PMP450x Release 21.1 is now available

Cambium is officially releasing the PMP450x Radio 21.1 software.

Radio software and documentation can be found at, and will be available on cnMaestro cloud within 24 hours.

System Release 21.1 is primarily a bug fix release. It also includes some CBRS features, support for the new PMP 450m 3 GHz P7 hardware and support for PMP 450m 5 GHz P9 hardware.

First upgrade Subscriber Modules (SMs) to System Release 20.0 or later version and then upgrade the AP. Otherwise, SMs will connect but at a maximum modulation rate of 2X MIMO- B until both sides are running on System Release 20.0 or later version.

Features introduced in System Release 21.1

System Release 21.1 supports the following new features:

  • Channel Change if only SMs are impacted
  • Restriction of CBRS channel hunts to the same bandwidth, for PMP 450m operators who prefer to avoids an AP reboot
  • Handling of CBRS SAS channel enforcement

Channel Change if only SMs are impacted

The System Release 21.1 introduces a new feature that allows the AP to automatically find and move to a new channel or lower the bandwidth, when a significant number of SMs have been affected by termination or suspension, even though the AP itself has not been impacted.

Three new configuration parameters are added to the Configuration → CBRS → Configuration page as shown in this screenshot:

Change Channel if only SMs are impacted: When enabled, this feature allows the AP to automatically find and move to a new channel or decrease the bandwidth, when more than the SM Percentage Threshold for Channel Change percentage of SMs has been impacted by termination or suspension, even though the AP itself has not been impacted.

Note that the Alternate Channel Selection feature must also be enabled for the AP to hunt for a new channel due to the Change Channel if SMs are Impacted feature. If an operator elects to run with Alternate Channel Selection enabled but Change Channel if SMs are impacted feature is disabled, the AP still performs automatic channel selection, but only in cases where the AP is directly impacted by terminations or suspensions.

If the Alternate Channel Selection feature is disabled, but the Change Channel if Only SMs are Impacted feature is enabled, if enough SMs are impacted by terminations or suspensions, the AP will still reduce the Bandwidth if authorized grants are available, but it will not hunt for a new channel.

Original Channel Restore Time: When this feature is triggered via SM suspensions, the AP continues to heartbeat the original channels for itself and all the SMs, while operating on the temporary channels or reduced bandwidth for at least this length of a period after moving to these temporary channels or reducing bandwidth. When this timer expires, the AP can move back to the original channels and/or bandwidth if enough suspended SMs have become authorized on the original channels.

On the bottom of the HOME → Session Status page of the AP, a new counter associated with this feature has been introduced. It is a computation of the number of SMs that need to experience a termination or suspension before this feature is invoked. For example, if Threshold for Channel Change is left at its default value of 10%, the 4 shown in the screenshot below indicates that this is a sector with 40 SMs.

System Release 21.1 does not support this feature for PTP BHM/BHS setups. Such support is expected to be added later in 2022.

Restriction of CBRS channel hunts to the same bandwidth, for PMP 450m operators who prefer to avoid an AP reboot

The PMP 450m APs require a reboot when the channel bandwidth is changed. For PMP 450m, operators who use the CBRS Alternate Channel Selection feature, but prefer to avoid the outage caused when the bandwidth is automatically adjusted, they can now leave the Alternate Channel Selection feature enabled, while disabling the Reboot for Channel Bandwidth Change feature. When a channel hunt is automatically invoked due to terminations or suspensions, the AP will only hunt for channels with the same total bandwidth currently in use.

Handling of CBRS SAS channel enforcement

Both Google and Federated Wireless have plans to implement a feature that can enforce a pre-determined frequency plan. They will do the calculations at CPAS using the new frequencies, and right after CPAS, they will terminate the old frequencies. When such a SAS-initiated channel termination is sent to an AP/BHM, pre-System Release 21.1 software handles this without any issue if the channel the SAS is intending to move the sector to does not overlap in frequency with the current operating channel. If, however, the new target channel overlaps with the existing operating channel, pre-System Release 21.1 software shrinks the bandwidth rather than moving the sector to the entire new channel made available by the SAS. This System Release 21.1 AP/BHM CBRS feature is introduced to handle the SAS channel enforcement more optimally, by triggering a channel hunt even if the AP/BHM still has unterminated grants.

SAS support is expected likely sometime late in the 2nd quarter of 2022, although exact dates are not yet finalized.

Additional enhancements in System Release 21.1

Products Affected Tracking Description
All CPY-17968 Do not show the Reboot button after the reboot has been initiated.
All CPY-17963 Automatically Reboot upon out of memory failure.
AP CPY-17928 New OID for connected SMs Color Code Priority.
450m CPY-17872 Support for new Ethernet PHY device on 450m. The newer PHY chip 450m devices can be recognized by checking the Statistics → Ethernet entry for PHY ID on the AP GUI. The older devices shows Atheros 8033 while the new 450m devices shows Qualcomm 8081. These newer devices require a minimum software revision of System Release 21.1.
450m CPY-17870 Slight packet per second and throughput improvement.
All CPY-17855 Automatically reboot Radio with Bandwidth Phase Lock Loop (PLL) Lock lost to attempt recovery.
CBRS CPY-17231 Follow-Me does not work with multi grant.
CBRS CPY-16631 Move CBRS heartbeat timing to relative time instead of absolute time.

