Cisco GLC-LH-SM vs. GLC-LH-SMD: Key Differences & Compatibility Guide
Cisco GLC-LH-SM is the older 1000BASE-LX/LH SFP optic; GLC-LH-SMD is its DOM-enabled successor that adds real-time diagnostics. Both run 1 Gbps over single-mode fiber up to 10 km.
Engineers often grab the first “LH-SM” they see in the parts bin, unaware the “D” suffix unlocks DOM data—handy for spotting dying lasers before users complain. That silent “D” keeps NOC tickets from multiplying.
Key Differences
GLC-LH-SM lacks DOM; GLC-LH-SMD reports temp, voltage, and light levels via SNMP. The D model also supports a wider temp range (-5 to 85 °C) and is the only one still shipping new from Cisco.
Which One Should You Choose?
Buy GLC-LH-SMD unless legacy gear explicitly rejects it. DOM is free visibility; resale value is higher; and you avoid “EOS” notices that come with the non-D variant.
Can I mix both models in the same link?
Yes—both speak 1000BASE-LX/LH, so one end can be GLC-LH-SM and the other GLC-LH-SMD.
Does the “D” consume more power?
Negligible—under 0.1 W extra—so power budgets stay the same.