IPWAVE Working Group                                       J. Jeong, Ed.
Internet-Draft                                   Sungkyunkwan University
Intended status: Informational                            9 October 2021
Expires: 12 April 2022


    IPv6 Wireless Access in Vehicular Environments (IPWAVE): Problem
                        Statement and Use Cases
               draft-ietf-ipwave-vehicular-networking-24

Abstract

   This document discusses the problem statement and use cases of
   IPv6-based vehicular networking for Intelligent Transportation
   Systems (ITS).  The main scenarios of vehicular communications are
   vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), and
   vehicle-to-everything (V2X) communications.  First, this document
   explains use cases using V2V, V2I, and V2X networking.  Next, for
   IPv6-based vehicular networks, it makes a gap analysis of current
   IPv6 protocols (e.g., IPv6 Neighbor Discovery, Mobility Management,
   and Security & Privacy), and then enumerates requirements for the
   extensions of those IPv6 protocols for IPv6-based vehicular
   networking.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on 12 April 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.






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   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.1.  V2V . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.2.  V2I . . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     3.3.  V2X . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
   4.  Vehicular Networks  . . . . . . . . . . . . . . . . . . . . .  12
     4.1.  Vehicular Network Architecture  . . . . . . . . . . . . .  14
     4.2.  V2I-based Internetworking . . . . . . . . . . . . . . . .  15
     4.3.  V2V-based Internetworking . . . . . . . . . . . . . . . .  18
   5.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .  22
     5.1.  Neighbor Discovery  . . . . . . . . . . . . . . . . . . .  23
       5.1.1.  Link Model  . . . . . . . . . . . . . . . . . . . . .  25
       5.1.2.  MAC Address Pseudonym . . . . . . . . . . . . . . . .  27
       5.1.3.  Routing . . . . . . . . . . . . . . . . . . . . . . .  27
     5.2.  Mobility Management . . . . . . . . . . . . . . . . . . .  29
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  31
     6.1.  Security Threats in Neighbor Discovery  . . . . . . . . .  32
     6.2.  Security Threats in Mobility Management . . . . . . . . .  33
     6.3.  Other Threats . . . . . . . . . . . . . . . . . . . . . .  33
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  34
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  34
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  35
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  39
   Appendix A.  Support of Multiple Radio Technologies for V2V . . .  44
   Appendix B.  Support of Multihop V2X Networking . . . . . . . . .  45
   Appendix C.  Support of Mobility Management for V2I . . . . . . .  47
   Appendix D.  Acknowledgments  . . . . . . . . . . . . . . . . . .  48
   Appendix E.  Contributors . . . . . . . . . . . . . . . . . . . .  48
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  50










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1.  Introduction

   Vehicular networking studies have mainly focused on improving safety
   and efficiency, and also enabling entertainment in vehicular
   networks.  The Federal Communications Commission (FCC) in the US
   allocated wireless channels for Dedicated Short-Range Communications
   (DSRC) [DSRC] in the Intelligent Transportation Systems (ITS) with
   the frequency band of 5.850 - 5.925 GHz (i.e., 5.9 GHz band).  DSRC-
   based wireless communications can support vehicle-to-vehicle (V2V),
   vehicle-to-infrastructure (V2I), and vehicle-to-everything (V2X)
   networking.  The European Union (EU) allocated radio spectrum for
   safety-related and non-safety-related applications of ITS with the
   frequency band of 5.875 - 5.905 GHz, as part of the Commission
   Decision 2008/671/EC [EU-2008-671-EC].

   For direct inter-vehicular wireless connectivity, IEEE has amended
   standard 802.11 (commonly known as Wi-Fi) to enable safe driving
   services based on DSRC for the Wireless Access in Vehicular
   Environments (WAVE) system.  The Physical Layer (L1) and Data Link
   Layer (L2) issues are addressed in IEEE 802.11p [IEEE-802.11p] for
   the PHY and MAC of the DSRC, while IEEE 1609.2 [WAVE-1609.2] covers
   security aspects, IEEE 1609.3 [WAVE-1609.3] defines related services
   at network and transport layers, and IEEE 1609.4 [WAVE-1609.4]
   specifies the multi-channel operation.  IEEE 802.11p was first a
   separate amendment, but was later rolled into the base 802.11
   standard (IEEE 802.11-2012) as IEEE 802.11 Outside the Context of a
   Basic Service Set (OCB) in 2012 [IEEE-802.11-OCB].

   3GPP has standardized Cellular Vehicle-to-Everything (C-V2X)
   communications to support V2X in LTE mobile networks (called LTE V2X)
   and V2X in 5G mobile networks (called 5G V2X) [TS-23.285-3GPP]
   [TR-22.886-3GPP][TS-23.287-3GPP].  With C-V2X, vehicles can directly
   communicate with each other without relay nodes (e.g., eNodeB in LTE
   and gNodeB in 5G).

   Along with these WAVE standards and C-V2X standards, regardless of a
   wireless access technology under the IP stack of a vehicle, vehicular
   networks can operate IP mobility with IPv6 [RFC8200] and Mobile IPv6
   protocols (e.g., Mobile IPv6 (MIPv6) [RFC6275], Proxy MIPv6 (PMIPv6)
   [RFC5213], Distributed Mobility Management (DMM) [RFC7333], Network
   Mobility (NEMO) [RFC3963], Locator/ID Separation Protocol (LISP)
   [RFC6830BIS], and Automatic Extended Route Optimization (AERO)
   [AERO]).  In addition, ISO has approved a standard specifying the
   IPv6 network protocols and services to be used for Communications
   Access for Land Mobiles (CALM) [ISO-ITS-IPv6][ISO-ITS-IPv6-AMD1].






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   This document describes use cases and a problem statement about
   IPv6-based vehicular networking for ITS, which is named IPv6 Wireless
   Access in Vehicular Environments (IPWAVE).  First, it introduces the
   use cases for using V2V, V2I, and V2X networking in ITS.  Next, for
   IPv6-based vehicular networks, it makes a gap analysis of current
   IPv6 protocols (e.g., IPv6 Neighbor Discovery, Mobility Management,
   and Security & Privacy), and then enumerates requirements for the
   extensions of those IPv6 protocols, which are tailored to IPv6-based
   vehicular networking.  Thus, this document is intended to motivate
   development of key protocols for IPWAVE.

2.  Terminology

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

   *  Class-Based Safety Plan: A vehicle can make a safety plan by
      classifying the surrounding vehicles into different groups for
      safety purposes according to the geometrical relationship among
      them.  The vehicle groups can be classified as Line-of-Sight
      Unsafe, Non-Line-of-Sight Unsafe, and Safe groups [CASD].

   *  Context-Awareness: A vehicle can be aware of spatial-temporal
      mobility information (e.g., position, speed, direction, and
      acceleration/deceleration) of surrounding vehicles for both safety
      and non-safety uses through sensing or communication [CASD].

   *  DMM: "Distributed Mobility Management" [RFC7333][RFC7429].

   *  Edge Computing (EC): It is the local computing near an access
      network (i.e., edge network) for the sake of vehicles and
      pedestrians.

   *  Edge Computing Device (ECD): It is a computing device (or server)
      for edge computing for the sake of vehicles and pedestrians.

   *  Edge Network (EN): It is an access network that has an IP-RSU for
      wireless communication with other vehicles having an IP-OBU and
      wired communication with other network devices (e.g., routers, IP-
      RSUs, ECDs, servers, and MA).  It may have a Global Positioning
      System (GPS) radio receiver for its position recognition and the
      localization service for the sake of vehicles.

   *  IP-OBU: "Internet Protocol On-Board Unit": An IP-OBU denotes a
      computer situated in a vehicle (e.g., car, bicycle, autobike,
      motor cycle, and a similar one) and a device (e.g., smartphone and
      Internet-of-Things (IoT) device).  It has at least one IP
      interface that runs in IEEE 802.11-OCB and has an "OBU"



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      transceiver.  Also, it may have an IP interface that runs in
      Cellular V2X (C-V2X) [TS-23.285-3GPP]
      [TR-22.886-3GPP][TS-23.287-3GPP].  It can play a role of a router
      connecting multiple computers (or in-vehicle devices) inside a
      vehicle.  See the definition of the term "OBU" in [RFC8691].

   *  IP-RSU: "IP Roadside Unit": An IP-RSU is situated along the road.
      It has at least two distinct IP-enabled interfaces.  The wireless
      PHY/MAC layer of at least one of its IP-enabled interfaces is
      configured to operate in 802.11-OCB mode.  An IP-RSU communicates
      with the IP-OBU over an 802.11 wireless link operating in OCB
      mode.  Also, it may have an IP interface that runs in C-V2X along
      with an "RSU" transceiver.  An IP-RSU is similar to an Access
      Network Router (ANR), defined in [RFC3753], and a Wireless
      Termination Point (WTP), defined in [RFC5415].  See the definition
      of the term "RSU" in [RFC8691].

   *  LiDAR: "Light Detection and Ranging".  It is a scanning device to
      measure a distance to an object by emitting pulsed laser light and
      measuring the reflected pulsed light.

   *  Mobility Anchor (MA): A node that maintains IPv6 addresses and
      mobility information of vehicles in a road network to support
      their IPv6 address autoconfiguration and mobility management with
      a binding table.  An MA has End-to-End (E2E) connections (e.g.,
      tunnels) with IP-RSUs under its control for the address
      autoconfiguration and mobility management of the vehicles.  This
      MA is similar to a Local Mobility Anchor (LMA) in PMIPv6 [RFC5213]
      for network-based mobility management.

   *  OCB: "Outside the Context of a Basic Service Set - BSS".  It is a
      mode of operation in which a Station (STA) is not a member of a
      BSS and does not utilize IEEE Std 802.11 authentication,
      association, or data confidentiality [IEEE-802.11-OCB].

   *  802.11-OCB: It refers to the mode specified in IEEE Std
      802.11-2016 [IEEE-802.11-OCB] when the MIB attribute
      dot11OCBActivited is 'true'.

   *  Platooning: Moving vehicles can be grouped together to reduce air-
      resistance for energy efficiency and reduce the number of drivers
      such that only the leading vehicle has a driver, and the other
      vehicles are autonomous vehicles without a driver and closely
      follow the leading vehicle [Truck-Platooning].

   *  Traffic Control Center (TCC): A system that manages road
      infrastructure nodes (e.g., IP-RSUs, MAs, traffic signals, and
      loop detectors), and also maintains vehicular traffic statistics



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      (e.g., average vehicle speed and vehicle inter-arrival time per
      road segment) and vehicle information (e.g., a vehicle's
      identifier, position, direction, speed, and trajectory as a
      navigation path).  TCC is part of a vehicular cloud for vehicular
      networks.

   *  Vehicle: A Vehicle in this document is a node that has an IP-OBU
      for wireless communication with other vehicles and IP-RSUs.  It
      has a GPS radio navigation receiver for efficient navigation.  Any
      device having an IP-OBU and a GPS receiver (e.g., smartphone and
      tablet PC) can be regarded as a vehicle in this document.

   *  Vehicular Ad Hoc Network (VANET): A network that consists of
      vehicles interconnected by wireless communication.  Two vehicles
      in a VANET can communicate with each other using other vehicles as
      relays even where they are out of one-hop wireless communication
      range.

   *  Vehicular Cloud: A cloud infrastructure for vehicular networks,
      having compute nodes, storage nodes, and network forwarding
      elements (e.g., switch and router).

   *  V2D: "Vehicle to Device".  It is the wireless communication
      between a vehicle and a device (e.g., smartphone and IoT device).

   *  V2I2D: "Vehicle to Infrastructure to Device".  It is the wireless
      communication between a vehicle and a device (e.g., smartphone and
      IoT device) via an infrastructure node (e.g., IP-RSU).

   *  V2I2V: "Vehicle to Infrastructure to Vehicle".  It is the wireless
      communication between a vehicle and another vehicle via an
      infrastructure node (e.g., IP-RSU).

   *  V2I2X: "Vehicle to Infrastructure to Everything".  It is the
      wireless communication between a vehicle and another entity (e.g.,
      vehicle, smartphone, and IoT device) via an infrastructure node
      (e.g., IP-RSU).

   *  V2X: "Vehicle to Everything".  It is the wireless communication
      between a vehicle and any entity (e.g., vehicle, infrastructure
      node, smartphone, and IoT device), including V2V, V2I, and V2D.

   *  VIP: "Vehicular Internet Protocol".  It is an IPv6 extension for
      vehicular networks including V2V, V2I, and V2X.

   *  VMM: "Vehicular Mobility Management".  It is an IPv6-based
      mobility management for vehicular networks.




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   *  VND: "Vehicular Neighbor Discovery".  It is an IPv6 ND extension
      for vehicular networks.

   *  VSP: "Vehicular Security and Privacy".  It is an IPv6-based
      security and privacy for vehicular networks.

   *  WAVE: "Wireless Access in Vehicular Environments" [WAVE-1609.0].

3.  Use Cases

   This section explains use cases of V2V, V2I, and V2X networking.  The
   use cases of the V2X networking exclude the ones of the V2V and V2I
   networking, but include Vehicle-to-Pedestrian (V2P) and Vehicle-to-
   Device (V2D).

   IP is widely used among popular end-user devices (e.g., smartphone
   and tablet) in the Internet.  Applications (e.g., navigator
   application) for those devices can be extended such that the V2V use
   cases in this section can work with IPv6 as a network layer protocol
   and IEEE 802.11-OCB as a link layer protocol.  In addition, IPv6
   security needs to be extended to support those V2V use cases in a
   safe, secure, privacy-preserving way.

