Xn interface) for interconnecting NG RAN nodes.

[0112] The CN 1 10 can be an Evolved Packet Core (EPC) and / or a 5G core (5GC). Among other components, the EPC can include a Serving Gateway (SGW), a Mobility Management Entity (MME), and a Packet Data Network Gateway (PGW). The SGW in general is configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., and the MME is configured to manage authentication, registration, paging, and other related functions. The PGW provides connectivity from the UE to one or more external packet data networks, e.g., an Internet network and / or an Internet Protocol (IP) Multimedia Subsystem (IMS) network. The 5GC includes a User Plane Function (UPF) and an Access and Mobility Management Function (AMF), and / or Session Management Function (SMF). Generally speaking, the UPF is configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., the AMF is configured to manage authentication, registration, paging, and other related functions, and the SMF is configured to manage PDU sessions.

[0113] The base station 106 is equipped with processing hardware 1206 that can include a receiver 1207B configured to receive data in the uplink direction. The processing hardware 1206 can also include a transmitter 1207A configured to transmit data in the downlink direction. The processing hardware further can one or more general-purpose processor(s) 1207C (e.g., CPUs) and a non-transitory computer-readable memory 1207D storing instructions that the one or more general-purpose processors execute. Additionally, or alternatively, the processing hardware 2506 can include special-purpose processing units. The processor 1207C may include, for example, one or more central processing units, graphics processing units (GPUs), or other application-specific integrated circuits (ASIC), and the like. CRM 1207D may include any suitable memory or storage device such as random-access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), or flash memory usable to store device data of the BS 106.

[0114] The UE 102 is equipped with processing hardware 1202 that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory 1203D storing machine-readable instructions executable on the one or more general-purpose processors, and / or special -purpose processing units. The processing hardware 1202 can also include a transmitter 1203A configured to transmit data in the downlink direction. The processing hardware further can include a receiver 1203B configured to receive data in theuplink direction. The processing hardware 1202, in an example implementation, includes a processor 1203C to process data that the UE 102 will transmit in the uplink direction, or process data received by UE 102 in the downlink direction. The processor(s) 1203C may include, for example, one or more central processing units, GPUs, or other applicationspecific integrated circuits (ASIC), and the like. To illustrate, the processor(s) 1203C may include an application processor (AP) utilized by the UE 102 to execute an operating system and various user-level software applications, as well as one or more processors utilized by modems or a baseband processor. The CRM 1203D may include any suitable memory or storage device such as RAM, SRAM, DRAM, NVRAM, ROM, flash memory, solid-state drive (SSD) or other mass-storage devices, and the like useable to store one or more sets of executable software instructions and associated data that manipulate the one or more processor(s) 1203C and other components of the processing hardware 1202 to perform the various functions described herein and attributed to the UE 102. The sets of executable software instructions include, for example, an operating system (OS) and various drivers (not shown), and various software applications (not shown), which are executable by processor(s) 1203C to enable user-plane communication, control-plane signaling, and user interaction with the UE 102.

[0115] FIG. 1A through FIG. 12 and the operations described herein are examples meant to aid in understanding example implementations and should not be used to limit the potential implementations or limit the scope of the claims, some implementations may perform additional operations, fewer operations, operations in parallel or in a different order, and some operations differently.

[0116] The foregoing disclosure provides illustration and description but is not intended to be exhaustive or to limit the aspects to the precise form disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of the aspects. While the aspects of the disclosure have been described in terms of various examples, any combination of aspects from any of the examples is also within the scope of the disclosure. The examples in this disclosure are provided for pedagogical purposes. Alternatively, or in addition to the other examples described herein, examples include any combination of the following implementation options (enumerated as clauses for clarity).

[0117] Clause 1. A method for wireless communication by a user equipment (UE) (102), including: receiving (150, 350, 450A, 450B, 550A, 550B, 650, 750) a downlink (DL) non- access stratum (NAS) message for congestion control of a first data network or network slice, where the DL NAS message indicates a timer value for a back-off timer is deactivated; deactivating the back-off timer for the first data network or network slice based on the DL NAS message; refraining (154, 354, 454, 654, 754) from communicating session management (SM) requests for the first data network or network slice while the back-off timer is deactivated; and resetting (360, 470, 580, 670, 780) the back-off timer based on a reset condition being satisfied.

