The ISDN BRI S/T BRI leased line (S/T) WAN interface card is designed specifically for the Cisco 1603 and 1604 routers. It is intended for users which require a dial-up ISDN BRI line (from the Cisco 1603 or 1604 router's fixed-WAN port) and an ISDN leased line (from the ISDN BRI leased line card inserted into the Cisco 1603 or 1604 router).