Intro: Cellular systems. Communication Systems. by Petar Popovski & Hans Peter Schwefel. Mm1 Cellular concept (PP) Mm2 Multiple access techniques (PP)

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1 Communication Systems by Petar Popovski & Mm1 Cellular concept (PP) Mm2 Multiple access techniques (PP) Mm3 Introduction to GSM & GPRS (hps) Mm4 Wireless Personal Area Networks and Bluetooth (PP) Mm5 WLAN and WIMAX (PP/hps) Page 1 Intro: Cellular systems Geographic region subdivided in radio cells Base Station provides radio connectivity to Mobile Station within cell Handover to neighbouring base station when necessary Base Stations connected by some networking infrastructure Page 2

2 Cellular systems: technologies & subscribers Subscribers [million] GSM total TDMA total CDMA total PDC total Analogue total Total wireless Prediction (1998) year Page 3 Content 1. Introduction Cellular Concepts & Technologies 2. GSM Network Architecture, Air Interface Signalling/Call Setup, Mobility Support Data Services, HSCSD 3. GPRS & UMTS GPRS: Architecture, Air-Interface, Core-Network Modifications UMTS domains and architecture 4. IP transport in Packet Switched UMTS/GPRS Networks PDP contexts, APNs, TFTs Bearers full network architecture Exercise Page 4

3 GSM: Global System for Mobile Communication History: Today: 2nd Generation of Mobile Telephony Networks 1982: Groupe Spèciale Mobile (GSM) founded 1987: First Standards defined 1991: Global System for Mobile Communication, Standardisation by ETSI (European Telecommunications Standardisation Institute) - First European Standard 1995: Fully in Operation Deployed in more than 184 countries in Asia, Africa, Europe, Australia, America) more than 747 million subscribers more than 70% of all digital mobile phones use GSM over 10 billion SMS per month in Germany, > 360 billion/year worldwide Page 5 GSM Architecture Components: BTS: Base Transceiver Station BSC: Base Station Controller MSC: Mobile Switching Center HLR/VLR: Home/Visitor Location Register AuC: Authentication Center EIR: Equipment Identity Register OMC: Operation and Maintenance Center Transmission: Circuit switched transfer Radio link capacity: 9.6 kb/s (FDMA/TDMA) Duration based charging Radio Subsystem (RSS) MS MS MS U m Base Station Subsystem BTS BTS BTS A bis BSC BSC Network and Switchung Subsystem A MSC VLR HLR Connection to ISDN, PDN PSTN Operation Subsystem O AuC OMC EIR Radio Link Page 6

4 GSM Services Traditional voice services voice telephony primary goal of GSM was to enable mobile telephony offering the traditional bandwidth of 3.1 khz emergency number common number throughout Europe (112); mandatory for all service providers; free of charge; connection with the highest priority (preemption of other connections possible) Multinumbering several ISDN phone numbers per user possible voice mailbox (implemented in the fixed network supporting the mobile terminals) Supplementary services, e.g.: identification, call forwarding, number suppression, conferencing Non-Voice Services (examples) Fax Transmissions electronic mail (MHS, Message Handling System, implemented in the fixed network) Short Message Service (SMS) alphanumeric data transmission to/from the mobile terminal using the signaling channel, thus allowing simultaneous use of basic services and SMS Page 7 GSM: Radio Technology Cellular Concept: segmentation of geographical area into cells Cell sizes vary from some 100 m up to 35 km depending on user density, geography, transceiver power etc. hexagonal shape of cells is idealized (cells overlap, shapes depend on geography) use of several carrier frequencies avoid same frequency in adjoining cells if a mobile user changes cells handover of the connection to the neighbor cell cell possible radio coverage of the cell idealized shape of the cell Page 8

5 GSM: Air Interface I Frequency Division Multiple Access (FDMA) Separate up-link (MT BTS) and down-link (BTS MT) traffic Two 25MHZ bands Distinguish 124 adjacent channels within each band Each channel 200kHz Frequenzband der Mobilstation Frequenzband der Basisstation Uplink Downlink MHz Radio Network Planning: Determine location of BTS Determine number of TRX per BTS Multiple transceivers (TRX) per BTS (e.g. 1,4,or 12) simultaneous use of different FDMA channels Assign subsets of 124 channels to BTSs Kanäle: khz Page 9 GSM: Air Interface II Time Division Multiple Access (TDMA) Within each channel: sequence of TDMA frames TDMA frames subdivided into 8 time-sots time slot: TDMA Frame 4,615 ms data bits training data bits tail bits 1 toggle 1 toggle 3 tail bits bit bit burst 148 bit time slot 156,25 bit 0,577 ms Page 10

