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.

az8831

videomatic3 These are some pretty decent first hop latency numbers compared to what mine were. I typically had 10-15ms versus your 5-7.

videomatic3

az8831
that was only under load.
not under load i see the same as normal. and its just using around 50mbit right now. that screen shot above i was uploading at 600mbit
its just as crappy when the connection isnt being used. ive seen similar behaviors even with lower provisioned speeds too. i do not expect anything to change until map interval gets changed. the reason latency improves under load is theres more grants for sending data.

videomatic3

az8831 overall if you look at this samknows chart… the latency has actually gotten worse than before having fdx.

MacLeech

videomatic3 overall if you look at this samknows chart… the latency has actually gotten worse than before having fdx.

By 1 whole millisecond!!! It went from 13ms to 14ms. Oh, the horror….. 😉

hex0101

videomatic3 The upload speed is only 933 Mbps? (Gigabit).

az8831

videomatic3 lol yeah my latency got worse by a few ms when they switched me to a Harmonic node

videomatic3

MacLeech By 1 whole millisecond!!! It went from 13ms to 14ms. Oh, the horror….. 😉

aint nothing like real stats

hex0101 videomatic3 The upload speed is only 933 Mbps? (Gigabit).

thats just an average from before and after fdx also accounting for how many days. look at the actual line graph. its more like 2000+ 😃😃😃
i only put that in there because it shows the day i swapped out the modem.
totally unnecessary, but whatever. locked in for 5 years.

hex0101

videomatic3 Ah I see, thanks for clarifying!

fmd

A more recent n+x layout from Comcast (“only” supports X-2000):

hex0101

Compared to N+0:

hex0101

As of July 2025, there are over 33,000 FDX amplifiers deployed in the network!

And 45,000 FDX RPD’s, with the majority being in N+0 footprint.

cypherstream

hex0101 I wonder how many recent mid split upgrades were done with FDX nodes- just had to use mid split amps since that’s all they had.

Anyone know when the first Harmonic FDX ready RPD and launch amplifier shipped?

fmd

cypherstream Anyone know when the first Harmonic FDX ready RPD and launch amplifier shipped?

The timeline looks something like this:
2015: R-PHY specification
2017: Pebble-1 (RPD)
2017: Ripple-1 (Node)
2018: Comcast deploys R-PHY
2022: Pebble-2 (FDX)
2022: Ripple-2 (FDX)
2023: Comcast deploys FDX
2025: Pepple-2, Unified (Q1)
2025: Ripple-2, Unified (Q3)

Ripple-2 Unified:

Chris313AllNight

Looking at those pictures, what would they be able to do if they pulled out D3 and the video QAM slots? Thinking back, I feel old. I remember reading about Docsis 3 on DSLR. Cable was intro’d to me January 31, 2004. Time has flown.

hex0101

Chris313AllNight

Cable was intro’d to me January 31, 2004. Time has flown.

Was it you on DSLR who said that you got AT&T Fiber, after 20 years of cable? (Starting on January 31, 2004.)

Chris313AllNight

Yes, for 1.5 years, I had the light goodness that is Fiber. I waited for 20 years for that, too. Love the Surfboard 4200 pic. Oldie but a goodie. I started with a SB5100 3/384. Wow.

hex0101

fmd Is this FDX up to 1.8 Ghz capability or running FDX and ESD simultaneously? Cool to see even if it is going to be reserved for future use.

Now we have 1st gen FDX hardware (Orginal Pebble-2 and FDX amps), with 2nd gen FDX hardware on the horizon (Unified Pebble-2, and 2nd gen FDX amps). 2nd gen FDX amps will be more automatic in terms of setup compared to the 1st gen, and will support 1.8 Ghz operation.

Harmonic Unified Pebble-2 only supports up to a 2×2 config? There are Ripple-1 nodes with 2×4 operation. (Pebble-1.) This is accomplished by having two RPD’s in the housing?

Will upgrades go like this:
mid-split > FDX gen 2 hardware (Unified pebble-2 and 2nd gen FDX amps). Will sit on mid-split for a bit though due to recent investment into upgrading these nodes/amps to mid-split.
legacy sub-split > FDX hardware gen 1 (standard pebble-2 with 1st gen FDX amps while supplies last.)

cypherstream

fmd that timeline doesn’t bode well for a lot of the new expansions and upgraded areas in PA then. It was late fall of 2022 that they started installing these nodes both in new areas and then retrofit them in place of Aurora nodes in the adjacent areas. The Aurora nodes at one time were SA6940’s so who knows maybe they will spend the capital and upgrade these again.

They should have waited or just did FTTH in new builds. Now they have to come through and do it all over again. At least they don’t have to dig again. Conduits FTW.

fmd

hex0101 Is this FDX up to 1.8 Ghz capability or running FDX and ESD simultaneously?

Technically, it’s one or the other, but in FDX mode, the downstream also goes to 1.8 GHz.

Another interesting detail is that the diplex filter is now digital, with a < 1 MHz crossover region.

hex0101

cypherstream In Seattle Harmonic Ripple-1 nodes (with pebble-1 RPD) were being installed as far back as 2019 (prior to COVID pandemic!)

From a tech in Seattle- August 4th, 2019- RPHY cut in
Services were tested on the new RPHY node the day prior to cutover

Moffetts

The Aurora nodes at one time were SA6940’s so who knows maybe they will spend the capital and upgrade these again.

Well yeah, cable companies are in a perpetual upgrade cycle. I don’t know what makes them choose FTTH over HFC in new builds in 2025, but, they have no issues with “doing it all over again.” That is how they have always operated.

MacLeech

Moffetts Well yeah, cable companies are in a perpetual upgrade cycle. I don’t know what makes them choose FTTH over HFC in new builds in 2025, but, they have no issues with “doing it all over again.” That is how they have always operated.

Most residential internet service providers are in a perpetual upgrade cycle, even fiber. Verizon FiOS went from BPON to GPON to now NG-PON2. ATT went from ADSL to ADSL2+ (fiber to the lawn fridge) to XGS-PON. Before that dial-up migrated through multiple variants of V.xx from 1200 through 14.4k, 28.8k, 33k, to 56k.

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