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.

meerkathalon

Maintenance outage this morning 1:47-3:30AM. OFDM channels 193 and 194 have shifted to freqs I haven’t seen before. OFDMA also shifted. Does anyone know what this is?

Downstream OFDM Channels
Channel   LockedStatus  ProfileID  ChannelID    Frequency       Power       SNR/MER    ActiveSubcarrier    Unerror    Correctable   Uncorrectable
      1     Locked     0 ,1 ,2 ,3     193     150000000 Hz     7.18 dBmV     42.8 dB     148 ~ 3947     19283179656     13628215314     1
      2     Locked     0 ,1 ,2 ,3     194     900000000 Hz     -1.02 dBmV     38.3 dB     268 ~ 3827     21313001617     17872223642     290

Upstream OFDMA Channels
Channel   LockedStatus    ProfileID    ChannelID    Frequency       Power
      1     Locked     12 ,13     41     36200000 Hz     30.0 dBmV
      2     Not Locked     0      0     0 Hz     0 dBmV

fmd

meerkathalon It’s the same (pre) FDX frequencies that we have seen, but now we know that the 900 MHz OFDM is not 192 MHz wide (if the channel is “standard”). 🙂

hex0101

meerkathalon Pre-FDX channel/RF spectrum config, the QAM TV channels also moved, you can easily spot it if you look at your DOCSIS 3.0 downstream frequencies.

For me, it went like this:
August 6th= Pre-FDX config (what you are seeing now)
August 12th= FDX config (The few remaining D3.0 downstream channels were cleared out up to 387 MHz). FDX spectrum is now enabled, and your 3.1 modem will lose the 150 MHz OFDM and just keep the 900 MHz OFDM.
August 18th= FDX sales enabled. Customers can now have access to the FDX speed tiers.

cypherstream

fmd Are you telling by the Active Subcarrier numbers? Is each subcarrier either 25khz or 50khz and it says 268 - 3827, so thats 3559 subcarriers.
Channel 1 3947 -148 = 3799 subcarriers
3799 subcarriers x 50 (khz) = 189950.
189950 / 1000 (Khz to Mhz) = 189.95. Am I close? I think I’m close enough its usually 190 MHz plus 2 Mhz of guard band (192) max.

So the second channel would be 177.95 MHz give or take (if I’m remotely close).

blackhawkpr

Is there any way to check this with a bridged XB8? I feel like we’re so close here to FDX.

hex0101

blackhawkpr Yeah, if you can access the Admin Tool at 10.0.0.1. Some routers/firewalls don’t allow this outside of WAN by default. Also, you may have to enable your Admin Tool in the Xfinity app, which will require you to factory reset the gateway to get it out of Bridge Mode, and then the option to enable the Admin Tool will become available in the Xfinity app. But perhaps this was fixed- and the Admin Tool remains available when in Bridge Mode.

The XB8 supports High Split (Return 5-204 MHz), so maybe the first FDX OFDMA can be used by the XB8 for upstream traffic.

meerkathalon

hex0101 This is super exciting! I am N+X; specifically N+2 (LE & MB). I’m not sure about the QAM TV channels. This is my full layout.

