Additional Disclaimers: There is no specific answer to what constitutes a successful connection. It is possible to disconnect with green (high) values – or connect with red (low) values for several reasons, including:
Modems may vary.
Not all modems have the same ranges of acceptable values, which can affect your connection.
You must factor in both signal strength and signal quality.
It is possible to have excellent RSSI but disconnect because of poor quality (and vice versa).
Signal strength and signal quality values do not hold constant.
The variance of a signal is a significant factor in the success of a connection. A particular reading represents one moment, but these values may vary dramatically over time. A stable connection requires consistency. This sample graph of RSSI values shows how much the values can jump (from https://cradlepointecm.com):
Environmental factors can affect all of the above values.
Everything from other network hardware to heavy machinery to the weather can have any affect on RSSI, SINR, Ec/Io, RSRP, and RSRQ.
Other factors can cause issues, such as tower load, signal going through a repeater or booster, and so on.
Some factors that don't show up in the signal strength and quality values can greatly impact a connection.