diff --git a/service-t/src/com/android/server/connectivity/mdns/MdnsServiceCache.java b/service-t/src/com/android/server/connectivity/mdns/MdnsServiceCache.java
new file mode 100644
index 0000000..bfda535
--- /dev/null
+++ b/service-t/src/com/android/server/connectivity/mdns/MdnsServiceCache.java
@@ -0,0 +1,178 @@
+/*
+ * Copyright (C) 2023 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 com.android.server.connectivity.mdns;
+
+import static com.android.server.connectivity.mdns.MdnsSocketProvider.ensureRunningOnHandlerThread;
+import static com.android.server.connectivity.mdns.util.MdnsUtils.equalsIgnoreDnsCase;
+import static com.android.server.connectivity.mdns.util.MdnsUtils.toDnsLowerCase;
+
+import android.annotation.NonNull;
+import android.annotation.Nullable;
+import android.net.Network;
+import android.os.Handler;
+import android.os.Looper;
+import android.util.ArrayMap;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Objects;
+
+/**
+ * The {@link MdnsServiceCache} manages the service which discovers from each socket and cache these
+ * services to reduce duplicated queries.
+ *
+ * <p>This class is not thread safe, it is intended to be used only from the looper thread.
+ *  However, the constructor is an exception, as it is called on another thread;
+ *  therefore for thread safety all members of this class MUST either be final or initialized
+ *  to their default value (0, false or null).
+ */
+public class MdnsServiceCache {
+    private static class CacheKey {
+        @NonNull final String mLowercaseServiceType;
+        @Nullable final Network mNetwork;
+
+        CacheKey(@NonNull String serviceType, @Nullable Network network) {
+            mLowercaseServiceType = toDnsLowerCase(serviceType);
+            mNetwork = network;
+        }
+
+        @Override public int hashCode() {
+            return Objects.hash(mLowercaseServiceType, mNetwork);
+        }
+
+        @Override public boolean equals(Object other) {
+            if (this == other) {
+                return true;
+            }
+            if (!(other instanceof CacheKey)) {
+                return false;
+            }
+            return Objects.equals(mLowercaseServiceType, ((CacheKey) other).mLowercaseServiceType)
+                    && Objects.equals(mNetwork, ((CacheKey) other).mNetwork);
+        }
+    }
+    /**
+     * A map of cached services. Key is composed of service name, type and network. Value is the
+     * service which use the service type to discover from each socket.
+     */
+    @NonNull
+    private final ArrayMap<CacheKey, List<MdnsResponse>> mCachedServices = new ArrayMap<>();
+    @NonNull
+    private final Handler mHandler;
+
+    public MdnsServiceCache(@NonNull Looper looper) {
+        mHandler = new Handler(looper);
+    }
+
+    /**
+     * Get the cache services which are queried from given service type and network.
+     *
+     * @param serviceType the target service type.
+     * @param network the target network
+     * @return the set of services which matches the given service type.
+     */
+    @NonNull
+    public List<MdnsResponse> getCachedServices(@NonNull String serviceType,
+            @Nullable Network network) {
+        ensureRunningOnHandlerThread(mHandler);
+        final CacheKey key = new CacheKey(serviceType, network);
+        return mCachedServices.containsKey(key)
+                ? Collections.unmodifiableList(new ArrayList<>(mCachedServices.get(key)))
+                : Collections.emptyList();
+    }
+
+    private MdnsResponse findMatchedResponse(@NonNull List<MdnsResponse> responses,
+            @NonNull String serviceName) {
+        for (MdnsResponse response : responses) {
+            if (equalsIgnoreDnsCase(serviceName, response.getServiceInstanceName())) {
+                return response;
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Get the cache service.
+     *
+     * @param serviceName the target service name.
+     * @param serviceType the target service type.
+     * @param network the target network
+     * @return the service which matches given conditions.
+     */
+    @Nullable
+    public MdnsResponse getCachedService(@NonNull String serviceName,
+            @NonNull String serviceType, @Nullable Network network) {
+        ensureRunningOnHandlerThread(mHandler);
+        final List<MdnsResponse> responses =
+                mCachedServices.get(new CacheKey(serviceType, network));
+        if (responses == null) {
+            return null;
+        }
+        final MdnsResponse response = findMatchedResponse(responses, serviceName);
+        return response != null ? new MdnsResponse(response) : null;
+    }
+
+    /**
+     * Add or update a service.
+     *
+     * @param serviceType the service type.
+     * @param network the target network
+     * @param response the response of the discovered service.
