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IPWAVE Working Group                                            J. Jeong
Internet-Draft                                                   Y. Shen
Intended status: Standards Track                                Z. Xiang
Expires: May 7, 2020                             Sungkyunkwan University
                                                             S. Cespedes
                                                 NIC Chile Research Labs
                                                        November 4, 2019


      Vehicular Neighbor Discovery for IP-Based Vehicular Networks
           draft-jeong-ipwave-vehicular-neighbor-discovery-08

Abstract

   This document specifies a Vehicular Neighbor Discovery (VND) as an
   extension of IPv6 Neighbor Discovery (ND) for IP-based vehicular
   networks.  An optimized Address Registration and a multihop Duplicate
   Address Detection (DAD) mechanism are performed for having operation
   efficiency and also saving both wireless bandwidth and vehicle
   energy.  Also, three new ND options for prefix discovery, service
   discovery, and mobility information report are defined to announce
   the network prefixes and services inside a vehicle (i.e., a vehicle's
   internal network).

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 7, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents



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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Link Model  . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  ND Optimization . . . . . . . . . . . . . . . . . . . . .   6
     4.3.  Design Goals  . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Vehicular Network Architecture  . . . . . . . . . . . . . . .   7
   6.  ND Extension for Prefix and Service Discovery . . . . . . . .   8
     6.1.  Vehicular Prefix Information Option . . . . . . . . . . .   8
     6.2.  Vehicular Service Information Option  . . . . . . . . . .   9
     6.3.  Vehicular Mobility Information Option . . . . . . . . . .  10
     6.4.  Vehicular Neighbor Discovery  . . . . . . . . . . . . . .  11
     6.5.  Message Exchange Procedure for V2I Networking . . . . . .  12
   7.  Address Registration and Duplicate Address Detection  . . . .  13
     7.1.  Address Autoconfiguration . . . . . . . . . . . . . . . .  14
     7.2.  Address Registration  . . . . . . . . . . . . . . . . . .  14
     7.3.  Multihop Duplicate Address Detection  . . . . . . . . . .  15
       7.3.1.  DAD without Intermediate Vehicle  . . . . . . . . . .  15
       7.3.2.  DAD with one Intermediate Vehicle . . . . . . . . . .  17
       7.3.3.  DAD with multiple Intermediate Vehicles . . . . . . .  18
     7.4.  Pseudonym Handling  . . . . . . . . . . . . . . . . . . .  19
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  20
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  21
   Appendix A.  Changes from draft-jeong-ipwave-vehicular-neighbor-
                discovery-07 . . . . . . . . . . . . . . . . . . . .  23
   Appendix B.  Acknowledgments  . . . . . . . . . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

1.  Introduction

   Vehicular Ad Hoc Networks (VANET) have been researched for
   Intelligent Transportation System (ITS) such as driving safety,
   efficient driving and entertainment.  Considering the high-speed
   mobility of vehicular network based on Dedicated Short-Range
   Communications (DSRC), IEEE has standardized IEEE 802.11p



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   [IEEE-802.11p] as a MAC protocol for vehicles in Wireless Access in
   Vehicular Environments (WAVE).  IEEE 802.11p was renamed IEEE 802.11
   Outside the Context of a Basic Service Set (OCB) [IEEE-802.11-OCB] in
   2012.  IEEE has standardized a family standard suite of WAVE
   [DSRC-WAVE] as IEEE 1609.  This IEEE 1609 is considered as a key
   component in ITS.  IEEE 1609 standards include IEEE 1609.0
   [WAVE-1609.0], 1609.2 [WAVE-1609.2], 1609.3 [WAVE-1609.3], and 1609.4
   [WAVE-1609.4] to provide a low-latency and alternative network for
   vehicular communications.  What is more, IP-based vehicular networks
   specialized as IP Wireless Access in Vehicular Environments (IPWAVE)
   [ID-IPWAVE-PS] can enable many use cases over vehicle-to-vehicle
   (V2V), vehicle-to-infrastructure (V2I), and vehicle-to-everything
   (V2X) communications.  IETF has standardized an IPv6 packet delivery
   protocol over IEEE 802.11-OCB [ID-IPv6-802.11-OCB].

   VANET features high mobility dynamics, asymmetric and lossy
   connections, and moderate power constraint (e.g., electric cars and
   unmanned aerial vehicles).  Links among hosts and routers in VANET
   can be considered as undetermined connectivities with constantly
   changing neighbors described in [RFC5889].  IPv6 [RFC8200] is
   selected as the network-layer protocol for Internet applications by
   IEEE 1609.0 and 1609.3.  However, the relatively long-time Neighbor
   Discovery (ND) process in IPv6 [RFC4861] is not suitable in VANET
   scenarios.

   To support the interaction between vehicles or between vehicles and
   Rode-Side Units (RSUs), this document specifies a Vehicular Neighbor
   Discovery (VND) as an extension of IPv6 ND for IP-based vehicular
   networks.  VND provides vehicles with an optimized Address
   Registration and a multihop Duplicate Address Detection (DAD)
   mechanism.  In addition, an efficient mobility management scheme is
   specified to support efficient V2V, V2I, and V2X communications.
   Detailed statements of the mobility management are addressed in
   [ID-IPWAVE-VMM] .

