IP Wireless Access in Vehicular Environments (IPWAVE): Problem Statement and Use Cases
draft-ietf-ipwave-vehicular-networking-04

Abstract

This document discusses the problem statement and use cases on IP-based vehicular networks, which are considered a key component of Intelligent Transportation Systems (ITS). The main topics of vehicular networking are vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), and vehicle-to-everything (V2X) networking. First, this document surveys use cases using V2V, V2I, and V2X networking. Second, it analyzes proposed protocols for IP-based vehicular networking and highlights the limitations and difficulties found on those protocols. Third, it presents a problem exploration for key aspects in IP-based vehicular networking, such as IPv6 Neighbor Discovery, Mobility Management, and Security & Privacy. For each key aspect, this document discusses a problem statement to analyze the gap between the state-of-the-art techniques and requirements in IP-based vehicular networking.

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This Internet-Draft will expire on January 17, 2019.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Use Cases
• 3.1. V2V
• 3.2. V2I
• 3.3. V2X
• 4. Analysis for Current Protocols
• 4.1. Current Protocols for Vehicular Networking
• 4.1.1. IPv6 over 802.11-OCB
• 4.1.2. IP Address Autoconfiguration
• 4.1.3. Routing
• 4.1.4. Mobility Management
• 4.1.5. DNS Naming Service
• 4.1.6. Service Discovery
• 4.1.7. Security and Privacy
• 4.2. General Problems
• 4.2.1. Vehicular Network Architecture
• 4.2.2. Latency
• 4.2.3. Security
• 4.2.4. Pseudonym Handling
• 5. Problem Exploration
• 5.1. Neighbor Discovery
• 5.1.1. Link Model
• 5.1.2. MAC Address Pseudonym
• 5.1.3. Prefix Dissemination/Exchange
• 5.1.4. Routing
• 5.2. Mobility Management
• 5.3. Security and Privacy
• 6. Security Considerations
• 7. Informative References
• Appendix A. Relevant Work Items to IPWAVE
• A.1. Vehicle Identity Management
• A.2. Multihop V2X
• A.3. Multicast
• A.4. DNS Naming Services and Service Discovery
• A.5. IPv6 over Cellular Networks
• A.5.1. Cellular V2X (C-V2X) Using 4G-LTE
• A.5.2. Cellular V2X (C-V2X) Using 5G
• Appendix B. Changes from draft-ietf-ipwave-vehicular-networking-03
• Appendix C. Acknowledgments
• Appendix D. Contributors
• Author's Address

1. Introduction

Vehicular networks have been focused on the driving safety, driving efficiency, and entertainment in road networks. The Federal Communications Commission (FCC) in the US allocated wireless channels for Dedicated Short-Range Communications (DSRC) [DSRC], service in the Intelligent Transportation Systems (ITS) Radio Service in the 5.850 - 5.925 GHz band (5.9 GHz band). DSRC-based wireless communications can support vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), and vehicle-to-everything (V2X) networking. Also, the European Union (EU) made a law for radio spectrum for safety-related applications of ITS with the frequency band of 5.875 - 5.905 GHz, which is called Commission Decision 2008/671/EC [EU-2008-671-EC].

For driving safety services based on the DSRC, IEEE has standardized Wireless Access in Vehicular Environments (WAVE) standards, such as IEEE 802.11p [IEEE-802.11p], IEEE 1609.2 [WAVE-1609.2], IEEE 1609.3 [WAVE-1609.3], and IEEE 1609.4 [WAVE-1609.4]. Note that IEEE 802.11p has been published as IEEE 802.11 Outside the Context of a Basic Service Set (OCB) [IEEE-802.11-OCB] in 2012. Along with these WAVE standards, IPv6 and Mobile IP protocols (e.g., MIPv4 and MIPv6) can be extended to vehicular networks [RFC8200][RFC5944][RFC6275]. Also, ETSI has standardized a GeoNetworking (GN) protocol [ETSI-GeoNetworking] and a protocol adaptation sub-layer from GeoNetworking to IPv6 [ETSI-GeoNetwork-IP]. In addition, ISO has standardized a standard specifying the IPv6 network protocols and services for Communications Access for Land Mobiles (CALM) [ISO-ITS-IPv6].

