diff --git a/framework-t/src/android/app/usage/NetworkStats.java b/framework-t/src/android/app/usage/NetworkStats.java
index 2b6570a..74fe4bd 100644
--- a/framework-t/src/android/app/usage/NetworkStats.java
+++ b/framework-t/src/android/app/usage/NetworkStats.java
@@ -17,6 +17,7 @@
 package android.app.usage;
 
 import android.annotation.IntDef;
+import android.annotation.Nullable;
 import android.content.Context;
 import android.net.INetworkStatsService;
 import android.net.INetworkStatsSession;
@@ -474,10 +475,11 @@
 
     /**
      * Fills the recycled bucket with data of the next bin in the enumeration.
-     * @param bucketOut Bucket to be filled with data.
+     * @param bucketOut Bucket to be filled with data. If null, the method does
+     *                  nothing and returning false.
      * @return true if successfully filled the bucket, false otherwise.
      */
-    public boolean getNextBucket(Bucket bucketOut) {
+    public boolean getNextBucket(@Nullable Bucket bucketOut) {
         if (mSummary != null) {
             return getNextSummaryBucket(bucketOut);
         } else {
@@ -651,7 +653,7 @@
      * @param bucketOut Next item will be set here.
      * @return true if a next item could be set.
      */
-    private boolean getNextSummaryBucket(Bucket bucketOut) {
+    private boolean getNextSummaryBucket(@Nullable Bucket bucketOut) {
         if (bucketOut != null && mEnumerationIndex < mSummary.size()) {
             mRecycledSummaryEntry = mSummary.getValues(mEnumerationIndex++, mRecycledSummaryEntry);
             fillBucketFromSummaryEntry(bucketOut);
@@ -678,7 +680,7 @@
      * @param bucketOut Next item will be set here.
      * @return true if a next item could be set.
      */
-    private boolean getNextHistoryBucket(Bucket bucketOut) {
+    private boolean getNextHistoryBucket(@Nullable Bucket bucketOut) {
         if (bucketOut != null && mHistory != null) {
             if (mEnumerationIndex < mHistory.size()) {
                 mRecycledHistoryEntry = mHistory.getValues(mEnumerationIndex++,
diff --git a/framework-t/src/android/app/usage/NetworkStatsManager.java b/framework-t/src/android/app/usage/NetworkStatsManager.java
index bf518b2..f41475b 100644
--- a/framework-t/src/android/app/usage/NetworkStatsManager.java
+++ b/framework-t/src/android/app/usage/NetworkStatsManager.java
@@ -290,7 +290,7 @@
      *         statistics collection.
      */
     @WorkerThread
-    public Bucket querySummaryForDevice(int networkType, String subscriberId,
+    public Bucket querySummaryForDevice(int networkType, @Nullable String subscriberId,
             long startTime, long endTime) throws SecurityException, RemoteException {
         NetworkTemplate template;
         try {
@@ -335,8 +335,8 @@
      *         statistics collection.
      */
     @WorkerThread
-    public Bucket querySummaryForUser(int networkType, String subscriberId, long startTime,
-            long endTime) throws SecurityException, RemoteException {
+    public Bucket querySummaryForUser(int networkType, @Nullable String subscriberId,
+            long startTime, long endTime) throws SecurityException, RemoteException {
         NetworkTemplate template;
         try {
             template = createTemplate(networkType, subscriberId);
@@ -384,7 +384,7 @@
      *         statistics collection.
      */
     @WorkerThread
-    public NetworkStats querySummary(int networkType, String subscriberId, long startTime,
+    public NetworkStats querySummary(int networkType, @Nullable String subscriberId, long startTime,
             long endTime) throws SecurityException, RemoteException {
         NetworkTemplate template;
         try {
@@ -508,15 +508,17 @@
      *
      * @see #queryDetailsForUidTagState(int, String, long, long, int, int, int)
      */
+    @NonNull
     @WorkerThread
-    public NetworkStats queryDetailsForUid(int networkType, String subscriberId,
+    public NetworkStats queryDetailsForUid(int networkType, @Nullable String subscriberId,
             long startTime, long endTime, int uid) throws SecurityException {
         return queryDetailsForUidTagState(networkType, subscriberId, startTime, endTime, uid,
             NetworkStats.Bucket.TAG_NONE, NetworkStats.Bucket.STATE_ALL);
     }
 
