From d1d8558d65db3250425055b20da7dba48d89a6d2 Mon Sep 17 00:00:00 2001
From: Stefano Avallone <stavallo@unina.it>
Date: Fri, 21 Feb 2020 16:13:13 +0100
Subject: [PATCH] wifi: Update backoff before checking for immediate access

---
 .../test/aodv-chain-regression-test-0-0.pcap  | Bin 1448 -> 1448 bytes
 .../test/aodv-chain-regression-test-1-0.pcap  | Bin 1024 -> 1024 bytes
 .../test/aodv-chain-regression-test-2-0.pcap  | Bin 1024 -> 1024 bytes
 .../test/aodv-chain-regression-test-3-0.pcap  | Bin 1024 -> 1024 bytes
 .../test/aodv-chain-regression-test-4-0.pcap  | Bin 1024 -> 1024 bytes
 src/aodv/test/bug-606-test-0-0.pcap           | Bin 1448 -> 1448 bytes
 src/aodv/test/bug-606-test-1-0.pcap           | Bin 1024 -> 1024 bytes
 src/aodv/test/bug-606-test-2-0.pcap           | Bin 1024 -> 1024 bytes
 .../hwmp-simplest-regression-test-0-1.pcap    | Bin 77637 -> 77637 bytes
 .../hwmp-simplest-regression-test-1-1.pcap    | Bin 81416 -> 81416 bytes
 .../test/flame/flame-regression-test-2-1.pcap | Bin 448 -> 448 bytes
 src/wifi/model/channel-access-manager.cc      |  50 ++++++++++++++++++
 src/wifi/model/channel-access-manager.h       |   9 ++++
 src/wifi/model/txop.cc                        |  49 ++---------------
 src/wifi/model/txop.h                         |   4 --
 src/wifi/test/channel-access-manager-test.cc  |   5 +-
 src/wifi/test/wifi-test.cc                    |   9 ++--
 17 files changed, 73 insertions(+), 53 deletions(-)

diff --git a/src/aodv/test/aodv-chain-regression-test-0-0.pcap b/src/aodv/test/aodv-chain-regression-test-0-0.pcap
index 9c8c800479b0eaf59174e4c5656618c4a4ba4a07..3108090bad9b469e7960a637f42a0e27034df648 100644
GIT binary patch
delta 103
zcmZ3%y@Go}3$s-v!{ql&@)MUiG5<QkJW*bLG8dy8<EP1ijOQ7%CMz<fGjZuoe#fLR
zc@>ir<EF`PnUWb#P7Y*FXO86H25Fppi`i*%1B=pRJC<c&nvK<oxsw4Rm&Ixa05Pv3
A3jhEB

delta 107
zcmZ3%y@Go}3$sKe!{ql&@)MUiG2b}CJW*bLG8dy8<AuqAjOQ6WCMz<fGriE6{EkUs
z@+u}L#tD<(G9@!EpB%`X&TP)X4bnLI7PAwh|Kvs%#mROo%b+YaRww3k28etXs~rHP
CW+He1

diff --git a/src/aodv/test/aodv-chain-regression-test-1-0.pcap b/src/aodv/test/aodv-chain-regression-test-1-0.pcap
index 4d6410f9d61b3c62c2b29a29390cab4f634b15ba..bcd1f00f4b818d56cbcab32bfce491b6673bb56e 100644
GIT binary patch
delta 80
zcmZqRXyBO8z$A2eqMX9SMNSaLWHv@8reD{9LX)!?oftPwUdx!wm^E3DDS4ud(&TAO
TPGFAW<X>=B95YC4A#*$cA|e?w

delta 82
zcmZqRXyBO8!1UqLL^*|ti<}^g$!v^HOgF9pg(hb)Ix$X|yp}PU(POe8Q!-=4L|Mhj
V)0mvVT*b-1;H)@ikk~@zcmT358kqn9

diff --git a/src/aodv/test/aodv-chain-regression-test-2-0.pcap b/src/aodv/test/aodv-chain-regression-test-2-0.pcap
index 0ee28de79f4ddc43a9eac734f3bbfbe77d064174..9d233047f86593ba1f43ff050c1d9858c96031af 100644
GIT binary patch
delta 78
zcmZqRXyBM2!z2_iQSKPitmKJu3X|CwotV08K&&iAr-=<plg}|aF+Q3s$dnA?Ok;9_
Vs{6$R5muZW$Lz!yHF+U(JOINA80r83