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  Terminology

   This document uses the terminology described in [RFC4861], [RFC4862],
   and [RFC6775].  In addition, the following new terms are defined as
   below:





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   o  WAVE: Acronym for "Wireless Access in Vehicular Environments"
      [WAVE-1609.0].

   o  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 typically deployed on the road
      infrastructure, either at an intersection or in a road segment,
      but may also be located in car parking areas.

   o  On-Board Unit (OBU): A node that has a DSRC device for wireless
      communications with other OBUs and RSUs, and may be connected to
      in-vehicle devices or networks.  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.

   o  Mobility Anchor (MA): A node that maintains IP addresses and
      mobility information of vehicles in a road network to support the
      address autoconfiguration and mobility management of them.  It has
      end-to-end connections with RSUs under its control.  It maintains
      a DAD Table recording the IP addresses of vehicles moving within
      the communication coverage of its RSUs.

   o  Vehicular Cloud: A cloud infrastructure for vehicular networks,
      including compute nodes, storage nodes, and network nodes.

   o  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 and has MAs
      under its management.

4.  Overview

   This document proposes an optimized ND with a more adaptive structure
   for vehicular networks compared to [RFC4861] considering fast vehicle
   mobility and wireless control traffic overhead.  Furthermore, prefix
   and service discovery can be implemented as part of the ND's process
   along with an efficient Address Registration procedure and DAD
   mechanism for moving vehicles.  This document specifies a set of
   behaviors between vehicles and RSUs to accomplish these goals.





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4.1.  Link Model

   There is a relationship between a link and a network prefix along
   with reachability scopes, such as link-local and global scopes.  The
   legacy IPv6 ND protocol [RFC4861] has the following link model.  All
   IPv6 nodes in the same on-link subnet, which use the same subnet
   prefix with the on-link bit set, are reachable with each other by
   one-hop links.  The symmetry of the connectivity among the nodes is
   assumed, that is, bidirectional connectivity between two on-link
   nodes.  However, a link model in vehicular networks (called vehicular
   link model) should consider the asymmetry of the connectivity that
   unidirectional links can exist due to interference in wireless
   channels and the different levels of transmission power employed by
   wireless network interfaces.

   The on-link subnet can be constructed by one link (as a basic service
   set) or multiple links (as an extended service set) called a multi-
   link subnet [RFC6775].  In this multi-link subnet, an all-node-
   multicasted packet is copied and related to other links by an ND
   proxy.  On the other hand, in vehicular networks having fast moving
   vehicles, multiple links can share the same subnet prefix for
   operation efficiency.  For example, if two wireless links under two
   adjacent RSUs are in the same subnet, a vehicle as an IPv6 host does
   not need to reconfigure its IPv6 address during handover between
   those RSUs.  However, the packet relay by an RSU as an ND proxy is
   not required because such a relay can cause a broadcast storm in the
   extended subnet.  Thus, in the multi-link subnet, all-node-
   multicasting needs to be well-calibrated to either being confined to
   multicasting in the current link or being disseminated to other links
   in the same subnet.

   In a connected multihop VANET, for efficient communication, vehicles
   in the same link of an RSU can communicate directly with each other,
   not through the serving RSU.  This direct wireless communication is
   similar to the direct wired communication in an on-link subnet using
   Ethernet as a wired network.  The vehicular link model needs to
   accommodate both the ad-hoc communication between vehicles and
   infrastructure communication between a vehicle and an RSU in an
   efficient and flexible way.  Therefore, the IPv6 ND should be
   extended to accommodate the concept of a new IPv6 link model in
   vehicular networks.

   To support multi-link subnet, this specification employs the Shared-
   Prefix model for prefix assignments.  A Shared-Prefix model refers to
   an addressing model where the prefix(es) are shared by more than one
   node.  In this document, we assume that in a specified subnet, all
   interfaces of RSUs responding for prefix assignments to vehicles hold




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   the same prefix, which ensure vehicles obtain and maintain the same
   prefix in this subnet scope.

4.2.  ND Optimization

   This document takes advantage of the optimized ND for Low-Power
   Wireless Personal Area Network (6LoWPAN) [RFC6775] because vehicular
   environments have common parts with 6LoWPAN, such as the reduction of
   unnecessary wireless traffic by multicasting and the energy saving in
   battery.  Note that vehicles tend to be electric vehicles whose
   energy source is from their battery.

   In the optimized IPv6 ND for 6LoWPAN, the connections among nodes are
   assumed to be asymmetric and unidirectional because of changing radio
   environment and loss signal.  The authors proposed an optimized IPv6
   ND which greatly eliminates link-scope multicast to save energy by
   constructing new options and a new scheme for address configurations.
   Similarly, this document proposes an improved IPv6 ND by eliminating
   many link-scope-multicast-based ND operations, such as DAD for IPv6
   Stateless Address Autoconfiguration (SLAAC) [RFC4862].  Thus, this
   document suggests an extension of IPv6 ND as vehicular ND tailored
   for vehicular networks along with new ND options (e.g., prefix
   discovery, service discovery, and mobility information options).

