6.1 Control and user plane stacks
23.3043GPPProximity based Services (ProSe) in the 5G System (5GS)Release 17TS
6.1.1 Control Plane
6.1.1.1 General
The control plane stack consists of protocols for controlling:
– 5G ProSe Direct Discovery, specified in clause 6.1.1.2.1, clause 6.1.1.3, clause 6.1.1.4, clause 6.1.1.5 and clause 6.1.1.6;
– 5G ProSe Direct Communication, specified in clause 6.1.1.2.2;
– 5G ProSe UE-to-Network Relay, specified in clause 6.1.1.7.
6.1.1.2 UE – UE
6.1.1.2.1 Discovery plane PC5 interface
The PC5 communication channel is used to carry the discovery messages over PC5 which are differentiated from other PC5 messages by the AS layer.
Figure 6.1.1.2.1-1 depicts a discovery plane for NR PC5 reference point.
Legend:
– PC5-D: The PDCP/RLC/MAC/PHY functionality is specified in TS 38.300 [12].
– The "ProSe Discovery protocol" is used for handling ProSe Direct Discovery as specified in clause 6.3.2.
Figure 6.1.1.2.1-1: Discovery Plane PC5 Interface
6.1.1.2.2 PC5 Signalling Protocol
The PC5 Signalling Protocol stack specified in clause 6.1.2 of TS 23.287 [2] is used. The protocol used for the control plane signalling over the PC5 reference point for the secure layer-2 link is specified in clauses 6.4.3, 6.5.1 and 6.5.2.
6.1.1.3 UE – 5G DDNMF
Legend:
– ProSe Control Signalling between UE and 5G DDNMF is carried over the user plane and using the PC3a protocol as specified in TS 24.554 [23].
NOTE 1: PC3a may be realized with one or more protocols.
NOTE 2: If 5G DDNMF is integrated with ProSe Application Server, 5G DDNMF provides PC3a interface towards UE and ProSe Application Server provides PC1 interface towards UE.
Figure 6.1.1.3-1 Control Plane for PC3a Interface
6.1.1.4 5G DDNMF – UDM
5G DDNMF uses Nudm interface defined in TS 23.501 [4] to obtain the UE’s subscription information for the authorization of the 5G ProSe Direct Discovery requests.
6.1.1.5 5G DDNMF – 5G DDNMF
The control plane protocol(s) between 5G DDNMFs are defined in TS 29.500 [30].
The 5G DDNMFs uses N5g-ddnmf 5G DDNMF services defined in clause 7.1 to access the services provided by the other 5G DDNMF(s). The 5G DDNMF in HPLMN uses NRF to discover the 5G DDNMFs in VPLMN and Local PLMNs.
6.1.1.6 5G DDNMF – ProSe Application Server
The 5G System architecture supports the service based Npc2 interface between 5G DDNMF and ProSe Application Server and optionally supports PC2 interface between 5G DDNMF and ProSe Application Server, to enable Proximity Services. See TS 23.501 [4] and TS 23.303 [3].
NOTE: PC2 support between 5G DDNMF and ProSe Application Server is for backwards compatibility for early deployments using Diameter. PC2 interface is used for 5G ProSe Direct Discovery authorization.
6.1.1.7 5G ProSe UE-to-Network Relay
6.1.1.7.1 5G ProSe Layer-3 UE-to-Network Relay
The UE-UE protocol stacks for discovery and PC5 link management as defined in clause 6.1.1.2 apply to 5G ProSe Remote UE and 5G ProSe Layer-3 UE-to-Network Relay.
Additionally, when N3IWF is supported by the 5G ProSe Layer-3 UE-to-Network Relay, the following control plane protocol stack apply.
Legend:
– NAS, EAP-5G, and IKEv2 between the Remote UE and the N3IWF are defined in clause 8.2.4 of TS 23.501 [4].
Figure 6.1.1.7.1-1: Control plane protocol stacks between 5G ProSe Layer-3 Remote UE and N3IWF over 5G ProSe Layer-3 UE-to-Network Relay before the signalling IPSec SA is established
Legend:
– NAS, TCP, and IPsec between the Remote UE and the N3IWF are defined in TS 23.501 [4] clause 8.2.4.
