We are operating several Cambium ePMP 4600 base stations in PTMP mode and have encountered a difficult-to-isolate issue.
At subscribers located farther from the base station (around 15–17 km, approximately -68 dBm signal level), we observe the following:
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On the CPE web interface, no disconnection is visible; the session time continues without resetting.
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However, CnMaestro reports a disconnection event.
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The customer experiences a real service interruption with no data traffic.
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When a Mikrotik router is connected behind the CPE, the connection does not automatically recover. It only comes back after rebooting the Mikrotik router.
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At sites without a router behind the CPE, short, intermittent drops occur.
We are running the latest firmware on all devices.
We have tried disabling the Hardware Acceleration Engine on both AP and CPE sides, but the issue persists.
Router replacements were also performed at the affected sites to rule out CPE-router compatibility problems, but the issue remained.
At some locations, a Tarana link was previously operating without any problems, and the issue appeared only after replacing Tarana with Cambium.
We have now seen the same behavior at two independent sites, which rules out a local network issue.
If the router is removed, the connection becomes stable and stays up.
Common characteristics at affected sites:
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Distance typically 14–18 km
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Signal level around -67 to -70 dBm
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PTMP mode
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Client devices are mixed: ePMP 4625 and ePMP 4600c
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VLAN traffic is typically used through the radios
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When the link is up, throughput is excellent (300–400 Mbps)
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The problem appears intermittently and unpredictably
Has anyone experienced something similar?
Could it be that at certain distance/SNR thresholds the radio silently drops sessions without re-registration?
Or could this be related to TCP session handling, keepalive behavior, or an incompatibility caused by hardware acceleration or VLAN traffic behind routers?
Any feedback, logs, or workarounds would be appreciated.
