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QoS not working

normalice
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QoS not working

I have my computer set to 'highest' priority, and all other devices set to low. Yet when I play an online game, I get lag while other devices take up 2+Mbps bandwidth. This is not a functioning feature.

Model: R7800|Nighthawk X4S AC2600 WiFi Router
Message 1 of 4
ka9q
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Re: QoS not working

You're probably a victim of "buffer bloat". It cannot be easily and definitively fixed in any one device.

 

The problem is that the connection from your router to your cable modem is much faster than the link from your cable modem to the cable company's routers. The cable modem contains buffers that can hold several seconds of outgoing traffic waiting to be transmitted. But your router doesn't know this; it only knows that when it gets a packet from your computer to send to the cable modem, it goes out very quickly without waiting long in the router. So even if the router correctly implements QoS, it won't do any good.

 

We need cable modems that will notify their routers when more than a very small amount of data is queued for transmission so the router will hold onto it long enough for its QoS mechanisms to actually work. Lacking this, the only workaround is to tell the router to artificially slow down the rate at which it sends to the cable modem. This is what I do in my own home-grown (Linux-based) router, but it is not entirely satisfactory because the speed of my cable channel varies and the router has no way to know what it actually is at any given moment. Set the limit too high and you'll risk long latencies when the cable network slows down; set it too low and you'll avoid buffer bloat but then risk latency by simply not using the full capacity of your cable modem.

Message 2 of 4
normalice
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Re: QoS not working

Sure. It's a DSL network with about 3Mbps (I know. highest available in my area..). I have roomates who use the wifi that I pay for, and I don't mind. But I get lag when I play any video game while they are downloading something. I (and they) wanted a router that specifically prioritizes my computer in such cases, slowing down their download when necissary, to prevent lag in my games. That's the sole reason I bought this router, and it doesn't do that.

 

Message 3 of 4
ka9q
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Re: QoS not working

I build my own routers using small Linux boxes, and I used existing Linux tools to solve my QoS problems years ago. I was briefly involved in the initial work on buffer bloat years ago, but I drifted away when I thought the proposed solutions were getting too elaborate and ignored a few simple fixes that solve 99% of the problem. I am also unfamiliar with the specific QoS features of Netgear routers, but I can say that they're unlikely to help unless you really understand what's going on.

 

As I said, the real problem is the excessive upstream buffering in most cable and DSL modems that let large FIFO queues build without any way to apply QoS. Your router connected to that modem can have all the QoS mechanisms in the world and they won't help you if the router sends everything to the modem via Ethernet at 1 Gb/s so the router queues remain empty. The outbound queues *must* be pushed back into the router where the router can manage them intelligently.

 

That requires one of two things: some form of flow control in the modem (preferred), or outbound rate limiting in the router. The modems are closed source and the vendors seem completely uninterested in helping (as far as I know), so that leaves outbound rate limiting. You have to estimate the outbound data rate of your modem and set the rate limit in the router to something slightly less than that rate. This will keep queues from ever building in the modem; they'll build up in the router where you can properly manage them.

 

Note I've talked only about upstream flow control. Downstream QoS is much more difficult because they're controlled by the router at your ISP, not yours. But fixing the upstream takes care of most of the problem because a) it is usually much slower than the downstream and 2) the upstream carries the requests and acknowledgements needed to make downstream flows happen.

 

So look for something about "rate limiting" in your router QoS settings.

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