'***************************************************

 '* This code belongs to Terry R. Olsen

 '* You are free to use this code in whole or

 '* in part for your own programs. But you may

 '* not use this code in any way to create

 '* the same type of program for public release.

 '* My Email: tolsen64@hotmail.com

 '***************************************************

 Imports System.Net

 Imports System.Net.Sockets

 Imports System.Windows.forms

 Imports System.Text.ASCIIEncoding

 Imports System.IO

 Imports System.IO.Ports

 Module Module1

 #Region "Telnet Commands"

 ' Telnet main commands - list copied from somewhere on the net - thank you to them

 Const TN_IAC As Int32 = 255 ' Interpret as command escape sequence, Prefix to all telnet commands. 1, 2 or sometimes more commands normally follow this character

 Const TN_DONT As Int32 = 254 ' You are not to use this option

 Const TN_DO As Int32 = 253 ' Please, you use this option

 Const TN_WONT As Int32 = 252 ' I won't use option

 Const TN_WILL As Int32 = 251 ' I will use option

 Const TN_SB As Int32 = 250 ' Subnegotiate, X number of commands follow

 Const TN_GA As Int32 = 249 ' Go ahead

 Const TN_EL As Int32 = 248 ' Erase line

 Const TN_EC As Int32 = 247 ' Erase character

 Const TN_AYT As Int32 = 246 ' Are you there

 Const TN_AO As Int32 = 245 ' Abort output

 Const TN_IP As Int32 = 244 ' Interrupt process

 Const TN_BRK As Int32 = 243 ' Break[1]InternetModem

 Const TN_DM As Int32 = 242 ' Data mark

 Const TN_NOP As Int32 = 241 ' No operation.

