GSM Architecture-The Network Switching Subsystem (NSS) - GSM

What is Network switching subsystem?

Network switching system (NSS) is the main component of the Mobile Switching Center (MSC). It deploys the switching of calls between the mobile and other fixed or mobile network users, along with the management of mobile services like authentication.

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Switching system will include below functional elements:

Home Location Register (HLR)

HLR is a database which is used for storing and managing subscriptions. HLR is a popular database as it is used for storing permanent data about subscribers, like a subscriber's service profile, location information, and activity status. When a person subscribes in the form of SIM, then all the information about this subscription will be registered in the HLR of that operator.

Mobile Services Switching Center (MSC)

MSC is known as the Central component of the Network Subsystem. MSC will perform the switching of calls between the mobile and other fixed or mobile network users, as well as management of mobile services such as registration, authentication, location updating, handovers, and call routing to a roaming subscriber. It also facilitates various functions as toll ticketing, network interfacing, common channel signaling, and others. MSC can be identified with a unique ID

Visitor Location Register (VLR)

VLR is known as a database which includes temporary information about the subscribers required by the MSC to serve the visiting subscribers. VLR is always combined with MSC. When a mobile station roams into a new MSC area, VLR connected to that MSC requests data about the mobile station from HLR. Later, if the mobile station makes a call, VLR will have the information required for call setup without having to investigate HLR each time.

Authentication Center (AUC)

Authentication Center is a protected database which is used for storing a copy of the secret key stored in each subscriber's SIM card. It is used for authentication and ciphering of the radio channel. AUC will protect the network operators from different types of fraud found in today's cellular world.

Equipment Identity Register (EIR)

Equipment Identity Register (EIR) is also known as a database which includes a list of all valid mobile equipment on the network, where its International Mobile Equipment Identity (IMEI) identifies each MS. An IMEI will be marked as invalid if it is reported stolen or is not type approved.

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