Problems and limitations corrected in System Release 21.1

Products Affected Tracking Description
CBRS CPY-18004 CBRS AP, running System Release 21.0, reset due to SAS empty responseData.
SM CPY-17996 The Reboot Required message was not displayed when a certificate was uploaded successfully.
CBRS CPY-17983 In termination case, no longer restricting Bandwidth in channel hunting algorithm as a function of the number of available channels.

Note: This is needed to support the SAS channel enforcement feature.
450m CPY-17971 Watchdog Reset due to buffer gather error.
AP CPY-17951 Rename the AP MIB OIDs, that had the same name in SM MIB: spatialFrequency, adaptRate, platformVer.
CBRS CPY-17940 AP does not send Spectrum Inquiry request and grant request for target frequency when relinquished AP is operating in the temporary channel.
450m CPY-17896 Uplink sounding reassessments more frequent with over 128 slots in the uplink.
CBRS CPY-17947 Do not relinquish the original channel in SM while operating on a temporary channel.
All CPY-17922 In some instances, SM sends PPPoE PADI as a unicast packet instead of sending it as a broadcast packet.
CBRS CPY-17920 calloc1 failed: out of heap and Internal error due to memory leak with CBRS when changing the configuration or exporting configuration.
All CPY-17908 Removed SM and PTP EIRP limits in 900 MHz bands for Brazil.
450m CPY-17897 40 MHz 5 ms Downlink Data percentage 33% or lower results in 1X modulation.
All CPY-17892 Updated Vietnam regulatory requirements for PMP products.
SM CPY-17887 NAT DNS Server Relay stopped working.
SM CPY-17881 Maximum Receive Power was incorrect on UI.
All CPY-17869 After every 17 days of uptime on System Release 21.0, uptime reads 1 year and SYSUPTIME OID was not correct.
PTP BHM CPY-17862 Receive Target Level configuration parameter was missing in the configuration file.
450m CPY-17854 Added more detail logging for 450m Watchdog resets due to canopy abort.
450m CPY-17842 Occasional invalid Ethernet TX frame, CRC mismatch.
PMP 450 CPY-17823 Follow-Me feature was not following hardware frequency limits.
CBRS CPY-17819 Channel hunt algorithm should consider SI response sorted, if any 5 MHz slices were present.
All CPY-17817 IPv6 configurations were missing from the configuration file.
AP CPY-17792 AP LAN2 Private Radio Network Interface must end in .1.
All CPY-17586 FatalError reset due to Invalid NiBuff error when processing DHCP Relay packet with no DHCP End Option (Code 255).
All CPY-17341 Memory leak when exporting user certificates when exporting the configuration file that can lead to calloc1 failed and Internal Error.
CBRS CPY-17172 Device Agent socket connection goes down on CBRS sync from cnMaestro.
450m CPY-17060 450m crashed due to GPS buffer overrun with bad serial input.
All CPY-17016 No HTTP access and/or occasional reset with security scans.
All CPY-16965 SM NAT mode with VPN on its LAN stops passing traffic when NAT table entries are greater than 1500.
450m CPY-16487 Downlink beamformed powers require a reboot to update correctly.
1 Like

Awesome! Please remember to update cloud with the new firmware! Thanks!

anyone else have trouble upgrading to 21.1? I upgraded one of my AP’s a 450m last night after the update no SM’s would connect. I had to roll the 450m back to to get the SM’s to reconnect. The AP was showing normal transmit but had an error code in red reason 2 transmit disabled on the general status page.

@ahults thanks for posting this. I’m sorry to hear about 21.1 giving this error.

Overnight we had one more customer report the same thing. They downgraded to 21.0 and the error went away. We are looking into it and will get back to you with more info.

I had the same thing, I also have the support file during the error. After several reboots the unit returned to normal.

@jnovak, would you be able to get the field_diags file from this unit?

Hi Lena,

I just pulled the ‘tech support’ file from cnMaestro. If that can be of help, let me know. This was ‘during’ the error.



Hi @jnovak, the tech support file cnMaestro would not have the history of when the issue happened. If you could help get the field_diags that would be best. From AP UI, type: http:///<IP_ADDRESS>/field_diags.cgi, then, download the *.gz file and send to us.

I have it, is it safe to upload this to the forum?

Hi @jnovak, if you have not already opened a support ticket, could you open one and upload it to this ticket? If that might be better that way.



I’ve got it sent over. Thanks!

Does this mean that the 40/30MHz channel width in combination with 5ms timing slowness has been resolved? or does Cambium still recommend using 2.5ms timing for 30 and 40 MHz channel widths?

No, that has not been resolved… that will take a very large overhaul. And yes, if you’re running 30 or 40MHz channel widths, 2.5ms frames is preferred. I think the only reason they’re recommending 5ms at this point is if you need LTE sync compatibility on their 3GHz radios.

I thought the 5ms was only an issue with 40MHz channels. Is it an issue with 30MHz channels as well?

Yes, please see this post:


I am running 21.1 on a 5Ghz production Medusa feeding my own home.
20Mhz, 5ms, 9 SMs total on this unit, downlink 75%, control slots at 6
SFP fiber fed data port
SM side is a new RETRO SM on a reflector
8./7 B on the downlink and 8/8 B on the uplink
Getting a little over 60 on a link test - full flood
My PPPoE session from the router barely crosses 30Mbps now whereas before it seemed in line with the link test

This 450m problem has been fixed by BETA-1:

I installed Beta-1 on one of our AP’s last night. I had to roll it back to 21.0 this morning due to poor throughput and high uplink frame rate maxing out at 100%. I have the field diags that I can submit.

@ahults, please help upload the field_diags log your existing support ticket #310015.


in what band? 3.5? 5?