[Ns-developers] A possible bug in ns2, capture() function in mac-802_11.cc

[Tom Henderson]

Mayur wrote:
> Dear NS experts,
> 
> There seems to be a BUG in ns2 (till latest version ns2.33) :
> 
> _*Abstract: *_
> 
> capture() function should treat errored_pkts and normal_pkts 
> differently. Viz., the NAV should be set to only EIFS for errored 
> packets and for normal packets to { EIFS + txtime(pkt) }.
> 
> _*More elaboration :*_
> 
>   * When a sender is far such that the received power (Pr) is [
>     RXThresh_ < Pr <= CSThresh_ ], the packet is sensed but bot
>     understood. As per the 802.11 std, for such sensed_only packet the
>     receiver node should wait for EIFS. In NS2 presently (till ns2.33)
>     this is done so far as this is the only packet being received.
>     (PHY makes the packet ERRORED and MAC sets NAV to EIFS. (see
>     recv_timer() function.)
> 
>   * But when more than one packets are being received, (COLLISION or
>     CAPTURE case) then, there (seems to be) is a bug in the code. viz.
>     The capture() function always sets NAV to (EIFS + txtime(pkt)),
>     without checking if the packet is marked with 'errored' or not.
> 
> 
> I have tried to rectify the bug (If I am correct). The corrected 
> mac-802_11.cc is attached herewith. [Note: The original and modified 
> versions can be toggled by just commenting/uncommenting the 
> corresponding "#define" .]
> 
> As observed I have modified the capture() function to take a second 
> argument for if the pkt is errored and the function acts accordingly.
> 
> Obviously, the mac-802_11.h needs one line correction for the new 
> declaration of capture().
> 
> The results in the two cases (original_capture and modified_capture) are 
> drastically different depending upon the scenario being tested.
> 
> Your suggestions are welcomed.
> 
> regards,
> Mayur
> 

I entered a new bug report in the ns-2 tracker:
https://sourceforge.net/tracker/index.php?func=detail&aid=2180792&group_id=149743&atid=775392

Are there any reviewers for this patch?

Thanks,
Tom