Change NetworkTimeUpdateServiceImpl behavior

This change moves some logic associated with time detection out of the
NetworkTimeUpdateServiceImpl and moves it to the TimeDetectorStrategy
called by the TimeDetectorService.

The TimeDetectorStategy implementation now decides when to use an
NTP-derived time instead. The logic implemented here is effectively the
same as it was: NITZ takes priority over NTP until the latest NITZ
signal becomes "too old".

The motivating reasons for the change:
1) The "what signal is used when several are available?" logic should be
in one place: the TimeDetectoryStrategy not scattered around the
platform. Centralizing will enable different strategies and time sources
to be introduced over time.

2) It will allow removal of the ACTION_NETWORK_SET_TIME intent in a
follow-up commit; this intent was used to coordinate the NTP vs NITZ
logic should no longer be required.

The "bonus" effect of this change is that NetworkTimeUpdateServiceImpl
becomes more general: It can now be the authority for the NTP time on a
device independently of how the system clock should be set. e.g. it
could be used in future to back the
AlarmManager.currentNetworkTimeMillis() API call.  Anything that needs a
"what is the best time according to NTP?" answer could use this service.

Note: The NetworkTimeUpdateServiceImpl still observes the AUTO_TIME
setting and will perform an NTP lookup "on demand" (if required) when
the user enables the setting. This should be a temporary state and
likely to be removed in future; knowledge of AUTO_TIME shouldn't be
required for the NTP info to be correct and if
NetworkTimeUpdateServiceImpl is doing the right thing.

Bug: 140712361
Test: atest com.android.server.timedetector
Test: atest android.app.timedetector
Change-Id: I4b2936a42c552c4dd4cb55010306bb81bca0c712

14 files changed, 741 insertions, 199 deletions

diff --git a/core/java/android/app/timedetector/ITimeDetectorService.aidl b/core/java/android/app/timedetector/ITimeDetectorService.aidl
index 9877fc741b7b..de8f4700de2d 100644
--- a/core/java/android/app/timedetector/ITimeDetectorService.aidl
+++ b/core/java/android/app/timedetector/ITimeDetectorService.aidl
@@ -17,6 +17,7 @@
 package android.app.timedetector;
 
 import android.app.timedetector.ManualTimeSuggestion;
+import android.app.timedetector.NetworkTimeSuggestion;
 import android.app.timedetector.PhoneTimeSuggestion;
 
 /**
@@ -35,4 +36,5 @@ import android.app.timedetector.PhoneTimeSuggestion;
 interface ITimeDetectorService {
   void suggestPhoneTime(in PhoneTimeSuggestion timeSuggestion);
   void suggestManualTime(in ManualTimeSuggestion timeSuggestion);
+  void suggestNetworkTime(in NetworkTimeSuggestion timeSuggestion);
 }
diff --git a/core/java/android/app/timedetector/NetworkTimeSuggestion.aidl b/core/java/android/app/timedetector/NetworkTimeSuggestion.aidl
new file mode 100644
index 000000000000..731c907f6837
--- /dev/null
+++ b/core/java/android/app/timedetector/NetworkTimeSuggestion.aidl
@@ -0,0 +1,19 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.app.timedetector;
+
+parcelable NetworkTimeSuggestion;
diff --git a/core/java/android/app/timedetector/NetworkTimeSuggestion.java b/core/java/android/app/timedetector/NetworkTimeSuggestion.java
new file mode 100644
index 000000000000..4c55ba12d881
--- /dev/null
+++ b/core/java/android/app/timedetector/NetworkTimeSuggestion.java
@@ -0,0 +1,129 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.app.timedetector;
+
+import android.annotation.NonNull;
+import android.annotation.Nullable;
+import android.os.Parcel;
+import android.os.Parcelable;
+import android.util.TimestampedValue;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.Objects;
+
+/**
+ * A time signal from a network time source like NTP. The value consists of the number of
+ * milliseconds elapsed since 1/1/1970 00:00:00 UTC and the time according to the elapsed realtime
+ * clock when that number was established. The elapsed realtime clock is considered accurate but
+ * volatile, so time signals must not be persisted across device resets.
+ *
+ * @hide
+ */
+public final class NetworkTimeSuggestion implements Parcelable {
+
+    public static final @NonNull Creator<NetworkTimeSuggestion> CREATOR =
+            new Creator<NetworkTimeSuggestion>() {
+                public NetworkTimeSuggestion createFromParcel(Parcel in) {
+                    return NetworkTimeSuggestion.createFromParcel(in);
+                }
+
+                public NetworkTimeSuggestion[] newArray(int size) {
+                    return new NetworkTimeSuggestion[size];
+                }
+            };
+
+    @NonNull
+    private final TimestampedValue<Long> mUtcTime;
+    @Nullable
+    private ArrayList<String> mDebugInfo;
+
+    public NetworkTimeSuggestion(@NonNull TimestampedValue<Long> utcTime) {
+        mUtcTime = Objects.requireNonNull(utcTime);
+        Objects.requireNonNull(utcTime.getValue());
+    }
+
+    private static NetworkTimeSuggestion createFromParcel(Parcel in) {
+        TimestampedValue<Long> utcTime = in.readParcelable(null /* classLoader */);
+        NetworkTimeSuggestion suggestion = new NetworkTimeSuggestion(utcTime);
+        @SuppressWarnings("unchecked")
+        ArrayList<String> debugInfo = (ArrayList<String>) in.readArrayList(null /* classLoader */);
+        suggestion.mDebugInfo = debugInfo;
+        return suggestion;
+    }
+
+    @Override
+    public int describeContents() {
+        return 0;
+    }
+
+    @Override
+    public void writeToParcel(@NonNull Parcel dest, int flags) {
+        dest.writeParcelable(mUtcTime, 0);
+        dest.writeList(mDebugInfo);
+    }
+
+    @NonNull
+    public TimestampedValue<Long> getUtcTime() {
+        return mUtcTime;
+    }
+
+    @NonNull
+    public List<String> getDebugInfo() {
+        return mDebugInfo == null
+                ? Collections.emptyList() : Collections.unmodifiableList(mDebugInfo);
+    }
+
+    /**
+     * Associates information with the instance that can be useful for debugging / logging. The
+     * information is present in {@link #toString()} but is not considered for
+     * {@link #equals(Object)} and {@link #hashCode()}.
+     */
+    public void addDebugInfo(String... debugInfos) {
+        if (mDebugInfo == null) {
+            mDebugInfo = new ArrayList<>();
+        }
+        mDebugInfo.addAll(Arrays.asList(debugInfos));
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        NetworkTimeSuggestion that = (NetworkTimeSuggestion) o;
+        return Objects.equals(mUtcTime, that.mUtcTime);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(mUtcTime);
+    }
+
+    @Override
+    public String toString() {
+        return "NetworkTimeSuggestion{"
+                + "mUtcTime=" + mUtcTime
+                + ", mDebugInfo=" + mDebugInfo
+                + '}';
+    }
+}
diff --git a/core/java/android/app/timedetector/TimeDetector.java b/core/java/android/app/timedetector/TimeDetector.java
index 48d5cd2d65a5..4976466e1c04 100644
--- a/core/java/android/app/timedetector/TimeDetector.java
+++ b/core/java/android/app/timedetector/TimeDetector.java
@@ -85,4 +85,19 @@ public class TimeDetector {
         manualTimeSuggestion.addDebugInfo(why);
         return manualTimeSuggestion;
     }
+
+    /**
+     * Suggests the time according to a network time source like NTP.
+     */
+    @RequiresPermission(android.Manifest.permission.SET_TIME)
+    public void suggestNetworkTime(NetworkTimeSuggestion timeSuggestion) {
+        if (DEBUG) {
+            Log.d(TAG, "suggestNetworkTime called: " + timeSuggestion);
+        }
+        try {
+            mITimeDetectorService.suggestNetworkTime(timeSuggestion);
+        } catch (RemoteException e) {
+            throw e.rethrowFromSystemServer();
+        }
+    }
 }
diff --git a/core/java/android/util/NtpTrustedTime.java b/core/java/android/util/NtpTrustedTime.java
index da566c934ef7..524078678460 100644
--- a/core/java/android/util/NtpTrustedTime.java
+++ b/core/java/android/util/NtpTrustedTime.java
@@ -175,4 +175,22 @@ public class NtpTrustedTime implements TrustedTime {
     public long getCachedNtpTimeReference() {
         return mCachedNtpElapsedRealtime;
     }
+
+    /**
+     * Returns the combination of {@link #getCachedNtpTime()} and {@link
+     * #getCachedNtpTimeReference()} as a {@link TimestampedValue}. This method is useful when
+     * passing the time to another component that will adjust for elapsed time.
+     *
+     * @throws IllegalStateException if there is no cached value
+     */
+    @UnsupportedAppUsage
+    public TimestampedValue<Long> getCachedNtpTimeSignal() {
+        if (!mHasCache) {
+            throw new IllegalStateException("Missing authoritative time source");
+        }
+        if (LOGD) Log.d(TAG, "currentTimeMillis() cache hit");
+
+        return new TimestampedValue<>(mCachedNtpElapsedRealtime, mCachedNtpTime);
+    }
+
 }
diff --git a/core/res/res/values/config.xml b/core/res/res/values/config.xml
index b516c41f3fb6..3f6bb225c5a5 100644
--- a/core/res/res/values/config.xml
+++ b/core/res/res/values/config.xml
@@ -2266,9 +2266,6 @@
     <!-- Number of times to try again with the shorter interval, before backing
          off until the normal polling interval. A value < 0 indicates infinite. -->
     <integer name="config_ntpRetry">3</integer>
-    <!-- If the time difference is greater than this threshold in milliseconds,
-         then update the time. -->
-    <integer name="config_ntpThreshold">5000</integer>
     <!-- Timeout to wait for NTP server response in milliseconds. -->
     <integer name="config_ntpTimeout">5000</integer>
 
