class Program
    {
        const int port = XXXX;
        static TcpListener listener;
        static void Main(string[] args)
        {
            try
            {
                listener = new TcpListener(IPAddress.Parse("XX.XXX.XX.XX"), port);
                listener.Start();
                Console.WriteLine("Listening...");

                while (true)
                {
                    TcpClient client = listener.AcceptTcpClient();
                    ClientObject clientObject = new ClientObject(client);

                    Thread clientThread = new Thread(new ThreadStart(clientObject.EndPoint));
                    clientThread.Start();
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            finally
            {
                if (listener != null)
                    listener.Stop();
            }
        }
    }

public class ClientObject
        {
            public TcpClient client;
            public ClientObject(TcpClient tcpClient)
            {
                client = tcpClient;
            }

            public void Process()
            {
                NetworkStream stream = null;
                try
                {  
                    stream = client.GetStream();
                    byte[] data = new byte[64];
                    while (true)
                    {
                        StringBuilder builder = new StringBuilder();
                        int bytes = 0;
                        do
                        {
                            bytes = stream.Read(data, 0, data.Length);
                            builder.Append(Encoding.Unicode.GetString(data, 0, bytes));
                        }
                        while (stream.DataAvailable);

                        string message = builder.ToString();

                        Console.WriteLine(message);
                        message = message.Substring(message.IndexOf(':') + 1).Trim().ToUpper();
                        data = Encoding.Unicode.GetBytes(message);
                        stream.Write(data, 0, data.Length);
                    }
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex.Message);
                }
                finally
                {
                    if (stream != null)
                        stream.Close();
                    if (client != null)
                        client.Close();
                }
            }

        public void EndPoint()
        {
            string MYIpClient;
            try
            {
                MYIpClient = Convert.ToString(((System.Net.IPEndPoint)client.Client.RemoteEndPoint).Address);
                Console.WriteLine(MYIpClient);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            finally
            {
                if (client != null)
                    client.Close();
            }
        }
        }

 public class Connect
    {
        const int port = XXXX;
        const string address = "XX.XXX.XXX.XX";
        public void Client()
        {
            Console.Write("Введите свое имя:");
            string userName = Console.ReadLine();
            TcpClient client = null;
            try
            {
                client = new TcpClient(address, port);
                NetworkStream stream = client.GetStream();

                while (true)
                {
                    Console.Write(userName + ": ");
                    string message = Console.ReadLine();
                    message = String.Format("{0}: {1}", userName, message);
                    byte[] data = Encoding.Unicode.GetBytes(message);
                    stream.Write(data, 0, data.Length);

                    data = new byte[64];
                    StringBuilder builder = new StringBuilder();
                    int bytes = 0;
                    do
                    {
                        bytes = stream.Read(data, 0, data.Length);
                        builder.Append(Encoding.Unicode.GetString(data, 0, bytes));
                    }
                    while (stream.DataAvailable);

                    message = builder.ToString();
                    Console.WriteLine("Сервер: {0}", message);
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            finally
            {
                client.Close();
            }
        }
    }