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spiceygas
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CRS312-4C+8XG-RM -- Jittery Network Latency During VR Gameplay

Fri Mar 19, 2021 4:42 pm

CRS312-4C+8XG-RM
SWoS v1.11 (Not using v1.12 because it has a bug with 2.5gbps devices)

Network:
Desktop PC (10gbps) ==> CRS312-4C+8XG-RM ==> (2.5gbps) Wireless AP (802.11ax) ==> Oculus Quest 2

Symptom:
When using Virtual Desktop (Oculus App) to play a VR game wirelessly (rendered on PC, played on the the Quest 2), I get a bunch of network latency spikes. Every 4-6 seconds the latency spikes up, causes jitters in VR (which is very disorienting). Then it settles back down and is good for a few seconds before again spiking back up.

When not gaming, the ping time is 1ms between the devices. Latency is only an issue when the VR game is streaming.

Cause:
The CRS312-4C+8XG-RM is definitely the cause. When I swap it out for an old Netgear 1gbps switch, all latency problems disappear and the games play silky smooth.

Ping times (when not playing) are reliably 1ms. The problem only happens when streaming VR games. I *presume* it has something to do with the rate at which network traffic is coming through the switch...?

The Ask:
While swapping the switch is functional, that means that my desktop PC is no longer running at 10gbps. Does anyone have suggestions of what might be causing the problem? Or settings within SWoS that I should tinker with?
 
maigonis
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Re: CRS312-4C+8XG-RM -- Jittery Network Latency During VR Gameplay

Fri Mar 19, 2021 7:57 pm

I would blame Wi-Fi first. You have setup Wi-Fi properly?
 
spiceygas
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Re: CRS312-4C+8XG-RM -- Jittery Network Latency During VR Gameplay

Fri Mar 19, 2021 8:15 pm

I would blame Wi-Fi first. You have setup Wi-Fi properly?
Yep, and it's not WiFi. I've tested with two different access points, both 802.11ax, from two different manufacturers. On multiple firmware versions each. And I've tried every permutation of channel, channel width, 802.11ax disabled, etc. that you'll think of.

I've also tested on multiple versions of the VR streaming application.

It's is comically easy to reproduce & solve the problem just by swapping the network switch. 20 seconds to swap the network cables from the Mikrotik switch to the old Netgear switch and the problem is immediately fixed. Swap the network cables back to the Mikrotik switch and the problem reappears. Tested swapping back-and-forth a dozen times.

I'm 99% confident it's the switch. (The 1% being that I always accept the possibility of being wrong)


The switch is the last thing I tested because I didn't honestly believe it could be the cause of the problem. I've spent 3 weeks debugging everything else, swapping parts, changing configuration, etc. to rule out everything I could think of. I tried changing the switch out of desperation because all other ideas were exhausted. And I was in disbelief when it worked. But it did. By process of elimination, I'm very confident I've demonstrated that the switch is the problem.
 
FezzFest
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Re: CRS312-4C+8XG-RM -- Jittery Network Latency During VR Gameplay

Sat Mar 20, 2021 1:52 am

It really is time MikroTik mentions the switch buffer size of their switches on the specifications page.

Your issue is related to the speed difference between the ports. When you send traffic from a 10Gbps device (desktop) to a 2.5Gbps device (AP) through the switch, it needs to buffer packets. If the buffer size is too small, this leads to dropped packets and/or added latency. Try to disable the higher rates on the switch (so all devices negotiate e.g. 1Gbps) and the issue will probably disappear.
 
mducharme
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Re: CRS312-4C+8XG-RM -- Jittery Network Latency During VR Gameplay

Sun Mar 21, 2021 4:35 am

SWoS v1.11 (Not using v1.12 because it has a bug with 2.5gbps devices)
Have you tried using RouterOS instead of SwOS? The switch supports either. RouterOS has more features and may handle this better than SwOS.
 
spiceygas
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Re: CRS312-4C+8XG-RM -- Jittery Network Latency During VR Gameplay

Sun Mar 21, 2021 11:52 pm

It really is time MikroTik mentions the switch buffer size of their switches on the specifications page.

Your issue is related to the speed difference between the ports. When you send traffic from a 10Gbps device (desktop) to a 2.5Gbps device (AP) through the switch, it needs to buffer packets. If the buffer size is too small, this leads to dropped packets and/or added latency. Try to disable the higher rates on the switch (so all devices negotiate e.g. 1Gbps) and the issue will probably disappear.
Confirmed that forcing both ports to 1gbps fixes the problem. It's only an issue when the speeds are mismatched, which would support your hypothesis on the root cause.

If only I could force both to 2.5gbps.
 
Cablenut9
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Re: CRS312-4C+8XG-RM -- Jittery Network Latency During VR Gameplay

Sun Mar 21, 2021 11:55 pm

It's only an issue when the speeds are mismatched
Image

For some reason, Mikrotik switches have a problem with buffers getting overloaded when differing 1+ gigabit speeds are used.
 
spiceygas
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Re: CRS312-4C+8XG-RM -- Jittery Network Latency During VR Gameplay

Mon Mar 22, 2021 3:47 pm

For some reason, Mikrotik switches have a problem with buffers getting overloaded when differing 1+ gigabit speeds are used.
Is that true on both SwOS and RouterOS?

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