Yes as described the mast is in charge. It measures your signal quality and puts you on the one most likely to give you a usable signal. It does not care about internet speed.
Carrier Aggregation only activates when the mast allows. (4G+ as you see it)
If that's the case and all the device is doing is looking for is signal quality then why does what I describe above work, and work every time?
Leaving the device alone after switching on / restarting can lead to CA never being activated, or taking many hours. I am not saying it's the device that is deciding to give CA / 4g+, however it's the device choosing to stay on a band 20 cell where CA will never work until the device switches to the band 3 cell.
By example my closest cell gives an RSRP of -90db / 5 bars but on band 20. Where as the cell further away gives a RSRP of -103db or worse however is on band 3.
Yet, as above if you disconnect the B525 for 30secs (using router page not by turning device off) then reconnect to network the device switches to the "poorer" strength signal and quality cell (neighbouring)l which has band 3. As soon as it hits this cell with band 3 then CA is activated by that cell site.
I think the B525 simply goes for the strongest signal upon start up. When disconnected from network it must free up resources on the device to do further computation. I think it's likely that it uses this time to work out if neighboring cell sites have better bandwidth available which still fall within whatever pre-programmed upper and lower control limits it wants to accept. The device clearly has say on which cell it connects to, and must be using some internal logic to move over to a poorer cell site that will support ultimately better throughput.
IMO it's likely the B535 has a better processor and can do this computation quicker and thus move over to a more suitable "better" cells far quicker. It seems to me that if the B525 doesn't have available resource to process the base station & cell data within a couple of seconds of starting up it just gives up. Doing what I said seems to kick the B525 in to having another go working out the "best" cell where multiple are available.
Edited by gary333 (Mon 16-Dec-19 22:05:22)