 Const TN_SE As Int32 = 240 ' End of subnegotiation, from above

 Const TN_EOR As Int32 = 239 ' End of record

 Const TN_ABORT As Int32 = 238 ' About process

 Const TN_SUSP As Int32 = 237 ' Suspend process

 Const TO_EOF As Int32 = 236 ' End of file

 ' Telnet (option) mainly return commands from above

 Const TN_BIN As Int32 = 0 ' Binary transmission

 Const TN_ECHO As Int32 = 1 ' Echo

 Const TN_RECN As Int32 = 2 ' Reconnection

 Const TN_SUPP As Int32 = 3 ' Suppress go ahead

 Const TN_APRX As Int32 = 4 ' Approx message size negotiation

 Const TN_STAT As Int32 = 5 ' Status

 Const TN_TIM As Int32 = 6 ' Timing mark

 Const TN_REM As Int32 = 7 ' Remote controlled trans/echo

 Const TN_OLW As Int32 = 8 ' Output line width

 Const TN_OPS As Int32 = 9 ' Output page size

 Const TN_OCRD As Int32 = 10 ' Out carriage-return disposition

 Const TN_OHT As Int32 = 11 ' Output horizontal tabstops

 Const TN_OHTD As Int32 = 12 ' Out horizontal tab disposition

 Const TN_OFD As Int32 = 13 ' Output formfeed disposition

 Const TN_OVT As Int32 = 14 ' Output vertical tabstops

 Const TN_OVTD As Int32 = 15 ' Output vertical tab disposition

 Const TN_OLD As Int32 = 16 ' Output linefeed disposition

 Const TN_EXT As Int32 = 17 ' Extended ascii character set

 Const TN_LOGO As Int32 = 18 ' Logout

 Const TN_BYTE As Int32 = 19 ' Byte macro

 Const TN_DATA As Int32 = 20 ' Data entry terminal

 Const TN_SUP As Int32 = 21 ' supdup protocol

 Const TN_SUPO As Int32 = 22 ' supdup output

 Const TN_SNDL As Int32 = 23 ' Send location

 Const TN_TERM As Int32 = 24 ' Terminal type

 Const TO_EOR As Int32 = 25 ' End of record

 Const TN_TACACS As Int32 = 26 ' Tacacs user identification

 Const TN_OM As Int32 = 27 ' Output marking

 Const TN_TLN As Int32 = 28 ' Terminal location number

 Const TN_3270 As Int32 = 29 ' Telnet 3270 regime

 Const TN_X3 As Int32 = 30 ' X.3 PAD

 Const TN_NAWS As Int32 = 31 ' Negotiate about window size

 Const TN_TS As Int32 = 32 ' Terminal speed

 Const TN_RFC As Int32 = 33 ' Remote flow control

 Const TN_LINE As Int32 = 34 ' Linemode

 Const TN_XDL As Int32 = 35 ' X display location

 Const TN_ENVIR As Int32 = 36 ' Telnet environment option

 Const TN_AUTH As Int32 = 37 ' Telnet authentication option

 Const TN_NENVIR As Int32 = 39 ' Telnet environment option

 Const TN_EXTOP As Int32 = 25 ' Extended-options-list

 #End Region

 'Serial Port Stuff

 Dim WithEvents Ser As New SerialPort

 'Telnet Stuff

 Dim LineSize As Integer

 Dim TcpPort As Integer = 23

 Dim TcpSvr As Socket 'TCP Listener Socket, listens for incoming calls

 Dim TcpClt As Socket 'TCP Client Socket, handles incoming calls

 Dim TcpMsg As Socket 'Tells Clients that we're busy right now...

 'Send & Receive Buffers

 Dim RcvBuf() As Byte 'In from TCP/Out to Serial

 Dim XmtBuf() As Byte 'In from Serial/Out to TCP

 Dim SerByt As Integer 'Bytes to read from serial port

 Dim Throttle As Integer 'Some slower terminals may need to slow it down

 'BBS not available message

 Dim msg() As Byte = ASCII.GetBytes("The line is busy. Please try again later.")

 'Stopwatch for measuring +++ Guard Time

 Dim swGuardTimer As New System.Timers.Timer

 'Application variables

 Dim logFile As String

 Dim iniFile As String

 Dim keepLog As Boolean = False

 Dim ver As String = "6.7.29.1"

 'Modem Emulator Stuff

 Enum ModemEcho

 EchoOff = 0

 EchoOn = 1

 End Enum

 Enum ModemResultCodeFormat

 Numeric = 0

 Text = 1

 End Enum

 Enum ModemResultCodes

 Enabled = 0

 Disabled = 1

 End Enum

 Enum ModemRingMode

 SendRing = 0

 SendConnect = 1

 End Enum

 Enum ModemHookState

 OnHook = 0

 OffHook = 1

 End Enum

 Const OK As Integer = 0

 Const CONNECT As Integer = 1

 Const RING As Integer = 2

 Const NO_CARRIER As Integer = 3

 Const ERR As Integer = 4

 Const NO_DIAL_TONE As Integer = 6

 Const BUSY As Integer = 7

 Const NO_ANSWER As Integer = 8

 Dim MdmErr As Integer

 Dim MdmErrorCode() As String = {"OK", "CONNECT", "RING", "NO CARRIER", "ERROR", "", "NO DIAL TONE", "BUSY", "NO ANSWER"}

 Dim MdmCmdMode As Boolean = True 'Are we in command mode?

 Dim MdmCmdStr As String

 Dim MdmResultCodeFormat As ModemResultCodeFormat = ModemResultCodeFormat.Numeric

 Dim MdmEcho As ModemEcho = ModemEcho.EchoOn

 Dim MdmResultCodes As ModemResultCodes = ModemResultCodes.Enabled

 Dim MdmRingMode As ModemRingMode = ModemRingMode.SendConnect

 Dim MdmHookState As ModemHookState = ModemHookState.OnHook

 Dim MdmBaud As String

 Sub Main()

 'Display Program & Author Information

 Console.WriteLine("Internet Modem v" & ver & " by Terry R. Olsen")

 Console.WriteLine("Call The BoycoT BBS: telnet://boycot.no-ip.com:9999")

 Console.WriteLine("Get the latest version of this program: http://boycot.no-ip.com/InternetModem")

 Console.WriteLine("Email: tolsen64@hotmail.com")

 Console.WriteLine("=============================================================================")

 'Load the INI file. This defines our variables.

