diff --git a/websocket-sharp/Ext.cs b/websocket-sharp/Ext.cs
index 7e90ebf1..7ecb912c 100644
--- a/websocket-sharp/Ext.cs
+++ b/websocket-sharp/Ext.cs
@@ -223,18 +223,24 @@ namespace WebSocketSharp
                  : null;
     }
 
-    internal static string CheckIfStarted (this ServerState state)
+    internal static string CheckIfStart (this ServerState state)
     {
-      return state != ServerState.START
-             ? "Any of not started, on shutdown or stopped."
-             : null;
+      return state == ServerState.READY
+             ? "The server hasn't started yet."
+             : state == ServerState.SHUTDOWN
+               ? "The server is shutting down."
+               : state == ServerState.STOP
+                 ? "The server has already stopped."
+                 : null;
     }
 
     internal static string CheckIfStopped (this ServerState state)
     {
-      return state == ServerState.START || state == ServerState.SHUTDOWN
-             ? "Already started or on shutdown."
-             : null;
+      return state == ServerState.START
+             ? "The server has already started."
+             : state == ServerState.SHUTDOWN
+               ? "The server is shutting down."
+               : null;
     }
 
     internal static string CheckIfValidCloseStatusCode (this ushort code)
@@ -259,6 +265,13 @@ namespace WebSocketSharp
              : null;
     }
 
+    internal static string CheckIfValidSendData (this FileInfo file)
+    {
+      return file == null
+             ? "'file' must not be null."
+             : null;
+    }
+
     internal static string CheckIfValidSendData (this string data)
     {
       return data == null
diff --git a/websocket-sharp/Server/HttpServer.cs b/websocket-sharp/Server/HttpServer.cs
index 80876224..99d99b17 100644
--- a/websocket-sharp/Server/HttpServer.cs
+++ b/websocket-sharp/Server/HttpServer.cs
@@ -537,7 +537,7 @@ namespace WebSocketSharp.Server
 
     private string checkIfCanStop (Func<string> checkParams)
     {
-      return _state.CheckIfStarted () ?? checkParams ();
+      return _state.CheckIfStart () ?? checkParams ();
     }
 
     private string checkIfCertExists ()
@@ -742,7 +742,7 @@ namespace WebSocketSharp.Server
     public void Stop ()
     {
       lock (_sync) {
-        var msg = _state.CheckIfStarted ();
+        var msg = _state.CheckIfStart ();
         if (msg != null) {
           _logger.Error (String.Format ("{0}\nstate: {1}", msg, _state));
           return;
diff --git a/websocket-sharp/Server/WebSocketServer.cs b/websocket-sharp/Server/WebSocketServer.cs
index 9d2f83cf..8b127d64 100644
--- a/websocket-sharp/Server/WebSocketServer.cs
+++ b/websocket-sharp/Server/WebSocketServer.cs
@@ -551,7 +551,7 @@ namespace WebSocketSharp.Server
 
     private string checkIfCanStop (Func<string> checkParams)
     {
-      return _state.CheckIfStarted () ?? checkParams ();
+      return _state.CheckIfStart () ?? checkParams ();
     }
 
