WO2019193184A1

WO2019193184A1 - Extended buffering of downlink (dl) data in a communications network

Info

Publication number: WO2019193184A1
Application number: PCT/EP2019/058712
Authority: WO
Inventors: Qian Chen; Paul Schliwa-Bertling; Stefan Rommer; Hans Bertil RÖNNEKE; Roland Gustafsson
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2018-04-05
Filing date: 2019-04-05
Publication date: 2019-10-10
Also published as: EP3777350A1

Abstract

The embodiments herein relate to the extended buffering of downlink (DL) in a communications network. The embodiments comprises methods performed by an Access Network, AN, an Access and Mobility Management Function, AMF, as well as a Core Network Function, CNF, respectively. Further, the embodiments comprises a corresponding AN, AMF, and CNF, respectively configured to perform the methods.

Description

EXTENDED BUFFERING OF DOWNLINK (DL) DATA IN A COMMUNICATIONS

NETWORK

TECHNICAL FIELD

Disclosed are embodiments related to the extended buffering of downlink (DL) in a

communications network.

BACKGROUND

As described in 3GPP TR 23.724 v.0.2.0, extended buffering of downlink data in the network is one mechanism for handling high latency communication. High latency refers to the initial response time before normal exchange of packets is performed. That is, the time it takes before a user equipment (UE) (i.e., a device capable of wireless communication with an access point (e.g., a 5G base station (gNB)) has woken up from its power saving state and responded to the initial downlink packet(s).

Extended buffering encompasses a network node storing downlink (DL) data (i.e., data addressed to a UE) until the UE wakes up or is expected to wake up from a power saving state and moves to a connected state (e.g., ECM-CONNECTED), at which time the DL data is conveyed to the UE. For example, extended buffering encompasses a network node storing DL data for a UE at least until i) the network node receives a notification that the UE is reachable, at which time the network node transmits the DL data toward the UE or ii) a buffer duration time has expired.

SUMMARY

A new Radio Resource Control (RRC) state is defined in New Radio (NR). This new state is the RRC Inactive state. A UE can transition to the RRC Inactive state from the RRC

Connected stated, and the UE can transition to the RRC Connected state from the RRC

Inactive state. When the UE is in the RRC Inactive state the UE is not reachable, and it would be advantageous for the communications network to store downlink data for the UE until the UE becomes reachable. Implementing extended buffering in the access network (AN) (e.g., radio access network (RAN)) portion of the communications network when the UE is in RRC Inactive, however, is not ideal. A better approach is to implement the extended buffering in the core network portion of the communications network (e.g., in the User Plane Function (UPF) or in the Session Management Function (SMF)) not only when the UE is in CM-IDFE but also when the UE is in CM-CONNECTED-with-RRC-Inaetive. Such an approach simplifies the overall system architecture. Additionally, this approach is advantageous for at least the reason that it avoids DL data being sent to the RAN when the UE is in CM-CONNECED-with-RRC Inactive and not reachable due to that it is in a power saving state such as Extended DRX (eDRX) or DRX set with a long DRX time (in terms of minutes or hours). Furthermore, buffering in SMF/UPF avoids data being forwarded from one AN node to another if the UE wakes up in another AN node after its power saving interval.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments.

FIG. 1 illustrates a communications network according to one embodiment.

FIG. 2 is a flow chart illustrating a process according to one embodiment.

FIG. 3 is a message flow diagram according to one embodiment.

FIG. 4 is a flow chart illustrating a process according to one embodiment.

FIG. 5 is a message flow diagram according to one embodiment.

FIG. 6 is a flow chart illustrating a process according to one embodiment.

FIG. 7 is a message flow diagram according to one embodiment.

FIG. 8 is a flow chart illustrating a process according to one embodiment.

FIG. 9 is a flow chart illustrating a process according to one embodiment.

FIG. 10 is a flow chart illustrating a process according to one embodiment.

FIG. 11 is a flow chart illustrating a process according to one embodiment. FIG. 12 is a flow chart illustrating a process according to one embodiment.

FIG. 13 is a block diagram of a network node according to one embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a communications network 100 according to one embodiment. More specifically, FIG. 1 illustrates a UE 101 that is connected to an access network (AN) 103, which may be a RAN. AN 103 is connected to an Access and Mobility Management Function (AMF) 105 via a N2 reference point, and UE 101 is connected to AMF 105 via a Nl reference point. AMF 105 is adapted to be connected to a Session Management Function (SMF) 108 via a Nl 1 reference point. SMF 108 is adapted to be connected to a User plane Function (UPF) 125 via an N4 reference point, and AN 103 is adapted to be connected to UPF 125 via a N3 reference point. UPF 125 is adapted to be connected to a data network (DN) 120 via a N6 reference point. The DN may be e.g. operator services, Internet access or 3rd party services. The AMF 105 is adapted to be connected to an Authentication Server Function (AUSF) 128 via a N12 reference point. The AMF 105 is adapted to be connected to a Network Slice Selection Function (NSSF) 129 via a N22 reference point. The AMF 105 is adapted to be connected to a Unified Data Management (UDM) 130 via a N8 reference point. The AUSF 128 is adapted to be connected to the UDM 130 via the N13 reference point. The SMF 108 is adapted to be connected to the UDM 130 via a N10 reference point. The SMF 108 is adapted to be connected to a Policy Control function (PCF) 133 via a N7 reference point. The PCF 133 is adapted to be connected to an Application Function (AF) 135 via a N5 reference point. The PCF 133 is adapted to be connected to the AMF 105 via a N15 reference point. A reference point may also be referred to as an interface.

