서버코드
public class PLOG_Server 
{
        private final int SERVER_PORT=6001;
        private String st = "서버연결";
        private int test =0;
        public void server() throws IOException
        {
                DatagramSocket Socket = new DatagramSocket(SERVER_PORT);
                byte [] data = new byte[8];
                byte [] data1 = new byte[8];

                DatagramPacket OutPacket , InPacket;
                
                while(true)
                {
                        System.out.println("서버작동중");
                        InPacket = new DatagramPacket(data, data.length);
                        Socket.receive(InPacket);
                        
                        InetAddress adress = InPacket.getAddress();
                        int port =InPacket.getPort();
                        
                        String a = "1"+test;
                        
                        data1 = a.getBytes();
                        OutPacket = new DatagramPacket(data1, data1.length,adress,port);
                        Socket.send(OutPacket);
                        test++;
                }

        } 
        public static void main(String[] args)
        {
                try {
                        new PLOG_Server().server();
                } catch (IOException e) {
                        // TODO 자동 생성된 catch 블록
                        e.printStackTrace();
                }
        }
        
}

클라소스
class test extends Thread
{
private final String SERVER_IP="000.000.000.000";
private final int SERVER_PORT=6001;
        private String a;
        @Override
        public void run() {
                while(true){
                        try{
                        DatagramSocket Socket = new DatagramSocket();
                        InetAddress Adress = InetAddress.getByName(SERVER_IP);
                        byte [] data = new byte[8];
                        byte [] data1 = new byte[8];
                        
                        DatagramPacket OutPacket = new DatagramPacket(data, 1, Adress, SERVER_PORT);
                        DatagramPacket InPacket = new DatagramPacket(data, data.length);
                        
                        Socket.send(OutPacket);
                        Socket.receive(InPacket);
                        
                        data1=InPacket.getData();
                        a = new String(data1);
                        
                        char[] stt3 = new char[4];
                        a.getChars(0,4, stt3, 0);
                        String rst3 = String.valueOf(stt3);
                        
                        System.out.println("클라이언트작동중 :" + rst3 );
                        Thread.sleep(1000);
                        }catch (IOException | InterruptedException e){
                                System.out.println("에러남");
                        }
                }

        }
        
}

public class Client 
{                
        
        public static void main(String[] args)
        {
                new test().run();
        }
}

이거로 udp통신테스트하는데 잘되다가 그냥 갑자기멈추는데 이유가뭐냐??
에러도안나오고 그냥말그대로멈춤

테스트할때 데스크탑으로 서버키고
노트북은 휴대폰 테더링으로 클라연결함