Introduction to Mobile Cellular Networks Part I: 3G Mobile Core Network in a Nutshell

1. Introduction to Mobile Cellular NetworksPart I: 3G Mobile Core Network in a Nutshell VU 389.134 Video and Multimedia Transmissions over Cellular Networks 3.10.2011

2. What this lecture is about … • Video and Multimedia Transmissions over Cellular Networks • Cellular networks (GSM, UMTS, LTE, LTE-A) • Packet switched data transmission • Video and other services • Cross layer approaches • How to measure/analyze/optimize such services • What you should already know • Cellular network (basics) • UDP, TCP, IP, … • eMail / HTTP / streaming (basics) HTTP HyperText Transport Protocol IP Internet Protocol TCP Transport Control Protocol UDP User Datagram Protocol

3. The Problem • Today data services generate more traffic than voice • Radio link is expensive and limit resource • Data services • consume more bandwidth at less revenue • QoS definition is problematic • Looking for ways to offer constant QoS at reduced data-rate/bandwidth needs • Measurement and analysis of existing traffic • Link layer modeling from IP point of view • Cross layer optimization (video streaming, …) • Traffic modeling with respect to cellular networks QoS Quality of Service

4. Possible Solutions • Communication system are split into independent atomic layers • Open Systems Interconnection (OSI) reference model • Data transmission • Two consecutive layers: payload • Two corresponding layers: payload, signaling • Processing information stays within the layer

5. Some (more) Motivation • Today every layer is optimized to a large extend • e.g.: receivers fight for < 1dB improvement • Idea: use processing information from multiple layers • Soften the boundaries between two layers • e.g.: variable priority for video streaming and web browsing • Optimization problems get much harder • Optimum often hard to prove X X X TB Transport Block

6. Outline of this Lecture • Cellular Mobile Networks: (5.10.2009 - 16.11.2009 / Svoboda) • PS-Core Network • Link Error Analysis • Link Error Prediction • Measurement and Analysis • Video in Error Prone Environments (23.11.2009 - 14.12.2009 / Rupp) • Principles of Video Encoding • Error Detection and Concealment • Cross Layer Error Resilience in Video Streaming • End to End Video Quality Estimation • Traffic in Mobile Networks (11.01.2010 - 25.01.2010 / Svoboda) • Detection of Anomalies in a Network • Traffic Flows • Traffic Modeling in High-Delay Environments

7. Outline of today's talk • Evolution of mobile cellular networks • 3G Network Hierarchy • 3G core network Elements • 3G protocol Hierarchy • Simple procedures in mobile cellular networks • Journey of a packet through the network

8. Network Architecture • Hierarchical ordering of functional groups • Functional structures/groups • Defined by “functions” / procedures • Consist of one or several physical elements • Interfaces (reference points) • Points allowing for interconnection between functional structures IP Internet Protocol MS Mobile Station UE User Equipment

9. Network Architecture: Example GSM/GPRS • GSM (2G): digital circuit switched network for voice • All services reserve the same fixed bandwidth • Charging on time unit basis • Data rate: 9.6 kbit/s • GPRS (2.5G): extension for packet switched traffic • Packet switched (PS) domain is introduced • PS oriented shared data channels at the radio link • Data rate: ~114 kbit/s GSM Global System for Mobile Communication GPRS General Packet Radio Service SIM Subscriber Identity Module BTS Base Transceiver Station BSC Base Station Controller PCU Packet Control Unit MSC Mobile Switching Center SGSN Serving GPRS Support Node GGSN Gateway SGSN

10. Network Architecture: Example UMTS/HSPA • UMTS (3G): • The UTRAN (UMTS RAN) is added to existing 2.5G networks • WCDMA, soft handover, QoS, … • Link speed is variable but fixed to certain values. • Data rate: 384 kbit/s • HSPA (3.5G): • Real packet switched radio bearers (similar to GPRS) • No more soft handover • Data rate: 7.2 Mbit/s PS Packet Switched UMTSUniversal Mobile Telecommunications System HSPA High Speed Packet Access USIM Universal SIM NodeBNodeB RNC Radio Network Controller

11. Evolution of (digital) Cellular Networks • GSM (2G)  GPRS (2.5G) • No changes on the radio interface • Large changes in RAN • Birth of the PS-Core (!) • GPRS (2.5G) UMTS (3G) • Large changes in the RAN • The first network designed for PS traffic • Small changes in the Core • UMTS R99 (3G)  HSPA (3.5G) • Changes in the radio interface • No changes in the Core RAN Radio Access Network PS Packet Switched GSM Global System for Mobile Communication GPRS General Packet Radio Service UMTS Universal Mobile Telecommunications System HSPA High Speed Packet Access

