Leviton: 24-fiber connector ‘yellow flags’ are misconceptions

Sept. 5, 2013
Company says the 24-fiber MPO remains a more-efficient choice for 4x25 100G, and the higher fiber count does not translate to higher insertion loss.

A document from Leviton titled “Misconceptions about 24-fiber MTP/MPO Connectivity” seeks to set the record straight on a couple technical issues related to the use of 24-fiber MPO-style fiber connectors as opposed to 12-fiber MPO-style connectors. “With the growth of 24-fiber MPO/MTP solutions, some confusion and misinformation has emerged within industry circles,” the document says. Although no particular piece of information or individual source is named, the publication of this document from Leviton followed the publication of a blog post by Belden’s Dwayne Crawford, in which he points to the forthcoming 4x25-Gbit version of 100G as well as concern over optical loss budgets as reasons he recommends the use of the 12-fiber rather than the 24-fiber MPO. We covered that blog post here.

Related story:MPO, MTP terminology clarified

The document from Leviton names and addresses two misconceptions. Specifically, and quoted directly:

  • Misconception #1—New proposed standards define 100GbE over fewer fibers, as opposed to 20 fibers today. This makes 24-fiber connections superfluous.
  • Misconception #2—24-fiber connectors don’t perform as well as 12-fiber connectors, as higher fiber counts translate into higher insertion loss.

Leviton addresses both directly. About 4x25 100G, the document says, “This 4x25 solution would only require 8 fibers (4 transmit, 4 receive)—the same as the current 40GBase-SR4. That means a 12-fiber connector can support a single 100G channel. However, a 12-fiber connector for an 8-fiber channel is inefficient, as 4 strands in the 12-fiber connector are not used. Alternatively, by using a 24-fiber MTP connector in the horizontal cabling, it can then be converted into three, 8-fiber 100G channels that run over one cable, with all 24 fibers used to support traffic.”

It then provides an example: “Say you need to support twelve 100GbE channels using the next-gen 4x25 Gb/s standard. With 12-fiber MPO/MTP connectors, you would need to install 12 connectors, or 144 fibers total, with 33% of the fiber wasted. However, when supporting the same 12 channels with 24-fiber connectors, only 4 cables would be required, using 96 fibers total, at 100% fiber utilization.”

Concerning the connectors’ performance, Leviton took this shot across the bow: “Some have mistakenly claimed that higher fiber count leads to higher loss, and one cable vendor pointed to a ‘typical’ loss of 0.5 dB for 24-fiber connectors as evidence.” It immediately followed with: “In fact, the industry standard product rating for MPO/MTP connector performance of both 12-fiber and 24-fiber is 0.5 dB maximum. When using proper polishing techniques, 24-fiber MPO/MTP terminations can meet the same performance levels as 12-fiber assemblies. Improved performance can be achieved using low-loss ferrules for both 12-fiber and 24-fiber MPO/MTP connectors rated at 0.35 dB maximum.”

It then adds that its own OM3 and OM4 24-fiber assemblies have a maximum insertion loss of 0.35 dB—“the same as in a premium/low-loss 12-fiber MTP assembly.”

The document concludes with a section titled “24-fiber is here to stay.” Within that portion of the document Leviton says, “We understand that many aspects of data centers are unique to each client, designed around not just ‘cable and connectors,’ but also inclusive of variables such as facility purpose and administrative styles. Any vendor is well-advised to listen to the client and view this complex environment as a total ecosystem—inclusive of many external drivers. This is why Leviton also offers a full end-to-end 12-fiber MTP solution alongside our 24-fiber end-to-end solution.”

You can access the complete document from Leviton here.

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