6 GSM: TDMA hierarchy of frames hyperframe h 28 min s superframe s multiframe ms ms frame slot burst Page ms 577 µs GSM Air Interface: Combination of TDMA & FDMA frequency MHz 124 channels (200 khz) downlink MHz 124 channels (200 khz) uplink higher GSM frame structures time GSM TDMA frame ms GSM time-slot (normal burst) guard space tail user data S Training S user data tail 3 bits 57 bits 1 26 bits 1 57 bits 3 guard space µs 577 µs Page 12

7 GSM: Logical Channels Page 13 Functionalities in Radio Subsystem BTS comprises radio specific functions BSC is the switching center for radio channels Functions BTS BSC Management of radio channels X Frequency hopping (FH) X X Management of terrestrial channels X Mapping of terrestrial onto radio channels X Channel coding and decoding X Rate adaptation X Encryption and decryption X X Paging X X Uplink signal measurements X Traffic measurement X Authentication X Location registry, location update X Handover management X Page 14

8 Overview: GSM protocol layers for signaling U m A bis A MS BTS BSC MSC CM CM MM MM RR LAPD m RR LAPD m BTSM LAPD RR BTSM LAPD BSSAP SS7 BSSAP SS7 radio radio PCM PCM PCM PCM 16/64 kbit/s 64 kbit/s / Mbit/s Page 15 Example: Mobile Terminated Call 1. calling a GSM subscriber 2. forwarding call to GMSC 3. signal call setup to HLR 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 calling station 4 HLR VLR PSTN GMSC 1 2 MSC BSS BSS BSS MS Page 16

9 Example: Message flow between MS and BTS for Mobile Terminated Call MS MTC BTS paging request channel request immediate assignment paging response authentication request authentication response ciphering command ciphering complete setup call confirmed assignment command assignment complete alerting connect connect acknowledge data/speech exchange Page 17 Mobility Support I: Types of handover MS MS MS MS BTS BTS BTS BTS BSC BSC BSC MSC MSC Page 18

10 Mobility Support II: Handover decision receive level BTS old receive level BTS old HO_MARGIN MS MS BTS old BTS new Page 19 Mobility support III: Handover procedure MS measurement report HO command BTS old measurement result BSC old HO decision HO required HO command HO command HO access Link establishment clear command clear complete clear command clear complete MSC HO request BSC new resource allocation ch. activation HO request ack ch. activation ack HO complete HO complete BTS new Page 20

11 Mobile Communication & Data Traffic The future Internet will mainly be accessed by mobile devices Subscriptions worldwide (millions) Mobile Fixed Mobile Internet Fixed Internet Mobile Subscribers Mobile Internet Subscribers Page 21 Data services in GSM Data transmission standardized with only 9.6 kbit/s advanced coding allows 14,4 kbit/s not enough for Internet and multimedia applications HSCSD (High-Speed Circuit Switched Data) mainly software update bundling of several time-slots to get higher AIUR (Air Interface User Rate) (e.g., 57.6 kbit/s using 4 slots, 14.4 each) advantage: ready to use, constant quality, simple disadvantage: channels blocked for voice transmission AIUR [kbit/s] TCH/F4.8 TCH/F9.6 TCH/F Page 22

12 Content 1. Introduction Cellular Concepts & Technologies 2. GSM Network Architecture, Air Interface Signalling/Call Setup, Mobility Support Data Services, HSCSD 3. GPRS & UMTS GPRS: Architecture, Air-Interface, Core-Network Modifications UMTS domains and architecture 4. IP transport in Packet Switched UMTS/GPRS Networks PDP contexts, APNs, TFTs Bearers full network architecture Exercise Page 23 GPRS: General Packet Radio Service Packet Switched Extension of GSM 1996: new standard developed by ETSI Components integrated in GSM architecture Improvements: Packet-switched transmission Higher transmission rates on radio link (multiple time-slots) Volume based charging Always ON mode possible Operation started in 2001 (Germany) Page 24

