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_Sp04/
Wireless Networks II, Lecture 1, Spring 04
Page 1
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
Wireless Networks II, Lecture 1, Spring 04
Page 2
Hans Peter Schwefel
Cellular systems: technologies & subscribers
1200
Subscribers [million]
1000
GSM total
800
TDMA total
CDMA total
600
PDC total
Analogue total
Total wireless
400
Prediction (1998)
200
0
1996
1997
Wireless Networks II, Lecture 1, Spring 04
1998
1999
2000
2001
Page 3
2002
year
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
Wireless Networks II, Lecture 1, Spring 04
Page 4
Hans Peter Schwefel
GSM: Global System for Mobile Communication
History:
•
•
•
•
•
Today:
•
•
•
•
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
Wireless Networks II, Lecture 1, Spring 04
Page 5
Hans Peter Schwefel
GSM – Architecture
Radio Subsystem (RSS)
•
•
•
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
Operation
Subsystem
Base Station
Subsystem
Components:
•
•
•
•
Network and
Switchung Subsystem
Um
Abis
A
VLR
MS
BTS
BSC
HLR
AuC
O
MS
BTS
OMC
BSC
Transmission:
•
•
•
Circuit switched transfer
Radio link capacity: 9.6 kb/s
(FDMA/TDMA)
Duration based charging
MSC
EIR
MS
BTS
Connection to
ISDN, PDN
PSTN
Radio Link
Wireless Networks II, Lecture 1, Spring 04
Page 6
Hans Peter Schwefel
GSM Services
‘Traditional’ voice services
– voice telephony
primary goal of GSM was to enable mobile telephony offering the traditional bandwidth of 3.1 kHz
– emergency number
common number throughout Europe (112); mandatory for all service providers; free of charge; connection
with the highest priority (preemption of other connections possible)
– Multinumbering
several 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
Wireless Networks II, Lecture 1, Spring 04
Page 7
Hans Peter Schwefel
GSM: Radio Technology
Cellular 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)
•
•
cell
possible radio coverage
of the cell
idealized shape of the cell
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
Wireless Networks II, Lecture 1, Spring 04
Page 8
Hans Peter Schwefel
GSM: Air Interface I
Frequency 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
890
Frequenzband der
Mobilstation
Frequenzband der
Basisstation
Uplink
Downlink
915
MHz
935
960
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
Wireless Networks II, Lecture 1, Spring 04
Page 9
Kanäle:
1
2
3
124
200 kHz
Hans Peter Schwefel
GSM: Air Interface II
TDMA Frame
Time Division Multiple
Access (TDMA)
•
•
Within each channel: sequence
of TDMA frames
TDMA frames subdivided into 8
time-slots
4,615 ms
0
4
3
2
1
5
6
7
time slot:
3 tail bits
data bits
training
data bits
57
26
57
1 toggle
bit
1 toggle
bit
3 tail bits
burst 148 bit
time slot 156,25 bit
0,577 ms
Wireless Networks II, Lecture 1, Spring 04
Page 10
Hans Peter Schwefel
GSM: TDMA hierarchy of frames
hyperframe
0
1
2
2045 2046 2047 3 h 28 min 53.76 s
...
superframe
0
1
0
2
...
1
48
...
49
24
50
6.12 s
25
multiframe
0
1
...
0
1
24
2
120 ms
25
...
48
49
50
235.4 ms
frame
0
1
...
6
7
4.615 ms
slot
577 µs
burst
Wireless Networks II, Lecture 1, Spring 04
Page 11
Hans Peter Schwefel
GSM Air Interface: Combination of
TDMA & FDMA
935-960 MHz
124 channels (200 kHz)
downlink
890-915 MHz
124 channels (200 kHz)
uplink
higher GSM frame structures
time
GSM TDMA frame
1
2
3
4
5
6
7
8
4.615 ms
GSM time-slot (normal burst)
guard
space
tail
3 bits
Wireless Networks II, Lecture 1, Spring 04
user data
57 bits
S
user data
tail
1 26 bits 1
57 bits
3
S Training
Page 12
guard
space
546.5 µs
577 µs
Hans Peter Schwefel
GSM: Logical
Channels
