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1. (WO2019063086) TRANSFERT DE CONTEXTE PAR L'INTERMÉDIAIRE DU DERNIER NŒUD RAN VISITÉ
Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

CONTEXT TRANSFER VIA LAST VISITED RAN NODE

Field of t e invention

The present invention relates to an apparatus, a method, and a computer program product related to context transfer, and in particular to context transfer in mobile networks.

Abbreviations

3GPP 3rd Generation Partnership Project

5G 5th Generation

5GC 5G Core Network

AMF Access and Mobility Function

CN Core Network

D2D Device-to-Device (Communication)

eNB evolved NB

gNB Next Generation NB

HW Hardware

ID Identifier

IOT Internet of Things

LTE Long Term Evolution

LV gNB Last visited gNB

MTC Machine-type Communication

NB NodeB

NG Next Generation

NGCI NG Cell Identity

RAN Radio Access Network

RNA RAN Notification Area

RRC Radio Resource Control

UE User Equipment

Xn Direct interface between two gNBs

XnAP Xn application part

Background of the invention

3GPP Standards is designing a new RRC state called RRC_inactive state (an example of an inactive state). For this RRC_inactive state, the concept of RAN Notification Area (RNA) has been designed (an example of a notification area). RNA is an area where the UE can move across cells substantially without requiring any signalling unless it has data to send. In particular, the UE does not send any location update indication when it moves within the boundaries of the RNA, but updates its location to the RAN when it leaves the RNA. In detail, if the terminal is in the inactive state in the notification area, the terminal does not inform another cell of the notification area on a location update when it moves from the last visited cell of the notification area to the other cell of the notification area, and, the terminal informs a new cell (or its base station) outside the notification area on the location update when it moves from the last visited cell of the notification area to the new cell outside the notification area.

The inactive state intends to limit battery consumption for the UE similarly to the idle state, while at the same time the UE may reach the connected state with little signalling (less signalling compared to transition from idle state to connected state) when to send data. In inactive state, the UE remains ECM-connected from 5GC (5G core network) point of view and therefore the NG connection between 5GC and gNB is maintained. This means that, when a packet arrives for paging the UE (mobile terminating call), the packet gets routed directly to the last serving gNB (called anchor gNB) which triggers itself the RAN paging in the RNA. I.e. the anchor gNB pages the UE in its cells of the RNA and sends an Xn Paging message (a paging message over the Xn interface) to its neighbour gNBs of the RNA, which in turn page the UE in their cells. The Xn interface is a direct interface between two base stations acting as peers, wherein the peers terminate the XnAP protocol.

In inactive state, the location of the UE is monitored by the RAN. More precisely, whenever the UE moves out of the RNA it must inform the anchor gNB with an RRC Location Update message: If in this case the UE is located under a new gNB, the anchor function is relocated and the new gNB becomes the new anchor gNB.

A UE is configured from connected state into inactive state by its last serving gNB which sends to the UE an RRC Suspend message including the applicable RNA. The last serving gNB becomes the anchor gNB for the UE keeping the UE context when the UE is in inactive state. This last serving gNB would typically configure an RNA comprising a list of cells or a list of "RAN Areas" which in general includes one or more cells of the last serving gNB and possibly includes one or more cells of one or more neighbour gNBs with which the last serving gNB has a direct connection (Xn connectivity). The last requirement is set to make the paging

successful. Indeed, if t e RNA comprised a cell whose gNB is not Xn-connected to the anchor gNB, then the RAN paging would not reach that gNB and therefore would not reach the UE.

When the UE moves out of the RNA it must inform the anchor gNB so that a new RNA can be configured to the UE and possibly the anchor function may be relocated. However, the first cell seen (reached) by the UE out of the RNA can be a cell of a new gNB (i.e. UE changes gNB when moving out of the RNA). In that case, the RRC Location Update message sent by the UE is received by this new gNB which must relay it to the anchor gNB over Xn. The new gNB typically triggers an Xn context fetch procedure to also retrieve the UE context (or part thereof).

A problem arises if that new gNB does not have Xn connectivity with the anchor gNB. Then the new gNB cannot trigger the Xn context fetch procedure and the anchor gNB cannot be informed of the new gNB and also cannot transfer any context. This situation is possible because even if the anchor gNB has configured the UE with an RNA with Xn reachability (i.e. comprising either its own cells or cells of neighbour gNBs with which it has Xn connectivity), nothing guarantees that the new gNB which UE has reached when moving out of the RNA has Xn connectivity with the anchor gNB, too.

