Content for TS 23.255 Word version: 19.0.0
7.4 C2 Communication mode selection and switching
7.4.1 General
7.4.2 Procedures
7.4.2.1 Management of C2 mode selection / switching capability
7.4.2.2 C2 communication modes configuration
7.4.2.3 C2 communication mode selection by UAE Client
7.4.2.4 UAE-layer assisted dynamic C2 mode switching
7.4.2.5 UAS application specific server triggered C2 communication mode switching
7.4.3 Information flows
7.4.3.1 C2 operation mode management request
7.4.3.2 C2 operation mode management response
7.4.3.3 C2 operation mode management complete
7.4.3.4 C2-related trigger event report
7.4.3.5 C2 mode switching confirmation request
7.4.3.6 C2 mode switching confirmation response
7.4.3.7 C2 operation mode switching
7.4.3.8 C2 communication modes configuration request
7.4.3.9 C2 communication modes configuration response
7.4.3.10 C2 communication mode notification
7.4.3.11 C2 communication mode notification acknowledgement
7.4.3.12 C2 operation mode switching performed
...
...
7.4 C2 Communication mode selection and switching p. 35
7.4.1 General p. 35
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 two Network-Assisted C2 communications (via different subscriptions/networks) or between a Network-Assisted C2 communication and a 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: 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 and in the UAE client performed using procedures described respectively in clause 7.4.2.1 and clause 7.4.2.2.
- Support for C2 direct mode availability reporting to provide the awareness to the UAE server to switch to direct C2 communication if it is possible, as described in clause 7.4.2.4.
7.4.2 Procedures p. 35
7.4.2.1 Management of C2 mode selection / switching capability p. 35
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.
Step 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. If the C2 operation mode management container is provided, the request shall include the allowed C2 communication modes, the primary C2 communication mode and the policy for C2 switching, and may include the secondary C2 communication mode and the C2 service area. If ProSe/PC5 is supported for direct C2 communications, such request may also include a C2 direct mode availability reporting requirement including the ProSe configuration information for direct C2 operation, the UAV and UAV-C IDs and addresses, and the time for which the monitoring of availability will apply. If Dual Network-Assisted C2 communication link is supported (dual subscription functionality), such request may also include a C2 active/standby configuration information for C2 connectivity of the UAV to select the specific network based on QoS or specific time and also the area for which the respective network connectivity should be valid. Such request may also include a C2 connectivity via both active links via different networks.
Step 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.
Step 3.
UAE server executes C2 communication modes configuration according to clause 7.4.2.2.
Step 4.
After 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 p. 36
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. For redundancy purposes, two links can be activated to work simultaneously or as active/standby. These links can belong to the same or different networks (e.g., dual subscription functionality) see Figure B.2.1-3.
Figure 7.4.2.2-1 illustrates the C2 communication modes configuration procedure.
Pre-conditions:
- The UAS UEs are connected to 5GS and authenticated and authorized by UAS application specific server as specified in clause 5.2 of TS 23.256.
- UAE Server has established a UAE session with the respective UAE Clients as the UAE clients are successfully registered to the UAE server.
- UAE Server has performed the C2 mode selection/switching capability initiation as in clause 7.4.2.1.
Step 1.
The UAE Server sends a C2 communication modes configuration request including the UAS identifier. If the C2 operation mode management container is provided, the request shall include the allowed C2 communication modes (e.g., direct, network assisted, UTM-Navigated), the primary C2 communication mode and the policy for C2 switching, and may include the secondary C2 communication mode. The UAE server may configure multiple Network-Assisted C2 communication links if the UAE client has indicated this capability to the UAE server at the UAE layer registration and if the UAE server has received such configuration via procedure described in clause 7.4.2.1. 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.
Step 2.
The UAE Client stores or removes the C2 communication mode configuration parameters as per the information received in step 1.
Step 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 p. 37
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. If two links are activated to work simultaneously or as active/standby, these links can belong to the same or different networks (dual subscription functionality). The UAE server can then have access to both networks (using deployment option shown in Figure B.2.1-3 (deployment of UAE server with connections to 3GPP network systems in multiple PLMN operator (network) domains)).
Figure 7.4.2.3-1 illustrates the C2 communication mode selection and redundant C2 link negotiation.
Pre-conditions:
- The UAE Clients are configured with a C2 communication modes configuration as described in clause 7.4.2.2.
- UAE Server has activated the dynamic C2 mode switching capability, as described in clause 7.4.2.1.
