La classe clSocket

using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Web.UI.WebControls;
namespace MyApps
{
  /// <summary>
  /// Classe per la connessione via socket
  /// </summary>
  public class clSocket
  {
    private Socket s;

    private string Fdns;
    public string dns
    {
      get {return Fdns;}
    }

    private int Fport;
    public int port
    {
      get {return Fport;}
    }

    private string Fuser;
    public string user
    {
      get {return Fuser;}
    }

    private string Fpassword;
    public string password
    {
      get {return Fpassword;}
    }

    public clSocket(){}

    /// <summary>
    /// Costruttore
    /// </summary>
    /// <param name="dns">Il server a cui collegarsi</param>
    /// <param name="port">La porta</param>
    /// <param name="user">Nome utente</param>
    /// <param name="password">Password</param>
    public clSocket(string dns, int port, string user, string password)
    {
      Fdns = dns;
      Fport = port;
      Fuser = user;
      Fpassword = password;
      Connect();
    }

    /// <summary>
    /// Crea la connessione al socket
    /// </summary>
    /// <returns>True se va a buon fine</returns>
    public bool Connect()
    {
      s = null;
      IPEndPoint hostEndPoint;
      IPAddress hostAddress = null;
      IPHostEntry hostInfo = Dns.Resolve(this.dns);
      IPAddress[] IPaddresses = hostInfo.AddressList;
      hostAddress = IPaddresses[0];
      hostEndPoint = new IPEndPoint(hostAddress, this.port);
      try
      {
        s = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        s.Connect(hostEndPoint);
        return s.Connected;
      }
      catch (Exception err)
      {
        s.Shutdown(SocketShutdown.Both);
        s.Close();
        throw err;
      }
    }

    /// <summary>
    /// Esegue il login
    /// </summary>
    /// <returns>True se va a buon fine</returns>
    public bool login()
    {
      SendCommand("USER " + this.user);
      SendCommand("PASS " + this.password);
      if (ReceiveCommand("login").IndexOf("200 login OK, proceed\r\n\0")>-1)
      {
        clearBuffer();
        return true;
      }
      else
        return false;
    }

    /// <summary>
    /// Esegue la disconnessione
    /// </summary>
    public void Disconnect()
    {
      s.Shutdown(SocketShutdown.Both);
      s.Close();
      s = null;
    }

    /// <summary>
    /// Invia un comando via socket
    /// </summary>
    /// <param name="command">Il nome del comando inviato</param>
    public void SendCommand(string command)
    {
      byte[] msg;
      msg = Encoding.ASCII.GetBytes(command + "\r\n");
      s.Send(msg, 0, msg.Length, SocketFlags.None);
    }

    /// <summary>
    /// Legge la risposta (dopo l'invio di un comando
    /// </summary>
    /// <param name="sTerminate">Il carattere di fine che cia aspettiamo</param>
    /// <returns>La risposta</returns>
    public string ReceiveCommand(string sTerminate)
    {
      string str = "";
      int iRx = 0;
      byte[] buffer;
      while (true)
      {
        if (s.Available > 0)
        {
            buffer = new byte[1024];
            iRx = s.Receive(buffer);
            str += Encoding.ASCII.GetString(buffer);
            if ( str.IndexOf(sTerminate) > -1 || str.IndexOf("512") > -1 )
              return str;
        }
      }
    }

    /// <summary>
    /// Svuota il buffer di ricazione
    /// </summary>
    public void clearBuffer()
    {
      int iRx;
      byte[] buffer;
      while (s.Poll(100000, SelectMode.SelectRead))
      {
        buffer = new byte[1024];
        iRx = s.Receive(buffer);
      }
    }
  }
}

Un esempio di utilizzo

//istanzio la classe
clSocket cs = new clSocket("web.myDomain.com", port, user, password);
try
{
  //eseguo il login
  cs.login();
  //invio un comando
  cs.SendCommand("NOMECOMANDO");
  //leggo la risposta
  cs.ReceiveCommand("ENDCHAR")
}
catch
{
  //gestione eccezioni
}
finally
{
  cs.Disconnect();
}