4.3.  Design Goals

   The vehicular ND in this document has the following design goals:

   o  To perform prefix and service discovery through ND procedure;

   o  To implement host-initiated refresh of Router Advertisement (RA)
      and remove the necessity for routers to use periodic or
      unsolicited multicast RA to find hosts;

   o  To replace Neighbor Unreachable Detection(NUD), create Neighbor
      Cache Entries (NCE) for all registered vehicles in RSUs and MA by
      appending Address Registration Option (ARO) in Neighbor
      Solicitation (NS), Neighbor Advertisement (NA) messages;

   o  To support a multihop DAD by conveying ND messages received from
      vehicles to MA to eliminate multicast storms and save energy; and

   o  To support multi-hop communication for vehicles outside the
      coverage of RSUs to communicate with the serving RSU via a relay
      neighbor.






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5.  Vehicular Network Architecture

   A vehicular network architecture for V2I and V2V is illustrated in
   Figure 1.  Three RSUs are deployed along roadsides and are connected
   to an MA through wired links.  There are two subnets such as Subnet1
   and Subnet2.  The wireless links of RSU1 and RSU2 belong to the same
   subnet named Subnet1, but the wireless link of RSU3 belongs to
   another subnet named Subnet2.  Vehicle2 is wirelessly connected to
   RSU1 while Vehicle3 and Vehicle4 are connected to RSU2 and RSU3,
   respectively.  Vehicles can directly communicate with each other
   through V2V connection (e.g., Vehicle1 and Vehicle2) to share driving
   information.  In addition, vehicles not in the range of any RSU may
   connect with RSU in multi-hop connection via relay vehicle (e.g.,
   Vehicle1 can contact RSU1 via Vehicle2).  Vehicles are assumed to
   start the connection to an RSU when they entered the coverage of the
   RSU.

   The document recommends a multi-link subnet involving multiple RSUs
   as shown in Figure 1.  This recommendation aims at the reduction of
   the frequency with which vehicles have to change their IP address
   during handover between two adjacent RSUs.  To construct this multi-
   link subnet, a Shared-Prefix model is proposed.  That is, for RSUs in
   the same subnet, the interfaces responsible for prefix assignment for
   vehicles should hold the same prefix in their global address.  This
   also promises vehicles achieve the same prefix in this scope.  When
   they pass through RSUs in the same subnet, vehicles do not need to
   perform the Address Registration and DAD again because they can use
   their current IP address in the wireless coverage of the next RSU.
   Moreover, this proposal accords with the assumption that nodes
   belonging to the same IP prefix domain are able to communicate with
   each other directly without the intervention of RSUs if they are
   within the wireless communication range of each other.  On the other
   hand, if vehicles enter the wireless coverage of an RSU belonging to
   another subnet with a different prefix, they repeat the Address
   Registration and DAD procedure to update their IP address with the
   new prefix.

   In Figure 1, RSU1 and RSU2 are deployed in a multi-link subnet with
   the same prefix address in their interfaces responding for connection
   with vehicles.  When vehicle2 leaves the coverage of RSU1 and enters
   RSU2, it maintains its address configuration and ignores Address
   Registration and DAD steps.  If vehicle2 moves into the coverage of
   RSU3, since RSU3 belongs to another subnet and holds a different
   prefix from RSU1 and RSU2, so vehicle2 must do Address Registration
   and DAD just as connecting to a new RSU.  Note that vehicles and RSUs
   have their internal networks including in-vehicle devices and
   servers, respectively.  The structures of the internal networks are
   described in [ID-IPWAVE-PS].



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                     Traffic Control Center in Vehicular Cloud
                    *-----------------------------------------*
                   *                                           *
                  *             +----------------+              *
                 *              | Mobility Anchor|               *
                 *              +----------------+               *
                  *                    ^                        *
                   *                   |                       *
                    *------------------v----------------------*
                    ^                  ^                     ^
                    |                  |                     |
                    |                  |                     |
                    v                  v                     v
               +--------+ Ethernet +--------+            +--------+
               |  RSU1  |<-------->|  RSU2  |<---------->|  RSU3  |
               +--------+          +--------+            +--------+
                  ^                     ^                    ^
                  :                     :                    :
           +-------------------------------------+   +-----------------+
           |      : V2I             V2I :        |   |   V2I :         |
           |      v                     v        |   |       v         |
+--------+ |   +--------+          +--------+    |   |   +--------+    |
|Vehicle1|===> |Vehicle2|===>      |Vehicle3|===>|   |   |Vehicle4|===>|
|        |<...>|        |<........>|        |    |   |   |        |    |
+--------+ V2V +--------+    V2V   +--------+    |   |   +--------+    |
           |                                     |   |                 |
           +-------------------------------------+   +-----------------+
                           Subnet1                         Subnet2

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

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

6.  ND Extension for Prefix and Service Discovery

   This section specifies an IPv6 ND extension for vehicle-to-vehicle
   (V2V) or vehicle-to-infrastructure (V2I) networking.  This section
   also defines three new ND options for prefix discovery, service
   discovery, and mobility information report: (i) Vehicular Prefix
   Information (VPI) option, (ii) Vehicular Service Information (VSI)
   option, and (iii) Vehicular Mobility Information (VMI) option.  It
   also describes the procedure of the ND protocol with those options.