     private string checkIfCertExists ()
@@ -758,7 +758,7 @@ namespace WebSocketSharp.Server
     public void Stop ()
     {
       lock (_sync) {
-        var msg = _state.CheckIfStarted ();
+        var msg = _state.CheckIfStart ();
         if (msg != null) {
           _logger.Error (String.Format ("{0}\nstate: {1}", msg, _state));
           return;
diff --git a/websocket-sharp/Server/WebSocketService.cs b/websocket-sharp/Server/WebSocketService.cs
index 2089c49a..906283e3 100644
--- a/websocket-sharp/Server/WebSocketService.cs
+++ b/websocket-sharp/Server/WebSocketService.cs
@@ -270,11 +270,11 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Sends a binary <paramref name="data"/> to the client of the current
-    /// <see cref="WebSocketService"/> instance.
+    /// Sends a binary <paramref name="data"/> to the client on the current
+    /// session in the WebSocket service.
     /// </summary>
     /// <param name="data">
-    /// An array of <see cref="byte"/> that contains the binary data to send.
+    /// An array of <see cref="byte"/> that represents the binary data to send.
     /// </param>
     protected void Send (byte [] data)
     {
@@ -283,11 +283,11 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Sends a binary data from the specified <see cref="FileInfo"/> to
-    /// the client of the current <see cref="WebSocketService"/> instance.
+    /// Sends the specified <paramref name="file"/> as a binary data
+    /// to the client on the current session in the WebSocket service.
     /// </summary>
     /// <param name="file">
-    /// A <see cref="FileInfo"/> from which contains the binary data to send.
+    /// A <see cref="FileInfo"/> that represents the file to send.
     /// </param>
     protected void Send (FileInfo file)
     {
@@ -296,8 +296,8 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Sends a text <paramref name="data"/> to the client of the current
-    /// <see cref="WebSocketService"/> instance.
+    /// Sends a text <paramref name="data"/> to the client on the current
+    /// session in the WebSocket service.
     /// </summary>
     /// <param name="data">
     /// A <see cref="string"/> that represents the text data to send.
@@ -309,20 +309,19 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Sends a binary <paramref name="data"/> asynchronously to the client of the
-    /// current <see cref="WebSocketService"/> instance.
+    /// Sends a binary <paramref name="data"/> asynchronously to the client
+    /// on the current session in the WebSocket service.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the send to be complete.
     /// </remarks>
     /// <param name="data">
-    /// An array of <see cref="byte"/> that contains the binary data to send.
+    /// An array of <see cref="byte"/> that represents the binary data to send.
     /// </param>
     /// <param name="completed">
     /// An Action&lt;bool&gt; delegate that references the method(s) called when
-    /// the send is complete.
-    /// A <see cref="bool"/> passed to this delegate is <c>true</c> if the send is
-    /// complete successfully; otherwise, <c>false</c>.
+    /// the send is complete. A <see cref="bool"/> passed to this delegate is
+    /// <c>true</c> if the send is complete successfully; otherwise, <c>false</c>.
     /// </param>
     protected void SendAsync (byte [] data, Action<bool> completed)
     {
@@ -331,21 +330,20 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Sends a binary data from the specified <see cref="FileInfo"/>
-    /// asynchronously to the client of the current <see cref="WebSocketService"/>
-    /// instance.
+    /// Sends the specified <paramref name="file"/> as a binary data
+    /// asynchronously to the client on the current session in the WebSocket
+    /// service.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the send to be complete.
     /// </remarks>
     /// <param name="file">
-    /// A <see cref="FileInfo"/> from which contains the binary data to send.
+    /// A <see cref="FileInfo"/> that represents the file to send.
     /// </param>
     /// <param name="completed">
     /// An Action&lt;bool&gt; delegate that references the method(s) called when
-    /// the send is complete.
-    /// A <see cref="bool"/> passed to this delegate is <c>true</c> if the send is
-    /// complete successfully; otherwise, <c>false</c>.
+    /// the send is complete. A <see cref="bool"/> passed to this delegate is
+    /// <c>true</c> if the send is complete successfully; otherwise, <c>false</c>.
     /// </param>
     protected void SendAsync (FileInfo file, Action<bool> completed)
     {
@@ -354,8 +352,8 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Sends a text <paramref name="data"/> asynchronously to the client of the
-    /// current <see cref="WebSocketService"/> instance.
+    /// Sends a text <paramref name="data"/> asynchronously to the client
+    /// on the current session in the WebSocket service.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the send to be complete.
@@ -365,9 +363,8 @@ namespace WebSocketSharp.Server
     /// </param>
     /// <param name="completed">
     /// An Action&lt;bool&gt; delegate that references the method(s) called when
-    /// the send is complete.
-    /// A <see cref="bool"/> passed to this delegate is <c>true</c> if the send is
-    /// complete successfully; otherwise, <c>false</c>.
+    /// the send is complete. A <see cref="bool"/> passed to this delegate is
+    /// <c>true</c> if the send is complete successfully; otherwise, <c>false</c>.
     /// </param>
     protected void SendAsync (string data, Action<bool> completed)
     {
@@ -377,22 +374,21 @@ namespace WebSocketSharp.Server
 
     /// <summary>
     /// Sends a binary data from the specified <see cref="Stream"/> asynchronously
-    /// to the client of the current <see cref="WebSocketService"/> instance.
+    /// to the client on the current session in the WebSocket service.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the send to be complete.
     /// </remarks>
     /// <param name="stream">
-    /// A <see cref="Stream"/> object from which contains the binary data to send.
+    /// A <see cref="Stream"/> from which contains the binary data to send.
     /// </param>
     /// <param name="length">
     /// An <see cref="int"/> that represents the number of bytes to send.
     /// </param>
     /// <param name="completed">
     /// An Action&lt;bool&gt; delegate that references the method(s) called when
-    /// the send is complete.
-    /// A <see cref="bool"/> passed to this delegate is <c>true</c> if the send is
-    /// complete successfully; otherwise, <c>false</c>.
+    /// the send is complete. A <see cref="bool"/> passed to this delegate is
+    /// <c>true</c> if the send is complete successfully; otherwise, <c>false</c>.
     /// </param>
     protected void SendAsync (Stream stream, int length, Action<bool> completed)
     {
diff --git a/websocket-sharp/Server/WebSocketServiceHostManager.cs b/websocket-sharp/Server/WebSocketServiceHostManager.cs
index 36c55eed..90a72fe1 100644
--- a/websocket-sharp/Server/WebSocketServiceHostManager.cs
+++ b/websocket-sharp/Server/WebSocketServiceHostManager.cs
@@ -263,6 +263,11 @@ namespace WebSocketSharp.Server
       return result;
     }
 
+    private string checkIfCanSend (Func<string> checkParams)
+    {
+      return _state.CheckIfStart () ?? checkParams ();
+    }
+
     #endregion
 
     #region Internal Methods
@@ -359,15 +364,16 @@ namespace WebSocketSharp.Server
     #region Public Methods
 
