Four versions of the ISDN Basic Rate Interface (BRI) S/T WAN interface card (WIC) exist (product numbers: WIC36-1B-S/T, WIC-1B-S/T, and WIC-1B-S/T-LL. Offering a single ISDN BRI S/T interface, these WICs may require an external Network Termination 1 (NT1), depending on the region of the world. The WICs insert into a mixed-media network module or directly into the WIC slot on the Cisco 1600, 1700, 2600, 3600, or 3700 chassis. The ability to add BRI connectivity through a WIC enables administrators to maximize valuable slot space while providing additional connectivity options, such as Ethernet, on the same module.