GSM - Architecture
A GSM network consists of several functional entities, whose functions and interfaces are defined. The GSM network can be divided into following broad parts.
Following is the simple architecture diagram of GSM Network:
The added components of the GSM architecture include the functions of the databases and messaging systems:
- Home Location Register (HLR)
- Visitor Location Register (VLR)
- Equipment Identity Register (EIR)
- Authentication Center (AuC)
- SMS Serving Center (SMS SC)
- Gateway MSC (GMSC)
- Chargeback Center (CBC)
- Transcoder and Adaptation Unit (TRAU)
Following is the diagram of GSM Netwrok along with added elements:
The MS and the BSS communicate across the Um interface, also known as the air interface or radio link. The BSS communicates with the Network Service Switching center across the A interface.
GSM network areas:
In a GSM network, the following areas are defined:
Cell: Cell is the basic service area: one BTS covers one cell. Each cell is given a Cell Global Identity (CGI), a number that uniquely identifies the cell.
Location Area: A group of cells form a Location Area. This is the area that is paged when a subscriber gets an incoming call. Each Location Area is assigned a Location Area Identity (LAI). Each Location Area is served by one or more BSCs.
MSC/VLR Service Area: The area covered by one MSC is called the MSC/VLR service area.
PLMN: The area covered by one network operator is called PLMN. A PLMN can contain one or more MSCs.