Considerations for ID/Location Separation Protocols in IPv6-based Vehicular Networks
draft-kjsun-ipwave-id-loc-separation-02

Abstract

ID/Location separation protocols are proposed for scalable routing, enhancing mobility and privacy in IPv6-based vehicular networks. In IPv6-based vehicular networks, ID/Location separation architecture is expected to offer benefits. This document analyzes how ID/Location separation protocols can adjust into IP based vehicular networks and suggests requirements for efficient ID/Location separation in vehicular networks.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Use Cases for ID/Location Separation Protocols
• 3.1. Locator/ID Separation Protocol (LISP)
• 3.2. Identifier-Locator Network Protocol (ILNP)
• 4. Gap Analysis
• 4.1. Neighbor Discovery
• 4.2. Mobility Management
• 4.3. Security and Privacy
• 5. Acknkowledgement
• 6. Informative References
• Authors' Addresses

1. Introduction

For vehicular networks, it is required to provide connection to the Intelligent Transport Systems (ITS) for the driver's safety, efficient driving and entertainment with fast mobility management. Other scenarios besides V2I communication, like V2V and V2X communication are also considered. Link layer protocols such as IEEE 802.11-OCB [IEEE-802.11-OCB] are already defined for low-latency and alternative networks, and it is designed for enabling IPv6 as a network layer protocol. Nevertheless, for using IPv6 in the vehicular network, there are some requirements for optimization as described in [ietf-ipwave-vehicular-networking]. These issues are classified into IPv6 neighbor discovery, mobility management, security and privacy.

In IETF, there are two major ID/Location separation protocols such as LISP [RFC6830] and ILNP [RFC6740] for scalable routing, enhancing privacy and mobility management. Currently ID/Location separation concept is useful not only for decomposing ID/Location from an IP address, but also for control/data plane separation which is a major evolution of the Internet infrastructure. For the vehicular networks, ID/Location separation protocols can be expected to meet requirements and solve problem statements discussed in IPWAVE WG. This document describes use cases for applying ID/Location separation architecture to IPv6-based vehicular networks, and analyzes how such protocols can meet requirements for IPv6 in vehicular networks.

2. Terminology

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 [RFC2119]. This document uses the terminology described in [ietf-ipwave-vehicular-networking], [RFC6830], [RFC6740].

3. Use Cases for ID/Location Separation Protocols

3.1. Locator/ID Separation Protocol (LISP)

                    Traffic Control Center in Vehicular Cloud
                   *-----------------------------------------*
                  *                                           *
                 *             +----------------+              *
                *              | Mapping System |               *
                *              +----------------+               *
                 *                      ^                      *
                  *               MS/MR |                     *
                   *--------------------v--------------------*
                   ^               ^                        ^
                   |               |                        |
                   |               |                        |
            RLOC1  v               v RLOC2                  v RLOC3   
              +--------+  Ethernet  +--------+ Tunneling  +--------+    
              |  RSU1  |<---------->|  RSU2  |<---------->|  RSU3  |    
              |  (xTR) |            |  (xTR) |            |  (xTR) |    
              +--------+            +--------+            +--------+    
                    ^                  ^                    ^         
               +----:------------------:---------+ +--------:---------+
               |    : V2I          V2I :         | |    V2I :         |
               |    v                  v         | |        v         |
   +--------+  |   +--------+      +--------+    | |    +--------+    |
   |Vehicle1|===>  |Vehicle2|===>  |Vehicle3|===>| |    |Vehicle4|===>|
   |  (EID) |<....>|  (EID) |<....>|  (EID) |    | |    |  (EID) |    |
   +--------+ V2V  +--------+ V2V  +--------+    | |    +--------+    |
               |                                 | |                  |
               +---------------------------------+ +------------------+
                   LISP Site-1                          LISP Site-2 

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

			            

Figure 1: LISP Use Case Scenario in IP-based Vehicular Network Architecture

Figure 1 describes a vehicular network architecture with the LISP protocol. A single LISP site can have multiple RSUs with the function of LISP Tunnel Router (xTR) to communicate with other LISP sites. In the figure, we assume that Vehicles 1, 2 and 3 belong to LISP site 1 and Vehicle 4 to LISP site 2. IPv6 addresses for wireless interfaces of each vehicle are mapped to unique End-Point IDs (EIDs), which can communicate with other EIDs in the same LISP site same as a legacy IPv6 operation. That is, vehicles are able to communicate with an RSU by V2I communication at the same time with other vehicles in the same LISP site by V2V communication.

