Nortel NTBB24GA MICS Services Cartridge (Refurbished)This cartridge uses slot "B" in the core Modular ICS unit. It provides the clocking service that is required for digital networks. It is required if you are using DTI cartridges or ISDN BRI Interface cartridges. One Services Cartridge supports all clocking that is needed on the system, regardless of the quantity or mixture of DTIs or ISDN BRI cartridges. Key Features: Mfr. Part #: NTBB24GA Provides the clocking service necessary for digital networks