QoS / R8500 / XFINITY testing and results

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DaveTheNerd
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Joined: 15 Jul 2008
Posts: 317

PostPosted: Sun Jan 22, 2017 18:17    Post subject: QoS / R8500 / XFINITY testing and results Reply with quote
I have an XFINITY connection that, without QoS enabled, reports raw speeds of about 230Mbps down and 12Mbps up, and I run an R8500 as my main router.

For years I've had both downstream and upstream QoS enabled and felt good about that.

Today I did some re-testing and have found that, for these speeds, setting my downstream kbps Qos "limit" to 0 (i.e. no limit) actually results in better ping-during-test times.

To test, I started pinging www.apple.com from my computer, then ran XFINITY's own speed tests, which test both IPv4 and IPv6. Default pings were about 17ms. Then I ran some speed tests and monitored the relative changes in those pings during each upstream and downstream tests to see if "buffer bloat" was an issue, and where.

QoS disabled entirely: during both IPv4 and IPv6 downstream tests my pings doubled to about 35ms. During upstream tests they went much higher, 70-100ms.

QoS enabled with 220000kbps downstream and 11000kbps upstream set: pings during IPv4 downstream test increased to 50ms, during downstream IPv6 test pings went to 35ms, pings during both IPv4 and IPv6 upstream tests stayed at 17ms.

QoS enabled with 0kbps downstream and 11000kbps upstream: pings during both IPv4 and IPv6 downstream tests went to 35ms, pings during both upstream tests stayed at 17ms.

Seems, at least on my R8500 running Kong's current firmware, my downstream connection is too fast for QoS to properly process and not impose its own delays. Better to let XFINITY's head-end and cable modem do the downstream QoS, so I now have this set to 0kbps. For upstream, it's obvious that my cable modem's brick wall bandwidth limiter will cause packet retries and impose significant delays, so setting my upstream at 11000kbps (or even 12000kbps) works well for me.

YMMV, of course, but just figured I'd share my findings and set you off on your own tests. Fun stuff!

(related: during these tests I also found that YaMon seems to limit my R8500's downstream bandwidth to about 150Mbps)
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