From ea0166feae203b52ca134b21ebdd2b6b710b01ad Mon Sep 17 00:00:00 2001
From: Stefano Avallone <stavallo@gmail.com>
Date: Fri, 19 Jul 2024 19:54:55 +0200
Subject: [PATCH] wifi: Store per-STA/per-AC SSRC/QSRC in the Txop class and
 fix CW update

---
 src/wifi/model/txop.cc | 31 ++++++++++++++++++++++----
 src/wifi/model/txop.h  | 50 +++++++++++++++++++++++++++---------------
 2 files changed, 59 insertions(+), 22 deletions(-)

diff --git a/src/wifi/model/txop.cc b/src/wifi/model/txop.cc
index bae65cfb9..abf999b71 100644
--- a/src/wifi/model/txop.cc
+++ b/src/wifi/model/txop.cc
@@ -358,6 +358,12 @@ Txop::GetCw(uint8_t linkId) const
     return GetLink(linkId).cw;
 }
 
+std::size_t
+Txop::GetStaRetryCount(uint8_t linkId) const
+{
+    return GetLink(linkId).staRetryCount;
+}
+
 void
 Txop::ResetCw(uint8_t linkId)
 {
@@ -365,6 +371,7 @@ Txop::ResetCw(uint8_t linkId)
     auto& link = GetLink(linkId);
     link.cw = GetMinCw(linkId);
     m_cwTrace(link.cw, linkId);
+    link.staRetryCount = 0;
 }
 
 void
@@ -372,10 +379,26 @@ Txop::UpdateFailedCw(uint8_t linkId)
 {
     NS_LOG_FUNCTION(this << linkId);
     auto& link = GetLink(linkId);
-    // see 802.11-2012, section 9.19.2.5
-    link.cw = std::min(2 * (link.cw + 1) - 1, GetMaxCw(linkId));
-    // if the MU EDCA timer is running, CW cannot be less than MU CW min
-    link.cw = std::max(link.cw, GetMinCw(linkId));
+
+    if (link.staRetryCount < m_mac->GetFrameRetryLimit())
+    {
+        // If QSRC[AC] is less than dot11ShortRetryLimit,
+        // - QSRC[AC] shall be incremented by 1.
+        // - CW[AC] shall be set to the lesser of CWmax[AC] and 2^QSRC[AC] × (CWmin[AC] + 1) – 1.
+        // (Section 10.23.2.2 of 802.11-2020)
+        ++link.staRetryCount;
+        link.cw =
+            std::min(GetMaxCw(linkId), (1 << link.staRetryCount) * (GetMinCw(linkId) + 1) - 1);
+    }
+    else
+    {
+        //  Else
+        // - QSRC[AC] shall be set to 0.
+        // - CW[AC] shall be set to CWmin[AC].
+        link.staRetryCount = 0;
+        link.cw = GetMinCw(linkId);
+    }
+
     m_cwTrace(link.cw, linkId);
 }
 
diff --git a/src/wifi/model/txop.h b/src/wifi/model/txop.h
index cf0fba64d..186f634a3 100644
--- a/src/wifi/model/txop.h
+++ b/src/wifi/model/txop.h
@@ -304,6 +304,25 @@ class Txop : public Object
      */
     void UpdateFailedCw(uint8_t linkId);
 
+    /**
+     * Get the current value of the CW variable for the given link. The initial
+     * value is minCw.
+     *
+     * @param linkId the ID of the given link
+     * @return the current value of the CW variable for the given link
+     */
+    uint32_t GetCw(uint8_t linkId) const;
+
+    /**
+     * Get the Station Short Retry Count (SSRC) maintained by non-QoS stations or the QoS STA
+     * Retry Count (QSRC) maintained by QoS STAs for each AC on the given link.
+     *
+     * @param linkId the ID of the given link
+     * @return the Station Short Retry Count (SSRC) maintained by non-QoS stations or the QoS STA
+     *         Retry Count (QSRC) maintained by QoS STAs for each AC on the given link
+     */
+    std::size_t GetStaRetryCount(uint8_t linkId) const;
+
     /**
      * Notify that the given link switched to sleep mode.
      *
@@ -475,14 +494,6 @@ class Txop : public Object
      */
     void RequestAccess(uint8_t linkId);
 
-    /**
-     * Get the current value of the CW variable for the given link. The initial
-     * value is minCw.
-     *
-     * @param linkId the ID of the given link
-     * @return the current value of the CW variable for the given link
-     */
-    uint32_t GetCw(uint8_t linkId) const;
     /**
      * Return the current number of backoff slots on the given link.
      *
@@ -516,16 +527,19 @@ class Txop : public Object
         /// Destructor (a virtual method is needed to make this struct polymorphic)
         virtual ~LinkEntity() = default;
 
-        uint32_t backoffSlots{0};                  //!< the number of backoff slots
-        Time backoffStart{0};                      /**< the backoffStart variable is used to keep
-                                                        track of the time at which a backoff was
-                                                        started or the time at which the backoff
-                                                        counter was last updated */
-        uint32_t cw{0};                            //!< the current contention window
-        uint32_t cwMin{0};                         //!< the minimum contention window
-        uint32_t cwMax{0};                         //!< the maximum contention window
-        uint8_t aifsn{0};                          //!< the AIFSN
-        Time txopLimit{0};                         //!< the TXOP limit time
+        uint32_t backoffSlots{0};     //!< the number of backoff slots
+        Time backoffStart{0};         /**< the backoffStart variable is used to keep
+                                           track of the time at which a backoff was
+                                           started or the time at which the backoff
+                                           counter was last updated */
+        uint32_t cw{0};               //!< the current contention window
+        uint32_t cwMin{0};            //!< the minimum contention window
+        uint32_t cwMax{0};            //!< the maximum contention window
+        uint8_t aifsn{0};             //!< the AIFSN
+        Time txopLimit{0};            //!< the TXOP limit time
+        std::size_t staRetryCount{0}; //!< the Station Short Retry Count (SSRC) maintained by
+                                      //!< non-QoS stations or the QoS STA Retry Count (QSRC)
+                                      //!< maintained by QoS STAs for each AC
         ChannelAccessStatus access{NOT_REQUESTED}; //!< channel access status
 
         mutable class