Mobile networks

A mobile network is composed by the following parts:

Mobile Station (MS):

the mobile equipment (Ex: phone)
the SIM (Subscriber identity Module) card that uniquely identified the card by the IMSI (International Mobile Subscriber Identity).

The base station subsystem (BSS):

base station (BTS) - it defines a cell in the network
base station controller (BSC) - controls a group of BTSs. Does handoffs, frequency hoppings, exchange functions and power control over each managed BTS

The network and switching subsystem(NSS)

Home location register (HLR)
- holds all subscribers in a network.
- keeps subscriber specific information like MSISDN, IMSI, current location of the MS, roaming restrictions, additional features.
Authentication Center (AuC)
- handles the authentications and encryption in a network.
- it is typically located with the HLR
Equipment inquiry register (EIR)
- tracks of handsets on the network using the International Mobile Equipment Identity (IMEI).
- there is only one EIR per network.
- It is composed of three lists. The white list, the gray list, and the black list.
Mobile switching center (MSC)
- handles call routing, call setup, and basic switching functions.
- does inter BSC handoffs and coordinates inter MSC handoffs
GMSC
Visitor location register (VLR)
- is associated a local area(LA).
- Keeps information similar to the one in the HLR for the users in it's current local area