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.

fmd

hex0101 Comcast published a top 25 chart a while back:

Based on that and your last SC-QAM, your 2nd OFDM has a width of maybe ~160 MHz. That can give you ~1.5 Gbps @ 4096-QAM.

hex0101

fmd Full Mid-Split/1 GHz plant operation now then!

Previously was just the one OFDM at 957 MHz. (and 690 MHz previously with the old Remote PHY Shelf and NC4000 node setup, also was pre node-split)

Wonder how wide the OFDM was then with the old node setup.

Thanks for sharing!

Next Stop: DOCSIS 4.0 FDX

fmd

hex0101 There is a different chart showing that a 96 MHz OFDM was common before mid-split 🙂

hex0101

only my node segment
and I haven’t noticed any issues.
still though just because you don’t notice anything doesn’t mean there aren’t any issues in the HFC world.
could be an issue on a particular frequency

Edit: resolved

hex0101

FDX testing on N+X architecture set to begin soon in some test markets! FDX amps will be put to the the test in in the real world and not in a lab enviroment. On 20+ year old Coax probably too. Good test bed.

videomatic3 is on a N+0 plant (upgraded to N+0 in 2020), and has been enjoying FDX since 2025 iirc.

meanwhile me and @Aceq2jot are on N+X FDX plants.

videomatic3

hex0101
i cant even repeat how many times its nice to not need limits on things because i come nowhere close to maxing out the connection. just set and forget.
im convinced that aqm is working, i only get latency this low + stable under high upload usage. still hoping pgs becomes a thing sooner than later.

cypherstream

hex0101 oh nice. There’s a lot of FDX amps installed in Comcast Freedom region to the east of me. Spot checking some addresses only ever pull up mid split plans. I’d imagine in those areas in east of my county, they will want to turn up x-class plans to compete with SECV fiber. Then in Montgomery county east, they have to compete with Verizon Fios.

crucialcolin

hex0101 meanwhile me and @Aceq2jot are on N+X FDX plants.

I’m assuming N+X means more one or more amp? My mid-split neighborhood has chains of up to about 6 amps between nodes.

It would be sweet if they could figure out how to bring FDX to a setup like that however as of march the 3rd party contractor still seems to still be installing Arris Starline MB120 amps in neighborhoods of the city that had yet to be upgraded over course of past two years. So I doubt I’ll be seeing FDX for many years to come.

XFINITY has been far more aggressive in Sacramento county on the south side of our citys border with the FDX rollout having just turning on X Class for Carmichael. It’s weird as it seems to be the same contractor CableCom LLC doing the work all over.

Meanwhile at the northern edge of our city someone I’m assuming either Aspire or AT&T has different contractor busy burying a ton of fiber conduit along the blvds branching out in all directions.

It feels like central Roseville, CA is going to end up being a black hole for internet 😞

fmd

videomatic3 How about LLD? I remember something about it being broken a while back…?

Edit: I forgot for a sec that your router is marking the icmp packets. Do you notice a change with and without marking?

videomatic3

fmd
no difference with the packet marking, ive disabled it. and that trace was done without packet marking.

fmd

videomatic3 It’s interesting that a load on the C queue affects the L queue like that (grant sharing between queues is not specified for LLD in the latest specification).

Do you know, if Jason has confirmed that LLD is working?

videomatic3

fmd
no idea on that end, but i can tell you that the queue was always affected from grants and current usage.

fmd

videomatic3 Grant sharing was introduced alongside LLX, a service that carries cellular traffic. To this date, the specifiction only mentions it in relation to LLX.

If Jason was here, maybe he could shed some light on it. What are we seeing, Jason? 🙂

Grant sharing can also help lower PGS overhead.

hex0101

crucialcolin I’m assuming N+X means more one or more amp? My mid-split neighborhood has chains of up to about 6 amps between nodes.

HFC plant with amps, yes. FDX can work up to at least N+6. 6 amps pass the node on the cable run.

