Readings
Global System for Mobile
Communication (GSM)
Recommended
Mobile Communications (2nd Edition) by Jochen Schiller
Chapter 4: Telecommunications Systems
Reference
“GSM Switching, Services, and Protocols” by Jörg Eberspächer,
Hans-Jörg Vögel, Christian Bettstetter. New York : Wiley, c2001.
Dr K.Sandrasegaran
Special Acknowledgements to Jochen Schiller
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
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What are the trends with mobile phone subscribers worldwide? (Schiller)
1200
GSM Markets & Evolution
Distinguish between 1G, 2G, 2.5G, 3G and 4G mobile technologies.
Tabulate the differences between GSM 900, 1800 and 1900.
What was the primary goal during the setting up of GSM standards?
Subscribers [million]
1000
GSM total
800
TDMA total
CDMA total
600
PDC total
Analogue total
Total wireless
400
Prediction (1998)
200
0
1996
1997
1998
1999
2000
2001
2002
year
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
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1
CT0/1
AMPS
NMT
GSM: Overview
GSM
CT2
IS-136
TDMA
D-AMPS
GSM
PDC
TDMA
FDMA
Development of mobile telecommunication systems
EDGE
GPRS
IMT-FT
DECT
IMT-SC
IS-136HS
UWC-136
IMT-DS
UTRA FDD / W-CDMA
CDMA
IMT-TC
UTRA TDD / TD-CDMA
IMT-TC
TD-SCDMA
1G
IS-95
cdmaOne
cdma2000 1X
2G
2.5G
IMT-MC
cdma2000 1X EV-DO
1X EV-DV
(3X)
3G
formerly: Groupe Spéciale Mobile (founded 1982)
now: Global System for Mobile Communication
Pan-European standard (ETSI, European Telecommunications
Standardisation Institute)
simultaneous introduction of essential services in three phases (1991,
1994, 1996) by the European telecommunication administrations
(Germany: D1 and D2)
seamless roaming within Europe possible
today many providers all over the world use GSM (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
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
What are performance characteristics of GSM (wrt. analog sys.)?
Communication
mobile, wireless communication; support for voice and data services
Total mobility
GSM Introduction
international access, chip-card enables use of access points of different
providers
Worldwide connectivity
one number, the network handles localization
High capacity if needed
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
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
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2
What are some of 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, no transparent Bchannel
reduced concentration while driving
electromagnetic radiation
abuse of private data possible
roaming profiles accessible
high complexity of the system
several incompatibilities within the GSM standards
GSM Services
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
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GSM Services: What type of services does GSM offer?
Services
GSM offers
several types of connections: voice connections, data
connections, SMS
multi-service options (combination of basic services)
Services
Three service domains
Bearer Services (i.e. pipes) refers to transport data between
access points
Supplementary
Services
Basic
Services
Telematic Services: enable communication via mobile phones
eg voice, data bearers.
eg telephony, emergency number, multinumbering, group 3 fax,
voice mailbox, email, SMS
Teleservices
Bearer
Services
Bearer Services transport data between access points
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
Supplementary Services: Services in addition to the basic
services, which cannot be offered stand-alone
eg CLI Caller Line Identifcation, suppression of number forwarding,
automatic call-back, conferencing, locking mobile terminal
(incoming or outgoing calls), ...
bearer services
MS
TE
MT
R, S
GSM-PLMN
Um
transit
network
(PSTN, ISDN)
source/
destination
TE
network
(U, S, R)
Telematic Services
Mobile telephony
Emergency number
Multinumbering
group 3 fax
voice mailbox
electronic mail
Short Message Service
(SMS)
bearer services
MS
TE
MT
R, S
GSM-PLMN
Um
transit
network
(PSTN, ISDN)
source/
destination
TE
network (U, S, R)
tele services
Supplementary services may include:
Voice mail
Acknowledgements to Schiller, Nokia, Ericsson,
Alcatel,
ETSI, 3GPP, IEEE,
tele
services
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
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3
What is a bearer service? What type of bearer services does
GSM offer?
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)
What are Tele Services? Types?
