What is the difference between GLC-T and SFP-GE-T?

What is the difference between SFP-GE-T and GLC-T? I have some information from Cisco Support Forums:

• GLC-T, 1000BASE-T SFP transceiver module for Category 5 copper wire, RJ-45 connector.
• SFP-GE-T, 1000BASE-T SFP transceiver module for Category 5 copper wire, extended operating temperature range, RJ-45 connector

GLC-T SFP copper SFP is a fiber optic transceiver module via Category 5 copper lines, Cisco GLC-T fiber transceivers provide 1Gbps data transfer and it provides full-duplex Gigabit Ethernet connectivity to high-end workstations and between wiring closets over existing copper network infrastructure. GLC-T SFP is compliant to IEEE 802.3 and its dimension is 0.6 in x 2.8 in x 0.6 in. GLC-T is with plug in module type Mini-GBIC.

3rd-party GLC-T Key Features

• Support 1000BASE-T Operation in Host Systems
• For 100m reach over Cat 5 UTP Cable
• Hot-Pluggable SFP Footprint
• Support RX_LOS as Link indication function
• Fully metallic enclosure for low EMI
• Low power dissipation (1.05 W typical)
• Compact RJ-45 connector assembly
• Compliant with SFP MSA and IEEE Std 802.3-2002
• Detailed product information in EEPROM
• Commercial temperature range (COM): 0 to 70°C

Cisco SFP-GE-T fiber optic transceiver that works with 1000BASE-T. SFP-GE-T is with extended working temperature and it is with DOM support. SFP-GE-T is small form transceiver with RJ45 connector interface and it is with spring latch for high density applications.

3rd-party SFP-GE-T Key Features

• Support 1000BASE-T Operation in Host Systems
• For 100m reach over Cat 5 UTP Cable
• Hot-Pluggable SFP Footprint
• Support RX_LOS as Link indication function
• Fully metallic enclosure for low EMI
• Low power dissipation (1.05 W typical)
• Compact RJ-45 connector assembly
• Compliant with SFP MSA and IEEE Std 802.3-2002
• Detailed product information in EEPROM
• Commercial temperature range (COM):0 to 70°C

The third-party GLC-T and SFP-GE-T have the same Key Features. So no difference between them? I think that they are operationally identical and can be interchanged with no problems - the only difference is that the SFP-GE-T conforms to NEBS Level 3 and the GLC-T doesn't. And Then question is what is NEBS Level 3? I'll also add that the SFP-GE-T is a little bit more expensive...maybe $40 more (retail) but it works in switches or routers like the ASR while the GLC-T is for switches only.

What is NEBS and why is it important?

Long a requirement for equipment used in the Central Office in the North American Public Switched Network, the rigorous Network Equipment Building System (NEBS) criteria have become a universal measure of network product excellence. The NEBS compliance of GDC's products is a key advantage for access providers including Local Exchange Carriers (LECs), Competitive Access Providers (CAPs), Competitive Local Exchange Carriers (CLECs), Internet Service Providers (ISPs), and Access Service Providers (ASPs). Products that are NEBS certified are also expected to be top performers in enterprise net- work environments as well.

What does NEBS Level 3 Certified mean?

NEBS has three levels, Level 1, Level 2, and Level 3. Level 1 refers to cases where minimum compatibility with the environment is needed. Level 2 applies for limited operability of the product. 

Finally, NEBS Level 3 certification guarantees the maximum operability of the equipment. It also certifies that the equipment will perform well in harsh environmental conditions and will not interfere with other electronic devices around. NEBS Level 3 certified networking equipment is vital in mission-critical applications. More information about NEBS please Google it.

In a word, GLC-T with 1000BASE-T standard, SFP-GE-T with 1000BASE-T NEBS 3 ESD. But, for a 3rd-party SFP module, I still don't know what the difference between them.