Downstream Bonded Channels
Channel LockedStatus Modulation ChannelID  Frequency     Power    SNR   Correctables Uncorrectables     
      1     Locked     QAM256      4     321000000 Hz     3     42.3     189     589
      2     Locked     QAM256      1     303000000 Hz     3.4     42.3     237     1095
      3     Locked     QAM256      2     309000000 Hz     3.1     42.4     202     1104
      4     Locked     QAM256      3     315000000 Hz     3     42.4     223     1032
      5     Locked     QAM256      5     327000000 Hz     2.9     42.3     248     1028
      6     Locked     QAM256      6     333000000 Hz     2.6     42.2     244     1064
      7     Locked     QAM256      7     339000000 Hz     2.7     41.8     250     1060
      8     Locked     QAM256      8     345000000 Hz     2.6     42.1     235     1119
      9     Locked     QAM256      9     351000000 Hz     2.7     42.1     251     1086
     10     Locked     QAM256     10     357000000 Hz     2.7     42.1     248     1113
     11     Locked     QAM256     11     363000000 Hz     2.7     42.1     223     1143
     12     Locked     QAM256     12     369000000 Hz     2.6     42     227     1047
     13     Locked     QAM256     13     375000000 Hz     2.8     42     226     1134
     14     Locked     QAM256     14     381000000 Hz     2.7     42     242     1121
     15     Locked     QAM256     15     387000000 Hz     2.6     42     240     1133
     16     Locked     QAM256     16     393000000 Hz     2.5     42     229     1061
     17     Locked     QAM256     17     399000000 Hz     2.3     41.9     236     1059
     18     Locked     QAM256     18     405000000 Hz     2.2     41.8     231     1070
     19     Locked     QAM256     19     411000000 Hz     2.1     41.5     220     1038
     20     Locked     QAM256     20     417000000 Hz     1.9     41.7     249     1105
     21     Locked     QAM256     21     423000000 Hz     1.8     41.7     214     1046
     22     Locked     QAM256     22     429000000 Hz     1.6     41.6     198     1080
     23     Locked     QAM256     23     435000000 Hz     1.5     41.6     235     1048
     24     Locked     QAM256     24     441000000 Hz     1.4     41.6     233     1116
     25     Locked     QAM256     25     447000000 Hz     1.3     41.5     229     1111
     26     Locked     QAM256     26     453000000 Hz     1.2     41.4     233     1091
     27     Locked     QAM256     27     459000000 Hz     1.2     41.5     216     1070
     28     Locked     QAM256     28     465000000 Hz     1.2     41.4     202     1074
     29     Locked     QAM256     29     471000000 Hz     1.3     41.5     246     1073
     30     Locked     QAM256     30     477000000 Hz     1.4     41.5     224     1078
     31     Locked     QAM256     31     483000000 Hz     1.5     41.5     248     1047
     32     Locked     QAM256     32     489000000 Hz     1.6     41.4     220     1113

Upstream Bonded Channels
Channel   LockedStatus  ChannelType ChannelID   SymbolRate        Frequency       Power     
      1       Locked       ATDMA      1       5120 Ksym/sec       16400000 Hz       36.3 dBmV
      2       Locked       ATDMA      2       5120 Ksym/sec       22800000 Hz       36.0 dBmV
      3       Locked       ATDMA      3       5120 Ksym/sec       29200000 Hz       36.3 dBmV
      4       Locked       ATDMA      4       5120 Ksym/sec       35600000 Hz       36.3 dBmV
      5       Not Locked       Unknown      0       0       0       0.0
      6       Not Locked       Unknown      0       0       0       0.0
      7       Not Locked       Unknown      0       0       0       0.0
      8       Not Locked       Unknown      0       0       0       0.0

Downstream OFDM Channels
Channel   LockedStatus  ProfileID  ChannelID    Frequency       Power       SNR/MER    ActiveSubcarrier    Unerror    Correctable   Uncorrectable
      1     Locked     0 ,1 ,2 ,3     193     150000000 Hz     6.68 dBmV     42.8 dB     148 ~ 3947     19663017497     13843825408     1
      2     Locked     0 ,1 ,2 ,3     194     900000000 Hz     -2.42 dBmV     37.9 dB     268 ~ 3827     21673420103     18135918398     290

Upstream OFDMA Channels
Channel   LockedStatus    ProfileID    ChannelID    Frequency       Power
      1     Locked     12 ,13     41     36200000 Hz     30.3 dBmV
      2     Not Locked     0      0     0 Hz     0 dBmV

fmd

cypherstream So the second channel would be 177.95 MHz give or take (if I’m remotely close)

You are a single subcarrier off: 3827 - 268 + 1. So it can carry ~1500-1600 Mbps @ 4096-QAM, depending on the other channel internals.

cypherstream I think I’m close enough its usually 190 MHz plus 2 Mhz of guard band (192) max.