     /// <summary>
-    /// Broadcasts a binary <paramref name="data"/> to all clients of the
-    /// WebSocket services provided by the server.
+    /// Broadcasts a binary <paramref name="data"/> to all clients
+    /// of the WebSocket services provided by the server.
     /// </summary>
     /// <param name="data">
-    /// An array of <see cref="byte"/> that contains the binary data to broadcast.
+    /// An array of <see cref="byte"/> that represents the binary data
+    /// to broadcast.
     /// </param>
     public void Broadcast (byte [] data)
     {
-      var msg = _state.CheckIfStarted () ?? data.CheckIfValidSendData ();
+      var msg = checkIfCanSend (() => data.CheckIfValidSendData ());
       if (msg != null) {
         _logger.Error (msg);
         return;
@@ -380,15 +386,15 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Broadcasts a text <paramref name="data"/> to all clients of the WebSocket
-    /// services provided by the server.
+    /// Broadcasts a text <paramref name="data"/> to all clients
+    /// of the WebSocket services provided by the server.
     /// </summary>
     /// <param name="data">
     /// A <see cref="string"/> that represents the text data to broadcast.
     /// </param>
     public void Broadcast (string data)
     {
-      var msg = _state.CheckIfStarted () ?? data.CheckIfValidSendData ();
+      var msg = checkIfCanSend (() => data.CheckIfValidSendData ());
       if (msg != null) {
         _logger.Error (msg);
         return;
@@ -409,7 +415,8 @@ namespace WebSocketSharp.Server
     /// This method doesn't wait for the broadcast to be complete.
     /// </remarks>
     /// <param name="data">
-    /// An array of <see cref="byte"/> that contains the binary data to broadcast.
+    /// An array of <see cref="byte"/> that represents the binary data
+    /// to broadcast.
     /// </param>
     /// <param name="completed">
     /// A <see cref="Action"/> delegate that references the method(s) called when
@@ -417,7 +424,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public void BroadcastAsync (byte [] data, Action completed)
     {
-      var msg = _state.CheckIfStarted () ?? data.CheckIfValidSendData ();
+      var msg = checkIfCanSend (() => data.CheckIfValidSendData ());
       if (msg != null) {
         _logger.Error (msg);
         return;
@@ -430,8 +437,8 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Broadcasts a text <paramref name="data"/> asynchronously to all clients of
-    /// the WebSocket services provided by the server.
+    /// Broadcasts a text <paramref name="data"/> asynchronously to all clients
+    /// of the WebSocket services provided by the server.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the broadcast to be complete.
@@ -445,7 +452,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public void BroadcastAsync (string data, Action completed)
     {
-      var msg = _state.CheckIfStarted () ?? data.CheckIfValidSendData ();
+      var msg = checkIfCanSend (() => data.CheckIfValidSendData ());
       if (msg != null) {
         _logger.Error (msg);
         return;
@@ -460,15 +467,14 @@ namespace WebSocketSharp.Server
 
     /// <summary>
     /// Broadcasts a binary data from the specified <see cref="Stream"/>
-    /// asynchronously to all clients of the WebSocket services provided by the
-    /// server.
+    /// asynchronously to all clients of the WebSocket services provided
+    /// by the server.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the broadcast to be complete.
     /// </remarks>
     /// <param name="stream">
-    /// A <see cref="Stream"/> object from which contains the binary data to
-    /// broadcast.
+    /// A <see cref="Stream"/> from which contains the binary data to broadcast.
     /// </param>
     /// <param name="length">
     /// An <see cref="int"/> that represents the number of bytes to broadcast.
@@ -479,9 +485,9 @@ namespace WebSocketSharp.Server
     /// </param>
     public void BroadcastAsync (Stream stream, int length, Action completed)
     {
-      var msg = _state.CheckIfStarted () ??
-                stream.CheckIfCanRead () ??
-                (length < 1 ? "'length' must be greater than 0." : null);
+      var msg = checkIfCanSend (
+        () => stream.CheckIfCanRead () ??
+              (length < 1 ? "'length' must be greater than 0." : null));
 
       if (msg != null) {
         _logger.Error (msg);
@@ -521,7 +527,8 @@ namespace WebSocketSharp.Server
     /// service to find.
     /// </param>
     /// <param name="data">
-    /// An array of <see cref="byte"/> that contains the binary data to broadcast.
+    /// An array of <see cref="byte"/> that represents the binary data
+    /// to broadcast.
     /// </param>
     public void BroadcastTo (string servicePath, byte [] data)
     {
@@ -531,8 +538,8 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Broadcasts a text <paramref name="data"/> to all clients of the WebSocket
-    /// service with the specified <paramref name="servicePath"/>.
+    /// Broadcasts a text <paramref name="data"/> to all clients of the
+    /// WebSocket service with the specified <paramref name="servicePath"/>.
     /// </summary>
     /// <param name="servicePath">
     /// A <see cref="string"/> that represents the absolute path to the WebSocket
@@ -560,7 +567,8 @@ namespace WebSocketSharp.Server
     /// service to find.
     /// </param>
     /// <param name="data">
-    /// An array of <see cref="byte"/> that contains the binary data to broadcast.
+    /// An array of <see cref="byte"/> that represents the binary data
+    /// to broadcast.
     /// </param>
     /// <param name="completed">
     /// A <see cref="Action"/> delegate that references the method(s) called when
@@ -575,8 +583,8 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Broadcasts a text <paramref name="data"/> asynchronously to all clients of
-    /// the WebSocket service with the specified <paramref name="servicePath"/>.
+    /// Broadcasts a text <paramref name="data"/> asynchronously to all clients
+    /// of the WebSocket service with the specified <paramref name="servicePath"/>.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the broadcast to be complete.
@@ -602,8 +610,8 @@ namespace WebSocketSharp.Server
 
