whether or not there is interface queue in hardware?

Jouni Malinen jkmaline
Sun Feb 1 09:17:40 PST 2004

On Sun, Feb 01, 2004 at 11:50:16AM +0800, lphao wrote:

> I read the hostap driver and linux kernel, I know the queue discipline(include red fifo etc.) existing at the top of driver. But I do not know whether or not there is interface queue between the driver and the MAC layer. If existing, does the queue implement in hardware? And what is the queue length?

There is a TX queue in the hardware/firmware. The maximum size of this
queue depends on the implementation and on how much memory is available
in the wlan card. However, in case of Host AP driver the length of this
queue is limited by PRISM2_TXFID_COUNT definition (in prism2_wlan.h, by
default 8) for most frames. The driver waits to get an acknowledgement
from the wlan card and limits the total number of pending frames by

Broadcast/multicast frames may not follow this rule, because they do not
wait for IEEE 802.11 ACK frame. I'm not sure about the STA f/w behavior,
but it may tell the driver that the frame is already processed even
before it has been sent. In this case, the queue could get more than

Jouni Malinen                                            PGP id EFC895FA

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