[ns] <Sorry Wrong File Sent> A possible BUG in ns2, in capture() function in mac/mac-802_11.cc

[Mayur]

Dear all,

[Sorry, I attached wrong file, Pl find the modified_mac-802_11.cc 
attached herewith. Kindly discard the earlier sent mac-802_11.cc file.]


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