6.1.  Vehicular Prefix Information Option

   The VPI option contains IPv6 prefix informations in the internal
   network.  Figure 2 shows the format of the VPI option.




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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |    Length     | Prefix Length |   Distance    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Reserved                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     :                            Prefix                             :
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 2: Vehicular Prefix Information (VPI) Option Format

   Fields:
    Type           8-bit identifier of the VPI option type as assigned
                   by the IANA: TBD

    Length         8-bit unsigned integer.  The length of the option
                   (including the Type and Length fields) is in units of
                   8 octets.  The value is 3.

    Prefix Length  8-bit unsigned integer.  The number of leading bits
                   in the Prefix that are valid.  The value ranges
                   from 0 to 128.

    Distance       8-bit unsigned integer. The distance between the
                   subnet announcing this prefix and the subnet
                   corresponding to this prefix in terms of the number
                   of hops.

    Reserved       This field is unused.  It MUST be initialized to
                   zero by the sender and MUST be ignored by the
                   receiver.

    Prefix         An IP address or a prefix of an IP address.  The
                   Prefix Length field contains the number of valid
                   leading bits in the prefix.  The bits in the prefix
                   after the prefix length are reserved and MUST be
                   initialized to zero by the sender and ignored by
                   the receiver.

6.2.  Vehicular Service Information Option

   The VSI option contains vehicular service information in the internal
   network.  Figure 3 shows the format of the VSI option.





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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |     Length    |           Reserved1           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Protocol    |   Reserved2   |          Port Number          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     :                          Node Address                         :
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 3: Vehicular Service Information (VSI) Option Format

 Fields:
  Type           8-bit identifier of the VSI option type as assigned
                 by the IANA: TBD

  Length         8-bit unsigned integer.  The length of the option
                 (including the Type and Length fields) is in units of
                 8 octets.  The value is 3.

  Reserved1      This field is unused.  It MUST be initialized to
                 zero by the sender and MUST be ignored by the
                 receiver.

  Protocol       8-bit unsigned integer to indicate the upper-layer
                 protocol, such as transport-layer protocol (e.g.,
                 TCP, UDP, and SCTP).

  Reserved2      This field is unused.  It MUST be initialized to
                 zero by the sender and MUST be ignored by the
                 receiver.

  Port Number    16-bit unsigned integer to indicate the port number
                 for this protocol.

  Service Address
                 128-bit IPv6 address of a node providing this vehicular
                 service.

6.3.  Vehicular Mobility Information Option

   The VMI option contains one vehicular mobility information of a
   vehicle or an RSU.  Figure 4 shows the format of the VMI option.






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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |     Length    |           Reserved1           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Reserved2                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     :                      Mobility Information                     :
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Figure 4: Vehicular Mobility Information (VMI) Option Format

   Fields:
    Type           8-bit identifier of the VMI option type as assigned
                   by the IANA: TBD

    Length         8-bit unsigned integer.  The length of the option
                   (including the Type and Length fields) is in units of
                   8 octets.  The value is 3.

    Reserved1      This field is unused.  It MUST be initialized to
                   zero by the sender and MUST be ignored by the
                   receiver.

    Reserved2      This field is unused.  It MUST be initialized to
                   zero by the sender and MUST be ignored by the
                   receiver.

    Mobility Information
                   128-bit mobility information, such as position,
                   speed, acceleration/deceleration, and direction.

6.4.  Vehicular Neighbor Discovery

   Prefix discovery enables hosts (e.g., vehicles and in-vehicle
   devices) to distinguish destinations on the same link from those only
   reachable via RSUs.  A vehicle (or its in-vehicle devices) can
   directly communicate with on-link vehicles (or their in-vehicle
   devices) without the relay of an RSU, but through V2V communications
   along with VPI ND option.  This VPI option contains IPv6 prefixes in
   a vehicle's internal network.

   Vehicles announce services in their internal networks to other
   vehicles through an VSI ND option.  The VSI option contains a list of
   vehicular services in a vehicle's or an RSU's internal network.




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   A vehicle periodically announces an NS message containing VPI and VSI
   options with its prefixes and services in all-nodes multicast address
   to reach all neighboring nodes.  When it receives this NS message,
   another neighboring node responds to this NS message by sending an NA
   message containing the VPI and VSI options with its prefixes and
   services via unicast towards the NS-originating node.

