1. GSM Architecture 1 1 1

2. Network Components
Switching System(SS)
Base Station System(BSS)

3. ( BSC A Interface A-bis interface OSS PSTN ISDN Data Networks
HLR
PSTN
ISDN B T S
MSC VLR
Data
Networks B T S
BSC
A Interface
A-bis interface
MSC VLR
Air interface

4. ERICSSON’S GSM SYSTEM ARCHITECTURE
BGW
SOG
OSS
ERICSSON’S GSM SYSTEM ARCHITECTURE
SCF
MIN
SDP
EIR
AUC
HLR
Switching System
ILR
MSC/VLR
DTI
SSF MC
(MXE)
GMSC
Other PLMNsz
ISDN
PSTN
Public Data
Networks

5. TRC
BSC
RBS
Base Station System

6. Basic or Additional Abbrev. System Full component name Platform Basic
MSC/VLR
GMSC
HLR
ILR
AUC
EIR
DTI
TRC
BSC
BTS
OMC
NMC MC
SSP
SCP
SDP
SOG
BGW SS
BSS
OSS
Mobile service Switching Center/Visitor Location Register
Gateway MSC
Home Location Register
Interworking Location Register
Authentication Center
Equipment Identity Register
Data Transmission Interface
TRanscoder Controller
Base Station Controller
Base Transceiver Station
Operation and Maintenance Center
Network Management Center
Message Center
Service Switching Point
Service Control Point
Service Data Point
Service Order Gateway
Billing Gateway
AXE
Unix/AXE
Unix
RBS
TMOS
MXE

7. Network Structure Cell
A cell is the basic unit of a cellular system and is defined as the radio coverage given by one BS antenna system.
Each cell is assigned a unique CGI.

8. Network Structure LOCATION AREA
A LA is defined as a group of cells.Within the network, a subsriber’s location is known by the LA which they are in.
The identity of the LA in which an MS is currently located is stored in the VLR. (LAI)

9. Cells & LA
LA2
LA3
LA1
VLR
LA6 C3
LA4 C2 C1
MSC C4 C5
LA5 C6
C=CELL

10. Network Structure MSC Service Area
An MSC Service Area is made up of LAs and represents the geographical part of the network controlled by one MSC.

11. MSC Service Area
LA2
LA3
LA1
VLR
MSC
LA4
LA6
LA5

12. Network Structure PLMN SERVICE AREA
A PLMN service area is the entire set of cells served by one network operator
and is defined as the area in which an operator offers radio coverage and access to its network.

13. PLMN Service Area I II V I
MSC
MSC
VLR
VLR
MSC
MSC
VLR
III IV

14. Network Structure GSM SERVICE AREA
The GSM service area is the entire geographical area in which a subscriber can gain access to a GSM network.

15. Relation between areas in GSM
Location Area
Cell
Location Area
MSC Service Area
PLMN Service Area
GSM Service Area

16. Mobile Station GSM MSs consist of: Mobile Equipment
Subscriber Identity Module

17. Functions of Mobile Station
Voice and data transmission& receipt
Frequency and time synchronization
Monitoring of power and signal quality of the surrounding cells
Provision of location updates even during inactive state

18. Mobile Station Discontinuous Transmission(DTX)
Discontinuous reception(DRX)
MS identified by unique IMEI
STAR#06#

19. SIM Fixed data stored for the subscription: IMSI,
Authentication Key, Ki
Security Algorithms:kc,A3,A8
PIN&PUK

20. SIM Temporary network data:
Location area of subscriber and forbidden PLMNs
Service data:
language preference, advice of charge

21. KEY TERMS An MS can have one of the following states :
Idle: the MS is ON but a call is not in progress.
Active: the MS is ON and a call is in progress.
Detached: the MS is OFF.

22. The following table defined the key terms used to describe GSM mobile traffic cases (there are no traffic cases in detached mode):
Mode
Term
Description
Idle
Registration
Roaming
International Roaming
This is the process in which an MS informs a network that it is attached.
When an MS moves around a network in idle mode, it is referred to as roaming.
When an MS moves into a network which is not its home network, it is referred to as international roaming. MSs can only roam into networks with which the home network has a roaming agreement.

23. Mode Term Description Active Location Updating Paging Handover
An MS roaming around the network must inform the network when it enters a new LA. This is called location updating.
This is the process whereby a network attempts to contact a particular MS. This is achieved by broadcasting a paging message containing the identity of that MS.
This is the process in which control of a call is passed from one cell to another while the MS moves between cells.

24. Network Identities
MSISDN
IMSI
TMSI
MSRN
IMEI

25. MSISDN Mobile Station ISDN Number 1 to 3 digits Variable Variable CC
The MSISDN is registered in the telephone directory and used by the calling party for dialing.
MSISDN shall not exceed 15 digits.
NDC--National Destination Code
SN--Subscriber Number
1 to 3 digits
Variable
Variable CC
NDC SN
MSISDN : not more than 15 digits

26. IMSI International mobile subscriber Identity
The IMSI is an unique identity which is used internationally and used within the network to identify the mobile subscribers.
The IMSI is stored in the subscriber identity module (SIM), the HLR, VLR database.

