Re: [ipwave] Intdir last call review of draft-ietf-ipwave-vehicular-networking-20

["Pascal Thubert (pthubert)" <[e-mail]>]

Hello Paul

This is absolutely excellent. I’m very happy will all the changes and your attached pdf made my life as a reviewer a lot simpler.

This is really a great way of progressing together. Many thanks for that!

I’m all good but for a little snippet in the new text which is actually incorrect, and denotes a usual misunderstanding of RPL that your doc may help correct for the future:

“
Although RPL can be used in IPv6-based vehicular networks, it is primarily designed for lossy
networks, which puts energy efficiency first. In addition, the topology it considers may not
quickly scale up and down for IPv6-based vehicular networks, since the mobility of vehicles is
much more diverse with a high speed, so it can frequently alter a tree-like topology formed by
RPL, which may cause network fragmentation and merging with more control traffic
“


The roots of my contribution to RPL are in vehicular networks, exactly the use case you describe. Based on that experience (including some actual test with NASA) I’d change the text above with:


“
RPL is primarily designed to minimize the control plane activity, that is the relative amount of routing protocol exchanges vs. data traffic; this approach is beneficial for situations where the power and bandwidth are scarce (e.g., an IoT LLN where RPL is typically used today), but also in situations of high relative mobility between the nodes in the network (aka swarming, e.g., within a variable set of vehicles with a similar global motion, or a toon of drones).
To reduce the routing exchanges, RPL leverages a Distance Vector approach, which does not need a global knowledge of the topology, and only optimizes the routes to and from the root, allowing P2P paths to be stretched. Although RPL installs its routes proactively, it only maintains them lazily, in reaction to actual traffic, or as a slow background activity. Additionally, RPL leverages the concept of an objective function, which allows to adapt the activity of the routing protocol to the use case, e.g., type, speed, and quality of the radios. RPL does not need converge, and provides connectivity to most nodes most of the time. The default route towards the Root is maintained aggressively and may change while a packet progresses without causing loops, so the packet will still reach the root. In non-storing mode, a node inside the mesh/swarm that changes its point(s) of attachment to the graph informs the root with a single unicast packet the flows along the default route, and the connectivity is restored immediately; this mode is preferable for use cases where internet connectivity is dominant. OTOH, in storing mode, the routing stretch is reduced, for a better P2P connectivity, while the internet connectivity is restored more slowly, time for the DV operation to operate hop-by-hop. While a RPL topology can quickly scale up and down and fits the needs of mobility of vehicles, the total performance of the system will also depend on how quickly a node can form an address, join the mesh (including AAA), and manage its global mobility to become reachable from outside the mesh.
“

Otherwise, all good!

Take care,

Pascal


From: Mr. Jaehoon Paul Jeong <[e-mail]>
Sent: lundi 30 août 2021 15:12
To: Pascal Thubert (pthubert) <[e-mail]>
Cc: [e-mail]; Last Call <[e-mail]>; [e-mail]; [e-mail]; Russ Housley <[e-mail]>; CARLOS JESUS BERNARDOS CANO <[e-mail]>; skku-iotlab-members <[e-mail]>; Chris Shen <[e-mail]>; Mr. Jaehoon Paul Jeong <[e-mail]>
Subject: Re: [ipwave] Intdir last call review of draft-ietf-ipwave-vehicular-networking-20

Hi Pascal,
Here is the revision (-21) of IPWAVE PS Draft:
https://datatracker.ietf.org/doc/html/draft-ietf-ipwave-vehicular-networking-21

I attach the revision letter to show how I have addressed your comments on the revision.

Chris and I have worked for this revision together.

If you have further comments, please let me know.

Thanks.

Best Regards,
Paul



On Fri, Jun 18, 2021 at 4:42 PM Pascal Thubert via Datatracker <[e-mail]<mailto:[e-mail]>> wrote:
Reviewer: Pascal Thubert
Review result: Not Ready

Dear authors

In summary:

I read a number of very good drafts collated in one, from the use cases that
very complete and ready to publish, to the architecture and protocol solution
in section 4 that would require more work for completeness.

There are multiple instances in the use cases where protocols are listed coming
out of the blue, e.g., the references to OMNI that seem artificially spread
regardless of the context of the section. OMNI is used throughout, both as an
open ended toolbox, and as a carpet under which all problems can be hidden.

Reading this doc, OMNI shows as an interface to a software mobile router, with
multiple of the device physical interfaces connected to the mobile router. This
makes the stack very simple as the complexity moves to the router. But now you
have to implement the router. Presented as that, the OMNI router deserves its
name, it’s indeed very rich; it seems to cover all forms of MANET (many to
choose from) and NEMO (and all the MIP protocol family across address
families), all the possible radio interfaces on which the ND problems go away
by magic, and whatever else you want to put in there. Is that the intention?

Instead of referring to OMNI for virtually anything, the doc should refer to
MANET for MANET things (like BYOD), NEMO for NEMO things (like MNP),
draft-nordmark-intarea-ippl for split subnets, and
draft-thubert-6man-ipv6-over-wireless for P2MP/NBMA link and subnet models. And
then you can say that all those components can be plugged in the OMNI router,
and you can discuss which MANET and which MIP you want, including using OMNI’s
built in mobility.

Note that my objections are not against the OMNI design, it might be the
perfect thing and I am already aware of use cases that could be served by a
P2MP interface like OMNI in conjunction with RFC8505 on the P2P subinterfaces
(recycling the high level design we’ve been shipping for IPv4 / frame relay for
the last 30 years). My objection is of the way the draft uses [OMNI] as the
magic wand that solves all the problems when what you really do is throw them
over the fence. I’d rather you focus on problems and use cases, for which
there’s excellent text, and indicate what needs to be done without making
assumption on how the needful things will be solved.