The "best existing" solution proposed so far in 3GPP is to use the 5GC (5G Core Network) as a relay. In that solution often called "NG context fetch" the new gNB reaches the anchor gNB over NG interface between RAN and CN. When receiving the RRC Location Update message from the UE, the new gNB typically triggers an NG message "context fetch request" towards an AMF including an anchor gNB ID and its own new gNB ID. The AMF recognizes the anchor gNB ID and relays this request over NG interface towards the anchor gNB. The anchor gNB ID replies with NG Context fetch response message towards the AMF including the context of the UE and setting the received new gNB ID as destination. The AMF recognizes the new gNB ID and is able to propagate the NG Context fetch response message towards the new gNB. New gNB gets the UE context.

This solution is however not efficient because:

1 . it involves lots of signalling for the 5GC whereas one purpose of moving the paging function from the 5GC to the RAN was originally intended to relieve the core network from signalling load.

2. the context retrieval involving the core network will introduce an extra delay which is critical, especially for paging time.

3. the UE access stratum context transfer does not remain confined within the RAN while the UE is RRC-INACTIVE, which is not consistent with the fact that the UE is perceived to be connected to a certain gNB with no need to transfer state transitions to the CN.

4. it is possible that the new gNB and the anchor gNB do not share a AMF. In this case, the right peer CN node has to be found where to send the context transfer request if this was via the CN and if the new AMF does not have a NG relationship with the anchor gNB (for sure the NG relationship to the same AMF exists inside the RNA, but this is not guaranteed outside). There is a problem of routing via two AMFs in these occasions.

A context comprises information (e.g. parameters) which are relevant for at least one of authenticaton, authorization, accounting, security information, radio bearer information, header compression, QoS, Policy, sub-IP protocols, and services for the UE.

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 at least one processor, at least one memory including computer program code, and the at least one processor, with the at least one memory and the computer program code, being arranged to cause the apparatus to at least perform checking if a terminal is in an inactive state in a notification area, monitoring if the terminal moves from a last visited cell of the notification area to a new cell outside the notification area; instructing the terminal to provide an anchor base station identifier of an anchor base station, a context identifier of a context for the terminal, and at least one of a last visited cell identifier of the last visited cell and a last visited base station identifier of a last visited base station to the new base station if the terminal is in the inactive state and moves from the last visited cell to the new cell; wherein

the last visited cell belongs to the last visited base station;

the new cell belongs to the new base station.

At least one of the anchor base station identifier, the context identifier, and the at least one of the last visited cell identifier and the last visited base station identifier may be provided along with the informing of the new cell on the location update of the terminal from the last visited cell to the new cell.

Acording to a second aspect of the invention, there is provided an apparatus, comprising at least one processor, at least one memory including computer program code, and the at least one processor, with the at least one memory and the computer program code, being arranged to cause the apparatus to at least perform monitoring if a new base station receives, from a terminal, location update information for the terminal, an anchor base station identifier of an anchor base station, a context identifier of a context, and at least one of a last visited cell identifier of a last visited cell and a last visited base station identifier of a last visited base station; checking if a first direct connection between the new base station and the anchor base station exists if the location update information and the anchor base station identifier are received; instructing the new base station to request the context from the anchor base station via the last visited base station if the first direct connection does not exist and the at least one of the last visited cell identifier and the last visited base station identifier is received; wherein the request for the context from the anchor base station comprises the anchor base station identifier and the context identifier.

The at least one processor, with the at least one memory and the computer program code, may be arranged to cause the apparatus to further perform, if the last visited cell identifier of the last visited cell is received and the last visited base station identifier is not received, identifying the last visited base station based on the last visited cell identifier, wherein the last visited cell belongs to the last visited base station.

At least one of the anchor base station identifier, the context identifier, and the at least one of the last visited cell identifier and the last visited base station identifier may be comprised in the location update information from the terminal.

The context may be requested via a second direct connection between the new base station and the last visited base station.

At least one of the first direct connection and the second direct connection may be based on an Xn interface.

