Basic Support for IPv6 over IEEE Std 802.11 Networks Operating Outside the Context of a Basic Service Set
(IPv6-over-80211-OCB)
Moulay Ismail University of Meknes
Morocco
+212670832236
n.benamar@est.umi.ac.ma
Eurecom Sophia-Antipolis
06904
France
+33493008134
Jerome.Haerri@eurecom.fr
Sangmyung University
31, Sangmyeongdae-gil, Dongnam-gu
31066
Cheonan
Republic of Korea
jonghyouk@smu.ac.kr
YoGoKo
France
thierry.ernst@yogoko.fr
Internet
IPWAVE Working Group
IPv6 over 802.11p, OCB, IPv6 over 802.11-OCB
This document provides methods and settings, and describes limitations,
for using IPv6 to communicate among nodes in range of one another
over a single IEEE 802.11-OCB link. This support does only require minimal changes to
existing stacks. Optimizations and usage of IPv6 over more complex scenarios
is not covered in this specification and is subject of future work.
This document provides a baseline with limitations for using IPv6 to
communicate among nodes in range of one another over a single IEEE 802.11-OCB link
(a.k.a., "802.11p" see ,
and )
with minimal changes to existing stacks. Moreover, the document identifies limitations
of such usage. Concretely, the document describes the layering
of IPv6 networking on top of the IEEE Std 802.11 MAC layer or an IEEE Std 802.3
MAC layer with a frame translation underneath. The resulting stack inherits from IPv6
over Ethernet , but operates over 802.11-OCB to provide at least P2P (Point to Point) connectivity
using IPv6 ND and link-local addresses.
The IPv6 network layer operates on 802.11-OCB in the same
manner as operating on Ethernet with the following
exceptions:
Exceptions due to different operation of IPv6 network
layer on 802.11 than on Ethernet. The operation of IP
on Ethernet is described in and .
Exceptions due to the OCB nature of 802.11-OCB compared to
802.11. This has impacts on security, privacy, subnet
structure and movement detection. Security and
privacy recommendations are discussed in and
. The subnet structure is described
in . The movement
detection on OCB links is not described in this document.
Likewise, ND Extensions and IPWAVE optimizations for vehicular communications are
not in scope. The expectation is that further specifications will be edited to cover
more complex vehicular networking scenarios.
The reader may refer to for an overview of
problems related to running IPv6 over 802.11-OCB. It is out of scope of this document to reiterate those.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
interpreted as described in BCP 14
when, and
only when, they appear in all capitals, as shown here.
The document makes uses of the following terms:
IP-OBU (Internet Protocol On-Board Unit): an IP-OBU denotes a
computer situated in a vehicle such as a car, bicycle,
or similar. It has at least one IP interface that runs in
mode OCB of 802.11, and that has an "OBU" transceiver. See
the definition of the term "OBU" in section .
IP-RSU (IP Road-Side Unit): an IP-RSU is situated along the
road. It has at least two distinct IP-enabled interfaces. The
wireless PHY/MAC layer of at least one of its IP-enabled
interfaces is configured to operate in 802.11-OCB mode. An
IP-RSU communicates with the IP-OBU in the vehicle over 802.11
wireless link operating in OCB mode. An IP-RSU is similar to
an Access Network Router (ANR) defined in , and a Wireless Termination Point (WTP)
defined in .
OCB (outside the context of a basic service set - BSS): is a mode
of operation in which a STA is not a member of a BSS and does
not utilize IEEE Std 802.11 authentication, association, or
data confidentiality.
802.11-OCB: refers to the mode specified in IEEE Std 802.11-2016 when the
MIB attribute dot11OCBActivited is 'true'.
The IEEE 802.11-OCB networks are used for vehicular
communications, as 'Wireless Access in Vehicular
Environments'. In particular, we refer the reader to , that lists
some scenarios and requirements for IP in Intelligent
Transportation Systems (ITS).
The link model is the following: STA --- 802.11-OCB --- STA.
In vehicular networks, STAs can be IP-RSUs and/or IP-OBUs.
All links are assumed to be P2P and multiple links can be on one radio
interface. While 802.11-OCB is clearly specified, and a legacy IPv6
stack can operate on such links, the use of the operating environment
(vehicular networks) brings in new perspectives.
The default MTU for IP packets on 802.11-OCB is inherited
from and is, as such, 1500 octets. This value
of the MTU respects the recommendation that every link on
the Internet must have a minimum MTU of 1280 octets (stated
in , and the recommendations
therein, especially with respect to fragmentation).
