The general procedure to decode an ASN.1 OER message involves the following three steps:

The first step is the creation of a decode message buffer object. The Asn1OerDecodeBuffer object contains constructors that can either accept a message as a byte array or as an I/O input stream. The input stream option makes it possible to decode messages directly from other mediums other than a memory buffer (for example, a message can be decoded directly from a file or a socket).

Unlike some other encoding rules, OER encodings do not indicate the ASN.1 type that was encoded. The ASN.1 type must be known prior to decoding in order to successfully decode it. A common approach in specifications is to have a specific outer level type known as a "Protocol Data Unit" (PDU) that encompasses all of the different message types that might be received. This is typically a CHOICE construct with each option representing a different type of message.

Whatever the message type is, the generated decode method for that message is invoked to decode the message. The calling arguments were described earlier.

The final step is to process the data. All data is contained within public member variables so access is quite easy. All of the primitive data type classes contain a public member variable called mValue that contains decoded data. This can be accessed in nested structures by prefixing mValue with each of the element names from the top down. For example, the given name element in the Name type shown earlier would be accessed as follows: name.givenName.mValue (this assumes an instance of the Name class was created using the variable name name).

A complete example showing how to invoke a decode method is as follows:

   try {

      // Step 1: create a decode message buffer object to describe the
      // message to be decoded. This example will use a file input
      // stream to decode a message directly from a binary file..

      // Create an input file stream object

      System.IO.FileStream ins = new System.IO.FileStream(
         filename, System.IO.FileMode.Open, System.IO.FileAccess.Read);

      // Create a decode buffer object

      Asn1OerDecodeBuffer decodeBuffer = new Asn1OerDecodeBuffer (ins);

      // Step 2: create an object of the generated type and invoke the
      // decode method..

      PersonnelRecord personnelRecord = new PersonnelRecord ();
      personnelRecord.Decode (decodeBuffer);

      // Step 3: process the data

      if (trace) {
         System.Console.Out.WriteLine ("Decode was successful");
         personnelRecord.Print ("personnelRecord");
      }
   }
   catch (Exception e) {
      System.Console.Out.WriteLine (e.Message);
      Asn1Util.WriteStackTrace(e, Console.Error);
      return;
   }