ACN GSM. Global System for Mobile communication. Rainer Bernhard. Rainer Bernhard Graz, GSM

Transcription

1 ACN GSM Global System for Mobile communication Rainer Bernhard 1

2 History GSM Architecture Radio Interface GSM Security GSM Services GPRS EDGE Possible Questions References Content 2

3 History of GSM 1982: Groupe Spécial Mobile created by CEPT 1987: GSM MoU (Memorandum of Understanding) 1989: Groupe Spécial Mobile becomes part of ETSI (European Telecommunications Standards Institute) 1990: GSM-900 Standard 1991: DCS-1800 Standard 1992: Launch of commercial GSM-900 providers 2000: Standardization activities transferred to 3GPP (3rd Generation Partnership Project) 3

4 GSM Architecture Overview 4

5 GSM Architecture Base Station Subsystem (BSS) The BSS is responsible for handling traffic and signaling between a mobile station (MS) and the Network Switching Subsystem (NSS). Base Transceiver Station (BTS) - Equipment for transmitting and receiving radio signals - Antennas - Encrypting and decrypting communications with the BSC. Base Station Controller (BSC) - Allocation of radio channels - Receives measurement from the mobile phones - Controls handovers from BTS to BTS - Transcoding (compressing/decompressing) Packet Control Unit (PCU) - Processing tasks for packet data. 5

6 GSM Architecture (2) Network Switching Subsystem (NSS) The NSS carries out switching functions and manages the communications between mobile phones and the Publich Switched Telephone Network (PSTN). Mobile Switching Center (MSC) - Provides circuit switched calling - mobility management (roaming) - (traditional) GSM services Home Location Register (HLR) - central database containing details of each mobile phone subscriber Authentication Center (AUC) - function to authenticate each SIM card that attempts to connect to the GSM core network. Visitor Location Register (VLR) - temporary database of the subscribers who have roamed into the area it serves. Equipment Identity Register (EIR) 6

7 GPRS Core Network GSM Architecture (3) The GPRS Core Network is the centralised part of the GPRS system and provides mobility managment, session management and transport for Internet Protocol packet services. Serving GPRS Support Node (SGSN) - packet routing and transfer - mobility management (roaming) - logical link management - authentication and charging functions Gateway GPRS Support Node (GGSN) - interface to external packet data networks - packet conversion - IP address assignment - authentication and charging functions 7

8 GSM Architecture (4) Operation and Maintenance Center (OMC) The OMC is used to secure the operation of the GSM network. In case of big (regional) networks many OMCs are administrated by a Network Management Center (NMC). Mobile Station (MS) The MS is the mobile equipment with antenna, power supply, speaker, microphone used for communication. Subscriber Identity Module (SIM) - GSM network (provider) specific data Transmission Power - 2 watts for GSM watt for DSC

9 GSM Radio Interface GSM uses two multiplexing methods: FDMA-frequency multiplexing and TDMAtime multiplexing. Frequency Division Multiple Access Duplex distance 45 MHz Time Division Multiple Access uplink downlink MHz GSM-900: 124 carrier frequency channels á 200kHz TDMA Frame frame duration ms 8 time slots Duplex distance 95 MHz uplink downlink MHz DCS-1800: 374 carrier frequency channels á 200kHz 9

10 Channel Codecs GSM Radio Interface (2) Full Rate (FR) - 13 kbit/s Half Rate (HR) - 6 kbit/s Enhanced Full Rate (GSM-EFR) kbit/s Adaptive Multi-rate (AMR-NB) - 8 codecs with 4.75 to 12.2 kbit/s - uses optimized link adaptation (selects one codec based on link conditions) 10

11 GSM Security designed with a moderate level of security several cryptographic algorithms - A5/1 (stronger) and A5/2 (weaker) stream ciphers Authentication using shared-secret cryptography - Key stored on SIM card - Key never sent over air interface Serious weaknesses in both algorithms - Possible to break A5/2 in real-time 11

12 GSM Services Standard collection of applications and features available to mobile phone subscribers all over the world. Voice calls outgoing calls - handled by the Visited MSC (Mobile Switching Center) incoming calls - handled by the Gateway MSC 12

13 Data transmission GSM Services (2) Circuit-switched data protocols - Circuit Switched Data (CSD) - uses single radio time slot kbit/s - High-Speed Circuit Switched Data (HSCD) kbit/s (single time slot) by using different error correction - can use multiple time slots General Packet Radio Service (GPRS) - packet-switched data transmission protocol - incorporated into GSM standard in 1997 Short Message Service (SMS) - means of sending messages of up to 160 characters 13

14 GSM Services (3) GSM supports a comprehensive set of supplemenatry services that complement and support the telephony and data services shown before. Supplementary Services -CallForwarding - Barring of Outgoing/Incoming Calls -CallHold - Call Waiting - Mulitparty Service (Conference) - Calling Line Identification 14

15 General Packet Radio Service (GPRS) Enhancement to GSM standard introduced in 1997 GPRS is packet-switched - Supports Point-to-Point service (IP and X.25 networks) Multiple users share same transmission channel - theoretical limit is 160 kbit/s (using 8 time slots á 20 kbit/s) - practical bit rates are kbit/s (max. 4 time slots depending on channel coding) 15

16 General Packet Radio Service (GPRS) (2) GPRS data services GPRS upgrades GSM data services providing: - Multimedia Messaging Service (MMS) - Push to Talk (PTT) - Instant Messaging - Wireless Application Protocol (WAP) - Point-to-Point (PTP) service 16

17 EDGE Enhanced Datarate for GSM Evolution (also EGPRS) Technology that allows to increase data transmission and improve data transmission quality. bolt-on enhancement to GSM/GPRS networks introduced in requires no HW or SW changes in the GSM core networks uses 8 phase shift keying (8PSK) - produces a 3-bit word for every change in carrier phase data rates up to kbit/s for 4 timeslots (theoretical max kbit/s for 8 timeslots) accepted as part of the IMT-2000 family of 3G standards 17

18 Possible Questions What are the components of a GSM network? Describe the GSM architecture. What GSM services do you know? Name some GSM services. What is the main advantage of GPRS? 18

19 References UMTSlink.at Das Mobilefunkportal GSM World Wikipedia