Network Working Group                                        A. Petrescu
Internet-Draft                                                 CEA, LIST
Intended status: Informational                                P. Pfister
Expires: December 18, 2014                                   only at -00
                                                              N. Benamar
                                                Moulay Ismail University
                                                          T. Leinmueller
                                              DENSO INTERNATIONAL EUROPE
                                                           June 16, 2014

        Transmission of IPv6 Packets over IEEE 802.11p Networks


   In order to transmit IPv6 packets on IEEE 802.11p networks there is a
   need to define a few parameters such as the recommended Maximum
   Transmission Unit size, the header format preceding the IPv6 base
   header, the Type value within it, and others.  This document
   describes these parameters for IPv6 and IEEE 802.11p networks; it
   portrays the layering of IPv6 on 802.11p similarly to other known
   802.11 and Ethernet layers, by using an existing Ethernet Adaptation

   In addition, the document attempts to list what is different in
   802.11p compared to more 'traditional' 802.11a/b/g/n layers, layers
   over which IPv6 protocols run ok.  Most notably, the operation
   outside the context of a BSS (OCB) has impact on IPv6 handover
   behaviour and on IPv6 security.

   An example of an IPv6 packet captured while transmitted over an IEEE
   802.11p link is given.

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
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   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

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   This Internet-Draft will expire on December 18, 2014.

Copyright Notice

   Copyright (c) 2014 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
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   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.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Communication Scenarios where IEEE 802.11p Links are Used  . .  6
   4.  Aspects introduced by 802.11p to 802.11  . . . . . . . . . . .  6
   5.  Layering of IPv6 over 802.11p as over Ethernet . . . . . . . .  9
     5.1.  Maximum Transmission Unit (MTU)  . . . . . . . . . . . . .  9
     5.2.  Frame Format . . . . . . . . . . . . . . . . . . . . . . .  9
       5.2.1.  Ethernet Adaptation Layer  . . . . . . . . . . . . . . 10
     5.3.  Link-Local Addresses . . . . . . . . . . . . . . . . . . . 11
     5.4.  Address Mapping  . . . . . . . . . . . . . . . . . . . . . 11
     5.5.  Stateless Autoconfiguration  . . . . . . . . . . . . . . . 11
     5.6.  Subnet Structure . . . . . . . . . . . . . . . . . . . . . 12
   6.  Handovers between OCB links  . . . . . . . . . . . . . . . . . 13
   7.  Example IPv6 Packet captured over a IEEE 802.11p link  . . . . 15
     7.1.  Capture in Monitor Mode  . . . . . . . . . . . . . . . . . 16
     7.2.  Capture in Normal Mode . . . . . . . . . . . . . . . . . . 18
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 20
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 21
   10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 21
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 21
     12.2. Informative References . . . . . . . . . . . . . . . . . . 22
   Appendix A.  ChangeLog . . . . . . . . . . . . . . . . . . . . . . 25
   Appendix B.  Explicit Prohibition of IPv6 on Channels Related
                to ITS Scenarios using 802.11p Networks - an
                Analysis  . . . . . . . . . . . . . . . . . . . . . . 26
     B.1.  Interpretation of FCC and ETSI documents with respect
           to running IP on particular channels . . . . . . . . . . . 26
     B.2.  Interpretations of Latencies of IP datagrams . . . . . . . 27
   Appendix C.  Changes Needed on a software driver 802.11a to
                become a 802.11p driver . . . . . . . . . . . . . . . 27
   Appendix D.  Use of IPv6 over 802.11p for distribution of
                certificates  . . . . . . . . . . . . . . . . . . . . 28
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29

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1.  Introduction

   This document describes the transmission of IPv6 packets on IEEE
   802.11p networks.  This involves the layering of IPv6 networking on
   top of the IEEE 802.11p MAC layer (with an LLC layer).  Compared to
   running IPv6 over the Ethernet MAC layer, or over other 802.11 links,
   there is no modification required to the standards: IPv6 works fine
   directly over 802.11p too (with an LLC layer).

   As an overview, we illustrate how an IPv6 stack runs over 802.11p by
   layering different protocols on top of each other.  The IPv6
   Networking is layered on top of the IEEE 802.2 Logical-Link Control
   (LLC) layer; this is itself layered on top of the 802.11p MAC; this
   layering illustration is similar to that of running IPv6 over 802.2
   LLC over the 802.11 MAC, or over Ethernet MAC.

                +-----------------+      +-----------------+
                |       ...       |      |       ...       |
                +-----------------+      +-----------------+
                | IPv6 Networking |      | IPv6 Networking |
                +-----------------+      +-----------------+
                |    802.2 LLC    |  vs. |    802.2 LLC    |
                +-----------------+      +-----------------+
                |   802.11p MAC   |      |   802.11b MAC   |
                +-----------------+      +-----------------+
                |   802.11p PHY   |      |   802.11b PHY   |
                +-----------------+      +-----------------+

   But, there are several deployment considerations to optimize the
   performances of running IPv6 over 802.11p (e.g. in the case of
   handovers between 802.11p Access Points, or the consideration of
   using the IP security layer).

   We briefly introduce the vehicular communication scenarios where IEEE
   802.11p links are used.  This is followed by a description of
   differences in specification terms, between 802.11p and 802.11a/b/g/n
   (and the same differences expressed in terms of requirements to
   software implementation are listed in Appendix C.)

   The document then concentrates on the parameters of layering IPv6
   over 802.11p as over Ethernet: MTU, Frame Format, Interface
   Identifier, Address Mapping, State-less Address Auto-configuration.
   The values of these parameters are precisely the same as IPv6 over
   Ethernet [RFC2464]: the recommended value of MTU to be 1500 octets,
   the Frame Format containing the Type 0x86DD, the rules for forming an

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   Interface Identifier, the Address Mapping mechanism and the Stateless
   Address Auto-Configuration.

   As an example, these characteristics of layering IPv6 straight over
   LLC over 802.11p MAC are illustrated by dissecting an IPv6 packet
   captured over a 802.11p link; this is described in the section titled
   "Example of IPv6 Packet captured over an IEEE 802.11p link".

