GSM System Architecture by BSNL(Bharat Sanchar Nigam Limited)
Comments
Content
Cellular Mobile Communication System
DGM(BSS), BSNL
15-Feb-06
1
GSM
Global System for Mobile Communication
DGM(BSS), BSNL
15-Feb-06
2
PART-I : Brief History of GSM
PART-II : GSM Architecture
DGM(BSS), BSNL
15-Feb-06
3
History of GSM
Date Activities of development of Mobile Communication 1982 Conference Europeenne des postes et Telecommunication – (CEPT)began specifying a European digital telecommunications 1985 standard in the 900 MHz frequency band. This standard later became known as Global System for Mobile Communication (GSM) 1986 Field tests were held in Paris to select which digital transmission technology to use. The choice was TDMA or FDMA 1987 A combination of TDMA and FDMA was selected as the transmission technology for GSM Operation from 12 countries signed a Memorandum of understanding committing themselves to introducing GSM by 1991. 1988 CEPT began producing GSM specifications for a phased implementation.Another five countries signed the MOU
DGM(BSS), BSNL
15-Feb-06
4
History
Date 1989 1990 1991 1992 Activity European Telecommunication Standards Institute (ETSI) took over responsibility for GSM Phase 1 specifications were frozen to allow manufacturers to develop network equipment. The GSM 1800 standard was released. An addendum was added to the MoU allowing Countries outside CEPT to sign. Phase 1 specifications were completed. First commercial Ph-I GSM networks were launched. The first international roaming agreement was established between Finland & Vodafone in UK. Australia becomes the first non-European country to sign the MoU. The first commercial DCS 1800 system was launched in UK
1993
DGM(BSS), BSNL
15-Feb-06
5
History
Date 1995 Activity The specification for Personal Communication Services (PCS) was developed in USA. This version of GSM operates at 1900MHz The first GSM 1900 system became available. These comply with the PCS 1900 standerd. At the beginning of 1998 the MoU has a total of 253 members in over 100 countries and there are over 70 million GSM subscribers worldwide. GSM subscribers account for 31% of the world’s mobile market
1996 1998
DGM(BSS), BSNL
15-Feb-06
6
GSM Specifications
• Designed to be Platform- Independent • Specify Network functions & Interfaces in details, not Actual Hardware requirements • Allows hardware manufacturers to be creative in providing actual functionality. • Allows operators to buy equipment from different suppliers.
DGM(BSS), BSNL
15-Feb-06
7
GSM SPECIFICATIONS
Recommended by Groups organized by ETSI
System Frequecies: Wave Length Bandwidth Duplex Distance Carrier Separation Radio Channels Transmission Rate P-GSM 900 UP Link : 890-915 MHz, Down Link : 935-960 MHz ~ 33 cm 25 MHz 45 MHz 200 KHz 125 270 Kbits/s (Over Air Interface)
PART - II :GSM Architecture
It Includes following Subsystems: 1. Switching Subsystem(SS) is responsible for
performing switching functions related to call processing & Subscriber related functions.
2. Radio Subsystem includes the equipments and
functions related to the management of the connections on the radio path. It performs all radio related functions
3. Operations and Maintenance subsystem
includes the operation and maintenance of GSM equipment for the radio and network interface.
