Network Switching Subsystem (NSS), handels the switching of GSM calls between external networks and the BSCs in the radio subsystem. This system is responsible for managing and providing external access to the several customer database. NSS is one of the most important part of GSM architecture. The major parts of Network Switching Subsystem are MSC (Mobile Switching Centre) and the database which includes HLR ( Home Location Resistor), VLR (Visitor Location Register). Here in this, you will find Wireless Communication Notes on Network Switching Subsystem in GSM Network in detail to understand the concept in a better way.
Block Diagram in GSM Architecture including Network Switching Subsystem:
Mobile Switching Centre ( MSC) :
The MSC is the most central unit in the NSS and thus MSC is responsible for controlling the traffic among all of the present BSCs. A MSC is the hardware part of any wireless communication switch which communicate with the PSTN switch using signalling system-7 protocol. In addition to this with all other MSCs in the coverage of a service provider.
MSC is responsible for
- Mobility management and Registration.
- Location Updating Process.
- Interconnecting BSS and MSC call handoff situations.
Data Base in NSS
There are basically three database in the NSS Network Switching Subsystem of GSM Network
- Home Location Resistor
- Visitor Location Register
- Authentication Centre
Home Location Resistor:
It is abbreviated as HLR, it is the database which is responsible for containing the subscriber information and location information for each user who reside in the same city as the city of the MSC. Each subscriber is assigned a Unique International Identity (IMSI) and this is the number which is used to identify the home user. We can say that HLR is the person using the mobile in the local area .
Visitor Location Register:
VLR is the database which temporaraily stores the IMSI an customer information for each roaming subscriber who is visiting the coverage information for each and a particular MSC. The VLR is linked between several adjoining MSCs in a particular market or a geographical n/w that contain the particular information of every visiting user in that area.
Once a roaming mobile is logged in the VLR, the MSC sends the necessary information to the visiting subscriber’s HLR so that calls to the roaming mobile can be appropriately routed over the PSTN by the roaming user’s HLR.
The Authentication centre is a strongly protected database that is responsible for handling the authentication and encryption keys for every single subscriber in the HLR and VLR. The Authentication center contains a register called Equipment Identity Register (EIR) which is the identification stolen which is used to transmit identity of data that does not match with the information containing the HLR or VLR.
Equipment Identity Register
This database is used in NSS in order to track the handsets using the IMEI (International Mobile Equipment Identity) number. EIR is made up of three sub-classes:
- The White List
- The Black List
- The Gray List
There are only one EIR (Equipment Identity Register) present in the set as per PLMN.
- Handover Mechanism in GSM Cellular System
- Important questions on GSM
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