Page 1 Hans Peter Schwefel Wireless Networks II, Lecture 1, Spring 05 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/WirelessNetworksII_Sp05/ Page 2 Hans Peter Schwefel Wireless Networks II, Lecture 1, Spring 05 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
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Page 1 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
4. IP transport in Packet Switched UMTS/GPRS Networks• PDP contexts, APNs, TFTs• Bearers• ’full’ network architecture
Exercise
Page 5 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
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 05
GSM – Architecture
Components:• BTS: Base Transceiver Station• BSC: Base Station Controller• MSC: Mobile Switching Center• HLR/VLR: Home/Visitor Location
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 05
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 05
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 05
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 05
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 05
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 05
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 05
GSM: Logical Channels
Page 14 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
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 05
• 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 05
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 05
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 05
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 05
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 05
Page 31 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
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 32 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
GPRS architecture and interfaces
MS BSS GGSNSGSN
MSC
Um
EIR
HLR/GR
VLR
PDN
Gb Gn Gi
Page 33 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
Packet Handling
MobilityManagement
SessionManagement
InterceptionHandling
ConfigurationManagement
SMS HandlingProtocols
&Interfaces
PerformanceManagement
Fault & MaintenanceManagement
AccountingResourceManagement
Handover Controland
SGSN ChangeHandling
Functions in SGSN and GGSNFunctions in SGSN
GPRS Core Network Functions
Page 34 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
GPRS: Protocol Stack
• RLC: Radio Link Control– Acknowledged mode (reliable) or unacked
• LLC: Logical Link Control– Acknowledged mode (reliable) or unacked
• 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,
4. IP transport in Packet Switched UMTS/GPRS Networks• PDP contexts, APNs, TFTs• Bearers• ’full’ network architecture
Exercise
Page 46 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
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 47 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
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 48 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
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 49 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
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 50 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
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
DN S G n-PRI
G n N etw ork
D N S E xt
B G
G i N etw ork
D M Z
D NSExt
E -m ail
HT T Pproxy
D N S NS
D N S IM S
P-C S C F
I/S -C S CF
MN O 1`s B ackbone
AS N etw o rk
M essages
FT P
V ideo
DN SAS
C orp. Network
VPN -G W Y
AS
B G
IDS
ID S
M N O 1`s N etw ork
B G
1 2 3 4 5 6 7 8 9 * 0 # U E1
BG
In ternetAS
M N O 3
UE3
M N O 2
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)
Page 51 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
Message Flow: PDP Context Setup
…
…
Page 52 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
Summary
1. Introduction• Cellular Concepts & Technologies
2. GSM• Network Architecture, Air Interface• Signalling/Call Setup, Mobility Support• Data Services, HSCSD
4. IP transport in Packet Switched UMTS/GPRS Networks• PDP contexts, APNs, TFTs• Bearers• ’full’ network architecture
Exercise
Page 53 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
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
Page 54 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
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 55 Hans Peter SchwefelWireless Networks II, Lecture 1, Spring 05
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 sessions are started according to a Poisson process with rate λ=2/min and with an exponentially distributed session duration of on average 2min, during which they transmit with maximum data rate (CS-2).Use the given simulation program to obtain average cell throughput, average throughput per session, session blocking probability for the following strategies:• Newly starting sessions either obtain the number of time-slots which they are
asking for, or they get blocked. Existing sessions are never downgraded.• [If a session 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 session. ]
Define a fairness criterion and evaluate it in the simulation.