7 Procedures and information flows

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

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

7.1 Usage of SEAL services

7.1.1 General

The UAE capabilities (UAE client and UAE server) utilize the SEAL services. Also the UAS application specific server(s) may directly utilize the SEAL services. All SEAL services specified in 3GPP TS 23.434 [5] are available to the UAS application layer (i.e. the UAE layer and the UAS application specific layer).

In this clause, the details of the information flows, procedures and APIs utilized by the UAS application layer are described.

7.1.2 Group management service

7.1.2.1 General

The UAE capabilities (UAE client and UAE server) utilize the group management service procedures (e.g. creation, join, leave) of SEAL based on the group configuration information (e.g. group join policy, group leader) provided by the UAS application specific layer. The decisions and corresponding triggers (e.g. group creation, join, leave) for group management are responsibility of the UAS application specific layer. The group management service of SEAL provides support for creating group for UAS for supporting UAS applications and C2 communications.

The UAS application specific server(s) may directly utilize the group management service procedures of SEAL.

7.1.2.2 Information flows

The following information flows of group management service of SEAL as specified in 3GPP TS 23.434 [5] are applicable for the UAS applications:

– Group creation request specified in clause 10.3.2.1;

– Group creation response specified in clause 10.3.2.2;

– Group creation notification specified in clause 10.3.2.3;

– Group information query request specified in clause 10.3.2.4;

– Group information query response specified in clause 10.3.2.5;

– Group membership update request specified in clause 10.3.2.6;

– Group membership update response specified in clause 10.3.2.7;

– Group membership notification specified in clause 10.3.2.8;

– Group deletion request specified in clause 10.3.2.9;

– Group deletion response specified in clause 10.3.2.10;

– Group deletion notification specified in clause 10.3.2.11;

– Group information request specified in clause 10.3.2.12;

– Group information response specified in clause 10.3.2.13;

– Group information subscribe request specified in clause 10.3.2.14;

– Group information subscribe response specified in clause 10.3.2.15;

– Group information notify request specified in clause 10.3.2.16;

– Group information notify response specified in clause 10.3.2.17;

– Store group configuration request specified in clause 10.3.2.18;

– Store group configuration response specified in clause 10.3.2.19;

– Get group configuration request specified in clause 10.3.2.20;

– Get group configuration response specified in clause 10.3.2.21;

– Subscribe group configuration request specified in clause 10.3.2.22;

– Subscribe group configuration response specified in clause 10.3.2.23;

– Notify group configuration request specified in clause 10.3.2.24;

– Notify group configuration response specified in clause 10.3.2.25;

– Configure VAL group request specified in clause 10.3.2.26;

– Configure VAL group response specified in clause 10.3.2.27;

– Group announcement specified in clause 10.3.2.28;

– Group registration request specified in clause 10.3.2.29;

– Group registration response specified in clause 10.3.2.30;

– Identity list notification specified in clause 10.3.2.31;

– Group de-registration request specified in clause 10.3.2.32;

– Group de-registration response specified in clause 10.3.2.33;

The usage of the above information flows are clarified as below:

– The identity is the UE ID or CAA Level ID;

– The identity list or identities list is the list of UE IDs or CAA Level IDs; and

– The VAL server is the UAE server or the UAS application specific server.

7.1.2.3 Procedures

The following procedures of group management service of SEAL as specified in 3GPP TS 23.434 [5] are applicable for the UAS applications:

– Group creation specified in clause 10.3.3;

– Group information query specified in clause 10.3.4;

– Group membership specified in clause 10.3.5;

– Group configuration management specified in clause 10.3.6;

– Group announcement and join specified in clause 10.3.8;

– Group member leave specified in clause 10.3.9;

7.1.2.4 APIs

The following APIs of group management service of SEAL as specified in 3GPP TS 23.434 [5] are applicable for the UAS applications:

– SS_GroupManagement API specified in clause 10.4.2;

7.1.3 Location management service

7.1.3.1 General

The UAE capabilities (UAE client and UAE server) utilize location management (e.g. network location of UEs) service procedures of SEAL to support UAS applications.

The UAS application specific server(s) may directly utilize the location management service procedures of SEAL.

7.1.3.2 Information flows

The following information flows of location management service of SEAL as specified in 3GPP TS 23.434 [5] are applicable for the UAS applications:

– Location reporting configuration request specified in clause 9.3.2.0;

– Location reporting configuration response specified in clause 9.3.2.1;

– Location information report specified in clause 9.3.2.2;

– Location information request specified in clause 9.3.2.3;

– Location reporting trigger specified in clause 9.3.2.4;

– Location information subscription request specified in clause 9.3.2.5;

– Location information subscription response specified in clause 9.3.2.6;

– Location information notification specified in clause 9.3.2.7;

– Location reporting configuration cancel specified in clause 9.3.2.8;

– Get UE(s) information request specified in clause 9.3.2.9;

– Get UE(s) information response specified in clause 9.3.2.10;

– Monitor location subscription request specified in clause 9.3.2.11;

– Monitor location subscription response specified in clause 9.3.2.12;

– Notify location monitoring event specified in clause 9.3.2.13;

The usage of the above information flows are clarified as below:

– The identity is the UE ID or CAA Level ID;

– The identity list or identities list is the list of UE IDs or CAA Level IDs; and

– The VAL server is the UAE server or the UAS application specific server.

7.1.3.3 Procedures

The following procedures of location management service of SEAL as specified in 3GPP TS 23.434 [5] are applicable for the UAS applications:

– Event-triggered location reporting procedure specified in clause 9.3.3;

– On-demand location reporting procedure specified in clause 9.3.4;

– Location reporting event triggers configuration cancel specified in clause 9.3.6;

– Location information subscription procedure specified in clause 9.3.7;

– Event-trigger location information notification procedure specified in clause 9.3.8;

– On-demand usage of location information procedure specified in clause 9.3.9;

– Obtaining UE(s) information at a location specified in clause 9.3.10;

– Monitoring Location Deviation specified in clause 9.3.11

7.1.3.4 APIs

The following APIs of location management service of SEAL as specified in 3GPP TS 23.434 [5] are applicable for the UAS applications:

– SS_LocationReporting API as specified in clause 9.4.2;

– SS_LocationInfoEvent API as specified in clause 9.4.3;

– SS_LocationInfoRetrieval API as specified in clause 9.4.4;

– SS_LocationAreaInfoRetrieval API as specified in clause 9.4.5;

– SS_LocationMonitoring API as specified in clause 9.4.6;

7.1.4 Network resource management service

7.1.4.1 General

The UAE capabilities (UAE client and UAE server) and UAS application specific servers utilize network resource management service procedures of SEAL to support UAS applications and C2 communications.