This document discusses problem statements and use cases related to IP-based vehicular networking for Intelligent Transportation Systems (ITS), which is IP Wireless Access in Vehicular Environments (IPWAVE). First, it surveys the use cases for using V2V, V2I, and V2X networking in the ITS. Second, for literature review, it analyzes proposed protocols for IP-based vehicular networking and highlights the limitations and difficulties found on those protocols. Third, for problem statement, it presents a problem exploration with key aspects in IPWAVE, such as IPv6 Neighbor Discovery, Mobility Management, and Security & Privacy. For each key aspect, it discusses a problem statement to analyze the gap between the state-of-the-art techniques and requirements in IP-based vehicular networking. Also, it also discusses relevant work items to IPWAVE, such as Vehicle Identities Management, Multihop V2X Communications, Multicast, DNS Naming Services, Service Discovery, and IPv6 over Cellular Networks. Therefore, with the problem statement, this document will open a door to develop key protocols for IPWAVE that will be essential to IP-based vehicular networks.

2. Terminology

This document uses the following definitions:

• WAVE: Acronym for "Wireless Access in Vehicular Environments" [WAVE-1609.0].
• DMM: Acronym for "Distributed Mobility Management" [RFC7333][RFC7429].
• Road-Side Unit (RSU): A node that has physical communication devices (e.g., DSRC, Visible Light Communication, 802.15.4, LTE-V2X, etc.) for wireless communications with vehicles and is also connected to the Internet as a router or switch for packet forwarding. An RSU is deployed either at an intersection or in a road segment.
• On-Board Unit (OBU): A node that has a DSRC device for wireless communications with other OBUs and RSUs. An OBU is mounted on a vehicle. It is assumed that a radio navigation receiver (e.g., Global Positioning System (GPS)) is included in a vehicle with an OBU for efficient navigation.
• Vehicle Detection Loop (or Loop Detector): An inductive device used for detecting vehicles passing or arriving at a certain point, for instance approaching a traffic light or in motorway traffic. The relatively crude nature of the loop's structure means that only metal masses above a certain size are capable of triggering the detection.
• Traffic Control Center (TCC): A node that maintains road infrastructure information (e.g., RSUs, traffic signals, and loop detectors), vehicular traffic statistics (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 included in a vehicular cloud for vehicular networks.

3. Use Cases

This section provides 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).

3.1. V2V

The use cases of V2V networking discussed in this section include

• Context-aware navigation for driving safety and collision avoidance;
• Cooperative adaptive cruise control in an urban roadway;
• Platooning in a highway;
• Cooperative environment sensing.

These four techniques will be important elements for self-driving vehicles.

Context-Aware Safety Driving (CASD) navigator [CASD] can help drivers to drive safely by letting the drivers recognize dangerous obstacles and situations. That is, CASD navigator displays obstables 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, such as the Line-of-Sight unsafe, Non-Line-of-Sight unsafe and safe situations. This action plan can be performed among vehicles through V2V networking.

Cooperative Adaptive Cruise Control (CACC) [CA-Cuise-Control] helps 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. CACC can help adjacent vehicles to efficiently adjust their speed in a cascade way through V2V networking.

Platooning [Truck-Platooning] allows a series of vehicles (e.g., trucks) to move together with a very short inter-distance. 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). This 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 from various sensors, such as radars, LiDARs and cameras, mounted on them with other vehicles and pedestrians. [Automotive-Sensing] introduces a millimeter-wave vehicular communication for massive automotive sensing. Data generated by those sensors can be substantially large, and these data shall be routed to different destinations. In addition, from the perspective of driverless vehicles, it is expected that driverless vehicles can be mixed with driver vehicles. Through cooperative environment sensing, driver vehicles can use environmental information sensed by driverless vehicles for better interaction with the context.

3.2. V2I

The use cases of V2I networking discussed in this section include

• Navigation service;
• Energy-efficient speed recommendation service;
• Accident notification service.

A navigation service, such as the Self-Adaptive Interactive Navigation Tool (called SAINT) [SAINT], using V2I networking interacts with TCC for the global road traffic optimization and can guide individual vehicles for appropriate navigation paths in real time. The enhanced SAINT (called SAINT+) [SAINTplus] can give the fast moving paths for emergency vehicles (e.g., ambulance and fire engine) toward accident spots while providing other vehicles with efficient detour paths.

A TCC can recommend an energy-efficient speed to a vehicle driving in different traffic environments. [Fuel-Efficient] studies fuel-efficient route and speed plans for platooned trucks.

