Fiber is all the rage but DOCSIS isn’t dead: CableLabs

It feels as if all eyes are on fiber at the moment, with money pouring in and deployment commitments piling up. Operators playing in this space have largely dismissed cable as obsolete, with Frontier Communications CEO Nick Jeffery stating this week cable won’t be able to keep up with multi-gigabit speeds on fiber. But an expert from CableLabs contended DOCSIS isn’t dead – and won’t be for a while.

CableLabs is the entity responsible for putting out DOCSIS specifications. But it also provides several different specifications for point-to-point coherent optics. Curtis Knittle is VP of wired technologies at CableLabs, with oversight of “all things DOCSIS, all things fiber and all things PON [passive optical networking].” He told Fierce all the talk about DOCSIS not being able to keep up with fiber is nonsense. He pointed to the performance offered by DOCSIS 4.0, the most recently released specification, as proof.

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“The DOCSIS 4.0 specification, at least in the downstream, will be able to provide higher usable throughout than 10-gig PON,” he said. Knittle explained if you take the theoretical capacity of each technology and subtract the expected overhead necessary to implement forward error correction you’re left “more or less with usable throughput.” In the case of 10G PON, that factors out to around 8.7 Gbps downstream, whereas DOCSIS 4.0 provides 10 Gbps of usable throughput.

“Right off the bat, you can see that the statement that today’s 10-gig PON, that DOCSIS won’t be able to keep up with that is just not true,” he said. While it has become challenging for an older technology like DSL to deliver the higher speeds expected today, “it should be pretty clear to everybody that coaxial cable has not reached that point yet.”

“The number of bits that you can push down a pipe is directly proportional to the amount of spectrum that that pipe can accommodate,” he continued. “We are still exploiting the spectral capacity of coaxial cable. And that’s the beauty of what cable operators are doing today. They don’t have to put fiber in the ground to meet these speeds.”

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The DOCSIS 4.0 specification was finalized in March 2020 and will enable downlink speeds of up to 10 Gbps and uplink speeds of up to 6 Gbps once deployed. Knittle said the industry is still working to hammer out a few more items before it hits prime time, including out-of-band requirements, leakage detection and neighbor interference. CableLabs is also planning a series of interoperability test events to allow vendors to check their DOCSIS 4.0 kit, with a few set for later this year and more coming in early 2022.

While 10-gig technologies are gaining steam, some fiber players are already pursuing 25G PON technology. Asked about just how much more performance operators will be able to squeeze out of coaxial beyond what’s enabled by DOCSIS 4.0, Knittle said “it’s hard to say where we might end up, but there’s been companies that have demonstrated 25 Gbps over coaxial cable or higher even.”

Knittle was careful not to definitively state whether or not CableLabs has started work on a specification beyond DOCSIS 4.0. But he noted that given how long the process takes “if we wait until the demand is there to start a new spec development, then we’re too late.”