Cisco offers a wide variety of connectivity, expansion and upgrade modules to accommodate the range of application needs in customer networks. The network modules assure customers that they can choose a connectivity solution that fits their requirements. As modular components, they are easily and inexpensively field upgradeable as customer's requirements change.??Cisco System`s T1 DSU/CSU WAN interface card is an integrated, fully managed DSU/CSU for T1 or fractional T1 service. It is supported on the Cisco 1600, Cisco 1720, Cisco 2600 and 3600 Series routers, and it provides a cost effective router-DSU/CSU combination.