Presentation on: GSM BASICS Presented by: Sandip Thakkar Saurabh Gandhi

Fixed line telephones What are the drawbacks ? No mobility Delay in new connections Security Hazards Prone to failures (line disconnection, etc) Very less value added services

What is GSM?  Global system for Mobile communication  Standard defined by ETSI (European Telecommunications Standards Institute)  Global System for Mobile (GSM) is a second generation cellular standard developed to cater voice services and data delivery using digital modulation

GSM: History 1982 CEPT initiated a new cellular system (GSM) in the 900 Mhz band CEPT tested 8 experimental systems in Paris MoU of allocations of frequencies.(uplink and downlink) 1991 First official call in the world with GSM on 1 st July New freq. allocation for GSM There were 117 GSM networks operating around the world >1300 miilion subscribers in the world & >45 millions subscribers in india. Aim : to replace the incompatible analog system

Evolution 1G3G2G+2G

5.973% Idea 2.075%

GSM Specifications-1  RF Spectrum GSM 900 Mobile to BTS (uplink): Mhz BTS to Mobile(downlink): Mhz Bandwidth : 2* 25 Mhz GSM 1800 Mobile to BTS (uplink): Mhz BTS to Mobile(downlink): Mhz Bandwidth : 2* 75 Mhz

GSM-900 System Specifications  Frequency Range : 890 MHz to 915 MHz for Uplink 935 MHz to 960 MHz for Downlink.  Uses TDMA technology for Downlink / Uplink.  124 Reusable Spot frequencies of 200 kHz bandwidth each.  Each Spot Frequency carries 8 Time slots for Traffic/Signalling.  Compatible to ISDN & PSPDN.  Modulation Method : GMSK  Modulation data rate : Kbps

Performance characteristics of GSM  Communication  Total mobility  Worldwide connectivity  High capacity  High transmission quality  Security functions  Greater QOS

CONSIDERATIONS [ FREQUENCY [ CAPACITY [ COVERAGE

The Cell Cellular Radio involves dividing a large service area into regions called “cells.” BTS Cell Size:  LARGE CELL(35 Km)  SMALL CELL(1 Km)

Frequency & ARFCN ul= 890 to 915 MHz dl= 935 to 960 MHz F ul (n) = (0.2) *n MHz F dl (n) = F ul + 45 MHz where n =ARFCN ; 1  n  124

GSM Services  Tele-services  Bearer or Data Services  Supplementary services

Tele Services  Telecommunication services that enable voice communication via mobile phones  Offered services - Mobile telephony - Emergency calling

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  Unified Messaging Services(UMS)  Voice mailbox  Electronic mail

Supplementary Services Call related services : o Call Waiting- Notification of an incoming call while on the handset o Call Hold- Put a caller on hold to take another call o Call Barring- All calls, outgoing calls, or incoming calls o Call Forwarding- Calls can be sent to various numbers defined by the user o Multi Party Call Conferencing - Link multiple calls together o CLIP – Caller line identification presentation o CLIR – Caller line identification restriction o CUG – Closed user group

GSM System Architecture

BSC MSC MS BTS GMSC PSTN ISDN PDN EIR AUC HLR VLR OMC SMSC VMSC

GSM System Architecture-I  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)

Mobile Station  Mobile Station consist of two units 1)Mobile handset 2) SIM(Subscriber Identity Module)

Mobile Station (MS) A Typical Handset Consists of the following parts : A microscopic microphone, A speaker, An LCD or plasma display, A mini keyboard, An Antenna, A battery, A Circuit board, SIM  MS is the radio mobile terminal carried by the subscriber  MS consists of  User independent HW and SW  SIM (Subscriber Identity Module)  MS can be identified by IMEI (Intl Mobile Equipment Identity)  MSs have transmit power of 2W and 1W

IMEI  The Mobile Equipment is identified inside any GSM network by the International Mobile Equipment Identity (IMEI) The IMEI is a 15-digit number IMEI = TAC/ FAC/ SNR/ SP TAC = Type Approval Code, determined by the main body of the GSM (6 digits) FAC = Final Assembly Code, identifies the maker (2 digits) SNR = Serial Number (6 digits) SP = A spare supplementary number (1digit)

 SIM stands for "Subscriber Identification Module"  SIM cards are small ‘smart’ cards that fit inside phones based on GSM technology. SIM

