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Difference between GLC-SX-MM and GLC-SX-MMD


The GLC-SX-MM 1000BASE-SX Ethernet transceiver is a Duplex SFP transceiver for optical communications, rated for distances up to 500m and a maximum bandwidth of 1Gbps. The GLC-SX-MM transceiver operates at 850nm wavelength. 



The glc-sx-mm is used in the 1000BASE-SX Ethernet and Gigabit Ethernet. One can use the GLC-SX-MMD with OM-3 fiber. The specs for OM-3 fiber are for laser-optimized 50 µm fiber with a minimum of 2000 MHz-km effective modal bandwidth (laser band-width). It also supports digital optical monitoring (DOM) functions according to the industry-standard SFF-8472 multi-source agreement (MSA). This feature gives the end user the ability to monitor real-time parameters of the SFP, such as optical output power, optical input power, temperature, laser bias current, and transceiver supply voltage.

GLC-SX-MMD compatibility

The GLC-SX-MMD 1000BASE-SX SFP, compatible with the IEEE 802.3z 1000BASE-SX standard, operates on legacy 50 μm multi-mode fiber links up to 550 m and on 62.5 μm Fiber Distributed Data Interface (FDDI)-grade multi-mode fibers up to 220 m. It can support up to 1km over laser-optimized 50 μm multi-mode fiber cable. 850-nm wavelength extended operating temperature range and DOM support, dual LC/PC connector.

GLC-SX-MMD fiber cable

A cable that uses glass (or plastic) threads (fibers) to transmit data. A fiber optic cable consists of a bundle of glass threads, each of which is capable of transmitting messages modulated onto light waves

Digital optical monitoring

Digital Optical Monitoring or DOM is an industry-wide standard, intended to define a digital interface to access real-time operating parameters such as:

Optical Tx power

Optical Rx power

Laser bias current


Transceiver supplies voltage


DOM or Digital Optical Monitoring as the words imply is used for monitoring some parameters of the transceiver, which can help to identify the location of the fiber link failure, simplify maintenance, improve system reliability. Obviously, an SFP with DOM function is high-ender than one without it. This is why most of modern optical SFP transceivers support DOM functions. Both the transceivers and receivers are functional and are provided by vendors like Cisco a done of the component is EOL and replaced by the other.

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