WO2020147972A1

WO2020147972A1 - Reachability of temporarily not-reachable ue

Info

Publication number: WO2020147972A1
Application number: PCT/EP2019/051285
Authority: WO
Inventors: Hannu Hietalahti; Philippe Godin; Anna SILLANPÄÄ
Original assignee: Nokia Technologies Oy
Priority date: 2019-01-18
Filing date: 2019-01-18
Publication date: 2020-07-23

Abstract

It is provided a method, comprising monitoring if a packet for a terminal is received from a core network; checking whether, according to stored status data, the terminal is temporarily not reachable; informing the core network that the terminal is temporarily not reachable if the packet for the terminal is received and, according to the stored status data, the terminal is temporarily not reachable.

Description

Reachability of temporarily not-reachable UE

Field of the invention

The present invention relates to a temporarily not-reachable UE. For example, it relates to UEs in DRX, eDRX, MICO, PSM, or to a congested RAN node serving the UE.

Abbreviations

3GPP 3^rd Generation Partnership Project

3G / 4G / 5G 3^rd / 4^th / 5^th Generation

5GS 5G System

AF Application Function

AMF Access and Mobility Management Function

AN Access Node

AS Access Stratum

AS Application Server

BS Base Station

CloT Cellular loT

CM Connection Management

CN Core Network

D2D Device-to-device (communication)

DDN Downlink Data Notification

DL Downlink

DRX Discontinuous Reception

eDRX Extended idle mode DRX

eNB evolved NodeB (base Station in 4G)

EPS Evolved Packet System

gNB Base Station in 5G/NR

(h) home

HLcom High Latency Communications

loT Internet of Things

IP Internet Protocol

LTE Long Term Evolution

MICO Mobile Initiated Connection Only

MME Mobility Management Entity NAS Non-Access Stratum

NB-IOT Narrowband-loT

NEF Network Exposure Function

NG Next Generation

NR New Radio (air interface standard of 5G systems)

PDU Packet Data Unit

PSM Power Saving Mode

QoS Quality of Service

RAN Radio Access Network

Rel Release

RNA RAN Notification Area

RRC Radio Resource Control

SMF Session Management Function

TAU Tracki n g Area U pd ate

TDD Time Division Duplex

TR Technical Report

TS Technical Specification

Tx Transmit

UE User Equipment

UL Uplink

UPF User Plane Function

(v) visited

V2X Vehicle to anything

Background of the invention

3GPP has included so called RRC Inactive state in Rel-15 5GS specifications. The main characteristic of RRC Inactive is that when the RAN has placed the UE in RRC Inactive state, the Core Network (AMF) considers the UE to be in NAS state CM-CONNECTED. No dedicated radio connection exists in RRC Inactive state, but the CN behaves as if the UE was in RRC CONNECTED state. Consequently, the CN considers the UE to be reachable, and sends any downlink signalling or data directly to the UE without initiating CN paging procedure. In this state, the UE reachability is however the responsibility of the serving RAN node, which -if it knows the UE to be reachable - initiates the RAN paging in order to deliver the downlink packet to the UE, which the CN expects to be connected all the time. This makes substantial difference to previous 3GPP releases, where the CN node, e.g. MME, had accurate information on any periodically unreachable UE via protocol parameters related with periodic updates, eDRX, and UE Power Saving Mode. The Introduction of RRC Inactive state delegates the negotiation and maintenance of some of the UE reachability parameters to the RAN node, so the AMF cannot be aware of all protocol parameters affecting the UE reachability any longer.

No issues arise when the UE is reachable by RAN paging and the CN request for downlink data transmission (e.g. control plane data encapsulated in NAS signalling) or signalling can be satisfied within the NAS re-transmission timers run in the CN. In that successful case, the AMF in the CN need not be aware that RAN had to page the UE in order to re-establish RRC connection towards the UE that the CN assumes to be in CM-CONNECTED.

A problem will arise, if the RAN for some reason fails to reach the target UE by RAN paging, as follows:

As stated above, the RAN and CN states for the UE differ intentionally in RRC Inactive state. The problem arises, if for any reason the RAN is not able to restore the RRC connectivity when requested by the CN sending a packet for the UE comprising downlink data or signalling.

