diff --git a/Tethering/tests/unit/src/com/android/networkstack/tethering/TestConnectivityManager.java b/Tethering/tests/unit/src/com/android/networkstack/tethering/TestConnectivityManager.java
index 6090213..b8389ea 100644
--- a/Tethering/tests/unit/src/com/android/networkstack/tethering/TestConnectivityManager.java
+++ b/Tethering/tests/unit/src/com/android/networkstack/tethering/TestConnectivityManager.java
@@ -36,6 +36,7 @@
 import android.os.UserHandle;
 import android.util.ArrayMap;
 
+import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 
 import java.util.Map;
@@ -67,10 +68,10 @@
     public static final boolean BROADCAST_FIRST = false;
     public static final boolean CALLBACKS_FIRST = true;
 
-    final Map<NetworkCallback, NetworkRequestInfo> mAllCallbacks = new ArrayMap<>();
+    final Map<NetworkCallback, NetworkCallbackInfo> mAllCallbacks = new ArrayMap<>();
     // This contains the callbacks tracking the system default network, whether it's registered
     // with registerSystemDefaultNetworkCallback (S+) or with a custom request (R-).
-    final Map<NetworkCallback, NetworkRequestInfo> mTrackingDefault = new ArrayMap<>();
+    final Map<NetworkCallback, NetworkCallbackInfo> mTrackingDefault = new ArrayMap<>();
     final Map<NetworkCallback, NetworkRequestInfo> mListening = new ArrayMap<>();
     final Map<NetworkCallback, NetworkRequestInfo> mRequested = new ArrayMap<>();
     final Map<NetworkCallback, Integer> mLegacyTypeMap = new ArrayMap<>();
@@ -91,15 +92,21 @@
         mContext = ctx;
     }
 
-    class NetworkRequestInfo {
-        public final NetworkRequest request;
+    static class NetworkCallbackInfo {
         public final Handler handler;
-        NetworkRequestInfo(NetworkRequest r, Handler h) {
-            request = r;
+        NetworkCallbackInfo(Handler h) {
             handler = h;
         }
     }
 
+    static class NetworkRequestInfo extends NetworkCallbackInfo {
+        public final NetworkRequest request;
+        NetworkRequestInfo(NetworkRequest r, Handler h) {
+            super(h);
+            request = r;
+        }
+    }
+
     boolean hasNoCallbacks() {
         return mAllCallbacks.isEmpty()
                 && mTrackingDefault.isEmpty()
@@ -145,7 +152,7 @@
     private void sendDefaultNetworkCallbacks(TestNetworkAgent formerDefault,
             TestNetworkAgent defaultNetwork) {
         for (NetworkCallback cb : mTrackingDefault.keySet()) {
-            final NetworkRequestInfo nri = mTrackingDefault.get(cb);
+            final NetworkCallbackInfo nri = mTrackingDefault.get(cb);
             if (defaultNetwork != null) {
                 nri.handler.post(() -> cb.onAvailable(defaultNetwork.networkId));
                 nri.handler.post(() -> cb.onCapabilitiesChanged(
@@ -191,20 +198,28 @@
 
     @Override
     public void requestNetwork(NetworkRequest req, NetworkCallback cb, Handler h) {
-        assertFalse(mAllCallbacks.containsKey(cb));
-        mAllCallbacks.put(cb, new NetworkRequestInfo(req, h));
         // For R- devices, Tethering will invoke this function in 2 cases, one is to request mobile
         // network, the other is to track system default network.
         if (looksLikeDefaultRequest(req)) {
-            assertFalse(mTrackingDefault.containsKey(cb));
-            mTrackingDefault.put(cb, new NetworkRequestInfo(req, h));
+            registerSystemDefaultNetworkCallback(cb, h);
         } else {
+            assertFalse(mAllCallbacks.containsKey(cb));
+            mAllCallbacks.put(cb, new NetworkRequestInfo(req, h));
             assertFalse(mRequested.containsKey(cb));
             mRequested.put(cb, new NetworkRequestInfo(req, h));
         }
     }
 