UE 101 may be any device, mobile or stationary, enabled to communicate over a radio channel in the communications network, for instance but not limited to e.g. user equipment, mobile phone, smart phone, sensors, meters, vehicles, household appliances, medical appliances, media players, cameras, Machine to Machine (M2M) device or any type of consumer electronic, for instance but not limited to television, radio, lighting arrangements, tablet computer, laptop or Personal Computer (PC). UE 101 may be portable, pocket storable, hand held, computer comprised, or vehicle mounted devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another UE or a server.

The (R)AN 103 may comprise a RAN node (not shown in figure 1) such as a NodeB, an eNodeB, a gNB or any other network unit capable to communicate over a radio carrier with the UE 101. The abbreviations AN and RAN may be used interchangeably herein when referring to an access network, a radio access network, or a node (e.g., gNB or other base station) comprised in the access network. The AN may include both 3GPP radio access network and non-3GPP access network. A typical non-3GPP access network is a Wi-Fi network. The embodiments in this application apply to both 3GPP radio access network and non-3GPP access network.

Described herein are various options for extended buffering of DL data for UE 101 .

FIG. 2 is flowchart illustrating a process 200 for extended buffering of DL data according to one embodiment. Process 200 may begin in step s202.

In step s202, SMF/UPF 125 receives DL data 302 (see FIG. 3) for UE 101 that originated from, for example, an application server (AS), and the SMF/UPF delivers the DL data 302 to RAN 103 (e.g., UPF 125 may deliver the DL data to AN 103 using an existing N3 tunnel).

In step s204, RAN 103 receives the DL data and checks the UE reachability in RRC Inactive mode. If UE is not reachable (e.g., due to Key Issue 4 (eDRX/DRX) or if RAN paging fails), the RAN sends to AMF 105 a notification 304 (e.g. an N2 Notification) to indicate the

unreachability and data delivery failure. RAN 103 may also provide buffering support information.

An example of buffering support information that RAN 103 may provide to the AMF 105 is information indicating a time at which the UE is expected to be reachable (“expected wake up time” for the UE). If the UE applies eDRX, the AMF may know how long the UE“sleeps” in between the wake windows (i.e. the eDRX/DRX interval), but the AMF does not know the exact “phase”, i.e. when a wake up interval ends or starts. So, at a given point in time when the RAN provides“buffering support information” to the AMF, the RAN can tell the AMF how much time it is left before the UE wakes up and listens to paging (i.e., is expected to be reachable). Another possible“buffering support information” is the length of time the UE is awake and listening for paging (“Paging Time Window”). The RAN knows this but not always the AMF.

If the UE was not reachable due to eDRX/DRX (Key Issue 4), the RAN schedules a paging of the UE 101 next time it will be reachable by paging. If the UE was not reachable for other reasons (e.g., RAN paging failed when UE was unreachable (e.g. the UE was located

underground or in a tunnel)), RAN may schedule additional paging(s) until a certain duration which is notified as buffering supporting info to AMF in step s204.

In step s206, AMF 105 sends to SMF 108 a notification 306 indicating UE unreachability and data delivery failure. AMF 105 also provides extended data buffering support information (e.g. buffering duration and/or information indicating the time at which the UE is expected to become reachable) based on known info (e.g. negotiated eDRX interval or DRX interval) and/or buffering supporting info from RAN in step s204. The AMF can use the existing

Nsmf_PDUSession_UpdateSMContext service, Namf_EventExpousre_Notify service, or any new service to deliver the notification and buffering support information to SMF 108. Similarly, if the UPF is buffering the data rather than the SMF 108, the SMF 108 sends to the UPF a notification 306 indicating the UE unreachability and data delivery failure, which notification may include the buffering support information.

In step s208, in response to receiving the data delivery failure notification, SMF/UPF initiates extended data buffering of the DF data. For example, the SMF/UPF may provide data forwarding tunnel info 308 to RAN via AMF through

Namf_Communication_NlN2MessageTransfer. The N2 message contains UF forwarding tunnel information. The message can either be new N2 message or modification of an existing N2 message, i.e. PDU session resource modification. The RAN forwards the DF data 302 received in step s202 to SMF/UPF where it is then stored for at least a certain amount of time denoted the “buffer duration time.”

After step s208, either steps s2l0 and s2l2 are performed or steps s2l4 and s2l6 are performed.

In step s2l0, at next UE contact with the network (e.g. after a paging initiated at step s204 or after a mobile originated (MO) event), AMF receives a N2 notification 310 triggered by an RRC resume or a N2 Path Switch Request if RRC resume triggers a RAN node change, and the AMF then notifies SMF/UPF of the UE reachability.

In step s2l2, as a result of receiving the UE reachability notification transmitted by the AMF in step s2l0 before the buffered DL data has been discarded, SMF/UPF delivers the buffered DF data 302 to UE (i.e., delivers the DF data to the RAN, which then provides the data to the UE).

In step s2l6, the SMF/UPF discards the DF data as a result of not receiving a UE reachability notification within a certain window of time. For example, the SMF/UPF may start a buffer duration timer after receiving the UE data delivery failure notification and if the buffer duration timer reaches a certain value before the reachability notification is received, then the SMF/UPF discards the DF data. For example, as shown in FIG. 2, in step s2l4 SMF/UPF detects that a buffer duration timer has expired and, as a consequence, performs step s2l6 (i.e., discards the buffered DF data 302).

FIG. 4 is flowchart illustrating a process 400 for extended buffering of DF data according to one embodiment. Process 400 may begin in step s402. In step s402, RAN 103 sends a notification 502 (see FIG. 5) to AMF 105 regarding UE 101. In this example, the notification is a notification (e.g., an N2 notification) indicating that the RAN has placed the UE 101 in RRC Inactive state and the UE is in power save mode due to KI4 (e.g., eDRX/DRX). The notification may include buffering support information.