IP packets MUST be transmitted over 802.11-OCB media as QoS
Data frames whose format is specified in IEEE 802.11 spec
.
The IPv6 packet transmitted on 802.11-OCB are
immediately preceded by a Logical Link Control (LLC) header
and an 802.11 header. In the LLC header, and in accordance
with the EtherType Protocol Discrimination (EPD, see ), the value of the Type field MUST be set to
0x86DD (IPv6). The mapping to the 802.11 data service SHOULD
use a 'priority' value of 1 (QoS with a 'Background' user priority),
reserving higher priority values for safety-critical and time-sensitive
traffic, including the ones listed in [ETSI-sec-archi].
To simplify the Application Programming Interface (API)
between the operating system and the 802.11-OCB media,
device drivers MAY implement IPv6-over-Ethernet as per
and then a frame translation from 802.3 to 802.11 in order
to minimize the code changes.
There are several types of IPv6 addresses , , that may be
assigned to an 802.11-OCB interface. Among these types of
addresses only the IPv6 link-local addresses can be formed
using an EUI-64 identifier, in particular during transition
time.
If the IPv6 link-local address is formed using an EUI-64
identifier, then the mechanism of forming that address is
the same mechanism as used to form an IPv6 link-local
address on Ethernet links. Moreover, whether or not the interface
identifier is derived from the EUI-64
identifier, its length is 64 bits as is the case for Ethernet .
The steps a host takes in deciding how to
autoconfigure its interfaces in IPv6 are described
in . This section describes
the formation of Interface Identifiers for IPv6 addresses of
type 'Global' or 'Unique Local'. Interface Identifiers
for IPv6 address of type 'Link-Local' are discussed in .
The RECOMMENDED method for forming
stable Interface Identifiers (IIDs) is described in . The method of forming IIDs described in
Section 4 of MAY be used during
transition time, in particular for IPv6 link-local
addresses. Regardless of how to form the IID,
its length is 64 bits, similarely to IPv6 over Ethernet .
The bits in the IID have no specific meaning
and the identifier should be treated as an opaque value.
The bits 'Universal' and 'Group' in the identifier of an
802.11-OCB interface are significant, as this is an IEEE
link-layer address. The details of this significance are
described in .
Semantically opaque IIDs, instead of
meaningful IIDs derived from a valid and
meaningful MAC address (, Section
4), help avoid certain privacy risks (see the risks
mentioned in ). If
semantically opaque IIDs are needed, they
may be generated using the method for generating
semantically opaque IIDs with IPv6
Stateless Address Autoconfiguration given in . Typically, an opaque IID is formed starting from identifiers different
than the MAC addresses, and from cryptographically strong
material. Thus, privacy sensitive information is absent
from Interface IDs, because it is impossible to calculate
back the initial value from which the Interface ID was first
generated.
Some applications that use IPv6 packets on 802.11-OCB links
(among other link types) may benefit from IPv6 addresses
whose IIDs don't change too often. It is
RECOMMENDED to use the mechanisms described in RFC 7217 to
permit the use of Stable IIDs that do not
change within one subnet prefix. A possible source for the
Net-Iface Parameter is a virtual interface name, or logical
interface name, that is decided by a local administrator.
Unicast and multicast address mapping MUST follow the
procedures specified for Ethernet interfaces specified in Sections 6
and 7 of .
This document is scoped for Address Resolution (AR) and Duplicate Address Detection (DAD) per .
The multicast address mapping is performed according to
the method specified in section 7 of . The meaning of the value "3333"
mentioned there is
defined in section 2.3.1 of .
Transmitting IPv6 packets to multicast destinations over
802.11 links proved to have some performance issues . These
issues may be exacerbated in OCB mode. A future improvement
to this specification should consider solutions for these problems.
When vehicles are in close range, a subnet may be formed over
802.11-OCB interfaces (not by their in-vehicle interfaces).
A Prefix List conceptual data structure ( Section 5.1) is maintained for each
802.11-OCB interface.
IPv6 Neighbor Discovery protocol (ND) requires reflexive properties
(bidirectional connectivity) which is generally, though not always, the case for P2P OCB links.
IPv6 ND also requires transitive properties for DAD and AR, so an IPv6 subnet can be mapped
on an OCB network only if all nodes in the network share a single physical broadcast domain.
The extension to IPv6 ND operating on a subnet that covers multiple OCB links
and not fully overlapping (NBMA) is not in scope.
Finally, IPv6 ND requires a permanent connectivity of all nodes in the subnet
to defend their addresses, in other words very stable network conditions.
