5 Functional model

23.2553GPPApplication layer support for Uncrewed Aerial System (UAS)Functional architecture and information flowsRelease 18TS

5.1 General

The functional model for the UAS application layer is organized into functional entities to describe a functional architecture which addresses the application layer support aspects for UAS applications.

5.2 Functional model description

Figures 5.2-1 and 5.2-2 illustrates the simplified architectural models for the UAS application layer.

Figure 5.2-1: Simplified architectural model for the UAS application layer

Figure 5.2-2: Simplified architectural model for U2 connectivity between UAS UE1 and UAS UE2 at the UAS application layer

The UAS UE1 communicates with UAS application server over U1 reference point. The UAS UE1 and UAS UE2 communicate over U2 reference point.

NOTE 1: Support for UE-to-network relay architecture for UAS communications is out of scope of the present document.

The UAS UE1 and the UAS UE2 may be a UAV Controller or a UAV.

NOTE 2: The UAV Controller can connect to the UAV via a transport independent of 3GPP. Such UAV Controller is not a 3GPP UE and is out of scope of the present document.

NOTE 3: Support of PC5 at the U2 reference point for 5GS is out of scope of the present document.

The reference point U1 supports the UAS application related interactions between UAS UE and UAS application server. It is expected that this reference point is supported at least for unicast delivery mode, and may support multicast delivery mode. The reference point U2 supports the interactions between the UAS UEs. The UAS application server can be the USS/UTM.

The reference point U1 is based on Uu connectivity as specified in 3GPP TS 23.256 [4].

The reference point U2 is based on Uu connectivity as specified in 3GPP TS 23.256 [4].

NOTE 4: Support of multicast delivery over Uu for 5GS is out of scope of the present document.

Figure 5.2-3 illustrates the detailed UAS application layer functional model. It enhances the simplified architectural model for the UAS application layer by specifying the functional entities at the UAS application layer.

Figure 5.2-3: UAS application layer functional model

Figure 5.2-4 illustrates the detailed UAS application layer functional model where the UAV-C has a network‑assisted connectivity with the UAV.

Figure 5.2-4: UAS application layer functional model with UAV-C having network-assisted connectivity with UAV

The UAS application layer functional entities for the UAS UE and the UAS application server are grouped into the UAS application specific layer and the UAE layer. The UAE layer offers the UAE capabilities to the UAS application specific layer. The UAS application layer functional model utilizes the SEAL services as specified in 3GPP TS 23.434 [5].

The UAE server is located in the UAE layer. The SEAL services/UAS application specific layer utilized by UAE layer may include location management, group management, configuration management, identity management, key management and network resource management. The UAS application specific layer consists of the UAS application specific functionalities.

NOTE 5: The functionalities of the UAS application specific layer include the USS/UTM and are out of scope of the present document.

The following connectivity path for the UAS is supported when both the UAV-C and the UAV are 3GPP UEs:

– UAV-C to UAV over U2 (Uu connectivity).

The UAS application server consists of the UAE server, the SEAL servers and the UAS application specific server. The UAE server provides the UAS application layer support functions to the UAS application specific server over Us reference point. The SEAL servers provide the SEAL services to the UAS application specific server/UAE server over SEAL-S reference point.

The UAS UE consists of the UAE client, the SEAL clients and the UAS application specific client. The UAE client provides the UAS application layer support functions to the UAS application specific client over Uc reference point. The SEAL clients provide the SEAL services to the UAS application specific client/UAE client over SEAL-C reference point.

NOTE 6: In some deployments, the client and server entities of SEAL can be part of UAE client and UAE server respectively.

The UAS application specific client/UAE client acts as a VAL client for its interaction with the SEAL clients as specified in 3GPP TS 23.434 [5]. The UAS application specific server/UAE server acts as a VAL server for its interaction with the SEAL servers as specified in 3GPP TS 23.434 [5].

In the UAE layer, the UAE client communicates with the UAE server over U1-AE reference point. In the UAS application specific layer, the UAS application specific client communicates with UAS application specific server over U1-APP reference point.

NOTE 7: The U1-APP reference point includes UAV Controller/UAV to USS/UTM communication and is out of scope of the present document.

In the UAE layer, the UAE client of UAS UE2 communicates with UAE client of UAS UE1 over U2-AE reference point. In the UAS application specific layer, the UAS application specific client of UAS UE2 communicates with UAE client of UAS UE1 over U2-APP reference point.

NOTE 8: The U2-APP reference point is out of scope of the present document.

