Maulana Azad National Institute of Technology,BhopalDepartment of Computer Science & Engineering GSM Guided By: Mrs. NAMITA TIWARI Presented By: Priyanka Chhabra 082112120
HISTORY • GSM criteria – • Good subjective speech quality • Low terminal and service cost • Support for international roaming • Ability to support handheld terminals • Support for range of new services and facilities • Enhanced Features • ISDN compatibility • Enhance privacy • Security against fraud
HISTORYcontd. • Phase I of GSM specifications was published in 1990 • International demand was so great that the system name was changed from Groupe Special Mobile to Global Systems for Mobile Communications (still GSM) • Commercial service started in mid-1991 • 1992 first paying customers were signed up for service • By 1993 there were 36 GSM networks in 22 countries • Early 1994 there were 1.3 million subscribers worldwide • By 1996 there were more than 25 million subscribers worldwide • By October 1997 it had grown to more than 55 million subscribers worldwide
Building Blocks • AMPS – Advanced Mobile Phone System • TACS – Total Access Communication System • NMT – Nordic Mobile Telephone System
Building Blockscontd. AMPS – Advanced Mobile Phone System • analog technology • used in North and South America and approximately 35 other countries • operates in the 800 MHz band using FDMA technology
Building Blockscontd. TACS – Total Access Communication System • variant of AMPS • deployed in a number of countries • primarily in the UK
Building Blockscontd. NMT – Nordic Mobile Telephone System • analog technology • deployed in the Benelux countries and Russia • operates in the 450 and 900 MHz band • first technology to offer international roaming – only within the Nordic countries
The GSM Services • Teleservices (TS) • Bearer services (BS) • Supplementary Services (SS)
Tele Services • • Telecommunication services that enable voice communication • via mobile phones • • Offered services • - Telephony • - Emergency calling • Voice messaging
Bearer Services • Include various data services for information transfer between GSM and other networks like PSTN, ISDN etc at rates from 300 to 9600 bps • Short Message Service (SMS) • up to 160 character alphanumeric data transmission to/from the mobile terminal • Group 3 fax • Voice mailbox • Electronic mail
Supplementary Services • Call forwarding. • Barring of Outgoing Calls. • Barring of Incoming Calls. • Advice of Charge (AoC). • Call Hold.. • Call Waiting. • Multiparty service. • Calling Line Identification presentation/restriction.. • Closed User Groups (CUGs). • Explicit Call Transfer (ECT).
The Four blocks • Mobile Station Subsystem (MSS) – Mobile Termination (MT) and SIM card (SIM) • Base Station Subsystem (BSS) – BSC and BTS • Network and Switching Subsystem (NSS) – MSC, HLR, VLR, EIR and AuC • Operation and Support Subsystem (OSS) – OMC and NMC
System ArchitectureMobile Station (MS) The Mobile Station is made up of two entities: • Mobile Equipment (ME) 2. Subscriber Identity Module (SIM)
System ArchitectureMobile Station (MS) contd. Mobile Equipment • Produced by many different manufacturers • Must obtain approval from the standardization body • Uniquely identified by an IMEI (International Mobile Equipment Identity)
System ArchitectureMobile Station (MS) contd. Subscriber Identity Module (SIM) • Smart card containing the International Mobile Subscriber Identity (IMSI) • Allows user to send and receive calls and receive other subscribed services • Encoded network identification details • Protected by a password or PIN • Can be moved from phone to phone – contains key information to activate the phone
Base Station Subsystem Consists of • • Base Transceiver Station (BTS) • – radio equipments responsible for radio coverage • • Base Station Controller • Controls a few BTS • Manages Resources for BTS • Handles call set up • Location update • Handover for each MS • Manage radio resource management, signaling transmission, • power control, handover control, frequency hopping control etc. • • Transcoder/Rate Adapter Unit (optional) • – A device placed between GSM elements (BTS, BSC and MSC) • to conserve bandwidth resources. • – Combines four 13 kbps speech channels to one 64 kbps data • stream. Thirty 64 kbps channels can then be multiplexed to a E1 • channel. Located at BTS, BSC (more often) or MSC.
Network and Switching Subsystem (NSS) • Perform functions such as call setup, paging, resource allocation, location registration, encryption, interfacing with other networks, handoff control, billing, synchronization, echo canceling and interface with external networks. • Consist of 4 elements – MSC, HLR, VLR, AuC and EIR – MSC is the processor, the others are database units.
