diff --git a/core/java/android/net/NetworkCapabilities.java b/core/java/android/net/NetworkCapabilities.java
index 0bdfca7..0c44a56 100644
--- a/core/java/android/net/NetworkCapabilities.java
+++ b/core/java/android/net/NetworkCapabilities.java
@@ -17,6 +17,7 @@
 package android.net;
 
 import android.annotation.IntDef;
+import android.annotation.Nullable;
 import android.annotation.SystemApi;
 import android.annotation.TestApi;
 import android.annotation.UnsupportedAppUsage;
@@ -79,6 +80,7 @@
         mNetworkCapabilities = mTransportTypes = mUnwantedNetworkCapabilities = 0;
         mLinkUpBandwidthKbps = mLinkDownBandwidthKbps = LINK_BANDWIDTH_UNSPECIFIED;
         mNetworkSpecifier = null;
+        mTransportInfo = null;
         mSignalStrength = SIGNAL_STRENGTH_UNSPECIFIED;
         mUids = null;
         mEstablishingVpnAppUid = INVALID_UID;
@@ -95,6 +97,7 @@
         mLinkUpBandwidthKbps = nc.mLinkUpBandwidthKbps;
         mLinkDownBandwidthKbps = nc.mLinkDownBandwidthKbps;
         mNetworkSpecifier = nc.mNetworkSpecifier;
+        mTransportInfo = nc.mTransportInfo;
         mSignalStrength = nc.mSignalStrength;
         setUids(nc.mUids); // Will make the defensive copy
         mEstablishingVpnAppUid = nc.mEstablishingVpnAppUid;
@@ -874,6 +877,7 @@
     }
 
     private NetworkSpecifier mNetworkSpecifier = null;
+    private TransportInfo mTransportInfo = null;
 
     /**
      * Sets the optional bearer specific network specifier.
@@ -899,6 +903,19 @@
     }
 
     /**
+     * Sets the optional transport specific information.
+     *
+     * @param transportInfo A concrete, parcelable framework class that extends
+     * {@link TransportInfo}.
+     * @return This NetworkCapabilities instance, to facilitate chaining.
+     * @hide
+     */
+    public NetworkCapabilities setTransportInfo(TransportInfo transportInfo) {
+        mTransportInfo = transportInfo;
+        return this;
+    }
+
+    /**
      * Gets the optional bearer specific network specifier.
      *
      * @return The optional {@link NetworkSpecifier} specifying the bearer specific network
@@ -910,6 +927,19 @@
         return mNetworkSpecifier;
     }
 
+    /**
+     * Returns a transport-specific information container. The application may cast this
+     * container to a concrete sub-class based on its knowledge of the network request. The
+     * application should be able to deal with a {@code null} return value or an invalid case,
+     * e.g. use {@code instanceof} operation to verify expected type.
+     *
+     * @return A concrete implementation of the {@link TransportInfo} class or null if not
+     * available for the network.
+     */
+    @Nullable public TransportInfo getTransportInfo() {
+        return mTransportInfo;
+    }
+
     private void combineSpecifiers(NetworkCapabilities nc) {
         if (mNetworkSpecifier != null && !mNetworkSpecifier.equals(nc.mNetworkSpecifier)) {
             throw new IllegalStateException("Can't combine two networkSpecifiers");
@@ -926,6 +956,17 @@
         return Objects.equals(mNetworkSpecifier, nc.mNetworkSpecifier);
     }
 