DGM(BSS), BSNL 15-Feb-06 10
Network Architecture
OMC
OSS EIR
B T S B T S
SS
AUC
HLR PSTN ISDN
MS
BSC BSC
GMSC/VLR
Data Networks
B T S
BSS
15-Feb-06
MSC
Air interface
DGM(BSS), BSNL 11
Architecture of the GSM system
• Several providers setup mobile networks following the GSM standard within each country • Components
– – – – MS (mobile station) BS (base station) MSC (mobile switching center) LR (location register)
• Subsystems
– RSS (radio subsystem): covers all radio aspects
• Base station subsystem
– NSS (network and switching subsystem): call forwarding, handover, switching DGM(BSS), BSNL 15-Feb-06 – OSS (operation subsystem): management of the
12
GSM: system architecture
radio subsystem MS MS Um BTS BTS Abis BSC SS7 MSC ISDN PSTN network and switching subsystem Fixed partner networks
EIR HLR
BTS BTS BSC A BSS MSC IWF
VLR ISDN PSTN PDN
Radio subsystem
radio subsystem MS MS Um BTS BTS Abis BSC MSC
• network and switching subsystem
Components
– MS (Mobile Station) – BSS (Base Station Subsystem): consisting of
• BTS (Base Transceiver Station): sender and receiver • BSC (Base Station Controller): controlling several transceivers
•
BTS BSC BTS BSS A MSC
Interfaces
– Um : radio interface – Abis : standardized, open interface with 16 kbit/s user channels – A: standardized, open interface with 64 kbit/s user channels
Network Subsystems
1. Network Subsystem(NSS) includes the equipments and functions related to end-to-end call. 2. Base Subsystem(BSS) includes the equipments and functions related to the management of the connections on the radio path. 3. Operations and Maintenance subsystem(OMC) includes the operation and maintenance of GSM equipment for the radio and network interface.
DGM(BSS), BSNL 15-Feb-06 15
SS Components:
• • • • • Mobile Services switching Center (MSC) Home Location Register (HLR) Visitor Location Register (VLR) Authentication Center(AUC) Equipment Identity Register(EIR)
DGM(BSS), BSNL
15-Feb-06
16
BSS Components:
• Base Station Controller (BSC) • Base Transceiver (BTS)
DGM(BSS), BSNL
15-Feb-06
17
GSM Network Structure
• • • • • GSM Service Area PLMN Service Area MSC Service Area Location Area Cells
DGM(BSS), BSNL 15-Feb-06 18
GSM
PLMN Service Area
I MSC VLR VLR MSC III IV VLR II MSC VLR
MSC
DGM(BSS), BSNL
15-Feb-06
19
GSM
MSC Service Area
LA2 LA1 VLR MSC LA3
LA4
LA6 LA5
DGM(BSS), BSNL
15-Feb-06
20
GSM
Cells
LA2 LA1
MSC/VLR
LA3 C2 C7 C3 C1 LA5 C4 C5 C=CELL C6
LA6
LA4
DGM(BSS), BSNL
15-Feb-06
21
GSM
Relation between areas in GSM
Cell Location Area Area served by a BTS Location Area MSC Service Area PLMN Service Area GSM Service Area
DGM(BSS), BSNL 15-Feb-06 22
Typical Engineering Groups and Activities
Marketing
RF Design & Planning OMC/NMC O&M Engineering
Customer Care
Optimization Quality Assurance Switching Operations
Site Planning
Faults Management
BTS Maintenance
Statistics Analysis
Performance Verification
Maintenance
Core Design
Statitics Generation
Air Interface Troubleshooting
RF Tests
Benchmarking
Planning
RF Planning
Databse Management
RF and Parametric Tuning
Transmission
Implementing Changes
DGM(BSS), BSNL 15-Feb-06
Value Added Services
23
RF Planning and Design – Site Planning
Reject Acquire
Action Steps
Search Area Selection Site Physical Qualification
Site Planning
Test Transmission
DGM(BSS), BSNL
Band Clearance
15-Feb-06
Coverage Prediction
24
RF Planning and Design – Frequency Planning
GSM uses concept of cells One cell covers small part of network Network has many cells Frequency used in one cell can be used in another cells This is known as Frequency Re-use
F4 F3 F1 F4 F3 F1 F2 F2
Interference
Interference in GSM systems are classified into three major categories . Co-Channel Interference Adjacent Channel Interference External Interference
DGM(BSS), BSNL
15-Feb-06
26
Co - Channel interference
Interference on a channel caused by another cell/mobile using the same frequency. C/Ic is the measure of co-channel interference GSM specifies the C/Ic threshold of 9dB for a service quality of 0.4% BER. 9db also includes 2db implementation margin 9db is decided considering the implementation of Synthesised Frequency Hopping Without SFH, the preferred threshold is 12 dB.
C / Ic 9 db
Ic
C
DGM(BSS), BSNL
15-Feb-06
27
Co-Channel Interference
Noise
C
Ic
ARFCN "N"
ARFCN "N"
Causes
Distant Cells due to tight frequency re-use patterns. Distant Cells due to errors in frequency planning. Mulitpath from Distant cells( strong reflector, Water). C/Ic will degrade the Ec/No, so if Noise floor itself is high, then even a high value of C/Ic can deteriorate quality.
