[ns] backoff decrement and transmission in 802.11e tkn code

[Sven Wiethoelter]

On Mar 15, 2006, at 1:40 PM, Jongman Heo wrote:

>
> According to section 9.9.1.3 in the IEEE 802.11e standard,
>
> one and only one of the following actions is allowed at slot  
> boundaries:
>  - decrement of backoff timer, or
>  - initiate transmission, or
>  - backoff procedure due to internal collision, or
>  - do nothing.
>
>
> So,
>
> 1.
> Backoff counter is resumed one slot time before the AIFS expiration.
>
> 2.
> However, since a single MAC operation per slot is permitted
> (backoff decrement or packet transmission),
>
> when the backoff counter decrements to 0, the station cannot
> transmit immediately, but has to wait for a further backoff
> slot if the medium is idle, or a further AIFS expiration if
> the medium is busy.
Hi,

exactly this has been included in the new EDCA model for ns-2.28. The  
updated backoff code can be found in mac-timers_802_11e.cc/h.

Best  regards,
Sven
>
>
> I think that 802.11e TKN code is a good implementation of IEEE  
> 802.11e.
>
> However, it seems that the implementation conforms to the requirement
> 1, but do not to the requirement 2.
>
> Am I correct?
>
>
> ps.
> The following paper can be a good guide.
>
> Giuseppe Bianchi, "Understanding 802.11e Contention-Based
> Prioritization Mechanisms and Their Coexistence with Legacy 802.11
> Stations", IEEE Network, 2005
>
>