   The use cases presented in this section serve as the description and
   motivation for the need to extend IPv6 and its protocols to
   facilitate "Vehicular IPv6".  Section 5 summarizes the overall
   problem statement and IPv6 requirements.  Note that the adjective
   "Vehicular" in this document is used to represent extensions of
   existing protocols such as IPv6 Neighbor Discovery, IPv6 Mobility
   Management (e.g., PMIPv6 [RFC5213] and DMM [RFC7429]), and IPv6
   Security and Privacy Mechanisms rather than new "vehicular-specific"
   functions.

3.1.  V2V

   The use cases of V2V networking discussed in this section include

   *  Context-aware navigation for safe driving and collision avoidance;

   *  Cooperative adaptive cruise control in a roadway;

   *  Platooning in a highway;

   *  Cooperative environment sensing;

   *  Collision avoidance service of end systems of Urban Air Mobility
      (UAM) [UAM-ITS].




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   These five techniques will be important elements for autonomous
   vehicles, which may be either terrestrial vehicles or UAM end
   systems.

   Context-Aware Safety Driving (CASD) navigator [CASD] can help drivers
   to drive safely by alerting them to dangerous obstacles and
   situations.  That is, a CASD navigator displays obstacles or
   neighboring vehicles relevant to possible collisions in real-time
   through V2V networking.  CASD provides vehicles with a class-based
   automatic safety action plan, which considers three situations,
   namely, the Line-of-Sight unsafe, Non-Line-of-Sight unsafe, and safe
   situations.  This action plan can be put into action among multiple
   vehicles using V2V networking.

   Cooperative Adaptive Cruise Control (CACC) [CA-Cruise-Control] helps
   individual vehicles to adapt their speed autonomously through V2V
   communication among vehicles according to the mobility of their
   predecessor and successor vehicles in an urban roadway or a highway.
   Thus, CACC can help adjacent vehicles to efficiently adjust their
   speed in an interactive way through V2V networking in order to avoid
   a collision.

   Platooning [Truck-Platooning] allows a series (or group) of vehicles
   (e.g., trucks) to follow each other very closely.  Trucks can use V2V
   communication in addition to forward sensors in order to maintain
   constant clearance between two consecutive vehicles at very short
   gaps (from 3 meters to 10 meters).  Platooning can maximize the
   throughput of vehicular traffic in a highway and reduce the gas
   consumption because the leading vehicle can help the following
   vehicles to experience less air resistance.

   Cooperative-environment-sensing use cases suggest that vehicles can
   share environmental information (e.g., air pollution, hazards/
   obstacles, slippery areas by snow or rain, road accidents, traffic
   congestion, and driving behaviors of neighboring vehicles) from
   various vehicle-mounted sensors, such as radars, LiDARs, and cameras,
   with other vehicles and pedestrians.  [Automotive-Sensing] introduces
   millimeter-wave vehicular communication for massive automotive
   sensing.  A lot of data can be generated by those sensors, and these
   data typically need to be routed to different destinations.  In
   addition, from the perspective of driverless vehicles, it is expected
   that driverless vehicles can be mixed with driver-operated vehicles.
   Through cooperative environment sensing, driver-operated vehicles can
   use environmental information sensed by driverless vehicles for
   better interaction with the other vehicles and environment.  Vehicles
   can also share their intended maneuvering information (e.g., lane
   change, speed change, ramp in-and-out, cut-in, and abrupt braking)
   with neighboring vehicles.  Thus, this information sharing can help



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   the vehicles behave as more efficient traffic flows and minimize
   unnecessary acceleration and deceleration to achieve the best ride
   comfort.

   A collision avoidance service of UAM end systems in air can be
   envisioned as a use case in air vehicular environments.  This use
   case is similar to the context-aware navigator for terrestrial
   vehicles.  Through V2V coordination, those UAM end systems (e.g.,
   drones) can avoid a dangerous situation (e.g., collision) in three-
   dimensional space rather than two-dimensional space for terrestrial
   vehicles.  Also, UAM end systems (e.g., flying car) with only a few
   meters off the ground can communicate with terrestrial vehicles with
   wireless communication technologies (e.g., DSRC, LTE, and C-V2X).
   Thus, V2V means any vehicle to any vehicle, whether the vehicles are
   ground-level or not.

   To encourage more vehicles to participate in this cooperative
   environmental sensing, a reward system will be needed.  Sensing
   activities of each vehicle need to be logged in either a central way
   through a logging server (e.g., TCC) in the vehicular cloud or a
   distributed way (e.g., blockchain [Bitcoin]) through other vehicles
   or infrastructure.  In the case of a blockchain, each sensing message
   from a vehicle can be treated as a transaction and the neighboring
   vehicles can play the role of peers in a consensus method of a
   blockchain [Bitcoin][Vehicular-BlockChain].

   To support applications of these V2V use cases, the required
   functions of IPv6 include IPv6-based packet exchange and secure, safe
   communication between two vehicles.  For the support of V2V under
   multiple radio technologies (e.g., DSRC and 5G V2X), refer to
   Appendix A.

3.2.  V2I

   The use cases of V2I networking discussed in this section include

   *  Navigation service;

   *  Energy-efficient speed recommendation service;

   *  Accident notification service;

   *  Electric vehicle (EV) charging service;

   *  UAM navigation service with efficient battery charging.






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   A navigation service, for example, the Self-Adaptive Interactive
   Navigation Tool(SAINT) [SAINT], using V2I networking interacts with a
   TCC for the large-scale/long-range road traffic optimization and can
   guide individual vehicles along appropriate navigation paths in real
   time.  The enhanced version of SAINT [SAINTplus] can give fast moving
   paths to emergency vehicles (e.g., ambulance and fire engine) to let
   them reach an accident spot while redirecting other vehicles near the
   accident spot into efficient detour paths.

   Either a TCC or an ECD can recommend an energy-efficient speed to a
   vehicle that depends on its traffic environment and traffic signal
   scheduling [SignalGuru].  For example, when a vehicle approaches an
   intersection area and a red traffic light for the vehicle becomes
   turned on, it needs to reduce its speed to save fuel consumption.  In
   this case, either a TCC or an ECD, which has the up-to-date
   trajectory of the vehicle and the traffic light schedule, can notify
   the vehicle of an appropriate speed for fuel efficiency.
   [Fuel-Efficient] studies fuel-efficient route and speed plans for
   platooned trucks.

   The emergency communication between accident vehicles (or emergency
   vehicles) and a TCC can be performed via either IP-RSU or 4G-LTE
   networks.  The First Responder Network Authority (FirstNet)
   [FirstNet] is provided by the US government to establish, operate,
   and maintain an interoperable public safety broadband network for
   safety and security network services, e.g., emergency calls.  The
   construction of the nationwide FirstNet network requires each state
   in the US to have a Radio Access Network (RAN) that will connect to
   the FirstNet's network core.  The current RAN is mainly constructed
   using 4G-LTE for the communication between a vehicle and an
   infrastructure node (i.e., V2I) [FirstNet-Report], but it is expected
   that DSRC-based vehicular networks [DSRC] will be available for V2I
   and V2V in the near future.

   An EV charging service with V2I can facilitate the efficient battery
   charging of EVs.  In the case where an EV charging station is
   connected to an IP-RSU, an EV can be guided toward the deck of the EV
   charging station through a battery charging server connected to the
   IP-RSU.  In addition to this EV charging service, other value-added
   services (e.g., air firmware/software update and media streaming) can
   be provided to an EV while it is charging its battery at the EV
   charging station.

   A UAM navigation service with efficient battery charging can plan the
   battery charging schedule of UAM end systems (e.g., drone) for long-
   distance flying [CBDN].  For this battery charging schedule, a UAM
   end system can communicate with an infrastructure node (e.g., IP-RSU)
   toward a cloud server via V2I communications.  This cloud server can



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   coordinate the battery charging schedules of multiple UAM end systems
   for their efficient navigation path, considering flight time from
   their current position to a battery charging station, waiting time in
   a waiting queue at the station, and battery charging time at the
   station.

   The existing IPv6 protocol must be augmented through protocol changes
   in order to support wireless multihop V2I communications in a highway
   where RSUs are sparsely deployed, so a vehicle can reach the wireless
   coverage of an RSU through the multihop data forwarding of
   intermediate vehicles.  Thus, IPv6 needs to be extended for multihop
   V2I communications.

   To support applications of these V2I use cases, the required
   functions of IPv6 include IPv6-based packet exchange, transport-layer
   session continuity, and secure, safe communication between a vehicle
   and an infrastructure node (e.g., IP-RSU) in the vehicular network.

3.3.  V2X

   The use case of V2X networking discussed in this section is for a
   pedestrian protection service.

   A pedestrian protection service, such as Safety-Aware Navigation
   Application (SANA) [SANA], using V2I2P networking can reduce the
   collision of a vehicle and a pedestrian carrying a smartphone
   equipped with a network device for wireless communication (e.g., Wi-
   Fi) with an IP-RSU.  Vehicles and pedestrians can also communicate
   with each other via an IP-RSU.  An edge computing device behind the
   IP-RSU can collect the mobility information from vehicles and
   pedestrians, compute wireless communication scheduling for the sake
   of them.  This scheduling can save the battery of each pedestrian's
   smartphone by allowing it to work in sleeping mode before the
   communication with vehicles, considering their mobility.

   For Vehicle-to-Pedestrian (V2P), a vehicle can directly communicate
   with a pedestrian's smartphone by V2X without IP-RSU relaying.
   Light-weight mobile nodes such as bicycles may also communicate
   directly with a vehicle for collision avoidance using V2V.

   The existing IPv6 protocol must be augmented through protocol changes
   in order to support wireless multihop V2X or V2I2X communications in
   an urban road network where RSUs are deployed at intersections, so a
   vehicle (or a pedestrian's smartphone) can reach the wireless
   coverage of an RSU through the multihop data forwarding of
   intermediate vehicles (or pedestrians' smartphones) as packet
   forwarders.  Thus, IPv6 needs to be extended for multihop V2X or
   V2I2X communications.



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   To support applications of these V2X use cases, the required
   functions of IPv6 include IPv6-based packet exchange, transport-layer
   session continuity, and secure, safe communication between a vehicle
   and a pedestrian either directly or indirectly via an IP-RSU.

4.  Vehicular Networks

   This section describes the context for vehicular networks supporting
   V2V, V2I, and V2X communications.  It describes an internal network
   within a vehicle or an edge network (called EN).  It explains not
   only the internetworking between the internal networks of a vehicle
   and an EN via wireless links, but also the internetworking between
   the internal networks of two vehicles via wireless links.






































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                     Traffic Control Center in Vehicular Cloud
                    *******************************************
+-------------+    *                                           *
|Corresponding|   *             +-----------------+             *
|    Node     |<->*             | Mobility Anchor |             *
+-------------+   *             +-----------------+             *
                  *                      ^                      *
                  *                      |                      *
                   *                     v                     *
                    *******************************************
                    ^                   ^                     ^
                    |                   |                     |
                    |                   |                     |
                    v                   v                     v
              +---------+           +---------+           +---------+
              | IP-RSU1 |<--------->| IP-RSU2 |<--------->| IP-RSU3 |
              +---------+           +---------+           +---------+
                  ^                     ^                    ^
                  :                     :                    :
           +-----------------+ +-----------------+   +-----------------+
           |      : V2I      | |        : V2I    |   |       : V2I     |
           |      v          | |        v        |   |       v         |
+--------+ |   +--------+    | |   +--------+    |   |   +--------+    |
|Vehicle1|===> |Vehicle2|===>| |   |Vehicle3|===>|   |   |Vehicle4|===>|
+--------+<...>+--------+<........>+--------+    |   |   +--------+    |
           V2V     ^         V2V        ^        |   |        ^        |
           |       : V2V     | |        : V2V    |   |        : V2V    |
           |       v         | |        v        |   |        v        |
           |  +--------+     | |   +--------+    |   |    +--------+   |
           |  |Vehicle5|===> | |   |Vehicle6|===>|   |    |Vehicle7|==>|
           |  +--------+     | |   +--------+    |   |    +--------+   |
           +-----------------+ +-----------------+   +-----------------+
                 Subnet1              Subnet2              Subnet3
                (Prefix1)            (Prefix2)            (Prefix3)

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

 Figure 1: An Example Vehicular Network Architecture for V2I and V2V













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4.1.  Vehicular Network Architecture

   Figure 1 shows an example vehicular network architecture for V2I and
   V2V in a road network.  The vehicular network architecture contains
   vehicles (including IP-OBU), IP-RSUs, Mobility Anchor, Traffic
   Control Center, and Vehicular Cloud as components.  These components
   are not mandatory, and they can be deployed into vehicular networks
   in various ways.  Some of them (e.g., Mobility Anchor, Traffic
   Control Center, and Vehicular Cloud) may not be needed for the
   vehicular networks according to target use cases in Section 3.

   Existing network architectures, such as the network architectures of
   PMIPv6 [RFC5213], RPL (IPv6 Routing Protocol for Low-Power and Lossy
   Networks) [RFC6550], and OMNI (Overlay Multilink Network Interface)
   [OMNI], can be extended to a vehicular network architecture for
   multihop V2V, V2I, and V2X, as shown in Figure 1.  Refer to
   Appendix B for the detailed discussion on multihop V2X networking by
   RPL and OMNI.

   As shown in this figure, IP-RSUs as routers and vehicles with IP-OBU
   have wireless media interfaces for VANET.  Furthermore, the wireless
   media interfaces are autoconfigured with a global IPv6 prefix (e.g.,
   2001:DB8:1:1::/64) to support both V2V and V2I networking.  Note that
   2001:DB8::/32 is a documentation prefix [RFC3849] for example
   prefixes in this document, and also that any routable IPv6 address
   needs to be routable in a VANET and a vehicular network including IP-
   RSUs.