   A few points can be considered as different, although they do not
   seem required in order to have a working implementation of IPv6-over-
   802.11p.  These points are consequences of the OCB operation which is
   particular to 802.11p (Outside the Context of a BSS).  The handovers
   between OCB links need specific behaviour for IP Router
   Advertisements, or otherwise 802.11p's Time Advertisement, or of
   higher layer messages such as the 'Basic Safety Message' (in the US)
   or the 'Cooperative Awareness Message' (in the EU) or the 'WAVE
   Routing Advertisement' ; second, the IP security should be considered
   of utmost importance, since OCB means that 802.11p is stripped of all
   802.11 link-layer security; a small additional security aspect which
   is shared between 802.11p and other 802.11 links is the privacy
   concerns related to the address formation mechanisms.  These two
   points (OCB handovers and security) are described each in a section
   of its own: OCB handovers in Section 6 and security in Section 8.

   In standards, the operation of IPv6 as a 'data plane' over 802.11p is
   specified in [ieeep1609.3-D9-2010].  For example, it mentions that
   "Networking services also specifies the use of the Internet protocol
   IPv6, and supports transport protocols such as UDP and TCP. [...]  A
   Networking Services implementation shall support either IPv6 or WSMP
   or both." and "IP traffic is sent and received through the LLC
   sublayer as specified in [...]".  Also, the operation of IPv6 over a
   GeoNetworking layer and over G5 is described in

   In the published literature, three documents describe aspects related
   to running IPv6 over 802.11p: [vip-wave], [ipv6-80211p-its] and

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

   RSU stands for Road Side Unit.

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3.  Communication Scenarios where IEEE 802.11p Links are Used

   The IEEE 802.11p Networks are used for vehicular communications, as
   'Wireless Access in Vehicular Environments'.  The IP communication
   scenarios for these environments have been described in several
   documents, among which we refer the reader to one recently updated
   [I-D.petrescu-its-scenarios-reqs], about scenarios and requirements
   for IP in Intelligent Transportation Systems.

4.  Aspects introduced by 802.11p to 802.11

   The link 802.11p is specified in IEEE Std 802.11p(TM)-2010
   [ieee802.11p-2010] as an amendment to the 802.11 specifications,
   titled "Amendment 6: Wireless Access in Vehicular Environments".
   Since then, these 802.11p amendments have been included in IEEE
   802.11(TM)-2012 [ieee802.11-2012], titled "IEEE Standard for
   Information technology--Telecommunications and information exchange
   between systems Local and metropolitan area networks--Specific
   requirements Part 11: Wireless LAN Medium Access Control (MAC) and
   Physical Layer (PHY) Specifications"; the modifications are diffused
   throughout various sections (e.g. 802.11p's Time Advertisement
   message is described in section 'Frame formats', and the operation
   outside the context of a BSS described in section 'MLME').

   In order to delineate the aspects introduced by 802.11p to 802.11, we
   refer to the earlier [ieee802.11p-2010].  The amendment is concerned
   with vehicular communications, where the wireless link is similar to
   that of Wireless LAN (using a PHY layer specified by 802.11a/b/g/n),
   but which needs to cope with the high mobility factor inherent in
   scenarios of communications between moving vehicles, and between
   vehicles and fixed infrastructure deployed along roads.  Whereas 'p'
   is a letter just like 'a, b, g' and 'n' are, 'p' is concerned more
   with MAC modifications, and a little with PHY modifications; the
   others are mainly about PHY modifications.  It is possible in
   practice to combine a 'p' MAC with an 'a' PHY by operating outside
   the context of a BSS with OFDM at 5.4GHz.

   The 802.11p links are specified to be compatible as much as possible
   with the behaviour of 802.11a/b/g/n and future generation IEEE WLAN
   links.  From the IP perspective, an 802.11p MAC layer offers
   practically the same interface to IP as the WiFi and Ethernet layers
   do (802.11a/b/g/n and 802.3).

   To support this similarity statement (IPv6 is layered on top of LLC
   on top of 802.11p similarly as on top of LLC on top of 802.11a/b/g/n,
   and as on top of LLC on top of 802.3) it is useful to analyze the
   802.11p differences compared to non-p 802.11 specifications.  Whereas

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   the 802.11p amendment specifies relatively complex and numerous
   changes to the MAC layer (and very little to the PHY layer), we note
   here only a few characteristics which may be important for an
   implementation transmitting IPv6 packets on 802.11p links.

   In the list below, the only 802.11p fundamental points which
   influence IPv6 are the OCB operation and the 12Mbit/s maximum which
   may be afforded by the IPv6 applications.

   o  Operation Outside the Context of a BSS (OCB): the 802.11p links
      are operated without a Basic Service Set (BSS).  This means that
      the messages Beacon, Association Request/Response, Authentication
      Request/Response, and similar, are not used.  The used identifier
      of BSS (BSSID) has a hexadecimal value always ff:ff:ff:ff:ff:ff
      (48 '1' bits, or the 'wildcard' BSSID), as opposed to an arbitrary
      BSSID value set by administrator (e.g.  'My-Home-AccessPoint').
      The OCB operation - namely the lack of beacon-based scanning and
      lack of authentication - has potentially strong impact on the use
      of protocol Mobile IPv6 and protocols for IP layer security.

   o  Timing Advertisement: is a new message defined in 802.11p, which
      does not exist in 802.11a/b/g/n.  This message is used by stations
      to inform other stations about the value of time.  It is similar
      to the time as delivered by a GNSS system (Galileo, GPS, ...) or
      by a cellular system.  This message is optional for
      implementation.  At the date of writing, an experienced reviewer
      considers that currently no field testing has used this message.
      Another implementor considers this feature implemented in an
      initial manner.  In the future, it is speculated that this message
      may be useful for very simple devices which may not have their own
      hardware source of time (Galileo, GPS, cellular network), or by
      vehicular devices situated in areas not covered by such network
      (in tunnels, underground, outdoors but shaded by foliage or
      buildings, in remote areas, etc.)

   o  Frequency range: this is a characteristic of the PHY layer, with
      almost no impact to the interface between MAC and IP.  However, it
      is worth considering that the frequency range is regulated by a
      regional authority (ARCEP, ETSI, FCC, etc.); as part of the
      regulation process, specific applications are associated with
      specific frequency ranges.  In the case of 802.11p, the regulator
      associates a set of frequency ranges, or slots within a band, to
      the use of applications of vehicular communications, in a band
      known as "5.9GHz".  This band is "5.9GHz" which is different than
      the bands "2.4GHz" or "5GHz" used for the Wireless LAN.  But, as
      with Wireless LAN, the operation of 802.11p in "5.9GHz" bands is
      exempt from owning a license in EU (in US the 5.9GHz is a licensed
      band of spectrum; for the the fixed infrastructure an explicit FCC

