IMSI and TMSI are two of the many different types of identifiers used in global system for mobile (GSM) communications.
IMSI (International Mobile Subscriber Identity) is an international subscriber identity used only by the network. Each registered user is uniquely identified by ISMI which is stored in subscriber identity module (SIM)
TMSI (Temporary Mobile Subscriber Identity) covers IMSI to prevent over-the-air interception and tracing. A visitor location register (VLR), which is responsible for current location of the subscriber can assign TMSI, which has only local significance in the area handled by VLR. This allows unique identification of a subscriber using a combination of TMSI and current location area.
what is pmln? what is its function where it is to be used