[0118] Clause 2. The method of clause 1, further including: transmitting (194, 394, 494, 694), an uplink (UL) NAS message including an SM request for the first data network or network slice after the resetting the back-off timer.

[0119] Clause 3. The method of clause 1 or 2, further including: determining that the reset condition is satisfied based on at least one of: expiration of a reset timer, reception of a subsequent DL NAS message indicating that the first data network or network slice is available, or reception of the subsequent DL NAS message explicitly or implicitly resetting the back-off timer.

[0120] Clause 4. The method of clause 1, where the reset condition is based on a reset timer, the method further including: starting the reset timer in association with the deactivating the back-off timer; and resetting the back-off timer based on an expiration of the reset timer.

[0121] Clause 5. The method of clause 4, where a duration of the reset timer between the starting and the expiration of the reset timer is based on a reset timer value.

[0122] Clause 6. The method of clause 5, further including: receiving the reset timer value from a core network.

[0123] Clause 7. The method of clause 5, further including: obtaining the reset timer value from a pre-configured or default setting of the UE.

[0124] Clause 8. The method of any one of clauses 5 to 7, where the reset timer value is specific to the first data network or network slice.

[0125] Clause 9. The method of any one of clauses 5 to 8, where the reset timer value is specific to the back-off timer.

[0126] Clause 10. The method of clause 1 , where the reset condition is satisfied based on receiving a subsequent DL NAS message while the back-off timer is deactivated, the method further including: resetting the back-off timer based the subsequent DL NAS message including at least one of: an identification of the first data network or network slice, an indication of an existing session or packet data network connection associated with the first data network or network slice, an indication of a radio access technology (RAT) or type of UE for which the back-off timer is to be reset, or additional information to explicitly or implicitly instruct the UE to reset the back-off timer.

[0127] Clause 11. The method of any one of clauses 1 to 10, where the DL NAS message for congestion control is one of: a protocol data unit (PDU) session modification message, a PDU session establishment rejection message, a DL NAS transport message, a DL NAS response message.

[0128] Clause 12. The method of any one of clauses 1 to 11, further including: transmitting a first SM request message before the receiving the DL NAS message, where the DL NAS message is in response to the first SM request message.

[0129] Clause 13. A method for wireless communication by a core network (110), including: transmitting (150, 350, 450A, 450B, 550A, 550B, 450A, 450B, 850) a downlink (DL) non- access stratum (NAS) message to a user equipment (UE) (102) based on congestion control of a first data network or network slice, where the DL NAS message indicates a timer value for a back-off timer is deactivated; and causing the UE to reset (360, 470, 580, 670, 780) the back-off timer based on a reset condition being satisfied.

[0130] Clause 14. The method of clause 13, further including: receiving a first session management (SM) request from the UE; determining (448, 848) a congestion of the first data network or network slice; and transmitting the DL NAS message for congestion control in response to the first SM request.

[0131] Clause 15. The method of clause 13 or 14, further including: receiving (194, 394, 494, 694), an uplink (UL) NAS message from the UE after the causing the UE to reset the back-off timer.

[0132] Clause 16. The method of any one of clauses 13 to 15, where the causing the UE to reset the back-off timer includes: communicating a reset timer value to the UE before thetransmitting the DL NAS message, where a duration of a reset timer is based on the reset timer value.

[0133] Clause 17. The method of clause 16, where the reset timer value is specific to the first data network or network slice.

[0134] Clause 18. The method of any one of clauses 13 to 16, where the causing the UE to reset the back-off timer includes: communicating a subsequent DL NAS message to the UE to cause the UE to reset the back-off timer.

[0135] Clause 19. The method of clause 18, where the subsequent DL NAS message includes at least one of: an identification of the first data network or network slice, an indication of an existing session or packet data network connection that associated with the first data network or network slice, an indication of a radio access technology (RAT) or type of UE for which the back-off timer is to be reset, or additional information to explicitly or implicitly instruct the UE to reset the back-off timer.

