From 60b4feb74dfdf83656fe131358ea739c01730aaf Mon Sep 17 00:00:00 2001
From: Stefano Avallone <stavallo@gmail.com>
Date: Sat, 28 Sep 2024 19:12:51 +0200
Subject: [PATCH] wifi: Interrupt switch main PHY back timer if medium gets
 busy for too long

---
 src/wifi/model/eht/advanced-emlsr-manager.cc | 119 +++++++++++++++++++
 src/wifi/model/eht/advanced-emlsr-manager.h  |  15 +++
 2 files changed, 134 insertions(+)

diff --git a/src/wifi/model/eht/advanced-emlsr-manager.cc b/src/wifi/model/eht/advanced-emlsr-manager.cc
index 36992cc49..4c85ae84c 100644
--- a/src/wifi/model/eht/advanced-emlsr-manager.cc
+++ b/src/wifi/model/eht/advanced-emlsr-manager.cc
@@ -13,6 +13,7 @@
 #include "ns3/boolean.h"
 #include "ns3/log.h"
 #include "ns3/wifi-net-device.h"
+#include "ns3/wifi-phy-listener.h"
 #include "ns3/wifi-phy.h"
 
 #include <algorithm>
@@ -24,6 +25,85 @@ NS_LOG_COMPONENT_DEFINE("AdvancedEmlsrManager");
 
 NS_OBJECT_ENSURE_REGISTERED(AdvancedEmlsrManager);
 
+/**
+ * PHY listener connected to the main PHY while operating on the link of an aux PHY that is
+ * not TX capable.
+ *
+ * PHY notifications are forwarded to this EMLSR manager one timestep later because this EMLSR
+ * manager may then decide to switch the main PHY back to the preferred link. Given that notifying
+ * a PHY listener is only one of the actions that are performed when handling events such as RX end
+ * or CCA busy start, it is not a good idea to request a main PHY switch while performing other
+ * actions. Forwarding notifications a timestep later allows to first complete the handling of the
+ * given event and then (possibly) starting a main PHY switch.
+ */
+class EmlsrPhyListener : public WifiPhyListener
+{
+  public:
+    /**
+     * Constructor
+     *
+     * @param emlsrManager the EMLSR manager
+     */
+    EmlsrPhyListener(Ptr<AdvancedEmlsrManager> emlsrManager)
+        : m_emlsrManager(emlsrManager)
+    {
+    }
+
+    void NotifyRxStart(Time /* duration */) override
+    {
+        Simulator::Schedule(TimeStep(1),
+                            &AdvancedEmlsrManager::InterruptSwitchMainPhyBackTimerIfNeeded,
+                            m_emlsrManager);
+    }
+
+    void NotifyRxEndOk() override
+    {
+        Simulator::Schedule(TimeStep(1),
+                            &AdvancedEmlsrManager::InterruptSwitchMainPhyBackTimerIfNeeded,
+                            m_emlsrManager);
+    }
+
+    void NotifyRxEndError() override
+    {
+    }
+
+    void NotifyTxStart(Time /* duration */, dBm_u /* txPower */) override
+    {
+    }
+
+    void NotifyCcaBusyStart(Time /* duration */,
+                            WifiChannelListType /* channelType */,
+                            const std::vector<Time>& /* per20MhzDurations */) override
+    {
+        Simulator::Schedule(TimeStep(1),
+                            &AdvancedEmlsrManager::InterruptSwitchMainPhyBackTimerIfNeeded,
+                            m_emlsrManager);
+    }
+
+    void NotifySwitchingStart(Time /* duration */) override
+    {
+    }
+
+    void NotifySleep() override
+    {
+    }
+
+    void NotifyOff() override
+    {
+    }
+
+    void NotifyWakeup() override
+    {
+    }
+
+    void NotifyOn() override
+    {
+    }
+
+  private:
+    Ptr<AdvancedEmlsrManager> m_emlsrManager; //!< the EMLSR manager
+};
+
 TypeId
 AdvancedEmlsrManager::GetTypeId()
 {
@@ -74,6 +154,7 @@ AdvancedEmlsrManager::GetTypeId()
 AdvancedEmlsrManager::AdvancedEmlsrManager()
 {
     NS_LOG_FUNCTION(this);
+    m_phyListener = std::make_shared<EmlsrPhyListener>(this);
 }
 
