Week4 Handout
Transcript of Week4 Handout
University of Technology, Sydney 31275 Mobile Networking
Week 4: GSM
Dr Peter Leijdekkers 4.1
Peter Leijdekkers UTS – Mobile Networking (31275) 4.1
Overview of GSM
Week 4
Peter Leijdekkers
Peter Leijdekkers UTS – Mobile Networking (31275) 4.2
Influence of mobile communication to the layer model
service location
new applications, multimedia
adaptive applications
congestion and flow control
quality of service
addressing, routing, device location
hand-over
SDMA, FDMA, TDMA, Aloha
Reservation schemes
Collision avoidance, MACA
Polling
Frequencies
Signals
Antenna
Signal propagation
Multiplexing Spread spectrum
Application layer
Transport layer
Network layer
Data link layer
Physical layer
Peter Leijdekkers UTS – Mobile Networking (31275) 4.3
Overview
Market
GSM Services
GSM components
Air Interface
Call Setup
Handover
University of Technology, Sydney 31275 Mobile Networking
Week 4: GSM
Dr Peter Leijdekkers 4.2
Peter Leijdekkers UTS – Mobile Networking (31275) 4.4
3G wireless Standards
3rd Generation mobile systems
3G: Wireless Wide Area Networks (WWANs) are the broadest range wireless networks. Most widely deployed today in the cellular voice infrastructure - also have the ability to transmit data. Includes UMTS (Universal Mobile Telecommunications Service), EV-DO Evolution-Data Optimized wireless high-speed data network. Applications: Multimedia such as full-motion video, video conferencing and Internet access. High-speed data transmissions of 144Kbps and higher (2Mbit/s).
http://www.youtube.com/watch?v=hX0i6pXzsLE&NR=1
5
Peter Leijdekkers UTS – Mobile Networking (31275) 4.6
Performance characteristics of GSM (wrt. analog sys.)
Communication
mobile, wireless communication; support for voice and data services
Total mobility
international access, chip-card enables use of access points of different providers
Worldwide connectivity
one number, the network handles localization
High capacity
better frequency efficiency, smaller cells, more customers per cell
High transmission quality
high audio quality and reliability for wireless, uninterrupted phone calls at higher speeds (e.g., from cars, trains)
Security functions
access control, authentication via chip-card and PIN
University of Technology, Sydney 31275 Mobile Networking
Week 4: GSM
Dr Peter Leijdekkers 4.3
Peter Leijdekkers UTS – Mobile Networking (31275) 4.7
Disadvantages of GSM
There is no perfect system!!
no end-to-end encryption of user data
no full ISDN bandwidth of 64 kbit/s to the user
reduced concentration while driving
abuse of private data possible
roaming profiles accessible
high complexity of the system
several incompatibilities within the GSM standards
limited access to American market
Peter Leijdekkers UTS – Mobile Networking (31275) 4.8
Overview
Market
GSM Services
GSM components
Air Interface
Call Setup
Handover
Peter Leijdekkers UTS – Mobile Networking (31275) 4.9
Mobile Services
GSM offers
several types of connections
voice connections, data connections, short message service
multi-service options (combination of basic services)
Three service domains
Bearer Services
Telematic Services
Supplementary Services
GSM-PLMN
transit
network
(PSTN, ISDN)
source/
destination
network
TE TE
bearer services
tele services
R, S (U, S, R)Um
MT
MS
TE: Terminal MT: Mobile Termination PSTN: Public Switched Telephone Network
MS: Mobile Station PLMN: Public Land Mobile network ISDN: Integrated Services Digital Network
University of Technology, Sydney 31275 Mobile Networking
Week 4: GSM
Dr Peter Leijdekkers 4.4
Peter Leijdekkers UTS – Mobile Networking (31275) 4.10
Bearer Services
Telecommunication services to transfer data between access points
Specification of services up to the terminal interface (OSI layers 1-3)
Different data rates for voice and data (original standard)
data service (circuit switched)
synchronous: 2.4, 4.8 or 9.6 kbit/s
asynchronous: 300 - 1200 bit/s
data service (packet switched)
synchronous: 2.4, 4.8 or 9.6 kbit/s
asynchronous: 300 - 9600 bit/s
Today: data rates of approx. 50 kbit/s possible
Peter Leijdekkers UTS – Mobile Networking (31275) 4.11
Tele Services I
Telecommunication services that enable voice communication via mobile phones
All these basic services have to obey cellular functions, security measurements etc.
