WO2019219752A1

WO2019219752A1 - Conditional connection and tunnel setup for small data transmission

Info

Publication number: WO2019219752A1
Application number: PCT/EP2019/062491
Authority: WO
Inventors: Qian Chen; Paul Schliwa-Bertling; Hans Bertil RÖNNEKE; Roland Gustafsson
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2018-05-18
Filing date: 2019-05-15
Publication date: 2019-11-21

Abstract

A method performed by a radio access node, RAN, in a radio access network of a cellular communications system adapted for communicating with a User Entity, UE, a User Plane Function, UPF, an Access and mobility management Function, AMF, and a Session Management Function, SMF. The method comprising: communicating (9_1) with a User Equipment, UE, to establish a Radio Resource Control, RRC, connection for small data fast path, SDFP, uplink data transmission; and conditionally allocating (9_1B) a downlink tunnel for a downlink data transmission to the UE and sending respective downlink tunnel information to a core network function.

Description

CONDITIONAL CONNECTION AND TUNNEL SETUP FOR SMALL DATA

TRANSMISSION

Technical Field

The present application is directed to transmission of small data packet data in 5G networks. More particularly, the invention relates to Infrequent Small Data user plane transmission in the uplink direction in 5G networks.

Background

Generally, all terms used herein are to be interpreted according to their ordinary meaning in the relevant technical field, unless a different meaning is clearly given and/or is implied from the context in which it is used. All references to a/an/the element, apparatus, component, means, step, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any methods disclosed herein do not have to be performed in the exact order disclosed, unless a step is explicitly described as following or preceding another step and/or where it is implicit that a step must follow or precede another step. Any feature of any of the embodiments disclosed herein may be applied to any other embodiment, wherever appropriate.

Likewise, any advantage of any of the embodiments may apply to any other embodiments, and vice versa. Other objectives, features, and advantages of the enclosed embodiments will be apparent from the following description.

The Third Generation Partnership Project (3GPP) has started Internet of Things (loT) study item for Fifth Generation (5G) networks through Technical Report (TR) 23.724 VO.3.0 [1]. One of the key issues is how to handle small data in an efficient way as documented below in TR 23.724 [1]

A first key issue (Key Issue 1 ) is support for infrequent small data

transmission. This key issue aims to provide solutions to support efficient infrequent small data transmissions for at least low complexity, power constrained, and low data-rate Cellular loT (CloT) User Equipment devices (UEs). In some of the usage scenarios, the devices (e.g., utility meters) may not be mobile throughout their lifetime. It is expected that the number of CloT devices will increase exponentially but the data size per device will remain small.

A second key issue (Key Issue 2) is frequent small data communication. This key issue aims at providing a solution to support efficient frequent small data transmissions for CloT, e.g. tracking devices for both Mobile Originated (MO) and Mobile Terminated (MT) use cases. It is expected that the number of such devices can increase exponentially, but the data size per device will remain small. Traffic characteristics for UEs used for CloT using frequent small data transmissions may lead to inefficient use of resources in the 3GPP system and high UE power consumption without use of appropriate

optimization.

Frequent small data communication targets optimizations that can meet both architecture requirements on UE power consumption and resource efficient system signaling in a balanced way. A traffic pattern is assumed where small data transmissions may occur from a few small data transmissions per hour to multiple small data transmissions per minute.

The objective of this key issue is to ensure optimized transmission with Internet Protocol (IP) based and non-IP based protocols. Failure to do so may lead to sub-optimal transmission characteristics with increased signaling and UE power consumption.

Different proposals are provided by different companies during 3GPP meetings including solution in S2-183041 [4] (further improved by S2-183214 [5]) and S2-184413 [6]

Summary

It is a first object to set forth a methods and apparatuses for providing improved and more reliable services for such dual connectivity UE’s.

This object has been solved by at least one of the following methods:

A method performed by a radio access node, RAN, in a radio access network of a cellular communications system adapted for communicating with a User Entity, UE, a User Plane Function, UPF, an Access and mobility management Function, AMF, and a Session Management Function, SMF,

the method comprising:

communicating with a User Equipment, UE, to establish a Radio Resource Control, RRC, connection for small data fast path, SDFP, uplink data transmission; and

conditionally allocating a downlink tunnel for a downlink data transmission to the UE and sending respective downlink tunnel information to a core network function.

The object mentioned above has moreover been solved by at least one of:

A method performed by a radio access node in a radio access network of a cellular communications system, the method comprising:

Sending, to an Access and Mobility management Function, AMF, in a core network of the cellular communications system, information that indicates a capability of the radio access node related to maintaining a tunnel between the radio access node and a User Plane Function, UPF, in the core network.

A method performed by an Access and Mobility management Function, AMF, in a core network of a cellular communications system, the method

comprising:

sending, to a radio access node, a paging request and an indication as to whether the paging request is due to signaling or data to the radio access network.

A method performed by a Session Management Function, SMF, in a core network of a cellular communications system, the method comprising:

Receiving, from an Access and Mobility management Function, AMF, during Protocol Data Unit, PDU, session establishment, information that indicates a capability of a radio access node related to maintaining a tunnel between the radio access node and a User Plane Function, UPF, in the core network; and moreover, storing the information. The invention also concerns various apparatuses adapted to carry out the methods above.

There currently exist certain challenges. The solutions provided in S2-183041 (c.f. fig. 1 and 2) and S2-184413 are both agreed in 3GPP meetings and documented as possible solutions in TR 23.724 [1] (i.e., solution 5 for S2- 183041 ) and solution 19 for S2-184413).

The solution in S2-183041 is about 1 ) exposing User Plane Function (UPF) tunnel information to the UE, 2) no N2 control plane signaling is needed during uplink (UL) data sending, 3) downlink (DL) data handling is the same as UE in Connection Management (CM) idle mode (CM-IDLE mode) after a certain time (e.g., UPF does not have DL N3 tunnel information and Core Network (CN) paging is to be triggered). Note that the UPF tunnel information includes, e.g., the N3 tunnel address information from the UPF. For instance, Technical Specification (TS) 23.501 [2] says“[t]he CN Tunnel Info

corresponds to the Core Network Address of the N3 tunnel corresponding to the PDU Session.” Figs. 1 and 2 show the basic concept of this solution.

