code: public void activate() {
          // Notify ActivationListeners
      	SipSessionEvent event = null;
      	if(sipSessionAttributeMap != null) {
  	        Set<String> keySet = getAttributeMap().keySet();
  	        for (String key : keySet) {
  	        	Object attribute = getAttributeMap().get(key);
  	            if (attribute instanceof SipSessionActivationListener) {
  	                if (event == null)
  	                	event = new SipSessionActivationEvent(this, SessionActivationNotificationCause.ACTIVATION);
  	                try {
  	                    ((SipSessionActivationListener)attribute)
  	                        .sessionDidActivate(event);
  	                } catch (Throwable t) {
  	                    logger.error("SipSessionActivationListener threw exception", t);
  	                }
  	            }
  			}
  	    }
      }
docs: Perform internal processing required to activate this
  session.