The emergency communication between accident vehicles (or emergency vehicles) and TCC can be performed via either 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, such as 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 FirstNet's network core. The current RAN is mainly constructed by 4G-LTE for the communication between a vehicle and an infrastructure node (i.e., V2I) [FirstNet-Report], but DSRC-based vehicular networks can be used for V2I in near future [DSRC].

3.3. V2X

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

A pedestrian protection service, such as Safety-Aware Navigation Application (called SANA) [SANA], using V2I2P networking can reduce the collision of a pedestrian and a vehicle, which have a smartphone, in a road network. Vehicles and pedestrians can communicate with each other via an RSU that delivers scheduling information for wireless communication to save the smartphones' battery.

4. Analysis for Current Protocols

4.1. Current Protocols for Vehicular Networking

We analyze the current protocols from the following aspects:

• IPv6 over 802.11-OCB;
• IP address autoconfiguration;
• Routing;
• Mobility management;
• DNS naming service;
• Service discovery;
• Security and privacy.

4.1.1. IPv6 over 802.11-OCB

For IPv6 packets transporting over IEEE 802.11-OCB, [IPv6-over-802.11-OCB] specifies several details, such as Maximum Transmission Unit (MTU), frame format, link-local address, address mapping for unicast and multicast, stateless autoconfiguration, and subnet structure. Especially, an Ethernet Adaptation (EA) layer is in charge of transforming some parameters between IEEE 802.11 MAC layer and IPv6 network layer, which is located between IEEE 802.11-OCB's logical link control layer and IPv6 network layer.

4.1.2. IP Address Autoconfiguration

For IP address autoconfiguration, Fazio et al. proposed a vehicular address configuration (VAC) scheme using DHCP where elected leader-vehicles provide unique identifiers for IP address configurations [Address-Autoconf]. Kato et al. proposed an IPv6 address assignment scheme using lane and position information [Address-Assignment]. Baldessari et al. proposed an IPv6 scalable address autoconfiguration scheme called GeoSAC for vehicular networks [GeoSAC]. Wetterwald et al. conducted a comprehensive study of the cross-layer identities management in vehicular networks using multiple access network technologies, which constitutes a fundamental element of the ITS architecture [Identity-Management].

4.1.3. Routing

For routing, Tsukada et al. presented a work that aims at combining IPv6 networking and a Car-to-Car Network routing protocol (called C2CNet) proposed by the Car2Car Communication Consortium (C2C-CC), which is an architecture using a geographic routing protocol [VANET-Geo-Routing]. Abrougui et al. presented a gateway discovery scheme for VANET, called Location-Aided Gateway Advertisement and Discovery (LAGAD) mechanism [LAGAD].

4.1.4. Mobility Management

For mobility management, Chen et al. tackled the issue of network fragmentation in VANET environments [IP-Passing-Protocol] by proposing a protocol that can postpone the time to release IP addresses to the DHCP server and select a faster way to get the vehicle's new IP address, when the vehicle density is low or the speeds of vehicles are varied. Nguyen et al. proposed a hybrid centralized-distributed mobility management called H-DMM to support highly mobile vehicles [H-DMM]. [NEMO-LMS] proposed an architecture to enable IP mobility for moving networks using a network-based mobility scheme based on PMIPv6. Chen et al. proposed a network mobility protocol to reduce handoff delay and maintain Internet connectivity to moving vehicles in a highway [NEMO-VANET]. Lee et al. proposed P-NEMO, which is a PMIPv6-based IP mobility management scheme to maintain the Internet connectivity at the vehicle as a mobile network, and provides a make-before-break mechanism when vehicles switch to a new access network [PMIP-NEMO-Analysis]. Peng et al. proposed a novel mobility management scheme for integration of VANET and fixed IP networks [VNET-MM]. Nguyen et al. extended their previous works on a vehicular adapted DMM considering a Software-Defined Networking (SDN) architecture [SDN-DMM].

4.1.5. DNS Naming Service

For DNS naming service, Multicast DNS (mDNS) [RFC6762] allows devices in one-hop communication range to resolve each other's DNS name into the corresponding IP address in multicast. DNS Name Autoconfiguration (DNSNA) [ID-DNSNA] proposes a DNS naming service for Internet-of-Things (IoT) devices in a large-scale network.

4.1.6. Service Discovery

For service discovery, as a popular existing service discovery protocol, DNS-based Service Discovery (DNS-SD) [RFC6763] with mDNS [RFC6762] provides service discovery. Vehicular ND [ID-Vehicular-ND] proposes an extension of IPv6 ND for the prefix and service discovery.