delta 82
zcmZqRXyBM2!}P&_qTDg2isXrM3X|CwotQFgK&&iAC&qw@jf#`c0T~A-3o<1`xYL-N
WplW|HK_nC>$1yuGT1;NZ91j35xEY-Q

diff --git a/src/aodv/test/aodv-chain-regression-test-3-0.pcap b/src/aodv/test/aodv-chain-regression-test-3-0.pcap
index 30c4ea28a6800f9d6aef6c88f3f44e05d3cffed9..ad5ae327f4fd4db8c134fea2a13c871fba9d222a 100644
GIT binary patch
delta 80
zcmZqRXyBM2!)P^8HkonO#KvT%tn7($3X|CwofwrS3o<EA&H}P-O<v2G4Cce+r!hG(
YaaDs<{$g@s{508?Ihk?O<b}-f0HuN$8~^|S

delta 80
zcmZqRXyBM2!zeLPHkq+vVq-FsNA^THg~@D;PK*qb1(_5lX8~C|Ca+~o2J>O^)0mu?
YUQ~fp{$g@syfE38Ihk?7<b}-f0EDC$#{d8T

diff --git a/src/aodv/test/aodv-chain-regression-test-4-0.pcap b/src/aodv/test/aodv-chain-regression-test-4-0.pcap
index ab9bb4adf840df72fea9a643102012d03c7797c9..977c4accef7a930eeff303e23c4ca8d160d376ae 100644
GIT binary patch
delta 88
zcmZqRXyBM2!?<grY%&v*=0rJ#iHn?=iX4E9$!v@;Ru-cZ<EzOFnH49W1G2Ox3o<1$
YIeCE8Ok;w{`~tFeO}1rD2CIw*0EA>4g#Z8m

delta 88
zcmZqRXyBM2!#HE2Y%<dWjfrv!6Bju#1vmg1li3(ytSm++#uJklGAm9#2V`+f7Gz3h
YQt$w&nZ^W@`2}Rnm~6|O3|1Kr0G5{<FaQ7m

diff --git a/src/aodv/test/bug-606-test-0-0.pcap b/src/aodv/test/bug-606-test-0-0.pcap
index cf91f88e88768343c6aeb428761726a4e807dcb6..97e12d6415380e9b9c6a410174547307ae490b51 100644
GIT binary patch
delta 112
zcmZ3%y@Gp!3}ezn*>q;5T87E*ndB!fb7Ee!l6j)M{A4ahH^x<y0~yaVo|>%4l+L82
zIr$xv!sJy<PK=u-zhz2h+&DRqIi2~WJU2+=<Xg;6lN(r+Cfl(rV_x`&3oORQ>cp%m
K0FlpPwF3Y$>m>64

delta 114
zcmZ3%y@Gp!45PzD*>q-xT87E*ndB!fb7F2-$vjbBeli!M8)L`hK*sZoD<&&4r86;T
zPJYLvFnJY|6XS%*Z<&%A`zHr7r!y~?=LTt<e2dwM(R^|vi{fNEmSxQKf4IP+Y^+Yq
L>;e!KS*&&d5zHgC

diff --git a/src/aodv/test/bug-606-test-1-0.pcap b/src/aodv/test/bug-606-test-1-0.pcap
index e44c9bf1b58d4c1a1cdc2b57a4e14823af40c72d..6b4c7e3b4a52deeda5d6ed5dabf2d6bc0118a127 100644
GIT binary patch
delta 72
zcmZqRXyBO8z!){LF?phl(quM9ClHmz=)~AHS&&I_@;N9gnTbh%qMX9yX-rNa#fp=E
S0U1S;ZJCo9y(TYYjt2k|suhg@

delta 78
zcmZqRXyBO8z-TeCF`4Oy)<ijl$!v^HP*xVB6Jy3?K_<n?=b)@)rU!Z;HPe`!Kw1<h
T{{k`sCfhP6Gipp;$Q%y<y80L9

