I run into the same problem and have figured out a workaround that works for as. It is not a perfect solution. I use a regular expressions substituions between the TCP buffer and the Telnet protocol because the firmware sometimes use unknow esc sequnences that bother the telnet/terminal protocol. I use Perl for switch automation but i try to translate it to C# (The orginal is a Perl module

Regexp::Common::ANSIescape

). I use this expression

\x1BE/\n

before the big one and this after

\[[0-9]+;[0-9]+H

because the firmware use sometimes esc secuences that does not exist.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

namespace ProcurevAnsiFilter {
class Program {
const string CHAR_STR = @"(.|\n)*?";

const string CSI\_7BIT    = @"\\x1B\\\\\\x5B";
const string CSI\_8BIT    = @"\\x9B";

const string CSI\_7OR8    = @"(?:" + CSI\_7BIT + "|" + CSI\_8BIT + ")";

const string C1\_NST\_8BIT = @"\[\\x80-\\x8F\\x91-\\x97\\x99\\x9A\\x9C\]";
const string C1\_NST\_7BIT = @"\\x1B\[\\x40-\\x4F\\x51-\\x57\\x59\\x5A\\\\\\x5C\]";

const string C1\_STR\_7BIT = @"\\x1B\[\\x5D\\x50\\x58\\x5E\\x5F\]";
const string C1\_STR\_8BIT = @"\[\\x9D\\x90\\x98\\x9E\\x9F\]";

const string C1\_STR\_7OR8 = @"(?:" + C1\_STR\_7BIT + "|" + C1\_STR\_8BIT + ")";

const string ST\_7BIT     = @"\\x1B\\\\\\\\";
const string ST\_8BIT     = @"\\x9C";
const string ST\_7OR8     = @"(?:" + ST\_7BIT     + "|" + ST\_8BIT     + ")";


static void Main(string\[\] args) {
string\[\] tmp = new string\[\] {
  @"(?:\[\\x30-\\x3F\]\*)(?:\[\\x20-\\x2F\]\*\[\\x40-\\x7E\])",
  C1\_NST\_7BIT,
  C1\_NST\_8BIT,
  C1\_STR\_7OR8 + CHAR\_STR + ST\_7OR8
};
  string regex = "(?:" + string.Join("|", tmp) + ")";

  Regex reg = new Regex(regex);
}

}
}