Transmission of IPv6 Packets over IEEE 802.11 Networks operating
in mode Outside the Context of a Basic Service Set
(IPv6-over-80211-OCB)
CEA, LIST
CEA Saclay
Gif-sur-Yvette
Ile-de-France
91190
France
+33169089223
Alexandre.Petrescu@cea.fr
Moulay Ismail University
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
Network Working Group
IPv6 over 802.11p, OCB, IPv6 over 802.11-OCB
In order to transmit IPv6 packets on IEEE 802.11 networks
running outside the context of a basic service set (OCB,
earlier "802.11p") there is a need to define a few parameters
such as the supported Maximum Transmission Unit size on the
802.11-OCB link, the header format preceding the IPv6 header,
the Type value within it, and others. This document describes
these parameters for IPv6 and IEEE 802.11-OCB networks; it
portrays the layering of IPv6 on 802.11-OCB similarly to other
known 802.11 and Ethernet layers - by using an Ethernet
Adaptation Layer.
This document describes the transmission of IPv6 packets on
IEEE Std 802.11-OCB networks
(a.k.a "802.11p" see ). This
involves the layering of IPv6 networking on top of the IEEE
802.11 MAC layer, with an LLC layer. Compared to running IPv6
over the Ethernet MAC layer, there is no modification expected
to IEEE Std 802.11 MAC and Logical Link sublayers: IPv6 works
fine directly over 802.11-OCB too, with an LLC layer.
The IPv6 network layer operates on 802.11-OCB in the same
manner as operating on Ethernet, but there are two kinds of
exceptions:
Exceptions due to different operation of IPv6 network
layer on 802.11 than on Ethernet. To satisfy these
exceptions, this document describes an Ethernet Adaptation
Layer between Ethernet headers and 802.11 headers. The
Ethernet Adaptation Layer is described . 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 handover behaviour. For security and
privacy recommendations see and
. The subnet structure is described
in . The handover
behaviour on OCB links is not described in this document.
In the published literature, many documents describe aspects
and problems related to running IPv6 over 802.11-OCB: .
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.
IP-OBU (Internet Protocol On-Board Unit): an IP-OBU is a
computer situated in a vehicle such as an automobile, 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. An IP-RSU has at least two distinct IP-enabled
interfaces; at least one interface is operated in mode OCB of
IEEE 802.11 and is IP-enabled. An IP-RSU is similar to a
Wireless Termination Point (WTP), as defined in , or an Access Point (AP), as defined in
IEEE documents, or an Access Network Router (ANR) defined in
, with one key particularity: the
wireless PHY/MAC layer of at least one of its IP-enabled
interfaces is configured to operate in 802.11-OCB mode. The
IP-RSU communicates with the IP-OBU in the vehicle over 802.11
wireless link operating in OCB mode.
OCB (outside the context of a basic service set - BSS): 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: mode specified in IEEE Std 802.11-2016 when the
MIB attribute dot11OCBActivited is true. The OCB mode
requires transmission of QoS data frames (IEEE Std 802.11e),
half-clocked operation (IEEE Std 802.11j), and use of 5.9 GHz
frequency band. Nota: any implementation should comply with
standards and regulations set in the different countries for
using that frequency band.
The IEEE 802.11-OCB 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; in
particular, we refer the reader to , that
lists some scenarios and requirements for IP in Intelligent
Transportation Systems.
The link model is the following: STA --- 802.11-OCB --- STA.
In vehicular networks, STAs can be IP-RSUs and/or IP-OBUs. While
802.11-OCB is clearly specified, and the use of IPv6 over such
link is not radically new, the operating environment
(vehicular networks) brings in new perspectives.
The mechanisms for forming and terminating, discovering,
peering and mobility management for 802.11-OCB links are not
described in this document.
The default MTU for IP packets on 802.11-OCB MUST be 1500
octets. It is the same value as IPv6 packets on Ethernet
links, as specified in . 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). If IPv6
packets of size larger than 1500 bytes are sent on an
802.11-OCB interface card then the IP stack MUST fragment.
In case there are IP fragments, the field "Sequence number"
of the 802.11 Data header containing the IP fragment field
MUST be increased.
Non-IP packets such as WAVE Short Message Protocol (WSMP)
can be delivered on 802.11-OCB links. Specifications of
these packets are out of scope of this document, and do not
impose any limit on the MTU size, allowing an arbitrary
number of 'containers'. Non-IP packets such as ETSI
GeoNetworking packets have an MTU of 1492 bytes. The
operation of IPv6 over GeoNetworking is specified at .
