The Cisco High-Density Analog and Digital Extension Module for Voice and Fax provides enterprises, managed service providers and service providers the ability to directly connect public-switched telephone networks (PSTNs) and existing telephony equipment to Cisco 2821, Cisco 2851, Cisco 3825, and Cisco 3845 integrated services routers.The EVM-HD-8FXS/DID is an 8-port extension module - baseboard with 8 ports that can be configured individually for FXS or DID signaling.