diff --git a/framework/src/android/net/ConnectivityManager.java b/framework/src/android/net/ConnectivityManager.java
index c7bb2a7..adab6e3 100644
--- a/framework/src/android/net/ConnectivityManager.java
+++ b/framework/src/android/net/ConnectivityManager.java
@@ -50,7 +50,6 @@
 import android.os.Handler;
 import android.os.IBinder;
 import android.os.INetworkActivityListener;
-import android.os.INetworkManagementService;
 import android.os.Looper;
 import android.os.Message;
 import android.os.Messenger;
@@ -835,7 +834,6 @@
 
     private final Context mContext;
 
-    private INetworkManagementService mNMService;
     private INetworkPolicyManager mNPManager;
     private final TetheringManager mTetheringManager;
 
@@ -2211,17 +2209,6 @@
         void onNetworkActive();
     }
 
-    private INetworkManagementService getNetworkManagementService() {
-        synchronized (this) {
-            if (mNMService != null) {
-                return mNMService;
-            }
-            IBinder b = ServiceManager.getService(Context.NETWORKMANAGEMENT_SERVICE);
-            mNMService = INetworkManagementService.Stub.asInterface(b);
-            return mNMService;
-        }
-    }
-
     private final ArrayMap<OnNetworkActiveListener, INetworkActivityListener>
             mNetworkActivityListeners = new ArrayMap<>();
 
@@ -2246,7 +2233,7 @@
         };
 
         try {
-            getNetworkManagementService().registerNetworkActivityListener(rl);
+            mService.registerNetworkActivityListener(rl);
             mNetworkActivityListeners.put(l, rl);
         } catch (RemoteException e) {
             throw e.rethrowFromSystemServer();
@@ -2263,7 +2250,7 @@
         INetworkActivityListener rl = mNetworkActivityListeners.get(l);
         Preconditions.checkArgument(rl != null, "Listener was not registered.");
         try {
-            getNetworkManagementService().unregisterNetworkActivityListener(rl);
+            mService.registerNetworkActivityListener(rl);
         } catch (RemoteException e) {
             throw e.rethrowFromSystemServer();
         }
@@ -2279,7 +2266,7 @@
      */
     public boolean isDefaultNetworkActive() {
         try {
-            return getNetworkManagementService().isNetworkActive();
+            return mService.isDefaultNetworkActive();
         } catch (RemoteException e) {
             throw e.rethrowFromSystemServer();
         }
diff --git a/services/core/java/com/android/server/ConnectivityService.java b/services/core/java/com/android/server/ConnectivityService.java
index 460fa6d..389b579 100644
--- a/services/core/java/com/android/server/ConnectivityService.java
+++ b/services/core/java/com/android/server/ConnectivityService.java
@@ -164,6 +164,7 @@
 import android.os.PersistableBundle;
 import android.os.PowerManager;
 import android.os.Process;
+import android.os.RemoteCallbackList;
 import android.os.RemoteException;
 import android.os.ServiceSpecificException;
 import android.os.SystemClock;
@@ -173,6 +174,7 @@
 import android.provider.Settings;
 import android.telephony.TelephonyManager;
 import android.text.TextUtils;
+import android.util.ArrayMap;
 import android.util.ArraySet;
 import android.util.LocalLog;
 import android.util.Log;
@@ -560,6 +562,11 @@
     private static final int EVENT_SET_OEM_NETWORK_PREFERENCE = 48;
 
     /**
+     * Used to indicate the system default network becomes active.
+     */
+    private static final int EVENT_REPORT_NETWORK_ACTIVITY = 49;
+
+    /**
      * Argument for {@link #EVENT_PROVISIONING_NOTIFICATION} to indicate that the notification
      * should be shown.
      */
@@ -1193,7 +1200,7 @@
         mUserAllContext.registerReceiver(mIntentReceiver, intentFilter,
                 null /* broadcastPermission */, mHandler);
 
-        mNetworkActivityTracker = new LegacyNetworkActivityTracker(mContext, mNMS);
+        mNetworkActivityTracker = new LegacyNetworkActivityTracker(mContext, mHandler, mNMS, mNetd);
 
         mSettingsObserver = new SettingsObserver(mContext, mHandler);
         registerSettingsCallbacks();
@@ -2405,7 +2412,7 @@
      */
     @Override
     public void registerNetworkActivityListener(@NonNull INetworkActivityListener l) {
-        // TODO: Replace network activity listener registry in ConnectivityManager from NMS to here
+        mNetworkActivityTracker.registerNetworkActivityListener(l);
     }
 