12. The Complete Picture of a 3G Core Network 2G 3G

13. Summary of (digital) Cellular Networks • Main Components of a Cellular Network • User equipment • Radio access network • Core network • GSM: digital and circuit switched • GPRS: adds the CN PS-domain to GSM • UMTS: pseudo PS radio links, RAN  UTRAN • HSPA: PS radio links for UMTS, no soft handover RAN Radio Access Network PS Packet Switched GSM Global System for Mobile Communication GPRS General Packet Radio Service UMTS Universal Mobile Telecommunications System HSPA High Speed Packet Access

14. The Core Network Elements

15. TheMobile Switching Center (MSC) • Routing grid for Circuit Switched (CS) services • Main functions: • Interconnect of CS services • Mobility Management • Localization • Signaling • Protocols: • PCM30 / PCM30 (not AMR!) • Interfaces: • IuCS / SS7(E)

16. The Serving GPRS Support Node • Counter part to the MSC in the Packet Switched (PS) domain • Main functions: • Security / authentication • Mobility Management (MM): cell update, etc. • Handling of data sessions (routing) • Caching user subscriber data • Protocols: • GTP / GTP (not terminated in SGSN!) • Interfaces: • IuPS / Gn

17. The Gateway GPRS Supporting Node (GGSN) • „The Gatekeeper to the outer Territories“ • GGSN ‘hides’ the GPRS infrastructure • Main functions: • Handling of the PDP Context • Building a bridge to the external networks – eg. Internet • Converting the IP packets to GTP protocol • Billing, QoS, … • Protocols: • GTP / IP • Interfaces: • Gn (GTP) / Gi(IP)

18. The Home Location Register (HLR) • Database holding static user information • Telephone number (MSISDN = CC + NDC + SN) • Subscriber number (IMSI = MCC + MNC + MSIN) • Security issues – AUC (key) • QoSparameters • Available services (voice, packet....) • Position information: Visitor Location Register (VLR) • Protocols: • IP • Interfaces: • Gr, C MSISDN = MS - ISDN CC Country Code NDC National Dest. Code SN Subscriber Number IMSI Int. Mobile Subscriber Id MCC Mobile Country Code MNC Mobile Network Code MSIN Mobile Station IdNumber

19. Summary of Core Network Elements • Core Network Elements • CS: MSC, G-MSC • PS: SGSN, GGSN • OM: HLR, VLR, EIR, … • MSC / SGSN interconnect RAN to the CN • G-MSC / GGSN interconnect CN with other networks • HLR holds all “static” user information • VLR local copy of HLR in SGSN • Further Management units: • EIR, OMC, … CS Circuit Switched PS Packet Switched OM Operation and Maintenance MSC Mobile Switching Center G-MSC Gateway MSC SGSN Serving GPRS Supporting Node GGSN Gateway GPRS Supporting Node HLR Home Location Register VLR Visiting Location Register

20. The Protocols

21. The Protocol Hierarchy

22. The Control Plane SDH

23. The User Plane SDH

24. The GPRS Mobility Management (GMM) • GPRS version of the MM protocol (MM still needed) • Managing the mobility of the terminals • Present location • Connections management services • User identity confidentiality • User states: • Idle: the subscriber is not attached • Standby: the subscriber is attached • Ready: the subscriber is active

25. The RAN Application Part (RANAP) • Handles the signaling between UTRAN and PS-CN (Iu) • Booking ATM lines, Changing Setup, …. • Includes all control information for UTRAN • 3 Classes of elementary procedures: • General control services • Notification services • Dedicated control services • Some functions: • Iu Release (1) • Overload Control (2) • RAB Assignment (3) RAB Radio Access Bearer

26. The Signaling Connection Control Part (SCCP) • Task: • Abstraction between UMTS and transport system (ATM, IP) •  Transport System is hidden. • Supports • connection -less and –oriented extension to MTP • Address translation • Full OSI layer 3 compatibility • Below SS7 protocol

27. The GPRS Tunneling Protocol (GTP v0) • For the connection between RNC, SGSN, GGSN • Payload is attached to GTP headers (8Bytes) • Used for signaling and data • Fields: • Version: GTP v0 or v1 • Protocol Type: GTP, GTP’ (GTP’ protocol is used to transfer charging data to the Charging Gateway Function) • Flags: Extension, Sequence, N-PDU • Message Type: What is this GTP message about • Length: length of payload • Tunnel Endpoint Identifier: Start/End point of the GTP tunnel (user, APN)

