Hi every one

     I am integrating USPS for my shipping rate calculator. I need to pass the country name and zip code as the request and get back the response in my site. the data is XML . I am using the following coding,

    Dim uri As New Uri(url)
        Dim data As String = pass_str
        If uri.Scheme = uri.UriSchemeHttp Then

            Dim request As Net.WebRequest = Net.WebRequest.Create(uri)
            request.Method = "POST"
            request.ContentType = "text/xml"
            request.ContentLength = data.Length
           
            Dim writer As New IO.StreamWriter(request.GetRequestStream)
            writer.Write(data)
            writer.Close() 

            Dim oResponse As Net.WebResponse = request.GetResponse()
            Dim reader As IO.StreamReader = New IO.StreamReader(oResponse.GetResponseStream())
            Dim tmp As String = reader.ReadToEnd()
            oResponse.Close()
           
            Response.Write(tmp)        

        End If

      I am receiving the following error,

      Exception Details: System.Net.WebException: The remote server returned an error: (501) Not Implemented.

     Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

       Please help me to solve this problem and exlain me the concept of "Http request" and "Http response"

   Thank you...........