diff --git a/core/res/res/values/symbols.xml b/core/res/res/values/symbols.xml
index 5cd5c8c930fd..5ac1093115c2 100644
--- a/core/res/res/values/symbols.xml
+++ b/core/res/res/values/symbols.xml
@@ -489,7 +489,6 @@
   <java-symbol type="integer" name="config_ntpPollingInterval" />
   <java-symbol type="integer" name="config_ntpPollingIntervalShorter" />
   <java-symbol type="integer" name="config_ntpRetry" />
-  <java-symbol type="integer" name="config_ntpThreshold" />
   <java-symbol type="integer" name="config_ntpTimeout" />
   <java-symbol type="integer" name="config_shortPressOnPowerBehavior" />
   <java-symbol type="integer" name="config_toastDefaultGravity" />
diff --git a/core/tests/coretests/src/android/app/timedetector/NetworkTimeSuggestionTest.java b/core/tests/coretests/src/android/app/timedetector/NetworkTimeSuggestionTest.java
new file mode 100644
index 000000000000..9b3d0c9eaff6
--- /dev/null
+++ b/core/tests/coretests/src/android/app/timedetector/NetworkTimeSuggestionTest.java
@@ -0,0 +1,66 @@
+/*
+ * Copyright 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.app.timedetector;
+
+import static android.app.timezonedetector.ParcelableTestSupport.assertRoundTripParcelable;
+import static android.app.timezonedetector.ParcelableTestSupport.roundTripParcelable;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+
+import android.util.TimestampedValue;
+
+import org.junit.Test;
+
+public class NetworkTimeSuggestionTest {
+
+    private static final TimestampedValue<Long> ARBITRARY_TIME =
+            new TimestampedValue<>(1111L, 2222L);
+
+    @Test
+    public void testEquals() {
+        NetworkTimeSuggestion one = new NetworkTimeSuggestion(ARBITRARY_TIME);
+        assertEquals(one, one);
+
+        NetworkTimeSuggestion two = new NetworkTimeSuggestion(ARBITRARY_TIME);
+        assertEquals(one, two);
+        assertEquals(two, one);
+
+        TimestampedValue<Long> differentTime = new TimestampedValue<>(
+                ARBITRARY_TIME.getReferenceTimeMillis() + 1,
+                ARBITRARY_TIME.getValue());
+        NetworkTimeSuggestion three = new NetworkTimeSuggestion(differentTime);
+        assertNotEquals(one, three);
+        assertNotEquals(three, one);
+
+        // DebugInfo must not be considered in equals().
+        one.addDebugInfo("Debug info 1");
+        two.addDebugInfo("Debug info 2");
+        assertEquals(one, two);
+    }
+
+    @Test
+    public void testParcelable() {
+        NetworkTimeSuggestion suggestion = new NetworkTimeSuggestion(ARBITRARY_TIME);
+        assertRoundTripParcelable(suggestion);
+
+        // DebugInfo should also be stored (but is not checked by equals()
+        suggestion.addDebugInfo("This is debug info");
+        NetworkTimeSuggestion rtSuggestion = roundTripParcelable(suggestion);
+        assertEquals(suggestion.getDebugInfo(), rtSuggestion.getDebugInfo());
+    }
+}
diff --git a/services/core/java/com/android/server/NetworkTimeUpdateServiceImpl.java b/services/core/java/com/android/server/NetworkTimeUpdateServiceImpl.java
index 39be311e902d..cfe56052118f 100644
--- a/services/core/java/com/android/server/NetworkTimeUpdateServiceImpl.java
+++ b/services/core/java/com/android/server/NetworkTimeUpdateServiceImpl.java
@@ -18,6 +18,8 @@ package com.android.server;
 
 import android.app.AlarmManager;
 import android.app.PendingIntent;
+import android.app.timedetector.NetworkTimeSuggestion;
+import android.app.timedetector.TimeDetector;
 import android.content.BroadcastReceiver;
 import android.content.ContentResolver;
 import android.content.Context;
@@ -35,10 +37,10 @@ import android.os.Message;
 import android.os.PowerManager;
 import android.os.SystemClock;
 import android.provider.Settings;
-import android.telephony.TelephonyManager;
 import android.util.Log;
 import android.util.NtpTrustedTime;
 import android.util.TimeUtils;
+import android.util.TimestampedValue;
 
 import com.android.internal.util.DumpUtils;
 
@@ -46,21 +48,19 @@ import java.io.FileDescriptor;
 import java.io.PrintWriter;
 
 /**
- * Monitors the network time and updates the system time if it is out of sync
- * and there hasn't been any NITZ update from the carrier recently.
- * If looking up the network time fails for some reason, it tries a few times with a short
- * interval and then resets to checking on longer intervals.
- * <p>
- * If the user enables AUTO_TIME, it will check immediately for the network time, if NITZ wasn't
- * available.
- * </p>
+ * Monitors the network time. If looking up the network time fails for some reason, it tries a few
+ * times with a short interval and then resets to checking on longer intervals.
+ *
+ * <p>When available, the time is always suggested to the {@link
+ * com.android.server.timedetector.TimeDetectorService} where it may be used to set the device
+ * system clock, depending on user settings and what other signals are available.
  */
 public class NetworkTimeUpdateServiceImpl extends Binder implements NetworkTimeUpdateService {
 
     private static final String TAG = "NetworkTimeUpdateService";
     private static final boolean DBG = false;
 
-    private static final int EVENT_AUTO_TIME_CHANGED = 1;
+    private static final int EVENT_AUTO_TIME_ENABLED = 1;
     private static final int EVENT_POLL_NETWORK_TIME = 2;
     private static final int EVENT_NETWORK_CHANGED = 3;
 
@@ -69,20 +69,19 @@ public class NetworkTimeUpdateServiceImpl extends Binder implements NetworkTimeU
 
     private static final int POLL_REQUEST = 0;
 
-    private static final long NOT_SET = -1;
-    private long mNitzTimeSetTime = NOT_SET;
     private Network mDefaultNetwork = null;
 
     private final Context mContext;
     private final NtpTrustedTime mTime;
     private final AlarmManager mAlarmManager;
+    private final TimeDetector mTimeDetector;
     private final ConnectivityManager mCM;
     private final PendingIntent mPendingPollIntent;
     private final PowerManager.WakeLock mWakeLock;
 
     // NTP lookup is done on this thread and handler
     private Handler mHandler;
-    private SettingsObserver mSettingsObserver;
+    private AutoTimeSettingObserver mAutoTimeSettingObserver;
     private NetworkTimeUpdateCallback mNetworkTimeUpdateCallback;
 
     // Normal polling frequency
@@ -91,8 +90,6 @@ public class NetworkTimeUpdateServiceImpl extends Binder implements NetworkTimeU
     private final long mPollingIntervalShorterMs;
     // Number of times to try again
     private final int mTryAgainTimesMax;
-    // If the time difference is greater than this threshold, then update the time.
-    private final int mTimeErrorThresholdMs;
     // Keeps track of how many quick attempts were made to fetch NTP time.
     // During bootup, the network may not have been up yet, or it's taking time for the
     // connection to happen.
@@ -102,6 +99,7 @@ public class NetworkTimeUpdateServiceImpl extends Binder implements NetworkTimeU
         mContext = context;
         mTime = NtpTrustedTime.getInstance(context);
         mAlarmManager = mContext.getSystemService(AlarmManager.class);
+        mTimeDetector = mContext.getSystemService(TimeDetector.class);
         mCM = mContext.getSystemService(ConnectivityManager.class);
 
         Intent pollIntent = new Intent(ACTION_POLL, null);
@@ -113,8 +111,6 @@ public class NetworkTimeUpdateServiceImpl extends Binder implements NetworkTimeU
                 com.android.internal.R.integer.config_ntpPollingIntervalShorter);
         mTryAgainTimesMax = mContext.getResources().getInteger(
                 com.android.internal.R.integer.config_ntpRetry);
-        mTimeErrorThresholdMs = mContext.getResources().getInteger(
-                com.android.internal.R.integer.config_ntpThreshold);
 
         mWakeLock = context.getSystemService(PowerManager.class).newWakeLock(
                 PowerManager.PARTIAL_WAKE_LOCK, TAG);
@@ -122,7 +118,6 @@ public class NetworkTimeUpdateServiceImpl extends Binder implements NetworkTimeU
 
     @Override
     public void systemRunning() {
-        registerForTelephonyIntents();
         registerForAlarms();
 
         HandlerThread thread = new HandlerThread(TAG);
@@ -131,14 +126,9 @@ public class NetworkTimeUpdateServiceImpl extends Binder implements NetworkTimeU
         mNetworkTimeUpdateCallback = new NetworkTimeUpdateCallback();
         mCM.registerDefaultNetworkCallback(mNetworkTimeUpdateCallback, mHandler);
 
-        mSettingsObserver = new SettingsObserver(mHandler, EVENT_AUTO_TIME_CHANGED);
-        mSettingsObserver.observe(mContext);
-    }
-
-    private void registerForTelephonyIntents() {
-        IntentFilter intentFilter = new IntentFilter();
-        intentFilter.addAction(TelephonyManager.ACTION_NETWORK_SET_TIME);
-        mContext.registerReceiver(mNitzReceiver, intentFilter);
+        mAutoTimeSettingObserver = new AutoTimeSettingObserver(mContext, mHandler,
+                EVENT_AUTO_TIME_ENABLED);
+        mAutoTimeSettingObserver.observe();
     }
 
     private void registerForAlarms() {
@@ -152,8 +142,7 @@ public class NetworkTimeUpdateServiceImpl extends Binder implements NetworkTimeU
     }
 
     private void onPollNetworkTime(int event) {
-        // If Automatic time is not set, don't bother. Similarly, if we don't
-        // have any default network, don't bother.
+        // If we don't have any default network, don't bother.
         if (mDefaultNetwork == null) return;
         mWakeLock.acquire();
         try {
@@ -173,10 +162,12 @@ public class NetworkTimeUpdateServiceImpl extends Binder implements NetworkTimeU
         if (mTime.getCacheAge() < mPollingIntervalMs) {
             // Obtained fresh fix; schedule next normal update
             resetAlarm(mPollingIntervalMs);
-            if (isAutomaticTimeRequested()) {
-                updateSystemClock(event);
-            }
 