The structure of this subnet is ephemeral, in that it is
strongly influenced by the mobility of vehicles: the hidden
terminal effects appear; the 802.11 networks in OCB mode may
be considered as 'ad-hoc' networks with an addressing model
as described in . On another hand,
the structure of the internal subnets in each vehicle is
relatively stable.
As recommended in , when the timing
requirements are very strict (e.g., fast-drive-through IP-RSU
coverage), no on-link subnet prefix should be configured on
an 802.11-OCB interface. In such cases, the exclusive use
of IPv6 link-local addresses is RECOMMENDED.
Additionally, even if the timing requirements are not very
strict (e.g., the moving subnet formed by two following
vehicles is stable, a fixed IP-RSU is absent), the subnet is
disconnected from the Internet (i.e., a default route is absent),
and the addressing peers are equally qualified (that is, it is impossible
to determine that some vehicle owns and distributes
addresses to others) the use of link-local addresses is
RECOMMENDED.
The baseline ND protocol MUST be supported over 802.11-OCB links.
Transmitting ND packets may prove to have some performance
issues as mentioned in , and
.
These issues may be exacerbated in OCB mode.
Solutions for these problems should consider the OCB mode
of operation. Future solutions to OCB should consider solutions
for avoiding broadcast. The best of current knowledge
indicates the kinds of issues that may arise with ND in
OCB mode; they are described in .
Protocols like Mobile IPv6 , and
DNAv6 , which depend on a timely
movement detection, might need additional tuning work to
handle the lack of link-layer notifications during handover.
This is for further study.
Any security mechanism at the IP layer or above that may be
carried out for the general case of IPv6 may also be carried
out for IPv6 operating over 802.11-OCB.
The OCB operation does not use existing 802.11
link-layer security mechanisms. There is no encryption
applied below the network layer running on 802.11-OCB. At
the application layer, the IEEE 1609.2 document provides security services for
certain applications to use; application-layer mechanisms are
out of scope of this document. On another hand, a security
mechanism provided at networking layer, such as IPsec , may provide data security protection to a
wider range of applications.
802.11-OCB does not provide any cryptographic protection,
because it operates outside the context of a BSS (no
Association Request/Response, no Challenge messages).
Therefore, an attacker can sniff or inject traffic while within
range of a vehicle or IP-RSU (by setting an interface card’s frequency to the proper range).
Also, an attacker may not heed to legal limits
for radio power and can use a very sensitive directional antenna;
if attackers wishe to attack a given exchange they do not necessarily
need to be in close physical proximity. Hence, such a link is less protected than
commonly used links (wired link or protected 802.11).
Therefore, any node can join a subnet, directly communicate with any nodes
on the subset to include potentially impersonating another node.
This design allows for a number of threats outlined in Section 3 of .
While not widely deployed, SeND , is a solution
that can address Spoof-Based Attack Vectors.
As with all Ethernet and 802.11 interface identifiers (), the identifier of an 802.11-OCB
interface may involve privacy, MAC address spoofing and IP
hijacking risks. A vehicle embarking an IP-OBU
whose egress interface is 802.11-OCB may expose itself to
eavesdropping and subsequent correlation of data. This may
reveal data considered private by the vehicle owner; there
is a risk of being tracked. In outdoors public
environments, where vehicles typically circulate, the
privacy risks are more important than in indoors settings.
It is highly likely that attacker sniffers are deployed
along routes which listen for IEEE frames, including IP
packets, of vehicles passing by. For this reason, in the
802.11-OCB deployments, there is a strong necessity to use
protection tools such as dynamically changing MAC addresses
, semantically opaque Interface
Identifiers and stable Interface Identifiers . An example of change policy is to change the MAC
address of the OCB interface each time the system boots up.
This may help mitigate privacy risks to a
certain level.
Futhermore, for pricavy concerns, () recommends using an address
generation scheme rather than addresses generated from a fixed link-layer address.
However, there are some specificities related to vehicles. Since roaming is an important
characteristic of moving vehicles, the use of the same Link-Local Address over time
can indicate the presence of the same vehicle in different places and thus leads to location tracking.
Hence, a vehicle should get hints about a change of environment (e.g. , engine running, GPS, etc..)
and renew the IID in its LLAs.
The privacy risks of using MAC addresses displayed in
Interface Identifiers are important. The IPv6 packets can
be captured easily in the Internet and on-link in public
roads. For this reason, an attacker may realize many
attacks on privacy. One such attack on 802.11-OCB is to
capture, store and correlate Company ID information
present in MAC addresses of many cars (e.g. listen for
Router Advertisements, or other IPv6 application data
packets, and record the value of the source address in
these packets). Further correlation of this information
with other data captured by other means, or other visual
information (car color, others) may constitute privacy
risks.