The cons with this solution are:

That UPF information is exposed to the UE and subject to attack.

No N2 control plane establishment is a problem if MT signaling comes since the Access and Mobility management Function (AMF) will consider the UE to be in CM-IDLE and trigger paging while the UE is transferring data through the Small Data Fast Path (SDFP) tunnel.

The solution in S2-184413 is about 1 ) the Radio Access Node (RAN) keeps UPF tunnel information (i.e., the UL UPF N3 tunnel information) and exposes the“RAN information” (which can be used to find the UL UPF N3 tunnel) to the UE, 2) always performing N2 control plane signaling even when UL data sending is possible, 3) DL data handling is the same as UE in CM-IDLE mode always (e.g., the UPF does not have DL N3 tunnel information and CN paging is triggered). Note that the RAN information is, e.g., the Resume-ID defined in 3GPP TS 38.300, which is the RAN node Identifier (ID) plus a random allocated unique ID. Figs. 3 through 5 show the main concept of this solution. The cons with this solution are: Every UL data transfer will trigger the N2 signaling connection setup and also the DL N3 tunnel re-establishment, even when there is no need of MT- signaling or MT data.

Triggering of CN paging always during MT data seems not optimized.

Certain aspects of the present disclosure and their embodiments may provide solutions to the aforementioned or other challenges. Systems and methods are disclosed herein that provide condition based N2 control plane signaling and N3 tunnel setup and capability communication between the RAN and the AMF/ Session Management Function (SMF).

Certain embodiments may provide one or more of the following technical advantage(s). Using the embodiments disclosed herein, the following advantages are provided: only“RAN information” is exposed to the UE, UL/DL data transmission can be transferred without Control Plane signaling involvement, and N2 signaling connection setup and N3 tunnel re- establishment are conditional.

Using the embodiments disclosed herein, it will be possible to offer only one solution for infrequent small data transmission in 5G System (5GS) based on user plane instead of using data over Non-Access Stratum (NAS) which is not the preferable solution.

Brief description of the Drawings

Fig. 1 , 2 show a prior art solution known according to document S2-183041 , figs. 3 - 5 show various aspects of another known solution known according to S2-184413, fig. 6 illustrates one example of known non-roaming 5G system architecture for a cellular communications network, fig. 7 illustrates a known wireless communication system represented as a 5G network architecture composed of core Network Functions (NFs), fig. 8 illustrates a known 5G network architecture using service-based interfaces between the NFs in the control plane, fig. 9 shows an embodiment of the invention, fig. 10 shows a known split of user plane and control plane for a New Radio

(NR) base station, figs. 11 , 12A and 12B illustrate procedures according to further embodiments of the invention, fig. 13 - 15 illustrate example embodiments of a network node in which

embodiments of the present disclosure may be implemented.

Detailed description

Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Other embodiments, however, are contained within the scope of the subject matter disclosed herein, the disclosed subject matter should not be construed as limited to only the embodiments set forth herein; rather, these embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art. Additional information may also be found in the document(s) provided in the Appendix.

Radio Node: As used herein, a“radio node” is either a radio access node or a wireless device.

Radio Access Node: As used herein, a“radio access node” or“radio network node” is any node in a radio access network of a cellular communications network that operates to wirelessly transmit and/or receive signals. Some examples of a radio access node include, but are not limited to, a base station (e.g., a New Radio (NR) base station (gNB) in a 3GPP 5G NR network or an enhanced or evolved Node B (eNB) in a 3GPP Long Term Evolution (LTE) network), a high-power or macro base station, a low-power base station (e.g., a micro base station, a pico base station, a home eNB, or the like), and a relay node.

Core Network Node: As used herein, a“core network node” is any type of node in a core network. Some examples of a core network node include, e.g., a Mobility Management Entity (MME), a Packet Data Network Gateway (P- GW), a Service Capability Exposure Function (SCEF), an AMF (Access and Mobility management Function), a SMF (Session Management Function), a UPF (User Plane Function), or the like.

Wireless Device: As used herein, a“wireless device” is any type of device that has access to (i.e., is served by) a cellular communications network by wirelessly transmitting and/or receiving signals to a radio access node(s). Some examples of a wireless device include, but are not limited to, a UE in a 3GPP network and a Machine Type Communication (MTC) device.

Network Node: As used herein, a“network node” is any node that is either part of the radio access network or the core network of a cellular

communications network/system.

Note that the description given herein focuses on a 3GPP cellular

communications system and, as such, 3GPP terminology or terminology similar to 3GPP terminology is oftentimes used. Flowever, the concepts disclosed herein are not limited to a 3GPP system.

Note that, in the description herein, reference may be made to the term“cell;” however, particularly with respect to 5G NR concepts, beams may be used instead of cells and, as such, it is important to note that the concepts described herein are equally applicable to both cells and beams.

Fig. 6 illustrates one example of a cellular communications network 600 according to some embodiments of the present disclosure. In the

embodiments described herein, the cellular communications network 600 is a 5G NR network. In this example, the cellular communications network 600 includes base stations 602-1 and 602-2, which in LTE are referred to as eNBs and in 5G NR are referred to as gNBs, controlling corresponding macro cells 604-1 and 604-2. The base stations 602-1 and 602-2 are generally referred to herein collectively as base stations 602 and individually as base station 602. Likewise, the macro cells 604-1 and 604-2 are generally referred to herein collectively as macro cells 604 and individually as macro cell 604. The cellular communications network 600 may also include a number of low power nodes 606-1 through 606-4 controlling corresponding small cells 608-1 through 608-4. The low power nodes 606-1 through 606-4 can be small base stations (such as pico or femto base stations) or Remote Radio Heads

(RRHs), or the like. Notably, while not illustrated, one or more of the small cells 608-1 through 608-4 may alternatively be provided by the base stations 602. The low power nodes 606-1 through 606-4 are generally referred to herein collectively as low power nodes 606 and individually as low power node 606. Likewise, the small cells 608-1 through 608-4 are generally referred to herein collectively as small cells 608 and individually as small cell 608. The base stations 602 (and optionally the low power nodes 606) are connected to a core network 610.

