protected NgnPublicationSession(NgnSipStack sipStack, String toUri) {
    super(sipStack);
    mSession = new PublicationSession(sipStack);

    super.init();
    super.setSigCompId(sipStack.getSigCompId());
    super.setToUri(toUri);
    super.setFromUri(toUri);

    // default
    mSession.addHeader("Event", "presence");
    mSession.addHeader("Content-Type", NgnContentType.PIDF);
  }
 public boolean setContentType(String contentType) {
   return mSession.addHeader("Content-Type", contentType);
 }
 public boolean setEvent(String event) {
   return mSession.addHeader("Event", event);
 }