 WriteStatus("Loading Initialization Data")

 Dim tmpPth As String = My.Application.Info.DirectoryPath

 If Right(tmpPth, 1) <> "\" Then tmpPth += "\"

 iniFile = tmpPth + "InternetModem.ini"

 logFile = tmpPth + "InternetModem.log"

 Dim r As New StreamReader(iniFile)

 Dim tmp() As String

 While r.Peek > 0

 tmp = Split(r.ReadLine, "=")

 Select Case tmp(0)

 Case "TcpPort"

 TcpPort = CInt(tmp(1))

 Case "SerPort"

 Ser.PortName = "COM" & Trim(tmp(1))

 Case "SerBaud"

 Ser.BaudRate = CInt(tmp(1))

 MdmBaud = Trim(tmp(1))

 Case "SerDataBits"

 Ser.DataBits = CInt(tmp(1))

 Case "SerParity"

 If tmp(1) = "None" Then Ser.Parity = Parity.None

 If tmp(1) = "Odd" Then Ser.Parity = Parity.Odd

 If tmp(1) = "Even" Then Ser.Parity = Parity.Even

 If tmp(1) = "Mark" Then Ser.Parity = Parity.Mark

 If tmp(1) = "Space" Then Ser.Parity = Parity.Space

 Case "SerStopBits"

 If tmp(1) = 1 Then Ser.StopBits = StopBits.One

 If tmp(1) = 1.5 Then Ser.StopBits = StopBits.OnePointFive

 If tmp(1) = 2 Then Ser.StopBits = StopBits.Two

 Case "Handshake"

 If tmp(1) = "None" Then Ser.Handshake = Handshake.None

 If tmp(1) = "RTS" Then Ser.Handshake = Handshake.RequestToSend

 If tmp(1) = "RTS/XonXoff" Then Ser.Handshake = Handshake.RequestToSendXOnXOff

 If tmp(1) = "XonXoff" Then Ser.Handshake = Handshake.XOnXOff

 Case "RcvBuf"

 Ser.WriteBufferSize = CInt(tmp(1))

 ReDim RcvBuf(CInt(tmp(1)))

 Case "XmtBuf"

 Ser.ReadBufferSize = CInt(tmp(1))

 ReDim XmtBuf(CInt(tmp(1)))

 Case "KeepLog"

 keepLog = CBool(tmp(1))

 Case "BBSName"

 msg = ASCII.GetBytes(tmp(1) & " is currently in use." & vbCrLf & vbCrLf & _

 "Please try again soon!" & vbCrLf & vbCrLf & _

 "While you're waiting...give The BoycoT BBS a call..." & vbCrLf & _

 "telnet://boycot.no-ip.com:9999")

 Case "Throttle"

 Throttle = CInt(tmp(1))

 Case "LineSize"

 LineSize = CInt(tmp(1))

 End Select

 End While

 r.Close()

 Ser.ReceivedBytesThreshold = 1 'Raise an event for each character received

 'Open the serial port

 WriteStatus("Opening " & Ser.PortName & "," & Ser.BaudRate & "," & Ser.DataBits & _

 "," & Ser.Parity.ToString & "," & Ser.StopBits & "," & Ser.Handshake.ToString)

 Try

 Ser.Open()

 Ser.DtrEnable = True

 Ser.RtsEnable = True

 Catch ex As Exception

 WriteStatus(ex.Message)

 WriteStatus("Failed!")

 Console.WriteLine("Press ENTER to exit.")

 Console.ReadLine()

 Exit Sub

 End Try

 StartTCPServer()

 AddHandler swGuardTimer.Elapsed, AddressOf swGuardTimerFired

 swGuardTimer.Interval = 1000

 'swGuardTimer.Enabled = True

 swGuardTimer.Stop()

 Application.Run() 'Keeps us running...

 End Sub

 '====================================================================

 'Our TCP Server Routines.