Mobile Switching Center (MSC) • Switch speech and data connections between: • Base Station Controllers • Mobile Switching Centers • GSM-networks • Other external networks • Heart of the network • Three main jobs: • 1) connects calls from sender to receiver • 2) collects details of the calls made and received • 3) supervises operation of the rest of the network components
Home Location Register (HLR) • • HLR contains a list of subscribers belonging to • one or more MSC areas. • • Permanent subscriber data including IMSI, MSISDN, • roaming restriction, permitted • supplementary services and authentication key. • • Temporary subscriber data consist of MSRN, • data related to encryption, VLR address, MSC • address and roaming restriction. • • HLR is usually centralized within a network. • Visitor Location Register (VLR) • • Similar to HLR but for visitors • • When a roamer appears, his HLR data is • transferred to the local VLR. • • VLR is usually co-located with MSC.
Authentication Center (AuC) • • Performs authentication function for each • subscriber within the system. • • A key Ki kept in SIM and AuC. This key is never • transmitted over air. • • Authenticate by using a random challenge. • • Vulnerability is present when encrypted • authentication keys must be transmitted from • HLR to VLR. • Equipment Identity Register (EIR) • • Records the IMEI of all subscribers in three lists. • • White list ---- clean equipment • • Black list ---- stolen equipment • • Gray list ---- equipment with minor problems
Operation and Support Subsystem (OSS) • OSS consists of two entities not fully specified in GSM. They are – Operation and Maintenance Center (OMC) – Network Management Center (NMC) • Performs alarm handling, fault management, performance management, configuration management, traffic data acquisition, activate and deactivate functions, and long term planning. Normally centralized in a network. • Implementation of these functions are operator specific.
Open Interfaces • A-Interface ---- between BSC and MSC, E1 link. • Abis-Interface ---- between BTS and BSC using LADP (Link Access Data Protocol) protocol. • B-Interface ---- between MSC and VLR • C-Interface ---- between MSC and HLR • D-Interface ---- between HLR and VLR • E-Interface ---- between MSCs • F-Interface ---- between MSC and EIR • Um-Interface ---- between MSS and BSS.
Call Routing • Call Originating from MS • Call termination to MS
Outgoing Call • MS sends dialled number to BSS • BSS sends dialled number to MSC • 3,4 MSC checks VLR if MS is allowed the requested service.Ifso,MSC asks BSS to allocate resources for call. • MSC routes the call to GMSC • GMSC routes the call to local exchange of called user • 7, 8, • 9,10 Answer back(ring back) tone is routed from called user to MS via GMSC,MSC,BSS
Incoming Call • Calling a GSM subscribers • Forwarding call to GSMC • Signal Setup to HLR • 5. Request MSRN from VLR • Forward responsible MSC to GMSC • Forward Call to current MSC • 9. Get current status of MS • 11. Paging of MS • 13. MS answers • 15. Security checks • 17. Set up connection
Handovers • Between 1 and 2 – Inter BTS / Intra BSC • Between 1 and 3 – Inter BSC/ Intra MSC • Between 1 and 4 – Inter MSC
Security in GSM • On air interface, GSM uses encryption and TMSI instead of IMSI. • SIM is provided 4-8 digit PIN to validate the ownership of SIM • 3 algorithms are specified : - A3(Authentication) algorithm for authentication - A5(Ciphering) algorithm for encryption • - A8(Ciphering Key Generation) algorithm for key generation
Call Management (CM) and Mobility Management (MM) • CM consists of setup, emergency setup, call proceeding, progress, call confirm, alerting, connect, user information, disconnect, release, status, congestion control, etc all together 18 messages. • MM consists of authentication request, authentication response, identify request, location update request, etc
GSM Mobile Services A prepaid mobile phone (also commonly referred to as pay-as-you-go or prepaid wireless) is a mobile phone for which service is purchased in advance of use. • Advantages • Lower cost for low usage • Easier to control spending • Available to those who do not have an address • Limitations • Every time pay before • No balance means cant make any call
Advantages of GSM over Analog system • Capacity increases • Reduced RF transmission power and longer battery life. • International roaming capability. • Better security against fraud (through terminal validation and user authentication). • Encryption capability for information security and privacy. • Compatibility with ISDN,leading to wider range of services
Future Of GSM • 2nd Generation • GSM -9.6 Kbps (data rate) • 2.5 Generation ( Future of GSM) • HSCSD (High Speed ckt Switched data) • Data rate : 76.8 Kbps (9.6 x 8 kbps) • GPRS (General Packet Radio service) • Data rate: 14.4 - 115.2 Kbps • EDGE (Enhanced data rate for GSM Evolution) • Data rate: 547.2 Kbps (max) • 3 Generation • WCDMA(Wide band CDMA) • Data rate : 0.348 – 2.0 Mbps
Future -- UMTS (Universal Mobile Telephone System • Reasons for innovations • new service requirements • availability of new radio bands