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      is required; for an onboard device a 'licensed-by-rule' concept
      applies: rule certification conformity is required); however
      technical conditions are different than those of the bands
      "2.4GHz" or "5GHz".  On one hand, the allowed power levels, and
      implicitly the maximum allowed distance between vehicles, is of
      33dBm for 802.11p (in Europe), compared to 20 dBm for Wireless LAN
      802.11a/b/g/n; this leads to maximum distance of approximately
      1km, compared to approximately 50m.  On another hand, specific
      conditions related to congestion avoidance, jamming avoidance, and
      radar detection are imposed on the use of DSRC (in US) and on the
      use of frequencies for Intelligent Transportation Systems (in EU),
      compared to Wireless LAN (802.11a/b/g/n).

   o  Explicit prohibition of IPv6 on some channels relevant for the PHY
      of IEEE 802.11p, as opposed to IPv6 not being prohibited on any
      channel on which 802.11a/b/g/n runs; for example, IPv6 is
      prohibited on the 'Control Channel' (number 178 at FCC/IEEE, and
      180 at ETSI); for a detailed analysis of IEEE and ETSI prohibition
      of IP in particular channels see Appendix B.

   o  'Half-rate' encoding: as the frequency range, this parameter is
      related to PHY, and thus has not much impact on the interface
      between the IP layer and the MAC layer.  The standard IEEE 802.11p
      uses OFDM encoding at PHY, as other non-b 802.11 variants do.
      This considers 20MHz encoding to be 'full-rate' encoding, as the
      earlier 20MHz encoding which is used extensively by 802.11b.  In
      addition to the full-rate encoding, the OFDM rates also involve
      5MHz and 10MHz.  The 10MHz encoding is named 'half-rate'.  The
      encoding dictates the bandwidth and latency characteristics that
      can be afforded by the higher-layer applications of IP
      communications.  The half-rate means that each symbol takes twice
      the time to be transmitted; for this to work, all 802.11 software
      timer values are doubled.  With this, in certain channels of the
      "5.9GHz" band, a maximum bandwidth of 12Mbit/s is possible,
      whereas in other "5.9GHz" channels a minimal bandwidth of 1Mbit/s
      may be used.  It is worth mentioning the half-rate encoding is an
      optional feature characteristic of OFDM PHY (compared to 802.11b's
      full-rate 20MHz), used by 802.11a before 802.11p used it.  In
      addition to the half-rate (10MHz) used by 802.11p in some
      channels, some other 802.11p channels may use full-rate (20MHz) or
      quarter-rate(?) (5MHz) encoding instead.


      *  It is worth mentioning that more precise interpretations of the
         'half-rate' term suggest that a maximum throughput be 27Mbit/s
         (which is half of 802.11g's 54Mbit/s), whereas 6Mbit/s or
         12Mbit/s throughputs represent effects of further 802.11p-

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         specific PHY reductions in the throughput necessary to better
         accommodate vehicle-class speeds and distance ranges.

   o  In vehicular communications where 802.11p links, there are strong
      privacy concerns with respect to addressing.  Whereas the 802.11p
      standard does not specify anything in particular with respect to
      MAC addresses, in these settings there exist a strong need for
      dynamic change of these addresses (as opposed to the non-vehicular
      settings - real wall protection - where fixed MAC addresses do not
      currently pose same privacy risks).  This is further described in
      section Section 8.

   Other aspects particular to 802.11p which are also particular to
   802.11 (e.g. the 'hidden node' operation) may have an influence on
   the use of transmission of IPv6 packets on 802.11p networks.  The
   subnet structure which may assumed in 802.11p networks is strongly
   influenced by the mobility of vehicles.

5.  Layering of IPv6 over 802.11p as over Ethernet

5.1.  Maximum Transmission Unit (MTU)

   The default MTU for IPv6 packets on 802.11p is 1500 octets.  It is
   the same value as IPv6 packets on Ethernet links, as specified in
   [RFC2464].  This value of the MTU respects the recommendation that
   every link in the Internet must have a minimum MTU of 1280 octets
   (stated in [RFC2460], and the recommendations therein, especially
   with respect to fragmentation).

5.2.  Frame Format

   IPv6 packets are transmitted over 802.11p as standard Ethernet
   packets.  As with all 802.11 frames, an Ethernet adaptation layer is
   used with 802.11p as well.  This Ethernet Adaptation Layer 802.11-to-
   Ethernet is described in Section 5.2.1.  The Ethernet Type code
   (EtherType) is 0x86DD (hexadecimal 86DD, or otherwise #86DD).

   The Frame format for transmitting IPv6 on 802.11p networks is the
   same as transmitting IPv6 on Ethernet networks, and is described in
   section 3 of [RFC2464].  For sake of completeness, the frame format
   for transmitting IPv6 over Ethernet is illustrated below:

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                      0                   1
                      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                     |          Destination          |
                     +-                             -+
                     |            Ethernet           |
                     +-                             -+
                     |            Address            |
                     |             Source            |
                     +-                             -+
                     |            Ethernet           |
                     +-                             -+
                     |            Address            |
                     |1 0 0 0 0 1 1 0 1 1 0 1 1 1 0 1|
                     |             IPv6              |
                     +-                             -+
                     |            header             |
                     +-                             -+
                     |             and               |
                     +-                             -+
                     /            payload ...        /

                     (Each tic mark represents one bit.)

5.2.1.  Ethernet Adaptation Layer

   In general, an 'adaptation' layer is inserted between a MAC layer and
   the Networking layer.  This is used to transform some parameters
   between their form expected by the IP stack and the form provided by
   the MAC layer.  For example, an 802.15.4 adaptation layer may perform
   fragmentation and reassembly operations on a MAC whose maximum Packet
   Data Unit size is smaller than the minimum MTU recognized by the IPv6
   Networking layer.  Other examples involve link-layer address
   transformation, packet header insertion/removal, and so on.

   An Ethernet Adaptation Layer makes an 802.11 MAC look to IP
   Networking layer as a more traditional Ethernet layer.  At reception,
   this layer takes as input the IEEE 802.11 Data Header and the
   Logical-Link Layer Control Header and produces an Ethernet II Header.
   At sending, the reverse operation is performed.

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        | 802.11 Data Header | LLC Header  | IPv6 Header | Payload |

                         802.11-to-Ethernet Adaptation Layer

                     | Ethernet II Header  | IPv6 Header | Payload |

   The Receiver and Transmitter Address fields in the 802.11 Data Header
   contain the same values as the Destination and the Source Address
   fields in the Ethernet II Header, respectively.  The value of the
   Type field in the LLC Header is the same as the value of the Type
   field in the Ethernet II Header.  The other fields in the Data and
   LLC Headers are not used by the IPv6 stack.

