AC68U: Internet using WiFi can't hit 400mbps. Is this CPU limited?

[hoegaarden]

Recently upgraded Xfinity to 600/15 plan. AC68U running lastest Merlin. In router, CTF and FA are enabled. Qos, AiProtection, etc are all turned off. Before the upgrade I was using 100/5 plan. Both wired and wireless client hit 110/6 mbps consistently using ookla speed test.

After the upgrade wired client still hit ~700/17 internet speed without problem, but wireless clients mostly got ~300/17, the best seen was around 350.

The tested wireless clients (including Windows laptop, Macbook Pro, Iphones) generally connect at 80Mhz 5G band with 886.6 mbps or 1300 mbps line rate. When doing tests I was at the same desk where the router is.

LAN->LAN speed test using iperf3 are good. Wired<->wired reaches 940mbps. Wireless client (Macbook Pro connected at 1300mbps) to wired server reaches ~650mbps. However the same client trying Ookla internet speed test can't get more than 350 mbps.

So, am I hitting the hardware limit (CPU) of AC68U???

 

[pirx73]

I suggest you observe router's CPU usage while running speedtest. That will answer your question.

 

[hoegaarden]

Thanks. This is what it looks like when doing Ookla speed test. It doesn't seem to reach the 100% CPU level.

 

[pirx73]

1300mpbs should be divided by 2 because WiFi is a half-duplex (sort of) medium. So 650Mbps.
That is "theoretical maximum" from which you should subtract overhead and also take into account that other active WiFi clients consume bandwidth too.
So those ~600Mbps are divided among all active WiFi clients. If you have other active WiFi clients they might prevent Mac from achieving those ~600Mbps
I am not sure about hardware limitation since i don't have 3x3 capable WiFi clients, only 2x2 they can reach 400+ mbps on my 500Mbit uplink
But i agree that this number a a bit small.
600/15... you must've been living in UK... country whose ISPs still think noone needs upstream, or upstream=torrents=piracy

 

[ColinTaylor]

The tested wireless clients (including Windows laptop, Macbook Pro, Iphones) generally connect at 80Mhz 5G band with 886.6 mbps or 1300 mbps line rate. When doing tests I was at the same desk where the router is.

I have an AC68U also and at 80MHz on 5G with a 886.6Mbps link speed I get >550Mbps from my 660Mbps line.

 

[hoegaarden]

Thanks again. I do understand the wifi overhead will drop the throughput to about half. And the iperf3 LAN speed test confirmed that, so I thought at least the wifi quality is good, and the slow internet speed had to come from some bottleneck in WAN->LAN.

The 600/15 speed tier is from glorious Xfinity, the "Extreme Pro+" plan, available early this year in California, maybe other spaces as well.

 

[hoegaarden]

I have an AC68U also and at 80MHz on 5G with a 886.6Mbps link speed I get >550Mbps from my 660Mbps line.

Thanks for the information. I will keep digging into the settings to see if I can improve mine.

 

[thiggins]

@pirx73 Wi-Fi is a half-duplex technology. But link rate is specified for a Transmit or Receive session. So you don't divide the link rate by half.

It's doubtful that your throughput is CPU limited, Wi-Fi radios have their own processors and memory and routers today all use some form of cut-through-forwarding, which can support full gigabit speed, or close to it.

What are you getting for uplink speed?

A thought: Have you tried running speedtest simultaneously on two machines?

 

[bluzfanmr1]

Thanks for the information. I will keep digging into the settings to see if I can improve mine.

What cable modem brand and model are you using? Is it your own or is it from Xfinity? If it's your own and it only supports DOCSIS 3.0, that may be the issue. I would think at your new speed you will need a DOCSIS 3.1 cable modem.

 

[hoegaarden]

@pirx73 Wi-Fi is a half-duplex technology. But link rate is specified for a Transmit or Receive session. So you don't divide the link rate by half.

It's doubtful that your throughput is CPU limited, Wi-Fi radios have their own processors and memory and routers today all use some form of cut-through-forwarding, which can support full gigabit speed, or close to it.

What are you getting for uplink speed?

A thought: Have you tried running speedtest simultaneously on two machines?

The plan is 600/15, so the uplink speed is really slow at 17mbps, and all speed tests can reach that.

Regarding running simultaneously on two machines -- I didn't think of that. What would that do -- adding the two speeds to see if the total is higher?

 

[hoegaarden]

What cable modem brand and model are you using? Is it your own or is it from Xfinity? If it's your own and it only supports DOCSIS 3.0, that may be the issue. I would think at your new speed you will need a DOCSIS 3.1 cable modem.

I am using a new Motorola DOCSIS 3.1 modem. Also a wired connection (desktop connected to one LAN port of the router) reaches ~700mbps.

 

[hoegaarden]

The plan is 600/15, so the uplink speed is really slow at 17mbps, and all speed tests can reach that.

Regarding running simultaneously on two machines -- I didn't think of that. What would that do -- adding the two speeds to see if the total is higher?

Just did two machines running speed test at the same time. Interesting to see each one gets about 150mbps, about half of ~300mbps either machine can get if running alone.

 

[anotherengineer]

1300mpbs should be divided by 2 because WiFi is a half-duplex (sort of) medium. So 650Mbps.
That is "theoretical maximum" from which you should subtract overhead and also take into account that other active WiFi clients consume bandwidth too.
So those ~600Mbps are divided among all active WiFi clients. If you have other active WiFi clients they might prevent Mac from achieving those ~600Mbps
I am not sure about hardware limitation since i don't have 3x3 capable WiFi clients, only 2x2 they can reach 400+ mbps on my 500Mbit uplink
But i agree that this number a a bit small.
600/15... you must've been living in UK... country whose ISPs still think noone needs upstream, or upstream=torrents=piracy

Same here in Canada well northern Ontario anyway.........fibre on pole, coax to home. 350/10. Back in the day I would say this was fine, but now, like you say, uploading videos, photos to the cloud, or trying to have an HD webcast, more upload bandwidth is definitely needed.