The Nortel Norstar NT7B74AAAA T1 Digital Trunk Interface Card provides access for up to 24 digital T1 or ISDN PRI channels. It comes equipped with built-in Channel Service Unit (CSU) functionality to support the integrity of digital signaling. The Modular ICS can support up to 2 DTI cards for a total of 48 T1 or ISDN-PRI (digital) lines. DTI cards cannot be installed in Trunk Modules. Requires either the Services Cartridge or the Combination Fiber 6-Port Services Cartridge. Compatible with the Modular ICS KSU only. The ISDN PRI Enabler Soft Key is required in order to configure the Digital Trunk Cartridge (DTI Card) as a PRI card.