IP packets are transmitted over 802.11-OCB as standard
Ethernet packets. As with all 802.11 frames, an Ethernet
adaptation layer is used with 802.11-OCB as well. This
Ethernet Adaptation Layer performing 802.11-to-Ethernet is
described in . The Ethernet Type code
(EtherType) for IPv6 MUST be 0x86DD (hexadecimal 86DD, or
otherwise #86DD).
The Frame format for transmitting IPv6 on 802.11-OCB
networks is the same as transmitting IPv6 on Ethernet
networks, and is described in section 3 of .
is the binary representation of the EtherType value
0x86DD.
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.
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.
The operation of the Ethernet Adaptation Layer is depicted
by the double arrow in .
The Receiver and Transmitter Address fields in the 802.11
Data Header MUST 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 MUST be the same as the value of the Type
field in the Ethernet II Header.
The ".11 Trailer" contains solely a 4-byte Frame Check
Sequence.
Additionally, the Ethernet Adaptation Layer performs
operations in relation to IP fragmentation and MTU. One
of these operations is briefly described in .
In OCB mode, IPv6 packets MAY be transmitted either as
"IEEE 802.11 Data" or alternatively as "IEEE 802.11 QoS
Data", as illustrated in .
The distinction between the two formats is given by the
value of the field "Type/Subtype". The value of the field
"Type/Subtype" in the 802.11 Data header is 0x0020. The
value of the field "Type/Subtype" in the 802.11 QoS header
is 0x0028.
The mapping between qos-related fields in the IPv6 header
(e.g. "Traffic Class", "Flow label") and fields in the
"802.11 QoS Data Header" (e.g. "QoS Control") are not
specified in this document. Guidance for a potential
mapping is provided in , although it is not
specific to OCB mode.
The placement of IPv6 networking layer on Ethernet
Adaptation Layer is illustrated in .
(in the above figure, a 802.11 profile is represented;
this is used also for 802.11 OCB profile.)
Other alternative views of layering are EtherType Protocol
Discrimination (EPD), see , and SNAP
see .
The link-local address of an 802.11-OCB interface is formed
in the same manner as on an Ethernet interface. This manner
is described in section 5 of .
Additionally, if stable identifiers are needed, it is
recommended to follow the Recommendation on Stable IPv6
Interface Identifiers .
Additionally, if semantically opaque Interface Identifiers
are needed, a potential method for generating semantically
opaque Interface Identifiers with IPv6 Stateless Address
Autoconfiguration is given in .
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 .
The procedure for mapping IPv6 unicast addresses into
Ethernet link-layer addresses is described in .
The multicast address mapping is performed according to
the method specified in section 7 of . The meaning of the value "3333"
mentioned in that section 7 of 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. Solutions for
these problems should consider the OCB mode of operation.
The Interface Identifier for an 802.11-OCB interface is
formed using the same rules as the Interface Identifier for
an Ethernet interface; this is described in section 4 of
. No changes are needed, but some
care must be taken when considering the use of the Stateless
Address Auto-Configuration procedure.
The bits in 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 802.11-OCB interface are significant, as this is an
IEEE link-layer address. The details of this significance
are described in .
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
address hijacking risks. A vehicle embarking an OBU or 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; see the privacy
considerations described in .
If stable Interface Identifiers are needed in order to form
IPv6 addresses on 802.11-OCB links, it is recommended to
follow the recommendation in .
Additionally, if semantically opaque Interface Identifiers
are needed, a potential method for generating semantically
opaque Interface Identifiers with IPv6 Stateless Address
Autoconfiguration is given in .
A subnet is formed by the external 802.11-OCB interfaces of
vehicles that are in close range (not their on-board
interfaces). This ephemeral subnet structure is strongly
influenced by the mobility of vehicles: the 802.11 hidden
node effects appear. On another hand, the structure of the
internal subnets in each car is relatively stable.
The 802.11 networks in OCB mode may be considered as
'ad-hoc' networks. The addressing model for such networks
is described in .
An addressing model involves several types of addresses,
like Globally-unique Addresses (GUA), Link-Local Addresses
(LL) and Unique Local Addresses (ULA). The subnet structure
in 'ad-hoc' networks may have characteristics that lead to
difficulty of using GUAs derived from a received prefix, but
the LL addresses may be easier to use since the prefix is
constant.