In agreement with a discussion on the 6MAN list, I’d suggest to split, keep all
that’s use case and problem description and ship it, remove references to
protocols envisioned in the solution, and start the work on architecture of the
solution and the protocol applicability statements separately. An alternate
would be to centralize the discussion on protocols to annex, and explain that
protocol A or B could be envisioned in solution space because to over this gap
or implement that function.

In any fashion, the current text is not ready for publication as applicability
statement, architecture and or/solution, so the related work should be removed
from the main text. But I find it mostly ready for use case and problem
statement, more below.

Review:

Abstract

   This document discusses the problem statement and use cases of
   IPv6-based vehicular networking for Intelligent Transportation
   Systems (ITS).

>>> The document goes beyond that; there was actually a thread at 6MAN where
Bob Hinden said “ This document says it is a problem statement, but then
becomes a solution document.   Might be better to cut it down to only the
problem statement part. “ >>> Would you consider doing this? If not, why? Note:
you may want to respond on 6MAN as well. >>> >>>I would have thought that the
traditional steps of problem statement and applicability statement of existing
work could be expected from IPWAVE too. >>> Please clarify the steps that you
intend to follow next with this work.

<snip>

1.  Introduction

>>> Very readable and informative section, many thanks!

   Along with these WAVE standards and C-V2X standards, regardless of a
   wireless access technology under the IP stack of a vehicle, vehicular
   networks can operate IP mobility with IPv6 [RFC8200] and Mobile IPv6
   protocols (e.g., Mobile IPv6 (MIPv6) [RFC6275], Proxy MIPv6 (PMIPv6)
   [RFC5213], Distributed Mobility Management (DMM) [RFC7333], Locator/
   ID Separation Protocol (LISP) [RFC6830BIS], and Asymmetric Extended
   Route Optimization (AERO) [RFC6706BIS]).

>>> NEMO (RFC 3963) is not cited. Any reason why the vehicle would not
transport a network?

<snip>

   This document describes use cases and a problem statement about
   IPv6-based vehicular networking for ITS, which is named IPv6 Wireless
   Access in Vehicular Environments (IPWAVE).  First, it introduces the
   use cases for using V2V, V2I, and V2X networking in ITS.  Next, for
   IPv6-based vehicular networks, it makes a gap analysis of current
   IPv6 protocols (e.g., IPv6 Neighbor Discovery, Mobility Management,
   and Security & Privacy), and then enumerates requirements for the
   extensions of those IPv6 protocols, which are tailored to IPv6-based
   vehicular networking.  Thus, this document is intended to motivate
   development of key protocols for IPWAVE.

>>>

<snip>

2.  Terminology

>>>

<snip>

   o  IP-OBU: "Internet Protocol On-Board Unit": An IP-OBU denotes a
      computer situated in a vehicle (e.g., car, bicycle, autobike,
      motor cycle, and a similar one) and a device (e.g., smartphone and
      IoT device).  It has at least one IP interface that runs in IEEE
      802.11-OCB and has an "OBU" transceiver.  Also, it may have an IP
      interface that runs in Cellular V2X (C-V2X) [TS-23.285-3GPP]
      [TR-22.886-3GPP][TS-23.287-3GPP].  See the definition of the term
      "OBU" in [RFC8691].

>>> Can that be a router connecting multiple computers?

<snip>

3.  Use Cases

>>> This is another great read and an enlightening section. Maybe mention in
the abstract that the doc also covers use cases?

<snip>

   Although a Layer-2 solution can provide a support for multihop
   communications in vehicular networks, the scalability issue related
   to multihop forwarding still remains when vehicles need to
   disseminate or forward packets toward multihop-away destinations.  In
   addition, the IPv6-based approach for V2V as a network layer protocol
   can accommodate multiple radio technologies as MAC protocols, such as
   5G V2X and DSRC.  Therefore, the existing IPv6 protocol can be
   augmented through the addition of an Overlay Multilink Network (OMNI)
   Interface [OMNI] and/or protocol changes in order to support both
   wireless single-hop/multihop V2V communications and multiple radio
   technologies in vehicular networks.  In such a way, vehicles can
   communicate with each other by V2V communications to share either an
   emergency situation or road hazard in a highway having multiple kinds
   of radio technologies, such as 5G V2X and DSRC.

>>> This text appears in the middle of high level use case, with a crude list
of protocols; this is not a place for it

>>> On a 6MAN Thread, Brian Carpenter said that the above:
“
is of concern regardless of the mention of OMNI. Does it mean "can be" or
"needs to be"? This paragraph seems like a very short summary of a big problem
area. At the end of page 13 there is some related discussion, which mentions
RPL as part of the solution (good choice, IMHO) but again seems to depend on
OMNI. I don't think the fix of simply removing references to OMNI works,
because it would leave a gap. In an informational document, that is not a
formal problem but as far as this draft describes architecture, I don't think
that big a gap is reasonable. "OMNI" is mentioned more than 20 times in the
document. There are also several references to AERO, which is strongly
associated with OMNI. “ >>> I agree with Brian. Here the document seems to be
mixing solution with problem and putting the cart before the horse. My
recommendation is to stick to what needs to be done that IPv6 does not do yet
-the reqs and gaps-; but the doc should not step in the how things will be done
unless the group already decided to do it. The logical next steps to a PS are
an applicability statement of existing work, and if the gaps cannot be filled,
there may be one or more WG chartered to fill those gaps.

>>> I’d still be happy to see an annex with leads on where the solution might
come from like RFC 8691 does.

