[Bloat] Xfinity Flex streaming box starves on cake?

[Bloat] Xfinity Flex streaming box starves on cake?

[Kenneth Porter]

I suspect that my Xfinity Flex box has too small an internal buffer and is 
starving when fed by my cake-enabled OpenWrt router.

For the last few weeks, I've been streaming Amazon Prime Video shows and 
movies and the box tends to go to black screen after 5-10 minutes of 
viewing, followed by a jump to the Flex main menu (which selects which 
streaming service to view). I thought perhaps the box was overheating or 
that there was a bug in the Amazon app that caused it to crash to the home 
screen. This week the same thing happened when I watched a show on HBO Max.

On a hunch, I disabled SQM on the router and was able to watch an hour of 
TV with no interruption, using a different service on successive nights. My 
next test will be to re-enable SQM and try viewing to see if I get a black 
screen and crash to home screen again.

Sometimes instead of a black screen I get a "problem with connection" 
message. So my theory is that the Flex box has too little buffer to handle 
hiccups in the feed, and is depending on a deep buffer in the Xfinity 
modem. Except that I have the modem set to bridge mode so I can disable its 
DHCP server and let my LAN server handle DHCP and DNS and other services.

My SQM config follows:

config queue 'eth1'
        option itarget 'auto'
        option etarget 'auto'
        option linklayer 'none'
        option interface 'eth1.2'
        option debug_logging '0'
        option verbosity '5'
        option qdisc 'cake'
        option qdisc_advanced '1'
        option squash_dscp '1'
        option squash_ingress '1'
        option qdisc_really_really_advanced '1'
        option script 'layer_cake.qos'
        option iqdisc_opts 'docsis wash besteffort nat ingress'
        option eqdisc_opts 'docsis ack-filter nat'
        option ingress_ecn 'NOECN'
        option egress_ecn 'NOECN'
        option download '170000'
        option upload '9000'
        option enabled '1'

Re: [Bloat] Xfinity Flex streaming box starves on cake?

[Toke Høiland-Jørgensen]

Kenneth Porter <shiva@sewingwitch.com> writes:

> I suspect that my Xfinity Flex box has too small an internal buffer and is 
> starving when fed by my cake-enabled OpenWrt router.

From your config you have around 10x the downstream bandwidth you need
for streaming, so unless you are really hitting your connection hard
with other things I would not expect packets to buffer in the
modem/router at all while you're streaming.

So if this really is caused by sqm-scripts (which I think you should do
a few more tests to definitely confirm), I would think it more likely it
was due to some other weird interaction. Streaming box expecting a
certain DSCP marking? Server choking on ACK stream due to filtering?
Hard to say... A packet dump of the stream going to the box while the
black screen happens may be illuminating, but could be hard to pull off
if it's not reliably reproducible...

-Toke