socket客户端的问题。

我想写一个socket的客户端。
连接已经写好，可是不知道怎么收、发数据。
代码如下，请哪位高手指点一下。using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Net;
using System.Net.Sockets;
using System.Threading;namespace testclient
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }        Socket client;
        Thread th1;
        private void Form1_Load(object sender, EventArgs e)
        {
            string pcname = Dns.GetHostName();
            IPAddress[] ip = Dns.GetHostAddresses(pcname);
            textBox5.Text = Convert.ToString(ip[0]);
            textBox1.Text = "192.168.0.99";
            textBox2.Text = "81";
            button2.Enabled = false;
        }        private void button1_Click(object sender, EventArgs e)
        {
            client = new Socket(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);
            th1 = new Thread(new ThreadStart(start));
            th1.IsBackground = true;
            th1.Start();
            button1.Enabled = false;
            button2.Enabled = true;
        }
        private void start()
        {
            try
            {
                IPAddress ip = IPAddress.Parse(this.textBox1.Text);
                int port = Convert.ToInt32(this.textBox2.Text);
                IPEndPoint IEp = new IPEndPoint(ip, port);                try
                {
                    client.Connect(IEp);
                }
                catch
                {
                    MessageBox.Show("服务器端未开启连接，请联系系统管理员");
                }
            }
            catch
            {
                MessageBox.Show("您输入的IP无效请重新输入");
            }
            if (client.Connected)
            {
                MessageBox.Show("连接成功可以开始通讯!");
            } 
        }        private void button2_Click(object sender, EventArgs e)
        {
            try
            {
                string str = textBox3.Text;
                ASCIIEncoding ascii = new ASCIIEncoding();
                byte[] msg = ascii.GetBytes(str);
                client.Send(msg);
            }
            catch
            {
                MessageBox.Show("没有连接或命令输入错误！"); 
            }
                        
        }        private void Form1_FormClosed(object sender, FormClosedEventArgs e)
        {
            th1.Abort();
        }
    }
}