The base stations 602 and the low power nodes 606 provide service to wireless devices 612-1 through 612-5 in the corresponding cells 604 and 608. The wireless devices 612-1 through 612-5 are generally referred to herein collectively as wireless devices 612 and individually as wireless device 612. The wireless devices 612 are also sometimes referred to herein as UEs.

Fig. 7 illustrates a wireless communication system represented as a 5G network architecture composed of core Network Functions (NFs), where interaction between any two NFs is represented by a point-to-point reference point/interface. Fig. 7 can be viewed as one particular implementation of the system 600 of Fig. 6.

Seen from the access side the 5G network architecture shown in Fig. 7 comprises a plurality of UEs connected to either a RAN or an Access Network (AN) as well as an AMF. Typically, the R(AN) comprises base stations, e.g. such as eNBs or gNBs or similar. Seen from the core network side, the 5G core NFs shown in Fig. 7 include a Network Slice Selection Function (NSSF), an Authentication Server Function (AUSF), a Unified Data Management (UDM), an AMF, a SMF, a Policy Control Function (PCF), and an Application Function (AF).

Reference point representations of the 5G network architecture are used to develop detailed call flows in the normative standardization. The N1 reference point is defined to carry signaling between the UE and AMF. The reference points for connecting between the AN and AMF and between the AN and UPF are defined as N2 and N3, respectively. There is a reference point, N 11 , between the AMF and SMF, which implies that the SMF is at least partly controlled by the AMF. N4 is used by the SMF and UPF so that the UPF can be set using the control signal generated by the SMF, and the UPF can report its state to the SMF. N9 is the reference point for the connection between different UPFs, and N14 is the reference point connecting between different AMFs, respectively. N15 and N7 are defined since the PCF applies policy to the AMF and SMP, respectively. N 12 is required for the AMF to perform authentication of the UE. N8 and N10 are defined because the subscription data of the UE is required for the AMF and SMF.

The 5G core network aims at separating user plane and control plane. The user plane carries user traffic while the control plane carries signaling in the network. In Fig. 7, the UPF is in the user plane and all other NFs, i.e., the AMF, SMF, PCF, AF, AUSF, and UDM, are in the control plane. Separating the user and control planes guarantees each plane resource to be scaled independently. It also allows UPFs to be deployed separately from control plane functions in a distributed fashion. In this architecture, UPFs may be deployed very close to UEs to shorten the Round Trip Time (RTT) between UEs and data network for some applications requiring low latency.

The core 5G network architecture is composed of modularized functions. For example, the AMF and SMF are independent functions in the control plane. Separated AMF and SMF allow independent evolution and scaling. Other control plane functions like the PCF and AUSF can be separated as shown in Fig. 7. Modularized function design enables the 5G core network to support various services flexibly.

Each NF interacts with another NF directly. It is possible to use intermediate functions to route messages from one NF to another NF. In the control plane, a set of interactions between two NFs is defined as service so that its reuse is possible. This service enables support for modularity. The user plane supports interactions such as forwarding operations between different UPFs. Fig. 8 illustrates a 5G network architecture using service-based interfaces between the NFs in the control plane, instead of the point-to-point reference points/interfaces used in the 5G network architecture of Fig. 7. Flowever, the NFs described above with reference to Fig. 7 correspond to the NFs shown in Fig. 8. The service(s) etc. that a NF provides to other authorized NFs can be exposed to the authorized NFs through the service-based interface. In Fig. 8 the service based interfaces are indicated by the letter“N” followed by the name of the NF, e.g. Namf for the service based interface of the AMF and Nsmf for the service based interface of the SMF etc. The Network Exposure Function (NEF) and the Network Repository Function (NRF) in Fig. 8 are not shown in Fig. 7 discussed above. Flowever, it should be clarified that all NFs depicted in Fig. 7 can interact with the NEF and the NRF of Fig. 8 as necessary, though not explicitly indicated in Fig. 7.

Some properties of the NFs shown in Figs. 7 and 8 may be described in the following manner. The AMF provides UE-based authentication, authorization, mobility management, etc. A UE even using multiple access technologies is basically connected to a single AMF because the AMF is independent of the access technologies. The SMF is responsible for session management and allocates IP addresses to UEs. It also selects and controls the UPF for data transfer. If a UE has multiple sessions, different SMFs may be allocated to each session to manage them individually and possibly provide different functionalities per session. The AF provides information on the packet flow to the PCF responsible for policy control in order to support Quality of Service (QoS). Based on the information, the PCF determines policies about mobility and session management to make the AMF and SMF operate properly. The AUSF supports authentication function for UEs or similar and thus stores data for authentication of UEs or similar while the UDM stores subscription data of the UE. The Data Network (DN), not part of the 5G core network, provides Internet access or operator services and similar.

An NF may be implemented either as a network element on a dedicated hardware, as a software instance running on a dedicated hardware, or as a virtualized function instantiated on an appropriate platform, e.g., a cloud infrastructure.

Systems and methods are disclosed herein that provide condition based N2 control plane signaling and N3 tunnel setup and capability communication between RAN and AMF/SMF. In this regard, the following discussion describes several procedures in which aspects of the present disclosure may be implemented. Note, however, that these procedures are examples.

Aspects of the present disclosure related to providing condition based N2 control plane signaling and N3 tunnel setup and capability communication between RAN and AMF/SMF may be implemented in other procedures or in other variations of the illustrated procedures.

