Inconsistent upload with DOCSIS 3.1 modems
Figured I would post here, since I have also posted on the DSLReports Community about this with my Gigabit Internet service, as seen here: https://www.dslreports.com/forum/r32249948-
it seems for the past few months, the upload on Gig service has gotten a bit inconsistent with TCP traffic. I can still get 42Mbps if I saturate the upstream by performing an upload and also running a download that can run at a Gigabit. If I have a standalone upload happening, such as if i am uploading a YouTube video, streaming, or in a video call, the upload will jump between 12Mbps and 42Mbps. Packet captures show a high amount of TCP Re-transmits and TCP Duplicate Acks when uploading.
The interesting bit is if I were to perform an upload using the UDP Protocol. Such as what games use, and some VPNs. Uploads over UDP will run at a full 42Mbps. Also, if I run an iperf3 test over the connection at 41Mbps, I will be able to transfer packets without an issue at the full 41Mbps rate, with no out of order packets or packet loss observed.
This almost looks like an issue with the DOCSIS-PIE Configuration (For Active Queue Management) or a problem with the CMTS. i've had a few techs out to check signals as well as change out modems. At this point I've used four different modems (Hitron E31H2V1, two of these, Technicolor E31T2V1, and now my current Ubee E31U2V1) and have been visited by plant maintenance close to three times. All of the coax between my modem to the cable tap has been changed. My grounded coupler (as I do not have splitters) has been checked and replaced. Fittings have also been changed out. A supervisor even stopped by on my last tech visit to see what was going on, and agreed something was wrong when I demonstrated the problem, and would escalate to engineering at the headend. My last visit was a few months ago, and I have not seen much action since. A lot of the techs continue to blame the tilt on my node, although plant maintenance keeps saying that's not a problem.
For the record, my service is also Residential. Others on DSLReports seem to be reporting similar behavior, even on lower speed tiers like the 400Mbps/20Mbps Spectrum Ultra plan, and that switching to a DOCSIS 3.0 modem resolves the issues with upstream. I also have a Spectrum Business Gig with Static IP connection I'm monitoring, and it, too, has similar behavior with the upload. Rebooting the modem does seem to allow the upload to occasionally remain consistent and work correctly, but this often doesn't last more than an hour. At times, the upload will correct itself for a few minutes, then return back to being inconsistent and broken, again with TCP traffic.
I've not been able to correlate this issue with any source/destination issue, with any configuration issue on my end, with IPv4 vs IPv6, with time of day, or weather. I use a UniFi Security Gateway 3P which reports active bandiwdth usage, and I can confirm it is not some other device on my network causing issues.
This is what the upload looks like when it is misbehaving.
This is what the upload looks like when it's working correctly.
This is what the upload looks like when it switches from "working correctly" to "broken"
The only other consideration for this problem is that, prior to having the upload issue, I was seeing a lot of download issues with the Gigabit service. The download would have a hard time getting above 340Mbps for again.... TCP Traffic. UDP traffic could saturate the Gigabit connection without issue every time. This was fixed after some overnight maintenance, but I don't know if the upload broke after the last maintenance.
These are my signals:
CM Downstream Channel Info
Channel Lock Status Channel Type Channel ID Frequency Width Power SNR Modulation Profile ID Correctables Uncorrectables
1 Locked OFDM Downstream 25 314000000 Hz 94000 kHz 8.1 dBmV 42.5 dB 0 1 2 0 0
2 Locked SC-QAM Downstream 1 507000000 Hz 6000000 Hz 5.2 dBmV 43.6 dB QAM256 0 0
3 Locked SC-QAM Downstream 2 513000000 Hz 6000000 Hz 5 dBmV 43.5 dB QAM256 0 0
4 Locked SC-QAM Downstream 3 519000000 Hz 6000000 Hz 4.6 dBmV 43.3 dB QAM256 0 0
5 Locked SC-QAM Downstream 4 525000000 Hz 6000000 Hz 4.1 dBmV 43.1 dB QAM256 0 0
6 Locked SC-QAM Downstream 5 633000000 Hz 6000000 Hz -0.7 dBmV 40.2 dB QAM256 0 0
7 Locked SC-QAM Downstream 6 639000000 Hz 6000000 Hz -0.1 dBmV 40.6 dB QAM256 0 0
8 Locked SC-QAM Downstream 7 645000000 Hz 6000000 Hz -0.5 dBmV 40.2 dB QAM256 0 0
9 Locked SC-QAM Downstream 8 651000000 Hz 6000000 Hz -0.1 dBmV 40.5 dB QAM256 0 0
10 Locked SC-QAM Downstream 9 657000000 Hz 6000000 Hz -0.8 dBmV 40.2 dB QAM256 0 0
11 Locked SC-QAM Downstream 10 663000000 Hz 6000000 Hz -0.8 dBmV 40.1 dB QAM256 0 0
12 Locked SC-QAM Downstream 11 669000000 Hz 6000000 Hz -1 dBmV 40.1 dB QAM256 0 0
13 Locked SC-QAM Downstream 12 675000000 Hz 6000000 Hz -1 dBmV 39 dB QAM256 0 0
14 Locked SC-QAM Downstream 13 681000000 Hz 6000000 Hz -0.8 dBmV 40.2 dB QAM256 0 0
15 Locked SC-QAM Downstream 14 687000000 Hz 6000000 Hz -0.8 dBmV 40 dB QAM256 0 0
16 Locked SC-QAM Downstream 15 693000000 Hz 6000000 Hz -0.7 dBmV 40.1 dB QAM256 0 0
17 Locked SC-QAM Downstream 16 699000000 Hz 6000000 Hz -1 dBmV 40 dB QAM256 0 0
18 Locked SC-QAM Downstream 17 705000000 Hz 6000000 Hz -0.5 dBmV 40.4 dB QAM256 0 0
19 Locked SC-QAM Downstream 18 711000000 Hz 6000000 Hz -0.4 dBmV 40.3 dB QAM256 0 0
20 Locked SC-QAM Downstream 19 717000000 Hz 6000000 Hz -0.3 dBmV 40.4 dB QAM256 0 0
21 Locked SC-QAM Downstream 20 723000000 Hz 6000000 Hz -0.3 dBmV 40.4 dB QAM256 0 0
22 Locked SC-QAM Downstream 21 729000000 Hz 6000000 Hz -0.6 dBmV 40.1 dB QAM256 0 0
23 Locked SC-QAM Downstream 22 735000000 Hz 6000000 Hz -0.5 dBmV 40.2 dB QAM256 0 0
24 Locked SC-QAM Downstream 23 741000000 Hz 6000000 Hz -0.8 dBmV 40.1 dB QAM256 0 0
25 Locked SC-QAM Downstream 24 747000000 Hz 6000000 Hz -0.8 dBmV 39.9 dB QAM256 0 0
CM Upstream Channel Info
Channel Lock Status Channel Type Channel ID Frequency Width Power Modulation/Profile ID
1 Locked ATDMA 25 19400000 Hz 3200000 Hz 36.3 dBmV 1
2 Locked ATDMA 26 24200000 Hz 6400000 Hz 37 dBmV 2
3 Locked ATDMA 27 30600000 Hz 6400000 Hz 37.5 dBmV 2
4 Locked ATDMA 28 37000000 Hz 6400000 Hz 37.8 dBmV 2
For signal junkies out there - I am on a Value 12 two-port tap, and between me and the node there is a single post-node amp. The majority of the plant is underground, and only goes arial for 800 feet before it reaches the node. My cable plant is 860Mhz but operates at 750Mhz.