On 12/28/06, Daniel Drake <[EMAIL PROTECTED]> wrote:
> Jon Smirl wrote:
> > First thing I need to figure out is why I can't finish a 250MB copy
> > over pure 802.11g without dropping the connection. I am getting
> > hundreds of these in the logs:
> > kernel: usb 5-1.3: handle_retry_failed_int() retry failed interrupt
> This interrupt occurs when the device failed to transmit a unicast
> frame. It retries several times (and gives us an interrupt for each
> retry) and then sends a final interrupt saying that it's given up. The
> definition of "failed to transmit" is "did not receive an ACK within a
> predefined timeframe".
> It has nothing to do with software or protocol retry. Lowering the rate
> would be a sensible experiment.

If the 802.11 MAC fails to transmit the frame or signals an error
because of a missing MAC level ack, then TCP will do the retry at
layer 4. That's part of the sliding window code in the TCP/IP
protocol. Retries at the TCP layer can be pretty slow.

I tried all rates from 18M to 54M and couldn't get a 250MB copy
without dropping the link. That was with the router set to 802.11g
only. If I turn on 802.11bg the copy works every time. Dropping the
link means that there were so many retries that TCP closed the socket
and caused the layer 7 SMB copy to fail.

So why am I dropping so many packets with the router at 802.11g and
not with the router at 802.11bg? I'll record a session with Ethereal
and see if it gives me any clues.

I just noticed my Nokia 770 sitting on my desk in sleep mode. It may
be waking up and causing interference I'll turn it off and do some
more experiments. Nokia 770 is 802.11bg so it's not likely causing

> > The nodes in my test are 5ft apart with 100% strength, 99% quality at
> > 54M on a clear channel. I would hope that they can exchange packets
> > without dropping them.
> Pay little attention to the strength/quality values, they are very
> fictitious.
> Daniel

Jon Smirl

Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys - and earn cash
Zd1211-devs mailing list - http://zd1211.ath.cx/
Unsubscribe: https://lists.sourceforge.net/lists/listinfo/zd1211-devs

Reply via email to