diff --git a/src/aodv/test/bug-606-test-2-0.pcap b/src/aodv/test/bug-606-test-2-0.pcap
index d364a162f3fbb400edf4ba754c08e3227b06aeb6..73a18baccdc877779dee5e560e89e00569fef0ff 100644
GIT binary patch
delta 74
zcmZqRXyBM2!x%MD_BfN2_Cz^_$!v^HOhs-WRu-cZ<EzPQ8Iu{kCJQnpgA^%Fp2p<F
W#H0_B{>226wq;Icyfk?sb36bNbQT`~

delta 74
zcmZqRXyBM2!)P&4_BhiIt%-69li3)Zm;&5DtSm++#uJm*GA1)>OcrEH1}RdUJdMeT
W>46?d`WF*O+Lk$)al_<=%<%v@*B0vl

diff --git a/src/mesh/test/dot11s/hwmp-simplest-regression-test-0-1.pcap b/src/mesh/test/dot11s/hwmp-simplest-regression-test-0-1.pcap
index c8fe30e0fd59c7a5b67c1aad418ddb63b1567fbd..16e37045dcf8456b3a5064cf678f579414333a99 100644
GIT binary patch
delta 4741
zcmYM1dvsLQ6^FA=GRX{*$eT=(F>`?=D59iDsUR-_0eLhm6`>S?T2rx#5vr&NL{U_P
zkYq~^5A8h>6|6yHM@<ox+y#h_T9cw8P(o5vPz15q0<w_qz0bYFTKdO)Yu|HE_WjOp
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z-mC4T`c}uN%U{Lj3X7K#=IW6>j9O5SudT9p?!1enx@S+L7SF?~N{c@u%+;yAjQU_c
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delta 4768
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diff --git a/src/mesh/test/dot11s/hwmp-simplest-regression-test-1-1.pcap b/src/mesh/test/dot11s/hwmp-simplest-regression-test-1-1.pcap
index 53a6e6093529f56396f824a991da45a6f2921bb5..3bb49f0d70a4f528c5a5fc2bba147acded37a4f0 100644
GIT binary patch
delta 4861
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diff --git a/src/mesh/test/flame/flame-regression-test-2-1.pcap b/src/mesh/test/flame/flame-regression-test-2-1.pcap
index cc5204dbea8a2fdbaf2c3ca1e32e51e54285fc17..588cb4b6e00c4463a7b80c73c3ba5cce6db527c6 100644
GIT binary patch
delta 28
jcmX@We1LgE8zb|?kBSplcrbEK{Fuqe2INexVRQiipFRq>

delta 28
ecmX@We1LgE8zaNSkBSplc!20kFlTZNqYD6@S_-BB

diff --git a/src/wifi/model/channel-access-manager.cc b/src/wifi/model/channel-access-manager.cc
index bcdeae75e..ee64cb5a3 100644
--- a/src/wifi/model/channel-access-manager.cc
+++ b/src/wifi/model/channel-access-manager.cc
@@ -242,6 +242,56 @@ ChannelAccessManager::IsBusy (void) const
   return false;
 }
 
+bool
+ChannelAccessManager::NeedBackoffUponAccess (Ptr<Txop> txop)
+{
+  NS_LOG_FUNCTION (this << txop);
+
+  // the Txop might have a stale value of remaining backoff slots
+  UpdateBackoff ();
+
+  /*
+   * From section 10.3.4.2 "Basic access" of IEEE 802.11-2016:
+   *
+   * A STA may transmit an MPDU when it is operating under the DCF access
+   * method, either in the absence of a PC, or in the CP of the PCF access
+   * method, when the STA determines that the medium is idle when a frame is
+   * queued for transmission, and remains idle for a period of a DIFS, or an
+   * EIFS (10.3.2.3.7) from the end of the immediately preceding medium-busy
+   * event, whichever is the greater, and the backoff timer is zero. Otherwise
+   * the random backoff procedure described in 10.3.4.3 shall be followed.
+   *
+   * From section 10.22.2.2 "EDCA backoff procedure" of IEEE 802.11-2016:
+   *
+   * The backoff procedure shall be invoked by an EDCAF when any of the following
+   * events occurs:
+   * a) An MA-UNITDATA.request primitive is received that causes a frame with that AC
+   *    to be queued for transmission such that one of the transmit queues associated
+   *    with that AC has now become non-empty and any other transmit queues
+   *    associated with that AC are empty; the medium is busy on the primary channel
+   */
+  if (!txop->HasFramesToTransmit () && !txop->GetLow ()->IsCfPeriod () && txop->GetBackoffSlots () == 0)
+    {
+      if (!IsBusy ())
+        {
+          // medium idle. If this is a DCF, use immediate access (we can transmit
+          // in a DIFS if the medium remains idle). If this is an EDCAF, update
+          // the backoff start time kept by the EDCAF to the current time in order
+          // to correctly align the backoff start time at the next slot boundary
+          // (performed by the next call to ChannelAccessManager::RequestAccess())
+          Time delay = (txop->IsQosTxop () ? Seconds (0)
+                                           : m_sifs + txop->GetAifsn () * m_slot);
+          txop->UpdateBackoffSlotsNow (0, Simulator::Now () + delay);
+        }
+      else
+        {
+          // medium busy, backoff is neeeded
+          return true;
+        }
+    }
+  return false;
+}
+
 void
 ChannelAccessManager::RequestAccess (Ptr<Txop> state, bool isCfPeriod)
 {
diff --git a/src/wifi/model/channel-access-manager.h b/src/wifi/model/channel-access-manager.h
index ad0dbd56c..7d68376f9 100644
--- a/src/wifi/model/channel-access-manager.h
+++ b/src/wifi/model/channel-access-manager.h
@@ -112,6 +112,15 @@ public:
    */
   void Add (Ptr<Txop> dcf);
 