That discrepancy is worth underlining. 192 MHz is usually quoted as being the maximum width, but that includes the guard bands. The active subcarrier count cannot be larger than 3800 (50 kHz spacing).

blackhawkpr

hex0101 Thanks. I looked in to it more and I’d have to upend my network to do the firewall thing since I use 10.0.0.0/24.

There’s another scheduled maintenance tomorrow at 1am so maybe it’ll be the last network enhancement needed. If not, I’ll just reset the gateway and check when I have some more time to tinker.

crucialcolin

blackhawkpr

I always forget to reset the gateway myself whenever they do scheduled maintenance. With the nearby construction activity that’s been going on in my city of late I wonder when I will first see signs of FDX prep.

So far crews haven’t swapped the actual physical amps + LE’s on my node either but everything seems peeped for them do so any day now.

They finished mid-split rollout early Sept 2024 in a similar upgrade pattern. Here it is almost exactly two years later.

blackhawkpr

I think I’m in the later stages of the rollout but not yet there. Might be weeks or months, or just a few days. Nobody knows.

ikoul

blackhawkpr

I think that’s just a standard mid-split configuration, it looks pretty similar to mine. And with pretty borderline signal levels - does your house have an 8 way splitter between the drop and modem?

blackhawkpr

ikoul I’m in an apartment complex, so most likely?

Devious

blackhawkpr I think I’m in the later stages of the rollout but not yet there.

Your signals are on the weak side and a few are less then minimum.

Ideal range: -7 dBmV to +7 dBmV.

Info reposted from the now dead dslreports site.

https://linustechtips.com/topic/1597858-guide-to-cable-modem-signals/

jsterling

jsterling So I received a call from corporate escalations this morning that the engineering team had lab tested a fix and would be rolling it out soon. Just checked a bit ago and I am receiving the 2Gig up and down now from the 1.5 Gig down issue. I’ll post the channel layout in a bit but ai went from 5 QAM and 1 OFDM to 28 QAM and 1 OFDM DS. This is essentially what I had with the mid-split previously.

Still have 4 QAM and 4 OFDMA US.

So they apparently got creative to resolve it for now. Still not sure what the actual issue is and I assume they will clean this up eventually.

fmd

jsterling A band-aid. The real fix is when you start bonding more OFDM channels - those that share spectrum with OFDMA.

HardlyWorthit

Maybe progress here:

enhancing-the-xfinity-network.pdf

46kB

Moffetts

HardlyWorthit Yeah those emails are worth their weight in gold.

crucialcolin

Devious Your signals are on the weak side and a few are less then minimum.

Ideal range: -7 dBmV to +7 dBmV.

Info reposted from the now dead dslreports site.

https://linustechtips.com/topic/1597858-guide-to-cable-modem-signals/

Mine rolls of a bit on the upper freqs. One of the OFDM channels usually floats somewhere around -9 - 10 dBmV.

It seems to be a mid split thing which hopefully wont get any worse with FDX(Assuming they will be able to balance the plant better once upgraded).

meerkathalon

meerkathalon Maintenance this morning. I believe FDX mode is now enabled?