According to a third aspect of the invention, there is provided an apparatus, comprising at least one processor, at least one memory including computer program code, and the at least one processor, with the at least one memory and the computer program code, being arranged to cause the apparatus to at least perform supervising if a last visited base station receives a request for a context from a new base station, wherein the request for the context comprises

an anchor base station identifier of an anchor base station and a context identifier of the context; instructing the last visited base station to ask the anchor base station for the context if the last visited base station receives the request; monitoring if the last visited base station receives the context from the anchor base station in response to the asking for the context; prompting the last visited base station to forward the context to the new base station in response to the received request if the last visited base station receives the context.

The anchor base station may be asked for the context via a first direct connection between the last visited base station and the anchor base station; and/or the request may be received and the context may be forwarded via a second direct connection between the last visited base station and the new base station.

At least one of the first direct connection and the second direct connection may be based on an Xn interface.

The at least one processor, with the at least one memory and the computer program code, may be arranged to cause the apparatus to further perform checking, if the request is received, if the anchor base station identifier identifies the last visited base station; inhibiting the instructing of the last visited base station if the anchor base station identifier identifies the last visited base station.

According to a fourth aspect of the invention, there is provided a method, comprising checking if a terminal is in an inactive state in a notification area, monitoring if the terminal moves from a last visited cell of the notification area to a new cell outside the notification area; instructing the terminal to provide an anchor base station identifier of an anchor base station, a context identifier of a context for the terminal, and at least one of a last visited cell identifier of the last visited cell and a last visited base station identifier of a last visited base station to the new base station if the terminal is in the inactive state and moves from the last visited cell to the new cell; wherein the last visited cell belongs to the last visited base station; the new cell belongs to the new base station.

At least one of the anchor base station identifier, the context identifier, and the at least one of the last visited cell identifier and the last visited base station identifier may be provided along with the informing of the new cell on the location update of the terminal from the last visited cell to the new cell.

According to a fifth aspect of the invention, there is provided a method, comprising monitoring if a new base station receives, from a terminal, location update information for the terminal, an anchor base station identifier of an anchor base station, a context identifier of a context, and at least one of a last visited cell identifier of a last visited cell and a last visited base station identifier of a last visited base station; checking if a first direct connection between the new base station and the anchor base station exists if the location update information and the anchor base station identifier are received; instructing the new base station to request the context from the anchor base station via the last visited base station if the first direct connection does not exist and the at least one of the last visited cell identifier and the last visited base station identifier is received; wherein the request for the context from the anchor base station comprises the anchor base station identifier and the context identifier.

The method may further comprise, if the last visited cell identifier of the last visited cell is received and the last visited base station identifier is not received, identifying the last visited base station based on the last visited cell identifier, wherein the last visited cell belongs to the last visited base station.

At least one of the anchor base station identifier, the context identifier, and the at least one of the last visited cell identifier and the last visited base station identifier may be comprised in the location update information from the terminal.

The context may be requested via a second direct connection between the new base station and the last visited base station.

At least one of the first direct connection and the second direct connection may be based on an Xn interface.

According to a sixth aspect of the invention, there is provided a method, comprising supervising if a last visited base station receives a request for a context from a new base station, wherein the request for the context comprises an anchor base station identifier of an anchor base station and a context identifier of the context; instructing the last visited base station to ask the anchor base station for the context if the last visited base station receives the request; monitoring if the last visited base station receives the context from the anchor base station in response to the asking for the context; prompting the last visited base station to forward the context to the new base station in response to the received request if the last visited base station receives the context.

The anchor base station may be asked for the context via a first direct connection between the last visited base station and the anchor base station; and/or the request may be received and the context may be forwarded via a second direct connection between the last visited base station and the new base station.

At least one of the first direct connection and the second direct connection may be based on an Xn interface.

The method may further comprise checking, if the request is received, if the anchor base station identifier identifies the last visited base station; inhibiting the instructing of the last visited base station if the anchor base station identifier identifies the last visited base station.

Each of the methods of the fourth to sixth aspects may be a method of context fetching.

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 embodiments of the invention, at least one of the following advantages may be achieved:

• The concentration of processing load in the AMF central node is avoided by using a distributed mechanism. Thus, the processing load is spread across many gNBs instead of being concentrated in the AMF.

• The delay for the transfer of the context is reduced compared to that when the central AMF is involved.

• Routing via multiple AMFs is avoided for a case that the new gNB and the anchor gNB do not share the AMF.

• Signalling load on CN and between RAN and CN is reduced.

• The solution is backward compatible for the anchor gNB.