In step s404, in response to receiving the notification 502, The AMF sends to SMF/UPF a notification 504 that a PDU session for UE 101 is subject for extended data buffering and provides buffering support information (e.g. buffering duration) based on known info (e.g.

negotiated eDRX/DRX interval) and/or buffering supporting info from RAN. The message used by AMF to send to SMF/UPF the notification and buffer support information can be the existing Nsmf_PDUSession_UpdateSMContext service or Namf_EventExpousre_Notify service, or any new service to deliver the information. If data is buffered in the UPF and not in SMF, the SMF can send the notification 504 to the UPF.

In step s406, the AS sends downlink (DF) data for the UE 101, which DF data is received by the SMF/UPF. In step s408, rather than provide the received DL data to the AN 103 without delay, the

SMF/UPF will start to apply extended data buffering for the received DL data based on the indication received in step s404 (e.g. using the duration for the extended buffering). For example, in step s408, based on the indication received in step s404, the SMF/UPF in response to receiving the DL data stores the DL data and then begins monitoring how long the data has been buffered (e.g., the SMF/UPF starts a buffer duration timer). If the DL data is still“in” the buffer (e.g., the memory locations holding the DL data are not marked as being free) when the timer indicates that a certain amount of time (buffer duration time) has elapsed since the DL data was placed in the buffer, the SMF/UPF will discard the data from the buffer (e.g., mark the memory location that is storing the DL data as being free).

In step s4l0, the SMF/UPF may enable UE reachability reporting. For example, in response to receiving a notification from the UPF (which notification from the UPF can be similar to the downlink data notification (DDN) in CM-IDLE mode or a modification of the existing DDN message), the SMF may transmit to the AMF a Namf_MT_EnableUEReachability service message 508 (see FIG 5.) to enable the UE reachability reporting.

In response to receiving message 508, the AMF may use the N2 Notification procedure to retrieve UE reachability information from the RAN (see message 510 in FIG. 5). In reply to message 510, RAN may send message 512, which may include information indicating whether or not UE 101 is reachable and new buffering support information, if there is any.

In step s4l2, the AMF notifies the SMF/UPF with the latest reachability information (see message 514). If the UE is still not reachable then message 514 may include new buffering support information (e.g., information identifying an updated buffering duration time). If message 514 indicates that the UE is reachable, then the process may jump to step s4l6, where the SMF/UPF delivers the buffered DF data to the UE.

As further shown in FIG. 5, at next UE contact with the network (e.g. after a paging or after a mobile originated (MO) event), the AMF receives a N2 notification 516 triggered by an RRC resume or a N2 Path Switch Request if RRC resume triggers a RAN node change, and the AMF then notifies SMF/UPF of the UE reachability. Assuming, the SMF/UPF has not discarded the DL data, then SMF/UPF performs step s4l6 in response to receiving from the AMF the message indicating that the UE is now reachable.

In step s4l8, the SMF/UPF determines that the buffer duration timer has expired. In response, the SMF/UPF discards the buffered DL data (step s420).

FIG. 6 is flowchart illustrating a process 600 for extended buffering of DL data according to one embodiment. Process 600 may begin in step s602.

In step s602, RAN 103 sends a notification 702 (see PIG. 7) to AMP 105 regarding UE 101. In this example, the notification is an notification (e.g., an N2 notification) indicating that the RAN has placed the UE 101 in RRC Inactive state and the UE is in power save mode due to KI4 (e.g., eDRX/DRX). The notification may include buffering support information.

In step s604, in response to receiving the notification 702, The AMF sends to SMF/UPF a notification 704 that a PDU session for UE 101 is subject for extended data buffering and provides buffering support information (e.g. buffering duration) based on known info (e.g.

negotiated eDRX/DRX interval) and/or buffering supporting info from RAN. The message used by AMF to send to SMF/UPF the notification and buffer support information can be the existing Nsmf_PDUSession_UpdateSMContext service or Namf_EventExpousre_Notify service, or any new service to deliver the information. If data is buffered in the UPF and not in SMF, the SMF can send the notification 704 to the UPF.

In step s606, the AS sends downlink data 706 for the UE 101, which DL data 706 is received and stored by the SMF/UPF.

In step s608, the SMF/UPF will start to apply extended data buffering for the received DL data 706 based on the indication received in step s604 (e.g. using the duration for the extended buffering), and the SMF/UPF provides at least some of the DL data 706 to the RAN.

In step s6l0, RAN 103 receives the DL data provided in step s608 and checks the UE reachability in RRC Inactive mode. If UE is not reachable (e.g., due to Key Issue 4

(eDRX/DRX) or if RAN paging fails), the RAN sends to AMF 105 a notification 710 (e.g. an N2 Notification) to indicate the unreachability and data delivery failure. RAN 103 also provides buffering support information, if there is any. If the UE was not reachable due to eDRX/DRX (Key Issue 4), the RAN schedules a paging of the UE 101 next time it will be reachable by paging. If the UE was not reachable for other reasons (e.g., RAN paging failed when UE was unreachable (e.g. the UE was located underground or in a tunnel)), RAN may schedule additional paging(s) until a certain duration which is notified as buffering supporting info to AMF in step s6l0.

