--- a/src/wifi/model/regular-wifi-mac.cc	Thu May 29 21:37:33 2014 +0200
+++ b/src/wifi/model/regular-wifi-mac.cc	Thu May 29 22:51:05 2014 -0700
@@ -57,6 +57,7 @@
   m_dca = CreateObject<DcaTxop> ();
   m_dca->SetLow (m_low);
   m_dca->SetManager (m_dcfManager);
+  m_dca->SetTxMiddle(m_txMiddle);
   m_dca->SetTxOkCallback (MakeCallback (&RegularWifiMac::TxOk, this));
   m_dca->SetTxFailedCallback (MakeCallback (&RegularWifiMac::TxFailed, this));