     @Override
+    public void registerSystemDefaultNetworkCallback(
+            @NonNull NetworkCallback cb, @NonNull Handler h) {
+        assertFalse(mAllCallbacks.containsKey(cb));
+        mAllCallbacks.put(cb, new NetworkCallbackInfo(h));
+        assertFalse(mTrackingDefault.containsKey(cb));
+        mTrackingDefault.put(cb, new NetworkCallbackInfo(h));
+    }
+
+    @Override
     public void requestNetwork(NetworkRequest req, NetworkCallback cb) {
         fail("Should never be called.");
     }
diff --git a/Tethering/tests/unit/src/com/android/networkstack/tethering/TetheringTest.java b/Tethering/tests/unit/src/com/android/networkstack/tethering/TetheringTest.java
index f1d8c0f..c636384 100644
--- a/Tethering/tests/unit/src/com/android/networkstack/tethering/TetheringTest.java
+++ b/Tethering/tests/unit/src/com/android/networkstack/tethering/TetheringTest.java
@@ -60,6 +60,7 @@
 import static android.system.OsConstants.RT_SCOPE_UNIVERSE;
 import static android.telephony.SubscriptionManager.INVALID_SUBSCRIPTION_ID;
 
+import static com.android.modules.utils.build.SdkLevel.isAtLeastS;
 import static com.android.net.module.util.Inet4AddressUtils.inet4AddressToIntHTH;
 import static com.android.net.module.util.Inet4AddressUtils.intToInet4AddressHTH;
 import static com.android.networkstack.tethering.OffloadHardwareInterface.OFFLOAD_HAL_VERSION_1_0;
@@ -779,10 +780,17 @@
     }
 
     private void verifyDefaultNetworkRequestFiled() {
-        ArgumentCaptor<NetworkRequest> reqCaptor = ArgumentCaptor.forClass(NetworkRequest.class);
-        verify(mCm, times(1)).requestNetwork(reqCaptor.capture(),
-                any(NetworkCallback.class), any(Handler.class));
-        assertTrue(TestConnectivityManager.looksLikeDefaultRequest(reqCaptor.getValue()));
+        if (isAtLeastS()) {
+            verify(mCm, times(1)).registerSystemDefaultNetworkCallback(
+                    any(NetworkCallback.class), any(Handler.class));
+        } else {
+            ArgumentCaptor<NetworkRequest> reqCaptor = ArgumentCaptor.forClass(
+                    NetworkRequest.class);
+            verify(mCm, times(1)).requestNetwork(reqCaptor.capture(),
+                    any(NetworkCallback.class), any(Handler.class));
+            assertTrue(TestConnectivityManager.looksLikeDefaultRequest(reqCaptor.getValue()));
+        }
+
         // The default network request is only ever filed once.
         verifyNoMoreInteractions(mCm);
     }
diff --git a/Tethering/tests/unit/src/com/android/networkstack/tethering/UpstreamNetworkMonitorTest.java b/Tethering/tests/unit/src/com/android/networkstack/tethering/UpstreamNetworkMonitorTest.java
index ce4ba85..173679d 100644
--- a/Tethering/tests/unit/src/com/android/networkstack/tethering/UpstreamNetworkMonitorTest.java
+++ b/Tethering/tests/unit/src/com/android/networkstack/tethering/UpstreamNetworkMonitorTest.java
@@ -24,6 +24,7 @@
 import static android.net.NetworkCapabilities.TRANSPORT_CELLULAR;
 import static android.net.NetworkCapabilities.TRANSPORT_WIFI;
 
+import static com.android.modules.utils.build.SdkLevel.isAtLeastS;
 import static com.android.networkstack.tethering.UpstreamNetworkMonitor.TYPE_NONE;
 
 import static org.junit.Assert.assertEquals;
@@ -172,12 +173,17 @@
         // Verify the fired default request matches expectation.
         final ArgumentCaptor<NetworkRequest> requestCaptor =
                 ArgumentCaptor.forClass(NetworkRequest.class);
-        verify(mCM, times(1)).requestNetwork(
-                requestCaptor.capture(), any(NetworkCallback.class), any(Handler.class));
-        // For R- devices, Tethering will invoke this function in 2 cases, one is to
-        // request mobile network, the other is to track system default network. Verify
-        // the request is the one tracks default network.
-        assertTrue(TestConnectivityManager.looksLikeDefaultRequest(requestCaptor.getValue()));
+
+        if (isAtLeastS()) {
+            verify(mCM).registerSystemDefaultNetworkCallback(any(), any());
+        } else {
+            verify(mCM).requestNetwork(
+                    requestCaptor.capture(), any(NetworkCallback.class), any(Handler.class));
+            // For R- devices, Tethering will invoke this function in 2 cases, one is to
+            // request mobile network, the other is to track system default network. Verify
+            // the request is the one tracks default network.
+            assertTrue(TestConnectivityManager.looksLikeDefaultRequest(requestCaptor.getValue()));
+        }
 
         mUNM.startObserveAllNetworks();
         verify(mCM, times(1)).registerNetworkCallback(