     /**
@@ -2413,7 +2420,7 @@
      */
     @Override
     public void unregisterNetworkActivityListener(@NonNull INetworkActivityListener l) {
-        // TODO: Replace network activity listener registry in ConnectivityManager from NMS to here
+        mNetworkActivityTracker.unregisterNetworkActivityListener(l);
     }
 
     /**
@@ -2421,8 +2428,7 @@
      */
     @Override
     public boolean isDefaultNetworkActive() {
-        // TODO: Replace isNetworkActive() in NMS.
-        return false;
+        return mNetworkActivityTracker.isDefaultNetworkActive();
     }
 
     /**
@@ -4448,6 +4454,9 @@
                         loge("handleMessage.EVENT_SET_OEM_NETWORK_PREFERENCE failed", e);
                     }
                     break;
+                case EVENT_REPORT_NETWORK_ACTIVITY:
+                    mNetworkActivityTracker.handleReportNetworkActivity();
+                    break;
             }
         }
     }
@@ -8637,12 +8646,33 @@
     private static final class LegacyNetworkActivityTracker {
         private static final int NO_UID = -1;
         private final Context mContext;
+        private final INetd mNetd;
         private final INetworkManagementService mNMS;
+        private final RemoteCallbackList<INetworkActivityListener> mNetworkActivityListeners =
+                new RemoteCallbackList<>();
+        // Indicate the current system default network activity is active or not.
+        @GuardedBy("mActiveIdleTimers")
+        private boolean mNetworkActive;
+        @GuardedBy("mActiveIdleTimers")
+        private final ArrayMap<String, IdleTimerParams> mActiveIdleTimers = new ArrayMap();
+        private final Handler mHandler;
 
-        LegacyNetworkActivityTracker(@NonNull Context context,
-                @NonNull INetworkManagementService nms) {
+        private class IdleTimerParams {
+            public final int timeout;
+            public final int transportType;
+
+            IdleTimerParams(int timeout, int transport) {
+                this.timeout = timeout;
+                this.transportType = transport;
+            }
+        }
+
+        LegacyNetworkActivityTracker(@NonNull Context context, @NonNull Handler handler,
+                @NonNull INetworkManagementService nms, @NonNull INetd netd) {
             mContext = context;
             mNMS = nms;
+            mNetd = netd;
+            mHandler = handler;
             try {
                 mNMS.registerObserver(mDataActivityObserver);
             } catch (RemoteException e) {
@@ -8658,9 +8688,50 @@
                             long tsNanos, int uid) {
                         sendDataActivityBroadcast(transportTypeToLegacyType(transportType), active,
                                 tsNanos);
+                        synchronized (mActiveIdleTimers) {
+                            mNetworkActive = active;
+                            // If there are no idle timers, it means that system is not monitoring
+                            // activity, so the system default network for those default network
+                            // unspecified apps is always considered active.
+                            //
+                            // TODO: If the mActiveIdleTimers is empty, netd will actually not send
+                            // any network activity change event. Whenever this event is received,
+                            // the mActiveIdleTimers should be always not empty. The legacy behavior
+                            // is no-op. Remove to refer to mNetworkActive only.
+                            if (mNetworkActive || mActiveIdleTimers.isEmpty()) {
+                                mHandler.sendMessage(
+                                        mHandler.obtainMessage(EVENT_REPORT_NETWORK_ACTIVITY));
+                            }
+                        }
                     }
                 };
 
+        // The network activity should only be updated from ConnectivityService handler thread
+        // when mActiveIdleTimers lock is held.
+        @GuardedBy("mActiveIdleTimers")
+        private void reportNetworkActive() {
+            final int length = mNetworkActivityListeners.beginBroadcast();
+            if (DDBG) log("reportNetworkActive, notify " + length + " listeners");
+            try {
+                for (int i = 0; i < length; i++) {
+                    try {
+                        mNetworkActivityListeners.getBroadcastItem(i).onNetworkActive();
+                    } catch (RemoteException | RuntimeException e) {
+                        loge("Fail to send network activie to listener " + e);
+                    }
+                }
+            } finally {
+                mNetworkActivityListeners.finishBroadcast();
+            }
+        }
+
+        @GuardedBy("mActiveIdleTimers")
+        public void handleReportNetworkActivity() {
+            synchronized (mActiveIdleTimers) {
+                reportNetworkActive();
+            }
+        }
+
         // This is deprecated and only to support legacy use cases.
         private int transportTypeToLegacyType(int type) {
             switch (type) {
@@ -8729,8 +8800,13 @@
 
