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Education
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The GSM Network Architecture can be divided into 4 parts:
• The Mobile Station (MS)
• The Base Station Subsystem (BSS)
• The Network and Switching Subsystem (NSS)
• The Operation and Support Subsystem (OSS)
GSM Network Architecture
MSC
VLR
AuC
EIR
HLR
MSBTS
OSS
BSC
PSDN
ISDN
PSTN
PLMN
BSSNSS
Abis interface A interfaceUm interface
Mobile Station
A Mobile Station consists of two main elements:
• The Mobile Equipment or terminal
• The Subscriber Identity Module (SIM)
The Terminal
• Portable, vehicle mounted or fixed, hand helddevice
• Uniquely identified by an IMEI (InternationalMobile Equipment Identity)
• Voice and data transmission
• Monitoring power and signal quality ofsurrounding cells for optimum handover
• Power level : 0.8W – 20 W
The SIM
• Smart card contains the International Mobile Subscriber Identity (IMSI)
• Allows user to send and receive calls and receive other subscribed services
• Normally 25 by 15 millimeters
• Protected by a password or PIN
• Can be moved from phone to phone –contains key information to activate the phone
The Base Station Subsystem
• The BSS connects the MS and the NSS.
It is in charge of the transmission and
reception. The BSS can be divided into
2 parts:
a. The Base Transceiver Station (BTS)or
Base Station
b. The Base Station Controller (BSC)
The Base Transceiver Station
• Contains the equipment for
transmitting and receiving of radio
signals (transceivers), antennas, and
equipment for encrypting and
decrypting communications with the
BSC
• Usually placed in the center of the cell
The Base Station Controller
• Manages Radio resources for BTS
• Assigns Frequency and time slots for all MS’s in its area
• Handles call set up
• Handover for each MS
• Radio Power control
• It communicates with MSC and BTS
• Frequency hopping
The Network and Switching Subsystem
The Network and Switching Subsystem
• manage the communications between the
mobile users and other users, such as
mobile users, ISDN (Integrated Services
Digital Network) users, fixed telephony
users, etc.
• it also includes data bases needed in
order to store information about the
subscribers and to manage their mobility.
Components of the NSS
Mobile Services Switching Center (MSC)
• Heart of the network
• Manages communication between GSM and other networks
• Call setup function and basic switching
• Call routing
• Billing information and collection
• Mobility management
- Registration
- Location Updating
- Inter BSS and inter MSC call handoff
• MSC does gateway function while its customer roams to other network by using HLR/VLR.
Gateway Mobile Services and Switching Center (GMSC)
• Gateway – is a node connecting two
networks.
• The interface between the mobile
cellular network and the PSTN
• Is in charge of routing calls
Home Location Register (HLR)
• Permanent database about mobile subscribers in a large service area (generally one per GSM network operator)
• Database contains:
IMSI (International Mobile Subscriber Identity)
MSISDN (Mobile Subscriber Integrated Services Digital Network Number)
prepaid/postpaid roaming restrictions
supplementary services
Visitor Location Register (VLR)
• Temporary database which updates whenever new MS enters its area, by HLR database
• Controls those mobiles roaming in its area
• Reduces number of queries to HLR
Authentication Center (AuC)
• Protects against intruders in air interface
• Maintains authentication keys and algorithms and provides security triplets. (Ki, Kc, etc.)
• Generally associated with HLR
Equipment Identity Register (EIR)
• Also used for security purposes
• Is a register containing information
about the mobile equipments
• A terminal is identified by its
International Mobile Equipment Identity
(IMEI)
• Forbids calls from unauthorized
terminals
GSM Interworking Unit
• Corresponds to an interface to various
data communications
• During these communications, the
transmission of speech and data can
be alternated
The Operation and Support Subsystem
Operation and Support Subsystem
• Is connected to the different components
of the NSS and BSC, in order to control
and monitor the GSM system
• Is also in charge of controlling the traffic
load in the BSS
• However, the increasing number of base
stations has provoked that some of the
maintenance tasks be transferred to the
BTS