CSMA/CA in Nqos or Qos

[Odil]

Hello folks, 

I have one doubtful point about CSMA/CA process in Wireless communication in ns-3. I have seen some documents and discussion about CSMA process in wireless communication.

Most of these materials make you assure that csma is already exist in Nqos or Qos  -Wifi-Mac-Helpers. But it happens when you really testing it around, it seems these two 

helpers are not containing any media access model inside, I tried sending broadcast message from two moving vehicles (nodes) continuously but other receivers only getting less than half of 

these sent packet within simulation time (for example 10 packet sent but only 4 packet received by all nodes). 

o->iiiii_____o_____o

___o_____o_____iiiii<-o     

So if anybody knows the answer for this problem, Please drop me here your precious comments. 

Thanks a lot !

Cheers, Odil  

[Tommaso Pecorella]

Hi,

you should take a better look at how QoS is implemented in Wi-Fi (I mean the global standard). QoS is reached by varying the internal device queues (4 instead of 1) and giving different backoff and access probabilities to each of them.

You low packet reception rate has (probably) nothing to do with QoS.

T.

[Odil]

Hi 

I am not asking about the QoS and I have already aware about EDCA (Enhanced Dedicated Channel Allocation). I know what is the reason 

to lost of my packet. It is because these helpers seems do not have any MAC mechanism installed. One thing I was wondering to know whether CSMA/CA is there or not.

 I thought CSMA/CA as a simple MAC mechanism had already installed in Nqos and Qos helpers but unfortunately, that seems was only delusion. 

Could you just answer for this question !

Thanks for help !

Cheers  

[Tommaso Pecorella]

Hi,

I see... perhaps you are confused by the names.

You'd better read this: https://en.wikipedia.org/wiki/Distributed_coordination_function and in particular this statement:

"Distributed coordination function (DCF) is the fundamental MAC technique of the IEEE 802.11 based WLAN standard. DCF employs a CSMA/CA with binary exponential backoff algorithm."

Now, if you look carefully, DCA and EDCA are two DCF subclasses.

T.

[Odil]

Hi 

I get it. 

Thank you !