The voice/fax modules enable packet voice technologies including voice over IP (VoIP), voice over Frame Relay (VoFR) and voice over ATM (VoATM). Cisco voice solutions provide the means for integrating both voice and data within a single network allowing users to take advantage of services, such as toll-bypass, without sacrificing voice quality.Cisco offers this four-port FXO voice/fax expansion module for High-Density Analog Voice and Fax Network Module with four FXS ports (NM-HDA-4FXS).