Re: [ipwave] Hidden terminal problem

[Abdussalam Baryun <[e-mail]>]

On Thu, Apr 18, 2019 at 10:21 AM Alexandre Petrescu <
[e-mail]> wrote:

>
>
> Le 18/04/2019 à 04:43, Abdussalam Baryun a écrit :
> >
> >
> > On Tue, Apr 16, 2019 at 5:50 PM Charlie Perkins
> > <[e-mail] <mailto:[e-mail]>>
> > wrote:
> >
> >     Hello Alex,
> >
> >     Consider the following three nodes with radio links as shown:
> >
> >     A----------B----------C
> >
> >     Suppose that A and B are at 80% of their signal range, and also that
> B
> >     and C are at 80% of their signal range.
> >
> >     So A and C are not in range.  So A is 'hidden' from C, and C is
> >     'hidden'
> >     from A.
> >
> >     That's the hidden terminal problem.  It's not specific to OCB or
> WiFi,
> >     and it is not a hypothetical problem.  It's just physics. It's not at
> >     all difficult to understand, but it is very important to understand.
> >
> >
> > Yes but it has been reduced its effects of collisions by CSMA/CA, and by
> > using control frames,
>
> Is OCB using CSMA/CA?
>

Yes,


> Is the OFDM that I see in OCB packet dumps an alternative to CSMA/CA?
>

one in PHY layer and the other protocol in MAC layer,


> Is OFDM solving the hidden terminal problem?
>

Yes when using MIMO and multi directional antennas, but some only think in
Omni-directional antenna use cases, and they think only in SISO use cases.


>
> In OCB there are no control frames; so the absence of the control frames
> can not help with the hidden terminal problem - on the contrary, it may
> worsen it.
>

In all cases of IEEE802.11 and application there are management messages
and control messages and data messages, so Do you say there is no Control
messages and no Management messages in OCB use cases, I disagree,

IMHO, it is ok to configure OCB with RTS/CTS and poll technique to solve
some applications services needed.


AB

>
> >
> >     One question below...
> >
> >     On 4/16/2019 3:18 AM, Alexandre Petrescu wrote:
> >      >
> >      > ...
> >
> >      >
> >      > I do not know how the hidden terminal problem works.  I feel like
> >     if I
> >      > start looking into it I will grow additional white hairs.  I feel
> >     like I
> >      > better avoid  it.
> >
> >
> > usually it is the IEEE problem to solve not this WG problem. I believe
> > they solved it.
>
> IT's good to know if it were that way.
>
> >      >
> >      > I think other people have some experience with the hidden terminal
> >      > problem in non-OCB WiFi and 802.15.4.  I am listening to them.
> >
> >
> > usually MIMO technology has change many issues, but 802.15.4 is big
> > different MAC than 802.11,
>
> I agree.
>
> >
> >      >
> >      > I think nobody has any experience with the hidden terminal
> problem in
> >      > OCB settings.  I have some doubts, but still I think it is almost
> >     nobody.
> >      >
> >      >
> >     I find this very surprising!  What do others think?
> >
> >
> > I think usually this hidden terminal is old problem now IEEE802.11 has
> > been updated, solving many old problems including that. It is called now
> > hidden station in IEEE802.11 new docs. In old sunets and terminals they
> > have no intelligence but now the stations are smart especially when it
> > is a Car not a sensor, because a Car has big storage and power
> > capabilities that can help to increase intelligence and decision making.
>
> I think both points are worth mentioning: (1) 802.11 new docs
> (presumably year 2016) do have solutions for hidden station problem and
> (2) car may have more computing capability than a small temperature
> sensor and hence may use it to alleviate the hidden station problem.
>
> I think there is much that can be put together about this.
>
> Pascal described an A-B-C-D problem.
> Charles described an A-B-C hidden terminal problem.
> I described a hidden car problem.
> You mention the IEEE hidden station problem and the IEEE 802.11 new
> solutions to it.
>
> It makes for a beautiful section "Hidden-icity Problems" (sorry I dont
> know a good term about Hidden).
>
> Alex
>