Patent Publication Number: US-2022217808-A1

Title: Handling an Attempt to Resume a Wireless Connection Using a Base Station that Supports a Different Core-Network Type

Description:
RELATED APPLICATION(S) 
     This application is a continuation of and claims priority to U.S. Non-Provisional patent application Ser. No. 16/759,258, filed on Apr. 24, 2020, which in turn is a National Stage Entry and claims priority to International Patent Application Serial No. PCT/US2019/045224, filed on Aug. 6, 2019, which in turn claims priority to U.S. Provisional Patent Application Ser. No. 62/716,725, filed on Aug. 9, 2018, the disclosures of which are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     The evolution of wireless communication to Fifth-Generation (5G) standards and technologies provide higher data rates and greater capacity, with improved reliability and lower latency, which enhances mobile broadband services. 5G technologies also provide new classes of services for vehicular, fixed wireless broadband, and the Internet of Things (IoT). The specification of the features in the 5G air interface is defined as 5G New Radio (5G NR). 
     To communicate wirelessly with a network, a user equipment (UE) may establish a connection to the network using a base station (e.g., a serving cell) that supports a Fifth-Generation core network (5GC), an Evolved Packet Core (EPC), or both. After suspending the connection to the network, the UE may perform a cell-selection procedure that selects a different base station. If the selected base station supports a different core-network type than the previous base station, however, an attempt to resume the connection to the network using the selected base station may fail. 
     SUMMARY 
     Techniques and apparatuses are described that handle an attempt to resume a connection using a base station that supports a different core-network type. In particular, a resource control module of a UE determines whether or not a core-network type supported by a currently selected base station differs from a core-network type supported by a previously-selected base station before performing a connection-resume procedure. If the core-network types differ, the resource control module performs another action prior to or instead of performing the connection-resume procedure. As an example action, the resource control module releases the wireless connection to the network, performs a connection-establishment procedure with the second base station, postpones the connection-resume procedure, or sends a message to an upper layer. In this way, the resource control module takes steps to proactively avoid performing a connection-resume procedure that may fail due to differences in core-network types. 
     Aspects described below include a method performed by a user equipment for handling an attempt to resume a wireless connection using a base station that supports a different core-network type. The method includes establishing a wireless connection to a network using a first base station that supports a first core-network type. The method also includes suspending the wireless connection to the network and performing a cell-selection procedure that selects a second base station. The method additionally includes processing system information received from the second base station to determine that the second base station supports a second core-network type and determining that the second core-network type differs from the first core-network type. The method further includes detecting a trigger that initiates a connection-resume procedure. Responsive to detecting the trigger and determining that the second core-network type is different, the method includes performing one or more operations comprising: releasing the wireless connection to the network; performing a connection-establishment procedure using the second base station; postponing the connection-resume procedure; or sending a message to an upper layer. 
     Aspects described below also include a user equipment comprising a radio-frequency transceiver. The UE also includes a processor and memory system configured to perform any of the methods described. 
     Aspects described below also include a system with means for handling an attempt to resume a wireless connection to a network using a base station that supports a different core-network type by performing at least one of the following: releasing the connection to the network, performing a connection-establishment procedure using the cell, postponing a connection-resume procedure, or sending a message to an upper layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Apparatuses of and techniques for handling an attempt to resume a wireless connection using a base station that supports a different core-network type are described with reference to the following drawings. The same numbers are used throughout the drawings to reference like features and components: 
         FIG. 1  illustrates an example wireless network environment in which handling an attempt to resume a wireless connection using a base station that supports a different core-network type can be implemented. 
         FIG. 2  illustrates an example user equipment for handling an attempt to resume a wireless connection using a base station that supports a different core-network type. 
         FIG. 3  illustrates another example environment in which a user equipment may attempt to resume a connection using a base station that supports a different core-network type. 
         FIG. 4  illustrates example data and control transactions between a user equipment, a first base station, and a second base station. 
         FIG. 5  illustrates an example method for handling an attempt to resume a wireless connection using a base station that supports a different core-network type. 
     
    
    
     DETAILED DESCRIPTION 
     Overview 
     This document describes techniques and devices for handling an attempt to resume a wireless connection using a base station that supports a different core-network type. While in a current resource control state, such as an inactive state, a user equipment (UE) can select a base station that supports a different core-network type than a previous base station. In some cases, this selected base station may not support the current resource control state or may not enable the UE to transition to a different resource control state, such as a connected state. Consequently, if the UE attempts to perform a procedure to transition the UE to a different resource control state, the procedure may fail. The failure may result in wasted network resources or delayed communications with the UE. 