   In Figure 1, three IP-RSUs (IP-RSU1, IP-RSU2, and IP-RSU3) are
   deployed in the road network and are connected with each other
   through the wired networks (e.g., Ethernet).  A Traffic Control
   Center (TCC) is connected to the Vehicular Cloud for the management
   of IP-RSUs and vehicles in the road network.  A Mobility Anchor (MA)
   may be located in the TCC as a mobility management controller.
   Vehicle2, Vehicle3, and Vehicle4 are wirelessly connected to IP-RSU1,
   IP-RSU2, and IP-RSU3, respectively.  The three wireless networks of
   IP-RSU1, IP-RSU2, and IP-RSU3 can belong to three different subnets
   (i.e., Subnet1, Subnet2, and Subnet3), respectively.  Those three
   subnets use three different prefixes (i.e., Prefix1, Prefix2, and
   Prefix3).

   Multiple vehicles under the coverage of an RSU share a prefix just as
   mobile nodes share a prefix of a Wi-Fi access point in a wireless
   LAN.  This is a natural characteristic in infrastructure-based
   wireless networks.  For example, in Figure 1, two vehicles (i.e.,
   Vehicle2, and Vehicle5) can use Prefix 1 to configure their IPv6
   global addresses for V2I communication.  Alternatively, mobile nodes
   can employ a "Bring-Your-Own-Addresses (BYOA)" technique using their



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   own IPv6 Unique Local Addresses (ULAs) [RFC4193] over the wireless
   network, which does not require the messaging (e.g., Duplicate
   Address Detection (DAD)) of IPv6 Stateless Address Autoconfiguration
   (SLAAC) [RFC4862].

   In wireless subnets in vehicular networks (e.g., Subnet1 and Subnet2
   in Figure 1), vehicles can construct a connected VANET (with an
   arbitrary graph topology) and can communicate with each other via V2V
   communication.  Vehicle1 can communicate with Vehicle2 via V2V
   communication, and Vehicle2 can communicate with Vehicle3 via V2V
   communication because they are within the wireless communication
   range of each other.  On the other hand, Vehicle3 can communicate
   with Vehicle4 via the vehicular infrastructure (i.e., IP-RSU2 and IP-
   RSU3) by employing V2I (i.e., V2I2V) communication because they are
   not within the wireless communication range of each other.

   As a basic definition for IPv6 packets transported over IEEE
   802.11-OCB, [RFC8691] specifies several details, including Maximum
   Transmission Unit (MTU), frame format, link-local address, address
   mapping for unicast and multicast, stateless autoconfiguration, and
   subnet structure.

   An IPv6 mobility solution is needed for the guarantee of
   communication continuity in vehicular networks so that a vehicle's
   TCP session can be continued, or UDP packets can be delivered to a
   vehicle as a destination without loss while it moves from an IP-RSU's
   wireless coverage to another IP-RSU's wireless coverage.  In
   Figure 1, assuming that Vehicle2 has a TCP session (or a UDP session)
   with a corresponding node in the vehicular cloud, Vehicle2 can move
   from IP-RSU1's wireless coverage to IP-RSU2's wireless coverage.  In
   this case, a handover for Vehicle2 needs to be performed by either a
   host-based mobility management scheme (e.g., MIPv6 [RFC6275]) or a
   network-based mobility management scheme (e.g., PMIPv6 [RFC5213] and
   AERO [AERO]).  This document describes issues in mobility management
   for vehicular networks in Section 5.2.

4.2.  V2I-based Internetworking

   This section discusses the internetworking between a vehicle's
   internal network (i.e., moving network) and an EN's internal network
   (i.e., fixed network) via V2I communication.  The internal network of
   a vehicle is nowadays constructed with Ethernet by many automotive
   vendors [In-Car-Network].  Note that an EN can accommodate multiple
   routers (or switches) and servers (e.g., ECDs, navigation server, and
   DNS server) in its internal network.






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   A vehicle's internal network often uses Ethernet to interconnect
   Electronic Control Units (ECUs) in the vehicle.  The internal network
   can support Wi-Fi and Bluetooth to accommodate a driver's and
   passenger's mobile devices (e.g., smartphone or tablet).  The network
   topology and subnetting depend on each vendor's network configuration
   for a vehicle and an EN.  It is reasonable to consider the
   interaction between the internal network and an external network
   within another vehicle or an EN.

                                                    +-----------------+
                           (*)<........>(*)  +----->| Vehicular Cloud |
        (2001:DB8:1:1::/64) |            |   |      +-----------------+
   +------------------------------+  +---------------------------------+
   |                        v     |  |   v   v                         |
   | +-------+          +-------+ |  | +-------+          +-------+    |
   | | Host1 |          |IP-OBU1| |  | |IP-RSU1|          | Host3 |    |
   | +-------+          +-------+ |  | +-------+          +-------+    |
   |     ^                  ^     |  |     ^                  ^        |
   |     |                  |     |  |     |                  |        |
   |     v                  v     |  |     v                  v        |
   | ---------------------------- |  | ------------------------------- |
   | 2001:DB8:10:1::/64 ^         |  |     ^ 2001:DB8:20:1::/64        |
   |                    |         |  |     |                           |
   |                    v         |  |     v                           |
   | +-------+      +-------+     |  | +-------+ +-------+   +-------+ |
   | | Host2 |      |Router1|     |  | |Router2| |Server1|...|ServerN| |
   | +-------+      +-------+     |  | +-------+ +-------+   +-------+ |
   |     ^              ^         |  |     ^         ^           ^     |
   |     |              |         |  |     |         |           |     |
   |     v              v         |  |     v         v           v     |
   | ---------------------------- |  | ------------------------------- |
   |      2001:DB8:10:2::/64      |  |       2001:DB8:20:2::/64        |
   +------------------------------+  +---------------------------------+
      Vehicle1 (Moving Network1)            EN1 (Fixed Network1)

      <----> Wired Link   <....> Wireless Link   (*) Antenna

         Figure 2: Internetworking between Vehicle and Edge Network













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   As shown in Figure 2, as internal networks, a vehicle's moving
   network and an EN's fixed network are self-contained networks having
   multiple subnets and having an edge router (e.g., IP-OBU and IP-RSU)
   for the communication with another vehicle or another EN.  The
   internetworking between two internal networks via V2I communication
   requires the exchange of the network parameters and the network
   prefixes of the internal networks.  For the efficiency, the network
   prefixes of the internal networks (as a moving network) in a vehicle
   need to be delegated and configured automatically.  Note that a
   moving network's network prefix can be called a Mobile Network Prefix
   (MNP) [RFC3963].

   Figure 2 also shows the internetworking between the vehicle's moving
   network and the EN's fixed network.  There exists an internal network
   (Moving Network1) inside Vehicle1.  Vehicle1 has two hosts (Host1 and
   Host2), and two routers (IP-OBU1 and Router1).  There exists another
   internal network (Fixed Network1) inside EN1.  EN1 has one host
   (Host3), two routers (IP-RSU1 and Router2), and the collection of
   servers (Server1 to ServerN) for various services in the road
   networks, such as the emergency notification and navigation.
   Vehicle1's IP-OBU1 (as a mobile router) and EN1's IP-RSU1 (as a fixed
   router) use 2001:DB8:1:1::/64 for an external link (e.g., DSRC) for
   V2I networking.  Thus, a host (Host1) in Vehicle1 can communicate
   with a server (Server1) in EN1 for a vehicular service through
   Vehicle1's moving network, a wireless link between IP-OBU1 and IP-
   RSU1, and EN1's fixed network.

   For the IPv6 communication between an IP-OBU and an IP-RSU or between
   two neighboring IP-OBUs, they need to know the network parameters,
   which include MAC layer and IPv6 layer information.  The MAC layer
   information includes wireless link layer parameters, transmission
   power level, and the MAC address of an external network interface for
   the internetworking with another IP-OBU or IP-RSU.  The IPv6 layer
   information includes the IPv6 address and network prefix of an
   external network interface for the internetworking with another IP-
   OBU or IP-RSU.

   Through the mutual knowledge of the network parameters of internal
   networks, packets can be transmitted between the vehicle's moving
   network and the EN's fixed network.  Thus, V2I requires an efficient
   protocol for the mutual knowledge of network parameters.










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   As shown in Figure 2, the addresses used for IPv6 transmissions over
   the wireless link interfaces for IP-OBU and IP-RSU can be link-local
   IPv6 addresses, ULAs, or global IPv6 addresses.  When global IPv6
   addresses are used, wireless interface configuration and control
   overhead for DAD [RFC4862] and Multicast Listener Discovery (MLD)
   [RFC2710][RFC3810] should be minimized to support V2I and V2X
   communications for vehicles moving fast along roadways.

   Let us consider the upload/download time of a vehicle when it passes
   through the wireless communication coverage of an IP-RSU.  For a
   given typical setting where 1km is the maximum DSRC communication
   range [DSRC] and 100km/h is the speed limit in highway, the dwelling
   time can be calculated to be 72 seconds by dividing the diameter of
   the 2km (i.e., two times of DSRC communication range where an IP-RSU
   is located in the center of the circle of wireless communication) by
   the speed limit of 100km/h (i.e., about 28m/s).  For the 72 seconds,
   a vehicle passing through the coverage of an IP-RSU can upload and
   download data packets to/from the IP-RSU.

4.3.  V2V-based Internetworking

   This section discusses the internetworking between the moving
   networks of two neighboring vehicles via V2V communication.




























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                           (*)<..........>(*)
        (2001:DB8:1:1::/64) |              |
   +------------------------------+  +------------------------------+
   |                        v     |  |     v                        |
   | +-------+          +-------+ |  | +-------+          +-------+ |
   | | Host1 |          |IP-OBU1| |  | |IP-OBU2|          | Host3 | |
   | +-------+          +-------+ |  | +-------+          +-------+ |
   |     ^                  ^     |  |     ^                  ^     |
   |     |                  |     |  |     |                  |     |
   |     v                  v     |  |     v                  v     |
   | ---------------------------- |  | ---------------------------- |
   | 2001:DB8:10:1::/64 ^         |  |         ^ 2001:DB8:30:1::/64 |
   |                    |         |  |         |                    |
   |                    v         |  |         v                    |
   | +-------+      +-------+     |  |     +-------+      +-------+ |
   | | Host2 |      |Router1|     |  |     |Router2|      | Host4 | |
   | +-------+      +-------+     |  |     +-------+      +-------+ |
   |     ^              ^         |  |         ^              ^     |
   |     |              |         |  |         |              |     |
   |     v              v         |  |         v              v     |
   | ---------------------------- |  | ---------------------------- |
   |      2001:DB8:10:2::/64      |  |       2001:DB8:30:2::/64     |
   +------------------------------+  +------------------------------+
      Vehicle1 (Moving Network1)        Vehicle2 (Moving Network2)

      <----> Wired Link   <....> Wireless Link   (*) Antenna

               Figure 3: Internetworking between Two Vehicles

   Figure 3 shows the internetworking between the moving networks of two
   neighboring vehicles.  There exists an internal network (Moving
   Network1) inside Vehicle1.  Vehicle1 has two hosts (Host1 and Host2),
   and two routers (IP-OBU1 and Router1).  There exists another internal
   network (Moving Network2) inside Vehicle2.  Vehicle2 has two hosts
   (Host3 and Host4), and two routers (IP-OBU2 and Router2).  Vehicle1's
   IP-OBU1 (as a mobile router) and Vehicle2's IP-OBU2 (as a mobile
   router) use 2001:DB8:1:1::/64 for an external link (e.g., DSRC) for
   V2V networking.  Thus, a host (Host1) in Vehicle1 can communicate
   with another host (Host3) in Vehicle2 for a vehicular service through
   Vehicle1's moving network, a wireless link between IP-OBU1 and IP-
   OBU2, and Vehicle2's moving network.

   As a V2V use case in Section 3.1, Figure 4 shows the linear network
   topology of platooning vehicles for V2V communications where Vehicle3
   is the leading vehicle with a driver, and Vehicle2 and Vehicle1 are
   the following vehicles without drivers.





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        (*)<..................>(*)<..................>(*)
         |                      |                      |
   +-----------+          +-----------+          +-----------+
   |           |          |           |          |           |
   | +-------+ |          | +-------+ |          | +-------+ |
   | |IP-OBU1| |          | |IP-OBU2| |          | |IP-OBU3| |
   | +-------+ |          | +-------+ |          | +-------+ |
   |     ^     |          |     ^     |          |     ^     |
   |     |     |=====>    |     |     |=====>    |     |     |=====>
   |     v     |          |     v     |          |     v     |
   | +-------+ |          | +-------+ |          | +-------+ |
   | | Host1 | |          | | Host2 | |          | | Host3 | |
   | +-------+ |          | +-------+ |          | +-------+ |
   |           |          |           |          |           |
   +-----------+          +-----------+          +-----------+
      Vehicle1               Vehicle2               Vehicle3

    <----> Wired Link   <....> Wireless Link   ===> Moving Direction
    (*) Antenna

      Figure 4: Multihop Internetworking between Two Vehicle Networks

   As shown in Figure 4, multihop internetworking is feasible among the
   moving networks of three vehicles in the same VANET.  For example,
   Host1 in Vehicle1 can communicate with Host3 in Vehicle3 via IP-OBU1
   in Vehicle1, IP-OBU2 in Vehicle2, and IP-OBU3 in Vehicle3 in the
   VANET, as shown in the figure.

