Understand the transport layer protocol - tcp/udp

Catalog

Two important protocols in the transport layer

UDP： User message protocol

TCP： Transmission control protocol

UDP And TCP contrast

The same thing ：

Difference ：

Five tuple information

Socket (Socket)

Java Used in UDP agreement

class DatagramSocket ( Message socket ) ： be used for UDP signal communication

1.UDP The server

2.UDP client

3. Receive and send

4. close

class DatagramPakcet( Packet )： Data abstraction in the communication process

1. The receiving party

2. The sender

3. Generally used as a server

4. Generally used as the method of receiver

Server and client

Common patterns

1. request (Request)- Respond to (Response) Pattern

2. subscribe (subsrcipt) - radio broadcast (broadcase) Pattern

UDP summary

TCP

1. Construction method

As a server , We need to create our own Socket object

Use Socket object

2.accept

3.close

4.Socket Get communication information

5. Input stream

6. Output stream

About the use of input and output streams

The difference between data message oriented and byte stream oriented  

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Two important protocols in the transport layer

First of all, make it clear , Now what to say UDP, And what I'm about to say TCP, These are the types of protocols that work at the transport layer .

UDP： User message protocol

Transport layer protocol , Need to implement the process to Interprocess communication .

Use UDP The two ends of the agreement are not really connected , It's just the dissemination of data .

UDP Nothing has been done , Keep the original ecological state of the network , There is no role to protect the network , So it's not reliable .

TCP： Transmission control protocol

Transport layer protocol , Need to implement the process to Interprocess communication .

Use TCP The protocol will connect the server and the client .

TCP Will do some transmission control , Make communication reliable .

UDP And TCP contrast

The same thing ：

It's all transport layer protocols , Need to implement the process to Interprocess communication .

Difference ：

UDP： unreliable , There is no connection , A protocol for datagram .

TCP： reliable , There is a connection , A protocol for byte stream .

Five tuple information

Both sides of the communication IP Address + The two sides port( port ) Address + Transport layer protocol = Five tuple information .

Through five tuple information, we can uniquely determine a communication line on the network

Socket (Socket)

Socket The keyword is standing on the application layer , Doing network programming is a very important concept .

Simply speaking , Below the application layer , The computer operating system hardware provides communication ,

And the application layer wants to use network services , Need to use OS Network service window provided Socket To enjoy the service .

Java Used in UDP agreement

class DatagramSocket ( Message socket ) ： be used for UDP signal communication

This class is Socket A subclass of class , Copy UDP signal communication , There are two ways to construct it ,

A parameter with port , For servers

A nonparametric structure , For clients

1.UDP The server

We use Socket Constructor creates objects for server-side communication

DatagramSocket socket = new DatagramSocket(PORT);

Use a fixed port , To facilitate client communication , There may be a risk of mistakes , For example, when you want to communicate, you find that the port is occupied by other processes .

2.UDP client

Is still Socket Construction method , But there is no need to pass parameters , We only send data to the server as a client , And receive the data replied by the server .

DatagramSocket socket = new DatagramSocket();

3. Receive and send

The content sent is the next packet class

// Receiving method 
socket.receive(receivedPacket);
// Sending method 
socket.send(sentPacket);

4. close

After use , Remember to turn off

socket.close();

class DatagramPakcet( Packet )： Data abstraction in the communication process

This thing is equivalent to Socket Class to send packets

It contains five tuple information and The data content

1. The receiving party

Just receive a letter , So just take one byte Just receive the package .

// 1.  Receiving request 
byte[] buf = new byte[1024];    // 1024  Represents the maximum data size we receive （ byte ）
DatagramPacket receivedPacket = new DatagramPacket(buf, buf.length);

2. The sender

The sender needs to provide the current data content , Already the other party's IP and port

        DatagramPacket sentPacket = new DatagramPacket(
                bytes, 0, bytes.length, //  Data to send 
                loopbackAddress, TranslateServer.PORT   //  The other person's  ip + port
        );

3. Generally used as a server

            InetAddress address = receivedPacket.getAddress();
            Log.println(" The other person's  IP  Address : " + address);
            //  Remove the port of the other party 
            int port = receivedPacket.getPort();
            Log.println(" The other person's  port: " + port);
            //  Pull out the other party's  ip  Address  + port
            SocketAddress socketAddress = receivedPacket.getSocketAddress();

We can get new port , ip As well as data .

obtain port and ip You can send the data back , So this is a common method for servers .

