From e97cab8ab870dec456480a65aae3e7f6d5dbbab3 Mon Sep 17 00:00:00 2001
From: Stefano Avallone <stavallo@unina.it>
Date: Thu, 29 Jun 2023 11:00:04 +0200
Subject: [PATCH] wifi: EMLSR client drops ICF if received while terminating a
 TXOP on another link

---
 .../model/eht/eht-frame-exchange-manager.cc   | 40 +++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/src/wifi/model/eht/eht-frame-exchange-manager.cc b/src/wifi/model/eht/eht-frame-exchange-manager.cc
index 4dc685614..860df84fb 100644
--- a/src/wifi/model/eht/eht-frame-exchange-manager.cc
+++ b/src/wifi/model/eht/eht-frame-exchange-manager.cc
@@ -786,6 +786,46 @@ EhtFrameExchangeManager::ReceiveMpdu(Ptr<const WifiMpdu> mpdu,
                 return;
             }
 
+            /**
+             * It might happen that the AP MLD has not yet received a data frame being transmitted
+             * by us on another link and starts sending an ICF on this link. The transmission of
+             * the ICF might be long enough to terminate after the subsequent acknowledgment, which
+             * terminates the TXOP on the other link. Consequently, no TXOP is ongoing when the
+             * reception of the ICF ends, hence the ICF is not dropped and a DL TXOP can start on
+             * this link. However, even if the aux PHY is able to receive the ICF, we need to allow
+             * enough time for the main PHY to switch to this link. Therefore, we assume that the
+             * ICF is successfully received (by an aux PHY) if the TXOP on the other link ended
+             * before the padding of the ICF. In order to determine when the TXOP ended, we can
+             * determine when the medium sync delay timer started on this link.
+             *
+             *                        TXOP end
+             *                            │
+             *                        ┌───┐                               another
+             *   AP MLD               │ACK│                               link
+             *  ───────────┬─────────┬┴───┴───────────────────────────────────────
+             *   EMLSR     │   QoS   │    │                            main PHY
+             *   client    │  Data   │    │
+             *             └─────────┘    │
+             *                            │- medium sync delay timer -│
+             *                      ┌─────┬───┐                           this
+             *   AP MLD             │ ICF │pad│                           link
+             *  ────────────────────┴─────┴───┴───────────────────────────────────
+             *                                                          aux PHY
+             */
+
+            if (auto elapsed =
+                    m_staMac->GetEmlsrManager()->GetElapsedMediumSyncDelayTimer(m_linkId))
+            {
+                TimeValue padding;
+                m_staMac->GetEmlsrManager()->GetAttribute("EmlsrPaddingDelay", padding);
+
+                if (*elapsed < padding.Get())
+                {
+                    NS_LOG_DEBUG("Drop ICF due to not enough time for the main PHY to switch link");
+                    return;
+                }
+            }
+
             NS_ASSERT(m_staMac->GetEmlsrManager());
             Simulator::ScheduleNow(&EmlsrManager::NotifyIcfReceived,
                                    m_staMac->GetEmlsrManager(),