   In this section, the link between two vehicles is assumed to be
   stable for single-hop wireless communication regardless of the sight
   relationship such as line of sight and non-line of sight, as shown in
   Figure 3.  Even in Figure 4, the three vehicles are connected to each
   other with a linear topology, however, multihop V2V communication can
   accommodate any network topology (i.e., an arbitrary graph) over
   VANET routing protocols.
















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        (*)<..................>(*)<..................>(*)
         |                      |                      |
   +-----------+          +-----------+          +-----------+
   |           |          |           |          |           |
   | +-------+ |          | +-------+ |          | +-------+ |
   | |IP-OBU1| |          | |IP-RSU1| |          | |IP-OBU3| |
   | +-------+ |          | +-------+ |          | +-------+ |
   |     ^     |          |     ^     |          |     ^     |
   |     |     |=====>    |     |     |          |     |     |=====>
   |     v     |          |     v     |          |     v     |
   | +-------+ |          | +-------+ |          | +-------+ |
   | | Host1 | |          | | Host2 | |          | | Host3 | |
   | +-------+ |          | +-------+ |          | +-------+ |
   |           |          |           |          |           |
   +-----------+          +-----------+          +-----------+
      Vehicle1                 EN1                  Vehicle3

    <----> Wired Link   <....> Wireless Link   ===> Moving Direction
    (*) Antenna

      Figure 5: Multihop Internetworking between Two Vehicle Networks
                             via IP-RSU (V2I2V)

   As shown in Figure 5, multihop internetworking between two vehicles
   is feasible via an infrastructure node (i.e., IP-RSU) with wireless
   connectivity among the moving networks of two vehicles and the fixed
   network of an edge network (denoted as EN1) in the same VANET.  For
   example, Host1 in Vehicle1 can communicate with Host3 in Vehicle3 via
   IP-OBU1 in Vehicle1, IP-RSU1 in EN1, and IP-OBU3 in Vehicle3 in the
   VANET, as shown in the figure.

   For the reliability required in V2V networking, the ND optimization
   defined in MANET [RFC6130] [RFC7466] improves the classical IPv6 ND
   in terms of tracking neighbor information with up to two hops and
   introducing several extensible Information Bases, which serves the
   MANET routing protocols such as the difference versions of Optimized
   Link State Routing Protocol (OLSR) [RFC3626] [RFC7181] [RFC7188]
   [RFC7722] [RFC7779] [RFC8218] and the Dynamic Link Exchange Protocol
   (DLEP) with its extensions [RFC8175] [RFC8629] [RFC8651] [RFC8703]
   [RFC8757].  In short, the MANET ND mainly deals with maintaining
   extended network neighbors.  However, an ND protocol in vehicular
   networks shall consider more about the geographical mobility
   information of vehicles as an important resource for serving various
   purposes to improve the reliability, e.g., vehicle driving safety,
   intelligent transportation implementations, and advanced mobility
   services.  For a more reliable V2V networking, some redundancy
   mechanisms should be provided in L3 in the case of the failure of L2.




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5.  Problem Statement

   In order to specify protocols using the architecture mentioned in
   Section 4.1, IPv6 core protocols have to be adapted to overcome
   certain challenging aspects of vehicular networking.  Since the
   vehicles are likely to be moving at great speed, protocol exchanges
   need to be completed in a time relatively short compared to the
   lifetime of a link between a vehicle and an IP-RSU, or between two
   vehicles.

   For safe driving, vehicles need to exchange application messages
   every 0.5 second [NHTSA-ACAS-Report] to let drivers take an action to
   avoid a dangerous situation (e.g., vehicle collision), so IPv6
   protocol exchanges need to support this order of magnitude for
   application message exchanges.  Also, considering the communication
   range of DSRC (up to 1km) and 100km/h as the speed limit in highway,
   the lifetime of a link between a vehicle and an IP-RSU is 72 seconds,
   and the lifetime of a link between two vehicles is 36 seconds.  Note
   that if two vehicles are moving in the opposite directions in a
   roadway, the relative speed of this case is two times the relative
   speed of a vehicle passing through an RSU.  This relative speed leads
   the half of the link lifetime between the vehicle and the IP-RSU.  In
   reality, the DSRC communication range is around 500m, so the link
   lifetime will be a half of the maximum time.  The time constraint of
   a wireless link between two nodes (e.g., vehicle and IP-RSU) needs to
   be considered because it may affect the lifetime of a session
   involving the link.  The lifetime of a session varies depending on
   the session's type such as a web surfing, voice call over IP, DNS
   query, and context-aware navigation (in Section 3.1).  Regardless of
   a session's type, to guide all the IPv6 packets to their destination
   host(s), IP mobility should be supported for the session.  In a V2V
   scenario (e.g., context-aware navigation), the IPv6 packets of a
   vehicle should be delivered to relevant vehicles in an efficient way
   (e.g., multicasting).  With this observation, IPv6 protocol exchanges
   need to be done as short as possible to support the message exchanges
   of various applications in vehicular networks.

   Therefore, the time constraint of a wireless link has a major impact
   on IPv6 Neighbor Discovery (ND).  Mobility Management (MM) is also
   vulnerable to disconnections that occur before the completion of
   identity verification and tunnel management.  This is especially true
   given the unreliable nature of wireless communication.  Meanwhile,
   the bandwidth of the wireless link determined by the lower layers
   (i.e., link and PHY layers) can affect the transmission time of
   control messages of the upper layers (e.g., IPv6) and the continuity
   of sessions in the higher layers (e.g., IPv6, TCP, and UDP).  Hence
   the bandwidth selection according to Modulation and Coding Scheme
   (MCS) also affects the vehicular network connectivity.  Note that



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   usually the higher bandwidth gives the shorter communication range
   and the higher packet error rate at the receiving side, which may
   reduce the reliability of control message exchanges of the higher
   layers (e.g., IPv6).  This section presents key topics such as
   neighbor discovery and mobility management for links and sessions in
   IPv6-based vehicular networks.

5.1.  Neighbor Discovery

   IPv6 ND [RFC4861][RFC4862] is a core part of the IPv6 protocol suite.
   IPv6 ND is designed for link types including point-to-point,
   multicast-capable (e.g., Ethernet) and Non-Broadcast Multiple Access
   (NBMA).  It assumes the efficient and reliable support of multicast
   and unicast from the link layer for various network operations such
   as MAC Address Resolution (AR), DAD, MLD and Neighbor Unreachability
   Detection (NUD).

   Vehicles move quickly within the communication coverage of any
   particular vehicle or IP-RSU.  Before the vehicles can exchange
   application messages with each other, they need to be configured with
   a link-local IPv6 address or a global IPv6 address, and run IPv6 ND.

   The requirements for IPv6 ND for vehicular networks are efficient DAD
   and NUD operations.  An efficient DAD is required to reduce the
   overhead of the DAD packets during a vehicle's travel in a road
   network, which can guarantee the uniqueness of a vehicle's global
   IPv6 address.  An efficient NUD is required to reduce the overhead of
   the NUD packets during a vehicle's travel in a road network, which
   can guarantee the accurate neighborhood information of a vehicle in
   terms of adjacent vehicles and RSUs.

   The legacy DAD assumes that a node with an IPv6 address can reach any
   other node with the scope of its address at the time it claims its
   address, and can hear any future claim for that address by another
   party within the scope of its address for the duration of the address
   ownership.  However, the partitioning and merging of VANETs makes
   this assumption frequently invalid in vehicular networks.  The
   merging and partitioning of VANETs frequently occurs in vehicular
   networks.  This merging and partitioning should be considered for the
   IPv6 ND such as IPv6 Stateless Address Autoconfiguration (SLAAC)
   [RFC4862].  Due to the merging of VANETs, two IPv6 addresses may
   conflict with each other though they were unique before the merging.
   An address lookup operation may be conducted by an MA or IP-RSU (as
   Registrar in RPL) to check the uniqueness of an IPv6 address that
   will be configured by a vehicle as DAD.  Also, the partitioning of a
   VANET may make vehicles with the same prefix be physically
   unreachable.  An address lookup operation may be conducted by an MA
   or IP-RSU (as Registrar in RPL) to check the existence of a vehicle



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   under the network coverage of the MA or IP-RSU as NUD.  Thus, SLAAC
   needs to prevent IPv6 address duplication due to the merging of
   VANETs, and IPv6 ND needs to detect unreachable neighboring vehicles
   due to the partitioning of a VANET.  According to the merging and
   partitioning, a destination vehicle (as an IPv6 host) needs to be
   distinguished as either an on-link host or an off-link host even
   though the source vehicle can use the same prefix as the destination
   vehicle [ID-IPPL].

   To efficiently prevent IPv6 address duplication due to the VANET
   partitioning and merging from happening in vehicular networks, the
   vehicular networks need to support a vehicular-network-wide DAD by
   defining a scope that is compatible with the legacy DAD.  In this
   case, two vehicles can communicate with each other when there exists
   a communication path over VANET or a combination of VANETs and IP-
   RSUs, as shown in Figure 1.  By using the vehicular-network-wide DAD,
   vehicles can assure that their IPv6 addresses are unique in the
   vehicular network whenever they are connected to the vehicular
   infrastructure or become disconnected from it in the form of VANET.

   For vehicular networks with high mobility and density, the DAD needs
   to be performed efficiently with minimum overhead so that the
   vehicles can exchange driving safety messages (e.g., collision
   avoidance and accident notification) with each other with a short
   interval suggested by NHTSA (National Highway Traffic Safety
   Administration) [NHTSA-ACAS-Report].  Since the partitioning and
   merging of vehicular networks may require re-perform the DAD process
   repeatedly, the link scope of vehicles may be limited to a small
   area, which may delay the exchange of driving safety messages.
   Driving safety messages can include a vehicle's mobility information
   (i.e., position, speed, direction, and acceleration/deceleration)
   that is critical to other vehicles.  The exchange interval of this
   message is recommended to be less than 0.5 second, which is required
   for a driver to avoid an emergency situation, such as a rear-end
   crash.

   ND time-related parameters such as router lifetime and Neighbor
   Advertisement (NA) interval need to be adjusted for vehicle speed and
   vehicle density.  For example, the NA interval needs to be
   dynamically adjusted according to a vehicle's speed so that the
   vehicle can maintain its neighboring vehicles in a stable way,
   considering the collision probability with the NA messages sent by
   other vehicles.  The ND time-related parameters can be an operational
   setting or an optimization point particularly for vehicular networks.







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   For IPv6-based safety applications (e.g., context-aware navigation,
   adaptive cruise control, and platooning) in vehicular networks, the
   delay-bounded data delivery is critical.  IPv6 ND needs to work to
   support those IPv6-based safety applications efficiently.

   From the interoperability point of view, in IPv6-based vehicular
   networking, IPv6 ND should have minimum changes with the legacy IPv6
   ND used in the Internet, including the DAD and NUD operations, so
   that IPv6-based vehicular networks can be seamlessly connected to
   other intelligent transportation elements (e.g., traffic signals,
   pedestrian wearable devices, electric scooters, and bus stops) that
   use the standard IPv6 network settings.

5.1.1.  Link Model

   A subnet model for a vehicular network needs to facilitate the
   communication between two vehicles with the same prefix regardless of
   the vehicular network topology as long as there exist bidirectional
   E2E paths between them in the vehicular network including VANETs and
   IP-RSUs.  This subnet model allows vehicles with the same prefix to
   communicate with each other via a combination of multihop V2V and
   multihop V2I with VANETs and IP-RSUs.  [IPoWIRELESS] introduces other
   issues in an IPv6 subnet model.

   IPv6 protocols work under certain assumptions that do not necessarily
   hold for vehicular wireless access link types [VIP-WAVE][RFC5889].
   For instance, some IPv6 protocols assume symmetry in the connectivity
   among neighboring interfaces [RFC6250].  However, radio interference
   and different levels of transmission power may cause asymmetric links
   to appear in vehicular wireless links.  As a result, a new vehicular
   link model needs to consider the asymmetry of dynamically changing
   vehicular wireless links.

   There is a relationship between a link and a prefix, besides the
   different scopes that are expected from the link-local and global
   types of IPv6 addresses.  In an IPv6 link, it is defined that all
   interfaces which are configured with the same subnet prefix and with
   on-link bit set can communicate with each other on an IPv6 link.
   However, the vehicular link model needs to define the relationship
   between a link and a prefix, considering the dynamics of wireless
   links and the characteristics of VANET.

   A VANET can have a single link between each vehicle pair within
   wireless communication range, as shown in Figure 4.  When two
   vehicles belong to the same VANET, but they are out of wireless
   communication range, they cannot communicate directly with each
   other.  Suppose that a global-scope IPv6 prefix (or an IPv6 ULA
   prefix) is assigned to VANETs in vehicular networks.  Even though two



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   vehicles in the same VANET configure their IPv6 addresses with the
   same IPv6 prefix, they may not communicate with each other not in one
   hop in the same VANET because of the multihop network connectivity
   between them.  Thus, in this case, the concept of an on-link IPv6
   prefix does not hold because two vehicles with the same on-link IPv6
   prefix cannot communicate directly with each other.  Also, when two
   vehicles are located in two different VANETs with the same IPv6
   prefix, they cannot communicate with each other.  When these two
   VANETs converge to one VANET, the two vehicles can communicate with
   each other in a multihop fashion, for example, when they are Vehicle1
   and Vehicle3, as shown in Figure 4.