<snip>

   The existing IPv6 protocol must be augmented through the addition of
   an OMNI interface and/or protocol changes in order to support
   wireless multihop V2I communications in a highway where RSUs are
   sparsely deployed, so a vehicle can reach the wireless coverage of an
   RSU through the multihop data forwarding of intermediate vehicles.
   Thus, IPv6 needs to be extended for multihop V2I communications.

>>> Note that I have no clue on how well OMNI applies in that space, maybe it
does very well; but here it comes out of the blue with no justification. If you
mention OMNI you need to detail what it is and which of the V2V  problems you
expect it to solve. But then, that’s beyond the scope of a PS.

<snip>

   The existing IPv6 protocol must be augmented through the addition of
   an OMNI interface and/or protocol changes in order to support
   wireless multihop V2X (or V2I2X) communications in an urban road
   network where RSUs are deployed at intersections, so a vehicle (or a
   pedestrian's smartphone) can reach the wireless coverage of an RSU
   through the multihop data forwarding of intermediate vehicles (or
   pedestrians' smartphones).  Thus, IPv6 needs to be extended for
   multihop V2X (or V2I2X) communications.

>>> Please be more specific on what the missing functions are and whether they
are missing from the stack development standpoint or if there’s work needed
from the IETF. 1)      If something is really missing in our specs, the text to
prove from the use case above is missing 2)      how OMNI serves the use case
could be elaborated in an applicability statement of OMNI for V2xyz, but it is
a bit blunt to present it as panacea when the problems to be solved are not
listed. 3)      If you look at it, OMNI seems like a software mobile router
within a bump in the stack. Can that become too big?

>>> my view is that the text above and the similar occasions should be replaced
by something like :

   The existing IPv6 protocol must be augmented to provide the following
   functions: 1) …

>>> and / or something like:

   In addition to the IPv6 node requirements [RFC 8504], the IPv6 protocol
   stack for use in a vehicle must support 1) RFC blah, 2) …

<snip>

   To support applications of these V2X use cases, the functions of IPv6
   such as VND, VMM, and VSP are prerequisites for IPv6-based packet
   exchange, transport-layer session continuity, and secure, safe
   communication between a vehicle and a pedestrian either directly or
   indirectly via an IP-RSU.

>>> “the functions of IPv6 such as VND, VMM, and VSP” does not parse. There’s
no IPv6 reference that provides those functions. If the intention is to say
that there’s stuff to add to IPv6 to support, like, say,  VND, then this
document fails to define how an IPv6 VND should behave, though it’s precisely
what I’d expect from a problem statement.

<snip>

4.  Vehicular Networks

>>> What is the purpose of section 4 as a whole, problem statement or
applicability statement of the listed protocols? In the former case what’s the
problem? In the latter case it is incomplete and needs to be exported to an
applicability statement doc with all the possible technologies evaluated.

   This section describes an example vehicular network architecture
   supporting V2V, V2I, and V2X communications in vehicular networks.

>>> I read this as presenting a context to explain what the problems are
instead of presenting the IPVAWE “architecture”. Maybe using the term
“Architecture” here is misleading and led to Bob’s comment.

<snip>

4.1.  Vehicular Network Architecture

   Figure 1 shows an example vehicular network architecture for V2I and
   V2V in a road network [OMNI].

a.      Is using OMNI a decision that the WG made for the future work ? what
does it do and what does it not do? b.      Is there work left to be done? Who
will do that work? Or is it the expectation that OMNI has it all defined
already?

<snip>

   An existing network architecture (e.g., an IP-based aeronautical
   network architecture [OMNI][UAM-ITS], a network architecture of
   PMIPv6 [RFC5213], and a low-power and lossy network architecture
   [RFC6550]) can be extended to a vehicular network architecture for
   multihop V2V, V2I, and V2X, as shown in Figure 1.  In a highway
   scenario, a vehicle may not access an RSU directly because of the
   distance of the DSRC coverage (up to 1 km).  For example, the OMNI
   interface and/or RPL (IPv6 Routing Protocol for Low-Power and Lossy
   Networks) [RFC6550] can be extended to support a multihop V2I since a
   vehicle can take advantage of other vehicles as relay nodes to reach
   the RSU.  Also, RPL can be extended to support both multihop V2V and
   V2X in the similar way.

>>> all this could fit well in annex; anyway you need to explain what you
expect the protocols to do and which extension is needed. In the case of RPL at
least you indicate that it would do routing, but not why you cannot use it of
the shelf; for OMNI, what you expect is less clear, though there’s text
elsewhere about the many radio interfaces that could be used for the purpose,
and the text in the UAM below that is enlightening.

<snip>

                                  To support not only the mobility
   management of the UAM end systems, but also the multihop and
   multilink communications of the UAM interfaces, the UAM end systems
   can employ an Overlay Multilink Network (OMNI) interface [OMNI] as a
   virtual Non-Broadcast Multiple Access (NBMA) connection to a serving
   ground domain infrastructure.

>>> Again, what is the expectation for OMNI? As an overlay it requires an
underlay; when connecting to a MANET it needs support for that MANET. The text
above seems to imply that is solves everything in V2xyz like magic; reminds me
of the IPv6 multicast abstraction that was supposed to solve the broadcast
problem and ended up worsening it.

<snip>

                            This infrastructure can be configured
   over the underlying data links.  The OMNI interface and its link
   model provide a means of multilink, multihop and mobility
   coordination to the legacy IPv6 ND messaging [RFC4861] according to
   the NBMA principle.  Thus, the OMNI link model can support efficient
   UAM internetworking services without additional mobility messaging,
   and without any modification to the IPv6 ND messaging services or
   link model.

>>> Again, what is the expectation for OMNI? As an overlay it requires an
underlay; the text above seems to imply that is solves everything in V2xyz like
magic; that would be a stretch, that reminds me of IPv6 multicast that was
supposed to solve the broadcast problem and ended up worsening it.

