[Socket]两个外网ip通过socket通信失败的问题

我想做一个手机P2P通信的app，手机既做客户端也做服务端，服务端A有一个ServerSocket，它比如说在监听8192端口，ip是49.74.79.155，然后又有一个手机B，比如说B的ip为210.52.23.14，它作为客户端去连接A的8192端口。理论上是不是这样就是一个P2P程序？但是我的app客户端一直无法成功连接服务端，代码如下：

        //发送消息的异步类

	public class SendTask extends AsyncTask<UserInfo,Void,Boolean>

	{



		@Override

		protected void onPostExecute(Boolean aBoolean)

		{

			if(aBoolean)

				Toast.makeText(MainActivity.this,"SendAccessed",Toast.LENGTH_SHORT).show();

			else

				Toast.makeText(MainActivity.this,"SendFailed",Toast.LENGTH_SHORT).show();

		}



		@Override

		protected Boolean doInBackground(UserInfo... model)

		{

			//建立连接

			Socket socket=new Socket();

			try

			{

				InetAddress addr = InetAddress.getByName(model[0].ip);  //这是服务端的ip，外网ip。

				SocketAddress remoteAddr=new InetSocketAddress(addr,model[0].port);



				socket.connect(remoteAddr,5000);        //   <---------------   就是这句，一直连接失败。

				//发送消息

				PrintStream outStream=new PrintStream(socket.getOutputStream());

				outStream.println( ebMsg.getText().toString() );



				outStream.close();

				socket.close();

				return true;

			}

			catch (IOException e)

			{

				e.printStackTrace();

				return false;

			}





		}

	}

然后监听的代码如下：

	public class SocketListener implements Runnable

	{

		Socket socket;

		ServerSocket serverSocket;

		BufferedReader br;

		public SocketListener(ServerSocket serverSocket)

		{

			this.serverSocket = serverSocket;

		}



		public String ReadLine()

		{

			try

			{

				return br.readLine();

			}

			catch (IOException e)

			{

				e.printStackTrace();

			}

			return null;

		}

		@Override

		public void run()

		{

			while (true)

			{

				try

				{

					socket = serverSocket.accept();

                                        //------------读出消息---------------------

					br = new BufferedReader(new InputStreamReader(socket.getInputStream()));

					String temp = ReadLine();

					String content = "";

					while (temp != null)

					{

						content += temp;

						temp = ReadLine();

					}

                                        //--------------------------------------------------

                                        //回送给主线程以显示

					Message msg = new Message();

					msg.what = Global.MessageTag.MSG_NEW_MESSAGE;

					Bundle bundle = new Bundle();

					bundle.putString("Content", content);

					msg.setData(bundle);

					handler.sendMessage(msg);

				}

				catch (IOException e)

				{

					e.printStackTrace();

				}

			}

		}

	}

然后一些调试信息：

03-06 19:30:52.837  12482-12600/org.helloworld W/System.err﹕ java.net.ConnectException: failed to connect to /49.74.79.155 (port 8192) after 5000ms: isConnected failed: ECONNREFUSED (Connection refused)

03-06 19:30:52.838  12482-12600/org.helloworld W/System.err﹕ at libcore.io.IoBridge.isConnected(IoBridge.java:249)

03-06 19:30:52.840  12482-12600/org.helloworld W/System.err﹕ at libcore.io.IoBridge.connectErrno(IoBridge.java:181)

03-06 19:30:52.841  12482-12600/org.helloworld W/System.err﹕ at libcore.io.IoBridge.connect(IoBridge.java:112)

03-06 19:30:52.843  12482-12600/org.helloworld W/System.err﹕ at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:192)

03-06 19:30:52.845  12482-12600/org.helloworld W/System.err﹕ at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:459)

03-06 19:30:52.846  12482-12600/org.helloworld W/System.err﹕ at java.net.Socket.connect(Socket.java:851)

03-06 19:30:52.848  12482-12600/org.helloworld W/System.err﹕ at org.helloworld.MainActivity$SendTask.doInBackground(MainActivity.java:112)

03-06 19:30:52.848  12482-12600/org.helloworld W/System.err﹕ at org.helloworld.MainActivity$SendTask.doInBackground(MainActivity.java:90)

03-06 19:30:52.848  12482-12600/org.helloworld W/System.err﹕ at android.os.AsyncTask$2.call(AsyncTask.java:264)

03-06 19:30:52.849  12482-12600/org.helloworld W/System.err﹕ at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)

03-06 19:30:52.849  12482-12600/org.helloworld W/System.err﹕ at java.util.concurrent.FutureTask.run(FutureTask.java:137)

03-06 19:30:52.850  12482-12600/org.helloworld W/System.err﹕ at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)

03-06 19:30:52.852  12482-12600/org.helloworld W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)

03-06 19:30:52.853  12482-12600/org.helloworld W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)

03-06 19:30:52.854  12482-12600/org.helloworld W/System.err﹕ at java.lang.Thread.run(Thread.java:856)

03-06 19:30:52.855  12482-12600/org.helloworld W/System.err﹕ Caused by: libcore.io.ErrnoException: isConnected failed: ECONNREFUSED (Connection refused)

03-06 19:30:52.857  12482-12600/org.helloworld W/System.err﹕ at libcore.io.IoBridge.isConnected(IoBridge.java:236)

03-06 19:30:52.858  12482-12600/org.helloworld W/System.err﹕ ... 14 more

03-06 19:31:06.676  12665-12665/org.helloworld W/ActivityThread﹕ Application org.helloworld is waiting for the debugger on port 8100...

我想请教各位老师，为什么会出现这样的问题？如何正确实现一个公网下可以p2p通信的app，比如说移动版的QQ？