7 Network Functions

If the mobile starts a call, its position and the serving BS are known as the latter is contacted by the MS for connection setup. After the MS requests a call service, authentication and ciphering are initiated and a new TMSI is provided. The information about the called party are transferred in ciphered mode. The MSC assigns a dedicated channel (this is when you hear the first ringtone) and finds a route to the called party (this is when the first ringtone is sent there, this may be later as at the MS).