Patent Description:
Non patent literature <NUM> (TS23. <NUM>) shows <NUM> System Architecture (see <FIG>) and some overload/congestion control methods. One example of the control methods is AMF Overload Control as below.

Under unusual circumstances, if AMF has reached overload situation, the AMF activates NAS level congestion control as specified in Clause <NUM>. <NUM> of the Non patent literature <NUM> and AMF restricts the load that the AN node(s) are generating, if the AN is configured to support overload control. N2 overload control can be achieved by the AMF invoking the N2 overload procedure (see TS <NUM> and TS <NUM>) to all or to a proportion of the AN nodes with which the AMF has N2 connections. The AMF may include the S-NSSAI(s) in N2 overload control message sent to AN node(s) to indicate the congestion of the Network Slice(s) at the CN part. To reflect the amount of load that the AMF wishes to reduce, the AMF can adjust the proportion of AN nodes which are sent NGAP OVERLOAD START message, and the content of the overload start procedure.

The AMF should select the <NUM>-AN node(s) to which it triggers overload start procedure at random to avoid that multiple AMFs in an AMF Set request reduction of load from the same subset of <NUM>-AN node(s).

An AN node supports rejecting of AN signalling connection establishments for certain UEs as specified in TS <NUM>. Additionally, an AN node provides support for the barring of UEs as described in TS <NUM>. These mechanisms are further specified in TS <NUM>.

Using the overload start procedure, the AMF can request the AN node to:.

The AN signaling connection requests listed in this clause also include the request from UE in RRC-Inactive state.

The AMF can provide percentage value that indicates how much amount of signalling traffic to be rejected in the overload start message, and the AN node may consider this value for congestion control.

When rejecting an AN signaling connection request for overload reasons the AN indicates to the UE an appropriate wait timer value that limits further AN signaling connection requests for a while.

During an overload situation, the AMF should attempt to maintain support for emergency services and for MPS.

When the AMF is recovering, the AMF can either:.

PTL <NUM>: <CIT> discloses a communication method and apparatus using network slicing. A communication method of a communication apparatus performing communication with a UE receives a predetermined request from the UE, selects a single network slice instance to be allocated to the UE from among a plurality of network slice instances in the communication apparatus in response to the request, selects a single network function instance to be allocated to the UE from among a plurality of network function instances included in the selected network slice instance. The network slice instance is in an instantiated form of a network slice that includes at least one network function and resource for providing a network service having a predetermined capability and characteristic to the UE.

According to the description of the AMF Overload Control in the non-patent document <NUM>, the AMF may include the S-NSSAI(s) in N2 overload control message sent to AN node(s). However, in the current procedure, the UE cannot perform an appropriate behaviour regarding the congestion as information which is sent from the AN node is insufficient.

Embodiments of the invention solve the following five issues which are related to general NAS level congestion control mechanism and network slice congestion control mechanism.

No information is sent with wait timer to the UE to identify if wait timer is related to General NAS level congestion or a network slice congestion.

Under general overload condition the network applies General NAS congestion control mechanism and sends a message to NG-RAN instructing NG-RAN to reject a request to establish an AN signalling connection. Following this, the NG-RAN rejects AN Signalling connection and sends wait timer in an AN signalling message.

Under a network slice overload condition, the AMF sends a message including network slice id (S-NSSAI(s)) of the congested network slice to the NG-RAN to reject the AN signalling connection. The NG RAN will reject the AN signalling connection and send wait time to the UE in a AN signalling connection.

So a wait timer is sent to the UE under two situations when a AMF applies General NAS level congestion control and a network slice related congestion control. The UE doesn't know whether the wait timer is related to a network slice congestion or a general NAS level congestion. Therefore, the UE behaviour becomes non deterministic when it receives a wait time without an indication identifying whether the wait timer is related to general NAS level congestion timer or a network slice congestion.

Network Slice Identifier of the congested network slice with wait timer is not being sent to the UE.

When the NG-RAN receives a message containing network slice identifier of the congested network slice to start the overload control procedure, then NG-RAN is releasing or rejecting the AN signalling connection without sending the wait time and a network slice identifier of the congested network. The UE may again initiate procedure (NAS or AS) related to congested network slice and may again congest the network (AMF/SMF/NG-RAN).

No mechanism is defined to handle a scenario at NG-RAN for a UE when some network slice related to the UE are congested and some network slice related to the UE are not congested.

