Full Duplex DOCSIS (FDX), an extension to DOCSIS 3.1 that will enable symmetric multi-gigabit speeds, took another step forward following the addition of MAC Layer support, CableLabs announced Tuesday.

MAC Layer support arrives more than three months after CableLabs released the physical layer specs for FDX.

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The addition is focused on the MAC management messaging and operation needed to enable FDX between the cable modem termination system and the cable modem, and includes new processes such as sounding, echo cancellation training, and resource block assignment, Karthik Sundaresan, a principal architect at CableLabs, explained in this blog post.

Notably, an FDX-capable CMTS will receive and transmit in the same spectrum, while FDX modems can either receive or transmit in the same FDX spectrum. The FDX band, Sundaresan explained, is divided into sub-bands that the CMTS assigns which sub-band or sub-bands each modem uses for upstream or downstream operation.

Among the FDX processes, sounding is a method used to identify groups of cable modems, called Interference Groups, that would interfere with each other if they were allowed to transmit and receive at the same time in a specific sub-band. Those Interference Groups are then grouped into smaller Transmission Groups.

“The new FDX capability and functions are introduced as changes across the MULPI (MAC and Upper Layer Protocols Interface) specification and is now an official part of the specification,” Sundaresan explained.

As the new FDX specs mature, CableLabs expects it will start to see products with that capability emerge over the next year as silicon is developed and built into product designs. Meanwhile, CableLabs will host a series of FDX interoperability events, with the first one slated for Feb. 5-9 in Louisville, Colo.

“These will start from basic node level echo cancellation and gradually progress into full-blown product interoperability,” Sundaresan wrote.

CableLabs is also working on OSS changes needed for FDX and has started work on changes required to support FDX when deployed with new remote PHY architectures (FDX assumes the use of a distributed, node-plus-zero architecture).

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Some industry experts expect to see FDX trials get underway sometime this year and into 2019, with 2020 viewed as the technology’s first significant deployment year.

CableLabs introduced the concept in February 2016. Per the specs, the FDX band will reside between 108 MHz and 684 MHz (regardless of whether FDX channels occupy the whole band), so it’s possible for existing D3.1 modems to also use some spectrum set aside for D3.1.