how to add PDU encoder and decoder to allow send SMS more than 160?

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VB

hi
how to add PDU encoder and PDU decoder in below code?
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Sub SendSMS()

        If Modem.IsOpen = False Then
            MsgBox("Port not Open!!")
            Exit Sub
        End If
        If Me.TxtTo.Text = "" Then
            MsgBox("No recepient number!!")
            Exit Sub

        End If

        If Me.TxtSMS.Text = "" Then
            MsgBox("Blank text message are not allowed!!")
            Exit Sub

        End If

        sendbutton.Enabled = False
        Sending = True
        SendAttempt = 0
        Do
            ATSend("AT+CMGF=1")
            Result = ATRead(1000)
        Loop While Result.Contains("COMMAND NOT SUPPORT")
        Do
            ATSend("AT+CSMP=17,167,0,0")
            Result = ATRead(1000)
        Loop While Result.Contains("COMMAND NOT SUPPORT")
        Do
            Do
                ATSend("AT+CMGS=""" & TxtTo.Text & """")
                Result = ATRead(1000)
            Loop While Result.Contains("COMMAND NOT SUPPORT")
            ATSend(TxtSMS.Text & Char.ConvertFromUtf32(26) & vbCr)
            'ATSend(MyMessage & Char.ConvertFromUtf32(26) & vbCr)
            'ATSend(MyMessage & vbCrLf & Chr(26))

            Result = ATRead(10000)
            SendAttempt += 1
        Loop While Result.Contains("COMMAND NOT SUPPORT") Or (Result.Contains("ERROR") And SendAttempt < 5)
        If Result.EndsWith(vbCrLf & "OK" & vbCrLf) Then
            TxtSMS.Text = ""
            TxtTo.Text = ""
            '  MsgBox("Message Successfully Sent")
        Else
            '  MsgBox("Message Could Not Be Sent", MsgBoxStyle.Critical, "Error")
        End If
        sendbutton.Enabled = True
        Sending = False


    End Sub

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