[Ns-bugs] [Bug 595] New: PHY may start receive packet inside SIFS

[code@nsnam.ece.gatech.edu]

http://www.nsnam.org/bugzilla/show_bug.cgi?id=595

           Summary: PHY may start receive packet inside SIFS
           Product: ns-3
           Version: ns-3.4
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P5
         Component: wifi
        AssignedTo: ns-bugs at isi.edu
        ReportedBy: kirillano at yandex.ru
   Estimated Hours: 0.0


Created an attachment (id=467)
 --> (http://www.nsnam.org/bugzilla/attachment.cgi?id=467)
Proposed fix

PHY passes information to DcfManager about PHY events, and DCF manager must
catch situation, when PHY starts to transmit and m_rxing is true. This may
occur only after the following steps:
1. PHY has started to receive a packet inside SIFS.
2. MacLow has started to transmit an ACK frame (or any other frame) when SIFS
has expired.
3. PHY has started to transmit this ACK frame and has cancelled previously
started receiving:
  if (m_state->IsStateSync ())
    {
      m_endSyncEvent.Cancel ();
    }
and has not tell anything to DcfManager.
4. IsBusy method of DcfManager decides that the medium is busy (because m_rxing
was not unset)
5. Next transmission causes collision at DcfManager layer due to IsBusy () (see
DcfManager::RequestAccess)


The idea to solve this problem is to check m_rxing flag when running
DcfManager::NotifyTxStartNow (see patch)


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