[Ns-developers] questions and patch

[Francesco Gringoli]

On Jan 18, 2006, at 07:17, mathieu lacage wrote:

>
> Maybe it woul be worth asking the 802.11 commitee for a  
> clarification. I don't care that much though.
>
I think for the moment that if we agree on that we can ask later.

>>> number of packets in TXOP1:
>>>
>>> TXOP1 transmission:
>>> CFPOLL1+SIFS+ACK+PKT1+SIFS+ACK1+SIFS+...+PKTN1+SIFS+ACKN1+SIFS
>>
>>
>> Uhm, what is the first ACK? Do you mean (ACK+PKT1) is a single  
>> packet?
>
>
> no, it is the ACK for CFPOLL1. If you don't send it, the QAP thinks  
> the TXOP is not used and switches to the next TXOP.
>
Mathieu, I'm not sure on that: your code too sends just a single  
packet after the POLL with data, if this is available. In the draft  
ACK+DATA is ok. My doubt was on the lack of a SIFS between ACK and PKT1.
>> I would remove the last SIFS and if N1 is the maximum number of   
>> "nominal" packet QSTA1 can send inside its TXOP, I will say that
>>
>> TXOP1 must contain [ CFPOLL+SIFS+(N1-1)*(PKT+SIFS+ACK+SIFS)  
>> +PKT_N1 +SIFS+ACK ]
>>
>> Hence we can fix
>>
>> TXOP1=duration(CFPOLL)+N1*duration(PKT)+N1*duration(ACK)+2*N1*SIFS
>>
>> However (this is the key point) to calculate the CFP duration we  
>> have  to add PIFS between every consecutive TXOPs plus a PIFS at  
>> the end of  the CFP. Only if we calculate CFP duration in this way  
>> everything is  ok. Imagine what happens if we don't count the  
>> PIFS: if we have a lot  of backlogged traffic in all stations,  
>> every one will not send  QOSNULL since there is no time. The last  
>> station however will never  be polled because the m_txopTimer  
>> always added up PIFS to the TXOP  and if the CFP=TXOP1+TXOP2+TXOP3 
>> +... all the added PIFSs have  consumed time that should be  
>> granted to last station. Then it has no  time to complete the TXOP  
>> inside the CFP.
>
>
> yes, hence my suggestion to add PIFS somewhere :)

> regards,
> Mathieu

Regards,
FG