Wireless Networks II, Lecture 1, Spring 04
Page 13
Hans Peter Schwefel
Functionalities in Radio Subsystem
• BTS comprises radio specific functions
• BSC is the switching center for radio channels
Functions
Management of radio channels
Frequency hopping (FH)
Management of terrestrial channels
Mapping of terrestrial onto radio channels
Channel coding and decoding
Rate adaptation
Encryption and decryption
Paging
Uplink signal measurements
Traffic measurement
Authentication
Location registry, location update
Handover management
Wireless Networks II, Lecture 1, Spring 04
Page 14
BTS
X
X
X
X
X
X
BSC
X
X
X
X
X
X
X
X
X
X
Hans Peter Schwefel
Overview: GSM protocol layers for signaling
Um
Abis
MS
A
BTS
BSC
MSC
CM
CM
MM
MM
RR
LAPDm
RR’
LAPDm
radio
radio
BTSM
LAPD
PCM
RR’
BTSM
LAPD
SS7
SS7
PCM
PCM
PCM
16/64 kbit/s
•
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
Wireless Networks II, Lecture 1, Spring 04
•
PCM: Pulse
Code Modulation
64 kbit/s /
2.048 Mbit/s
–
•
•
•
BSSAP
BSSAP
Page 15
•
•
MM: Mobility Management
CM: Call Management:
–
–
–
Call control
Short Message Service (SDCCH, SACCH)
Supplementary service
Hans Peter Schwefel
Example: Mobile Terminated Call
1. 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
Wireless Networks II, Lecture 1, Spring 04
HLR
4
5
3 6
calling
station 1
PSTN
2
GMSC
10
7
VLR
8 9
14 15
MSC
10 13
16
10
BSS
BSS
BSS
11
11
11
11 12
17
MS
Page 16
Hans Peter Schwefel
Example: Message flow
MS
MTC
BTS
paging request
between MS and BTS
for Mobile Terminated Call
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
Wireless Networks II, Lecture 1, Spring 04
Page 17
Hans Peter Schwefel
Mobility Support I: Types of handover
1
MS
BTS
Wireless Networks II, Lecture 1, Spring 04
2
4
3
MS
MS
MS
BTS
BTS
BTS
BSC
BSC
BSC
MSC
MSC
Page 18
Hans Peter Schwefel
Mobility Support II: Handover decision
receive level
BTSold
receive level
BTSold
HO_MARGIN
MS
MS
BTSold
Wireless Networks II, Lecture 1, Spring 04
BTSnew
Page 19
Hans Peter Schwefel
Mobility support III: Handover procedure
MSC
MS
BTSold
BSCold
measurement
measurement
report
result
BSCnew
HO decision
HO required
BTSnew
HO request
resource allocation
ch. activation
HO command
HO command
HO command
HO request ack ch. activation ack
HO access
Link establishment
clear command
clear command
clear complete
clear complete
Wireless Networks II, Lecture 1, Spring 04
Page 20
HO complete
HO complete
Hans Peter Schwefel
Mobile Communication & Data Traffic
• The future Internet will mainly be accessed by mobile devices
1800 Subscriptions worldwide (millions)
1600
Mobile
1400
Fixed
Mobile
Subscribers
Mobile Internet
1200
Fixed Internet
1000
Mobile Internet
Subscribers
800
600
400
200
0
1995
Wireless Networks II, Lecture 1, Spring 04
2000
2005
Page 21
2010
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]
4.8
9.6
14.4
19.2
28.8
38.4
43.2
57.6
Wireless Networks II, Lecture 1, Spring 04
TCH/F4.8
1
2
3
4
TCH/F9.6
TCH/F14.4
1
1
2
3
4
2
3
4
Page 22
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
Wireless Networks II, Lecture 1, Spring 04
Page 23
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)
Wireless Networks II, Lecture 1, Spring 04
Page 24
Hans Peter Schwefel
GPRS - Architecture
Components:
• CCU: Channel Coding Unit
• PCU: Packet Control Unit
• SGSN: Serving GPRS Support Node
• GGSN: Gateway GPRS Support Node
• GR: GPRS Register
GPRS
GSM
Components
Um
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
MS
BSS
A
Abis
B
T
S
C
C
U
Gp
Gb
Other
B
S
C
P
C
U
PLMN
Gn
Gs
SGSN
MSC
GGSN
Gi
HLR
G
Wireless Networks II, Lecture 1, Spring 04
Page 25
GR
PDN
Gr
Hans Peter Schwefel
GPRS: Channel Coding and Multiplexing
