450m Prioritization Configuration

I’m working with one of our customers to improve his gaming experience.

Normally it is fine, but at peak hour, when our 22.0 3GHz 450m is stressed, his gameplay lags. For a nice visual, he sends me videos of the game lagging along with corresponding ping latency spikes, seen on a graph, to various places on the internet.

I thought I’d use this as a test case to learn more about the prioritization features of the 450 platform. I read the End-to-End QOS Document, and can see entries in the AP’s Logs>DSCP Priority Streams when our customer is gaming. We’re using the Legacy Scheduler.

In the SM, I have set up all 4 data channels. High and Ultra High are set for 1024 kbps, which maybe is too low, but DSCP 45 traffic we identified with the Game does not seem to require much throughput.

I have also set the SM to be in the High Prioritization Group in the SM>Configuration>QOS menu. The gameplay and latency issues are still happening, and none of the changes I’ve tried seem to have any real effect.

Am I missing something with the configuration, or maybe when the 450m is loaded at peak hour, the prioritization mechanisms don’t help much?

For all the other SM’s are you just using the default/low priority group for them? If yes, then don’t setup any other groups. Just try giving them a low priority CIR. This should give them a dedicated CIR and give them the highest priority within the low priority group.

Setting the “SM Prioritization Configuration” to High doesn’t do anything on PMP450m. This feature only works on PMP450 and PMP450i AP’s.

Lastly, have you updated your AP to R22.0.1, or even better, the new R22.1 beta? There are some significant performance increases for loaded up PMP450m AP’s in those releases that can help reduce latency during periods of high utilization.

1 Like

All the other SMs’ Data Channel Priority Settings have not been touched, so they’re all Low still. I’ll remove the other priority channels from this one customer and configure a few Mbps for the Low Priority. Good idea to test.

As for the SM Prioritization Group, I recall seeing somewhere that the 450m does not support that, and then was able to find it again in the 450 Platform Configuration Guide as a note at the SM Prioritization section. It’d be nice if the note in the SM had this detail as well.

The release notes for 22.0.1 don’t state any major performance improvements, but I will try the 22.1 beta next week. I’ll collect some more data and report back.

Quick Update–

On 22.1 Beta2 customer still was experiencing gameplay problems with 2/1 Mbps DL/UL set in the Low Priority CIR, with all other customers having no CIR set.

I have just increased that to customer’s full speeds of 10/4 Mbps in the Low Priority CIR and will report if there are still issues.

There are still latency issues for this customer when he’s set for 10/4 CIR in Low Priority.

It seems the CIR settings are not working as intended. I’ve opened a Cambium ticket to see if they can determine what we’re missing in the configuration.

The root of our issue turned out to be a lack of contention slots set on the 450m.

We had the default of 3 set, when there were around 30 SMs attached. Cambium recommends setting 8 contention slots when there are 11-50 SMs. Here’s an image of what the pings would look like when there were “collisions” due to lack of contention slots. This is an graph of ping times, 10 pings per second. There will be clumps of high duration pings.

With the contention slots set properly, we will resume testing various prioritization settings.

Thanks to the Cambium support team for helping us find this issue.



From the Cambium white paper on the contention slots:

The paper says 4 contention slots for 11 to 50 SMs and 6 contention slots for 51 to 150 SMs for 450M 5G. Has that changed or is it different for 3G? If so, Cambium should let us know so we can update our APs.

1 Like

The guidelines given are only guidelines, because the actual data traversing the network might affect the usage of contention slots. In this case, the latency demands of this particular customer required additional contention slots to be added, which might not be the case for a sector in which there aren’t such demanding subscribers. I am glad to hear that support was able to identify the issue and help optimize the network.

1 Like

Thanks Matt - at what latency range would one expect to investigate changing contention slot values?

So @LuciaCambium gives a good explanation of how to fine tune your contention slots HERE.

1 Like


I should have included we’re using 5ms frames…which changes the recommended values:

The majority of our APs have between 11 and 50 subscribers, so we’re planning to set them all that way for ease of synchronizing.


Thank you! What document is that table from?

Edit: Nevermind found it in the 22.0 user guide. Thanks!

Matt, does the new 22.x firmware and the 450M co-locate calculator account for the new 5.0 contention slot table in auto contention for the 450i series?

So, as stated, the contention slot table is just a recommendation. For the 450 and 450i AP’s, the auto contention slot feature does not use that table to derive its value, it is automatically adjusted based on traffic conditions. You still need to set the contention slot value so that the AP can be sync’d with whatever value is used for PMP450m. The PMP450m series does not have an auto contention feature because of the complexity in calculating the contention slots across multiple groupings.


Ah that’s right - forgot about setting the value. Thanks Eric!

This topic was automatically closed 365 days after the last reply. New replies are no longer allowed.