Offered services
mobile 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)
Peter Leijdekkers UTS – Mobile Networking (31275) 4.12
Tele Services II
Non-Voice-Teleservices
group 3 fax
voice mailbox (implemented in the fixed network supporting the mobile terminals)
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
Multimedia Message Service (MMS)
University of Technology, Sydney 31275 Mobile Networking
Week 4: GSM
Dr Peter Leijdekkers 4.5
Peter Leijdekkers UTS – Mobile Networking (31275) 4.13
Supplementary services
Similar to ISDN services besides lower bandwidth due to the radio link
May differ between different service providers, countries and protocol versions
Important services
User Identification
Call Redirection or forwarding
suppression of number forwarding
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
...
Peter Leijdekkers UTS – Mobile Networking (31275) 4.14
Overview
Market
GSM Services
GSM components
Air Interface
Call Setup
Handover
Peter Leijdekkers UTS – Mobile Networking (31275) 4.15
Cellular Network Reference Model
BTS: Base Transceiver Station BSC: Base Station ControllerMS: Mobile Station AC: Authentication Centre EIR: Equipment Identity Register HLR: Home Location Register VLR: Visitor Location Register
MSC: Mobile Services Switching Center EIR: Equipment Identity RegisterAC: Authentication Centre OMC: Operation & Maintenance Center
MSCHLR
VLR
MS
VLR
EIR
AC
MSC PSTN ISDN
UmA
B
C
D
G
H
E
AiDi
F
NSS/OSS (Network & Switching Subsystem)
OMC
BTS
BTS
BSC
University of Technology, Sydney 31275 Mobile Networking
Week 4: GSM
Dr Peter Leijdekkers 4.6
Peter Leijdekkers UTS – Mobile Networking (31275) 4.16
NNS: Network and Switching subsystem
NSS: the main component of the public mobile network GSM Connects wireless network to fixed networks Performs handovers between different BSCs Functions to worldwide localisation of users Charging, accounting functions Roaming of users between different providers in different countries
Mobile Services Switching Center (MSC)
High performance digital ISDN switches Manages several BSCs in a geographical region Connects to other networks (PSTN,ISDN,X25) Uses standard signalling system SS7
Databases (important: scalability, high capacity, low delay) Home Location Register (HLR)
central master database containing user data, permanent and semi-permanent data of all subscribers assigned to the HLR (one provider can have several HLRs)
Visitor Location Register (VLR)local database for a subset of user data, including data about all user currently in the domain of the VLR. Each MSC has a VLR database
Peter Leijdekkers UTS – Mobile Networking (31275) 4.17
Mobile Services Switching Center (MSC)
The MSC plays a central role in GSM
switching functions
additional functions for mobility support
management of network resources
interworking functions via Gateway MSC (GMSC)
integration of several databases
Functions of a MSC
specific functions for paging and call forwarding
termination of SS7 (signaling system no. 7)
mobility specific signaling
location registration and forwarding of location information
provision of new services (fax, data calls)
support of short message service (SMS)
generation and forwarding of accounting and billing information
Peter Leijdekkers UTS – Mobile Networking (31275) 4.18
Operation subsystem
The OSS (Operation Subsystem) enables centralized operation, management, and maintenance of all GSM subsystems Communication with other components via SS7 signaling
Authentication Center (AC) generates user specific authentication parameters on request of a VLR authentication parameters used for authentication of mobile terminals and
encryption of user data on the air interface within the GSM system
Equipment Identity Register (EIR) registers GSM mobile stations and user rights stolen or malfunctioning mobile stations can be locked and sometimes even
localized
Operation and Maintenance Center (OMC) traffic monitoring status reports of network entities accounting and billing …
