Virtual WiFi on Linux?

Jim Thompson jim at netgate.com
Thu Oct 20 08:24:04 EDT 2005


On Oct 20, 2005, at 2:20 AM, Dan Searle wrote:

> Hi,
>
> Sorry if I'm using the wrong terms here, please correct me....
>
> Thursday, October 20, 2005, 1:06:16 PM, you wrote:
>
>
>>> Then, run 16 separate MAC layers with some kind of modification  
>>> to the
>>> HAL to share (schedule) the PHY layer between the 16 MAC layers.
>>>
>
>
>> No, you 'multiplex' 16 instances of the "upper MAC" over a single
>> instance of the "lower MAC".
>>
>
> But if you just use simple multiplexing, would you not end up with
> contention between the different upper MAC instances? I'm thinking a
> more intelligent scheduling scheme would be needed to ensure the 16
> upper MAC stacks share the lower MAC in a "fair" manner?

Sure, you probably want something like this, so the set of clients on  
one VAP don't dominate the
transmit queues.

> I.e. if we are the lower MAC and have basically 16 incoming queues of
> transmit traffic from the 16 upper MACs, how do we decide which frames
> to transmit first? Do we simply round robin the 16 queue's
its an approach!

> or would some kind of intelligent scheduling achieve better  
> throughput/sharing
> of the lower MAC and ultimately the PHY??

now factor in 802.11e (EDCF) and wonder 'why?'  Or perhaps "when?" as  
in "when will the linux 802.11 stack
have support for 802.11e?
>
>>> Received frames are not under our control, so all the scheduler  
>>> would
>>> have to do is share out the PHY transmit buffer (e.g. SFQ?).
>>>
>
>
>> Huh?
>>
>
> Sorry, was just trying to point out that we would only have to
> multiplex/schedule the transmit buffers as the radio can't control
> what frames arrive on the PHY, and hence in what order/priority the
> upper MAC layers get on the receive side of things.

If I'm reading you correctly, this is true even for one MAC instance.
>
>>> I think this would require either modifying any existing lower MAC
>>> (HAL), or perhaps writing a completely new lower MAC (HAL).
>>>
>
>
>> The HAL (in madwifi anyway) is not the "lower MAC".
>>
>
> Sorry, I'm getting my HAL and lower MAC boundries confused here.
>
> Regards, Dan...
>
>




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