In 802.11-OCB networks, the MAC addresses may change during
well defined renumbering events. In the moment the MAC
address is changed on an 802.11-OCB interface all the
Interface Identifiers of IPv6 addresses assigned to that
interface MUST change.
Implementations should use a policy dictating when the MAC address is changed on the 802.11-OCB interface.
For more information on the motivation of this policy please refer to
the privacy discussion in .
A 'randomized' MAC address has the following
characteristics:
Bit "Local/Global" set to "locally admninistered".
Bit "Unicast/Multicast" set to "Unicast".
The 46 remaining bits are set to a random value, using a
random number generator that meets the requirements of
.
To meet the randomization requirements for the 46 remaining
bits, a hash function may be used. For example, the SHA256
hash function may be used with input a 256 bit local secret,
the 'nominal' MAC Address of the interface, and a
representation of the date and time of the renumbering
event.
A randomized Interface ID has the same characteristics of a
randomized MAC address, except the length in bits.
The demand for privacy protection of vehicles' and drivers'
identities, which could be granted by using a pseudonym or
alias identity at the same time, may hamper the required
confidentiality of messages and trust between participants -
especially in safety critical vehicular
communication.
Particular challenges arise when the pseudonymization
mechanism used relies on (randomized) re-addressing.
A proper pseudonymization tool operated by a trusted
third party may be needed to ensure both aspects
simultaneously (privacy protection on one hand and trust
between participants on another hand).
This is discussed in and of this document.
Pseudonymity is also discussed in
in its sections 4.2.4 and 5.1.2.
No request to IANA.
Christian Huitema, Tony Li.
Romain Kuntz contributed extensively about IPv6 handovers
between links running outside the context of a BSS (802.11-OCB
links).
Tim Leinmueller contributed the idea of the use of IPv6 over
802.11-OCB for distribution of certificates.
Marios Makassikis, Jose Santa Lozano, Albin Severinson and
Alexey Voronov provided significant feedback on the experience
of using IP messages over 802.11-OCB in initial trials.
Michelle Wetterwald contributed extensively the MTU
discussion, offered the ETSI ITS perspective, and reviewed
other parts of the document.
The authors would like to thank Alexandre Petrescu for
initiating this work and for being the lead author until
the version 43 of this draft.
The authors would like to thank Pascal Thubert for reviewing,
proofreading and suggesting modifications of this document.
The authors would like to thank Mohamed Boucadair for
proofreading and suggesting modifications of this document.
The authors would like to thank Witold Klaudel, Ryuji
Wakikawa, Emmanuel Baccelli, John Kenney, John Moring,
Francois Simon, Dan Romascanu, Konstantin Khait, Ralph Droms,
Richard 'Dick' Roy, Ray Hunter, Tom Kurihara, Michal Sojka,
Jan de Jongh, Suresh Krishnan, Dino Farinacci, Vincent Park,
Jaehoon Paul Jeong, Gloria Gwynne, Hans-Joachim Fischer, Russ
Housley, Rex Buddenberg, Erik Nordmark, Bob Moskowitz, Andrew
Dryden, Georg Mayer, Dorothy Stanley, Sandra Cespedes, Mariano
Falcitelli, Sri Gundavelli, Abdussalam Baryun, Margaret
Cullen, Erik Kline, Carlos Jesus Bernardos Cano, Ronald in 't
Velt, Katrin Sjoberg, Roland Bless, Tijink Jasja, Kevin Smith,
Brian Carpenter, Julian Reschke, Mikael Abrahamsson, Dirk von
Hugo, Lorenzo Colitti, Pascal Thubert, Ole Troan, Jinmei
Tatuya, Joel Halpern, Eric Gray and William Whyte. Their
valuable comments clarified particular issues and generally
helped to improve the document.
Pierre Pfister, Rostislav Lisovy, and others, wrote 802.11-OCB
drivers for linux and described how.
For the multicast discussion, the authors would like to thank
Owen DeLong, Joe Touch, Jen Linkova, Erik Kline, Brian
Haberman and participants to discussions in network working
groups.
The authors would like to thank participants to the
Birds-of-a-Feather "Intelligent Transportation Systems"
meetings held at IETF in 2016.
Human Rights Protocol Considerations review by Amelia
Andersdotter.