5.3.  Link-Local Addresses

   The link-local address of an 802.11p interface is formed in the same
   manner as on an Ethernet interface.  This manner is described in
   section 5 of [RFC2464].

5.4.  Address Mapping

   For unicast as for multicast, there is no change from the unicast and
   multicast address mapping format of Ethernet interfaces, as defined
   by sections 6 and 7 of [RFC2464].

   (however, there is discussion about geography, networking and IPv6
   multicast addresses: geographical dissemination of IPv6 data over
   802.11p may be useful in traffic jams, for example).

5.5.  Stateless Autoconfiguration

   The Interface Identifier for an 802.11p interface is formed using the
   same rules as the Interface Identifier for an Ethernet interface;
   this is described in section 4 of [RFC2464].  No changes are needed,
   but some care must be taken when considering the use of the SLAAC

   For example, the Interface Identifier for an 802.11p interface whose
   built-in address is, in hexadecimal:

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   would be


   The bits in the the interface identifier have no generic meaning and
   the identifier should be treated as an opaque value.  The bits
   'Universal' and 'Group' in the identifier of an 802.11p interface are
   significant, as this is a IEEE link-layer address.  The details of
   this significance are described in [I-D.ietf-6man-ug].

   As with all Ethernet and 802.11 interface identifiers, the identifier
   of an 802.11p interface may involve privacy risks.  A vehicle
   embarking an On-Board Unit whose egress interface is 802.11p may
   expose itself to eavesdropping and subsequent correlation of data;
   this may reveal data considered private by the vehicle owner.  The
   address generation mechanism should consider these aspects, as
   described in [I-D.ietf-6man-ipv6-address-generation-privacy].

5.6.  Subnet Structure

   In this section the subnet structure may be described: the addressing
   model (are multi-link subnets considered?), address resolution,
   multicast handling, packet forwarding between IP subnets.
   Alternatively, this section may be spinned off into a separate

   The 802.11p networks, much like other 802.11 networks, may be
   considered as 'ad-hoc' networks.  The addressing model for such
   networks is described in [RFC5889].

   The SLAAC procedure makes the assumption that if a packet is
   retransmitted a fixed number of times (typically 3, but it is link
   dependent), any connected host receives the packet with high
   probability.  On ad-hoc links (when 802.11p is operated in OCB mode,
   the link can be considered as 'ad-hoc'), both the hidden terminal
   problem and mobility-range considerations make this assumption
   incorrect.  Therefore, SLAAC should not be used when address
   collisions can induce critical errors in upper layers.

   Some aspects of multi-hop ad-hoc wireless communications which are
   relevant to the use of 802.11p (e.g. the 'hidden' node) are described
   in [I-D.baccelli-multi-hop-wireless-communication].

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   When operating in OCB mode, it may be appropriate to use a 6LoWPAN
   adaptation layer [RFC6775].  However, it should be noted that the use
   6lowpan adaptation layer may compete with the use of Ethernet to
   802.11 adaptation layer.

6.  Handovers between OCB links

   A station operating IEEE 802.11p in the 5.9 GHz band in US or EU is
   required to send data frames outside the context of a BSS.  In this
   case, the station does not utilize the IEEE 802.11 authentication,
   association, or data confidentiality services.  This avoids the
   latency associated with establishing a BSS and is particularly suited
   to communications between mobile stations or between a mobile station
   and a fixed one playing the role of the default router (e.g. a fixed
   Road-Side Unit a.k.a RSU acting as an infrastructure router).

   The process of movement detection is described in section 11.5.1 of
   [RFC6275].  In the context of 802.11p deployments, detecting
   movements between two adjacent RSUs becomes harder for the moving
   stations: they cannot rely on Layer-2 triggers (such as L2
   association/de-association phases) to detect when they leave the
   vicinity of an RSU and move within coverage of another RSU.  In such
   case, the movement detection algorithms require other triggers.  We
   detail below the potential other indications that can be used by a
   moving station in order to detect handovers between OCB ("Outside the
   Context of a BSS") links.

   A movement detection mechanism may take advantage of positioning data
   (latitude and longitude).

   Mobile IPv6 [RFC6275] specifies a new Router Advertisement option
   called the "Advertisement Interval Option".  It can be used by an RSU
   to indicate the maximum interval between two consecutive unsolicited
   Router Advertisement messages sent by this RSU.  With this option, a
   moving station can learn when it is supposed to receive the next RA
   from the same RSU.  This can help movement detection: if the
   specified amount of time elapses without the moving station receiving
   any RA from that RSU, this means that the RA has been lost.  It is up
   to the moving node to determine how many lost RAs from that RSU
   constitutes a handover trigger.

   In addition to the Mobile IPv6 "Advertisement Interval Option", the
   Neighbor Unreachability Detection (NUD) [RFC4861] can be used to
   determine whether the RSU is still reachable or not.  In this
   context, reachability confirmation would basically consist in
   receiving a Neighbor Advertisement message from a RSU, in response to
   a Neighbor Solicitation message sent by the moving station.  The RSU

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   should also configure a low Reachable Time value in its RA in order
   to ensure that a moving station does not assume an RSU to be
   reachable for too long.

   The Mobile IPv6 "Advertisement Interval Option" as well as the NUD
   procedure only help knowing if the RSU is still reachable by the
   moving station.  It does not provide the moving station with
   information about other potential RSUs that might be in range.  For
   this purpose, increasing the RA frequency could reduce the delay to
   discover the next RSU.  The Neighbor Discovery protocol [RFC4861]
   limits the unsolicited multicast RA interval to a minimum of 3
   seconds (the MinRtrAdvInterval variable).  This value is too high for
   dense deployments of Access Routers deployed along fast roads.  The
   protocol Mobile IPv6 [RFC6275] allows routers to send such RA more
   frequently, with a minimum possible of 0.03 seconds (the same
   MinRtrAdvInterval variable): this should be preferred to ensure a
   faster detection of the potential RSUs in range.

