wireless communication protocols and technologies

Hans Peter Schwefel

Wireless Networks I, Lecture 5, Spring 04

Wireless Communication Protocols and Technologies

by Tatiana Madsen & Hans Peter Schwefel

• Mm1 Introduction. Wireless LANs (TKM)

• Mm2 Wireless Personal Area Networks and Bluetooth (TKM)

• Mm3 IP Mobility Support (HPS)

• Mm4 Ad hoc Networks (TKM)

• Mm5 Overview of GSM, GPRS, UMTS (HPS)

www.kom.auc.dk/~tatiana/ www.kom.auc.dk/~hps/

Hans Peter Schwefel


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

Hans Peter Schwefel


Cellular systems: technologies & subscribers

0

200

400

600

800

1000

1200

1996 1997 1998 1999 2000 2001 2002 year

Su

bsc

rib

ers

[mill

ion

] GSM total

TDMA total

CDMA total

PDC total

Analogue total

Total wireless

Prediction (1998)

Hans Peter Schwefel


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

Hans Peter Schwefel


GSM: Global System for Mobile Communication

• 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

History:

Today:

Hans Peter Schwefel


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

BSC

BSC

MS

BTS

BTS

BTS

MS

MS

MSC

HLR

VLR

OMC

EIR

AuC

O

Abis AUm

Radio Link

Base StationSubsystem

Network andSwitchung Subsystem

OperationSubsystem

Connection toISDN, PDNPSTN

Radio Subsystem (RSS)

Hans Peter Schwefel


GSM Services ‘Traditional’ voice services

– voice telephonyprimary goal of GSM was to enable mobile telephony offering the traditional bandwidth of 3.1 kHz

– emergency numbercommon number throughout Europe (112); mandatory for all service providers; free of charge; connection with the highest priority (preemption of other connections possible)

– Multinumberingseveral 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

Hans Peter Schwefel


possible radio coverage of the cell

idealized shape of the cell

cell

GSM: Radio TechnologyCellular 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

Hans Peter Schwefel


1 2 3 124

890 915Uplink Downlink

MHz 935 960

Kanäle:

200 kHz

Frequenzband derMobilstation

Frequenzband derBasisstation

GSM: Air Interface IFrequency Division Multiple Access (FDMA)• Separate up-link (MTBTS) and down-link (BTSMT) traffic

– Two 25MHZ bands

• Distinguish 124 adjacent channels within each band– Each channel 200kHz

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

Hans Peter Schwefel


0 1 2 3 4 5 6 7

4,615 ms

data bits data bitstraining

57 26 57

time slot:

3 tail bits 3 tail bits1 togglebit

1 togglebit

burst 148 bit

time slot 156,25 bit

0,577 ms

GSM: Air Interface IITime Division Multiple

Access (TDMA)• Within each channel: sequence

of TDMA frames• TDMA frames subdivided into

8 time-sots

TDMA Frame

Hans Peter Schwefel


GSM: TDMA hierarchy of frames0 1 2 2045 2046 2047...

hyperframe

0 1 2 48 49 50...

0 1 24 25...

superframe

0 1 24 25...

0 1 2 48 49 50...

0 1 6 7...

multiframe

frame

burst

slot

577 µs

4.615 ms

120 ms

235.4 ms

6.12 s

3 h 28 min 53.76 s

Hans Peter Schwefel


1 2 3 4 5 6 7 8

higher GSM frame structures

935-960 MHz124 channels (200 kHz)downlink

890-915 MHz124 channels (200 kHz)uplink

frequ

ency

time

GSM TDMA frame

GSM time-slot (normal burst)

4.615 ms

546.5 µs577 µs

tail user data TrainingSguardspace S user data tail

guardspace

3 bits 57 bits 26 bits 57 bits1 1 3

GSM Air Interface: Combination of TDMA & FDMA

Hans Peter Schwefel


Functionalities in Radio Subsystem• BTS comprises radio specific functions• BSC is the switching center for radio channels

Functions BTS BSCManagement of radio channels XFrequency hopping (FH) X XManagement of terrestrial channels XMapping of terrestrial onto radio channels XChannel coding and decoding XRate adaptation XEncryption and decryption X XPaging X XUplink signal measurements XTraffic measurement XAuthentication XLocation registry, location update XHandover management X

