450i APs intermittently lose Cambium sync

I know Matt has said that how Cambium Sync works is proprietary, but how robust is it? If there are no Ethernet errors, should Cambium Sync also work reliably?

I’m trying to figure out why some 450i APs show intermittent loss of power port sync in the Event log. When this happens, some (not all) SMs have to rereg, I know this has always been the case with 450 when switching between sync sources or sync and free run. But it can cause a several minute outage for customers if the SM has to scan a lot of frequencies and channel widths.

In this case, sync is coming from a Packetflux Rackinjector, and it is not a problem with losing GPS from the satellites. And whenever I log into the affected APs, they say 100% sync pulses received, so it’s not a case of pulses constantly missing.

These are 300 ft cables, but I had assumed the Cambium Sync protocol was more robust than Ethernet and not finicky about cable conditions, maybe that’s a wrong assumption.

I have been seeing the same behavior more and more on 450i 3Ghz APs with the syncport aux edition. Often it will only affect 1 or 2 of the APs connected to the same sync injector, but never all of them at the same time. In my case the cables are usually under 10’ between the sync injector and the aux port of the radios.

I haven’t done any further diagnosis, and can’t add anything else helpful at this time other than that I see the same behavior. Rebooting the affected AP(s) always resolves the issue for some length of time.

Here’s an example right now:

Jacob, that’s interesting that you are seeing problems with AUX port timing and short cables. In your screenshot, it actually says receiving sync, but not using it. Strange. Are these APs on latest firmware? I know we’re better about keeping our 3 GHz stuff on latest FW than the 5 GHz radios.

How often does this happen? I checked one site where we have two CBRS APs, a sector and an omni. using AUX port sync. One has a Cambium cnPulse, one has a Packetflux Syncbox Junior AUX port version. In the Event Log, they both show an occasional brief loss of timing port sync, but maybe once every 2-3 months.

I have one particularly problematic 5 GHz AP that loses power port sync several times per day. It has also saying it acquired then lost timing port sync even though nothing is connected to the AUX port. I am trying a FW update, if that doesn’t help, I’m going to see if I can telnet in and disable timing port sync and see if that changes anything.

We did have one older site with 4 x 450 APs that all started having sync go flaky or die, both external and internal sync. We tried literally everything, finally replaced all 4 APs with 450i and the sync problems went away, so I have to conclude something just died over time. That was 450 though, not 450i.

I’m currently running 22.1.1 on all of the radios, so current.

I haven’t kept good enough track of how often it happens, but it is often enough that I notice. I notice on this particular AP more often, because it gets constant DPA events.

The radios I’ve had this happen on (which are spread across sites) will stay in the state in the screenshot until rebooted. They don’t appear to be able to “fix” themselves.

Oh, that’s different from what I see. Just a momentary loss of power port sync.

The problem is that Cambium doesn’t seem to do a graceful transition to free run. SMs are likely to rereg even if the sync loss is just a few seconds. I also remember using SNMP to graph InSync and OutSync counts on SMs and they would increment when AP went between power port or timing port sync and free run.

22 hours since disabling timing port sync from the CLI (why has Cambium still not put this in the web interface?).

No event log entries about loss of power port sync. No SM reregs. I’m going to need to see 3-5 days, but given that it was happening every 1-3 hours before, I think this made a difference.

Not sure why the AP thinks it sees timing port sync when there is not and has never been anything plugged into its timing (AUX) port. Note that AUX port power is not enabled.