Patent Description:
The present disclosure relates to registration of a User Equipment (UE) using Single-Network Slice Selection Assistance Information (S-NSSAI) in a cellular communication system.

Support for network slices in a registration area (RA) is homogenous in Third Generation Partnership Project (3GPP) Technical Report (TR) <NUM>-<NUM> Release <NUM>. In 3GPP TR <NUM>-<NUM> Release <NUM>, Solution #<NUM> (and Solution #<NUM>, which mimics #<NUM> but uses one or more rejected Single-Network Slice Selection Assistance Information (S-NSSAI) for redirection and also includes info to a User Equipment (UE) for cell reselection) enables the network to redirect the UE to a new tracking area (TA) when current TA does not support the S-NSSAI requested by the UE. The solution works in most cases, as it relies upon TA borders of S-NSSAI availability. An unsupported network slice is put in a Rejected S-NSSAI for the registration area (RA), and the UE then is assumed to retry per existing logic. In both Solutions #<NUM> and #<NUM>, the registration accept occurs prior to the RwR (Release with Redirection, i.e., with cell reselection priorities), and then the UE attempts a new registration because the UE is in a new RA. Both solutions rely on the RwR succeeding, or, if done in CM-CONNECTED, that the handover (HO) succeeds.

Solution #<NUM> avoids the need for the core network (CN) to know whether there actually is overlapping coverage or not. However, discussions in 3GPP are also focusing on whether the CN should have more information about Radio Access Network (RAN) coverage.

The Network Slice Selection Function (NSSF) can make use of the fact that a same Fifth Generation (<NUM>) New Radio (NR) base station (gNB) reports support for "rejected S-NSSAIs. " A Next Generation Radio Access Network (NG-RAN) reports supported S-NSSAIs per TA during NG SETUP, and that information is propagated to the NSSF. There is a difference in that an Access and Mobility Management Function (AMF) can know per gNB basis about supported S-NSSAIs per TA, and then better assume if there is a high likelihood of overlap as the same gNB supports some S-NSSAIs. However, the NSSF only gets supported S-NSSAIs per TA, and not which gNB indicated it.

Non-patent literature CMCC: "<NPL>), discloses a discussion on RAN support of network slicing, wherein, a registration accept is send before a Release with Redirection (RwR) reconfiguration.

Non-patent literature <NPL>), discloses a "REGISTRATION REJECT" and "that if there is an S-NSSAI which is in the configured or Allowed NSSAI but not in the rejected NSSAI, the UE can re-attempt registration on the same PLMN". In addition, "the UE reattempts initial registration" and "if the UE had included requested NSSAI in the REGISTRATION REQUEST message and if the network decides to reject the request with cause #<NUM>, then the network also needs to include the relevant rejected NSSAI entries" and "it is necessary for the network to tell the UE whether the S-NSSAI is rejected for the registration area or for the entire PLMN/SNPN".

Methods and apparatus are disclosed herein for providing redirection and retry of registration. According to the present disclosure, there are provided methods, a user equipment and an access node according to the independent claims. Developments are set forth in the dependent claims. Embodiments of a method performed by a User Equipment (UE) of a Next Generation Radio Access Network (NG-RAN) of a cellular communication system to enable redirection and retry of registration are disclosed herein. The method comprises transmitting a Non-Access Stratum (NAS) registration request comprising one or more Single-Network Slice Selection Assistance Information (S-NSSAI) indicated as one or more requested S-NSSAI. The method further comprises receiving, in an Access Stratum (AS) protocol, an AS-level registration reattempt indication to instruct the UE to reattempt the NAS registration request in a target cell. The method also comprises reattempting the NAS registration in the target cell, responsive to receiving the AS-level registration reattempt indication.

In some embodiments disclosed herein, the AS protocol comprises a Radio Resource Control (RRC) protocol. Some embodiments disclosed herein provide that the method further comprises receiving a Release with Redirection (RwR) or RRC reconfiguration to redirect the UE to the target cell. According to some embodiments disclosed herein, the method further comprises receiving, by the UE, a NAS registration accept message. In some embodiments disclosed herein, the AS-level registration reattempt indication includes at least one S-NSSAI of the one or more S-NSSAI that caused a redirection from an original serving cell.