 Uniquely associated to a user Not to an equipment, as in first generation cellular networks  Stores user addresses  IMSI  MSISDN  Temporary addresses for location, roaming, etc  Authentication and encryption feature s All security features of GSM are stored in the SIM for max. protection  subscriber’s secret authentication key ( Ki)  Authentication algorithm (“secret” algorithm - A3 – not unique)  Cipher key generation algorithm (A8)  Personalization  SIM stores user profile (subscribed services)  RAM available for SMS, short numbers, user’s directory, etc  Protection codes  PIN (Personal Identification Number, 4-8 digits)  PUK (PIN Unblocking Key, 8 digits)

MSISDN (Mobile Subscriber ISDN Number) MSISDN : the “usual” telephone number Structure: CC/NDC/SN CC : Country Code(up to 3 digits) NDC : National Destination Code (3 digits,for PLMN) SN : Subscriber Number (max 10 digits) IMSI The IMSI has the following: MCC / MNC / MSIN where MCC: Mobile Country Code (2 or 3 digits, 404 for INDIA) MNC: Mobile Network Code (2 digits) MSIN: Mobile Station Identification Number (max 13 digits)

Temporary addresses TMSI – Temporary Mobile Subscriber Identity 32 bits assigned by VLR within an administrative area has significance only in this area transmitted on the radio interface instead of IMSI reduces problem of“eavesdropping” MSRN – Mobile Station Roaming Number An MSISDN number CC, NDC of the visited network SN assigned by VLR Used to route calls to a roaming MS Subscriber Number (SN) assigned to provide routing information towards actually responsible

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 ) BTS TC BSC TC BTS

Base Transceiver Station (BTS): SHELTER +Transmission Medium +TOWER

 BTS has a set of Transceivers to talk to MS.  One BTS covers one or more than one cell.  Capacity of BTS depends on no of Transceivers.  BTS is connected to BSC via A’bis interface.  Transmission rate on A’bis is 2 Mbps (G.703).  Interface between MS & BTS is called Air I/f.  Transmission rate on Air interface is 13 Kbps.  BTS controls RF parameters of MS.  Each TRx has 8 TDMA channels to carry Voice & signalling BTS

 A BTS in general has the following units: Transceiver (TRX) Power unit Combiner Duplexer Antenna Alarm extension system Transmission unit Baseband receiver unit (BBxx)

Nokia BTS’s Nokia ultrasite Nokia metrosite Nokia flexisite TRx capacity Max Tx power(dBm)

Base Station Controller (BSC) BSC controls several BTSs. BSC manages channel allocation, & Handover of calls from one BTS to another BTS. BSC is connected to MSC via A interface. Transmission rate on A I/f is 2 Mbps (G.703). Interface between BSC & BTS is called A’bis I/f. BSC has database for all of its BTS’s parameters. BSC provides path from MS to MSC. 1 BSC may control up to 40 BTS BSC

BTS & BSC  Tasks of a BSS are distributed over BSC and BTS

Transcoder and Sub multiplexer TC 64 kbps 16 (13+3) kbps 13 kbps 16 kbps (90 Channels) 16 kbps TCSM MSC BTS BSC SMUXSMUX TC

 Taking care of speech transcoding,  For transmission over the air interface, the speech signal is compressed by the mobile station to 13Kbits/s (Full Rate) or 5.6Kbits/s (Half Rate).  TCSM incorporates the transcoder and the sub-multiplexer into one piece of hardware.  Minimum possible PCM line: 4  Maximum (half rate channel): 7  TC enable also (DTx=discontinous transmssion)  In NOKIA =TCSM2E(European version) or TCSM2A(American version)

Network Switching Sub-System (NSS) Elements:  Mobile Switching Center (MSC) / Gateway MSC (GMSC)  Home Location Register (HLR ) / Authentication Center (AuC)  Visitor Location Register (VLR)  Equipment Identity Register (EIR) Functions:  Call control  User management Inter-component communication:  Via SS7 signalling network  With suitable extensions (e.g. MAP – Mobile Application Part)

Mobile Switching Center (MSC )  Heart of the network  Manages communication between GSM and other networks  Call setup function and basic switching  Call routing  Billing information and collection  Mobility management - Registration - Location Updating - Inter BSS and inter MSC call handoff  MSC does gateway function while its customer roams to other network by using HLR/VLR.

 database per operator (PLMN)  HLR entries: Every user / MSISDN that has subscribed to the operator  Stores: Permanent information associated to the user IMSI, MSISDN Services subscribed Service restrictions (e.g. roaming restrictions) Parameters for additional services info about user equipment (IMEI) Authentication data Temporary information associated to the user Link to current location of the user: Current VLR address (if avail) Current MSC address (if avail) MSRN (if user outside PLMN) Home location register (HLR)