IEEE Standard 802.11-2016 - 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. Status - Active Standard. Description
retrieved freely; the document itself is also freely
available, but with some difficulty (requires
registration); description and document retrieved on April
8th, 2019, starting from URL
https://standards.ieee.org/findstds/standard/802.11-2016.html
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.
IEEE SA - 1609.2-2016 - IEEE Standard for Wireless Access
in Vehicular Environments (WAVE) -- Security Services for
Applications and Management Messages. Example URL
http://ieeexplore.ieee.org/document/7426684/ accessed on
August 17th, 2017.
IEEE SA - 1609.3-2016 - IEEE Standard for Wireless Access
in Vehicular Environments (WAVE) -- Networking Services.
Example URL http://ieeexplore.ieee.org/document/7458115/
accessed on August 17th, 2017.
IEEE SA - 1609.4-2016 - IEEE Standard for Wireless Access
in Vehicular Environments (WAVE) -- Multi-Channel
Operation. Example URL
http://ieeexplore.ieee.org/document/7435228/ accessed on
August 17th, 2017.
ETSI TS 102 940 V1.2.1 (2016-11), ETSI Technical
Specification, Intelligent Transport Systems (ITS);
Security; ITS communications security architecture and
security management, November 2016. Downloaded on
September 9th, 2017, freely available from ETSI website at
URL
http://www.etsi.org/deliver/etsi_ts/102900_102999/102940/01.02.01_60/ts_102940v010201p.pdf
The term "802.11p" is an earlier definition. The behaviour of
"802.11p" networks is rolled in the document IEEE Std
802.11-2016. In that document the term 802.11p disappears.
Instead, each 802.11p feature is conditioned by the IEEE
Management Information Base (MIB) attribute "OCBActivated"
. Whenever OCBActivated is
set to true the IEEE Std 802.11-OCB state is activated. 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, uses a BSS identifier equal
to ff:ff:ff:ff:ff:ff.
In the IEEE 802.11-OCB mode, all nodes in the wireless range
can directly communicate with each other without involving
authentication or association procedures. In OCB mode, the
manner in which channels are selected and used is simplified
compared to when in BSS mode. Contrary to BSS mode, at link
layer, it is necessary to set statically the same channel
number (or frequency) on two stations that need to communicate
with each other (in BSS mode this channel set operation is
performed automatically during 'scanning'). The manner in
which stations set their channel number in OCB mode is not
specified in this document. Stations STA1 and STA2 can
exchange IP packets only if they are set on the same channel.
At IP layer, they then discover each other by using the IPv6
Neighbor Discovery protocol. The allocation of a particular
channel for a particular use is defined statically in
standards authored by ETSI (in Europe), FCC in America, and
similar organisations in South Korea, Japan and other parts of
the world.
Briefly, the IEEE 802.11-OCB mode has the following
properties:
The use by each node of a 'wildcard' BSSID (i.e., each bit
of the BSSID is set to 1)
No IEEE 802.11 Beacon frames are transmitted No authentication is required in order to be able to communicate No association is needed in order to be able to communicate No encryption is provided in order to be able to communicate Flag dot11OCBActivated is set to true
All the nodes in the radio communication range (IP-OBU and IP-RSU)
receive all the messages transmitted (IP-OBU and IP-RSU) within the
radio communications range. The eventual conflict(s) are
resolved by the MAC CDMA function.
The message exchange diagram in
illustrates a comparison between traditional 802.11 and 802.11
in OCB mode. The 'Data' messages can be IP packets such as
HTTP or others. Other 802.11 management and control frames
(non IP) may be transmitted, as specified in the 802.11
standard. For information, the names of these messages as
currently specified by the 802.11 standard are listed in .
The interface 802.11-OCB was specified in IEEE Std 802.11p
(TM) -2010 as an amendment
to IEEE Std 802.11 (TM) -2007, titled "Amendment 6: Wireless
Access in Vehicular Environments". Since then, this amendment
has been integrated in IEEE 802.11(TM) -2012 and -2016 .
In document 802.11-2016, anything qualified specifically as
"OCBActivated", or "outside the context of a basic service"
set to be true, then it is actually referring to OCB aspects
introduced to 802.11.
In order to delineate the aspects introduced by 802.11-OCB to
802.11, we refer to the earlier . 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. While 'p' is a letter identifying the
Amendment, 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 and 5.9GHz.
The 802.11-OCB 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
802.11-OCB MAC layer offers practically the same interface to
IP as the 802.11a/b/g/n and 802.3. A packet sent by an IP-OBU
may be received by one or multiple IP-RSUs. The link-layer
resolution is performed by using the IPv6 Neighbor Discovery
protocol.