     /** @hide */
-    public NetworkStats queryDetailsForUid(NetworkTemplate template,
+    @NonNull
+    public NetworkStats queryDetailsForUid(@NonNull NetworkTemplate template,
             long startTime, long endTime, int uid) throws SecurityException {
         return queryDetailsForUidTagState(template, startTime, endTime, uid,
                 NetworkStats.Bucket.TAG_NONE, NetworkStats.Bucket.STATE_ALL);
@@ -524,23 +526,59 @@
 
     /**
      * Query network usage statistics details for a given uid and tag.
+     *
+     * This may take a long time, and apps should avoid calling this on their main thread.
+     * Only usable for uids belonging to calling user. Result is not aggregated over time.
+     * This means buckets' start and end timestamps are going to be between 'startTime' and
+     * 'endTime' parameters. The uid is going to be the same as the 'uid' parameter, the tag
+     * the same as the 'tag' parameter, and the state the same as the 'state' parameter.
+     * defaultNetwork is going to be {@link NetworkStats.Bucket#DEFAULT_NETWORK_ALL},
+     * metered is going to be {@link NetworkStats.Bucket#METERED_ALL}, and
+     * roaming is going to be {@link NetworkStats.Bucket#ROAMING_ALL}.
+     * <p>Only includes buckets that atomically occur in the inclusive time range. Doesn't
+     * interpolate across partial buckets. Since bucket length is in the order of hours, this
+     * method cannot be used to measure data usage on a fine grained time scale.
      * This may take a long time, and apps should avoid calling this on their main thread.
      *
-     * @see #queryDetailsForUidTagState(int, String, long, long, int, int, int)
+     * @param networkType As defined in {@link ConnectivityManager}, e.g.
+     *            {@link ConnectivityManager#TYPE_MOBILE}, {@link ConnectivityManager#TYPE_WIFI}
+     *            etc.
+     * @param subscriberId If applicable, the subscriber id of the network interface.
+     *                     <p>Starting with API level 29, the {@code subscriberId} is guarded by
+     *                     additional restrictions. Calling apps that do not meet the new
+     *                     requirements to access the {@code subscriberId} can provide a {@code
+     *                     null} value when querying for the mobile network type to receive usage
+     *                     for all mobile networks. For additional details see {@link
+     *                     TelephonyManager#getSubscriberId()}.
+     *                     <p>Starting with API level 31, calling apps can provide a
+     *                     {@code subscriberId} with wifi network type to receive usage for
+     *                     wifi networks which is under the given subscription if applicable.
+     *                     Otherwise, pass {@code null} when querying all wifi networks.
+     * @param startTime Start of period. Defined in terms of "Unix time", see
+     *            {@link java.lang.System#currentTimeMillis}.
+     * @param endTime End of period. Defined in terms of "Unix time", see
+     *            {@link java.lang.System#currentTimeMillis}.
+     * @param uid UID of app
+     * @param tag TAG of interest. Use {@link NetworkStats.Bucket#TAG_NONE} for aggregated data
+     *            across all the tags.
+     * @return Statistics which is described above.
+     * @throws SecurityException if permissions are insufficient to read network statistics.
      */
+    @NonNull
     @WorkerThread
-    public NetworkStats queryDetailsForUidTag(int networkType, String subscriberId,
+    public NetworkStats queryDetailsForUidTag(int networkType, @Nullable String subscriberId,
             long startTime, long endTime, int uid, int tag) throws SecurityException {
         return queryDetailsForUidTagState(networkType, subscriberId, startTime, endTime, uid,
             tag, NetworkStats.Bucket.STATE_ALL);
     }
 
