Download while Live Streaming kills upload bitrate

I've been happily running Openwrt on my Netgear R7800 for the past year and a half. Over the course of this time, I've noticed that whenever I am live streaming to Twitch (~6000 kb/s upload) and start a big download (usually something over 1GB), my streaming bitrate takes a huge blow, and goes down to about 300 kb/s. It is so bad, I typically don't stream when performing these downloads, or am forced to postpone certain software updates that are encountered during stream.

I don't run any QoS software, but I imagine that would be a way towards a solution. I've never used such software. Do you think that would help me?

If anyone could point me in the right direction to solve this issue, I would greatly appreciate it.


P.S. If there is anything logs or anything I should provide from my running router, please let me know! Thanks

Can you run Booferbloat Tests on the following 2 sites, when nothing happens on the network and when you stream:

Mmmh, how fast is your internet access, and how assymmetric? I ask because TCP will always have packets traversing in both directions, as even for Downloads, the receiver needs to periodically signal the sender about the received data via so called ACKnowledge packets (short ACKs), this reverse traffic for an internet download then causes traffic/load in the upload direction. For TCP Reno the naive expectation is to see ~1/40 of the data traffic as reverse ACK traffic, so for a 1Gbps downlink, that will be 1000/40 = 25 Mbps (most modern systems use fewer ACKs, but even then normal ACK traffic still needs room in the reverse direction). And ACK traffic is not 'elastic' that is dropping ACKs at the bottleneck will not reduce the rate of incoming ACKs in any meaningful way, so typically more responsive traffic will give way...

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I performed one of these tests after starting stream with nothing else happening on the network, generally speaking.

And, just as per my previous experiences, while running the test my stream bitrate dipped to the hundreds, and then fluctuates around the low thousands. Once the test was finishing, the bitrate sky rockets to several thousand over the specified bitrate (I assume to 'Catch up'), and eventually comes back to specified bitrate.

I am aware you might prefer further tests from me as specified. I will postpone these a day or two.

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Thanks for the quick reply.

how fast is your internet access?

Perhaps the test in my reply to ASFP would help shine some light on your question. My plan is also listed as:

Download speeds: up to 800 Mbps
Upload speeds: up to 15 Mbps

And how assymetric?

I cannot speak for its assymetric properties.

And ACK traffic is not 'elastic' that is dropping ACKs at the bottleneck will not reduce the rate of incoming ACKs in any meaningful way, so typically more responsive traffic will give way...

Are you saying that one cannot limit the download speed (conditionally) to avoid overuse of the upload bandwidth? I feel like it's possible to reserve the critical 6Mb/s in my setup.

Here is the info in text form.

Grade: A

Download: 62 Mb/s
Upload: 9.22 Mb/s

A: Quality
B: Bufferbloat

Ping: 27-67 ms
Streams: 24/6
Link: Cable

Your upload bandwidth is too low. I think you experience exactly what @moeller0 mentioned above. If you're downloading big files and updates that take up the most or whole of your 800Mbit download bandwidth the ACK traffic is using to much of your upload bandwidth.
I don't think QoS will be able to get you better results with this. Either continue to postpone updates and big file downloads while streaming or get a better upload bandwidth. I have never seen someone having a 15Mbit upload and a 800Mbit download. Your ISP is a joke for providing such a low upload bandwidth.


800/15 is not balanced you have way more down than up speed. That is what I meant with asymmetric.

Oh even better, you can go and reserve enough rate for your video streaming, at the cost of potentially somewhat reduced download rates.

The easiest way to get there would be to install SQM (on a ssh shell on the router: opkg update ; opkg install luci-app-sqm', then edit /etc/config/sqm either with your editor of choice (e.g. opkg uddate ; opkg install nano`) or via the luci GUI) to look like:

config queue                                                                                                                        
        option verbosity '5'                                                                                                        
        option qdisc_advanced '1'                                                                                                   
        option squash_dscp '0'                                                                                                      
        option squash_ingress '0'                                                                                                   
        option ingress_ecn 'ECN'                                                                                                    
        option egress_ecn 'ECN'                                                                                                     
        option qdisc_really_really_advanced '1'                                                                                     
        option linklayer 'ethernet'                                                                                                 
        option overhead '18'                                                                                                        
        option linklayer_advanced '1'                                                                                               
        option tcMTU '2047'                                                                                                         
        option tcTSIZE '128'                                                                                                        
        option linklayer_adaptation_mechanism 'default'                                                                             
        option iqdisc_opts 'nat dual-dsthost ingress'                                                                               
        option eqdisc_opts 'nat dual-srchost ack-filter'                                                                                       
        option interface 'pppoe-wan'                                                                                                
        option script 'layer_cake.qos'                                                                                              
        option tcMPU '64'                                                                                                           
        option download '720000'                                                                                                     
        option qdisc 'cake'                                                                                                         
        option debug_logging '1'                                                                                                    
        option upload '14000'                                                                                                       
        option enabled '1'  

Then replace pppoe-wan with your treu wan interface, and start that new config:
SQM_DEBUG=1 SQM_VERBOSITY_MAX=8 /etc/init.d/sqm restart
copy and paste the output from the terminal here into this thread

Please also post the output of
tc -s qdisc
ifstatus wan

This config will already implement per internal IP fairness, so if you only use two computers (one for streaming and for downloading each one should get 7000 Kbps for its own use which might already be enough*. If however you have more users internally we would need to play with DSCP marking for the streaming data, but let's first see whether that is required.

*) The calculation is simple each active computer will get its fair share of the capacity so with three fully active machines each can use 14000/3 = 4666.66666667 Kbps of gross upstream.

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