Time Slot (MS-> BTS)
Selection of Coding
depending on quality
of radio connection
Coding Scheme 1
9,05 kbit/s
Coding Scheme 2
13,4 kbit/s
Coding Scheme 3
‚optimal‘ radio quality:
no interference, etc.
1
Coding Scheme 4
2
9,05 kbit/s
9,05 kbit/s
13,4 kbit/s
15,6 kbit/s
21,4 kbit/s
Overall transmission rate
Wireless Networks II, Lecture 1, Spring 04
3
15,6 kbit/s
21,4 kbit/s
.....
8
.....
9,05 kbit/s
.....
13,4 kbit/s
.....
.....
15,6 kbit/s
21,4 kbit/s
72.4.......171,2 kbit/s
Page 26
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
Wireless Networks II, Lecture 1, Spring 04
Page 27
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
Wireless Networks II, Lecture 1, Spring 04
Page 28
Hans Peter Schwefel
GPRS:
channel
types
Wireless Networks II, Lecture 1, Spring 04
Page 29
Hans Peter Schwefel
Example: Channel Assignment
•
•
•
4 TRX  4 FDMA channels
 32 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
Wireless Networks II, Lecture 1, Spring 04
Page 30
Hans Peter Schwefel
Performance Measurements in BSS
(examples)
User data throughput
Signalling Data Throughput
Transmitted PDUs
Retransmitted PDUs
Transmitted LLC Frames
Service Upgrade/Downgrade Measurements
Number of discarded LLC PDU
Number of Successful GPRS Paging Procedures
Number of available and assigned PDCH/cell
Number of used PDCH per Cell
Attempted, Rejected Packet Ressource Reassignments
Successful Packet Ressource Reassignements
.
.
.
Wireless Networks II, Lecture 1, Spring 04
Page 31
Hans Peter Schwefel
GPRS architecture and interfaces
BSS
MS
Um
SGSN
Gb
Gn
Wireless Networks II, Lecture 1, Spring 04
Gi
HLR/
GR
MSC
VLR
PDN
GGSN
EIR
Page 32
Hans Peter Schwefel
GPRS Core Network Functions
Packet Handling
Resource
Management
Accounting
Configuration
Management
Mobility
Management
Handover Control
and
SGSN Change
Handling
Interception
Handling
Performance
Management
Session
Management
SMS Handling
Protocols
&
Interfaces
Fault & Maintenance
Management
Functions in SGSN and GGSN
Functions in SGSN
Wireless Networks II, Lecture 1, Spring 04
Page 33
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
Wireless Networks II, Lecture 1, Spring 04
•
SNDCP: Sub-Network Dependent
Convergence Protocol
GTP: GPRS Tunneling Protocol
– Mobility Support
– GTP-C and GTP-U
Page 34
Hans Peter Schwefel
Data Units
in GPRS
Wireless Networks II, Lecture 1, Spring 04
Page 35
Hans Peter Schwefel
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)
Wireless Networks II, Lecture 1, Spring 04
Page 36
Hans Peter Schwefel
Mapping TBFs to Timeslots
Wireless Networks II, Lecture 1, Spring 04
Page 37
Hans Peter Schwefel
GPRS: Obtaining IP Connectivity
•
GPRS attach
– Authentication of
MS
– Establishment/Ini
tialization of
security functions
SGSN
BSS
Um
Gb
HLR
Gr
Attach Request
(NSAPI,TI,PDP Type)
Authentication/Ciphering
Authentication/Ciphering
Insert Subscriber Data
•
(NSAPI,TI,PDP Type)
PDP Context Setup
– Obtain IP
address
– Connect to
‚external‘ network
[see later]
Wireless Networks II, Lecture 1, Spring 04
Insert Subscriber Data Ack
(NSAPI,TI,PDP Type)
Attach Accept
(NSAPI,TI,PDP Type)
Attach Complete
(NSAPI,TI,PDP Type)
Page 38
Hans Peter Schwefel
Enhanced Data rates for the GSM Evolution
(EDGE)
Time Slot (MS-> BTS)
New Modulation
Scheme
8 PSK
1
2
48 kbit/s
48 kbit/s
.... 8
....
Transmission Rate
48 kbit/s
48.......384 kbit/s
•
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
Wireless Networks II, Lecture 1, Spring 04
Page 39
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
1850
1900
1950
2000
2050
Frequencies
ITU allocation
(WRC 1992)
Europe
China
GSM DE
1800 CT
GSM
1800
Japan
MSS