27. IMSI 3 digits MCC MNC MSIN 3 digits Not more than 9 digits NMSI
IMSI : Max. 15 digits
MCC--Mobile Country Code, MNC--Mobile N/W Code, MSIN--Mobile Station Identification Number
NMSI--National Mobile Station Identity,assigned by Individual Administration.
Mobile station Identification Number. It identifies the subs. In a PLMN. First 3 digit identifies the Logical HLR-id of Mobile subs.

28. Temporary Mobile subscriber Identity
TMSI is a temporary IMSI no. made known to an MS at registration.
The VLR assigns a TMSI to each mobile subscribers entering the VLR area.
Assigned only after successful authentication.
TMSI has only local significance i.e. within VLR area & controlled by the VLR.
TMSI changes on location updation.
TMSI is less than 8 digit.

29. MSRN Mobile Station Roaming Number
The MSRN is used in the GMSC to set up a connection to the visited MSC/VLR.
MSRN--is a temporary identity which is assigned during the establishment of a call to a roaming subs. CC SN
NDC
CC--Country Code, NDC--National Destination Code, SN– Servicing Node

30. IMEI International Mobile Equipment Identity
The IMEI is an unique code allocated to each mobile equipment. It is checked in the EIR.
IMEI check List
White List
Grey List
Black List

31. BASE STATION SYSTEM (BSS)
MSC/VLR
n BTS
BSC
BSS

32. FUNCTIONS OF BTS Radio resources Signal Processing
Signaling link management
Synchronization
Local maintenance handling
Functional supervision and Testing

33. FUNCTIONS OF BSC Radio Network management RBS Management TRC Handling
Tx. Network Management
Internal BSC O&M
Handling of MS connections

34. MSC-BSS Configurations
BTS
MSC A
BSS
A-bis
BTS
BTS
BSC
BTS
BTS
A-bis
BTS

35. Transcoder Configurations
64Kbps
16 Kbps
To MS
BTS
BSC
TRAU
MSC
To fixed networks
A-bis
Interface
To MS
BTS
BSC
TRAU
MSC
To fixed networks
RF Air Interface
A Interface
16 kbps transmission
64 kbps transmission
Transcoder (XC) configurations

36. Switching System (SS) SS7 Signalling Traffic Path MSC (PSTN) (BSS) D
VLR
HLR
AUC C F E
Other
MSC
EIR A
MSC
(PSTN)
(BSS)

37. MSC Functions Switcing and call routing Charging Service provisioning
Communication with HLR
Communication with VLR
Communication with other MSCs
Control of connected BSCs

38. MSC Functions Echo canceller operation control
Signaling interface to databases like HLR, VLR.
Gateway to SMS between SMS centers and subscribers
Handle interworking function while working as GMSC

39. VISITOR LOCATION REGISTER (VLR)
It controls those mobiles roaming in its area.
VLR reduces the number of queries to HLR
One VLR may be incharge of one or more LA.
VLR is updated by HLR on entry of MS its area.
VLR assigns TMSI which keeps on changing.
IMSI detach and attach operation

40. Data in VLR IMSI & TMSI MSISDN MSRN. Location Area
Supplementary service parameters
MS category
Authentication Key

41. Home Location Register(HLR)
Reference store for subscriber’s parameters, numbers, authentication & Encryption values.
Current subscriber status and associated VLR.
Both VLR and HLR can be implemented in the
same equipment in an MSC.
one PLMN may contain one or several HLR.

42. Home Location Register(HLR)
Permanent data in HLR
Data stored is changed only by commands.
IMSI, MS-ISDN number.
Category of MS ( whether pay phone or not )
Roaming restriction ( allowed or not ).
Supplementary services like call forwarding

43. Home Location Register(HLR)
Temporary data in HLR
The data changes from call to call & is dynamic
MSRN
RAND /SRES and Kc
VLR address , MSC address.
Messages waiting data used for SMS

44. EQUIPMENT IDENTITY REGISTER ( EIR )
This data base stores IMEI for all registered mobile equipments and is unique to every ME.
Only one EIR per PLMN.
White list : IMEI, assigned to valid ME.
Black list : IMEI reported stolen
Gray list : IMEI having problems like faulty software, wrong make of equipment etc.

45. AUthentication Center (AUC)
To authenticate the subs. attempting to use a network.
AUC is connected to HLR which provides it with authentication parameters and ciphering keys used to ensure network security.

46. AUC Functions
To perform subscriber authentication and to establish ciphering procedures on the radio link between the network and MS.

47. AUC Functions Information provided is called a TRIPLET consists of:
RAND(non predictable random number)
SRES(Signed response)
Kc(ciphering key)

48. Operations and Maintenance Centre OMC
The centralized operation of the various units in the system and functions needed to maintain the subsystems.
Dynamic monitoring and controlling of the network

49. Functions Of OMC -Configuration management
-O&M data function
-Configuration management
--Fault report and alarm handling
-Performance supervision/management
-Storage of system software and data