   From the previous observation, a vehicular link model should consider
   the frequent partitioning and merging of VANETs due to vehicle
   mobility.  Therefore, the vehicular link model needs to use an on-
   link prefix and off-link prefix according to the network topology of
   vehicles such as a one-hop reachable network and a multihop reachable
   network (or partitioned networks).  If the vehicles with the same
   prefix are reachable from each other in one hop, the prefix should be
   on-link.  On the other hand, if some of the vehicles with the same
   prefix are not reachable from each other in one hop due to either the
   multihop topology in the VANET or multiple partitions, the prefix
   should be off-link.  In most cases in vehicular networks, due to the
   partitioning and merging of VANETs, and the multihop network topology
   of VANETS, off-link prefixes will be used for vehicles as default.

   The vehicular link model needs to support multihop routing in a
   connected VANET where the vehicles with the same global-scope IPv6
   prefix (or the same IPv6 ULA prefix) are connected in one hop or
   multiple hops.  It also needs to support the multihop routing in
   multiple connected VANETs through infrastructure nodes (e.g., IP-RSU)
   where they are connected to the infrastructure.  For example, in
   Figure 1, suppose that Vehicle1, Vehicle2, and Vehicle3 are
   configured with their IPv6 addresses based on the same global-scope
   IPv6 prefix.  Vehicle1 and Vehicle3 can also communicate with each
   other via either multihop V2V or multihop V2I2V.  When Vehicle1 and
   Vehicle3 are connected in a VANET, it will be more efficient for them
   to communicate with each other directly via VANET rather than
   indirectly via IP-RSUs.  On the other hand, when Vehicle1 and
   Vehicle3 are far away from direct communication range in separate
   VANETs and under two different IP-RSUs, they can communicate with
   each other through the relay of IP-RSUs via V2I2V.  Thus, two
   separate VANETs can merge into one network via IP-RSU(s).  Also,
   newly arriving vehicles can merge two separate VANETs into one VANET
   if they can play the role of a relay node for those VANETs.






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   Thus, in IPv6-based vehicular networking, the vehicular link model
   should have minimum changes for interoperability with standard IPv6
   links in an efficient fashion to support IPv6 DAD, MLD and NUD
   operations.

5.1.2.  MAC Address Pseudonym

   For the protection of drivers' privacy, a pseudonym of a MAC address
   of a vehicle's network interface should be used, so that the MAC
   address can be changed periodically.  However, although such a
   pseudonym of a MAC address can protect to some extent the privacy of
   a vehicle, it may not be able to resist attacks on vehicle
   identification by other fingerprint information, for example, the
   scrambler seed embedded in IEEE 802.11-OCB frames [Scrambler-Attack].
   The pseudonym of a MAC address affects an IPv6 address based on the
   MAC address, and a transport-layer (e.g., TCP and SCTP) session with
   an IPv6 address pair.  However, the pseudonym handling is not
   implemented and tested yet for applications on IP-based vehicular
   networking.

   In the ETSI standards, for the sake of security and privacy, an ITS
   station (e.g., vehicle) can use pseudonyms for its network interface
   identities (e.g., MAC address) and the corresponding IPv6 addresses
   [Identity-Management].  Whenever the network interface identifier
   changes, the IPv6 address based on the network interface identifier
   needs to be updated, and the uniqueness of the address needs to be
   checked through the DAD procedure.

5.1.3.  Routing

   For multihop V2V communications in either a VANET or VANETs via IP-
   RSUs, a vehicular Mobile Ad Hoc Networks (MANET) routing protocol may
   be required to support both unicast and multicast in the links of the
   subnet with the same IPv6 prefix.  However, it will be costly to run
   both vehicular ND and a vehicular ad hoc routing protocol in terms of
   control traffic overhead [ID-Multicast-Problems].

   A routing protocol for a VANET may cause redundant wireless frames in
   the air to check the neighborhood of each vehicle and compute the
   routing information in a VANET with a dynamic network topology
   because the IPv6 ND is used to check the neighborhood of each
   vehicle.  Thus, the vehicular routing needs to take advantage of the
   IPv6 ND to minimize its control overhead.

   RPL [RFC6550] defines a routing protocol for low-power and lossy
   networks, which constructs and maintains Destination-Oriented
   Directed Acyclic Graphs (DODAGs) optimized by an Objective Function
   (OF).  A defined OF provides route selection and optimization within



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   an RPL topology.  The RPL nodes use an anisotropic Distance Vector
   (DV) approach to form a DODAG by discovering and aggressively
   maintaining the upward default route toward the root of the DODAG.
   Downward routes follow the same DODAG, with lazy maintenance and
   stretched Peer-to-Peer (P2P) routing in the so-called storing mode.
   It is well-designed to reduce the topological knowledge and routing
   state that needs to be exchanged.  As a result, the routing protocol
   overhead is minimized, which allows either highly constrained stable
   networks or less constrained, highly dynamic networks.  Refer to
   Appendix B for the detailed description of RPL for multihop V2X
   networking.

   An address registration extension for 6LoWPAN (IPv6 over Low-Power
   Wireless Personal Area Network) in [RFC8505] can support light-weight
   mobility for nodes moving through different parents.  [RFC8505], as
   opposed to [RFC4861], is stateful and proactively installs the ND
   cache entries, which saves broadcasts and provides a deterministic
   presence information for IPv6 addresses.  Mainly it updates the
   Address Registration Option (ARO) of ND defined in [RFC6775] to
   include a status field that can indicate the movement of a node and
   optionally a Transaction ID (TID) field, i.e., a sequence number that
   can be used to determine the most recent location of a node.  Thus,
   RPL can use the information provided by the Extended ARO (EARO)
   defined in [RFC8505] to deal with a certain level of node mobility.
   When a leaf node moves to the coverage of another parent node, it
   should de-register its addresses to the previous parent node and
   register itself with a new parent node along with an incremented TID.

   RPL can be used in IPv6-based vehicular networks, but it is primarily
   designed for lossy networks, which puts energy efficiency first.  For
   using it in IPv6-based vehicular networks, there have not been actual
   experiences and practical implementations for vehicular networks,
   though it was tested in IoT low-power and lossy networks (LLN)
   scenarios.

   Moreover, due to bandwidth and energy constraints, RPL does not
   suggest to use a proactive mechanism (e.g., keepalive) to maintain
   accurate routing adjacencies such as Bidirectional Forwarding
   Detection [RFC5881] and MANET Neighborhood Discovery Protocol
   [RFC6130].  As a result, due to the mobility of vehicles, network
   fragmentation may not be detected quickly and the routing of packets
   between vehicles or between a vehicle and an infrastructure node may
   fail.








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5.2.  Mobility Management

   The seamless connectivity and timely data exchange between two end
   points requires efficient mobility management including location
   management and handover.  Most vehicles are equipped with a GPS
   receiver as part of a dedicated navigation system or a corresponding
   smartphone App.  Note that the GPS receiver may not provide vehicles
   with accurate location information in adverse environments such as a
   building area or a tunnel.  The location precision can be improved
   with assistance of the IP-RSUs or a cellular system with a GPS
   receiver for location information.

   With a GPS navigator, efficient mobility management can be performed
   with the help of vehicles periodically reporting their current
   position and trajectory (i.e., navigation path) to the vehicular
   infrastructure (having IP-RSUs and an MA in TCC).  This vehicular
   infrastructure can predict the future positions of the vehicles from
   their mobility information (i.e., the current position, speed,
   direction, and trajectory) for efficient mobility management (e.g.,
   proactive handover).  For a better proactive handover, link-layer
   parameters, such as the signal strength of a link-layer frame (e.g.,
   Received Channel Power Indicator (RCPI) [VIP-WAVE]), can be used to
   determine the moment of a handover between IP-RSUs along with
   mobility information.

   By predicting a vehicle's mobility, the vehicular infrastructure
   needs to better support IP-RSUs to perform efficient SLAAC, data
   forwarding, horizontal handover (i.e., handover in wireless links
   using a homogeneous radio technology), and vertical handover (i.e.,
   handover in wireless links using heterogeneous radio technologies) in
   advance along with the movement of the vehicle.

   For example, as shown in Figure 1, when a vehicle (e.g., Vehicle2) is
   moving from the coverage of an IP-RSU (e.g., IP-RSU1) into the
   coverage of another IP-RSU (e.g., IP-RSU2) belonging to a different
   subnet, the IP-RSUs can proactively support the IPv6 mobility of the
   vehicle, while performing the SLAAC, data forwarding, and handover
   for the sake of the vehicle.













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   For a mobility management scheme in a domain, where the wireless
   subnets of multiple IP-RSUs share the same prefix, an efficient
   vehicular-network-wide DAD is required.  If DHCPv6 is used to assign
   a unique IPv6 address to each vehicle in this shared link, the DAD is
   not required.  On the other hand, for a mobility management scheme
   with a unique prefix per mobile node (e.g., PMIPv6 [RFC5213]), DAD is
   not required because the IPv6 address of a vehicle's external
   wireless interface is guaranteed to be unique.  There is a tradeoff
   between the prefix usage efficiency and DAD overhead.  Thus, the IPv6
   address autoconfiguration for vehicular networks needs to consider
   this tradeoff to support efficient mobility management.

   Even though the SLAAC with classic ND costs a DAD during mobility
   management, the SLAAC with [RFC8505] does not cost a DAD.  SLAAC for
   vehicular networks needs to consider the minimization of the cost of
   DAD with the help of an infrastructure node (e.g., IP-RSU and MA).
   Using an infrastructure prefix over VANET allows direct routability
   to the Internet through the multihop V2I toward an IP-RSU.  On the
   other hand, a BYOA does not allow such direct routability to the
   Internet since the BYOA is not topologically correct, that is, not
   routable in the Internet.  In addition, a vehicle configured with a
   BYOA needs a tunnel home (e.g., IP-RSU) connected to the Internet,
   and the vehicle needs to know which neighboring vehicle is reachable
   inside the VANET toward the tunnel home.  There is nonnegligible
   control overhead to set up and maintain routes to such a tunnel home
   over the VANET.

   For the case of a multihomed network, a vehicle can follow the first-
   hop router selection rule described in [RFC8028].  For example, an
   IP-OBU inside a vehicle may connect to an IP-RSU that has multiple
   routers behind.  In this scenario, because the IP-OBU can have
   multiple prefixes from those routers, the default router selection,
   source address selection, and packet redirect process should follow
   the guidelines in [RFC8028].  That is, the vehicle should select its
   default router for each prefix by preferring the router that
   advertised the prefix.

   Vehicles can use the TCC as their Home Network having a home agent
   for mobility management as in MIPv6 [RFC6275] and PMIPv6 [RFC5213],
   so the TCC (or an MA inside the TCC) maintains the mobility
   information of vehicles for location management.  IP tunneling over
   the wireless link should be avoided for performance efficiency.
   Also, in vehicular networks, asymmetric links sometimes exist and
   must be considered for wireless communications such as V2V and V2I.

   Therefore, for the proactive and seamless IPv6 mobility of vehicles,
   the vehicular infrastructure (including IP-RSUs and MA) needs to
   efficiently perform the mobility management of the vehicles with



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   their mobility information and link-layer information.  Also, in
   IPv6-based vehicular networking, IPv6 mobility management should have
   minimum changes for the interoperability with the legacy IPv6
   mobility management schemes such as PMIPv6, DMM, LISP, and AERO.

6.  Security Considerations

   This section discusses security and privacy for IPv6-based vehicular
   networking.  Security and privacy are paramount in V2I, V2V, and V2X
   networking along with neighbor discovery and mobility management.

   Vehicles and infrastructure must be authenticated in order to
   participate in vehicular networking.  For the authentication in
   vehicular networks, vehicular cloud needs to support a kind of Public
   Key Infrastructure (PKI) in an efficient way.  To provide safe
   interaction between vehicles or between a vehicle and infrastructure,
   only authenticated nodes (i.e., vehicle and infrastructure node) can
   participate in vehicular networks.  Also, in-vehicle devices (e.g.,
   ECU) and a driver/passenger's mobile devices (e.g., smartphone and
   tablet PC) in a vehicle need to communicate with other in-vehicle
   devices and another driver/passenger's mobile devices in another
   vehicle, or other servers behind an IP-RSU in a secure way.  Even
   though a vehicle is perfectly authenticated and legitimate, it may be
   hacked for running malicious applications to track and collect its
   and other vehicles' information.  In this case, an attack mitigation
   process may be required to reduce the aftermath of malicious
   behaviors.

   For secure V2I communication, a secure channel (e.g., IPsec) between
   a mobile router (i.e., IP-OBU) in a vehicle and a fixed router (i.e.,
   IP-RSU) in an EN needs to be established, as shown in Figure 2
   [RFC4301][RFC4302] [RFC4303][RFC4308] [RFC7296].  Also, for secure
   V2V communication, a secure channel (e.g., IPsec) between a mobile
   router (i.e., IP-OBU) in a vehicle and a mobile router (i.e., IP-OBU)
   in another vehicle needs to be established, as shown in Figure 3.
   For secure communication, an element in a vehicle (e.g., an in-
   vehicle device and a driver/passenger's mobile device) needs to
   establish a secure connection (e.g., TLS) with another element in
   another vehicle or another element in a vehicular cloud (e.g., a
   server).  IEEE 1609.2 [WAVE-1609.2] specifies security services for
   applications and management messages, but this WAVE specification is
   optional.  Thus, if the link layer does not support the security of a
   WAVE frame, either the network layer or the transport layer needs to
   support security services for the WAVE frames.