The handling of RAN paging failure is covered in 3GPP TS 23.501 , clause 5.3.3.2.5, which states that the RAN paging failure leads to RAN node releasing the CN connections. Thus, the RRC Inactive state is cancelled, and the RAN connection state and the CN connection state for the UE are moved to RRC idle and CN idle, respectively. Consequently, the packet whose DL transport led to the paging failure is lost, and re-transmission is up to the appropriate application layer. Signalling messages need to be repeated by the appropriate NAS signalling layer, and data packet would need to be re-transmitted by the application function that sent the data. These re-transmissions need to be done on sheer brutal force method without any awareness of UEs foreseen reachability, that is not known by the CN node (AMF) in the RRC Inactive state.

3GPP TS 23.502 disclose that a CN paging failure in RRC Idle state leads to notification of the UE unreachability towards the Application Server (AS) or Application Function (AF).

3GPP TS 23.501 , clause 5.3.3.2.5, specifies that in RRC Inactive / CM-CONNECTED state, the recovery from RAN paging failure is done via RRC Idle state and CM-IDLE state:

“If the RAN paging procedure, as defined in TS 38.300 [27], is not successful in establishing contact with the UE the procedure shall be handled by the network as follows: If NG-RAN has at least one pending NAS PDU for transmission, the RAN node shall initiate the AN Release procedure (see TS 23.502 [3], clause 4.2.6,) to move the UE CM state in the AMF to CM-IDLE state and indicate to the AMF the NAS non-delivery.

If NG RAN has only pending user plane data for transmission, the NG-RAN node may keep the N2 connection active or initiate the AN Release procedure (see TS 23.502 [3], clause 4.2.6) based on local configuration in NG-RAN."

3GPP TR 23.724, clause 6.50.4.2, specifies the handling of CN paging in CM-IDLE state, with AMF informing AF of unreachable UE, as shown in Fig. 1. In the CN paging call flow according to Fig. 1 , the DDN failure observed between steps 3 and 4 is detected by the AMF based on the UE not responding to paging.

There are several options to allow the UE to save energy because it is dormant for some time:

The LTE DRX allows the UE to sleep for 10.24s between paging cycle. The eDRX of NR (5G) allows the UE to tell the network how many“hyper frames” (HF) of 10.24s it would like to sleep before waking up and listening again. The maximum number of HFs a UE can sleep is settable by the mobile network operator.

Power Saving Mode (PSM) is an EPS UE mode where the UE is not reachable based on negotiation between UE and CN in NAS signaling. CN (MME) may assign a so called Active Time timer value for the UE to remain pageable for a short period of time after the RRC Connection release, but after that time has elapsed, the MME considers the UE not reachable and does not page it for any DL traffic, as the negotiated PSM means the UE need not listen to paging at all. The MME may also indicate to the UE a Periodic Tracking Area Update timer, which will force the UE to initiate periodic TAU procedure in order to remain registered. This establishes a predictable UE unreachability period that is known by the CN.

The corresponding 5GS feature Mobile Initiated Connection Only (MICO) mode allows the 5G UE to request the AMF to enter UE power saving state corresponding to PSM in EPS. The main difference is that in Rel-15 MICO, there is no option to indicate any Active Time for the UE to apply after RRC Connection release. Once the RRC connection goes to idle, it’s not possible to inform the MICO device of incoming (IP) packets. A server may send DL packets, but those can be delivered to the UE only when the UE sets up a connection on its own initiative. The CN (AMF) may assign a Periodic Registration Update timer for predictable but delayed reachability of MICO UE. 3GPP TR 23.724, clause 6.7, specifies a RAN method of informing the CN node of UE being in power saving mode in step 0, “N2 notification”. It should be noted that this is stateful processing with pre-requisite notifications from RAN to AMF-SMF-UPF and NEF for each UE that enters power saving mode. Furthermore, in this method, AMF polls the RAN for the UE reachability. It does not get the information on event-driven basis when trying to send a DL packet. The method is typically not adopted.

CN cannot control eDRX in RRC Inactive state. The AMF negotiates the eDRX value with UE. However, AMF is not aware of RAN Notification Area (RNA) updates. Hence, the AMF cannot know when the UE’s eDRX cycle started after the latest RNA update signaling. Accordingly, with eDRX in RRC Inactive state, CN (represented by AMF) does not know when the UE is reachable.

Summary of the invention

It is an object of the present invention to improve the prior art.

According to a first aspect of the invention, there is provided an apparatus, comprising means for monitoring configured to monitor if a packet for a terminal is received from a core network; means for checking configured to check whether, according to stored status data, the terminal is temporarily not reachable; means for informing configured to inform the core network that the terminal is temporarily not reachable if the packet for the terminal is received and, according to the stored status data, the terminal is temporarily not reachable.

