Page 1 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Wireless Networks II: Performance & Cross-Layer Aspects
by Hans Peter Schwefel
• Mm1 Cellular Networks: GSM, GPRS, and UMTS
• Mm2 Network Performance: Methodology
• Mm3 Quality of Service, content & header compression
• Mm4 Security aspects of wireless networks
• Mm5 Reliability aspects
www.kom.auc.dk/~hps/
Page 2 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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 3 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Cellular systems: technologies & subscribers
0
200
400
600
800
1000
1200
1996 1997 1998 1999 2000 2001 2002 year
Subs
crib
ers
[mill
ion] GSM total
TDMA totalCDMA totalPDC totalAnalogue totalTotal wirelessPrediction (1998)
Page 4 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Content
1. Introduction• Cellular Concepts & Technologies
2. GSM (revision)• Network Architecture, Air Interface• Signalling/Call Setup, Mobility Support• Data Services, HSCSD
3. GPRS [& UMTS]• GPRS: Architecture, Air-Interface, Core-Network Modifications• Radio Resource Management in GPRS• UMTS domains and architecture
4. IP transport in Packet Switched UMTS/GPRS Networks• PDP contexts, APNs, TFTs• Bearers, Admission Control• ’full’ network architecture
Exercise
Page 5 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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:
Page 6 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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)
Page 7 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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
Page 8 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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 cellshandover of the connection to the neighbor cell
Page 9 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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 (MT BTS) and down-link (BTS MT) 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
Page 10 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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-slots
TDMA Frame
Page 11 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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
burstslot
577 µs
4.615 ms
120 ms
235.4 ms
6.12 s
3 h 28 min 53.76 s
Page 12 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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
Page 13 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
GSM: Logical Channels
Page 14 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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
Page 15 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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
• Layer 1, Um: Radio– Creation & multiplexing of bursts, synchronisation,
modulation, en/decryption, channel coding, error detection/correction
• LAPDm: variant ofLink Access Procedure for the D-Channel• RR: Radio Resource Management• BTSM: BTS Management
• MM: Mobility Management• CM: Call Management:
– Call control– Short Message Service (SDCCH, SACCH)– Supplementary service
• PCM: Pulse Code Modulation
Page 16 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Example: Mobile Terminated Call1. calling a GSM subscriber2. forwarding call to GMSC3. signal call setup to HLR4. 5. request MSRN from VLR6. forward responsible
MSC to GMSC7. forward call to current MSC8, 9. get current status of MS10, 11. paging of MS12, 13. MS answers14, 15. security checks16, 17. set up connection
PSTNcallingstation GMSC
HLR VLR
BSSBSSBSS
MSC
MS
1 2
3
45
6
7
8 9
10
11 12
1316
10 10
11 11 11
14 15
17
Page 17 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Example: Message flow between MS and BTS for Mobile Terminated Call
BTSMS
paging request
channel request
immediate assignment
paging responseauthentication request
authentication response
ciphering command
ciphering complete
setupcall confirmed
assignment command
assignment complete
alerting
connectconnect acknowledge
data/speech exchange
MTC
Page 18 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Mobility Support I: Types of handover
MSC MSC
BSC BSCBSC
BTS BTS BTSBTS
MS MS MS MS
1
23 4
Page 19 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Mobility Support II: Handover decisionreceive level
BTSold
receive levelBTSold
MS MS
HO_MARGIN
BTSold BTSnew
Page 20 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Mobility support III: Handover procedure
HO access
BTSold BSCnew
measurementresult
BSCold
Link establishment
MSCMS
measurementreport
HO decisionHO required
BTSnew
HO request
resource allocationch. activation
ch. activation ackHO request ackHO commandHO commandHO command
HO completeHO completeclear commandclear command
clear complete clear complete
Page 21 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
0
200
400
600
800
1000
1200
1400
1600
1800
1995 2000 2005 2010
Subscriptions worldwide (millions)
Mobile InternetSubscribers
MobileSubscribersMobile
FixedMobile InternetFixed Internet
• The future Internet will mainly be accessed by mobile devices
Mobile Communication & Data Traffic
Page 22 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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
Page 23 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Content
1. Introduction• Cellular Concepts & Technologies
2. GSM (revision)• Network Architecture, Air Interface• Signalling/Call Setup, Mobility Support• Data Services, HSCSD
3. GPRS [& UMTS]• GPRS: Architecture, Air-Interface, Core-Network Modifications• Radio Resource Management in GPRS• UMTS domains and architecture
4. IP transport in Packet Switched UMTS/GPRS Networks• PDP contexts, APNs, TFTs• Bearers, Admission Control• ’full’ network architecture
Exercise
Page 24 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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 25 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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 – On-demand allocation of time-slots
• Volume Based Charging
Page 26 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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– GTP-C and GTP-U
Page 27 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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
Page 28 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Examples for GPRS device classes
54412
52410
5148
4225
3223
3122
2111
Maximum number of slotsSending slotsReceiving slotsClass
Page 29 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
GPRS user data rates in kbit/s
171.2149.8128.410785.664.242.821.4CS-4
124.8109.293.67862.446.831.215.6CS-3
107.293.880.46753.640.226.813.4CS-2
72.463.3554.345.2536.227.1518.29.05CS-1
8 slots7 slots6 slots5 slots4 slots3 slots2 slots1 slotCoding scheme
Page 30 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
GPRS: channel types
Page 31 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Example: Channel Assignment
• 4 TRX 4 FDMA channels32 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 32 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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 33 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Data Units in GPRS
Page 34 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Mapping TBFs to Timeslots
Page 35 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Radio Resource Management in GPRS• ‘connection’ admission control (CAC)
• PDP context set-up signalling (BSC, SGSN, GGSN), see later• Temporary Block Flow (TBF) allocation
• delayed TBF de-allocation as opposed to immediate• impact on signalling volumes, delays (‘access’ delays), cell throughput
• Packet scheduling• downlink
• decision by BSC• standard methods: Round-Robin, weighted Fair Queueing• channel dependent scheduling• potential consideration of QoS requirements (delay bounds, etc.)• impact on total throughput, user throughput, fairness, packet-delays, etc.
