GLC-LH-SM vs. GLC-LH-SMD Similarities

Cisco SFP GLC-LH-SM and Cisco SFP GLC-LH-SMD are both used for 1Gbps Ethernet network. They support with IEEE 802.3 1000BASE-LX/LH standard and are compatible with each other. The two Cisco SFP modules can be connected with single mode and multimode LC fiber patch cable. If one switch supports Cisco SFP GLC-LH-SM, then it can also support Cisco SFP GLC-LH-SMD. Here are supported switches for these two Cisco SFP modules: Catalyst Express 500, Catalyst Express 520, Cisco ME 3400, Cisco ME 4900 series, Cisco ME 6500 series, Catalyst 2940 series, Catalyst 2950 series, Catalyst 2960 series, Catalyst 2960 S series, Catalyst 2970 series, Catalyst 3560 series, Catalyst 3560 E series, Catalyst 3560-X series, Catalyst 3750 series, Catalyst 3750-E series, Catalyst 3750-X series, Catalyst 4500series, Catalyst 4900 series, Catalyst 6500 series, cisco IE3010 series.

GLC-LH-SM vs. GLC-LH-SMD Differences

The difference between Cisco SFP GLC-LH-SM and Cisco SFP GLC-LH-SMD is that Cisco SFP GLC-LH-SMD has additional letter “D”. What does “D” mean?

There are two kinds of misunderstanding about “D”. Some think “D” represent “duplex”. Cisco SFP GLC-LH-SMD supports duplex interface. But Cisco SFP GLC-LH-SM should be connected with duplex LC patch cable. And nearly all SFP transceiver modules, except copper SFPs, are interfaced with duplex ports. So this understanding is obvious wrong. Some think that “D” means “ruggged”. This opinion is not true either. “Rugged” is abbreviated to “RGD”, for example, Cisco GLC-LX-SM-RGD Compatible 1000BASE-LX/LH SFP 1310nm 10km DOM Transceiver.

“D” of GLC-LH-SMD transceiver has additional support for Digital Optical Monitoring (DOM) capability. From the features stated above, Cisco SFP GLC-LH-SMD can support DOM function while Cisco SFP GLC-LH-SM can’t. DOM provides a diagnostic monitoring interface for optical transceiver modules. DOM supports monitoring of optic output power, optic input power, temperature, laser bias current, and transceiver voltage. When DOM is enabled, the system monitors the temperature and signal power levels for the optical transceiver modules in the specified ports. Console messages and syslog messages are sent when optical operating conditions fall below or rise above the SFP manufacturer-recommended thresholds.