     /// <summary>
     /// Broadcasts a binary data from the specified <see cref="Stream"/>
-    /// asynchronously to all clients of the WebSocket service with the specified
-    /// <paramref name="servicePath"/>.
+    /// asynchronously to all clients of the WebSocket service with the
+    /// specified <paramref name="servicePath"/>.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the broadcast to be complete.
@@ -613,8 +621,7 @@ namespace WebSocketSharp.Server
     /// service to find.
     /// </param>
     /// <param name="stream">
-    /// A <see cref="Stream"/> object from which contains the binary data to
-    /// broadcast.
+    /// A <see cref="Stream"/> from which contains the binary data to broadcast.
     /// </param>
     /// <param name="length">
     /// An <see cref="int"/> that represents the number of bytes to broadcast.
@@ -643,7 +650,7 @@ namespace WebSocketSharp.Server
     /// </returns>
     public Dictionary<string, Dictionary<string, bool>> Broadping ()
     {
-      var msg = _state.CheckIfStarted ();
+      var msg = _state.CheckIfStart ();
       if (msg != null) {
         _logger.Error (msg);
         return null;
@@ -671,8 +678,9 @@ namespace WebSocketSharp.Server
         return Broadping ();
 
       byte [] data = null;
-      var msg = _state.CheckIfStarted () ??
-                (data = Encoding.UTF8.GetBytes (message)).CheckIfValidControlData ("message");
+      var msg = checkIfCanSend (
+        () => (data = Encoding.UTF8.GetBytes (message))
+              .CheckIfValidControlData ("message"));
 
       if (msg != null) {
         _logger.Error (msg);
@@ -851,19 +859,19 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Sends a binary <paramref name="data"/> to the client associated with the
-    /// specified <paramref name="servicePath"/> and <paramref name="id"/>.
+    /// Sends a binary <paramref name="data"/> to the client on the session with
+    /// the specified <paramref name="id"/>, in the WebSocket service with the
+    /// specified <paramref name="servicePath"/>.
     /// </summary>
     /// <param name="servicePath">
     /// A <see cref="string"/> that represents the absolute path to the WebSocket
     /// service to find.
     /// </param>
     /// <param name="id">
-    /// A <see cref="string"/> that represents the ID of the session to send the
-    /// data to.
+    /// A <see cref="string"/> that represents the ID of the session to find.
     /// </param>
     /// <param name="data">
-    /// An array of <see cref="byte"/> that contains the binary data to send.
+    /// An array of <see cref="byte"/> that represents the binary data to send.
     /// </param>
     public void SendTo (string servicePath, string id, byte [] data)
     {
@@ -873,16 +881,16 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Sends a text <paramref name="data"/> to the client associated with the
-    /// specified <paramref name="servicePath"/> and <paramref name="id"/>.
+    /// Sends a text <paramref name="data"/> to the client on the session with
+    /// the specified <paramref name="id"/>, in the WebSocket service with the
+    /// specified <paramref name="servicePath"/>.
     /// </summary>
     /// <param name="servicePath">
     /// A <see cref="string"/> that represents the absolute path to the WebSocket
     /// service to find.
     /// </param>
     /// <param name="id">
-    /// A <see cref="string"/> that represents the ID of the session to send the
-    /// data to.
+    /// A <see cref="string"/> that represents the ID of the session to find.
     /// </param>
     /// <param name="data">
     /// A <see cref="string"/> that represents the text data to send.
@@ -895,9 +903,9 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Sends a binary <paramref name="data"/> asynchronously to the client
-    /// associated with the specified <paramref name="servicePath"/> and
-    /// <paramref name="id"/>.
+    /// Sends a binary <paramref name="data"/> asynchronously to the client on the
+    /// session with the specified <paramref name="id"/>, in the WebSocket service
+    /// with the specified <paramref name="servicePath"/>.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the send to be complete.
@@ -907,11 +915,10 @@ namespace WebSocketSharp.Server
     /// service to find.
     /// </param>
     /// <param name="id">
-    /// A <see cref="string"/> that represents the ID of the session to send the
-    /// data to.
+    /// A <see cref="string"/> that represents the ID of the session to find.
     /// </param>
     /// <param name="data">
-    /// An array of <see cref="byte"/> that contains the binary data to send.
+    /// An array of <see cref="byte"/> that represents the binary data to send.
     /// </param>
     /// <param name="completed">
     /// An Action&lt;bool&gt; delegate that references the method(s) called when
@@ -928,9 +935,9 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Sends a text <paramref name="data"/> asynchronously to the client
-    /// associated with the specified <paramref name="servicePath"/> and
-    /// <paramref name="id"/>.
+    /// Sends a text <paramref name="data"/> asynchronously to the client on the
+    /// session with the specified <paramref name="id"/>, in the WebSocket service
+    /// with the specified <paramref name="servicePath"/>.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the send to be complete.
@@ -940,8 +947,7 @@ namespace WebSocketSharp.Server
     /// service to find.
     /// </param>
     /// <param name="id">
-    /// A <see cref="string"/> that represents the ID of the session to send the
-    /// data to.
+    /// A <see cref="string"/> that represents the ID of the session to find.
     /// </param>
     /// <param name="data">
     /// A <see cref="string"/> that represents the text data to send.
@@ -962,8 +968,8 @@ namespace WebSocketSharp.Server
 