Condition Based N2 Control Plane Signaling

In prior solutions (e.g., in solution 19 in TR 23.724 [1]), at UL small data (step 2), a tunnel update in the UPF (i.e., providing the RAN DL Tunnel information to the UPF) is always done. That is, the step 1 B + 1 C (see Fig. 9) or step 2/3/4 in Fig. 3 signaling (RAN-AMF-SMF-UPF). The solution proposed herein is that this tunnel update is only done when DL small data is expected. In other words, the tunnel update is conditional. For the common use case of sensor devices that only send one UL packet that is unconfirmed /

unacknowledged, the UPF tunnel update is not done.

In this solution, the RAN would by default NOT send (i.e., refrain from sending) any signaling with tunnel update (i.e., RAN DL N3 Tunnel Info) to the AMF-SMF-UPF. The RAN DL N3 Tunnel Info normally includes General Packet Radio Service Tunneling Protocol User Plane (GTP-U) Tunnel Endpoint ID (TEID) + IP address. Signaling with tunnel update would only be sent when any of the following conditions are met:

A prior request (e.g., Paging) has been received for the UE, e.g., due to DL small data or DL NAS signaling

The UE provided Assistance Information indicates that DL data transmissions are expected

The RAN has earlier received Communication Pattern parameters with, e.g., Traffic Profile Type indicating“dual packet transmission” (UL with subsequent DL or DL with subsequent UL) or“multiple packets transmission.” The Communication Pattern parameter may have been received in the RAN as part of Core Network Assisted eNB Parameters Tuning (TS 23.401 clause 4.3.21 ).

Fig. 9 illustrates one example procedure in which condition based (i.e., conditional) N2 control plane signaling is performed in accordance with some embodiments of the present disclosure. The procedure includes the following steps:

Pre-condition: The UE enters CM-IDLE mode with RAN and UPF kept N3 tunnel information with N3 tunnel release timer running as specified above Step 9_1 : The UE establishes an RRC connection for SDFP transfer. The parameters needed to route the UL data Protocol Data Unit (PDU), i.e. User Plane Index (UPI) allocated for the SDFP PDU Session and for the UE are passed to the RAN.

Based on the received UPI, the RAN determines the Central Unit of the User Plane (CU-UP) entity and UL N3 Tunnel (i.e., N3 tunnel release timer is still running) allocated for that UE and SDFP PDU Session. This enables the PDCP layer in CU-UP to perform decryption, integrity check, and header decompression. Note that the RAN node (e.g., gNB) includes the Central Unit of the Control Plane (CU-CP), CU-UP, and Digital Unit (DU) as illustrated in Fig. 10.

Note: An alternative would be to transfer the parameters as part of the UL data PDU.

Step 9_1 A: As specified in A) above, in case the AMF can trigger paging towards the RAN (e.g., due to N1 CP signaling or DL data) for the UE with a SDFP PDU session, the AMF restricts the paging request only towards the latest known RAN node.

The AMF may also include a flag to indicate if the paging request is due to CP signaling or DL data.

Step 9_1 B: If the RAN has the UE context based on the 5G System

Architecture Evolution (SAE) Temporary Mobile Subscriber ID (S-TMSI) in the paging request, the RAN (i.e., the radio access node) sets up N2 connection and provides the AMF with Next Generation Application Protocol (NGAP) UE ID. The RAN also allocates DL N3 tunnel if the flag in the paging request indicates that the paging request is for DL data. The AMF replies with Next Generation (NG) AMF ID.

Note: The RAN may, also based on the conditions B) and C) above, trigger step 1 B without step 1 A. Thus, in this regard, the establishment of the control plane N2 connection and allocation of the DL N3 tunnel by the RAN node and the sending of the respective DL N3 tunnel information to the AMF are conditional (i.e., performed only if any one of condition A, condition B, or condition C is satisfied). The NG-RAN may conditionally (e.g. AMF has paged UE or NG-RAN knows new N3 tunnel that need to be allocated) notify AMF of UE's connection resume without depending on timing of UL data forwarding. Step 9_1 C: If the AMF received DL N3 tunnel information from the RAN in step 1 B, the AMF sends the tunnel information to the SMF/UPF.

Note: Step 1 A/1 B can be performed at any time between step 1 and step 6. Step 9_2: The UE encrypts, and if needed integrity protects a UL data PDU and sends it to the RAN.

Based on the received UPI, the RAN (i.e., the radio access node) determines the CU-UP entity and N3 Tunnel allocated for that UE and SDFP PDU

Session. If the CP-UP is not available (e.g., after the N3 tunnel release timer expired and UE context is released), a fallback procedure (e.g., NAS Service Request) to user plane setup is initiated, see section 4.2.3.2 in TS 23.502.

The processed UL data PDU is forwarded on the N3 tunnel to the UPF. If the N3 tunnel release timer is running, the timer is stopped. The timer is re- started each time there is no user plane data associated with the SDFP PDU Session in the CP-UP. It is assumed that the N3 tunnel release timer in RAN and UPF (step 5) are initialized with same timeout values.

Step 9_3: The UPF verifies the QoS Flow Identity (QFI) in UL data PDU. If verified, the UPF forwards the UL data on the N6/N9 interface. If the N3 tunnel release timer is running, it is stopped. In addition, based on the reception of the UP data, the UPF enables subsequent DL data transmissions to the RAN on the N3 tunnel, either based on the previous DL N3 tunnel info or new DL N3 tunnel information from step 1 C above. The N3 tunnel release timer is re-started each time when there is no user plane data associated with the SDFP PDU Session in the UPF. It is assumed that the N3 tunnel release timer in the RAN and UPF are initialized with same timeout values. Step 9_4: A DL data packet may arrive on N6/N9 shortly after, e.g., an acknowledgement.

The UPF inserts the QFI into the N3 packet header and passes it to the RAN node on the N3 tunnel, which was enabled in step 3.

Step 9_5: The RAN (i.e., the radio access node) processes (e.g., encryption) and forwards the DL data PDU to the UE.

Step 9_6: Based on expiration of N3 tunnel release timer in the RAN/UPF,

N3 tunnel information is released at both the RAN and UPF.