Some embodiments disclosed herein provide that reattempting the NAS registration in the target cell comprises attempting to establish an AS connection in the target cell. In such examples, the method further comprises, responsive to successfully attempting to establish the AS connection in the target cell, determining, by the UE based on the AS-level registration reattempt indication, to request a NAS registration requesting the one or more S-NSSAI, and sending, to an access node, another NAS registration request containing the one or more S-NSSAI. According to some embodiments disclosed herein, reattempting the NAS registration in the target cell comprises attempting to establish an AS connection in the target cell. According to such examples, the method further comprises, responsive to unsuccessfully attempting to establish the AS connection in the target cell, determining, by the UE based on the AS-level registration reattempt indication, whether to reconnect to the original serving cell or to any cell in range with a same Tracking Area Identity (TAI) as the original serving cell.

Embodiments of a UE of a NG-RAN of a cellular communication system to enable redirection and retry of registration are also disclosed herein. In some embodiments disclosed herein, the UE comprises one or more transmitters, one or more receivers, and processing circuitry associated with the one or more transmitters and the one or more receivers. The processing circuitry is configured to cause the UE to transmit a NAS registration request comprising one or more S-NSSAI indicated as one or more requested S-NSSAI. The processing circuitry is further configured to cause the UE to receive, in an AS protocol, an AS-level registration reattempt indication to instruct the UE to reattempt the NAS registration request in a target cell. The processing circuitry is also configured to cause the UE to reattempt the NAS registration in the target cell, responsive to receiving the AS-level registration reattempt indication. Some embodiments disclosed herein provide that the processing circuitry is additionally configured to cause the UE to perform the steps of any of the above-disclosed methods attributed to the UE.

Embodiments of a UE of a NG-RAN of a cellular communication system to enable redirection and retry of registration are also disclosed herein. According to some embodiments disclosed herein, the UE is adapted to transmit a NAS registration request comprising one or more S-NSSAI indicated as one or more requested S-NSSAI. The UE is further adapted to receive, in an AS protocol, an AS-level registration reattempt indication to instruct the UE to reattempt the NAS registration request in a target cell. The UE is also adapted to reattempt the NAS registration in the target cell, responsive to receiving the AS-level registration reattempt indication. In some embodiments disclosed herein, the UE is additionally adapted to perform the steps of any of the above-disclosed methods attributed to the UE.

Embodiments of a method performed in an access node of an NG-RAN of a cellular communication system to enable redirection and retry of a NAS registration. The method comprises determining that one or more of S-NSSAI requested by a UE in a NAS registration request cannot be served by an original serving cell or cannot be served at the NG-RAN. The method further comprises determining that the S-NSSAI requested by the UE in the NAS registration request can be served by a target cell in range. The method also comprises performing AS RwR or AS reconfiguration to redirect the UE to the target cell. The method additionally comprises transmitting, to the UE, an AS-level registration reattempt indication to instruct the UE to reattempt the NAS registration.

Some embodiments disclosed herein provide that the AS-level registration reattempt indication includes at least one of the one or more S-NSSAI causing redirection. According to some embodiments disclosed herein, the AS-level registration reattempt indication comprises the S-NSSAI causing redirection. In some embodiments disclosed herein, the AS-level registration reattempt indication comprises a list of S-NSSAIs that the UE can use in the target cell as requested Network Slice Selection Assistance Information (NSSAI). In some embodiments disclosed herein, the method further comprises receiving the one or more S-NSSAI from the UE in an RRC Setup Complete message or an RRC Resume Complete message. Some embodiments disclosed herein provide that the method further comprises receiving the one or more S-NSSAI causing redirection from an Access and Mobility Management Function (AMF).

Embodiments of an access node of a NG-RAN of a cellular communication system to enable redirection and retry of a NAS registration are also disclosed herein. According to some embodiments disclosed herein, the access node comprises at least one communication interface, and processing circuitry associated with the at least one communication interface. The processing circuitry is configured to cause the access node to determine that the S-NSSAI requested by the UE in the NAS registration request can be served by a target cell in range. The processing circuitry is further configured to cause the access node to determine that the S-NSSAI requested by the UE can be served by a target cell in range. The processing circuitry is also configured to cause the access node to perform AS RwR or AS reconfiguration to redirect the UE to the target cell. The processing circuitry is additionally configured to cause the access node to transmit, to the UE, an AS-level registration reattempt indication to instruct the UE to reattempt the NAS registration. In some embodiments disclosed herein, the processing circuitry is further configured to cause the access node to perform to perform the steps of any of the above-disclosed methods attributed to the access node.

