EM-HDA-6FXO This 6-port FXO voice and fax expansion module provides off-premises connection to the central office. This module supports FXO power failover. If power to the router fails, this feature helps enable a direct metallic path between an FXO port and a special "red". It also supports analog Centralized Automated Message Accounting (CAMA) on any port. telephone to provide a direct line to the PSTN.