            InetAddress address = receivedPacket.getAddress();
            Log.println(" The other person's  IP  Address : " + address);
            //  Remove the port of the other party 
            int port = receivedPacket.getPort();
            Log.println(" The other person's  port: " + port);

With these , We can send the data back

First get the information of the other party

//  Pull out the other party's  ip  Address  + port
            SocketAddress socketAddress = receivedPacket.getSocketAddress();

And then use Packet Package and send back

DatagramPacket sentPacket = new DatagramPacket(
       sendBuf, 0, sendBuf.length,     //  Data to send 
       socketAddress                         //  The address of the object removed from the request envelope （ip + port）
);

4. Generally used as the method of receiver

The receiver needs data , therefore getData Methods are commonly used

byte[] data = receivedPacket.getData();

Server and client

Servers are generally said from the perspective of the application layer , Serve the goal

The client is the end that enjoys the service

Common patterns

1. request (Request)- Respond to (Response) Pattern

One request , One response

That means , The client sends the request , The server receives and responds , In this process, the server is passive .

The following figure shows the simple sending of updates , There is no client , Servers , Send data by the sender , The receiving end receives and updates data .

  The following figure is more in line with the interaction between the server and the client , The client sends data to the server first , After a series of processing by the server, it will be sent back to the client .

  Communication data are all binary data communication , It is shown here as byte[] Spread by .

2. subscribe (subsrcipt) - radio broadcast (broadcase) Pattern

The client subscribes at one time , The server will actively push information to the client regularly .

The server here is relatively active .

UDP summary

1. Network programming

2. How to use ip + port

3.socket Use

4.UDP Characteristics ： unreliable , There is no connection , Data oriented message （ The data content is not unpacked during communication , That is, I won't open this letter , There is no problem of data change , The other party can receive the data completely , Of course, the premise is that it spreads ）

TCP

TCP It's a reliable , There is a connection , Byte stream oriented protocol

1. Construction method

As a server , We need to create our own Socket object

Use ServerSocket object

ServerSocket serverSocket = new ServerSocket(PORT);

As a client, you need to connect to the server

Use Socket object

        //  Create directly  Socket, Use the server  IP + PORT
        Log.println(" Ready to create  socket(TCP  Connect )");
        Socket socket = new Socket("127.0.0.1", TranslateServerShortConnection.PORT);

2.accept

Server's Socket The object is what the receiving client gets , You don't need to create

Listen to the client port , Once there is a client connection , Return a server-side Socket object , And connect with this client until it is closed , In this process, other clients can only block and wait .

            Log.println(" Wait for the other party to connect ");
            Socket socket = serverSocket.accept();
            Log.println(" There is a client connection ");

Socket Objects are equivalent to established connections ：

3.close

  Both client and server can call this method to close communication

socket.close();

4.Socket Get communication information

When the server gets Socket Object time , You can call methods to determine each other's information .

            //  The other person's information ：
            InetAddress inetAddress = socket.getInetAddress();  // ip
            Log.println(" The other person's  ip: " + inetAddress);
            int port = socket.getPort();    // port
            Log.println(" The other person's  port: " + port);
            SocketAddress remoteSocketAddress = socket.getRemoteSocketAddress();    // ip + port
            Log.println(" The other person's  ip + port: " + remoteSocketAddress);

5. Input stream

When the receiving end receives information , You need to use the input stream to receive

InputStream inputStream = socket.getInputStream();
Scanner scanner = new Scanner(inputStream, "UTF-8");

6. Output stream

Send data using output stream

        OutputStream os = socket.getOutputStream();
        OutputStreamWriter osWriter = new OutputStreamWriter(os, "UTF-8");
        PrintWriter writer = new PrintWriter(osWriter);

About the use of input and output streams

The difference between data message oriented and byte stream oriented