Embodiments of an access node of a NG-RAN of a cellular communication system to enable redirection and retry of a NAS registration are also disclosed herein. Some embodiments disclosed herein provide that the access node is adapted to determine that one or more of S-NSSAI requested by a UE in a NAS registration request cannot be served by an original serving cell or cannot be served at the NG-RAN. The access node is further adapted to determine that the S-NSSAI requested by the UE in the NAS registration request can be served by a target cell in range. The access node is also adapted to perform AS RwR or AS reconfiguration to redirect the UE to the target cell. The access node is additionally adapted to transmit, to the UE, an AS-level registration reattempt indication to instruct the UE to reattempt the NAS registration. According to some embodiments disclosed herein, the access node is further adapted to perform to perform the steps of any of the above-disclosed methods attributed to the access node.

There currently exist certain challenge(s). In particular, in some scenarios a User Equipment (UE) may register using one or more Single-Network Slice Selection Assistance Information (S-NSSAI) in Requested NSSAI, one of which is not supported on the currently used cell or band. If the registration is rejected and the New Radio (NR) Base Station (NR Node B or "gNB") redirects the UE to a new cell or band where the network slice is supported, however, it is unclear how to ensure that the UE performs registration with the rejected S-NSSAI when the Release with Redirection (RwR) or Handover (HO) succeeds, and what happens if the RwR or HO does not succeed. If the UE tries to add an S-NSSAI to Allowed NSSAI and is denied by an Access and Mobility Function (AMF), the S-NSSAI slice is added to Rejected NSSAI, and UE is only allowed to request it again if it enters a new Registration Area (RA).

If the slice is available at another co-located cell, the Radio Access Network (RAN) may use Solution #<NUM> in 3GPP TR <NUM>-<NUM> to re-direct the UE to the other cell. This cell will have different slice support, and is therefore in another RA, so the RA is changed. This change, though, does not necessarily trigger the desired UE behavior.

There are, proposed herein, various embodiments which address one or more of the issues disclosed herein. One embodiment provides that, if the gNB detects that there is a not supported S-NSSAI in the Requested NSSAI (e.g., provided by the UE in Radio Resource Control (RRC) Setup Complete or RRC Resume Complete, or provided by the Core Network (CN) to the RAN via specific signaling after the UE performed a request for the S-NSSAI over Non-Access Stratum (NAS)), the gNB performs RwR or RRC reconfiguration (e.g., for handover) and sends a new indication to the UE (referred to herein as a "registration reattempt indication"), informing the UE that the redirection is for the purpose of allowing the UE to access the network slices as requested. The gNB indicates the S-NSSAI causing the redirection (i.e., the "redirect S-NSSAI"). If RwR succeeds, this new indication forces the UE to attempt registration in the new cell/band including all S-NSSAIs the UE may need to access (including the redirect S-NSSAI). If RwR fails, the UE stays on the current cell (i.e., the cell serving the UE before the RwR) or on a cell within the RA, and the UE removes the redirect S-NSSAI from Requested NSSAI and attempts registration again.

Another embodiment provides that, if the gNB detects that there are S-NSSAIs in the Rejected NSSAI (e.g., provided by the AMF to the RAN after the UE performed a request for the S-NSSAI over NAS) for which a redirect is possible, the gNB performs RwR or RRC reconfiguration (e.g., for Hand Over) and sends a new indication to the UE, informing the UE that the redirection is for the purpose of allowing the UE to access the rejected slice in the target cell of the RwR or HO. If the RwR or HO to new cell and TA succeeds, this new indication forces the UE to attempt registration in the new cell or band including the S-NSSAI(s) that was/were rejected for the previous RA. If the RwR or HO fails, the UE stays on current cell (i.e., the cell serving the UE before the RwR) or on a cell within the RA, knowing that it was forced to perform RwR due to S-NSSAI in requested NSSAI. The UE can then continue using the Allowed NSSAI without the rejected S-NSSAI.