+     */
+    public void addOrUpdateService(@NonNull String serviceType, @Nullable Network network,
+            @NonNull MdnsResponse response) {
+        ensureRunningOnHandlerThread(mHandler);
+        final List<MdnsResponse> responses = mCachedServices.computeIfAbsent(
+                new CacheKey(serviceType, network), key -> new ArrayList<>());
+        // Remove existing service if present.
+        final MdnsResponse existing =
+                findMatchedResponse(responses, response.getServiceInstanceName());
+        responses.remove(existing);
+        responses.add(response);
+    }
+
+    /**
+     * Remove a service which matches the given service name, type and network.
+     *
+     * @param serviceName the target service name.
+     * @param serviceType the target service type.
+     * @param network the target network.
+     */
+    @Nullable
+    public MdnsResponse removeService(@NonNull String serviceName, @NonNull String serviceType,
+            @Nullable Network network) {
+        ensureRunningOnHandlerThread(mHandler);
+        final List<MdnsResponse> responses =
+                mCachedServices.get(new CacheKey(serviceType, network));
+        if (responses == null) {
+            return null;
+        }
+        final Iterator<MdnsResponse> iterator = responses.iterator();
+        while (iterator.hasNext()) {
+            final MdnsResponse response = iterator.next();
+            if (equalsIgnoreDnsCase(serviceName, response.getServiceInstanceName())) {
+                iterator.remove();
+                return response;
+            }
+        }
+        return null;
+    }
+
+    // TODO: check ttl expiration for each service and notify to the clients.
+}
diff --git a/service-t/src/com/android/server/connectivity/mdns/util/MdnsUtils.java b/service-t/src/com/android/server/connectivity/mdns/util/MdnsUtils.java
new file mode 100644
index 0000000..4b0f2a4
--- /dev/null
+++ b/service-t/src/com/android/server/connectivity/mdns/util/MdnsUtils.java
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2023 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 com.android.server.connectivity.mdns.util;
+
+import android.annotation.NonNull;
+
+/**
+ * Mdns utility functions.
+ */
+public class MdnsUtils {
+
+    private MdnsUtils() { }
+
+    /**
+     * Convert the string to DNS case-insensitive lowercase
+     *
+     * Per rfc6762#page-46, accented characters are not defined to be automatically equivalent to
+     * their unaccented counterparts. So the "DNS lowercase" should be if character is A-Z then they
+     * transform into a-z. Otherwise, they are kept as-is.
+     */
+    public static String toDnsLowerCase(@NonNull String string) {
+        final char[] outChars = new char[string.length()];
+        for (int i = 0; i < string.length(); i++) {
+            outChars[i] = toDnsLowerCase(string.charAt(i));
+        }
+        return new String(outChars);
+    }
+
+    /**
+     * Compare two strings by DNS case-insensitive lowercase.
+     */
+    public static boolean equalsIgnoreDnsCase(@NonNull String a, @NonNull String b) {
+        if (a.length() != b.length()) return false;
+        for (int i = 0; i < a.length(); i++) {
+            if (toDnsLowerCase(a.charAt(i)) != toDnsLowerCase(b.charAt(i))) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private static char toDnsLowerCase(char a) {
+        return a >= 'A' && a <= 'Z' ? (char) (a + ('a' - 'A')) : a;
+    }
+}
diff --git a/service-t/src/com/android/server/net/NetworkStatsService.java b/service-t/src/com/android/server/net/NetworkStatsService.java
index 961337d..c660792 100644
--- a/service-t/src/com/android/server/net/NetworkStatsService.java
+++ b/service-t/src/com/android/server/net/NetworkStatsService.java
@@ -946,7 +946,11 @@
     @GuardedBy("mStatsLock")
     private void shutdownLocked() {
         final TetheringManager tetheringManager = mContext.getSystemService(TetheringManager.class);
-        tetheringManager.unregisterTetheringEventCallback(mTetherListener);
+        try {
+            tetheringManager.unregisterTetheringEventCallback(mTetherListener);
+        } catch (IllegalStateException e) {