   If multiple RSUs are in the vicinity of a moving station at the same
   time, the station may not be able to choose the "best" one (i.e. the
   one that would afford the moving station spending the longest time in
   its vicinity, in order to avoid too frequent handovers).  In this
   case, it would be helpful to base the decision on the signal quality
   (e.g. the RSSI of the received RA provided by the radio driver).  A
   better signal would probably offer a longer coverage.  If, in terms
   of RA frequency, it is not possible to adopt the recommendations of
   protocol Mobile IPv6 (but only the Neighbor Discovery specification
   ones, for whatever reason), then another message than the RA could be
   emitted periodically by the Access Router (provided its specification
   allows to send it very often), in order to help the Host determine
   the signal quality.  One such message may be the 802.11p's Time
   Advertisement, or higher layer messages such as the "Basic Safety
   Message" (in the US) or the "Cooperative Awareness Message " (in the
   EU), that are usually sent several times per second.  Another
   alternative replacement for the IPv6 Router Advertisement may be the
   message 'WAVE Routing Advertisement' (WRA), which is part of the WAVE
   Service Advertisement and which may contain optionally the
   transmitter location; this message is described in section 8.2.5 of

   Once the choice of the default router has been performed by the
   moving node, it can be interesting to use Optimistic DAD [RFC4429] in
   order to speed-up the address auto-configuration and ensure the
   fastest possible Layer-3 handover.

   To summarize, efficient handovers between OCB links can be performed
   by using a combination of existing mechanisms.  In order to improve
   the default router unreachability detection, the RSU and moving

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   stations should use the Mobile IPv6 "Advertisement Interval Option"
   as well as rely on the NUD mechanism.  In order to allow the moving
   station to detect potential default router faster, the RSU should
   also be able to be configured with a smaller minimum RA interval such
   as the one recommended by Mobile IPv6.  When multiple RSUs are
   available at the same time, the moving station should perform the
   handover decision based on the signal quality.  Finally, optimistic
   DAD can be used to reduce the handover delay.

7.  Example IPv6 Packet captured over a IEEE 802.11p link

   We remind that a main goal of this document is to make the case that
   IPv6 works fine over 802.11p networks.  Consequently, this section is
   an illustration of this concept and thus can help the implementer
   when it comes to running IPv6 over IEEE 802.11p.  By way of example
   we show that there is no modification in the headers when transmitted
   over 802.11p networks - they are transmitted like any other 802.11
   and Ethernet packets.

   We describe an experiment of capturing an IPv6 packet captured on an
   802.11p link.  In this experiment, the packet is an IPv6 Router
   Advertisement.  This packet is emitted by a Router on its 802.11p
   interface.  The packet is captured on the Host, using a network
   protocol analyzer (e.g.  Wireshark); the capture is performed in two
   different modes: direct mode and 'monitor' mode.  The topology used
   during the capture is depicted below.

                   ##########                    ########
                   #        #                    #      #
                   # Router #--------------------# Host #
                   #        #    802.11p Link    #      #
                   ##########                    ########
                     /   \                         o  o

   During several capture operations running from a few moments to
   several hours, no message relevant to the BSSID contexts were
   captured (no Association Request/Response, Authentication Req/Resp,
   Beacon).  This shows that the operation of 802.11p is outside the
   context of a BSSID.

   Overall, the captured message is precisely similar with a capture of
   an IPv6 packet emitted on a 802.11b interface.  The contents are
   precisely similar.

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7.1.  Capture in Monitor Mode

   The IPv6 RA packet captured in monitor mode is illustrated below.
   The radio tap header provides more flexibility for reporting the
   characteristics of frames.  The Radiotap Header is prepended by this
   particular stack and operating system on the Host machine to the RA
   packet received from the network (the Radiotap Header is not present
   on the air).  The implementation-dependent Radiotap Header is useful
   for piggybacking PHY information from the chip's registers as data in
   a packet understandable by userland applications using Socket
   interfaces (the PHY interface can be, for example: power levels, data
   rate, ratio of signal to noise).

   The packet present on the air is formed by IEEE 802.11 Data Header,
   Logical Link Control Header, IPv6 Base Header and ICMPv6 Header.

     Radiotap Header v0
     |Header Revision|  Header Pad   |    Header length              |
     |                         Present flags                         |
     | Data Rate     |             Pad                               |

     IEEE 802.11 Data Header
     |  Type/Subtype and Frame Ctrl  |          Duration             |
     |                      Receiver Address...
     ... Receiver Address           |      Transmitter Address...
     ... Transmitter Address                                        |
     |                            BSS Id...
     ... BSS Id                     |  Frag Number and Seq Number   |

     Logical-Link Control Header
     |      DSAP   |I|     SSAP    |C| Control field | Org. code...
     ... Organizational Code        |             Type              |

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     IPv6 Base Header
     |Version| Traffic Class |           Flow Label                  |
     |         Payload Length        |  Next Header  |   Hop Limit   |
     |                                                               |
     +                                                               +
     |                                                               |
     +                         Source Address                        +
     |                                                               |
     +                                                               +
     |                                                               |
     |                                                               |
     +                                                               +
     |                                                               |
     +                      Destination Address                      +
     |                                                               |
     +                                                               +
     |                                                               |

     Router Advertisement
     |     Type      |     Code      |          Checksum             |
     | Cur Hop Limit |M|O|  Reserved |       Router Lifetime         |
     |                         Reachable Time                        |
     |                          Retrans Timer                        |
     |   Options ...

   The value of the Data Rate field in the Radiotap header is set to 6
   Mb/s.  This indicates the rate at which this RA was received.

   The value of the Transmitter address in the IEEE 802.11 Data Header
   is set to a 48bit value.  The value of the destination address is 33:
   33:00:00:00:1 (all-nodes multicast address).  The value of the BSS Id
   field is ff:ff:ff:ff:ff:ff, which is recognized by the network
   protocol analyzer as being "broadcast".  The Fragment number and
   sequence number fields are together set to 0x90C6.

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   The value of the Organization Code field in the Logical-Link Control
   Header is set to 0x0, recognized as "Encapsulated Ethernet".  The
   value of the Type field is 0x86DD (hexadecimal 86DD, or otherwise
   #86DD), recognized as "IPv6".

   A Router Advertisement is periodically sent by the router to
   multicast group address ff02::1.  It is an icmp packet type 134.  The
   IPv6 Neighbor Discovery's Router Advertisement message contains an
   8-bit field reserved for single-bit flags, as described in [RFC4861].

   The IPv6 header contains the link local address of the router
   (source) configured via EUI-64 algorithm, and destination address set
   to ff02::1.  Recent versions of network protocol analyzers (e.g.
   Wireshark) provide additional informations for an IP address, if a
   geolocalization database is present.  In this example, the
   geolocalization database is absent, and the "GeoIP" information is
   set to unknown for both source and destination addresses (although
   the IPv6 source and destination addresses are set to useful values).
   This "GeoIP" can be a useful information to look up the city,
   country, AS number, and other information for an IP address.

