mobile and cellular communication
January 19, 2020
GSM SYSTEM ARCHITECTURE
GSM
SYSTEM ARCHITECTURE
· Mobile Station (MS)
Mobile Equipment (ME)
Subscriber Identity Module (SIM)
· Base Station Subsystem (BSS)
Base Transceiver Station (BTS)
Base Station Controller (BSC)
· Network Switching Subsystem(NSS)
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitor Location Register (VLR)
Authentication Center (AUC)
Equipment Identity Register(EIR)
· Operational Support Subsystem (OSS)
SYSTEM ARCHITECTURE MOBILE STATION (MS):
The Mobile Station is made up of
two entities:
1. Mobile Equipment (ME)
2. Subscriber Identity Module (SIM)
1. MOBILE EQUIPMENT (ME):
·
Portable, vehicle mounted, hand held device
·
Uniquely identified by an IMEI (International Mobile Equipment Identity)
·
Voice and data transmission
·
Monitoring power and signal quality of surrounding
cells for optimum handover
·
Power level : 0.8W – 20 W 160 character long
SMS.
2. SUBSCRIBER IDENTITY MODULE (SIM)
·
Smart card contains the International Mobile
Subscriber Identity (IMSI)
·
Allows user to send and receive calls and
receive other subscribed services
·
Protected by a password or PIN
·
Can be moved from phone to phone – contains key
information to activate the phone
SYSTEM ARCHITECTURE BASE STATION SUBSYSTEM (BSS):
·
Base Station Subsystem is composed of two parts
that communicate across the standardized Abis
interface allowing operation between components made by different suppliers
1.Base Transceiver Station (BTS)
2.Base Station Controller (BSC)
1. BASE TRANSCEIVER STATION (BTS):
·
Encodes, encrypts, multiplexes, modulates and
feeds the RF signals to the antenna.
·
Communicates with Mobile station and BSC
·
Consists of Transceivers (TRX) units
2. BASE STATION CONTROLLER (BSC):
·
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
·
It communicates with MSC and BTS
SYSTEM ARCHITECTURE NETWORK SWITCHING SUBSYSTEM(NSS)
Manages the switching functions of
the system and allows the MSCs to communicate with other networks such as PSTN
and ISDN. It consist of
1. MOBILE SWITCHING CENTER (MSC)
·
Heart of the network
·
Manages communication between GSM and other
networks
·
Billing information and collection
·
Mobility management
-Registration
-Location Updating
-Inter BSS and inter MSC call handoff
2. HOME LOCATION REGISTERS (HLR)
·
Stores information about each subscriber that belongs
to it MSC in permanent and temporary fashion.
·
As soon as mobile subscriber leaves its current
local area, the information in the HLR is updated.
·
database contains IMSI, IMSISDN, prepaid/
postpaid, roaming restrictions, supplementary services.
3. VISITOR LOCATION REGISTERS (VLR)
·
Temporary database which updates whenever new MS
enters its area, by HLR database
·
Assigns a TMSI to each MS entering the VLR area
which keeps on changing.
·
Controls those mobiles roaming in its area o
Database contains IMSI, MSISDN, Location Area, authentication key
4. AUTHENTICATION CENTER (AUC)
·
Contains
the algorithms for authentication as well as the keys for encryption.
·
Protects
network operators from fraud.
·
Situated
in special protected part of the HLR.
5. EQUIPMENT IDENTITY REGISTER (EIR)
·
Stores
all devices identifications registered for this network.
·
Database
that is used to track handsets using the IMEI (International Mobile Equipment
Identity)
·
Prevents
calls from stolen, unauthorised or defective mobile devices
OPERATIONAL SUPPORT SUBSYSTEM (OSS):
It supports the operation
and maintenance of GSM and allows system engineers to monitor, diagnose and
troubleshoot all aspects of GSM system. It supports one or more Operation
Maintenance Centres (OMC) which are used to monitor the performance of each MS,
Bs, BSC and MSC within a GSM system. It has three main functions:
• To maintain all
telecommunication hardware and network operations with a particular market.
• To manage all charging and billing procedures
• To manage all mobile equipment in the system.
Interfaces used for GSM network: (fig
2)
1)UM Interface -Used to communicate
between BTS with MS
2)Abis Interface- Used to
communicate BSC TO BTS
3)A Interface-- Used to communicate
BSC and MSC
4)Singling protocol (SS 7)- Used to
communicate MSC with other network.