According to a second aspect of the invention, there is provided an apparatus, comprising means for monitoring configured to monitor if, in response to transmitting a packet to a terminal via an access network, an indication is received from the access network that the terminal is temporarily not reachable; means for informing configured to inform a sender of the packet that the terminal is temporarily not reachable if the indication is received, wherein the packet is received from the sender for transmitting the packet to the terminal.

According to a third aspect of the invention, there is provided an apparatus, comprising means for monitoring configured to monitor if an indication is received in response to transmitting a packet towards a terminal, wherein the indication indicates that the terminal is temporarily not reachable; means for inhibiting configured to inhibit re-transmitting the packet for a waiting duration if the indication is received.

According to a fourth aspect of the invention, there is provided a method, comprising monitoring if a packet for a terminal is received from a core network; checking whether, according to stored status data, the terminal is temporarily not reachable; informing the core network that the terminal is temporarily not reachable if the packet for the terminal is received and, according to the stored status data, the terminal is temporarily not reachable.

According to a fifth aspect of the invention, there is provided a method, comprising monitoring if, in response to transmitting a packet to a terminal via an access network, an indication is received from the access network that the terminal is temporarily not reachable; informing a sender of the packet that the terminal is temporarily not reachable if the indication is received, wherein the packet is received from the sender for transmitting the packet to the terminal.

According to a sixth aspect of the invention, there is provided a method, comprising monitoring if an indication is received in response to transmitting a packet towards a terminal, wherein the indication indicates that the terminal is temporarily not reachable; inhibiting re-transmitting the packet for a waiting duration if the indication is received.

Each of the methods of the fourth to sixth aspects may be a method for reachability in inactive state.

According to a seventh aspect of the invention, there is provided a computer program product comprising a set of instructions which, when executed on an apparatus, is configured to cause the apparatus to carry out the method according to any of the fourth to sixth aspects. The computer program product may be embodied as a computer-readable medium or directly loadable into a computer.

According to some example embodiments of the invention, at least one of the following advantages may be achieved:

• Signalling effort is reduced via event driven UE reachability procedures;

• Applications awareness of the power saving UE’s reachability is increased;

• Success rate of transmissions may be increased;

• Reduced number of pagings;

• Allows adaptation of applications to energy saving measures of the UE. It is to be understood that any of the above modifications can be applied singly or in combination to the respective aspects to which they refer, unless they are explicitly stated as excluding alternatives.

Brief description of the drawings

Further details, features, objects, and advantages are apparent from the following detailed description of the preferred example embodiments of the present invention which is to be taken in conjunction with the appended drawings, wherein:

Fig. 1 shows a message flow according to 3GPP TR 23.724, clause 6.50.4.2;

Fig. 2 shows a message flow according to 3GPP TR 23.724, clause 6.7;

Fig. 3 shows a message flow according to some example embodiments of the invention;

Fig. 4 shows an apparatus according to an example embodiment of the invention;

Fig. 5 shows a method according to an example embodiment of the invention;

Fig. 6 shows an apparatus according to an example embodiment of the invention;

Fig. 7 shows a method according to an example embodiment of the invention;

Fig. 8 shows an apparatus according to an example embodiment of the invention;

Fig. 9 shows a method according to an example embodiment of the invention; and

Fig. 10 shows an apparatus according to an example embodiment of the invention.

Detailed description of certain example embodiments

Herein below, certain example embodiments of the present invention are described in detail with reference to the accompanying drawings, wherein the features of the example embodiments can be freely combined with each other unless otherwise described. However, it is to be expressly understood that the description of certain example embodiments is given by way of example only, and that it is by no way intended to be understood as limiting the invention to the disclosed details.

Moreover, it is to be understood that the apparatus is configured to perform the corresponding method, although in some cases only the apparatus or only the method are described.

The conventional method of Fig. 1 does not consider that the RAN node may have more information on the UE than just occurrence of a RAN paging failure. In the CN paging call flow of Fig. 1 , there isn’t any active analysis to detect a reason or duration of the UE unreachability in RAN, or any indication of an expected reachability time when the UE might be reachable in the future.