Traffic control center in the vehicular cloud is appropriate to deploy a mapping system, since it is a point accessible from all RSUs. When vehicles enter each LISP site and attach to an RSU, the RSU sends a Map-Register message to the mapping system including vehicle's EID and RLOC of the attached RSU. After registration, the vehicle can be provided with reachability from other LISP sites or non-LISP sites. In the figure, for the communication between vehicle 4 and vehicle 3, RSU 3 which is the attachment point of Vehicle 4 should request for the RLOC of vehicle 3 from the mapping system by sending Map-Requests message. After receiving mapping information of Vehicle 3's EID and its RLOC in Map-Reply message, RLOC 3 can forward packets via the IP tunnel between xTR (e.g., RSU 2 in this figure) assigned to vehicle 3. Note that several data plane protocols (e.g., SRv6, etc.) can be used with LISP control plane functions.

3.2. Identifier-Locator Network Protocol (ILNP)

In the ILNPv6, an IPv6 address is replaced with an Identifier-Locator Vector (I-LV). The I-LV has a 128-bit length allowing it to be applied to the current IPv6 header without modification. [RFC6740] describes in detail how an I-LV value can replace an IPv6 address at the same time how it can work in the current IPv6-based infrastructure. In [RFC6741], the details of the ILNPv6 packet header, locator subnetting and new DNS resource record type for mapping I-LV values are defined.

A vehicular network architecture for supporting ILNP is shown in Figure 2. Most of the components are similar with the architecture described in [ietf-ipwave-vehicular-networking]. Every Vehicle can have more than one NID to connect to a network, and the IPv6 address for communication is represented as a combination of Node Identifier (NID) and Locator. Site Border Router (SBR) can be implemented in an RSU or border of ILNP subnet site, which should have a routing table having the mapping information of I-LV values for forwarding packets. A DNS server can be deployed in the vehicular cloud which is accessible from both in ILNP site and external Internet.

                    Traffic Control Center in Vehicular Cloud
                   *-----------------------------------------*
                  *                                           *
                 *            +-----------------+              *
                *             |    DNS Server   |               *
                *             +-----------------+               *
                 *                      ^                      *
                  *                     |                     *
                   *--------------------v--------------------*
                   ^               ^                        ^
                   |               |                        |
               +---------------------+                      |
               |         SBR         |                      |
               +---------------------+                      |
                   |               |                        |
                   v               v                        v         
              +--------+   Ethernet  +--------+         +--------+    
              |  RSU1  |<----------->|  RSU2  |<------->|RSU3/SBR|    
              +--------+             +--------+         +--------+    
                    ^                  ^                    ^         
               +----:------------------:---------+ +--------:---------+
               |    : V2I          V2I :         | |    V2I :         |
               |    v                  v         | |        v         |
   +--------+  |   +--------+      +--------+    | |    +--------+    |
   |Vehicle1|===>  |Vehicle2|===>  |Vehicle3|===>| |    |Vehicle4|===>|
   | (I-LV) |<....>| (I-LV) |<....>| (I-LV) |    | |    | (I-LV) |    |
   +--------+ V2V  +--------+ V2V  +--------+    | |    +--------+    |
               |                                 | |                  |
               +---------------------------------+ +------------------+
                           Subnet-1                      Subnet-2 

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

			            

Figure 2: ILNP Use Case Scenario in IP-based Vehicular Network Architecture

4. Gap Analysis

4.1. Neighbor Discovery

In both cases of LISP and ILNP, the usage of the existing neighbor discovery message defined in [RFC4861] is possible without modification. In LISP, Vehicles and RSUs in the same LISP site can exchange ND/NA messages for routing by EID configured as IPv6 format. Also, ILNP can operate the neighbor discovery for the configuration of an I-LV value as the I-LV for ILNPv6 occupies the same bits as the IPv6 address in the IPv6 header[RFC6740]. Thus, for vehicular networking, it is expected that the same solutions already mentioned in [ietf-ipwave-vehicular-networking] (e.g., new ND option [ID-Vehicular-ND]) can also be applicable in the ID/Location separation architecture.

