Evolving test capabilities for 40G cabling systems

The growing interest in and deployment of 40-Gbit/sec transmission systems in data centers has brought the concept of ...

From the January, 2013 Issue of Cabling Installation & Maintenance Magazine

New products offer capabilities for MPO-based parallel-optics systems. Meanwhile, copper looms.

by Patrick McLaughlin

The growing interest in and deployment of 40-Gbit/sec transmission systems in data centers has brought the concept of parallel-optic transmission technology to the forefront. In simple, practical terms, a 40-Gbit/sec Ethernet transmission scheme combines four, 10-Gbit/sec transmission paths (in parallel, hence the nomenclature).

Because the transmission of 40G requires four paths, and the reception of 40G also requires four paths, the multi-fiber push-on (MPO) optical connector has emerged as the interface of choice for the installers, technicians and managers of 40G-capable fiber-optic cabling systems in data centers. As authors Jeff Bullion and Gordon Wiegand point out elsewhere in this issue (see page 25), the MPO has not yet been widely adopted as a transceiver interface. Even so, its use within the backbone and horizontal cabling infrastructures of data center networks is significant and growing. The most popular style of MPO connector has 12 fibers, though 24-fiber MPOs are available and have been put forth by some system providers as the better long-term option for migration to speeds beyond 40G. (See “Are you ready for 40 and 100G?” October 2011; and “A 24-fiber interconnect solution: The right migration path to 40/100G,” September 2012).

Parallel optics

While the 24-fiber MPO connector might emerge as the market’s choice, the current state-of-the-market, or state-of-the-technology, is the 12-fiber MPO. Until recently, conducting tests of MPO-connected cabling systems has been an impractical proposition and frequently has been passed over. The vast majority of MPO-based systems are factory-terminated, not field-terminated. And providers of preterminated MPO-based fiber-optic cabling systems generally have assured users of their systems’ performance without requiring that they be tested. Considering that one of the incentives driving the certification testing of any installed cabling system is to obtain the manufacturer’s warranty, getting an OK from the manufacturer to skip the testing process is likely to be welcomed with open arms by users.

But another significant incentive of testing a system is to ensure it actually performs at the specified and expected level. Cabling-test-equipment manufacturer Fluke Networks (www.flukentworks.com) has embarked on a campaign to raise that issue with users of preterminated systems. Among the lessons in Fluke Networks’ campaign was the concept of total cable certification for a preterminated system. The company stated, “Preterminated fiber is an important innovation that offers the ease of installing high-performance fiber networks with reduced hassles in the installation process. However, if you simply rely on the factory guarantee but ignore fthe ield testing aspect of certification, the fiber link installed can fail the industry performance standards and/or customer requirements. It is always important to complete the following steps to ensure total cable certification: 1) Confirm the fiber trunks are as specified. 2) Clean and inspect the fiber before installation. 3) Certify the fiber loss against the loss budget (Tier 1 certification) and then characterize the end-to-end fiber link (Tier 2 certification) to complete the total certification process.”

Testing the MPO

In October 2011 fiber-optic test-equipment manufacturer Kingfisher (www.kingfisher.com.au) introduced an MPO test-equipment kit, containing cleaning, inspection and test equipment. When it made the introduction, Kingfisher noted, “MPO/MTP ribbon fiber connectors are rapidly gaining popularity in many areas of fiber optics, from LAN to telco and others. They provide a practical method of reducing the cost and complexity of handling cabling and connectivity in high-fiber-count environments, which are becoming much more common. However, to date they have been poorly supported by appropriate test kits.”

The Kingfisher kit is available in three levels of functionality, including cleaning and inspection, clean/inspect/multimode test, and clean/inspect/multimode and singlemode test. The company added that the kit includes “multimode test sources which feature encircled flux compliance for improved loss testing accuracy, and Multi-Fiber ID, which gives improved continuity/polarity test capability across 12 fibers.”

The development of MPO-based test equipment opens up the possibility of alleviating the burdensome process of testing fiber trunk systems, as MPO-based multifiber cabling infrastructures are frequently called. When Fluke Networks introduced an MPO-based test kit in July, it provided detail on research it had done into the existing processes for testing fiber trunks. On average, its research found, it takes 6.5 minutes to setup and test the 12 fibers in an MPO trunk. “In today’s market, few MPO fiber trunks are tested in the field,” given the time it takes to conduct such tests, the company said. Its recently introduced product, MultiFiber Pro, reduces the test time to approximately 20 seconds—14 seconds for setup and 6 seconds for testing—the company said. “For the average data center with 1,600 MPO trunks, the MultiFiber Pro tester can save contractors more than 155 hours of labor and $17,000 USD in costs, assuming an average burdened labor rate of $55 USD,” the company noted.

The MultiFiber Pro includes a “scan-all” test functionality that autotests all 12 fibers in an MPO connector, in addition to the ability to troubleshoot a single fiber. The tester also provides built-in polarity verification and other capabilities.

Citing Cisco’s Market Need for 40 Gigabit Ethernet Market Report, published in 2012, Fluke Networks’ vice president of datacom cabling and installation tools Jason Wilbur commented, “With rates of 40-Gbits/sec in data centers expected to grow by more than 175 percent by 2016, it’s critical that we provide our customers with a solution that makes the MPO testing process both easy and cost-efficient. That need is compounded by the fact that preterminated MPO cables can be damaged or contaminated during transport and installation, and industry best practices dictate that validating performance is a critical step in ensuring data center performance.”

Other recent technological developments may further drive the need for MPO-based test equipment. In December Sumitomo Electric Lightwave announced that in January it would begin shipping a jacketed MPO ribbon splice-on connector. When making the announcement, the company said its “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.”

The advent of field-splicing MPO-style fiber connectors is likely to fuel the desire for field testing of those connections.

Here comes copper

Meanwhile, fiber-optic transmission evidently will not be the proverbial only-game-in-town forever when it comes to 40G transmission. The Telecommunications Industry Association’s (TIA; www.tiaonline.org) forging ahead with a Category 8 cabling specification will be geared specifically for the transmission of 40-Gbit/sec Ethernet to some distance that is likely to be less than 100 meters. Preliminary information from the TIA’s TR-42.7 Telecommunications Copper Cabling Systems Subcommittee indicates that Category 8 cabling performance will be specified to 2 GHz.

The certification of a twisted-pair copper cabling system to 2 GHz is one of many challenging initiatives that TR-42.7 will intend to tackle. As 2013 moves along, more specifics about Category 8 and the testing for it are likely to emerge. We will keep you informed of those activities as we obtain such information. ::

Patrick McLaughlin is chief editor of Cabling Installation & Maintenance.

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