On the other hand, the method of Fig. 2 is not very efficient, as it involves a lot of signalling to pre-configure the AMF, SMF, UPF and NEF to be prepared to handle the DL data towards a power saving UE. It also assumes CN buffering in all cases, including UE unreachability that is not predictable by the network (such as PSM or MICO mode without periodic update timer set by the CN). The approach of Fig. 2 prepares the network for efficient DL data transmission towards a UE that is applying aggressive power saving methods such as PSM. Consequently, a lot of network signalling and storing of UE state is done in order to serve a large number of Clot UEs, many of which probably won’t receive much DL traffic during its sleep cycles anyway. The long unreachability periods do not serve the needs of bi-directional interactive applications too well, so preparation of network resources for UEs that may not receive any downlink data or signalling at all during the sleep period is less efficient than on-demand method that only deals with the actual DL data or signalling when it arrives.

For a UE in RRCJnactive state, a reason for the UE unreachability (RAN will not even try to page) may be (but is not limited to):

UE using eDRX (in particular with long eDRX cycle); and/or

RAN node being congested (and the UE having low priority in the paging queue)

According to some example embodiments of the invention, if the UE unreachability is caused by one of the above examples, the RAN node (e.g. gNB) could indicate to the CN attempting to pass a packet (DL message) via RAN towards the UE in RRC Inactive state that the target UE is temporarily not reachable. “Temporarily not reachable” means that the UE is not reachable right now, but it is expected to become reachable later on. At least in some cases, such as eDRX, the expected time of UE reachability can be predicted with reasonable accuracy. Then, RAN may inform on the reachability time when the UE is expected to be reachable again, too.

More in detail, according to some example embodiments of the invention, the RAN node that is responsible for paging operates as follows: When receiving DL data or signaling towards the UE, the RAN node dynamically determines that the target UE is not reachable immediately, but is expected to become reachable later on (“temporary unreachable”).

RAN node informs the CN node ^*explicitly^* of the UE being temporarily unreachable . In addition, RAN node may optionally inform the CN node of expected UE reachability time:

o RAN node may derive the predicted UE reachability time based on the remaining time of UE power saving cycle that can be eDRX or RAN Notification Area Update timer

o RAN node may derive the predicted UE reachability time based on any other AS or NAS timer value that is known by the RAN node

o RAN node may derive the predicted UE reachability based on RAN node load conditions (in case UE is temporarily not reachable because of RAN overload) or estimated evolution of these RAN load conditions

o Even if RAN node is not able to estimate next UE reachability time, it may still indicate a minimum expected time duration before CN may attempt again to reach the UE.

As explained above, according to some example embodiments of the invention, the RAN node serving a UE in RRC Inactive state responds to the CN node providing a packet (DL signalling or DL data e.g. user data embedded in DL signalling) for the UE by indicating that the UE is not immediately reachable (temporarily not reachable). It may also indicate a reachability time when RAN node expects the UE to become reachable. The reachability time may be derived by the RAN node as shown above.

If RAN node is not able to determine when UE will become reachable again but has an estimation (with sufficiently high probability) that UE will not become reachable for a certain time (e.g. due to congestion), RAN node may indicate a minimum expected time. In some example embodiments of the invention, network functions of CN (AMF, SMF, UPF, AF, etc.) must not attempt to reach the UE before the minimum expected time has elapsed.

A call flow diagram of a method according to some example embodiments of the invention is shown in Fig. 3. Dashed arrows indicate optional messages (steps).

Steps 1 to 3 correspond to steps 1 to 3 of Fig. 1 , wherein step 2 is shown at greater detail (steps 2a to 2c). I.e., in step 1 , AF comprises downlink data to UPF. Then, in step 2a, UPF informs SMF on the data and requests setting up a session. SMF, in step 2b, acknowledges the request and provides parameters of the session. Then, in step 2c, UPF sends the downlink data in the session to SMF. In step 3a, SMF sends the DL data to AMF. The AMF may optionally provide a provisional response confirming receipt of a syntactically correct message (step 3b), but at this point it is not yet possible to give the final response, as the outcome of the DL data delivery is not yet known.

In step 4a, AMF sends the data encapsulated in DL signalling to RAN for transfer towards the UE. In step 4b, RAN determines that the UE is temporarily not reachable. This determination is made based on the status information stored for the UE, without paging the UE. If the status information comprises an expected reachability time, RAN may retrieve it from the status information, too. As an alternative or in addition, RAN may estimate an estimated reachability time from other parameters such as the load of the RAN, or any AS or NAS timer value related to the UE.

If RAN determines both the expected reachability time and the estimated reachability time, it may select one of these times as the reachability time according to some predefined criterion. For example, it may determine the shortest of these times in order to avoid an unnecessary long waiting time, or the longest of these times in order to avoid more safely that the UE is still temporarily unavailable. The expected reachability time may have prevalence over the estimated reachability time.

