wifi: Send CTS-to-self over the bandwidth of the frame it protects

Assisted-by: Claude Code (claude-fable-5)

Author: DvdMgr

CHANGES.md

@@ -25,6 +25,7 @@ This file is a best-effort approach to solving this issue; we will do our best b
 * Pcap helpers now use ``LinkType`` enum contained in the ``iana`` namespace (``iana-link-type-numbers.h``).
 * (network) After the introduction of the `iana::` enumerations for L2 protocol numbers, the old ones (e.g., `Ipv4L3Protocol::PROT_NUMBER`) have been deprecated.
 * Centralized IANA numbers list in ``network/utils`` is now used instead of the constexpr ``PROT_NUMBER`` found in the definition of multiple protocols.
+* (wifi) `WifiRemoteStationManager::GetCtsToSelfTxVector()` now takes the channel width of the data frame being protected, so that the returned TXVECTOR covers that bandwidth (using the non-HT duplicate format if wider than 20 MHz).
 
 ### Changes to build system
 

RELEASE_NOTES.md

@@ -45,6 +45,7 @@ been tested on Linux. As of this release, the latest known version to work with
 - (sixlowpan) #1342 Fixed a deserialization error in the MESH header.
 - (dsr) !2762 Fixes header format to comply with RFC4728. Also other minor bug fixes and modernization.
 - (zigbee) In the NWK, broadcast initiator devices are now registered in the BTT to avoid receiving retransmissions.
+- (wifi) !2945 CTS-to-self frames are now transmitted over the bandwidth of the frame they protect, so that transmissions in the rest of the TXOP are no longer limited to 20 MHz.
 
 ## Release 3.48
 

src/wifi/model/wifi-default-protection-manager.cc

@@ -222,7 +222,8 @@ WifiDefaultProtectionManager::GetPsduProtection(const WifiMacHeader& hdr,
     if (GetWifiRemoteStationManager()->NeedCtsToSelf(txParams.m_txVector, hdr))
     {
         auto protection = std::make_unique<WifiCtsToSelfProtection>();
-        protection->ctsTxVector = GetWifiRemoteStationManager()->GetCtsToSelfTxVector();
+        protection->ctsTxVector = GetWifiRemoteStationManager()->GetCtsToSelfTxVector(
+            txParams.m_txVector.GetChannelWidth());
         return protection;
     }
 

src/wifi/model/wifi-remote-station-manager.cc

@@ -669,7 +669,7 @@ WifiRemoteStationManager::GetDataTxVector(const WifiMacHeader& header, MHz_u all
 }
 
 WifiTxVector
-WifiRemoteStationManager::GetCtsToSelfTxVector()
+WifiRemoteStationManager::GetCtsToSelfTxVector(MHz_u allowedWidth)
 {
     WifiMode defaultMode = GetDefaultMode();
     WifiPreamble defaultPreamble;
@@ -694,15 +694,23 @@ WifiRemoteStationManager::GetCtsToSelfTxVector()
         defaultPreamble = WIFI_PREAMBLE_LONG;
     }
 
-    return WifiTxVector(defaultMode,
-                        GetDefaultTxPowerLevel(),
-                        defaultPreamble,
-                        GetGuardIntervalForMode(defaultMode, m_wifiPhy->GetDevice()),
-                        GetNumberOfAntennas(),
-                        1,
-                        0,
-                        m_wifiPhy->GetTxBandwidth(defaultMode),
-                        false);
+    WifiTxVector v(defaultMode,
+                   GetDefaultTxPowerLevel(),
+                   defaultPreamble,
+                   GetGuardIntervalForMode(defaultMode, m_wifiPhy->GetDevice()),
+                   GetNumberOfAntennas(),
+                   1,
+                   0,
+                   m_wifiPhy->GetTxBandwidth(defaultMode),
+                   false);
+
+    // The CTS-to-self must cover the bandwidth of the data transmission it protects,
+    // because the TXOP holder shall not transmit any PPDU in the TXOP with a bandwidth
+    // exceeding that of the CTS-to-self frame (Sec. 10.23.2.8 of 802.11-2024); use the
+    // non-HT duplicate format for bandwidths wider than 20 MHz
+    AdjustTxVectorForCtlResponse(v, allowedWidth);
+
+    return v;
 }
 
 void

src/wifi/model/wifi-remote-station-manager.h

@@ -949,10 +949,13 @@ class WifiRemoteStationManager : public Object
      * Since CTS-to-self parameters are not dependent on the station,
      * it is implemented in wifi remote station manager
      *
+     * @param allowedWidth the width of the data frame being protected, which the
+     *        CTS-to-self must cover (using the non-HT duplicate format if wider
+     *        than 20 MHz)
      * @return the transmission mode to use to send the CTS-to-self prior to the
      *         transmission of the data packet itself.
      */
-    WifiTxVector GetCtsToSelfTxVector();
+    WifiTxVector GetCtsToSelfTxVector(MHz_u allowedWidth);
     /**
      * Adjust the TXVECTOR for a control response frame to ensure that, if appropriate, the non-HT
      * duplicate format is used and the TX width matches that of the data frame transmitted (in case

src/wifi/test/wifi-gcr-test.cc

@@ -446,6 +446,19 @@ GcrTestBase::Transmit(std::string context,
                 NS_TEST_EXPECT_MSG_EQ(mpdu->GetHeader().GetAddr1(),
                                       m_apWifiMac->GetAddress(),
                                       "Incorrect Address1 set for CTS-to-self frame");
+                // the CTS-to-self must cover the bandwidth of the protected groupcast frame,
+                // since no PPDU in the TXOP may be wider than the CTS-to-self frame
+                // (Sec. 10.23.2.8 of 802.11-2024)
+                const auto expectedCtsWidth =
+                    std::min_element(m_params.stas.cbegin(),
+                                     m_params.stas.cend(),
+                                     [](const auto& sta1, const auto& sta2) {
+                                         return sta1.maxChannelWidth < sta2.maxChannelWidth;
+                                     })
+                        ->maxChannelWidth;
+                NS_TEST_EXPECT_MSG_EQ(txVector.GetChannelWidth(),
+                                      expectedCtsWidth,
+                                      "Incorrect channel width for CTS-to-self frame");
                 m_nTxApCts++;
             }
             else