Yet another embodiment operates the same as the previously described embodiment, but instead of a single indication, the Next Generation Radio Access Network (NG-RAN) provides a list of S-NSSAIs that the UE uses in the target cell (if redirection per RwR or HO succeeds) as Requested NSSAI. Namely, such list consists of a list of remapping S-NSSAIs that can be used instead of the requested S-NSSAI for establishment of the PDU Session resources needed for the UE.

Embodiments disclosed herein thus provide one or more of the following technical advantage(s). The point of signaling to the UE is that the RwR is for the purpose of connecting to the S-NSSAI(s) requested, but not possible to serve at the serving gNB. By sending the Target NSSAI indication, the UE knows that it needs to request for those slices again after redirection, and if redirection fails, the UE needs to connect back to the old cell for connection to any slice that was in use (or in the allowed NSSAI) before the RwR. The additional information proposed by solution #<NUM> in TR23. <NUM>-<NUM> implies the addition of much more information which makes the RRC message much larger (noting that UE could use the Frequency band per S-NSSAI information proposed by solution #<NUM> to derive that the UE should request the same S-NSSAI again at the target RA).

Before discussing methods and apparatus for providing redirection and retry of registration in greater detail, exemplary cellular communications systems in which some embodiments of the present disclosure may be implemented are first discussed. In this regard, the following terms are defined:.

Core Network Node: As used herein, a "core network node" is any type of node in a core network or any node that implements a core network function. Some examples of a core network node include, e.g., a Mobility Management Entity (MME), a Packet Data Network Gateway (P-GW), a Service Capability Exposure Function (SCEF), a Home Subscriber Server (HSS), or the like. Some other examples of a core network node include a node implementing an Access and Mobility Management Function (AMF), a User Plane Function (UPF), a Session Management Function (SMF), an Authentication Server Function (AUSF), a Network Slice Selection Function (NSSF), a Network Exposure Function (NEF), a Network Function (NF) Repository Function (NRF), a Policy Control Function (PCF), a Unified Data Management (UDM), or the like.

Transmission/Reception Point (TRP): In some embodiments, a TRP may be either a network node, a radio head, a spatial relation, or a Transmission Configuration Indicator (TCI) state. A TRP may be represented by a spatial relation or a TCI state in some embodiments. In some embodiments, a TRP may be using multiple TCI states.

<FIG> illustrates one example of a cellular communications system <NUM> in which embodiments of the present disclosure may be implemented. In the embodiments described herein, the cellular communications system <NUM> is a <NUM> system (5GS) including a NG-RAN and a <NUM> Core (5GC) or an Evolved Packet System (EPS) including an Evolved Universal Terrestrial RAN (E-UTRAN) and an Evolved Packet Core (EPC). In this example, the RAN includes base stations <NUM>-<NUM> and <NUM>-<NUM>, which in the 5GS include gNBs and optionally next generation eNBs (ng-eNBs) (e.g., LTE RAN nodes connected to the 5GC) and in the EPS include eNBs, controlling corresponding (macro) cells <NUM>-<NUM> and <NUM>-<NUM>. The base stations <NUM>-<NUM> and <NUM>-<NUM> are generally referred to herein collectively as base stations <NUM> and individually as base station <NUM>. Likewise, the (macro) cells <NUM>-<NUM> and <NUM>-<NUM> are generally referred to herein collectively as (macro) cells <NUM> and individually as (macro) cell <NUM>. The RAN may also include a number of low power nodes <NUM>-<NUM> through <NUM>-<NUM> controlling corresponding small cells <NUM>-<NUM> through <NUM>-<NUM>. The low power nodes <NUM>-<NUM> through <NUM>-<NUM> can be small base stations (such as pico or femto base stations) or Remote Radio Heads (RRHs), or the like. Notably, while not illustrated, one or more of the small cells <NUM>-<NUM> through <NUM>-<NUM> may alternatively be provided by the base stations <NUM>. The low power nodes <NUM>-<NUM> through <NUM>-<NUM> are generally referred to herein collectively as low power nodes <NUM> and individually as low power node <NUM>. Likewise, the small cells <NUM>-<NUM> through <NUM>-<NUM> are generally referred to herein collectively as small cells <NUM> and individually as small cell <NUM>. The cellular communications system <NUM> also includes a core network <NUM>, which in the 5GS is referred to as the 5GC. The base stations <NUM> (and optionally the low power nodes <NUM>) are connected to the core network <NUM>.