 Private Sub StartTCPServer()

 Dim addr As IPAddress = IPAddress.Parse("0.0.0.0")

 Dim ep As New IPEndPoint(addr, TcpPort)

 TcpSvr = New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)

 TcpSvr.Bind(ep)

 TcpSvr.Listen(2)

 TcpSvr.BeginAccept(AddressOf AcceptCallback, TcpSvr)

 WriteStatus("Listening for calls on TCP Port " & TcpPort)

 End Sub

 Private Sub AcceptCallback(ByVal ar As IAsyncResult)

 System.Threading.Thread.CurrentThread.Name = "AcceptCallback"

 Debug.WriteLine(Now.ToLongTimeString & " AcceptCallback")

 If TcpClt Is Nothing And MdmHookState = ModemHookState.OnHook Then

 Debug.WriteLine("TcpClt=Nothing, MdmHookState=" & MdmHookState.ToString)

 TcpClt = TcpSvr.EndAccept(ar)

 WriteStatus("Connected to " & CType(TcpClt.RemoteEndPoint, IPEndPoint).ToString)

 TcpClt.BeginReceive(RcvBuf, 0, RcvBuf.Length, SocketFlags.None, AddressOf ReceiveCallback, RcvBuf)

 MdmCmdMode = False

 MdmHookState = ModemHookState.OffHook

 ModemError(1)

 Else

 Debug.WriteLine(Now.ToLongTimeString & " TcpMsg started")

 TcpMsg = TcpSvr.EndAccept(ar)

 TcpMsg.Send(msg)

 WriteStatus("Sent busy message to " & CType(TcpMsg.RemoteEndPoint, IPEndPoint).ToString)

 TcpMsg.Shutdown(SocketShutdown.Both)

 TcpMsg.Close()

 TcpMsg = Nothing

 End If

 TcpSvr.BeginAccept(AddressOf AcceptCallback, TcpSvr)

 WriteStatus("Listening for calls on TCP Port " & TcpPort)

 End Sub

 Private Sub ReceiveCallback(ByVal ar As IAsyncResult)

 System.Threading.Thread.CurrentThread.Name = "ReceiveCallback"

 RcvBuf = CType(ar.AsyncState, Byte())

 Dim numbytes As Int32

 Try

 numbytes = TcpClt.EndReceive(ar)

 Catch

 Exit Sub

 End Try

 If numbytes = 0 Then 'client has disconnected.

 Ser.DtrEnable = False

 Ser.RtsEnable = False

 HangUp(False) 'False = Remote initiated disconnect

 MdmHookState = ModemHookState.OnHook

 Ser.DtrEnable = True

 Ser.RtsEnable = True

 ModemError(NO_CARRIER)

 Exit Sub

 End If

 If MdmCmdMode = False Then ProcessIncoming(numbytes)

 TcpClt.BeginReceive(RcvBuf, 0, RcvBuf.Length, SocketFlags.None, AddressOf ReceiveCallback, RcvBuf)

 End Sub

 Sub ProcessIncoming(ByVal numbytes As Int32)

 For i As Integer = 0 To numbytes - 1

 Select Case RcvBuf(i)

 Case TN_IAC

 'WriteStatus("Telnet Protocol in use.")

 Dim byt(0 To 2) As Byte

 byt(0) = TN_IAC

 i += 1

 Select Case RcvBuf(i)

 Case TN_SB

 'ToChatWindow(" TN_SB" & vbCrLf)

 WriteStatus("TN_SB Received! Subnegotiate Incomplete.")

 Do

 i += 1

 Loop Until RcvBuf(i) = TN_SE Or i = numbytes - 1

 Case TN_DO 'Server asking you to do something

 'ToChatWindow(" TN_DO " & Str(buffer(i + 1)) & vbCrLf)

 i += 1

 Select Case RcvBuf(i)

 Case TN_NAWS

 byt(1) = TN_WILL

 byt(2) = RcvBuf(i)

 SendBytesToHost(byt)

 SetLineSize()

 Case Else

 byt(1) = TN_WONT

 byt(2) = RcvBuf(i)

 SendBytesToHost(byt)

 End Select

 Case TN_DONT 'Server asking you to NOT do something

 'ToChatWindow(" TN_DONT" & Str(buffer(i + 1)) & vbCrLf)

 byt(1) = TN_WONT

 i += 1

 byt(2) = RcvBuf(i)

 SendBytesToHost(byt)

 Case TN_WILL 'Server telling you it will do something

 'ToChatWindow(" TN_WILL" & Str(buffer(i + 1)) & vbCrLf)

 byt(1) = TN_DONT

 i += 1

 byt(2) = RcvBuf(i)

 SendBytesToHost(byt)