     /**
-     * Query network usage statistics details for a given uid, tag, and state. Only usable for uids
-     * belonging to calling user. Result is not aggregated over time. This means buckets' start and
-     * end timestamps are going to be between 'startTime' and 'endTime' parameters. The uid is going
-     * to be the same as the 'uid' parameter, the tag the same as the 'tag' parameter, and the state
-     * the same as the 'state' parameter.
+     * Query network usage statistics details for a given uid, tag, and state.
+     *
+     * Only usable for uids belonging to calling user. Result is not aggregated over time.
+     * This means buckets' start and end timestamps are going to be between 'startTime' and
+     * 'endTime' parameters. The uid is going to be the same as the 'uid' parameter, the tag
+     * the same as the 'tag' parameter, and the state the same as the 'state' parameter.
      * defaultNetwork is going to be {@link NetworkStats.Bucket#DEFAULT_NETWORK_ALL},
      * metered is going to be {@link NetworkStats.Bucket#METERED_ALL}, and
      * roaming is going to be {@link NetworkStats.Bucket#ROAMING_ALL}.
@@ -572,11 +610,12 @@
      *            across all the tags.
      * @param state state of interest. Use {@link NetworkStats.Bucket#STATE_ALL} to aggregate
      *            traffic from all states.
-     * @return Statistics object or null if an error happened during statistics collection.
+     * @return Statistics which is described above.
      * @throws SecurityException if permissions are insufficient to read network statistics.
      */
+    @NonNull
     @WorkerThread
-    public NetworkStats queryDetailsForUidTagState(int networkType, String subscriberId,
+    public NetworkStats queryDetailsForUidTagState(int networkType, @Nullable String subscriberId,
             long startTime, long endTime, int uid, int tag, int state) throws SecurityException {
         NetworkTemplate template;
         template = createTemplate(networkType, subscriberId);
@@ -669,7 +708,7 @@
      *         statistics collection.
      */
     @WorkerThread
-    public NetworkStats queryDetails(int networkType, String subscriberId, long startTime,
+    public NetworkStats queryDetails(int networkType, @Nullable String subscriberId, long startTime,
             long endTime) throws SecurityException, RemoteException {
         NetworkTemplate template;
         try {
@@ -698,7 +737,7 @@
      *
      * @hide
      */
-    @SystemApi
+    @SystemApi(client = MODULE_LIBRARIES)
     @RequiresPermission(anyOf = {
             NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK,
             android.Manifest.permission.NETWORK_STACK})
@@ -724,7 +763,7 @@
      *
      * @hide
      */
-    @SystemApi
+    @SystemApi(client = MODULE_LIBRARIES)
     @RequiresPermission(anyOf = {
             NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK,
             android.Manifest.permission.NETWORK_STACK})
@@ -785,10 +824,28 @@
     /**
      * Registers to receive notifications about data usage on specified networks.
      *
-     * @see #registerUsageCallback(int, String, long, UsageCallback, Handler)
+     * <p>The callbacks will continue to be called as long as the process is live or
+     * {@link #unregisterUsageCallback} is called.
+     *
+     * @param networkType Type of network to monitor. Either
+    {@link ConnectivityManager#TYPE_MOBILE} or {@link ConnectivityManager#TYPE_WIFI}.
+     * @param subscriberId If applicable, the subscriber id of the network interface.
+     *                     <p>Starting with API level 29, the {@code subscriberId} is guarded by
+     *                     additional restrictions. Calling apps that do not meet the new
+     *                     requirements to access the {@code subscriberId} can provide a {@code
+     *                     null} value when registering for the mobile network type to receive
+     *                     notifications for all mobile networks. For additional details see {@link
+     *                     TelephonyManager#getSubscriberId()}.
+     *                     <p>Starting with API level 31, calling apps can provide a
+     *                     {@code subscriberId} with wifi network type to receive usage for
+     *                     wifi networks which is under the given subscription if applicable.
+     *                     Otherwise, pass {@code null} when querying all wifi networks.
+     * @param thresholdBytes Threshold in bytes to be notified on.
+     * @param callback The {@link UsageCallback} that the system will call when data usage
+     *            has exceeded the specified threshold.
      */
-    public void registerUsageCallback(int networkType, String subscriberId, long thresholdBytes,
-            UsageCallback callback) {
+    public void registerUsageCallback(int networkType, @Nullable String subscriberId,
+            long thresholdBytes, @NonNull UsageCallback callback) {
         registerUsageCallback(networkType, subscriberId, thresholdBytes, callback,
                 null /* handler */);
     }
@@ -818,8 +875,8 @@
      * @param handler to dispatch callback events through, otherwise if {@code null} it uses
      *            the calling thread.
      */
-    public void registerUsageCallback(int networkType, String subscriberId, long thresholdBytes,
-            UsageCallback callback, @Nullable Handler handler) {
+    public void registerUsageCallback(int networkType, @Nullable String subscriberId,
+            long thresholdBytes, @NonNull UsageCallback callback, @Nullable Handler handler) {
         NetworkTemplate template = createTemplate(networkType, subscriberId);
         if (DBG) {
             Log.d(TAG, "registerUsageCallback called with: {"
@@ -839,7 +896,7 @@
      *
      * @param callback The {@link UsageCallback} used when registering.
      */
-    public void unregisterUsageCallback(UsageCallback callback) {
+    public void unregisterUsageCallback(@NonNull UsageCallback callback) {
         if (callback == null || callback.request == null
                 || callback.request.requestId == DataUsageRequest.REQUEST_ID_UNSET) {
             throw new IllegalArgumentException("Invalid UsageCallback");
@@ -880,7 +937,7 @@
         /**
          * Called when data usage has reached the given threshold.
          */
-        public abstract void onThresholdReached(int networkType, String subscriberId);
+        public abstract void onThresholdReached(int networkType, @Nullable String subscriberId);
 