     /// <summary>
     /// Sends a binary data from the specified <see cref="Stream"/> asynchronously
-    /// to the client associated with the specified <paramref name="servicePath"/>
-    /// and <paramref name="id"/>.
+    /// to the client on the session with the specified <paramref name="id"/>, in
+    /// the WebSocket service with the specified <paramref name="servicePath"/>.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the send to be complete.
@@ -973,11 +979,10 @@ namespace WebSocketSharp.Server
     /// service to find.
     /// </param>
     /// <param name="id">
-    /// A <see cref="string"/> that represents the ID of the session to send the
-    /// data to.
+    /// A <see cref="string"/> that represents the ID of the session to find.
     /// </param>
     /// <param name="stream">
-    /// A <see cref="Stream"/> object from which contains the binary data to send.
+    /// A <see cref="Stream"/> from which contains the binary data to send.
     /// </param>
     /// <param name="length">
     /// An <see cref="int"/> that represents the number of bytes to send.
@@ -1016,7 +1021,7 @@ namespace WebSocketSharp.Server
     public bool TryGetServiceHost (
       string servicePath, out WebSocketServiceHost serviceHost)
     {
-      var msg = _state.CheckIfStarted () ?? servicePath.CheckIfValidServicePath ();
+      var msg = _state.CheckIfStart () ?? servicePath.CheckIfValidServicePath ();
       if (msg != null) {
         _logger.Error (msg);
         serviceHost = null;
diff --git a/websocket-sharp/Server/WebSocketSessionManager.cs b/websocket-sharp/Server/WebSocketSessionManager.cs
index 9b20cad2..28d72313 100644
--- a/websocket-sharp/Server/WebSocketSessionManager.cs
+++ b/websocket-sharp/Server/WebSocketSessionManager.cs
@@ -276,6 +276,11 @@ namespace WebSocketSharp.Server
         state => broadcast (opcode, stream, completed));
     }
 
+    private string checkIfCanSend (Func<string> checkParams)
+    {
+      return _state.CheckIfStart () ?? checkParams ();
+    }
+
     private static string createID ()
     {
       return Guid.NewGuid ().ToString ("N");
@@ -398,15 +403,16 @@ namespace WebSocketSharp.Server
     #region Public Methods
 
     /// <summary>
-    /// Broadcasts a binary <paramref name="data"/> to all clients of the
-    /// WebSocket service.
+    /// Broadcasts a binary <paramref name="data"/> to all clients
+    /// of the WebSocket service.
     /// </summary>
     /// <param name="data">
-    /// An array of <see cref="byte"/> that contains the binary data to broadcast.
+    /// An array of <see cref="byte"/> that represents the binary data
+    /// to broadcast.
     /// </param>
     public void Broadcast (byte [] data)
     {
-      var msg = _state.CheckIfStarted () ?? data.CheckIfValidSendData ();
+      var msg = checkIfCanSend (() => data.CheckIfValidSendData ());
       if (msg != null) {
         _logger.Error (msg);
         return;
@@ -419,15 +425,15 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Broadcasts a text <paramref name="data"/> to all clients of the WebSocket
-    /// service.
+    /// Broadcasts a text <paramref name="data"/> to all clients
+    /// of the WebSocket service.
     /// </summary>
     /// <param name="data">
     /// A <see cref="string"/> that represents the text data to broadcast.
     /// </param>
     public void Broadcast (string data)
     {
-      var msg = _state.CheckIfStarted () ?? data.CheckIfValidSendData ();
+      var msg = checkIfCanSend (() => data.CheckIfValidSendData ());
       if (msg != null) {
         _logger.Error (msg);
         return;
@@ -448,7 +454,8 @@ namespace WebSocketSharp.Server
     /// This method doesn't wait for the broadcast to be complete.
     /// </remarks>
     /// <param name="data">
-    /// An array of <see cref="byte"/> that contains the binary data to broadcast.
+    /// An array of <see cref="byte"/> that represents the binary data
+    /// to broadcast.
     /// </param>
     /// <param name="completed">
     /// A <see cref="Action"/> delegate that references the method(s) called when
@@ -456,7 +463,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public void BroadcastAsync (byte [] data, Action completed)
     {
-      var msg = _state.CheckIfStarted () ?? data.CheckIfValidSendData ();
+      var msg = checkIfCanSend (() => data.CheckIfValidSendData ());
       if (msg != null) {
         _logger.Error (msg);
         return;
@@ -469,8 +476,8 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Broadcasts a text <paramref name="data"/> asynchronously to all clients of
-    /// the WebSocket service.
+    /// Broadcasts a text <paramref name="data"/> asynchronously to all clients
+    /// of the WebSocket service.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the broadcast to be complete.
@@ -484,7 +491,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public void BroadcastAsync (string data, Action completed)
     {
-      var msg = _state.CheckIfStarted () ?? data.CheckIfValidSendData ();
+      var msg = checkIfCanSend (() => data.CheckIfValidSendData ());
       if (msg != null) {
         _logger.Error (msg);
         return;
@@ -505,8 +512,7 @@ namespace WebSocketSharp.Server
     /// This method doesn't wait for the broadcast to be complete.
     /// </remarks>
     /// <param name="stream">
-    /// A <see cref="Stream"/> object from which contains the binary data to
-    /// broadcast.
+    /// A <see cref="Stream"/> from which contains the binary data to broadcast.
     /// </param>
     /// <param name="length">
     /// An <see cref="int"/> that represents the number of bytes to broadcast.
@@ -517,9 +523,9 @@ namespace WebSocketSharp.Server
     /// </param>
     public void BroadcastAsync (Stream stream, int length, Action completed)
     {
-      var msg = _state.CheckIfStarted () ??
-                stream.CheckIfCanRead () ??
-                (length < 1 ? "'length' must be greater than 0." : null);
+      var msg = checkIfCanSend (
+        () => stream.CheckIfCanRead () ??
+              (length < 1 ? "'length' must be greater than 0." : null));
 