 Case TN_WONT 'Server telling you it won't do someting

 'ToChatWindow(" TN_WONT" & Str(buffer(i + 1)) & vbCrLf)

 byt(1) = TN_DONT

 i += 1

 byt(2) = RcvBuf(i)

 SendBytesToHost(byt)

 End Select

 Case Else

 Try

 Threading.Thread.Sleep(Throttle)

 'Debug.Write(ASCII.GetString(RcvBuf, i, 1))

 Ser.Write(RcvBuf, i, 1)

 Catch ex As Exception

 WriteStatus("----------------------------")

 WriteStatus("Routine: ReceiveCallBack")

 WriteStatus("Exception: " & ex.Message)

 WriteStatus("Chat Msg: " & Chr(RcvBuf(i)))

 End Try

 End Select

 Next

 End Sub

 Private Sub SetLineSize()

 'The syntax for the subnegotiation is: IAC SB NAWS WIDTH[1] WIDTH[0] HEIGHT[1] HEIGHT[0] IAC SE

 Dim byt() As Byte = {TN_IAC, TN_SB, TN_NAWS, LineSize \ 256, LineSize Mod 256, 0, 24, TN_IAC, TN_SE}

 SendBytesToHost(byt)

 End Sub

 Private Sub SendBytesToHost(ByVal byt() As Byte)

 TcpClt.Send(byt, byt.Length, SocketFlags.None)

 End Sub

 Private Sub HangUp(ByVal local As Boolean)

 MdmErr = OK

 If Not TcpClt Is Nothing Then

 Try

 TcpClt.Shutdown(SocketShutdown.Both)

 TcpClt.Close()

 TcpClt = Nothing

 MdmErr = NO_CARRIER

 If local = True Then

 WriteStatus("Locally initiated disconnect")

 Else

 WriteStatus("Remote initiated disconnect")

 End If

 Catch ex As Exception

 WriteStatus("Locally initiated disconnect, already offline")

 End Try

 Else

 WriteStatus("Locally initiated disconnect, already offline")

 End If

 MdmCmdMode = True

 Debug.WriteLine(MdmCmdMode.ToString)

 End Sub

 'Routine to write status to console window...

 'and to log file if set.

 Private Sub WriteStatus(ByVal msg As String)

 Dim dt As String = Date.Now.ToShortDateString & " " & Date.Now.ToShortTimeString

 msg = dt & " - " & msg

 Console.WriteLine(msg)

 Exit Sub

 If keepLog = True Then

 Dim sw As New StreamWriter(logFile, True)

 'w = My.Computer.FileSystem.OpenTextFileWriter(logFile, True)

 sw.WriteLine(msg)

 sw.Close()

 End If

 End Sub

 Private Sub SerRcvEvent(ByVal sender As Object, ByVal e As SerialDataReceivedEventArgs) Handles Ser.DataReceived

 SerByt = Ser.BytesToRead

 Ser.Read(XmtBuf, 0, SerByt)

 Dim rcvString As String = ASCII.GetString(XmtBuf, 0, SerByt)

 Debug.Write(rcvString)

 ' --Did we get a Modem Esc Command?

 ' If so, start the 1 second timer.

 If InStr(rcvString, "+++") Then

 swGuardTimer.Start()

 End If

 ' --If we're in command mode, send characters received to be processed

 If MdmCmdMode = True Then

 ProcessMdmCmd(rcvString)

 Exit Sub

 End If

 ' --Otherwise, send it out to our connected user.

 If TcpClt Is Nothing Then Exit Sub

 Try

 TcpClt.Send(XmtBuf, SerByt, SocketFlags.None)

 Catch

 End Try

 End Sub

 Private Sub ProcessMdmCmd(ByVal CmdStr As String)

 MdmErr = OK

 MdmCmdStr += UCase(CmdStr)

 If MdmEcho = ModemEcho.EchoOn Then Ser.Write(CmdStr)

 '--Command is still coming in if we haven't received the CR

 If Right(MdmCmdStr, 1) <> Chr(13) Then Exit Sub

 '--CR only does not a command make...