13 GPRS - Architecture Components: CCU: Channel Coding Unit PCU: Packet Control Unit SGSN: Serving GPRS Support Node GGSN: Gateway GPRS Support Node GR: GPRS Register GSM GPRS Components BSS Um MS Transmission: Packet Based Transmission Radio link: Radio transmission identical to GSM Different coding schemes (CS1-4) Use of Multiple Time Slots Volume Based Charging MSC B T S B S C C C U A Abis Gb Gp Gs P C U SGSN Gn Other PLMN GGSN Gi HLR GR PDN G Gr Page 25 GPRS: Channel Coding and Multiplexing Selection of Coding depending on quality of radio connection Time Slot (MS-> BTS) Coding Scheme 1 Coding Scheme 2 Coding Scheme 3 9,05 kbit/s 9,05 kbit/s 9,05 kbit/s 13,4 kbit/s ,05 kbit/s 13,4 kbit/s 13,4 kbit/s... 15,6 kbit/s 15,6 kbit/s 15,6 kbit/s optimal radio quality: no interference, etc. Coding Scheme 4 21,4 kbit/s 21,4 kbit/s 21,4 kbit/s... Overall transmission rate ,2 kbit/s Page 26

14 Examples for GPRS device classes Class Receiving slots Sending slots Maximum number of slots Page 27 GPRS user data rates in kbit/s Coding scheme 1 slot 2 slots 3 slots 4 slots 5 slots 6 slots 7 slots 8 slots CS CS CS CS Page 28

15 GPRS: channel types Page 29 Example: Channel Assignment 4 TRX 4 FDMA channels 32 time slots 3 Signalling Channels 1TS: FCCH, SCH, BCCH (PBCCH), PAGCH, RACH (PRACH) 2 TS: SDCCH 29 Tracffic Channels (TCH/PDTCH) GSM calls only GPRS calls only Common channels Page 30

16 GPRS architecture and interfaces SGSN G n MS BSS SGSN GGSN PDN U m G b G n G i MSC HLR/ GR VLR EIR Page 31 GPRS Core Network Functions Packet Handling Resource Management Accounting Configuration Management Mobility Management Handover Control and SGSN Change Handling Interception Handling Performance Management Session Management SMS Handling Protocols & Interfaces Fault & Maintenance Management Functions in SGSN and GGSN Functions in SGSN Page 32

17 GPRS: Protocol Stack RLC: Radio Link Control Acknowledged mode (reliable) or unacked LLC: Logical Link Control Acknowledged mode (reliable) or unacked BSSGRP: BSS GPRS Protocol SNDCP: Sub-Network Dependent Convergence Protocol GTP: GPRS Tunneling Protocol Mobility Support Page 33 Data Units in GPRS Page 34

18 Coding Schemes USF = Uplink State Flag owner of time-slot in next uplink TDMA frame Allows multiplexing of up to 8 MS on one time-slot Block header contains Temporary Flow Identifier (TFI) TFI and direction identifies Temporary Block Flow (TBF) Page 35 GPRS: Obtaining IP Connectivity GPRS attach Authentication of MS Establishment/Ini tialization of security functions SGSN BSS U m G b G r Attach Request (NSAPI,TI,PDP Type) HLR PDP Context Setup Obtain IP address Connect to external network [see later] Authentication/Ciphering Attach Accept (NSAPI,TI,PDP Type) Attach Complete (NSAPI,TI,PDP Type) Authentication/Ciphering Insert Subscriber Data (NSAPI,TI,PDP Type) Insert Subscriber Data Ack (NSAPI,TI,PDP Type) Page 36

19 Enhanced Data rates for the GSM Evolution (EDGE) Time Slot (MS-> BTS) Transmission Rate New Modulation Scheme 8 PSK 48 kbit/s 48 kbit/s 48 kbit/s kbit/s Advantages Increased Data Rate No Modificatíons in Core Network (SGSN/GGSN) required Disadvantages New Modulationscheme(8 PSK), not compatible to GSMK HW Changes in the BTS required Page 37 3 rd Generation Systems: IMT-2000 Proposals for IMT-2000 (International Mobile Telecommunications) UWC-136, cdma2000, WP-CDMA UMTS (Universal Mobile Telecommunications System) from ETSI Frequencies ITU allocation (WRC 1992) MHz IMT-2000 MSS IMT-2000 MSS Europe GSM 1800 DE CT T D D UTRA FDD T MSS D D UTRA FDD MSS China GSM 1800 IMT-2000 MSS IMT-2000 MSS Japan cdma2000 PHS W-CDMA MSS cdma2000 W-CDMA MSS North America PCS MHz Page 38 MSS rsv. MSS

