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