GLC-SX-MM vs GLC-SX-MMD: What’s the Difference?

With the widespread used with the Cisco switches and routers, Cisco’s GBIC transceivers and Small Form-factor Pluggables (SFP) transceivers for Gigabit Ethernet and Fibre Channel applications have also been popular in the market. These small, modular optical interface transceivers offer a convenient and cost effective solution for the adoption of Gigabit Ethernet and Fibre Channel in data center, campus, metropolitan area access and ring networks, and storage area networks. The 1000BASE-SX SFP (ie, the GLC-SX-MM and GLC-SX-MMD) is one of the common types of Cisco SFPs. Compatible with the IEEE 802.3z 1000BASE-SX standard, it operates on legacy 50 μm multimode fiber links up to 550 m and on 62.5 μm Fiber Distributed Data Interface (FDDI)-grade multimode fibers up to 220 m. It can support up to 1km over laser-optimized 50 μm multimode fiber cable.

GLC-SX-MM vs GLC-SX-MMD: What’s the Difference?

Due to the similar model, users are usually confused with the Cisco GLC-SX-MM and Cisco GLC-SX-MMD when they are choosing the SFP modules. So, what’s the difference between them? We are going to talk something about the difference between GLC-SX-MM and GLC-SX-MMD in this paper. (Note: Cisco GLC-SX-MMD= which refers SFP transceiver with the “FRU” part doesn’t be included here.)

As their models suggest, there is only little difference between GLC-SX-MM and GLC-SX-MMD, Obviously the “D”. Here, letter D in the model means the DOM functionality. DOM stands for Digital Optical Monitoring. Digital Optical Monitoring (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
  • Temperature
  • Transceiver supply voltage

Which means you can configure your device to monitor optical transceivers in the system, either globally or by specified ports. When this feature is enabled, the system will monitor the temperature and signal power levels for the optical transceivers in the specified ports. Console messages and syslog messages are sent when optical operating conditions fall below or rise above the XFP or SFP manufacturer’s recommended thresholds. It is an useful function and now is very popular with users.

It is worth noting that the GLC-SX-MM SFP has been no longer for sale since March 8, 2013 in Cisco. It is entirely replaced by GLC-SX-MMD. Cisco official encourages the customers to migrate to new model SFP transceiver modules. However, for usage and cost considerations, many users still use the old model SFPs. GLC-SX-MMD is much more expensive than GLC-SX-MM, but except the additional DOM function, they work as the same when use in the switch. This is why GLC-SX-MM is still used by many users. To a great extent, this situation is caused by the cost. Fiberstore offers a low cost option for you in both GLC-SX-MM and GLC-SX-MMD. No matter you still like to use the GLC-SX-MM, or wanna replace the new version GLC-SX-MMD, you can find the corresponding products in Fiberstore with a very low price and do not worry about the quality because all of Fiberstore’s Cisco compatible SFP modules are tested in-house prior to shipment to guarantee that they will arrive in perfect physical and working condition before delivered worldwide. In addition, there is a big stock of these two products, you can enjoy the same-day shipping when you order them in Fiberstore.


NEW Cisco GLC-SX-MMD Compatible 1000BASE-SX SFP 850nm 550m EXT DDM Transceiver Module


Key Features

  • Data-rate of 1.25Gbps/1.063Gbps operation
  • 850nm VCSEL laser and PIN photodetector for 550m transmission
  • Hot-pluggable SFP footprint duplex LC connector Interface
  • Class 1 FDA and IEC60825-1 Laser Safety Compliant
  • Compatible with SFP MSA
  • Compatible with SFF-8472
  • +3.3V single power supply and TTL Logic Interface
  • Average Output Power:-9.5~ -3dBm
  • Receiver Sensitivity:-17dBm
  • Extended temperature range (EXT):-5 to 85°C
  • Built-in Digital Diagnostic Function


  • Fiber Channel Links
  • Gigabit Ethernet Links
  • Fast Ethernet Links
  • Other Optical Links

Related Article:
Top 3 Cisco Catalyst Switches & Compatible SFP+ Options
A Quick Overview of Cisco GLC-LH-SM SFP Module
A Quick Overview of Cisco 1000BASE-T GLC-T SFP Copper Module

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