DGM(BSS), BSNL 15-Feb-06 28
Adjacent Channel Interference
Interference caused when wanted and unwanted GSM RF channels co-exist.
Ia C
GSM receivers are designed for an Adjacent Channel Suppression of minimum 18db at an offset of 200 Khz, 50db at 400 Khz and 58db at 600 Khz.
DGM(BSS), BSNL
15-Feb-06
29
GSM LA Coding
MCC 3 digit
MNC 3 digit LAI
LAC 2 Octets
DGM(BSS), BSNL
15-Feb-06
30
GSM Functions of Mobile Station
• Voice and data transmission • Frequency and time synchronization • Monitoring of power and signal quality of the surrounding cells • Provision of location updates even during inactive state • Equalization of multi path distortions
DGM(BSS), BSNL 15-Feb-06 31
GSM Mobile Station
• Portable, vehicle mounted, hand held • MS identified by unique IMEI (*#06#) • Shall display at least last ten received, dialled and missed calls • Minimum talk time of 1hr 30 min. and standby time of 80 hrs
• 160 characters long SMS
DGM(BSS), BSNL
15-Feb-06
32
GSM Mobile Station - Power Levels
Power Class 1 2 3 4 5
DGM(BSS), BSNL
GSM MSISDN
• Mobile Subscriber’s ISDN Number • The MSISDN is registered in the telephone directory and used by the calling party for dialing.
1 to 3 digits CC=+91 Variable NDC=94170 Variable SN=12345
N(S)N MSISDN : not more than 15 digits
DGM(BSS), BSNL 15-Feb-06 36
GSM IMSI
• International mobile subscriber’s 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 on the subscriber identity module (SIM), the HLR, VLR and AC database.
DGM(BSS), BSNL
15-Feb-06
37
GSM IMSI
3 digits MCC 2 digits MNC NMSI
MSC in HLR Area (1); Pre/Post (1); Vendor ID (1); Running Counter=6
Not more than 9 digits MSIN
IMSI : Not more than 15 digits
DGM(BSS), BSNL
15-Feb-06
38
GSM TMSI
• Temporary Mobile subscriber’s Identity
• The TMSI is an identity which guarantees the integrity of the mobile subscribers on the radio interface. • The VLR assigns a TMSI to each mobile subscribers entering the VLR area.
DGM(BSS), BSNL
15-Feb-06
39
GSM MSRN
Mobile Station Roaming Number
• The MSRN is used in the GMSC to set up a connection to the visited MSC/VLR.
DGM(BSS), BSNL
15-Feb-06
40
GSM IMEI
• International Mobile Equipment Identity
• The IMEI is an unique code allocated to each mobile equipment. It is checked in the EIR. • IMEI check • White List • Grey List • Black List
DGM(BSS), BSNL
15-Feb-06
41
RADIO SUB SYSTEM (RSS)
MSC/VLR
BSC BSC
BSC
RSS RSS
n BTS
DGM(BSS), BSNL 15-Feb-06
n BTS
42
GSM
FUNCTION OF BTS -I
• Encodes, encrypts, multiplexes, modulates and feeds the RF signals to the antenna Transcoding and rate adaption Functionality Time and frequency synchronisation signals transmission. 11 power classes from .01 watts (Micro cell) to 320 watts (Umbrella cell)
15-Feb-06 43
• •
•
DGM(BSS), BSNL
GSM
FUNCTIONS OF BSC-I
• It is connected to BTS and offloads MSC • Radio resource management • Inter-cell handover • Reallocation of frequencies • Power control
DGM(BSS), BSNL
15-Feb-06
44
GSM
FUNCTION OF BTS -II
• Frequency hopping • Random access detection • Uplink radio channel measurements • BTS mainly consists of a set of transceivers (TRX). Can accommodate 1 to 7 TRX per Sector
DGM(BSS), BSNL
15-Feb-06
45
GSM
FUNCTIONS OF BSC-II
• Time delay measurement of the received signals from MS with respect to BTS clock. • Performs traffic concentration to reduce the number of lines from BSC to MSC. • Provide interface TCP/IP X.25 to the OMS
DGM(BSS), BSNL
15-Feb-06
46
GSM MSC-BSS Configurations
