Weighing the costs and benefits of preterminated fiber-optic systems

The ability to quickly turn up networking services has propelled preterminated cabling systems--particularly including fiber-optic systems--to a technology of choice in many data center environments.

From the May, 2014 Issue of Cabling Installation & Maintenance Magazine

Their surge in deployment indicates value, but the ability to field-terminate multifiber connections offers an alternative.

The ability to quickly turn up networking services has propelled preterminated cabling systems--particularly including fiber-optic systems--to a technology of choice in many data center environments. The rationale behind deploying preterminated systems is simple on the surface: They epitomize "plug and play" in that their setup time is significantly lower than that of field-terminated systems with the same numbers of connections. Some calculations put the installation time of a preterminated system at 10 percent of that of a field-terminated system in a from-scratch installation. For moves/adds/changes, preterminated systems are estimated to be 50 percent faster than field-terminated. Generally speaking, the greater the number of fiber connections, the greater the value preterm represents.

Pros and cons

The pros and cons of each type are more complicated than that simplistic time-based perspective. As part of a Standards Frequently Asked Questions page on its website, BICSI (www.bicsi.org) provides information on "Factors of Preterminated Versus Custom Terminated Network Cables." There, BICSI explains, "Cabling standards do not necessarily provide pros and cons of installation methodologies such as the use of trunking assemblies or field termination of cabling components." It then provides a set of pros and cons for the trunking (preterminated) approach, stating, "While not necessarily a complete list, please consider the following."

Within that list, the "cons" of trunking are its initial cost and lead time; BICSI points out those factors can be true for both fiber-optic and twisted-pair copper cabling systems. However, the "pros" list outnumbers the "cons" list by a count of 6 to 2, with the following "pros" listed and explained: rapid deployment; risk abatement ("… potentially less risk of improperly terminated connections …"); high-performance assurance; greater predictability ("… installation schedules may be completed with greater predictability …"); comprehensive solution; and aesthetic appeal ("… a consistent, clean appearance that may improve manageability …").

In a white paper, Excel's (www.excel-networking.com) technical manager Paul Cave details several of preterminated systems' benefits. Cave says data centers are "one area that is very competitive, not only the cost but also the delivery schedules required to satisfy the very quick turnaround of the modern data centre (DC) deployment. It is not uncommon for a DC operator to want to turn an empty data hall into a fully functioning and revenue-generating suite in a matter of weeks. Time is money, and as soon as the decision is made they want to start earning revenue.

"Therefore, the time pressure quite simply dictates that pretermination is essential for the rapid commissioning of new data halls. This involves both copper and fibre connectivity; MPO/MTP fibre is fast becoming the de-facto system for both single and multimode connectivity in this space due to ease of use and speed, not to mention the high density."

Earlier this year, cabling market-intelligence firm BSRIA (www.bsria.co.uk) reported preliminary results on the sale of MPO connectors in 2013. BSRIA said, "MPO sales in 2012 were at $290 million," with "increasing sales of MPOs in 2013." The Americas region accounted for 73 percent of the world market for MPOs, with the United States alone accounting for two-thirds of it.

In the field

The MPO-style multifiber connector is the component upon which the conversation can turn. Many professionals may think of MPOs exclusively as components of preterminated fiber systems, but field-terminated MPOs have been available for more than three years. In January 2011 2011 Sumitomo Electric Lightwave (www.sumitomoelectric.com) added the MPO connector for ribbon fiber to its Lynx2 CustomFit Splice-On Connector product line. In March 2011 it added an MPO for loose-tube fiber to the line as well. At that time, Sumitomo Electric Lightwave said, "This 12-fiber connector completes full terminations in less than five minutes, including a streamlined ribbonized process … The on-site customization facilitated by the Lynx2 connectivity method eliminates the risk of shorts and slack, and the logistic delays associated with preterminated cables and pigtails."