+  /**
+   * Determine if a new backoff needs to be generated when a packet is queued
+   * for transmission.
+   *
+   * \param txop the Txop requesting to generate a backoff
+   * \return true if backoff needs to be generated, false otherwise
+   */
+  bool NeedBackoffUponAccess (Ptr<Txop> txop);
+
   /**
    * \param state a Txop
    * \param isCfPeriod flag whether it is called during the CF period
diff --git a/src/wifi/model/txop.cc b/src/wifi/model/txop.cc
index dc387659b..7b15b7bd0 100644
--- a/src/wifi/model/txop.cc
+++ b/src/wifi/model/txop.cc
@@ -312,50 +312,6 @@ Txop::HasFramesToTransmit (void)
   return ret;
 }
 
-void
-Txop::GenerateBackoffUponAccessIfNeeded (void)
-{
-  NS_LOG_FUNCTION (this);
-  /*
-   * From section 10.3.4.2 "Basic access" of IEEE 802.11-2016:
-   *
-   * A STA may transmit an MPDU when it is operating under the DCF access
-   * method, either in the absence of a PC, or in the CP of the PCF access
-   * method, when the STA determines that the medium is idle when a frame is
-   * queued for transmission, and remains idle for a period of a DIFS, or an
-   * EIFS (10.3.2.3.7) from the end of the immediately preceding medium-busy
-   * event, whichever is the greater, and the backoff timer is zero. Otherwise
-   * the random backoff procedure described in 10.3.4.3 shall be followed.
-   *
-   * From section 10.22.2.2 "EDCA backoff procedure" of IEEE 802.11-2016:
-   *
-   * The backoff procedure shall be invoked by an EDCAF when any of the following
-   * events occurs:
-   * a) An MA-UNITDATA.request primitive is received that causes a frame with that AC
-   *    to be queued for transmission such that one of the transmit queues associated
-   *    with that AC has now become non-empty and any other transmit queues
-   *    associated with that AC are empty; the medium is busy on the primary channel
-   */
-  if (!HasFramesToTransmit () && !m_low->IsCfPeriod () && m_backoffSlots == 0)
-    {
-      if (!m_channelAccessManager->IsBusy ())
-        {
-          // medium idle. If this is a DCF, use immediate access (we can transmit
-          // in a DIFS if the medium remains idle). If this is an EDCAF, update
-          // the backoff start time kept by the EDCAF to the current time in order
-          // to correctly align the backoff start time at the next slot boundary
-          // (performed by the next call to ChannelAccessManager::RequestAccess())
-          Time delay = (IsQosTxop () ? Seconds (0) : m_low->GetSifs () + GetAifsn () * m_low->GetSlotTime ());
-          UpdateBackoffSlotsNow (0, Simulator::Now () + delay);
-        }
-      else
-        {
-          // medium busy, generate backoff
-          GenerateBackoff ();
-        }
-    }
-}
-
 void
 Txop::Queue (Ptr<const Packet> packet, const WifiMacHeader &hdr)
 {
@@ -365,7 +321,10 @@ Txop::Queue (Ptr<const Packet> packet, const WifiMacHeader &hdr)
   SocketPriorityTag priorityTag;
   packetCopy->RemovePacketTag (priorityTag);
   m_stationManager->PrepareForQueue (hdr.GetAddr1 (), &hdr, packetCopy);
-  GenerateBackoffUponAccessIfNeeded ();
