public String getAttribute(String attribName) {
        if ((pdu.getPdu().equals("PSSRR")) || (pdu.getPdu().equals("PSSDR"))) {
            ArrayList attribs = pdu.getAttribs();
            for (int i=0; i < attribs.size(); i++){
                String[] attrib = (String[])attribs.get(i);
                if (attrib[0].equals(attribName)) return attrib[1];
            }
        }
        return null;
    }