The low density voice/fax network modules slide into Cisco 2600, 3600, and 3700 network module slots and contain either one or two voice interface card (VIC) slots. The VICs are daughter cards that slide into the voice/fax network modules and provide the interface to the telephony equipment and the PSTN. Just as the Cisco WAN interface cards can be swapped with other WAN interface cards, the Cisco VICs can be deployed interchangeably with other VICs in the voice/fax network modules. This built-in flexibility and investment protection are key reasons for the world-wide popularity of Cisco modular branch office router products.
VICs currently available include two-port foreign exchange station (FXS), direct inward dial (DID), foreign exchange office (FXO), Centralized Automated Message Accounting (CAMA) and E&M analog interface cards. Also available are a two-port ISDN Basic Rate Interface (BRI) digital interface card providing no phantom power and a two-port ISDN Basic Rate Interface (BRI) digital interface card providing -48V phantom power. These cards cover the entire range of analog connectivity options along with user side Q.931 and QSIG digital BRI connections (see chart). A Cisco 2600 series, including 2691 and 2600XM, or a Cisco 3620 can house one voice/fax module that contains up to two VICs, a Cisco 3640 can house up to three modules with a total of six VICs, and the 3660 holds up to six network modules providing a maximum of 24 analog voice ports. In addition, a Cisco 3725 can house two voice/fax modules with a total of four VICs and a Cisco 3745 can house up to four modules with a total of eight VICs.