From 942e0baca3c3ab9a34bef9741713f0fd8b9eae1a Mon Sep 17 00:00:00 2001
From: Stefano Avallone <stavallo@unina.it>
Date: Fri, 17 Nov 2023 17:25:43 +0100
Subject: [PATCH] wifi: Reset backoff and request access if needed when
 switching EMLSR links

---
 src/wifi/model/eht/default-emlsr-manager.cc |  8 +++-
 src/wifi/model/eht/emlsr-manager.cc         | 53 +++++++++++++++++++--
 src/wifi/model/eht/emlsr-manager.h          | 12 ++++-
 3 files changed, 66 insertions(+), 7 deletions(-)

diff --git a/src/wifi/model/eht/default-emlsr-manager.cc b/src/wifi/model/eht/default-emlsr-manager.cc
index 7befd67be..f7e750df6 100644
--- a/src/wifi/model/eht/default-emlsr-manager.cc
+++ b/src/wifi/model/eht/default-emlsr-manager.cc
@@ -153,9 +153,11 @@ DefaultEmlsrManager::DoNotifyTxopEnd(uint8_t linkId)
         // is not received and the UL TXOP ends before the main PHY channel switch is completed.
         // In such cases, wait until the main PHY channel switch is completed before requesting
         // a new channel switch.
+        // Backoff shall not be reset on the link left by the main PHY because a TXOP ended and
+        // a new backoff value must be generated.
         if (!mainPhy->IsStateSwitching())
         {
-            SwitchMainPhy(GetMainPhyId(), false);
+            SwitchMainPhy(GetMainPhyId(), false, DONT_RESET_BACKOFF, REQUEST_ACCESS);
         }
         else
         {
@@ -163,7 +165,9 @@ DefaultEmlsrManager::DoNotifyTxopEnd(uint8_t linkId)
                                 &DefaultEmlsrManager::SwitchMainPhy,
                                 this,
                                 GetMainPhyId(),
-                                false);
+                                false,
+                                DONT_RESET_BACKOFF,
+                                REQUEST_ACCESS);
         }
         return;
     }
diff --git a/src/wifi/model/eht/emlsr-manager.cc b/src/wifi/model/eht/emlsr-manager.cc
index 0e3387d25..12e1dd4d3 100644
--- a/src/wifi/model/eht/emlsr-manager.cc
+++ b/src/wifi/model/eht/emlsr-manager.cc
@@ -372,7 +372,10 @@ EmlsrManager::NotifyIcfReceived(uint8_t linkId)
     }
 
     Simulator::ScheduleNow([=, this]() {
-        SwitchMainPhy(linkId, true); // channel switch should occur instantaneously
+        SwitchMainPhy(linkId,
+                      true, // channel switch should occur instantaneously
+                      RESET_BACKOFF,
+                      DONT_REQUEST_ACCESS);
 
         // aux PHY received the ICF but main PHY will send the response
         auto uid = auxPhy->GetPreviouslyRxPpduUid();
@@ -423,7 +426,13 @@ EmlsrManager::NotifyUlTxopStart(uint8_t linkId, std::optional<Time> timeToCtsEnd
 
         NS_ASSERT(delay.IsPositive());
         NS_LOG_DEBUG("Schedule main Phy switch in " << delay.As(Time::US));
-        Simulator::Schedule(delay, &EmlsrManager::SwitchMainPhy, this, linkId, false);
+        Simulator::Schedule(delay,
+                            &EmlsrManager::SwitchMainPhy,
+                            this,
+                            linkId,
+                            false,
+                            RESET_BACKOFF,
+                            DONT_REQUEST_ACCESS);
     }
 