The UAS application specific server(s) may directly utilize the network management service procedures of SEAL.

7.1.4.2 Information flows

The following information flows of network resource management service of SEAL as specified in 3GPP TS 23.434 [5] are applicable for the UAS applications:

– Network resource adaptation request specified in clause 14.3.2.1;

– Network resource adaptation response specified in clause 14.3.2.2;

– Resource request specified in clause 14.3.2.6;

– Resource response specified in clause 14.3.2.7;

– Resource modification request specified in clause 14.3.2.8;

– Resource modification response specified in clause 14.3.2.9;

– Monitoring Events Subscription Request specified in clause 14.3.2.17;

– Monitoring Events Subscription Response specified in clause 14.3.2.18;

– Monitoring Events Notification message specified in clause 14.3.2.19;

The usage of the information flows are clarified as below:

– The identity is the 3GPP UE ID or CAA Level UAV ID;

– The identity list or identities list is the list of 3GPP UE IDs or CAA Level UAV IDs; and

– The VAL server is the UAE server or the UAS application specific server.

7.1.4.3 Procedures

The following procedures of network resource management service of SEAL specified 3GPP TS 23.434 [5] are applicable for the UAS applications and C2 communications:

– Request for unicast resources at VAL service communication establishment specified in clause 14.3.3.2.1;

– Request for modification of unicast resources specified in clause 14.3.3.2.2;

– Network resource adaptation specified in clause 14.3.3.3.1;

– QoS/resource management capability initiation in network assisted UE-to-UE communications procedure specified in clause 14.3.5.2;

– Coordinated QoS provisioning operation in network assisted UE-to-UE communications procedure specified in clause 14.3.5.3;

– Monitoring Events Subscription procedure specified in clause 14.3.6.2;

– Monitoring Events Notification procedure specified in clause 14.3.6.3;

7.1.4.4 APIs

The following APIs of network resource management service of SEAL specified 3GPP TS 23.434 [5] are applicable for the UAS applications and C2 communications:

– SS_NetworkResourceAdaptation API specified in clause 14.4.2;

– SS_EventsMonitoring API specified in clause 14.4.3;

7.1a UAE layer registration

7.1a.1 General

The UAE capabilities provide support for registering UAV/UAV-C at the UAE server. The UAE server uses the registration information to distribute UAE layer messages or UAS application specific layer messages to the appropriate UAS UEs.

7.1a.2 Procedures

7.1a.2.1 UAS UE registration

7.1a.2.1.1 General

This clause describes the procedure for UAS UE (UAV/UAV-C) to register with the UAE server.

7.1a.2.1.2 Procedure

Pre-conditions:

– The UAE client has discovered the UAE server and is aware of the address of the UAE server (e.g. FDQN).

NOTE: How the UAE client is provisioned with the UAE server information is outside the scope of the current document.

– The UAV/UAV-C has already been assigned with the UAV ID.

Figure 7.1a.2.1.1-1: Procedure for registering the UAE client at the UAE server

1. The UAE client sends a registration request to the UAE server.

2. The UAE server performs authentication and authorization check (e.g. based on pre-provisioned security information or by interacting with UAS application specific server (e.g. USS/UTM)).

3. The UAE server sends a registration response to the UAE client indicating success or failure of the registration.

7.1a.2.2 UAS UE deregistration

7.1a.2.2.1 General

This clause describes the procedures for UAS UE (UAV/UAV-C) to deregister at the UAE server.

7.1a.2.2.2 Procedure

Pre-condition:

– The UAE client has already registered with the UAE server as described in subclause 7.1a.2.1.

Figure 7.1a.2.2.2-1: Procedure for deregistering the UAE client at the UAE server

1. The UAE client sends a deregistration request to the UAE server.

2. The UAE server sends a deregistration response to the UAE client.

7.1a.2.3 UAS UE registration update

7.1a.2.3.1 General

This clause describes the procedures for UAS UE (UAV/UAV-C) to update its registration with the UAE server.

7.1a.2.3.2 Procedure

Pre-conditions:

– The UAE client has already registered with the UAE server as described in subclause 7.1a.2.1.

Figure 7.1a.2.3.1-1: Procedure for registration update by the UAE client at the UAE server

1. The UAE client sends a registration update request to the UAE server.

2. The UAE server sends an acknowledgement to the UAE client.

7.1a.3 Information flows

7.1a.3.1 Registration request

Table 7.1a.3.1-1 describes the information flow for a UAE client to register with the UAE server.

Table 7.1a.3.1-1: Registration request

Information element	Status	Description
UAV ID	M	The identifier of the UAV/UAV-C (e.g. 3GPP UE ID or CAA level UAV ID) which initiates the registration request
UAS UE information	O	UAS UE information like IP address, Multi-USS capability, etc.
Proposed registration lifetime (NOTE)	O	Proposed registration lifetime.
NOTE: If Proposed registration lifetime IE is not included, then the registration lifetime is valid until explicit deregistration is performed.

7.1a.3.2 Registration response

Table 7.1a.3.2-1 describes the information flow for UAE server to respond for registration request from the UAE client.

Table 7.1a.3.2-1: Registration response

Information element	Status	Description
Result	M	Result from the UAE server in response to registration request indicating success or failure
Registration lifetime	O	The registration lifetime provided by UAE server if registration is successful

7.1a.3.3 Deregistration request

Table 7.1a.3.3-1 describes the information flow for a UAE client to deregister at the UAE server.