<snip>

   Multiple vehicles under the coverage of an RSU share a prefix just as
   mobile nodes share a prefix of a Wi-Fi access point in a wireless
   LAN.  This is a natural characteristic in infrastructure-based
   wireless networks.  For example, in Figure 1, two vehicles (i.e.,
   Vehicle2, and Vehicle5) can use Prefix 1 to configure their IPv6
   global addresses for V2I communication.  Alternatively, mobile nodes
   can employ an OMNI interface and use their own IPv6 Unique Local
   Addresses (ULAs) [RFC4193] over the wireless network without
   requiring the messaging of IPv6 Stateless Address Autoconfiguration
  (SLAAC) [RFC4862], which uses an on-link prefix provided by the
   (visited) wireless LAN; this technique is known as "Bring-Your-Own-
   Addresses".

>>>  Is OMNI the only way to "Bring-Your-Own-Addresses”? Else the text could be
more generic, at least use e.g., like the ref to AERO later. >>> What are the
implications / limitations of doing that – like they can do line of sight V2V
but not reach the internet, or the need of  a local MANET / RPL that will
accept to route those addresses, or the security / address ownership validation
issues ?

<snip>

   A single subnet prefix announced by an RSU can span multiple vehicles
   in VANET.  For example, in Figure 1, for Prefix 1, three vehicles
   (i.e., Vehicle1, Vehicle2, and Vehicle5) can construct a connected
   VANET.  Also, for Prefix 2, two vehicles (i.e., Vehicle3 and
   Vehicle6) can construct another connected VANET, and for Prefix 3,
   two vehicles (i.e., Vehicle4 and Vehicle7) can construct another
   connected VANET.  Alternatively, each vehicle could employ an OMNI
   interface with their own ULAs such that no topologically-oriented
   subnet prefixes need be announced by the RSU.

>>>  same as above. This seems to restate the same thing, derive an address
from a topologically correct prefix or use your own with limitations to be
described.

<snip>

   For IPv6 packets transported over IEEE 802.11-OCB, [RFC8691]
   specifies several details, including Maximum Transmission Unit (MTU),
   frame format, link-local address, address mapping for unicast and
   multicast, stateless autoconfiguration, and subnet structure.  An
   Ethernet Adaptation (EA) layer is in charge of transforming some
   parameters between the IEEE 802.11 MAC layer and the IPv6 network
   layer, which is located between the IEEE 802.11-OCB's logical link
   control layer and the IPv6 network layer.  This IPv6 over 802.11-OCB
   can be used for both V2V and V2I in IPv6-based vehicular networks.

>>>  solution space.

<snip>

   An IPv6 mobility solution is needed for the guarantee of
   communication continuity in vehicular networks so that a vehicle's
   TCP session can be continued, or UDP packets can be delivered to a
   vehicle as a destination without loss while it moves from an IP-RSU's
   wireless coverage to another IP-RSU's wireless coverage.  In
   Figure 1, assuming that Vehicle2 has a TCP session (or a UDP session)
   with a corresponding node in the vehicular cloud, Vehicle2 can move
   from IP-RSU1's wireless coverage to IP-RSU2's wireless coverage.  In
   this case, a handover for Vehicle2 needs to be performed by either a
   host-based mobility management scheme (e.g., MIPv6 [RFC6275]) or a
   network-based mobility management scheme (e.g., PMIPv6 [RFC5213] and
   AERO [RFC6706BIS]).

   In the host-based mobility scheme (e.g., MIPv6), an IP-RSU plays a
   role of a home agent.  On the other hand, in the network-based
   mobility scheme (e.g., PMIPv6, an MA plays a role of a mobility
   management controller such as a Local Mobility Anchor (LMA) in
   PMIPv6, which also serves vehicles as a home agent, and an IP-RSU
   plays a role of an access router such as a Mobile Access Gateway
   (MAG) in PMIPv6 [RFC5213].  The host-based mobility scheme needs
   client functionality in IPv6 stack of a vehicle as a mobile node for
   mobility signaling message exchange between the vehicle and home
   agent.  On the other hand, the network-based mobility scheme does not
   need such a client functionality for a vehicle because the network
   infrastructure node (e.g., MAG in PMIPv6) as a proxy mobility agent
   handles the mobility signaling message exchange with the home agent
   (e.g., LMA in PMIPv6) for the sake of the vehicle.

   There are a scalability issue and a route optimization issue in the
   network-based mobility scheme (e.g., PMIPv6) when an MA covers a
   large vehicular network governing many IP-RSUs.  In this case, a
   distributed mobility scheme (e.g., DMM [RFC7429]) can mitigate the
   scalability issue by distributing multiple MAs in the vehicular
   network such that they are positioned closer to vehicles for route
   optimization and bottleneck mitigation in a central MA in the
   network-based mobility scheme.  All these mobility approaches (i.e.,
   a host-based mobility scheme, network-based mobility scheme, and
   distributed mobility scheme) and a hybrid approach of a combination
   of them need to provide an efficient mobility service to vehicles
   moving fast and moving along with the relatively predictable
   trajectories along the roadways.

   In vehicular networks, the control plane can be separated from the
   data plane for efficient mobility management and data forwarding by
   using the concept of Software-Defined Networking (SDN)
   [RFC7149][DMM-FPC].  Note that Forwarding Policy Configuration (FPC)
   in [DMM-FPC], which is a flexible mobility management system, can
   manage the separation of data-plane and control-plane in DMM.  In
   SDN, the control plane and data plane are separated for the efficient
   management of forwarding elements (e.g., switches and routers) where
   an SDN controller configures the forwarding elements in a centralized
   way and they perform packet forwarding according to their forwarding
   tables that are configured by the SDN controller.  An MA as an SDN
   controller needs to efficiently configure and monitor its IP-RSUs and
   vehicles for mobility management, location management, and security
   services.