     DoNotifyUlTxopStart(linkId);
@@ -487,9 +496,12 @@ EmlsrManager::SetCcaEdThresholdOnLinkSwitch(Ptr<WifiPhy> phy, uint8_t linkId)
 }
 
 void
-EmlsrManager::SwitchMainPhy(uint8_t linkId, bool noSwitchDelay)
+EmlsrManager::SwitchMainPhy(uint8_t linkId,
+                            bool noSwitchDelay,
+                            bool resetBackoff,
+                            bool requestAccess)
 {
-    NS_LOG_FUNCTION(this << linkId << noSwitchDelay);
+    NS_LOG_FUNCTION(this << linkId << noSwitchDelay << resetBackoff << requestAccess);
 
     auto mainPhy = m_staMac->GetDevice()->GetPhy(m_mainPhyId);
 
@@ -535,6 +547,28 @@ EmlsrManager::SwitchMainPhy(uint8_t linkId, bool noSwitchDelay)
         mainPhy->SetSlot(MicroSeconds(9));
     }
 
+    if (resetBackoff)
+    {
+        // reset the backoffs on the link left by the main PHY
+        m_staMac->GetChannelAccessManager(*currMainPhyLinkId)->ResetAllBackoffs();
+    }
+
+    const auto timeToSwitchEnd = noSwitchDelay ? Seconds(0) : mainPhy->GetChannelSwitchDelay();
+
+    if (requestAccess)
+    {
+        // schedule channel access request on the new link when switch is completed
+        Simulator::Schedule(timeToSwitchEnd, [=, this]() {
+            for (const auto& [acIndex, ac] : wifiAcList)
+            {
+                m_staMac->GetQosTxop(acIndex)->StartAccessAfterEvent(
+                    linkId,
+                    Txop::DIDNT_HAVE_FRAMES_TO_TRANSMIT,
+                    Txop::CHECK_MEDIUM_BUSY);
+            }
+        });
+    }
+
     SetCcaEdThresholdOnLinkSwitch(mainPhy, linkId);
     NotifyMainPhySwitch(*currMainPhyLinkId, linkId);
 }
@@ -562,6 +596,17 @@ EmlsrManager::SwitchAuxPhy(uint8_t currLinkId, uint8_t nextLinkId)
         auxPhy->SetSlot(MicroSeconds(9));
     }
 
+    // schedule channel access request on the new link when switch is completed
+    Simulator::Schedule(auxPhy->GetChannelSwitchDelay(), [=, this]() {
+        for (const auto& [acIndex, ac] : wifiAcList)
+        {
+            m_staMac->GetQosTxop(acIndex)->StartAccessAfterEvent(
+                nextLinkId,
+                Txop::DIDNT_HAVE_FRAMES_TO_TRANSMIT,
+                Txop::CHECK_MEDIUM_BUSY);
+        }
+    });
+
     SetCcaEdThresholdOnLinkSwitch(auxPhy, nextLinkId);
 }
 
diff --git a/src/wifi/model/eht/emlsr-manager.h b/src/wifi/model/eht/emlsr-manager.h
index 7d25b8c4a..4cc4a8b87 100644
--- a/src/wifi/model/eht/emlsr-manager.h
+++ b/src/wifi/model/eht/emlsr-manager.h
@@ -285,8 +285,18 @@ class EmlsrManager : public Object
      *
      * \param linkId the ID of the link on which the main PHY has to operate
      * \param noSwitchDelay whether switching delay should be zero
+     * \param resetBackoff whether backoff should be reset on the link on which the main PHY
+     *                     is operating
+     * \param requestAccess whether channel access should be requested on the link on which the
+     *                      main PHY is moving onto
      */
-    void SwitchMainPhy(uint8_t linkId, bool noSwitchDelay);
+    void SwitchMainPhy(uint8_t linkId, bool noSwitchDelay, bool resetBackoff, bool requestAccess);
+
+    static constexpr bool RESET_BACKOFF = true;       //!< reset backoff on main PHY switch
+    static constexpr bool DONT_RESET_BACKOFF = false; //!< do not reset backoff on main PHY switch
+    static constexpr bool REQUEST_ACCESS = true; //!< request channel access when PHY switch ends
+    static constexpr bool DONT_REQUEST_ACCESS =
+        false; //!< do not request channel access when PHY switch ends
 
     /**
      * Switch channel on the Aux PHY operating on the given current link so that it operates