Table 7.1a.3.3-1: Deregistration request

Information element	Status	Description
UAV ID	M	The identifier of the UAV/UAV-C (e.g. 3GPP UE ID or CAA level UAV ID) which initiates the deregistration request

7.1a.3.4 Deregistration response

Table 7.1a.3.4-1 describes the information flow for UAE server to respond for deregistration request from the UAE client.

Table 7.1a.3.4-1: Deregistration response

Information element	Status	Description
Result	M	Result from the UAE server in response to the deregistration request

7.1a.3.5 Registration update request

Table 7.1a.3.5-1 describes the information flow for a UAE client to update registration with the UAE server.

Table 7.1a.3.5-1: Registration update request

Information element	Status	Description
UAV ID	M	The identifier of the UAV/UAV-C (e.g. 3GPP UE ID or CAA level UAV ID) which initiates the registration request
UAS UE information	M	UAS UE information like IP address, Multi-USS capability, etc.
Proposed registration lifetime	O	Proposed registration lifetime.

7.1a.3.6 Registration update response

Table 7.1a.3.6-1 describes the information flow for UAE server to respond for registration update request from the UAE client.

Table 7.1a.3.6-1: Registration update response

Information element	Status	Description
Result	M	Result from the UAE server in response to registration update request indicating success or failure
Registration lifetime	O	The registration lifetime provided by UAE server if registration update is successful

7.2 Communications between UAVs within a geographical area

7.2.1 General

This clause describes the procedure for communications between UAVs within a geographical area. The geographical area is from the perspective of the UAV initiating the communication with other UAVs.

The following transport mechanisms can be supported for communications between UAVs within a geographical area:

a. Using unicast Uu.

NOTE: The mechanisms for communications between UAVs using multicast/broadcast Uu and ProSe are out of scope of the current release of the present document.

7.2.2 Procedures

7.2.2.1 Communications between UAVs within a geographical area using unicast Uu

Figure 7.2.2.1-1 illustrates the procedure for communications between UAVs within a geographical area using unicast Uu.

Pre-conditions:

1. The UAE clients of UAVs have successfully registered and connected to the UAE server.

2. The SEAL’s LM server information is configured at the UAE server.

Figure 7.2.2.1-1: Communications between UAVs within a geographical area using unicast Uu

1. The UAE client of UAV sends a UAV application message to the UAE server in order to communicate the payload information of the UAV application message to other UAVs in a range of the location corresponding to the UAV.

2. The UAE server obtains the other UAV(s) information in the location of the UAV from the LMS as specified in 3GPP TS 23.434 [5].

3. Upon receiving the list of other UAV(s), the UAE server sends the payload in UAV application message to each of the UAV via unicast channel.

4. Upon completing step 3, the UAE server may send an acknowledgement to the UAE client.

7.2.3 Information flows

7.2.3.1 UAV application message

Table 7.2.3.1-1 describes the information flow for the UAV application message from UAE client to UAE server and from UAE server to UAE client.

Table 7.2.3.1-1: UAV application message

Information element	Status	Description
UAV ID	M	The identifier of the UAV (e.g. 3GPP UE ID or CAA level UAV ID) which initiates the UAV application message.
Application defined proximity range information (NOTE 2)	M	Description of the range information over which the UAV application message is to be sent.
Application Payload (NOTE 1)	M	Application payload that is to be delivered to the other UAVs
NOTE 1: This IE is provided by the UAS application specific client and its details are out of scope of 3GPP. NOTE 2: This IE is not included when the UAV application message is sent from UAE server to UAE client.

7.3 UAV and UAV-C Pairing and C2 QoS Provisioning using Group ID

7.3.1 General

This clause describes the procedure for UAV and UAV-C grouping C2 QoS provisioning using subsequent group ID. It also provides the procedure for UAV replacement resulting in group ID update.

7.3.2 Procedures

7.3.2.1 Procedure for group creation for one pair of UAV and UAV-C

Figure 7.3.2.1-1 illustrates a high-level procedure for group creation.

Pre-conditions:

– Both UAV-C and UAV have successfully registered and connected to the UAE server.

– A CAA-level UAV ID is already assigned to the UAV-C and UAV.

Figure 7.3.2.1-1: Procedure for group creation for one pair of UAV and UAV-C

1. The UAE server recognizes a unique pair of UAV and UAV-C either by 3GPP UE ID or CAA-level UAV ID.

NOTE: The mechanisms for how the UAE server recognizes a pair of UAV-C and UAV is out of scope of the present document.

2. The UAE server sends a group creation request to the SEAL GM server, if there is no pre-assigned group ID, by using the GM-S reference link as specified in 3GPP TS 23.434 [5] using the procedure defined in clause 10.3. The SEAL GM server creates one group ID for one pair of UAV and UAV-C as specified in 3GPP TS 23.434 [5].

3. The UAE server uses the returned group ID for UAS for QoS management.

7.3.2.2 Procedure for group-based approach for C2 QoS provisioning

Figure 7.3.2.2-1 illustrates a high-level workflow of group-based C2 QoS provisioning.

Pre-conditions:

– Both UAV and UAV-C have registered to 3GPP 5G network respectively. C2 communication is established.

– The procedure specified in clause 7.3.2.1 is performed and the group ID for the UAS group is available at the UAE server.

Figure 7.3.2.2-1: Procedure of group-based approach for C2 QoS provisioning.

1. The UAE server monitors the QoS for the UAS group (which includes a UAV and UAV-C) by SEAL NRM as specified in 3GPP TS 23.434 [5].

2. In cases where the network condition for C2 communication does not satisfy the pre-defined QoS requirement, the UAE server may choose to send QoS adaptation request to the SEAL NRM server using the NRM-S reference point as specified in 3GPP TS 23.434 [5]. The QoS adaptation request needs to be sent per group ID for a pair of UAV and UAV-C created in the procedure specified in clause 7.3.2.1. The subsequent network resource adaptation procedure is triggered by the UAE server as specified in clause 14.3.3.3.1 of 3GPP TS 23.434 [5].

3. The UAE client and UAE server established communication based on new QoS requirements as specified in clause 14.3.3.2.1.2 of 3GPP TS 23.434 [5].

