Fritzbox 7520 low SQM Speed

Hey, I'm new to OpenWRT. I spend the last 2 days trying to learn and understand how to setup the router, I basically want to mitigate bufferbloat in my network. I have a 250/40 VDSL connection (somehow I'm able to get 47 up). I use the intergrated Modem (VRX518) and basically everything works fine and it can hold around 230mbps Up and 40 down. Now I have setup SQM, nomatter what I put in "Download speed (ingress)" and which "Queue setup script" I use I can't really get above 150mbps down. Upload speed is perfectly fine. The best result I got working so far was with fq_codel + simplest.qos, which got me around 150mbps and 38mbps up and low jitter (A+ 0ms). I still want to try higher Speeds which I just can't achieve. And help would be apprectiated!

SQM config:

config queue 'eth1'
	option enabled '1'
	option interface 'dsl0.7'
	option download '180000'
	option upload '38000'
	option qdisc 'fq_codel'
	option script 'simplest.qos'
	option linklayer 'ethernet'
	option debug_logging '0'
	option verbosity '5'
	option overhead '34'

A 716 MHz cortex a7 (sqm is mostly single threaded, so is PPP, so the other three cores don't help you much) isn't exactly a performance monster, 150 MBit/s with PPPoE and sqm/cake is already more than you can expect from this hardware.


ohh okay, thank you for the quick response anyways! There is no possible way to improve performance to push the max out of it by using external dsl modem (tbh idk if dsl modem offload work to cpu) or editing config for cpu clocking as an example?

External modem might help, but as far as I can tell the FB7520 going for ~50-60 EUR second hand is already one of the cheapest VDSL2 modems capable of using profile 35b (required for most 250/40 services). I actually use a FB7520 as bridged modem (running OpenWrt) in front of my primary router, and the 7520 is a great modem for my 100/40 line...

I was asking cause I have a speedport smart 3 laying around which has a "DSL Modem Mode" so I can easilly use the speedport as a dsl modem. Might try that tomorrow and see if it changes anything. If not what should I look for in routers that could theoretically keep up the speed (w/o modem, as I can use the speeport for that aswell), or how do I specify if the CPU is strong enough?

Ah, okay. The thing that is really nice about the 7520 (under OpenWrt) is that is return really decent diagnostics (using luci_mod_dsl) and works well with @janh 's go-dsl. Not sure whether the speedport in modem mode will return anything. However on a stable link this information typically is not really necessary.

So 250/40 already requires a pretty beefy CPU if you need to to software traffic shaping a la SQM. Something like a raspberry pi 4B will do (but really wants a USB3 ethernet dongle) or a friendlyElec nanoPi (not sure which are supported by OpenWrt out of the box) or an intel N95 or N100 device.
I operate a turris omnia (it still is a decent performer given its arm A9 hardware and age I would not recommend buying one new, there are rumors for a refresh next year or 2025) which for my 100/40 link seems to work well, and which I benchmarked up to 550/550, but I am not sure whether it would do for a 250/40 link (given the other stuff I run on the router).

my connection is really really stable tbh. But I need a router that supports wifi for sure (since I'm not the only one using the network) which is not possible with a raspberry pi(?). So I need to do some research on other peoples reports with their routers, also looking for one that doesn't kost me a kidney :smile:

Yes the pi's WiFi is not suitable for AP duty, but one can always add a dedicated AP to handle WiFi.

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Yeah lemme see which is the best/ least costs intensive option. Also I found some people improving CPU performance with irqbalance and packetsteering, I'm gonna find out what they do and see if this can help me temporary improving my "problem".

just shape outbound with cake nat ack-filter and the right dsl options.

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