+    private void combineTransportInfos(NetworkCapabilities nc) {
+        if (mTransportInfo != null && !mTransportInfo.equals(nc.mTransportInfo)) {
+            throw new IllegalStateException("Can't combine two TransportInfos");
+        }
+        setTransportInfo(nc.mTransportInfo);
+    }
+
+    private boolean equalsTransportInfo(NetworkCapabilities nc) {
+        return Objects.equals(mTransportInfo, nc.mTransportInfo);
+    }
+
     /**
      * Magic value that indicates no signal strength provided. A request specifying this value is
      * always satisfied.
@@ -1238,6 +1279,7 @@
         combineTransportTypes(nc);
         combineLinkBandwidths(nc);
         combineSpecifiers(nc);
+        combineTransportInfos(nc);
         combineSignalStrength(nc);
         combineUids(nc);
         combineSSIDs(nc);
@@ -1347,6 +1389,7 @@
                 && equalsLinkBandwidths(that)
                 && equalsSignalStrength(that)
                 && equalsSpecifier(that)
+                && equalsTransportInfo(that)
                 && equalsUids(that)
                 && equalsSSID(that));
     }
@@ -1364,7 +1407,8 @@
                 + Objects.hashCode(mNetworkSpecifier) * 23
                 + (mSignalStrength * 29)
                 + Objects.hashCode(mUids) * 31
-                + Objects.hashCode(mSSID) * 37;
+                + Objects.hashCode(mSSID) * 37
+                + Objects.hashCode(mTransportInfo) * 41;
     }
 
     @Override
@@ -1379,6 +1423,7 @@
         dest.writeInt(mLinkUpBandwidthKbps);
         dest.writeInt(mLinkDownBandwidthKbps);
         dest.writeParcelable((Parcelable) mNetworkSpecifier, flags);
+        dest.writeParcelable((Parcelable) mTransportInfo, flags);
         dest.writeInt(mSignalStrength);
         dest.writeArraySet(mUids);
         dest.writeString(mSSID);
@@ -1396,6 +1441,7 @@
                 netCap.mLinkUpBandwidthKbps = in.readInt();
                 netCap.mLinkDownBandwidthKbps = in.readInt();
                 netCap.mNetworkSpecifier = in.readParcelable(null);
+                netCap.mTransportInfo = in.readParcelable(null);
                 netCap.mSignalStrength = in.readInt();
                 netCap.mUids = (ArraySet<UidRange>) in.readArraySet(
                         null /* ClassLoader, null for default */);
@@ -1435,6 +1481,9 @@
         if (mNetworkSpecifier != null) {
             sb.append(" Specifier: <").append(mNetworkSpecifier).append(">");
         }
+        if (mTransportInfo != null) {
+            sb.append(" TransportInfo: <").append(mTransportInfo).append(">");
+        }
         if (hasSignalStrength()) {
             sb.append(" SignalStrength: ").append(mSignalStrength);
         }
@@ -1501,6 +1550,9 @@
         if (mNetworkSpecifier != null) {
             proto.write(NetworkCapabilitiesProto.NETWORK_SPECIFIER, mNetworkSpecifier.toString());
         }
+        if (mTransportInfo != null) {
+            // TODO b/120653863: write transport-specific info to proto?
+        }
 
         proto.write(NetworkCapabilitiesProto.CAN_REPORT_SIGNAL_STRENGTH, hasSignalStrength());
         proto.write(NetworkCapabilitiesProto.SIGNAL_STRENGTH, mSignalStrength);
diff --git a/core/java/android/net/TransportInfo.java b/core/java/android/net/TransportInfo.java
new file mode 100644
index 0000000..b78d3fe
--- /dev/null
+++ b/core/java/android/net/TransportInfo.java
@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2018 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.net;
+
+/**
+ * A container for transport-specific capabilities which is returned by
+ * {@link NetworkCapabilities#getTransportInfo()}. Specific networks
+ * may provide concrete implementations of this interface.
+ */
+public interface TransportInfo {
+}
diff --git a/services/core/java/com/android/server/ConnectivityService.java b/services/core/java/com/android/server/ConnectivityService.java
index bb3b9f7..14503f9 100644
--- a/services/core/java/com/android/server/ConnectivityService.java
+++ b/services/core/java/com/android/server/ConnectivityService.java
@@ -274,7 +274,8 @@
     private int mDefaultInetConditionPublished = 0;
 
     private INetworkManagementService mNMS;
-    private INetd mNetd;
+    @VisibleForTesting
+    protected INetd mNetd;
     private INetworkStatsService mStatsService;
     private INetworkPolicyManager mPolicyManager;
     private NetworkPolicyManagerInternal mPolicyManagerInternal;
@@ -2090,7 +2091,8 @@
         }
     }
 