To support this similarity statement (IPv6 is layered on top
of LLC on top of 802.11-OCB, in the same way that IPv6 is
layered on top of LLC on top of 802.11a/b/g/n (for WLAN) or
layered on top of LLC on top of 802.3 (for Ethernet)) it is
useful to analyze the differences between 802.11-OCB and
802.11 specifications. During this analysis, we note that
whereas 802.11-OCB lists relatively complex and numerous
changes to the MAC layer (and very little to the PHY layer),
there are only a few characteristics which may be important
for an implementation transmitting IPv6 packets on 802.11-OCB
links.
The most important 802.11-OCB point which influences the IPv6
functioning is the OCB characteristic; an additional, less
direct influence, is the maximum bandwidth afforded by the PHY
modulation/demodulation methods and channel access specified
by 802.11-OCB. The maximum bandwidth theoretically possible
in 802.11-OCB is 54 Mbit/s (when using, for example, the
following parameters: 20 MHz channel; modulation 64-QAM;
coding rate R is 3/4); in practice of IP-over-802.11-OCB a
commonly observed figure is 12Mbit/s; this bandwidth allows
the operation of a wide range of protocols relying on IPv6.
Operation Outside the Context of a BSS (OCB): the (earlier
802.11p) 802.11-OCB links are operated without a Basic
Service Set (BSS). This means that the frames IEEE 802.11
Beacon, Association Request/Response, Authentication
Request/Response, and similar, are not used. The used
identifier of BSS (BSSID) has a hexadecimal value always
0xffffffffffff (48 '1' bits, represented as MAC address
ff:ff:ff:ff:ff:ff, or otherwise 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 - should be taken into account when the
Mobile IPv6 protocol and the
protocols for IP layer security
are used. The way these protocols adapt to OCB is not
described in this document.
Timing Advertisement: is a new message defined in
802.11-OCB, 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.
Frequency range: this is a characteristic of the PHY
layer, with almost no impact on the interface between MAC
and IP. However, it is worth considering that the
frequency range is regulated by a regional authority
(ARCEP, ECC/CEPT based on ENs from ETSI, FCC, etc.); as
part of the regulation process, specific applications are
associated with specific frequency ranges. In the case of
802.11-OCB, 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".
The 5.9GHz band is different from the 2.4GHz and 5GHz
bands used by Wireless LAN. However, as with Wireless
LAN, the operation of 802.11-OCB 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 fixed infrastructure an
explicit FCC authorization is required; for an on-board
device a 'licensed-by-rule' concept applies: rule
certification conformity is required.) Technical
conditions are different than those of the bands "2.4GHz"
or "5GHz". The allowed power levels, and implicitly the
maximum allowed distance between vehicles, is of 33dBm for
802.11-OCB (in Europe), compared to 20 dBm for Wireless
LAN 802.11a/b/g/n; this leads to a maximum distance of
approximately 1km, compared to approximately 50m.
Additionally, 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).
'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.
In vehicular communications using 802.11-OCB links, there
are strong privacy requirements with respect to
addressing. While the 802.11-OCB standard does not
specify anything in particular with respect to MAC
addresses, in these settings there exists 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 some privacy
risks). This is further described in . A relevant function is described in
documents IEEE 1609.3-2016
and IEEE 1609.4-2016 .
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 802.11-OCB compliant:
The PHY entity shall be an orthogonal frequency division
multiplexing (OFDM) system. It must support the frequency
bands on which the regulator recommends the use of ITS
communications, for example using IEEE 802.11-OCB layer,
in France: 5875MHz to 5925MHz.
The OFDM system must provide a "half-clocked" operation
using 10 MHz channel spacings.
The chip transmit spectrum mask must be compliant to the
"Transmit spectrum mask" from the IEEE 802.11p amendment
(but experimental environments tolerate otherwise).
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:
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 local computer file that
describes regulatory domains rules, if used by the
kernel to enforce local specific restrictions. Such
modifications to the local computer file must respect
the location-specific regulatory rules.
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.
A more theoretical and detailed view of layer stacking, and
interfaces between the IP layer and 802.11-OCB layers, is
illustrated in . The IP layer
operates on top of the EtherType Protocol Discrimination
(EPD); this Discrimination layer is described in IEEE Std
802.3-2012; the interface between IPv6 and EPD is the LLC_SAP
(Link Layer Control Service Access Point).