<FIG> illustrates a wireless communication system represented as a <NUM> network architecture composed of core Network Functions (NFs), where interaction between any two NFs is represented by a point-to-point reference point/interface. <FIG> can be viewed as one particular implementation of the system <NUM> of <FIG>.

Seen from the access side the <NUM> network architecture shown in <FIG> comprises a plurality of UEs <NUM> connected to either a RAN <NUM> or an Access Network (AN) as well as an AMF <NUM>. Typically, the R(AN) <NUM> comprises base stations, e.g., such as eNBs or gNBs or similar. Seen from the core network side, the 5GC NFs shown in <FIG> include a NSSF <NUM>, an AUSF <NUM>, a UDM <NUM>, the AMF <NUM>, a SMF <NUM>, a PCF <NUM>, and an Application Function (AF) <NUM>.

Reference point representations of the <NUM> network architecture are used to develop detailed call flows in the normative standardization. The N1 reference point is defined to carry signaling between the UE <NUM> and AMF <NUM>. The reference points for connecting between the AN <NUM> and AMF <NUM> and between the AN <NUM> and UPF <NUM> are defined as N2 and N3, respectively. There is a reference point, N11, between the AMF <NUM> and SMF <NUM>, which implies that the SMF <NUM> is at least partly controlled by the AMF <NUM>. N4 is used by the SMF <NUM> and UPF <NUM> so that the UPF <NUM> can be set using the control signal generated by the SMF <NUM>, and the UPF <NUM> can report its state to the SMF <NUM>. N9 is the reference point for the connection between different UPFs <NUM>, and N14 is the reference point connecting between different AMFs <NUM>, respectively. N15 and N7 are defined since the PCF <NUM> applies policy to the AMF <NUM> and SMF <NUM>, respectively. N12 is required for the AMF <NUM> to perform authentication of the UE <NUM>. N8 and N10 are defined because the subscription data of the UE <NUM> is required for the AMF <NUM> and SMF <NUM>.

The 5GC network aims at separating UP and CP. The UP carries user traffic while the CP carries signaling in the network. In <FIG>, the UPF <NUM> is in the UP and all other NFs, i.e., the AMF <NUM>, SMF <NUM>, PCF <NUM>, AF <NUM>, NSSF <NUM>, AUSF <NUM>, and UDM <NUM>, are in the CP. Separating the UP and CP guarantees each plane resource to be scaled independently. It also allows UPFs to be deployed separately from CP functions in a distributed fashion. In this architecture, UPFs may be deployed very close to UEs to shorten the Round Trip Time (RTT) between UEs and a Data Network (DN) <NUM> (which provides Internet access, operator services, and/or the like) for some applications requiring low latency.

The core <NUM> network architecture is composed of modularized functions. For example, the AMF <NUM> and SMF <NUM> are independent functions in the CP. Separated AMF <NUM> and SMF <NUM> allow independent evolution and scaling. Other CP functions like the PCF <NUM> and AUSF <NUM> can be separated as shown in <FIG>. Modularized function design enables the 5GC network to support various services flexibly.

In the CP, a set of interactions between two NFs is defined as service so that its reuse is possible. The UP supports interactions such as forwarding operations between different UPFs.

<FIG> illustrates a <NUM> network architecture using service-based interfaces between the NFs in the CP, instead of the point-to-point reference points/interfaces used in the <NUM> network architecture of <FIG>. However, the NFs described above with reference to <FIG> correspond to the NFs shown in <FIG>. The service(s) etc. that a NF provides to other authorized NFs can be exposed to the authorized NFs through the service-based interface. In <FIG> the service based interfaces are indicated by the letter "N" followed by the name of the NF, e.g., Namf for the service based interface of the AMF <NUM> and Nsmf for the service based interface of the SMF <NUM>, etc. The NEF <NUM> and the NRF <NUM> in <FIG> are not shown in <FIG> discussed above. However, it should be clarified that all NFs depicted in <FIG> can interact with the NEF <NUM> and the NRF <NUM> of <FIG> as necessary, though not explicitly indicated in <FIG>.

