On Wed, 2013-01-09 at 00:38 +0100, Christian Lamparter wrote: > > My feeling is that nothing in 802.11-2012 covers this scenario. There > > are some paragraphs that deal with similar situations when using the > > other flavour of BlockAcks (originally defined in 802.11e I believe), > > but in my experience, you can't assume much based in this. > > > > And even if the DELBA in 6 is sent ok, there is a race between 5 and > > 6, where the originator has block ack state, but the recipient does not. > > Yes, this sounds wrong. Was there a historic reason why RX_STOP was put before > DELBA? I've traced the code back to Intel's initial A-MPDU RX contribution: I'm not aware of any particular reason. However, not all devices/drivers properly report TX status, so waiting for TX status won't be feasible with all devices/drivers. > > So, my question now is: Does this reasoning make sense, or have I > > missed anything? > > I think reordering 5 and 6 won't stop the race entirely. ACKs are > usually generated by hardware (or firmware) right away when the received > frame passed the CRC checks and found a place to stay in the HW's FIFOs. > However by the time DELBA is processed by the peers' 802.11 stack, some > frames on the tx-path might have left the DELBA in the dust [keep-alives > and friends]. > > [Note: Action frames like DELBA have to be encrypted/decrypted when > MFP/802.11w is enabled on the link and some HW/FW can't do that. So > it takes even longer to react to those.] Actually no: HT action frames aren't robust management frames. FWIW, our (Intel's) firmware will send frames from the aggregation queues unaggregated as soon as it receives a DelBA frame from the peer, so as long as it receives it there's no issue. > [Note2: Some hardware (rtlwifi) only have some sort of "fire and forget" > TX. The we don't know when, or even if a frame (like a DELBA) was received...] > > [Note3: What will happen to DELBAs if they aren't acked? Is there a timeout > or are they retried until the peer is dropped by other means? > I'm asking this because with some hardware we have to be greedy with the > number of open BA Agreements. For example ti's wl12xx can only support a > limited number of open RX BA Agreements.] DelBA frames are unicast frames, so they're retried normally. johannes -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
