[SPAM] Re: fragmentation threshold support

Actually dot11RTSThreshold isn't what you want it's the 
dot11FragmentationThreshold (Pizza: typo?)

The MAC will fragment the frames at the 802.11 layer.  To see the 
fragmentation, you will need to sniff the traffic in the air.  This 
fragmentation has nothing to do with IP fragmentation.

It sounds like you may be trying to use 802.11 fragmentation for some kind 
of traffic control purposes, that's not what it's meant for.  802.11 
fragmentation was added to the MAC behavior to mitigate the effect of 
periodic inteferers on the medium.  The classic example of a periodic 
interferer is a microwave oven, they transmit spikes of power with a 
fairly long period.  The idea is to only do retries on the portion of the 
frame that was lost rather than the whole frame.

-M



On Wed, 25 May 2005, P Laurent wrote:

> I forgot something: i'm using broadcasted frames so
> RTS/CTS mechanism is not used and therefore setting
> RTSThreshold does not help.
>
> Laurent
>
>> if I let the default mtu=1500 and I try to send
>> fragments of 1800 bytes then it looks like no frame
>> at
>> all is transmitted.
>>
>> if I change the mtu with ifconfig wlan0 mtu=2000 and
>> then I try to send 1800 bytes long frames I get:
>>  hfa384x_usbin_callback: wlan0 rx pipe stalled:
>> requesting reset
>>  hfa384x_usbin_ctlx: Could not match IN
>> URB(0x0001,-75) to CTLX - ignored
>>  wlan0 rx pipe reset complete.
>>
>> I set the RTSThreshold to 1000 but I could still
>> send
>> fragments of 1500 bytes as before. Actually I don't
>> really understand why you mentionned this
>> mibattribute. Thus I also set
>> mibattribute=FragmentationThreshold=1000 but once
>> again I could still send frames with 1500 bytes
>> payload.
>>
>> I send frames using a SOCK_RAW socket.
>>
>> any idea?
>>
>> Laurent
>>
>>>> I'm using wlan-ng 0.2.1 pre26.
>>>> I'd like to control the length of the frames I
>>>> send(to set a fragmentation threshold).
>>>
>>> wlanctl wlan0 dot11req_mibset
>>> mibattribute=dot11RTSThreshold=<whatever>
>>>
>>>> frames. But at the same time i can't send frames
>>>> much longer than 1500 bytes.
>>>
>>> ifconfig wlan0 mtu <whatever>
>>>
>>> mtu is not the same thing as dot11 fragmentation;
>> if
>>> you're bridging to
>>> ethernet anywhere you'll want to leave it no
>> greater
>>> than 1500.
>>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
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>
>
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-- 

Mark S. Mathews

AbsoluteValue Systems      Web:    http://www.linux-wlan.com
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