In step s6l2, AMF 105 sends to SMF 108 a notification 306 indicating UE unreachability and data delivery failure. AMF 105 also provides extended data buffering support information (e.g. buffering duration) based on known info (e.g. negotiated eDRX interval or DRX interval) and/or buffering supporting info from RAN in step s6l0. The AMF can use the existing

Nsmf_PDUSession_UpdateSMContext service, Namf_EventExpousre_Notify service, or any new service to deliver the notification and buffering support information to SMF 108. Similarly, if the UPF is buffering the data rather than the SMF 108, the SMF 108 sends to the UPF a notification 306 indicating the UE unreachability and data delivery failure, which notification may include the buffering support information. After step s6l2, either steps s6l4 and s6l6 are performed or steps s6l8 and s620 are performed.

In step s6l4, at next UE contact with the network (e.g. after a paging initiated at step s204 or after a mobile originated (MO) event), AMF receives from the RAN a N2 notification 310 triggered by an RRC resume or a N2 Path Switch Request if RRC resume triggers a RAN node change, and the AMF then notifies SMF/UPF of the UE reachability.

In step s6l6, as a result of receiving the UE reachability notification transmitted by the AMF in step s6l4 before the buffered DF data has been discarded, SMF/UPF delivers the buffered DF data 706 to the UE (i.e., delivers the DF data to the RAN, which then provides the data to the UE).

In step s620, the SMF/UPF discards the buffered data as a result of not receiving a UE reachability notification within a certain window of time (i.e. buffer duration time). For example, the SMF/UPF may start a timer after receiving the UE data delivery failure notification and if the timer reaches a certain value before the reachability notification is received, then the SMF/UPF discards the buffered DF data. For example, as shown in FIG. 6, in step s6l8 SMF/UPF detects that a buffer duration timer has expired and, as a consequence, performs step s620 (i.e., discards the buffered DL data 302).

FIG. 8 is a flow chart illustrating a process 800, according to one embodiment, that is performed by AN 103 (e.g., performed by a node of AN 103, such as a gNB or other node). Process 800 may begin in step s802.

In step s802, the AN receives DL data for UE 101.

In step s804, the AN determines that the UE is in the RRC Inactive state and determines that the UE is not reachable (e.g., determines that the UE is currently in a temporary power savings mode or determines that the UE has not responded to a page).

In step s806, as a result of determining that the UE is in the RRC Inactive state and is not reachable, the AN provides to AMF 105 a notification (e.g., an N2 Notification) indicating that the UE is not reachable. In step s806, the AN may also provide to the AMF buffering support information for the UE (e.g., information comprising a value indicating a time duration for buffering DL data for the UE). In some embodiments, the AN may also schedule a paging of the UE (step s8l0). For example, as a result of the AN determining that the UE is not reachable because the UE is in a temporary power saving mode (e.g., eDRX/DRX) (Key issue 4), the AN may schedule a paging of the UE to occur at a time when the UE is no longer in the power saving mode. As another example, the AN may, during a certain window of time, schedule paging for the UE. This certain window of time may correspond to the time duration identified by the buffering support information.

In some embodiments, the AN may receive data forwarding tunnel information transmitted by a network function (e.g., SMF 108 or UPF 125) (step s8l2). In such an embodiment, as a result of determining that the UE is in the RRC Inactive state and is not reachable, the AN uses the data forwarding tunnel information to forward to a network function the received DL data so that the network function can buffer the DL data for an extended period of time.

FIG. 9 is a flow chart illustrating a process 900, according to one embodiment, that is performed by AN 103 (e.g., performed by a node of AN 103, such as a gNB or other node). Process 900 may begin in step s902. In step s902, the AN decides to place UE 101 in the RRC Inactive state. For example, the AN may place the UE in the RRC Inactive state at a time during which the UE 101 is in a power savings mode or about to enter the power savings mode.

In step s904, the AN provides to AMF 105 a notification (e.g., an N2 Notification) indicating that the UE is not reachable. In step s904, the AN may also provide to the AMF buffering support information for the UE (e.g., information comprising a value indicating a time duration for buffering DL data for the UE).

In some embodiments, in response to a request from AMF 105, the AN may provide to the AMF updated buffering support information for the UE (step s906). In some embodiments, process 900 may further includes steps s908-s9l2. In step s908,

In step s908, the AN receives DL data for the UE.

In step s9l0, the AN determines that the UE is in the RRC Inactive state and determines that the UE is not reachable (e.g., determines that the UE is currently in a temporary power savings mode or determines that the UE has not responded to a page).

In step s9l2, as a result of determining that the UE is in the RRC Inactive state and is not reachable, the AN provides to AMF 105 a notification (e.g., an N2 Notification) indicating that the UE is not reachable.

FIG. 10 is a flow chart illustrating a process 1000, according to one embodiment, that is performed by AMF 105. Process 1000 may begin in step sl002.

In step sl002, the AMF receives a notification transmitted by AN 103, wherein the notification includes information indicating that UE 101 is not reachable (e.g., information indicating that the UE has been placed in the RRC Inactive state and is not reachable). The information may further include a data delivery failure indication if the AN was unable to deliver DL data to the UE. The information may also include buffering support information.

In step sl004, the AMF, in response to receiving the notification transmitted by the AN, sends a notification to SMF 108, wherein the notification sent to SMF 108 comprises information indicating that the UE is not reachable (i.e., information indicating that DL data for the UE is subject to extended data buffering). The notification sent in step sl004 may further include buffering support information. For example, the buffering support information included in the notification sent in step sl004 may be based on the UE’s eDRX or DRX interval.

FIG. 11 is a flow chart illustrating a process 1100, according to one embodiment, that is performed by a core network function (CNF) (e.g., SMF 108 or UPF 115). Process 1100 may begin in step s 1102.

In step sl 102, the CNF receives DL data for UE 101.

