Content for  TS 23.287  Word version:  18.4.0

For V2X communication, two types of PC5 reference points exist: the LTE based PC5 reference point as defined in TS 23.285, and the NR based PC5 reference point as defined in clause 4.2.3. A UE may use either type of PC5 or both for V2X communication depending on the services the UE supports. The V2X communication over PC5 reference point supports roaming and inter-PLMN operations. V2X communication over PC5 reference point is supported when UE is "served by NR or E-UTRA" or when the UE is "not served by NR or E-UTRA". A UE is authorized to transmit and receive V2X messages when it has valid authorization and configuration as specified in clause 5.1.2. The V2X communication over PC5 reference point has the following characteristics:

• V2X communication over LTE based PC5 reference point is connectionless, i.e. broadcast mode at Access Stratum (AS) layer, and there is no signalling over PC5 for connection establishment.
• V2X communication over NR based PC5 reference point supports broadcast mode, groupcast mode, and unicast mode at AS layer. If V2X application layer of the UE indicates the mode of communication to V2X layer, the V2X layer shall set the mode of communication based on the request of the V2X application layer; otherwise, the V2X layer sets the mode of communication based on the mapping information for a V2X service type defined in clause 5.1.2.1. The V2X layer indicates the mode of communication for the V2X service type to the AS layer. Signalling over control plane over PC5 reference point for unicast mode communication management is supported.
• V2X services communication support between UEs over PC5 user plane.
  • Both IP based and non-IP based V2X services communication are supported over PC5 reference point.
  • For IP based V2X services communication, only IPv6 is used. IPv4 is not supported.
• V2X messages are exchanged between UEs over PC5 user plane.
  • Both IP based and non-IP based V2X messages are supported over PC5 reference point.
  • For IP based V2X messages, only IPv6 is used. IPv4 is not supported.

The identifiers used in the V2X communication over PC5 reference point are described in clause 5.6.1. UE decides on the type of PC5 reference point and the Tx Profile for the transmission of a particular packet based on the configuration described in clause 5.1.2. When the LTE based PC5 reference point is selected, the QoS handling corresponding procedures are defined in TS 23.285. When NR based PC5 reference point is selected, the QoS handling and procedures are defined in clauses 5.4.1 and 6.3. If the UE has an ongoing emergency session via IMS, the ongoing emergency session via IMS shall be prioritized over V2X communication over PC5 reference point. The security for V2X communication over PC5 reference point is provided with mechanisms defined in TS 33.536. For broadcast and groupcast mode communication, security is supported in the V2X application layer schemes developed in other SDOs. The pedestrian UEs may use the PC5 DRX mechanism to perform V2X communication over PC5 reference point with power efficiency as specified in clause 5.9.

Broadcast mode of communication is supported over both LTE based PC5 reference point and NR based PC5 reference point. Therefore, when broadcast mode is selected for transmission over PC5 reference point, PC5 RAT selection needs to be performed based on configuration described in clause 5.1.2. Based on configuration described in clause 5.1.2 and the availability of the corresponding PC5 RAT(s) for the specific V2X service type, the V2X layer in the UE determines PC5 RAT(s) and passes the packet to the applicable PC5 AS (Access Stratum) layer(s) with the appropriate PC5 QoS parameters as defined in clause 5.4.1.1.1 For LTE based PC5 reference point, broadcast mode is the only supported communication mode, and the operation details are defined in TS 23.285. For NR based PC5 reference point, the broadcast mode also supports enhanced QoS handling as defined in clause 5.4.1.

Groupcast mode communication is only supported over NR based PC5 reference point and applies to all types of groups, i.e. Application Layer connection-less group and Application Layer managed group. For Application Layer managed group, the following applies:

• If the V2X application layer provides a group size and a member ID, the V2X layer passes them to the AS layer for groupcast control, as defined in TS 38.300.

QoS handling for groupcast mode communication is defined in clause 5.4.1.

Unicast mode of communication is only supported over NR based PC5 reference point. Figure 5.2.1.4-1 illustrates an example of PC5 unicast links.