-    private static final String DEFAULT_TCP_BUFFER_SIZES = "4096,87380,110208,4096,16384,110208";
+    @VisibleForTesting
+    protected static final String DEFAULT_TCP_BUFFER_SIZES = "4096,87380,110208,4096,16384,110208";
     private static final String DEFAULT_TCP_RWND_KEY = "net.tcp.default_init_rwnd";
 
     // Overridden for testing purposes to avoid writing to SystemProperties.
@@ -2116,15 +2118,11 @@
         try {
             if (VDBG || DDBG) Slog.d(TAG, "Setting tx/rx TCP buffers to " + tcpBufferSizes);
 
-            final String prefix = "/sys/kernel/ipv4/tcp_";
-            FileUtils.stringToFile(prefix + "rmem_min", values[0]);
-            FileUtils.stringToFile(prefix + "rmem_def", values[1]);
-            FileUtils.stringToFile(prefix + "rmem_max", values[2]);
-            FileUtils.stringToFile(prefix + "wmem_min", values[3]);
-            FileUtils.stringToFile(prefix + "wmem_def", values[4]);
-            FileUtils.stringToFile(prefix + "wmem_max", values[5]);
+            String rmemValues = String.join(" ", values[0], values[1], values[2]);
+            String wmemValues = String.join(" ", values[3], values[4], values[5]);
+            mNetd.setTcpRWmemorySize(rmemValues, wmemValues);
             mCurrentTcpBufferSizes = tcpBufferSizes;
-        } catch (IOException e) {
+        } catch (RemoteException | ServiceSpecificException e) {
             loge("Can't set TCP buffer sizes:" + e);
         }
 
diff --git a/tests/net/java/android/net/NetworkCapabilitiesTest.java b/tests/net/java/android/net/NetworkCapabilitiesTest.java
index b40921f..50aef1d 100644
--- a/tests/net/java/android/net/NetworkCapabilitiesTest.java
+++ b/tests/net/java/android/net/NetworkCapabilitiesTest.java
@@ -24,9 +24,9 @@
 import static android.net.NetworkCapabilities.NET_CAPABILITY_MMS;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_NOT_METERED;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_NOT_RESTRICTED;
-import static android.net.NetworkCapabilities.NET_CAPABILITY_OEM_PAID;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_NOT_ROAMING;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_NOT_VPN;
+import static android.net.NetworkCapabilities.NET_CAPABILITY_OEM_PAID;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_VALIDATED;
 import static android.net.NetworkCapabilities.NET_CAPABILITY_WIFI_P2P;
 import static android.net.NetworkCapabilities.RESTRICTED_CAPABILITIES;
@@ -46,7 +46,6 @@
 import android.test.suitebuilder.annotation.SmallTest;
 import android.util.ArraySet;
 
-
 import org.junit.Test;
 import org.junit.runner.RunWith;
 
