Benefits of Fiber Optic Zero-U Adaptors in a Data Center Design
Fiber optic zero-U adapters have been available for a few years from various manufacturers. However, the value they can provide specifically in the data center does not seem to be widely realized. There is a consistent theme within the data center design criteria for the network cable plant, and that is; owners want improved management, flexibility and scalability. We will review how zero-U adapters can assist in providing all these sought after attributes.
First let’s identify what challenges zero-U adapters were meant to solve. Many data center managers have tried to find suitable methods of managing equipment which terminate high port counts of fiber optic connections, including core/distribution LAN or SAN switches. Effectively managing all the fiber optic interconnects and the significant quantity of associated patch cable “slack” when using the traditional fiber shelf approach can be overwhelming.

Troubleshooting or dealing with moves, adds and changes within a non-structured fiber optic distribution system that has a significant congestion of fiber optic patch cables puts the network at risk.
Zero-U adapters provide improved management to deal with the congestion typically seen at high-density fiber optic interconnect terminations. The zero-U adapters, terminating industry standard MTP connectors, are connected on the rear side of the adapter to the structured fiber optic cabling system with 12 strands of backbone fiber optic cabling to each MTP connector within the zero-U adapter. The IT equipment served from the zero-U adapter are connected with a breakout cable from each MTP connector, providing six LC pairs to connect to the individual ports on the LAN/SAN switch ports. Patch cord “slack” is eliminated if the quantity and location of the zero-U adapters, and the breakout cables are appropriately designed and specified to meet the requirements of the application.

In order for the implementation of zero-U adapters to improve flexibility and scalability of the fiber optic infrastructure, it is important to know where and how they are to be used, and where traditional high-density fiber shelves may be more appropriate. Again, the zero-U adapters are well suited at IT equipment with high counts of high-density fiber terminations. The IT equipment with high fiber port counts within the MDA typically consists of LAN core switches, the HDA typically consists of LAN distribution switches, and the SAN directors can be located within the MDA or HDA depending on the network architect preference.

 

The use of zero-U adapters in the MDA and HDA at these high fiber port count IT equipment, with a backbone fiber infrastructure cabled back to a centralized intermediate cross connect, helps provide improved flexibility and scalability. The server processing and storage equipment within the EDA would be provisioned with structured horizontal fiber infrastructure, also cabled back to the centralized intermediate cross connect. The use of zero-U adapters in the EDA would depend on the quantity of fiber ports within each server or storage cabinet.

The placement of the zero-U adapters, as shown above, needs to be closely coordinated not only with the location of each piece of IT network equipment, but also the slot the line cards occupy within the chassis. This requires more up-front planning and design time, but the reward can be an easy to manage flexible and scalable solution.

 

We recommend installing the quantity of zero-U adapters and associated MTP connectors to match the quantity of ports on the line cards. This will extend all ports from the network cabinets to the IDA centralized fiber cross connect field. The network cabinets can then be locked as there will be no need to access the network cabinets when managing moves, ads or changes.

 

Note the technology refresh cabinets adjacent to the production LAN core & distribution switches, and the SAN director. Planning for technology refresh ensures that migration to newer LAN/SAN technology in the future will be easily accommodated. The flexibility that the zero-U adapter provides for technology refresh is that the adapter and associated backbone fiber optic cabling can be easily and quickly moved to an adjacent cabinet. This enables the network administrator to install the new network chassis hardware, configure, test and validate the system is functioning as intended prior to disconnecting the legacy chassis. Once the new system has finished being commissioned and is ready to be placed into production the physical MTP connections can be quickly migrated to the adjacent cabinet shortening the maintenance window required to refresh a large network chassis.
One challenge with using the zero-U adapters and MTP connectors within the MDA & HDA cabinet lineup is that the centralized fiber optic cross connect field in the IDA will require excellent cable management to accommodate the quantity of fiber optic patch cords. The complexity of high density patching hasn’t been eliminated, it has just been moved from the network equipment cabinets where it is difficult to implement suitable cable management, to the IDA. One of the methods we have used to implement excellent fiber optic cable management is to field assemble off the shelf commercially available (from several manufacturers, no vendor lock-in required) components into a customized management solution for high density fiber optic cross connect fields. The solution shown utilizes one standard length of patch cord to cross connect any-to-any port between adjacent cabinets. Field installed fiber management is installed within the vertical manager to dress all the fiber patch cord slack. If there is a requirement to terminate more fibers than two adjacent cabinets can accommodate, we also have designed solutions that can efficiently manage patch cord cable management between cabinets that are not adjacent to each other while still taking advantage of the vertical slack manager.
The zero-U adapter solutions presented in this white paper are not meant to imply they are recommended for all applications. This is one of several methods of implementing a structured network cable plant to provide a flexible, scalable infrastructure that is easy to manage.
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