FDX/Unified DOCSIS

fmd · 2025-02-13T20:05:09+00:00

While we wait for the announcement that N+X deployment has officially begun... Unified is the new version of FDX that has downstream going all the way to 1.8 GHz (currently limited by old taps). The return still stops at 684 MHz. Comcast has presented this spectrum layout to begin with: This is sufficient to offer symmetrical 2 Gbps. When more of the legacy channels go away, higher speeds can be offered. 3.1 modems that get FDX-L (limited) firmware can use the FDX channels.

badtlc4

Man-of-Leisure Fiber upgrades are actually costing MORE than companies were expected. at&t, verizon, GF have all run into this uncomfortable reality.

Man-of-Leisure

badtlc4 Fiber upgrades are actually costing MORE than companies were expected.

More than they expected maybe, but still far less than doing a complete DAA overhaul and replacing every node, amp, and tap nationwide. Sometimes even needing to go into people’s homes to remove old amps and splitters too.

The maintenance and upgrade costs for fiber are way less than cable. It’s only the up-front installation costs that are high.

badtlc4

swilliams RG-6 doesnt really have a known hard limit. It is really about signal processing and how far you can go with certain speeds. There are data centers that can pump terabit/s through RG-6.

CommunityMember

badtlc4 RG-6 doesnt really have a known hard limit.

Belden even has specs for the 1694a RG-6 type coax at 6GHz (as would be expected for RG-6 type coax, the attenuation at 6GHz is quite high).

MacLeech

Man-of-Leisure More than they expected maybe, but still far less than doing a complete DAA overhaul and replacing every node, amp, and tap nationwide. Sometimes even needing to go into people’s homes to remove old amps and splitters too.

The huge problem is getting last mile from copper to fiber. That’s the expensive part being talked about. That’s the part you gloss over, not the maintenance after going to fiber. That copper to fiber change means running dual networks for a decade.

If that change over was cheaper, cable companies would’ve done it by now.

Man-of-Leisure

MacLeech The huge problem is getting last mile from copper to fiber.

I’m not talking about upgrading DSL to fiber or coax to fiber, I was talking about upgrading existing fiber like going from GPON to XGS-PON, which can be done far more easily and quickly than these DOCSIS upgrades.

Fiber’s been doing 2Gbps for many years now, and cable companies are just now in 2025 slowly rolling it out, and with only 250Mb upload in Comcast’s case lol

I suspect the next logical step for DOCSIS will be Node+0 and eventually fiber to the tap, especially if they’re talking about going to 3GHz, 6GHz, and even higher.

I don’t think fiber into the home is necessary. Fiber to the tap may be the end stage for DOCSIS, and just use coax drops into the homes from there. That would save them a lot of effort/money also. But eventually those coax drops will need to be replaced anyway.

cypherstream

SpottedCat A press release came out in our local newspaper in May 2022 that Comcast was going to expand into our township, and we were one of the first subdivisions to get it. Funny because I moved here in 2010 and when I left my apartment I told Comcast I was sorry to leave because they just did this huge HD channel expansion and I was beta testing 100mbps docsis 3 at the time.

From May 2022 to late 2024 Comcast did a lot of new overbuilding and edge out expansions. But in 2022 when the conduit was being put in, FDX amps didn’t exist. They also didn’t do Node+0 or FTTH, despite spending all that labor right then and there. The last mile is the hardest to get to all fiber, but in our greenfield when the ditch witch was out and all the conduit was going in… they just didn’t want to use that as an opportunity.

I do think its Node+2 though. Theres MB-120’s and BLE-120’s along with 3 Harmonic nodes in my development. Two populated power supplies and one Power supply cabinet they placed but nothing in it.

Meanwhile my operator SECV is doing FTTH. In fact I saw a fiber tap in front of an Italian restaurant we like. A tech I know for them says my area should get the fiber lit in 2026.

Stuff

Man-of-Leisure You state that fiber has moved on to 8Gb and beyond. Can you please let Verizon know this? They only are offering 1Gb in my area so Comcast Xfinity wins with 1.2Gb in the advertising space.

Man-of-Leisure

Stuff You state that fiber has moved on to 8Gb and beyond. Can you please let Verizon know this?

They actually have upgraded a lot of their footprint to NG-PON2 and are doing 2Gb there, with the ability to go all the way up to 40Gb.

You can see their progress on the FCC map if you filter by speed.

videomatic3

Stuff at least verizon has symmetrical with low latency. Most likely cheaper too without data caps Id take that over comcast any day.

telcodad

Well, this is on the Light Reading site today:

CableLabs sees 14-Gig speeds at latest DOCSIS 4.0 interop
CableLabs said its latest DOCSIS 4.0 interop of cable modems, remote PHY devices and virtual CMTSs delivered downstream speeds of 14 Gbit/s – a 55% increase when compared to recent D4.0 interops.
By Jeff Baumgartner, Senior Editor, Light Reading - June 30, 2025
https://www.lightreading.com/cable-technology/cablelabs-sees-14-gig-speeds-at-latest-docsis-4-0-interop

Far exceeding the speed goal of cable’s “10G” mandate established in January 2019, CableLabs said it saw downstream speeds of 14 Gbit/s at a recent DOCSIS 4.0 interop that tested various components, including distributed access architecture (DAA) equipment, virtual cable modem termination systems (vCMTSs) and DOCSIS 4.0-capable cable modems from several vendors.