       if (msg != null) {
         _logger.Error (msg);
@@ -560,7 +566,7 @@ namespace WebSocketSharp.Server
     /// </returns>
     public Dictionary<string, bool> Broadping ()
     {
-      var msg = _state.CheckIfStarted ();
+      var msg = _state.CheckIfStart ();
       if (msg != null) {
         _logger.Error (msg);
         return null;
@@ -587,8 +593,9 @@ namespace WebSocketSharp.Server
         return Broadping ();
 
       byte [] data = null;
-      var msg = _state.CheckIfStarted () ??
-                (data = Encoding.UTF8.GetBytes (message)).CheckIfValidControlData ("message");
+      var msg = checkIfCanSend (
+        () => (data = Encoding.UTF8.GetBytes (message))
+              .CheckIfValidControlData ("message"));
 
       if (msg != null) {
         _logger.Error (msg);
@@ -695,15 +702,14 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Sends a binary <paramref name="data"/> to the client associated with the
-    /// specified <paramref name="id"/>.
+    /// Sends a binary <paramref name="data"/> to the client on the session
+    /// with the specified <paramref name="id"/>.
     /// </summary>
     /// <param name="id">
-    /// A <see cref="string"/> that represents the ID of the session to send the
-    /// data to.
+    /// A <see cref="string"/> that represents the ID of the session to find.
     /// </param>
     /// <param name="data">
-    /// An array of <see cref="byte"/> that contains the binary data to send.
+    /// An array of <see cref="byte"/> that represents the binary data to send.
     /// </param>
     public void SendTo (string id, byte [] data)
     {
@@ -713,11 +719,11 @@ namespace WebSocketSharp.Server
     }
 
     /// <summary>
-    /// Sends a text <paramref name="data"/> to the client associated with the
-    /// specified <paramref name="id"/>.
+    /// Sends a text <paramref name="data"/> to the client on the session
+    /// with the specified <paramref name="id"/>.
     /// </summary>
     /// <param name="id">
-    /// A <see cref="string"/> that represents the ID of the session to send the
+    /// A <see cref="string"/> that represents the ID of the session to find.
     /// data to.
     /// </param>
     /// <param name="data">
@@ -732,17 +738,16 @@ namespace WebSocketSharp.Server
 
     /// <summary>
     /// Sends a binary <paramref name="data"/> asynchronously to the client
-    /// associated with the specified <paramref name="id"/>.
+    /// on the session with the specified <paramref name="id"/>.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the send to be complete.
     /// </remarks>
     /// <param name="id">
-    /// A <see cref="string"/> that represents the ID of the session to send the
-    /// data to.
+    /// A <see cref="string"/> that represents the ID of the session to find.
     /// </param>
     /// <param name="data">
-    /// An array of <see cref="byte"/> that contains the binary data to send.
+    /// An array of <see cref="byte"/> that represents the binary data to send.
     /// </param>
     /// <param name="completed">
     /// An Action&lt;bool&gt; delegate that references the method(s) called when
@@ -759,14 +764,13 @@ namespace WebSocketSharp.Server
 
     /// <summary>
     /// Sends a text <paramref name="data"/> asynchronously to the client
-    /// associated with the specified <paramref name="id"/>.
+    /// on the session with the specified <paramref name="id"/>.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the send to be complete.
     /// </remarks>
     /// <param name="id">
-    /// A <see cref="string"/> that represents the ID of the session to send the
-    /// data to.
+    /// A <see cref="string"/> that represents the ID of the session to find.
     /// </param>
     /// <param name="data">
     /// A <see cref="string"/> that represents the text data to send.
@@ -786,17 +790,16 @@ namespace WebSocketSharp.Server
 