             if (timeout > 0 && iface != null) {
                 try {
-                    // TODO: Access INetd directly instead of NMS
-                    mNMS.addIdleTimer(iface, timeout, type);
+                    synchronized (mActiveIdleTimers) {
+                        // Networks start up.
+                        mNetworkActive = true;
+                        mActiveIdleTimers.put(iface, new IdleTimerParams(timeout, type));
+                        mNetd.idletimerAddInterface(iface, timeout, Integer.toString(type));
+                        reportNetworkActive();
+                    }
                 } catch (Exception e) {
                     // You shall not crash!
                     loge("Exception in setupDataActivityTracking " + e);
@@ -8758,9 +8834,12 @@
 
             try {
                 updateRadioPowerState(false /* isActive */, type);
-                // The call fails silently if no idle timer setup for this interface.
-                // TODO: Access INetd directly instead of NMS
-                mNMS.removeIdleTimer(iface);
+                synchronized (mActiveIdleTimers) {
+                    final IdleTimerParams params = mActiveIdleTimers.remove(iface);
+                    // The call fails silently if no idle timer setup for this interface
+                    mNetd.idletimerRemoveInterface(iface, params.timeout,
+                            Integer.toString(params.transportType));
+                }
             } catch (Exception e) {
                 // You shall not crash!
                 loge("Exception in removeDataActivityTracking " + e);
@@ -8793,6 +8872,26 @@
                     logw("Untracked transport type:" + transportType);
             }
         }
+
+        public boolean isDefaultNetworkActive() {
+            synchronized (mActiveIdleTimers) {
+                // If there are no idle timers, it means that system is not monitoring activity,
+                // so the default network is always considered active.
+                //
+                // TODO : Distinguish between the cases where mActiveIdleTimers is empty because
+                // tracking is disabled (negative idle timer value configured), or no active default
+                // network. In the latter case, this reports active but it should report inactive.
+                return mNetworkActive || mActiveIdleTimers.isEmpty();
+            }
+        }
+
+        public void registerNetworkActivityListener(@NonNull INetworkActivityListener l) {
+            mNetworkActivityListeners.register(l);
+        }
+
+        public void unregisterNetworkActivityListener(@NonNull INetworkActivityListener l) {
+            mNetworkActivityListeners.unregister(l);
+        }
     }
 
     /**
diff --git a/tests/net/java/com/android/server/ConnectivityServiceTest.java b/tests/net/java/com/android/server/ConnectivityServiceTest.java
index 182897e..e9c3577 100644
--- a/tests/net/java/com/android/server/ConnectivityServiceTest.java
+++ b/tests/net/java/com/android/server/ConnectivityServiceTest.java
@@ -8205,8 +8205,8 @@
         reset(mNetworkManagementService);
         mCellNetworkAgent.connect(true);
         networkCallback.expectAvailableThenValidatedCallbacks(mCellNetworkAgent);
-        verify(mNetworkManagementService, times(1)).addIdleTimer(eq(MOBILE_IFNAME), anyInt(),
-                eq(NetworkCapabilities.TRANSPORT_CELLULAR));
+        verify(mMockNetd, times(1)).idletimerAddInterface(eq(MOBILE_IFNAME), anyInt(),
+                eq(Integer.toString(TRANSPORT_CELLULAR)));
 
         mWiFiNetworkAgent = new TestNetworkAgentWrapper(TRANSPORT_WIFI);
         final LinkProperties wifiLp = new LinkProperties();
@@ -8214,25 +8214,27 @@
         mWiFiNetworkAgent.sendLinkProperties(wifiLp);
 