+            // Suggest the time to the time detector. It may choose use it to set the system clock.
+            TimestampedValue<Long> timeSignal = mTime.getCachedNtpTimeSignal();
+            NetworkTimeSuggestion timeSuggestion = new NetworkTimeSuggestion(timeSignal);
+            timeSuggestion.addDebugInfo("Origin: NetworkTimeUpdateServiceImpl. event=" + event);
+            mTimeDetector.suggestNetworkTime(timeSuggestion);
         } else {
             // No fresh fix; schedule retry
             mTryAgainCounter++;
@@ -190,36 +181,6 @@ public class NetworkTimeUpdateServiceImpl extends Binder implements NetworkTimeU
         }
     }
 
-    private long getNitzAge() {
-        if (mNitzTimeSetTime == NOT_SET) {
-            return Long.MAX_VALUE;
-        } else {
-            return SystemClock.elapsedRealtime() - mNitzTimeSetTime;
-        }
-    }
-
-    /**
-     * Consider updating system clock based on current NTP fix, if requested by
-     * user, significant enough delta, and we don't have a recent NITZ.
-     */
-    private void updateSystemClock(int event) {
-        final boolean forceUpdate = (event == EVENT_AUTO_TIME_CHANGED);
-        if (!forceUpdate) {
-            if (getNitzAge() < mPollingIntervalMs) {
-                if (DBG) Log.d(TAG, "Ignoring NTP update due to recent NITZ");
-                return;
-            }
-
-            final long skew = Math.abs(mTime.currentTimeMillis() - System.currentTimeMillis());
-            if (skew < mTimeErrorThresholdMs) {
-                if (DBG) Log.d(TAG, "Ignoring NTP update due to low skew");
-                return;
-            }
-        }
-
-        SystemClock.setCurrentTimeMillis(mTime.currentTimeMillis());
-    }
-
     /**
      * Cancel old alarm and starts a new one for the specified interval.
      *
@@ -232,27 +193,6 @@ public class NetworkTimeUpdateServiceImpl extends Binder implements NetworkTimeU
         mAlarmManager.set(AlarmManager.ELAPSED_REALTIME, next, mPendingPollIntent);
     }
 
-    /**
-     * Checks if the user prefers to automatically set the time.
-     */
-    private boolean isAutomaticTimeRequested() {
-        return Settings.Global.getInt(
-                mContext.getContentResolver(), Settings.Global.AUTO_TIME, 0) != 0;
-    }
-
-    /** Receiver for Nitz time events */
-    private BroadcastReceiver mNitzReceiver = new BroadcastReceiver() {
-
-        @Override
-        public void onReceive(Context context, Intent intent) {
-            String action = intent.getAction();
-            if (DBG) Log.d(TAG, "Received " + action);
-            if (TelephonyManager.ACTION_NETWORK_SET_TIME.equals(action)) {
-                mNitzTimeSetTime = SystemClock.elapsedRealtime();
-            }
-        }
-    };
-
     /** Handler to do the network accesses on */
     private class MyHandler extends Handler {
 
@@ -263,7 +203,7 @@ public class NetworkTimeUpdateServiceImpl extends Binder implements NetworkTimeU
         @Override
         public void handleMessage(Message msg) {
             switch (msg.what) {
-                case EVENT_AUTO_TIME_CHANGED:
+                case EVENT_AUTO_TIME_ENABLED:
                 case EVENT_POLL_NETWORK_TIME:
                 case EVENT_NETWORK_CHANGED:
                     onPollNetworkTime(msg.what);
@@ -287,27 +227,42 @@ public class NetworkTimeUpdateServiceImpl extends Binder implements NetworkTimeU
         }
     }
 
-    /** Observer to watch for changes to the AUTO_TIME setting */
-    private static class SettingsObserver extends ContentObserver {
+    /**
+     * Observer to watch for changes to the AUTO_TIME setting. It only triggers when the setting
+     * is enabled.
+     */
+    private static class AutoTimeSettingObserver extends ContentObserver {
 
-        private int mMsg;
-        private Handler mHandler;
+        private final Context mContext;
+        private final int mMsg;
+        private final Handler mHandler;
 
-        SettingsObserver(Handler handler, int msg) {
+        AutoTimeSettingObserver(Context context, Handler handler, int msg) {
             super(handler);
+            mContext = context;
             mHandler = handler;
             mMsg = msg;
         }
 
-        void observe(Context context) {
-            ContentResolver resolver = context.getContentResolver();
+        void observe() {
+            ContentResolver resolver = mContext.getContentResolver();
             resolver.registerContentObserver(Settings.Global.getUriFor(Settings.Global.AUTO_TIME),
                     false, this);
         }
 
         @Override
         public void onChange(boolean selfChange) {
-            mHandler.obtainMessage(mMsg).sendToTarget();
+            if (isAutomaticTimeEnabled()) {
+                mHandler.obtainMessage(mMsg).sendToTarget();
+            }
+        }
+
+        /**
+         * Checks if the user prefers to automatically set the time.
+         */
+        private boolean isAutomaticTimeEnabled() {
+            ContentResolver resolver = mContext.getContentResolver();
+            return Settings.Global.getInt(resolver, Settings.Global.AUTO_TIME, 0) != 0;
         }
     }
 
@@ -319,8 +274,6 @@ public class NetworkTimeUpdateServiceImpl extends Binder implements NetworkTimeU
         pw.print("\nPollingIntervalShorterMs: ");
         TimeUtils.formatDuration(mPollingIntervalShorterMs, pw);
         pw.println("\nTryAgainTimesMax: " + mTryAgainTimesMax);
-        pw.print("TimeErrorThresholdMs: ");
-        TimeUtils.formatDuration(mTimeErrorThresholdMs, pw);
         pw.println("\nTryAgainCounter: " + mTryAgainCounter);
         pw.println("NTP cache age: " + mTime.getCacheAge());
         pw.println("NTP cache certainty: " + mTime.getCacheCertainty());
diff --git a/services/core/java/com/android/server/timedetector/TimeDetectorService.java b/services/core/java/com/android/server/timedetector/TimeDetectorService.java
index 172367a128cc..2bd4acb8e532 100644
--- a/services/core/java/com/android/server/timedetector/TimeDetectorService.java
+++ b/services/core/java/com/android/server/timedetector/TimeDetectorService.java
@@ -20,6 +20,7 @@ import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.app.timedetector.ITimeDetectorService;
 import android.app.timedetector.ManualTimeSuggestion;
+import android.app.timedetector.NetworkTimeSuggestion;
 import android.app.timedetector.PhoneTimeSuggestion;
 import android.content.ContentResolver;
 import android.content.Context;
@@ -105,6 +106,14 @@ public final class TimeDetectorService extends ITimeDetectorService.Stub {
         mHandler.post(() -> mTimeDetectorStrategy.suggestManualTime(timeSignal));
     }
 
+    @Override
+    public void suggestNetworkTime(@NonNull NetworkTimeSuggestion timeSignal) {
+        enforceSuggestNetworkTimePermission();
+        Objects.requireNonNull(timeSignal);
+
+        mHandler.post(() -> mTimeDetectorStrategy.suggestNetworkTime(timeSignal));
+    }
+
     @VisibleForTesting
     public void handleAutoTimeDetectionToggle() {
         mHandler.post(mTimeDetectorStrategy::handleAutoTimeDetectionChanged);
@@ -125,4 +134,10 @@ public final class TimeDetectorService extends ITimeDetectorService.Stub {
     private void enforceSuggestManualTimePermission() {
         mContext.enforceCallingOrSelfPermission(android.Manifest.permission.SET_TIME, "set time");
     }
+
+    private void enforceSuggestNetworkTimePermission() {
+        mContext.enforceCallingOrSelfPermission(
+                android.Manifest.permission.SET_TIME,
+                "set time");
+    }
 }
diff --git a/services/core/java/com/android/server/timedetector/TimeDetectorStrategy.java b/services/core/java/com/android/server/timedetector/TimeDetectorStrategy.java
index 0a6c2e776072..b4f4eca5f188 100644
--- a/services/core/java/com/android/server/timedetector/TimeDetectorStrategy.java
+++ b/services/core/java/com/android/server/timedetector/TimeDetectorStrategy.java
@@ -19,6 +19,7 @@ package com.android.server.timedetector;
 import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.app.timedetector.ManualTimeSuggestion;
+import android.app.timedetector.NetworkTimeSuggestion;
 import android.app.timedetector.PhoneTimeSuggestion;
 import android.content.Intent;
 import android.util.TimestampedValue;
@@ -86,6 +87,9 @@ public interface TimeDetectorStrategy {
     /** Process the suggested manually entered time. */
     void suggestManualTime(@NonNull ManualTimeSuggestion timeSuggestion);
 