   The Ethernet Type field in the logical-link control header is set to
   0x86dd which indicates that the frame transports an IPv6 packet.  In
   the IEEE 802.11 data, the destination address is 33:33:00:00:00:01
   which is he corresponding multicast MAC address.  The BSS id is a
   broadcast address of ff:ff:ff:ff:ff:ff.  Due to the short link
   duration between vehicles and the roadside infrastructure, there is
   no need in IEEE 802.11p to wait for the completion of association and
   authentication procedures before exchanging data.  IEEE 802.11p
   enabled nodes use the wildcard BSSID (a value of all 1s) and may
   start communicating as soon as they arrive on the communication

7.2.  Capture in Normal Mode

   The same IPv6 Router Advertisement packet described above (monitor
   mode) is captured on the Host, in the Normal mode, and depicted

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     Ethernet II Header
     |                       Destination...
     ...Destination                 |           Source...
     ...Source                                                      |
     |          Type                 |

     IPv6 Base Header
     |Version| Traffic Class |           Flow Label                  |
     |         Payload Length        |  Next Header  |   Hop Limit   |
     |                                                               |
     +                                                               +
     |                                                               |
     +                         Source Address                        +
     |                                                               |
     +                                                               +
     |                                                               |
     |                                                               |
     +                                                               +
     |                                                               |
     +                      Destination Address                      +
     |                                                               |
     +                                                               +
     |                                                               |

     Router Advertisement
     |     Type      |     Code      |          Checksum             |
     | Cur Hop Limit |M|O|  Reserved |       Router Lifetime         |
     |                         Reachable Time                        |
     |                          Retrans Timer                        |
     |   Options ...

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   One notices that the Radiotap Header is not prepended, and that the
   IEEE 802.11 Data Header and the Logical-Link Control Headers are not
   present.  On another hand, a new header named Ethernet II Header is

   The Destination and Source addresses in the Ethernet II header
   contain the same values as the fields Receiver Address and
   Transmitter Address present in the IEEE 802.11 Data Header in the
   "monitor" mode capture.

   The value of the Type field in the Ethernet II header is 0x86DD
   (recognized as "IPv6"); this value is the same value as the value of
   the field Type in the Logical-Link Control Header in the "monitor"
   mode capture.

   The knowledgeable experimenter will no doubt notice the similarity of
   this Ethernet II Header with a capture in normal mode on a pure
   Ethernet cable interface.

   It may be interpreted that an Adaptation layer is inserted in a pure
   IEEE 802.11 MAC packets in the air, before delivering to the
   applications.  In detail, this adaptation layer may consist in
   elimination of the Radiotap, 802.11 and LLC headers and insertion of
   the Ethernet II header.  In this way, it can be stated that IPv6 runs
   naturally straight over LLC over the 802.11p MAC layer, as shown by
   the use of the Type 0x86DD, and assuming an adaptation layer
   (adapting 802.11 LLC/MAC to Ethernet II header).

8.  Security Considerations

   802.11p does not provide any cryptographic protection, because it
   operates outside the context of a BSS (no Association Request/
   Response, no Challenge messages).  Any attacker can therefore just
   sit in the near range of vehicles, sniff the network (just set the
   interface card's frequency to the proper range) and perform attacks
   without needing to physically break any wall.  Such a link is way
   less protected than commonly used links (wired link or protected

   At the IP layer, IPsec can be used to protect unicast communications,
   and SeND can be used for multicast communications.  If no protection
   is used by the IP layer, upper layers should be protected.
   Otherwise, the end-user or system should be warned about the risks
   they run.

   The WAVE protocol stack provides for strong security when using the
   WAVE Short Message Protocol and the WAVE Service Advertisement

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   As with all Ethernet and 802.11 interface identifiers, there may
   exist privacy risks in the use of 802.11p interface identifiers.
   However, in outdoors vehicular settings, the privacy risks are more
   important than in indoors settings.  New risks are induced by the
   possibility of attacker sniffers deployed along routes which listen
   for IP packets of vehicles passing by.  For this reason, in the
   802.11p deployments, there is a strong necessity to use protection
   tools such as dynamically changing MAC addresses.  This may help
   mitigate privacy risks to a certain level.  On another hand, it may
   have an impact in the way typical IPv6 address auto-configuration is
   performed for vehicles (SLAAC would rely on MAC addresses amd would
   hence dynamically change the affected IP address), in the way the
   IPv6 Privacy addresses were used, and other effects.

9.  IANA Considerations

10.  Contributors

   Romain Kuntz contributed extensively the concepts described in
   Section 6 about IPv6 handovers between links running outside the
   context of a BSS (802.11p links).

11.  Acknowledgements

   The authors would like to acknowledge Witold Klaudel, Ryuji Wakikawa,
   Emmanuel Baccelli, John Kenney, John Moring, Francois Simon, Dan
   Romascanu, Konstantin Khait, Ralph Droms, Richard Roy and Ray Hunter.
   Their supportive comments clarified certain issues and generally
   helped to improve the document.

12.  References

12.1.  Normative References

              Cooper, A., Gont, F., and D. Thaler, "Privacy
              Considerations for IPv6 Address Generation Mechanisms",
              draft-ietf-6man-ipv6-address-generation-privacy-01 (work
              in progress), February 2014.

              Carpenter, B. and S. Jiang, "Significance of IPv6

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              Interface Identifiers", draft-ietf-6man-ug-06 (work in
              progress), December 2013.

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

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC2464]  Crawford, M., "Transmission of IPv6 Packets over Ethernet
              Networks", RFC 2464, December 1998.

   [RFC4429]  Moore, N., "Optimistic Duplicate Address Detection (DAD)
              for IPv6", RFC 4429, April 2006.

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

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

   [RFC6275]  Perkins, C., Johnson, D., and J. Arkko, "Mobility Support
              in IPv6", RFC 6275, July 2011.

   [RFC6775]  Shelby, Z., Chakrabarti, S., Nordmark, E., and C. Bormann,
              "Neighbor Discovery Optimization for IPv6 over Low-Power
              Wireless Personal Area Networks (6LoWPANs)", RFC 6775,
              November 2012.

12.2.  Informative References

              Baccelli, E. and C. Perkins, "Multi-hop Ad Hoc Wireless
              draft-baccelli-multi-hop-wireless-communication-06 (work
              in progress), July 2011.

              Petrescu, A., Janneteau, C., Boc, M., and W. Klaudel,
              "Scenarios and Requirements for IP in Intelligent
              Transportation Systems",
              draft-petrescu-its-scenarios-reqs-03 (work in progress),
              October 2013.

