Intermittent latency / packet-loss–like behavior under upload load (signals clean)

Hi everyone,

I’m hoping to get some guidance or escalation help. I’ve been experiencing intermittent issues that feel like packet loss (gaming lag, voice calls cutting out, spikes in latency), even though speeds and signal levels look good.

A Comcast tech already came out and checked:

• Drop line, inside wiring, splitters

• Signal levels and SNR

• Modem status and error counters

He said everything looks clean and there are no T3/T4 errors or uncorrectables, which I understand.

However, the problem only appears under upstream load, not at idle.

What I’m seeing:

• Baseline latency ~15–20 ms (stable)

• As soon as upload traffic starts, latency spikes to 140–180+ ms

• This happens wired directly to the modem (no Wi-Fi, no router)

Tests I’ve run:

• Waveform Bufferbloat Test

  • Download bufferbloat: +~17 ms (A)

  • Upload bufferbloat: +140 ms (C)

• PingPlotter (ICMP) to 1.1.1.1 and 8.8.8.8

  • Clean routing and no sustained packet loss at idle

  • Large latency spikes when upload traffic is present

• WinMTR

  • No packet loss to final destination

  • Confirms the issue is not present at rest

So from what I can tell, this doesn’t look like a wiring or modem signal issue, but more like upstream congestion / queueing (bufferbloat) somewhere past the modem (possibly node or CMTS behavior).

My question:

Is this something that can be escalated to maintenance to check:

• Upstream utilization on the node

• Latency or congestion at the CMTS

• Intermittent upstream noise that only appears under load

Thanks in advance to anyone who can point me in the right direction.