= GSM =

GSM or the global system for mobile communications is a standard developed to
standardize cellphones and their communication and infrastructure.

== IMSI ==

International Mobile Subscriber Identity is a way for devices to id themselves
on a GSM network. An IMSI is a secret key that is stored on the SIM card.

=== IMSI catcher ===

A spoofed GSM tower. In GSM the base station (tower) picks all settings
including Tx power, Rx gain, encryption, etc