         // Network switch
-        reset(mNetworkManagementService);
         mWiFiNetworkAgent.connect(true);
         networkCallback.expectAvailableCallbacksUnvalidated(mWiFiNetworkAgent);
         networkCallback.expectCallback(CallbackEntry.LOSING, mCellNetworkAgent);
         networkCallback.expectCapabilitiesWith(NET_CAPABILITY_VALIDATED, mWiFiNetworkAgent);
-        verify(mNetworkManagementService, times(1)).addIdleTimer(eq(WIFI_IFNAME), anyInt(),
-                eq(NetworkCapabilities.TRANSPORT_WIFI));
-        verify(mNetworkManagementService, times(1)).removeIdleTimer(eq(MOBILE_IFNAME));
+        verify(mMockNetd, times(1)).idletimerAddInterface(eq(WIFI_IFNAME), anyInt(),
+                eq(Integer.toString(TRANSPORT_WIFI)));
+        verify(mMockNetd, times(1)).idletimerRemoveInterface(eq(MOBILE_IFNAME), anyInt(),
+                eq(Integer.toString(TRANSPORT_CELLULAR)));
 
         // Disconnect wifi and switch back to cell
-        reset(mNetworkManagementService);
+        reset(mMockNetd);
         mWiFiNetworkAgent.disconnect();
         networkCallback.expectCallback(CallbackEntry.LOST, mWiFiNetworkAgent);
         assertNoCallbacks(networkCallback);
-        verify(mNetworkManagementService, times(1)).removeIdleTimer(eq(WIFI_IFNAME));
-        verify(mNetworkManagementService, times(1)).addIdleTimer(eq(MOBILE_IFNAME), anyInt(),
-                eq(NetworkCapabilities.TRANSPORT_CELLULAR));
+        verify(mMockNetd, times(1)).idletimerRemoveInterface(eq(WIFI_IFNAME), anyInt(),
+                eq(Integer.toString(TRANSPORT_WIFI)));
+        verify(mMockNetd, times(1)).idletimerAddInterface(eq(MOBILE_IFNAME), anyInt(),
+                eq(Integer.toString(TRANSPORT_CELLULAR)));
 
         // reconnect wifi
+        reset(mMockNetd);
         mWiFiNetworkAgent = new TestNetworkAgentWrapper(TRANSPORT_WIFI);
         wifiLp.setInterfaceName(WIFI_IFNAME);
         mWiFiNetworkAgent.sendLinkProperties(wifiLp);
@@ -8240,9 +8242,12 @@
         networkCallback.expectAvailableCallbacksUnvalidated(mWiFiNetworkAgent);
         networkCallback.expectCallback(CallbackEntry.LOSING, mCellNetworkAgent);
         networkCallback.expectCapabilitiesWith(NET_CAPABILITY_VALIDATED, mWiFiNetworkAgent);
+        verify(mMockNetd, times(1)).idletimerAddInterface(eq(WIFI_IFNAME), anyInt(),
+                eq(Integer.toString(TRANSPORT_WIFI)));
+        verify(mMockNetd, times(1)).idletimerRemoveInterface(eq(MOBILE_IFNAME), anyInt(),
+                eq(Integer.toString(TRANSPORT_CELLULAR)));
 
         // Disconnect cell
-        reset(mNetworkManagementService);
         reset(mMockNetd);
         mCellNetworkAgent.disconnect();
         networkCallback.expectCallback(CallbackEntry.LOST, mCellNetworkAgent);
@@ -8250,17 +8255,18 @@
         // sent as network being switched. Ensure rule removal for cell will not be triggered
         // unexpectedly before network being removed.
         waitForIdle();
-        verify(mNetworkManagementService, times(0)).removeIdleTimer(eq(MOBILE_IFNAME));
+        verify(mMockNetd, times(0)).idletimerRemoveInterface(eq(MOBILE_IFNAME), anyInt(),
+                eq(Integer.toString(TRANSPORT_CELLULAR)));
         verify(mMockNetd, times(1)).networkDestroy(eq(mCellNetworkAgent.getNetwork().netId));
         verify(mMockDnsResolver, times(1))
                 .destroyNetworkCache(eq(mCellNetworkAgent.getNetwork().netId));
 
         // Disconnect wifi
         ExpectedBroadcast b = expectConnectivityAction(TYPE_WIFI, DetailedState.DISCONNECTED);
-        reset(mNetworkManagementService);
         mWiFiNetworkAgent.disconnect();
         b.expectBroadcast();
-        verify(mNetworkManagementService, times(1)).removeIdleTimer(eq(WIFI_IFNAME));
+        verify(mMockNetd, times(1)).idletimerRemoveInterface(eq(WIFI_IFNAME), anyInt(),
+                eq(Integer.toString(TRANSPORT_WIFI)));
 
         // Clean up
         mCm.unregisterNetworkCallback(networkCallback);