   The mobility information of a GPS receiver mounted in its vehicle
   (e.g., position, speed, and direction) can be used to accommodate
   mobility-aware proactive handover schemes, which can perform the
   handover of a vehicle according to its mobility and the wireless
   signal strength of a vehicle and an IP-RSU in a proactive way.

   Vehicles can use the TCC as their Home Network having a home agent
   for mobility management as in MIPv6 [RFC6275] and PMIPv6 [RFC5213],
   so the TCC (or an MA inside the TCC) maintains the mobility
   information of vehicles for location management.  IP tunneling over
   the wireless link should be avoided for performance efficiency.
   Also, in vehicular networks, asymmetric links sometimes exist and
   must be considered for wireless communications such as V2V and V2I.

>>>  This is all very informative text but does not state a problem. Is there a
problem is left to be solved or are we assessing the applicability of
protocols? Could it for instance, forward point to issues discussed in section
5?

<snip>

   As shown in Figure 3, as internal networks, a vehicle's moving
   network and an EN's fixed network are self-contained networks having
   multiple subnets and having an edge router (e.g., IP-OBU and IP-RSU)
   for the communication with another vehicle or another EN.  The
   internetworking between two internal networks via V2I communication
   requires the exchange of the network parameters and the network
   prefixes of the internal networks.  For the efficiency, the network
   prefixes of the internal networks (as a moving network) in a vehicle
   need to be delegated and configured automatically.  Note that a
   moving network's network prefix can be called a Mobile Network Prefix
   (MNP) [OMNI].

>>> Then again you’re overselling OMNI. MNP is originally defined here
https://datatracker.ietf.org/doc/html/rfc3963#section-2 and that’s a reference
you can use normatively.

<snip>

   As shown in Figure 3, the addresses used for IPv6 transmissions over
   the wireless link interfaces for IP-OBU and IP-RSU can be either
   global IPv6 addresses, or IPv6 ULAs as long as IPv6 packets can be
   routed within vehicular networks [OMNI].

>>> Then again you’re overselling OMNI. There needs to  be a routing protocol
like a MANET that will accept to carry the
 MNPs, and that must be implemented by the infra and both cars. The OMNI spec
 is clear on that. This is why at first glance I see OMNI as a full mobile
 router in a bump in the stack. Now what is the problem behind this? No such
 protocol at IETF? Too many to choose from? No deployment?
<snip>

When global IPv6 addresses
   are used, wireless interface configuration and control overhead for
   Duplicate Address Detection (DAD) [RFC4862] and Multicast Listener
   Discovery (MLD) [RFC2710][RFC3810] should be minimized to support V2I
   and V2X communications for vehicles moving fast along roadways; when
   ULAs and the OMNI interface are used, no DAD nor MLD messaging is
   needed.

>>> Then again you’re overselling OMNI. Isn’t it the no dad needed a property
of injecting a BYOA in the fabric for an GUA MIP Home Address which is known to
be unique at home? >>> OTOH, autoconf’ing a random ULA “FD…”prefix has lesser
DAD properties than autoconf’ing a random 64bit IID in a classical subnet. So
who says DAD isn’t required for OMNI ULA? >>> note that IMHO DAD on wireless is
a lot more harm than good, and I agree that with a good pseudo random generator
the ULA has no chance to collision in the real world, as OMNI claims. It’s just
that your argument here plays the other way, because there are less random bits
(56)  in the ULA prefix than in the IID (62), and if one starts using more
prefix bits to be non-random, there will be a time when DAD on prefix is needed.

<snip>

   Let us consider the upload/download time of a vehicle when it passes
   through the wireless communication coverage of an IP-RSU.  For a
   given typical setting where 1km is the maximum DSRC communication
   range [DSRC] and 100km/h is the speed limit in highway, the dwelling
   time can be calculated to be 72 seconds by dividing the diameter of
   the 2km (i.e., two times of DSRC communication range where an IP-RSU
   is located in the center of the circle of wireless communication) by
   the speed limit of 100km/h (i.e., about 28m/s).  For the 72 seconds,
   a vehicle passing through the coverage of an IP-RSU can upload and
   download data packets to/from the IP-RSU.

<snip>

4.3.  V2V-based Internetworking

>>> In this section it looks like the cars are in a stable line of sight
relationship. Which is probably fine for a platoon, but when you drive along
with friends in different cars, you realize that the line of sight assumption
does not stand over time. Soon enough, other cars meddle in, and possibly one
of the cars drives faster and too far ahead so you need the infra to relay,
possibly over multiple infra hops.

>>> so in this section, I’d expect to see a Vehicle communicating with another
one and using either line of sight or V2V relaying but also using relay via V2I
(multihop I2I not just hub and spoke V2I2V ), alternatively to together for
redundancy. Is that part of the problem?

>>> reading deeper section 5 I found excellent text on routing via V and via I.
This tells that section 4 does not play a good role at justifying section 5.
Maybe keep section 4 for another doc?

>>> What kind or reliability is required in a V2V use case? Do you think ND can
handle it? Or MANET? What would be the assumption on L2 (roaming time, unicast
vs P2MP) and on L3 (reliability ala DetNet/RAW). Should we have some L3
redundancy?

<snip>

5.  Problem Statement

<snip>

   In order to specify protocols using the architecture mentioned in
   Section 4.1, IPv6 core protocols have to be adapted to overcome
   certain challenging aspects of vehicular networking.  Since the
   vehicles are likely to be moving at great speed, protocol exchanges
   need to be completed in a time relatively short compared to the
   lifetime of a link between a vehicle and an IP-RSU, or between two
   vehicles.

