Re: [LARTC] QoS in wireless networks

[Michael Renzmann <lartc@nospam.otaku42.de>]

Hi.

Francisco Javier Simo Reigadas wrote:
>> IEEE 802.11 provides a fair channel access for all the nodes including 
>> APs and clients. (I do not know about PCF mode implemented)
> It seems that it was abandoned because it didn't work as expected, 

It's not abandoned, but it's an optional feature that mostly none AP has 
implemented. And it's not a complete protocol afair, but only a 
framework that leaves much room for the actual implementation.

> only private extensions like Karlnet's Turbocell can do that (polling
 > from a central point)

While Karlnet's Turbocell implements central polling, it does not make 
use of PCF. Instead, the stations work in DCF, and all traffic is 
transmitted as broadcasts (thus getting rid of 802.11 ACKs which gives 
some additional bandwidth). Downside: they loose the ability to have 
automatic rate selection.

> and I am not interested in private extensions.

Maybe you'll also consider this as private extension, but you might be 
interested in some "DCF-based polling protocol" implementations running 
under Linux:
frottle: http://frottle.sourceforge.net/
WiCCP: http://patraswireless.net/software.html
pewit: http://savannah.nongnu.org/projects/pewit

While they all perform a similar goal (implementation of a polling 
protocol on top of a normal ethernet link) they use different techniques 
to achieve their goal. But they all are not depending on a special 
device driver, so you can still choose your hardware freely.


And maybe also this link is of interest:
http://wsched.sourceforge.net/

"While the H-FSC qdisc can be used in a usual wireline environment (e.g. 
replacing the standard CBQ scheduler), the purpose of the port to Linux 
was to use it as a basis for the prototype implementation of a new form 
of wireless link-sharing. The basic problem is that in a wireless 
environment the amount of resources consumed in order to transmit X 
bytes to a mobile destination depends on the quality of the link to this 
station. The link-sharing model developed during the project allows the 
integration of goodput and resource-consumption oriented criteria in 
hierarchies for wireless link-sharing. Furthermore, the model can be 
used with currently available hardware because it can be implemented 
above the link layer. For detailed information take a look at the 
documents listed in the Documentation section."

They have two interesting papers about their work online:
"Packet scheduling for bandwidth sharing and quality of service support 
in wireless local area networks" and "A resource-based approach to MAC 
layer independent hierarchical link-sharing in wireless local area 
networks", explaining the ideas behind their scheduler.

Bye, Mike
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