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 t e drawings

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

Fig. 1 shows a call flow according to an embodiment of the invention;

Fig. 2 shows an apparatus according to an embodiment of the invention;

Fig. 3 shows a method according to an embodiment of the invention;

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

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

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

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

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

Detailed description of certain embodiments

Herein below, certain embodiments of the present invention are described in detail with reference to the accompanying drawings, wherein the features of the embodiments can be freely combined with each other unless otherwise described. However, it is to be expressly understood that the description of certain 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.

Some embodiments of the invention provide mechanisms to inform the anchor gNB on the location update of the UE to a new gNB outside the RNA and to transfer the context for the UE to the new gNB.

According to some embodiments of the invention, when the UE moves out of the RNA it includes the identity of the last cell (e.g. NGCI) which it has visited in the RNA in the RRC Location Update message to the new gNB, in addition to anchor gNB ID and UE context ID. According to current discussion in 3GPP, it is planned to send only the last two pieces of information.

The new gNB extracts from the identity of the last visited cell (its NGCI) the identity of the gNB serving the last visited cell in the RNA, i.e. the identity of the Last Visited gNB (LV gNB) in the last used RNA. The new gNB sends over a direct Xn interface to the LV gNB (also named relay gNB) an Xn message (called e.g. Xn Relay message) which includes the anchor gNB ID as destination, the new gNB ID as source, and the Xn context fetch request comprising the UE context ID. When receiving this Xn Relay message, the LV gNB propagates the Xn Context fetch request towards the anchor gNB over a second direct interface between the LV gNB and the anchor gNB.

The new gNB may provide to the Anchor gNB, via the relay gNB (LV gNB), all the information a new gNB being Xn connected with the Anhor gNB would provide, in order for the Anchor gNB e.g. to compute the security keys for the UE in the New gNB.

In return, the same mechanism is used by the anchor gNB to reply via the LV gNB to the new gNB by sending a Relay Response Xn message including the new gNB ID as destination, the anchor gNB ID as source and including the UE context.

Embodiments of the invention avoid at least some of the drawbacks mentioned above of the "best existing" solution. In particular, if the request for the context and the response via the relay gNB (LV gNB) are transmitted via respective direct interfaces (i.e. a first Xn interface between anchor gNB and relay gNB and a second Xn interface between the relay gNB and the new gNB in the case of Xn interfaces), the context fetch is confined to the RAN such that one of the purposes of the inactive state feature are fulfilled. The term "direct interface" relates to the logical structure of the interface which does not comprise an intervening node on the top layer. However, on the lower layers, the interface may be based on intervening nodes such as routers, bridges, etc.

However, even if, for some reasons, one of the connections between the new gNB and the relay gNB or between the relay gNB and the anchor gNB goes via the CN (e.g. 5GC), it might still have the advantage that the risk for routing via multiple AMFs in the CN is reduced.

In some embodiments, the UE provides the ID of the anchor gNB, the context ID, and the ID of the previous visited cell in the location update message to the new gNB. However, in some embodiments, the UE provides one or more of these information elements in one or more additional messages different from the location update message to the new gNB. Preferably,

such additional message(s) follow the location update message, but they may precede the location update message instead.

Fig. 1 shows a call flow according to an embodiment of the invention. The call flow may be performed when the UE moves from a cell of the LV gNB in the RNA to a cell of the new gNB outside the RNA, wherein the anchor gNB and the new gNB are not Xn connected. As shown in Fig. 1 , the UE provides in the RRC location update message to the new gNB an ID of the last visited cell (LV NGCI), an ID of the anchor gNB, and a UE context ID, which identifies the context for the UE kept in the anchor gNB.

The new gNB derives the ID of the gNB to which the last visited cell belongs (LV gNB-ID) from LV NGCI. Then, it issues, via XN interface to the LV gNB (relay gNB), an Xn relay request containing a context fetch request, which comprises the ID of the new gNB, the ID of the anchor gNB, and context fetch information including at least the UE context ID.

The LV gNB propagates the Xn context fetch request to the Anchor gNB via the Xn interface between LV gNB and anchor gNB. In response, the anchor gNB provides the context to the LV gNB, which forwards the context to the new gNB in response to the Xn relay request.