>>> Any order of magnitude?
>>> Can you indicate whether this already rules out certain procedures, e.g.
DAD ?

   The lifetime of a session varies depending on the session's type such
   as a web surfing, voice call over IP, and DNS query.  Regardless of a
   session's type, to guide all the IPv6 packets to their destination
   host, IP mobility should be supported for the session.

>>> this seems to be for unicast when you know who to talk to. Is there a need
some multicast groups like anybody around interested in topic blah like I could
be multicasting the speed of vehicles coming the other way that I crossed
recently, for use of vehicles that I’m crossing now, so they can see a slowdown
on advance

   Thus, the time constraint of a wireless link has a major impact on
   IPv6 Neighbor Discovery (ND).  Mobility Management (MM) is also
   vulnerable to disconnections that occur before the completion of
   identity verification and tunnel management.  This is especially true
   given the unreliable nature of wireless communication.  This section
   presents key topics such as neighbor discovery and mobility
   management.

>>> Only ND? What about the MANET?
>>> how fast should ND be to be suitable?
>>> is there also a bandwidth check? You can make things much faster if you
dedicate a lot of spectrum to it. But that can also be a waste.

5.1.  Neighbor Discovery

<snip>

   The requirements for IPv6 ND for vehicular networks are efficient DAD
   and NUD operations.

>>> Not lookup? Is it the intention to use IP unicast over MAC broadcast, which
is a good idea in my book?

 <snip>

      This merging and partitioning should be considered for the
   IPv6 ND such as IPv6 Stateless Address Autoconfiguration (SLAAC)
   [RFC4862].

>>> Not lookup? Is it the intention to use IP unicast over MAC broadcast, which
is a good idea in my book?

 <snip>

   Also, the partitioning of a VANET may make vehicles with the same
   prefix be physically unreachable.  Also, SLAAC needs to prevent IPv6
   address duplication due to the merging of VANETs.  According to the
   merging and partitioning, a destination vehicle (as an IPv6 host)
   needs to be distinguished as either an on-link host or an off-link
   host even though the source vehicle uses the same prefix as the
   destination vehicle.

>>> should reference to draft-nordmark-intarea-ippl

   To efficiently prevent IPv6 address duplication due to the VANET
   partitioning and merging from happening in vehicular networks, the
   vehicular networks need to support a vehicular-network-wide DAD by
   defining a scope that is compatible with the legacy DAD.  In this
   case, two vehicles can communicate with each other when there exists
   a communication path over VANET or a combination of VANETs and IP-
   RSUs, as shown in Figure 1.  By using the vehicular-network-wide DAD,
   vehicles can assure that their IPv6 addresses are unique in the
   vehicular network whenever they are connected to the vehicular
   infrastructure or become disconnected from it in the form of VANET.

>>> Excellent

   ND time-related parameters such as router lifetime and Neighbor
   Advertisement (NA) interval need to be adjusted for vehicle speed and
   vehicle density.  For example, the NA interval needs to be
   dynamically adjusted according to a vehicle's speed so that the
   vehicle can maintain its neighboring vehicles in a stable way,
   considering the collision probability with the NA messages sent by
   other vehicles.

>>> Is that a problem or just an operational setting that needs to be found?
>>> Do we need to reconsider the concepts of those timers?

<snip>

   Thus, in IPv6-based vehicular networking, IPv6 ND should have minimum
   changes for the interoperability with the legacy IPv6 ND used in the
   Internet, including the DAD and NUD operations.

>>> I do not find the logical link with the text before, why is this a “thus”?
>>> why should the ND inside the VANET be constrained to be interoperable? This
may place constraints on the solution.

5.1.1.  Link Model

   A prefix model for a vehicular network needs to facilitate the

>>> Do you mean a “subnet model” as opposed to “prefix model”.
>>> it would make this piece and the next should refer to
draft-thubert-6man-ipv6-over-wireless for IPv6 over P2MP /NBMA, for both link
and subnet issues. The general ideas are the same, but the gory details here
are slightly incorrect, like this notion of prefix model than comes out of the
blue. The model is really the subnet model for the subnet associated to P2MP.

   communication between two vehicles with the same prefix regardless of
   the vehicular network topology as long as there exist bidirectional
   E2E paths between them in the vehicular network including VANETs and
   IP-RSUs.  This prefix model allows vehicles with the same prefix to
   communicate with each other via a combination of multihop V2V and
   multihop V2I with VANETs and IP-RSUs.  Note that the OMNI interface
   supports an NBMA link model where multihop V2V and V2I communications
   use each mobile node's ULAs without need for any DAD or MLD
   messaging.

>>> again overselling OMNI.
>>> I kinda agree about the OMNI interface model, nothing against that. But you
must see that there needs a lot more than what the OMNI interface to get
packets across V and I hops to the destination. Like routing ala MANET,
redundancy handling ala DetNet because it will be very lossy, path management
ala RAW to optimize delivery vs. spectrum… And OMNI ignores ND so it does not
solve the ND problems above.

   IPv6 protocols work under certain assumptions that do not necessarily
   hold for vehicular wireless access link types other than OMNI/NBMA
   [VIP-WAVE][RFC5889]; the rest of this section discusses implications
   for those link types that do not apply when the OMNI/NBMA link model

>>> again overselling OMNI.
>>> The keyword here is P2MP / NBMA, and OMNI is one interface that accepts
that. There are others. IBM’s IPv4 over Frame relay was already P2MP / NBMA,
using routing to complete the partial mesh in P2MP. The text seems to imply
that OMNI is the only way to do that and that’s wrong. Also OMNI is loaded with
other stuff than a plain P2MP capable interface. And ND over P2MP is not done
by OMNI, OMNI only makes classical ND worse and only works in a full mesh. OTOH
RFC 8505, which is designed to do ND for P2MP /NBMA would indeed work very well
within an OMNI interface and solve those problems. >>> My point is that you
need to tell the full story or refrain from entering solution space in this doc

<snip>

   There is a relationship between a link and a prefix, besides the
   different scopes that are expected from the link-local and global
   types of IPv6 addresses.  In an IPv6 link, it is assumed that all
   interfaces which are configured with the same subnet prefix and with
   on-link bit set can communicate with each other on an IPv6 link.