4.2. Mobility Management

One of the advantages for using LISP is that mobility management can be provided efficiently, when a device is roaming across different LISP sites while maintaining its EID. The existing IP mobilty management schemes such as MIP or PMIP require an anchor function (e.g., Home Agent and Local Mobility Anchor) to maintain the IP address of a mobile node when the mobile node moves. They can construct a non-optimized forwarding path between the anchor and current attachment point of the mobile node. In LISP, however, a forwarding path can be optimized by updating EID-RLOC mapping information and establishing an IP tunnel between the xTR of the coresponding node and the xTR of the current mobile node's attachement point. This provides advantages for easly optimizing a forwarding path especially the vehicular networks where the connection point of the mobile node can be move fast away from its initial attachment point. In the vehicular networks, a vehicle with an EID will roam much faster and it means that the mapped RLOC will be changed more frequently. For faster RLOC assignment, a predictive RLOC algorithm for roaming-EID is proposed in LISP WG [draft-ietf-lisp-predictive-rlocs]. Using this algorithm, it predicts the moving direction of a vehicle with a roaming-EID, registers predictive RLOCs as a list to the mapping system, and replicates packets to each RLOC in the list. It can minimize packet loss while maintaining transport session continuity.

In ILNP, mobility management is classified into host mobility and network (or site) mobility. For vehicular networks, host mobility scenario is suitable [RFC6740]. When the vehicle moves to its network attachment point and locator, it shortly becomes to belong to a new site, it may send a Locator Update (LU) message to the Corresponding Node (CN) and also send a request to the DNS server to change its entry. Even though LU procedure is necessary, it causes delay and packet loss during handover, and it may become a more critical issue in the vehicular networks where the locator of a vehicle is updated faster and more frequently. Therefore, ILNP needs to minimize LU process including DNS updates for seamless mobility management in vehicular networks. For example, [ILNP-Sol-Wireless-Net] may be one possible solution that defines a geological information server, which gives information of attachment points nearby to devices to prepare handover, deliver its predictive locator to the CN so that it can reduce packet loss and latency for updating DNS.

4.3. Security and Privacy

For supporting applications such as autonomous driving, the vehicular networks require not only low latency and high bandwidth but also a high level of security and privacy. The IPWAVE working group is facing a mobility management challenge due to latency and management complexity due to the exchange of signaling messages with mobility anchor to establish a tunnel. In the ID/Location separation approach, all vehicles maintain their unique ID while they are allocated a locator in the fastest way without binding update procedure. Nevertheless, a privacy problem still exists due to the eacy access to the mapping system. Even though it is difficult to track a device using a single RLOC or locator value since its locator changes while moving across sites, on the other hand, since an EID or identifier is defined as permanent, additional methodologies need to be considered to secure device identifier information.

Another consideration is various communication links. In the vehicular networks, not only V2I communication but also V2X communication are required. It means that vehicles can directly communicate with each other only with an ID value without a locator which is allocated from the infrastructure. In this scenario, the exposure of vehicle IDs to others (including hackers) occurs frequently even though they do not access mapping system. In [draft-iannone-pidloc-privacy], they describe about privacy issues and requirements in ID/Location separation architecture.

Several existing works can provide enhanced privacy mechanisms in ID/Location separation architectures. For example, [draft-ietf-lisp-eid-anonymity] defines Ephemeral-EID which is frequently changed by the device. For ILNP, identity privacy supports using IPv6 privacy extensions for stateless address autoconfiguration [RFC4941] and Locator Rewriting Relay (LRR) component for locator privacy [RFC6748], can be solutions for enhancing privacy in vehicular networks.

5. Acknkowledgement

We would like to thank Jahoon Paul Jeong as a contributor who reviewed and gave comments for this version.

6. Informative References

Authors' Addresses