[0136] Clause 20. The method of any one of clauses 13 to 19, where the DL NAS message for congestion control is one of: a protocol data unit (PDU) session modification message, a PDU session establishment rejection message, a DL NAS transport message, a DL NAS response message.

[0137] Clause 21. The method of any one of clauses 13 to 20, where the causing the UE to reset the back-off timer includes: configuring a reset mechanism of the UE to reset the backoff timer based on a determination that the UE matches a particular type of UE, category of service, or subscription.

[0138] Clause 22. The method of clause 21, where the configuring the reset mechanism includes configuring a reset timer value for a reset timer.

[0139] Clause 23. The method of clause 21, where the configuring the reset mechanism includes: transmitting a subsequent DL NAS message to the UE to cause the UE to reset the back-off timer based on a determination that the congestion of the first data network or network slice is resolved.

[0140] Clause 24. An apparatus, including: a communication unit; and a processing system configured to control the communication unit to implement any one of the methods of any one of clauses 1 to 23.

[0141] Another innovative aspect of the subject matter described in this disclosure can be implemented as a computer-readable medium having stored therein instructions which, when executed by a processor, causes the processor to perform any one of the above-mentioned functionalities.

[0142] Another innovative aspect of the subject matter described in this disclosure can be implemented as a system having means for implementing any one of the above-mentioned functionalities.

[0143] Another innovative aspect of the subject matter described in this disclosure can be implemented as an apparatus having one or more processors configured to perform one or more operations from any one of the above-mentioned methods.

[0144] The following description may be applied to the description above.

[0145] Generally speaking, description for one of the above figures can apply to another of the above figures. Examples, implementations and methods described above can be combined, if there is no conflict. An event or block described above can be optional or omitted. For example, an event or block with dashed lines in the figures can be optional. In some implementations, “message” is used and can be replaced by “information element (IE),” and vice versa. In some implementations, “IE” is used and can be replaced by “field,” and vice versa. In some implementations, “configuration” can be replaced by “configurations” or “configuration parameters,” and vice versa. In some implementations, “some” means “one or more.” In some implementations, “at least one” means “one or more.”

[0146] A user device in which the techniques of this disclosure can be implemented (e.g, the UE 102) can be any suitable device capable of wireless communications such as a smartphone, a tablet computer, a laptop computer, a mobile gaming console, a point-of-sale (POS) terminal, a health monitoring device, a drone, a camera, a media-streaming dongle or another personal media device, a wearable device such as a smartwatch, a wireless hotspot, a femtocell, or a broadband router. Further, the user device in some cases may be embedded in an electronic system such as the head unit of a vehicle or an advanced driver assistance system (ADAS). Still further, the user device can operate as an internet-of-things (loT) device or a mobile-internet device (MID). Depending on the type, the user device can include one or moregeneral-purpose processors, a computer-readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0147] Certain embodiments are described in this disclosure as including logic or a number of components or modules. Modules can be software modules (e.g., code, or machine-readable instructions stored on non-transitory machine-readable medium) or hardware modules. A hardware module is a tangible unit capable of performing certain operations and may be configured or arranged in a certain manner. A hardware module can comprise dedicated circuitry or logic that is permanently configured (e.g., as a special-purpose processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), a digital signal processor (DSP), etc.) to perform certain operations. A hardware module may also comprise programmable logic or circuitry e.g., as encompassed within a general-purpose processor or other programmable processor) that is temporarily configured by software to perform certain operations. The decision to implement a hardware module in dedicated and permanently configured circuitry, or in temporarily configured circuitry (e.g., configured by software) may be driven by cost and time considerations.

[0148] When implemented in software, the techniques can be provided as part of the operating system, a library used by multiple applications, a particular software application, etc. The software can be executed by one or more general -purpose processors or one or more special-purpose processors.

[0149] Upon reading this disclosure, those of skill in the art will appreciate additional and alternative structural and functional designs for handling mobility between base stations through the principles disclosed herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those of ordinary skill in the art, may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the spirit and scope defined in the appended claims.