+    /** Process the suggested time from network sources. */
+    void suggestNetworkTime(@NonNull NetworkTimeSuggestion timeSuggestion);
+
     /** Handle the auto-time setting being toggled on or off. */
     void handleAutoTimeDetectionChanged();
 
diff --git a/services/core/java/com/android/server/timedetector/TimeDetectorStrategyImpl.java b/services/core/java/com/android/server/timedetector/TimeDetectorStrategyImpl.java
index c50248d4b402..02656eaf5c6c 100644
--- a/services/core/java/com/android/server/timedetector/TimeDetectorStrategyImpl.java
+++ b/services/core/java/com/android/server/timedetector/TimeDetectorStrategyImpl.java
@@ -21,6 +21,7 @@ import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.app.AlarmManager;
 import android.app.timedetector.ManualTimeSuggestion;
+import android.app.timedetector.NetworkTimeSuggestion;
 import android.app.timedetector.PhoneTimeSuggestion;
 import android.content.Intent;
 import android.telephony.TelephonyManager;
@@ -32,6 +33,7 @@ import com.android.internal.annotations.GuardedBy;
 import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.util.IndentingPrintWriter;
 import com.android.server.timezonedetector.ArrayMapWithHistory;
+import com.android.server.timezonedetector.ReferenceWithHistory;
 
 import java.io.PrintWriter;
 import java.lang.annotation.Retention;
@@ -56,11 +58,11 @@ public final class TimeDetectorStrategyImpl implements TimeDetectorStrategy {
     /** Each bucket is this size. All buckets are equally sized. */
     @VisibleForTesting
     static final int PHONE_BUCKET_SIZE_MILLIS = 60 * 60 * 1000;
-    /** Phone suggestions older than this value are considered too old. */
+    /** Phone and network suggestions older than this value are considered too old to be used. */
     @VisibleForTesting
-    static final long PHONE_MAX_AGE_MILLIS = PHONE_BUCKET_COUNT * PHONE_BUCKET_SIZE_MILLIS;
+    static final long MAX_UTC_TIME_AGE_MILLIS = PHONE_BUCKET_COUNT * PHONE_BUCKET_SIZE_MILLIS;
 
-    @IntDef({ ORIGIN_PHONE, ORIGIN_MANUAL })
+    @IntDef({ ORIGIN_PHONE, ORIGIN_MANUAL, ORIGIN_NETWORK })
     @Retention(RetentionPolicy.SOURCE)
     public @interface Origin {}
 
@@ -72,6 +74,10 @@ public final class TimeDetectorStrategyImpl implements TimeDetectorStrategy {
     @Origin
     private static final int ORIGIN_MANUAL = 2;
 
+    /** Used when a time value originated from a network signal. */
+    @Origin
+    private static final int ORIGIN_NETWORK = 3;
+
     /**
      * CLOCK_PARANOIA: The maximum difference allowed between the expected system clock time and the
      * actual system clock time before a warning is logged. Used to help identify situations where
@@ -101,9 +107,13 @@ public final class TimeDetectorStrategyImpl implements TimeDetectorStrategy {
      * will have a small number of telephony devices and phoneIds are assumed to be stable.
      */
     @GuardedBy("this")
-    private ArrayMapWithHistory<Integer, PhoneTimeSuggestion> mSuggestionByPhoneId =
+    private final ArrayMapWithHistory<Integer, PhoneTimeSuggestion> mSuggestionByPhoneId =
             new ArrayMapWithHistory<>(KEEP_SUGGESTION_HISTORY_SIZE);
 
+    @GuardedBy("this")
+    private final ReferenceWithHistory<NetworkTimeSuggestion> mLastNetworkSuggestion =
+            new ReferenceWithHistory<>(KEEP_SUGGESTION_HISTORY_SIZE);
+
     @Override
     public void initialize(@NonNull Callback callback) {
         mCallback = callback;
@@ -122,6 +132,19 @@ public final class TimeDetectorStrategyImpl implements TimeDetectorStrategy {
     }
 
     @Override
+    public synchronized void suggestNetworkTime(@NonNull NetworkTimeSuggestion timeSuggestion) {
+        if (!validateSuggestionTime(timeSuggestion.getUtcTime(), timeSuggestion)) {
+            return;
+        }
+        mLastNetworkSuggestion.set(timeSuggestion);
+
+        // Now perform auto time detection. The new suggestion may be used to modify the system
+        // clock.
+        String reason = "New network time suggested. timeSuggestion=" + timeSuggestion;
+        doAutoTimeDetection(reason);
+    }
+
+    @Override
     public synchronized void suggestPhoneTime(@NonNull PhoneTimeSuggestion timeSuggestion) {
         // Empty time suggestion means that telephony network connectivity has been lost.
         // The passage of time is relentless, and we don't expect our users to use a time machine,
@@ -167,6 +190,12 @@ public final class TimeDetectorStrategyImpl implements TimeDetectorStrategy {
         ipw.increaseIndent(); // level 1
 
         ipw.println("mLastAutoSystemClockTimeSet=" + mLastAutoSystemClockTimeSet);
+        ipw.println("mCallback.isAutoTimeDetectionEnabled()="
+                + mCallback.isAutoTimeDetectionEnabled());
+        ipw.println("mCallback.elapsedRealtimeMillis()=" + mCallback.elapsedRealtimeMillis());
+        ipw.println("mCallback.systemClockMillis()=" + mCallback.systemClockMillis());
+        ipw.println("mCallback.systemClockUpdateThresholdMillis()="
+                + mCallback.systemClockUpdateThresholdMillis());
 
         ipw.println("Time change log:");
         ipw.increaseIndent(); // level 2
@@ -178,6 +207,11 @@ public final class TimeDetectorStrategyImpl implements TimeDetectorStrategy {
         mSuggestionByPhoneId.dump(ipw);
         ipw.decreaseIndent(); // level 2
 
+        ipw.println("Network suggestion history:");
+        ipw.increaseIndent(); // level 2
+        mLastNetworkSuggestion.dump(ipw);
+        ipw.decreaseIndent(); // level 2
+
         ipw.decreaseIndent(); // level 1
         ipw.flush();
     }
@@ -247,23 +281,34 @@ public final class TimeDetectorStrategyImpl implements TimeDetectorStrategy {
             return;
         }
 
+        // Android devices currently prioritize any telephony over network signals. There are
+        // carrier compliance tests that would need to be changed before we could ignore NITZ or
+        // prefer NTP generally. This check is cheap on devices without phone hardware.
         PhoneTimeSuggestion bestPhoneSuggestion = findBestPhoneSuggestion();
+        if (bestPhoneSuggestion != null) {
+            final TimestampedValue<Long> newUtcTime = bestPhoneSuggestion.getUtcTime();
+            String cause = "Found good phone suggestion."
+                    + ", bestPhoneSuggestion=" + bestPhoneSuggestion
+                    + ", detectionReason=" + detectionReason;
+            setSystemClockIfRequired(ORIGIN_PHONE, newUtcTime, cause);
+            return;
+        }
 
-        // Work out what to do with the best suggestion.
-        if (bestPhoneSuggestion == null) {
-            // There is no good phone suggestion.
-            if (DBG) {
-                Slog.d(LOG_TAG, "Could not determine time: No best phone suggestion."
-                        + " detectionReason=" + detectionReason);
-            }
+        // There is no good phone suggestion, try network.
+        NetworkTimeSuggestion networkSuggestion = findLatestValidNetworkSuggestion();
+        if (networkSuggestion != null) {
+            final TimestampedValue<Long> newUtcTime = networkSuggestion.getUtcTime();
+            String cause = "Found good network suggestion."
+                    + ", networkSuggestion=" + networkSuggestion
+                    + ", detectionReason=" + detectionReason;
+            setSystemClockIfRequired(ORIGIN_NETWORK, newUtcTime, cause);
             return;
         }
 
-        final TimestampedValue<Long> newUtcTime = bestPhoneSuggestion.getUtcTime();
-        String cause = "Found good suggestion."
-                + ", bestPhoneSuggestion=" + bestPhoneSuggestion
-                + ", detectionReason=" + detectionReason;
-        setSystemClockIfRequired(ORIGIN_PHONE, newUtcTime, cause);
+        if (DBG) {
+            Slog.d(LOG_TAG, "Could not determine time: No best phone or network suggestion."
+                    + " detectionReason=" + detectionReason);
+        }
     }
 
     @GuardedBy("this")
@@ -342,37 +387,50 @@ public final class TimeDetectorStrategyImpl implements TimeDetectorStrategy {
 
     private static int scorePhoneSuggestion(
             long elapsedRealtimeMillis, @NonNull PhoneTimeSuggestion timeSuggestion) {
-        // The score is based on the age since receipt. Suggestions are bucketed so two
-        // suggestions in the same bucket from different phoneIds are scored the same.
+
+        // Validate first.
         TimestampedValue<Long> utcTime = timeSuggestion.getUtcTime();
-        long referenceTimeMillis = utcTime.getReferenceTimeMillis();
-        if (referenceTimeMillis > elapsedRealtimeMillis) {
-            // Future times are ignored. They imply the reference time was wrong, or the elapsed
-            // realtime clock has gone backwards, neither of which are supportable situations.
-            Slog.w(LOG_TAG, "Existing suggestion found to be in the future. "
+        if (!validateSuggestionUtcTime(elapsedRealtimeMillis, utcTime)) {
+            Slog.w(LOG_TAG, "Existing suggestion found to be invalid "
                     + " elapsedRealtimeMillis=" + elapsedRealtimeMillis
                     + ", timeSuggestion=" + timeSuggestion);
             return PHONE_INVALID_SCORE;
         }
 
-        long ageMillis = elapsedRealtimeMillis - referenceTimeMillis;
+        // The score is based on the age since receipt. Suggestions are bucketed so two
+        // suggestions in the same bucket from different phoneIds are scored the same.
+        long ageMillis = elapsedRealtimeMillis - utcTime.getReferenceTimeMillis();
 
-        // Any suggestion > MAX_AGE_MILLIS is treated as too old. Although time is relentless and
-        // predictable, the accuracy of the reference time clock may be poor over long periods which
-        // would lead to errors creeping in. Also, in edge cases where a bad suggestion has been
-        // made and never replaced, it could also mean that the time detection code remains
-        // opinionated using a bad invalid suggestion. This caps that edge case at MAX_AGE_MILLIS.
-        if (ageMillis > PHONE_MAX_AGE_MILLIS) {
+        // Turn the age into a discrete value: 0 <= bucketIndex < PHONE_BUCKET_COUNT.
+        int bucketIndex = (int) (ageMillis / PHONE_BUCKET_SIZE_MILLIS);
+        if (bucketIndex >= PHONE_BUCKET_COUNT) {
             return PHONE_INVALID_SCORE;
         }
 