     These techniques and devices enable handling an attempt to resume a wireless connection using a base station that supports a different core-network type. In particular, a resource control module of a UE determines whether or not a core-network type supported by a currently selected base station differs from a core-network type supported by a previously-selected base station before performing a connection-resume procedure. If the core-network types differ, the resource control module performs another action prior to or instead of performing the connection-resume procedure. As an example action, the resource control module releases the wireless connection to the network, performs a connection-establishment procedure with the second base station, postpones the connection-resume procedure, or sends a message to an upper layer. In this way, the resource control module takes steps to proactively avoid performing a connection-resume procedure that may fail due to differences in core-network types. 
     Example Environment 
       FIG. 1  illustrates an example environment  100 , in which handling an attempt to resume a wireless connection using a base station that supports a different core-network type can be implemented. The environment  100  includes multiple UEs  110 , illustrated as UE  111 , UE  112 , and UE  113 . Each UE  110  communicates with one or more base stations  120  (illustrated as base stations  121 ,  122 ,  123 , and  124 ) through one or more wireless communication links  130  (wireless link  130 ), illustrated as wireless links  131  and  132 . Although illustrated as a smartphone, the UE  110  can be implemented as any suitable computing or electronic device, such as a mobile communication device, a modem, a cellular phone, a gaming device, a navigation device, a media device, a laptop computer, a desktop computer, a tablet computer, a smart appliance, a vehicle-based communication system, and the like. The base station  120  (e.g., an Evolved Universal Terrestrial Radio Access Network Node B, E-UTRAN Node B, evolved Node B, eNodeB, eNB, Next Generation Evolved Node B, ng-eNB, Next Generation Node B, gNode B, gNB, or the like) can be implemented in a macrocell, microcell, small cell, picocell, or the like, or any combination thereof. 
     The base stations  120  communicate with the UE  110  using the wireless links  131  and  132 , which may be implemented as any suitable type of wireless link. The wireless link  131  and  132  can include a downlink of data and control information communicated from the base stations  120  to the UE  110 , an uplink of other data and control information communicated from the UE  110  to the base stations  120 , or both. The wireless links  130  include one or more wireless links or bearers implemented using any suitable communication protocol or standard, or combination of communication protocols or standards such as 3rd Generation Partnership Project Long-Term Evolution (3GPP LTE), Enhanced Long-Term Evolution (eLTE), Fifth-Generation New Radio (5G NR), Fourth-Generation (4G) standard, and so forth. Multiple wireless links  130  can be aggregated in a carrier aggregation to provide a higher data rate for the UE  110 . Multiple wireless links  130  from multiple base stations  120  can be configured for Coordinated Multipoint (CoMP) communication with the UE  110 . 
     The base stations  120  are collectively a Radio Access Network  140  (RAN, Evolved Universal Terrestrial Radio Access Network, E-UTRAN, 5G NR RAN or NR RAN) that each use a Radio Access Technology (RAT). The RANs  140  include an NR RAN  141  and an E-UTRAN  142 . In  FIG. 1 , core networks  190  include a Fifth-Generation Core (5GC) network  150  (5GC  150 ) and an Evolved Packet Core (EPC) network  160  (EPC  160 ), which are different types of core networks. The base stations  121  and  123  in the NR RAN  141  are connected to the 5GC  150 . The base stations  122  and  124  in the E-UTRAN  142  connect to the EPC  160 . Optionally or additionally, the base station  122  connects to both the 5GC  150  and EPC  160 . 
     The base stations  121  and  123  connect, at  102  and  104  respectively, to the 5GC  150  using an NG2 interface for control-plane signaling and using an NG3 interface for user-plane data communications. The base stations  122  and  124  connect, at  106  and  108  respectively, to the EPC  160  using an S1 interface for control-plane signaling and user-plane data communications. If the base station  122  connects to both the 5GC  150  and EPC  160 , the base station  122  can connect to the 5GC  150  using an NG2 interface for control-plane signaling and using an NG3 interface for user-plane data communications, at  180 . In addition to connections to core networks  190 , base stations  120  can communicate with each other. The base stations  121  and  123  communicate using an Xn interface at  112 , for instance. The base stations  122  and  124  communicate using an X2 interface at  114 . The base stations  122  and  123  can communicate using an Xn interface at  116  to execute a handover procedure. 
