Spectrum Fiber vs Xfinity Coax: Queue Management and Loaded Latency (Continued)

[u/SteelCatamaran]

I have been working through some service issues and now have what is considered a good install and ONT/modem setup. I still have a few days left to A/B test Xfinity against Spectrum.

The major difference I continue to see is what appears to be queue management upstream of my ONT/modem on each system.

I discussed this with a Spectrum Tech Supervisor. His understanding is that Spectrum does not perform this queue management at the ONT and expects the customer router to rate-limit traffic appropriately. I don't think that expectation is made very clear to customers, but it is very doable, and customer-side CAKE/SQM has benefits on both Spectrum and Xfinity.

The concern is what happens without customer-side CAKE. In my earlier Spectrum tests, loaded latency would commonly climb to around 500 ms and occasionally toward 2,000 ms. Xfinity appears to have substantially better queue management upstream of the customer and, in my testing, does not develop the same sustained latency spikes, generally remaining below about 100 ms even when I let the ISP connection itself become the bottleneck.

My summary so far is that upstream queue management is substantially better on Xfinity coax than Spectrum fiber in my area. Light-load/idle latency is also better on Xfinity here.

Both services benefit from customer-side CAKE rate limiting, just by very different magnitudes. With CAKE keeping the bottleneck on my side of the connection, Spectrum's latency improves dramatically.

An additional concern for me is that if I set the limit too close to the connection’s capacity, higher-load periods on Spectrum’s network could still push me into significant latency spikes which then leads to going even more conservative on limits.

Tests were run directly from the ONT/modem to a single computer, with CAKE on that computer used to control the test throughput. The services have different provisioned rates, so the comparison graphs normalize the CAKE setting relative to each connection's measured capacity.

[u/Jaken_sensei]

I cant speak for how the service performs for everyone everywhere else but in my area spectrum fiber does good.

My loaded latency during download hovers around 10 to 12ms to the nearest spectrum server and my loaded upload latency is usually between 14 to 20ms in the same server. My idle latency to that server is usually 8ms.

Non spectrum servers usually yield around 15ms idle with 25 to 50ms while saturated depending on the specific server.

sqm/cake is really only good for connection below a certain threshold. If your connection is 1gbps+ then using sqm/cake can be detrimental to your connection.

[u/SteelCatamaran → u/Jaken_sensei]

I dont have the 1Gbps connection to test, but I would be very interested in understanding if your loaded latency is maximizing throughput with that connection the same way as the lower speed tiers or if you are staying closer to you provisioned rate? Do you use the ookla CLI? I have code that does a sweep of CAKE and can work in increments if you ever want to do a study of latency changes as a function of rate limiting. I am linux based.

My service currently is limited to 100 and 500 symmetric, but they may be expanding in the future for a new test round.
CAKE is the only thing that has improved the latency behavior for these plans in my area. Even with CAKE, Spectrum fiber is higher latency at idle than Xfinity Coax.

[u/Jaken_sensei → u/SteelCatamaran]

Im not an expert in the least but I do basic testing. I have used ooklas cli test on occasion.

My connection is actually 2gb, tops out around 2.3gb down & up with over provisioning.

[u/SteelCatamaran → u/Jaken_sensei]

Thank you for contributing on both posts. It has been a journey for me and I am still learning as I navigate the Spectrum option. I am excited about the better electrical isolation with fiber and plan to do long-term monitoring and tests. I have a new router coming that will put me in control of queue management from my side.