              "Intelligent Transport Systems (ITS); Access layer
              specification for Intelligent Transport Systems operating

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              in the 5 GHz frequency band, 2013-07, document
              en_302663v010201p.pdf, document freely available at URL
              01.02.01_60/en_302663v010201p.pdf downloaded on October
              17th, 2013.".

              "Electromagnetic compatibility and Radio spectrum Matters
              (ERM); Intelligent Transport Systems (ITS); Part 2:
              Technical characteristics for pan European harmonized
              communications equipment operating in the 5 GHz frequency
              range intended for road safety and traffic management, and
              for non-safety related ITS applications; System Reference
              Document, Draft ETSI TR 102 492-2 V1.1.1, 2006-07,
              document tr_10249202v010101p.pdf freely available at URL
              10249202/01.01.01_60/tr_10249202v010101p.pdf downloaded on
              October 18th, 2013.".

   [fcc-cc]   "'Report and Order, Before the Federal Communications
              Commission Washington, D.C. 20554', FCC 03-324, Released
              on February 10, 2004, document FCC-03-324A1.pdf, document
              freely available at URL
     downloaded on
              October 17th, 2013.".

              "'Memorandum Opinion and Order, Before the Federal
              Communications Commission Washington, D.C. 20554', FCC
              06-10, Released on July 26, 2006, document FCC-06-
              110A1.pdf, document freely available at URL http://
              FCC-06-110A1.pdf downloaded on June 5th, 2014.".

              "802.11-2012 - IEEE Standard for Information technology--
              Telecommunications and information exchange between
              systems Local and metropolitan area networks--Specific
              requirements Part 11: Wireless LAN Medium Access Control
              (MAC) and Physical Layer (PHY) Specifications.  Downloaded
              on October 17th, 2013, from IEEE Standards, document
              freely available at URL
              findstds/standard/802.11-2012.html retrieved on October
              17th, 2013.".

              "IEEE Std 802.11p(TM)-2010, IEEE Standard for Information
              Technology - Telecommunications and information exchange

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              between systems - Local and metropolitan area networks -
              Specific requirements, Part 11: Wireless LAN Medium Access
              Control (MAC) and Physical Layer (PHY) Specifications,
              Amendment 6: Wireless Access in Vehicular Environments;
              document freely available at URL http://
              retrieved on September 20th, 2013.".

              "IEEE P1609.2(tm)/D17 Draft Standard for Wireless Access
              in Vehicular Environments - Security Services for
              Applications and Management Messages.  pdf, length 2558
              Kb.  Restrictions apply.".

              "IEEE P1609.3(tm)/D9, Draft Standard for Wireless Access
              in Vehicular Environments (WAVE) - Networking Services,
              August 2010.  Authorized licensed use limited to: CEA.
              Downloaded on June 19, 2013 at 07:32:34 UTC from IEEE
              Xplore. Restrictions apply, document at persistent link

              "IEEE P1609.4(tm)/D9 Draft Standard for Wireless Access in
              Vehicular Environments (WAVE) - Multi-channel Operation.
              Authorized licensed use limited to: CEA. Downloaded on
              June 19, 2013 at 07:34:48 UTC from IEEE Xplore.
              Restrictions apply.  Document at persistent link

              Shagdar, O., Tsukada, M., Kakiuchi, M., Toukabri, T., and
              T. Ernst, "Experimentation Towards IPv6 over IEEE 802.11p
              with ITS Station Architecture", International Workshop on
              IPv6-based Vehicular Networks, (colocated with IEEE
              Intelligent Vehicles Symposium), URL:
     , Downloaded on:  24
              October 2013, Availability: free at some sites, paying at
              others, May 2012.

              Clausen, T., Baccelli, E., and R. Wakikawa, "IPv6
              Operation for WAVE - Wireless Access in Vehicular
              Environments", Rapport de Recherche INRIA, number 7383,
              URL:, Downloaded on:
               24 October 2013, Availability: free at some sites,
              September 2010.

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              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, Volume 14, Issue 1, URL and Digital Object
              Downloaded on:  24 October 2013, Availability: free at
              some sites, paying at others, March 2013.

Appendix A.  ChangeLog

   The changes are listed in reverse chronological order, most recent
   changes appearing at the top of the list.

   From draft-petrescu-ipv6-over-80211p-01.txt to

   o  updated authorship.

   o  added explanation about FCC not prohibiting IP on channels, and
      comments about engineering advice and reliability of IP messages.

   o  added possibility to use 6lowpan adaptation layer when in OCB

   o  added appendix about the distribution of certificates to vehicles
      by using IPv6-over-802.11p single-hop communications.

   o  refined the explanation of 'half-rate' mode.

   o  added the privacy concerns and necessity of and potential effects
      of dynamically changing MAC addresses.

   From draft-petrescu-ipv6-over-80211p-00.txt to

   o  updated one author's affiliation detail.

   o  added 2 more references to published literature about IPv6 over

   From draft-petrescu-ipv6-over-80211p-00.txt to

   o  first version.

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Appendix B.  Explicit Prohibition of IPv6 on Channels Related to ITS
             Scenarios using 802.11p Networks - an Analysis

B.1.  Interpretation of FCC and ETSI documents with respect to running
      IP on particular channels

   o  The FCC created the term "Control Channel" [fcc-cc].  For it, it
      defines the channel number to be 178 decimal, and positions it
      with a 10MHz width from 5885MHz to 5895MHz.  The FCC rules point
      to standards document ASTM-E2213 (not freely available at the time
      of writing of this draft); in an interpretation of a reviewer of
      this document, this means not making any restrictions to the use
      of IP on the control channel.

   o  The FCC created two more terms for particular channels
      [fcc-cc-172-184], among others.  The channel 172 (5855MHz to
      5865MHz)) is designated "exclusively for [V2V] safety
      communications for accident avoidance and mitigation, and safety
      of life and property applications", and the channel 184 (5915MHz
      to 5925MHz) is designated "exclusively for high-power, longer-
      distance communications to be used for public-safety applications
      involving safety of life and property, including road-intersection
      collision mitigation".  However, they are not named "control"
      channels, and the document does not mention any particular
      restriction on the use of IP on either of these channels.

   o  On another hand, at IEEE, IPv6 is explicitely prohibited on
      channel number 178 decimal - the FCC's 'Control Channel'.  The
      document [ieeep1609.4-D9-2010] prohibits upfront the use of IPv6
      traffic on the Control Channel: 'data frames containing IP
      datagrams are only allowed on service channels'.  Other 'Service
      Channels' are allowed to use IP, but the Control Channel is not.