4. UAS application layer adapts the updated QoS assignment.

NOTE: The mechanisms for how the UAS application layer is adapting newly assigned QoS is out of scope of the present document.

7.3.2.3 Procedure for group update

Figure 7.3.2.3-1 illustrates the group membership update when UAV-2 is used to replace UAV-1.

Pre-conditions:

– The UAV-C, UAV-1, and UAV-2 are all previously successfully subscribed with 3GPP Core Network and UAS application specific server (e.g. USS/UTM) and have received a 3GPP UE ID (e.g. GPSI) and a CAA-level UAV ID.

– The UAV-1 and UAV-C have been grouped by a group ID by SEAL GMS as specified in clause 7.3.2.1.

Figure 7.3.2.3-1: Procedure for group update

1. The UAE server recognizes a new pair of UAV-2 and UAV-C by the new CAA-level UAV ID.

NOTE: The mechanisms for how the UAE server recognizes a new pair of UAV-C and UAV is out of scope of the present document.

2. The UAE server sends a group membership update request to the SEAL GM server using the procedure specified in clause 10.3.2.6 of 3GPP TS 23.434 [5]. The SEAL GM server sends a group membership update response as specified in clause 10.3.2.7 of 3GPP TS 23.434 [5].

7.3.3 Information flows

The usage of information flows between UAE server and SEAL’s Group management Server is specified in clause 7.1.2.2.

The usage of information flows between UAE server and SEAL’s Network Resource Management Server is specified in clause 7.1.4.2.

7.4 C2 Communication mode selection and switching

7.4.1 General

This feature introduces the UAS application enablement services for supporting the selection and re-selection of C2 communication modes. In particular, the UAE layer provides support for the following operations:

– Support the switch between the Network-Assisted C2 communication and Direct C2 communication (e.g. when the direct link becomes feasible/available, or when a UAV is moving towards BVLOS or has poor direct link conditions, etc.) as described in clause 7.4.2.4.

– Support the switch between the Network-Assisted/Direct C2 communication and UTM-navigated C2 communication (e.g. for air traffic control, the UAV is approaching a No Drone Zone, and detected potential security threats, etc.) as described in clause 7.4.2.5.

– Support the selection of the communication mode between: utilizing more than one C2 communication links, and among applicable C2 communication links, selecting a mode as the primary one as described in clause 7.4.2.3.

– Activation for the support of the above operations in the UAE Server in the UAE client is performed using procedure described respectively in clause 7.4.2.1 and clause 7.4.2.2.

Below, the different procedures for C2 communication mode selection and switching are described using UAE Client assisted and UAE Server controlled based mechanisms. Such functionality is supported by means of policies delivered to the UAV/UAV-C via the UAE layer and assisting the dynamic switching of C2 modes.

NOTE: For direct C2 communication mode, usage of ProSe/PC5 is not considered in the present specification (e.g. direct wireless communication over a technology outside the scope of 3GPP is assumed).

7.4.2 Procedures

7.4.2.1 Management of C2 mode selection / switching capability

This procedure manages the C2 mode selection/switching capability at the UAE server, based on an application request from UAS application specific server (which can be the USS/UTM) to manage the C2 operation modes (direct, network-assisted) of C2 communication for a UAS.

Figure 7.4.2.1-1 illustrates the procedure where the UAE server receives an application request for managing the operation mode for C2 communications for a UAS.

Pre-condition:

– The UAV has received its UAS ID from the UAS application specific server.

Figure 7.4.2.1-1: C2 operation mode management request / response

1. The UAS application specific server sends to the UAE Server a C2 operation mode management request for managing the operation modes for the C2 communication for a UAS (consisting a UAV and a UAV-C) and to subscribe for UAE notifications.

2. The UAE Server sends to the UAS application specific server a C2 operation mode management response with a positive or negative acknowledgement of the request, based on capability of UAE server to undertake this task.

3. UAE server executes C2 communication modes configuration according to clause 7.4.2.2.

4. After successful execution of C2 communication modes configuration, the UAE server notifies the UAS application specific server with a C2 operation mode management complete.

7.4.2.2 C2 communication modes configuration

This procedure enables the configuration of the UAE Client, based on an application request from UAS application specific server (which can be the USS/UTM) to manage the C2 operation modes (direct, network-assisted) of C2 communication for a UAS.

Figure 7.4.2.2-1 illustrates the C2 communication modes configuration procedure.

Pre-conditions:

1. The UAS UEs are connected to 5GS and authenticated and authorized by UAS application specific server as specified in clause 5.2 of 3GPP TS 23.256 [4].

2. UAE Server has established a UAE session with the respective UAE Clients as the UAE clients are successfully registered to the UAE server.

3. UAE Server has performed the C2 mode switching/selection capability initiation as in clause 7.4.2.1.

Figure 7.4.2.2-1: C2 communication modes configuration

1. The UAE Server sends a C2 communication modes configuration request including the UAS identifier, allowed C2 communication modes (e.g., direct, network assisted, USS/UTM navigated), primary and optionally secondary C2 communication mode and policy for switching. In the case of removal of C2 communication mode configuration parameters from the UAV or UAV-C, then the request shall only include the UAS identifier.

2. The UAE Client stores or removes the C2 communication mode configuration parameters as per the information received in step 1.

3. The UAE Client sends a C2 communication modes configuration response to the UAE Server.

7.4.2.3 C2 communication mode selection by UAE Client

This procedure provides a mechanism for the UAE client to select a primary C2 communication mode and optional secondary C2 communication mode based on C2 communication mode configuration enabled as described in clause 7.4.2.2.

Figure 7.4.2.3-1 illustrates the C2 communication mode selection and redundant C2 link negotiation.

Pre-conditions:

1. The UAE Clients are configured with a C2 communication modes configuration as described in clause 7.4.2.2.

2. UAE Server has activated the dynamic C2 mode switching capability, as described in clause 7.4.2.1.

Figure 7.4.2.3-1: C2 communication mode selection

1. UAE Clients (UAV and UAV-C) select a primary and secondary C2 communication mode based on C2 communication mode configuration.