In step 4c, RAN informs AMF that UE is temporarily not reachable. This notification may comprise the indication of the (selected) reachability time. This notification may also encapsulate the DL signalling that RAN could not send or that DL signalling may be sent back as a separate message. This failure indication may be propagated back to SMF (step 5), and onwards to UPF via SMF (steps 6 and 7). The back-propagating informs the respective sender of UE’s temporary non-reachability. Based on this knowledge, the respective sender may decide whether or not to buffer the DL data (as in HLcom).ln case of NAS signalling the respective sender may dynamically adjust the re-transmission policy.

Instead of back-propagating the failure indication in steps 5 - 7, one of AMF, SMF, and UPF may buffer the DL signalling or the data for the UE and initiate a retransmission of the DL signalling or data later after some waiting duration, if the time constraint of the request to the respective network function allow such behaviour. Only if the re-transmission (or even plural re-transmission attempts) fails, too, the respective network function may back-propagate the failure indication. Due to the failure indication, the CN may distinguish between paging failure and a RAN controlled UE sleep cycle after which the UE is expected to be reachable.

Preferably, the waiting duration may be determined based on the reachability time if the same is indicated in the failure indication from RAN. I.e., the waiting duration may elapse at the reachability time. Alternatively, the waiting time may be predefined or determined based on other parameters available to the respective network function.

Even if a re-transmission after the waiting duration is not possible within the required time constraint, one of AMF, SMF, and UPF may buffer the packet (DL data or signalling) for later re-transmission and inform the respective upstream network function (i.e., the sender from which the packet is received) on the buffering and (optionally) on the expected reachability time. Thus, the upstream network function is informed about the failure but need not retransmit the packet. If a predefined number of re-transmissions fails, and/or if the expected re transmission time is more than a predefined time duration later than the initial transmission attempt, the buffering network function may indicate to the upstream network function that the transmission has finally failed.

In CM-CONNECTED state, especially when combined with RRC Inactive, the UE reachability is determined based on RAN Notification in step 4c of Fig. 3 instead of UE state stored in the AMF. That notification of reachability is event driven, and it applies only on those UEs for which DL signalling or DL data is attempted to be delivered. More precisely it is sent either as an acknowledgement of a CN request to deliver DL signalling or corresponds to a signalling event related to DL signalling being sent by the CN to the RAN.

Some example embodiments of the invention may be used with various core network initiated signalling procedures: e.g. Network initiated deregistration, network initiated PDU session, network initiated QoS flow establishment, modification and release (see 3GPP TS 23.502 for Release 15), sending of NAS PDU, or sending of user data encapsulated over NAS.

Some embodiments of the invention may be used for RRC connected mode UEs while using eDRX.

In some embodiments, AMF may change the UE state in the AMF to CM-IDLE state if the indication is received that the UE is temporarily not reachable. In some embodiments, AMF may maintain the UE state in the AMF in CM-CONNECTED state if the indication is received that the UE is temporarily not reachable. In some embodiment, AMF may decide whether or not to change the UE state in the AMF based on a condition such as the cause value or foreseen UE reachability indicated by the RAN or Expected UE behaviour information that is either pre-configured or observed by the network.

Fig. 4 shows an apparatus according to an example embodiment of the invention. The apparatus may be a RAN (e.g. represented by a base station or base station controller such as a gNB) or an element thereof. Fig. 5 shows a method according to an example embodiment of the invention. The apparatus according to Fig. 4 may perform the method of Fig. 5 but is not limited to this method. The method of Fig. 5 may be performed by the apparatus of Fig. 4 but is not limited to being performed by this apparatus.

The apparatus comprises means for monitoring 10, means for checking 20, and means for informing 30. The means for monitoring 10, means for checking 20, and means for informing 30 may be a monitoring means, checking means, and informing means, respectively. The means for monitoring 10, means for checking 20, and means for informing 30 may be an monitor, checker, and informer, respectively. The means for monitoring 10, means for checking 20, and means for informing 30 may be a monitoring processor, checking processor, and informing processor, respectively.

The means for monitoring 10 monitors if a packet for a terminal is received from a core network (S10). The means for checking 20 checks whether, according to stored status data, the terminal is temporarily not reachable (S20).

S10 and S20 may be performed in an arbitrary sequence. They may be performed fully or partly in parallel.