>>> not assumed; that’s what the onlink but set tells. The conclusion should be
that the VANET cannot set the O bit.

   However, the vehicular link model needs to define the relationship
   between a link and a prefix, considering the dynamics of wireless
   links and the characteristics of VANET.

<snip>

   From the previous observation, a vehicular link model should consider
   the frequent partitioning and merging of VANETs due to vehicle
   mobility.  Therefore, the vehicular link model needs to use an on-
   link prefix and off-link prefix according to the network topology of
   vehicles such as a one-hop reachable network and a multihop reachable

>>> No, the once a node saw a O bit set that sticks even if it sees other
advertisements of the PIO with the O bit not set. >>> This is a global and
intrinsic property of the prefix (and an attack vector that could be mentioned
in the sec section). >>> the VANET prefix must never come with the O bit set.

<snip>

   network (or partitioned networks).  If the vehicles with the same
   prefix are reachable from each other in one hop, the prefix should be
   on-link.

>>>> No, see above; but the router may redirect though it is really risky
unless this is a stable situation like a parking place.

   Thus, in IPv6-based vehicular networking, the vehicular link model
   should have minimum changes for interoperability with standard IPv6
   links in an efficient fashion to support IPv6 DAD, MLD and NUD
   operations.  When the OMNI NBMA link model is used, there are no link
   model changes nor DAD/MLD messaging required.

>>>> again overselling OMNI.
>>>> You need a good P2MP subnet model with routing support when the mesh is
partial. My company alone has been shipping million of nodes that build subnets
of thousands, and that was done using IETF standards.

<snip>

   For vehicular networks with high mobility and density, the DAD needs
   to be performed efficiently with minimum overhead so that the
   vehicles can exchange a driving safety message (e.g., collision
   avoidance and accident notification) with each other with a short
   interval (e.g., 0.5 second) by a technical report from NHTSA
   (National Highway Traffic Safety Administration) [NHTSA-ACAS-Report].
   Such a driving safety message may include a vehicle's mobility
   information (i.e., position, speed, direction, and acceleration/
   deceleration).  The exchange interval of this message is 0.5 second,
   which is required to allow a driver to avoid a rear-end crash from
   another vehicle.

>>> IPv6 over broadcast MAC (used to be called internet 0, 10+ years ago)
solves that MAC issue since there is no MAC.

5.1.3.  Routing

   For multihop V2V communications in either a VANET or VANETs via IP-
   RSUs, a vehicular Mobile Ad Hoc Networks (MANET) routing protocol may
   be required to support both unicast and multicast in the links of the
   subnet with the same IPv6 prefix.  However, it will be costly to run
   both vehicular ND and a vehicular ad hoc routing protocol in terms of
   control traffic overhead [ID-Multicast-Problems].

>>> we do that with IETF standards on battery operated devices already. Using
RFC 8505 for the UNI and RPL for the NNI. It is scalable (we’ve seen 30 hops in
meshes of thousands in the real world though it’s not the normal operational
model, but can happen to maintain connectivity during the reboot of a root) and
does not use broadcast. RPL was initially designed as a V2V2V protocol but
found its market on the IoT. I’m sure the protocol would gladly come back to
its roots.

   A routing protocol for a VANET may cause redundant wireless frames in
   the air to check the neighborhood of each vehicle and compute the
   routing information in a VANET with a dynamic network topology
   because the IPv6 ND is used to check the neighborhood of each
   vehicle.  Thus, the vehicular routing needs to take advantage of the
   IPv6 ND to minimize its control overhead.

>>> A clean description of the interaction of RPL and RFC 8505 in our IoT
networks. Note that the speed of the PHY in VANET balanced the instability of
the topology, and RPL still applies. Note also that RPL uses DV with a routing
stretch in order to minimize the topology awareness that’s needed in each node,
which results in minimal signaling.

5.2.  Mobility Management

<snip>

   For a mobility management scheme in a shared link, where the wireless
   subnets of multiple IP-RSUs share the same prefix, an efficient
   vehicular-network-wide DAD is required.  If DHCPv6 is used to assign
   a unique IPv6 address to each vehicle in this shared link,

>>> I would not use the term link, or shared. Maybe shared link -> domain?
<snip>

the DAD is
   not required.  On the other hand, for a mobility management scheme
   with a unique prefix per mobile node (e.g., PMIPv6 [RFC5213] and OMNI
   [OMNI]), DAD is not required because the IPv6 address of a vehicle's
   external wireless interface is guaranteed to be unique.

>>> again overselling OMNI
>>> As I said earlier, this is wring there are (64*) more chances of a
collision in OMNI prefixes than in IPv6 IIDs. >>> OMNI prefixes can collision,
home addresses that are unique on a home network cannot. >>> Now if both the
OMNI prefix and the IID are good randoms, then obviously, the chances of
collisions round up to 0. >>> Collision is certainly not my worst fear.

  There is a
   tradeoff between the prefix usage efficiency and DAD overhead.  Thus,
   the IPv6 address autoconfiguration for vehicular networks needs to
   consider this tradeoff to support efficient mobility management.

