AutoSync: The AP automatically receives sync from one of the following sources: • GPS Sync over Timing Port (UGPS, co-located AP GPS sync output, or “Remote AP” feed from a registered SM’s GPS sync output) • GPS Sync over Power Port (CMM) • On-board GPS (internal GPS) Upon AP power on, the AP does not transmit until a valid synchronization pulse is received from one of the sources above. When there are synchronization sources on both the timing port and the power port, the power port GPS source will be chosen first. If there is a loss of GPS synchronization pulse, within two seconds the AP automatically attempts to source GPS signaling from another source. On-board GPS (internal GPS) is the last source checked for GPS signaling if there is no receipt of signaling from the timing port or from the power port (the on-board GPS module must not be used as the primary timing source). If no valid GPS signal is received, the AP ceases transmission and SM registration is lost until a valid GPS signal is received again on the AP.
AutoSync + Free Run: This mode operates similarly to mode “AutoSync”, but if a previously received synchronization signal is lost and no GPS signaling alternative is achieved (from the timing port, power port, or on-board GPS), the AP automatically changes to synchronization mode “Generate Sync”. While SM registration ins maintained, in this mode there is no synchronization of APs that can “hear” each other; the AP will only generate a sync signal for the local AP and its associated SMs. Once a valid GPS signal is obtained again, the AP automatically switches to receiving synchronization via the GPS source and SM registration is maintained.
In mode AutoSync + Free Run, if a GPS signal is never achieved initially, the system will not switch to “Free Run” mode, and SMs will not register to the AP. A valid GPS signal must be present initially for the AP to switch into “Free Run” mode (and to begin self-generating a synchronization pulse). Also, When an AP is operating in “Free Run” mode, over a short time it will no longer be synchronized with co-located or nearby APs (within radio range). Due to this lack of transmit and receive synchronization across APs or across systems, performance while in “Free Run” mode may be degraded until the APs operating in “Free Run” mode regain a external GPS synchronization source. Careful attention is required to ensure that all systems are properly receiving an external GPS synchronization pulse, and please consider “Free Run” mode as an emergency option.
Generate Sync (factory default): This option may be used when the AP is not receiving GPS synchronization pulses from either a CMM or UGPS module, and there are no other APs active within the link range. Using this option will not synchronize transmission of APs that can “hear” each other; it will only generate a sync signal for the local AP and its associated SMs.
This is the same kind of weird sync issues I see on multiple 3.6 450 APs almost every day. I've seen the sync status showing the timing port pulse flip-flopping on and off every second or two. There's nothing wrong with the GPS receiver. I reboot the AP and it's fixed right away. There's a problem in the code somewhere.
This issue arrived with the 13.2.1 software. Multiple radio's on my network switch to the on-board GPS even though the sync status is present on the power port. We run six cell clusters and at least three of the AP's in each cluster switch to the on-board GPS. Prior to 13.2.1 all AP's received timing reliably on the power port. A reboot will temporarily "fix" the issue for a few hours.