The Cisco GLC-SX-MMD is a Gigabit Small Form-factor Pluggable (SFP) transceiver module. It's a hot-swappable optical module used in network switches and routers to provide a Gigabit Ethernet (1 Gbps) connection over multimode fiber optic cable. The "MMD" in the name stands for "Multimode with Digital Diagnostics Monitoring," which is a key feature.

Key Features and Specifications

• Data Rate: 1 Gbps (1000BASE-SX).

• Media Type: Multimode Fiber (MMF). This is crucial as it only works with this type of fiber optic cable, which has a larger core and is designed for shorter distances.

• Wavelength: It operates at a short wavelength of 850 nm.

• Distance: The maximum distance depends on the type of multimode fiber used:

  • 550m over OM2 (50/125 µm) fiber.

  • 1000m over OM3 (50/125 µm) laser-optimized fiber.

  • 220m over legacy OM1 (62.5/125 µm) fiber.

• Digital Diagnostics Monitoring (DDM): This is a major selling point. The DDM function allows a network administrator to monitor real-time operating parameters of the module, such as temperature, voltage, and optical transmit and receive power levels. This is invaluable for troubleshooting and link health management.

• Connector: It uses a duplex LC connector to interface with the fiber optic cable.

• Compatibility: While it's a Cisco product, many third-party manufacturers produce MSA (Multi-Source Agreement) compliant versions that are 100% compatible with Cisco and other brands like Ubiquiti, D-Link, and Netgear.