diff --git a/hadoop-common-project/hadoop-common/CHANGES.txt b/hadoop-common-project/hadoop-common/CHANGES.txt
index ad2b336fb3..a1ac0440be 100644
--- a/hadoop-common-project/hadoop-common/CHANGES.txt
+++ b/hadoop-common-project/hadoop-common/CHANGES.txt
@@ -17,6 +17,8 @@ Trunk (Unreleased)
 
     HADOOP-9380 Add totalLength to rpc response  (sanjay Radia)
 
+    HADOOP-9194. RPC Support for QoS. (Junping Du via llu)
+
   NEW FEATURES
     
     HADOOP-8561. Introduce HADOOP_PROXY_USER for secure impersonation in child
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/Client.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/Client.java
index 5294aa3b94..986b1a2c15 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/Client.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/Client.java
@@ -257,6 +257,7 @@ private class Connection extends Thread {
     private final ConnectionId remoteId;                // connection id
     private AuthMethod authMethod; // authentication method
     private Token<? extends TokenIdentifier> token;
+    private int serviceClass;
     private SaslRpcClient saslRpcClient;
     
     private Socket socket = null;                 // connected socket
@@ -279,7 +280,7 @@ private class Connection extends Thread {
     
     private final Object sendRpcRequestLock = new Object();
 
-    public Connection(ConnectionId remoteId) throws IOException {
+    public Connection(ConnectionId remoteId, int serviceClass) throws IOException {
       this.remoteId = remoteId;
       this.server = remoteId.getAddress();
       if (server.isUnresolved()) {
@@ -296,6 +297,7 @@ public Connection(ConnectionId remoteId) throws IOException {
       this.tcpNoDelay = remoteId.getTcpNoDelay();
       this.doPing = remoteId.getDoPing();
       this.pingInterval = remoteId.getPingInterval();
+      this.serviceClass = serviceClass;
       if (LOG.isDebugEnabled()) {
         LOG.debug("The ping interval is " + this.pingInterval + " ms.");
       }
@@ -747,7 +749,9 @@ private void handleConnectionFailure(int curRetries, IOException ioe
      * +----------------------------------+
      * |  "hrpc" 4 bytes                  |      
      * +----------------------------------+
-     * |  Version (1 bytes)               |      
+     * |  Version (1 byte)                |
+     * +----------------------------------+
+     * |  Service Class (1 byte)          |
      * +----------------------------------+
      * |  Authmethod (1 byte)             |      
      * +----------------------------------+
@@ -760,6 +764,7 @@ private void writeConnectionHeader(OutputStream outStream)
       // Write out the header, version and authentication method
       out.write(Server.HEADER.array());
       out.write(Server.CURRENT_VERSION);
+      out.write(serviceClass);
       authMethod.write(out);
       Server.IpcSerializationType.PROTOBUF.write(out);
       out.flush();
@@ -1179,19 +1184,33 @@ public Writable call(RPC.RpcKind rpcKind, Writable param, InetSocketAddress addr
 
   
   /**
-   * Same as {@link #call(RPC.RpcKind, Writable, InetSocketAddress, 
+   * Same as {@link #call(RPC.RpcKind, Writable, InetSocketAddress,
    * Class, UserGroupInformation, int, Configuration)}
    * except that rpcKind is writable.
    */
-  public Writable call(Writable param, InetSocketAddress addr, 
+  public Writable call(Writable param, InetSocketAddress addr,
       Class<?> protocol, UserGroupInformation ticket,
-      int rpcTimeout, Configuration conf)  
+      int rpcTimeout, Configuration conf)
       throws InterruptedException, IOException {
-        ConnectionId remoteId = ConnectionId.getConnectionId(addr, protocol,
+    ConnectionId remoteId = ConnectionId.getConnectionId(addr, protocol,
         ticket, rpcTimeout, conf);
     return call(RPC.RpcKind.RPC_BUILTIN, param, remoteId);
   }
   
+  /**
+   * Same as {@link #call(Writable, InetSocketAddress,
+   * Class, UserGroupInformation, int, Configuration)}
+   * except that specifying serviceClass.
+   */
+  public Writable call(Writable param, InetSocketAddress addr,
+      Class<?> protocol, UserGroupInformation ticket,
+      int rpcTimeout, int serviceClass, Configuration conf)
+      throws InterruptedException, IOException {
+    ConnectionId remoteId = ConnectionId.getConnectionId(addr, protocol,
+        ticket, rpcTimeout, conf);
+    return call(RPC.RpcKind.RPC_BUILTIN, param, remoteId, serviceClass);
+  }
+
   /**
    * Make a call, passing <code>param</code>, to the IPC server running at
    * <code>address</code> which is servicing the <code>protocol</code> protocol,
@@ -1218,10 +1237,10 @@ public Writable call(Writable param, ConnectionId remoteId)
      return call(RPC.RpcKind.RPC_BUILTIN, param, remoteId);
   }
   
