contention slots - 450

hi cambium team,

i have 4-5 450m APs deployed. every night, they max out on frame utilization. during peak traffic time, i see the bandwidth requests as low as 85%. 

all of them are in 5.1/5.8 band, 5 ms frames, 8 contention slots, and have the MU-MIMO key. 

should i increase the contention slots? an image is attached. 

Hi Joshwehe,

Not sure if you need more contention slots or more UL slots (lower DL data %) from that graph.

On 450m Frame Utilization can be high without the link being overloaded in the DL direction. Indeed MU-MIMO will not start happening until frame utilization hits around 70% in most cases. The better/additional things to monitor on 450m are Sector Utilization, MUMIMO utilization and SUMIMIO utilization. Sector Utilization is more comparable to Frame Utilization on other 450 platforms to give an overall loading monitor and MU/SUMIMO show how it is being used. There is also the Slot Grouping (Group Size) stat which should show you how well groups are being formed as MUMIMO starts being utilized.

If Sector Utilization is showing spare capacity but UL Frame Utilization is near 100% then more UL slots would be recommended.

A couple of other threads (including have you maxed out a 450m) have discussions on these stats.

Let me know if you would like us to have a more detailed look at any of your 450m and we can collect some field diags to look at.

best regards,


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We have a similar question.  We have 71 clients off one 450M - cap per client is 20Mbps.  3 contention slots, low sector utilization.  DL frame utilization is at 99% (see attached image).  It is my understanding 3 contention slots should allow closer to 150 clients.  Is that correct or are there other factors to take into consideration?

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The pattern of traffic itself is also a consideration.  If lots of TCP ACK packets are required from many SMs, then more contention slots may be needed to optimize the sector during the busy hour... so some amount of trial and error is usually required, and things may change a bit over time.  This sounds a bit difficult to eek out the most the equipment can offer, but good news is on the way.

In an upcoming release, we will implement a feature called Auto Contention Slots, where the sector will optimally set the level based on all the factors that affect it, alleviating the user from the consternation of this parameter. So stay tuned!


Yes auto-contention slots should be great. UL-MUMIMO will also be coming soon for a great boost in UL performance.

In the mean time here are links to a couple of threads with some good discussions on contention slots.



best regards,