University of Technology, Sydney 31275 Mobile Networking
Week 4: GSM
Dr Peter Leijdekkers 4.7
Peter Leijdekkers UTS – Mobile Networking (31275) 4.19
Base Station System and Mobile Station
MS
Um
MSC
A
BSC
MS
UmAbis
Abis
Base Station System
BTS
BTS
Radio cell
Radio cell
Base Transceiver Station (BTS):
• radio components (sender, receiver,
antenna)
• if directed antennas are used one BTS can
cover several cells
Base Station Controller (BSC):
• switching between BTSs,
• controlling BTSs,
• managing of network resources,
• mapping of radio channels (Um) onto
terrestrial channels (A interface)
• Handles handover between BTSs
• Paging of MS
Peter Leijdekkers UTS – Mobile Networking (31275) 4.20
possible radio coverage of the cell
idealized shape of the cellcell
segmentation of the area into cells
Radio Cells
use of several carrier frequencies
not the same frequency in adjoining 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)
if a mobile user changes cells handover of the connection to the neighbor cell
Peter Leijdekkers UTS – Mobile Networking (31275) 4.21
Mobile Station (MS)
Terminal for the use of GSM services
A mobile station (MS) comprises several functional groups
MT (Mobile Terminal):
offers common functions used by all services the MS offers
corresponds to the network termination (NT) of an ISDN access
end-point of the radio interface (Um)
TA (Terminal Adapter):
terminal adaptation, hides radio specific characteristics
TE (Terminal Equipment):
peripheral device of the MS, offers services to a user
does not contain GSM specific functions
R SUm
TE TA MT
University of Technology, Sydney 31275 Mobile Networking
Week 4: GSM
Dr Peter Leijdekkers 4.8
Peter Leijdekkers UTS – Mobile Networking (31275) 4.22
Identifiers Used in GSM
SIM (Subscriber Identity Module) personalization of the mobile terminal, stores user parameters
IMSI (international mobile subscriber identification) IMSI identifies a subscriber worldwide. Mobile country code + mobile network node + ms identification nr E.g 240 + 23415 + 123456
TMSI (temporary mobile subscriber identification): TMSI identifies a subscriber. Used over the air only to hide identity of the user. Used by VLR is only valid for a certain period
MSISDN (mobile station ISDN number) MSISDN is a dialable number assigned to a given subscriber. +61 4 2456 1842
IMEI (international mobile station equipment identity) IMEI identifies a particular handset.
This is also called mobile identity number (MIN).
Peter Leijdekkers UTS – Mobile Networking (31275) 4.23
Overview
Market
GSM Services
GSM components
Air Interface
Call Setup
Handover
Peter Leijdekkers UTS – Mobile Networking (31275) 4.24
The GSM Radio Interface
MOBILE
BASE TRANSCEIVER STATION
University of Technology, Sydney 31275 Mobile Networking
Week 4: GSM
Dr Peter Leijdekkers 4.9
Peter Leijdekkers UTS – Mobile Networking (31275) 4.25
Air Interface
Radio Transmission Techniques
FDMA
TDMA
CDMA
Channels
Physical channels
Logical channels
Peter Leijdekkers UTS – Mobile Networking (31275) 4.26
FDMA
Time
Frequency
Channel
Peter Leijdekkers UTS – Mobile Networking (31275) 4.27
TDMA
Time
Frequency
0 1 2 3 4 5 6 7
Channel
Time Slot
University of Technology, Sydney 31275 Mobile Networking
Week 4: GSM
Dr Peter Leijdekkers 4.10
Peter Leijdekkers UTS – Mobile Networking (31275) 4.28
GSM uses paired radio channels
TDMA
GSM900: 124 radio carriers, inter carrier spacing 200khz.
890 to 915mhz mobile to base - UPLINK
935 to 960mhz base to mobile - DOWNLINK
0 124 0 124
890MHz 915MHz 935MHz 960MHz
Peter Leijdekkers UTS – Mobile Networking (31275) 4.29
1 2 3 4 5 6 7 8
higher GSM frame structures
935-960 MHz
124 channels (200 kHz)
downlink
890-915 MHz
124 channels (200 kHz)
uplink
time
GSM TDMA frame
GSM time-slot (normal burst)
4.615 ms
546.5 µs577 µs
tail user data TrainingSguard
space S user data tailguard
space
3 bits 57 bits 26 bits 57 bits1 1 3
GSM - TDMA/FDMA
Peter Leijdekkers UTS – Mobile Networking (31275) 4.30
Burst and Frames
The information contained in one time slot on the TDMA frame is called a burst.