Telecommunication services that enable voice communication via
mobile phones
All these basic services have to obey cellular functions, security
measurements etc.
Offered services
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 – will be covered later!
mobile 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
Q. Distinguish the terms transparent vs. non-transparent, and synchronous vs.
asynchronous.
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
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Tele Services II
Additional services
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)
...
What are supplementary services?
Services in addition to the basic services, which cannot be offered
stand-alone
May differ between different service providers, countries and protocol
versions
Some examples of services
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
identification: forwarding of caller number
suppression of number forwarding
automatic call-back
conferencing with up to 7 participants
locking of the mobile terminal (incoming or outgoing calls)
...
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
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4
Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network)
GSM Architecture
several providers setup mobile networks following the GSM standard within
each country
Encourages competition which lowers prices and speeds up development of
new services
Open interfaces (eg Um, A, Abis) encourages vendor competition
What are the subsystems of GSM?
Distinguish between the following GSM subsystems: RSS, BSS, NSS and OSS.
Using an A3 page, draw and name the main elements of the GSM system architecture
(BTS, BSC, MSC, VLR, HLR, AuC, EIR, GMSC, SMSC (SMS), IWF, etc.
What are the functions of network elements?
Draw the external entities to which GSM connect to including MS, PSTN, PSPDN. Etc.
On the same diagram, sketch all the interfaces A, Abis, B, C, D, E, F, G, Um, R and S.
Draw the protocol stack that is used on each interface above.
What are the advantages of specifying all internal interfaces of the GSM system?
RSS (radio subsystem): covers all radio aspects
NSS (network and switching subsystem): call forwarding, handover, switching
OSS (operation subsystem): management of the network
Um
A
NSS
Network and Switching
Subsystem
Location and call
handling
RSS
Radio Subsystem
Radio and mobility
How and where is user-related data represented/stored in the GSM system?
Distinguish between the HLR and VLR.
OSS
Operation Subsystem
Network Management
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
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GSM: system architecture
network and
switching subsystem
radio
subsystem
MS
Network Elements
fixed
partner networks
OSS
Operation Subsystem
Network Management
MS
ISDN
PSTN
MSC
Um
BTS
Abis
Um
TC
BSC
EIR
BTS
BSS
Base Station
Subsystem
SS7
Abis
Mobile
Terminals
HLR
A
NSS
Network and
Switching Subsystem
Ater
BTS
BTS
EIR
BSC
MSC
HLR
TC
BTS
BSS
BSC
A
MSC
IWF
VLR
BTS
VLR
TC
BTS
ISDN
PSTN
BTS
Fixed
Partner
Networks
BSC
MSC
ISDN
PSTN
PSPDN
CSPDN
IWF
AUC
PSPDN
CSPDN
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
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5
GSM: overview
What is RSS? Components? Functions?
OMC, EIR,
AUC
HLR
NSS
with OSS
VLR
MSC
GMSC
VLR
fixed network
MSC
radio
subsystem
The Radio Subsystem (RSS) consists of one
or more BSS.
Components of Base Station Subsystem
BSS = BSC + sum(BTS) + TC
+interconnection
1. Base Transceiver Station (BTS):
BSC
MS
network and switching
subsystem
MS
Um
BTS
radio components including sender,
receiver, antenna
Signal and protocol processing limited to
error protection, encryption, link level
signalling
BTS
Abis
BSC
MSC
2. Base Station Controller (BSC):
BSC
RSS
Controlling and switching between BTSs,
Manages radio channels – handover,
paging, radio slot reservation and
assignment
mapping of radio channels (Um) onto
terrestrial channels (A interface)
A
BTS
MSC
BSC
BTS
BSS
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Interfaces
Um : radio interface
Abis : standardized, open interface with
16 kbit/s user channels
A: standardized, open interface with
64 kbit/s user channels
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3. Transcoder (TC) :
translates GSM speech channels (13kbit/s) to
PCM speech channels (64kbit/s),
handles comfort noise generation, discontinuous
transmission
Distinguish between the tasks of the BTS and BSC
Mobile station (MS), Mobile Terminal and SIM
Tasks of a BSS are distributed over BSC and BTS
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
BTS
X
X
X
X
X
X
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 )
BSC
X
X
X
X
personalization of the mobile station, stores user parameters
Provides separation of personal and terminal mobility.