-        // Turn the age into a discrete value: 0 <= bucketIndex < MAX_AGE_HOURS.
-        int bucketIndex = (int) (ageMillis / PHONE_BUCKET_SIZE_MILLIS);
-
         // We want the lowest bucket index to have the highest score. 0 > score >= BUCKET_COUNT.
         return PHONE_BUCKET_COUNT - bucketIndex;
     }
 
+    /** Returns the latest, valid, network suggestion. Returns {@code null} if there isn't one. */
+    @GuardedBy("this")
+    @Nullable
+    private NetworkTimeSuggestion findLatestValidNetworkSuggestion() {
+        NetworkTimeSuggestion networkSuggestion = mLastNetworkSuggestion.get();
+        if (networkSuggestion == null) {
+            // No network suggestions received. This is normal if there's no connectivity.
+            return null;
+        }
+
+        TimestampedValue<Long> utcTime = networkSuggestion.getUtcTime();
+        long elapsedRealTimeMillis = mCallback.elapsedRealtimeMillis();
+        if (!validateSuggestionUtcTime(elapsedRealTimeMillis, utcTime)) {
+            // The latest suggestion is not valid, usually due to its age.
+            return null;
+        }
+
+        return networkSuggestion;
+    }
+
     @GuardedBy("this")
     private void setSystemClockIfRequired(
             @Origin int origin, @NonNull TimestampedValue<Long> time, @NonNull String cause) {
@@ -409,7 +467,7 @@ public final class TimeDetectorStrategyImpl implements TimeDetectorStrategy {
     }
 
     private static boolean isOriginAutomatic(@Origin int origin) {
-        return origin == ORIGIN_PHONE;
+        return origin != ORIGIN_MANUAL;
     }
 
     @GuardedBy("this")
@@ -501,6 +559,16 @@ public final class TimeDetectorStrategyImpl implements TimeDetectorStrategy {
     }
 
     /**
+     * Returns the latest valid network suggestion. Not intended for general use: it is used during
+     * tests to check strategy behavior.
+     */
+    @VisibleForTesting
+    @Nullable
+    public NetworkTimeSuggestion findLatestValidNetworkSuggestionForTests() {
+        return findLatestValidNetworkSuggestion();
+    }
+
+    /**
      * A method used to inspect state during tests. Not intended for general use.
      */
     @VisibleForTesting
@@ -508,4 +576,32 @@ public final class TimeDetectorStrategyImpl implements TimeDetectorStrategy {
     public synchronized PhoneTimeSuggestion getLatestPhoneSuggestion(int phoneId) {
         return mSuggestionByPhoneId.get(phoneId);
     }
+
+    /**
+     * A method used to inspect state during tests. Not intended for general use.
+     */
+    @VisibleForTesting
+    @Nullable
+    public NetworkTimeSuggestion getLatestNetworkSuggestion() {
+        return mLastNetworkSuggestion.get();
+    }
+
+    private static boolean validateSuggestionUtcTime(
+            long elapsedRealtimeMillis, TimestampedValue<Long> utcTime) {
+        long referenceTimeMillis = utcTime.getReferenceTimeMillis();
+        if (referenceTimeMillis > elapsedRealtimeMillis) {
+            // Future reference times are ignored. They imply the reference time was wrong, or the
+            // elapsed realtime clock used to derive it has gone backwards, neither of which are
+            // supportable situations.
+            return false;
+        }
+
+        // Any suggestion > MAX_AGE_MILLIS is treated as too old. Although time is relentless and
+        // predictable, the accuracy of the reference time clock may be poor over long periods which
+        // would lead to errors creeping in. Also, in edge cases where a bad suggestion has been
+        // made and never replaced, it could also mean that the time detection code remains
+        // opinionated using a bad invalid suggestion. This caps that edge case at MAX_AGE_MILLIS.
+        long ageMillis = elapsedRealtimeMillis - referenceTimeMillis;
+        return ageMillis <= MAX_UTC_TIME_AGE_MILLIS;
+    }
 }
diff --git a/services/tests/servicestests/src/com/android/server/timedetector/TimeDetectorServiceTest.java b/services/tests/servicestests/src/com/android/server/timedetector/TimeDetectorServiceTest.java
index 72a7f508772b..624053f5b9c3 100644
--- a/services/tests/servicestests/src/com/android/server/timedetector/TimeDetectorServiceTest.java
+++ b/services/tests/servicestests/src/com/android/server/timedetector/TimeDetectorServiceTest.java
@@ -18,15 +18,18 @@ package com.android.server.timedetector;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.doNothing;
+import static org.mockito.Mockito.doThrow;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 import android.app.timedetector.ManualTimeSuggestion;
+import android.app.timedetector.NetworkTimeSuggestion;
 import android.app.timedetector.PhoneTimeSuggestion;
 import android.content.Context;
 import android.content.pm.PackageManager;
@@ -109,6 +112,36 @@ public class TimeDetectorServiceTest {
         mStubbedTimeDetectorStrategy.verifySuggestManualTimeCalled(manualTimeSuggestion);
     }
 
+    @Test(expected = SecurityException.class)
+    public void testSuggestNetworkTime_withoutPermission() {
+        doThrow(new SecurityException("Mock"))
+                .when(mMockContext).enforceCallingOrSelfPermission(anyString(), any());
+        NetworkTimeSuggestion NetworkTimeSuggestion = createNetworkTimeSuggestion();
+
+        try {
+            mTimeDetectorService.suggestNetworkTime(NetworkTimeSuggestion);
+            fail();
+        } finally {
+            verify(mMockContext).enforceCallingOrSelfPermission(
+                    eq(android.Manifest.permission.SET_TIME), anyString());
+        }
+    }
+
+    @Test
+    public void testSuggestNetworkTime() throws Exception {
+        doNothing().when(mMockContext).enforceCallingOrSelfPermission(anyString(), any());
+
+        NetworkTimeSuggestion NetworkTimeSuggestion = createNetworkTimeSuggestion();
+        mTimeDetectorService.suggestNetworkTime(NetworkTimeSuggestion);
+        mTestHandler.assertTotalMessagesEnqueued(1);
+
+        verify(mMockContext).enforceCallingOrSelfPermission(
+                eq(android.Manifest.permission.SET_TIME), anyString());
+
+        mTestHandler.waitForEmptyQueue();
+        mStubbedTimeDetectorStrategy.verifySuggestNetworkTimeCalled(NetworkTimeSuggestion);
+    }
+
     @Test
     public void testDump() {
         when(mMockContext.checkCallingOrSelfPermission(android.Manifest.permission.DUMP))
@@ -146,11 +179,17 @@ public class TimeDetectorServiceTest {
         return new ManualTimeSuggestion(timeValue);
     }
 
+    private static NetworkTimeSuggestion createNetworkTimeSuggestion() {
+        TimestampedValue<Long> timeValue = new TimestampedValue<>(100L, 1_000_000L);
+        return new NetworkTimeSuggestion(timeValue);
+    }
+
     private static class StubbedTimeDetectorStrategy implements TimeDetectorStrategy {
 
         // Call tracking.
         private PhoneTimeSuggestion mLastPhoneSuggestion;
         private ManualTimeSuggestion mLastManualSuggestion;
+        private NetworkTimeSuggestion mLastNetworkSuggestion;
         private boolean mLastAutoTimeDetectionToggleCalled;
         private boolean mDumpCalled;
 
@@ -171,6 +210,12 @@ public class TimeDetectorServiceTest {
         }
 
         @Override
+        public void suggestNetworkTime(NetworkTimeSuggestion timeSuggestion) {
+            resetCallTracking();
+            mLastNetworkSuggestion = timeSuggestion;
+        }
+
+        @Override
         public void handleAutoTimeDetectionChanged() {
             resetCallTracking();
             mLastAutoTimeDetectionToggleCalled = true;
@@ -185,6 +230,7 @@ public class TimeDetectorServiceTest {
         void resetCallTracking() {
             mLastPhoneSuggestion = null;
             mLastManualSuggestion = null;
+            mLastNetworkSuggestion = null;
             mLastAutoTimeDetectionToggleCalled = false;
             mDumpCalled = false;
         }
@@ -197,6 +243,10 @@ public class TimeDetectorServiceTest {
             assertEquals(expectedSuggestion, mLastManualSuggestion);
         }
 
+        public void verifySuggestNetworkTimeCalled(NetworkTimeSuggestion expectedSuggestion) {
+            assertEquals(expectedSuggestion, mLastNetworkSuggestion);
+        }
+
         void verifyHandleAutoTimeDetectionToggleCalled() {
             assertTrue(mLastAutoTimeDetectionToggleCalled);
         }
diff --git a/services/tests/servicestests/src/com/android/server/timedetector/TimeDetectorStrategyImplTest.java b/services/tests/servicestests/src/com/android/server/timedetector/TimeDetectorStrategyImplTest.java
index 1aa3d8fe654b..ca6fd08092df 100644
--- a/services/tests/servicestests/src/com/android/server/timedetector/TimeDetectorStrategyImplTest.java
+++ b/services/tests/servicestests/src/com/android/server/timedetector/TimeDetectorStrategyImplTest.java
@@ -24,6 +24,7 @@ import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
 import android.app.timedetector.ManualTimeSuggestion;
+import android.app.timedetector.NetworkTimeSuggestion;
 import android.app.timedetector.PhoneTimeSuggestion;
 import android.content.Intent;
 import android.icu.util.Calendar;
@@ -45,14 +46,16 @@ public class TimeDetectorStrategyImplTest {
     private static final TimestampedValue<Long> ARBITRARY_CLOCK_INITIALIZATION_INFO =
             new TimestampedValue<>(
                     123456789L /* realtimeClockMillis */,
-                    createUtcTime(1977, 1, 1, 12, 0, 0));
+                    createUtcTime(2008, 5, 23, 12, 0, 0));
 
+    /**
+     * An arbitrary time, very different from the {@link #ARBITRARY_CLOCK_INITIALIZATION_INFO}
+     * time. Can be used as the basis for time suggestions.
+     */
     private static final long ARBITRARY_TEST_TIME_MILLIS = createUtcTime(2018, 1, 1, 12, 0, 0);
 
     private static final int ARBITRARY_PHONE_ID = 123456;
 