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6.1.  Security Threats in Neighbor Discovery

   For the classical IPv6 ND, the DAD is required to ensure the
   uniqueness of the IPv6 address of a vehicle's wireless interface.
   This DAD can be used as a flooding attack that uses the DAD-related
   ND packets disseminated over the VANET or vehicular networks.
   [RFC6959] introduces threats enabled by IP source address spoofing.
   This possibility indicates that vehicles and IP-RSUs need to filter
   out suspicious ND traffic in advance.  [RFC8928] introduces a
   mechanism that protects the ownership of an address for 6loWPAN ND
   from address theft and impersonation attacks.  Based on the SEND
   [RFC3971] mechanism, the authentication for routers (i.e., IP-RSUs)
   can be conducted by only selecting an IP-RSU that has a certification
   path toward trusted parties.  For authenticating other vehicles, the
   cryptographically generated address (CGA) can be used to verify the
   true owner of a received ND message, which requires to use the CGA ND
   option in the ND protocols.  For a general protection of the ND
   mechanism, the RSA Signature ND option can also be used to protect
   the integrity of the messages by public key signatures.  For a more
   advanced authentication mechanism, a distributed blockchain-based
   approach [Vehicular-BlockChain] can be used.  However, for a scenario
   where a trustable router or an authentication path cannot be
   obtained, it is desirable to find a solution in which vehicles and
   infrastructures can authenticate each other without any support from
   a third party.

   When applying the classical IPv6 ND process to VANET, one of the
   security issues is that an IP-RSU (or an IP-OBU) as a router may
   receive deliberate or accidental DoS attacks from network scans that
   probe devices on a VANET.  In this scenario, the IP-RSU can be
   overwhelmed for processing the network scan requests so that the
   capacity and resources of IP-RSU are exhausted, causing the failure
   of receiving normal ND messages from other hosts for network address
   resolution.  [RFC6583] describes more about the operational problems
   in the classical IPv6 ND mechanism that can be vulnerable to
   deliberate or accidental DoS attacks and suggests several
   implementation guidelines and operational mitigation techniques for
   those problems.  Nevertheless, for running IPv6 ND in VANET, those
   issues can be more acute since the movements of vehicles can be so
   diverse that it leaves a large room for rogue behaviors, and the
   failure of networking among vehicles may cause grave consequences.

   Strong security measures shall protect vehicles roaming in road
   networks from the attacks of malicious nodes, which are controlled by
   hackers.  For safe driving applications (e.g., context-aware
   navigation, cooperative adaptive cruise control, and platooning), as
   explained in Section 3.1, the cooperative action among vehicles is
   assumed.  Malicious nodes may disseminate wrong driving information



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   (e.g., location, speed, and direction) for disturbing safe driving.
   For example, a Sybil attack, which tries to confuse a vehicle with
   multiple false identities, may disturb a vehicle from taking a safe
   maneuver.

   To identify malicious vehicles among vehicles, an authentication
   method may be required.  A Vehicle Identification Number (VIN) and a
   user certificate (e.g., X.509 certificate [RFC5280]) along with an
   in-vehicle device's identifier generation can be used to efficiently
   authenticate a vehicle or its driver (having a user certificate)
   through a road infrastructure node (e.g., IP-RSU) connected to an
   authentication server in the vehicular cloud.  This authentication
   can be used to identify the vehicle that will communicate with an
   infrastructure node or another vehicle.  In the case where a vehicle
   has an internal network (called Moving Network) and elements in the
   network (e.g., in-vehicle devices and a user's mobile devices), as
   shown in Figure 2, the elements in the network need to be
   authenticated individually for safe authentication.  Also, Transport
   Layer Security (TLS) certificates [RFC8446][RFC5280] can be used for
   an element's authentication to allow secure E2E vehicular
   communications between an element in a vehicle and another element in
   a server in a vehicular cloud, or between an element in a vehicle and
   another element in another vehicle.

6.2.  Security Threats in Mobility Management

   For mobility management, a malicious vehicle can construct multiple
   virtual bogus vehicles, and register them with IP-RSUs and MA.  This
   registration makes the IP-RSUs and MA waste their resources.  The IP-
   RSUs and MA need to determine whether a vehicle is genuine or bogus
   in mobility management.  Also, the confidentiality of control packets
   and data packets among IP-RSUs and MA, the E2E paths (e.g., tunnels)
   need to be protected by secure communication channels.  In addition,
   to prevent bogus IP-RSUs and MA from interfering with the IPv6
   mobility of vehicles, mutual authentication among them needs to be
   performed by certificates (e.g., TLS certificate).

6.3.  Other Threats

   For the setup of a secure channel over IPsec or TLS, the multihop V2I
   communications over DSRC or 5G V2X (or LTE V2X) is required in a
   highway.  In this case, multiple intermediate vehicles as relay nodes
   can help forward association and authentication messages toward an
   IP-RSU (gNodeB, or eNodeB) connected to an authentication server in
   the vehicular cloud.  In this kind of process, the authentication
   messages forwarded by each vehicle can be delayed or lost, which may
   increase the construction time of a connection or some vehicles may
   not be able to be authenticated.



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   Even though vehicles can be authenticated with valid certificates by
   an authentication server in the vehicular cloud, the authenticated
   vehicles may harm other vehicles.  To deal with this kind of security
   issue, for monitoring suspicious behaviors, vehicles' communication
   activities can be recorded in either a central way through a logging
   server (e.g., TCC) in the vehicular cloud or a distributed way (e.g.,
   blockchain [Bitcoin]) along with other vehicles or infrastructure.
   To solve the issue ultimately, we need a solution where, without
   privacy breakage, vehicles may observe activities of each other to
   identify any misbehavior.  Once identifying a misbehavior, a vehicle
   shall have a way to either isolate itself from others or isolate a
   suspicious vehicle by informing other vehicles.  Alternatively, for
   completely secure vehicular networks, we shall embrace the concept of
   "zero-trust" for vehicles in which no vehicle is trustable and
   verifying every message is necessary.  For doing so, we shall have an
   efficient zero-trust framework or mechanism for vehicular networks.

   For the non-repudiation of the harmful activities of malicious nodes,
   a blockchain technology can be used [Bitcoin].  Each message from a
   vehicle can be treated as a transaction and the neighboring vehicles
   can play the role of peers in a consensus method of a blockchain
   [Bitcoin] [Vehicular-BlockChain].  For a blockchain's efficient
   consensus in vehicular networks having fast moving vehicles, a new
   consensus algorithm needs to be developed or an existing consensus
   algorithm needs to be enhanced.

   To prevent an adversary from tracking a vehicle with its MAC address
   or IPv6 address, especially for a long-living transport-layer session
   (e.g., voice call over IP and video streaming service), a MAC address
   pseudonym needs to be provided to each vehicle; that is, each vehicle
   periodically updates its MAC address and its IPv6 address needs to be
   updated accordingly by the MAC address change [RFC4086][RFC4941].
   Such an update of the MAC and IPv6 addresses should not interrupt the
   E2E communications between two vehicles (or between a vehicle and an
   IP-RSU) for a long-living transport-layer session.  However, if this
   pseudonym is performed without strong E2E confidentiality (using
   either IPsec or TLS), there will be no privacy benefit from changing
   MAC and IPv6 addresses, because an adversary can observe the change
   of the MAC and IPv6 addresses and track the vehicle with those
   addresses.  Thus, the MAC address pseudonym and the IPv6 address
   update should be performed with strong E2E confidentiality.

7.  IANA Considerations

   This document does not require any IANA actions.

8.  References




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8.1.  Normative References

   [RFC8691]  Benamar, N., Haerri, J., Lee, J., and T. Ernst, "Basic
              Support for IPv6 Networks Operating Outside the Context of
              a Basic Service Set over IEEE Std 802.11", RFC 8691,
              December 2019, <https://www.rfc-editor.org/rfc/rfc8691>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 8200, July 2017,
              <https://www.rfc-editor.org/rfc/rfc8200>.

   [RFC6275]  Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
              Support in IPv6", RFC 6275, July 2011,
              <https://www.rfc-editor.org/rfc/rfc6275>.

   [RFC5213]  Gundavelli, S., Ed., Leung, K., Devarapalli, V.,
              Chowdhury, K., and B. Patil, "Proxy Mobile IPv6",
              RFC 5213, August 2008,
              <https://www.rfc-editor.org/rfc/rfc5213>.

   [RFC7333]  Chan, H., Liu, D., Seite, P., Yokota, H., and J. Korhonen,
              "Requirements for Distributed Mobility Management",
              RFC 7333, August 2014,
              <https://www.rfc-editor.org/rfc/rfc7333>.

   [RFC7429]  Liu, D., Zuniga, JC., Seite, P., Chan, H., and CJ.
              Bernardos, "Distributed Mobility Management: Current
              Practices and Gap Analysis", RFC 7429, January 2015,
              <https://www.rfc-editor.org/rfc/rfc7429>.

   [RFC3963]  Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
              Thubert, "Network Mobility (NEMO) Basic Support Protocol",
              RFC 3963, January 2005,
              <https://www.rfc-editor.org/rfc/rfc3963>.

   [RFC6550]  Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R.,
              Levis, P., Pister, K., Struik, R., Vasseur, JP., and R.
              Alexander, "RPL: IPv6 Routing Protocol for Low-Power and
              Lossy Networks", RFC 6550, March 2012,
              <https://www.rfc-editor.org/rfc/rfc6550>.

   [RFC3753]  Manner, J. and M. Kojo, "Mobility Related Terminology",
              RFC 3753, June 2004,
              <https://www.rfc-editor.org/rfc/rfc3753>.







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   [RFC5415]  Calhoun, P., Montemurro, M., and D. Stanley, "Control And
              Provisioning of Wireless Access Points (CAPWAP) Protocol
              Specification", RFC 5415, March 2009,
              <https://www.rfc-editor.org/rfc/rfc5415>.

   [RFC7149]  Boucadair, M. and C. Jacquenet, "Software-Defined
              Networking: A Perspective from within a Service Provider
              Environment", RFC 7149, March 2014,
              <https://www.rfc-editor.org/rfc/rfc7149>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP Version 6 (IPv6)", RFC 4861,
              September 2007, <https://www.rfc-editor.org/rfc/rfc4861>.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007,
              <https://www.rfc-editor.org/rfc/rfc4862>.

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, October 2005,
              <https://www.rfc-editor.org/rfc/rfc4193>.

   [RFC2710]  Deering, S., Fenner, W., and B. Haberman, "Multicast
              Listener Discovery (MLD) for IPv6", RFC 2710, October
              1999, <https://www.rfc-editor.org/rfc/rfc2710>.

   [RFC3810]  Vida, R. and L. Costa, "Multicast Listener Discovery
              Version 2 (MLDv2) for IPv6", RFC 3810, June 2004,
              <https://www.rfc-editor.org/rfc/rfc3810>.

   [RFC5889]  Baccelli, E. and M. Townsley, "IP Addressing Model in Ad
              Hoc Networks", RFC 5889, September 2010,
              <https://www.rfc-editor.org/rfc/rfc5889>.

   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", RFC 4086, June
              2005, <https://www.rfc-editor.org/rfc/rfc4086>.

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, September 2007,
              <https://www.rfc-editor.org/rfc/rfc4941>.

   [RFC3849]  Huston, G., Lord, A., and P. Smith, "IPv6 Address Prefix
              Reserved for Documentation", RFC 3849, July 2004,
              <https://www.rfc-editor.org/rfc/rfc3849>.





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   [RFC6250]  Thaler, D., "Evolution of the IP Model", RFC 6250, May
              2011, <https://www.rfc-editor.org/rfc/rfc6250>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, August 2018,
              <https://www.rfc-editor.org/rfc/rfc8446>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008,
              <https://www.rfc-editor.org/rfc/rfc5280>.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005,
              <https://www.rfc-editor.org/rfc/rfc4301>.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302, December
              2005, <https://www.rfc-editor.org/rfc/rfc4302>.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, December 2005,
              <https://www.rfc-editor.org/rfc/rfc4303>.

   [RFC4308]  Hoffman, P., "Cryptographic Suites for IPsec", RFC 4308,
              December 2005, <https://www.rfc-editor.org/rfc/rfc4308>.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", RFC 7296, October 2014,
              <https://www.rfc-editor.org/rfc/rfc7296>.

   [RFC8028]  Baker, F. and B. Carpenter, "First-Hop Router Selection by
              Hosts in a Multi-Prefix Network", RFC 8028, November 2016,
              <https://www.rfc-editor.org/rfc/rfc8028>.

   [RFC3971]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
              Neighbor Discovery (SEND)", RFC 3971, March 2005,
              <https://www.rfc-editor.org/rfc/rfc3971>.

   [RFC8505]  Thubert, P., Nordmark, E., Chakrabarti, S., and C.
              Perkins, "Registration Extensions for IPv6 over Low-Power
              Wireless Personal Area Network (6LoWPAN) Neighbor
              Discovery", RFC 8505, November 2018,
              <https://www.rfc-editor.org/rfc/rfc8505>.






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   [RFC6775]  Shelby, Z., Chakrabarti, S., Nordmark, E., and C. Bormann,
              "Neighbor Discovery Optimization for IPv6 over Low-Power
              Wireless Personal Area Networks (6LoWPANs)", RFC 6775,
              November 2012, <https://www.rfc-editor.org/rfc/rfc6775>.

   [RFC5881]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, June
              2010, <https://www.rfc-editor.org/rfc/rfc5881>.

   [RFC6130]  Clausen, T., Dearlove, C., and J. Dean, "Mobile Ad Hoc
              Network (MANET) Neighborhood Discovery Protocol (NHDP)",
              RFC 6130, April 2011,
              <https://www.rfc-editor.org/rfc/rfc6130>.