Someone in a N+0 area would have had fiber optic cable pulled deeper throughout the neighborhood and all existing amplifiers removed. This makes everything after the RF leaves the node completely passive. No more actives.

crucialcolin

hex0101 HFC plant with amps, yes. FDX can work up to at least N+6. 6 amps pass the node on the cable run.

Someone in a N+0 area would have had fiber optic cable pulled deeper throughout the neighborhood and all existing amplifiers removed. This makes everything after the RF leaves the node completely passive. No

Well I’m hopeful they will come back around a second time and at least do the modular lid swaps on the MB120s. I’ve heard that’s how those amps can be upgraded to FDX capabilities.

The thing is will they though with the contractor at it for over two years slowly rolling mid-split upgrades in my city I don’t see them getting back to my neighborhood for quite some time.

lesmikesell

Having outages for ‘network improvements’ in my area today. We are already mid-split so maybe FDX is coming. They must have broken something because originally the outage details said they expected to be back at 10:32 AM, and then it jumped to 2 PM. Running on my phone hotspot now.

I switched to antenna TV and my ATSC 3.0 channels are still playing but without an internet connection there is a little box in the corner that says ’Cannot view channel because the TV’s license is being updated or another problem has occurred.' That can’t be good…

crucialcolin

lesmikesell
Interestingly also already on mid-split I just opened up the Xfinity Assistant and got this message myself:

A planned outage is scheduled on 2026-06-18 from 8:00:00 AM to 10:00:00 AM. A planned outage is scheduled on 2026-06-18 from 8:00:00 AM to 10:00:00 AM. A planned outage is scheduled on 2026-06-17 from 9:00:00 AM to 11:00:00 AM. A planned outage is scheduled on 2026-06-17 from 9:00:00 AM to 11:00:00 A.M.

In addition to that there is scheduled maintenance for 2am PST on 6/17 according to the outage map.

bigcoda

lesmikesell Having outages for ‘network improvements’ in my area today. We are already mid-split so maybe FDX is coming.

Yea it definitly sounds like there upgrading you too FDX. Have you noticed them replacing the amps around your area?
I noticed they have marked the street in front of the amp doghouses recently on my street, like there getting ready to dig them up. I’m hoping this is a sign, there getting ready to replace the amps for the FDX upgrade. I have been noticing the new CommScope amps popping up around my city. I’ve also noticed a lot more Network Improvements popping up during the day lately around my city.

crucialcolin

bigcoda Yea it definitly sounds like there upgrading you too FDX. Have you noticed them replacing the amps around your area?
I noticed they have marked the street in front of the amp doghouses recently on my street, like there getting ready to dig them up. I’m hoping this is a sign, there getting ready to replace the amps for the FDX upgrade. I have been noticing the new CommScope amps popping up around my city. I’ve also noticed a lot more Network Improvements popping up during the day lately around my city.

Since you said that I had to check my neighborhood tonight in Roseville, CA.

You are right they recently marked all the horizontal doghouses.
Example:

What’s odd is most of vertical style housings don’t seem to have the same recent markings (including the two on my circle).
Those look like this:

Both doghouse styles have the same Arris MB120 mid-split amps in them however. Maybe the marking crew just missed a couple 🤷‍♂️ It’s also concerning because that means the contractor’s line crew might not see them now either.

crucialcolin

bigcoda I noticed they seemingly were back out today in my neighborhood marking some of the vertical housings now.

From the looks of thing it would appear they are relocating a couple of them about 50-100 ft in either direction along the roadway.

I feel sorry for the house who’s likely to end up with a larger horizontal enclosure literally right in line with their front door at the corner of their lawn though. Also the homeowners are liable to run it over while backing their vehicle out of the driveway. It’s essential the worst possible spot to put one.

This all has me wondering if they decided to replace the majority of the currently installed mid-split amps with nodes in the neighborhood bringing them closer to achieving a node+0 FDX setup?

fmd

crucialcolin Could they be big enough for FDX amps/nodes?

crucialcolin

fmd Could they be big enough for FDX amps/nodes?

Maybe that has something to do with it. Currently the nodes in the neighborhood are in larger Amphenol enclosures like these.

Suppose we will find out soon enough 🤞

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