Capability Communication between RAN and AMF/SMF

When a UE wants to setup a PDU session where the RAN may maintain certain Context (e.g., maintain N3 tunnel information) for later quick setup of the N3 tunnel, the RAN may provide respective support information (e.g., SDFP support capability, N3 tunnel release timer) to the AMF and the AMF may provide the support information to the SMF during establishment of the PDU session.

In this regard, Figs. 11 and Figs. 12A and 12B illustrate procedures for communicating such capability information from the RAN toward the

AMF/SMF and for subsequently using this capability information in the system.

Specifically, Fig. 11 illustrates a procedure in which a NG-RAN node (i.e., a radio access node) provides such capability information to an AMF in accordance with some embodiments of the present disclosure. As illustrated, when NG-RAN node initiates NG signaling towards the AMF, the NG-RAN node may indicate N3 tunnel maintaining capability information to the AMF. The N3 tunnel maintaining capability information includes, e.g., information that indicates capabilities of the NG-RAN node related to a N3 tunnel maintaining timer, RRC for SDFP, and/or the like. Further, the NG-RAN node may send this indication using non-UE related signaling (e.g., NG setup RequesT, 11_1 ) or using UE related signaling (e.g., Initial UE message, or other messages).

The AMF stores this capability information either at the RAN node level or as individual UE context information based on the selected message (i.e., if the message is non-UE related signaling then it is RAN node level information or if the message is UE related signaling then it is UE context level information). The AMF passes this information to the SMF during PDU session

establishment (see, e.g., Figs. 12A and 12B). The AMF may respond to the 5G-RAN node, e.g., to acknowledge receipt.

Figs. 12A and 12B illustrate a procedure for PDU session establishment that utilize the aforementioned capability information in accordance with some embodiments of the present disclosure. The procedure of Figs. 12A and 12B includes the following:

Step 1 : The UE provides an indication that it wants to establish a SDFP PDU session. Additionally, it is assumed that the UE could provide Network Slice Selection Assistance Information (NSSAI) indicating a specific network slice for SDFP which could be used by the RAN to select an AMF that supports SDFP.

Step 2: The AMF selects an SMF that supports SDFP.

Step 3: The AMF will generate a SDFP security context, which will be forwarded to the SMF. The AMF may also indicate the RAN N3 tunnel maintaining capability information previously received from the radio access node.

Step 8: The SMF selects a UPF that supports SDFP. The SMF will take the RAN N3 tunnel maintaining capability into consideration and provide N3 tunnel release timer information based on RAN maintaining capability information and other available local information. The N3 tunnel release timer information comprises, e.g., the timer value to be used by the UPF to monitor the N3 tunnel release (the SMF will take the maintaining capability information from the RAN into consideration as well).

Steps 10A and 10B: The SMF performs N4 Session Establishment including setting up the SDFP security context in the UPF. During this procedure the UE UPF and PDU Session information will be generated.

Step 11 : The SMF will include the UE UPF and PDU Session information in an N1 SM message to the UE. If the SMF decides to use the RAN N3 tunnel maintaining capability for SDFP, the SDFP related information (e.g., N3 tunnel release timer information) is provided in the N2 SM message to the RAN. SMF/UPF may start the DL N3 tunnel timer when there is no data traffic on the N3 tunnel.

Step 12: The AMF to RAN: N2 PDU Session Request (N2 SM information, NAS message (PDU Session ID, N1 SM container (PDU Session

Establishment Accept))).

The AMF sends the NAS message containing PDU Session ID and PDU Session Establishment Accept targeted to the UE and the N2 SM information received from the SMF within the N2 PDU Session Request to the RAN. In N2 SM information, the SMF indicates that this is SDFP PDU Session and the N3 tunnel release timer if provided.

Step 13: The RAN initiates bearer setup. In this step the RAN allocates a UPI used by the RAN to determine the CU-UP and the UL N3 tunnel allocated for that UE and PDU Session. The RAN also allocates RAN DL N3 Tunnel Info for the PDU Session.

Step 14: RAN to UE: RRC signaling establishing a Data Radio Bearer (DRB) used for the SDFP PDU Session. In this procedure the RAN forwards to the UE the N1 SM container received in step 12 and the UPI allocated in step 13. The RAN forwards the NAS message (PDU Session ID, N1 SM container (PDU Session Establishment Accept)) provided in step 12 and the UPI allocated in step 13 to the UE. The RAN shall only provide the NAS message and the UPI to the UE if the necessary RAN resources are established and the allocation of RAN Tunnel Info are successful.

Step 15: RAN to AMF: N2 PDU Session Response (PDU Session ID, Cause, N2 SM information (PDU Session ID, RAN Tunnel Info, List of

accepted/rejected QFI(s))).

The RAN Tunnel Info corresponds to the Access Network address of the DL N3 tunnel for the PDU Session.

User plane data transfer.

Step 21 : RAN to UE: Release of the RRC connection.

The RAN issues signaling to the UE releasing the RRC connection. The UE enters RRCJDLE and CM-IDLE.

Step 22: RAN to AMF: N2 UE Context release (or N2 suspend) The RAN indicates if N3 tunnel is kept and the N3 tunnel release timer is started. If there is still no data after timer expires, the RAN releases the UL N3 tunnel information.

Note: the message used to signal to the AMF can be either an existing NGAP message (e.g., UE context release with extra parameters) or a new message (e.g., N2 suspended)

The AMF releases the N2 connection and enters CM-IDLE state with specific marking (or a new state such as“Suspend”) where the AMF is responsible for paging if any MT signaling comes (see Fig./9 step 1A. The SMF/UPF starts the N3 tunnel release timer previously provided to the RAN when no data on N3 tunnel. If there is still no data after the timer expires, the SMF/UPF releases the DL N3 tunnel information. The SMF/UPF may be notified by the AMF with the suspend. If for any reason (e.g., operator policy configuration) the AMF wants to trigger the SMF/UPF to release the DL N3 tunnel

information, the AMF send notification to the SMF/UPF. If the SMF/UPF is notified with the suspend notification, the SMF/UPF releases the DL N3 tunnel info immediately.

