Internet DRAFT - draft-petrescu-ipv6-over-80211p
draft-petrescu-ipv6-over-80211p
Network Working Group A. Petrescu
Internet-Draft CEA, LIST
Intended status: Informational N. Benamar
Expires: October 21, 2016 Moulay Ismail University
T. Leinmueller
DENSO INTERNATIONAL EUROPE
April 19, 2016
Transmission of IPv6 Packets over IEEE 802.11 Networks Outside the
Context of a Basic Service Set
draft-petrescu-ipv6-over-80211p-04.txt
Abstract
In order to transmit IPv6 packets on IEEE 802.11 networks run outside
the context of a basic service set (OCB, earlier "802.11p") there is
a need to define a few parameters such as the recommended Maximum
Transmission Unit size, the header format preceding the IPv6 header,
the Type value within it, and others. This document describes these
parameters for IPv6 and IEEE 802.11 OCB networks; it portrays the
layering of IPv6 on 802.11 OCB similarly to other known 802.11 and
Ethernet layers - by using an Ethernet Adaptation Layer.
In addition, the document attempts to list what is different in
802.11 OCB (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
802.11 OCB link (802.11p) is given.
Status of This Memo
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This Internet-Draft will expire on October 21, 2016.
Copyright Notice
Copyright (c) 2016 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Communication Scenarios where IEEE 802.11p Links are Used . . 5
4. Aspects introduced by 802.11p to 802.11 . . . . . . . . . . . 5
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
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B.2. Interpretations of Latencies of IP datagrams . . . . . . 28
Appendix C. Changes Needed on a software driver 802.11a to
become a 802.11p driver . . . . . . . . . . 28
Appendix D. Use of IPv6 over 802.11p for distribution of
certificates . . . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction
This document describes the transmission of IPv6 packets on IEEE Std
802.11 OCB networks (earlier known as 802.11p). This involves the
layering of IPv6 networking on top of the IEEE 802.11 MAC layer (with
an LLC layer). Compared to running IPv6 over the Ethernet MAC layer,
there is no modification required to the standards: IPv6 works fine
directly over 802.11 OCB too (with an LLC layer).
The term "802.11p" is an earlier definition. As of year 2012, the
behaviour of "802.11p" networks has been rolled in the document IEEE
Std 802.11-2012. In this document the term 802.11p disappears.
Instead, each 802.11p feature is conditioned by a flag in the
Management Information Base. That flag is named "OCBActivated".
Whenever OCBActivated is set to true the feature it relates to
represents an earlier 802.11p feature. For example, an 802.11
STAtion operating outside the context of a basic service set has the
OCBActivated flag set. Such a station, when it has the flag set, it
uses ta BSS identifier equal to ff:ff:ff:ff:ff.
In the following text we use the term "802.11p" to mean 802.11-2012
OCB.
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.
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+-----------------+ +-----------------+
| ... | | ... |
+-----------------+ +-----------------+
| 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
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
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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
[etsi-302663-v1.2.1p-2013].
In the published literature, three documents describe aspects related
to running IPv6 over 802.11p: [vip-wave], [ipv6-80211p-its] and
[ipv6-wave].
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 RFC 2119 [RFC2119].
RSU: Road Side Unit.
OCB: Outside the Context of a Basic Service Set identifier.
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
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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 document 802.11-2012, specifically anything referring
"OCBActivated", or "outside the context of a basic service set" is
actually referring to the 802.11p aspects introduced to 802.11. Note
in earlier 802.11p documents the term "OCBEnabled" was used instead.
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
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
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(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
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).
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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.
o
* 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-
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.
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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
|
v
+---------------------+-------------+---------+
| 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
procedure.
For example, the Interface Identifier for an 802.11p interface whose
built-in address is, in hexadecimal:
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30-14-4A-D9-F9-6C
would be
32-14-4A-FF-FE-D9-F9-6C.
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
document.
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 is comparable 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
should also configure a low Reachable Time value in its RA in order
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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
[ieeep1609.3-D9-2010].
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
stations should use the Mobile IPv6 "Advertisement Interval Option"
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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.
The Received Frame Power Level (RCPI) defined in IEEE Std
802.11-2012, conditioned by the dotOCBActived flag, is an information
element which contains a value expressing the power level at which
that frame was received. This value may be used in comparing power
levels when triggering IP handovers.
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.
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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.
The popular wireshark network protocol analyzer is a free software
tool for Windows and Unix. It includes a dissector for 802.11p
features along with all other 802.11 features (i.e. it displays these
features in a human-readable format).
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...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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... BSS Id | Frag Number and Seq Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Logical-Link Control Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DSAP |I| SSAP |C| Control field | Org. code...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... Organizational Code | 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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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.
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
channel.
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
below.
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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
present.
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
802.11).
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
[ieeep1609.2-D17].
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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, Ray Hunter,
Tom Kurihara and Gloria Gwynne. Their supportive comments clarified
certain issues and generally helped to improve the document.
Pierre Pfister wrote an 802.11p driver for linux and described how.
12. References
12.1. Normative References
[I-D.ietf-6man-ipv6-address-generation-privacy]
Cooper, A., Gont, F., and D. Thaler, "Privacy
Considerations for IPv6 Address Generation Mechanisms",
draft-ietf-6man-ipv6-address-generation-privacy-08 (work
in progress), September 2015.