Subscriber and subscription data  IMSI, MSISDN  Parameters for additional services  info about user equipment (IMEI)  Authentication data Tracking & routing information  Mobile Station Roaming No(MSRN)  Temporary Mobile Station Identity  Location Area Identity (LAI) where MS has registered  Used for paging and call setup Visitor Location Register (VLR)  At most 1 database per MSC VLR entries:  Every user / MSISDN actually staying in the administrative area of the associated MSC  Entry created when an MS enters the MSC area (registration) NOTE: may store data for roaming users (subscribed to different operators) Stores:

Authentication Centre (AUC) HLR MSC  Authentication is a process to verify the subscriber SIM.  Secret data & verification algorithm are stored in to the AUC.  AUC & HLR combined to authenticate the subscribers.  Subscriber authentication can be done on every call, if required. AUC

Equipment Identity Register (EIR ) EIR MSC  All subscriber's mobile handset data is stored in EIR.  MSC asks mobile to send it IMEI & then checks it with data available in EIR.  EIR has different classification for mobile handset like, White list, Grey list & Black list.  According to category the MS can make calls or can be stopped from making calls.

VMSC & SMSC MSC SMSC VMSC  Voice Mail Service Centre : To provide Voice Mail service.  It has database for all the VMS subscribers & also stores voice messages for them.  Short Message Service Centre : To provide text message service.  To send short messages from mobile to another mobile subscriber.  Messages can also be sent by Manual Terminal connected to SMSC.0

OMC  All the network elements are connected to OMC.  OMC monitors health of all network elements & carry out maintenance operation, if required.  OMC link to BTSs are via parent BSC.  OMC keeps records of all the faults occurred.  OMC can also do Traffic analysis.  OMC may prepares MIS Report for the network. OMC

GSM Terrestrial Interfaces

Broadly classified into two types of interfaces - Standard Interfaces  2 Mbps Trunks (E1)  Signalling System No. 7 SS7 ( CCS7)  X.25 (Packet Switched Mode) GSM Interfaces  Air interface: MS-BTS  Abis interface: BTS-BSC  Ater interface: BSC-TCSM  A interface: TCSM-MSC  Gb interface: MSC-SGSN  X.25(protocol): MSC-DCN

GSM Operation Speech decoding Channel decoding De-interleaving Burst Formatting De-ciphering DemodulationModulation Ciphering Burst Formatting Interleaving Channel Coding Speech coding Radio Interface Speech 13 Kbps 22.8 Kbps 33.6 Kbps Kbps

GSM Framing

Tail bits 57 Coded data 1 Steali ng bit 26 midamble 1 Steali ng bit 57 Coded data 3 Tail bits 8.25 Guard period 120 ms ms 6.12 ms micro sec 51 Multiframes 26 frames 8 time slots Superframe Multiframe Frame

Multiple access Techniques In GSM

FDD / TDMA In GSM FDD/TDMA is used. f c t

 FDD is used to separate downlink and uplink. GSM TDMA System: In TDMA one radio freq. channel is devides into consecutive periods of time.  124 traffic channels * 8 slots/Ch = 992 simultaneous conversations  13 kbps coding data rate  Each TDMA frame contain 8 shorter periods of time known as Time slots.  TDMA time slots are called physical channel

GSM Channels

GSM Channel PhysicalLogical CommonDedicated SCH FCCHBCCH SDCCH Broadcast Common control Dedicated control Traffic SACCHFACCH RACH PCH AGCH TCH/HTCH/F TCH/ EFR

Incoming Call & Outgoing Call

PSTN calling station GMSC HLR VLR BSS MSC MS : Calling a GSM subscriber 2: Forwarding call to GMSC 3: Signal call setup to HLR 4, 5: Request MSRN from VLR 6: Forward responsible MSC to GMSC 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 Incoming Call

PSTN GMSC VLR BSS MSC MS MS sends dialled number to BSS 2. BSS sends dialled number to MSC 3,4 MSC checks VLR if MS is allowed the requested service.If so,MSC asks BSS to allocate resources for call. 5 MSC routes the call to GMSC 6 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 Outgoing C all

Handover What is the purpose of HO? Call continuity Call quality Others... Call continuity Call quality Others...

Reasons:  Handover due to traffic reasons  Handover due to Signal quality and strength Four Possible Handover Scenarios: Intra-cell handover Inter-cell, intra-BSC handover Inter-BSC, intra-MSC handover Inter MSC handover

Handovers Hard Handoff Analog, TDMA and GSM Soft Handoff CDMA Break before MakeMake before Break

GSM Data HSCSD GPRS EDGE EGPRS WCDMA WCDMA Phase I Time Evolution 14.4 kbps 14.4 – 57.6 kbps 64 ~ 170 kbps 384 kbps kbps kbps Technology Upgradation The Evolutionary Path

Thanking You……