Belden raises yellow flag on use of 24-fiber MPO connectors

Aug. 7, 2013
Blog post says ‘the technology is not all it’s cracked up to be,’ citing limitations caused by the connector’s loss performance.

In a blog post, Belden fiber-connectivity solutions product manager Dwayne Crawford raises a yellow flag on the idea of implementing the 24-fiber MPO connector in data center environments. Several cabling providers, including Leviton Network Solutions (here) and TE Connectivity (here), have advocated the use of the 24-fiber MPO and made the case for that interface’s benefits in accommodating the migration from 10- to 40- and 100-Gbit/sec Ethernet transmission over multimode fiber.

Not so fast, says Belden’s Crawford. Citing the forthcoming 100GBase-SR4 specification—sometimes referred to as the 4x25 version of 100G because it will transmit 25-Gbit/sec data per pair over 4 fibers, and receive 25-Gbit/sec data over another 4 fibers—Crawford says that once 100G can run over 8 fibers rather than the 20 multimode fibers it currently requires, “We’re back to using the 12-fiber MPO solutions.” He says that is “precisely why I do not recommend the use of 24-fiber MPO solutions today.”

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But there’s more than fiber counts to consider, he emphasizes. “Optical loss budget is a big concern among data center managers,” he says, “and due to limitations in the protocol, standards now require a total connector loss budget of 1.0 dB for 40 and 100 Gigabit Ethernet channels.” That’s an issue because, as Crawford explains, “A 24-fiber MPO connector typically has a loss of 0.5 dB.” He contrasts that with the 0.2-dB loss performance of Belden’s 12-fiber MPOs. The disparity, he says, “is mainly due to the fact that the more fibers in a connector, the higher the loss, and the 24-fiber MPO connector and its endface geometry are more difficult to manufacture and control than a 12-fiber MPO.”

A 24-fiber MPO with such high loss limits a channel to having 2 mated pairs, eliminating the flexibility of a crossconnect architecture or the use of a zone distribution area, Crawford points out. He sums up by saying, “While a 24-fiber MPO solution might work for simple, point-to-point architecture, the reality is that the technology is not all it’s cracked up to be.”

You can read his full blog post, titled “24-fiber MPO solutions: A true caveat emptor,” here.

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