/**
  * @return string
  */
 public static final function getProtocol()
 {
     if (self::$_protocol === null) {
         self::$_protocol = defined('AMQP_STRICT_FLD_TYPES') && AMQP_STRICT_FLD_TYPES ? PhpAmqpLib_Channel_AbstractChannel::getProtocolVersion() : self::PROTOCOL_RBT;
     }
     return self::$_protocol;
 }