By comparison, CableLabs’ D4.0 interop held in November 2024 saw downstream speeds of 9 Gbit/s-plus. That speed milestone was achieved via a “live, multi-vendor network” using top-end modulation of 4096 QAM, Doug Jones, principal architect at CableLabs, explained in this blog post about the event.
:
The cable industry is already pursuing a possible successor to DOCSIS 4.0 that would target downstream speeds of 25 Gbit/s by elevating spectrum to 3GHz (D4.0 envisions HFC plant built to 1.8GHz). ….

Man-of-Leisure

telcodad CableLabs said it saw downstream speeds of 14 Gbit/s

I’m guessing this was using ESD, by reducing the number of upstream channels in exchange for additional downstream, but the trade-off for 15Gb download is you’re then capped at high-split upload, so like 1Gb.

The cable companies seem more interested in doing symmetrical tiers to match fiber.

But if they extend FDX to 1.8GHz, then they could do 15Gb down and 6Gb up.

At 1.2GHz, Comcast would be limited to ~ 9.5Gb download.

telcodad

telcodad Well, this is on the Light Reading site today:

CableLabs sees 14-Gig speeds at latest DOCSIS 4.0 interop
CableLabs said its latest DOCSIS 4.0 interop of cable modems, remote PHY devices and virtual CMTSs delivered downstream speeds of 14 Gbit/s – a 55% increase when compared to recent D4.0 interops.
By Jeff Baumgartner, Senior Editor, Light Reading - June 30, 2025
https://www.lightreading.com/cable-technology/cablelabs-sees-14-gig-speeds-at-latest-docsis-4-0-interop

FYI - Latest update from CableLabs on D4.0/D3.1 interoperability:

CableLabs advances on coherent PON and DOCSIS 4.0
Advancing the ball on both FTTP and HFC, CableLabs has issued specs for a 100-Gig coherent PON platform and verified that a DOCSIS 4.0 modem interoperates with DOCSIS 3.1 networks.
By Jeff Baumgartner, Senior Editor, Light Reading - January 26, 2026
https://www.lightreading.com/cable-technology/cablelabs-advances-on-coherent-pon-and-docsis-4-0

:
Seeding the network for DOCSIS 4.0
CableLabs also reached a milestone on the DOCSIS 4.0 front as it issued the first DOCSIS 3.1 Verified for Interoperability (VFI) with a DOCSIS 4.0 modem.

Boiled down, that means that a DOCSIS 4.0 modem works on DOCSIS 3.1 plant, a designation that should give cable operators confidence that they can begin to seed their network with D4.0 modems ahead of future DOCSIS 4.0 network upgrades that involve DAA and virtual cable modem termination systems (vCMTSs).

According to CableLabs documentation, a modem powered by MaxLinear’s new Puma 8 chipset is the device that has been verified for interoperability. MaxLinear’s Puma 8 can support both D4.0 and DOCSIS 3.1+, an enhanced form of DOCSIS 3.1 that boosts cable downstream speeds by supporting additional orthogonal frequency-division multiplexing (OFDM) channels.

Knittle said the interoperability achievement also marks an important step in the broader DOCSIS 4.0 certification program, which kicked off back in June 2023. To date, no products have been certified by CableLabs for D4.0.
“Once we get VFI certification we’ll move more into DOCSIS 4.0-specific testing,” Knittle said.

Meanwhile, cable operators such as Comcast and Mediacom have started their respective D4.0 network upgrades. …

Man-of-Leisure

videomatic3 Most likely cheaper too without data caps Id

Comcast starts at $30 and recently got rid of their data cap nationwide.

kmax

Man-of-Leisure Meanwhile, Comcast is slowly upgrading to 2Gb with 250Mb upload lol

They are in panic mode I imagine. Warms the heart.

hex0101

Man-of-Leisure Ziply Fiber is doing 50Gb residential using some type of Ethernet over fiber, since 50G-PON wasn’t available yet.

This is cool, basically since every home has their own fiber strand back to the PFP, Ziply can change a home’s fiber strand over to Ethernet for 10 and 50 Gig customers (dedicated fiber), and change it back to PON for 5 gig and below speed tiers. No outside plant changes needed in the neighborhood, you only need extra fiber from the CO to be available at the PFP.

fmd

swilliams Ron Hranac talks about top frequency vs attenuation in this article: https://broadbandlibrary.com/the-untapped-capacity-of-coaxial-cable/

Two takeaways: 1) Coax can go pretty high (actual frequency response must be measured). 2) You don’t get both. Increase the top frequency and you lose on distance, and vice versa.

Capacity… That depends on the modulation. It may be lowered on very high frequencies to deal with the high signal loss (one way to deal with 1.8 GHz, depending on amplifiers and the spacing between them).

Man-of-Leisure

fmd Removing amps will be the next step, going Node+0 everywhere.

After that, fiber to the tap unless the cable companies jump straight to FTTH after 4.0.

Fiber to the tap would let them do the same speeds as FTTH for a while, but without needing to run fiber drops to everyone’s homes. Also very useful in MDUs where they can’t always easily run fiber to each unit.

Tito79

so, what was the outcome of the install?

hex0101

Tito79 @videomatic3’s installation date for FDX is July 5th.

badtlc4

Man-of-Leisure being able to use coax inside the home would be a big advantage, IMO. It gives people in existing homes a lot more flexibility where they can put their gateways and get better wifi coverage with a single unit.

videomatic3

badtlc4 this is exactly why I like separate things for everything. Such as stand alone cable modem. Most modern houses have ethernet everywhere. It wont matter where the fiber drop is.

Man-of-Leisure
Fiber to the tap will only let them match fiber speeds if it was done yesterday By the time they get around to it, it wont. But im not sure how many people need 50-100gbit+ connections yet if any.

hex0101

badtlc4 What if those interior coax runs are only RG-59 cables from a long time ago?

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