In step sl 104, the CNF provides the DL data for the UE to AN 103.

In step sl 106, after performing step sl 104, the CNF receives a first notification comprising information indicating that the DL data for the UE that was provided to the AN has not been delivered to the UE. The notification may further comprise buffering support information.

In step sl 108, after receiving the first notification, the CNF initiates extended buffering of the DL data. In some embodiments, initiating extended buffering of the DL data includes the CNF providing address information (e.g., tunnel endpoint information) to the AN so that the AN can send the DL data back to the CNF so that the CNF can receive the DL data and then store the DL data. In some embodiments, initiating extended buffering of the DL data includes the CNF obtaining a buffer duration time for the DL data (i.e., obtaining information specifying the buffer duration time) and setting a buffer duration timer to expire at the end of the buffer duration time. Obtaining the buffer duration time for the DL data may be performed by determining the buffer duration time based on the received buffering support information.

After step sl 108, the CNF either performs step sl 110 or it performs step sl 112.

In step sl 110, the CNF discards the buffered DL data in response to detecting that the buffer duration time for the DL data has elapsed (e.g., in response to detecting the expiration of the buffer duration timer).

In step sl 112, the CNF provides the buffered DL data to an AN in response to receiving a second notification indicating that the UE is reachable. The AN to which the DL data is provided in step sl 112 may be the same AN to which the DL data was provided in step sl 104 or it may be a different AN (e.g., the UE may have moved from one AN to another AN while it was unreachable). FIG. 12 is a flow chart illustrating a process 1200, according to one embodiment, that is performed by a core network function (CNF) (e.g., SMF 108 or UPF 125). Process 1200 may begin in step sl202.

In step sl202, the CNF receives a first notification concerning UE 101 as a result of AN 103 placing the UE in the RRC Inactive state. The first notification may comprise buffering support information.

In step sl204, after the CNF receives the first notification, the CNF receives DL data for the UE and stores the received DL data.

In step sl206, after receiving the DL data and based on the first notification, the CNF initiates the extended buffering of the received DL data. In some embodiment, initiating the extended buffering of the received DL data includes the CNF obtaining a buffer duration time for the DL data and setting a buffer duration timer to expire at the end of the buffer duration time.

Obtaining the buffer duration time for the DL data may be performed by determining the buffer duration time based on the received buffering support information. After step sl206, the CNF either performs step sl208 or it performs step sl2l0.

In step sl208, the CNF discards the stored DL data in response to detecting that a buffer duration time for the DL data has elapsed (e.g., in response to detecting the expiration of a timer).

In step sl2l0, the CNF provides the buffered DL data to an AN in response to receiving a second notification indicating that the UE is reachable.

FIG. 13 is a block diagram of network node 1301, according to some embodiments, that can implement any one or more of: AN 103, AMF 105, SMF 108, UPF 125. As shown in FIG. 13, network node 1301 may comprise: processing circuitry (PC) 1302, which may include one or more processors (P) 1355 (e.g., a general purpose microprocessor and/or one or more other processors, such as an application specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like); a network interface 1348 comprising a transmitter (Tx) 1345 and a receiver (Rx) 1347 for enabling network node 1301 to transmit data to and receive data from other nodes connected to a network 110 (e.g., an Internet Protocol (IP) network) to which network interface 1348 is connected; and a local storage unit (a.k.a.,“data storage system”) 1308, which may include one or more non-volatile storage devices and/or one or more volatile storage devices. In embodiments where PC 1302 includes a programmable processor, a computer program product (CPP) 1341 may be provided. CPP 1341 includes a computer readable medium (CRM) 1342 storing a computer program (CP) 1343 comprising computer readable instructions (CRI) 1344. CRM 1342 may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI 1344 of computer program 1343 is configured such that when executed by PC 1302, the CRI causes network node 1301 to perform steps described herein (e.g., steps described herein with reference to the flow charts). In other embodiments, network node 1301 may be configured to perform steps described herein without the need for code. That is, for example, PC 1302 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and/or software.

Embodiments

I. (R)AN Embodiments

Al . A method performed by an AN (e.g., performed by a gNB), the method comprising: the AN receiving DL data for UE 101;

the AN determining that the UE is in the RRC Inactive state and that the UE is not reachable (e.g., determines that the UE is currently in a temporary power savings mode or determines that the UE has not responded to a page); and

after receiving the DL data for the UE and determining that the UE is in the RRC Inactive state and is not reachable, the AN providing to AMF 105 a notification (e.g., an N2 Notification) indicating that the UE is not reachable (in some embodiments, the AN may also provide to the AMF buffering support information for the UE (e.g., information comprising a value indicating a time duration for buffering DL data for the UE)).

A2. The method of embodiment Al, further comprising, after receiving the DL data for the UE and determining that the UE is in the RRC Inactive state and is not reachable, the AN scheduling a paging of the UE. A3. The method of embodiment Al or A2, further comprising, after receiving the DL data for the UE and determining that the UE is in the RRC Inactive state and is not reachable: the AN receiving data forwarding tunnel information transmitted by a network function (e.g., SMF 108 or UPF 125); and

the AN using the data forwarding tunnel information to forward to a network function the received DL data so that the network function can buffer the DL data for an extended period of time.

B1. A method performed by an AN, the method comprising:

the AN deciding to place UE 101 in the RRC Inactive state (e.g., the AN may place the UE in the RRC Inactive state at a time during which the UE 101 is in a power savings mode or about to enter the power savings mode); and

after deciding to place the UE in the RRC Inactive state, the AN providing to AMF 105 a notification (e.g., an N2 Notification) indicating that the UE is not reachable (the AN may also provide to the AMF with the notification buffering support information for the UE (e.g., information comprising a value indicating a time duration for buffering DL data for the UE)).

