[Ns-developers] management of wifi association in infrastructure mode

[Gustavo Carneiro]

2008/11/26 Mathieu Lacage <mathieu.lacage at sophia.inria.fr>

> hi,
>
> A while ago, gustavo reported bug 396 which describes a rather
> pathological case:
>
> a) ASSOCIATION_REQUEST: STA -> AP
> b) ACK: AP -> STA
> c) ASSOCIATION_RESPONSE (OK): AP -> STA
> d) ACK: STA -> AP
>
> The main problem is that the last transmission (d) fails which means
> that the AP assumes that the station is not associated (because it did
> not receive an ACK for the RESPONSE) and the STA believes that it is
> associated (because it received the ASSOCIATION_RESPONSE and sent the
> ACK).
>
> The question, then, is, what should we do ? A couple of options:
>
> 1) assume that association is successful even when we don't receive the
> ACK from the STA. This means that, at least in this case, the AP and the
> STA will maintain the same state (association successful)
>
> 2) in the STA, periodically attempt to verify that it is associated. How
> should it do this ?


Maybe,

3) In the AP, if it doesn't receive an ACK for the ASSOCIATION_RESPONSE,
re-send the ASSOCIATION_RESPONSE when the ACK timer expires or the ACK is
received with error; repeat this until 7 times or until the ACK is received.

I think this is the most logical solution.  We know that management frames
have to follow the same basic DCF transmission rules as normal data frames.
And for both management and data frames it makes perfect sense to treat a
unreadable ACK as a missing ACK and trigger a retransmission accordingly.




>
>
> Comments and bright ideas would be welcome.
>
> Mathieu
>
>


-- 
Gustavo J. A. M. Carneiro
INESC Porto, Telecommunications and Multimedia Unit
"The universe is always one step beyond logic." -- Frank Herbert