Friday, August 29, 2014

New Comcast Speeds -> New CeroWRT SQM Settings

Comcast upped their line-rates in my area recently, which meant I needed to up the settings I use with CeroWRT to harness that bandwidth with reasonable latency (vs. the unreasonable latency that the cablemodems have by default).

Our service was previously 50/10 Mbps (nominal), although in practice I saw that it was a bit above that (maybe 10% or so).  Comcast just upped that to 100/10 (nominal).

Raw testing:


The raw rates (laptop plugged directly into the modem) show 120Mbps down, 10 up, and 120ms of bufferbloat latency.  These are both improvements over the previous setup.  I'm wondering if the modem is now running PIE...  The latency is about half what it was when I set the service up back in May.

And 120Mbps is awfully nice...

But the WNDR3800 was set for slower settings:

Wonderful (lack of) latency, but 50Mbps is a lot less than 120Mbps, so time to start upping the download rate limiting and see what the unit can do:

Unfortunately, the WNDR3800 just doesn't have the processing power to pull off much more than 50Mbps (as I previously knew).  Setting the download rate at 100Mbps, it can only manage about 70-75Mbps, and the graphs are noisy enough to show that the unit isn't able to correctly run the algorithms.

Final settings:
CeroWrt Toronto 3.10.36-4
100000 Kbps ingress limit
12000 Kbps egress limit
ECN enabled (both directions)

Addendum:  I tried to disable downstream shaping, to see if that would control latency well enough on the upstream side.  The results were not confidence-inspiring:

Certainly much better than with no upstream shaping, but the extra latency goes from 5ms to 15ms, and the sharing/fairness of the streams comes apart.

If only Comcast would just fix this in the CMTS and in the modems, instead of forcing us to do this on our own...

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