From 370dbb04d573f6acddbc7b4c0d44e14099c77231 Mon Sep 17 00:00:00 2001
From: Stefano Avallone <stavallo@gmail.com>
Date: Mon, 11 Mar 2024 23:08:30 +0100
Subject: [PATCH] wifi: Advanced EMLSR manager can interrupt main PHY switch
 after CTS timeout

---
 src/wifi/model/eht/advanced-emlsr-manager.cc | 62 ++++++++++++++++++++
 src/wifi/model/eht/advanced-emlsr-manager.h  | 12 ++--
 2 files changed, 70 insertions(+), 4 deletions(-)

diff --git a/src/wifi/model/eht/advanced-emlsr-manager.cc b/src/wifi/model/eht/advanced-emlsr-manager.cc
index f19560aed..4f6fc4f22 100644
--- a/src/wifi/model/eht/advanced-emlsr-manager.cc
+++ b/src/wifi/model/eht/advanced-emlsr-manager.cc
@@ -42,6 +42,12 @@ AdvancedEmlsrManager::GetTypeId()
                           "If this attribute is true, the PPDU may be dropped.",
                           BooleanValue(false),
                           MakeBooleanAccessor(&AdvancedEmlsrManager::m_allowUlTxopInRx),
+                          MakeBooleanChecker())
+            .AddAttribute("InterruptSwitch",
+                          "Whether the main PHY can be interrupted while switching to start "
+                          "switching to another link.",
+                          BooleanValue(false),
+                          MakeBooleanAccessor(&AdvancedEmlsrManager::m_interruptSwitching),
                           MakeBooleanChecker());
     return tid;
 }
@@ -209,4 +215,60 @@ AdvancedEmlsrManager::ReceivedMacHdr(Ptr<WifiPhy> phy,
     }
 }
 
+void
+AdvancedEmlsrManager::DoNotifyTxopEnd(uint8_t linkId)
+{
+    NS_LOG_FUNCTION(this << linkId);
+
+    auto mainPhy = GetStaMac()->GetDevice()->GetPhy(m_mainPhyId);
+
+    if (m_switchAuxPhy && (!mainPhy->IsStateSwitching() || !m_interruptSwitching))
+    {
+        NS_LOG_DEBUG("SwitchAuxPhy true, nothing to do");
+        return;
+    }
+
+    if (!m_switchAuxPhy && !m_auxPhyToReconnect)
+    {
+        NS_LOG_DEBUG("SwitchAuxPhy false, nothing to do");
+        return;
+    }
+
+    // we get here if:
+    // - SwitchAuxPhy is true, the main PHY is switching and switching can be interrupted
+    // or
+    // - SwitchAuxPhy is false and there is an aux PHY to reconnect
+
+    // Note that the main PHY may be switching at the end of a TXOP when, e.g., the main PHY
+    // starts switching to a link on which an aux PHY gained a TXOP and sent an RTS, but the CTS
+    // 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 (unless the channel
+    // switching can be interrupted) before requesting a new channel switch. Given that the
+    // TXOP ended, the event to put the aux PHY to sleep can be cancelled.
+    // 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.
+    m_auxPhyToSleepEvent.Cancel();
+
+    if (m_switchAuxPhy || !mainPhy->IsStateSwitching() || m_interruptSwitching)
+    {
+        NS_ASSERT_MSG(
+            !m_switchAuxPhy || m_mainPhySwitchInfo.end >= Simulator::Now(),
+            "Aux PHY next link ID should have a value when interrupting a main PHY switch");
+        uint8_t nextLinkId = m_switchAuxPhy ? m_mainPhySwitchInfo.from : GetMainPhyId();
+        SwitchMainPhy(nextLinkId, false, DONT_RESET_BACKOFF, REQUEST_ACCESS);
+    }
+    else
+    {
+        // delay link switch until current channel switching is completed
+        Simulator::Schedule(mainPhy->GetDelayUntilIdle(), [=, this]() {
+            // request the main PHY to switch back to the primary link only if in the meantime
+            // no TXOP started on another link (which will require the main PHY to switch link)
+            if (!GetEhtFem(linkId)->UsingOtherEmlsrLink())
+            {
+                SwitchMainPhy(GetMainPhyId(), false, DONT_RESET_BACKOFF, REQUEST_ACCESS);
+            }
+        });
+    }
+}
+
 } // namespace ns3
diff --git a/src/wifi/model/eht/advanced-emlsr-manager.h b/src/wifi/model/eht/advanced-emlsr-manager.h
index ed21f9d41..0eb47e3a5 100644
--- a/src/wifi/model/eht/advanced-emlsr-manager.h
+++ b/src/wifi/model/eht/advanced-emlsr-manager.h
@@ -52,10 +52,14 @@ class AdvancedEmlsrManager : public DefaultEmlsrManager
                         Time psduDuration);
 
   private:
-    bool m_useNotifiedMacHdr; //!< whether to use the information about the MAC header of
-                              //!< the MPDU being received (if notified by the PHY)
-    bool m_allowUlTxopInRx;   //!< whether a (main or aux) PHY is allowed to start an UL
-                              //!< TXOP if another PHY is receiving a PPDU
+    void DoNotifyTxopEnd(uint8_t linkId) override;
+
+    bool m_useNotifiedMacHdr;        //!< whether to use the information about the MAC header of
+                                     //!< the MPDU being received (if notified by the PHY)
+    bool m_allowUlTxopInRx;          //!< whether a (main or aux) PHY is allowed to start an UL
+                                     //!< TXOP if another PHY is receiving a PPDU
+    bool m_interruptSwitching;       //!< whether a main PHY switching can be interrupted to start
+                                     //!< switching to another link
 };
 
 } // namespace ns3