Step 1.
UAE Clients (UAV and UAV-C) select a primary and optionally a secondary C2 communication mode based on C2 communication mode configuration. The UAE Client (UAV) may select active connectivity via network 1 or network 2 based on the preconfigured policy for C2 and payload communication. The two links may have been activated to work simultaneously based on specific QoS threshold. The UAE Client (UAV) may also select active/standby connectivity via network 1 or network 2 based on the preconfigured policy for C2 and payload communication or activate both links via both networks simultaneously. The two links can belong to the same or different networks (e.g., dual subscription functionality).
Step 2.
The UAE Client sends a C2 communication mode notification to the UAE Server indicating the selected primary and secondary C2 communication modes or the selected active/standby communication modes and the associated C2 link information which may include UAE Client and peer address information (e.g., IP/MAC address).
Step 3.
The UAE Server stores the C2 communication modes and links information.
Step 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.
Step 5.
The UAE Server may forward the C2 communication mode notification acknowledgement to the UAE Client.
Step 6.
The UAV and UAV-C start C2 communication using the selected C2 communication mode.
7.4.2.4 UAE-layer assisted dynamic C2 mode switching p. 38
This procedure provides a mechanism for supporting dynamic switching between two Network-Assisted C2 communications (via different networks) or between a direct and a network assisted C2 communication, 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:
- UAE Server has activated the dynamic C2 mode switching capability, as described in clause 7.4.2.1
- UAE Server has subscribed for using SEAL/LMS services and has configured the location event reporting, based on TS 23.434. If two links are configured to work simultaneously or as active/standby, SEAL/LMS must have access to both networks (using deployment option shown in Figure 8.2.2-2 of TS 23.434 - deployment of SEAL servers with connections to 3GPP network system in multiple PLMN operators (networks) domains).
- 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. Two links may have been activated to work simultaneously or as active/standby.
Step 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. The report shall include 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 links or the direct link (e.g. packet loss greater than a pre-defined threshold).
If a C2 direct mode availability reporting requirement exists based on clause 7.4.2.1 step 1, the detection of UAV/UAV-C(s) can be based on the PC5 discovery due to the configurations received due procedures in clause 7.4.2.1 and clause 7.4.2.2. In this case, the C2-related trigger event report message shall include also a C2 direct mode availability report including PC5 related configuration information.
Step 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 TS 23.434 SEAL's LM server procedures (UAE Server acting as a VAL server).
Step 3.
The UAE Server determines the switching of the C2 mode between network 1 and network 2, from direct to network assisted or vice versa or to 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.
Step 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 (active links between network 1 and network 2, direct to network-assisted or network-assisted to direct or to UTM-Navigated). The UAE Server sends this request to obtain confirmation from the UAS application specific server before proceeding with switching to UTM-Navigated. This step is optional in the case of switching from direct to network assisted or vice versa.
Step 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.
Step 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 between the networks, to network-assisted mode or to direct mode or to UTM-Navigated. The UAV and UAV-C start C2 communication using the indicated C2 communication mode (e.g., active link via network 1 or network 2, direct, network assisted, UTM-Navigated).
Step 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 p. 40
This procedure provides a mechanism for supporting dynamic switching between direct or network assisted C2 communications to 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 clause 4.2 of TS 22.125).
Figure 7.4.2.5-1 illustrates a UAS application specific server triggered C2 communication mode switching.
Pre-conditions:
- UAE Server has activated the dynamic C2 mode switching capability, as described in clause 7.4.2.1. If two links can be activated to work simultaneously or as active/standby, these links can belong to the same or different networks.
- 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. Two links may have been activated to work simultaneously.
Figure 7.4.2.5-1: UAS application specific server triggered C2 communication mode switching
(⇒ copy of original 3GPP image)
(⇒ copy of original 3GPP image)
Step 1.
The UAS application specific client is instructed directly by a command from the UAS application specific server to switch to UTM-Navigated mode.
Step 2.
The UAE Client initiates the procedure described in clause 7.4.2.4.