         /**
          * @hide used for internal bookkeeping
@@ -924,7 +981,7 @@
     @RequiresPermission(anyOf = {
             android.Manifest.permission.NETWORK_STATS_PROVIDER,
             NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK})
-    @NonNull public void registerNetworkStatsProvider(
+    public void registerNetworkStatsProvider(
             @NonNull String tag,
             @NonNull NetworkStatsProvider provider) {
         try {
@@ -950,7 +1007,7 @@
     @RequiresPermission(anyOf = {
             android.Manifest.permission.NETWORK_STATS_PROVIDER,
             NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK})
-    @NonNull public void unregisterNetworkStatsProvider(@NonNull NetworkStatsProvider provider) {
+    public void unregisterNetworkStatsProvider(@NonNull NetworkStatsProvider provider) {
         try {
             provider.getProviderCallbackBinderOrThrow().unregister();
         } catch (RemoteException e) {
@@ -958,7 +1015,7 @@
         }
     }
 
-    private static NetworkTemplate createTemplate(int networkType, String subscriberId) {
+    private static NetworkTemplate createTemplate(int networkType, @Nullable String subscriberId) {
         final NetworkTemplate template;
         switch (networkType) {
             case ConnectivityManager.TYPE_MOBILE:
diff --git a/framework-t/src/android/net/NetworkStats.java b/framework-t/src/android/net/NetworkStats.java
index 06f2a62..bcfeab9 100644
--- a/framework-t/src/android/net/NetworkStats.java
+++ b/framework-t/src/android/net/NetworkStats.java
@@ -16,6 +16,8 @@
 
 package android.net;
 
+import static android.annotation.SystemApi.Client.MODULE_LIBRARIES;
+
 import static com.android.net.module.util.NetworkStatsUtils.multiplySafeByRational;
 
 import android.annotation.IntDef;
@@ -124,7 +126,6 @@
     public @Nullable static final String[] INTERFACES_ALL = null;
 
     /** {@link #tag} value for total data across all tags. */
-    // TODO: Rename TAG_NONE to TAG_ALL.
     public static final int TAG_NONE = 0;
 
     /** {@link #metered} value to account for all metered states. */
@@ -390,77 +391,102 @@
 
         /**
          * @return the uid of this entry.
+         * @hide
          */
+        @SystemApi(client = MODULE_LIBRARIES)
         public int getUid() {
             return uid;
         }
 
         /**
          * @return the set state of this entry.
+         * @hide
          */
+        @SystemApi(client = MODULE_LIBRARIES)
         @State public int getSet() {
             return set;
         }
 
         /**
          * @return the tag value of this entry.
+         * @hide
          */
+        @SystemApi(client = MODULE_LIBRARIES)
         public int getTag() {
             return tag;
         }
 
         /**
          * @return the metered state.
+         * @hide
          */
-        @Meteredness public int getMetered() {
+        @Meteredness
+        @SystemApi(client = MODULE_LIBRARIES)
+        public int getMetered() {
             return metered;
         }
 
         /**
          * @return the roaming state.
+         * @hide
          */
-        @Roaming public int getRoaming() {
+        @Roaming
+        @SystemApi(client = MODULE_LIBRARIES)
+        public int getRoaming() {
             return roaming;
         }
 
         /**
          * @return the default network state.
+         * @hide
          */
-        @DefaultNetwork public int getDefaultNetwork() {
+        @DefaultNetwork
+        @SystemApi(client = MODULE_LIBRARIES)
+        public int getDefaultNetwork() {
             return defaultNetwork;
         }
 