4.1.7. Security and Privacy

For security and privacy, Fernandez et al. proposed a secure vehicular IPv6 communication scheme using Internet Key Exchange version 2 (IKEv2) and Internet Protocol Security (IPsec) [Securing-VCOMM]. Moustafa et al. proposed a security scheme providing authentication, authorization, and accounting (AAA) services in vehicular networks [VNET-AAA].

4.2. General Problems

This section describes a vehicular network architecture for V2V, V2I, and V2X communications. Then it analyzes the limitations of the current protocols for vehicular networking.

4.2.1. Vehicular Network Architecture

Figure 1 shows an architecture for V2I and V2V networking in a road network. The two RSUs (RSU1 and RSU2) are deployed in the road network and are connected to a Vehicular Cloud through the Internet. TCC is connected to the Vehicular Cloud and the two vehicles (Vehicle1 and Vehicle2) are wirelessly connected to RSU1, and the last vehicle (Vehicle3) is wirelessly connected to RSU2. Vehicle1 can communicate with Vehicle2 via V2V communication, and Vehicle2 can communicate with Vehicle3 via V2V communication. Vehicle1 can communicate with Vehicle3 via RSU1 and RSU2 via V2I communication.

In vehicular networks, unidirectional links exist and must be considered for wireless communications. Also, in the vehicular networks, control plane must be separated from data plane for efficient mobility management and data forwarding. ID/Pseudonym change for privacy requires a lightweight DAD. IP tunneling over the wireless link should be avoided for performance efficiency. The mobility information of a mobile device (e.g., vehicle), such as trajectory, position, speed, and direction, can be used by the mobile device and infrastructure nodes (e.g., TCC and RSU) for the accommodation of proactive protocols because it is usually equipped with a GPS receiver. Vehicles can use the TCC as its Home Network, so the TCC maintains the mobility information of vehicles for location management.

                            *-------------*
                           *               *         .-------.
                          * Vehicular Cloud *<------>|  TCC  |
                           *               *         ._______.
                            *-------------*
                           ^               ^
                           |               |
                           |               |
                           v               v
                   .--------.             .--------.
                   |  RSU1  |<----------->|  RSU2  |
                   .________.             .________.
                   ^        ^                  ^
                   :        :                  :
                   :        :                  :
                   v        v                  v
           .--------.      .--------.      .--------. 
           |Vehicle1|=>    |Vehicle2|=>    |Vehicle3|=>
           |        |<....>|        |<....>|        |
           .________.      .________.      .________.


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

Figure 1: A Vehicular Network Architecture for V2I and V2V Networking

Cespedes et al. proposed a vehicular IP in WAVE called VIP-WAVE for I2V and V2I networking [VIP-WAVE]. The standard WAVE does not support both seamless communications for Internet services and multi-hop communications between a vehicle and an infrastructure node (e.g., RSU), either. To overcome these limitations of the standard WAVE, VIP-WAVE enhances the standard WAVE by the following three schemes: (i) an efficient mechanism for the IPv6 address assignment and DAD, (ii) on-demand IP mobility based on Proxy Mobile IPv6 (PMIPv6), and (iii) one-hop and two-hop communications for I2V and V2I networking.

Baccelli et al. provided an analysis of the operation of IPv6 as it has been described by the IEEE WAVE standards 1609 [IPv6-WAVE]. This analysis confirms that the use of the standard IPv6 protocol stack in WAVE is not sufficient. It recommebs that the IPv6 addressing assignment should follow considerations for ad-hoc link models, defined in [RFC5889] for nodes' mobility and link variability.

Petrescu et al. proposed the joint IP networking and radio architecture for V2V and V2I communication in [Joint-IP-Networking]. The proposed architecture considers an IP topology in a similar way as a radio link topology, in the sense that an IP subnet would correspond to the range of 1-hop vehicular communication. This architecture defines three types of vehicles: Leaf Vehicle, Range Extending Vehicle, and Internet Vehicle.

4.2.1.1. V2I-based Internetworking

This section discusses the internetworking between a vehicle's moving network and an RSU's fixed network.

