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The Mobile services Switching Center (MSC)
It is the central component of the NSS. The MSC
performs the switching functions of the network. It also
provides connection to other networks.
The Gateway Mobile services Switching Center (GMSC)
A gateway is a node interconnecting two networks.
The GMSC is the interface between the mobile cellular
network and the PSTN. It is in charge of routing calls
from the fixed network towards a GSM user. The
GMSC is often implemented in the same machines as
the MSC.
The Network and Switching Subsystem
Like a normal PSTN/ISDN switch with added mobile functionality:
- (^) Registration
- (^) Authentication
- (^) Location updating
- (^) Handovers
- (^) Integrates VLR
- (^) Call routing to roaming sub…
Mobile Switching Center - MSC
MSC is the interface which interconnects various BSCs The functionality of the MSC is to perform switching MSC handles various databases for operational management
Home Location Register - HLR
IMSI 1^9848922122 /^ Paul^ /^ SS – Code / NRU^ /^ HYD - 100111001
9848923415 / Dubey / SS – Code / IRU / BLR - 010010001
IMSI 3 ---------^ ----------^ ----------^ ---------^ -----------^ --------
MSISDN / User Details /Access List / Address of Current VLR
IMSI 2
IMSI Number The HLR is considered as a very important database that stores information of the subscribers belonging to the covering area of a MSC. It also stores the current location of these subscribers and the services to which they have access. The location of the subscriber corresponds to the SS address of the Visitor Location Register (VLR) associated to the terminal.
BSC MSC
HLR VLR EIR AC BSC MSC
GMSC PST
N PST N Um Um Abis A
GSM - Architecture
BTS BTS VLR – Visitor Location Register VLR
The VLR contains information from a subscriber's
HLR necessary in order to provide the subscribed
services to visiting users. When a subscriber
enters the covering area of a new MSC, the VLR
associated to this MSC will request information
about the new subscriber to its corresponding
HLR. The VLR will then have enough information
in order to assure the subscribed services without
needing to ask the HLR each time a
communication is established.
The VLR is always implemented together with a
MSC; so the area under control of the MSC is
also the area under control of the VLR.
Visitor Location Register - VLR
BSC MSC
HLR VLR EIR AC BSC MSC
GMSC PST
N PST N Um Um Abis A
GSM - Architecture
BTS BTS EIR – Equipment Identification Register EIR
BSC MSC
HLR VLR EIR AC BSC MSC
GMSC PST
N PST N Um Um Abis A
GSM - Architecture
BTS BTS AC – Authentication Center AC
Authentication Center - AC
IMSI 1 SIM / Ki / Kc / A3 / A8……
IMSI 2 SIM / Ki / Kc / A3 / A8……
IMSI 3 SIM / Ki / Kc / A3 / A8……
IMSI 4 SIM / Ki / Kc / A3 / A8……
IMSI (^) Authentication Codes The AuC register is used for security purposes. It provides the parameters needed for authentication and encryption functions. These parameters help to verify the user's identity.
BSC MSC
HLR VLR EIR AC BSC MSC
GMSC PST
N PST N Um Um Abis A
GSM - Architecture
BTS BTS PSTN - The PSTN Gateway (eg., 091 for India)
The Operations and Maintenance Center (OMC) is the centralized maintenance and diagnostic heart of the Base Station System (BSS). It allows the network provider to operate, administer, and monitor the functioning of the BSS. Operations and Maintenance Center - OMC
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