Andy Johnson <johnsonzjo@xxxxxxxxx> writes: > Hello, Hi, > I had encountered the recent PS-POLL patches from Kalle Valo and I > have three questions about PS-Poll mechanism. I hope that I did not > miss something. In fact, the first question, which is about the > design of this mechanism, seems to me the most important. I'll try to answer them. > As I understand, when a station in power save mode (dozed) gets a > beacon TIM from its AP which tells it that the AP has kept unicast > packets for it, that station wakes up and starts sending PS-Poll > frames. It sends PS-POLL one by one; each such packet, which is > received in the AP, will cause it to send an skb from its buffer > (ps_tx_buf skb queue, in sta_info struct). This packet has a > MOREDATA flag set. > > The stations send PS Poll packets one by one, until the ps_tx_buf is > emptied; when the last skb from ps_tx_buf is sent from the AP, it does > not have the MOREDATA flag set, as opposed to all the previous > sk_buffs which were retrieved from the ps_tx_buf. Yes, this is the case when the station is in power save mode all the time. But most of the implementations don't use ps-poll, instead they wakeup from power save mode by sending a null frame. So there are two ways to handle this. > (I believe that it should be the IEEE80211_FCTL_MOREDATA flag, not sure). Correct. > In the period from when the first skb is retrieved to when the last > skb, the station must not got to sleep. After the last one is > received, it may go to sleep or stay awake (I wonder on what this > depends). If ps-poll is used, the assumption is that it should go to sleep immediately. > My questions are: > > 1) Why not send **one** PS-POLL which will signal the AP to start > sending sk_buffs from the ps_tx_buf until is it emptied ? why do we > send PS Poll packets > one by one ? Sending only one PS poll, as suggested, will reduce > traffic (take in accordance that we have ACKs also). That's how ps-poll is defined in the spec in chapter 11.2. If throughput is concern, then it's better to wakeup with a null frame and AP will start sending all the frames to the station. > 2) In the sceario depicted above, when sending PS polls one by one, > what happens if there are packets sent to that station from the same > source as packets > that were kept in the buffer - will they be received in the > destination (the client that awoke)? don't we loose here the order of > the packets? I would assume that the ap will take care of the ordering. > 3) should the station send ACK to the AP for each skb it receives (as > a response to PS Poll) using this mechanism? Yes, all frames (including ps-poll to the ap) need to be acked. -- Kalle Valo -- 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