                        (*)<..........>(*)
                         |              | 2001:DB8:1:1::/64 
.------------------------------.  .---------------------------------.
|                        |     |  |     |                           |
| .-------. .------. .-------. |  | .-------. .------. .-------.    |
| | Host1 | |RDNSS1| |Router1| |  | |Router3| |RDNSS2| | Host3 |    |
| ._______. .______. ._______. |  | ._______. .______. ._______.    |
|     ^        ^         ^     |  |     ^         ^        ^        |
|     |        |         |     |  |     |         |        |        |
|     v        v         v     |  |     v         v        v        |
| ---------------------------- |  | ------------------------------- |
| 2001:DB8:10:1::/64 ^         |  |     ^ 2001:DB8:20:1::/64        | 
|                    |         |  |     |                           |
|                    v         |  |     v                           |
| .-------.      .-------.     |  | .-------. .-------.   .-------. |
| | Host2 |      |Router2|     |  | |Router4| |Server1|...|ServerN| |
| ._______.      ._______.     |  | ._______. ._______.   ._______. |
|     ^              ^         |  |     ^         ^           ^     |
|     |              |         |  |     |         |           |     |
|     v              v         |  |     v         v           v     |
| ---------------------------- |  | ------------------------------- |
|  2001:DB8:10:2::/64          |  |       2001:DB8:20:2::/64        |
.______________________________.  ._________________________________.
   Vehicle1 (Moving Network1)            RSU1 (Fixed Network1)

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

Figure 2: Internetworking between Vehicle Network and RSU Network

As shown in Figure 2, the vehicle's moving network and the RSU's fixed network are self-contained networks having multiple subnets and having an edge router for the communication with another vehicle or RSU. The method of prefix assignment for each subnet inside the vehicle's mobile network and the RSU's fixed network is out of scope for this document. Internetworking between two internal networks via either V2I or V2V communication requires an exchange of network prefix and other parameters.

The network parameter discovery collects networking information for an IP communication between a vehicle and an RSU or between two neighboring vehicles, such as link layer, MAC layer, and IP layer information. The link layer information includes wireless link layer parameters, such as wireless media (e.g., IEEE 802.11-OCB, LTE D2D (Device to Device), Bluetooth, and LiFi (Light Fidelity)) and a transmission power level. Note that LiFi is a technology for light-based wireless communication between devices in order to transmit both data and position. The MAC layer information includes the MAC address of an external network interface for the internetworking with another vehicle or RSU. The IP layer information includes the IP address and prefix of an external network interface for the internetworking with another vehicle or RSU.

Once the network parameter discovery and prefix exchange operations have been performed, packets can be transmitted between the vehicle's moving network and the RSU's fixed network. DNS services should be supported to enable name resolution for hosts or servers residing either in the vehicle's moving network or the RSU's fixed network. For these DNS services, a recursive DNS server (RDNSS) within each internal network of a vehicle or RSU can be used for the hosts or servers.

Figure 2 shows internetworking between the vehicle's moving network and the RSU's fixed network. There exists an internal network (Moving Network1) inside Vehicle1. Vehicle1 has the DNS Server (RDNSS1), the two hosts (Host1 and Host2), and the two routers (Router1 and Router2). There exists another internal network (Fixed Network1) inside RSU1. RSU1 has the DNS Server (RDNSS2), one host (Host3), the two routers (Router3 and Router4), and the collection of servers (Server1 to ServerN) for various services in the road networks, such as the emergency notification and navigation. Vehicle1's Router1 (called mobile router) and RSU1's Router3 (called fixed router) use 2001:DB8:1:1::/64 for an external link (e.g., DSRC) for I2V networking.

4.2.1.2. V2V-based Internetworking

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

Figure 3 shows internetworking between the moving networks of two neighboring vehicles. There exists an internal network (Moving Network1) inside Vehicle1. Vehicle1 has the DNS Server (RDNSS1), the two hosts (Host1 and Host2), and the two routers (Router1 and Router2). There exists another internal network (Moving Network2) inside Vehicle2. Vehicle2 has the DNS Server (RDNSS2), the two hosts (Host3 and Host4), and the two routers (Router3 and Router4). Vehicle1's Router1 (called mobile router) and Vehicle2's Router3 (called mobile router) use 2001:DB8:1:1::/64 for an external link (e.g., DSRC) for V2V networking.