B2. The method of embodiment Bl, further comprising:

receiving a request from the AMF;

in response to the request from AMF, the AN providing to the AMF updated buffering support information for the UE and reachability information for the UE.

B3. The method of embodiment Bl or B2, further comprising:

the AN receiving DL data for the UE;

the AN determining that the UE is in the RRC Inactive state and that the UE is not reachable (e.g., determines that the UE is currently in a temporary power savings mode or determines that the UE has not responded to a page);

as a result of determining that the UE is in the RRC Inactive state and is not reachable, the AN providing to the AMF a notification (e.g., an N2 Notification) indicating that the UE is not reachable. II. AMF Embodiments

C 1. A method performed by an AMF, the method comprising:

the AMF receives a first notification transmitted by AN 103, wherein the first notification includes information indicating that UE 101 is not reachable (e.g., information indicating that the UE has been placed in the RRC Inactive state and is not reachable); and

the AMF, in response to receiving the notification transmitted by the AN, sends a second notification to SMF 108, wherein the second notification sent to SMF 108 comprises information indicating that the UE is not reachable (i.e., information indicating that DL data for the UE is subject to extended data buffering).

C2. The method of embodiment Cl, wherein the second notification sent to the SMF further includes buffering support information (buffering support information based on the UE’s eDRX or DRX interval).

C3. The method of embodiment Cl or C2, wherein first notification further includes a data delivery failure indication.

C4. The method of embodiment Cl, C2 or C3, wherein the first notification further includes buffering support information.

III. SMF/UPF Embodiments

Dl . A method for buffering DF data, the method being performed by a CNF (e.g., SMF or UPF) and the method comprising:

the CNF receiving DF data for UE 101;

the CNF providing the DF data for the UE to AN 103;

after providing the DF data for the UE to the AN, the CNF receives a first notification comprising information indicating that the DF data for the UE that was provided to the AN has not been delivered to the UE (the notification may further comprise buffering support

information); and

after receiving the first notification, the CNF initiating extended buffering of the DF data. D2. The method of embodiment Dl, further comprising:

after providing the DL data for the UE to the AN, the CNF discarding the DL data, wherein

initiating the extended buffering of the DL data comprises, the CNF providing address information (e.g., tunnel endpoint information) to the AN so that the AN can send the DL data back to the CNF so that the CNF can receive the DL data and then store the DL data.

D3. The method of embodiment Dl or D2, wherein

initiating the extended buffering of the DL data comprises obtaining a buffer duration time for the DL data.

D4. The method of embodiment D3, further comprising

the CNF discarding the DL data in response to detecting that the buffer duration time for the DL data has elapsed (e.g., in response to detecting the expiration of a buffer duration timer).

D5. The method of embodiment Dl, D2, or D3, further comprising

the CNF provides the buffered DL data to an AN in response to receiving a second notification indicating that the UE is reachable.

El . A method for buffering DL data, the method being performed by a CNF (e.g., SMF or UPF) and the method comprising:

the CNF receiving a first notification concerning UE 101 as a result of an AN placing the UE in the RRC Inactive state (the first notification may comprise buffering support information); after the CNF receives the first notification, the CNF receiving DL data for the UE;

after receiving the DL data and based on the first notification, the CNF initiating extended buffering of the received DL data; and

the CNF either:

discarding the DL data in response to detecting that a buffer duration time for the DL data has elapsed (e.g., in response to detecting the expiration of a timer), or providing the DL data to an AN in response to receiving a second notification indicating that the UE is reachable.

E2. The method of embodiment El, wherein initiating extended buffering of the received DL data comprises obtaining a buffer duration time for the DL data.

E3. The method of embodiment E2, further comprising setting a buffer duration timer to expire at the end of the buffer duration time. E4. The method of embodiment E2 or E3, wherein obtaining a buffer duration time for the DL data comprises determining the buffer duration time from received buffering support information.

Fl. A network node 1301 (e.g., RAN, AMF, SMF or UPF) adapted to perform any one of the above described methods.

While various embodiments are described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of this disclosure should not be limited by any of the above-described exemplary embodiments.

Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is

contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel. ABBREVIATIONS

AN Access Network

AMF Access and Mobility Management Function

AUSF Authentication Server Function

CNF Core Network Function

UDM Unified Data Management

DF Downlink

UF Uplink

DN Data Network

PCF Policy Control function

AF Application Function

MO mobile originated

RRC Radio Resource Control

NR New Radio

NSSF Network Slice Selection Function

UE User Equipment

RAN radio access network

UPF User Plane Function

SMF Session Management Function

Claims

1. A method performed by an Access Network, AN (103), the method comprising:

the AN (103) receiving DownLink, DL, data for User Equipment, UE (101);

the AN (103) determining that the UE (101) is in the Radio Resource Control, RRC, Inactive state and that the UE (101) is not reachable; and

after receiving the DL data for the UE (101) and determining that the UE (101) is in the RRC Inactive state and is not reachable, the AN (103) providing to an Access and Mobility Management Function, AMF (105), a notification indicating that the UE (101) is not reachable. 2. The method of claim 1 , further comprising the AN (103) providing to the AMF (105) buffering support information for the UE (101).

3. The method of claim 1 or 2, further comprising, after receiving the DL data for the UE (101) and determining that the UE (101) is in the RRC Inactive state and is not reachable, the AN (103) scheduling a paging of the UE (101).

