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Question about Oculus Link bandwidth

JParra75
Level 4

I have a question about the connection speeds between the Oculus Quest 2 and the PC.

 

My USB cable gives 2.1 Gbps in Oculus Home tests.
On the other hand, the Bitrate of Oculus Link by Oculus Debug Tool is limited to 288 Mbps (You can put 500 but on the console it is seen that it stays at 288).

 

My Wifi (In Virtual Desktop) gives a connection between PC and Quest 2 of 1.2Gbps
But it only lets you configure up to a 150 Mbps bitrate


Are we wasting bandwidth?
Is there something else besides the bitrate of the video that travels through the connection?
Is it a limit of the Oculus Quest 2 device itself?


Thanks for the clarifications.

1 ACCEPTED SOLUTION

Accepted Solutions

nalex66
Volunteer Moderator
Volunteer Moderator

The main limitation (for both Link and Virtual Desktop) is the speed at which the GPU can encode the signal, and the speed at which the Quest's processor can decode the signal. This is what is controlled by the bitrate setting. The cable's bandwidth is mostly irrelevant, which is why Link will also work over USB2.

 

In addition to the video signal, there is also audio being sent to the headset, microphone input being sent back, tracking data from the headset and the controllers, and input information (buttons and triggers) from the controllers. This where USB3 helps--it allows full duplex communication (data going both ways at the same time), which means that tracking and input data from the headset doesn't have to wait to be queued between packets of video and audio data from the PC. Link is pretty good at managing the queue, but occasionally it will cause some slight latency over USB2.

 

The Quest 2 processor can handle higher bitrates than the original Quest, and newer GPUs (like Nvidia's 2000 or 3000 series) are built to handle more streaming bandwidth through their hardware encoders than older GPU models. Depending on your hardware, one or the other will be the limiting factor for the video bitrate.

i7 5820K @ 4.25GHz | EVGA GTX 1080 SC | Gigabyte GA-X99-UD4 | Corsair DDR4 3000 32GB | Corsair HX 750W
SSDs: Intel 660p M.2 2TB, 3x Samsung Evo 1TB | Startech PCIe 4x USB 3.0 | Startech PCIe 2x USB C 3.1 gen2

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16 REPLIES 16

nalex66
Volunteer Moderator
Volunteer Moderator

The main limitation (for both Link and Virtual Desktop) is the speed at which the GPU can encode the signal, and the speed at which the Quest's processor can decode the signal. This is what is controlled by the bitrate setting. The cable's bandwidth is mostly irrelevant, which is why Link will also work over USB2.

 

In addition to the video signal, there is also audio being sent to the headset, microphone input being sent back, tracking data from the headset and the controllers, and input information (buttons and triggers) from the controllers. This where USB3 helps--it allows full duplex communication (data going both ways at the same time), which means that tracking and input data from the headset doesn't have to wait to be queued between packets of video and audio data from the PC. Link is pretty good at managing the queue, but occasionally it will cause some slight latency over USB2.

 

The Quest 2 processor can handle higher bitrates than the original Quest, and newer GPUs (like Nvidia's 2000 or 3000 series) are built to handle more streaming bandwidth through their hardware encoders than older GPU models. Depending on your hardware, one or the other will be the limiting factor for the video bitrate.

i7 5820K @ 4.25GHz | EVGA GTX 1080 SC | Gigabyte GA-X99-UD4 | Corsair DDR4 3000 32GB | Corsair HX 750W
SSDs: Intel 660p M.2 2TB, 3x Samsung Evo 1TB | Startech PCIe 4x USB 3.0 | Startech PCIe 2x USB C 3.1 gen2

View solution in original post

JParra75
Level 4

Thank you for your prompt and extensive response.

If the bandwidth of the connection is not relevant and the limit is on the different hardware components. Can we dream that the next Air Link offers a quality similar to what the Oculus Link offers?


Greetings.

JParra75
Level 4

And if you allow me to expand the debate, I would like to know what reason there is to allow the bitrate to be configured in the Oculus Debug Tool up to 500, if later from the console you can see how it is configured internally to a maximum of 288.

Thanks again

loregnum
Level 5

Virtual Desktop already offers quality similar to link (iMO, better on the high quality setting than all but the top 2 resolution multipliers in link) so unless air link is some shoddy option, it will as well.

 

You also seem to be too focused on bitrates and don't realize there is minimal, if any, difference once you reach a certain point. Virtual Desktop also allows the option of HEVC encoding which means you get similar quality at a lower bitrate compared to h.264. It's said that it is about half so in theory, HEVC in Virtual Desktop at the 150 you mentioned would be equal to link at 300...not that one needs to try and play at 150 though.

PITTCANNA
Level 12

Don't get hung up on bandwidth, the link cable is all about the latency it reduces due to the usb 3.1 connection.

For example youtube can stream 4khdr video 60 frames a second at 56mbps.  So 500 link, and 150 virtual desktop is more than sufficent to transmit video.

 

https://www.youtube.com/watch?v=GjF1m2OzcIA

nalex66
Volunteer Moderator
Volunteer Moderator

What video card are you using? That 288 Mbps max bitrate that you mention might be limited by your GPU. I've experimented with various rates, and I can definitely see the difference in image quality as I raise the bitrate. I settled on either 250 or 300 (can't remember offhand, and not at my VR PC right now) as the point at which I could no longer see compression artifacts. I've seen an Oculus dev comment that above 250 you get into the territory of diminishing returns.

 

Based on my experience with Virtual Desktop, I definitely think they can achieve a quality level similar to Link. there may be other factors that impact the overall experience (higher latency over WiFi than USB, or hiccups due to network traffic, for instance), but certainly image quality can be very good over WiFi.

i7 5820K @ 4.25GHz | EVGA GTX 1080 SC | Gigabyte GA-X99-UD4 | Corsair DDR4 3000 32GB | Corsair HX 750W
SSDs: Intel 660p M.2 2TB, 3x Samsung Evo 1TB | Startech PCIe 4x USB 3.0 | Startech PCIe 2x USB C 3.1 gen2

I understand perfectly, but although Virtual Desktop can achieve a quality similar to Oculus Link, it is at the cost of a higher power requirement, therefore in a balanced point, the cable is better. In fact, I use Virtual Desktop for everything except for Simracing, where I use Oculus Link.

The issue of the limitation to 288 is not my hardware, as I have read on multiple sites showing the same limitation and they did not have the same hardware.
If you show the Oculus Debug Tool console, when applying the changes you can see how the instruction for the Bitrate is 288, even if you have put 500, 400, 300 in the configuration.

I know it is enough, even as you comment with 250, I am just curious to know why it is allowed to enter up to 500 when in reality the real "internal" limit is 288.

Thanks.

nalex66
Volunteer Moderator
Volunteer Moderator

I recall that after v23 came out, they had reworked some aspects of how Link works, and people who had set their bitrate to 500 started reporting performance issues. Oculus devs on Reddit recommended reducing it back to default (150) and bumping it up in small increments to find a new sweet spot. That's also when they suggested that going above 250 was getting into diminishing returns. Perhaps in one of the updates since then, they decided to just cap it at 288 to eliminate problems with the Quest 2 decoder.

i7 5820K @ 4.25GHz | EVGA GTX 1080 SC | Gigabyte GA-X99-UD4 | Corsair DDR4 3000 32GB | Corsair HX 750W
SSDs: Intel 660p M.2 2TB, 3x Samsung Evo 1TB | Startech PCIe 4x USB 3.0 | Startech PCIe 2x USB C 3.1 gen2