code: int getAssembledLengthIfKnown() {
      if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled()) SibTr.entry(this, tc, "getAssembledLengthIfKnown");
      int flatSize = -1;
      if (jmfPart instanceof JMFMessage) {
        flatSize = ((JMFMessage)jmfPart).originalFrame();
      }
      if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled()) SibTr.exit(this, tc, "getAssembledLengthIfKnown",  flatSize);
      return flatSize;
    }
docs: getAssembledLengthIfKnown
  Return the flattened length of the JMF Message contained by this part.
  The originalFrame() method of JMFMessageData returns the assembled length of the
  JMF message if it is known, i.e. if it arrived assembled and has not been updated
  in such away to make the length invalid.
  This length will include the length of any sub-messages.
  
  @return int The flattened size of the message, or -1 if it is not known.