         /**
          * @return the number of received bytes.
+         * @hide
          */
+        @SystemApi(client = MODULE_LIBRARIES)
         public long getRxBytes() {
             return rxBytes;
         }
 
         /**
          * @return the number of received packets.
+         * @hide
          */
+        @SystemApi(client = MODULE_LIBRARIES)
         public long getRxPackets() {
             return rxPackets;
         }
 
         /**
          * @return the number of transmitted bytes.
+         * @hide
          */
+        @SystemApi(client = MODULE_LIBRARIES)
         public long getTxBytes() {
             return txBytes;
         }
 
         /**
          * @return the number of transmitted packets.
+         * @hide
          */
+        @SystemApi(client = MODULE_LIBRARIES)
         public long getTxPackets() {
             return txPackets;
         }
 
         /**
          * @return the count of network operations performed for this entry.
+         * @hide
          */
+        @SystemApi(client = MODULE_LIBRARIES)
         public long getOperations() {
             return operations;
         }
@@ -682,7 +708,7 @@
      * The remove() method is not implemented and will throw UnsupportedOperationException.
      * @hide
      */
-    @SystemApi
+    @SystemApi(client = MODULE_LIBRARIES)
     @NonNull public Iterator<Entry> iterator() {
         return new Iterator<Entry>() {
             int mIndex = 0;
diff --git a/framework-t/src/android/net/TrafficStats.java b/framework-t/src/android/net/TrafficStats.java
index bc836d8..dc4ac55 100644
--- a/framework-t/src/android/net/TrafficStats.java
+++ b/framework-t/src/android/net/TrafficStats.java
@@ -205,7 +205,7 @@
      *                server context.
      * @hide
      */
-    @SystemApi(client = SystemApi.Client.MODULE_LIBRARIES)
+    @SystemApi(client = MODULE_LIBRARIES)
     @SuppressLint("VisiblySynchronized")
     public static synchronized void init(@NonNull final Context context) {
         if (sStatsService != null) {
@@ -376,7 +376,7 @@
      *
      * @hide
      */
-    @SystemApi
+    @SystemApi(client = MODULE_LIBRARIES)
     public static void setThreadStatsTagDownload() {
         setThreadStatsTag(TAG_SYSTEM_DOWNLOAD);
     }
@@ -468,7 +468,7 @@
      *
      * @see #setThreadStatsTag(int)
      */
-    public static void tagSocket(Socket socket) throws SocketException {
+    public static void tagSocket(@NonNull Socket socket) throws SocketException {
         SocketTagger.get().tag(socket);
     }
 
@@ -483,7 +483,7 @@
      * calling {@code untagSocket()} before sending the socket to another
      * process.
      */
-    public static void untagSocket(Socket socket) throws SocketException {
+    public static void untagSocket(@NonNull Socket socket) throws SocketException {
         SocketTagger.get().untag(socket);
     }
 
@@ -496,14 +496,14 @@
      *
      * @see #setThreadStatsTag(int)
      */
-    public static void tagDatagramSocket(DatagramSocket socket) throws SocketException {
+    public static void tagDatagramSocket(@NonNull DatagramSocket socket) throws SocketException {
         SocketTagger.get().tag(socket);
     }
 
     /**
      * Remove any statistics parameters from the given {@link DatagramSocket}.
      */
-    public static void untagDatagramSocket(DatagramSocket socket) throws SocketException {
+    public static void untagDatagramSocket(@NonNull DatagramSocket socket) throws SocketException {
         SocketTagger.get().untag(socket);
     }
 
@@ -516,7 +516,7 @@
      *
      * @see #setThreadStatsTag(int)
      */
-    public static void tagFileDescriptor(FileDescriptor fd) throws IOException {
+    public static void tagFileDescriptor(@NonNull FileDescriptor fd) throws IOException {
         SocketTagger.get().tag(fd);
     }
 
@@ -524,7 +524,7 @@
      * Remove any statistics parameters from the given {@link FileDescriptor}
      * socket.
      */
-    public static void untagFileDescriptor(FileDescriptor fd) throws IOException {
+    public static void untagFileDescriptor(@NonNull FileDescriptor fd) throws IOException {
         SocketTagger.get().untag(fd);
     }