Wireless Telecommunication System

Contd.. AMPS: Advanced Mobile Phone System DECT: Digital Enhanced Cordless Telephone NMT : Nordic Mobile Telephone PDC : Personnal Digital Cellular IMT : International Mobile Telecommunication GPRS: General Packet Radio Service EDGE: Enhanced Data Rates for GSM Evolution UMTS: Universal Mobile Telecommunication System EVDO: Evolution Data Optimized EVDV: Evolution Data and Voice UTRA: UMTS Terrestrial Radio Access

GSM Groupe Speciale Mobile Global System for Mobile Communication ->Goal: Roam and Provide Voice Services (But not offering high world wide data rates that 3G/UMTS are promising) MHZ for Uplinks MHZ for Downlinks

Performance Characteristics of GSM

DisAdvantagesin GSM

GSM : MOBILE SERVICE

BEARER SERVICE Transparent transmission of data between the interfaces to the network (TE-TE) Within MS,MT(Mobile Termination- TDMA,FDMA,Coding etc) Increasing Transmission Quality-Forward Error Correction(FEC) PLMN –Public Land Mobile Network ISDN -Integrated Service Digital Network PSDN –Public SwitcedDigital Network

Contd..

TELE SERVICES Mobile Telephony Emergency Number Multinumbering SMS –160 Characters EMS –760 Characters MMS –(GIF,JPG,WBMP) Group 3 Fax

Supplementary Services User Identification Call Redirection or Forwarding Closed User Groups(Multi Party Communication)

GSM :Architecture

GSM Architecture

Radio Sub System

Mobile Station SIM (Stores User Specific Data) IMEI PIN IMSI

Network & Switching SubSystem

NSS Msc –High Performance Digital ISDN Switches GMsc–Gateway Msc-Fixed SS7-Standard SIGNALLING SYSTEM -> Connection Setup, Release & HO

HLR STATIC IMSI CALL FORWARDING,ROAMING Dynamic Information (Location Area (LA)) MSRN --Mobile SubsciberRoaming Number MSLeave <- Update

VLR Dynamic Database Associated with each Msc MSCurrentLocation Area Copies from HLR

Operation Subsystem OMC -Traffic Moinitoring -Status Report of N/W Entities -Accounting&Billing,Security MGT AUC -User Identity and Data Transmission EIR -DB for IMEI,Black list,WhiteList,Gray List -Synchronization not done

GSM

Radio Interface Um interface-Multiplexing,Media Access FDD –Separate UP&DOWN Links Channels each 200 Khz 32 Channels for organization Data Remaining for Customer Use -90 channels 248 Channels –additionaly seperated by GSM TDMA Frame Each 200Khz carrier is divided into frames

Contd.. Duration of each frame is ms 8 GSM Time Slots ( 577 μs) Data –BURSTS(NORMAL BURST) Each Burst is μs long & remaining is 30.5 μs(GuardSpace) Whole Data is bit with 577 μs

GSM-TDMA/FDMA

GSM :FDMA/TDMA Tail-> Enhance the Receiver Performance Training Sequence-> Select Strongest Signal(mpp) Flag S -> Data Field contains user data or Network Data

Other Bursts Frequency Correction Burst MS to correct local oscillator to avoid interferences in neighbor channel Synchronization Burst synchronization burst (BTS-MS) Access Burst Initial Connection Setup (BTS-MS) Dummy Burst if no data is available for slot

GSM: Logical Channels Traffic Channels (TCH) (i) Full Rate (ii) Half Rate Control Channels ->Control Medium Access ->Allocation of Traffic Channels ->Mobility Management

Control Channels Broadcast Control Channel (BCCH) ->BTS signals all information to MS Synchronization in time(Cell) –SCH Frequency Correction (Cell) -FCH Common Control Channel (CCCH) Connection Setup(MS-BTS) Paging Channel(PCH)-BTS-Pages-MS Random Access Channel(RAC)-MS-BTS Dedicated Control Channel (DCCH) -> Bidirectional MS uses Stand-Alone Dedicated Control Channel(SDCCH) with low data rate for signaling; if (Ms using TCH not estabilished –BTS) TCH & SDCCH is associated with SLOW ASSOCIATED DEDICATED CONTROL CHANNEL(SACCH)

