Cisco 4400 Series Integrated Services Router Network Interface Modules (ISRNIMs) provide highly reliable synchronous serial WAN connections for remote sites. These interfaces use well-known point-to-point WAN protocols such as High-Level Data Link Control (HDLC) and Point-to-Point Protocol (PPP) as well as Frame Relay, offering cost-effective virtualized WAN connections in both point-to-point and point-to-multipoint designs. You can mix and match NIMs to tailor cost-effective solutions for common networking solutions for low- and high-density WAN aggregation.