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NBase-T maps out spec ahead of products in 2016

MAC/PHY specs released, plugfest in the pipeline

By Richard Chirgwin, 10 Dec 2015

A year after its launch, the NBase-T 2.5 / 5 Gbps Ethernet alliance's 802.3bz IEEE specification is drawing closer to reality.

Peter Jones, chair of the alliance (he's also a principal engineer at Cisco, but members of the alliance do so as individuals, not as company reps), told The Register the 2016 agenda will be led by getting key specifications into place.

The second version of the NBase-T physical layer (PHY) specification has been settled, he said, but to turn that into product also requires that the PHY-MAC (Media Access Control) layer be agreed.

For those that haven't been following it, NBase-T was kicked off in 2014 to fill a gap created by faster Wi-Fi: boost the speed of the wired Ethernet serving beyond-gigabit Wave 2 access points without demanding an expensive cabling upgrade.

Jones said 2016 is the year that deployments will start, and that makes two things important: a rapid completion of the standards, and certainty that pre-standard products won't be made obsolete when the specs are wrapped up.

The USXGMII MAC-PHY specification the group released today is important to both of these, Jones said.

“You need a system that plugs the PHY-layer silicon into the CPU silicon,” he explained.

Usually, that's handled by vendors rather than by the IEEE, but there are reasons that the NBase-T group decided it should be in the specification.

“We wanted to get the information defined and available, so system builders can get going,” he said – so Cisco released its internal MAC-PHY work to the alliance members in general.

A graceful downgrade in the system is particularly important, Jones said, for interoperability between 2.5 / 5 Gbps systems and 1 Gbps switches.

“There are times [in Ethernet] where the autonegotiation process chooses the highest common speed. This has come up before, and it's usually solved by ISVs,” he said.

“We want this codified: if you plug in something at 1000Base-T, we can't have a situation where it doesn't work.”

There's also a boatload of analogue and digital signal processor (DSP) work for OEMs and merchant silicon vendors to work on, which a common MAC/PHY spec should help with.

The first version of the specification defines a single-port interface, with dual and multi-port versions are expected in Q1 2016.

That will get tested by a plugfest early in 2016, Jones added.

The alliance is now closing in on 50 members, with coverage extending to cabling companies, test equipment vendors and others.

The alliance's announcement is here. ®

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