     The 5GC  150  includes an Access and Mobility Management Function  152  (AMF  152 ) that provides control-plane functions such as registration and authentication of multiple UE  110 , authorization, mobility management, or the like in the 5G NR network. The EPC  160  includes a Mobility Management Entity  162  (MME  162 ) that provides control-plane functions such as registration and authentication of multiple UE  110 , authorization, mobility management, or the like in the E-UTRA network. The AMF  152  and the MME  162  communicate with the base stations  120  in the RANs  140  and also communicate with multiple UE  110  through the base stations  120 . 
     The UE  110  supports eLTE or a variety of different RATs, such as 5G NR and 4G. Different situations can cause the UE  110  to transition among different resource control states as determined by the RAT. Example resource control states include a connected state in which the UE  110  establishes a wireless connection to a network using the base station  120 , an inactive state in which the UE  110  suspends the wireless connection to the network, or an idle state in which the UE  110  releases the wireless connection to the network. While in the inactive state, for example, the UE  110  performs the cell-selection procedure. In some cases, the cell-selection procedure selects a second base station that supports a core-network type that is different from the core-network type supported by the previous cell. As such, the selected base station may not support the inactive state or may not enable a wireless connection to a network to be resumed from the inactive state through a connection-resume procedure (e.g., a radio-resource-control (RRC) connection-resume procedure). In general, the connection-resume procedure enables the UE  110  to transition from the inactive state to the connected state and resume the connection to the RAN  140 . Components of the UE  110  are further described with respect to  FIG. 2 . 
     Example Device 
       FIG. 2  illustrates an example device diagram  200  of the UE  110 . The UE  110  can include additional functions and interfaces that are omitted from  FIG. 2  for the sake of clarity. In the depicted configuration, the UE  110  includes antennas  202 , a radio-frequency (RF) front end  204  (RF front end  204 ), a radio-frequency transceiver, including, for example, an LTE transceiver  206 , and/or a 5G NR transceiver  208  for communicating with one or more base stations  120  in the RAN  140 . The RF front end  204  couples or connects the LTE transceiver  206  and the 5G NR transceiver  208  to the antennas  202  to facilitate various types of wireless communication. The antennas  202  can include an array of multiple antennas that are configured similar to or differently from each other. The antennas  202  and the RF front end  204  are tuned to one or more frequency bands defined by the 3GPP LTE and 5G NR communication standards and implemented by the LTE transceiver  206  and/or the 5G NR transceiver  208 . 
     The UE  110  also includes one or more processors  210  and memory system including, for example, computer-readable storage media  212  (CRM  212 ). The processor  210  can be a single core processor or a multiple core processor composed of a variety of materials, such as silicon, polysilicon, high-K dielectric, copper, and so on. The computer-readable storage media excludes propagating signals and the CRM  212  includes 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 useable to store device data  214  of the UE  110 . The device data  214  includes user data, multimedia data, beamforming codebooks, applications, and/or an operating system of the UE  110 , which are executable by the processor  210  to enable user-plane communication, control-plane signaling, and user interaction with the UE  110 . 
     The CRM  212  also includes a resource control module  216 . Alternately or additionally, the resource control module  216  can be implemented in whole or part as hardware logic or circuitry integrated with or separate from other components of the UE  110 . The resource control module  216  implements an RRC layer, as described according to the wireless communication standard. The resource control module  216  determines the resource control state (e.g., the connected state, the inactive state, or the idle state) and performs operations according to the resource control state. Instead of directly performing a connection-resume procedure, the resource control module  216  evaluates a core-network type of a currently selected cell. If the core-network type does not support the current resource control state or differs from a previous cell&#39;s core-network type, the resource control module  216  performs other actions prior to or instead of performing the connection-resume procedure. The resource control module  216  can at least partially implement handling an attempt to resume a wireless connection using a base station that supports a different core-network type, as further described in  FIGS. 3-5 . 
     Handling an Attempt to Resume a Wireless Connection Using a Base Station that Supports a Different Core-Network Type 
       FIG. 3  illustrates another example environment  300  in which the UEs  111  and  112  move to different geographical locations that are serviced by different base stations  121 ,  122 , and  124  of  FIG. 1 . In this example, the base station  121  is a gNB and supports the 5GC  150 . In contrast, the base station  124  is an ng-eNB or an eNB that supports the EPC  160 . The base station  122  is another ng-eNB that supports both the 5GC  150  and EPC  160 . 