   Therefore, prefix and service discovery can be achieved via ND
   messages (e.g., NS and NA) by vehicular ND with VPI and VSI options.
   This VND-based discovery eliminates an additional prefix and service
   discovery scheme, such as DNS-based Service Discovery [RFC6763]
   (e.g., Multicast DNS (mDNS) [RFC6762] and DNSNA [ID-DNSNA]), other
   than ND.  That is, vehicles and RSUs can rapidly discover the network
   prefixes and services of the other party without any additional
   service discovery protocol.

6.5.  Message Exchange Procedure for V2I Networking

   This subsection explains a message exchange procedure for VND in V2I
   networking, where a vehicle communicates with its corresponding node
   in the Internet via an RSU.

   Figure 5 shows an example of message exchange procedure in V2I
   networking.  Detailed steps of the procedure are explained in
   Section 7.  The mobility management part is described in
   [ID-IPWAVE-VMM].

   Note that a vehicle could also perform the prefix and service
   discovery simultaneously along with Address Registration procedure,
   as shown in Figure 7.

   This document specified that RSUs as routers do not transmit
   periodical and unsolicited multicast RA messages including a prefix
   for energy saving in vehicular networks.  Vehicles as hosts
   periodically initiate an RS message according to a time interval
   (considering its position and an RSU's coverage).  Since they have a
   digital road map with the information of RSUs (e.g., position and
   communication coverage), vehicles can know when they will go out of
   the communication range of an RSU along with the signal strength
   (e.g., Received Channel Power Indicator (RCPI) [VIP-WAVE]) from the
   RSU.  RSUs replies with a solicited RA in unicast only when they
   receive an RS message.









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             Vehicle                    RSU                      MA
                |                        |                        |
                |-RS with Mobility Info->|                        |
                |         [VMI]          |                        |
                |                        |                        |
                |                        |-----------PBU--------->|
                |                        |                        |
                |                        |                        |
                |                        |<----------PBA----------|
                |                        |                        |
                |                        |                        |
                |                        |======Bi-Dir Tunnel=====|
                |                        |                        |
                |                        |                        |
                |<----RA with prefix-----|                        |
                |                        |                        |
                |                        |                        |
                |                        |                        |
                |--NS with Address Reg-->|                        |
                |     [ARO+VPI+VSI]      |                        |
                |                        |                        |
                |                        |---Forward NS for DAD-->|
                |                        |                        |
                |                        |                        |
                |                        |<--NA with DAD result---|
                |                        |    [ARO+VPI+VSI]       |
                |<------Forward NA-------|                        |
                |                        |                        |

      Figure 5: Message Interaction for Vehicular Neighbor Discovery

7.  Address Registration and Duplicate Address Detection

   This section explains address configuration, consisting of IP Address
   Autoconfiguration, Address Registration, and multihop DAD via V2I or
   V2V.

   This document recommends a new Address Registration and DAD scheme in
   order to avoid multicast flooding and decrease link-scope multicast
   for energy and wireless channel conservation on a large-scale
   vehicular network.  Host-initiated refresh of RA removes the
   necessity for routers to use frequent and unsolicited multicast RAs
   to accommodate hosts.  This also enables the same IPv6 address
   prefix(es) to be used across a subnet.

   There are three scenarios feasible in Address Registration scheme:





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   1.  Vehicle enters the subnet for the first time or the current RSU
       belongs to another subnet: Vehicles need to perform the Address
       Registration and multihop DAD as described in the following
       subsections.

   2.  Vehicle has already configured its IP addresses with prefix
       obtained from the previous RSU, and the current RSU located in
       the same subnet: This means RSUs have the same prefix and the
       vehicle has no need to repeat the Address Registration and
       multihop DAD.

   3.  Vehicle is not in the coverage of RSU but has a neighbor
       registered in RSU: This document proposes a new V2V scenario for
       vehicles which are currently not in the range of the RSU.  If a
       user vehicle failed to find an on-link RSU, it starts to look for
       adjacent vehicle neighbors which can work as a relay neighbor to
       share the prefix obtained from RSU and undertake DAD of the user
       vehicle by forwarding DAD messages to RSU.

7.1.  Address Autoconfiguration

   A vehicle as an IPv6 host creates its link-local IPv6 address and
   global IPv6 address as follows [RFC4862].  When they receive RS
   messages from vehicles, RSUs send back RA messages containing prefix
   information.  The vehicle makes its global IPv6 addresses by
   combining the prefix for its current link and its link-layer address.

   The address autoconfiguration does not perform the legacy DAD as
   defined in [RFC4862].  Instead, a new multihop DAD is performed in
   Section 7.3.

7.2.  Address Registration

   After its IP tentative address autoconfiguration with the known
   prefix from an RSU and its link-layer address, a vehicle starts to
   register its IP address to the serving RSU along with multihop DAD.
   Address Register Option (ARO) is used in this step and its format is
   defined in [RFC6775].

   ARO is always host-initiated by vehicles.  Information such as
   registration time and registration status contained in ARO are
   applied to indicate the registration duration and result.  ARO will
   also be forwarded to MA together with NS by RSUs.

   An example message exchange procedure of Address Registration is
   presented in Figure 6.  Since Address Registration is performed
   simultaneously with the multihop DAD, the specific procedure is
   together described with the DAD mechanism in Section 7.3.