@@ -457,6 +456,62 @@
         assertEquals(nc1, nc2);
     }
 
+    @Test
+    public void testSetNetworkSpecifierOnMultiTransportNc() {
+        // Sequence 1: Transport + Transport + NetworkSpecifier
+        NetworkCapabilities nc1 = new NetworkCapabilities();
+        nc1.addTransportType(TRANSPORT_CELLULAR).addTransportType(TRANSPORT_WIFI);
+        try {
+            nc1.setNetworkSpecifier(new StringNetworkSpecifier("specs"));
+            fail("Cannot set NetworkSpecifier on a NetworkCapability with multiple transports!");
+        } catch (IllegalStateException expected) {
+            // empty
+        }
+
+        // Sequence 2: Transport + NetworkSpecifier + Transport
+        NetworkCapabilities nc2 = new NetworkCapabilities();
+        nc2.addTransportType(TRANSPORT_CELLULAR).setNetworkSpecifier(
+                new StringNetworkSpecifier("specs"));
+        try {
+            nc2.addTransportType(TRANSPORT_WIFI);
+            fail("Cannot set NetworkSpecifier on a NetworkCapability with multiple transports!");
+        } catch (IllegalStateException expected) {
+            // empty
+        }
+    }
+
+    @Test
+    public void testSetTransportInfoOnMultiTransportNc() {
+        // Sequence 1: Transport + Transport + TransportInfo
+        NetworkCapabilities nc1 = new NetworkCapabilities();
+        nc1.addTransportType(TRANSPORT_CELLULAR).addTransportType(TRANSPORT_WIFI)
+                .setTransportInfo(new TransportInfo() {});
+
+        // Sequence 2: Transport + NetworkSpecifier + Transport
+        NetworkCapabilities nc2 = new NetworkCapabilities();
+        nc2.addTransportType(TRANSPORT_CELLULAR).setTransportInfo(new TransportInfo() {})
+                .addTransportType(TRANSPORT_WIFI);
+    }
+
+    @Test
+    public void testCombineTransportInfo() {
+        NetworkCapabilities nc1 = new NetworkCapabilities();
+        nc1.setTransportInfo(new TransportInfo() {
+            // empty
+        });
+        NetworkCapabilities nc2 = new NetworkCapabilities();
+        nc2.setTransportInfo(new TransportInfo() {
+            // empty
+        });
+
+        try {
+            nc1.combineCapabilities(nc2);
+            fail("Should not be able to combine NetworkCaabilities which contain TransportInfos");
+        } catch (IllegalStateException expected) {
+            // empty
+        }
+    }
+
     private void assertEqualsThroughMarshalling(NetworkCapabilities netCap) {
         Parcel p = Parcel.obtain();
         netCap.writeToParcel(p, /* flags */ 0);
diff --git a/tests/net/java/com/android/server/ConnectivityServiceTest.java b/tests/net/java/com/android/server/ConnectivityServiceTest.java
index 17bcea0..71529fd 100644
--- a/tests/net/java/com/android/server/ConnectivityServiceTest.java
+++ b/tests/net/java/com/android/server/ConnectivityServiceTest.java
@@ -96,6 +96,7 @@
 import android.net.ConnectivityManager.PacketKeepaliveCallback;
 import android.net.ConnectivityManager.TooManyRequestsException;
 import android.net.ConnectivityThread;
+import android.net.INetd;
 import android.net.INetworkPolicyListener;
 import android.net.INetworkPolicyManager;
 import android.net.INetworkStatsService;
@@ -228,6 +229,7 @@
     @Mock INetworkManagementService mNetworkManagementService;
     @Mock INetworkStatsService mStatsService;
     @Mock INetworkPolicyManager mNpm;
+    @Mock INetd mMockNetd;
 
     private ArgumentCaptor<String[]> mStringArrayCaptor = ArgumentCaptor.forClass(String[].class);
 
@@ -926,8 +928,9 @@
 
         public WrappedConnectivityService(Context context, INetworkManagementService netManager,
                 INetworkStatsService statsService, INetworkPolicyManager policyManager,
-                IpConnectivityLog log) {
+                IpConnectivityLog log, INetd netd) {
             super(context, netManager, statsService, policyManager, log);
+            mNetd = netd;
             mLingerDelayMs = TEST_LINGER_DELAY_MS;
         }
 
@@ -1087,7 +1090,8 @@
                 mNetworkManagementService,
                 mStatsService,
                 mNpm,
-                mock(IpConnectivityLog.class));
+                mock(IpConnectivityLog.class),
+                mMockNetd);
 