The following SEAL services for UAS applications may include:

– Location management as specified in 3GPP TS 23.434 [5];

– Group management as specified in 3GPP TS 23.434 [5];

– Configuration management as specified in 3GPP TS 23.434 [5];

– Identity management as specified in 3GPP TS 23.434 [5];

– Key management as specified in 3GPP TS 23.434 [5]; and

– Network resource management as specified in 3GPP TS 23.434 [5].

The UAS application specific client/UAE client interacts with SEAL clients over the SEAL-C reference point specified for each SEAL service. The UAS application specific server/UAE server interacts with SEAL servers over the SEAL-S reference point specified for each SEAL service. The interaction between the SEAL clients is supported by SEAL-PC5 reference point specified for each SEAL service. The interaction between a SEAL client and the corresponding SEAL server is supported by SEAL-UU reference point specified for each SEAL service.

NOTE 9: The SEAL-C, SEAL-S, SEAL-PC5, SEAL-UU reference points for each SEAL service is specified in 3GPP TS 23.434 [5].

To support distributed UAE server deployments, the UAE server interacts with another UAE server over UAE-E reference point.

A U1-AE message can be sent over at least unicast, and may be sent over transparent multicast via xMB or transparent multicast via MB2. The non-transparent multicast via xMB (as specified in 3GPP TS 26.348 [10]) is triggered by a U1-AE message. Multicast distribution can be supported by both transparent and non-transparent multicast modes.

The UAE server interacts with the 3GPP network system over U2, MB2, xMB, Rx, T8 and Nnef reference points.

5.3 Functional entities description

5.3.1 General

Each clause specifies a description of a functional entity corresponding to UAS application layer and does not imply a physical entity.

5.3.2 UAS application specific client

The UAS application specific client provides the client side functionalities corresponding to the UAS applications (e.g. Client interacting with USS/UTM). The UAS application specific client utilizes the UAE client for the UAS application layer support functions.

NOTE: The details of the UAS application specific client is out of scope of the present document.

5.3.3 UAS application specific server

The UAS application specific server provides the server side functionalities corresponding to the UAS applications (e.g. USS/UTM). The UAS application specific server utilizes the UAE server for the UAS application layer support functions. If CAPIF is supported, the UAS application specific server acts as CAPIF’s API invoker as specified in 3GPP TS 23.222 [3].

NOTE: The details of the UAS application specific server is out of scope of the present document.

5.3.4 UAE client

The UAE client supports interactions with the UAS application specific client(s).

The UAE client provides the client side UAS application layer support functions as below:

– receiving and storing C2 operation mode configurations;

– selecting primary and secondary C2 communication modes based on the configurations;

– switching of C2 communication in emergency scenarios;

– supporting UAV application message communication handling;

– providing the UAE server with the Multi-USS capability;

– receiving and storing Multi-USS policies; and

– based on Multi-USS policies, switching of UAS application specific server in emergency scenarios.

5.3.5 UAE server

If CAPIF is supported, the UAE server acts as CAPIF’s API exposing function to provide service APIs to the UAS application specific server (e.g. USS/UTM) or another UAE server as specified in 3GPP TS 23.222 [3], or acts as CAPIF’s API invoker to consume the service APIs provided by another UAE server.

The UAE server provides the server side UAS application layer support functions as below:

– performing group based QoS management for the UAS (i.e. pair of UAV and UAV-C) by using SEAL APIs.

– receiving C2 operation mode configuration from UAS application specific servers (e.g. USS/UTM) and further configuring the UAS UEs (i.e. UAV, UAV-C);

– triggering C2 communication mode switching with the UAS UEs;

– receiving and storing the selected C2 communication modes from the UAS UEs;

– monitoring the real-time status of UAS UEs by using SEAL APIs;

– supporting UAV application message communications between UAVs; and

– receiving Multi-USS policies from UAS application specific servers and further configuring the UAS UEs (i.e. UAV).

5.3.6 SEAL client

The following SEAL clients as specified in 3GPP TS 23.434 [5] are supported:

– Location management client;

– Group management client;

– Configuration management client;

– Identity management client;

– Key management client; and

– Network resource management client.

5.3.7 SEAL server

The following SEAL servers as specified in 3GPP TS 23.434 [5] are supported:

– Location management server;

– Group management server;

– Configuration management server;

– Identity management server;

– Key management server; and

– Network resource management server.

5.4 Reference points description

5.4.1 General

The reference points for the UAS application layer are described in the following clauses.

5.4.2 U1-AE

The interactions related to UAS application layer support functions between UAE client and UAE server are supported by U1-AE reference point.

