2G architecture

I'm gonna talk about the architectures of 2G, 3G and 4G one by one. I skipped 1Gs architecture since it's already extinct so there is no reason to talk about it. 2G is called GSM which stands for Global System for Mobile Communication.

GSM provides recommendations, not requirements. The GSM specifications define the functions and interface requirements in detail but don't address the hardware. The GSM network is divided into three major parts:

- Switching System (SS)

-Base Station System (BSS)

-Operation and Support System (OSS)

The basic GSM network elements are shown in the above figure. Now, I will talk briefly about each main part. The switching system is responsible for performing call processing and subscriber-related functions. It includes the following functional units:

- Mobile Services Switching Center (MSC):

The MSC performs the telephony switching functions of the system. It also performs such functions as toll ticketing, network interfacing, common channel signalling, and others.

- Gateway Mobile Switching Center (GMSC):

A gateway mobile services switching center (GMSC) is a node used to interconnect two networks.

- GSM Interworking Unit (GIWU):

The GIWU consists of both hardware and software that provides an interface to various networks for data communications. Through the GSM interworking unit (GIWU), users can alternate between speech and data during the same call.

- Message Center (MXE):

The MXE is a node that provides integrated voice, fax, and data messaging.

- Mobile Service Node (MSN):

The MSN is the node that handles the mobile intelligent network (IN) services.

- Home Location Register (HLR):

The HLR database is used for storage and management of subscriptions. The home location register stores permanent data about subscribers, including a subscriber's service profile, location information, and activity status.

- Visitor Location Register (VLR):

The VLR database contains temporary information about subscribers that is needed by the mobile services switching center (MSC) in order to service visiting subscribers. When a mobile station roams into a new mobile services switching center (MSC) area, the visitor location register (VLR) connected to that MSC will request data about the mobile station from the HLR, reducing the need for interrogation of the home location register (HLR).

-Authentication Center (AUC):

The AUC provides authentication and encryption parameters that verify the user's identity and ensure the confidentiality of each call. The authentication center (AUC) also protects network operators from fraud.

-Equipment Identity Register (EIR):

The EIR database contains information on the identity of mobile equipment to prevent calls from stolen, unauthorized or defective mobile stations.

The base station system is responsible for performing all radio-related functions. It includes the following functional units:

- Base Station Controller (BSC):

The BSC provides the control functions and physical links between the MSC and BTS. It provides functions such as handover, cell configuration data and control of RF power levels in base transceiver stations. A number of BSCs are served by a MSC.

- Base Tranceiver Station (BTS):

The base transceiver station (BTS) handles the radio interface to the mobile station. The base transceiver station is the radio equipment (transceivers and antennas)

The Operation and Support System (OSS) is is the functional entity from which the network operator monitors and controls the system. The purpose of operation and support system is to offer support for centralized, regional, and local operational and maintenance activities that are required for a GSM network.

The GSM mobile station (or mobile phone) communicates with other parts of the system through the base-station system.