The Data Guard Configuration feature allows to identify the current database as well as all the other databases in the configuration using LOG_ARCHIVE_CONFIG parameter.
LOG_ARCHIVE_CONFIG parameter defines the list of databases in this configuration. Log transport will not be allowed to any database not on the list . It is required for Dataguard configuration.
But FAL_CLIENT is Oracle TNS service of the local system and FAL_SERVER is Oracle TNS service of remote system. FAL_SERVER is fetch archive log for standby server and used for gap resolution.
FAL_CLIENT is not even needed in most Oracle 11 Data Guard setups