-    private static final long ONE_DAY_MILLIS = Duration.ofDays(1).toMillis();
-
     private Script mScript;
 
     @Before
@@ -67,15 +70,16 @@ public class TimeDetectorStrategyImplTest {
 
         int phoneId = ARBITRARY_PHONE_ID;
         long testTimeMillis = ARBITRARY_TEST_TIME_MILLIS;
+
         PhoneTimeSuggestion timeSuggestion =
                 mScript.generatePhoneTimeSuggestion(phoneId, testTimeMillis);
-        int clockIncrement = 1000;
-        long expectedSystemClockMillis = testTimeMillis + clockIncrement;
+        mScript.simulateTimePassing()
+                .simulatePhoneTimeSuggestion(timeSuggestion);
 
-        mScript.simulateTimePassing(clockIncrement)
-                .simulatePhoneTimeSuggestion(timeSuggestion)
-                .verifySystemClockWasSetAndResetCallTracking(
-                        expectedSystemClockMillis, true /* expectNetworkBroadcast */)
+        long expectedSystemClockMillis =
+                mScript.calculateTimeInMillisForNow(timeSuggestion.getUtcTime());
+        mScript.verifySystemClockWasSetAndResetCallTracking(
+                expectedSystemClockMillis, true /* expectNetworkBroadcast */)
                 .assertLatestPhoneSuggestion(phoneId, timeSuggestion);
     }
 
@@ -94,26 +98,24 @@ public class TimeDetectorStrategyImplTest {
 
     @Test
     public void testSuggestPhoneTime_systemClockThreshold() {
-        int systemClockUpdateThresholdMillis = 1000;
+        final int systemClockUpdateThresholdMillis = 1000;
+        final int clockIncrementMillis = 100;
         mScript.pokeFakeClocks(ARBITRARY_CLOCK_INITIALIZATION_INFO)
                 .pokeThresholds(systemClockUpdateThresholdMillis)
                 .pokeAutoTimeDetectionEnabled(true);
 
-        final int clockIncrement = 100;
         int phoneId = ARBITRARY_PHONE_ID;
 
         // Send the first time signal. It should be used.
         {
-            long testTimeMillis = ARBITRARY_TEST_TIME_MILLIS;
             PhoneTimeSuggestion timeSuggestion1 =
-                    mScript.generatePhoneTimeSuggestion(phoneId, testTimeMillis);
-            TimestampedValue<Long> utcTime1 = timeSuggestion1.getUtcTime();
+                    mScript.generatePhoneTimeSuggestion(phoneId, ARBITRARY_TEST_TIME_MILLIS);
 
             // Increment the the device clocks to simulate the passage of time.
-            mScript.simulateTimePassing(clockIncrement);
+            mScript.simulateTimePassing(clockIncrementMillis);
 
             long expectedSystemClockMillis1 =
-                    TimeDetectorStrategy.getTimeAt(utcTime1, mScript.peekElapsedRealtimeMillis());
+                    mScript.calculateTimeInMillisForNow(timeSuggestion1.getUtcTime());
 
             mScript.simulatePhoneTimeSuggestion(timeSuggestion1)
                     .verifySystemClockWasSetAndResetCallTracking(
@@ -127,7 +129,7 @@ public class TimeDetectorStrategyImplTest {
             int underThresholdMillis = systemClockUpdateThresholdMillis - 1;
             PhoneTimeSuggestion timeSuggestion2 = mScript.generatePhoneTimeSuggestion(
                     phoneId, mScript.peekSystemClockMillis() + underThresholdMillis);
-            mScript.simulateTimePassing(clockIncrement)
+            mScript.simulateTimePassing(clockIncrementMillis)
                     .simulatePhoneTimeSuggestion(timeSuggestion2)
                     .verifySystemClockWasNotSetAndResetCallTracking()
                     .assertLatestPhoneSuggestion(phoneId, timeSuggestion2);
@@ -138,11 +140,10 @@ public class TimeDetectorStrategyImplTest {
             PhoneTimeSuggestion timeSuggestion3 = mScript.generatePhoneTimeSuggestion(
                     phoneId,
                     mScript.peekSystemClockMillis() + systemClockUpdateThresholdMillis);
-            mScript.simulateTimePassing(clockIncrement);
+            mScript.simulateTimePassing(clockIncrementMillis);
 
             long expectedSystemClockMillis3 =
-                    TimeDetectorStrategy.getTimeAt(timeSuggestion3.getUtcTime(),
-                            mScript.peekElapsedRealtimeMillis());
+                    mScript.calculateTimeInMillisForNow(timeSuggestion3.getUtcTime());
 
             mScript.simulatePhoneTimeSuggestion(timeSuggestion3)
                     .verifySystemClockWasSetAndResetCallTracking(
@@ -162,17 +163,16 @@ public class TimeDetectorStrategyImplTest {
         int phone1Id = ARBITRARY_PHONE_ID;
         int phone2Id = ARBITRARY_PHONE_ID + 1;
         long phone1TimeMillis = ARBITRARY_TEST_TIME_MILLIS;
-        long phone2TimeMillis = phone1TimeMillis + 60000;
-
-        final int clockIncrement = 999;
+        long phone2TimeMillis = ARBITRARY_TEST_TIME_MILLIS + Duration.ofDays(1).toMillis();
 
         // Make a suggestion with phone2Id.
         {
             PhoneTimeSuggestion phone2TimeSuggestion =
                     mScript.generatePhoneTimeSuggestion(phone2Id, phone2TimeMillis);
-            mScript.simulateTimePassing(clockIncrement);
+            mScript.simulateTimePassing();
 
-            long expectedSystemClockMillis = phone2TimeMillis + clockIncrement;
+            long expectedSystemClockMillis =
+                    mScript.calculateTimeInMillisForNow(phone2TimeSuggestion.getUtcTime());
 
             mScript.simulatePhoneTimeSuggestion(phone2TimeSuggestion)
                     .verifySystemClockWasSetAndResetCallTracking(
@@ -181,15 +181,16 @@ public class TimeDetectorStrategyImplTest {
                     .assertLatestPhoneSuggestion(phone2Id, phone2TimeSuggestion);
         }
 
-        mScript.simulateTimePassing(clockIncrement);
+        mScript.simulateTimePassing();
 
         // Now make a different suggestion with phone1Id.
         {
             PhoneTimeSuggestion phone1TimeSuggestion =
                     mScript.generatePhoneTimeSuggestion(phone1Id, phone1TimeMillis);
-            mScript.simulateTimePassing(clockIncrement);
+            mScript.simulateTimePassing();
 
-            long expectedSystemClockMillis = phone1TimeMillis + clockIncrement;
+            long expectedSystemClockMillis =
+                    mScript.calculateTimeInMillisForNow(phone1TimeSuggestion.getUtcTime());
 
             mScript.simulatePhoneTimeSuggestion(phone1TimeSuggestion)
                     .verifySystemClockWasSetAndResetCallTracking(
@@ -198,14 +199,14 @@ public class TimeDetectorStrategyImplTest {
 
         }
 
-        mScript.simulateTimePassing(clockIncrement);
+        mScript.simulateTimePassing();
 
         // Make another suggestion with phone2Id. It should be stored but not used because the
         // phone1Id suggestion will still "win".
         {
             PhoneTimeSuggestion phone2TimeSuggestion =
                     mScript.generatePhoneTimeSuggestion(phone2Id, phone2TimeMillis);
-            mScript.simulateTimePassing(clockIncrement);
+            mScript.simulateTimePassing();
 
             mScript.simulatePhoneTimeSuggestion(phone2TimeSuggestion)
                     .verifySystemClockWasNotSetAndResetCallTracking()
@@ -220,9 +221,10 @@ public class TimeDetectorStrategyImplTest {
         {
             PhoneTimeSuggestion phone2TimeSuggestion =
                     mScript.generatePhoneTimeSuggestion(phone2Id, phone2TimeMillis);
-            mScript.simulateTimePassing(clockIncrement);
+            mScript.simulateTimePassing();
 
-            long expectedSystemClockMillis = phone2TimeMillis + clockIncrement;
+            long expectedSystemClockMillis =
+                    mScript.calculateTimeInMillisForNow(phone2TimeSuggestion.getUtcTime());
 
             mScript.simulatePhoneTimeSuggestion(phone2TimeSuggestion)
                     .verifySystemClockWasSetAndResetCallTracking(
@@ -239,7 +241,7 @@ public class TimeDetectorStrategyImplTest {
         int phoneId = ARBITRARY_PHONE_ID;
         PhoneTimeSuggestion timeSuggestion =
                 mScript.generatePhoneTimeSuggestion(phoneId, ARBITRARY_TEST_TIME_MILLIS);
-        mScript.simulateTimePassing(1000)
+        mScript.simulateTimePassing()
                 .simulatePhoneTimeSuggestion(timeSuggestion)
                 .verifySystemClockWasNotSetAndResetCallTracking()
                 .assertLatestPhoneSuggestion(phoneId, timeSuggestion);
@@ -260,9 +262,8 @@ public class TimeDetectorStrategyImplTest {
         TimestampedValue<Long> utcTime1 = timeSuggestion1.getUtcTime();
 