+  if (m_channelAccessManager->NeedBackoffUponAccess (this))
+    {
+      GenerateBackoff ();
+    }
   m_queue->Enqueue (Create<WifiMacQueueItem> (packetCopy, hdr));
   StartAccessIfNeeded ();
 }
diff --git a/src/wifi/model/txop.h b/src/wifi/model/txop.h
index 606f8078c..0fb0c6dec 100644
--- a/src/wifi/model/txop.h
+++ b/src/wifi/model/txop.h
@@ -376,10 +376,6 @@ protected:
    * \return true if the DCF has frames to transmit.
    */
   virtual bool HasFramesToTransmit (void);
-  /**
-   * Generate a new backoff, if needed, when a packet is queued for transmission.
-   */
-  virtual void GenerateBackoffUponAccessIfNeeded (void);
   /**
    * Generate a new backoff now.
    */
diff --git a/src/wifi/test/channel-access-manager-test.cc b/src/wifi/test/channel-access-manager-test.cc
index a6126a557..758c567a3 100644
--- a/src/wifi/test/channel-access-manager-test.cc
+++ b/src/wifi/test/channel-access-manager-test.cc
@@ -679,7 +679,10 @@ void
 ChannelAccessManagerTest<TxopType>::DoAccessRequest (uint64_t txTime, uint64_t expectedGrantTime,
                                                      Ptr<TxopTest<TxopType>> state)
 {
-  state->GenerateBackoffUponAccessIfNeeded ();
+  if (m_ChannelAccessManager->NeedBackoffUponAccess (state))
+    {
+      state->GenerateBackoff ();
+    }
   state->QueueTx (txTime, expectedGrantTime);
   m_ChannelAccessManager->RequestAccess (state);
 }
diff --git a/src/wifi/test/wifi-test.cc b/src/wifi/test/wifi-test.cc
index 0be76272b..97533ddc9 100644
--- a/src/wifi/test/wifi-test.cc
+++ b/src/wifi/test/wifi-test.cc
@@ -460,7 +460,6 @@ DcfImmediateAccessBroadcastTestCase::NotifyPhyTxBegin (Ptr<const Packet> p, doub
 {
   if (m_numSentPackets == 0)
     {
-      NS_ASSERT_MSG (Simulator::Now () == Time (Seconds (1)), "Packet 0 not transmitted at 1 second");
       m_numSentPackets++;
       m_firstTransmissionTime = Simulator::Now ();
     }
@@ -536,13 +535,17 @@ DcfImmediateAccessBroadcastTestCase::DoRun (void)
   Simulator::Run ();
   Simulator::Destroy ();
 
+  // First packet is transmitted a DIFS after the packet is queued. A DIFS
+  // is 2 slots (2 * 9 = 18 us) plus a SIFS (16 us), i.e., 34 us
+  Time expectedFirstTransmissionTime = Seconds (1.0) + MicroSeconds (34);
+
   //First packet has 1408 us of transmit time.   Slot time is 9 us.
   //Backoff is 1 slots.  SIFS is 16 us.  DIFS is 2 slots = 18 us.
   //Should send next packet at 1408 us + (1 * 9 us) + 16 us + (2 * 9) us
   //1451 us after the first one.
   uint32_t expectedWait1 = 1408 + (1 * 9) + 16 + (2 * 9);
-  Time expectedSecondTransmissionTime = MicroSeconds (expectedWait1) + MilliSeconds (1000);
-  NS_TEST_ASSERT_MSG_EQ (m_firstTransmissionTime, MilliSeconds (1000), "The first transmission time not correct!");
+  Time expectedSecondTransmissionTime = expectedFirstTransmissionTime + MicroSeconds (expectedWait1);
+  NS_TEST_ASSERT_MSG_EQ (m_firstTransmissionTime, expectedFirstTransmissionTime, "The first transmission time not correct!");
 
   NS_TEST_ASSERT_MSG_EQ (m_secondTransmissionTime, expectedSecondTransmissionTime, "The second transmission time not correct!");
 }