4. The method of any of claims 1-3, further comprising, after receiving the DL data for the UE (101) and determining that the UE (101) is in the RRC Inactive state and is not reachable:

the AN (103) receiving data forwarding tunnel information transmitted by a network function; and

the AN (103) using the data forwarding tunnel information to forward to a network function the received DL data so that the network function can buffer the DL data for an extended period of time. 5. The method of claim 4, wherein the network function is one of Session Management

Function, SMF (108), or User Plane Function, UPF (125).

6. An Access Network, AN (103), configured to:

receive DownLink, DL, data for User Equipment, UE (101); determine that the UE (101) is in the Radio Resource Control, RRC, Inactive state and that the UE (101) is not reachable (e.g., determines that the UE (101) is currently in a temporary power savings mode or determines that the UE (101) has not responded to a page); and

provide to an Access and Mobility Management Function, AMF (105), a notification indicating that the UE (101) is not reachable, after receiving the DL data for the UE (101) and determining that the UE (101) is in the RRC Inactive state and is not reachable, the AN (103).

7. The AN (103) of claim 6, further being configured provide to the AMF (105) buffering support information for the UE (101).

8. The AN (103) of any of claims 6 or 7, further being configured to schedule a paging of the UE (101), after receiving the DL data for the UE (101) and determining that the UE (101) is in the RRC Inactive state and is not reachable.

9. The AN (103) of any of claims 6-8, further being configured to, after receiving the DL data for the UE (101) and determining that the UE (101) is in the RRC Inactive state and is not reachable: receive data forwarding tunnel information transmitted by a network function; and use the data forwarding tunnel information to forward to a network function the received DL data so that the network function can buffer the DL data for an extended period of time.

10. The AN (103) of claim 9, wherein the network function is one of Session Management Function, SMF (108), or User Plane Function, UPF (125).

11. A method performed by an Access Network, AN (103), the method comprising:

the AN (103) deciding to place a User Equipment, UE (101), in the Radio Resource Control, RRC, Inactive state; and

after deciding to place the UE in the RRC Inactive state, the AN (103) providing to an Access and Mobility Management Function, AMF (105), a notification indicating that the UE is not reachable.

12. The method of claim 11, further comprising the AN (103) providing to the AMF (105) buffering support information for the UE (101).

13. The method of claims 11 or 12, further comprising:

receiving a request from the AMF (105);

in response to the request from AMF (105), the AN (103) providing to the AMF (105) updated buffering support information for the UE (101) and reachability information for the UE (101). 14. The method of any of claim 11-13, further comprising:

the AN (103) receiving DF data for the UE (101);

the AN (103) determining that the UE (101) is in the RRC Inactive state and that the UE (101) is not reachable;

as a result of determining that the UE (101) is in the RRC Inactive state and is not reachable, the AN (103) providing to the AMF (105) a notification indicating that the UE (101) is not reachable.

15. An Access Network, AN (103), configured to:

decide to place a User Equipment, UE (101), in the Radio Resource Control, RRC, Inactive state; and

provide to an Access and Mobility Management Function, AMF (105), a notification indicating that the UE (101) is not reachable, after deciding to place the UE in the RRC Inactive state. 16. The AN (103) of claim 15, further being configured to provide to the AMF (105) buffering support information for the UE (101).

17. The AN (103) of claims 15 or 16, further being configured to:

receive a request from the AMF (105); in response to the request from AMF (105), provide to the AMF (105) updated buffering support information for the UE (101) and reachability information for the UE (101).

18. The AN (103) of any of claim 15-17 further being configured to:

receive DL data for the UE (101);

determine that the UE (101) is in the RRC Inactive state and that the UE (101) is not reachable;

provide to the AMF (105) a notification indicating that the UE (101) is not reachable, as a result of determining that the UE (101) is in the RRC Inactive state and is not reachable.

19. A method performed by an Access and Mobility Management Function, AMF (105), the method comprising:

the AMF (105) receives a first notification transmitted by an Access Network, AN (103) (103), wherein the first notification includes information indicating that a User Equipment, UE ( 101 ), is not reachable; and

the AMF (105), in response to receiving the notification transmitted by the AN (103), sends a second notification to Session Management Function, SMF (108), wherein the second notification sent to the SMF (108) comprises information indicating that the UE (101) is not reachable.

20. The method of claim 19, wherein the second notification comprises information indicating that DownLink, DL, data for the UE (101) is subject to extended data buffering.

21. The method of claim 19 or 20, wherein the second notification sent to the SMF (108) further includes buffering support information.

22. The method of claim 21, wherein the buffering support information is based on the UE’s (101) eDRX or DRX interval.

23. The method of any of claims 19-22, wherein first notification further includes a data delivery failure indication.

24. The method of any of claims 19-23, wherein the first notification further includes buffering support information.

25. An Access and Mobility Management Function, AMF (105), being configured to:

receive a first notification transmitted by an Access Network, AN (103), wherein the first notification includes information indicating that a User Equipment, UE (101), is not reachable; and

send a second notification to Session Management Function, SMF (108), in response to receiving the notification transmitted by the AN (103), wherein the second notification sent to the SMF (108) comprises information indicating that the UE is not reachable. 26. The AMF of claim 25, wherein the second notification comprises information indicating that

DownFink, DF, data for the UE (101) is subject to extended data buffering.

27. The AMF of claim 25 or 26, wherein the second notification sent to the SMF (108) further includes buffering support information.