The NG-RAN receives a message (e.g. NGAP OVERLOAD START) containing a network slice identifier of the congested network slice from the AMF to start congestion control related to the network slice. The UE has a PDU session(s) established related to the network slice and a PDU session(s) related to other network slice. In this scenario the NG-RAN behaviour regarding the UE is not clear or nondeterministic. It is not clear whether the NG-RAN will release all AN connection or only release the resources related to the congested network slice only.

When a AN connection is established during the service request procedure, the S-NSSAI for which the service request procedure is initiated is not included in the AN signalling message. Since a AN signalling Request message doesn't contain requested NSSAI during AN signalling establishment procedure therefore the RAN cannot perform RAN overload control procedure related to a congested network slice. If a lot of UE is initiating service request procedure to establish a PDU session then AN cannot reject AN connection establishment and send the message to AMF or SMF then the AMF/SMF gets further congested. This may lead to severe network failure.

When a UE is establishing a AN signalling connection related to a S-NSSAI to N3IWF for a non-3GPP access, then no procedure is defined to send a congested S-NSSAI and corresponding wait time.

The present invention provides a User Equipment, an Access Management Function, a Next Generation Radio Access Network node and associated methods as defined in the appended independent claims. Optional features are defined in the appended dependent claims.

For the purposes of the present document, the abbreviations given in TR <NUM> and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR <NUM>.

In order to make both general NAS level congestion control and network slice congestion control works together, a procedure is needed by a (R)AN node to send a congested S-NSSAI with wait time to the UE so that the UE does not need initiates any signaling related to the S-NSSAI for the duration of wait time due to following reasons:.

The reasons also include to protect the (R)AN node when it is congested or to prevent RAN node getting congested.

This invention discloses the following technical aspects to the overload control in the 5GS.

The <FIG> shows a procedure related to handling of congestion control at (R)AN node and the UE when AMF indicates that congestion related to network slice congestion or general NAS congestion.

The network ((R)AN and AMF) and the UE will follow the procedure as described in the <FIG> and procedure as described below.

In one scenario in above case of step <NUM>, the (R)AN node provides an additional information in a first information element (e.g. AN cause or RRC cause) indicating the reason for failure in establishing the AN signaling connection together with list of S-NSSAI and wait time in the second AN signaling message. The information element contains a value congestion if RAN detects general NAS level congestion or network slice congestion if RAN detects congestion in the network slice(s).

In case, the AN signaling connection establishment is rejected due to NAS level congestion then the AN node set the information element with value congestion and includes wait time in the first AN message and does not include list of S-NSSAI and their wait time. In one case it just includes wait time in the second AN signaling connection and does not include list of S-NSSAI and their wait time and the first information element.

In one scenario in the above case, the wait time sent for each S-NSSAI to the UE may be same as or based on the wait time provided by the AMF for this S-NSSAI.

In one scenario in the above case, the wait time sent for each S-NSSAI to the UE is derived by the (R )AN node by considering the wait time received from the AN node for this S-NSSAI as one input parameter in deriving the wait time.

In one scenario when the wait time is not received from the AMF then the (R)AN decides wait time for each S-NSSAI by itself or on some other parameters provided by AMF in the N2 message.

If the second AN signaling message contains the list of S-NSSAI and wait time for each S-NSSAI and does not contain the first information element then the UE does not initiate any NAS or AS procedure related to the S-NSSAI present in the list for the period of corresponding wait time i.e. the UE does not send any NAS or AS signaling related to the S-NSSAI present in the S-NSSAI present in the list for the period of corresponding wait time. The UE initiates NAS procedure or AS procedure related to a S-NSSAI not present in the list of S-NSSAI received from the (R )AN node i.e. the UE sends NAS or AS message related to a S-NSSAI not present in the list of S-NSSAI received from the (R)AN node. The UE may initiate NAS procedure or AS procedure related to a S-NSSAI present in the list of S-NSSAI received from the (R )AN node if the wait timer expires.

If the second AN signaling message contains wait time and does not contain the list of S-NSSAI and their wait time, and the first information element, then the UE does not initiates any NAS or AS procedure i.e. the UE does not send any AS or NAS signaling message to the network. The UE does not establish any AS or NAS signaling connection. The UE determines that the AN signaling connection establishment fails due to general NAS level congestion.

If the second AN signaling message contains the information element which value is set to congestion, and wait time but does not contain list of S-NSSAI and then the UE does not initiates any NAS or AS procedure i.e. the UE does not send any AS or NAS signaling message to the network. The UE does not establish any AS or NAS signaling connection. The UE determines that the AN signaling connection establishment fails due to general NAS level congestion with the network.