7.4.3 Information flows p. 40
7.4.3.1 C2 operation mode management request p. 40
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.
| 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, 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
|
| > 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. |
| > C2 direct mode availability reporting requirement | O | A requirement for C2 direct mode reporting. |
| >> ProSe application codes | O | The ProSe codes used for direct C2 communications. The ProSe codes are used for the ProSe Direct Discovery as specified in [4]. |
| >> Time of validity | O | The time for which the C2 direct mode availability/feasibility checking applies. |
| >> Reporting configuration | O | The configuration of the reporting and periodicity/frequency of reporting required. |
| > Dual Network-Assisted C2 communication links | O | Support for multiple Network-Assisted C2 communication links. |
| >> Policy of C2 switching in case of Network-Assisted C2 communication link 1 | O | Parameters for C2 switching for Network-Assisted C2 communication link 1:
|
| >> Policy of C2 switching in case of Network-Assisted C2 communication link 2 | O | Parameters for C2 switching for Network-Assisted C2 communication link 2:
|
| > C2 service area for Network-Assisted C2 communication link 1 | O | The area where the C2 operation mode management request applies. This can be geographical area, or topological area in which the connectivity via subscription/network 1 is active. |
| > C2 service area for Network-Assisted C2 communication link 2 | O | The area where the C2 operation mode management request applies. This can be geographical area, or topological area in which the connectivity via subscription/network 2 is active. |
|
NOTE 1:
Void
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 p. 42
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.
| 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 p. 42
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.
| 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 p. 42
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.
| Information element | Status | Description |
|---|---|---|
| UAE client ID | M | The identifier of the UAE client which indicates the QoS downgrade. |
| UAS UE ID(s) | O | The identifier of the UE ID(s) for which the PC5 connectivity is feasible/available. |
| 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) of Network-Assisted C2 communication link 1. The event configuration (thresholds, policies) is provided to the UAE client as described in clause 7.4.2.4. |
| Application QoS-related event of Network-Assisted C2 communication link 2 | O | The report including the expected or actual application QoS / QoE parameters which were changed (i.e. latency, throughput, reliability, jitter) of Network-Assisted C2 communication link 2. The event configuration (thresholds, policies) is provided to the UAE client as described in clause 7.4.2.4. |
| PC5 availability indication | O | The PC5 availability indication for the direct C2 mode. |
| > PC5 capabilities | O | The PC5/ProSe capabilities and configuration information of the involved UAS UEs. |
| > PC5 QoS/access information | O | The PC5 QoS (list of PQIs) and access related information (e.g. DRX cycles, resource pools). |
| > Time of validity | O | The time for which the direct mode is available. |
7.4.3.5 C2 mode switching confirmation request p. 43
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.
| 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 (network-assisted to network-assisted, direct to network-assisted, network-assisted to direct, or 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 p. 43
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.
| 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 p. 43
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.
| 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 (network-assisted to network-assisted, 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 p. 43
Table 7.4.3.8-1 describes the information flow C2 communication modes configuration request from the UAE server to the UAE client.
| 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, 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
|
| > Dual Network-Assisted C2 communication links | O | Support for multiple Network-Assisted C2 communication links. This information element may only be present if the UAE client has indicated this capability to the UAE server at the UAE layer registration. |
| >> Policy of C2 switching in case of Network-Assisted C2 communication link 1 | O | Parameters for C2 switching for Network-Assisted C2 communication link 1:
|
| >> Policy of C2 switching in case of Network-Assisted C2 communication link 2 | O | Parameters for C2 switching for Network-Assisted C2 communication link 2:
|
| > C2 service area for Network-Assisted C2 communication link 1 | O | The area where the C2 operation mode management request applies. This can be geographical area, or topological area in which the connectivity via subscription/network 1 is active. |
| > C2 service area for Network-Assisted C2 communication link 2 | O | The area where the C2 operation mode management request applies. This can be geographical area, or topological area in which the connectivity via subscription/network 2 is active. |
|
NOTE 1:
Void
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 p. 44
Table 7.4.3.9-1 describes the information flow C2 communication modes configuration response from the UAE client to the UAE server.
| 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 p. 45
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.
| 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, UTM-Navigated or via specific subscription). |
| Selected secondary C2 communication mode | O | Selected secondary C2 communication mode (direct, network assisted, UTM-Navigated or via specific subscription). |
7.4.3.11 C2 communication mode notification acknowledgement p. 45
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.
| Information element | Status | Description |
|---|---|---|
| Acknowledgement | M | Acknowledgement of selected C2 communication mode(s) |
7.4.3.12 C2 operation mode switching performed p. 45
Table 7.4.3.12-1 describes the information flow C2 operation mode switching performed from the UAE client to the UAE server.
| Information element | Status | Description |
|---|---|---|
| Result | M | The result of the C2 mode switching |