Fig. 13 is a schematic block diagram of a network node 1300 according to some embodiments of the present disclosure. The network node 1300 may be, for example, a radio access node (e.g., a base station 602 or 606) or a network node implementing a core network function (e.g., an AMF, SMF, or the like). As illustrated, the network node 1300 includes a control system 1302 that includes one or more processors 1304 (e.g., Central Processing Units (CPUs), Application Specific Integrated Circuits (ASICs), Field

Programmable Gate Arrays (FPGAs), and/or the like), memory 1306, and a network interface 1308. The one or more processors 1304 are also referred to herein as processing circuitry.

In addition, in embodiments in which the network node 1300 is a radio access node, the radio access node includes one or more radio units 1310 that each includes one or more transmitters 1312 and one or more receivers 1314 coupled to one or more antennas 1316. The radio units 1310 may be referred to or be part of radio interface circuitry. In some embodiments, the radio unit(s) 1310 is external to the control system 1302 and connected to the control system 1302 via, e.g., a wired connection (e.g., an optical cable).

However, in some other embodiments, the radio unit(s) 1310 and potentially the antenna(s) 1316 are integrated together with the control system 1302.

The one or more processors 1304 operate to provide one or more functions of a network node (e.g., a radio access node or a network node implementing a core network function) as described herein. In some embodiments, the function(s) are implemented in software that is stored, e.g., in the memory 1306 and executed by the one or more processors 1304.

Fig. 14 is a schematic block diagram that illustrates a virtualized embodiment of the network node 1300 according to some embodiments of the present disclosure. This discussion is equally applicable to other types of network nodes. Further, other types of network nodes may have similar virtualized architectures.

As used herein, a“virtualized” network node is an implementation of the network node 1300 in which at least a portion of the functionality of the network node 1300 is implemented as a virtual component(s) (e.g., via a virtual machine(s) executing on a physical processing node(s) in a

network(s)). As illustrated, in this example, the network node 1300 includes the control system 1302 that includes the one or more processors 1304 (e.g., CPUs, ASICs, FPGAs, and/or the like), the memory 1306, and the network interface 1308.

Also, in embodiments in which the network node 1300 is a radio access node, the radio access node further includes the one or more radio units 1310 that each includes the one or more transmitters 1312 and the one or more receivers 1314 coupled to the one or more antennas 1316, as described above. The control system 1302 is connected to the radio unit(s) 1310 via, for example, an optical cable, or the like. The control system 1302 is connected to one or more processing nodes 1400 coupled to or included as part of a network(s) 1402 via the network interface 1308.

Each processing node 1400 includes one or more processors 1404 (e.g., CPUs, ASICs, FPGAs, and/or the like), memory 1406, and a network interface 1408. In this example, functions 1410 of the network node 1300 (e.g., functions of a radio access node or a network node implementing a core network function) described herein are implemented at the one or more processing nodes 1400 or distributed across the control system 1302 and the one or more processing nodes 1400 in any desired manner. In some particular embodiments, some or all of the functions 1410 of the network node 1300 described herein are implemented as virtual components executed by one or more virtual machines implemented in a virtual environment(s) hosted by the processing node(s)

1400. As will be appreciated by one of ordinary skill in the art, additional signaling or communication between the processing node(s) 1400 and the control system 1302 is used in order to carry out at least some of the desired functions 1410. Notably, in some embodiments, the control system 1302 may not be included, in which case the radio unit(s) 1310 communicate directly with the processing node(s) 1400 via an appropriate network interface(s).

In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of network node 1300 or a node (e.g., a processing node 1400) implementing one or more of the functions 1410 of the network node 1300 in a virtual environment according to any of the

embodiments described herein is provided. In some embodiments, a carrier comprising the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory).

Fig. 15 is a schematic block diagram of the network node 1300 according to some other embodiments of the present disclosure. The network node 1300 includes one or more modules 1500, each of which is implemented in software. The module(s) 1500 provide the functionality of the network node 1300 described herein. This discussion is equally applicable to the

processing node 1400 of Fig. 14 where the modules 1500 may be

implemented at one of the processing nodes 1400 or distributed across multiple processing nodes 1400 and/or distributed across the processing node(s) 1400 and the control system 1302. Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include Digital Signal Processor (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as Read Only Memory (ROM), Random Access Memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more

telecommunications and/or data communications protocols as well as instructions for carrying out one or more of the techniques described herein.

In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according one or more embodiments of the present disclosure.

To reiterate, there is provided the following embodiments according to the invention:

the method comprising:

- communicating 9_1 with a User Equipment, UE, to establish a Radio

Resource Control, RRC, connection for small data fast path, SDFP, uplink data transmission; and

- conditionally allocating 9_1 B a downlink tunnel for a downlink data transmission to the UE and sending respective downlink tunnel information to a core network function.

The setup of a control plane (e.g., N2) connection may also be conditional. Moreover, it may be provided to conditionally allocating 9_1 B a downlink tunnel for a downlink data transmission to the UE and sending respective downlink tunnel information to a core network function comprises:

- determining whether any one of at least one predefined condition is satisfied;

- if any one of the at least one predefined condition is satisfied, allocating 9_1 B a downlink tunnel for a downlink data transmission to the UE and sending respective downlink tunnel information to a core network function; and

- if none of the at least one predefined condition are satisfied, refraining from allocating a downlink tunnel for a downlink data transmission to the UE and refraining from sending 3_2 respective downlink tunnel information to a core network function.

The at least one predefined condition may comprise:

- a condition that the radio access node has received a prior request for the UE; and/or

- a condition that the UE provided, to the radio access node, information that indicates that one or more downlink data transmissions to the UE are expected; and/or

- a condition that the radio access node has previously received at least one communication pattern parameter that indicates that one or more downlink data transmissions are expected for the UE.