>>> This is way too superficial and hides the reality of things.
- Using a VANET Infra prefix allows direct routability to the internet which
BYOA does not since the BYOA is not topologically correct. Yes, it costs a DAD
with classic ND, but it does not with RCF8505 and the draft fails to mention
that. - A BYOA needs a tunnel home, and the node needs to know who is reachable
inside the VANET and what is not to decide to tunnel or not; this is a
difficult problem (vs. control place overhead) that is not discussed here.

<snip>

   For the case of a multihomed network, a vehicle can follow the first-
   hop router selection rule described in [RFC8028].  That is, the
   vehicle should select its default router for each prefix by
   preferring the router that advertised the prefix.

>>> Still router discovery (in and out) must be very fast. Thing of the RA
intervale in MIPv6. Is that sufficient? Too expensive?

<snip>

6.  Security Considerations
>>> Any discussion on the security of classical ND and other operational issues
(rfc6583) ?

<snip>

   Security and privacy are paramount in V2I, V2V, and V2X networking.
   Vehicles and infrastructure must be authenticated in order to
   participate in vehicular networking.  Also, in-vehicle devices (e.g.,
   ECU) and a driver/passenger's mobile devices (e.g., smartphone and
   tablet PC) in a vehicle need to communicate with other in-vehicle
   devices and another driver/passenger's mobile devices in another
   vehicle, or other servers behind an IP-RSU in a secure way.  Even
   though a vehicle is perfectly authenticated and legitimate, it may be
   hacked for running malicious applications to track and collect its
   and other vehicles' information.  In this case, an attack mitigation
   process may be required to reduce the aftermath of malicious
   behaviors.

>>> The section should mention that both with classical ND and BYOA, addresses
can be impersonated, and RFC 8928 protects against that in both cases while
maintaining privacy.

   Even though vehicles can be authenticated with valid certificates by
   an authentication server in the vehicular cloud, the authenticated

>>> Is PKI feasible (deploying it in every car?). Is it fast enough? Is it
really what IPWAVE thinks vehicle should use????? >>> e.g. why would one need
to authenticate to a V2I network? >>> from the text earlier in the doc, it
seemed that what you really want is access that is fast to join, capable of
offering the reachability you want, anonymous, and innocuous (cars can not harm
one another).

   vehicles may harm other vehicles, so their communication activities
   need to be logged in either a central way through a logging server
   (e.g., TCC) in the vehicular cloud or a distributed way (e.g.,
   blockchain [Bitcoin]) along with other vehicles or infrastructure.
   For the non-repudiation of the harmful activities of malicious nodes,
   a blockchain technology can be used [Bitcoin].  Each message from a
   vehicle can be treated as a transaction and the neighboring vehicles
   can play the role of peers in a consensus method of a blockchain
   [Bitcoin][Vehicular-BlockChain].  For a blockchain's efficient
   consensus in vehicular networks having fast moving vehicles, a new
   consensus algorithm needs to be developed or an existing consensus
   algorithm needs to be enhanced.

>>> solution space; better express the  security needs since this is a PS.

<snip>

   To identify malicious vehicles among vehicles, an authentication
   method is required.

>>> No. As said earlier a vehicle can be infected. You need innocuousness.which
can come from things like isolation, zerotrust, and protocols that are
difficult to hack around. Classical IPv6 ND is open bar. RFC 8505/8928 is
protected by construction, anonymous, and fast.

<snip>

   For the setup of a secure channel over IPsec or TLS, the multihop V2I
   communications over DSRC is required in a highway for the
   authentication by involving multiple intermediate vehicles as relay
   nodes toward an IP-RSU connected to an authentication server in the
   vehicular cloud.  The V2I communications over 5G V2X (or LTE V2X) is
   required to allow a vehicle to communicate directly with a gNodeB (or
   eNodeB) connected to an authentication server in the vehicular cloud.

>>> solution space. Instead, you could mention that setting up secured channels
between cars that cross one another might not complete in time to establish the
communication channel, and that the innocuousness must come from zerotrust in
the transactions between the cars.
   For the IPv6 ND, the DAD is required to ensure the uniqueness of the
   IPv6 address of a vehicle's wireless interface.

>>> for classical ND (SLAAC) that’s true. That is not with RFC 8505, since the
infra maintains a table of all addresses in use in the prefix and blocks
duplicates without the RFC 4862 DAD method. The stateful autoconf address grant
is immediate.

                               This DAD can be used
   as a flooding attack that uses the DAD-related ND packets
   disseminated over the VANET or vehicular networks.

>>> also for DOS attacks. You can block a owner from using an address. A
reference to rfc6959 is much needed here.

<snip>

 This possibility
   indicates that the vehicles and IP-RSUs need to filter out suspicious
   ND traffic in advance.  Based on the SEND [RFC3971] mechanism, the
   authentication for routers (i.e., IP-RSUs) can be conducted by only
   selecting an IP-RSU that has a certification path toward trusted
   parties.  For authenticating other vehicles, the cryptographically
   generated address (CGA) can be used to verify the true owner of a
   received ND message, which requires to use the CGA ND option in the
   ND protocols.  For a general protection of the ND mechanism, the RSA
   Signature ND option can also be used to protect the integrity of the
   messages by public key signatures.  For a more advanced
   authentication mechanism, a distributed blockchain-based mechanism
   [Vehicular-BlockChain] can be used.

>>> solution space. Again, the draft should focus on problems and needs. The
problem here is that SEND is complex, and not implemented in the major stack.
It relies on PKI for trusting the router. The V2I need is a zerotrust model
where one V, the other local Vs, and the I, can help each other anonymously and
harmlessly. <snip>

8.  Informative References

>>> no normative reference?

>>> no normative reference?

<snip>

Voila!

Keep safe;

Pascal



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