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                   Vehicle                       RSU
                      |                           |
                      |                           |
               1.     |----NS with Address Reg--->|
                      |            [ARO]          |
                      |                           |
                      |                           |
                      |                           |
               2.     |<---NA with Address Reg----|
                      |            [ARO]          |



             Figure 6: Neighbor Discovery Address Registration

7.3.  Multihop Duplicate Address Detection

   Before it can exchange data, a node should determine whether its IP
   address is already used by another node or not.  In the legacy IPv6
   ND, hosts multicast NS messages to all nodes in the same on-link
   subnet for DAD.  Instead of this, an optimized multihop DAD is
   designed to eliminate multicast messages for energy-saving purpose.
   For this multihop DAD, Neighbor Cache and DAD Table are maintained by
   each RSU and an MA, respectively, for the duplicate address
   inspection during the multihop DAD process.  That is, each RSU makes
   Neighbor Cache Entries (NCE) of all the on-link hosts in its Neighbor
   Cache.  Similarly, the MA stores all the NCEs reported by the RSUs in
   its DAD Table.

   With the multihop DAD, a vehicle can skip the multicast-based DAD in
   its current wireless link whenever it enters the coverage of another
   RSU in the same subset, leading to the reduction of traffic overhead
   in vehicular wireless links.

   For the multihop DAD, we take advantage of the procedure of [RFC6775]
   but simplified the message flows by canceling the two new ICMPv6
   message types such as Duplicate Address Request (DAR) and the
   Duplicate Address Confirmation (DAC).  Instead, NS and NA containing
   ARO are directly forwarded between RSU and MA.  This idea is raised
   because DAR and DAC

7.3.1.  DAD without Intermediate Vehicle

   Figure 7 presents the procedure of Address Registration and multihop
   DAD.  The detailed steps are explained as follows.






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              Vehicle                    RSU                MA
                 |                        |                  |
                 |                        |                  |
          1.     |--NS with Address Reg-->|                  |
                 |     [ARO+VPI+VSI]      |                  |
                 |                        |                  |
          2.     |                        |----Forward NS--->|
                 |                        |                  |
                 |                        |                  |
          3.     |                        |<---Forward NA----|
                 |                        |                  |
                 |                        |                  |
          4.     |<--NA with Address Reg--|                  |
                 |     [ARO+VPI+VSI]      |                  |


    Figure 7: Neighbor Discovery Address Registration with Multihop DAD

   1.  A vehicle sends an NS message to the current RSU in unicast,
       containing the ARO to register its address.

   2.  The RSU receives the NS message, and then inspects its Neighbor
       Cache to check whether it is duplicate or not.  If there is no
       duplicate NCE, a tentative NCE is created for this address, and
       then the RSU forward the NS message containing the ARO to the MA
       for the multihop DAD.

   3.  When the MA receives NS from an RSU, it checks whether the
       register-requested address exists in its DAD Table or not.  If an
       entry with the same address exists in the DAD Table, which means
       that the address is considered "Duplicate Address", then MA
       returns a NA message containing the registration status in ARO to
       notify the RSU of the address duplication.  If no entry with the
       same address exists in the DAD Table, which means that an entry
       for the address is created, then MA replies a NA message to the
       RSU to confirm the uniqueness of the register-requested address
       to the RSU.

   4.  If the address duplication is notified by the MA, the RSU deletes
       the tentative NCE, and forward NA with to the address-
       registration vehicle to notify the registration failure.
       Otherwise, the RSU changes the tentative NCE into a registered
       NCE in its Neighbor Cache, and then forward NA to the vehicle to
       notify the registration success.

   Thus, the multihop DAD is processed simultaneously with the Address
   Registration.  Note that the tentative address is not considered




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   assigned to the vehicle until the MA confirms the uniqueness of the
   register-requested address in the multihop DAD.

7.3.2.  DAD with one Intermediate Vehicle

   If a vehicle failed to register a default router, it triggers
   neighbor discovery to look for vehicle neighbors which can provide
   relay service using multi-hop communication.  In this specification,
   we assumed vehicles would not emulate V2V communication and trigger
   relay scenario only if Router Discovery(RD) failed.

 User Vehicle          Relay Vehicle                RSU               MA
    |                        |                       |                 |
    |------------------------|                       |                 |
    |        RD failed       |                       |                 |
    |------------------------|                       |                 |
    |                        |                       |                 |
    |                        |                       |                 |
    |-----------NS---------->|                       |                 |
    |                        |                       |                 |
    |<--NA with Prefix Info--|                       |                 |
    |                        |                       |                 |
    |                        |                       |                 |
    |--NS with Address Reg-->|                       |                 |
    |    [ARO+VPI+VSI]       |                       |                 |
    |                        |----- Forward NS ----->|                 |
    |                        |                       |                 |
    |                        |                       |-----------------|
    |                        |                       | Same as Figure 9|
    |                        |                       |-----------------|
    |                        |                       |                 |
    |                        |<--NA with Address Reg-|                 |
    |                        |     [ARO+VPI+VSI]     |                 |
    |<------ Forward NA -----|                       |                 |
    |                        |                       |                 |

       Figure 8: Address Registration and Multihop DAD via V2V Relay

   Since vehicles have a digital road map with the information of RSUs
   (e.g., position and communication coverage), they can determine if
   they are available to serve as a relay vehicle.  Only vehicles with
   the ability to serve as temporary relays will take action when they
   receive relay service requests.  The user vehicle can process global
   address configuration, Address Registration and DAD through its relay
   vehicle before it enters the coverage of RSUs.  See Figure 8.