Five types of burst
Normal Burst(data transmission)
Frequency Correction Burst(correct local oscillator of MS to avoid interference with neighboring channels)
Synchronization Burst (training sequence to synchronize Ms with BTS)
Access Burst (initial connection setup between MS and BTS)
Dummy Burst (No Data is available for that slot)
University of Technology, Sydney 31275 Mobile Networking
Week 4: GSM
Dr Peter Leijdekkers 4.11
Peter Leijdekkers UTS – Mobile Networking (31275) 4.31
Channels
Physical Channels
Associated with frequency bands, time slots, codes
Physical channels transfer bits from one network element to another
Logical Channels
Distinguished by the nature of carried information and the way to assemble bits into data units
Three types
one-to-one: traffic channels between a BTS and a MS
one-to-many: synchronization signals from BTS to MSs in a cell
many-to-one: from MSs to the same BTS
Peter Leijdekkers UTS – Mobile Networking (31275) 4.32
Logical Channels
Control Channels
Broadcast Channels (BCH)
Common Control Channels (CCCH)
Dedicated Control Channels (DCCH)
Traffic Channels (TCH)
Full Rate (TCH/F)
Half Rate (TCH/H)
Peter Leijdekkers UTS – Mobile Networking (31275) 4.33
Control Channels
Broadcast Channels (BCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Broadcast Control Channel (BCCH)
Common Control Channels (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
Dedicated Control Channels (DCCH)
Stand alone Dedicated Control Channel (SDCCH)
Cell Broadcast Channel (CBCH)
Slow Associated Control Channel (SACCH)
Fast Associated Control Channel (FACCH)
University of Technology, Sydney 31275 Mobile Networking
Week 4: GSM
Dr Peter Leijdekkers 4.12
Peter Leijdekkers UTS – Mobile Networking (31275) 4.34
Overview
Market
GSM Services
GSM components
Air Interface
Call Setup
Handover
Peter Leijdekkers UTS – Mobile Networking (31275) 4.35
Mobile Terminated Call (MTC)
PSTNcalling
stationGMSC
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
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
BSS: Base Station System MS: Mobile Station HLR: Home Location Register VLR: Visitor Location RegisterGMSC: Gateway Mobile Services Switching Center
Peter Leijdekkers UTS – Mobile Networking (31275) 4.36
Mobile Originated Call (MOC)
PSTN GMSC
VLR
BSS
MSC
MS1
2
6 5
3 4
9
10
7 8
1, 2: connection request
3, 4: security check
5-8: check resources (free circuit)
9-10: set up call
University of Technology, Sydney 31275 Mobile Networking
Week 4: GSM
Dr Peter Leijdekkers 4.13
Peter Leijdekkers UTS – Mobile Networking (31275) 4.37
MTC/MOC call setup
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
BTSMS
channel request
immediate assignment
service request
authentication request
authentication response
ciphering command
ciphering complete
setup
call confirmed
assignment command
assignment complete
alerting
connect
connect acknowledge
data/speech exchange
Mobile Terminated Call Mobile Originated Call
Peter Leijdekkers UTS – Mobile Networking (31275) 4.38
Overview
Market
GSM Services
GSM components
Air Interface
Call Setup
Handover
Peter Leijdekkers UTS – Mobile Networking (31275) 4.39
4 types of handover
MSC MSC
BSC BSCBSC
BTS BTS BTSBTS
MS MS MS MS
12 3 4
1. Intra cell handover
2. Inter cell, intra BSC handover
3. Inter-BSC, intra MSC handover
4. Inter MSC handover
University of Technology, Sydney 31275 Mobile Networking
Week 4: GSM
Dr Peter Leijdekkers 4.14
Peter Leijdekkers UTS – Mobile Networking (31275) 4.40
Handover decision
receive level
BTSold
receive level
BTSold
MS MS
HO_MARGIN
BTSold BTSnew
Peter Leijdekkers UTS – Mobile Networking (31275) 4.41
Handover procedure
HO access
BTSold BSCnew
measurement
result
BSCold
Link establishment
MSCMSmeasurement
report
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