   [RFC6583]  Gashinsky, I., Jaeggli, J., and W. Kumari, "Operational
              Neighbor Discovery Problems", RFC 6583, March 2012,
              <https://www.rfc-editor.org/rfc/rfc6583>.

   [RFC8928]  Thubert, P., Sarikaya, B., Sethi, M., and R. Struik,
              "Address-Protected Neighbor Discovery for Low-Power and
              Lossy Networks", RFC 8928, November 2020,
              <https://www.rfc-editor.org/rfc/rfc8928>.

   [RFC3626]  Clausen, T. and P. Jacquet, "Optimized Link State Routing
              Protocol (OLSR)", RFC 3626, October 2003,
              <https://www.rfc-editor.org/rfc/rfc3626>.

   [RFC7181]  Clausen, T., Dearlove, C., Jacquet, P., and U. Herberg,
              "The Optimized Link State Routing Protocol Version 2",
              RFC 7181, April 2014,
              <https://www.rfc-editor.org/rfc/rfc7181>.

   [RFC7188]  Dearlove, C. and T. Clausen, "Optimized Link State Routing
              Protocol Version 2 (OLSRv2) and MANET Neighborhood
              Discovery Protocol (NHDP) Extension TLVs", RFC 7188, April
              2014, <https://www.rfc-editor.org/rfc/rfc7188>.

   [RFC7722]  Dearlove, C. and T. Clausen, "Multi-Topology Extension for
              the Optimized Link State Routing Protocol Version 2
              (OLSRv2)", RFC 7722, December 2015,
              <https://www.rfc-editor.org/rfc/rfc7722>.

   [RFC7779]  Rogge, H. and E. Baccelli, "Directional Airtime Metric
              Based on Packet Sequence Numbers for Optimized Link State
              Routing Version 2 (OLSRv2)", RFC 7779, April 2016,
              <https://www.rfc-editor.org/rfc/rfc7779>.





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   [RFC8218]  Yi, J. and B. Parrein, "Multipath Extension for the
              Optimized Link State Routing Protocol Version 2 (OLSRv2)",
              RFC 8218, August 2017,
              <https://www.rfc-editor.org/rfc/rfc8218>.

   [RFC8175]  Ratliff, S., Jury, S., Satterwhite, D., Taylor, R., and B.
              Berry, "Dynamic Link Exchange Protocol (DLEP)", RFC 8175,
              June 2017, <https://www.rfc-editor.org/rfc/rfc8175>.

   [RFC8629]  Cheng, B. and L. Berger, "Dynamic Link Exchange Protocol
              (DLEP) Multi-Hop Forwarding Extension", RFC 8629, July
              2019, <https://www.rfc-editor.org/rfc/rfc8629>.

   [RFC8651]  Cheng, B., Wiggins, D., and L. Berger, "Dynamic Link
              Exchange Protocol (DLEP) Control-Plane-Based Pause
              Extension", RFC 8651, October 2019,
              <https://www.rfc-editor.org/rfc/rfc8651>.

   [RFC8703]  Taylor, R. and S. Ratliff, "Dynamic Link Exchange Protocol
              (DLEP) Link Identifier Extension", RFC 8703, February
              2020, <https://www.rfc-editor.org/rfc/rfc8703>.

   [RFC8757]  Cheng, B. and L. Berger, "Dynamic Link Exchange Protocol
              (DLEP) Latency Range Extension", RFC 8757, March 2020,
              <https://www.rfc-editor.org/rfc/rfc8757>.

   [RFC7466]  Dearlove, C. and T. Clausen, "An Optimization for the
              Mobile Ad Hoc Network (MANET) Neighborhood Discovery
              Protocol (NHDP)", RFC 7466, March 2015,
              <https://www.rfc-editor.org/rfc/rfc7466>.

8.2.  Informative References

   [ID-IPPL]  Nordmark, E., "IP over Intentionally Partially Partitioned
              Links", Work in Progress, Internet-Draft, draft-ietf-
              intarea-ippl-00, March 2017,
              <https://datatracker.ietf.org/doc/html/draft-ietf-intarea-
              ippl-00>.

   [RFC6830BIS]
              Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
              Cabellos, "The Locator/ID Separation Protocol (LISP)",
              Work in Progress, Internet-Draft, draft-ietf-lisp-
              rfc6830bis-36, November 2020,
              <https://datatracker.ietf.org/doc/html/draft-ietf-lisp-
              rfc6830bis-36>.





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   [AERO]     Templin, F., "Automatic Extended Route Optimization
              (AERO)", Work in Progress, Internet-Draft, draft-templin-
              6man-aero-34, September 2021,
              <https://datatracker.ietf.org/doc/html/draft-templin-6man-
              aero-34>.

   [OMNI]     Templin, F. and A. Whyman, "Transmission of IP Packets
              over Overlay Multilink Network (OMNI) Interfaces", Work in
              Progress, Internet-Draft, draft-templin-6man-omni-47,
              September 2021, <https://datatracker.ietf.org/doc/html/
              draft-templin-6man-omni-47>.

   [UAM-ITS]  Templin, F., "Urban Air Mobility Implications for
              Intelligent Transportation Systems", Work in Progress,
              Internet-Draft, draft-templin-ipwave-uam-its-04, January
              2021, <https://datatracker.ietf.org/doc/html/draft-
              templin-ipwave-uam-its-04>.

   [DMM-FPC]  Matsushima, S., Bertz, L., Liebsch, M., Gundavelli, S.,
              Moses, D., and C. Perkins, "Protocol for Forwarding Policy
              Configuration (FPC) in DMM", Work in Progress, Internet-
              Draft, draft-ietf-dmm-fpc-cpdp-14, September 2020,
              <https://datatracker.ietf.org/doc/html/draft-ietf-dmm-fpc-
              cpdp-14>.

   [ID-Multicast-Problems]
              Perkins, C., McBride, M., Stanley, D., Kumari, W., and JC.
              Zuniga, "Multicast Considerations over IEEE 802 Wireless
              Media", Work in Progress, Internet-Draft, draft-ietf-
              mboned-ieee802-mcast-problems-15, July 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-mboned-
              ieee802-mcast-problems-15>.

   [DSRC]     ASTM International, "Standard Specification for
              Telecommunications and Information Exchange Between
              Roadside and Vehicle Systems - 5 GHz Band Dedicated Short
              Range Communications (DSRC) Medium Access Control (MAC)
              and Physical Layer (PHY) Specifications",
              ASTM E2213-03(2010), October 2010.

   [EU-2008-671-EC]
              European Union, "Commission Decision of 5 August 2008 on
              the Harmonised Use of Radio Spectrum in the 5875 - 5905
              MHz Frequency Band for Safety-related Applications of
              Intelligent Transport Systems (ITS)", EU 2008/671/EC,
              August 2008.





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   [IEEE-802.11p]
              "Part 11: Wireless LAN Medium Access Control (MAC) and
              Physical Layer (PHY) Specifications - Amendment 6:
              Wireless Access in Vehicular Environments", IEEE Std
              802.11p-2010, June 2010.

   [IEEE-802.11-OCB]
              "Part 11: Wireless LAN Medium Access Control (MAC) and
              Physical Layer (PHY) Specifications", IEEE Std
              802.11-2016, December 2016.

   [WAVE-1609.0]
              IEEE 1609 Working Group, "IEEE Guide for Wireless Access
              in Vehicular Environments (WAVE) - Architecture", IEEE Std
              1609.0-2013, March 2014.

   [WAVE-1609.2]
              IEEE 1609 Working Group, "IEEE Standard for Wireless
              Access in Vehicular Environments - Security Services for
              Applications and Management Messages", IEEE Std
              1609.2-2016, March 2016.

   [WAVE-1609.3]
              IEEE 1609 Working Group, "IEEE Standard for Wireless
              Access in Vehicular Environments (WAVE) - Networking
              Services", IEEE Std 1609.3-2016, April 2016.

   [WAVE-1609.4]
              IEEE 1609 Working Group, "IEEE Standard for Wireless
              Access in Vehicular Environments (WAVE) - Multi-Channel
              Operation", IEEE Std 1609.4-2016, March 2016.

   [ISO-ITS-IPv6]
              ISO/TC 204, "Intelligent Transport Systems -
              Communications Access for Land Mobiles (CALM) - IPv6
              Networking", ISO 21210:2012, June 2012.

   [ISO-ITS-IPv6-AMD1]
              ISO/TC 204, "Intelligent Transport Systems -
              Communications Access for Land Mobiles (CALM) - IPv6
              Networking - Amendment 1", ISO 21210:2012/AMD 1:2017,
              September 2017.

   [TS-23.285-3GPP]
              3GPP, "Architecture Enhancements for V2X Services", 3GPP
              TS 23.285/Version 16.2.0, December 2019.





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   [TR-22.886-3GPP]
              3GPP, "Study on Enhancement of 3GPP Support for 5G V2X
              Services", 3GPP TR 22.886/Version 16.2.0, December 2018.

   [TS-23.287-3GPP]
              3GPP, "Architecture Enhancements for 5G System (5GS) to
              Support Vehicle-to-Everything (V2X) Services", 3GPP
              TS 23.287/Version 16.2.0, March 2020.

   [VIP-WAVE] Cespedes, S., Lu, N., and X. Shen, "VIP-WAVE: On the
              Feasibility of IP Communications in 802.11p Vehicular
              Networks", IEEE Transactions on Intelligent Transportation
              Systems, vol. 14, no. 1, March 2013.

   [Identity-Management]
              Wetterwald, M., Hrizi, F., and P. Cataldi, "Cross-layer
              Identities Management in ITS Stations", The 10th
              International Conference on ITS Telecommunications,
              November 2010.

   [SAINT]    Jeong, J., Jeong, H., Lee, E., Oh, T., and D. Du, "SAINT:
              Self-Adaptive Interactive Navigation Tool for Cloud-Based
              Vehicular Traffic Optimization", IEEE Transactions on
              Vehicular Technology, Vol. 65, No. 6, June 2016.

   [SAINTplus]
              Shen, Y., Lee, J., Jeong, H., Jeong, J., Lee, E., and D.
              Du, "SAINT+: Self-Adaptive Interactive Navigation Tool+
              for Emergency Service Delivery Optimization",
              IEEE Transactions on Intelligent Transportation Systems,
              June 2017.

   [SANA]     Hwang, T. and J. Jeong, "SANA: Safety-Aware Navigation
              Application for Pedestrian Protection in Vehicular
              Networks", Springer Lecture Notes in Computer Science
              (LNCS), Vol. 9502, December 2015.

   [CASD]     Shen, Y., Jeong, J., Oh, T., and S. Son, "CASD: A
              Framework of Context-Awareness Safety Driving in Vehicular
              Networks", International Workshop on Device Centric Cloud
              (DC2), March 2016.

   [CA-Cruise-Control]
              California Partners for Advanced Transportation Technology
              (PATH), "Cooperative Adaptive Cruise Control", Available:
              http://www.path.berkeley.edu/research/automated-and-
              connected-vehicles/cooperative-adaptive-cruise-control,
              2017.



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   [Truck-Platooning]
              California Partners for Advanced Transportation Technology
              (PATH), "Automated Truck Platooning", Available:
              http://www.path.berkeley.edu/research/automated-and-
              connected-vehicles/truck-platooning, 2017.

   [FirstNet] U.S. National Telecommunications and Information
              Administration (NTIA), "First Responder Network Authority
              (FirstNet)", Available: https://www.firstnet.gov/, 2012.

   [FirstNet-Report]
              First Responder Network Authority, "FY 2017: ANNUAL REPORT
              TO CONGRESS, Advancing Public Safety Broadband
              Communications", FirstNet FY 2017, December 2017.

   [SignalGuru]
              Koukoumidis, E., Peh, L., and M. Martonosi, "SignalGuru:
              Leveraging Mobile Phones for Collaborative Traffic Signal
              Schedule Advisory", ACM MobiSys, June 2011.

   [Fuel-Efficient]
              van de Hoef, S., H. Johansson, K., and D. V. Dimarogonas,
              "Fuel-Efficient En Route Formation of Truck Platoons",
              IEEE Transactions on Intelligent Transportation Systems,
              January 2018.

   [Automotive-Sensing]
              Choi, J., Va, V., Gonzalez-Prelcic, N., Daniels, R., R.
              Bhat, C., and R. W. Heath, "Millimeter-Wave Vehicular
              Communication to Support Massive Automotive Sensing",
              IEEE Communications Magazine, December 2016.

   [NHTSA-ACAS-Report]
              National Highway Traffic Safety Administration (NHTSA),
              "Final Report of Automotive Collision Avoidance Systems
              (ACAS) Program", DOT HS 809 080, August 2000.

   [CBDN]     Kim, J., Kim, S., Jeong, J., Kim, H., Park, J., and T.
              Kim, "CBDN: Cloud-Based Drone Navigation for Efficient
              Battery Charging in Drone Networks", IEEE Transactions on
              Intelligent Transportation Systems, November 2019.

   [In-Car-Network]
              Lim, H., Volker, L., and D. Herrscher, "Challenges in a
              Future IP/Ethernet-based In-Car Network for Real-Time
              Applications", ACM/EDAC/IEEE Design Automation Conference
              (DAC), June 2011.




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   [Scrambler-Attack]
              Bloessl, B., Sommer, C., Dressier, F., and D. Eckhoff,
              "The Scrambler Attack: A Robust Physical Layer Attack on
              Location Privacy in Vehicular Networks", IEEE 2015
              International Conference on Computing, Networking and
              Communications (ICNC), February 2015.

   [Bitcoin]  Nakamoto, S., "Bitcoin: A Peer-to-Peer Electronic Cash
              System", URL: https://bitcoin.org/bitcoin.pdf, May 2009.