   When a user vehicle failed to directly register to an RSU, it
   initiates neighbor discovery to detect vehicle neighbors through V2V



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   communication.  Vehicle sends NS messages to connect with neighbors
   in range.  If neighbor can provide relay service, it creates a NCE
   for user vehicle, setting its own address as relay address, and sends
   back NA with prefix information received from RSU.

   To guarantee vehicles could find the nearest neighbor from multiple
   neighbors which can act as relay vehicles, a new time-out mechanism
   is presented to select the nearest neighbor by hop distance parameter
   carried in Prefix Information Option.  That is, a user vehicle
   multicast NS messages to look for relay vehicles after RD failed and
   wait for 1.5 seconds to receive all NA replies from neighbors.  Each
   NA carries its own global prefix(es) and the hop distance(s) in
   Prefix Information Option.  The user vehicle preserves every NA reply
   in a temporary router list and select the one with least hop counts
   as its relay vehicle after time out.

   With receipt of NA, user vehicle configures its global address with
   prefix information as mentioned in Section 7.1.  After this, user
   vehicle takes up to initiate the Address Registration along with DAD
   process via relay vehicle.  NS message is configured as specified in
   Section 7.2 but indicate the relay vehicle's address as next-hop to
   reach the RSU.  In such a case, when relay vehicle receives relay
   request message, it will forward NS message to RSU.  The procedure
   sets up on the rails except MA will include the relay vehicle's
   address as relay address in NCE to indicate that at this moment, it
   is not a directly attached vehicle, and sets the relay address as
   next-hop address.  Relay vehicle forwards DAD result information
   message to user vehicle as soon as it received.

7.3.3.  DAD with multiple Intermediate Vehicles

   This document supports multihop communications (e.g., multihop DAD
   and UDP/TCP transmission) for remote vehicles through multiple relay
   vehicles.  Vehicles which have already finished DAD process can serve
   as temporary routers and forward packets for remote vehicles.

   A new routing mechanism is specified to accomplish route selections
   among user vehicles and serving RSUs when multiple vehicles act as
   relay vehicles.  Taking advantage of the Destination-Sequenced
   Distance-Vector routing protocol (DSDV) [DSDV], this new routing
   approach supposes that each vehicle holds a Neighbor Routing
   Table which integrates the neighbor information in Neighbor Cache and
   forwarding records for remote vehicles.  Each vehicle which acts as a
   relay vehicle for this remote vehicle will make records in its
   Neighbor Routing Table.

   Figure 9 specifies an example of parameters in Neighbor Routing
   Table when more than one vehicle work as intermediate relay vehicles.



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   In Figure 9, Vehicle3 connects RSU1 indirectly via Vehicle2 and
   Vehicle1.  When Vehicle1 and Vehicle2 forward messages for Vehicle3,
   they make records in its Neighbor Routing Table including the next-
   hop node to indicate the route to Vehicle3.  This can ensure that the
   packets from a source vehicle can be successfully transmitted to an
   RSU as well as the reverse packet path exists from the RSU to the
   source vehicle.


  +--------+        +--------+          +--------+          +--------+
  |Vehicle3|<......>|Vehicle2|<........>|Vehicle1|<.......> |  RSU1  |
  |  (V3)  |   V2V  |  (V2)  |    V2V   |  (V1)  |   V2I    |        |
  +--------+        +--------+          +--------+          +--------+

+------------+    +------------+      +------------+      +------------+
|Node|NextHop|    |Node|NextHop|      |Node|NextHop|      |Node|NextHop|
+------------+    +------------+      +------------+      +------------+
| V2 |   V2  |    | V1 |   V1  |      |RSU1| RSU1  |      |  V1  |  V1 |
+------------+    | V3 |   V3  |      | V2 |  V2   |      |  V2  |  V1 |
                  +------------+      | V3 |  V2   |      |  V3  |  V1 |
                                      +------------+      +------------+

   Figure 9: An Example of Neighbor Routing Table when multiple Vehicles
                           act as Relay Vehicles

7.4.  Pseudonym Handling

   Considering the privacy protection of a vehicle, a pseudonym
   mechanism for its link-layer address is requested.  This mechanism
   periodically modifies the link-layer address, leading to the update
   of the corresponding IP address.  A random MAC Address Generation
   mechanism is proposed in Appendix F.4 of [IEEE-802.11-OCB] by
   generating the 46 remaining bits of MAC address using a random number
   generator.  When it changes its MAC address, a vehicle should ask the
   serving RSU to update its own NCE, and to register its IP address
   into the MA again.