Contains keys and algorithms needed for security.
X
X
X
X
X
X
SIM (Subscriber Identity Module):
TA (Terminal Adapter): e.g. Modem. Provides terminal adaptation, hides radio
specific characteristics.
TE (Terminal Equipment): e.g. Laptop
peripheral device of the MS, offers services to a user
does not contain GSM specific functions
TE
TA
R
MT
S
Um
Describe the functions of the MT and SIM. Why does GSM separate the MT and SIM?
Explain the difference between MT, TE, TA, SIM, MS?
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
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6
network
subsystem
Network and switching subsystem (NSS)
What are the function of NSS?
1.
main component of the GSM PLMN.
Performs switching, mobility management,
interconnection to other networks, system control,
charging
ISDN
PSTN
MSC
controls all connections via a separated network
to/from a mobile terminal within the domain of the
MSC - several BSC can belong to a MSC
HLR
2. Databases (scalability, high capacity, low delay)
The MSC (mobile switching center) plays a central role in GSM
EIR
What are the components of the NSS?
Mobile Services Switching Center (MSC)
What are functions of an Mobile Services Switching Center?
SS7
fixed partner
networks
VLR
Home Location Register (HLR): central master
database containing user data, permanent and
ISDN
semi-permanent data of all subscribers assigned to MSC
PSTN
IWF
the HLR (one provider can have several HLRs)
PSPDN
Visitor Location Register (VLR) : local database for
CSPDN
a subset of user data, including data about all user
MSC (Mobile Services Switching Center):
IWF (Interworking Functions)
currently in the domain of the VLR. Usually
ISDN (Integrated Services Digital Network)
combined with MSC.
PSTN (Public Switched Telephone Network)
PSPDN (Packet Switched Public Data Net.)
EIR (part of OSS)
CSPDN (Circuit Switched Public Data Net.)
AuC (part of OSS)
HLR (Home Location Register)
VLR (Visitor Location Register)
EIR (Equipment Identity Register)
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
switching functions
Mobility management
management of network resources
interworking functions via Gateway MSC (GMSC)
integration of several databases
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
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
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OSS Operation Subsystem
radio cell
The OSS (Operation Subsystem) enables
centralized operation, management, and
maintenance of all GSM subsystems
Components
1. Authentication Center (AUC)
2.
BSS
MS
Um
radio cell
RSS
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
MS
BTS
BTS
GSM Numbering
Abis
BSC
Equipment Identity Register (EIR)
registers GSM mobile stations
stolen or malfunctioning mobile stations
can be locked and sometimes even
localized
MS
BSC
A
3.
MSC
NSS
VLR
Operation and Maintenance Center
(OMC)
MSC
signaling
VLR
GMSC
HLR
IWF
different control capabilities for the radio
subsystem and the network subsystem
State the full name, composition, location(s) where it is kept, and purpose of
the following identifiers used in GSM: MSISDN, CC, NDC, SN, IMSI, MCC,
MNC, MSIN, TMSI, MSRN, VCC, VNDC, LAI, CGI (Cell Global Identity), BSIC,
IMEI? Distinguish between user related and system related identifiers.
ISDN, PSTN
PDN
O
OSS
EIR
AUC
OMC
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
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7
Identifiers Used in GSM
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)
IMSI identifies a subscriber worldwide.
Mobile country code + mobile network node + ms identification nr
E.g 240 + 23415 + 123456
TMSI (temporary mobile subscriber identification):
personalization of the mobile terminal, stores user parameters
IMSI (international mobile subscriber identification)
Numbering in Germany
SIM (Subscriber Identity Module)
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).
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
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IMSI vs MSISDN
IMSI – International Mobile Subscriber Identity
•Uniquely identifies a subscriber
•Used internally within the network
•Stored in the HLR, SIM, AUC
•IMSI = MCC + MNC + MSIN (Mobile Country Code +
Mobile Network Code + Mobile Subscriber Number)
MCC 3 digits
MNC 2 digits
Network name: Telstra Corporation Ltd.