   o  In Europe, basically ETSI considers FCC's "Control Channel" to be
      a "Service Channel", and defines a "Control Channel" to be in a
      slot considered by FCC as a "Service Channel".  In detail, FCC's
      "Control Channel" number 178 decimal with 10MHz width (5885MHz to
      5895MHz) is defined by ETSI to be a "Service Channel", and is
      named 'G5-SCH2' [etsi-302663-v1.2.1p-2013].  This channel is
      dedicated to 'ITS Road Safety' by ETSI.  Other channels are
      dedicated to 'ITS road traffic efficiency' by ETSI.  The ETSI's
      "Control Channel" - the "G5-CCH" - number 180 decimal (not 178) is
      reserved as a 10MHz-width centered on 5900MHz (5895MHz to 5905MHz)
      (the 5895MHz-5905MHz channel is a Service Channel for FCC).
      Compared to IEEE, ETSI makes no upfront statement with respect to
      IP and particular channels; yet it relates the 'In car Internet'
      applications ('When nearby a stationary public internet access
      point (hotspot), application can use standard IP services for

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      applications.') to the 'Non-safety-related ITS application'
      [etsi-draft-102492-2-v1.1.1-2006].  Under an interpretation of an
      author of this Internet Draft, this may mean ETSI may forbid IP on
      the 'ITS Road Safety' channels, but may allow IP on 'ITS road
      traffic efficiency' channels, or on other 5GHz channels re-used
      from BRAN (also dedicated to Broadband Radio Access Networks).

   o  At EU level in ETSI (but not some countries in EU with varying
      adoption levels) the highest power of transmission of 33 dBm is
      allowed, but only on two separate 10Mhz-width channels centered on
      5900MHz and 5880MHz respectively.  It may be that IPv6 is not
      allowed on these channels (in the other 'ITS' channels where IP
      may be allowed, the levels vary between 20dBm, 23 dBm and 30 dBm;
      in some of these channels IP is allowed).  A high-power of
      transmission means that vehicles may be distanced more
      (intuitively, for 33 dBm approximately 2km is possible, and for 20
      dBm approximately 50meter).

B.2.  Interpretations of Latencies of IP datagrams

   IPv6 may be "allowed" on any channel.  Certain interpretations
   consider that communicating IP datagrams may involve longer latencies
   than non-IP datagrams; this may make them little adapted for safety
   applications which require fast reaction.  Certain other views
   disagree with this, arguing that IP datagrams are transmitted at the
   same speed as any other non-IP datagram and may thus offer same level
   of reactivity for safety applications.

Appendix C.  Changes Needed on a software driver 802.11a to become a
             802.11p driver

   The 802.11p amendment modifies both the 802.11 stack's physical and
   MAC layers but all the induced modifications can be quite easily
   obtained by modifying an existing 802.11a ad-hoc stack.

   Conditions for a 802.11a hardware to be 802.11p compliant:

   o  The chip must support the frequency bands on which the regulator
      recommends the use of ITS communications, for example using IEEE
      802.11p layer, in France: 5875MHz to 5925MHz.

   o  The chip must support the half-rate mode (the internal clock
      should be able to be divided by two).

   o  The chip transmit spectrum mask must be compliant to the "Transmit
      spectrum mask" from the IEEE 802.11p amendment (but experimental
      environments tolerate otherwise).

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   o  The chip should be able to transmit up to 44.8 dBm when used by
      the US government in the United States, and up to 33 dBm in
      Europe; other regional conditions apply.

   Changes needed on the network stack in OCB mode:

   o  Physical layer:

      *  The chip must use the Orthogonal Frequency Multiple Access
         (OFDM) encoding mode.

      *  The chip must be set in half-mode rate mode (the internal clock
         frequency is divided by two).

      *  The chip must use dedicated channels and should allow the use
         of higher emission powers.  This may require modifications to
         the regulatory domains rules, if used by the kernel to enforce
         local specific restrictions.  Such modifications must respect
         the location-specific laws.

      MAC layer:

      *  All management frames (beacons, join, leave, etc...) emission
         and reception must be disabled except for frames of subtype
         Action and Timing Advertisement (defined below).

      *  No encryption key or method must be used.

      *  Packet emission and reception must be performed as in ad-hoc
         mode, using the wildcard BSSID (ff:ff:ff:ff:ff:ff).

      *  The functions related to joining a BSS (Association Request/
         Response) and for authentication (Authentication Request/Reply,
         Challenge) are not called.

      *  The beacon interval is always set to 0 (zero).

      *  Timing Advertisement frames, defined in the amendment, should
         be supported.  The upper layer should be able to trigger such
         frames emission and to retrieve information contained in
         received Timing Advertisements.

Appendix D.  Use of IPv6 over 802.11p for distribution of certificates

   Security of vehicular communications is one of the challenging tasks
   in the Intelligent Transport Systems.  The adoption of security
   procedures becomes an indispensable feature that cannot be neglected

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   when designing new protocols.  One of the interesting use cases of
   transmitting IPv6 packets over IEEE 802.11p links is the distribution
   of certificates between road side infrastructure and the vehicule
   (Figure below).

                   #         #
                   # Server  #
                   #         #
                        |  <-- link  (depending on the infrastructure)
                    ##########                    #############
                    #        #                    #           #
                    #  RSU   # - - - - - - - - - -#   Router  #
                    #        #    802.11p Link    # in-vehicle#
                    ##########                    #############
                                                       o  o

   Many security mechanisms have been proposed for the vehicular
   environment, mechanisms often relying on public key algorithms.
   Public key algorithms necessitate a public key infrastructure (PKI)
   to distribute and revoke certificates.  The server backend in the
   figure can play the role of a Certification Authority which will send
   certificates and revocation lists to the RSU which in turn
   retransmits certificates in messages directed to passing-by vehicles.
   The initiation distribution of certificates as IPv6 messages over
   802.11p links may be realized by WSA messages (WAVE Service
   Announcement, a non-IP message).  The certificate is sent as an IPv6
   messages over a single-hop 802.11p link.

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Authors' Addresses

   Alexandru Petrescu
   CEA Saclay
   Gif-sur-Yvette, Ile-de-France  91190

   Phone: +33169089223

   Pierre Pfister
   only at -00


   Nabil Benamar
   Moulay Ismail University

   Phone: +212670832236

   Tim Leinmueller


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