DESC: The Cisco 3600 platform offers a wide variety of serial connectivity modules to accommodate the range of application needs in customer networks. The serial network module family for the Cisco 3600 series assures customers that they can choose a serial connectivity solution that fits their requirements. Available as network modules or WAN interface cards, serial connectivity options offer several port densities, synchronous and asynchronous alternatives, and integrated channel service unit/data service unit (CSU/DSU). As modular components, they are easily and inexpensively field upgradeable as customer requirements change.