MCC / MNC: 505 / 01, / 11, / 71, / 72
Network name: Optus Mobile Pty. Ltd.
MCC / MNC: 505 / 02, /90
Network name: Vodafone Network Pty. Ltd.
MCC / MNC: 505 / 03, / 07
MSIN – 10 digits
MSISDN – Mobile Subscriber Identity Number
•Uniquely identifies a subscriber
•Stored in the HLR and SIM
•MSISDN = CC + NDC + SN (Country Code +
National Destination Code + Subscriber Number)
•Publicly known subscriber number
CC max 3 digits
NDC max 3 digits
SN – 10 digits
GSM Air Interface
Explain how GSM implements SDMA, FDMA, TDMA, FDD on its air interface.
Using a table, distinguish between the following in terms of composition, duration, types, and effective
data rate: Burst, Time Slot, Frame, Multiframe, Superframe, Hyperframe.
Why is there a need to standardize the framing structure?
Explain the purpose of the various fields of the GSM burst? Guard, tail, S, training, etc.
Explain the purpose of normal, synchronization, access, dummy, and frequency correction bursts.
Why is there a need to separate uplink and downlink channels by 3TS?
How is slow hopping implemented in GSM?
Distinguish between the terms physical channel and logical channel.
Explain how different logical channels can use the same physical channel.
Distinguish between TCH/F and TCH/H. What data rates are possible in each?
What is the difference between TCH and CCH?
Explain the purpose of BCCH, FCCH, SCH, CCCH, PCH, RACH, AGCH, DCCH, SDCCH, SACCH,
FACCH.
Prove that the TCH/F data rate is 22.8 kbits/sec. Why is the user data rate much less than 22.8 kbits/sec?
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
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8
Basic Structure of Air Interface
GSM – SDMA/TDMA/FDMA/FDD/TDD
935-960 MHz
124 channels (200 kHz)
downlink
890-915 MHz
124 channels (200 kHz)
uplink
f1
f5
higher GSM frame structures
time
2
4
3
5
6
7
f2
f2
f2
f4
8
f15
3 bits
57 bits
S Training
S
1
1
26 bits
T0
f6
T6
T7
T0
T1
T2
T1
T2
user data
tail
57 bits
3
5. To increase capacity,
several frequencies can be
used in a cell, or sector, and
only 1 TSL is needed for
broadcasting
f24
f3
user data
T7
T3
T4
T5
T6
T7
T0
T1
T3
T4
T5
T6
T7
T0
T1
f22
GSM time-slot (normal burst)
tail
T6
Entire network is synchronised
f10
4.615 ms
guard
space
f9
f18
f12
GSM TDMA frame
1
3. Transmission in each cell is
divided into 8 timeslots (TSL) –
TDMA frame
1. Geographic region
divided into areas called
cells or sectors
f19
guard
space
f7
546.5 µs
577 µs
2. Each cell is assigned a frequency –
FDMA. Consecutive frequency numbers
should be separated by distance so as
to reduce interference
148 bits + 8.25 bp =156.25bp (*3.69us) = 577us per RTSL
4. T0, the first TSL in each
sector is reserved for
broadcast signalling
Once the mobile has
identified the timing of the
network it will tune in to this
timeslot anywhere in the
network find out more info
These timeslots are known as
PHYSICAL channels
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
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GSM hierarchy of frames (Schiller)
Timeslot content – LOGICAL CHANNELS
T6
What is transmitted in a timeslot is categorised
and scheduled in a predictable manner
Each successive transmission of a timeslot
contains a Logical Channel in a given
order, as shown
T0 always contains the Control Channels so
that all mobiles can orient themselves
within any network
The control channels (CCH) are for signalling
only, whereas the Traffic Channels (TCH)
carry user voice and data traffic
CCH are grouped in a sequence of 51 frames,
called a multiframe and TCH are grouped
in a 26 frame multiframe
51 Frame
hyperframe
T7
0
T0
T1
T2
FCCH
T3
0
T4
T6
T7
T0
T1
0
1
2
0
1
2
SCH
2
BCCH
2
TCH
3
BCCH
3
TCH
4
BCCH
4
TCH
2045 2046 2047 3 h 28 min 53.76 s
...
superframe
TCH
1
1
T5
TCH
0
...
