The Nortel 12×0 Fiber Trunk Modules (NTBB20) may be connected to the Modular ICS by a fiber cable. Each Fiber Trunk Module holds up to three Trunk Cartridges. There is one emergency transfer port per Trunk Module. All analog trunk cartridges are supported in the Fiber Trunk Module. Digital Trunk Interface (DTI) Cartridges and the Services Cartridges are not supported in the Fiber Trunk Module. ISDN-BRI Cards are supported only on Trunk Modules 3 and 4 (2-port expansion), or Trunk Modules 7 or 8 (6 or 12-port expansion).