     Consider that the UE  111  supports eLTE and is positioned at a first location  310 , which is proximate to the base station  122 . The UE  111  performs a cell-selection procedure that selects the base station  122 , establishes a wireless link  132  with the base station  122 , and operates in a connected state  330 . After some period of time, the UE  111  transitions from the connected state  330  to an inactive state  332 . In some cases, the UE  111  receives a request message from the base station  122  (shown in  FIG. 4 ) that directs the UE  111  to transition from the connected state  330  to the inactive state  332 . The request message can be a radio-resource-control (RRC) connection-release message. 
     While in the inactive state  332 , the UE  111  moves to a second location  312 , which is proximate to the base station  124 . The UE  111  performs a second cell-selection procedure to select or determine a second base station. The cell-selection procedure can alternatively be referred to as a cell-reselection procedure, which enables the UE  111  to change or switch to a different base station  120  within the RAN  140 . In this example, the UE  111  selects the base station  124 , which supports the EPC  160  and not the 5GC  150 . Consequently, the base station  124  does not support the inactive state  332  and does not support a connection-resume procedure that enables the UE  111  to transition from the inactive state  332  to the connected state  330 . Since the currently selected base station  124  does not support the inactive state  332 , a future attempt to perform the connection-resume procedure will fail. 
     A similar problem occurs if the UE  110  performs an inter-RAT cell-selection procedure, as described with respect to UE  112 . Consider that the UE  112  is positioned at a third location  314 , which is proximate to the base station  121 . The UE  112  performs a cell-selection procedure that selects the base station  121 , establishes the wireless link  131  with the base station  121 , and operates in the connected state  330 . After some time period, the UE  112  transitions from the connected state  330  to the inactive state  332 , similar to the UE  111 . Additionally, the UE  112  moves to a fourth location  316 , which is proximate to the base station  124 . At the fourth location  316 , the UE  112  performs a cell-selection procedure that selects the base station  124 , which supports a different core-network type compared to the core-network type supported by the base station  121 . Since the core-network type supported by the base station  124  does not support the inactive state  332 , a future attempt to perform the connection-resume procedure while the base station  124  is selected will fail. 
     To avoid wasting network resources or delaying communications that could be caused by a connection-resume procedure failure, the UE  110  performs other actions prior to or instead of performing the connection-resume procedure, as further described in  FIG. 4 . Although the UEs  111  and  112  are described as being in the inactive state  332 , these techniques can be applied to other types of resource control states that may not be supported by the selected base station  120 . 
       FIG. 4  illustrates example data and control transactions  400  between the UE  110 , the first base station  121  or  122 , and the second base station  124 . In this example, the first base station  121  or  122  supports a first core-network (CN) type  402  and the second base station  124  supports a second core-network type  404 , which differs from the first core-network type  402 . As an example, the first core-network type  402  includes the 5GC  150  and the second core-network type  404  includes the EPC  160 . 
     At  405 , the first base station  121  or  122  and the UE  110  perform a connection-establishment procedure, which enables the UE  110  to wirelessly connect to the RAN  140  using the base station  121  or  122 . 
     At  410 , the UE  110  operates in the connected state  330 . 
     At  415 , the first base station  121  or  122  sends a request message  416  to the UE  110 . The request message  416  directs the UE  110  to transition from the connected state  330  to the inactive state  332 . In some cases, the request message  416  specifies a duration  418  for which the UE  110  operates in the inactive state  332  prior to performing a connection-resume procedure. An example request message  416  includes the RRC connection-release message, as described above with respect to  FIG. 3 . 
     At  420 , the UE  110  transitions from the connected state  330  to the inactive state  332  and operates in the inactive state  332  according to the request message  416 . 
     At  425 , the UE  110  additionally sets a timer that triggers a connection-resume procedure upon expiration. In some cases, the UE  110  sets a duration of the timer based on a predetermined amount of time that is specified by the computer-readable storage media  212  of the UE  110 . Alternatively, the UE  110  sets the duration of the timer according to the duration  418  specified by the request message  416 . 
     At  430 , the UE  110  performs a cell-selection procedure that selects the second base station  124 . In some cases, the UE  110  selects the second base station  124  instead of the first base station  121  or  122  because the UE  110  moved to a new location that is closer to the second base station  124  (relative to the first base station  121  or  122 ). As an example, the UE  110  moves to the second location  312  or the fourth location  316  shown in  FIG. 3 . 