Some properties of the NFs shown in <FIG> and <FIG> may be described in the following manner. The AMF <NUM> provides UE-based authentication, authorization, mobility management, etc. A UE <NUM> even using multiple access technologies is basically connected to a single AMF <NUM> because the AMF <NUM> is independent of the access technologies. The SMF <NUM> is responsible for session management and allocates Internet Protocol (IP) addresses to UEs. It also selects and controls the UPF <NUM> for data transfer. If a UE <NUM> has multiple sessions, different SMFs <NUM> may be allocated to each session to manage them individually and possibly provide different functionalities per session. The AF <NUM> provides information on the packet flow to the PCF <NUM> responsible for policy control in order to support Quality of Service (QoS). Based on the information, the PCF <NUM> determines policies about mobility and session management to make the AMF <NUM> and SMF <NUM> operate properly. The AUSF <NUM> supports authentication function for UEs or similar and thus stores data for authentication of UEs or similar while the UDM <NUM> stores subscription data of the UE <NUM>. The Data Network (DN) <NUM>, not part of the 5GC network, provides Internet access or operator services and similar.

Aspects of some embodiments will now be discussed. For the sake of illustration, <FIG> reproduces <FIG>. <NUM>-<NUM> of 3GPP TR <NUM> v. <NUM>, with the addition of the "Target NSSAI Indication" included in step <NUM>. The description of Figure <NUM>. <NUM>-<NUM> of 3GPP TR <NUM> v. <NUM> applies except as otherwise described herein.

In one embodiment, the UE at step <NUM> of <FIG> may, per existing specifications, include an s-NSSAI-List in the RRCSetupComplete (see 3GPP TR <NUM>). Note, whether the UE includes the s-NSSAI-List is dependent on the Access Stratum Connection Establishment NSSAI Inclusion Mode (see clause <NUM>. <NUM> of 3GPP TS <NUM>). When the NG-RAN receives an s-NSSAI-List, the NG-RAN checks that the S-NSSAIs are allowed to be served by the current cell, and if not, the NG-RAN determines whether the S-NSSAIs could be served by a different cell in range. If so, the NG-RAN initiates step <NUM> (i.e., triggers an RwR), with the intention of allowing the UE to connect to the target cell that could serve the S-NSSAIs in the s-NSSAI-List. In this case, the new indication tells the UE to re-send the s-NSSAI-List again at the target cell.

In another embodiment, in step <NUM> of <FIG>, it can be seen that the AMF signals to the RAN the Target NSSAI, which includes the S-NSSAI that the UE requested at the serving RAN and that could not be served at serving RAN. At reception of the Target NSSAI, the serving RAN is able to determine whether the Target NSSAI could be served by a different cell in range. The serving RAN thus triggers a RwR as in step <NUM> of <FIG>, with the intention of allowing the UE to connect to the target cell that could serve the Target NSSAI.

When the UE has been redirected and successfully establishes an RRC connection with the redirection target cell, the UE sends a Requested NSSAI as in step <NUM> of <FIG>. The UE uses the new indication received in the RwR of step <NUM> of <FIG> to determine whether to re-send, in step <NUM> of <FIG>, the S-NSSAI that was rejected for the RA in step <NUM> of <FIG>.

Alternatively, if the redirection of the UE is unsuccessful (i.e., the UE was not able to access the redirection target cell), then the UE uses the new indication received in the RwR of step <NUM> of <FIG> to determine that the redirection was for the purpose of letting the UE request the slice rejected in the source cell. With this information at hand, the UE is able to determine whether it should re-connect to the original serving cell or to any cell in range with the same TAI as the original serving cell, in order to access the slices in the Allowed NSSAI provided when in the source cell.

In another embodiment, and with respect to <FIG>, the procedures after step <NUM> may be modified as described below:.

Step <NUM>: The serving RAN decides to hand over the UE to another target cell in range that can serve the S-NSSAI(s) that were rejected for the UE at the registration in step <NUM> of <FIG>. As part of the HO command signaled to the UE to trigger mobility towards the selected target cell, the serving RAN includes the TargetNSSAI indication, which is received by the UE before handover execution.

