Low speed PMP450 15.1.1 when connected 6 and more SM (ethernet port on SM down)

When testing speed for PMP450 I have noticed that when it is connected from 6 and more SM speed in proportion decreases.


PMP450 AP configuration: Configuration Source: SM, Channel Bandwidth 30,  Max Range: 2 Downlink Data: 50

ALL PMP450 SM configuration: Sustained Downlink Data Rate: 155000, Sustained Uplink Data Rate 155000, Downlink and Uplink Burst Allocation: 2500000, Max Burst Downlink and Uplink Data Rate: 0

ALL SM connected 8x/8x

When in AP450 connected only 1 SM450(tested SM) - iperf test speed download 55Mbit/c,

Whent i else connected other 4 SM with ethernet port down  - after test spedd on Tested SM downlof speed 50Mbit/с

but if connected in AP450 esle 5 other SM with ethernet pord down and 1 tested SM total 6 SM - tested SM iperf speed download 35Mbit/с

Why in case of connection more than 5 SM even with switched off Ethernet ports speed on test SM considerably decreases?

Hi madmax,

Could you please let me know what is the "Frame Period" (Configuration -> Radio page) configured on the AP?



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2,5 ms

Thanks for bringing this to our notice.

This will be fixed in a future release.

What exactly is broken and can we avoid it in the mean time?  Is this affecting throughput overall for the whole AP or just on an SM by SM basis?  (Where it's just the max throughput of a single SM)  (Eg., this wouldn't matter if the largest package any given SM was configured for was 25mbps?)

Also, is this brand new to 15.1.1?  

What would be the ETA on a future release that fixes the issue?

Hi Steven

This does not effect the aggregate throughput of the AP.
It effects the max. throughput of individual SMs.

This is not new to 15.1.1. Release 14.1.2 or newer will have this issue.

I'm sorry, at this point I do not have a ETA on a future release, which fixes this issue.

Best Regards,



It's still not clear on the exact problem here.  Do the Ethernet ports on the "other" SM's need to be set to disabled, just "not linked", or does Ethernet port connection on the SM's not matter at all?  Is this just saying that 450 SM's are just limited by a software bug to some maximum bits-per-second or packets-per-second?

More clarity on the problem would be useful for the rest of us please.


This issue happens in the UL only.
Bandwidth allocation, in the UL, is optimized when there are 5 or fewer SM registerd to the AP.
When 6 or more SMs are registered to the AP, every SM has to randomly wait between 1 to 7 frames, before requesting the bandwidth. This introduces a delay in the UL traffic.
In madmax's case, he was seeing DL TCP throughput drop, because TCP Ack's in the UL were delayed.
Ethernet port status does not matter, it only matters if the SM is registered to the AP or not.

Please fix it is problems because if on AP registered 7 and more SM - Each SM passes no more 15-20mbit/s
Now it is big problems

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When we receive fixed version

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Inversion 15.1.2 fixed it is problems ?

This issue is not fixed in 15.1.2.

It will be fixed in 15.2.


When will we receive version 15.2??? Earlier promised us October-November, now December. Where?

Hi madmax,

We are sorry for the delay.

We will be releasing 15.1.3 this month.

This issue will be fixed in 15.1.3.

We appreciate your patience.

- Balaji


Am I correct in assuming this severely impacts VOIP traffic?

I'm having complaints from customers using Skype for Business.  Outgoing voice specifically.  Try as I might, I haven't been able to track it down, but this looks like a huge problem.

Is VOIP part of any of the pre-release tests - Beta or otherwise?

We perform all our link tests with bridging and MIR enabled and don't offer any packages over 20 Mbps, so never noticed the bandwidth restrictions.  Looks like this is the answer/problem with the multiple threads of slow/capped bandwidth despite correct results when performing the RF link tests.

This issue is fixed in 15.1.3 (BETA-3).
Beta build can be downloaded from here: https://support.cambiumnetworks.com/beta

For more info on 15.1.3 (BETA-3), please see this post.


I am also getting a lot of complaints with Skype Business. It seem only them for voice.

AP capacity seems less the 50%.

This issue is fixed in 15.1.3, which will be released in early January, 2018.

If you are interested, please try 15.1.3 BETA-5, available at https://support.cambiumnetworks.com/beta.