Re: [Autoconf] aspects of multi-hop wireless communication

[Alexandru Petrescu <[e-mail]>]

Emmanuel Baccelli wrote:

>>> Second, there is no guarantee that two given routers within S can
>>> directly communicate with one another.  In other words, even 
>>> though two routers R1 and R2 can both "hear" packets from router 
>>> A, there is no guarantee that R1 can hear packets from R2, and
>>> there is likewise no guarantee that R2 can hear packets from R1.
>>> Thus, multi-hop ad hoc wireless communications may be
>>> "non-transitive".
>> 
>> It is of paramount important for me to understand what is meant by 
>> "hearing".  Is it MAC level or IP level.
>> 
>> It is very possible for R1 to not receive from R2 (although the 
>> intermediary A receives from both) and this does not represent a
>> problem at all, even less a particular problem of wireless
>> communications.  When R1 doesn't hear from R2 it's because it's too
>> "far" from it; the solution could be A to bridge R1 to R2.  It is
>> the same problem in wired communication.
> 
> Actually this is out of the question because, as stated in the
> previous paragraph in the draft, there is no guarantee that A can
> hear either R1, or R2... (all we know is that R1 and R2 can hear A).

So this second issue is tightly bound to the first, it seems.

I agree a radio-through-air system may behave that way.

I think some solutions exist at PHY and MAC layers in the case of 802.11.

I doubt a solution is necessary at IP layer.

Maybe there's a need to discuss this radio-through-air problem more in 
terms of what IP could do for it.

Alex


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