The networks defined by 802.11-OCB are in many ways similar to
other networks of the 802.11 family. In theory, the
transportation of IPv6 over 802.11-OCB could be very similar to
the operation of IPv6 over other networks of the 802.11
family. However, the high mobility, strong link asymmetry and
very short connection makes the 802.11-OCB link significantly
different from other 802.11 networks. Also, the automotive
applications have specific requirements for reliability,
security and privacy, which further add to the particularity
of the 802.11-OCB link.
For information, at the time of writing, this is the list of
IEEE 802.11 messages that may be transmitted in OCB mode,
i.e. when dot11OCBActivated is true in a STA:
The STA may send management frames of subtype Action and,
if the STA maintains a TSF Timer, subtype Timing
Advertisement;
The STA may send control frames, except those of subtype
PS-Poll, CF-End, and CF-End plus CFAck;
The STA MUST send data frames of subtype QoS
Data.
This section describes an example of an IPv6 Packet captured
over a IEEE 802.11-OCB link.
By way of example we show that there is no modification in the
headers when transmitted over 802.11-OCB networks - they are
transmitted like any other 802.11 and Ethernet packets.
We describe an experiment of capturing an IPv6 packet on an
802.11-OCB link. In topology depicted in , the packet is an IPv6 Router Advertisement.
This packet is emitted by a Router on its 802.11-OCB
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.
The packet is captured on the Host. The Host is an IP-OBU
containing an 802.11 interface in format PCI express (an ITRI
product). The kernel runs the ath5k software driver with
modifications for OCB mode. The capture tool is Wireshark.
The file format for save and analyze is 'pcap'. The packet is
generated by the Router. The Router is an IP-RSU (ITRI
product).
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
802.11-OCB is outside the context of a BSSID.
Overall, the captured message is identical with a capture of
an IPv6 packet emitted on a 802.11b interface. The contents
are precisely similar.
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.
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 .
The IPv6 header contains the link local address of the router
(source) configured via EUI-64 algorithm, and destination
address set to ff02::1.
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 the 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 802.11-OCB to wait for the completion of association
and authentication procedures before exchanging data. IEEE
802.11-OCB enabled nodes use the wildcard BSSID (a value of
all 1s) and may start communicating as soon as they arrive
on the communication channel.
The same IPv6 Router Advertisement packet described above
(monitor mode) is captured on the Host, in the Normal mode,
and depicted below.
One notices that the Radiotap Header, the IEEE 802.11 Data
Header and the Logical-Link Control Headers are not present.
On the other 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.
A frame translation is inserted on top of a pure IEEE 802.11
MAC layer, in order to adapt packets, before delivering the
payload data to the applications. It adapts 802.11 LLC/MAC
headers to Ethernet II headers. In further detail, this
adaptation consists in the elimination of the Radiotap,
802.11 and LLC headers, and in the insertion of the Ethernet
II header. In this way, IPv6 runs straight over LLC over
the 802.11-OCB MAC layer; this is further confirmed by the
use of the unique Type 0x86DD.
The following terms are defined outside the IETF. They are
used to define the main terms in the main terminology section
.
DSRC (Dedicated Short Range Communication): a term defined
outside the IETF. The US Federal Communications Commission
(FCC) Dedicated Short Range Communication (DSRC) is defined in
the Code of Federal Regulations (CFR) 47, Parts 90 and 95.
This Code is referred in the definitions below. At the time
of the writing of this Internet Draft, the last update of this
Code was dated October 1st, 2010.
DSRCS (Dedicated Short-Range Communications Services): a term
defined outside the IETF. The use of radio techniques to
transfer data over short distances between roadside and mobile
units, between mobile units, and between portable and mobile
units to perform operations related to the improvement of
traffic flow, traffic safety, and other intelligent
transportation service applications in a variety of
environments. DSRCS systems may also transmit status and
instructional messages related to the units involve. [Ref. 47
CFR 90.7 - Definitions]
OBU (On-Board Unit): a term defined outside the IETF. An
On-Board Unit is a DSRCS transceiver that is normally mounted
in or on a vehicle, or which in some instances may be a
portable unit. An OBU can be operational while a vehicle or
person is either mobile or stationary. The OBUs receive and
contend for time to transmit on one or more radio frequency
(RF) channels. Except where specifically excluded, OBU
operation is permitted wherever vehicle operation or human
passage is permitted. The OBUs mounted in vehicles are
licensed by rule under part 95 of the respective chapter and
communicate with Roadside Units (RSUs) and other OBUs.
