So there are a bunch of settings depending on what FW the PMP100 AP is running and whether it uses timing port or power port sync.
My question is: if the timing depends on all those variables, how were we able to colocate PMP100 APs without factoring them in?
For example, if I was trying to coexist with another WISP's tower a mile away, why didn't I need to know what FW they were using and whether they were using timing or power port sync? And why didn't PMP100 need these settings?
And didn't I see discussion about CMM3 and CMM4 sync being different?
I don't think highly precise frame alignment was required on FSK. Now we have this OFDM stuff and we want the most bps possible.
There is definitely a difference in the pulses between CMM3 and CMM4 and their derviative 3rd party timing modules.
The 450 on-board GPS is CMM4 aligned. So if you have a CMM3 (or a SyncInjector) on the power port. If an AP loses that and switches to on-board, and you're doing ABAB, it will be slightly out of sync with the opposite AP. I believe this is one of the benefits of the new frame alignment feature.
Why you need to know what sync input a radio is using I believe is because of hardware delays. And software is because of slight changes in the frame structure over the years.
Thanks for posting! You're right that this setting did not exist in the past, but due to an unfortunate bug in prior releases which has made it into the wild, the Frame Alignment Legacy Mode setting became necessary to minimize impact on customers who are in the process of upgrading older radios, or installing new radios with the latest software.
In order to incorporate major improvements to frame alignment made in the latest software releases, while still maintaining compatibility with software/hardware in the wild, we added Frame Alignment Legacy Mode to allow as much flexibility as possible. To achieve the most accurate frame alignment and multi-sync-source operation, the best option is to upgrade all radios that are colocated or have potential to interfere across service areas to the latest 13.4.1 open beta or 14.1.1 release software. Alternatively, if some radios cannot be upgraded at this time, Frame Alignment Legacy Mode will ensure optimal operation in a mixed software scenario by behaving as closely like previous builds as possible while allowing a slower rollout of upgrades.
As George mentioned, the lastest software, including the frame alignment improvements, should greatly improve performance overall, so we recommend upgrading wherever possible. Using the latest software also means you don't have to worry about the Frame Alignment Legacy Mode setting at all, once all colocated radios are up-to-date.
Regarding CMM3 and CMM4 timing differences, there is a slight (on the order of 15μs) difference in timing pulse propagation, which is far below the threshold where any impact would be seen.