Re: [ipwave] Hidden terminal problem

[Alexandre Petrescu <[e-mail]>]

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?
Is the OFDM that I see in OCB packet dumps an alternative to CSMA/CA?
Is OFDM solving the hidden terminal problem?

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.

> 
>     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