The request from the LV gNB (relay gNB) arriving at the anchor gNB may have the same format as a corresponding request from a new gNB outside the RNA which is Xn connected to the anchor gNB. However, in the former case, the destination indicated in the request (new gNB) is different from the originator of the request (relay gNB) arriving at the anchor gNB, while, in the latter case, these identifiers may be the same. If the anchor gNB does not check if these IDs are the same, the anchor gNB need not to be modified over a conventional anchor gNB such that embodiments of the invention may be backwards compatible with respect to the anchor gNB.

In some embodiments of the invention, at least one of the request from the new gNB to the relay gNB and the request from the relay gNB to the anchor gNB may not comprise an indication of the final destination for the context (i.e. the ID of the new gNB). The anchor gNB may not need this information. The relay gNB knows the new gNB because it receives the request from the new gNB.

In some embodiments, the UE may provide to the new gNB an identifier of the LV gNB instead of or in addition to the LV NGCI. In these embodiments, the new gNB need not to derive the ID of the LV gNB from the LV NGCI. For example, the identifier of the LV gNB may be embedded in the cell identifier of the last visited cell.

Fig. 2 shows an apparatus according to an embodiment of the invention. The apparatus may be a terminal such as a UE, an loT device, a MTC device, or an element thereof. Fig. 3 shows a method according to an embodiment of the invention. The apparatus according to Fig. 2 may perform the method of Fig. 3 but is not limited to this method. The method of Fig. 3 may be performed by the apparatus of Fig. 2 but is not limited to being performed by this apparatus.

The apparatus comprises checking means 10, monitoring means 20, and instructing means 30. Each of the checking means 10, monitoring means 20, and instructing means 30 may be a checker, monitor, and instructor, respectively. Each of the checking means 10, monitoring means 20, and instructing means 30 may be a checking processor, monitoring processor, and instructing processor, respectively.

The checking means 10 checks if a terminal is in an inactive state (e.g. RRC_inactive state) in a notification area (e.g. RNA) (S10). If the terminal is in the inactive state in the notification area, the terminal does not inform another cell of the notification area on a location update when it moves from the last visited cell of the notification area to the other cell of the notification area, and, the terminal informs a new cell outside the notification area on the location update when it moves from the last visited cell of the notification area to the new cell outside the notification area.

The monitoring means 20 monitors if the terminal moves from a last visited cell of the notification area to a new cell outside the notification area (S20). The last visited cell belongs to a last visited base station (sometimes also called relay base station), and the new cell belongs to a new base station.

The sequence of S10 and S20 is arbitrary, i.e. S20 may follow S10, or S10 may follow S20. S10 and S20 may be performed fully or partly in parallel.

If the terminal moves from the last visited cell of the notification area to the new cell outside the notification area (S20 = "yes"), the terminal may provide a location update information to the new cell because it is in the inactive state in the notification area and the new cell is outside the notification area. However, this step may be outside the claimed method and may be controlled by another apparatus.

In addition, if the terminal is in the inactive state (S10 ="yes") and moves from the last visited cell of the notification area to the new cell outside the notification area (S20 = "yes"), the instructing means instructs the terminal to provide an anchor base station identifier of an anchor base station, a context identifier of a context for the terminal, and at least one of a last visited cell identifier of the last visited cell and a last visited base station identifier of a last visited base station to the new base station (S30).

Fig. 4 shows an apparatus according to an embodiment of the invention. The apparatus may be a base station such as a NB (e.g. gNB or eNB), or an element thereof. It may have the role of a new base station. Fig. 5 shows a method according to an 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 monitoring means 1 10, checking means 120, and instructing means 130. Each of the monitoring means 1 10, checking means 120, and instructing means 130 may be a monitor, checker, and instructor, respectively. Each of the monitoring means1 10, checking means 120, and instructing means 130 may be a monitoring processor, checking processor, and instructing processor, respectively.

The monitoring means 1 10 monitors if a new base station receives, from a terminal (e.g. UE), location update information for the terminal, an anchor base station identifier of an anchor base station, a context identifier of a context, and at least one of a last visited cell identifier of a last visited cell and a last visited base station identifier of a last visited base station (S1 10). If the last visited cell identifier is provided, the apparatus assumes that the last visited cell belongs to the last visited base station.

If, according to S110, the location update information and the anchor base station identifier are received, the checking means 120 checks if a first direct connection between the new base station and the anchor base station exists (S120).

The monitoring of S1 10 if the context identifier and the at least one of the last visited cell identifier and the last visited base station identifier are received may be performed in an arbitrary sequence with respect to S120. These steps may be performed fully or partly in parallel.