5.4.3 U1-APP

The interactions related to UAS applications between UAS application specific client and UAS application specific server are supported by U1-APP reference point. The details of U1-APP reference point is out of scope of the present document.

5.4.4 U2-AE

The interactions related to UAS application layer support functions between the UAE clients are supported by U2-AE reference point.

5.4.5 U2-APP

The interactions related to UAS applications between UAS application specific clients are supported by U2-APP reference point. The details of U2-APP reference point is out of scope of the present document.

5.4.6 Us

The interactions related to UAS application layer support functions between the UAE server and the UAS application specific server are supported by Us reference point. If CAPIF is supported, this reference point is an instance of CAPIF‑2/2e reference point as specified in 3GPP TS 23.222 [3].

5.4.7 Uc

The interactions related to UAS application layer support functions between the UAE client and the UAS application specific client are supported by Uc reference point.

5.4.8 SEAL-C

The following SEAL-C reference points specified in 3GPP TS 23.434 [5] are supported:

– LM-C reference point for location management;

– GM-C reference point for group management;

– CM-C reference point for configuration management;

– IM-C reference point for identity management;

– KM-C reference point for key management; and

– NRM-C reference point for network resource management.

5.4.9 SEAL-S

The following SEAL-S reference points specified in 3GPP TS 23.434 [5] are supported:

– LM-S reference point for location management;

– GM-S reference point for group management;

– CM-S reference point for configuration management;

– IM-S reference point for identity management;

– KM-S reference point for key management; and

– NRM-S reference point for network resource management.

5.4.10 SEAL-PC5

The following SEAL-PC5 reference points specified in 3GPP TS 23.434 [5] are supported:

– LM-PC5 reference point for location management;

– GM-PC5 reference point for group management;

– CM-PC5 reference point for configuration management;

– IM-PC5 reference point for identity management;

– KM-PC5 reference point for key management; and

– NRM-PC5 reference point for network resource management.

5.4.11 SEAL-UU

The following SEAL-UU reference points specified in 3GPP TS 23.434 [5] are supported:

– LM-UU reference point for location management;

– GM-UU reference point for group management;

– CM-UU reference point for configuration management;

– IM-UU reference point for identity management;

– KM-UU reference point for key management; and

– NRM-UU reference point for network resource management.

5.4.12 UAE-E

The interactions related to UAS application support functions between the UAE servers in a distributed deployment are supported by UAE-E reference point. If CAPIF is supported, this reference point is an instance of CAPIF-2/2e reference point as specified in 3GPP TS 23.222 [3].

5.5 External reference points

5.5.1 General

The reference points between the UAS application layer and the 3GPP network systems (EPS, 5GS) are described in the following clauses.

5.5.2 Rx

The reference point Rx supports the interactions between the UAS application server and the PCRF and is specified in 3GPP TS 29.214 [11]. The functions for Rx reference point are supported by the network resource management server of the SEAL.

5.5.3 MB2-C

The reference point MB2-C supports the control plane interactions between the UAS application server and the BM-SC and is specified in 3GPP TS 29.468 [12]. The functions for MB2-C reference point are supported by the network resource management server of the SEAL.

5.5.4 MB2-U

The reference point MB2-U supports the user plane interactions between the UAS application server and the BM-SC and is specified in 3GPP TS 29.468 [12]. The functions for MB2-U reference point are supported by the UAE server.

5.5.5 xMB-C

The reference point xMB-C supports the control plane interactions between the UAS application server and the BM-SC and is specified in 3GPP TS 26.346 [9]. The functions for xMB reference point are supported by the network resource management server of the SEAL.

5.5.6 xMB-U

The reference point xMB-U supports the user plane interactions between the UAS application server and the BM-SC and is specified in 3GPP TS 26.346 [9]. The functions for xMB-U reference point are supported by the UAE server.

5.5.7 T8

The reference point T8 supports the interactions between the UAS application server and the SCEF and is specified in 3GPP TS 23.682 [8]. The functions of T8 interface are supported by UAE server and the functions related to location management of T8 are supported by the location management server.

5.5.8 N5

The reference point N5 supports the interactions between the UAS application server and the PCF and is specified in 3GPP TS 23.501 [6]. The functions of N5 interface are supported by UAE server.

5.5.9 N33/Nnef

The reference point N33 supports the interactions between the UAS application server and the NEF and is specified in 3GPP TS 23.501 [6]. Nnef is the service based interface exposed by the NEF as per the N33 reference point. The functions of Nnef interface are supported by UAE server and the functions related to location management of Nnef are supported by the location management server.