public function connect($host = null, $port = null)
    {
        $this->_host = null !== $host ? $host : $this->_host;
        $this->_port = null !== $port ? $port : $this->_port;
        if (false === $this->_ssh_resource = ssh2_connect($this->_host, $this->_port)) {
            throw new TransportException(sprintf('Enable to connect to %s:%i.', $this->_host, $this->_port));
        }

        return $this;
    }