Basic Support for IPv6 Networks Operating over 5G Vehicle-to-Everything Communications

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Table of Contents

1. Introduction

This document provides a baseline for using IPv6 in the hosts communicating with each other by the 5th Generation New Radio (NR) Vehicle-to-Everything (5G NR V2X) links [TS23303] [TS23304] defined by the 3rd Generation Partnership Project (3GPP). The baseline defined in this document has the minimal changes to existing stacks. Moreover, the document identifies the limitations of such usage.¶

The 3GPP has published the long-term evolution V2X (LTE V2X) in its Release 14 to support V2X communications using the Uu and PC5 reference points for vehicle-to-infrastructure (V2I) and vehicle-to-vehicle (V2V), respectively. In the recent development, the 5G V2X has also been proposed to enhance the existing and future V2X use cases. Particularly, the 5G V2X improves the sidelink resource allocation and the handling of quality-of-service (QoS) in the current 5G networks, and beyond 5G networks, such as 6G networks. It also extends the communication modes for UE over PC5 from broadcast mode to groupcast and unicast mode [TS24587].¶

The motivation for this document is the service discovery that utilizes the specifications developed by 3GPP to enhance and broaden the connectivity in a vehicular environment. As the 5G Core (5GC) and 5G New Radio (5G-NR) with 5G User Equipment (UE) are being deployed world wide, they can be of great importance in creating a connected network for moving objects such as automobiles, motorcycles, drones etc.¶

However, for IPv6-based 5G V2X communications based on the 3GPP documents [TS23287] [TS24587] it is still not clear how the IPv6 addresses are well configured for multi-hop 5G V2X networks. Particularly, when the Stateless Address Autoconfiguration (SLAAC) process is used in IPv6-based 5G V2X communications, a vehicle as an IPv6 router, which assigns an IPv6 prefix to another vehicle in SLAAC, shall be selected or determined. For a scenario having ground moving vehicles, how to determine the IPv6 router for SLAAC is still not clear. In addition, the 3GPP 5G V2X specifications discourage the use of the Duplicate Address Detection (DAD) [RFC4862] [RFC7527] and Neighbor Discover (ND) messages [RFC4861], which arises the concern of unusable IPv6-based 5G V2X services in the future. On top of that, other issues such as multi-hop packet forwarding among non-IPv6 router vehicles and efficiency of mobility management may also occur [RFC9365].¶

Thus this document offers the basic support for IPv6-based 5G V2X communications to enable application services such as infotainment and cooperative driving safety through the driving context information sharing.¶

                       +------------+
                       |   NG-RAN   |  Base Station
                       +------------+ (e.g., gNodeB)
                             ^
                             :
                             : Uu
                             :
                             V
+------------+   PC5   +------------+   PC5   +------------+
| IP-VehUE A |<.......>| IP-VehUE B |<.......>|    UE C    |
+------------+         +------------+         +------------+
   Car A ==>              Car B ==>           Pedestrian ==>

      <....> Wireless Link   ===> Moving Direction

2. Terminology

This document uses the terminology described in [RFC8691]. In addition, the following terms are defined below:¶

• IP-VehUE (Internet Protocol Vehicle User Equipment): It is a UE device mounted on a vehicle such as car, motorcycle, and scooter that operates based on 5G V2X services to transmit IPv6 data packets. It can connect to the vehicle's internal networks.¶
• NG-RAN (Next Generation Radio Access Network) node: It is a base station node that provides user plane and control plane functions toward IP-VehUEs, and it also connects to 5GC networks. It can be a gNodeB (gNB) in 5G or an ng-eNobdB (ng-eNB) in E-UTRA per the 5G network definition [TS23501] [TS38300].¶
• 5G NR-PC5 RP (5G New Radio PC5 Reference Point): The 5G NR-PC5 RP is referred to as communication links among IP-VehUEs (i.e., V2V).¶
• 5G NR-Uu RP(5G New Radio Uu Reference Point): The 5G NR-Uu RP is referred to as communication links between an IP-VehUE and an NG-RAN node.¶

3. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶

4. Overview of 5G V2X Communications

  +-------------------+
  |  UDP/TCP V2X App  |
  +-------------------+
            |
  +===================+
  |       IPv6        |
  +===================+
            |
+-----------------------+
|3GPP Underlying Layers |
|   +--------------+    |
|   |      SDAP    |    |
|   +--------------+    |
|           |           |
|   +--------------+    |
|   |      PDCP    |    |
|   +--------------+    |
|           |           |
|   +--------------+    |
|   |      RLC     |    |
|   +--------------+    |
|           |           |
|   +--------------+    |
|   |      MAC     |    |
|   +--------------+    |
|           |           |
|   +--------------+    |
|   |      PHY     |    |
|   +--------------+    |
+-----------------------+

A high-level system architecture for V2X communication over PC5 and Uu reference points is shown in Figure 1. A modified sidelink interface allows IP-VehUEs to communicate with each other by the PC5 RP. An IP-VehUE can connect with a stationary NG-RAN through Uu interface. Both communications among IP-VehUEs and between IP-VehUEs and NG-RAN mainly rely on the lower layers shown in Figure 2.¶

The 5G V2X communications support both IP and non-IP based message exchanges in unicast, broadcast, and groupcast modes per 3GPP documents [TS23287] [TS24587]. For the IPv6-based 5G V2X communications via PC5 RP, only IPv6 is used for the communications. In the unicast mode of IPv6-based 5G V2X by PC5 RP, an IP-VehUE uses either the IPv6 Stateless Address Autoconfiguration (SLAAC) process or the IPv6 link-local addresses to generate usable IP addresses [RFC4862].¶

• When using SLAAC, an IP-VehUE uses an IPv6 prefix sent by another IP-VehUE acting as an IPv6 default router.¶
• When using IPv6 link-local addresses, an IP-VehUE forms the link-local addresses locally without Duplicate Address Detection (DAD) [TS23287].¶

In the broadcast and groupcast modes of 5G V2X over PC5 RP, an IP-VehUE configures a link-local IPv6 address as the source IP address. The configuration of the link-local IPv6 address does not send Neighbor Solicitation (NS) and Neighbor Advertisement (NA) messages for DAD per the 3GPP document [TS23287].¶

5. IPv6 over 5G V2X Links

                   +---------------------+
                   | Access and Mobility |
                   | Management Function |
                   +---------------------+
                              ^
                              |
                              |
                              |
                              V
+------------+        +------------+        +------------+
|  NG-RAN A  |<--Xn-->|  NG-RAN B  |<--Xn-->|  NG-RAN C  |
+------------+        +------------+        +------------+
      ^                       ^                    ^
      :                       :                    :
      : Uu                    : Uu                 : Uu
      :                       :                    :
      V                       V                    V
+-----------------------------------------+     +------------------+
|                                         |     |                  |
|  +------------+   PC5   +------------+  | PC5 |  +------------+  |
|  | IP-VehUE A |<.......>| IP-VehUE B |<.........>|    UE C    |  |
|  +------------+         +------------+  |     |  +------------+  |
|     Car A ==>              Car B ==>    |     |  Pedestrian ==>  |
+-----------------------------------------+     +------------------+
                 Subnet 1                             Subnet 2

  <----> Wired Link   <....> Wireless Link   ===> Moving Direction

6. Security Considerations

The security considerations in this document inherit those in [RFC8691][RFC9365].¶

7. IANA Considerations

This document does not require any IANA actions.¶

Appendix B. Contributors

This document is a group work, greatly benefiting from inputs and texts by Erik Kline (Aalyria) and Eric Vyncke (Cisco). The authors sincerely appreciate their contributions.¶

The following are coauthors of this document:¶

Authors' Addresses