                        (*)<..........>(*)
                         |              | 2001:DB8:1:1::/64 
.------------------------------.  .---------------------------------.
|                        |     |  |     |                           |
| .-------. .------. .-------. |  | .-------. .------. .-------.    |
| | Host1 | |RDNSS1| |Router1| |  | |Router3| |RDNSS2| | Host3 |    |
| ._______. .______. ._______. |  | ._______. .______. ._______.    |
|     ^        ^         ^     |  |     ^         ^        ^        |
|     |        |         |     |  |     |         |        |        |
|     v        v         v     |  |     v         v        v        |
| ---------------------------- |  | ------------------------------- |
| 2001:DB8:10:1::/64 ^         |  |     ^ 2001:DB8:30:1::/64        | 
|                    |         |  |     |                           |
|                    v         |  |     v                           |
| .-------.      .-------.     |  | .-------.      .-------.        |
| | Host2 |      |Router2|     |  | |Router4|      | 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 Vehicle Networks

The differences between IPWAVE (including Vehicular Ad Hoc Networks (VANET)) and Mobile Ad Hoc Networks (MANET) are as follows:

• IPWAVE is not power-constrained operation;
• Traffic can be sourced or sinked outside of IPWAVE;
• IPWAVE shall support both distributed and centralized operations;
• No "sleep" period operation is required for energy saving.

4.2.2. Latency

The communication delay (i.e., latency) between two vehicular nodes (vehicle and RSU) should be bounded to a certain threshold. For IP-based safety applications (e.g., context-aware navigation, adaptive cruise control, and platooning) in vehicular network, this bounded data delivery is critical. The real implementations for such applications are not available, so the feasibility of IP-based safety applications is not tested yet.

4.2.3. Security

Security protects vehicles roaming in road networks from the attacks of malicious vehicular nodes, which are controlled by hackers. For safety applications, the cooperation among vehicles is assumed. Malicious vehicular nodes may disseminate wrong driving information (e.g., location, speed, and direction) to make driving be unsafe. Sybil attack, which tries to illude a vehicle with multiple false identities, disturbs a vehicle in taking a safe maneuver. Applications on IP-based vehicular networking, which are resilient to such a sybil attack, are not developed and tested yet.

4.2.4. Pseudonym Handling

For the protection of privacy, pseudonym for a vehicle's network interface is used, which the interface's identifier is changed periodically. Such a pseudonym affects an IPv6 address based on the network interface's identifier, and a transport-layer session with an IPv6 address pair. The pseudonym handling is not implemented and test yet for applications on IP-based vehicular networking.

5. Problem Exploration

This section discusses key work items for IPWAVE, such as neighbor discovery, mobility management, and security & privacy.

5.1. Neighbor Discovery

Neighbor Discovery (ND) [RFC4861] is a core part of the IPv6 protocol suite. This section discusses the need for modifying ND for use with vehicular networking (e.g., V2V, V2I, and V2X). The vehicles are moving fast within the communication coverage of a vehicular node (e.g., vehicle and RSU). The external link between two vehicular nodes can be used for vehicular networking, as shown in Figure 2 and Figure 3.

ND time-related parameters such as router lifetime and Neighbor Advertisement (NA) interval should be adjusted for high-speed vehicles and vehicle density. As vehicles move faster, the NA interval should decrease for the NA messages to reach the neighboring vehicles promptly. Also, as vehicle density is higher, the NA interval should increase for the NA messages to collide with other NA messages with lower collision probability.

5.1.1. Link Model

IPv6 protocols work under certain assumptions for the link model that do not necessarily hold in WAVE [IPv6-WAVE]. For instance, some IPv6 protocols assume symmetry in the connectivity among neighboring interfaces. However, interference and different levels of transmission power may cause unidirectional links to appear in a WAVE link model.

Also, in an IPv6 link, it is assumed that all interfaces which are configured with the same subnet prefix are on the same IP link. Hence, there is a relationship between link and prefix, besides the different scopes that are expected from the link-local and global types of IPv6 addresses. Such a relationship does not hold in a WAVE link model due to node mobility and highly dynamic topology.

Thus, IPv6 ND should be extended to support the concept of a link for an IPv6 prefix in terms of multicast in VANET.

5.1.2. MAC Address Pseudonym

As the ETSI GeoNetworking, 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 should be updated. For the continuity of an end-to-end transport-layer (e.g., TCP, UDP, and SCTP) session, the IP addresses of the transport-layer session should be notified to both the end points and the packets of the session should be forwarded to their destinations with the changed network interface identifier and IPv6 address.