[0150] As used herein, the terms “component” and “module” are intended to be broadly construed as hardware, firmware, or a combination of hardware and software. As used herein, a processor is implemented in hardware, firmware, or a combination of hardware andsoftware. As used herein, the phrase “based on” is intended to be broadly construed to mean “based at least in part on.”

[0151] As used herein, a phrase referring to a list of items separated by “or” refers to any combination of those items, including single members. For example, “a, b, or c” is intended to cover the possibilities of: a only, b only, c only, a combination of a and b, a combination of a and c, a combination of b and c, and a combination of a and b and c.

[0152] In this disclosure, an expression of “X / Y” may include meaning of any of the following: “X or Y” or “X and Y” or “X and / or Y." An expression of “(A) B” or “B (A)” may include concept of “only B.” An expression of “(A) B” or “B (A)” may include the concept of“A+B” or “B+A.”

[0153] In this disclosure, the term "can" indicates a capability, or alternatively indicates a possible implementation option. The term "may" indicates a permission or a possible implementation option.

[0154] Some aspects are described herein in connection with thresholds. As used herein, satisfying a threshold may refer to a value being greater than the threshold, greater than or equal to the threshold, less than the threshold, less than or equal to the threshold, equal to the threshold, not equal to the threshold, or the like.

[0155] The various illustrative components, logic, logical blocks, modules, circuits, operations and algorithm processes described in connection with the implementations disclosed herein may be implemented as electronic hardware, firmware, software, or combinations of hardware, firmware or software, including the structures disclosed in this specification and the structural equivalents thereof. The interchangeability of hardware, firmware and software has been described generally, in terms of functionality, and illustrated in the various illustrative components, blocks, modules, circuits and processes described above. Whether such functionality is implemented in hardware, firmware or software depends upon the particular application and design constraints imposed on the overall system.

[0156] The hardware and data processing apparatus used to implement the various illustrative components, logics, logical blocks, modules and circuits described in connection with the aspects disclosed herein may be implemented or performed with a general purpose single- or multi-chip processor, a digital signal processor (DSP), an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, or any conventional processor, controller, microcontroller, or state machine. A processor also may be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. In some implementations, particular processes, operations and methods may be performed by circuitry that is specific to a given function.

[0157] As described above, some aspects of the subject matter described in this specification can be implemented as software. For example, various functions of components disclosed herein, or various blocks or steps of a method, operation, process or algorithm disclosed herein can be implemented as one or more modules of one or more computer programs. Such computer programs can include non-transitory processor-executable or computer-executable instructions encoded on one or more tangible processor-readable or computer-readable storage media for execution by, or to control the operation of, a data processing apparatus including the components of the devices described herein. By way of example, and not limitation, such storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that may be used to store program code in the form of instructions or data structures. Combinations of the above should also be included within the scope of storage media.

[0158] As used herein, the terms “user device”, “user equipment” (for example, UE 110), “wireless communication device”, “mobile communication device”, “communication device”, or “mobile device” refer to any one or all of cellular telephones, smartphones, portable computing devices, personal or mobile multi-media players, laptop computers, tablet computers, smartbooks, Internet-of-Things (loT) devices, palm-top computers, wireless electronic mail receivers, multimedia Internet enabled cellular telephones, wireless gaming controllers, display sub-systems, driver assistance systems, vehicle controllers, vehicle system controllers, vehicle communication system, infotainment systems, vehicle telematics systems or subsystems, vehicle display systems or subsystems, vehicle data controllers, point-of-sale (POS) terminals, health monitoring devices, drones, cameras, media-streaming dongles or another personal media devices, wearable devices such as smartwatches, wireless hotspots, femtocells, broadband routers or other types of routers, and similar electronic devices which include a programmable processor and memory and circuitry configured to perform operations as described herein. Further, the user device in some cases may be embedded in an electronic system such as the head unit of a vehicle or an advanced driver assistance system (ADAS). Still further, a mobile-internet device (MID). Depending on the type, the user device can include one or more general-purpose processors, a computer- readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0159] Various modifications to the implementations described in this disclosure may be readily apparent to persons having ordinary skill in the art, and the generic principles defined herein may be applied to other implementations without departing from the scope of this disclosure. Thus, the claims are not intended to be limited to the implementations shown herein but are to be accorded the widest scope consistent with this disclosure, the principles and the novel features disclosed herein.

