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

[Gustavo Carneiro]

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

>
> On Wed, 2008-11-26 at 15:55 +0000, Gustavo Carneiro wrote:
>
> > 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.
>
> We already do this


307565309ns NqstaWifiMac:Receive(): assoc completed
307581309ns MacLow:SendAckAfterData(0x8a8620)
307581309ns MacLow:ForwardDown(0x8a8620, 0x8aada0, 0x7fffde836c30, wifia-6mbs)
307581309ns MacLow:ForwardDown(): d0:00:00:00:00:02 send CTL_ACK,
to=d0:00:00:00:00:01, size=14, mode=wifia-6mbs, duration=0ns, seq=0x0
307625412ns MacLow:ReceiveError(0x899800, 0x8aaf90, 0.71913)
307625412ns MacLow:ReceiveError(): d0:00:00:00:00:01 rx failed
307640872ns MacLow:NormalAckTimeout(0x899800)
307640872ns MacLow:NormalAckTimeout(): d0:00:00:00:00:01 normal ack timeout
307640872ns NqapWifiMac:TxFailed(0x899650)
307640872ns NqapWifiMac:TxFailed(): assoc failed with sta=d0:00:00:00:00:02


According to my logs, we do not do this at all.  AssociationResponse is
transmitted once, the ACK is lost, and re-transmission is not attempted, the
AP simply gives up immediately.

but this does not solve the problem: we can still
> have the AP think that the frame was not sent successfully and thus
> decide that the STA is not associated and have the STA receive the
> ASSOCIATION_RESPONSE correctly and think that it is associated.


Yes, it is true that even after 7 retransmissions the ASSOCIATION_RESPONSE's
could all still lose the ACKs.  However, surely the probability of all 7
retransmissions failing decreases enormously and the problem is minimized.

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