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.

About the Author

Kevin Paschal

Kevin Paschal is Product Manager, Enterprise Fiber Optic Solutions for CommScope, Inc. He is responsible for the development and implementation of the global strategic plan for his solution set, managing the product portfolio life cycle and roadmap, and working with customers to define the infrastructure needs of next generation applications. Paschal received a Bachelor of Science degree in Mechanical Engineering from the North Carolina State University. He has more than 20 years of experience with fiber optic solutions, including proficiencies in product management, research & development, engineering, and manufacturing. Paschal holds 5 patents relating to fiber optic cable design. Paschal received a Bachelor of Science degree in Mechanical Engineering from the North Carolina State University. He has more than 20 years of experience with fiber optic solutions, including proficiencies in product management, research & development, engineering, and manufacturing. Paschal holds 5 patents relating to fiber optic cable design.

See all posts by this author

Comments

2 comments for "Polarity: Knowing Whether You’re Coming Or Going"
jamesdonovan

Nice summary Kevin. Heard rumours of a Method D being considered in standards. What is that about?

Kevin Paschal

James, In last week's TIA TR42.1 meeting, a Method D proposal was addressed. The proposed method covers only parallel connectivity. Comments on Method D did not gain consensus and will appear again on the second default ballot. It would appear that Method D is being proposed by a company that utilizes a proprietary polarity scheme for duplex connectivity. That scheme does not migrate to parallel transmission easily. We'll have to wait and see how the standards activity progresses. In any event Method B polarity is still the best choice for duplex and parallel connectivity.

Add Your Comment

Please submit your comment using the form below

 
(required)