The Cisco IP Communications voice/fax network modules provide enterprises, managed service providers, & service providers the ability to directly connect the public switched telephone network (PSTN) & traditional telephony equipment to existing Cisco 2600XM Series, Cisco 2691, 3640, & 3660, & Cisco 3700 Series voice gateway routers. This set of Cisco IP Communications voice/fax network modules delivers the most versatile combination of analog & digital voice & data capabilities in a single network module. The 2-port FXS voice/fax interface card generates battery polarity reversal & caller ID. FXS port is used to connect directly to phones, fax machines, & key systems.