         // Initialize the strategy / device with a time set from a phone suggestion.
-        mScript.simulateTimePassing(100);
-        long expectedSystemClockMillis1 =
-                TimeDetectorStrategy.getTimeAt(utcTime1, mScript.peekElapsedRealtimeMillis());
+        mScript.simulateTimePassing();
+        long expectedSystemClockMillis1 = mScript.calculateTimeInMillisForNow(utcTime1);
         mScript.simulatePhoneTimeSuggestion(timeSuggestion1)
                 .verifySystemClockWasSetAndResetCallTracking(
                         expectedSystemClockMillis1, true /* expectNetworkBroadcast */)
@@ -299,8 +300,7 @@ public class TimeDetectorStrategyImplTest {
         long validReferenceTimeMillis = utcTime1.getReferenceTimeMillis() + 100;
         TimestampedValue<Long> utcTime4 = new TimestampedValue<>(
                 validReferenceTimeMillis, validUtcTimeMillis);
-        long expectedSystemClockMillis4 =
-                TimeDetectorStrategy.getTimeAt(utcTime4, mScript.peekElapsedRealtimeMillis());
+        long expectedSystemClockMillis4 = mScript.calculateTimeInMillisForNow(utcTime4);
         PhoneTimeSuggestion timeSuggestion4 =
                 createPhoneTimeSuggestion(phoneId, utcTime4);
         mScript.simulatePhoneTimeSuggestion(timeSuggestion4)
@@ -335,8 +335,7 @@ public class TimeDetectorStrategyImplTest {
         // Simulate more time passing.
         mScript.simulateTimePassing(clockIncrementMillis);
 
-        long expectedSystemClockMillis1 =
-                TimeDetectorStrategy.getTimeAt(utcTime1, mScript.peekElapsedRealtimeMillis());
+        long expectedSystemClockMillis1 = mScript.calculateTimeInMillisForNow(utcTime1);
 
         // Turn on auto time detection.
         mScript.simulateAutoTimeDetectionToggle()
@@ -357,8 +356,8 @@ public class TimeDetectorStrategyImplTest {
         // Simulate more time passing.
         mScript.simulateTimePassing(clockIncrementMillis);
 
-        long expectedSystemClockMillis2 = TimeDetectorStrategy.getTimeAt(
-                timeSuggestion2.getUtcTime(), mScript.peekElapsedRealtimeMillis());
+        long expectedSystemClockMillis2 =
+                mScript.calculateTimeInMillisForNow(timeSuggestion2.getUtcTime());
 
         // The new time, though valid, should not be set in the system clock because auto time is
         // disabled.
@@ -382,19 +381,21 @@ public class TimeDetectorStrategyImplTest {
         long testTimeMillis = ARBITRARY_TEST_TIME_MILLIS;
         PhoneTimeSuggestion phoneSuggestion =
                 mScript.generatePhoneTimeSuggestion(phoneId, testTimeMillis);
-        int clockIncrementMillis = 1000;
 
-        mScript.simulateTimePassing(clockIncrementMillis)
-                .simulatePhoneTimeSuggestion(phoneSuggestion)
+        mScript.simulateTimePassing();
+
+        long expectedSystemClockMillis =
+                mScript.calculateTimeInMillisForNow(phoneSuggestion.getUtcTime());
+        mScript.simulatePhoneTimeSuggestion(phoneSuggestion)
                 .verifySystemClockWasSetAndResetCallTracking(
-                        testTimeMillis + clockIncrementMillis, true /* expectedNetworkBroadcast */)
+                        expectedSystemClockMillis, true /* expectedNetworkBroadcast */)
                 .assertLatestPhoneSuggestion(phoneId, phoneSuggestion);
 
         // Look inside and check what the strategy considers the current best phone suggestion.
         assertEquals(phoneSuggestion, mScript.peekBestPhoneSuggestion());
 
         // Simulate time passing, long enough that phoneSuggestion is now too old.
-        mScript.simulateTimePassing(TimeDetectorStrategyImpl.PHONE_MAX_AGE_MILLIS);
+        mScript.simulateTimePassing(TimeDetectorStrategyImpl.MAX_UTC_TIME_AGE_MILLIS);
 
         // Look inside and check what the strategy considers the current best phone suggestion. It
         // should still be the, it's just no longer used.
@@ -407,13 +408,14 @@ public class TimeDetectorStrategyImplTest {
         mScript.pokeFakeClocks(ARBITRARY_CLOCK_INITIALIZATION_INFO)
                 .pokeAutoTimeDetectionEnabled(false);
 
-        long testTimeMillis = ARBITRARY_TEST_TIME_MILLIS;
-        ManualTimeSuggestion timeSuggestion = mScript.generateManualTimeSuggestion(testTimeMillis);
-        final int clockIncrement = 1000;
-        long expectedSystemClockMillis = testTimeMillis + clockIncrement;
+        ManualTimeSuggestion timeSuggestion =
+                mScript.generateManualTimeSuggestion(ARBITRARY_TEST_TIME_MILLIS);
 
-        mScript.simulateTimePassing(clockIncrement)
-                .simulateManualTimeSuggestion(timeSuggestion)
+        mScript.simulateTimePassing();
+
+        long expectedSystemClockMillis =
+                mScript.calculateTimeInMillisForNow(timeSuggestion.getUtcTime());
+        mScript.simulateManualTimeSuggestion(timeSuggestion)
                 .verifySystemClockWasSetAndResetCallTracking(
                         expectedSystemClockMillis, false /* expectNetworkBroadcast */);
     }
@@ -430,21 +432,19 @@ public class TimeDetectorStrategyImplTest {
         long testTimeMillis = ARBITRARY_TEST_TIME_MILLIS;
         PhoneTimeSuggestion phoneTimeSuggestion =
                 mScript.generatePhoneTimeSuggestion(phoneId, testTimeMillis);
-        long expectedAutoClockMillis = phoneTimeSuggestion.getUtcTime().getValue();
-        final int clockIncrement = 1000;
 
         // Simulate the passage of time.
-        mScript.simulateTimePassing(clockIncrement);
-        expectedAutoClockMillis += clockIncrement;
+        mScript.simulateTimePassing();
 
+        long expectedAutoClockMillis =
+                mScript.calculateTimeInMillisForNow(phoneTimeSuggestion.getUtcTime());
         mScript.simulatePhoneTimeSuggestion(phoneTimeSuggestion)
                 .verifySystemClockWasSetAndResetCallTracking(
                         expectedAutoClockMillis, true /* expectNetworkBroadcast */)
                 .assertLatestPhoneSuggestion(phoneId, phoneTimeSuggestion);
 
         // Simulate the passage of time.
-        mScript.simulateTimePassing(clockIncrement);
-        expectedAutoClockMillis += clockIncrement;
+        mScript.simulateTimePassing();
 
         // Switch to manual.
         mScript.simulateAutoTimeDetectionToggle()
@@ -452,26 +452,29 @@ public class TimeDetectorStrategyImplTest {
                 .assertLatestPhoneSuggestion(phoneId, phoneTimeSuggestion);
 
         // Simulate the passage of time.
-        mScript.simulateTimePassing(clockIncrement);
-        expectedAutoClockMillis += clockIncrement;
+        mScript.simulateTimePassing();
 
         // Simulate a manual suggestion 1 day different from the auto suggestion.
-        long manualTimeMillis = testTimeMillis + ONE_DAY_MILLIS;
-        long expectedManualClockMillis = manualTimeMillis;
+        long manualTimeMillis = testTimeMillis + Duration.ofDays(1).toMillis();
         ManualTimeSuggestion manualTimeSuggestion =
                 mScript.generateManualTimeSuggestion(manualTimeMillis);
+        mScript.simulateTimePassing();
+
+        long expectedManualClockMillis =
+                mScript.calculateTimeInMillisForNow(manualTimeSuggestion.getUtcTime());
         mScript.simulateManualTimeSuggestion(manualTimeSuggestion)
                 .verifySystemClockWasSetAndResetCallTracking(
                         expectedManualClockMillis, false /* expectNetworkBroadcast */)
                 .assertLatestPhoneSuggestion(phoneId, phoneTimeSuggestion);
 
         // Simulate the passage of time.
-        mScript.simulateTimePassing(clockIncrement);
-        expectedAutoClockMillis += clockIncrement;
+        mScript.simulateTimePassing();
 
         // Switch back to auto.
         mScript.simulateAutoTimeDetectionToggle();
 
+        expectedAutoClockMillis =
+                mScript.calculateTimeInMillisForNow(phoneTimeSuggestion.getUtcTime());
         mScript.verifySystemClockWasSetAndResetCallTracking(
                         expectedAutoClockMillis, true /* expectNetworkBroadcast */)
                 .assertLatestPhoneSuggestion(phoneId, phoneTimeSuggestion);
@@ -492,13 +495,143 @@ public class TimeDetectorStrategyImplTest {
 
         ManualTimeSuggestion timeSuggestion =
                 mScript.generateManualTimeSuggestion(ARBITRARY_TEST_TIME_MILLIS);
-        final int clockIncrement = 1000;
 
-        mScript.simulateTimePassing(clockIncrement)
+        mScript.simulateTimePassing()
                 .simulateManualTimeSuggestion(timeSuggestion)
                 .verifySystemClockWasNotSetAndResetCallTracking();
     }
 