The "shorts and slack" reference brings up a "con" with respect to preterminated systems--namely, that a preterminated system too short for its application would be a fiasco, and many data center managers ensure against a too-short system by ordering a length exceeding what they need, thereby creating the need to manage slack in racks, overhead, and/or under floors.

In January 2013 Sumitomo began shipping a jacketed MPO ribbon splice-on connector. "The company's decision to design and launch the Lynx2-MPO Ribbon Jacket splice-on connector addresses the growing network migration from 10 Gbits/sec to 40 and 100 Gbits/sec, and the subsequent accelerated use of optical fiber ribbon cables that meet the larger fiber counts, real-time scalability, speed of installation, and cost efficiencies required for the migration," Sumitomo Electric Lightwave said when announcing the jacketed connector.

AFL (www.aflgobal.com) also offers fusion-terminated MPO connectors as part of its FuseConnect product line. In September 2011 it added the FuseConnect MPO to its connector lineup. AFL describes it as "a fusion-spliced, field-terminated connector designed with just six components. With a factory prepolished ferrule, gone are the concerns of operator error and expensive connector scrap," AFL continues.

8-fiber cores

With transmission-speed upgrades from 10 to 40 or 100 Gbits/sec becoming reality for some data center managers, attention has turned to the efficiency--or lack thereof--of using MPO connectors, which generally house 12 or 24 fibers. Existing 40-Gbit/sec and pending 100-Gbit/sec short-wave (multimode-based) Ethernet specifications use a total of 8 fibers--4 transmit and 4 receive--for each circuit. In the common scenario in which 12-fiber MPOs support these connections, 4 of the 12 fibers go unused. Similarly, when 24-fiber MPOs are used to support current-generation 100G connectivity, 4 fibers go unused because the "10x10" parallel-optic scheme uses 10 transmit and 10 receive fibers. Soon-to-publish specifications will call for a "4x25" 100G scheme, in which 4 fibers will transmit 25 Gbits/sec and 4 fibers will receive 25 Gbits/sec.

However, fiber-system providers are aiming to make use of all fibers in these MPO connectors by breaking out MPOs housing 12 or 24 fibers into assemblies housing 8 fibers. In these setups, the connector interface does not change, but a 12-fiber MPO houses only 8 fibers.

Corning Optical Communications (www.corning.com) introduced a set of components in July 2013 to accommodate these types of conversions. It calls its new product set the Pretium Edge Advanced Optics (AO) Solutions. When announcing the conversion modules and harnesses in the product set, Corning explained that they "allow networks to fully utilize base-12 fiber count trunks when migrating to 40G, which uses base-8 fiber counts." In describing the practical implementation of the AO Solutions set, Corning explained to users: "Use your existing Pretium Edge infrastructure and, when it's time, swap out today's modules and harnesses for the advanced optical components of the Pretium Edge AO Solutions. Leave your existing hardware and trunks in place."

The AO Conversion Module is the product set's core component. As the company explained, the module "has 12-fiber MTP brand adapters in the rear for mating backbone trunks, and breaks out to 8-fiber MTPs in the front for connectivity to electronics … The conversion module fully utilizes all fibers in each base-12 set by breaking out base-12 MTPs at the rear of the module into base-8 MTPs at the front, which can then use high-bandwidth 8-fiber MTP assemblies to connect to electronics." The modules are available in 2-by-3 (2, 12-fiber MTP adapters in the rear with 3, 8-fiber MTP adapters in the front), and 4x6 (4, 12-fiber adapters in the rear and 6, 8-fiber adapters in the front).

While Corning's product set is based on an even number of 12-fiber MPOs to amass a fiber count that is a multiple of 8, the breakout concept also can work smoothly with any number of 24-fiber MPOs.

The 8-fiber core concept is not so much a preterm-versus-field-term issue; it has been discussed and advanced by organizations that are agnostic to the termination type. Even so, it is shaping up to be a topic that current users of MPO-based systems will face.

Patrick McLaughlin is our chief editor.

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