The operation of the Neighbor Discovery protocol (ND) over
802.11 OCB links is different than over 802.11 links. In
OCB, the link layer does not ensure that all associated
members receive all messages, because there is no
association operation. The operation of ND over 802.11 OCB
is not specified in this document.
The operation of the Mobile IPv6 protocol over 802.11 OCB
links is different than on other links. The Movement
Detection operation (section 11.5.1 of ) can not rely on Neighbor Unreachability
Detection operation of the Neighbor Discovery protocol, for
the reason mentioned in the previous paragraph. Also, the
802.11 OCB link layer is not a lower layer that can provide
an indication that a link layer handover has occured. The
operation of the Mobile IPv6 protocol over 802.11 OCB is not
specified in this document.
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 is stripped off of all existing 802.11
link-layer security mechanisms. There is no encryption
applied below the network layer running on 802.11-OCB. At
application layer, the IEEE 1609.2 document does provide 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). 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 less protected than
commonly used links (wired link or protected 802.11).
The potential attack vectors are: MAC address spoofing, IP
address and session hijacking and privacy violation.
Within the IPsec Security Architecture , the IPsec AH and ESP headers and respectively,
its multicast extensions , HTTPS and SeND protocols
can be used to protect communications. Further, the
assistance of proper Public Key Infrastructure (PKI) protocols
is necessary to establish
credentials. More IETF protocols are available in the toolbox
of the IP security protocol designer. Certain ETSI protocols
related to security protocols in Intelligent Transportation
Systems are described in .
As with all Ethernet and 802.11 interface identifiers, there
may exist privacy risks in the use of 802.11-OCB interface
identifiers. Moreover, in outdoors vehicular settings, the
privacy risks are more important than in indoors settings.
New risks are induced by the possibility of attacker sniffers
deployed along routes which listen for IP packets of vehicles
passing by. For this reason, in the 802.11-OCB deployments,
there is a strong necessity to use protection tools such as
dynamically changing MAC addresses. This may help mitigate
privacy risks to a certain level. On another hand, it may
have an impact in the way typical IPv6 address
auto-configuration is performed for vehicles (SLAAC would rely
on MAC addresses and would hence dynamically change the
affected IP address), in the way the IPv6 Privacy addresses
were used, and other effects.
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 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 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.
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.
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 on September 12th, 2017, at URL
https://standards.ieee.org/findstds/standard/802.11-2016.html
ETSI EN 302 636-6-1 v1.2.1 (2014-05), ETSI, European
Standard, Intelligent Transportation Systems (ITS);
Vehicular Communications; Geonetworking; Part 6: Internet
Integration; Sub-part 1: Transmission of IPv6 Packets over
Geonetworking Protocols. Downloaded on September 9th,
2017, freely available from ETSI website at URL
http://www.etsi.org/deliver/etsi_en/302600_302699/30263601/01.02.01_60/en_30263601v010201p.pdf
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 changes are listed in reverse chronological order, most
recent changes appearing at the top of the list.
From draft-ietf-ipwave-ipv6-over-80211ocb-15 to
draft-ietf-ipwave-ipv6-over-80211ocb-16
Removed the definition of the 'WiFi' term and its
occurences. Clarified a phrase that used it in Appendix C
"Aspects introduced by the OCB mode to 802.11".
Added more normative words: MUST be 0x86DD, MUST fragment
if size larger than MTU, Sequence number in 802.11 Data
header MUST be increased.
From draft-ietf-ipwave-ipv6-over-80211ocb-14 to
draft-ietf-ipwave-ipv6-over-80211ocb-15
Added normative term MUST in two places in section
"Ethernet Adaptation Layer".
From draft-ietf-ipwave-ipv6-over-80211ocb-13 to
draft-ietf-ipwave-ipv6-over-80211ocb-14
Created a new Appendix titled "Extra Terminology" that
contains terms DSRC, DSRCS, OBU, RSU as defined outside
IETF. Some of them are used in the main Terminology
section.
Added two paragraphs explaining that ND and Mobile IPv6
have problems working over 802.11 OCB, yet their
adaptations is not specified in this document.
From draft-ietf-ipwave-ipv6-over-80211ocb-12 to
draft-ietf-ipwave-ipv6-over-80211ocb-13
Substituted "IP-OBU" for "OBRU", and "IP-RSU" for "RSRU"
throughout and improved OBU-related definitions in the
Terminology section.
