Reduce Your Losses

Pre-Term Assemblies and Cassettes for the Data Center

Pre-term Assembly smallOne of the main concerns with cable installations in today’s data centers is space efficiency, especially as it relates to airflow, which is critical for the safe and effective operation of the active equipment. This hot topic focuses on reducing cable congestion, which has opened the doors for installing MTP®/MPO pre-terminated fiber optic cabling systems because these systems increase port density and offer superior performance due to increased bandwidth over copper based systems. So, selecting smaller diameter pre-terminated fiber cable assemblies together with high-density MPO cassettes is the smart choice when designing your data center’s cabling infrastructure.
Fiber MTP®/MPO cassettes provide the transition from the multi-fiber array backbone to individual patching. This “plug and go” factory tested and terminated technology makes installation easier and provides more reliable performance. But when selecting fiber cassettes, link-loss budgets must be carefully considered. Since pre-terminated fiber solutions include many components, such as cassettes, cable, connectors and patch cords, the total loss needs to be less than the maximum specified by the networking system budget. 
Each application specification, such as 10GBASE-SR, dictates the allowable channel link loss. For example, within the 10G fiber optic standard, inhibitors such as intersymbol interference (ISI) have been recognized to cause bit errors when adjacent data pulses spread and overlap. The impact of ISI is affected by the cable’s modal bandwidth, which varies depending on the type of 50-micron laser-optimized fiber used. The modal bandwidth itself is limited by the fiber’s characteristic of differential modal delay (or DMD), which actually causes ISI.
Modular Cassette
Sum of its parts
The overall performance of a fiber-based cabling solution needs to be viewed at the system level, which is includes the sum of the performance of the individual components. Each component is allowed a certain loss budget that contributes to the overall system loss budget. Here are the components to a pre-terminated fiber assembly:
Patch Cord Selection: Make sure that you have selected the proper patch cords and cable types that mate to your cassettes to build the full fiber channel. There are a variety of adapter interface options available. The LC interface is the most popular (and recommended) because it allows the best combination of high-density, low-loss and compatibility with active equipment vendors.  
Low-loss Cassettes:
 Select a cassette that incorporates high-performing 50 micron laser-optimized multimode fiber (LOMF) with matching performance LC patch cords and backbone cables. For example, the MomentumÒ cassettes from Legrand/Ortronics offer two grades of low-loss cassettes which mate high perofming LC patch cords with Berk-Tek’s GIGAlite-10XB LOMF fiber. Lower insertion loss per channel,means more cassettes can be used in the channel – allowing greater flexibility in your data center.
Protect your array fibers. Multi-fiber backbone cables are terminated into the back of the cassettes through MTPÒ/MPO array connectors. These cables can tight buffered with ribbon fiber or even reduced-diameter loose tube round cables that have ribbonized ends that are terminated in the MTP/MPO connectors. Care needs to be taken to protect these cables when terminated into the cassettes. The cassettes are inserted into the fiber patch panels and can mount in standard 19-inch or 23-inch rack-mount cabinets, wall-mount enclosures and under-floor boxes. 
Internal fiber management. Not only do you need to make sure that the outside connectors are protected, it is equally important to make sure that the individual fibers, once broken out from the array within the cassette, adheres to proper bend radius.  
Outside Durability and SafetyIn addition to the internal protection of the fibers, make sure that the cassette housing is rugged – metal is better than plastic. Some are even available with front shutters and dust covers that not only protect the fibers, but also provide eye safety to the installers.
Performance Documentation. One of the biggest benefits to selecting fiber cassettes is that they are factory terminated and tested, so there is no time-consuming field preparation or testing involved during installation. Make sure that test data from all the components is provided in the form of a visible label affixed to the cassette housing. This way any field-testing results can be verified quickly and easily and you are getting what you thought you paid for.

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Carol Oliver Berk-Tek Marketing Analyst