-  /** 
+  /**
    * Make a call, passing <code>rpcRequest</code>, to the IPC server defined by
    * <code>remoteId</code>, returning the rpc respond.
-   * 
+   *
    * @param rpcKind
    * @param rpcRequest -  contains serialized method and method parameters
    * @param remoteId - the target rpc server
@@ -1231,8 +1250,26 @@ public Writable call(Writable param, ConnectionId remoteId)
    */
   public Writable call(RPC.RpcKind rpcKind, Writable rpcRequest,
       ConnectionId remoteId) throws InterruptedException, IOException {
+    return call(rpcKind, rpcRequest, remoteId, RPC.RPC_SERVICE_CLASS_DEFAULT);
+  }
+
+  /** 
+   * Make a call, passing <code>rpcRequest</code>, to the IPC server defined by
+   * <code>remoteId</code>, returning the rpc respond.
+   * 
+   * @param rpcKind
+   * @param rpcRequest -  contains serialized method and method parameters
+   * @param remoteId - the target rpc server
+   * @param serviceClass - service class for RPC
+   * @returns the rpc response
+   * Throws exceptions if there are network problems or if the remote code 
+   * threw an exception.
+   */
+  public Writable call(RPC.RpcKind rpcKind, Writable rpcRequest,
+      ConnectionId remoteId, int serviceClass)
+      throws InterruptedException, IOException {
     Call call = new Call(rpcKind, rpcRequest);
-    Connection connection = getConnection(remoteId, call);
+    Connection connection = getConnection(remoteId, call, serviceClass);
     try {
       connection.sendRpcRequest(call);                 // send the rpc request
     } catch (RejectedExecutionException e) {
@@ -1289,7 +1326,7 @@ Set<ConnectionId> getConnectionIds() {
   /** Get a connection from the pool, or create a new one and add it to the
    * pool.  Connections to a given ConnectionId are reused. */
   private Connection getConnection(ConnectionId remoteId,
-                                   Call call)
+                                   Call call, int serviceClass)
                                    throws IOException, InterruptedException {
     if (!running.get()) {
       // the client is stopped
@@ -1304,7 +1341,7 @@ private Connection getConnection(ConnectionId remoteId,
       synchronized (connections) {
         connection = connections.get(remoteId);
         if (connection == null) {
-          connection = new Connection(remoteId);
+          connection = new Connection(remoteId, serviceClass);
           connections.put(remoteId, connection);
         }
       }
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/RPC.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/RPC.java
index 8ee22aa415..3563e07dba 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/RPC.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/RPC.java
@@ -77,12 +77,12 @@
 @InterfaceAudience.LimitedPrivate(value = { "Common", "HDFS", "MapReduce", "Yarn" })
 @InterfaceStability.Evolving
 public class RPC {
+  final static int RPC_SERVICE_CLASS_DEFAULT = 0;
   public enum RpcKind {
     RPC_BUILTIN ((short) 1),         // Used for built in calls by tests
     RPC_WRITABLE ((short) 2),        // Use WritableRpcEngine 
     RPC_PROTOCOL_BUFFER ((short) 3); // Use ProtobufRpcEngine
     final static short MAX_INDEX = RPC_PROTOCOL_BUFFER.value; // used for array size
-    private static final short FIRST_INDEX = RPC_BUILTIN.value;    
     public final short value; //TODO make it private
 
     RpcKind(short val) {
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/Server.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/Server.java
index c44eb9426d..f76690c27f 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/Server.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/Server.java
@@ -438,6 +438,11 @@ Iterable<? extends Thread> getHandlers() {
     return Arrays.asList(handlers);
   }
 
+  @VisibleForTesting
+  List<Connection> getConnections() {
+    return connectionList;
+  }
+
   /**
    * Refresh the service authorization ACL for the service handled by this server.
    */
@@ -1104,6 +1109,7 @@ public class Connection {
     private ByteBuffer connectionHeaderBuf = null;
     private ByteBuffer unwrappedData;
     private ByteBuffer unwrappedDataLengthBuffer;
+    private int serviceClass;
     