From draft-ietf-ipwave-ipv6-over-80211ocb-11 to
draft-ietf-ipwave-ipv6-over-80211ocb-12
Improved the appendix about "MAC Address Generation" by
expressing the technique to be an optional suggestion, not
a mandatory mechanism.
From draft-ietf-ipwave-ipv6-over-80211ocb-10 to
draft-ietf-ipwave-ipv6-over-80211ocb-11
Shortened the paragraph on forming/terminating 802.11-OCB
links.
Moved the draft tsvwg-ieee-802-11 to Informative
References.
From draft-ietf-ipwave-ipv6-over-80211ocb-09 to
draft-ietf-ipwave-ipv6-over-80211ocb-10
Removed text requesting a new Group ID for multicast for
OCB.
Added a clarification of the meaning of value "3333" in
the section Address Mapping -- Multicast.
Added note clarifying that in Europe the regional
authority is not ETSI, but "ECC/CEPT based on ENs from
ETSI".
Added note stating that the manner in which two STAtions
set their communication channel is not described in this
document.
Added a time qualifier to state that the "each node is
represented uniquely at a certain point in time."
Removed text "This section may need to be moved" (the
"Reliability Requirements" section). This section stays
there at this time.
In the term definition "802.11-OCB" added a note stating
that "any implementation should comply with standards and
regulations set in the different countries for using that
frequency band."
In the RSU term definition, added a sentence explaining
the difference between RSU and RSRU: in terms of number of
interfaces and IP forwarding.
Replaced "with at least two IP interfaces" with "with at
least two real or virtual IP interfaces".
Added a term in the Terminology for "OBU". However the
definition is left empty, as this term is defined outside
IETF.
Added a clarification that it is an OBU or an OBRU in this
phrase "A vehicle embarking an OBU or an OBRU".
Checked the entire document for a consistent use of terms
OBU and OBRU.
Added note saying that "'p' is a letter identifying the
Ammendment".
Substituted lower case for capitals SHALL or MUST in the
Appendices.
Added reference to RFC7042, helpful in the 3333
explanation. Removed reference to individual submission
draft-petrescu-its-scenario-reqs and added reference to
draft-ietf-ipwave-vehicular-networking-survey.
Added figure captions, figure numbers, and references to
figure numbers instead of 'below'. Replaced "section
Section" with "section" throughout.
Minor typographical errors.
From draft-ietf-ipwave-ipv6-over-80211ocb-08 to
draft-ietf-ipwave-ipv6-over-80211ocb-09
Significantly shortened the Address Mapping sections, by
text copied from RFC2464, and rather referring to it.
Moved the EPD description to an Appendix on its own.
Shortened the Introduction and the Abstract.
Moved the tutorial section of OCB mode introduced to .11,
into an appendix.
Removed the statement that suggests that for routing
purposes a prefix exchange mechanism could be needed.
Removed refs to RFC3963, RFC4429 and RFC6775; these are
about ND, MIP/NEMO and oDAD; they were referred in the
handover discussion section, which is out.
Updated a reference from individual submission to now a WG
item in IPWAVE: the survey document.
Added term definition for WiFi.
Updated the authorship and expanded the Contributors
section.
Corrected typographical errors.
From draft-ietf-ipwave-ipv6-over-80211ocb-07 to
draft-ietf-ipwave-ipv6-over-80211ocb-08
Removed the per-channel IPv6 prohibition text.
Corrected typographical errors.
From draft-ietf-ipwave-ipv6-over-80211ocb-06 to
draft-ietf-ipwave-ipv6-over-80211ocb-07
Added new terms: OBRU and RSRU ('R' for Router). Refined
the existing terms RSU and OBU, which are no longer used
throughout the document.
Improved definition of term "802.11-OCB".
Clarified that OCB does not "strip" security, but that the
operation in OCB mode is "stripped off of all .11
security".
Clarified that theoretical OCB bandwidth speed is 54mbits,
but that a commonly observed bandwidth in IP-over-OCB is
12mbit/s.
Corrected typographical errors, and improved some
phrasing.
From draft-ietf-ipwave-ipv6-over-80211ocb-05 to
draft-ietf-ipwave-ipv6-over-80211ocb-06
Updated references of 802.11-OCB document from -2012 to
the IEEE 802.11-2016.
In the LL address section, and in SLAAC section, added
references to 7217 opaque IIDs and 8064 stable IIDs.
