using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Net.Sockets;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {

        const int port = 8888;
        const string address = "127.0.0.1";
        static void Main(string[] args)
        {

            List<Task> tasks = new List<Task>();

            Stopwatch sw = new Stopwatch();
            sw.Start();


            for (int i = 0; i < 100; i++)
            {
                int tmp = i;

                tasks.Add(Task.Factory.StartNew(async () =>
               {
                   TcpClient client = null;
                   try
                   {
                       client = new TcpClient(address, port);
                       NetworkStream stream = client.GetStream();

                       string message = $"qwertyuiop {tmp}";
                       // преобразуем сообщение в массив байтов
                       byte[] data = Encoding.Unicode.GetBytes(message);
                       // отправка сообщения
                       stream.Write(data, 0, data.Length);

                       // получаем ответ
                       data = new byte[64]; // буфер для получаемых данных
                       StringBuilder builder = new StringBuilder();
                       int bytes = 0;
                       do
                       {
                           Task<int> readtask = stream.ReadAsync(data, 0, data.Length);
                           await readtask;
                           //bytes = stream.Read(data, 0, data.Length);
                           bytes = readtask.Result;
                           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();
                   }



               }));
            }
            Task.WaitAll(tasks.ToArray());

            sw.Stop();
            Console.WriteLine(sw.ElapsedMilliseconds);
            Console.ReadLine();
        }
    }

}

using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;

namespace ConsoleServer
{
    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]; // буфер для получаемых данных

                // получаем сообщение
                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);
                // отправляем обратно сообщение в верхнем регистре

                Thread.Sleep(5000);

                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();
            }
        }
    }

    class Program
    {
        const int port = 8888;
        static TcpListener listener;
        static void Main(string[] args)
        {
            try
            {
                listener = new TcpListener(IPAddress.Parse("127.0.0.1"), port);
                listener.Start();
                Console.WriteLine("Ожидание подключений...");

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

                    // создаем новый поток для обслуживания нового клиента
                    Thread clientThread = new Thread(new ThreadStart(clientObject.Process));
                    clientThread.Start();
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            finally
            {
                if (listener != null)
                    listener.Stop();
            }
        }
    }



}