     UserGroupInformation user = null;
     public UserGroupInformation attemptingUser = null; // user name before auth
@@ -1314,14 +1320,17 @@ public int readAndProcess() throws IOException, InterruptedException {
         if (!connectionHeaderRead) {
           //Every connection is expected to send the header.
           if (connectionHeaderBuf == null) {
-            connectionHeaderBuf = ByteBuffer.allocate(3);
+            connectionHeaderBuf = ByteBuffer.allocate(4);
           }
           count = channelRead(channel, connectionHeaderBuf);
           if (count < 0 || connectionHeaderBuf.remaining() > 0) {
             return count;
           }
           int version = connectionHeaderBuf.get(0);
-          byte[] method = new byte[] {connectionHeaderBuf.get(1)};
+          // TODO we should add handler for service class later
+          this.setServiceClass(connectionHeaderBuf.get(1));
+
+          byte[] method = new byte[] {connectionHeaderBuf.get(2)};
           authMethod = AuthMethod.read(new DataInputStream(
               new ByteArrayInputStream(method)));
           dataLengthBuffer.flip();
@@ -1345,7 +1354,7 @@ public int readAndProcess() throws IOException, InterruptedException {
           }
           
           IpcSerializationType serializationType = IpcSerializationType
-              .fromByte(connectionHeaderBuf.get(2));
+              .fromByte(connectionHeaderBuf.get(3));
           if (serializationType != IpcSerializationType.PROTOBUF) {
             respondUnsupportedSerialization(serializationType);
             return -1;
@@ -1735,6 +1744,22 @@ private boolean authorizeConnection() throws IOException {
       return true;
     }
     
+    /**
+     * Get service class for connection
+     * @return the serviceClass
+     */
+    public int getServiceClass() {
+      return serviceClass;
+    }
+
+    /**
+     * Set service class for connection
+     * @param serviceClass the serviceClass to set
+     */
+    public void setServiceClass(int serviceClass) {
+      this.serviceClass = serviceClass;
+    }
+
     private synchronized void close() throws IOException {
       disposeSasl();
       data = null;
diff --git a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/ipc/TestIPC.java b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/ipc/TestIPC.java
index 3847bfd081..24b20f89ef 100644
--- a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/ipc/TestIPC.java
+++ b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/ipc/TestIPC.java
@@ -25,6 +25,7 @@
 import org.apache.hadoop.io.IntWritable;
 import org.apache.hadoop.io.Writable;
 import org.apache.hadoop.io.LongWritable;
+import org.apache.hadoop.ipc.Server.Connection;
 import org.apache.hadoop.util.StringUtils;
 import org.apache.hadoop.net.ConnectTimeoutException;
 import org.apache.hadoop.net.NetUtils;
@@ -520,11 +521,53 @@ public void testIpcConnectTimeout() throws Exception {
     }
   }
   
+  /**
+   * Check service class byte in IPC header is correct on wire.
+   */
+  @Test(timeout=60000)
+  public void testIpcWithServiceClass() throws Exception {
+    // start server
+    Server server = new TestServer(5, false);
+    InetSocketAddress addr = NetUtils.getConnectAddress(server);
+    server.start();
+
+    // start client
+    Client.setConnectTimeout(conf, 10000);
+
+    callAndVerify(server, addr, 0, true);
+    // Service Class is low to -128 as byte on wire.
+    // -128 shouldn't be casted on wire but -129 should.
+    callAndVerify(server, addr, -128, true);
+    callAndVerify(server, addr, -129, false);
+
+    // Service Class is up to 127.
+    // 127 shouldn't be casted on wire but 128 should.
+    callAndVerify(server, addr, 127, true);
+    callAndVerify(server, addr, 128, false);
+
+    server.stop();
+  }
+
+  /**
+   * Make a call from a client and verify if header info is changed in server side
+   */
+  private void callAndVerify(Server server, InetSocketAddress addr,
+      int serviceClass, boolean noChanged) throws Exception{
+    Client client = new Client(LongWritable.class, conf);
+
+    client.call(new LongWritable(RANDOM.nextLong()),
+        addr, null, null, MIN_SLEEP_TIME, serviceClass, conf);
+    Connection connection = server.getConnections().get(0);
+    int serviceClass2 = connection.getServiceClass();
+    assertFalse(noChanged ^ serviceClass == serviceClass2);
+    client.stop();
+  }
+
   /**
    * Check that file descriptors aren't leaked by starting
    * and stopping IPC servers.
    */
-  @Test
+  @Test(timeout=60000)
   public void testSocketLeak() throws Exception {
     Assume.assumeTrue(FD_DIR.exists()); // only run on Linux