[Ns-bugs] [Bug 555] DCF immediate access bug

[code@nsnam.ece.gatech.edu]

http://www.nsnam.org/bugzilla/show_bug.cgi?id=555





--- Comment #8 from Mathieu Lacage <mathieu.lacage at sophia.inria.fr>  2009-06-23 08:02:14 EDT ---
I have to confess that I really don't understand the purpose of this test:

  // Test case where two packets are queued at DcaTxop, the first send starts   
  // immediately and the second is also immediately indicated but has to wait   
  // for its backoff.                                                           
  //                                                                            
  //  20          60     66      70   80                                        
  //   | tx        | sifs | aifs  | tx |                                        
  //   |20: request access for both packets                                     
  StartTest (4, 6 , 10);
  AddDcfState (1);
  AddAccessRequest (20, 40, 20, 0, 0);
  AddAccessRequest (20, 10, 70, 0, 0);
  EndTest ();

If I read the code of dca-txop.cc correctly, I think that this set of access
requests is impossible. i.e., DcaTxop::StartAccessIfNeeded appears to be
checking for IsAccessRequested before calling RequestAccess so, it should not
be possible for a specific queue to request access again before the first
access has been resolved. 

Timo, could you explain what you are trying to test here and why you think that
the above is a sequence of events which can happen ?


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