From draft-ietf-ipwave-ipv6-over-80211ocb-04 to
draft-ietf-ipwave-ipv6-over-80211ocb-05
Lengthened the title and cleanded the abstract.
Added text suggesting LLs may be easy to use on OCB,
rather than GUAs based on received prefix.
Added the risks of spoofing and hijacking.
Removed the text speculation on adoption of the TSA
message.
Clarified that the ND protocol is used.
Clarified what it means "No association needed".
Added some text about how two STAs discover each other.
Added mention of external (OCB) and internal network
(stable), in the subnet structure section.
Added phrase explaining that both .11 Data and .11 QoS
Data headers are currently being used, and may be used in
the future.
Moved the packet capture example into an Appendix
Implementation Status.
Suggested moving the reliability requirements appendix out
into another document.
Added a IANA Consiserations section, with content,
requesting for a new multicast group "all OCB interfaces".
Added new OBU term, improved the RSU term definition,
removed the ETTC term, replaced more occurences of
802.11p, 802.11 OCB with 802.11-OCB.
References:
Added an informational reference to ETSI's
IPv6-over-GeoNetworking.
Added more references to IETF and ETSI security protocols.
Updated some references from I-D to RFC, and from old RFC
to new RFC numbers.
Added reference to multicast extensions to IPsec
architecture RFC.
Added a reference to 2464-bis.
Removed FCC informative references, because not used.
Updated the affiliation of one author.
Reformulation of some phrases for better readability, and
correction of typographical errors.
From draft-ietf-ipwave-ipv6-over-80211ocb-03 to
draft-ietf-ipwave-ipv6-over-80211ocb-04
Removed a few informative references pointing to Dx draft
IEEE 1609 documents.
Removed outdated informative references to ETSI documents.
Added citations to IEEE 1609.2, .3 and .4-2016.
Minor textual issues.
From draft-ietf-ipwave-ipv6-over-80211ocb-02 to
draft-ietf-ipwave-ipv6-over-80211ocb-03
Keep the previous text on multiple addresses, so remove
talk about MIP6, NEMOv6 and MCoA.
Clarified that a 'Beacon' is an IEEE 802.11 frame Beacon.
Clarified the figure showing Infrastructure mode and OCB
mode side by side.
Added a reference to the IP Security Architecture RFC.
Detailed the IPv6-per-channel prohibition paragraph which
reflects the discussion at the last IETF IPWAVE WG
meeting.
Added section "Address Mapping -- Unicast".
Added the ".11 Trailer" to pictures of 802.11 frames.
Added text about SNAP carrying the Ethertype.
New RSU definition allowing for it be both a Router and
not necessarily a Router some times.
Minor textual issues.
From draft-ietf-ipwave-ipv6-over-80211ocb-01 to
draft-ietf-ipwave-ipv6-over-80211ocb-02
Replaced almost all occurences of 802.11p with 802.11-OCB,
leaving only when explanation of evolution was necessary.
Shortened by removing parameter details from a paragraph
in the Introduction.
Moved a reference from Normative to Informative.
Added text in intro clarifying there is no handover spec
at IEEE, and that 1609.2 does provide security services.
Named the contents the fields of the EthernetII header
(including the Ethertype bitstring).
Improved relationship between two paragraphs describing
the increase of the Sequence Number in 802.11 header upon
IP fragmentation.
Added brief clarification of "tracking".
From draft-ietf-ipwave-ipv6-over-80211ocb-00 to
draft-ietf-ipwave-ipv6-over-80211ocb-01
Introduced message exchange diagram illustrating
differences between 802.11 and 802.11 in OCB mode.
Introduced an appendix listing for information the set of
802.11 messages that may be transmitted in OCB mode.
Removed appendix sections "Privacy Requirements",
"Authentication Requirements" and "Security Certificate
Generation".
Removed appendix section "Non IP Communications".
Introductory phrase in the Security Considerations
section.
Improved the definition of "OCB".
Introduced theoretical stacked layers about IPv6 and IEEE
layers including EPD.
Removed the appendix describing the details of prohibiting
IPv6 on certain channels relevant to 802.11-OCB.
Added a brief reference in the privacy text about a
precise clause in IEEE 1609.3 and .4.
Clarified the definition of a Road Side Unit.
Removed the discussion about security of WSA (because is
non-IP).
Removed mentioning of the GeoNetworking discussion.