• uplink• Polling by BSC (Uplink State Flag USF)• potential polling of ‘idle’ MS – optimization via ‘prediction’ of data availability
• Transmission ‘parameters’• Coding Scheme selection• Power Control• Frequency hopping
Page 36 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
GPRS RRM: Example (VTC’05)‘Best Effort’ Scheme
• FIFO access queue• assign time-slots with
smallest number of TBFs•Round-Robin Scheduling
Channel Model• no mobility• path-loss exponent 3.5• log-normal fading
Traffic Model• Poisson arrivals of GSM calls and TBFs• TBFs always have data to send until completed
Improved channel dependent credit-based scheme
• credit-assignment to TBFs based on C/I value• time-slots selected based on accumulated credit in TS• weighted round robin (proportional to credit of TBF)
Page 37 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
GPRS RRM (VTC’05): Results
Avg. throughput per cell Avg. throughput per user
Page 38 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
GPRS RRM (VTC’05): Results (cntd)
Avg. Access DelayFairness?
Page 39 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Performance Measurements in BSS (examples)
User data throughputSignalling Data ThroughputTransmitted PDUsRetransmitted PDUsTransmitted LLC FramesService Upgrade/Downgrade MeasurementsNumber of discarded LLC PDUNumber of Successful GPRS Paging ProceduresNumber of available and assigned PDCH/cellNumber of used PDCH per CellAttempted, Rejected Packet Ressource ReassignmentsSuccessful Packet Ressource Reassignements
.
.
.
Page 40 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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
Page 41 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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-2000 MSS↑
IMT-2000 MSS↓
GSM1800
cdma2000W-CDMA
MSS↓
MSS↓
MSS↑
MSS↑
cdma2000W-CDMAPHS
PCS rsv.
Page 42 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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)
Page 43 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
UMTS Domains
B S C
B T S
B T S
B S S (R A N /G E R A N )
R N C
N o d e B
N o d e B
U T R A N
M E
S IM
U S IM
M S
S G S N
P S D o m a in
G G S N
C S M G W
C S D o m a in
H S S /A u C
R N C
M S C -S e rv ./V L RA b is
S IM - M E
Iu b is C u
U m
U u
Iu C s G b
A
Iu P S
CD
Iu r
G n
G r G c
G s
C S M G W M S C -S e rv ./V L R
C S M G W
G M S C -S e rv .
