Transmission of IPv6 Packets over IEEE 802.11p Networks
draft-petrescu-ipv6-over-80211p-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
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|
|---|---|---|---|
| Authors | Alexandre Petrescu , Romain Kuntz , Pierre Pfister , Nabil Benamar | ||
| Last updated | 2013-10-21 | ||
| Replaced by | draft-ietf-ipwave-ipv6-over-80211ocb, draft-ietf-ipwave-ipv6-over-80211ocb, draft-ietf-ipwave-ipv6-over-80211ocb, draft-ietf-ipwave-ipv6-over-80211ocb, draft-ietf-ipwave-ipv6-over-80211ocb, RFC 8691 | ||
| RFC stream | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-petrescu-ipv6-over-80211p-00
Network Working Group A. Petrescu
Internet-Draft CEA
Intended status: Informational R. Kuntz
Expires: April 24, 2014 IP Flavors
P. Pfister
changing
N. Benamar
Moulay Ismail University
October 21, 2013
Transmission of IPv6 Packets over IEEE 802.11p Networks
draft-petrescu-ipv6-over-80211p-00.txt
Abstract
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
Layer.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on April 24, 2014.
Copyright Notice
Copyright (c) 2013 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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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 . . . . . . . . . . . . . . . . . 15
7.2. Capture in Normal Mode . . . . . . . . . . . . . . . . . . 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 20
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
11.1. Normative References . . . . . . . . . . . . . . . . . . . 21
11.2. Informative References . . . . . . . . . . . . . . . . . . 22
Appendix A. ChangeLog . . . . . . . . . . . . . . . . . . . . . . 24
Appendix B. Explicit Prohibition of IPv6 on Channels Related
to ITS Scenarios using 802.11p Networks - an
Analysis . . . . . . . . . . . . . . . . . . . . . . 24
Appendix C. Changes Needed on a software driver 802.11a to
become a 802.11p driver . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
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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 the published literature, the operation of IPv6 for WAVE (Wireless
Access In Vehicular Environments) was described in [ipv6-wave].
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].
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 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, and 180 at
ETSI); for a detailed analysis of FCC 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.
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.
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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
documents.
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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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
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
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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"
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
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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.
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
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPv6 Base Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Traffic Class | Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| 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.
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".
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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
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[ieeep1609.2-D17].
As with all Ethernet and 802.11 interface identifiers, there may
exist privacy risks in the use of 802.11p interface identifiers.
9. IANA Considerations
10. Acknowledgements
The authors would like to acknowledge Witold Klaudel, Ryuji Wakikawa,
Emmanuel Baccelli, John Kenney, John Moring, Francois Simon, Dan
Romascanu, Konstantin Khait and Ralph Droms. Their supportive
comments at the early stages enlightened and helped improve the
document. More comments from more persons are expected.
11. References
11.1. 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-00 (work
in progress), October 2013.
[I-D.ietf-6man-ug]
Carpenter, B. and S. Jiang, "Significance of IPv6
Interface Identifiers", draft-ietf-6man-ug-04 (work in
progress), October 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.
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[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.
11.2. Informative References
[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.
[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 ht
tp://www.etsi.org/deliver/etsi_en/302600_302699/302663/
01.02.01_60/en_302663v010201p.pdf downloaded on October
17th, 2013.".
[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 h
ttp://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
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October 17th, 2013.".
[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".
[ipv6-wave]
"Clausen, T., Baccelli, E. and R. Wakikawa, "IPv6
Petrescu, et al. Expires April 24, 2014 [Page 23]
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Operation for WAVE - Wireless Access in Vehicular
Environments", Rapport de recherche, INRIA, numero 7383,
September 2010.".
Appendix A. ChangeLog
The changes are listed in reverse chronological order, most recent
changes appearing at the top of the list.
From draft-authors-ipv6-over-80211p-00.txt to
draft-authors-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
o IPv6 is prohibited on channel number 178 decimal, named 'Control
Channel' at IEEE and FCC. 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'. The FCC names the Control Channel as being the channel
number 178 decimal, and positions it with a 10MHz width from
5885MHz to 5895MHz [fcc-cc]. Other 'Service Channels' are allowed
to use IP, but the Control Channel is not.
o The same channel number 178 decimal with 10MHz width (5885MHz to
5895MHz) is considered to be a Service Channel by ETSI and is
named 'G5-SCH2' [etsi-302663-v1.2.1p-2013]. This channel is
dedicated to 'ITS Road Safety'. Other channels are dedicated to
'ITS road traffic efficiency'. Also, a 'Control Channel G5-CCH'
number 180 decimal (not 178) is reserved by ETSI to be 10MHz-width
centered on 5900MHz. Compared to FCC, the 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]. This
means 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
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5900MHz and 5880MHz respectively. It appears 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).
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 can
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.
* 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.
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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.
Authors' Addresses
Alexandru Petrescu
CEA
http://www.cea.fr,
Phone:
Email: Alexandru.Petrescu@cea.fr
Romain Kuntz
IP Flavors
http://www.ipflavors.com,
Phone:
Email: r.kuntz@ipflavors.com
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Pierre Pfister
changing
Phone:
Email: pierre.pfister@polytechnique.org
Nabil Benamar
Moulay Ismail University
Morocco
Phone:
Email: benamar73@gmail.com
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