The IP Communications High-Density Digital Voice/Fax Network Modules are an addition to the Cisco Systems IP Communications suite of solutions. The IP Communications High-Density Digital Voice/Fax Network Modules deliver high-density digital voice connectivity, high-density WAN connectivity, analog voice connectivity, and conferencing and transcoding capability in a network module form factor. The network modules provide enterprises, managed service providers, and service providers with the ability to directly connect the public switched telephone network (PSTN), traditional telephony equipment (such as private branch exchange (PBX), key systems, analog telephones, and fax machines), and WAN to Cisco 2811, 2821, 2851, 2911, 2921, 2951, 3825, 3845 and 3925, 3945 Unified Communications Routers for either IP Communications capabilities or pure toll bypass.

The IP Communications High-Density Digital Voice/Fax Network Modules flexibly operates within two different Cisco Unified Communications (UC) environments-the Cisco Unified Communications Manager (UCM) system with Survivable Remote Site Telephony (SRST) or Cisco Unified Communications Manager Express (UCME). The network modules can be integrated with these IP Telephony solutions in a Unified Communications Router, to provide a complete IP Communications solution for full service branch customers.

FXS port is used to connect directly to phones, fax machines, and key systems. Generates battery polarity reversal and caller ID. VIC3-2FXS-E/DID is designated as an "Off-Premise Extension Lite" product offering. This means that while the module addresses a subset of the off-premise extension applications, it should be noted that the module is not in full compliance
for off-premise usage.

DID port is used to provide off-premises DID connection from central office. Serves only incoming calls from the PSTN. Does not support caller ID in DID mode.