[I-D.ietf-6man-ug]
Carpenter, B. and S. Jiang, "Significance of IPv6
Interface Identifiers", draft-ietf-6man-ug-06 (work in
progress), December 2013.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <http://www.rfc-editor.org/info/rfc2460>.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998,
<http://www.rfc-editor.org/info/rfc2464>.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,
<http://www.rfc-editor.org/info/rfc4429>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<http://www.rfc-editor.org/info/rfc4861>.
[RFC5889] Baccelli, E., Ed. and M. Townsley, Ed., "IP Addressing
Model in Ad Hoc Networks", RFC 5889, DOI 10.17487/RFC5889,
September 2010, <http://www.rfc-editor.org/info/rfc5889>.
[RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July
2011, <http://www.rfc-editor.org/info/rfc6275>.
[RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
Bormann, "Neighbor Discovery Optimization for IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)",
RFC 6775, DOI 10.17487/RFC6775, November 2012,
<http://www.rfc-editor.org/info/rfc6775>.
12.2. Informative References
[etsi-302663-v1.2.1p-2013]
"Intelligent Transport Systems (ITS); Access layer
specification for Intelligent Transport Systems operating
in the 5 GHz frequency band, 2013-07, document
en_302663v010201p.pdf, document freely available at URL
http://www.etsi.org/deliver/etsi_en/302600_302699/302663/
01.02.01_60/en_302663v010201p.pdf downloaded on October
17th, 2013.".
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[etsi-draft-102492-2-v1.1.1-2006]
"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
http://www.etsi.org/deliver/etsi_tr/102400_102499/
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
http://www.its.dot.gov/exit/fcc_edocs.htm downloaded on
October 17th, 2013.".
[fcc-cc-172-184]
"'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://hraunfoss.fcc.gov/edocs_public/attachmatch/
FCC-06-110A1.pdf downloaded on June 5th, 2014.".
[I-D.baccelli-multi-hop-wireless-communication]
Baccelli, E. and C. Perkins, "Multi-hop Ad Hoc Wireless
Communication", draft-baccelli-multi-hop-wireless-
communication-06 (work in progress), July 2011.
[I-D.petrescu-its-scenarios-reqs]
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.
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[ieee802.11-2012]
"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
http://standards.ieee.org/findstds/
standard/802.11-2012.html retrieved on October 17th,
2013.".
[ieee802.11p-2010]
"IEEE Std 802.11p(TM)-2010, 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,
Amendment 6: Wireless Access in Vehicular Environments;
document freely available at URL
http://standards.ieee.org/getieee802/
download/802.11p-2010.pdf retrieved on September 20th,
2013.".
[ieeep1609.2-D17]
"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.".
[ieeep1609.3-D9-2010]
"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
http://ieeexplore.ieee.org/servlet/opac?punumber=5562705".
[ieeep1609.4-D9-2010]
"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
http://ieeexplore.ieee.org/servlet/opac?punumber=5551097".
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[ipv6-80211p-its]
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:
http://hal.inria.fr/hal-00702923/en, Downloaded on: 24
October 2013, Availability: free at some sites, paying at
others, May 2012.
[ipv6-wave]
Clausen, T., Baccelli, E., and R. Wakikawa, "IPv6
Operation for WAVE - Wireless Access in Vehicular
Environments", Rapport de Recherche INRIA, number 7383,
URL: http://hal.inria.fr/inria-00517909/, Downloaded on:
24 October 2013, Availability: free at some sites,
September 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, Volume 14, Issue 1, URL and Digital Object
Identifier: http://dx.doi.org/10.1109/TITS.2012.2206387,
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-02.txt to draft-petrescu-ipv6-
over-80211p-03.txt:
o Added clarification about the "OCBActivated" qualifier in the the
new IEEE 802.11-2012 document; this IEEE document integrates now
all earlier 802.11p features; this also signifies the
dissapearance of an IEEE IEEE 802.11p document altogether.
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
mode.
o Added appendix about the distribution of certificates to vehicles
by using IPv6-over-802.11p single-hop communications.
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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-01.txt to draft-petrescu-ipv6-
over-80211p-02.txt:
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
mode.
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 draft-petrescu-ipv6-
over-80211p-01.txt:
o updated one author's affiliation detail.
o added 2 more references to published literature about IPv6 over
802.11p.
From draft-petrescu-ipv6-over-80211p-00.txt to draft-petrescu-ipv6-
over-80211p-00.txt:
o first version.
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
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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
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
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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).
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.
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* 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, and others)
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
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).
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###########
# #
# Server #
#(backend)#
# #
###########
|
|
| <-- 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.
Authors' Addresses
Alexandre Petrescu
CEA, LIST
CEA Saclay
Gif-sur-Yvette , Ile-de-France 91190
France
Phone: +33169089223
Email: Alexandre.Petrescu@cea.fr
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Nabil Benamar
Moulay Ismail University
Morocco
Phone: +212670832236
Email: benamar73@gmail.com
Tim Leinmueller
DENSO INTERNATIONAL EUROPE
Deutschland
Email: t.leinmueller@denso-auto.de
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