20 Universal Mobile Telecommunication System (UMTS) Currently standardized by 3rd Generation Partnership Project (3GPP), see [North America: 3GPP2] So far, four releases: R 99, R4, R5, R6 Modifications: New methods & protocols on radio link increased access bandwidth Coexistence of two domains in the core network Packets Switched (PS) Circuit Switched (CS) New Services IP Service Infrastructure: IP Based Multimedia Subsystems (IMS) (R5) Page 39 UMTS Domains CS MGW MSC-Serv./VLR BSS (RAN/GERAN) Nb G/E/Nc Mc BTS Abis A CS MGW M S C -Serv./VLR Nc BSC GMSC-Serv. Um BTS Gb Iu C s D C Nb Mc SIM-ME CS MGW SIM ME HSS/AuC CS Domain USIM Cu MS Node B Iu bis UTRAN RNC Gs Gr Cx Gc IM S D om ain (Release 5) Mb/Gi Uu Node B Gn Iur RNC Iu P S SGSN GGSN PS Domain Access Network Domain C ore N etw ork Domain User Equipm ent Domain Infrastructure Domain Page 40

21 UMTS Network Domains Radio Access Network Node B (Base station) Radio Network Controller (RNC) Mobile Core Network Serving GPRS Support Node (SGSN) Gateway GPRS Support Node (GGSN) Mobile Switching Center (MSC) Home/Visited Location Register (HLR/VLR) User User Equipment Equipment Domain Domain Routers/Switches, DNS Server, DHCP Server, Radius Server, NTP Server, Firewalls/VPN Gateways Application/Services IP-Based Multimedia Subsystem (IMS) [see 9 th Semester] Operation, Administration & Maintenance (OAM) Charging Network [Legal Interception] Access Access Network Network Domain Domain Service Service and and Application Application Domain Domain Core Core Network Network Domain Domain Charging/ Charging/ Lawful Lawful Interception/ Interception/ OAM OAM Other Other Networks Networks (IP/ (IP/ ISDN) ISDN) Page 41 UMTS Radio Access Network (UTRAN): architecture CDMA (Code Division Multiple Access) on Radio Link transmission rate theoretically up to 2Mbit/s (realistic up to 300kb/s) Page 42

22 Content 1. Introduction Cellular Concepts & Technologies 2. GSM Network Architecture, Air Interface Signalling/Call Setup, Mobility Support Data Services, HSCSD 3. GPRS & UMTS GPRS: Architecture, Air-Interface, Core-Network Modifications UMTS domains and architecture 4. IP transport in Packet Switched UMTS/GPRS Networks PDP contexts, APNs, TFTs Bearers full network architecture Exercise Page 43 Transport of IP packets IP tackets are tunnelled through the UMTS/GPRS network (GTP GPRS tunneling protocol) User IP (v4 or v6) Terminal UTRAN SGSN GGSN Application Server Radio Bearer GTP-U GTP-U Application IP v4 or v6 IP v4 or v6 IP v4 or v6 Relay Relay PDCP PDCP GTP-U GTP-U GTP-U GTP-U RLC MAC RLC MAC UDP/IP v4 or v6 AAL5 UDP/IP v4 or v6 AAL5 UDP/IP v4 or v6 L2 UDP/IP v4 or v6 L2 L2 L1 L1 ATM ATM L1 L1 L1 [Source: 3GPP] Uu Iu-PS Gn Gi Page 44

23 IP Transport: Concepts PDP contexts (Packet Data Protocol) activation done by UE before data transmission specification of APN and traffic parameters GGSN delivers IP address to UE set-up of bearers and mobility contexts in SGSN and GGSN activation of multiple PDP contexts possible Access Point Names (APN) APNs identify external networks (logical Gi interfaces of GGSN) At PDP context activation, the SGSN performs a DNS query to find out the GGSN(s) serving the APN requested by the terminal. The DNS response contains a list of GGSN addresses from which the SGSN selects one address in a round-robin fashion (for this APN). Traffic Flow Templates (TFTs) set of packet filters (source address, subnet mask, destination port range, source port range, SPI, TOS (IPv4), Traffic Class (v6), Flow Label (v6) used by GGSN to assign IP packets from external networks to proper PDP context GPRS tunneling protocol (GTP) For every UE, one GTP-C tunnel is established for signalling and a number of GTP-U tunnels, one per PDP context (i.e. session), are established for user traffic. Page 45 IP Transport: PDP Context & APNs Same PDP (IP) address and APN GGSN ISP X PDP Context X 1 (APN X, IP address X, QoS 1 ) Terminal PDP Context X 2 (APN X, IP address X, QoS 2 ) SGSN PDP Context selection based on TFT (downstream) PDP Context Y (APN Y, IP address Y, QoS) PDP Context Z (APN Z, IP address Z, QoS) GGSN APN Z APN Y APN X ISP Z ISP Y [Source: 3GPP] Page 46