Moved references to scientific articles to a separate
'overview' draft, and referred to it.
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 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. At link layer, it
is necessary to set the same channel number (or frequency) on
two stations that need to communicate with each other. The
manner in which stations set their channel number is not
specified in this document. Stations STA1 and STA2 can
exchange IP packets if they are set on the same channel. At
IP layer, they then discover each other by using the IPv6
Neighbor Discovery protocol.
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
Ammendment, 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
IEEE 1609.3-2016 , clause
5.5.1 and IEEE 1609.4-2016 ,
clause 6.7.
Other aspects particular to 802.11-OCB, 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 802.11-OCB networks. The OCB subnet structure is described
in .
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
encapsulation 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.
In automotive networks it is required that each node is
represented uniquely at a certain point in time.
Accordingly, a vehicle must be identified by at least one
unique identifier. The current specification at ETSI and at
IEEE 1609 identifies a vehicle by its MAC address, which is
obtained from the 802.11-OCB Network Interface Card (NIC).
In case multiple 802.11-OCB NICs are present in one car,
implicitely multiple vehicle IDs will be generated.
Additionally, some software generates a random MAC address
each time the computer boots; this constitutes an additional
difficulty.
A mechanim to uniquely identify a vehicle irrespectively to
the multiplicity of NICs, or frequent MAC address
generation, is necessary.
The dynamically changing topology, short connectivity,
mobile transmitter and receivers, different antenna heights,
and many-to-many communication types, make IEEE 802.11-OCB
links significantly different from other IEEE 802.11 links.
Any IPv6 mechanism operating on IEEE 802.11-OCB link must
support strong link asymmetry, spatio-temporal link quality,
fast address resolution and transmission.
IEEE 802.11-OCB strongly differs from other 802.11 systems
to operate outside of the context of a Basic Service Set.
This means in practice that IEEE 802.11-OCB does not rely on
a Base Station for all Basic Service Set management. In
particular, IEEE 802.11-OCB shall not use beacons. Any IPv6
mechanism requiring L2 services from IEEE 802.11 beacons
must support an alternative service.
Channel scanning being disabled, IPv6 over IEEE 802.11-OCB
must implement a mechanism for transmitter and receiver to
converge to a common channel.
Authentication not being possible, IPv6 over IEEE 802.11-OCB
must implement an distributed mechanism to authenticate
transmitters and receivers without the support of a DHCP
server.
Time synchronization not being available, IPv6 over IEEE
802.11-OCB must implement a higher layer mechanism for time
synchronization between transmitters and receivers without
the support of a NTP server.
The IEEE 802.11-OCB link being asymmetric, IPv6 over IEEE
802.11-OCB must disable management mechanisms requesting
acknowledgements or replies.
The IEEE 802.11-OCB link having a short duration time, IPv6
over IEEE 802.11-OCB should implement fast IPv6 mobility
management mechanisms.
There are considerations for 2 or more IEEE 802.11-OCB
interface cards per vehicle. For each vehicle taking part in
road traffic, one IEEE 802.11-OCB interface card could be
fully allocated for Non IP safety-critical communication.
Any other IEEE 802.11-OCB may be used for other type of
traffic.
The mode of operation of these other wireless interfaces is
not clearly defined yet. One possibility is to consider each
card as an independent network interface, with a specific
MAC Address and a set of IPv6 addresses. Another
possibility is to consider the set of these wireless
interfaces as a single network interface (not including the
IEEE 802.11-OCB interface used by Non IP safety critical
communications). This will require specific logic to ensure,
for example, that packets meant for a vehicle in front are
actually sent by the radio in the front, or that multiple
copies of the same packet received by multiple interfaces
are treated as a single packet. Treating each wireless
interface as a separate network interface pushes such issues
to the application layer.
Certain privacy requirements imply that if these multiple
interfaces are represented by many network interface, a
single renumbering event shall cause renumbering of all
these interfaces. If one MAC changed and another stayed
constant, external observers would be able to correlate old
and new values, and the privacy benefits of randomization
would be lost.
The privacy requirements of Non IP safety-critical
communications imply that if a change of pseudonyme occurs,
renumbering of all other interfaces shall also occur.
In 802.11-OCB networks, the MAC addresses may change during
well defined renumbering events. 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.
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 may send data frames of subtype Data, Null, QoS
Data, and QoS Null.
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. 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 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.
An Adaptation layer 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].