If the packet for the terminal is received (S10 =“yes”) and, according to the stored status data, the terminal is temporarily not reachable (S20 =“yes”), the means for informing 30 informs the core network that the terminal is temporarily not reachable (S30). The indication may comprise an indication of a reachability time when the terminal is expected to be reachable again and/or may also include the undelivered packet.

Fig. 6 shows an apparatus according to an example embodiment of the invention. The apparatus may be a core network function (e.g. AMF, SMF, or UPF) or an element thereof. Fig. 7 shows a method according to an example embodiment of the invention. The apparatus according to Fig. 6 may perform the method of Fig. 7 but is not limited to this method. The method of Fig. 7 may be performed by the apparatus of Fig. 6 but is not limited to being performed by this apparatus.

The apparatus comprises means for monitoring 1 10 and means for informing 120. The means for monitoring 1 10 and means for informing 120 may be a monitoring means and informing means, respectively. The means for monitoring 1 10 and means for informing 120 may be a monitor and informer, respectively. The means for monitoring 1 10 and means for informing 120 may be a monitoring processor and informing processor, respectively.

The means for monitoring 1 10 monitors if, in response to transmitting a packet, an indication is received from an access network that a terminal is temporarily not reachable (S1 10). The packet is from a sender and intended for transmission to the terminal via the access network. In other words, the packet is transmitted towards the terminal. If the indication is received (S1 10 =“yes”), the means for informing 120 informs the sender of the packet that the terminal is temporarily not reachable (S120). The indication may comprise an indication of a reachability time when the terminal is expected to be reachable again.

Fig. 8 shows an apparatus according to an example embodiment of the invention. The apparatus may be a application function or application server or an element thereof. In some example embodiments of the invention, the apparatus may be an AMF or SMF or UPF or an element thereof. Fig. 9 shows a method according to an example embodiment of the invention. The apparatus according to Fig. 8 may perform the method of Fig. 9 but is not limited to this method. The method of Fig. 9 may be performed by the apparatus of Fig. 8 but is not limited to being performed by this apparatus.

The apparatus comprises means for monitoring 210 and means for inhibiting 220. The means for monitoring 210 and means for inhibiting 220 may be a monitoring means and inhibiting means, respectively. The means for monitoring 210 and means for inhibiting 220 may be a monitor and inhibitor, respectively. The means for monitoring 210 and means for inhibiting 220 may be a monitoring processor and inhibiting processor, respectively.

The means for monitoring 210 monitors if an indication is received in response to transmitting a packet to a terminal (S210). The indication indicates that the terminal is temporarily not reachable. If the indication is received (S210 =“yes”), the means for inhibiting 220 inhibits re-transmitting the packet for a waiting duration (S220). In some example embodiments of the invention, the indication may comprise an indication of a reachability time indicating when the terminal is expected to be reachable again. It may also include the undelivered packet. Then, the waiting duration may be set such that it elapses at the reachability time.

Fig. 10 shows an apparatus according to an example embodiment of the invention. The apparatus comprises at least one processor 810, at least one memory 820 including computer program code, and the at least one processor 810, with the at least one memory 820 and the computer program code, being arranged to cause the apparatus to at least perform at least one of the methods according to Figs. 5, 7, and 9 and related description.

Some example embodiments of the invention are described which are based on a 3GPP network. It may be applied to any generation (3G, 4G, 5G, etc.) of 3GPP networks. However, the invention is not limited to 3GPP networks. It may be applied to other radio networks, too, which allow that the terminal may be temporarily not reachable although it remains in the same coverage region (e.g. tracking area). It may even be applied to fixed access networks and satellite systems if they allow that the terminal may be temporarily not reachable.

According to some embodiments of the invention, the duration of a hyperframe in eDRX may be arbitrary, i.e., it may be 10.24 ms or different from 10.24 ms. The number of hyperframes during which the UE is asleep is arbitrary, too. The number may be fixed (e.g. 1 ) or indicated by the UE to RAN. In general, eDRX, MICO, and PSM are described based on the numerical values according to current 3GPP standards. However, these numerical values are not limiting for the invention. They may be adapted according to future standards or according to specific needs.

A UE is an example of a terminal. However, the terminal (UE) may be any device capable to connect to the (3GPP) radio network such as a MTC device, an NBIOT device, a D2X device etc..

A cell may be represented by the base station (e.g. gNB, eNB, etc.) serving the cell. The base station (cell) may be connected to an antenna (array) serving the cell by a Remote Radio Head. A base station may be realized as a combination of a central unit (one or plural base stations) and a distributed unit (one per base station). The central unit and/or distributed unit(s) may be employed in the cloud. One piece of information may be transmitted in one or plural messages from one entity to another entity. Each of these messages may comprise further (different) pieces of information.

