Inline > On Jan 22, 2016, at 12:02 AM, George Skorup <[email protected]> wrote: > > Sounds like you mean that sector's frame timing is drifting? I haven't seen > that. But I have seen sectors go nuts where all of the SMs show 12dB SNR and > MIMO-A downlink. For no reason. Reboot the AP and it's gone. >
I do think the sector’s frame timing is drifting. The end result is exactly the same thing you are seeing - all the SM end up with low SNR and MIMO-A. Reboot it and it goes away for 8 to 12 hours before it’s back. It truly smells like timing drift. I don’t think it keeps drifting though - I think the AP works it’s way off to some sort of offset limit on the timing and then sits there. Cambium was playing around with something in the software with a ‘debounce timing’ that (I think) compared the incoming pulse with the internal clock for a sanity check and then rejected pulses outside the window. I’m not sure they didn’t end up putting some type of averaging or compensating calculation in that might be ending up working it’s way to a limit. > On full cluster sites, we're using SyncInjectors, and only SyncInjectors. > I.E. I disable the on-board and timing ports on all sectors. If the sync > pulse from the injector drops, oh well. FreeRun is a PITA especially with LBT. That’s my usual practice, for the same reasons. > > And I've said this many, many times. There's a difference between the > on-board GPS which is CMM4 aligned and PacketFlux stuff which is CMM3 > aligned. The frames don't match when you have a mix of this in a cluster. I don’t have any way to measure the on-board timing pulse so I can’t say where it’s at relative to a sync injector, but I am getting very good performance with the north AP on the same frequency as the south with one on a SyncInjector and the other on internal GPS. SNR on both sectors is stable and modulation is where I expect it to be. > > It's very obvious when this problem crops up. The AP session list shows most > SMs sitting at 8X/1X. And sessions with HP show the normal VC as 8X/1X, HP VC > as 1X/1X. Yep > > I know at one site in particular, the SyncInjector doesn't show any 1PPS > active events, yet the APs show a few inSync and outSync counts. Those could > be actual losses in timing, but Forrest said it needs to see something like > 3-4 in a row before it's logged in the event counter. However, at another > site, the timing is very stable and the APs show zero outSync and one inSync > count. But weird things are still happening. Same - the SyncInjector logs don’t show anything unusual, nor does the AP. > > Another thing I've noticed is that a loss in the sync pulse doesn't always > show up in the AP event log. Or I'll see a loss message, but no acquired > message after that. > > And I've been seeing this weird stuff for well over a year. I just don't know > what else to do. CMMs, CTMs and new radios do not fit in the budget. Using the internal GPS isn’t a viable permanent solution for this, but it’s working for the moment, and I have not seen a recurrence of the problem in a week. I’m going to try a CMM to see if it makes any difference, and if that fails I’ll probably resort to dragging a timing port device up there and using that. Mark