The at least one predefined condition may comprise the condition that the radio access node has received a prior request for the UE, and the prior request is a prior paging request for the UE.

The at least one predefined condition may comprise the condition that the radio access node has received a prior request for the UE, and the prior request is a prior request due to downlink small data for the UE. The at least one predefined condition may moreover comprise the condition that the radio access node has received a prior request for the UE, and the prior request is a prior request due to Non-Access Stratum, NAS, signaling.

The at least one predefined condition may comprise the condition that the UE provided, to the radio access node, information that indicates that one or more downlink data transmissions to the UE are expected, and the information is release assistance information that indicates that one or more downlink data transmissions to the UE are expected.

Moreover, the at least one predefined condition may comprise the condition that the radio access node has previously received at least one

communication pattern parameter that indicates that one or more downlink data transmissions are expected for the UE, and the at least one

communication pattern parameter comprises a traffic profile type that indicates dual packet transmission or multiple packet transmission.

The downlink tunnel may be a downlink N3 tunnel, and the core network function is an Access and Mobility management Function, AMF, Session Management Function, SMF, or User Plane Function, UPF.

Prior to establishment of the RRC connection it may apply that:

the UE is in Connection Management Idle, CM-IDLE, mode;

a UPF stores N3 tunnel information for the UE; and

a N3 tunnel release timer is running.

A Radio base station according to the invention 1310, 602, 606 may comprise at least one processor adapted for carrying out any of the steps noted above.

In an embodiment there is provided a method performed by a radio access node in a radio access network of a cellular communications system, the method comprising:

- sending 11_1 , to an Access and Mobility management Function, AMF, in a core network of the cellular communications system, information that indicates a capability of the radio access node related to maintaining a tunnel between the radio access node and a User Plane Function, UPF, in the core network.

The information may indicate a capability of the radio access node related to a timer for maintaining the tunnel.

The information may indicate a capability of the radio access node related to Radio Resource Control, RRC, for Small Data Fast Path, SDFP.

In another embodiment there is provided a method performed by an Access and Mobility management Function, AMF, in a core network of a cellular communications system, the method comprising:

- sending, to a radio access node, a paging request 9_1A and an indication as to whether the paging request is due to signaling or data to the radio access network.

Again, the information may indicate a capability of the radio access node related to a timer for maintaining the tunnel.

Storing the information may comprise storing the information at a radio access node level or storing the information as individual User Equipment, UE, context information.

It may also comprise providing the information to a Session Management Function, SMF, during Protocol Data Unit, PDU, session establishment.

An Access and Mobility management Function, AMF, for a core network of a cellular communications system, the AMF adapted to perform the method mentioned above. A method performed by a Session Management Function, SMF, in a core network of a cellular communications system, the method comprising:

- receiving 9_1 C, from an Access and Mobility management Function, AMF, during Protocol Data Unit, PDU, session establishment, information that indicates a capability of a radio access node related to maintaining a tunnel between the radio access node and a User Plane Function, UPF, in the core network; and

- storing the information.

The method may further comprise:

- selecting 8 an UPF for the PDU session that supports Small Data Fast Path, SDFP; and

- providing 11 , 9_1 C, to the UPF, information related to a tunnel release timer for maintaining the tunnel, taking into consideration the stored information.

A Session Management Function, SMF, is provided in a core network of a cellular communications system, the SMF adapted to perform the method noted above.

While processes in the figures may show a particular order of operations performed by certain embodiments of the present disclosure, it should be understood that such order is exemplary (e.g., alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, etc.).

Abbreviations

At least some of the following abbreviations may be used in this disclosure. If there is an inconsistency between abbreviations, preference should be given to how it is used above. If listed multiple times below, the first listing should be preferred over any subsequent listing(s).

3GPP Third Generation Partnership Project

5G Fifth Generation

5GS Fifth Generation System

AF Application Function

AMF Access and Mobility managment Function

AN Access Network

ASIC Application Specific Integrated Circuit

AUSF Authentication Server Function

CloT Cellular Internet of Things

CM Connection Management

CN Core Network

CPU Central Processing Unit

CU-CP Central Unit of the Control Plane

CU-UP Central Unit of the User Plane

DL Downlink

DN Data Network

DRB Data Radio Bearer

DSP Digital Signal Processor

DU Digital Unit

eNB Enhanced or Evolved Node B

FPGA Field Programmable Gate Array

gNB New Radio Base Station

GTP-U General Packet Radio Service Tunneling Protocol

User Plane

ID Identifier

loT Internet of Things

IP Internet Protocol • LTE Long Term Evolution

• MME Mobility Management Entity

• MO Mobile Originated

• MT Mobile Terminated

• MTC Machine Type Communication

• NAS Non-Access Stratum

• NEF Network Exposure Function

• NF Network Function

• NG Next Generation

• NGAP Next Generation Application Protocol

• NR New Radio

• NRF Network Repository Function

• NSSAI Network Slice Selection Assistance Information

• NSSF Network Slice Selection Function

• PCF Policy Control Function

• PDU Protocol Data Unit

• P-GW Packet Data Network Gateway

• QFI Duality of Service Flow Identity

• CoS Quality of Service

• RAM Random Access Memory

• RAN Radio Access Network

• ROM Read Only Memory

• RRH Remote Radio Head

• RTT Round Trip Time

• SAE System Architecture Evolution

• SCEF Service Capability Exposure Function

• SDFP Small Data Fast Path

• SMF Session Management Function

• S-TMSI System Architecture Evolution Temporary Mobile

Subscriber Identity

• TEID Tunnel Endpoint Identifier

• TR Technical Report • TS Technical Specification

• UDM Unified Data Management

• UE User Equipment

• UL Uplink

• UPF User Plane Function

• UPI User Plane Index

List of References

[1] 3GPP TR 23.724 nq.3.0

[2] 3GPP TS 23.501 v15.1.0

[3] 3GPP TS 23.502 v15.1.0

[4] Ericsson,“S2-183041 : PCR 23.724: Infrequent Small Data user plane transmission for CloT,” SA WG2 Meeting #126, February 26 - March 2, 2018, Montreal, Canada