Figure 6.1.1.7.1-2: Control plane protocol stacks between 5G ProSe Layer-3 Remote UE and N3IWF over 5G ProSe Layer-3 UE-to-Network Relay after the signalling IPSec SA is established
6.1.1.7.2 5G ProSe Layer-2 UE-to-Network Relay
The UE-UE protocol stacks for discovery and PC5 signalling defined in clause 6.1.1.2 apply to 5G ProSe Remote UE and 5G ProSe Layer-2 UE-to-Network Relay.
Figure 6.1.1.7.2-1 illustrates the protocol stack of the NAS connection for the 5G ProSe Layer-2 Remote UE for NAS-MM and NAS-SM. The NAS messages are transparently transferred between the 5G ProSe Layer-2 Remote UE and NG-RAN over the 5G ProSe Layer-2 UE-to-Network Relay using:
– PDCP end-to-end connection between the 5G ProSe Layer-2 Remote UE and NG-RAN, where the role of the 5G ProSe Layer-2 UE-to-Network Relay is to relay the PDUs over the signalling radio bear without any modifications and using the functionality of the adaptation layer as specified in TS 38.300 [12].
– Connection between NG-RAN and AMF over N2.
– Connection between AMF and SMF over N11.
Figure 6.1.1.7.2-1: End-to-End Control Plane for a Remote UE using Layer-2 UE-to-Network Relay
The control plane protocol stack used by the 5G ProSe Layer-2 UE-to-Network Relay is defined in clause 8.2.2 of TS 23.501 [4].
6.1.2 User Plane
6.1.2.1 General
The user plane stack consists of protocols for data transmission via:
– 5G ProSe Direct Communication, specified in clause 6.1.2.2;
– 5G ProSe UE-to-Network Relay, specified in clause 6.1.2.3.
6.1.2.2 UE – UE
Figure 6.1.2.2-1 depicts a user plane for NR PC5 reference point, i.e. PC5 User Plane Protocol stack.
Legend:
– PC5-U: The SDAP/PDCP/RLC/MAC/PHY functionality is specified in TS 38.300 [12].
Figure 6.1.2.2-1: User Plane for NR PC5 reference point
PDCP SDU types of IP, Ethernet, Unstructured and Address Resolution Protocol are supported. For IP PDCP SDU type, both IPv4 and IPv6 are supported.
NOTE: Address Resolution Protocol is only supported for broadcast and groupcast mode 5G ProSe Direct Communication.
The packets from ProSe application layer are handled by the ProSe layer before transmitting them to the AS layer, e.g. ProSe layer maps the IP, Ethernet and Unstructured packets to PC5 QoS Flow and marks the corresponding PFI.
6.1.2.3 5G ProSe UE-to-Network Relay
6.1.2.3.1 5G ProSe Layer-3 UE-to-Network Relay
Legend:
– GPRS Tunnelling Protocol for the user plane (GTP‑U): This protocol tunnels user data between NG-RAN node and UPF as well as between the UPFs in the backbone network (not shown in the figure). GTP-U shall encapsulate all end user PDU packets.
– SMF controls the user plane tunnel establishment and establishes User Plane Bearers between NG-RAN node and UPF.
– UDP/IP: These are the backbone network protocols used for routing user data and control signalling.
– Uu: The NR Uu radio protocols of NG-RAN between the UE-to-Network Relay and the NG-RAN node are specified in TS 38.300 [12].
– PC5-U: The radio protocols between the UE and the UE-to-Network Relay are specified in clause 6.1.2.2.
Figure 6.1.2.3.1-1: User plane protocol stack for Layer-3 UE-to-Network Relay
Legend:
– IPSec, Inner IP, and GRE between the UE and the N3IWF are defined in TS 23.501 [4] clause 8.3.2.
Figure 6.1.2.3.1-2: User plane protocol stacks for Layer-3 UE-to-Network Relay with N3IWF support
6.1.2.3.2 5G ProSe Layer-2 UE-to-Network Relay
Figure 6.1.2.2.2-1 illustrates the protocol stack for the user plane transport, related to a PDU Session, including a 5G ProSe Layer 2 UE-to-Network Relay. The PDU layer corresponds to the PDU carried between the 5G ProSe Layer-2 Remote UE and the Data Network (DN) over the PDU session. The SDAP and PDCP protocols are specified in TS 38.300 [12]. PDCP end-to-end connection is between the 5G ProSe Layer-2 Remote UE and NG-RAN. The functionality of the adaptation layer is specified in TS 38.351 [28].
Figure 6.1.2.3.2-1: End-to-End User Plane Stack for a 5G ProSe Remote UE using 5G ProSe Layer-2 UE-to-Network Relay