 If MdmCmdStr.Equals(vbCr) Then

 MdmCmdStr = ""

 Exit Sub

 End If

 '--Get rid of the +'s from the ESC sequence, and trim off the CR

 MdmCmdStr = MdmCmdStr.Replace("+", "").Trim(Chr(13))

 Debug.WriteLine("MdmCmdStr: " & MdmCmdStr)

 '--All good command strings begin with AT

 If Left(MdmCmdStr, 2) <> "AT" Then

 Debug.WriteLine("MdmCmdStr doesn't begin with AT")

 MdmCmdStr = ""

 ModemError(ERR)

 Exit Sub

 End If

 '--Sometimes they just type AT to see if the modem is responding.

 If MdmCmdStr = "AT" Then

 MdmCmdStr = ""

 ModemError(OK)

 Exit Sub

 End If

 '--Now start dealing with the command strings...

 Dim tmpCmd As String

 If InStr(MdmCmdStr, "ATA") Then

 MdmCmdStr = ""

 End If

 If InStr(MdmCmdStr, "ATD ") Or InStr(MdmCmdStr, "ATDT ") Then

 GoDialOut(MdmCmdStr)

 MdmCmdStr = ""

 Exit Sub

 End If

 If InStr(MdmCmdStr, "ATI") Then

 Ser.Write("Internet Modem Emulator v" & ver & " by Terry Olsen" & vbCr)

 MdmErr = OK

 MdmCmdStr = ""

 'Exit Sub

 End If

 If InStr(MdmCmdStr, "AT&V") Then

 Ser.Write("This will be our &V display page." & vbCr)

 MdmErr = OK

 MdmCmdStr = ""

 'Exit Sub

 End If

 If InStr(MdmCmdStr, "ATZ") Then

 HangUp(True)

 MdmCmdMode = True

 MdmHookState = ModemHookState.OnHook

 MdmCmdStr = ""

 End If

 If InStr(MdmCmdStr, "E") Then

 tmpCmd = Mid(MdmCmdStr, InStr(MdmCmdStr, "E") + 1, 1)

 Debug.Write("E" & tmpCmd & ":")

 If Val(tmpCmd) > 1 Then

 MdmErr = ERR

 Else

 MdmEcho = Val(tmpCmd)

 End If

 MdmCmdStr = ""

 End If

 If InStr(MdmCmdStr, "H") Then

 tmpCmd = Mid(MdmCmdStr, InStr(MdmCmdStr, "H") + 1, 1)

 Debug.Write("H" & tmpCmd & ":")

 If Val(tmpCmd) > 1 Then

 MdmErr = ERR

 Else

 MdmHookState = Val(tmpCmd)

 HangUp(True) 'True = Locally initiated disconnect

 End If

 MdmCmdStr = ""

 End If

 If InStr(MdmCmdStr, "Q") Then

 tmpCmd = Mid(MdmCmdStr, InStr(MdmCmdStr, "Q") + 1, 1)

 Debug.Write("Q" & tmpCmd & ":")

 If Val(tmpCmd) > 1 Then

 MdmErr = ERR

 Else

 MdmEcho = Val(tmpCmd)

 End If

 MdmCmdStr = ""

 End If

 If InStr(MdmCmdStr, "S0") Then

 tmpCmd = Mid(MdmCmdStr, InStr(MdmCmdStr, "S0=") + 3, 1)

 Debug.Write("S0=" & tmpCmd & ":")

 If Val(tmpCmd) > 1 Then

 MdmErr = ERR

 Else

 MdmRingMode = Val(tmpCmd)

 End If

 MdmCmdStr = ""

 End If

 If InStr(MdmCmdStr, "V") Then

 tmpCmd = Mid(MdmCmdStr, InStr(MdmCmdStr, "V") + 1, 1)

 Debug.Write("V" & tmpCmd & ":")

 If Val(tmpCmd) > 1 Then

 MdmErr = ERR

 Else

 MdmResultCodeFormat = Val(tmpCmd)

 End If

 MdmCmdStr = ""

 End If

 ModemError(MdmErr)

 End Sub

 Private Sub ModemError(ByVal code As Integer)

 If MdmResultCodes = ModemResultCodes.Enabled Then

 If MdmResultCodeFormat = ModemResultCodeFormat.Text Then

 Debug.WriteLine("MdmErrCode: " & MdmErrorCode(code))

 Ser.Write(vbCr & MdmErrorCode(code))

 If code = 1 Then Ser.Write(" " & MdmBaud)