     /// <summary>
     /// Sends a binary data from the specified <see cref="Stream"/> asynchronously
-    /// to the client associated with the specified <paramref name="id"/>.
+    /// to the client on the session with the specified <paramref name="id"/>.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the send to be complete.
     /// </remarks>
     /// <param name="id">
-    /// A <see cref="string"/> that represents the ID of the session to send the
-    /// data to.
+    /// A <see cref="string"/> that represents the ID of the session to find.
     /// </param>
     /// <param name="stream">
-    /// A <see cref="Stream"/> object from which contains the binary data to send.
+    /// A <see cref="Stream"/> from which contains the binary data to send.
     /// </param>
     /// <param name="length">
     /// An <see cref="int"/> that represents the number of bytes to send.
@@ -864,7 +867,7 @@ namespace WebSocketSharp.Server
     /// </param>
     public bool TryGetSession (string id, out IWebSocketSession session)
     {
-      var msg = _state.CheckIfStarted () ?? id.CheckIfValidSessionID ();
+      var msg = _state.CheckIfStart () ?? id.CheckIfValidSessionID ();
       if (msg != null) {
         _logger.Error (msg);
         session = null;
diff --git a/websocket-sharp/WebSocket.cs b/websocket-sharp/WebSocket.cs
index 190d1594..754c57fd 100644
--- a/websocket-sharp/WebSocket.cs
+++ b/websocket-sharp/WebSocket.cs
@@ -650,6 +650,11 @@ namespace WebSocketSharp
              : _readyState.CheckIfConnectable ();
     }
 
+    private string checkIfCanSend (Func<string> checkParams)
+    {
+      return _readyState.CheckIfOpen () ?? checkParams ();
+    }
+
     // As server
     private string checkIfValidHandshakeRequest (WebSocketContext context)
     {
@@ -1054,7 +1059,7 @@ namespace WebSocketSharp
       return res;
     }
 
-    private bool send (byte [] frameAsBytes)
+    private bool send (byte [] frame)
     {
       lock (_forConn) {
         if (_readyState != WebSocketState.OPEN) {
@@ -1065,7 +1070,7 @@ namespace WebSocketSharp
           return false;
         }
 
-        return _stream.Write (frameAsBytes);
+        return _stream.Write (frame);
       }
     }
 
@@ -1860,11 +1865,11 @@ namespace WebSocketSharp
     /// Sends a binary <paramref name="data"/> using the WebSocket connection.
     /// </summary>
     /// <param name="data">
-    /// An array of <see cref="byte"/> that contains the binary data to send.
+    /// An array of <see cref="byte"/> that represents the binary data to send.
     /// </param>
     public void Send (byte [] data)
     {
-      var msg = _readyState.CheckIfOpen () ?? data.CheckIfValidSendData ();
+      var msg = checkIfCanSend (() => data.CheckIfValidSendData ());
       if (msg != null) {
         _logger.Error (msg);
         error (msg);
@@ -1884,17 +1889,15 @@ namespace WebSocketSharp
     }
 
     /// <summary>
-    /// Sends a binary data from the specified <see cref="FileInfo"/> using the
-    /// WebSocket connection.
+    /// Sends the specified <paramref name="file"/> as a binary data
+    /// using the WebSocket connection.
     /// </summary>
     /// <param name="file">
-    /// A <see cref="FileInfo"/> from which contains the binary data to send.
+    /// A <see cref="FileInfo"/> that represents the file to send.
     /// </param>
     public void Send (FileInfo file)
     {
-      var msg = _readyState.CheckIfOpen () ??
-                (file == null ? "'file' must not be null." : null);
-
+      var msg = checkIfCanSend (() => file.CheckIfValidSendData ());
       if (msg != null) {
         _logger.Error (msg);
         error (msg);
@@ -1913,7 +1916,7 @@ namespace WebSocketSharp
     /// </param>
     public void Send (string data)
     {
-      var msg = _readyState.CheckIfOpen () ?? data.CheckIfValidSendData ();
+      var msg = checkIfCanSend (() => data.CheckIfValidSendData ());
       if (msg != null) {
         _logger.Error (msg);
         error (msg);
@@ -1929,24 +1932,23 @@ namespace WebSocketSharp
     }
 
     /// <summary>
-    /// Sends a binary <paramref name="data"/> asynchronously using the WebSocket
-    /// connection.
+    /// Sends a binary <paramref name="data"/> asynchronously
+    /// using the WebSocket connection.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the send to be complete.
     /// </remarks>
     /// <param name="data">
-    /// An array of <see cref="byte"/> that contains the binary data to send.
+    /// An array of <see cref="byte"/> that represents the binary data to send.
     /// </param>
     /// <param name="completed">
     /// An Action&lt;bool&gt; delegate that references the method(s) called when
-    /// the send is complete.
-    /// A <see cref="bool"/> passed to this delegate is <c>true</c> if the send is
-    /// complete successfully; otherwise, <c>false</c>.
+    /// the send is complete. A <see cref="bool"/> passed to this delegate is
+    /// <c>true</c> if the send is complete successfully; otherwise, <c>false</c>.
     /// </param>
     public void SendAsync (byte [] data, Action<bool> completed)
     {
-      var msg = _readyState.CheckIfOpen () ?? data.CheckIfValidSendData ();
+      var msg = checkIfCanSend (() => data.CheckIfValidSendData ());
       if (msg != null) {
         _logger.Error (msg);
         error (msg);
@@ -1967,26 +1969,23 @@ namespace WebSocketSharp
     }
 