In another scenario, the AN, the UE and the AMF may performs as following steps:.

In this embodiment, the AMF determines the timer value and the AMF optionally sends the timer value to the (R)AN node. However, the (R)AN node can determine the timer value instead of the AMF. The (R)AN node can determine the timer value based on information from the AMF. The information can be, for example, load level information(e.g. <NUM>. very high/high/middle/low <NUM>. percentage of the load),. The variation that the (R)AN node determines the timer value can be applied to other embodiment in this description.

The <FIG> shows a procedure for the scenario when the UE has NAS signaling connection established and has at least one PDU session established.

In the description above, AN signaling message is shown. An example of the AN signaling message is RRC connection release.

Also, in the description above, an example to release the network resources relates to S-NSSAI. The network resource can be identified by not only the S-NSSAI but also a current PDU session ID.

When the UE sends, to the AMF, a PDU session Establish Request which includes any one of parameters below after a back-off timer expires.

This resource identification in this embodiment can be applied to other embodiment in this description.

The <FIG> shows a procedure related to release of network resources of a congested network slice(s) only and keeping network resources of non-congested slice(s).

In this procedure the network resources are AN resources and CN resources. The AN and CN resources further comprise signalling resources and user plane resources. The example of AN resources is DRB and SRB and example of the CN resources are GTP-U resources and QoS flows. From another perspective, the AN resources may be all radio resources including at least one of the RLC entity, the MAC configuration and the associated PDCP entity for all established radio bearers.

If the first AN signaling message contains the list of S-NSSAI and wait time for each S-NSSAI and does not contain the first information element then the UE does not initiate any NAS or AS procedure related to the S-NSSAI present in the list for the period of corresponding wait time i.e. the UE does not send any NAS or AS signaling related to the S-NSSAI present in the S-NSSAI present in the list for the period of corresponding wait time. The UE initiates NAS procedure or AS procedure related to a S-NSSAI not present in the list of S-NSSAI received from the (R )AN node i.e. the UE sends NAS or AS message related to a S-NSSAI not present in the list of S-NSSAI received from the (R)AN node.

After step <NUM>, the (R)AN node sends a second N2 message to the AMF containing list of S-NSSAI and UE ID requesting AMF to release the network resources related to the PDU sessions established for the S-NSSAI(s) present in the list. The N2 message is a new N2 message.

The AMF receives the second N2 message and initiates network resources release procedure related to the PDU session(s) corresponding to the S-NSSAI(s) present in the list by sending a message to the related SMF.

The <FIG> shows a procedure releasing network resources related to all S-NSSAI if one S-NSSAI related to the UE is indicated as congested by the AMF. This procedure discloses the following technical aspects to the overload control in the 5GS.

In case the AN signaling connection establishment is rejected due to NAS level congestion then the AN node set the information element with value congestion and includes wait time in the first AN message and does not include list of S-NSSAI and their wait time. In one case it just includes wait time in the second AN signaling connection and does not include list of S-NSSAI and their wait time and the first information element.

In one scenario in the above case the wait time sent for each S-NSSAI to the UE is same as the wait time provided by the AMF for this S-NSSAI.

In one scenario in the above case the wait time sent for each S-NSSAI to the UE is derived by the (R )AN node by considering the wait time received from the AN node for this S-NSSAI as one input parameter in deriving the wait time.

If the second AN signaling message contains the list of S-NSSAI and wait time for each S-NSSAI and does not contain the first information element then the UE does not initiate any NAS or AS procedure related to the S-NSSAI present in the list for the period of corresponding wait time i.e. the UE does not send any NAS or AS signaling related to the S-NSSAI present in the S-NSSAI present in the list for the period of corresponding wait time. The UE initiates NAS procedure or AS procedure related to a S-NSSAI not present in the list of S-NSSAI received from the (R )AN node i.e. the UE sends NAS or AS message related to a S-NSSAI not present in the list of S-NSSAI received from the (R)AN node.

If the second AN signaling message contains wait time and does not contain the list of S-NSSAI and their wait time, and the first Information element, then the UE does not initiates any NAS or AS procedure i.e. the UE does not send any AS or NAS signaling message to the network. The UE does not establish any AS or NAS signaling connection.