Hans Peter Schwefel


Overview: GSM protocol layers for signaling

CM

MM

RR

MM

LAPDm

radio

LAPDm

radio

LAPD

PCM

RR’ BTSM

CM

LAPD

PCM

RR’BTSM

16/64 kbit/s

Um Abis A

SS7

PCM

SS7

PCM

64 kbit/s /2.048 Mbit/s

MS BTS BSC MSC

BSSAP BSSAP

Hans Peter Schwefel


Example: Mobile Terminated Call1. calling a GSM subscriber

2. forwarding call to GMSC

3. signal call setup to HLR

4. 5. 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

PSTNcallingstation

GMSC

HLR VLR

BSSBSSBSS

MSC

MS

1 2

3

4

5

6

7

8 9

10

11 12

1316

10 10

11 11 11

14 15

17

Hans Peter Schwefel


Example: Message flow between MS and BTS for Mobile Terminated Call

BTSMS

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

MTC

Hans Peter Schwefel


Mobility Support I: Types of handover

MSC MSC

BSC BSCBSC

BTS BTS BTSBTS

MS MS MS MS

1

23

4

Hans Peter Schwefel


Mobility Support II: Handover decision

receive levelBTSold

receive levelBTSold

MS MS

HO_MARGIN

BTSold BTSnew

Hans Peter Schwefel


Mobility support III: Handover procedure

HO access

BTSold BSCnew

measurementresult

BSCold

Link establishment

MSC

MSmeasurementreport

HO decision

HO required

BTSnew

HO request

resource allocation

ch. activation

ch. activation ackHO request ackHO commandHO commandHO command

HO completeHO completeclear commandclear command

clear complete clear complete

Hans Peter Schwefel


0

200

400

600

800

1000

1200

1400

1600

1800

1995 2000 2005 2010

Subscriptions worldwide (millions)

Mobile InternetSubscribers

MobileSubscribers

Mobile

Fixed

Mobile Internet

Fixed Internet

• The future Internet will mainly be accessed by mobile devices

Mobile Communication & Data Traffic

Hans Peter Schwefel


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/F14.44.8 19.6 2 1

14.4 3 119.2 4 228.8 3 238.4 443.2 357.6 4

Hans Peter Schwefel


Content





Exercise

Hans Peter Schwefel


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)

Hans Peter Schwefel


GPRS - Architecture

PDN

Other

PLMN

GSM GPRS

BTS

CCU

MSC

BSC

PCU

HLR GR

GGSN

Components

A Abis Gb Gp

Gs

Gn

G Gr

Gi

UmBSS

SGSN

MS

Components:• CCU: Channel Coding Unit

• PCU: Packet Control Unit

• SGSN: Serving GPRS Support Node

• GGSN: Gateway GPRS Support Node

• GR: GPRS Register

Transmission: • Packet Based Transmission• Radio link:

– Radio transmission identical to GSM– Different coding schemes (CS1-4)– Use of Multiple Time Slots

• Volume Based Charging

Hans Peter Schwefel


GPRS: Channel Coding and Multiplexing

9,05 kbit/s

.....

Time Slot (MS-> BTS)

Coding Scheme 1

72.4.......171,2 kbit/s

9,05 kbit/s

13,4 kbit/s

9,05 kbit/s

1 2 8

13,4 kbit/s 13,4 kbit/s

15,6 kbit/s 15,6 kbit/s 15,6 kbit/s

.....

.....

21,4 kbit/s .....21,4 kbit/s 21,4 kbit/s

9,05 kbit/s

3

Coding Scheme 2

Coding Scheme 3

Coding Scheme 4

.....

‚optimal‘ radio quality: no interference, etc.

Selection of Codingdepending on qualityof radio connection

Overall transmission rate

Hans Peter Schwefel


Examples for GPRS device classes

Class Receiving slots Sending slots Maximum number of slots

1 1 1 2

2 2 1 3

3 2 2 3

5 2 2 4

8 4 1 5

10 4 2 5

12 4 4 5

Hans Peter Schwefel


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-1 9.05 18.2 27.15 36.2 45.25 54.3 63.35 72.4

