GSM, GPRS, 3G, 4G (LTE), etc.. is built around signalling and State/Entity
Functions. As a result of a request an entity will move from one
state to another in a well defined sequence. In order for this to happen
timers must be used and supported. 3GPP has a lot of specified Timers that are required
for the system to work in a well co-ordinated manner.