Portable OBUs are also licensed by rule under part 95 of the
respective chapter. OBU operations in the Unlicensed National
Information Infrastructure (UNII) Bands follow the rules in
those bands. - [CFR 90.7 - Definitions].
RSU (Road-Side Unit): a term defined outside of IETF. A
Roadside Unit is a DSRC transceiver that is mounted along a
road or pedestrian passageway. An RSU may also be mounted on
a vehicle or is hand carried, but it may only operate when the
vehicle or hand- carried unit is stationary. Furthermore, an
RSU operating under the respectgive part is restricted to the
location where it is licensed to operate. However, portable
or hand-held RSUs are permitted to operate where they do not
interfere with a site-licensed operation. A RSU broadcasts
data to OBUs or exchanges data with OBUs in its communications
zone. An RSU also provides channel assignments and operating
instructions to OBUs in its communications zone, when
required. - [CFR 90.7 - Definitions].
IPv6 Neighbor Discovery (IPv6 ND) [RFC4861][RFC4862] was
designed for point-to-point and transit links such as
Ethernet, with the expectation of a cheap and reliable support
for multicast from the lower layer. Section 3.2 of RFC 4861
indicates that the operation on Shared Media and on
non-broadcast multi-access (NBMA) networks require additional
support, e.g., for Address Resolution (AR) and duplicate
address detection (DAD), which depend on multicast. An
infrastructureless radio network such as OCB shares properties
with both Shared Media and NBMA networks, and then adds its
own complexity, e.g., from movement and interference that
allow only transient and non-transitive reachability between
any set of peers.
The uniqueness of an address within a scoped domain is a key
pillar of IPv6 and the base for unicast IP communication. RFC
4861 details the DAD method to avoid that an address is
duplicated. For a link local address, the scope is the link,
whereas for a Globally Reachable address the scope is much
larger. The underlying assumption for DAD to operate
correctly is that the node that owns an IPv6 address can reach
any other node within the scope at the time it claims its
address, which is done by sending a NS multicast message, and
can hear any future claim for that address by another party
within the scope for the duration of the address ownership.
In the case of OCB, there is a potentially a need to define a
scope that is compatible with DAD, and that cannot be the set
of nodes that a transmitter can reach at a particular time,
because that set varies all the time and does not meet the DAD
requirements for a link local address that could possibly be
used anytime, anywhere. The generic expectation of a reliable
multicast is not ensured, and the operation of DAD and AR
(Address Resolution) as specified by RFC 4861 cannot be
guaranteed. Moreover, multicast transmissions that rely on
broadcast are not only unreliable but are also often
detrimental to unicast traffic (see
[draft-ietf-mboned-ieee802-mcast-problems]).
Early experience indicates that it should be possible to
exchange IPv6 packets over OCB while relying on IPv6 ND alone
for DAD and AR (Address Resolution) in good conditions. In the absence
of a correct DAD operation, a node that relies only on IPv6 ND
for AR and DAD over OCB should ensure that the addresses that
it uses are unique by means others than DAD. It must be noted
that deriving an IPv6 address from a globally unique MAC
address has this property but may yield privacy issues.
RFC 8505 provides a more recent approach to IPv6 ND and in
particular DAD. RFC 8505 is designed to fit wireless and
otherwise constrained networks whereby multicast and/or
continuous access to the medium may not be guaranteed. RFC
8505 Section 5.6 "Link-Local Addresses and Registration"
indicates that the scope of uniqueness for a link local
address is restricted to a pair of nodes that use it to
communicate, and provides a method to assert the uniqueness
and resolve the link-Layer address using a unicast exchange.
RFC 8505 also enables a router (acting as a 6LR) to own a
prefix and act as a registrar (acting as a 6LBR) for addresses
within the associated subnet. A peer host (acting as a 6LN)
registers an address derived from that prefix and can use it
for the lifetime of the registration. The prefix is advertised
as not onlink, which means that the 6LN uses the 6LR to relay
its packets within the subnet, and participation to the subnet
is constrained to the time of reachability to the 6LR. Note
that RSU that provides internet connectivity MAY announce a
default router preference , whereas a car that does
not provide that connectivity MUST NOT do so. This operation
presents similarities with that of an access point, but at
Layer-3. This is why RFC 8505 well-suited for wireless in
general.
Support of RFC 8505 may be implemented on OCB. OCB nodes
that support RFC 8505 SHOULD support the 6LN operation in order
to act as a host, and may support the 6LR and 6LBR operations
in order to act as a router and in particular own a prefix
that can be used by RFC 8505-compliant hosts for address
autoconfiguration and registration.