Re: [ipwave] Expertise on ND problems on OCB

[Alexandre Petrescu <[e-mail]>]

Hi Brian,

Le 14/04/2019 à 22:49, Brian E Carpenter a écrit :
> Hi Alexandre,
> 
> On 15-Apr-19 04:38, Alexandre Petrescu wrote:

[...]
>>>     The baseline Neighbor Discovery protocol (ND) [RFC4861] MUST be used
>>>     over 802.11-OCB links.  Transmitting ND packets may prove 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 best of current knowledge indicates the kinds of
>>>     issues that may arise with ND in OCB mode; they are described in
>>>     Appendix J.
> 
> That's exactly the text that I find problematic. I can't write a new
> version because I lack your expert knowledge, but IMHO it should be
> more specific:

I do have expert knowledge on ND on OCB, although only at a certain 
level.  It works.

Other people may claim ND does not work on OCB, but have they tried OCB 
at all?

It is the people who claim ND does not work on OCB should write the new 
version of the 'TBD' text.

It is very simple to try ND on OCB.  I published a howto on the email 
list.  A Hackathon w/o me was tried following that howto.  A few other 
organisations that I work with tried it (w/o me).  I did not received 
feedback from them about ND not working.

What is difficult to try is to reproduce the ND-over-OCB problem 
imagined by Pascal.  It is difficult to try because it involves 4 cars 
(I dont have that many).  It  is also difficult to try because it seems 
to miss the fact that OCB can do high power.  Maybe that high power 
solves the problems that appear in ND over low power.

For my part, I cant put text about ND on OCB without having an 
implementation of that problem.

It is for that reason that I asked Pascal, or anybody else claiming ND 
does not work on OCB, to try it and write that text 'TBD'.

Alex

> 
>      The baseline Neighbor Discovery protocol (ND) [RFC4861] MUST be used
>      over 802.11-OCB links.  However, as on any wireless link, transmission
>      of multicast ND packets may fail in OCB. In particular, scenarios
>      where TBD TBD TBD are likely to be unreliable and SHOULD NOT be
>      deployed until an alternative standardised solution is available.
>      The best of current knowledge indicates the kinds of issues that
>      may arise with ND in OCB mode; they are described in Appendix J.
> 
> Also I don't like this phrasing in Appendix J:
> 
>     Early experiences indicate that it should be possible to exchange
>     IPv6 packets over OCB while relying on IPv6 ND alone for DAD and AR
>     (Address Resolution).
> 
> Could you rather say the opposite:
> 
>     Early experience indicates that it is possible to exchange
>     IPv6 packets over OCB while relying on IPv6 ND alone for DAD and AR
>     (Address Resolution) in good conditions. However, this does not
>     apply if TBD TBD TBD...
> 
> Regards
>      Brian
> 
> 
>>
>>
>> Alex
>>
>>>
>>> Regards
>>>      Brian
>>>
>>> On 14-Apr-19 13:58, NABIL BENAMAR wrote:
>>>> +1 Sri
>>>>
>>>> On Sun, Apr 14, 2019, 00:06 Sri Gundavelli (sgundave) <[e-mail] <mailto:[e-mail]>> wrote:
>>>>
>>>>       I understand your point Brian, but IMO there are enough reasons not to
>>>>       delay this work.
>>>>
>>>>       There are many use-cases/applications where there is a stable topology of
>>>>       RSU¹s and OBU¹s. The regulations around 5.9 Ghz (DSRC) band allows the
>>>>       channel use for non-priority/non-traffic safety related applications. For
>>>>       example, a vehicle in a gas station can receive a coupon from the
>>>>       802.11-OCB radio (AP/RSU) in the gas station. There, its a stable topology
>>>>       that classic ND is designed for. In this operating mode, its perfectly
>>>>       reasonable to use classic ND and it works. The authors have shown enough
>>>>       lab data on the same.
>>>>
>>>>       Ideally, I agree with you that it makes lot more sense to publish both the
>>>>       specs at the same time. But, for what ever reasons the WG went on this
>>>>       path. Authors have spent incredible amount of efforts in getting the draft
>>>>       this far and we cannot ignore that. You can see the efforts from the
>>>>       version number; when did we last see a draft version -037?
>>>>
>>>>       We also need to distill the recent ND discussions and filter out the
>>>>       threads that are clearly motivated to insert a ND protocol that is
>>>>       designed for a totally different operating environment. An argument that a
>>>>       protocol designed for low-power environments is the solution for vehicular
>>>>       environments requires some serious vetting. Looking at the
>>>>       characteristics, always-sleeping, occasional internet connectivity,
>>>>       low-power, no memory, no processing power, no mobility ..etc, meeting
>>>>       vehicular requirements is some thing most people in the WG do not get it.
>>>>
>>>>       Bottom line, IMO, we should move this forward and publish the document.
>>>>       All we need is a simple statement in the spec which puts some scope
>>>>       limits, w.r.t the missing ND pieces and issues. There are other proposals
>>>>       in the WG that will address the gaps and bring closure to the work.
>>>>
>>>>       Sri
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>       On 4/12/19, 1:28 PM, "Brian E Carpenter" <[e-mail] <mailto:[e-mail]>>
>>>>       wrote:
>>>>
>>>>       >On 13-Apr-19 02:59, Sri Gundavelli (sgundave) wrote:
>>>>       >>If you go back and check 2017 archives, I did raise many of these
>>>>       >>issues.  But, we clearly decided to limit the scope excluding address
>>>>       >>configuration, DAD, ND aspect, link models. When there is such a scope
>>>>       >>statement, it should clearly move these comments to the draft that
>>>>       >>defines how ND works for 802.11-OCB links.
>>>>       >
>>>>       >This is of course possible. In general the IETF hasn't done that, but has
>>>>       >followed the lead set by RFC 2464 with the complete specification of
>>>>       >IPv6-over-foo in one document.
>>>>       >
>>>>       >However, I don't believe that publishing an RFC about the frame format
>>>>       >without *simultaneously* publishing an RFC about ND etc would be a good
>>>>       >idea. That would leave developers absolutely unable to write useful
>>>>       >code, and might easily lead to incompatible implementations. Since
>>>>       >we'd presumably like Fords to be able to communicate with Peugeots,
>>>>       >that seems like a bad idea.
>>>>       >
>>>>       >Regards
>>>>       >   Brian
>>>>
>>>
>>>
>> .
>>
> 
>