The following principles apply when the V2X communication is carried over PC5 unicast link:

• A PC5 unicast link between two UEs allows V2X communication between one or more pairs of peer V2X services in these UEs. All V2X services in the UE using the same PC5 unicast link use the same Application Layer ID.
• One PC5 unicast link supports one or more V2X service types) if these V2X service types are at least associated with the pair of peer Application Layer IDs for this PC5 unicast link. For example, as illustrated in Figure 5.2.1.4-1, UE A and UE B have two PC5 unicast links, one between peer Application Layer ID 1/UE A and Application Layer ID 2/UE B and one between peer Application Layer ID 3/UE A and Application Layer ID 4/UE B.
• A PC5 unicast link supports V2X communication using a single network layer protocol e.g. IP or non-IP.
• A PC5 unicast link supports per-flow QoS model as specified in clause 5.4.1.
• If multiple V2X service types use a PC5 unicast link, one PC5 QoS Flow identified by PFI may be associated with more than one V2X service types.

When the Application layer in the UE initiates data transfer for a V2X service type which requires unicast mode of communication over PC5 reference point:

• the UE shall reuse an existing PC5 unicast link if the pair of peer Application Layer IDs and the network layer protocol of this PC5 unicast link are identical to those required by the application layer in the UE for this V2X service, and modify the existing PC5 unicast link to add this V2X service type as specified in clause 6.3.3.4; otherwise
• the UE shall trigger the establishment of a new PC5 unicast link as specified in clause 6.3.3.1.

After successful PC5 unicast link establishment, UE A and UE B use the same pair of Layer-2 IDs for subsequent PC5-S signalling message exchange and V2X service data transmission as specified in clause 5.6.1.4. The V2X layer of the transmitting UE indicates to the AS layer whether a transmission is for a PC5-S signalling message (i.e. Direct Communication Request/Accept, Link Identifier Update Request/Response/Ack, Disconnect Request/Response, Link Modification Request/Accept, Keep-alive/Ack) or V2X service data. For every PC5 unicast link, a UE self-assigns a distinct PC5 Link Identifier that uniquely identifies the PC5 unicast link in the UE for the lifetime of the PC5 unicast link. Each PC5 unicast link is associated with a Unicast Link Profile which includes:

• Application Layer ID and Layer-2 ID of UE A; and
• Application Layer ID and Layer-2 ID of UE B; and
• network layer protocol used on the PC5 unicast link; and
• the information about PC5 QoS Flow(s). For each PC5 QoS Flow, the PC5 QoS Context and the PC5 QoS Rule(s) as defined in clause 5.4.1.1.3.

For privacy reason, the Application Layer IDs and Layer-2 IDs may change as described in clause 5.6.1.1 and clause 6.3.3.2 during the lifetime of the PC5 unicast link and, if so, shall be updated in the Unicast Link Profile accordingly. The UE uses PC5 Link Identifier to indicate the PC5 unicast link to V2X Application layer, therefore V2X Application layer identifies the corresponding PC5 unicast link even if there are more than one unicast link associated with one V2X service type (e.g. the UE establishes multiple unicast links with multiple UEs for a same V2X service type). The Unicast Link Profile shall be updated accordingly after a Layer-2 link modification for an established PC5 unicast link as specified in clause 6.3.3.4 or Layer-2 link identifier update as specified in clause 6.3.3.2. Upon receiving an indication from the AS layer that the PC5-RRC connection was released due to RLF, the V2X layer in the UE locally releases the PC5 unicast link associated with this PC5-RRC connection. The AS layer uses PC5 Link Identifier to indicate to the V2X layer the PC5 unicast link whose PC5-RRC connection was released. When the PC5 unicast link has been released as specified in clause 6.3.3.3, the V2X layer of each UE for the PC5 unicast link informs the AS layer that the PC5 unicast link has been released. The V2X layer uses PC5 Link Identifier to indicate the released unicast link. When the V2X layer determines that no radio frequency is available for any PC5 QoS Flow(s) over a PC5 unicast link based on indication about radio frequency failure from the AS layer, the V2X layer removes the PC5 QoS Flow(s) from the PC5 unicast link by performing Layer-2 link modification procedure as specified in clause 6.3.3.4. The AS layer uses PC5 Link Identifier to indicate to the V2X layer the PC5 unicast link whose radio frequency has failed for the PC5 QoS Flow(s).

