Introduction to Mobile Cellular Networks

Part I: 3G Mobile Core Network in a Nutshell

VU 389.134Video and Multimedia Transmissions over Cellular

Networks

3.10.2011

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Video and Multimedia Transmissions over Cellular Networks 389.134

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 ProtocolIP Internet ProtocolTCP Transport Control ProtocolUDP User Datagram Protocol

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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

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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

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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

TCP Packet

TB Transport Block

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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

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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

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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 ProtocolMS Mobile StationUE User Equipment

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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 ServiceSIM Subscriber Identity ModuleBTS Base Transceiver StationBSC Base Station ControllerPCU Packet Control UnitMSC Mobile Switching CenterSGSN Serving GPRS Support NodeGGSN Gateway SGSN

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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 SwitchedUMTS Universal Mobile

Telecommunications SystemHSPA High Speed Packet AccessUSIM Universal SIMNodeB NodeBRNC Radio Network Controller

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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 NetworkPS Packet SwitchedGSM Global System for Mobile

CommunicationGPRS General Packet Radio ServiceUMTS Universal Mobile

Telecommunications SystemHSPA High Speed Packet Access

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The Complete Picture of a 3G Core Network

2G

3G

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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 NetworkPS Packet SwitchedGSM Global System for Mobile

CommunicationGPRS General Packet Radio ServiceUMTS Universal Mobile

Telecommunications SystemHSPA High Speed Packet Access

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The Core Network Elements

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The Mobile 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)

RNC

MSC G-MSCE

Iu-cs

PSTN

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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 RNC SGSN GGSNIu-ps Gn

HLR

Gr

SGSN

Gn

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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)

SGSN GGSNGn INTERNETGi

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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)– QoS parameters– Available services (voice, packet....)– Position information: Visitor Location Register (VLR)

• Protocols:– IP

• Interfaces:– Gr, C

SGSNHLRGr

G-MSC

C

MSISDN = MS - ISDNCC Country CodeNDC National Dest. CodeSN Subscriber Number

IMSI Int. Mobile Subscriber IdMCC Mobile Country CodeMNC Mobile Network CodeMSIN Mobile Station Id Number

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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 SwitchedPS Packet SwitchedOM Operation and MaintenanceMSC Mobile Switching CenterG-MSC Gateway MSCSGSN Serving GPRS Supporting NodeGGSN Gateway GPRS Supporting NodeHLR Home Location RegisterVLR Visiting Location Register

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The Protocols

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The Protocol Hierarchy

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The Control Plane

L1

ATM

SCCP

RANAP

MAC

RLC

RRC

UDP/ATM

GTP-C

ATM

RANAP

SM/ GMM

UDP/ATM

GTP-C

SM

RNC SGSN GGSN

PDP context Management

SCTP/IP

SCCP

SCTP/IP

SDH

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The User Plane

L1

ATM/UDP

GTP-U

MAC

RLC

PDCP

UDP/ATM

ATM UDP/ATM

RNC SGSN GGSNUE

PDP context

GTP-U GTP-U GTP-U

IP

Iu - UP Iu - UP

SDH

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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

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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

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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

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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)

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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

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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 SwitchedPS Packet Switched

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Let's start the Journey . . .

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

PDH

ATM

AAL-5

IP

UDP

GTP

PDH

ATM

AAL-5

IP

UDP

GTP

PDH

ATM

AAL-5

IP

UDP

GTP

PDH

ATM

AAL-5

IP

UDP

GTP

UTRAN SGSN

GGSN

PDPPDP

PAYLOAD PAYLOAD

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Svoboda

Activating a PDP Context

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Protocol Mapping

Image Size = 2000 Bytes

Data1 (1472)

0 1500

TCP IP

201472 20

Data2

0 1500

TCP IP

20528 20

Original

IP – Layer USER

UTRAN

GTP Layer + UDP, IP Core GTP

8

UDP IP

8 20

GTP

8

UDP IP

8 20

ATM Layer

48 5

48 5

48 5

5

48 5

48 548

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Sending the Packet: UTRAN-SGSN

PAYLOAD (1500)

TCP Header (20)

IP Header (20)

GTP Header (8)

UDP (8)

IP (20)

ATM (5)

PDH (var)

RNC SGSN

SGSN

Iu-ps

Gn

UTRAN

PAYLOAD (1500)

TCP Header (20)

IP Header (20)

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Sending the Packet: SGSN-GGSN

PAYLOAD (1500)

TCP Header (20)

IP Header (20)

GTP Header (8)

SGSN GGSNGn

PAYLOAD (1500)

TCP Header (20)

IP Header (20)

PAYLOAD (1500)

TCP Header (20)

IP Header (20)

GTP Header (8)

UDP (8)

IP (20)

ATM (5)

PDH (var)

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Sending the Packet: Outer Regions

INTERNET

PAYLOAD (1500)

TCP Header (20)

IP Header (20)

Ethernet

PAYLOAD (1500)

TCP Header (20)

IP Header (20)

Ethernet

GGSN

Where is the bird?

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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

Thank you for your attention

Questions?psvoboda@nt.tuwien.ac.at

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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/

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Abbreviations (1)AAL2 ATM Adaptation Layer type 2ALCAP Access Link Control Application PartAPN Access Point NameAS Access StratumASN.1 Abstract Syntax Notation OneATM Asynchronous Transfer ModeBSC Base Station ControllerBTS Base Transceiver StationCC Call ControlCN Core NetworkCRNC Controlling RNCCS Circuit SwitchedDCH Dedicated ChannelDL DownlinkDRNC Drift RNCDRNS Drift RNSDSCH Downlink Shared ChannelEP Elementary ProcedureGERAN GSM/EDGE Radio Access NetworkGGSN Gateway GPRS Supporting NodeG-MSC Gateway Mobile Switching CenterGMM/SM GPRS Mobility Management / Session ManagementGPRS General Packet Radio SystemGSM Global System for Mobile communicationsGTP GPRS Tunneling ProtocolGWCN GateWay Core NetworkHLR Home Location RegisterIE Information ElementIMEI International Mobile Equipment IdentityIMSI International Mobile Subscriber Identity

IPv4 Internet Protocol (version 4)IPv6 Internet Protocol (version 6)MAC Media Access ControlMBMS Multimedia Broadcast Multicast ServiceMM Mobility ManagementMOCN Multi Operator Core NetworkMSC Mobile services Switching CentreMTP Message Transfer PartNACC Network Assisted Cell ChangeNAS Non Access StratumNRT Non-Real TimeN-PDU Network – Protocol Data UnitP-TMSI Packet TMSIPCM Puls Code ModulationPCU Packet Control UnitPDCP Packet Data Convergence ProtocolPDP Packet Data ProtocolPDU Protocol Data Unit PLMN Public Land Mobile NetworkPS Packet SwitchedPSTN Public Switched Telephone NetworkQoS Quality of ServiceRAB Radio Access BearerRANAP Radio Access Network Application PartRLC Radio Link ControlRNC Radio Network ControllerRNS Radio Network SubsystemRRC Radio Resource ControlRT Real Time