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.

GHz-Man

People prioritize different things. Personally, I’d never go with fixed wireless unless my only options were satellite or ADSL.

I lived in an apartment that could only get FTTB, then Verizon used VDSL2 to each unit. It was 50/10Mb but I still preferred it over wireless. The latency was good and the speed never slowed down at all.

clocks

Well, that has been my other shocker. I am getting better latency than I did with Astound. 13-15 with Tmo vs 18-19 with Astound. Anyway, I don’t want to derail this main topic. I’ve been watching regularly for signs of D4 in my area.

videomatic3

GHz-Man lucky you weren’t an area with congestion then.
My area has had issues since forever, there was about 500 customers on one node. They did a bunch of n+0 splits in 2020 to make it less than 100 customers per node and I still had issues with my house, then they split my n+0 to have 2 upstreams at the node, and then the issues went away mostly…, been in my house since 09 and the problems finally went away in like 2022 when mid split got enabled, and like 2024 when fdx got turned on. Sure as shit enjoy gigabit symmetrical now got 5 year guarantee price for 50 a month.

HardlyWorthit

clocks
Have you seen:

GHz-Man

videomatic3 My area has had issues since forever, there was about 500 customers on one node.

That’s wild. Is it a pretty rural area?

My family has had Comcast since 1998 and I can’t ever remember noticing congestion.

videomatic3

GHz-Man can’t imagine how they would get 500 customers on a single node in a rural area

clocks

HardlyWorthit Yeah, I think I had seen that before.

Moffetts

T-mobile home internet is deprioritized, but there is no speed cap. I don’t think the gateway supports mmwave (of which Tmob has some, but it is very uncommon) or C band/N77 (which is even more rare than mmwave is.) N41 does their heavy lifting, not N77.

GHz-Man

videomatic3 can’t imagine how they would get 500 customers on a single node in a rural area

With amplifiers, a single node can easily serve hundreds of homes spread out across a large suburban or semi-rural area.

Wasn’t there that guy on DSLReports who said his entire town of Redwood Valley, CA was served by one really old Comcast node that hadn’t been touched in ages, and a long cascade of amplifiers?

I think he said it was one of the last areas at the time that still couldn’t get 1Gb service because the node was so old.

hex0101

GHz-Man Well when the plant got rebuilt for HFC (if it was a pure coax system beforehand from the analog days) then there would be a limit on how many amps there could be. I can’t imagine any more than 15-20 amplifiers in cascade would work that well even for digital cable and sub-split DOCSIS service.

GHz-Man

hex0101 I can’t find the original post, but from what I remember it was a really old 450MHz node, and it was one of the final nodes to still not be upgraded to 3.1 when the other 99% had already been upgraded, so they weren’t doing gigabit on it.

The top speed you could subscribe to was only 400Mbps or something.

With a 20 amp cascade you could still reach 5-6 miles away from the node which is pretty far.

MacLeech

GHz-Man Wasn’t there that guy on DSLReports who said his entire town of Redwood Valley, CA was served by one really old Comcast node that hadn’t been touched in ages, and a long cascade of amplifiers?

I think he said it was one of the last areas at the time that still couldn’t get 1Gb service because the node was so old.

It wasn’t the node, there were many nodes in Redwood Valley. It was the backhaul/uplink out of the area. Adelphia had it on multiple bonded T1s because they couldn’t build a fiber backhaul link. Comcast finally secured one after many years fighting with CalTrans, the California government, and other providers.

High capacity communications links up that stretch of the northern California coast are still problematic and still being worked on.
https://www.pressdemocrat.com/2026/03/30/highway-101-shows-fiber-optic-broadband-progress/

GHz-Man

MacLeech But there was something limiting his area to DOCSIS 3.0, I thought it was the node.

I remember he said they could subscribe to all the speed tiers except gigabit.

Or maybe the fiber backhaul Comcast got was too slow for 1Gb service.

hex0101

GHz-Man The top speed you could subscribe to was only 400Mbps or something.

400/10 on the D3.0 plants, that was the max offering in some areas until 2021. Meanwhile by October 2018, most of the gigabit rollout was complete. Sub-Split DOCSIS 3.1 was live.

It is one of the reasons why Lon.TV started to pursue Gigabit Pro back in 2018, and got it installed back in 2020. 10 Mbps upload just wasn’t cutting it, nor was the current reliability of the old DOCSIS 3.0 plant.

Comcast Gigabit Pro Update- Fiber Installation Has Begun

Why Your Internet Sucks Right Now

Signal Levels at 6:22 ^

fmd

WinDBreak is trying Technetix’ “Direction Neutral Amplifier” in a FDX deployment. This amplifier (same size as a tap) differs greatly from the CommScope amplifiers. There is no advanced Broadcom chip and no echo cancellation.

Article: https://www.lightreading.com/cable-technology/small-operator-sets-sights-on-full-duplex-docsis
Amplifier: https://emea.technetix.com/broadband-cable/access-amplifiers/dna-1800-15/

Maybe Comcast could find some use for it, if the length of a coax span between two of the large FDX amplifiers is not ideal. Place a DNA between them…

Technetix has been working on a larger version of it, but I haven’t heard about that project for some time.

GHz-Man

I guess we’re seeing why they slightly reduced upload speeds on the mid-split residential tiers, lol

All of the business class tiers have 300Mb upload:

crucialcolin

GHz-Man I guess we’re seeing why they slightly reduced upload speeds on the mid-split residential tiers, lol

All of the business class tiers have 300Mb upload:

Yeah I’m still a little irked by that. Dropping Xfinity voice bumped us of a now legacy 2gig res plan with 300 mbps(Lost 50 mbps upload).

Also most likely that 300 on business is likely over provisioned in reality closer to 350 mbps which is the way mid-split residential had been until the new plans came along.

cypherstream

fmd Wow those areas are really remote. Pulled up their headend coordinates in google maps. What a trip back in time when headends were just little shacks, no generators, big dishes and no fencing.

Be interesting if they and other operators can get the technetix amps to work with fdx.

fmd

cypherstream I’ve been looking for FDX test results with this amplifier for a long time. I don’t know how likely it is for WinDBreak to publish a paper or something.

hex0101

Added into the system on 5/9/2026 at around 8-9 am.

Hope that FDX config gets enabled on the RPD and amps.

sub-split and mid-split nodes showing no maintenance upcoming, localized node maintenance for me and the node the next neighborhood over. (OM6000 FDX node cut in on 4/13, removed on 4/27 and replaced with Harmonic Ripple after intermittent service and all day outage). My OM6000 FDX node was cut in on 3/17 and has worked well. (probably wasn’t defective from the factory lol)

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