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The Difference Between Cisco SFP Optics GLC-SX-MMD and GLC-SX-MM
Cisco the announced the end-of-sale of some Cisco SFP transceivers for Gigabit Ethernet in 2012, among which is GLC-SX-MM transceiver. Meanwhile, Cisco also announced a replacement of GLC-SX-MM transceiver, which is GLC-SX-MMD transceiver. Then, GLC-SX-MMD gradually replaced its predecessor. And the GLC-SX-MMD transceiver is now still kind of popular in many places. The module number of the two Cisco SFP transceivers only differ in one letter—D. What does the “D” stands for? What the differences between them and makes the GLS-SX-MMD transceiver so popular? The following text is giving the answers.
Both of the two Cisco SFP are 1000Base-SX SFP transceivers for multi-mode fiber and can be operated on 850nm wavelength. In addition, both GLC-SX-MMD and its predecessor has a dual LC/PC connector interface. The GLC-SX-MMD transceiver consists of three sections: a VCSEL laser transmitter, a PIN photodiode integrated with a trans-impedance preamplifier (TIA) and MCU control unit. However, according to Cisco, GLC-SX-MMD supports digital optical monitoring (DOM) functions. Apparently, the D stands for DOM.
Digital optical monitoring is also known as DDM (digital diagnostics monitoring) according to the industry standard MSA (Multi-Source Agreement) SFF-8472. The modern optical transceivers usually support these functions with which the end user would have the ability to monitor real-time parameters of the optical transceiver, like optical output power, optical input power, temperature, laser bias current and transceiver supply voltage.
Currently SFP transceiver with DOM function is now something new. However, the DOM allows the user to view the threshold violation messages of the optical transceivers. This useful function is very helpful in the telecommunication network which reliability and stability are required. The main difference between GLS-SX-MMD transceiver and GLC-SX-MM transceiver is that GLC-SX-MMD transceiver has the DOM function. And this is the main reason why GLC-SX-MM transceiver is gradually replaced by GLC-SX-MMD transceiver.
Both of the two Cisco SFP are economic solutions to Gigabit Ethernet. Although GLS-SX-MMD transceivers are much popular than GLC-SX-MM transceivers, some users still use the older one in consideration of the costs. Even Cisco hasn’t provide GLC-SX-MM transceivers any more since March 8, 2013, many users seek the third party GLC-SX-MM transceivers. To satisfy the customers’ needs, vendors like Fiberstore provides both GLC-SX-MM OEM transceivers and GLS-SX-MMD transceivers with high quality and low price.