+            Log.i(TAG, "shutdownLocked: error when unregister tethering, ignored. e=" + e);
+        }
         mContext.unregisterReceiver(mPollReceiver);
         mContext.unregisterReceiver(mRemovedReceiver);
         mContext.unregisterReceiver(mUserReceiver);
diff --git a/tests/unit/java/com/android/server/connectivity/mdns/MdnsServiceCacheTest.kt b/tests/unit/java/com/android/server/connectivity/mdns/MdnsServiceCacheTest.kt
new file mode 100644
index 0000000..f091eea
--- /dev/null
+++ b/tests/unit/java/com/android/server/connectivity/mdns/MdnsServiceCacheTest.kt
@@ -0,0 +1,136 @@
+/*
+ * Copyright (C) 2023 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 com.android.server.connectivity.mdns
+
+import android.net.Network
+import android.os.Build
+import android.os.Handler
+import android.os.HandlerThread
+import com.android.testutils.DevSdkIgnoreRule
+import com.android.testutils.DevSdkIgnoreRunner
+import java.util.concurrent.CompletableFuture
+import java.util.concurrent.TimeUnit
+import kotlin.test.assertNotNull
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Assert.assertTrue
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.mockito.Mockito.mock
+
+private const val SERVICE_NAME_1 = "service-instance-1"
+private const val SERVICE_NAME_2 = "service-instance-2"
+private const val SERVICE_TYPE_1 = "_test1._tcp.local"
+private const val SERVICE_TYPE_2 = "_test2._tcp.local"
+private const val INTERFACE_INDEX = 999
+private const val DEFAULT_TIMEOUT_MS = 2000L
+
+@RunWith(DevSdkIgnoreRunner::class)
+@DevSdkIgnoreRule.IgnoreUpTo(Build.VERSION_CODES.S_V2)
+class MdnsServiceCacheTest {
+    private val network = mock(Network::class.java)
+    private val thread = HandlerThread(MdnsServiceCacheTest::class.simpleName)
+    private val handler by lazy {
+        Handler(thread.looper)
+    }
+    private val serviceCache by lazy {
+        MdnsServiceCache(thread.looper)
+    }
+
+    @Before
+    fun setUp() {
+        thread.start()
+    }
+
+    @After
+    fun tearDown() {
+        thread.quitSafely()
+    }
+
+    private fun <T> runningOnHandlerAndReturn(functor: (() -> T)): T {
+        val future = CompletableFuture<T>()
+        handler.post {
+            future.complete(functor())
+        }
+        return future.get(DEFAULT_TIMEOUT_MS, TimeUnit.MILLISECONDS)
+    }
+
+    private fun addOrUpdateService(serviceType: String, network: Network, service: MdnsResponse):
+            Unit = runningOnHandlerAndReturn {
+        serviceCache.addOrUpdateService(serviceType, network, service) }
+
+    private fun removeService(serviceName: String, serviceType: String, network: Network):
+            Unit = runningOnHandlerAndReturn {
+        serviceCache.removeService(serviceName, serviceType, network) }
+
+    private fun getService(serviceName: String, serviceType: String, network: Network):
+            MdnsResponse? = runningOnHandlerAndReturn {
+        serviceCache.getCachedService(serviceName, serviceType, network) }
+
+    private fun getServices(serviceType: String, network: Network): List<MdnsResponse> =
+        runningOnHandlerAndReturn { serviceCache.getCachedServices(serviceType, network) }
+
+    @Test
+    fun testAddAndRemoveService() {
+        addOrUpdateService(SERVICE_TYPE_1, network, createResponse(SERVICE_NAME_1, SERVICE_TYPE_1))
+        var response = getService(SERVICE_NAME_1, SERVICE_TYPE_1, network)
+        assertNotNull(response)
+        assertEquals(SERVICE_NAME_1, response.serviceInstanceName)
+        removeService(SERVICE_NAME_1, SERVICE_TYPE_1, network)
+        response = getService(SERVICE_NAME_1, SERVICE_TYPE_1, network)
+        assertNull(response)
+    }
+
+    @Test
+    fun testGetCachedServices_multipleServiceTypes() {
+        addOrUpdateService(SERVICE_TYPE_1, network, createResponse(SERVICE_NAME_1, SERVICE_TYPE_1))
+        addOrUpdateService(SERVICE_TYPE_1, network, createResponse(SERVICE_NAME_2, SERVICE_TYPE_1))
+        addOrUpdateService(SERVICE_TYPE_2, network, createResponse(SERVICE_NAME_2, SERVICE_TYPE_2))
+
+        val responses1 = getServices(SERVICE_TYPE_1, network)
+        assertEquals(2, responses1.size)
+        assertTrue(responses1.stream().anyMatch { response ->
