Cabletron FDMMIM-24 FDDI Concentrator Ethernet to FDDI Bridge Module UTP-PMD

Cabletron FDMMIM-24 FDDI Concentrator Ethernet to FDDI Bridge Module UTP-PMD

The Cabletron FDMMIM-24 is an Ethernet-to-FDDI bridge and concentrator module designed for installation in Cabletron MMAC-series chassis. It provides UTP-PMD FDDI connectivity — copper-based FDDI rather than fiber-optic — along with multiple Ethernet ports, enabling network segments to be bridged across FDDI backbone rings using standard unshielded twisted-pair cabling. The module is a dual-board assembly with dedicated management ports and an onboard Flash and DRAM module for configuration and operational storage.

Specifications & What's Included

• Model: Cabletron FDMMIM-24
• Type: Ethernet-to-FDDI Concentrator / Bridge Module
• FDDI Standard: UTP-PMD (copper-based FDDI, not optical fiber)
• FDDI Ports: 2 — FDDI A and FDDI B (MIC-style connectors)
• Ethernet Ports: 4 A-B port pairs (RJ-45)
• Management Ports: MODEM (RJ-45) and CONSOLE (RJ-45)
• BYPASS switch: present on front panel
• Status LEDs: RESET, ENET, FDDI, PWR, TWR, STBY, SOK, XMT, RCV, WRP, ROP, CLN, POK
• Onboard Flash Module (Intel E28F020 ICs visible on PCB)
• Onboard DRAM Module slot (populated)
• Form factor: Dual-board module for Cabletron MMAC chassis
• Physical note: FDDI A port connector housing is cracked and broken (see photos); FDDI B port intact with dust cover
• Includes: Module assembly only — no chassis, cables, or accessories

Applications

The FDMMIM-24 was designed for use in Cabletron's MMAC (Multi-Media Access Center) and MMAC-Plus modular chassis systems, which were widely deployed in enterprise and campus networks during the mid-to-late 1990s. FDDI (Fiber Distributed Data Interface) operated at 100 Mbps and served as a high-speed backbone technology bridging slower Ethernet segments before Fast Ethernet and Gigabit Ethernet rendered it obsolete. The UTP-PMD variant allowed FDDI to run over standard copper twisted-pair cabling rather than fiber, lowering installation cost in environments already wired for Ethernet. Bridge modules like the FDMMIM-24 allowed network administrators to interconnect legacy 10BASE-T Ethernet segments across a FDDI ring backbone, extending network reach and increasing aggregate throughput within the Cabletron chassis ecosystem. Today these modules are sought primarily by organizations maintaining legacy Cabletron MMAC infrastructure and by collectors of late-1990s enterprise networking equipment.