Names of network elements, protocols, and methods are based on current standards. In other versions or other technologies, the names of these network elements and/or protocols and/or methods may be different, as long as they provide a corresponding functionality.

If not otherwise stated or otherwise made clear from the context, the statement that two entities are different means that they perform different functions. It does not necessarily mean that they are based on different hardware. That is, each of the entities described in the present description may be based on a different hardware, or some or all of the entities may be based on the same hardware. It does not necessarily mean that they are based on different software. That is, each of the entities described in the present description may be based on different software, or some or all of the entities may be based on the same software. Each of the entities described in the present description may be embodied in the cloud.

According to the above description, it should thus be apparent that example embodiments of the present invention provide, for example, a function of an access network (in particular of a radio access network) (e.g. gNB, NG-eNB or eNB), or a component thereof, an apparatus embodying the same, a method for controlling and/or operating the same, and computer program(s) controlling and/or operating the same as well as mediums carrying such computer program(s) and forming computer program product(s). According to the above description, it should thus be apparent that example embodiments of the present invention provide, for example, a function of a core network (e.g. AMF or SMF), or a component thereof, an apparatus embodying the same, a method for controlling and/or operating the same, and computer program(s) controlling and/or operating the same as well as mediums carrying such computer program(s) and forming computer program product(s).

Implementations of any of the above described blocks, apparatuses, systems, techniques or methods include, as non-limiting examples, implementations as hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

It is to be understood that what is described above is what is presently considered the preferred example embodiments of the present invention. However, it should be noted that the description of the preferred example embodiments is given by way of example only and that various modifications may be made without departing from the scope of the invention as defined by the appended claims.

Claims

Claims:

1. Apparatus, comprising

means for monitoring configured to monitor if a packet for a terminal is received from a core network;

means for checking configured to check whether, according to stored status data, the terminal is temporarily not reachable;

means for informing configured to inform the core network that the terminal is temporarily not reachable if the packet for the terminal is received and, according to the stored status data, the terminal is temporarily not reachable.

2. The apparatus according to claim 1 , further comprising

means for paging configured to page the terminal if the packet for the terminal is received;

means for inhibiting configured to inhibit the means for paging from paging the terminal if, according to the stored status data, the terminal is temporarily not reachable.

3. The apparatus according to any of claims 1 and 2, further comprising at least one of

means for retrieving configured to retrieve from the stored status data an expected reachability time when the terminal is expected to be reachable again; and

means for estimating configured to estimate an estimated reachability time when the terminal is expected to be reachable again; wherein

the means for informing is configured to inform the core network on a reachability time being one of the expected reachability time and the estimated reachability time, respectively.

4. The apparatus according to any of claims 1 to 3, further comprising at least one of

means for encapsulating configured to encapsulate the packet to the core network together with the information that the terminal is temporarily not reachable; and

means for delivering configured to deliver the packet to the core network separately from the information that the terminal is temporarily not reachable.

5. Apparatus, comprising

means for monitoring configured to monitor if, in response to transmitting a packet to a terminal via an access network, an indication is received from the access network that the terminal is temporarily not reachable; means for informing configured to inform a sender of the packet that the terminal is temporarily not reachable if the indication is received, wherein

the packet is received from the sender for transmitting the packet to the terminal.

6. The apparatus according to claim 5, wherein

the indication comprises an indication of a reachability time indicating when the terminal is expected to be reachable again;

the means for informing is configured to inform the sender on the reachability time.

7. The apparatus according to any of claims 5 to 6, further comprising

means for buffering configured to buffer the packet for a waiting duration if the terminal is temporarily not reachable;

means for initiating configured to initiate a retransmission of the packet when the waiting duration has elapsed after the indication is received.

8. The apparatus according to claim 7 dependent on claim 6, wherein the waiting duration elapses at the reachability time.

9. Apparatus, comprising

means for monitoring configured to monitor if an indication is received in response to transmitting a packet towards a terminal, wherein the indication indicates that the terminal is temporarily not reachable;

means for inhibiting configured to inhibit re-transmitting the packet for a waiting duration if the indication is received.

10. The apparatus according to claim 9, wherein

the indication comprises an indication of a reachability time indicating when the terminal is expected to be reachable again; and

the waiting duration elapses at the reachability time.

