Gigabit broadband is installed, but internet access is slow
Early this month I went and switched my bundled plan, and now I’ve upgraded back to the gigabit broadband plan. The China Unicom app shows gigabit, but browsing the internet at home still feels like 100Mbps-level speeds. I’m not sure whether it takes effect next month or what.
The wiring in my walls is Cat7a, the router has all-gigabit Ethernet ports, and my PC has a 10Gbps Ethernet port. Testing with speedtest.cn on the PC connected directly by cable, I only get 181Mbps down / 28.3Mbps up, which looks the same as before the upgrade.
I asked China Unicom support for help. They told me to bypass my router and test the speed straight off the ONT, but it’s a pain to move my PC, and my laptop has no Ethernet port, so it’s awkward to do myself. He said he’d come by in the afternoon to test the speed for me.
Speed testing with iperf3
I ran a test on my LAN to check the state of the cabling and router at home.
MacStudio to PC = 940Mbps
MacBookPro (wireless) to PC = 393Mbps
D:\GreenSoft\iperf-3.1.3-win64>iperf3 -s
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Server listening on 5201
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Accepted connection from 192.168.50.3, port 57277
[ 5] local 192.168.50.8 port 5201 connected to 192.168.50.3 port 57278
[ ID] Interval Transfer Bandwidth
[ 5] 0.00-1.00 sec 112 MBytes 941 Mbits/sec
[ 5] 1.00-2.00 sec 112 MBytes 942 Mbits/sec
[ 5] 2.00-3.00 sec 112 MBytes 941 Mbits/sec
[ 5] 3.00-4.00 sec 112 MBytes 942 Mbits/sec
[ 5] 4.00-5.00 sec 110 MBytes 926 Mbits/sec
[ 5] 5.00-6.00 sec 112 MBytes 942 Mbits/sec
[ 5] 6.00-7.00 sec 112 MBytes 942 Mbits/sec
[ 5] 7.00-8.00 sec 112 MBytes 941 Mbits/sec
[ 5] 8.00-9.00 sec 112 MBytes 941 Mbits/sec
[ 5] 9.00-10.00 sec 112 MBytes 941 Mbits/sec
[ 5] 10.00-10.01 sec 612 KBytes 880 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth
[ 5] 0.00-10.01 sec 0.00 Bytes 0.00 bits/sec sender
[ 5] 0.00-10.01 sec 1.09 GBytes 940 Mbits/sec receiver
-----------------------------------------------------------
Server listening on 5201
-----------------------------------------------------------
Accepted connection from 192.168.50.18, port 61115
[ 5] local 192.168.50.8 port 5201 connected to 192.168.50.18 port 61116
[ ID] Interval Transfer Bandwidth
[ 5] 0.00-1.00 sec 47.2 MBytes 396 Mbits/sec
[ 5] 1.00-2.00 sec 45.2 MBytes 379 Mbits/sec
[ 5] 2.00-3.00 sec 47.2 MBytes 396 Mbits/sec
[ 5] 3.00-4.00 sec 48.8 MBytes 409 Mbits/sec
[ 5] 4.00-5.00 sec 50.6 MBytes 425 Mbits/sec
[ 5] 5.00-6.00 sec 46.9 MBytes 393 Mbits/sec
[ 5] 6.00-7.00 sec 45.5 MBytes 382 Mbits/sec
[ 5] 7.00-8.00 sec 44.3 MBytes 371 Mbits/sec
[ 5] 8.00-9.00 sec 46.3 MBytes 388 Mbits/sec
[ 5] 9.00-10.00 sec 46.7 MBytes 391 Mbits/sec
[ 5] 10.00-10.01 sec 201 KBytes 525 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth
[ 5] 0.00-10.01 sec 0.00 Bytes 0.00 bits/sec sender
[ 5] 0.00-10.01 sec 469 MBytes 393 Mbits/sec receiver
-----------------------------------------------------------
Server listening on 5201
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Using the MacBook Pro over Wi-Fi to test roaming speeds on a far-away node:
On the table outside 168Mbps, at the kitchen doorway 185Mbps
China Unicom technician comes to help with speed testing
The China Unicom technician came to help test speeds. Here are the measurements:
ONT port at the entrance, speed tester plugged in: 960Mbps+
Study wall port, speed tester plugged in: 960Mbps+
Study wall port with my own cable to the speed tester: 960Mbps+
With Linksys in the path, speed tester on the LAN port: 260Mbps
Combined with the earlier result that LAN-to-LAN can hit 960Mbps+
The test shows: the speed between the Linksys WAN port and its LAN ports is capped at 300
Is the Linksys router causing the slow speeds?
Strange — why would a Linksys router cause slow speeds? Every link in the chain really is gigabit.
After checking, my initial guess is that the Linksys router throttles speed between devices to keep any single device from hogging the bandwidth.
I went into the “Priority” settings and found it was allocating priority between devices based on 100Mbps speeds. I manually changed the prioritized speed to gigabit, then tested again in the browser on my Mac and got over 500Mbps! So it was splitting the bandwidth evenly and not giving any device permission to run at full speed.
Raising the priority further: after setting the Mac Studio as the priority device, the speed test hit 672Mbps down / 66Mbps up.
OK, so I just turned the priority feature off entirely. Speed came up to around 800M/62M.
Summary of the cause:
At this point, that’s honestly plenty for me. So the root cause is that the Linksys MX8400 has a certain protection mechanism, originally meant to keep the network stable by limiting speed between devices. But that mechanism depends on the measured internet connection speed, and the Linksys speed test itself isn’t accurate, so it reports a speed that’s too low, which in turn heavily restricts the speed allocated to devices at home. That’s what was capping the network speed.
Put plainly, it trades burst speed for stability.
So I need to set the internet speed correctly and turn off priority allocation, so that devices on the network can get higher burst speeds.