code: public Iterator<?> getSessions(String protocol) {
  		if(!isValid()) {
  			throw new IllegalStateException("SipApplicationSession already invalidated !");
  		}
  		if(protocol == null) {
  			throw new NullPointerException("protocol given in argument is null");
  		}
  		if("SIP".equalsIgnoreCase(protocol)) {
  			return getSipSessions(false).iterator();
  		} else if("HTTP".equalsIgnoreCase(protocol)) {
  			return getHttpSessions().iterator();
  		} else {
  			throw new IllegalArgumentException(protocol + " sessions are not handled by this container");
  		}
  	}
docs: /*
  (non-Javadoc)
  @see javax.servlet.sip.SipApplicationSession#getSessions(java.lang.String)