From aab9cbd2a535bb7128cbd3239d510b4fdccc63ff Mon Sep 17 00:00:00 2001
From: Yan Yan <evitayan@google.com>
Date: Tue, 9 Apr 2024 01:23:04 +0000
Subject: [PATCH] VCN: Ignore packet loss detection when there is too few
 traffic

When the expected received packet number is smaller than 10, the
packet loss detection result will be ignored because the sample
size is too small to ensure a reliable result.

This patch also fixes the bug where the detector does not update
ths packet loss threshold when carrier config updates

Bug: 332598276
Test: atest FrameworksVcnTests && atest CtsVcnTestCases
Change-Id: Iccc47e83c48699d139029420572e2a2616c357cd
---
 .../routeselection/IpSecPacketLossDetector.java  | 16 +++++++++++++++-
 .../IpSecPacketLossDetectorTest.java             | 16 ++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/Vcn/service-b/src/com/android/server/vcn/routeselection/IpSecPacketLossDetector.java b/Vcn/service-b/src/com/android/server/vcn/routeselection/IpSecPacketLossDetector.java
index 206523a6e9..3619253749 100644
--- a/Vcn/service-b/src/com/android/server/vcn/routeselection/IpSecPacketLossDetector.java
+++ b/Vcn/service-b/src/com/android/server/vcn/routeselection/IpSecPacketLossDetector.java
@@ -64,6 +64,12 @@ public class IpSecPacketLossDetector extends NetworkMetricMonitor {
 
     private static final int PACKET_LOSS_PERCENT_UNAVAILABLE = -1;
 
+    // Ignore the packet loss detection result if the expected packet number is smaller than 10.
+    // Solarwinds NPM uses 10 ICMP echos to calculate packet loss rate (as per
+    // https://thwack.solarwinds.com/products/network-performance-monitor-npm/f/forum/63829/how-is-packet-loss-calculated)
+    @VisibleForTesting(visibility = Visibility.PRIVATE)
+    static final int MIN_VALID_EXPECTED_RX_PACKET_NUM = 10;
+
     @Retention(RetentionPolicy.SOURCE)
     @IntDef(
             prefix = {"PACKET_LOSS_"},
@@ -85,6 +91,8 @@ public class IpSecPacketLossDetector extends NetworkMetricMonitor {
      * <ul>
      *   <li>The replay window did not proceed and thus all packets might have been delivered out of
      *       order
+     *   <li>The expected received packet number is too small and thus the detection result is not
+     *       reliable
      *   <li>There are unexpected errors
      * </ul>
      */
@@ -113,7 +121,7 @@ public class IpSecPacketLossDetector extends NetworkMetricMonitor {
     private static final int MAX_SEQ_NUM_INCREASE_DEFAULT_DISABLED = -1;
 
     private long mPollIpSecStateIntervalMs;
-    private final int mPacketLossRatePercentThreshold;
+    private int mPacketLossRatePercentThreshold;
     private int mMaxSeqNumIncreasePerSecond;
 
     @NonNull private final Handler mHandler;
@@ -273,6 +281,7 @@ public class IpSecPacketLossDetector extends NetworkMetricMonitor {
         mPollIpSecStateIntervalMs = getPollIpSecStateIntervalMs(carrierConfig);
 
         if (Flags.handleSeqNumLeap()) {
+            mPacketLossRatePercentThreshold = getPacketLossRatePercentThreshold(carrierConfig);
             mMaxSeqNumIncreasePerSecond = getMaxSeqNumIncreasePerSecond(carrierConfig);
         }
     }
@@ -476,6 +485,11 @@ public class IpSecPacketLossDetector extends NetworkMetricMonitor {
                             + " actualPktCntDiff: "
                             + actualPktCntDiff);
 
+            if (Flags.handleSeqNumLeap() && expectedPktCntDiff < MIN_VALID_EXPECTED_RX_PACKET_NUM) {
+                // The sample size is too small to ensure a reliable detection result
+                return PacketLossCalculationResult.invalid();
+            }
+
             if (expectedPktCntDiff < 0
                     || expectedPktCntDiff == 0
                     || actualPktCntDiff < 0
diff --git a/Vcn/tests/unit/java/com/android/server/vcn/routeselection/IpSecPacketLossDetectorTest.java b/Vcn/tests/unit/java/com/android/server/vcn/routeselection/IpSecPacketLossDetectorTest.java
index 68a2ad7e1a..c8b60e5c33 100644
--- a/Vcn/tests/unit/java/com/android/server/vcn/routeselection/IpSecPacketLossDetectorTest.java
+++ b/Vcn/tests/unit/java/com/android/server/vcn/routeselection/IpSecPacketLossDetectorTest.java
@@ -20,6 +20,7 @@ import static android.net.vcn.VcnManager.VCN_NETWORK_SELECTION_IPSEC_PACKET_LOSS
 import static android.net.vcn.VcnManager.VCN_NETWORK_SELECTION_MAX_SEQ_NUM_INCREASE_PER_SECOND_KEY;
 import static android.net.vcn.VcnManager.VCN_NETWORK_SELECTION_POLL_IPSEC_STATE_INTERVAL_SECONDS_KEY;
 
+import static com.android.server.vcn.routeselection.IpSecPacketLossDetector.MIN_VALID_EXPECTED_RX_PACKET_NUM;
 import static com.android.server.vcn.routeselection.IpSecPacketLossDetector.getMaxSeqNumIncreasePerSecond;
 import static com.android.server.vcn.util.PersistableBundleUtils.PersistableBundleWrapper;
 
@@ -436,6 +437,21 @@ public class IpSecPacketLossDetectorTest extends NetworkEvaluationTestBase {
                 mTransformStateInitial, 3000, 2000, 2000, PacketLossCalculationResult.invalid());
     }
 
+    @Test
+    public void testGetPacketLossRate_expectedPacketNumTooFew() throws Exception {
+        final int oldRxNo = 4096;
+        final int oldPktCnt = 4096;
+        final int pktCntDiff = MIN_VALID_EXPECTED_RX_PACKET_NUM - 1;
+        final byte[] bitmapReceiveAll = newReplayBitmap(4096);
+
+        final IpSecTransformState oldState =
+                newTransformState(oldRxNo, oldPktCnt, bitmapReceiveAll);
+        final IpSecTransformState newState =
+                newTransformState(oldRxNo + pktCntDiff, oldPktCnt + pktCntDiff, bitmapReceiveAll);
+
+        checkGetPacketLossRate(oldState, newState, PacketLossCalculationResult.invalid());
+    }
+
     @Test
     public void testGetPacketLossRate_againstInitialState() throws Exception {
         checkGetPacketLossRate(mTransformStateInitial, 7000, 7001, 4096, 0);