24 * 0 # UE1 UMTS Data Transport: Bearer Hierarchy Air Interface TE MT UTRAN/ GERAN CN Iu EDGE NODE End-to-End Service (IP Bearer Service) CN Gateway TE/AS TE/MT Local Bearer Service UMTS Bearer Service Service External Bearer Service Radio Access Bearer Service CN Bearer Service Radio Bearer Service Iu Bearer Service Backbone Bearer Service Physical Radio Service Physical Bearer Service RAN 3G SGSN 3G GGSN User Equipment Page 47 The full picture of the UMTS packet switched domain MNO1`s Network SS7, Gc SS7, Gr Network Services RADIUS DNS DHCP NS IMS Dom ain DNS IMS HSS P-CSCF I/S-CSCF AS Network V ideo Messages DNS FTP AS VPN -GWY Corp. Network A S HLR/AuC Gi Network Node B RNC DNS Gn-PRI DNS Gn-SEC DMZ IDS BG Internet AS Node B SGSN Gn Network GGSN IDS DNS Ext HTTP proxy BG MNO3 IMS DNS Ext BG MNO1`s Backbone UE3 GRX Network Page 48 BG MNO2 UE2 Roaming Support: UE attaches with SGSN in visited network PDP context is set-up to GGSN in home network (via Gp interface, GRX network)

25 Message Flow: PDP Context Setup Page 49 Summary 1. Introduction Cellular Concepts & Technologies 2. GSM Network Architecture, Air Interface Signalling/Call Setup, Mobility Support Data Services, HSCSD 3. GPRS & UMTS GPRS: Architecture, Air-Interface, Core-Network Modifications UMTS domains and architecture 4. IP transport in Packet Switched UMTS/GPRS Networks PDP contexts, APNs, TFTs Bearers full network architecture Exercise Page 50

26 Acknowledgements/References Lecture notes: Mobile Communciations, Jochen Schiller, Marco Hoffmann, Master Thesis, Simulation of a flow-control algorithm between two nodes of the GPRS network, TU Munich and Siemens AG, Tutorial: IP Technology in 3 rd Generation mobile networks, Siemens AG (J. Kross, L. Smith, H. Schwefel) Various 3GPP Presentations. J. Schiller: Mobile Communications. Addison-Wesley, GPRS books: T. Halonen, J. Romero, J. Melero: GSM, GRPS, EDGE Performance: Evolution towards 3G/UMTS, Wiley, 2003 Page 51 Exercises: 1. Data Rates: A user wants to do an FTP download of a 8MB Power-Point Presentation. Compute the duration of this download for the following access technologies GSM data service HSCSD, 4 timeslots GPRS, 4 timeslots (downlink) EDGE, 8 timeslots Wired ISDN access (64kbit/s) Give at least two reasons why the actual download times are likely to be longer than the ones just computed. Charging: The operator charges in GSM 15cent/min, in GPRS 0.1cent/kB. Compare the costs of the GSM and GPRS download in the FTP case as well as for a Web-session with duration of 1hour and overall data volume of 150kB. 2. IP transport in GPRS networks: a mobile user has set-up a PDP context to an ISP which has assigned him the IP address (private). The user now iniates a web access to the CNN server. Describe the header structure of the IP packet which is sent downstream from the GGSN to the SGSN (detailling the IP source and destination address). 3. GPRS overhead: Consider an FTP (over TCP over IP) download in a GPRS setting when a mobile device uses 3 timeslots downlink and CS-2. Assume a an IP-packet size of 1500 Bytes. Compute the necessary volume of header-information and FEC for one IP packet on the air-interface. Compute the theoretical maximal L4 payload throughput as allowed by the GPRS air-interface transmission! Compute the ratio of up-link and down-link traffic volumes as created by TCP (assuming delayed Acks). What L4 throughput do you expect to achieve in a download of a small file of 2000 Bytes? Page 52