 AdvancedEmlsrManager::~AdvancedEmlsrManager()
@@ -91,6 +172,11 @@ AdvancedEmlsrManager::DoDispose()
             "PhyRxMacHeaderEnd",
             MakeCallback(&AdvancedEmlsrManager::ReceivedMacHdr, this).Bind(phy));
     }
+    if (!GetAuxPhyTxCapable())
+    {
+        GetStaMac()->GetDevice()->GetPhy(GetMainPhyId())->UnregisterListener(m_phyListener);
+    }
+    m_phyListener.reset();
     DefaultEmlsrManager::DoDispose();
 }
 
@@ -131,6 +217,10 @@ AdvancedEmlsrManager::DoSetWifiMac(Ptr<StaWifiMac> mac)
             "PhyRxMacHeaderEnd",
             MakeCallback(&AdvancedEmlsrManager::ReceivedMacHdr, this).Bind(phy));
     }
+    if (!GetAuxPhyTxCapable())
+    {
+        mac->GetDevice()->GetPhy(GetMainPhyId())->RegisterListener(m_phyListener);
+    }
 }
 
 std::pair<bool, Time>
@@ -526,6 +616,35 @@ AdvancedEmlsrManager::SwitchMainPhyBackDelayExpired(uint8_t linkId)
     SwitchMainPhyBackToPreferredLink(linkId, EmlsrSwitchMainPhyBackTrace(false));
 }
 
+void
+AdvancedEmlsrManager::InterruptSwitchMainPhyBackTimerIfNeeded()
+{
+    NS_LOG_FUNCTION(this);
+
+    if (!m_switchMainPhyBackEvent.IsPending())
+    {
+        return; // nothing to do
+    }
+
+    // a busy event occurred, check if the main PHY has to switch back to the preferred link
+    auto mainPhy = GetStaMac()->GetDevice()->GetPhy(GetMainPhyId());
+    auto linkId = GetStaMac()->GetLinkForPhy(GetMainPhyId());
+
+    if (!linkId.has_value())
+    {
+        NS_LOG_DEBUG("Main PHY is not operating on any link");
+        return;
+    }
+
+    const auto delay =
+        Simulator::GetDelayLeft(m_switchMainPhyBackEvent) + mainPhy->GetChannelSwitchDelay();
+    if (!GetExpectedAccessWithinDelay(*linkId, delay))
+    {
+        m_switchMainPhyBackEvent.Cancel();
+        SwitchMainPhyBackDelayExpired(*linkId);
+    }
+}
+
 void
 AdvancedEmlsrManager::DoNotifyIcfReceived(uint8_t linkId)
 {
diff --git a/src/wifi/model/eht/advanced-emlsr-manager.h b/src/wifi/model/eht/advanced-emlsr-manager.h
index 5acc00222..517d4f1f8 100644
--- a/src/wifi/model/eht/advanced-emlsr-manager.h
+++ b/src/wifi/model/eht/advanced-emlsr-manager.h
@@ -11,9 +11,13 @@
 
 #include "default-emlsr-manager.h"
 
+#include <memory>
+
 namespace ns3
 {
 
+class WifiPhyListener;
+
 /**
  * @ingroup wifi
  *
@@ -31,6 +35,14 @@ class AdvancedEmlsrManager : public DefaultEmlsrManager
     AdvancedEmlsrManager();
     ~AdvancedEmlsrManager() override;
 
+    /**
+     * This method is called by the PHY listener attached to the main PHY when a switch main PHY
+     * back timer is started to notify of events that may delay the channel access for the main
+     * PHY on the current link. If the expected channel access is beyond the end of the switch
+     * main PHY timer expiration plus a channel switch delay, the timer is stopped immediately.
+     */
+    void InterruptSwitchMainPhyBackTimerIfNeeded();
+
   protected:
     void DoDispose() override;
     void DoSetWifiMac(Ptr<StaWifiMac> mac) override;
@@ -124,6 +136,9 @@ class AdvancedEmlsrManager : public DefaultEmlsrManager
     EventId m_switchMainPhyBackEvent; //!< event scheduled in case of non-TX capable aux PHY when
                                       //!< medium is sensed busy during the PIFS interval
                                       //!< preceding/following the main PHY switch end
+    std::shared_ptr<WifiPhyListener>
+        m_phyListener; //!< PHY listener connected to the main PHY while operating on the link of
+                       //!< an aux PHY that is not TX capable
 };
 
 /**