CS-2 13.4 26.8 40.2 53.6 67 80.4 93.8 107.2

CS-3 15.6 31.2 46.8 62.4 78 93.6 109.2 124.8

CS-4 21.4 42.8 64.2 85.6 107 128.4 149.8 171.2

Hans Peter Schwefel


GPRS architecture and interfaces

MS BSS GGSNSGSN

MSC

Um

EIR

HLR/GR

VLR

PDN

Gb Gn Gi

SGSN

Gn

Hans Peter Schwefel


Packet Handling

MobilityManagement

SessionManagement

InterceptionHandling

ConfigurationManagement

SMS HandlingProtocols

&Interfaces

PerformanceManagement

Fault & MaintenanceManagement

AccountingResource

Management

Handover Controland

SGSN ChangeHandling

Functions in SGSN and GGSN

Functions in SGSN

GPRS Core Network Functions

Hans Peter Schwefel


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

Hans Peter Schwefel


Data Units in GPRS

Hans Peter Schwefel


BSS

SGSN

Um GbGr

Insert Subscriber Data Ack(NSAPI,TI,PDP Type)

Insert Subscriber Data(NSAPI,TI,PDP Type)

Attach Request(NSAPI,TI,PDP Type)

Attach Accept(NSAPI,TI,PDP Type)

Attach Complete(NSAPI,TI,PDP Type)

HLR

Authentication/Ciphering Authentication/Ciphering

GPRS: Obtaining IP Connectivity

• GPRS attach– Authentication of

MS– Establishment/

Initialization of security functions

• PDP Context Setup– Obtain IP

address– Connect to

‚external‘ network[see later]

Hans Peter Schwefel


Enhanced Data rates for the GSM Evolution (EDGE)

Time Slot (MS-> BTS) Transmission Rate

48.......384 kbit/s

1 2 8

48 kbit/s ....48 kbit/s 48 kbit/s8 PSK

....

New Modulation Scheme

• 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

Hans Peter Schwefel


3rd Generation Systems: IMT-2000• Proposals for IMT-2000 (International Mobile Telecommunications)

– UWC-136, cdma2000, WP-CDMA– UMTS (Universal Mobile Telecommunications System) from ETSI

• Frequencies

IMT-2000

1850 1900 1950 2000 2050 2100 2150 2200 MHz

MSS

ITU allocation(WRC 1992) IMT-2000

MSS

Europe

China

Japan

NorthAmerica

UTRAFDD

UTRAFDD

TDD

TDD

MSS

MSS

DECT

GSM1800

1850 1900 1950 2000 2050 2100 2150 2200 MHz

IMT-2000MSS

IMT-2000MSS

GSM1800

cdma2000W-CDMA

MSS

MSS

MSS

MSS

cdma2000W-CDMA

PHS

PCS rsv.

Hans Peter Schwefel


Universal Mobile Telecommunication System (UMTS)

• Currently standardized by 3rd Generation Partnership Project (3GPP), see http://www.3GPP.org[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)

Hans Peter Schwefel


UMTS Domains

BSC

BTS

BTS

BSS (RAN/GERAN)

RNC

Node B

Node B

UTRAN

ME

SIM

USIM

MS

SGSN

PS Domain

GGSN

CS MGW

CS

Domain HSS/AuC

RNC

MSC-Serv./VLR Abis

SIM-ME

Iu bis Cu

Um

Uu

Iu Cs Gb

A

Iu PS

C

D

Iur

Gn

Gr Gc

Gs

CS MGW MSC-Serv./VLR

CS MGW

GMSC-Serv.

IMS Domain

(Release 5)

Mb/Gi

Cx

Mc

Nb

Nb

G/E/Nc

Nc

Mc

User Equipment Domain

Access Network Domain

Core Network Domain

Infrastructure Domain

Hans Peter Schwefel


User Equipment

Domain

User Equipment

DomainAccess

Network

Domain

Access

Network

Domain

Core

Network

Domain

Core

Network

Domain

Service and Application

Domain

Service and Application

Domain

Charging/ Lawful Interception/ OAMCharging/ Lawful Interception/ OAM

Other

Networks (IP/ ISDN)

Other

Networks (IP/ ISDN)

• 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)– Routers/Switches, DNS Server, DHCP Server,

Radius Server, NTP Server, Firewalls/VPN Gateways

• Application/Services• IP-Based Multimedia Subsystem (IMS)

– [see 9th Semester]• Operation, Administration & Maintenance (OAM)• Charging Network • [Legal Interception]

UMTS Network Domains

Hans Peter Schwefel


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)

