Your SIM is designed to connect to the best available network. However, any endpoint's connectivity will affect the ability of the SIM to establish a successful connection with a network operator or will be disconnected if there is a network coverage issue (for example, poor/weak signal, a dead spot which can be encountered commonly when a device is moving). In order to give you a better understanding of how it really works, our SIM is not the one which is getting the signal instead it is the RF module of the device. The SIM is just small apparatus with a DB in it which store the profiles that will help the device to register to a network. Also, our SIM depends on the behavior of the device.
Criteria when to Blacklist the operator
If the network operator has a weak coverage signal on the location of device.
If It has a network outage.
No roaming agreement between SAP Digital Interconnect and MNO.
No agreement between SAP Digital Interconnect and Channel Partners (IMSI not supported).
Symptoms in UI events that denotes unstable network
Frequent disconnection of PDP context such create PDP and delete PDP (Only if the device is not moving or in one place)
Established PDP but no data session.
Took long to initiate create PDP.
Shahzad Ismail Head of Knowledge Management and Community Engagement, Sinch