Multi - cell site (sector Cells Configuration -5 A BTS A BSS Single - cell site Configuration -1 BTS BTS BTS Many single cell sites
MSC
A
BSS
A-bis BSC A-bis
BTS
BTS
MCC: Mobile Switching Centre BSS: Base Station System BSC: Base Station Controller BTS: Base Transceiver Station
Configuration -6
BTS
Multi - cell site = multi--BTS site
DGM(BSS), BSNL
15-Feb-06
47
Network and Switching Subsystem (NSS)
SS7 Signalling Traffic Path
VLR D C HLR E EIR A AUC
F
MSC
Other MSC
(PSTN) (BSS)
DGM(BSS), BSNL 15-Feb-06 48
GSM
MSC ( MOBILE SWITCHING CENTRE)
• Manages communication between GSM & other network . • Call setup functions, basic switching are done. • MSC takes into account the RR allocation in addition to normal exchange functions. • MSC does gateway function while its customers roams to other network by using HLR /VLR .
DGM(BSS), BSNL 15-Feb-06 49
GSM MSC Functions - I
• Paging, specifically call handling • Location updation. • Handover management. • Billing for all subscribers based in its area. • Reallocation of frequencies to BTSs in its area to meet heavy demands.
DGM(BSS), BSNL 15-Feb-06 50
GSM MSC Functions - II
• 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
DGM(BSS), BSNL
15-Feb-06
51
GSM
VISITOR LOCATION REGISTER (VLR)-I
• 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
DGM(BSS), BSNL 15-Feb-06 52
GSM
Data in VLR
• • • • • • • IMSI & TMSI MSISDN MSRN. Location Area Supplementary service parameters MS category Authentication Key
DGM(BSS), BSNL
15-Feb-06
53
GSM
Home Location Register(HLR)-I
• 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.
DGM(BSS), BSNL
15-Feb-06
54
GSM
Home Location Register(HLR)-II
• Permanent data in HLR
• Data stored is changed only by man-machine. • IMSI, MS-ISDN number. • Category of MS ( whether pay phone or not ) • Roaming restriction ( allowed or not ). • Supplementary services like call forwarding
DGM(BSS), BSNL 15-Feb-06 55
GSM
Home Location Register(HLR)-III
• 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
DGM(BSS), BSNL 15-Feb-06 56
GSM
AUTHENTICATION CENTRE (AUC )-I
• AUC is a separate entity and physically included in HLR • Protect against intruders in air interface • Authentication (Ki) and ciphering (Kc) key are stored in this data base. • Keys change randomly with each call • Keys are never transmitted to MS on air Only calculated response are sent.
DGM(BSS), BSNL 15-Feb-06 57
GSM
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.
DGM(BSS), BSNL
15-Feb-06
58
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 Separate OMC-S and OMC-R for NSS and RSS
DGM(BSS), BSNL
15-Feb-06
59
Functions of OMC
- O&M data function
- Configuration management - Fault report and alarm handling - Performance supervision/management - Storage of system software and data - Support GUI for operation and Maintenance
DGM(BSS), BSNL 15-Feb-06 60
Mobile Terminated Call
• • • • • • • • • • • 1: calling a GSM subscriber 2: forwarding call to GMSC 3: signal call setup to HLR 4, 5: connect with current VLR 6: forward responsible MSC to GMSC calling station 1 7: forward call to current MSC 8, 9: get current status of MS 10, 11: paging of MS 12, 13: MS answers 14, 15: security checks 16, 17: set up connection
HLR
4 5 7
VLR
3 6
PSTN
8 9 14 15
MSC
2
GMSC
10
BSS
10 13 16
BSS
10
BSS
11
11 11 12 17
MS
11
DGM(BSS), BSNL
15-Feb-06
61
Mobile Originated Call
• 1, 2: connection request • 3, 4: security check • 5-8: check resources (free circuit) • 9-10: set up call
VLR