Downstream Bonded Channels
Channel LockedStatus Modulation ChannelID  Frequency     Power    SNR   Correctables Uncorrectables     
      1     Locked     QAM256      4     405000000 Hz     3.9     42.5     419     1583
      2     Locked     QAM256      1     387000000 Hz     4     42.6     1283     5633
      3     Locked     QAM256      2     393000000 Hz     4     42.6     1157     5524
      4     Locked     QAM256      3     399000000 Hz     3.9     42.5     833     4128
      5     Locked     QAM256      5     411000000 Hz     3.8     42.3     797     4060
      6     Locked     QAM256      6     417000000 Hz     3.7     42.5     770     3544
      7     Locked     QAM256      7     423000000 Hz     3.7     42.4     908     4557
      8     Locked     QAM256      8     429000000 Hz     3.5     42.3     946     4507
      9     Locked     QAM256      9     435000000 Hz     3.4     42.4     839     4055
     10     Locked     QAM256     10     441000000 Hz     3.3     42.3     986     4566
     11     Locked     QAM256     11     447000000 Hz     3.3     42.3     912     4636
     12     Locked     QAM256     12     453000000 Hz     3.1     42.2     243     1157
     13     Locked     QAM256     13     459000000 Hz     3.1     42.2     943     4585
     14     Locked     QAM256     14     465000000 Hz     3.1     42.2     932     4595
     15     Locked     QAM256     15     471000000 Hz     3.1     42.1     930     4565
     16     Locked     QAM256     16     477000000 Hz     3     42.1     1017     5082
     17     Locked     QAM256     17     483000000 Hz     3     42.2     1024     4937
     18     Locked     QAM256     18     489000000 Hz     3     42.2     1033     4839
     19     Locked     QAM256     19     495000000 Hz     3.1     42.3     995     4800
     20     Locked     QAM256     20     765000000 Hz     3     41.1     939     4499
     21     Locked     QAM256     21     771000000 Hz     3     41.1     1053     4795
     22     Locked     QAM256     22     777000000 Hz     2.9     41     774     3902
     23     Locked     QAM256     23     783000000 Hz     2.9     41.1     1027     4983
     24     Locked     QAM256     24     789000000 Hz     3     41.1     963     4581
     25     Locked     QAM256     25     801000000 Hz     2.8     41     1003     5000
     26     Locked     QAM256     26     807000000 Hz     2.9     41     900     4654
     27     Locked     QAM256     27     813000000 Hz     2.9     40.9     812     3873
     28     Locked     QAM256     28     819000000 Hz     2.7     40.7     1062     4940
     29     Not Locked     Unknown      0     0 Hz     0.0     0.0     0     0
     30     Not Locked     Unknown      0     0 Hz     0.0     0.0     0     0
     31     Not Locked     Unknown      0     0 Hz     0.0     0.0     0     0
     32     Not Locked     Unknown      0     0 Hz     0.0     0.0     0     0

Upstream Bonded Channels
Channel   LockedStatus  ChannelType ChannelID   SymbolRate        Frequency       Power     
      1       Locked       ATDMA      3       5120 Ksym/sec       29200000 Hz       36.8 dBmV
      2       Locked       ATDMA      2       5120 Ksym/sec       22800000 Hz       36.8 dBmV
      3       Locked       ATDMA      1       5120 Ksym/sec       16400000 Hz       36.8 dBmV
      4       Locked       ATDMA      4       5120 Ksym/sec       35600000 Hz       36.8 dBmV
      5       Not Locked       Unknown      0       0       0       0.0
      6       Not Locked       Unknown      0       0       0       0.0
      7       Not Locked       Unknown      0       0       0       0.0
      8       Not Locked       Unknown      0       0       0       0.0

Downstream OFDM Channels
Channel   LockedStatus  ProfileID  ChannelID    Frequency       Power       SNR/MER    ActiveSubcarrier    Unerror    Correctable   Uncorrectable
      1     Locked     0 ,1 ,2 ,3     193     900000000 Hz     2.58 dBmV     40.3 dB     268 ~ 3827     5866908953     3453987563     11509
      2     Not Locked     0      0     0 Hz     0 dBmV     0 dB     0 ~ 4095     0     0     0

Upstream OFDMA Channels
Channel   LockedStatus    ProfileID    ChannelID    Frequency       Power
      1     Locked     12 ,13     41     36200000 Hz     31.3 dBmV
      2     Not Locked     0      0     0 Hz     0 dBmV

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