2. The UAE Client sends a C2 communication mode notification to the UAE Server indicating the selected primary and secondary C2 communication modes and associated C2 link information which may include UAE Client and peer address information (e.g., IP/MAC address).

3. The UAE Server stores the C2 communication modes and links information.

4a-4b. The UAE Server forwards the C2 communication mode and links information to the UAS application specific server and receives a C2 communication mode notification acknowledgement from the UAS application specific server.

5. The UAE Server may forward the C2 communication mode notification acknowledgement to the UAE Client.

6. The UAV and UAV-C start C2 communication using the selected C2 communication mode.

NOTE: The details of step 6 are outside the scope of the present specification.

7.4.2.4 UAE-layer assisted dynamic C2 mode switching

This procedure provides a mechanism for supporting dynamic switching between direct and network assisted C2 communications, which may be required while the UAV flight is ongoing, due to possible change of network conditions, expected location/mobility of the UAV, unpredictable events etc.

Figure 7.4.2.4-1 illustrates the procedure where the UAE server supports the dynamic C2 mode switching for network-assisted C2 communications.

Pre-conditions:

1. UAE Server has activated the dynamic C2 mode switching capability, as described in clause 7.4.2.1

2. UAE Server has subscribed for using SEAL/LMS services and has configured the location event reporting, based on 3GPP TS 23.434 [5].

3. UAE Client has selected a C2 communication mode as described in clause 7.4.2.3, and UAV and UAV-C are engaged in C2 communication.

Figure 7.4.2.4-1: UAE-assisted dynamic C2 mode switching

1. The UAE Client detects a condition for switching C2 communication mode based on local conditions (e.g. using the C2 communication mode switching policy) or based on a command from the UAS application specific server (as described in clause 7.4.2.5). A C2-related trigger event report is sent from the UAE Client of the UAV and/or the UAV-C to the UAE Server, denoting a command from the UAS application specific server or an application QoS attribute change (experienced or expected) e.g. based on the experienced packet delay or packet loss for the Uu or direct link (e.g. packet loss greater than a pre-defined threshold).

2. Additionally, the UAE Server receives a location report for the UAV/UAV-C by the SEAL’s LM server. The report can be either periodical or event-based (e.g. UAV moving towards an area covered by a different cell or different operator), as specified in 3GPP TS 23.434 [5] SEAL’s LM server procedures (UAE Server acting as a VAL server).

3. The UAE Server determines the switching of the C2 mode from direct to network assisted or vice versa or to USS/UTM navigated. If the switching is from direct to network assisted or vice versa, this is done by calculating the relative actual or expected UAV-to-UAV-C location, as well as other factors like QoS fulfilment/unfulfilment, augmented location, mobility/speed, direction, topography, weather conditions.

4. The UAE Server sends a C2 mode switching confirmation request to the UAS application specific server, which includes the UAS identifier as well as the cause for switching and the switching option (direct to network-assisted or network-assisted to direct or to USS/UTM navigated). The UAE Server sends this request to obtain confirmation from the UAS application specific server before proceeding with switching to USS/UTM navigated. This step is optional in the case of switching from direct to network assisted or vice versa.

5. Conditional on Step 3, the UAE Server receives from the UAS application specific server a C2 mode switching confirmation response indicating a positive or negative result for the requested change.

6. The UAE Server sends to the involved UAE Clients, a C2 operation mode switching message which provides an instruction to the UAV and UAV-C to switch to network-assisted mode or to direct mode or to USS/UTM navigated. The UAV and UAV-C start C2 communication using the indicated C2 communication mode (e.g., direct, network assisted, USS/UTM navigated).

7. If an emergency switch of the C2 communication is deemed necessary by the UAE Client (e.g. sudden loss of the active C2 link), the UAE Client changes the link prior to the steps 1-6, which are skipped. The UAE Clients send a C2 operation mode switching performed message to the UAE Server to confirm the switching of the C2 communication mode.

7.4.2.5 UAS application specific server triggered C2 communication mode switching

This procedure provides a mechanism for supporting dynamic switching between direct or network assisted C2 communications to USS/UTM navigated, initiated by the UAS application specific server (which can be the USS/UTM) after detecting a C2 switching condition which may be required while the UAV enters a no-fly zone. For example, the UAS application specific server needs to take over the control of UAV and fly it to safety (see 3GPP TS 22.125 [2] clause 4.2).

Figure 7.4.2.5-1 illustrates a UAS application specific server triggered C2 communication mode switching.

Pre-conditions:

1. UAE Server has activated the dynamic C2 mode switching capability, as described in clause 7.4.2.1.

2. UAE Client has selected a primary C2 communication mode as described in clause 7.4.2.3, and UAV and UAV-C are engaged in (e.g., direct or network assisted) C2 communication.

Figure 7.4.2.5-1: UAS application specific server triggered C2 communication mode switching

1. The UAS application specific client is instructed directly by a command from the UAS application specific server to switch to USS/UTM navigated mode.

NOTE: This procedure between the UAS application specific server and the UAS application specific client is out of scope of the present document.

2. The UAE Client initiates the procedure described in clause 7.4.2.4.

7.4.3 Information flows

7.4.3.1 C2 operation mode management request

Table 7.4.3.1-1 describes the information flow C2 operation mode management request from the UAS application specific server to the UAE server.