5.1.3. Prefix Dissemination/Exchange

A vehicle and an RSU can have their internal network, as shown in Figure 2 and Figure 3. In this case, nodes in within the internal networks of two vehicular nodes (e.g., vehicle and RSU) want to communicate with each other. For this communication, the network prefix dissemination or exchange is required. It is assumed that a vehicular node has an external network interface and its internal network. The standard IPv6 ND needs to be extended for the communication between the internal-network vehicular nodes by letting each of them know the other side's prefix with a new ND option [ID-Vehicular-ND].

5.1.4. Routing

For Neighbor Discovery in vehicular networks (called vehicular ND), Ad Hoc routing is required for either unicast or multicast in the links in a connected VANET with the same IPv6 prefix [GeoSAC]. Also, a rapid DAD should be supported to prevent or reduce IPv6 address conflicts in such links.

5.2. Mobility Management

The seamless connectivity and timely data exchange between two end points requires an efficient mobility management including location management and handover. Most of vehicles are equipped with a GPS navigator as a dedicated navigation system or a smartphone App. With this GPS navigator, an efficient mobility management is possible by vehicles periodically reporting their current position and trajectory (i.e., navigation path) to TCC. TCC can predict the future positions of the vehicles with their mobility information (i.e., the current position, speed, direction, and trajectory) for location management.

With the prediction of the vehicle mobility, TCC can support RSUs to perform DAD, data packet routing, and horizontal/vertical handover in a proactive manner. When it is assigned a new IPv6 address belonging to a different subnet,a vehicle can skip the DAD operation, reducing IPv6 control traffic overhead. RSUs can efficiently forward data packets from the wired network to a moving destination vehicle along its trajectory. RSUs can smoothly perform handover for the sake of a moving vehicle along its trajectory.

5.3. Security and Privacy

Security and privacy are paramount in the V2I, V2V, and V2X networking in vehicular networks. Only authorized vehicles should be allowed to use vehicular networking. Also, in-vehicle devices and mobile devices in a vehicle need to communicate with other in-vehicle devices and mobile devices in another vehicle, and other servers in an RSU in a secure way.

A Vehicle Identification Number (VIN) and a user certificate along with in-vehicle device's identifier generation can be used to efficiently authenticate a vehicle or a user through a road infrastructure node (e.g., RSU) connected to an authentication server in TCC. Also, Transport Layer Security (TLS) certificates can be used for secure end-to-end vehicle communications.

For secure V2I communication, a secure channel between a mobile router in a vehicle and a fixed router in an RSU should be established, as shown in Figure 2. Also, for secure V2V communication, a secure channel between a mobile router in a vehicle and a mobile router in another vehicle should be established, as shown in Figure 3.

To prevent an adversary from tracking a vehicle with its MAC address or IPv6 address, MAC address pseudonym should be provided to the vehicle; that is, each vehicle should periodically update its MAC address and the corresponding IPv6 address as suggested in [RFC4086][RFC4941]. Such an update of the MAC and IPv6 addresses should not interrupt the end-to-end communications between two vehicular nodes (e.g., vehicle and RSU) in terms of transport layer.

6. Security Considerations

This document discussed security and privacy for IP-based vehicular networking.

The security and privacy for key components in IP-based vehicular networking, such as neighor discovery and mobility management, needs to be analyzed in depth.

7. Informative References

Appendix A. Relevant Work Items to IPWAVE

This section discusses relevant work items to IPWAVE: (i) vehicle identity management; (ii) multihop V2X; (iii) multicast; (iv) DNS naming services and service discovery; (v) IPv6 over cellular networks.

A.1. Vehicle Identity Management

A vehicle can have multiple network interfaces using different access network technologies [Identity-Management]. These multiple network interfaces mean multiple identities. To identify a vehicle with multiple indenties, a Vehicle Identification Number (VIN) can be used as a globally unique vehicle identifier.

To support the seamless connectivity over the multiple identities, a cross-layer network architecture is required with vertical handover functionality [Identity-Management]. Also, an AAA service for multiple identities should be provided to vehicles in an efficient way to allow horizontal handover as well as vertical handover; note that AAA stands for Authentication, Authorization, and Accounting.

A.2. Multihop V2X

Multihop packet forwarding among vehicles in 802.11-OCB mode shows an unfavorable performance due to the common known broadcast-storm problem [Broadcast-Storm]. This broadcast-storm problem can be mitigated by the coordination (or scheduling) of a cluster head in a connected VANET or an RSU in an intersection area, which is a coordinator for the access to wireless channels.