For unicast mode of V2X communication over PC5 reference point, the following mechanism for IP address/prefix allocation may be used:

1. IPv6 Stateless Address auto configuration specified in RFC 4862 for assignment of IPv6 prefix, with one of the two UEs acting as IPv6 default router.
2. IPv6 link-local addresses as defined in RFC 4862 are formed by UEs locally. The IPv6 link-local addresses are exchanged during the establishment of a secure layer-2 link over PC5 reference point as described in clause 6.3.3.1. The UEs shall disable duplicate address detection after the layer-2 link is established.

For broadcast and groupcast modes of V2X communication over PC5 reference point, the following source IP address management applies:

• The UE configures a link local IPv6 address to be used as the source IP address, as defined in clause 4.5.3 of TS 23.303. The UE may use this IP address for V2X communication over PC5 reference point without sending Neighbour Solicitation and Neighbour Advertisement message for Duplicate Address Detection.

The V2X communication via unicast over the Uu reference point supports non-roaming and roaming operations. For transport of V2X messages over Uu reference point:

• the mechanisms defined in TS 23.501 and TS 23.502 can be used to establish the suitable PDU Sessions, and V2X messages are routed towards V2X Application Server or towards UEs with existing unicast routing.

The mechanisms defined in TS 23.247 can be used to establish the suitable MBS sessions, and V2X messages are routed from the V2X Application Server towards UEs via broadcast MBS sessions or multicast MBS sessions. As defined in TS 23.247 multicast/broadcast service for roaming is not supported in this release. For MBS reception of V2X messages, announcement for V2X services is required for the UE. To provide the UE with the announcement, the following ways may be used:

• Existing announcement mechanisms specified in TS 23.247, TS 26.502 and TS 26.517.
• MBS session announcement provisioned as described in clauses 5.1.1 and 5.1.3.1.

The V2X Application Server providing the V2X service identified by V2X service type sends the V2X message via UDP/IP transport using information provided in the announcement. V2X message transfer via MBS may be achieved by locating the MBS CN NFs (e.g. MB-UPF) closer to the gNB to meet the latency requirement as defined for 5QI 75 specified in TS 23.501.

V2X communication over PC5 reference point may use different protocols and formats than V2X communication over Uu reference point. For a V2X service type that can use PC5 reference points or Uu reference point for the transmission of the same V2X messages, the following additional consideration apply for unicast transport of V2X messages over Uu reference point:

• for transport of non-IP based V2X messages from the application:
  • IP encapsulation (i.e. IP PDU Session type) or Unstructured PDU Session type is used.
  • The UE determines which method between IP encapsulation and Unstructured PDU Session type is used for non-IP based V2X messages based on the UE configuration as described in clause 5.1.3.1. If no such configuration is available, UE can use the method based on the UE implementation.
• when IP PDU Session type is used for transport of IP based or non-IP based V2X messages:
  • V2X messages are transported over UDP or TCP:
    • for non-IP based V2X messages from the application, UE may learn from V2X Application Server or UE may be configured explicitly about a transport layer protocol needs to be used or no restriction imposed by configuration.
    • for IP based V2X messages from the application, UE uses the transport layer protocol set by the upper layer.
  • the UE sends a V2X message to a V2X Application Server address. The destined V2X Application Server address is derived from the V2X service type and the UE configuration as described in clause 5.1.3.1, and the V2X Application Server receives the V2X message in a UDP/IP packet or a TCP/IP packet on a V2X Application Server address.
• when Unstructured PDU Session type is used for transport of non-IP based V2X messages:
  • V2X messages are transported to the V2X Application Server as defined in clause 5.6.10.3 of TS 23.501.

Latency reduction for V2X message transfer via unicast may be achieved by using various mechanisms, including via e.g., edge computing defined in clauses 5.6.7 and 5.13 of TS 23.501, where the V2X Application Server acts as an Application Function. For a network that has deployed MBS, additional information to assist V2X Application Server discovery can be provided via broadcast MBS session. When a UE has the configuration for receiving V2X Application Server information via broadcast MBS session as specified in clause 5.1.3.1, it can perform the procedure specified in clause 6.4.2 to obtain additional local V2X Application Server information. The local V2X Application Server information obtained by MBS as described in clause 6.4.2 takes precedence over the V2X Application Server information in the UE. As defined in TS 23.247 broadcast service for roaming is not supported in this Release.