1 1. The apparatus according to any of claims 9 to 10, further comprising

means for checking configured to check, if the indication is received, whether the waiting duration elapses earlier than a time constraint for transmitting the packet to the terminal;

means for buffering configured to buffer the packet for the waiting duration if the indication is received and the waiting duration elapses earlier than the time constraint; means for initiating configured to initiate a retransmission of the packet when the waiting duration has elapsed after the indication is received if the waiting duration elapses earlier than the time constraint.

12. The apparatus according to any of claims 5 to 1 1 , wherein

the indication includes the packet, or the packet is received from the access network in a message separate from the indication.

13. The apparatus according to any of claims 5 to 12 being an access and mobility function, wherein the packet is transmitted towards the terminal over an interface to a base station.

14. The apparatus according to any of claims 5 to 13, wherein the packet comprises one of downlink signaling and downlink user data encapsulated in downlink signaling.

15. The apparatus according to any of claims 5 to 14, further comprising

means for changing configured to change a context stored for the terminal into an idle mode if the indication is received.

16. The apparatus according to claim 15, further comprising

means for prohibiting configured to prohibit the changing of the context based on a condition.

17. The apparatus according to any of claims 5 to 14, further comprising

means for maintaining configured to maintain a context stored for the terminal to be a connected mode if the indication is received.

18. Method, comprising

monitoring if a packet for a terminal is received from a core network;

checking whether, according to stored status data, the terminal is temporarily not reachable;

informing the core network that the terminal is temporarily not reachable if the packet for the terminal is received and, according to the stored status data, the terminal is temporarily not reachable.

19. The method according to claim 18, further comprising

paging the terminal if the packet for the terminal is received; inhibiting the paging of the terminal if, according to the stored status data, the terminal is temporarily not reachable.

20. The method according to any of claims 18 and 19, further comprising at least one of

retrieving from the stored status data an expected reachability time when the terminal is expected to be reachable again; and

estimating an estimated reachability time when the terminal is expected to be reachable again; wherein

the informing comprises informing the core network on a reachability time being one of the expected reachability time and the estimated reachability time, respectively.

21. The method according to any of claims 18 to 20, further comprising at least one of

encapsulating the packet to the core network together with the information that the terminal is temporarily not reachable; and

delivering the packet to the core network separately from the information that the terminal is temporarily not reachable.

22. Method, comprising

monitoring if, in response to transmitting a packet to a terminal via an access network, an indication is received from the access network that the terminal is temporarily not reachable; informing a sender of the packet that the terminal is temporarily not reachable if the indication is received, wherein

23. The method according to claim 22, wherein

the informing comprises informing the sender on the reachability time.

24. The method according to any of claims 22 to 23, further comprising

buffering the packet for a waiting duration if the terminal is temporarily not reachable; initiating a retransmission of the packet when the waiting duration has elapsed after the indication is received.

25. The method according to claim 24 dependent on claim 23, wherein the waiting duration elapses at the reachability time.

26. Method, comprising

monitoring if an indication is received in response to transmitting a packet towards a terminal, wherein the indication indicates that the terminal is temporarily not reachable;

inhibiting re-transmitting the packet for a waiting duration if the indication is received.

27. The method according to claim 26, wherein

the waiting duration elapses at the reachability time.

28. The method according to any of claims 26 to 27, further comprising

checking, if the indication is received, whether the waiting duration elapses earlier than a time constraint for transmitting the packet to the terminal;

buffering the packet for the waiting duration if the indication is received and the waiting duration elapses earlier than the time constraint;

initiating a retransmission of the packet when the waiting duration has elapsed after the indication is received if the waiting duration elapses earlier than the time constraint.

29. The method according to any of claims 22 to 28, wherein

30. The method according to any of claims 22 to 29 being an access and mobility function, wherein the packet is transmitted towards the terminal over an interface to a base station.

31. The method according to any of claims 22 to 30, wherein the packet comprises one of downlink signaling and downlink user data encapsulated in downlink signaling.

32. The method according to any of claims 22 to 31 , further comprising

changing a context stored for the terminal into an idle mode if the indication is received.

33. The method according to claim 32, further comprising

prohibiting the changing of the context based on a condition.

34. The method according to any of claims 22 to 31 , further comprising

maintaining a context stored for the terminal to be a connected mode if the indication is received.

35. A computer program product comprising a set of instructions which, when executed on an apparatus, is configured to cause the apparatus to carry out the method according to any of claims 18 to 34.

36. The computer program product according to claim 35, embodied as a computer-readable medium or directly loadable into a computer.