     /// <summary>
-    /// Sends a binary data from the specified <see cref="FileInfo"/>
+    /// Sends the specified <paramref name="file"/> as a binary data
     /// asynchronously using the WebSocket connection.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the send to be complete.
     /// </remarks>
     /// <param name="file">
-    /// A <see cref="FileInfo"/> from which contains the binary data to send.
+    /// A <see cref="FileInfo"/> that represents the file to send.
     /// </param>
     /// <param name="completed">
     /// An Action&lt;bool&gt; delegate that references the method(s) called when
-    /// the send is complete.
-    /// A <see cref="bool"/> passed to this delegate is <c>true</c> if the send is
-    /// complete successfully; otherwise, <c>false</c>.
+    /// the send is complete. A <see cref="bool"/> passed to this delegate is
+    /// <c>true</c> if the send is complete successfully; otherwise, <c>false</c>.
     /// </param>
     public void SendAsync (FileInfo file, Action<bool> completed)
     {
-      var msg = _readyState.CheckIfOpen () ??
-                (file == null ? "'file' must not be null." : null);
-
+      var msg = checkIfCanSend (() => file.CheckIfValidSendData ());
       if (msg != null) {
         _logger.Error (msg);
         error (msg);
@@ -1998,8 +1997,8 @@ namespace WebSocketSharp
     }
 
     /// <summary>
-    /// Sends a text <paramref name="data"/> asynchronously using the WebSocket
-    /// connection.
+    /// Sends a text <paramref name="data"/> asynchronously
+    /// using the WebSocket connection.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the send to be complete.
@@ -2009,13 +2008,12 @@ namespace WebSocketSharp
     /// </param>
     /// <param name="completed">
     /// An Action&lt;bool&gt; delegate that references the method(s) called when
-    /// the send is complete.
-    /// A <see cref="bool"/> passed to this delegate is <c>true</c> if the send is
-    /// complete successfully; otherwise, <c>false</c>.
+    /// the send is complete. A <see cref="bool"/> passed to this delegate is
+    /// <c>true</c> if the send is complete successfully; otherwise, <c>false</c>.
     /// </param>
     public void SendAsync (string data, Action<bool> completed)
     {
-      var msg = _readyState.CheckIfOpen () ?? data.CheckIfValidSendData ();
+      var msg = checkIfCanSend (() => data.CheckIfValidSendData ());
       if (msg != null) {
         _logger.Error (msg);
         error (msg);
@@ -2031,29 +2029,28 @@ namespace WebSocketSharp
     }
 
     /// <summary>
-    /// Sends a binary data from the specified <see cref="Stream"/> asynchronously
-    /// using the WebSocket connection.
+    /// Sends a binary data from the specified <see cref="Stream"/>
+    /// asynchronously using the WebSocket connection.
     /// </summary>
     /// <remarks>
     /// This method doesn't wait for the send to be complete.
     /// </remarks>
     /// <param name="stream">
-    /// A <see cref="Stream"/> object from which contains the binary data to send.
+    /// A <see cref="Stream"/> from which contains the binary data to send.
     /// </param>
     /// <param name="length">
     /// An <see cref="int"/> that represents the number of bytes to send.
     /// </param>
     /// <param name="completed">
     /// An Action&lt;bool&gt; delegate that references the method(s) called when
-    /// the send is complete.
-    /// A <see cref="bool"/> passed to this delegate is <c>true</c> if the send is
-    /// complete successfully; otherwise, <c>false</c>.
+    /// the send is complete. A <see cref="bool"/> passed to this delegate is
+    /// <c>true</c> if the send is complete successfully; otherwise, <c>false</c>.
     /// </param>
     public void SendAsync (Stream stream, int length, Action<bool> completed)
     {
-      var msg = _readyState.CheckIfOpen () ??
-                stream.CheckIfCanRead () ??
-                (length < 1 ? "'length' must be greater than 0." : null);
+      var msg = checkIfCanSend (
+        () => stream.CheckIfCanRead () ??
+              (length < 1 ? "'length' must be greater than 0." : null));
 
       if (msg != null) {
         _logger.Error (msg);
@@ -2067,9 +2064,9 @@ namespace WebSocketSharp
         data => {
           var len = data.Length;
           if (len == 0) {
-            var err = "A data cannot be read from 'stream'.";
-            _logger.Error (err);
-            error (err);
+            msg = "A data cannot be read from 'stream'.";
+            _logger.Error (msg);
+            error (msg);
 
             return;
           }