Step <NUM>: The UE successfully executes the HO to the target cell. The UE uses the TargetNSSAI indication received in the HO Command in step <NUM> of <FIG> to determine whether to re-send in the new registration triggered at step <NUM> of <FIG> (as part of the RRC access to the target cell) the S-NSSAI that was rejected for the RA in step <NUM> of <FIG>.

Alternatively, if the handover execution was unsuccessful (i.e., the UE was not able to access the target cell), then the UE uses the new indication received in the HO Command in step <NUM> of <FIG> to determine that the handover was for the purpose of letting the UE request the slice rejected in the source cell. With this information at hand, the UE is able to determine that it should re-connect to the original serving cell or to any cell in range with the same TAI as the original serving cell, in order to access the slices in the Allowed NSSAI provided when in the source cell.

Tables <NUM>-<NUM> below illustrate an implementation of an indication of S-NSSAI to be accessed after RwR, according to some embodiments. This implementation is based on the RRCRelease message specified in 3GPP TR <NUM> v16. <NUM> which is used as reference, with the addition of the newly added TargetNSSAI:
<IMG>.

It is noted that information elements (IEs) similar to the ones provided above as part of the RRCRelease message could be used for the Target NSSAI indication (namely in cases where the RAN performs mobility of the UE to a target cell in order to let it access the requested s-NSSAI). In such a case, the IEs proposed in the example above may be added as part of the HandoverCommand or RRCReconfiguration message.

Tables <NUM>-<NUM> below illustrate another implementation of an indication of RwR to access a Rejected S-NSSAI according to some embodiments.

One possible way to implement the method based on release and redirection described above is shown below. In this embodiment, the RRCRelease message specified in 3GPP TR <NUM> v16. <NUM> is used as reference with a new flag added to indicate to the UE that the RwR is for the purpose of accessing the S-NSSAI(s) that was rejected in the source RAN. Note that some embodiments may provide that the new flag indicates that the RwR was due to an S-NSSAI not allowed in a current cell, and an additional list of S-NSSAIs may optionally be included as additional data.

<FIG> provides a flowchart <NUM> that illustrates exemplary operations performed by a network node, such as a base station <NUM> or <NUM>, for providing redirection and retry of registration. In <FIG>, operations begin with a network node determining that an S-NSSAI requested by a UE cannot be served by an original serving cell or cannot be served at a serving RAN (block <NUM>). The network node determines that the S-NSSAI can be served by a target cell in range (block <NUM>). The network node then performs RwR or RRC reconfiguration to redirect the UE to the target cell (block <NUM>). The network node then transmits, to the UE, a registration reattempt indication to instruct the UE to reattempt registration including the S-NSSAI causing the redirection (block <NUM>).

In some examples, the UE receives the registration reattempt indication (block <NUM>). The UE then attempts to establish an RRC connection with the target cell (block <NUM>). If the attempt is successful, the UE determines, based on the registration reattempt indication, whether to resend the S-NSSAI (block <NUM>). The UE then sends the S-NSSAI to a network node of the target cell (block <NUM>). For example, the UE may send the S-NSSAI as a list of S-NSSAIs in NAS as a requested NSSAI, and optionally in RRC message <NUM>. However, if the attempt is unsuccessful, the UE determines, based on the registration reattempt indication, whether to reconnect to the original serving cell or to any cell in range with a same TAI as the original serving cell (block <NUM>).

<FIG> is a schematic block diagram of a radio access node <NUM> according to some embodiments of the present disclosure. Optional features are represented by dashed boxes. The radio access node <NUM> may be, for example, a base station <NUM> or <NUM> or a network node that implements all or part of the functionality of the base station <NUM> or gNB described herein. As illustrated, the radio access node <NUM> includes a control system <NUM> that includes one or more processors <NUM> (e.g., Central Processing Units (CPUs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), and/or the like), memory <NUM>, and a network interface <NUM>. The one or more processors <NUM> are also referred to herein as processing circuitry. In addition, the radio access node <NUM> may include one or more radio units <NUM> that each includes one or more transmitters <NUM> and one or more receivers <NUM> coupled to one or more antennas <NUM>. The radio units <NUM> may be referred to or be part of radio interface circuitry. In some embodiments, the radio unit(s) <NUM> is external to the control system <NUM> and connected to the control system <NUM> via, e.g., a wired connection (e.g., an optical cable). However, in some other embodiments, the radio unit(s) <NUM> and potentially the antenna(s) <NUM> are integrated together with the control system <NUM>. The one or more processors <NUM> operate to provide one or more functions of a radio access node <NUM> as described herein. In some embodiments, the function(s) are implemented in software that is stored, e.g., in the memory <NUM> and executed by the one or more processors <NUM>.