8.  Security Considerations

   This document shares all the security issues of the neighbor
   discovery protocol and 6LoWPAN protocol.  This document can get
   benefits from secure neighbor discovery (SEND) [RFC3971] in order to
   protect ND from possible security attacks.








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9.  References

9.1.  Normative References

   [ID-IPv6-802.11-OCB]
              Benamar, N., Haerri, J., Lee, J., and T. Ernst, "Basic
              Support for IPv6 over IEEE Std 802.11 Networks Operating
              Outside the Context of a Basic Service Set (IPv6-over-
              80211-OCB)", draft-ietf-ipwave-ipv6-over-80211ocb-52 (work
              in progress), August 2019.

   [ID-IPWAVE-PS]
              Jeong, J., Ed., "IP Wireless Access in Vehicular
              Environments (IPWAVE): Problem Statement and Use Cases",
              draft-ietf-ipwave-vehicular-networking-12 (work in
              progress), October 2019.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3971]  Arkko, J., "SEcure Neighbor Discovery (SEND)", RFC 3971,
              March 2005.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP Version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

   [RFC5889]  Baccelli, E. and M. Townsley, "IP Addressing Model in Ad
              Hoc Networks", RFC 5889, September 2010.

   [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
              February 2013.

   [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
              Discovery", RFC 6763, February 2013.

   [RFC6775]  Shelby, Z., Ed., "Neighbor Discovery Optimization for IPv6
              over Low-Power Wireless Personal Area Networks
              (6LoWPANs)", RFC 6775, November 2012.

   [RFC8106]  Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
              "IPv6 Router Advertisement Options for DNS Configuration",
              RFC 8106, March 2017.





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   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 8200, July 2017.

9.2.  Informative References

   [DSDV]     Perkins, C. and P. Bhagwat, "Highly Dynamic Destination-
              Sequenced Distance-Vector Routing (DSDV) for Mobile
              Computers", ACM SIGCOMM, August 1994.

   [DSRC-WAVE]
              Morgan, Y., "Notes on DSRC & WAVE Standards Suite: Its
              Architecture, Design, and Characteristics",
              IEEE Communications Surveys & Tutorials, 12(4), 2012.

   [ID-DNSNA]
              Jeong, J., Ed., Lee, S., and J. Park, "DNS Name
              Autoconfiguration for Internet-of-Things Devices in IP-
              Based Vehicular Networks", draft-jeong-ipwave-iot-dns-
              autoconf-07 (work in progress), November 2019.

   [ID-IPWAVE-VMM]
              Jeong, J., Ed., Shen, Y., and Z. Xiang, "Vehicular
              Mobility Management for IP-Based Vehicular Networks",
              draft-jeong-ipwave-vehicular-mobility-management-02 (work
              in progress), November 2019.

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

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

   [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.

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





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   [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.




































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Appendix A.  Changes from draft-jeong-ipwave-vehicular-neighbor-
             discovery-07

   The following changes are made from draft-jeong-ipwave-vehicular-
   neighbor-discovery-07:

   o  In this version, Sandra Cespedes joined as a co-author.

   o  In this version, simplified message flows of DAD are proposed by
      removing the two new ICMPv6 message types such as Duplicate
      Address Request (DAR) and Duplicate Address Confirmation (DAC).
      Instead of them, an NS and an NA containing ARO are directly
      forwarded between an RSU and an MA.

   o  The V2I internetworking and V2V internetworking is removed from
      this version.  The detailed internetworkings are described in
      [ID-IPWAVE-PS].

   o  In Section 4.3, the explanation of the two new ICMPv6 message
      types is deleted.

   o  In Section 5, the description of the network architecture is
      revised with easily identifiable expressions to remove ambiguity.

   o  In Section 6.5, the message flow is revised according to the
      simplified message types.

   o  In Section 7.3, the explanation of two new ICMPv6 message types is
      deleted.

   o  Several typo errors are corrected.

Appendix B.  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 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 under the ITRC
   (Information Technology Research Center) support program (IITP-
   2019-2017-0-01633) supervised by the IITP.




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Authors' Addresses

   Jaehoon Paul Jeong
   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
   Fax:   +82 31 290 7996
   EMail: pauljeong@skku.edu
   URI:   http://iotlab.skku.edu/people-jaehoon-jeong.php


   Yiwen Chris Shen
   Department of Electrical and Computer 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


   Zhong Xiang
   Department of Electrical and Computer Engineering
   Sungkyunkwan University
   2066 Seobu-Ro, Jangan-Gu
   Suwon, Gyeonggi-Do  16419
   Republic of Korea

   Phone: +82 10 9895 1211
   Fax:   +82 31 290 7996
   EMail: xz618@skku.edu


   Sandra Cespedes
   NIC Chile Research Labs
   Universidad de Chile
   Av. Blanco Encalada 1975
   Santiago
   Chile

   Phone: +56 2 29784093
   EMail: scespede@niclabs.cl



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