A.3. Multicast

IP multicast in vehicular network environments is especially useful for various services. For instance, an automobile manufacturer can multicast a particular group/class/type of vehicles for service notification. As another example, a vehicle or an RSU can disseminate alert messages in a particular area [Multicast-Alert].

In general IEEE 802 wireless media, some performance issues about multicast are found in [Multicast-802]. Since serveral procedures and functions based on IPv6 use multicast for control-plane messages, such as Neighbor Discovery (called ND) and Service Discovery, [Multicast-802] describes that the ND process may fail due to unreliable wireless link, causing failure of the DAD process. Also, the Router Advertisement messages can be lost in multicasting.

A.4. DNS Naming Services and Service Discovery

When two vehicular nodes communicate with each other with the DNS name of the partner node, DNS naming service (i.e., DNS name resolution) is required. As shown in Figure 2 and Figure 3, a recursive DNS server (called RDNSS) within an internal network can perform such DNS name resolution for the sake of other vehicular nodes.

A service discovery service is required for an application in a vehicular node to search for another application or server in another vehicular node, which resides in either the same internal network or the other internal network. In V2I or V2V networking, as shown in Figure 2 and Figure 3, such a service discovery service can be provided by either DNS-based Service Discovery (DNS-SD) [RFC6763] with mDNS [RFC6762] or the vehicular ND with a new option for service discovery [ID-Vehicular-ND].

A.5. IPv6 over Cellular Networks

Recently, 3GPP has announced a new technical specification, Release 14 (3GPP-R14), which proposes an architecture enhancements for V2X services using the modified sidelink interface that originally is designed for the LTE-D2D communications. 3GPP-R14 regulates that the V2X services only support IPv6 implementation. 3GPP is also investigating and discussing the evolved V2X services in the next generation cellular networks, i.e., 5G new radio (5G-NR), for advanced V2X communications and automated vehicles' applications.

A.5.1. Cellular V2X (C-V2X) Using 4G-LTE

Before 3GPP-R14, some researchers have studied the potential usage of C-V2X communications. For example, [VMaSC-LTE] explores a multihop cluster-based hybrid architecture using both DSRC and LTE for safety message dissemination. Most of the research consider a short message service for safety instead of IP datagram forwarding. In other C-V2X research, the standard IPv6 is assumed.

The 3GPP technical specification [TS-23.285-3GPP] states that both IP based and non-IP based V2X messages are supported, and only IPv6 is supported for IP based messages. Moreover, [TS-23.285-3GPP] instructs that a UE autoconfigures a link- local IPv6 address by following [RFC4862], but without sending Neighbor Solicitation and Neighbor Advertisement messages for DAD.

A.5.2. Cellular V2X (C-V2X) Using 5G

The emerging services, functions and applications in automotive industry spurs ehhanced V2X (eV2X)-based services in the future 5G era. The 3GPP Technical Report [TR-22.886-3GPP] is studying new use cases for V2X using 5G in the future.

Appendix B. Changes from draft-ietf-ipwave-vehicular-networking-03

The following changes are made from draft-ietf-ipwave-vehicular-networking-03:

• EU wireless channel allocation (frequency band 5.875 - 5.905 GHz) for vehicular networking was specified in Section 1.
• Relevant work items to IPWAVE is discussed in Appendix A as follows: (i) vehicle identity management; (ii) multihop V2X; (iii) multicast; (iv) DNS naming services and service discovery; (v) IPv6 over cellular networks.

Appendix C. Acknowledgments

This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2017R1D1A1B03035885).

This work was supported in part by Global Research Laboratory Program through the NRF funded by the Ministry of Science and ICT (MSIT) (NRF-2013K1A1A2A02078326) and by the DGIST R&D Program of the MSIT (18-EE-01).

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).

Appendix D. 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), and Sri Gundavelli (Cisco). The authors sincerely appreciate their contributions.

The following are co-authors of this document:

Nabil Benamar
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
Department of Electrical Engineering
Universidad de Chile
Av. Tupper 2007, Of. 504
Santiago, 8370451
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: http://iotlab.skku.edu/people-chris-shen.php

Michelle Wetterwald
FBConsulting
21, Route de Luxembourg
Wasserbillig, Luxembourg L-6633
Luxembourg


EMail: Michelle.Wetterwald@gmail.com

Author's Address