Table 7.4.3.1-1: C2 operation mode management request

Information element	Status	Description
UASS ID	M	Identity of the UAS application specific server which requests the C2 operation mode management. This ID can be the USS/UTM identifier, when the UAS application specific server is the USS/UTM.
UAS ID	M	The identification of the UAS for which the C2 QoS management request applies. This could be in form of identifier for the UAS, e.g group ID; or collection of individual identifiers for the UAV and UAV-C, e.g. CAA level UAV ID, GPSI
C2 operation mode management container (see NOTE 2)	O	The C2 operation mode management container consists of the requirements and policy for C2 operation mode management
> C2 operation mode management requirement	M	Identification of the type of the C2 mode switching to be supported by the UAE server. This can be either from direct to network-assisted C2, or from network-assisted to direct C2 or to UTM navigated.
> Allowed C2 communication modes	M	direct, network assisted, USS/UTM navigated
> Primary C2 communication mode	M	Primary C2 communication mode (direct, network assisted)
> Secondary C2 communication mode	O	Secondary C2 communication mode (direct, network assisted)
> Policy of C2 switching	M	Parameters for C2 switching (see NOTE 1) – QoS thresholds on active link – QoS thresholds on target link
> C2 service area	O	The area where the C2 operation mode management request applies. This can be geographical area, or topological area in which the capability is active.
NOTE 1: A complete list of parameters for the QoS-policy of C2 switching is specified by stage 3. NOTE 2: If C2 operation mode management container IE is not included, it indicates removal of the C2 operation mode management related information.

7.4.3.2 C2 operation mode management response

Table 7.4.3.2-1 describes the information flow C2 operation mode management response from the UAE server to the UAS application specific server.

Table 7.4.3.2-1: C2 operation mode management response

Information element	Status	Description
Result	M	The positive or negative result of the C2 operation mode management request.

7.4.3.3 C2 operation mode management complete

Table 7.4.3.3-1 describes the information flow C2 operation mode management complete from the UAE server to the UAS application specific server.

Table 7.4.3.3-1: C2 operation mode management complete

Information element	Status	Description
Result	M	The positive or negative result of the C2 communication mode configuration.

7.4.3.4 C2-related trigger event report

Table 7.4.3.4-1 describes the information flow C2-related trigger event report from the UAE client (of the UAV or the UAV-C) to the UAE server.

Table 7.4.3.4-1: C2-related trigger event report

Information element	Status	Description
UAE client ID	M	The identifier of the UAE client which indicates the QoS downgrade
Application QoS-related event	M	The report including the expected or actual application QoS / QoE parameters which were change (i.e. latency, throughput, reliability, jitter). The event configuration (thresholds, policies) is provided to the UAE client as described in clause 7.3.2.2.

7.4.3.5 C2 mode switching confirmation request

Table 7.4.3.5-1 describes the information flow C2 mode switching confirmation request from the UAE server to the UAS application specific server.

Table 7.4.3.5-1: C2 mode switching confirmation request

Information element	Status	Description
UAE server ID	M	The identifier of the UAE server which requests the C2 mode switching confirmation from USS/UTM
UAS ID	M	The identification of the UAS. This could be in form of identifier for the UAS, e.g. group ID; or collection of individual identifiers for the UAV and UAV-C, e.g. CAA level UAV ID, GPSI.
C2 operation mode switching type	M	The type of the C2 mode switching to be applied (direct to network-assisted, or network-assisted to direct, or to USS/UTM navigated).
Switching cause	O	Cause information for initiating the switching (e.g. poor radio link quality)

7.4.3.6 C2 mode switching confirmation response

Table 7.4.3.6-1 describes the information flow C2 mode switching confirmation response from the UAS application specific server (USS/UTM) to the UAE server.

Table 7.4.3.6-1: C2 mode switching confirmation response

Information element	Status	Description
Result	M	The positive or negative result of the C2 mode switching confirmation response.

7.4.3.7 C2 operation mode switching

Table 7.4.3.7-1 describes the information flow C2 operation mode switching from the UAE server to the UAE client(s) of the affected UAS.

Table 7.4.3.7-1: C2 operation mode switching

Information element	Status	Description
UAE server ID	M	The identifier of the UAE server which instructs the UAS to apply the C2 mode switching.
C2 operation mode switching requirement	M	The type of the C2 mode switching to be applied (direct to network-assisted, or network-assisted to direct).
Time Validity	O	Time validity for the C2 switching requirement
Geographical Area	O	Area for which the C2 switching applies

7.4.3.8 C2 communication modes configuration request

Table 7.4.3.8-1 describes the information flow C2 communication modes configuration request from the UAE server to the UAE client.

Table 7.4.3.8-1: C2 communication modes configuration request

Information element	Status	Description
UAS ID	M	The identification of the UAS for which the C2 QoS management request applies. This could be in form of identifier for the UAS, e.g. group ID; or collection of individual identifiers for the UAV and UAV-C, e.g. CAA level UAV ID, GPSI.
C2 operation mode management configuration (see NOTE 2)	O	The C2 operation mode management configuration information to be configured at the UAS
> C2 operation mode management requirement	M	Identification of the type of the C2 mode switching to be supported by the UAE server. This can be either from direct to network-assisted C2, or from network-assisted to direct C2 or to UTM navigated.
> Allowed C2 communication modes	M	direct, network assisted, USS/UTM navigated
> Primary C2 communication mode	M	Primary C2 communication mode (direct, network assisted)
> Secondary C2 communication mode	O	Secondary C2 communication mode (direct, network assisted)
> Policy of C2 switching	M	Parameters for C2 switching (see NOTE 1) – QoS thresholds on active link – QoS thresholds on target link
NOTE 1: A complete list of parameters for the QoS-policy of C2 switching is specified by stage 3. NOTE 2: If C2 operation mode management configuration IE is not included, it indicates removal of the C2 operation mode management configuration at the UAS ID.

7.4.3.9 C2 communication modes configuration response

Table 7.4.3.9-1 describes the information flow C2 communication modes configuration response from the UAE client to the UAE server.

Table 7.4.3.9-1: C2 communication modes configuration response

Information element	Status	Description
Result	M	The positive or negative result of reception and storing or removal of the communication mode configuration parameters

7.4.3.10 C2 communication mode notification

Table 7.4.3.10-1 describes the information flow C2 communication mode notification from the UAE client to the UAE server and from the UAE server to the UAS application specific server.

Table 7.4.3.10-1: C2 communication mode notification

Information element	Status	Description
UAS ID	M	The identification of the UAS. This could be in form of identifier for the UAS, e.g. group ID; or collection of individual identifiers for the UAV and UAV-C, e.g. CAA level UAV ID, GPSI.
Selected primary C2 communication mode	M	Selected primary C2 communication mode (direct, network assisted)
Selected secondary C2 communication mode	O	Selected secondary C2 communication mode (direct, network assisted)

7.4.3.11 C2 communication mode notification acknowledgement

Table 7.4.3.11-1 describes the information flow C2 communication mode notification acknowledgement from the UAE server to the UAE client and from the UAS application specific server to the UAE server.