[5] Ericsson,“S2-183214: Kl 1 : Adding DL data handling in solution 5 SDFP,” SA WG2 Meeting #127, April 16-20, 2018, Sanya, P.R. China

[6] Samsung et al.,“S2-184413: Infrequent Small Data Transmission: Using Resume and Suspend procedure,” SA WG2 Meeting #127, April 16-20, 2018, Sanya, China

Claims

1. A method performed by a radio access node, RAN, in a radio access network of a cellular communications system adapted for communicating with a User Entity, UE, a User Plane Function, UPF, an Access and mobility management Function, AMF, and a Session Management Function, SMF, the method comprising:

communicating (9_1 ) with a User Equipment, UE, to establish a Radio Resource Control, RRC, connection for small data fast path, SDFP, uplink data transmission; and

conditionally allocating (9_1 B) a downlink tunnel for a downlink data transmission to the UE and sending respective downlink tunnel information to a core network function.

2. The method of claim 1 wherein setup of a control plane (e.g., N2) connection is also conditional.

3. The method of claim 1 or 2, wherein conditionally allocating (9_1 B) a downlink tunnel for a downlink data transmission to the UE and sending respective downlink tunnel information to a core network function comprises: determining whether any one of at least one predefined condition is satisfied;

if any one of the at least one predefined condition is satisfied, allocating (9_1 B) a downlink tunnel for a downlink data transmission to the UE and sending respective downlink tunnel information to a core network function; and

if none of the at least one predefined conditions is satisfied, refraining from allocating a downlink tunnel for a downlink data transmission to the UE and refraining from sending (3_2) respective downlink tunnel information to a core network function.

4. The method of claim 3 wherein the at least one predefined condition comprises: a condition that the radio access node has received a prior request for the UE; and/or

a condition that the UE provided, to the radio access node, information that indicates that one or more downlink data transmissions to the UE are expected; and/or

a condition that the radio access node has previously received at least one communication pattern parameter that indicates that one or more downlink data transmissions are expected for the UE.

5. The method of claim 4 wherein the at least one predefined condition comprises the condition that the radio access node has received a prior request for the UE, and the prior request is a prior paging request for the UE.

6. The method of claim 4 wherein the at least one predefined condition comprises the condition that the radio access node has received a prior request for the UE, and the prior request is a prior request due to downlink small data for the UE.

7. The method of claim 4 wherein the at least one predefined condition comprises the condition that the radio access node has received a prior request for the UE, and the prior request is a prior request due to Non-Access Stratum, NAS, signaling.

8. The method of claim 4 wherein the at least one predefined condition comprises the condition that the UE provided, to the radio access node, information that indicates that one or more downlink data transmissions to the UE are expected, and the information is release assistance information that indicates that one or more downlink data transmissions to the UE are expected.

9. The method of claim 4 wherein the at least one predefined condition comprises the condition that the radio access node has previously received at least one communication pattern parameter that indicates that one or more downlink data transmissions are expected for the UE, and the at least one communication pattern parameter comprises a traffic profile type that indicates dual packet transmission or multiple packet transmission.

10. The method of any one of claims 1 to 9 wherein the downlink tunnel is a downlink N3 tunnel, and the core network function is an Access and Mobility management Function, AMF, Session Management Function, SMF, or User Plane Function, UPF.

11. The method of any of claims 1 -10 wherein, prior to establishment of the RRC connection:

the UE is in Connection Management Idle, CM-IDLE, mode;

a UPF stores N3 tunnel information for the UE; and

a N3 tunnel release timer is running.

12. Radio base station (1310, 602, 606) comprising at least one processor adapted for carrying out any of the steps according to claims 1 - 11.

13. A method performed by a radio access node in a radio access network of a cellular communications system, the method comprising:

Sending (11_1 ), to an Access and Mobility management Function, AMF, in a core network of the cellular communications system, information that indicates a capability of the radio access node related to maintaining a tunnel between the radio access node and a User Plane Function, UPF, in the core network.

14. The method of claim 13 wherein the information indicates a capability of the radio access node related to a timer for maintaining the tunnel.

15. The method of claim 13 or 14 wherein the information indicates a capability of the radio access node related to Radio Resource Control, RRC, for Small Data Fast Path, SDFP.

16. A method performed by an Access and Mobility management Function, AMF, in a core network of a cellular communications system, the method comprising:

sending, to a radio access node, a paging request (9_1A) and an indication as to whether the paging request is due to signaling or data to the radio access network.

17. The method of claim 16 wherein the information indicates a capability of the radio access node related to a timer for maintaining the tunnel.

18. The method of claim 16 or 17 wherein the information indicates a capability of the radio access node related to Radio Resource Control, RRC, for Small Data Fast Path, SDFP.

19. The method of any one of claims 16 to 18 wherein storing the information comprises storing the information at a radio access node level or storing the information as individual User Equipment, UE, context information.

20. The method of any one of claims 16 to 19 further comprising providing the information to a Session Management Function, SMF, during Protocol Data Unit, PDU, session establishment.

21. An Access and Mobility management Function, AMF, for a core network of a cellular communications system, the AMF adapted to perform the method of any one of claims 16 to 20.

22. A method performed by a Session Management Function, SMF, in a core network of a cellular communications system, the method comprising: receiving (9_1 C), from an Access and Mobility management Function, AMF, during Protocol Data Unit, PDU, session establishment, information that indicates a capability of a radio access node related to maintaining a tunnel between the radio access node and a User Plane Function, UPF, in the core network; and

storing the information.

23. The method of claim 22 further comprising:

selecting (8) an UPF for the PDU session that supports Small Data Fast Path, SDFP; and

providing (11 , 9_1 C), to the UPF, information related to a tunnel release timer for maintaining the tunnel, taking into consideration the stored information.

24. A Session Management Function, SMF, in a core network of a cellular communications system, the SMF adapted to perform the method of any one of claims 22 or 23.