When planning for 40/100 Gigabit Ethernet (GbE) capability in your data center, it is important to select a polarity management method that will take care of your current and future needs. The Telecommunications Industry Association’s (TIA) Method B polarity management offers the best path forward.
According to the TIA, there are three standard-defined polarity methods—Methods A, B and C. While mutually exclusive and incompatible with each other, each method does manage polarity in duplex fiber systems. Ease of implementation may vary among the methods. Adding to the options, at least one main-stream supplier uses a proprietary method of polarity management.
When choosing a polarity management method, I believe a standardized method will offer more design flexibility when compared to a proprietary management scheme, and is more likely to be used by the industry for new applications. As an aside, in my experience proprietary usually means exclusive, making it difficult to change suppliers, update your electronics without recabling, maintain your system when that vendor goes a different direction, or maintain your system at an effective cost.
With regard to specialized components, it seems to be widely accepted that Method B has unique advantages over Methods A and C for 1 and 10GbE systems when it comes to both implementation and administration.
Method A requires the use of different duplex fiber patch cords on each end of the channel. Method C uses a pair flip within the trunk cable, making network extensions more complex. Method B, as well as the common proprietary method, use standard patch cords on both ends of the channel and do not contain “pair flips” in the trunk cables.
Of course, most current data center projects include requirements or considerations for migration to 40/100GbE. This application standard specifies the use of parallel optics when the chosen media is multimode fiber. This parallel optics requirement puts additional pressure on choosing the right polarity management method.
The advantages of Method B polarity management continue to hold true for parallel optics configurations. Simply by replacing the module used to aggregate/disaggregate the channels with an MPO pass-thru panel, the system is ready for use in a parallel optics system. In fact, the Method B system allows for the use of common equipment cords on both sides of the channel. This is where Method B polarity management is differentiated from all of the common standards compliant and proprietary schemes. For parallel optics configurations, the schemes that use a key-up to key-down mating (TIA Type A: 1-1 Trunk) will all require different equipment cords on each end of the network.
This benefit is likely a major reason why international standards, such as EN 50174-1, are focusing solely on Method B. In conclusion, to handle your polarity needs for duplex and parallel optics configurations, Method B should be strongly considered as the front runner for implementation.