Table 7.4.3.11-1: C2 communication mode notification acknowledgement

Information element	Status	Description
Acknowledgement	M	Acknowledgement of selected C2 communication mode(s)

7.4.3.12 C2 operation mode switching performed

Table 7.4.3.12-1 describes the information flow C2 operation mode switching performed from the UAE client to the UAE server.

Table 7.4.3.12-1: C2 operation mode switching performed

Information element	Status	Description
Result	M	The result of the C2 mode switching

7.5 Real-Time UAV Connection Status Monitoring and Location reporting

7.5.1 General

This clause enables the UAE server to provide a real-time view of UAV network status and location reporting based on current network connection status, in particular with the supporting of following use cases:

– Support of real-time monitor the 3GPP network connection with UAVs.

– Support of reporting of loss of communication with UAVs.

– Support of location reporting such as last known location after loss of communication.

7.5.2 Procedures

7.5.2.1 Procedure for real-time UAV network connection status monitoring and location update

Figure 7.5.2.1-1 illustrates the real-time network monitoring and location update support for UAV operations.

Pre-conditions:

– UAE server has subscribed to the monitoring event API for connection monitoring by the NRM server for both UAV and/or UAV client as specified in clause 14.3.6.2.2 of 3GPP TS 23.434 [5].

– UAE server has subscribed for the location information and location deviation monitoring events of UAV from LM server as per the clause 9.3.7 and clause 9.3.11.2 specified in 3GPP TS 23.434 [5].

– Subscription for real-time UAV status information is performed as specified in clause 7.5.2.2.

Figure 7.5.2.1-1: Real-time UAV network connection status monitoring and location update

1. The UAE server receives location report and location deviation monitoring event notifications from LM server as specified in clause 9.3.8 and clause 9.3.11.2 of 3GPP TS 23.434 [5]. UAE server shall record the current location reporting timestamp as specified in clause 9.3.2.2 of 3GPP TS 23.434 [5].

2. The UAE server receives monitoring events notification as specified in clause 14.3.6.3.2 of 3GPP TS 23.434 [5]. If events are regarding loss of UE reachability such as when received "Loss_of_connectivity_notification", the UAE server shall record such event with current timestamp.

3. NRM server sends notification when UE re-connected status is detected as specified in clause 14.3.6.3.2 of 3GPP TS 23.434 [5].

4. The UAE server shall record such event with current timestamp, plus with last known location information and timestamp as specified in clause 9.3.2.7 of 3GPP TS 23.434 [5] and trigger location update as specified in clause 9.3.4 of 3GPP TS 23.434 [5].

7.5.2.2 Subscription for real-time UAV status information

Figure 7.5.2.2-1 describes the procedure for subscription for real-time UAV status information.

Pre-condition:

– UAS application specific server has been provisioned with UAE server information.

Figure 7.5.2.2-1: Subscription for real-time UAV status information

1. The UAE application specific server sends subscribe real-time UAV status information request to the UAE server. The request includes the UAV ID.

2. The UAE server stores the subscription information.

3. The UAE server sends subscription response to the UAS application specific server.

7.5.2.3 Notification of real-time UAV status information

Pre-conditions:

– UAS application specific server has performed subscription as per procedure in clause 7.5.2.2 with UAE server and the procedure for processing real-time UAV status as specified in clause 7.5.2.1 has performed.

Figure 7.5.2.3-1: Notification for real-time UAV status information

1. When real-time UAV status information is available at the UAE as per the subscription then, the UAE server sends notification of real-time UAV status information to the UAS application specific server.

7.5.2.4 Unsubscription for real-time UAV status information

Figure 7.5.2.4-1 describes the procedure for unsubscription for real-time UAV status information.

Pre-condition:

– UAS application specific server has performed the subscription procedure as specified in clause 7.5.2.2.

Figure 7.5.2.4-1: Unsubscription for real-time UAV status information

1. The UAE application specific server sends unsubscribe real-time UAV status information request to the UAE server. The request includes the subscription ID.

2. The UAE server cancels the subscription information.

3. The UAE server sends unsubscription response to the UAS application specific server.

7.5.3 Information flows

7.5.3.1 Information flows between UAE server and SEAL servers

The usage of information flows between UAE server and SEAL’s Location Management Server is specified in clause 7.1.3.2.

The usage of information flows between UAE server and SEAL’s Network Resource Management Server is specified in clause 7.1.4.2.

7.5.3.2 Subscribe real-time UAV status information request

Table 7.5.3.2-1 describes the information flow for a UAS application specific server to subscribe to real-time UAV status information at the UAE server.

Table 7.5.3.2-1: Subscribe real-time UAV status information request

Information element	Status	Description
UASS ID	M	The identifier of the UAS application specific server which initiated this request.
UAV ID	M	The identifier of the UAV (e.g. 3GPP UE ID or CAA level UAV ID) for which the real-time UAV status is requested.
Area of Interest	M	Geographic area location information where the UASS server wishes to monitor the UAS’s location adherence.
Notification Target URI	M	Target URI where the UAS application specific server wishes to receive the notifications about real-time UAV status information.

7.5.3.3 Subscribe real-time UAV status information response

Table 7.5.3.3-1 describes the information flow for UAE server to respond for real-time UAV status subscription request from the UAS application specific server.

Table 7.5.3.3-1: Subscribe real-time UAV status information response

Information element	Status	Description
Result	M	Result from the UAE server in response to subscription request indicating success or failure
Subscription ID (NOTE)	O	Identifier of a successful subscription.
NOTE: This IE is included when the Result indicates success

7.5.3.4 Notify real-time UAV status information

Table 7.5.3.4-1 describes the information flow for a UAS application specific server to receive notification about real-time UAV status information from the UAE server.