If the second AN signaling message contains the information element which value is set to congestion, and wait time but does not contain list of S-NSSAI and then the UE does not initiates any NAS or AS procedure i.e. the UE does not send any AS or NAS signaling message to the network. The UE does not establish any AS or NAS signaling connection.

The (R)AN node initiate UE context release procedure as defined in sub clause <NUM>. <NUM> of TS Non patent literature <NUM>.

The <FIG> shows a handling of network slice related congestion at AN node during service request procedure. This procedure discloses the following technical aspects to the overload control in the 5GS.

The <FIG> shows a procedure to handle congestion control by N3IWF. This procedure discloses the following technical aspects to the overload control in the 5GS.

Step 4a may contains a parameter that indicates that this message is for the attach request or registration request as the IKE parameter or as the EAP parameter. Step 4b may contains a parameter that indicates that this message is for the service request as the IKE parameter or as the EAP parameter. Step 4b may contains an S-NSSAI parameter that indicates that an S-NSSAI that UE wishes to establish the PDU connection in the IKE parameter or in the EAP parameter.

Either step 5a or 5b takes place.

The N3IWF sends an IKE message containing a wait time and an optional information element AN cause which is set to a value (e.g. congestion )related to NAS congestion when it receives a N2 message in step 1a to perform NAS level congestion controlor.

The N3IWF sends an IKE message containing a list of S-NSSAI which present in the step 4a or 4b and indicated as congested in the first N2 message in step 1a. The IKE message also contains wait time for each S-NSSAI in present in the list. The IKE message optionally contains an information element indicating network slice related congestion.

The message is step <NUM> is as defined as follows:.

Either step 6a or 6b takes place in accordance with step <NUM>.

If the IKE message in step <NUM> contains the information element set to network slice congestion or congestion, and contains the list of S-NSSAI and wait time for each S-NSSAI then the UE does not initiate any NAS or AS procedure related to the S-NSSAI present in the list for the period of corresponding wait time i.e. the UE does not send any NAS or AS signaling related to the S-NSSAI present in the S-NSSAI present in the list for the period of corresponding wait time. The UE initiates NAS procedure or AS procedure related to a S-NSSAI not present in the list of S-NSSAI received from the (R)AN node i.e. the UE sends NAS or AS message related to a S-NSSAI not present in the list of S-NSSAI received from the (R)AN node.

If the IKE AN message is step <NUM> contains the list of S-NSSAI and wait time for each S-NSSAI and does not contain the first information element then the UE does not initiate any NAS or AS procedure related to the S-NSSAI present in the list for the period of corresponding wait time i.e. the UE does not send any NAS or AS signaling related to the S-NSSAI present in the S-NSSAI present in the list for the period of corresponding wait time. The UE initiates NAS procedure or AS procedure related to a S-NSSAI not present in the list of S-NSSAI received from the (R)AN node i.e. the UE sends NAS or AS message related to a S-NSSAI not present in the list of S-NSSAI received from the (R)AN node.

If the IKE message in step <NUM> contains wait time and does not contain the list of S-NSSAI and their wait time, and the first Information element, then the UE does not initiates any NAS or AS procedure i.e. the UE does not send any AS or NAS signaling message to the network. The UE does not establish any AS or NAS signaling connection.

If the IKE message in step <NUM> contains the information element which value is set to congestion, and wait time but does not contain list of S-NSSAI and then the UE does not initiates any NAS or AS procedure i.e. the UE does not send any AS or NAS signaling message to the network. The UE does not establish any AS or NAS signaling connection.

<FIG> is a block diagram illustrating the main components of the UE. As shown, the UE (<NUM>) includes a transceiver circuit (<NUM>) which is operable to transmit signals to and to receive signals from the connected node(s) via one or more antenna (<NUM>). Although not necessarily shown in <FIG>, the UE will of course have all the usual functionality of a conventional mobile device (such as a user interface (<NUM>)) and this may be provided by any one or any combination of hardware, software and firmware, as appropriate. Software may be pre-installed in the memory and/or may be downloaded via the telecommunication network or from a removable data storage device (RMD), for example.

A controller (<NUM>) controls the operation of the UE in accordance with software stored in a memory (<NUM>). The software includes, among other things, an operating system and a communications control module (<NUM>) having at least a transceiver control module (<NUM>). The communications control module (<NUM>) (using its transceiver control sub-module) is responsible for handling (generating/sending/receiving) signalling and uplink/downlink data packets between the UE and other nodes, such as the base station / (R)AN node, the AMF (and other core network nodes). Such signalling may include, for example, appropriately formatted signalling messages relating to connection establishment and maintenance (e.g. RRC connection establishment and other RRC messages), periodic location update related messages (e.g. tracking area update, paging area updates, location area update, RAN notification area (RNA) update) etc..