     At  435 , the UE  110  receives system information  436  from the second base station  124 . The system information  436  informs the UE  110  of the second core-network type  404  supported by the second base station  124 . 
     At  440 , the UE  110  determines that the first core-network type  402  supported by the first base station  121  or  122  differs from the second core-network type  404  supported by the second base station  124 . Consequently, a connection-resume procedure with the selected base station  124  may fail. The UE  110  can also determine that a future connection-resume procedure will fail based on a determination that the second core-network type  404  does not support the inactive state  332  (e.g., the current resource control state of the UE  110 ). 
     At  445 , the UE  110  detects a trigger that initiates a connection-resume procedure. One example trigger includes an expiration of the timer  446 , which was previously set at  425 . A second example trigger includes a request to perform a radio-access-network notification-area (RNA) update  447 . The RNA update  447  provides a single identity (e.g., a RAN area identity, a cell identity, or a Public Land Mobile Network (PLMN) identity) or a list of identities (e.g., a list of cell identities) to the UE  110 . In some situations, the RNA update  447  is triggered if a RAN notification area associated with the selected base station (e.g., the second base station  124 ) differs from the RAN notification area associated with the previously-selected base station (e.g., the first base station  121  or  122 ). The system information  436  can provide the RAN notification area associated with the second base station  124  to the UE  110 . A third example trigger includes a message  448  from an upper layer, which triggers the RNA update  447  or the connection-resume procedure. 
     At  450 , the UE  110  performs one or more operations prior to or instead of the connection-resume procedure. In particular, when it is determined that the first core-network type  402  differs from the second core-network type  404  and a trigger occurred, the UE  110  releases the wireless connection to the RAN  140  (e.g., transitions to the idle state), performs a connection-establishment procedure with the base station  124 , postpones the connection-resume procedure, and/or sends a message to an upper layer, as further described with respect to  FIG. 5 . By determining that the first core-network type  402  differs from the second core-network type  404  at  440 , the UE  110  can take action to avoid attempting a connection-resume procedure that wastes network resources or delays communications. 
     Example Method 
       FIG. 5  depicts an example method  500  for handling an attempt to resume a wireless connection using a base station that supports a different core-network type. Method  500  is shown as a set of operations (or acts) performed but not necessarily limited to the order or combinations in which the operations are illustrated. Further, any of one or more of the operations may be repeated, combined, reorganized, skipped, or linked to provide a wide array of additional and/or alternate methods. In portions of the following discussion, reference may be made to environment  100  of  FIG. 1 or 300  of  FIG. 3  and entities detailed in  FIG. 2 , reference to which is made for example only. The techniques are not limited to performance by one entity or multiple entities operating on one device. 
     At  502 , a UE establishes a wireless connection to a network using a first base station that supports a first core-network type. For example, the UE  110  establishes a wireless link  130  to the RAN  140  of  FIG. 1  using the base station  120 , as shown in  FIG. 1 . In particular, the UE  110  performs a connection-establishment procedure (shown in  FIG. 4 ) as specified by the wireless communication standard. The UE  110  also determines that the base station  122  supports the first core-network type  402 , such as the 5GC  150 , based on system information provided by the base station  120 . In  FIG. 3 , the UE  111  establishes a wireless link  132  to the RAN  142  using the base station  122 , which is implemented as a ng-eNB that supports both the 5GC  150  and the EPC  160 . Additionally, or alternatively, the UE  112  establishes a wireless link  131  to the RAN  141  using the base station  121 , which is implemented as a gNB that supports the 5GC  150 . 
     At  504 , the UE suspends the wireless connection to the network. For example, the UE  110  suspends the connection to the RAN  140 . In some cases, the UE  110  suspends the connection responsive to receiving the request message  416  of  FIG. 4  (e.g., an RRC connection-release message) from the base station  120 . The request message directs the UE  110  to transition from the connected state  330  to the inactive state  332 . Although described with respect to the inactive state  332 , this step may alternatively involve transitioning to any second resource control state that is not supported by a second core-network type  404 . 
     At  506 , the UE performs a cell-selection procedure that selects a second base station. For example, the UE  110  performs the cell-selection procedure, which selects the base station  124 . Continuing with the above example, the cell-selection procedure is performed while the UE  110  is in the inactive state  332 . 
     At  508 , the UE processes system information received from the second base station to determine that the second base station supports a second core-network type. For example, UE  110  processes the system information  436  to determine that the base station  124  supports the second core-network type  404 . The system information  436  is received from the base station  124 , as shown at  435  in  FIG. 4 . 