+            response.serviceInstanceName == SERVICE_NAME_1
+        })
+        assertTrue(responses1.any { response ->
+            response.serviceInstanceName == SERVICE_NAME_2
+        })
+        val responses2 = getServices(SERVICE_TYPE_2, network)
+        assertEquals(1, responses2.size)
+        assertTrue(responses2.any { response ->
+            response.serviceInstanceName == SERVICE_NAME_2
+        })
+
+        removeService(SERVICE_NAME_2, SERVICE_TYPE_1, network)
+        val responses3 = getServices(SERVICE_TYPE_1, network)
+        assertEquals(1, responses3.size)
+        assertTrue(responses3.any { response ->
+            response.serviceInstanceName == SERVICE_NAME_1
+        })
+        val responses4 = getServices(SERVICE_TYPE_2, network)
+        assertEquals(1, responses4.size)
+        assertTrue(responses4.any { response ->
+            response.serviceInstanceName == SERVICE_NAME_2
+        })
+    }
+
+    private fun createResponse(serviceInstanceName: String, serviceType: String) = MdnsResponse(
+        0 /* now */, "$serviceInstanceName.$serviceType".split(".").toTypedArray(),
+            INTERFACE_INDEX, network)
+}
diff --git a/tests/unit/java/com/android/server/connectivity/mdns/util/MdnsUtilsTest.kt b/tests/unit/java/com/android/server/connectivity/mdns/util/MdnsUtilsTest.kt
new file mode 100644
index 0000000..f584ed5
--- /dev/null
+++ b/tests/unit/java/com/android/server/connectivity/mdns/util/MdnsUtilsTest.kt
@@ -0,0 +1,68 @@
+/*
+ * Copyright (C) 2023 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 com.android.server.connectivity.mdns.util
+
+import android.os.Build
+import com.android.server.connectivity.mdns.util.MdnsUtils.equalsIgnoreDnsCase
+import com.android.server.connectivity.mdns.util.MdnsUtils.toDnsLowerCase
+import com.android.testutils.DevSdkIgnoreRule
+import com.android.testutils.DevSdkIgnoreRunner
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+import org.junit.runner.RunWith
+
+@RunWith(DevSdkIgnoreRunner::class)
+@DevSdkIgnoreRule.IgnoreUpTo(Build.VERSION_CODES.S_V2)
+class MdnsUtilsTest {
+    @Test
+    fun testToDnsLowerCase() {
+        assertEquals("test", toDnsLowerCase("TEST"))
+        assertEquals("test", toDnsLowerCase("TeSt"))
+        assertEquals("test", toDnsLowerCase("test"))
+        assertEquals("tÉst", toDnsLowerCase("TÉST"))
+        assertEquals("ţést", toDnsLowerCase("ţést"))
+        // Unicode characters 0x10000 (𐀀), 0x10001 (𐀁), 0x10041 (𐁁)
+        // Note the last 2 bytes of 0x10041 are identical to 'A', but it should remain unchanged.
+        assertEquals("test: -->\ud800\udc00 \ud800\udc01 \ud800\udc41<-- ",
+                toDnsLowerCase("Test: -->\ud800\udc00 \ud800\udc01 \ud800\udc41<-- "))
+        // Also test some characters where the first surrogate is not \ud800
+        assertEquals("test: >\ud83c\udff4\udb40\udc67\udb40\udc62\udb40" +
+                "\udc77\udb40\udc6c\udb40\udc73\udb40\udc7f<",
+                toDnsLowerCase("Test: >\ud83c\udff4\udb40\udc67\udb40\udc62\udb40" +
+                        "\udc77\udb40\udc6c\udb40\udc73\udb40\udc7f<"))
+    }
+
+    @Test
+    fun testEqualsIgnoreDnsCase() {
+        assertTrue(equalsIgnoreDnsCase("TEST", "Test"))
+        assertTrue(equalsIgnoreDnsCase("TEST", "test"))
+        assertTrue(equalsIgnoreDnsCase("test", "TeSt"))
+        assertTrue(equalsIgnoreDnsCase("Tést", "tést"))
+        assertFalse(equalsIgnoreDnsCase("ŢÉST", "ţést"))
+        // Unicode characters 0x10000 (𐀀), 0x10001 (𐀁), 0x10041 (𐁁)
+        // Note the last 2 bytes of 0x10041 are identical to 'A', but it should remain unchanged.
+        assertTrue(equalsIgnoreDnsCase("test: -->\ud800\udc00 \ud800\udc01 \ud800\udc41<-- ",
+                "Test: -->\ud800\udc00 \ud800\udc01 \ud800\udc41<-- "))
+        // Also test some characters where the first surrogate is not \ud800
+        assertTrue(equalsIgnoreDnsCase("test: >\ud83c\udff4\udb40\udc67\udb40\udc62\udb40" +
+                "\udc77\udb40\udc6c\udb40\udc73\udb40\udc7f<",
+                "Test: >\ud83c\udff4\udb40\udc67\udb40\udc62\udb40" +
+                        "\udc77\udb40\udc6c\udb40\udc73\udb40\udc7f<"))
+    }
+}