28. The GTP -U / -C • GTP-C(ontrol) • GPRS mobility management between GSNs • Logically attached to the GTP-U tunnel – physically separated • Functions: • Create/Update/Change PDP Context • Echo Request/Response • RAN Information • GTP-U(ser) • Hides mobility from IP layer • Supports reordering of T-PDUs • TEID is always unique • Functions: • Data Transmission • Tunnel Setup/Release/Error • Echo Request/Response TEID Tunnel Endpoint IDentifier

29. Summary of Core Network Protocols • Protocol hierarchy • Non-access / Access Stratum • Radio / Transport Network Layer • Core network protocols: • GMM: location, user mobility, … • RANAP: signaling between UTRAN and CN • SCCP: abstraction between UMTS layers and transport layer • GTP-U: transport of user data payload • GTP-C: managing of corresponding GTP-U (always in pairs) • Every user has a least one GTP tunnel (pair) active • SGSN records the states of these protocols for every user CS Circuit Switched PS Packet Switched

30. Let's start the Journey . . .

31. Processed Steps • Now we will use the basics. • GPRS attach • PDP context activation • Mobile Station starts to send data (IP Packets)

32. Svoboda Activating a PDP Context

33. Protocol Mapping

34. Sending the Packet: UTRAN-SGSN

35. Sending the Packet: SGSN-GGSN

36. Where is the bird? Sending the Packet: Outer Regions

37. Summary of this lecture • Network hierarchy • Core network elements • Protocol hierarchy • How a data (IP) transmission over mobile cellular networks works • Important things/abbreviations • Subscriber: IMSI, TIMSI, GTP • Elements: RNC, SGSN, GGSN, NodeB • Interfaces: Gi, Gn, IuCS, IuPS • Procedures: PDP, GMM • Next stop: UTRAN

38. Thank you for your attention Questions? psvoboda@nt.tuwien.ac.at

39. Where to look? [1] RANAP on Iu: 3gpp 25.413; 23.108 (E Interface) [2] Iu User Plane: 3gpp 25.415 [3] GTP: 3gpp 29.060 [4] Core Network Basics: 3gpp 23.002 [5] www.umtslink.at [6] http://www.techfest.com/networking/ [7] http://www.manualy.sk/protocols2/pbook/gprs.htm#GTP [8] http://www.manualy.sk/protocols2/pbook/umts.htm [9] http://www.tkn.tu-berlin.de/curricula/ws0405/vl-umts/

40. Abbreviations (1) AAL2 ATM Adaptation Layer type 2 ALCAP Access Link Control Application Part APN Access Point Name AS Access Stratum ASN.1 Abstract Syntax Notation One ATM Asynchronous Transfer Mode BSC Base Station Controller BTS Base Transceiver Station CC Call Control CN Core Network CRNC Controlling RNC CS Circuit Switched DCH Dedicated Channel DL Downlink DRNC Drift RNC DRNS Drift RNS DSCH Downlink Shared Channel EP Elementary Procedure GERAN GSM/EDGE Radio Access Network GGSN Gateway GPRS Supporting Node G-MSC Gateway Mobile Switching Center GMM/SM GPRS Mobility Management / Session Management GPRS General Packet Radio System GSM Global System for Mobile communications GTP GPRS Tunneling Protocol GWCN GateWay Core Network HLR Home Location Register IE Information Element IMEI International Mobile Equipment Identity IMSI International Mobile Subscriber Identity IPv4 Internet Protocol (version 4) IPv6 Internet Protocol (version 6) MAC Media Access Control MBMS Multimedia Broadcast Multicast Service MM Mobility Management MOCN Multi Operator Core Network MSC Mobile services Switching Centre MTP Message Transfer Part NACC Network Assisted Cell Change NAS Non Access Stratum NRT Non-Real Time N-PDU Network – Protocol Data Unit P-TMSI Packet TMSI PCM Puls Code Modulation PCU Packet Control Unit PDCP Packet Data Convergence Protocol PDP Packet Data Protocol PDU Protocol Data Unit PLMN Public Land Mobile Network PS Packet Switched PSTN Public Switched Telephone Network QoS Quality of Service RAB Radio Access Bearer RANAP Radio Access Network Application Part RLC Radio Link Control RNC Radio Network Controller RNS Radio Network Subsystem RRC Radio Resource Control RT Real Time