     At  510 , the UE determines that the second core-network type is different from the first core-network type. For example, the UE  110  determines that the second core-network type  404  is different from the first core-network type  402 . In particular, this can include determining that at least one difference between the first core-network type  402  and the second core-network type  404  is such that a connection-resume procedure with the second base station  124  may fail. In an example, determining that the second core-network type  404  is different from the first core-network type  402  includes determining that the second core-network type  404  and first core-network type  402  support different resource control states and/or different connection procedures. The UE  110  makes this determination based on system information  436  that is provided by the first base station  120  (e.g., the base station  121  or the base station  122 ) and the second base station  124 . 
     As an example, the second core-network type  404  includes the EPC  160  and the first core-network type  402  includes the 5GC  150 . Unlike the 5GC  150 , the EPC  160  does not support the UE  110  in an inactive state  332  and does not support a connection-resume procedure that enables the UE  110  to transition from the inactive state  332  to the connected state  330 . Therefore, the UE  110  determines that the second core-network type  404  is different from the first core-network type  402 . 
     At  512 , the UE detects a trigger that initiates a connection-resume procedure. For example, the UE  110  detects at least one of the following types of triggers: an expiration of a timer  446  that directs the UE  110  to perform the connection-resume procedure, a request to perform an RNA update  447 , or a message  448  from the upper layer that directs the UE  110  to perform the connection-resume procedure, as described above with respect to  FIG. 4 . To avoid performing a connection-resume procedure with the second base station  124 , which may fail due to the differences between the core-network types (e.g., differences between the EPC  160  and the 5GC  150 ), the UE  110  performs at least one of the operations at  514 - 520  prior to or instead of performing the connection-resume procedure. 
     At  514 , the UE releases the wireless connection to the network. For example, the UE  110  releases the wireless connection to the RAN  140  by performing an RRC connection-release procedure. The UE  110  performs the RRC connection-release procedure with the first base station  122  or the second base station  124 . This procedure causes the UE  110  to transition from the inactive state  332  to an idle state, which is supported by the EPC  160 . Upon entering the idle state, the UE  110  deletes a resume UE context (e.g., an inactive UE context), a related identity (e.g., a resume identity or RNA identity), a security context, and so forth. In general, this step transitions the UE  110  from a current state that is not supported by the second core-network type  404  to a second state that is supported by the second core-network type  404 . 
     At  516 , the UE performs a connection-establishment procedure with the second base station. For example, the UE  110  performs the connection-establishment procedure with the base station  124  of  FIG. 1 or 3  instead of performing the requested connection-resume procedure. The connection-establishment procedure is a procedure that is supported by the EPC  160 , and therefore may succeed. If the connection-establishment procedure fails, the UE  110  can proceed to release the connection at  514  and enter the idle state. 
     At  518 , the UE postpones the connection-resume procedure. For example, the UE  110  postpones the connection-resume procedure triggered at  512 . This postponement provides an opportunity for the UE  110  to perform a second cell-selection procedure. The UE  110  postpones the connection-resume procedure based on a predetermined amount of time or a timer. After the specified amount of time, the UE  110  proceeds to release the connection at  514 , perform the connection-establishment procedure at  516 , remain in the inactive state and send a message to an upper layer at  520 , or perform a second cell-selection procedure at  506 . In some cases, the UE  110  continues performing multiple cell-selection procedures  506  until a base station  120  is selected that supports the first core-network type  402  (e.g., the 5GC  150 ). In other cases, the UE  110  keeps track of a timer or a total quantity of attempts and proceeds according to  514 ,  516 , or  520  if a time limit or a maximum quantity of attempts has been reached. In some cases, the UE  110  continues performing cell-selection procedures at a predetermined time interval. 
     At  520 , the UE sends a message is sent to an upper layer. For example, the UE  110  sends a message from the RRC layer to a mobility management layer, such as a non-access stratum (NAS) layer. The message indicates an intent or determination of the UE  110  to not perform the connection-resume procedure. In this case, the UE  110  continues to operate in the inactive state  332 . In other cases, the UE  110  sends the message in response to the release of the connection at  514  or the connection-establishment procedure at  516 . 
     Conclusion 
     Although techniques for handling an attempt to resume a wireless connection using a base station that supports a different core-network type have been described in language specific to features and/or methods, it is to be understood that the subject of the appended claims is not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed as example implementations of handling an attempt to resume a wireless connection using a base station that supports a different core-network type.