 Ser.Write(vbCr)

 Else

 Ser.Write(vbCr & code & vbCr)

 Debug.WriteLine("MdmErrCode: " & code)

 End If

 End If

 End Sub

 Private Sub GoDialOut(ByVal cmd As String)

 Dim port As Integer

 Dim IP As IPAddress

 Dim host As String

 '--First, get rid of the AT command

 cmd = cmd.Replace("ATDT ", "").Trim

 cmd = cmd.Replace("ATD ", "").Trim

 cmd = cmd.Trim(Chr(13))

 'Debug.WriteLine("CMD=" & cmd)

 '--Next, see if a port is specified

 cmd = cmd.Replace(",", ":") 'Change comma separator to colon

 cmd = cmd.Replace(" ", ":") 'change space separator to colon

 'Debug.WriteLine("CMD=" & cmd)

 '--Define the port we'll use to dial out

 If cmd.Contains(":") Then

 port = Val(Mid(cmd, InStr(cmd, ":") + 1))

 cmd = cmd.Remove(cmd.IndexOf(":"))

 Else

 port = 23

 End If

 'Debug.WriteLine("CMD=" & cmd)

 'Debug.WriteLine("PORT=" & port)

 'Exit Sub

 '--Now we check what kind of address we have. It could be:

 ' hostname.com, xx.xxx.xx.x, or WWWXXXYYYZZZ

 Dim IpNoDots As Boolean = True

 If Not cmd.Contains(".") Then

 If cmd.Length = 12 Then

 For i As Integer = 1 To 12

 If Not (Mid(cmd, i, 1) >= "0" And Mid(cmd, i, 1) <= "9") Then

 IpNoDots = False : Exit For

 End If

 Next

 If IpNoDots = True Then

 cmd = cmd.Insert(9, ".")

 cmd = cmd.Insert(6, ".")

 cmd = cmd.Insert(3, ".")

 End If

 End If

 End If

 'Debug.WriteLine("CMD=" & cmd)

 'Debug.WriteLine("PORT=" & port)

 'Exit Sub

 '--By the time we get here, we should have either a hostname or

 ' an IP address in the form of xxx.xx.xx.x

 Try

 IP = Dns.GetHostEntry(cmd).AddressList(0)

 Try

 host = Dns.GetHostEntry(IP).HostName

 Catch

 host = cmd

 End Try

 WriteStatus("Dialing: " & host & " (" & IP.ToString & ") on port " & port.ToString)

 Catch ex As SocketException

 WriteStatus("Error dialing " & cmd & ":" & port.ToString)

 WriteStatus("Error message:" & ex.Message)

 ModemError(NO_DIAL_TONE)

 Exit Sub

 End Try

 MdmCmdMode = False

 Dim IPE As New IPEndPoint(IP, port)

 Try

 TcpClt = New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)

 TcpClt.BeginConnect(IPE, AddressOf DialOutConnected, Nothing)

 Catch ex As SocketException

 ModemError(NO_DIAL_TONE)

 WriteStatus(ex.Message)

 End Try

 End Sub

 Private Sub DialOutConnected(ByVal ar As IAsyncResult)

 Try

 TcpClt.EndConnect(ar)

 Catch ex As SocketException

 WriteStatus(ex.Message)

 MdmCmdMode = True

 ModemError(NO_ANSWER)

 Exit Sub

 End Try

 WriteStatus("Connection established.")

 ModemError(CONNECT)

 TcpClt.BeginReceive(RcvBuf, 0, RcvBuf.Length, SocketFlags.None, AddressOf ReceiveCallback, RcvBuf)

 End Sub

 Private Sub swGuardTimerFired(ByVal sender As Object, ByVal e As System.Timers.ElapsedEventArgs)

 swGuardTimer.Stop()

 If Ser.BytesToRead < 1 Then

 MdmCmdMode = True

 ModemError(OK)

 Else

 MdmCmdMode = False

 If TcpClt Is Nothing Then Exit Sub

 TcpClt.Send(XmtBuf, SerByt, SocketFlags.None)

 End If

 End Sub

 End Module

References

   Visible links
   1. http://icopiedyou.com/wp-content/uploads/2015/07/InternetModem.zip