Tổng quan Gsm

GSM is a Second Generation (2G) digital radio cellular network  Time Division Multiplexing / Multiple access (TDM/TDMA) are employed  TDM / TDMA allows:  One frequency channel to be subdivided  Multiple conversations over a single physical channe

04/2009

What is GSM?

 GSM (Global System for Mobile communication)

is a Worldwide Digital Cellular Communications Network

 formerly: Groupe Spéciale Mobile (founded 1982)

 used in over 184 countries

 The GSM network provides for

 mobile voice communication

 international roaming

 mobile fax

 text messaging

 One frequency channel to be subdivided

 Multiple conversations over a single physical

2 Data (Bearer services)

Capacity necessary to transmit appropriate data signals between two access points creating an interface to the network

GSM Subscriber Services

GSM supports the following subscriber services:

1 Dual tone multi frequency (DTMF)

tone signaling scheme used for control purposes E.g Remote control of an answering machine

2 Facsimile group III

GSM supports CCITT group III FacsimileSpecial fax converter forms junction between standard analogue fax and GSM FAX

GSM Subscriber Services

3 Short Message Services (SMS)

Messaging facility consisting of maximum 160 alphanumeric characters to or from a mobile

connection with the highest priority (pre-emption of other connections possible)

2 Barring of outgoing calls

3 Advice of charge (AoC)

GSM Supplementary Services

4 Call hold

5 Call waiting

6 Multiparty service

7 Calling line identification presentation / restriction

8 Closed user groups (CUGs)

Multiple incompatible networks

 Before GSM, the technical incompatibilities

between networks were due to:

 operation on different radio frequencies

 use of incompatible signals to control the call setup, handoff and end of the connection

 Even when the same technological standard existed between countries:

 there were usually organisational barriers

Analogue Networks

 An analogue cellular system:

 uses frequency modulation (FM) to send data and signals

 Divides the spectrum only into physical channels of different frequency

 Does not offer added services such as Caller ID or Messaging

1st Generation Analogue Networks

Japan 1978/88

NTT/NTT Hi Cap

Japan 1991

RTMS

France 1985

ETACS

Germany, Austria, Portugal, South Africa

1981 C-Netz

USA, Australia 1983

AMPS

How did GSM get established

 CEPT formed a technical study group named

 The group’s mandate was to:

 formulate a specification for a pan-European mobile cellular radio system in 900MHz band

 Tackle the associated technical, economic and

logistical problems

Objectives of GSM

 To provide a European “second

generation” digital network standard

 Increase the market for Equipment Manufacturers

 Allow Manufacturing to establish

economy of scale.

Development Timeline

 1985 – Digital Coded Speech over radio link chosen as basis for GSM

 1986 – Validation Trials held in Paris

 1988 – Following successful validation

multiple invitations to tender issued

 1992 – Commercial Networks Launched

First portable units

 First portable units

were really big and

heavy.

 Called transportables

or “luggables”.

“Curt” – The Hotline Pocket

 The first Ericsson

 Later adapted for

the ETACS network.

 Later adapted for

GSM, and is the first Ericsson GSM phone.

 First all digital

mobile

 First introduced by Ericsson in 1991

 First version used in NMT-900 networks, followed by version for ETACS, D-

AMPS/AMPS

 Adapted for GSM in 1993

 Introduced by

Ericsson in 1996

 Several version manufactured for AMPS, GSM, DCS, PCD1900/GSM

Gaussian Minimum Shift Keying (GMSK) Modulation

200 kHz Carrier Separation

45MHz / 95MHz Duplex distance

Uplink: 890 MHz – 915 MHz / 1710 MHz – 1785 MHz Downlink: 935 MHz – 960 MHz / 1805 MHz – 1880 MHz Frequency Band

 one number, the network handles localization

 High capacity if needed

 better frequency efficiency, smaller cells, more customers per cell

 High transmission quality

 high audio quality and reliability for wireless, uninterrupted phone calls at higher speeds (e.g., from cars, trains)

 Security functions

access control, authentication via chip-card and PIN

What are some of disadvantages

of GSM?

There is no perfect system!!

 no end-to-end encryption of user data

 reduced concentration while driving

 electromagnetic radiation

 abuse of private data possible

 roaming profiles accessible

 high complexity of the system

 several incompatibilities within the GSM standards

What are the trends with mobile phone subscribers worldwide?

Development of mobile

telecommunication systems

Components

GSM is a PLMN (Public Land Mobile Network)

 BSS (Base Station Subsystem): BSC, BTSs

 MS (Mobile Station)

handover, switching

 MSC (Mobile Switching Center)

 HLR (Home Location Register)

 VLR (Visitor Location Register)

 OMC (Operation and Maintenance Center)

 AuC (Authentication Center)

EIR (Equipment Identity Register)

BSC : Base Station Controller

Radio Subsystem

Radio Subsystem

Network and Switching

What are the components of the NSS?

 Mobile Services Switching Center (MSC)

 controls all connections via a separated network to/from a mobile terminal within the domain of the MSC - several BSC can belong to a MSC

 Home Location Register (HLR)

 central master database containing user data, permanent and semi-permanent data of all subscribers assigned to the HLR (one provider can have several HLRs)

 Visitor Location Register (VLR)

 local database for a subset of user data, including data about all user currently in the

Network and Switching

Subsystem

AuC : Authentication Center

EIR : Equipment Identity Register

OMC : Operation and Maintenance Center

Operation Subsystem

The OSS (Operation Subsystem) enables centralized operation,

management, and maintenance of all GSM subsystems Components

 generates user specific authentication parameters on request of a VLR

 authentication parameters used for authentication of mobile terminals and encryption of user data on the air interface within the GSM system

 registers GSM mobile stations and user rights

 stolen or malfunctioning mobile stations can be locked and sometimes even localized

 different control capabilities for the radio subsystem and the network

subsystem

Network Databases

Summary

Interfaces

Interfaces

Interfaces

Interfaces

Geographical network

organization

Location area (LA)

•The MSC service areas, in turn, consists of cells which are organized as Location Areas (LA)

•Allows MS to move freely without updating location information

•System uses LA’s to locate a MS using broadcast messages.

GSM numbering

Permanent subscriber numbering

MSRN & TMSI

IMEI, LAI & CI

Summary

a MOC (Mobile Originated Call)

b MTC (Mobile Terminated Call)

Mobile Originated Call

Mobile Originated Call

Mobile Terminated Call

 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

Mobile Terminated Call

Detail Sequence of MTC

Future mobile

telecommunication networks