The voice functionality built into Cisco IOS software enables modular access routers to carry voice traffic, such as telephone calls and faxes, as Voice over IP (VoIP) simultaneously with data traffic over LANs, MANs, and WANs. Voice network modules convert telephone voice signals into a form that can be transmitted over an IP network. Voice network modules convert telephone voice signals into a form that can be transmitted over an IP network. ??NM-HD-1V= is a 1-slot 4-channel High-Density Network Module.