<FIG> is a block diagram illustrating the main components of an exemplary (R)AN node (<NUM>), for example a base station ('gNB' in <NUM>). As shown, the (R)AN node (<NUM>) includes a transceiver circuit (<NUM>) which is operable to transmit signals to and to receive signals from connected UE(s) via one or more antenna (<NUM>) and to transmit signals to and to receive signals from other network nodes (either directly or indirectly) via a network interface (<NUM>). A controller (<NUM>) controls the operation of the (R)AN node in accordance with software stored in a memory (<NUM>). Software may be pre-installed in the memory and/or may be downloaded via the telecommunication network or from a removable data storage device (RMD), for example. The software includes, among other things, an operating system and a communications control module (<NUM>) having at least a transceiver control module.

The communications control module (<NUM>) (using its transceiver control sub-module) is responsible for handling (generating/sending/receiving) signalling between the (R)AN node and other nodes, such as the UE, the AMF, and the UDM/UDR (e.g. directly or indirectly). The signalling may include, for example, appropriately formatted signalling messages relating to a radio connection and location procedures (for a particular UE), and in particular, relating to connection establishment and maintenance (e.g. RRC connection establishment and other RRC messages), periodic location update related messages (e.g. tracking area update, paging area updates, location area update, RAN notification area (RNA) update), N2 messaging (e.g. to activate an N2 connection, to convey an NAS message from the UE, to provide any RRC Inactive state feature capability support information to the AMF, and related N2 request/response messages from the core network), etc..

The controller is also configured (by software or hardware) to handle related tasks such as, when implemented, RRC Inactive state optimisation, UE mobility estimate and/or moving trajectory estimation.

<FIG> is a block diagram illustrating the main components of the AMF (<NUM>). As shown, the AMF (<NUM>) includes a transceiver circuit (<NUM>) which is operable to transmit signals to and to receive signals from other nodes (including the UE) via a network interface (<NUM>). A controller (<NUM>) controls the operation of the AMF (<NUM>) in accordance with software stored in a memory (<NUM>). Software may be pre-installed in the memory (<NUM>) and/or may be downloaded via the telecommunication network or from a removable data storage device (RMD), for example. The software includes, among other things, an operating system and a communications control module (<NUM>) having at least a transceiver control module.

The communications control module (using its transceiver control sub-module) is responsible for handling (generating/sending/ receiving) signalling between the AMF and other nodes, such as the UE, base station/(R)AN node, and UDM/UDR (directly or indirectly). Such signalling may include, for example, appropriately formatted signalling messages relating to the procedures described herein, for example, N2 messaging (e.g. from the (R)AN to activate an N2 connection, to convey an NAS message from the UE, and to provide any RRC Inactive state feature capability support information to the AM, and related N2 request/response messages to the (R)AN to provide, if implemented, (further) RRC Inactive assistance information), signalling messages relating to UE subscription enquiries, etc..

AS (Access Stratum) may include an RRC layer, a SADP layer, a PDCP layer, a RLC layer, a MAC layer and PHY layer.

NG-RAN may include an eNB (evolved Node B) connected with 5GC and gNB.

The "wait time" as mentioned above may be denoted as "wait timer ".

The "AN signaling message" in downlink as mentioned above may be "RRCConnectionReject", "RRCConnectionRelease" or "RRCConnectionReestablishmentReject".

Claim 1:
A Next Generation Radio Access Network, NG-RAN, node (<NUM>) comprising:
means for receiving (<NUM>), from an Access-mobility Management Function, AMF, (<NUM>) an NGAP OVERLOAD START message,
wherein the NGAP OVERLOAD START message includes one or more first Single Network Slicing Selection Assistance Information, S-NSSAIs, identifying one or more overloaded network slices;
means for receiving (<NUM>), from a User Equipment, UE, (<NUM>) a Radio Resource Control, RRC, Setup Complete message,
wherein the RRC Setup Complete message includes a list of one or more second S-NSSAIs; and
means for transmitting (<NUM>), to the UE (<NUM>), an RRC Release message in a case where the list only includes the one or more first S-NSSAIs,
wherein the RRC Release message includes a value of a timer, and
wherein the timer limits further RRC connection request by the UE (<NUM>) until the timer expires.