If the first direct connection does not exist (S120 = "no") and, according to S1 10, the at least one of the last visited cell identifier and the last visited base station identifier is received, the instructing means 130 instructs the new base station to request the context from the anchor base station via the last visited base station (S130). The request for the context from the anchor base station comprises the anchor base station identifier and the context identifier. It may additionally comprise an identifier of the new base station. Due to S130, the last visited base station is sometimes called a relay base station.

Fig. 6 shows an apparatus according to an embodiment of the invention. The apparatus may be a base station such as a NB (e.g. gNB or eNB), or an element thereof. It may have the role of a relay base station and of the last visited base station in the RNA for a terminal. Fig. 7 shows a method according to an 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 supervising means 210, instructing means 230, monitoring means 240, and prompting means 250. Each of the supervising means 210, instructing means 230, monitoring means 240, and prompting means 250 may be a supervisor, instructor, monitor, and prompter, respectively. Each of the supervising means 210, instructing means 230, monitoring means 240, and prompting means 250 may be a supervising processor, instructing processor, monitoring processor, and prompting processor, respectively. Optionally (indicated by the dashed lines in Figs. 6 and 7), the apparatus may comprise checking means 220 which may be a checker or a checking processor.

The supervising means 210 supervises if a last visited base station (sometimes also named relay base station) receives a request for a context from a new base station (S210). The request for the context comprises an anchor base station identifier of an anchor base station and a context identifier of the context.

In some embodiments of the invention comprising the checking means 220, the checking means 220 checks if the last visited base station is the same as the anchor base station. In detail, if the request is received (S210 = "yes"), the checking means 220 checks if the anchor base station identifier identifies the last visited base station (S220), i.e. if the last visited base station is the anchor base station such that it may provide itself the context. Thus, the new

gNB may send t e same context fetch request, regardless of whether or not the anchor gNB is Xn connected to the new gNB.

The instructing means 230 instructs the last visited base station to ask the anchor base station for the context (S230). In embodiments without the checking means 220, S230 is performed by the instructing means 230 if the last visited base station receives the request (S210 = "yes"). In embodiments comprising the checking means 220, S230 may be performed by the instructing means 230 if the anchor base station identifier does not identify the last visited base station (S220 = "no"; i.e., the last visited base station is different from the anchor base station). Due to S230, the last visited base station is sometimes called relay base station.

The monitoring means 240 monitors if the last visited base station receives the context from the anchor base station in response to the asking for the context instructed in S230 (S240).

If the last visted base station receives the context (S240 = "yes"), the prompting means 250 prompts the last visited base station to forward the context to the new base station in response to the request received in S210 (S250).

Fig. 8 shows an apparatus according to an embodiment of the invention. The apparatus comprises at least one processor 410, at least one memory 420 including computer program code, and the at least one processor 410, with the at least one memory 420 and the computer program code, being arranged to cause the apparatus to at least perform at least one of the methods according to Figs. 3, 5, and 7.

In some embodiments of the invention, instead of the (full) context, only a portion of the context is transferred from the anchor gNB to the new gNB. Therefore, unless otherwise described or made clear from the context, the term "context" in the present application includes both the full context and a portion of the context.

Embodiments of the invention are described with respect to a UE. A UE is a particular kind of a terminal. All kinds of terminals may belong to embodiments of the invention. E.g., terminals in which embodiments of the invention are implemented may be a loT device, a MTC device, a laptop, a tablet, a smartphone, a mobile phone, etc.

The invention is described for a 5G network. However, it may be employed also in other networks of other radio technologies where a concept of an inactive state (such as

RRCjnactive state) in a notification area (such as a RAN notification area) exists, even if different terms may be used in other technologies. According to the concept, the terminal does not inform a new cell on a location update if the new cell is in the notification area, and informs the new cell on the location update if the new cell is not in the notification area, wherein the context of the terminal is kept at an anchor base station while the terminal moves in the notification area. Correspondingly, in other technologies than 5G, another direct interface between base stations than the Xn interface may be used, such as an X2 interface in LTE and LTE-A.

Accordingly, a base station may be a RAN node of the respective radio technology.

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 terminal such as a UE, an loT device, a MTC device etc., 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 base station such as a NB (e.g. gNB, 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).

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 embodiments of the present invention. However, it should be noted that the description of the preferred 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.