28. The AMF of claim 27, wherein the buffering support information is based on the UE’s (101) eDRX or DRX interval.

29. The AMF of any of claims 25-28, wherein first notification further includes a data delivery failure indication.

30. The AMF of any of claims 25-29, wherein the first notification further includes buffering support information.

31. A method for buffering Downlink, DL, data, the method being performed by a Core Network Function, CNF (108; 125), the method comprising:

the CNF (108; 125) receiving DL data for a User Equipment, UE, (101);

the CNF (108; 125) providing the DL data for the UE (101) to an Access Network, AN,

(103);

after providing the DL data for the UE (101) to the AN (103), the CNF (108; 125) receives a first notification comprising information indicating that the DL data for the UE (101) that was provided to the AN (103) has not been delivered to the UE (101); and

after receiving the first notification, the CNF (108; 125) initiating extended buffering of the DL data.

32. The method of claim 31, wherein the notification may further comprise buffering support information.

33. The method of claim 32, further comprising:

after providing the DL data for the UE (101) to the AN (103), the CNF (108; 125) discarding the DL data,

wherein initiating the extended buffering of the DL data comprises the CNF (108; 125) providing address information to the AN (103) so that the AN (103) can send the DL data back to the CNF (108; 125) so that the CNF (108; 125) can receive the DL data and then store the DL data.

34. The method of any of claims 31-33, wherein

35. The method of claim 34, further comprising

the CNF (108; 125) discarding the DL data in response to detecting that the buffer duration time for the DL data has elapsed.

36. The method of any of claims 31-34, further comprising

the CNF (108; 125) providing the buffered DL data to an AN (103) in response to receiving a second notification indicating that the UE (101) is reachable. 37. The method of any of claims 31-36, wherein the CNF (108; 125) is one of a Session

Management Function, SMF (108) or User Plane Function, UPF (125).

38. A Core Network Function, CNF (108; 125), configured to:

receive DL data for a User Equipment, UE, (101);

provide the DL data for the UE (101) to an Access Network, AN, (103);

receive a first notification comprising information indicating that the DL data for the UE (101) that was provided to the AN (103) has not been delivered to the UE (101), after providing the DL data for the UE (101) to the AN (103); and

initiate extended buffering of the DL data after receiving the first notification.

39. The CNF (108; 125) of claim 38, wherein the notification may further comprise buffering support information.

40. The CNF (108; 125) of claim 39, further being configured to:

discard the DL data after providing the DL data for the UE (101) to the AN (103), and wherein initiating the extended buffering of the DL data comprises the CNF (108; 125) providing address information to the AN (103) so that the AN (103) can send the DL data back to the CNF (108; 125) so that the CNF (108; 125) can receive the DL data and then store the DL data. 41. The CNF (108; 125) of any of claims 38-40, wherein

the CNF (108; 125) being configured to initiate the extended buffering of the DL data comprises the CNF (108; 125) being configured to obtain a buffer duration time for the DL data.

42. The CNF (108; 125) of claim 41, further being configured to discard the DL data in response to detecting that the buffer duration time for the DL data has elapsed.

43. The CNF (108; 125) of any of claims 38-40, further being configured to

provide the buffered DL data to an AN (103) in response to receiving a second notification indicating that the UE (101) is reachable.

44. The CNF (108; 125) of any of claims 38-43, wherein the CNF (108; 125) is one of a Session Management Function, SMF (108) or User Plane Function, UPF (125).

45. A method for buffering DownFink, DF, data, the method being performed by a Core Network Function, CNF (108; 125), and the method comprising:

the CNF (108; 125) receiving a first notification concerning a UE (101) as a result of an AN (103) placing the UE (101) in the Radio Resource Control, RRC, Inactive state;

after the CNF (108; 125) receives the first notification, the CNF (108; 125) receiving DF data for the UE (101);

after receiving the DF data and based on the first notification, the CNF (108; 125) initiating extended buffering of the received DF data; and

the CNF (108; 125) either:

discarding the DF data in response to detecting that a buffer duration time for the DF data has elapsed, or

providing the DF data to an AN (103) in response to receiving a second notification indicating that the UE (101) is reachable.

46. The method of claim 45, wherein the first notification comprises buffering support information.

47. The method of claim 45 or 46, wherein initiating extended buffering of the received DF data comprises obtaining a buffer duration time for the DF data.

48. The method of claim 47, further comprising setting a buffer duration timer to expire at the end of the buffer duration time.

49. The method of claim 47 or 48, wherein obtaining a buffer duration time for the DL data comprises determining the buffer duration time from received buffering support information.

50. The method of any of claims 45-49, wherein the CNF (108; 125) is one of a Session Management Function, SMF (108) or User Plane Function, UPF (125).

51. A Core Network Function, CNF (108; 125) configured to:

receive a first notification concerning a UE (101) as a result of an AN (103) placing the UE in the Radio Resource Control, RRC, Inactive state;

receive DL data for the UE after receiving the first notification;

initiate extended buffering of the received DL data after receiving the DL data and based on the first notification; and

either:

discard the DL data in response to detecting that a buffer duration time for the DL data has elapsed, or

provide the DL data to an AN (103) in response to receiving a second notification indicating that the UE (101) is reachable.

52 The CNL (108; 125) of claim 51, wherein the first notification may comprise buffering support information.

53. The CNL (108; 125) of claim 50 or 51, wherein being configured to initiate extended buffering of the received DL data comprises the CNL (108; 125) being configured to obtain a buffer duration time for the DL data.

54 The CNL (108; 125) of claim 53, further being configured to set a buffer duration timer to expire at the end of the buffer duration time.

55. The CNF (108; 125) of claim 53 or 54, wherein being configured to obtain a buffer duration time for the DL data comprises the CNF (108; 125) being configured to determine the buffer duration time from received buffering support information.

56. The CNF (108; 125) of any of claims 51-55, wherein the CNF (108; 125) is one of a Session Management Function, SMF (108) or User Plane Function, UPF (125).