การเชื่อมต่อ VBไปยังเว็บส่ง SMS ไม่เข้าใจตรง xmlhttp คืออะไรหรอครับ

 Public Function GetResponse(ByVal StrURL As String) As String
        Dim strReturn As String = ""
        Dim objRequest As HttpWebRequest = Nothing
        Dim ar As IAsyncResult = Nothing
        Dim objResponse As HttpWebResponse = Nothing
        Dim objs As StreamReader = Nothing
        Try

            objRequest = DirectCast(WebRequest.Create(StrURL), HttpWebRequest)
            ar = objRequest.BeginGetResponse(New AsyncCallback(AddressOf GetScrapingResponse), objRequest)

            'Wait for request to complete
            ar.AsyncWaitHandle.WaitOne(1000 * 60, True)
            If objRequest.HaveResponse = False Then
                Throw New Exception("No Response!!!")
            End If

            objResponse = DirectCast(objRequest.EndGetResponse(ar), HttpWebResponse)
            objs = New StreamReader(objResponse.GetResponseStream())
            strReturn = objs.ReadToEnd()
        Catch exp As Exception
            Throw exp
        Finally
            If objResponse IsNot Nothing Then
                objResponse.Close()
            End If
            objRequest = Nothing
            ar = Nothing
            objResponse = Nothing
            objs = Nothing
        End Try
        Return strReturn
    End Function

GetResponse("http://www.cat4sms.com/api/api.php?username=UserID&password=Password&msisdn=เบอร์โทร&message=ข้อความ")

Imports System.IO
Imports System.Net