IM S D o m a in (R e le a s e 5 )
M b /G i
C x
M c
N b
N b
G /E /N c
N c
M c
U s e r E q u ip m e n t D o m a in
A c c e s s N e tw o rk D o m a in
C o re N e tw o rk D o m a in
In f ra s tru c tu r e D o m a in
Page 44 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
User EquipmentDomain
User EquipmentDomain Access
NetworkDomain
AccessNetworkDomain
CoreNetworkDomain
CoreNetworkDomain
Service and ApplicationDomain
Service and ApplicationDomain
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
Page 45 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
UTRANUTRANRNSRNS
Core networkCore network
Circuit-switched core network
MSC
Packet-switched core network
SGNS
Iu
IubIur
Uu
UEUE UEUE UEUE UEUE
Cu Cu Cu Cu
RNC RNC
Node B Node B Node B Node B
ME ME ME ME
USIM USIM USIM USIM
Basic UMTS Architecture
Source: CSYS
Page 46 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
UE 1Time
Power
UE 2UE 3UE 4
Node BUE
Available resources: Spreading Codes (OVSF)
andTransmission Power
SoftHandover
non-orthogonal codes
orthogonal codes
Wideband Code Division Multiple Access
Source: CSYS
Page 47 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
I
u
b
I
u
b
Uu Iub
UE Node B RNC
PC
AC
LC
PS
RM
HC PC
PC LC
Radio Resource Management (RRM)
AC – Admission Control; PS – Packet Scheduler; LC – Load Control; RM Resource Manager; HC – Handover control; PC – Power Control
Source: CSYS
Page 48 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Time
free capacity, which canbe allocated forcontrollable load
Non-controllable load
RRM – AC, LC, PS
Received Power
Plannedtarget
General resource management – example for uplink
Page 49 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Content
1. Introduction• Cellular Concepts & Technologies
2. GSM (revision)• Network Architecture, Air Interface• Signalling/Call Setup, Mobility Support• Data Services, HSCSD
3. GPRS [& UMTS]• GPRS: Architecture, Air-Interface, Core-Network Modifications• Radio Resource Management in GPRS• UMTS domains and architecture
4. IP transport in Packet Switched UMTS/GPRS Networks• PDP contexts, APNs, TFTs• Bearers, Admission Control• ’full’ network architecture
Exercise
Page 50 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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
Page 51 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Transport of IP packets
ApplicationServerGGSNTerminal 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]
Page 52 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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 53 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
GGSN
IP Transport: PDP Context & APNs
Terminal SGSNGGSN
PDP Context X2 (APN X, IP address X, QoS2)
PDP Context X1 (APN X, IP address X, QoS1)
ISP X
ISP Z
ISP Y
PDP Context Z (APN Z, IP address Z, QoS)
PDP Context Y (APN Y, IP address Y, QoS)
APN
YA
PN Z
APN
X
Same PDP (IP) address and APN
PDP Context selectionbased on TFT (downstream)
[Source: 3GPP]
Page 54 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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
Page 55 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Connection Admission Control (CAC)• Goal: Avoid over-load (QoS degradation) while still allowing for multiplex-gain• Principle Approaches
– Easy for constant bit rate (CBR) flows– Difficult tasks for bursty traffic
Alternatives:• Peak-Rate Allocation no multiplex gain• Mean-rate allocation large delays and
losses possible• Intermediate solution: effective bandwidths
Frequently based on limit theorems• Large deviations theory• High multiplex degrees
• Example: CAC in GPRS/UMTS core networks [WPMC05]
Page 56 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
The ’full picture’ of the UMTS packet switched domain
G G SNSG SN
D HC P
R ADIU S
IM S D o m ain
H SS
H L R/AuC
RNC
Node B
Node B
N etw ork Services
SS7, G r
SS 7, G c
G RX Netw o rk
D N SG n-SEC
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Page 57 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Message Flow: PDP Context Setup
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Page 58 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
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 59 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Acknowledgements/References• Lecture notes: Mobile Communciations, Jochen Schiller, www.jochenschiller.de• HP Schwefel, T.B. Sørensen, ‘Cellular Networks and wireless applications’, ELITE Industrial
Course, Nov. 2004. • H. Wang et al., ‘Improved Channel Allocation and RLC block scheduling for downlink traffic in
GPRS’, Vehicular Technology Conference (VTC), May 2005.• 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
• H. Wang et al., ‘Performance Enhancements of UMTS networks using end-to-end QoS provsioning’, WPMC 2005, Aalborg, Sept. 2006.
Page 60 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Exercises I: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, CS-2 (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 header structure of the IP packet which is sent downstream from the GGSN to the SGSN (detailling the IP source and destination address).
Page 61 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 06
Exercises II:3. Channel Assignment: In a certain radio cells, 2 channels are allocated resulting in 16
available timeslots. 3 timeslots are always used for control channels, 8 timeslots are reserved for voice-calls (GSM) and the remaining time-slots are freely given to either GSM or GPRS users.
Assume that there are no GSM users in the cell. GPRS users with two types of devices are considered: i) 30% are supporting and asking for 2 down-link slots, ii) 70% are supporting and asking for 4 down-link slots. GPRS TBFs are started according to a Poisson process with rate λ=2/min and with an exponentially distributed TBF duration of on average 2min, during which they transmit with maximum data rate (CS-2). Assume that no TBF multiplexing is used, i.e. time-slots are not shared.Use the given simulation program to obtain average cell throughput, average throughput per TBF, TBF blocking probability for the following strategies:• Newly starting TBFs either obtain the number of time-slots which they are asking
for, or they get blocked. Existing TBFs are never downgraded.• [If a TBF comes in newly, it obtains the remaining available time-slots up to the
number which it is asking for. If none are left, a station with the maximum number of allocated time-slots is downgraded by one slot which is given to the new TBF. ]
Define a fairness criterion and evaluate it in the simulation.