Hans Peter Schwefel


Content





Exercise

Hans Peter Schwefel


Transport of IP packets

ApplicationServer

GGSNTerminal SGSNUTRAN

GTP-UGTP-U

User IP (v4 or v6)

Radio Bearer

IP tackets are tunnelled through the UMTS/GPRS network (GTP – GPRS tunneling protocol)

L1

RLC

PDCP

MAC

IPv4 or v6

Application

L1

RLC

PDCP

MAC

ATM

UDP/IPv4 or v6

GTP‑U

AAL5

Relay

L1

UDP/IPv4 or v6

L2

GTP‑U

IPv4 or v6

Iu-PSUu Gn Gi

ATM

UDP/IPv4 or v6

GTP‑U

AAL5

L1

UDP/IPv4 or v6

GTP‑U

L2

Relay

L1

L2

IPv4 or v6

[Source: 3GPP]

Hans Peter Schwefel


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.

Hans Peter Schwefel


GGSN

IP Transport: PDP Context & APNs

Terminal SGSNGGSN

PDP Context X 2 (APN X, IP address X, QoS 2)

PDP Context X 1 (APN X, IP address X, QoS 1)

ISP X

ISP Z

ISP Y

PDP Context Z (APN Z, IP address Z, QoS)

PDP Context Y (APN Y, IP address Y, QoS)

AP

N Y

AP

N Z

AP

N X

Same PDP (IP) address and APN

PDP Context selectionbased on TFT (downstream)

[Source: 3GPP]

Hans Peter Schwefel


UMTS Data Transport: Bearer Hierarchy

TE MT UTRAN/GERAN

CN IuEDGENODE

CNGateway

TE/AS

End-to-End Service(IP Bearer Service)

TE/MT LocalBearer Service

UMTS BearerService

External BearerService

UMTS Bearer Service

Radio Access BearerService

CN BearerService

BackboneBearer Service

Iu BearerService

Radio BearerService

PhysicalRadio

Service

PhysicalBearer Service

Air Interface

3G GGSN3G SGSNRAN

User Equipment

Hans Peter Schwefel


The ’full picture’ of the UMTS packet switched domain

GGSN SGSN

DHCP

RADIUS

IMS Domain

HSS

HLR/AuC

RNC

Node B

Node B

Network Services

SS7, Gr

SS7, Gc

GRX Network

DNS Gn-SEC

DNS Gn-PRI

Gn Network

DNS Ext

BG

Gi Network

DMZ

DNS Ext

E-mail

HTTP proxy

DNS NS

DNS IMS

P-CSCF

I/S-CSCF

MNO1̀s Backbone

AS Network

Messages

FTP

Video

DNS AS

Corp. Network

VPN -GWY

AS

BG

IDS

IDS

MNO1̀s Network

BG

1 2 3 4 5 6 7 8 9 * 0 # UE1

BG

Internet AS

MNO3

UE3

MNO2

UE2

IMS

Roaming Support: • UE attaches with SGSN in visited network• PDP context is set-up to GGSN in home network (via Gp interface, GRX network)

Hans Peter Schwefel


Message Flow: PDP Context Setup

…

…

Hans Peter Schwefel


Summary





Exercise

Hans Peter Schwefel


Acknowledgements/References

• Lecture notes: Mobile Communciations, Jochen Schiller, www.jochenschiller.de• Marco Hoffmann, Master Thesis, ‘Simulation of a flow-control algorithm between two nodes of

the GPRS network’, TU Munich and Siemens AG, 2001.• Tutorial: IP Technology in 3rd Generation mobile networks, Siemens AG (J. Kross, L. Smith, H.

Schwefel)• Various 3GPP Presentations. www.3gpp.org• J. Schiller: ’Mobile Communications’. Addison-Wesley, 2000.• GPRS books:

– T. Halonen, J. Romero, J. Melero: ‘GSM, GRPS, EDGE Performance: Evolution towards 3G/UMTS’, Wiley, 2003

Hans Peter Schwefel


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 10.10.123.45 (private). The user now iniates a web access to the CNN server. Describe the path of the IP packet through the mobile operator’s network, showing the header structure of the packet (detailling the IP source and destination address).

wireless communication protocols and technologies

Documents

ip address x

ip address z

ip address y

apn pdp context selection

pdp context activation

qospdp context y apn

proper pdp context gprs

qos2pdp context x1 apn