From 45473264459b9ac76b4c6ee65a0b07dc1bb5315e Mon Sep 17 00:00:00 2001
From: Stefano Avallone <stavallo@unina.it>
Date: Sun, 7 Jun 2020 23:06:03 +0200
Subject: [PATCH] wifi: (fixes #211) Remove MSDUs with expired lifetime when
 (re)starting channel access

---
 src/wifi/model/qos-txop.cc | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/src/wifi/model/qos-txop.cc b/src/wifi/model/qos-txop.cc
index 9ee3c5ae0..8222d6fee 100644
--- a/src/wifi/model/qos-txop.cc
+++ b/src/wifi/model/qos-txop.cc
@@ -985,11 +985,15 @@ void
 QosTxop::RestartAccessIfNeeded (void)
 {
   NS_LOG_FUNCTION (this);
-  if ((m_currentPacket != 0
-       // check first if the BA manager retransmit queue is empty, so that expired
-       // frames (if any) are removed and a BlockAckRequest is scheduled to advance
-       // the starting sequence number of the transmit (and receiver) window
-       || m_baManager->HasPackets () || !m_queue->IsEmpty ())
+
+  // check if the BA manager retransmit queue is empty, so that expired
+  // frames (if any) are removed and a BlockAckRequest is scheduled to advance
+  // the starting sequence number of the transmit (and receiver) window
+  bool baManagerHasPackets = m_baManager->HasPackets ();
+  // remove MSDUs with expired lifetime starting from the head of the queue
+  bool queueIsNotEmpty = !m_queue->IsEmpty ();
+
+  if ((m_currentPacket != 0 || baManagerHasPackets || queueIsNotEmpty)
       && !IsAccessRequested ())
     {
       Ptr<const Packet> packet;
@@ -1024,11 +1028,16 @@ void
 QosTxop::StartAccessIfNeeded (void)
 {
   NS_LOG_FUNCTION (this);
+
+  // check if the BA manager retransmit queue is empty, so that expired
+  // frames (if any) are removed and a BlockAckRequest is scheduled to advance
+  // the starting sequence number of the transmit (and receiver) window
+  bool baManagerHasPackets = m_baManager->HasPackets ();
+  // remove MSDUs with expired lifetime starting from the head of the queue
+  bool queueIsNotEmpty = !m_queue->IsEmpty ();
+
   if (m_currentPacket == 0
-      // check first if the BA manager retransmit queue is empty, so that expired
-      // frames (if any) are removed and a BlockAckRequest is scheduled to advance
-      // the starting sequence number of the transmit (and receiver) window
-      && (m_baManager->HasPackets () || !m_queue->IsEmpty ())
+      && (baManagerHasPackets || queueIsNotEmpty)
       && !IsAccessRequested ())
     {
       Ptr<const Packet> packet;