Definition

With the widespread of Cisco routers and switches, Cisco SFP transceiver modules for Gigabit Ethernet and Fiber Channel applications have also been popular in the market. The Cisco GLC-LH-SM/Cisco GLC-LH-SMD is one of the Cisco SFP transceiver modules. Cisco GLC-LH-SM is the Cisco 1000BASE LX/LH SFP transceiver module. In Match, 2013, Cisco announced the end-of-sale for GLC-LH-SM. It has been replaced by GLC-LH-SMD.

Similarities between the two will be set forth first. Both the Cisco GLC-LH-SM and Cisco GLC-LH-SMD are compatible with the IEEE 802.3z 1000BASE-LX standard. They operate on standard single-mode fiber-optic link spans of up to 10km and up to 550m on any multimode fibers. They are compatible with each other. When used over legacy multimode fiber type, the transmitter of Cisco GLC-LH-SM and Cisco GLC-LH-SMD should be coupled through a mode conditioning patch cable. In addition, both the two have dual LC/PC connector and work at 1300nm wavelength.

Difference between GLC-LH-SM and GLC-LH-SMD

The differences between Cisco GLC-LH-SM and Cisco GLC-LH-SMD will be stated in this part. Literally, there is little difference, obviously the “D”. Here, letter D means DOM functionality. DOM stands for digital optical monitoring. So Cisco GLC-LH-SMD has additional support for digital optical monitoring capability. DOM is utilized intending to define a digital interface to access real-time operating parameters, such as optical Tx power, optical Rx power, laser bias current, and temperature as well as transceiver supply voltage. More specifically, it means that you can configure your device to monitor optical transceivers in the system either globally or on 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. 

Application

These utilised in Ethernet switches, routers, firewalls and network interface cards. Storage interface cards, also called HBAs or Fibre Channel storage switches, also make use of these modules, supporting different speeds such as 2 GB, 4 GB, and 8 GB. Because of their low cost, low profile, and ability to provide a connection to different types of optical fiber, SFP provides such equipment with enhanced flexibility

GLC-LH-SM specification

The minimum transmit power for the module is -23.5 for 50/125 cabling and the overall power budget is about 10 dB.The rating changes as the component value changes and it are fixed for a particular kind of component.

Conclusion

Even though GLC-LH-SM has been no longer for sale in Cisco, many users still use it. Except the additional DOM function, Cisco GLC-LH-SM 1000BASE LX/LH SFP nearly has the same function with Cisco GLC-LH-SMD. And Cisco GLC-LH-SMD is more expensive than Cisco GLC-LH-SM 1000BASE LX/LH SFP. Fiberstore offers both GLC-LH-SM and GLC-LH-SMD. No matter you still like to use GLC-LH-SM, or would like to have the new version GLC-LH-SMD.