GSM:HIERARCHY OF FRAMES

GSM PROTOCOL LAYERS FOR SIGNALING

Layer –I (Radio Specific Function) Creation of Bursts; Multiplexing of Bursts in TDMA Frame Synchronization Detection of Idle Channel Measurement of Channel Quality Synchronization (Correction –Individual path delay)

Contd.. BTS –MS (RTT is short for near and.25ms for 35kms) VAD(Voice Activity Detection) Scheme for voice transmission During Period of Silence; COMFORT NOISE to fake a connection

Signaling Between two Entities- Layer 2 LAPD (Link Access Procedure for D-Channel) -> Reliable Data Transfer over connections -> Flow control,Segmentation&Reassembly of Data -> ACK for Data Transfer

Layer –3 Sub Layers RR-Radio Resource Management(RR) (Part of BTS Supported by BTSM) Setup,Maintenance & Release of Radio Channels MM-Mobility Management (MM) Registration,Authentication,Identification, Location Updating,TMSI(IMSI)

LAYER -3 Contd… CALL MANAGEMENT (CM) (i) Call Control (ii) SMS –SDCCH /SACCH (iii) Supplementary Services

MSC PULSE CODE MODULATION SS7 (BSC-MSC)->Transfer all MGT info between MSC(HLR,VLR,AUC,EIR,OMC) BSSAP: An MSC can also control a BSS (via) BSS Application Part.

Localization and Calling GSM System-Automatic Worldwide Localization of users Periodic Location Updates ROAMING *Changing VLR’s with uninterrupted Availability of all services *One Provider / Two providers in a Country/Two providers in a two different countries

Locating an MS Mobile Station International ISDN Number(MSISDN) CC + National Destination Code + Sub. Number(eg ) IMSI- Internal unique identification of a subscriber TMSI- current VLR- valid temporarily- LA- VLR changes periodically. Mobile Station Roaming Number (MSRN) -Hides the identity and location of the user -VLR-Generates on request from MSC –HLR -VCC –VNDC –SN -MSRN helps HLR to find user for an incoming call

Mobile Terminated

Visitor Location Register (VLR) Suppose your mobile is registered in Mumbai and you are currently in Delhi 1.What happens when your friend in Mumbai calls you?

Mobile Originated Call

Visitor Location Register (VLR) 2. What happens when you call to a friend (a)In the home network ? (Mumbai) (b)In the visitor network ? (Delhi) (c)Both are from Mumbai and currently in Delhi

HANDOVER Should not cause a Cut-off.(CALLDROP) Maximum Duration is 60 ms Basic Reason 1. Quality of the Radio Link 2. Load Balancing(MSC,BSC to decide – Traffic in an Cell –High) Error Rates and Signal Levels

Four Types of HandOver Intra-Cell Handover --Within a cell Inter-Cell, Intra-Bsc Handover --Cell to another cell –Bsc Inter-Bsc,Intra-Msc Handover --Bsc to Bsc ->Msc Inter Msc Handover --Msc to Msc

Types of Handover

Signal Flow-Inter-BSC,Intra- MSC

SECURITY Security to AUC and SIM A3 –Authentication A5 –Encryption A8 –Generation of Cipher Key

Authentication Any Service –GSM Authentication is based on Individual Authentication Key IMSI A3 Challenge-Response Method Generating a Random Number

Authentication

Key Generation and Encryption

GPRS Packet Mode Transfer Small /Medium/High Volumes of Data Broadcasting/Multicasting/Unicasting Services are charged on Volume of Usages “Always On”-No connection to setup prior to data transfer

GPRS-General Packet Radio Service

GPRS Architecture and Interfaces

GPRS –Protocol Architecture

GPRS GPRS Tunnelling Protocol (GTP) All data between GSN is transferred between GTP. GTP -> Reliable TCP,Unreilable UDP Sub Network Dependent Convergence Protocol (SNDCP) Used between SGSN and MS –to adapt different characterstics LLC –High Reliability of Packet Transfer Base Station Subsystem GPRS Protocol (BSSGP) ->Convey Routing & QOS related information between BSS and SGSN RLC –Reliable Link MAC –Mapping LLC Frames into GSM Channels