+    @Test
+    public void testSuggestNetworkTime_autoTimeEnabled() {
+        mScript.pokeFakeClocks(ARBITRARY_CLOCK_INITIALIZATION_INFO)
+                .pokeAutoTimeDetectionEnabled(true);
+
+        NetworkTimeSuggestion timeSuggestion =
+                mScript.generateNetworkTimeSuggestion(ARBITRARY_TEST_TIME_MILLIS);
+
+        mScript.simulateTimePassing();
+
+        long expectedSystemClockMillis =
+                mScript.calculateTimeInMillisForNow(timeSuggestion.getUtcTime());
+        mScript.simulateNetworkTimeSuggestion(timeSuggestion)
+                .verifySystemClockWasSetAndResetCallTracking(
+                        expectedSystemClockMillis, false /* expectNetworkBroadcast */);
+    }
+
+    @Test
+    public void testSuggestNetworkTime_autoTimeDisabled() {
+        mScript.pokeFakeClocks(ARBITRARY_CLOCK_INITIALIZATION_INFO)
+                .pokeAutoTimeDetectionEnabled(false);
+
+        NetworkTimeSuggestion timeSuggestion =
+                mScript.generateNetworkTimeSuggestion(ARBITRARY_TEST_TIME_MILLIS);
+
+        mScript.simulateTimePassing()
+                .simulateNetworkTimeSuggestion(timeSuggestion)
+                .verifySystemClockWasNotSetAndResetCallTracking();
+    }
+
+    @Test
+    public void testSuggestNetworkTime_phoneSuggestionsBeatNetworkSuggestions() {
+        mScript.pokeFakeClocks(ARBITRARY_CLOCK_INITIALIZATION_INFO)
+                .pokeAutoTimeDetectionEnabled(true);
+
+        // Three obviously different times that could not be mistaken for each other.
+        long networkTimeMillis1 = ARBITRARY_TEST_TIME_MILLIS;
+        long networkTimeMillis2 = ARBITRARY_TEST_TIME_MILLIS + Duration.ofDays(30).toMillis();
+        long phoneTimeMillis = ARBITRARY_TEST_TIME_MILLIS + Duration.ofDays(60).toMillis();
+        // A small increment used to simulate the passage of time, but not enough to interfere with
+        // macro-level time changes associated with suggestion age.
+        final long smallTimeIncrementMillis = 101;
+
+        // A network suggestion is made. It should be used because there is no phone suggestion.
+        NetworkTimeSuggestion networkTimeSuggestion1 =
+                mScript.generateNetworkTimeSuggestion(networkTimeMillis1);
+        mScript.simulateTimePassing(smallTimeIncrementMillis)
+                .simulateNetworkTimeSuggestion(networkTimeSuggestion1)
+                .verifySystemClockWasSetAndResetCallTracking(
+                        mScript.calculateTimeInMillisForNow(networkTimeSuggestion1.getUtcTime()),
+                        false /* expectNetworkBroadcast */);
+
+        // Check internal state.
+        mScript.assertLatestPhoneSuggestion(ARBITRARY_PHONE_ID, null)
+                .assertLatestNetworkSuggestion(networkTimeSuggestion1);
+        assertEquals(networkTimeSuggestion1, mScript.peekLatestValidNetworkSuggestion());
+        assertNull(mScript.peekBestPhoneSuggestion());
+
+        // Simulate a little time passing.
+        mScript.simulateTimePassing(smallTimeIncrementMillis)
+                .verifySystemClockWasNotSetAndResetCallTracking();
+
+        // Now a phone suggestion is made. Phone suggestions are prioritized over network
+        // suggestions so it should "win".
+        PhoneTimeSuggestion phoneTimeSuggestion =
+                mScript.generatePhoneTimeSuggestion(ARBITRARY_PHONE_ID, phoneTimeMillis);
+        mScript.simulateTimePassing(smallTimeIncrementMillis)
+                .simulatePhoneTimeSuggestion(phoneTimeSuggestion)
+                .verifySystemClockWasSetAndResetCallTracking(
+                        mScript.calculateTimeInMillisForNow(phoneTimeSuggestion.getUtcTime()),
+                        true /* expectNetworkBroadcast */);
+
+        // Check internal state.
+        mScript.assertLatestPhoneSuggestion(ARBITRARY_PHONE_ID, phoneTimeSuggestion)
+                .assertLatestNetworkSuggestion(networkTimeSuggestion1);
+        assertEquals(networkTimeSuggestion1, mScript.peekLatestValidNetworkSuggestion());
+        assertEquals(phoneTimeSuggestion, mScript.peekBestPhoneSuggestion());
+
+        // Simulate some significant time passing: half the time allowed before a time signal
+        // becomes "too old to use".
+        mScript.simulateTimePassing(TimeDetectorStrategyImpl.MAX_UTC_TIME_AGE_MILLIS / 2)
+                .verifySystemClockWasNotSetAndResetCallTracking();
+
+        // Now another network suggestion is made. Phone suggestions are prioritized over network
+        // suggestions so the latest phone suggestion should still "win".
+        NetworkTimeSuggestion networkTimeSuggestion2 =
+                mScript.generateNetworkTimeSuggestion(networkTimeMillis2);
+        mScript.simulateTimePassing(smallTimeIncrementMillis)
+                .simulateNetworkTimeSuggestion(networkTimeSuggestion2)
+                .verifySystemClockWasNotSetAndResetCallTracking();
+
+        // Check internal state.
+        mScript.assertLatestPhoneSuggestion(ARBITRARY_PHONE_ID, phoneTimeSuggestion)
+                .assertLatestNetworkSuggestion(networkTimeSuggestion2);
+        assertEquals(networkTimeSuggestion2, mScript.peekLatestValidNetworkSuggestion());
+        assertEquals(phoneTimeSuggestion, mScript.peekBestPhoneSuggestion());
+
+        // Simulate some significant time passing: half the time allowed before a time signal
+        // becomes "too old to use". This should mean that phoneTimeSuggestion is now too old to be
+        // used but networkTimeSuggestion2 is not.
+        mScript.simulateTimePassing(TimeDetectorStrategyImpl.MAX_UTC_TIME_AGE_MILLIS / 2);
+
+        // NOTE: The TimeDetectorStrategyImpl doesn't set an alarm for the point when the last
+        // suggestion it used becomes too old: it requires a new suggestion or an auto-time toggle
+        // to re-run the detection logic. This may change in future but until then we rely on a
+        // steady stream of suggestions to re-evaluate.
+        mScript.verifySystemClockWasNotSetAndResetCallTracking();
+
+        // Check internal state.
+        mScript.assertLatestPhoneSuggestion(ARBITRARY_PHONE_ID, phoneTimeSuggestion)
+                .assertLatestNetworkSuggestion(networkTimeSuggestion2);
+        assertEquals(networkTimeSuggestion2, mScript.peekLatestValidNetworkSuggestion());
+        assertNull(mScript.peekBestPhoneSuggestion());
+
+        // Toggle auto-time off and on to force the detection logic to run.
+        mScript.simulateAutoTimeDetectionToggle()
+                .simulateTimePassing(smallTimeIncrementMillis)
+                .simulateAutoTimeDetectionToggle();
+
+        // Verify the latest network time now wins.
+        mScript.verifySystemClockWasSetAndResetCallTracking(
+                mScript.calculateTimeInMillisForNow(networkTimeSuggestion2.getUtcTime()),
+                false /* expectNetworkTimeBroadcast */);
+
+        // Check internal state.
+        mScript.assertLatestPhoneSuggestion(ARBITRARY_PHONE_ID, phoneTimeSuggestion)
+                .assertLatestNetworkSuggestion(networkTimeSuggestion2);
+        assertEquals(networkTimeSuggestion2, mScript.peekLatestValidNetworkSuggestion());
+        assertNull(mScript.peekBestPhoneSuggestion());
+    }
+
     /**
      * A fake implementation of TimeDetectorStrategy.Callback. Besides tracking changes and behaving
      * like the real thing should, it also asserts preconditions.
@@ -674,6 +807,11 @@ public class TimeDetectorStrategyImplTest {
             return this;
         }
 
+        Script simulateNetworkTimeSuggestion(NetworkTimeSuggestion timeSuggestion) {
+            mTimeDetectorStrategy.suggestNetworkTime(timeSuggestion);
+            return this;
+        }
+
         Script simulateAutoTimeDetectionToggle() {
             mFakeCallback.simulateAutoTimeZoneDetectionToggle();
             mTimeDetectorStrategy.handleAutoTimeDetectionChanged();
@@ -685,6 +823,13 @@ public class TimeDetectorStrategyImplTest {
             return this;
         }
 
+        /**
+         * Simulates time passing by an arbitrary (but relatively small) amount.
+         */
+        Script simulateTimePassing() {
+            return simulateTimePassing(999);
+        }
+
         Script verifySystemClockWasNotSetAndResetCallTracking() {
             mFakeCallback.verifySystemClockNotSet();
             mFakeCallback.verifyIntentWasNotBroadcast();
@@ -711,14 +856,30 @@ public class TimeDetectorStrategyImplTest {
         }
 
         /**
+         * White box test info: Asserts the latest network suggestion is as expected.
+         */
+        Script assertLatestNetworkSuggestion(NetworkTimeSuggestion expected) {
+            assertEquals(expected, mTimeDetectorStrategy.getLatestNetworkSuggestion());
+            return this;
+        }
+
+        /**
          * White box test info: Returns the phone suggestion that would be used, if any, given the
-         * current elapsed real time clock.
+         * current elapsed real time clock and regardless of origin prioritization.
          */
         PhoneTimeSuggestion peekBestPhoneSuggestion() {
             return mTimeDetectorStrategy.findBestPhoneSuggestionForTests();
         }
 
         /**
+         * White box test info: Returns the network suggestion that would be used, if any, given the
+         * current elapsed real time clock and regardless of origin prioritization.
+         */
+        NetworkTimeSuggestion peekLatestValidNetworkSuggestion() {
+            return mTimeDetectorStrategy.findLatestValidNetworkSuggestionForTests();
+        }
+
+        /**
          * Generates a ManualTimeSuggestion using the current elapsed realtime clock for the
          * reference time.
          */
@@ -739,6 +900,24 @@ public class TimeDetectorStrategyImplTest {
             }
             return createPhoneTimeSuggestion(phoneId, time);
         }
+
+        /**
+         * Generates a NetworkTimeSuggestion using the current elapsed realtime clock for the
+         * reference time.
+         */
+        NetworkTimeSuggestion generateNetworkTimeSuggestion(long timeMillis) {
+            TimestampedValue<Long> utcTime =
+                    new TimestampedValue<>(mFakeCallback.peekElapsedRealtimeMillis(), timeMillis);
+            return new NetworkTimeSuggestion(utcTime);
+        }
+
+        /**
+         * Calculates what the supplied time would be when adjusted for the movement of the fake
+         * elapsed realtime clock.
+         */
+        long calculateTimeInMillisForNow(TimestampedValue<Long> utcTime) {
+            return TimeDetectorStrategy.getTimeAt(utcTime, peekElapsedRealtimeMillis());
+        }
     }
 
     private static PhoneTimeSuggestion createPhoneTimeSuggestion(int phoneId,