From 75df5d004dac5381ceedfd3f2aa067e1a76af884 Mon Sep 17 00:00:00 2001
From: Stefano Avallone <stavallo@gmail.com>
Date: Mon, 1 Jul 2024 13:50:39 +0200
Subject: [PATCH] wifi: Default ack manager returns that response is needed if
 TX window is stalled

Reported by Rami Abdallah
---
 .../model/originator-block-ack-agreement.cc   | 24 ++++++++++
 .../model/originator-block-ack-agreement.h    | 12 +++++
 src/wifi/model/wifi-default-ack-manager.cc    | 47 ++++++++++++++-----
 3 files changed, 71 insertions(+), 12 deletions(-)

diff --git a/src/wifi/model/originator-block-ack-agreement.cc b/src/wifi/model/originator-block-ack-agreement.cc
index 2d8fb3a4f..65d5cf34b 100644
--- a/src/wifi/model/originator-block-ack-agreement.cc
+++ b/src/wifi/model/originator-block-ack-agreement.cc
@@ -88,6 +88,30 @@ OriginatorBlockAckAgreement::InitTxWindow()
     m_txWindow.Init(m_startingSeq, m_bufferSize);
 }
 
+bool
+OriginatorBlockAckAgreement::AllAckedMpdusInTxWindow(const std::set<uint16_t>& seqNumbers) const
+{
+    std::set<std::size_t> distances;
+    for (const auto seqN : seqNumbers)
+    {
+        distances.insert(GetDistance(seqN));
+    }
+
+    for (std::size_t i = 0; i < m_txWindow.GetWinSize(); ++i)
+    {
+        if (distances.contains(i))
+        {
+            continue; // this is one of the positions to ignore
+        }
+        if (!m_txWindow.At(i))
+        {
+            return false; // this position is available or contains an unacknowledged MPDU
+        }
+    }
+    NS_LOG_INFO("TX window is blocked");
+    return true;
+}
+
 void
 OriginatorBlockAckAgreement::AdvanceTxWindow()
 {
diff --git a/src/wifi/model/originator-block-ack-agreement.h b/src/wifi/model/originator-block-ack-agreement.h
index b7da72370..9d4fb5af6 100644
--- a/src/wifi/model/originator-block-ack-agreement.h
+++ b/src/wifi/model/originator-block-ack-agreement.h
@@ -12,6 +12,8 @@
 #include "block-ack-agreement.h"
 #include "block-ack-window.h"
 
+#include <set>
+
 class OriginatorBlockAckWindowTest;
 
 namespace ns3
@@ -190,6 +192,16 @@ class OriginatorBlockAckAgreement : public BlockAckAgreement
      */
     void NotifyDiscardedMpdu(Ptr<const WifiMpdu> mpdu);
 
+    /**
+     * Check whether all the MPDUs in the TX window other than the given ones have been already
+     * acknowledged.
+     *
+     * \param seqNumbers the sequence numbers of the given MPDUs
+     * \return whether all the MPDUs in the TX window other than the given ones have been already
+     *         acknowledged
+     */
+    bool AllAckedMpdusInTxWindow(const std::set<uint16_t>& seqNumbers) const;
+
   private:
     /**
      * Advance the transmit window so that the starting sequence number is the
diff --git a/src/wifi/model/wifi-default-ack-manager.cc b/src/wifi/model/wifi-default-ack-manager.cc
index 48497c850..e4e51deff 100644
--- a/src/wifi/model/wifi-default-ack-manager.cc
+++ b/src/wifi/model/wifi-default-ack-manager.cc
@@ -133,27 +133,50 @@ WifiDefaultAckManager::IsResponseNeeded(Ptr<const WifiMpdu> mpdu,
     auto receiver = mpdu->GetHeader().GetAddr1();
     auto origReceiver = mpdu->GetOriginal()->GetHeader().GetAddr1();
     Ptr<QosTxop> edca = m_mac->GetQosTxop(tid);
+    const auto& seqNumbers = txParams.GetPsduInfo(receiver)->seqNumbers.at(tid);
 
     // An immediate response (Ack or Block Ack) is needed if any of the following holds:
+    // * the BA threshold is set to zero
+    if (m_baThreshold == 0.0)
+    {
+        return true;
+    }
     // * the maximum distance between the sequence number of an MPDU to transmit
     //   and the starting sequence number of the transmit window is greater than
     //   or equal to the window size multiplied by the BaThreshold
+    if (GetMaxDistFromStartingSeq(mpdu, txParams) >=
+        m_baThreshold * edca->GetBaBufferSize(origReceiver, tid))
+    {
+        return true;
+    }
     // * no other frame belonging to this BA agreement is queued (because, in such
     //   a case, a Block Ack is not going to be requested anytime soon)
+    if (auto queueId = WifiContainerQueueId(WIFI_QOSDATA_QUEUE, WIFI_UNICAST, origReceiver, tid);
+        edca->GetWifiMacQueue()->GetNPackets(queueId) -
+            edca->GetBaManager()->GetNBufferedPackets(origReceiver, tid) - seqNumbers.size() <
+        1)
+    {
+        return true;
+    }
+    // * the block ack TX window cannot advance because all the MPDUs in the TX window other than
+    //   those being transmitted have been already acknowledged
+    if (m_mac->GetBaAgreementEstablishedAsOriginator(origReceiver, tid)
+            ->get()
+            .AllAckedMpdusInTxWindow(seqNumbers))
+    {
+        return true;
+    }
+
     // * this is the initial frame of a transmission opportunity and it is not
     //   protected by RTS/CTS (see Annex G.3 of IEEE 802.11-2016)
-    return !(
-        m_baThreshold > 0 &&
-        GetMaxDistFromStartingSeq(mpdu, txParams) <
-            m_baThreshold * edca->GetBaBufferSize(origReceiver, tid) &&
-        (edca->GetWifiMacQueue()->GetNPackets(
-             {WIFI_QOSDATA_QUEUE, WIFI_UNICAST, origReceiver, tid}) -
-             edca->GetBaManager()->GetNBufferedPackets(origReceiver, tid) -
-             txParams.GetPsduInfo(receiver)->seqNumbers.at(tid).size() >=
-         1) &&
-        !(edca->GetTxopLimit(m_linkId).IsStrictlyPositive() &&
-          edca->GetRemainingTxop(m_linkId) == edca->GetTxopLimit(m_linkId) &&
-          !(txParams.m_protection && txParams.m_protection->method == WifiProtection::RTS_CTS)));
+    if (edca->GetTxopLimit(m_linkId).IsStrictlyPositive() &&
+        edca->GetRemainingTxop(m_linkId) == edca->GetTxopLimit(m_linkId) &&
+        !(txParams.m_protection && txParams.m_protection->method == WifiProtection::RTS_CTS))
+    {
+        return true;
+    }
+
+    return false;
 }
 
 bool