As used herein, a "virtualized" radio access node is an implementation of the radio access node <NUM> in which at least a portion of the functionality of the radio access node <NUM> is implemented as a virtual component(s) (e.g., via a virtual machine(s) executing on a physical processing node(s) in a network(s)). As illustrated, in this example, the radio access node <NUM> may include the control system <NUM> and/or the one or more radio units <NUM>, as described above. The control system <NUM> may be connected to the radio unit(s) <NUM> via, for example, an optical cable or the like. The radio access node <NUM> includes one or more processing nodes <NUM> coupled to or included as part of a network(s) <NUM>. If present, the control system <NUM> or the radio unit(s) are connected to the processing node(s) <NUM> via the network <NUM>. Each processing node <NUM> includes one or more processors <NUM> (e.g., CPUs, ASICs, FPGAs, and/or the like), memory <NUM>, and a network interface <NUM>.

In this example, functions <NUM> of the radio access node <NUM> described herein are implemented at the one or more processing nodes <NUM> or distributed across the one or more processing nodes <NUM> and the control system <NUM> and/or the radio unit(s) <NUM> in any desired manner. In some particular embodiments, some or all of the functions <NUM> of the radio access node <NUM> described herein are implemented as virtual components executed by one or more virtual machines implemented in a virtual environment(s) hosted by the processing node(s) <NUM>. As will be appreciated by one of ordinary skill in the art, additional signaling or communication between the processing node(s) <NUM> and the control system <NUM> is used in order to carry out at least some of the desired functions <NUM>. Notably, in some embodiments, the control system <NUM> may not be included, in which case the radio unit(s) <NUM> communicate directly with the processing node(s) <NUM> via an appropriate network interface(s).

<FIG> is a schematic block diagram of a wireless communication device <NUM> according to some embodiments of the present disclosure. As illustrated, the wireless communication device <NUM> includes one or more processors <NUM> (e.g., CPUs, ASICs, FPGAs, and/or the like), memory <NUM>, and one or more transceivers <NUM> each including one or more transmitters <NUM> and one or more receivers <NUM> coupled to one or more antennas <NUM>. The transceiver(s) <NUM> includes radio-front end circuitry connected to the antenna(s) <NUM> that is configured to condition signals communicated between the antenna(s) <NUM> and the processor(s) <NUM>, as will be appreciated by on of ordinary skill in the art. The processors <NUM> are also referred to herein as processing circuitry. The transceivers <NUM> are also referred to herein as radio circuitry. In some embodiments, the functionality of the wireless communication device <NUM> described above may be fully or partially implemented in software that is, e.g., stored in the memory <NUM> and executed by the processor(s) <NUM>. Note that the wireless communication device <NUM> may include additional components not illustrated in <FIG> such as, e.g., one or more user interface components (e.g., an input/output interface including a display, buttons, a touch screen, a microphone, a speaker(s), and/or the like and/or any other components for allowing input of information into the wireless communication device <NUM> and/or allowing output of information from the wireless communication device <NUM>), a power supply (e.g., a battery and associated power circuitry), etc..

implemented in software.

Claim 1:
A method performed in a User Equipment, UE, (<NUM>) of a Next Generation Radio Access Network, NG-RAN, of a cellular communication system to enable redirection and retry of registration, the method comprising:
transmitting (<NUM>) a Non-Access Stratum, NAS, registration request comprising one or more Single-Network Slice Selection Assistance Information, S-NSSAI, indicated as one or more requested S-NSSAI;
receiving (<NUM>), in an Access Stratum, AS, protocol, an AS-level registration reattempt indication to instruct the UE to reattempt the NAS registration request in a target cell; and
reattempting (<NUM>) the NAS registration in the target cell, responsive to receiving the AS-level registration reattempt indication.