Device component - IETF L2VPN Driver:

        """

        SETTINGS = {    # min_endpoints, max_endpoints, vpn_service_type

            'ELINE': (2,    2, 'vpws'), # Virtual Private Wire Service

            'ELAN' : (2, None, 'vpls'), # Virtual Private LAN  Service

            'ELAN' : (2, None, 'bgp-vpls'), # Virtual Private LAN  Service

        }

        settings = SETTINGS.get(service_type)

        if settings is None: raise NotImplementedError('Unsupported service_type({:s})'.format(str(service_type)))