         final ArgumentCaptor<INetworkPolicyListener> policyListenerCaptor =
                 ArgumentCaptor.forClass(INetworkPolicyListener.class);
@@ -4766,4 +4770,30 @@
         // Clean up
         mCm.unregisterNetworkCallback(networkCallback);
     }
+
+    private static final String TEST_TCP_BUFFER_SIZES = "1,2,3,4,5,6";
+
+    private void verifyTcpBufferSizeChange(String tcpBufferSizes) throws Exception {
+        String[] values = tcpBufferSizes.split(",");
+        String rmemValues = String.join(" ", values[0], values[1], values[2]);
+        String wmemValues = String.join(" ", values[3], values[4], values[5]);
+        waitForIdle();
+        verify(mMockNetd, atLeastOnce()).setTcpRWmemorySize(rmemValues, wmemValues);
+        reset(mMockNetd);
+    }
+
+    @Test
+    public void testTcpBufferReset() throws Exception {
+        mCellNetworkAgent = new MockNetworkAgent(TRANSPORT_CELLULAR);
+        reset(mMockNetd);
+        // Simple connection should have updated tcp buffer size.
+        mCellNetworkAgent.connect(false);
+        verifyTcpBufferSizeChange(ConnectivityService.DEFAULT_TCP_BUFFER_SIZES);
+
+        // Change link Properties should have updated tcp buffer size.
+        LinkProperties lp = new LinkProperties();
+        lp.setTcpBufferSizes(TEST_TCP_BUFFER_SIZES);
+        mCellNetworkAgent.sendLinkProperties(lp);
+        verifyTcpBufferSizeChange(TEST_TCP_BUFFER_SIZES);
+    }
 }
diff --git a/tests/net/java/com/android/server/IpSecServiceParameterizedTest.java b/tests/net/java/com/android/server/IpSecServiceParameterizedTest.java
index 4dc0341..d8f9618 100644
--- a/tests/net/java/com/android/server/IpSecServiceParameterizedTest.java
+++ b/tests/net/java/com/android/server/IpSecServiceParameterizedTest.java
@@ -542,7 +542,7 @@
 
         verify(mMockNetd)
                 .ipSecApplyTransportModeTransform(
-                        eq(pfd.getFileDescriptor()),
+                        eq(pfd),
                         eq(mUid),
                         eq(IpSecManager.DIRECTION_OUT),
                         anyString(),
@@ -555,7 +555,7 @@
         ParcelFileDescriptor pfd = ParcelFileDescriptor.fromSocket(new Socket());
         mIpSecService.removeTransportModeTransforms(pfd);
 
-        verify(mMockNetd).ipSecRemoveTransportModeTransform(pfd.getFileDescriptor());
+        verify(mMockNetd).ipSecRemoveTransportModeTransform(pfd);
     }
 
     private IpSecTunnelInterfaceResponse createAndValidateTunnel(
diff --git a/tests/net/java/com/android/server/IpSecServiceTest.java b/tests/net/java/com/android/server/IpSecServiceTest.java
index 2c94a60..724446e 100644
--- a/tests/net/java/com/android/server/IpSecServiceTest.java
+++ b/tests/net/java/com/android/server/IpSecServiceTest.java
@@ -425,7 +425,7 @@
         ParcelFileDescriptor pfd = ParcelFileDescriptor.fromSocket(new Socket());
         mIpSecService.removeTransportModeTransforms(pfd);
 
-        verify(mMockNetd).ipSecRemoveTransportModeTransform(pfd.getFileDescriptor());
+        verify(mMockNetd).ipSecRemoveTransportModeTransform(pfd);
     }
 
     @Test
@@ -620,10 +620,10 @@
                 mIpSecService.openUdpEncapsulationSocket(0, new Binder());
 
         FileDescriptor sockFd = udpEncapResp.fileDescriptor.getFileDescriptor();
-        ArgumentMatcher<FileDescriptor> fdMatcher = (arg) -> {
+        ArgumentMatcher<ParcelFileDescriptor> fdMatcher = (arg) -> {
                     try {
                         StructStat sockStat = Os.fstat(sockFd);
-                        StructStat argStat = Os.fstat(arg);
+                        StructStat argStat = Os.fstat(arg.getFileDescriptor());
 
                         return sockStat.st_ino == argStat.st_ino
                                 && sockStat.st_dev == argStat.st_dev;