   [Vehicular-BlockChain]
              Dorri, A., Steger, M., Kanhere, S., and R. Jurdak,
              "BlockChain: A Distributed Solution to Automotive Security
              and Privacy", IEEE Communications Magazine, Vol. 55, No.
              12, December 2017.

   [IPoWIRELESS]
              Thubert, P., "IPv6 Neighbor Discovery on Wireless
              Networks", Work in Progress, Internet-Draft, draft-
              thubert-6man-ipv6-over-wireless-09, May 2021,
              <https://datatracker.ietf.org/doc/html/draft-thubert-6man-
              ipv6-over-wireless-09>.

   [RFC6959]  McPherson, D., Baker, F., and J. Halpern, "Source Address
              Validation Improvement (SAVI) Threat Scope", RFC 6959, May
              2013, <https://www.rfc-editor.org/rfc/rfc6959>.

Appendix A.  Support of Multiple Radio Technologies for V2V

   Vehicular networks may consist of multiple radio technologies such as
   DSRC and 5G V2X.  Although a Layer-2 solution can provide a support
   for multihop communications in vehicular networks, the scalability
   issue related to multihop forwarding still remains when vehicles need
   to disseminate or forward packets toward multihop-away destinations.
   In addition, the IPv6-based approach for V2V as a network layer
   protocol can accommodate multiple radio technologies as MAC
   protocols, such as DSRC and 5G V2X.  Therefore, the existing IPv6
   protocol can be augmented through the addition of a virtual interface
   (e.g., Overlay Multilink Network (OMNI) Interface [OMNI]) and/or
   protocol changes in order to support both wireless single-hop/
   multihop V2V communications and multiple radio technologies in
   vehicular networks.  In such a way, vehicles can communicate with
   each other by V2V communications to share either an emergency
   situation or road hazard information in a highway having multiple
   kinds of radio technologies.






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Appendix B.  Support of Multihop V2X Networking

   The multihop V2X networking can be supported by RPL (IPv6 Routing
   Protocol for Low-Power and Lossy Networks) [RFC6550] and AERO
   (Automatic Extended Route Optimization) [AERO] over OMNI (Overlay
   Multilink Network Interface) [OMNI].

   RPL defines an IPv6 routing protocol for low-power and lossy networks
   (LLN), mostly designed for home automation routing, building
   automation routing, industrial routing, and urban LLN routing.  It
   uses a Destination-Oriented Directed Acyclic Graph (DODAG) to
   construct routing paths for hosts (e.g., IoT devices) in a network.
   The DODAG uses an objective function (OF) for route selection and
   optimization within the network.  A user can use different routing
   metrics to define an OF for a specific scenario.  RPL supports
   multipoint-to-point, point-to-multipoint, and point-to-point traffic,
   and the major traffic flow is the multipoint-to-point traffic.  For
   example, in a highway scenario, a vehicle may not access an RSU
   directly because of the distance of the DSRC coverage (up to 1 km).
   In this case, the RPL can be extended to support a multihop V2I since
   a vehicle can take advantage of other vehicles as relay nodes to
   reach the RSU.  Also, RPL can be extended to support both multihop
   V2V and V2X in the similar way.

   RPL is primarily designed to minimize the control plane activity,
   which is the relative amount of routing protocol exchanges versus
   data traffic; this approach is beneficial for situations where the
   power and bandwidth are scarce (e.g., an IoT LLN where RPL is
   typically used today), but also in situations of high relative
   mobility between the nodes in the network (also known as swarming,
   e.g., within a variable set of vehicles with a similar global motion,
   or a variable set of drones flying toward the same direction).

   To reduce the routing exchanges, RPL leverages a DV approach, which
   does not need a global knowledge of the topology, and only optimizes
   the routes to and from the root, allowing P2P paths to be stretched.
   Although RPL installs its routes proactively, it only maintains them
   lazily, that is, in reaction to actual traffic, or as a slow
   background activity.  Additionally, RPL leverages the concept of an
   objective function (called OF), which allows to adapt the activity of
   the routing protocol to use cases, e.g., type, speed, and quality of
   the radios.  RPL does not need converge, and provides connectivity to
   most nodes most of the time.  The default route toward the root is
   maintained aggressively and may change while a packet progresses
   without causing loops, so the packet will still reach the root.
   There are two modes for routing in RPL such as non-storing mode and
   storing mode.  In non-storing mode, a node inside the mesh/swarm that
   changes its point(s) of attachment to the graph informs the root with



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   a single unicast packet flowing along the default route, and the
   connectivity is restored immediately; this mode is preferable for use
   cases where Internet connectivity is dominant.  On the other hand, in
   storing mode, the routing stretch is reduced, for a better P2P
   connectivity, while the Internet connectivity is restored more
   slowly, during the time for the DV operation to operate hop-by-hop.
   While an RPL topology can quickly scale up and down and fits the
   needs of mobility of vehicles, the total performance of the system
   will also depend on how quickly a node can form an address, join the
   mesh (including Authentication, Authorization, and Accounting (AAA)),
   and manage its global mobility to become reachable from another node
   outside the mesh.

   AERO and OMNI together securely and efficiently address the following
   6 M's of Modern Internetworking for mobile V2V, V2I and V2X Clients:

   1.  Multilink: A Client's ability to coordinate multiple diverse
       underlying data links as a single logical unit (i.e., the OMNI
       interface) to achieve the required communications performance and
       reliability objectives.

   2.  Multinet: The ability to span the OMNI link over a segment
       routing topology with multiple diverse administrative domain
       network segments while maintaining seamless E2E communications
       between mobile Clients and correspondents such as air traffic
       controllers and fleet administrators.

   3.  Mobility: A Client's ability to change network points of
       attachment (e.g., moving between wireless base stations) which
       may result in an underlying interface address change without
       disruptions to ongoing communication sessions with peers over the
       OMNI link.

   4.  Multicast: The ability to send a single network transmission that
       reaches multiple Clients belonging to the same interest group
       without disturbing other Clients not subscribed to the interest
       group.

   5.  Multihop: A mobile Client's V2V relaying capability useful when
       multiple forwarding hops between vehicles may be necessary to
       reach back to an infrastructure access point connection to the
       OMNI link.

   6.  MTU Assurance: The ability to deliver packets of various robust
       sizes between peers without loss due to a link size restriction,
       and to dynamically adjust packet sizes in order to achieve the
       optimal performance for each independent traffic flow.




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Appendix C.  Support of Mobility Management for V2I

   The seamless application communication between two vehicles or
   between a vehicle and an infrastructure node requires mobility
   management in vehicular networks.  The mobility management schemes
   include a host-based mobility scheme, network-based mobility scheme,
   and software-defined networking scheme.

   In the host-based mobility scheme (e.g., MIPv6), an IP-RSU plays a
   role of a home agent.  On the other hand, in the network-based
   mobility scheme (e.g., PMIPv6, an MA plays a role of a mobility
   management controller such as a Local Mobility Anchor (LMA) in
   PMIPv6, which also serves vehicles as a home agent, and an IP-RSU
   plays a role of an access router such as a Mobile Access Gateway
   (MAG) in PMIPv6 [RFC5213].  The host-based mobility scheme needs
   client functionality in IPv6 stack of a vehicle as a mobile node for
   mobility signaling message exchange between the vehicle and home
   agent.  On the other hand, the network-based mobility scheme does not
   need such a client functionality for a vehicle because the network
   infrastructure node (e.g., MAG in PMIPv6) as a proxy mobility agent
   handles the mobility signaling message exchange with the home agent
   (e.g., LMA in PMIPv6) for the sake of the vehicle.

   There are a scalability issue and a route optimization issue in the
   network-based mobility scheme (e.g., PMIPv6) when an MA covers a
   large vehicular network governing many IP-RSUs.  In this case, a
   distributed mobility scheme (e.g., DMM [RFC7429]) can mitigate the
   scalability issue by distributing multiple MAs in the vehicular
   network such that they are positioned closer to vehicles for route
   optimization and bottleneck mitigation in a central MA in the
   network-based mobility scheme.  All these mobility approaches (i.e.,
   a host-based mobility scheme, network-based mobility scheme, and
   distributed mobility scheme) and a hybrid approach of a combination
   of them need to provide an efficient mobility service to vehicles
   moving fast and moving along with the relatively predictable
   trajectories along the roadways.

   In vehicular networks, the control plane can be separated from the
   data plane for efficient mobility management and data forwarding by
   using the concept of Software-Defined Networking (SDN)
   [RFC7149][DMM-FPC].  Note that Forwarding Policy Configuration (FPC)
   in [DMM-FPC], which is a flexible mobility management system, can
   manage the separation of data-plane and control-plane in DMM.  In
   SDN, the control plane and data plane are separated for the efficient
   management of forwarding elements (e.g., switches and routers) where
   an SDN controller configures the forwarding elements in a centralized
   way and they perform packet forwarding according to their forwarding
   tables that are configured by the SDN controller.  An MA as an SDN



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   controller needs to efficiently configure and monitor its IP-RSUs and
   vehicles for mobility management, location management, and security
   services.

Appendix D.  Acknowledgments

   This work was supported by Institute of Information & Communications
   Technology Planning & Evaluation (IITP) grant funded by the Korea
   MSIT (Ministry of Science and ICT) (R-20160222-002755, Cloud based
   Security Intelligence Technology Development for the Customized
   Security Service Provisioning).

   This work was supported in part by the MSIT, Korea, under the ITRC
   (Information Technology Research Center) support program (IITP-
   2021-2017-0-01633) supervised by the IITP.

   This work was supported in part by the IITP grant funded by the MSIT
   (2020-0-00395, Standard Development of Blockchain based Network
   Management Automation Technology).

   This work was supported in part by the French research project
   DataTweet (ANR-13-INFR-0008) and in part by the HIGHTS project funded
   by the European Commission I (636537-H2020).

   This work was supported in part by the Cisco University Research
   Program Fund, Grant # 2019-199458 (3696), and by ANID Chile Basal
   Project FB0008.

Appendix E.  Contributors

   This document is a group work of IPWAVE working group, greatly
   benefiting from inputs and texts by Rex Buddenberg (Naval
   Postgraduate School), Thierry Ernst (YoGoKo), Bokor Laszlo (Budapest
   University of Technology and Economics), Jose Santa Lozanoi
   (Universidad of Murcia), Richard Roy (MIT), Francois Simon (Pilot),
   Sri Gundavelli (Cisco), Erik Nordmark, Dirk von Hugo (Deutsche
   Telekom), Pascal Thubert (Cisco), Carlos Bernardos (UC3M), Russ
   Housley (Vigil Security), Suresh Krishnan (Kaloom), Nancy Cam-Winget
   (Cisco), Fred L.  Templin (The Boeing Company), Jung-Soo Park (ETRI),
   Zeungil (Ben) Kim (Hyundai Motors), Kyoungjae Sun (Soongsil
   University), Zhiwei Yan (CNNIC), YongJoon Joe (LSware), Peter E.  Yee
   (Akayla), and Erik Kline.  The authors sincerely appreciate their
   contributions.

   The following are co-authors of this document:

   Nabil Benamar




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   Department of Computer Sciences, High School of Technology of Meknes,
   Moulay Ismail University, Morocco, Phone: +212 6 70 83 22 36, EMail:
   benamar73@gmail.com

   Sandra Cespedes

   NIC Chile Research Labs, Universidad de Chile, Av.  Blanco Encalada
   1975, Santiago, Chile, Phone: +56 2 29784093, EMail:
   scespede@niclabs.cl

   Jerome Haerri

   Communication Systems Department, EURECOM, Sophia-Antipolis, France,
   Phone: +33 4 93 00 81 34, EMail: jerome.haerri@eurecom.fr

   Dapeng Liu

   Alibaba, Beijing, Beijing 100022, China, Phone: +86 13911788933,
   EMail: max.ldp@alibaba-inc.com

   Tae (Tom) Oh

   Department of Information Sciences and Technologies, Rochester
   Institute of Technology, One Lomb Memorial Drive, Rochester, NY
   14623-5603, USA, Phone: +1 585 475 7642, EMail: Tom.Oh@rit.edu

   Charles E.  Perkins

   Futurewei Inc., 2330 Central Expressway, Santa Clara, CA 95050, USA,
   Phone: +1 408 330 4586, EMail: charliep@computer.org

   Alexandre Petrescu

   CEA, LIST, CEA Saclay, Gif-sur-Yvette, Ile-de-France 91190, France,
   Phone: +33169089223, EMail: Alexandre.Petrescu@cea.fr

   Yiwen Chris Shen

   Department of Computer Science & Engineering, Sungkyunkwan
   University, 2066 Seobu-Ro, Jangan-Gu, Suwon, Gyeonggi-Do 16419,
   Republic of Korea, Phone: +82 31 299 4106, Fax: +82 31 290 7996,
   EMail: chrisshen@skku.edu, URI: https://chrisshen.github.io

   Michelle Wetterwald

   FBConsulting, 21, Route de Luxembourg, Wasserbillig, Luxembourg
   L-6633, Luxembourg, EMail: Michelle.Wetterwald@gmail.com




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Author's Address

   Jaehoon (Paul) Jeong (editor)
   Department of Computer Science and Engineering
   Sungkyunkwan University
   2066 Seobu-Ro, Jangan-Gu
   Suwon
   Gyeonggi-Do
   16419
   Republic of Korea

   Phone: +82 31 299 4957
   Email: pauljeong@skku.edu
   URI:   http://iotlab.skku.edu/people-jaehoon-jeong.php





































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