T
D
D
MSS T
D
 D
UTRA
FDD 
IMT-2000
PHS
North
America
MSS

cdma2000 MSS
W-CDMA

1900
1950
2000
Page 40
2150
2200
IMT-2000
MSS

UTRA
FDD 
MSS

IMT-2000
MSS

MHz
cdma2000 MSS
W-CDMA

MSS

PCS
1850
Wireless Networks II, Lecture 1, Spring 04
IMT-2000
2100
MSS

rsv.
2050
2100
2150
2200
MHz
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)
Wireless Networks II, Lecture 1, Spring 04
Page 41
Hans Peter Schwefel
UMTS Domains
MSC-Serv./VLR
CS MGW
G/E/Nc
BSS (RAN/GERAN)
Nb
Mc
Abis
A
BTS
MSC-Serv./VLR
CS MGW
BSC
GMSC-Serv.
Um
Mc
D
BTS
Gb
C
Iu Cs
Nb
SIM-ME
CS MGW
SIM
CS
HSS/AuC
ME
Domain
UTRAN
USIM
Nc
IMS Domain
Cx
Gs
Cu
(Release 5)
Iu bis
MS
Node B
Gc
Gr
RNC
Mb/Gi
Uu
Node B
Gn
Iur
Iu PS
SGSN
GGSN
RNC
PS Domain
Access
Network
Domain
User Equipment
Domain
Wireless Networks II, Lecture 1, Spring 04
Core Network
Domain
Infrastructure
Domain
Page 42
Hans Peter Schwefel
UMTS Network Domains
•
Service
Serviceand
andApplication
Application
Domain
Domain
Radio Access Network
– Node B (Base station)
– Radio Network Controller (RNC)
•
Mobile Core Network
–
–
–
–
–
•
•
•
•
•
User
UserEquipment
Equipment
Domain
Domain
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
Access
Access
Network
Network
Domain
Domain
Core
Core
Network
Network
Domain
Domain
Other
Other
Networks
Networks(IP/
(IP/ISDN)
ISDN)
Charging/
Charging/Lawful
LawfulInterception/
Interception/OAM
OAM
Application/Services
IP-Based Multimedia Subsystem (IMS)
– [see 9th Semester]
Operation, Administration & Maintenance (OAM)
Charging Network
[Legal Interception]
Wireless Networks II, Lecture 1, Spring 04
Page 43
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)
Wireless Networks II, Lecture 1, Spring 04
Page 44
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
Wireless Networks II, Lecture 1, Spring 04
Page 45
Hans Peter Schwefel
Transport of IP packets
IP tackets are tunnelled through the UMTS/GPRS network
(GTP – GPRS tunneling protocol)
User IP (v4 or v6)
UTRAN
Terminal
Radio Bearer
SGSN
GTP-U
Application
Server
GGSN
GTP-U
Application
IP
v4 or v6
IP
v4 or v6
Relay
IP
v4 or v6
Relay
PDCP
PDCP
GTP-U
GTP-U
GTP-U
GTP-U
RLC
RLC
UDP/IP
v4 or v6
UDP/IP
v4 or v6
UDP/IP
v4 or v6
MAC
MAC
UDP/IP
v4 or v6
AAL5
AAL5
L2
L2
L2
L1
L1
ATM
ATM
L1
L1
L1
Uu
Wireless Networks II, Lecture 1, Spring 04
Iu-PS
Gn
Page 46
[Source: 3GPP]
Gi
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.
Wireless Networks II, Lecture 1, Spring 04
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Hans Peter Schwefel
IP Transport: PDP Context & APNs
Same PDP (IP) address and APN
ISP X
GGSN
APN X
PDP Context X1 (APN X, IP address X, QoS1)
PDP Context X2 (APN X, IP address X, QoS2)
ISP Y
GGSN
PDP Context Y (APN Y, IP address Y, QoS)
APN Y
PDP Context selection
based on TFT (downstream)
PDP Context Z (APN Z, IP address Z, QoS)
APN Z
Terminal
SGSN
ISP Z
[Source: 3GPP]
Wireless Networks II, Lecture 1, Spring 04
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Hans Peter Schwefel
UMTS Data Transport: Bearer Hierarchy
Air
Interface
TE
MT
UTRAN/
GERAN
CN
Gateway
CN Iu
EDGE
NODE
TE/AS
End-to-End Service
(IP Bearer Service)
TE/MT Local
Bearer Service
External Bearer
Service
UMTS Bearer Service
Service
CN Bearer
Service
Radio Access Bearer
Service
Radio Bearer
Service
Iu Bearer
Service
Physical
Radio
Service
Physical
Bearer Service
RAN
Backbone
Bearer Service
3G SGSN
3G GGSN
User Equipment
Wireless Networks II, Lecture 1, Spring 04
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Hans Peter Schwefel
The ’full picture’ of the UMTS packet switched domain
Roaming Support:
•
•
UE attaches with SGSN in visited network
PDP context is set-up to GGSN in home network (via Gp interface, GRX network)
Wireless Networks II, Lecture 1, Spring 04
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Message Flow: PDP Context Setup
…
…
Wireless Networks II, Lecture 1, Spring 04
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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
Wireless Networks II, Lecture 1, Spring 04
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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
Wireless Networks II, Lecture 1, Spring 04
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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).
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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 =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.
Wireless Networks II, Lecture 1, Spring 04
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