[0160] Additionally, various features that are described in this specification in the context of separate implementations also can be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation also can be implemented in multiple implementations separately or in any suitable subcombination. As such, although features may be described above as acting in particular combinations, and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a sub combi nation.

[0161] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Further, the drawings may schematically depict one or more example processes in the form of a flowchart or flow diagram. However, other operations that are not depicted can be incorporated in the example processes that are schematically illustrated. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the illustrated operations. In some circumstances, multitasking and parallelprocessing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results.

Claims

CLAIMSWhat is claimed is:

1. A method for wireless communication by a user equipment (UE) (102), comprising: receiving (150, 350, 450A, 450B, 550A, 550B, 650, 750) a downlink (DL) non-access stratum (NAS) message for congestion control of a first data network or network slice, wherein the DL NAS message indicates to deactivate a back-off timer; deactivating the back-off timer for the first data network or network slice based on the DL NAS message; starting a reset timer in association with the deactivating the back-off timer; refraining (154, 354, 454, 654, 754) from communicating session management (SM) requests for the first data network or network slice while the back-off timer is deactivated; resetting (360, 470, 580, 670, 780) the back-off timer based on an expiration of the reset timer; and transmitting (194, 394, 494, 694), an uplink (UL) NAS message including an SM request for the first data network or network slice after the resetting the back-off timer.

2. The method of claim 1, wherein a duration of the reset timer between the starting and the expiration of the reset timer is based on a reset timer value.

3. The method of claim 2, further comprising: receiving the reset timer value from a core network.

4. The method of claim 2, further comprising: obtaining the reset timer value from a pre-configured or default setting of the UE.

5. The method of any one of claims 2 to 4, wherein the reset timer value is specific to the first data network or network slice.

6. The method of any one of claims 2 to 5, wherein the reset timer value is specific to the back-off timer.

7. The method of any one of claims 1 to 6, further comprising:resetting the back-off timer based on receiving a subsequent DL NAS message that includes at least one of: an identification of the first data network or network slice for which the backoff timer is to be reset, an indication of a radio access technology (RAT) or type of UE for which the back-off timer is to be reset, or additional information to explicitly or implicitly instruct the UE to reset the back-off timer.

8. The method of claim 7, wherein the DL NAS message for congestion control is one of: a protocol data unit (PDU) session modification message, a PDU session establishment rejection message, a DL NAS transport message, a DL NAS response message.

9. A method for wireless communication by a core network (110), comprising: configuring a user equipment (UE) (102) with a reset timer to override a deactivated back-off timer; transmitting (150, 350, 450A, 450B, 550A, 550B, 450A, 450B, 850) a downlink (DL) non-access stratum (NAS) message to the UE based on congestion control of a first data network or network slice, wherein the DL NAS message indicates deactivation of a back-off timer; and receiving (194, 394, 494, 694), an uplink (UL) NAS message from the UE after an expiration of the reset timer causes the UE to reset (360, 470, 580, 670, 780) the back-off timer.

10. The method of claim 9, wherein the configuring the UE with the reset timer includes: communicating a reset timer value to the UE before the transmitting the DL NAS message, wherein a duration of a reset timer is based on a reset timer value.

11. The method of claim 10, wherein the reset timer value is specific to the first data network or network slice.

12. The method of claim 9 or 10, further comprising: communicating a subsequent DL NAS message to the UE to cause the UE to reset the back-off timer, wherein the subsequent DL NAS message includes at least one of: an indication of a radio access technology (RAT) or type of UE for which the back-off timer is to be reset, or additional information to instruct the UE to reset the back-off timer.

13. The method of any one of claims 9 to 12, wherein the configuring the UE includes: configuring a reset mechanism of the UE to reset the back-off timer based on a determination that the UE matches a particular type of UE, category of service, or subscription.

14. The method of claim 13, wherein the configuring the reset mechanism includes configuring a reset timer value for the reset timer.

15. An apparatus, comprising: a communication unit; and a processing system configured to control the communication unit to implement any one of the methods of any one of claims 1 to 14.

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