Table 7.5.3.4-1: Notify real-time UAV status information

Information element	Status	Description
Subscription ID	M	Identifier of the subscription for this notification.
Real-time UAV status information	M	The real-time UAV status information
>UAV ID	M	The identifier of the UAV (e.g. 3GPP UE ID or CAA level UAV ID) for which the real-time UAV status information is notified.
>UAV status information	M	The UAV status information includes the UAV network connection status information, location information and timestamp.

7.5.3.5 Unsubscribe real-time UAV status information request

Table 7.5.3.5-1 describes the information flow for a UAS application specific server to unsubscribe to real-time UAV status information at the UAE server.

Table 7.5.3.5-1: Unsubscribe real-time UAV status information request

Information element	Status	Description
Subscription ID	M	Identifier of the subscription for this notification.

7.5.3.6 Unsubscribe real-time UAV status information response

Table 7.5.3.6-1 describes the information flow for UAE server to respond for real-time UAV status unsubscription request from the UAS application specific server.

Table 7.5.3.6-1: Unsubscribe real-time UAV status information response

Information element	Status	Description
Result	M	Result from the UAE server in response to unsubscription request indicating success or failure

7.6 Change of USS during flight

7.6.1 General

This feature introduces the UAS application enablement services for supporting change of UAS application specific server. In particular, the UAE layer provides support for the following operations:

– Support of the registration of the UAE clients multi-USS capability to the UAE server as described in clause 7.1a.

– Support the distribution of the for multi-USS policies from the UAS application specific server to the UAE server and the UAE client, as described in clause 7.6.2.1 and clause 7.6.2.2.

– Support the change of UAS application specific server, as described in clause 7.6.2.3.

NOTE: The functions of the USS are out of scope of the present specification.

7.6.2 Procedures

7.6.2.1 Management of multi-USS configuration

This procedure manages the multi-USS policies at the UAE server, based on an application request from UAS application specific server to support the change of USS for a UAS.

Figure 7.6.2.1-1 illustrates the procedure where the UAE server receives an application request for managing the multi-USS policies for a UAS from the UAS application specific server.

Pre-condition:

– The UAV has received its UAS ID from the UAS application specific server.

– The UAV has performed the UAS UE registration procedure.

Figure 7.6.2.1-1: Multi-USS management procedure

1. The UAS application specific server sends to the UAE server a Multi-USS management. The request includes the UAV (UAE client) identifier and the Multi-USS policies. The Multi-USS policy is: allowed USSes (identified by e.g. FQDN), serving USS information, and additional information for change of USS (USS change constraints parameter geo location/area threshold for change of USS by UAV). The UAE server stores the Multi-USS policies corresponding to the UAV ID. In case of removal of the Multi-USS policy for a USS from the UAE server, the request shall include the UAV identifier and a USS identifier (e.g. FQDN) for the USS that will be removed.

2. The UAE server sends to the UAS application specific server a Multi-USS management response with a positive or negative acknowledgement of the request.

3. UAE server executes the multi-USS configuration according to clause 7.6.2.2.

4. After successful execution of USS management configuration, the UAE server notifies the UAS application specific server with a Multi-USS management complete based on the configured capabilities of the UAE client.

7.6.2.2 Multi-USS configuration

This procedure enables the configuration of the UAE client, based on a request from UAS application specific server to configure multi-USS policies to the UAE client.

Figure 7.6.2.2-1 illustrates the Multi-USS configuration procedure.

Pre-conditions:

1. The UAS UEs are connected to 5GS and authenticated and authorized by UAS application specific server as specified in clause 5.2 of 3GPP TS 23.256 [4].

2. UAE server has established a UAE session with the respective UAE clients as the UAE clients are successfully registered to the UAE server.

3. UAE server has performed the Multi-USS management procedure according to clause 7.6.2.1.

Figure 7.6.2.2-1: Multi-USS configuration

1. The UAE server sends a Multi-USS configuration request to the UAE client. The UAE client receives a Multi-USS configuration request from the UAE server that includes the Multi-USS policies. In case of removal of the Multi-USS policy for a USS from the UAE client, then the request shall only include a USS identifier (e.g. FQDN) for the USS that will be removed.

Editor’s Note: Further details on the procedures of multi-USS configuration is FFS.

2. The UAE client stores or removes the Multi-USS policies as per the information received in step 1.

3. The UAE client sends a Multi-USS configuration response to the UAE server.

7.6.2.3 UAE-layer assisted change of USS

This procedure provides a mechanism for supporting dynamic change of USS which may be required while the UAV flight is ongoing, due to expected location/mobility of the UAV, emergency events, etc.

Figure 7.6.2.3-1 illustrates the procedure where the UAE server supports the change of USS.

Pre-conditions:

1. UAE client has indicated support of change of USS by the Multi-USS capability.

2. UAS application specific server has provided Multi-USS policies to the UAE client and the UAE server.

Figure 7.6.2.3-1: UAE-layer assisted change of USS

1. The UAE server receives a USS change request from a UAS application specific server. The request includes the UAV (UAE client) identification information, a new serving USS information and USS change authorization information (e.g. authorization token). Optionally, an updated Multi-USS policy for the USS can be included. The UAE server verifies that the request is authorized (e.g., Multi-USS capability is enabled, new USS part of the allowed USS information).

2. The UAE server forwards the USS change request to the UAE client including the new serving USS information and the updated Multi-USS policy.

3. Perform change of USS.

The UAE client initiates the communication with the new serving USS based on the USS change request and the Multi-USS policy.

If an emergency change of USS is deemed necessary by the UAE Client (e.g. sudden loss of contact with the serving USS), the UAE client initiates the change of USS (i.e. on behalf of the USS) based on the previously USS provided Multi-USS policy. In this case, the steps 1-2 are not performed.

4. The UAE client sends a USS change response/notification indicating to what USS the change of USS has been performed.

5. The UAE server sends a USS change response/notification to the UAS application specific server indicating that a change of USS has been performed.

7.6.3 Information flows

7.6.3.1 Multi-USS management request

Table 7.6.3.1-1 describes the information flow Multi-USS management request from the UAS application specific server to the UAE server.