1
48
...
49
24
50
6.12 s
25
multiframe
0
5
BCCH
5
TCH
6
CCCH
...
TCH
7
CCCH
11
TCH
8
CCCH
12
SACCH
9
CCCH
13
TCH
10
FCCH
...
TCH
11
SCH
25
idle
1
...
0
1
24
2
120 ms
25
...
48
49
50
235.4 ms
frame
26 Frame
0
1
...
6
7
4.615 ms
slot
burst
577 µs
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
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9
GSM Logical Channels
DCH
Dedicated Channels
CCH
Common Channels
BCH
CCCH
DCCH
Broadcast Channels
Common Control
Channels
Dedicated Control
Channels
Used to set up a point to point
connection
Used to set up a point to
point connection
Broadcast network information
DL Only
FCCH
Frequency Correction
Channel
Broadcasts carrier frequency
SDCCH
Full rate
Paging Channel
Slow Dedicated
Control Channel
User data rate of 13
kbit/s
SCH
TCH/H
Half rate
SACCH
Random Access
Channel
User data rate of 67 kbit/s
Slow Associated
Control Channel
Used by MS to gain DCCH
UL only
BCCH
Broadcast network information:
Used frequencies, Frequency
hopping sequence, Channel
combination, Paging groups,
surrounding cell information
Stand alone signalling
channel used to set up
connections
RACH
Contains BSIC and TDMA
frame no.
Broadcast Control
Channels
TCH/F
PCH
Broadcasts pages
DL only
Synchronisation
Channel
TCH
Traffic Channels
Used to set up a point to
point connection
Used to control a point
to point connection
AGCH
TCH/EFR
Enhanced Full
Rate
FACCH
Access Grant Channel
Fast Associated
Control Channel
Network assigns DCCH to Ms
DL only
User data rate of 13
kbit/s
Provides better
speech quality
Steals 20ms TCH channel
to exchange quick control
communication eg for
handovers
GSM Operation
4.1.4. Protocols
State the full names of the protocols shown in Figure 4.6. At which layer and interface are these protocols used on.
Explain the following functions of the physical layer (Layer 1) of the GSM Air interface: burst formatting, multiplexing,
synchronization (including timing advance), idle channel detection, measurements, modulation, encryption, channel
coding, error coding, interleaving.
What multiplexing schemes are used in GSM for what purposes?
How is synchronisation achieved in GSM? Who is responsible for synchronisation and why is synchronisation very
important? (Timing Advance)
How is error coding different in GSM and ISO/OSI model?
What are the important characteristics of channel coding in GSM?
Explain the role of voice activity detection (VAD) and comfort noise in GSM.
Why is a delay introduced due to interleaving in GSM?
What are the differences between LAPDm and LAPD?
Explain the function of RR, MM and CM in GSM?
Why is there a need to provide DTMF functionality in GSM?
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
GSM protocol layers for signaling
Um
Abis
MS
A
BTS
BSC
MSC
CM
CM
MM
MM
BSSAP
RR
RR’
BTSM
RR’
BTSM
LAPDm
LAPDm
LAPD
LAPD
radio
radio
PCM
PCM
16/64 kbit/s
BSSAP
SS7
SS7
PCM
PCM
64 kbit/s /
2.048 Mbit/s
GSM Session Management
4.1.5 Localization and Calling
How is localization performed in GSM? How does the HLR and VLR interact?
What is roaming? What are typical roaming scenarios?
Describe the steps involved in a Mobile Terminated Call (MTC)? Figure 4.4 &
4.9
Describe the steps involved in a Mobile Originated Call (MOC)? Figure 4.8 &
4.9
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
10
Mobile Terminated Call
Mobile Originated Call
VLR
1, 2: connection request
3, 4: security check
5-8: check resources (free circuit)
9-10: set up call
MS
MOC
3 4
6
PSTN
5
GMSC
7
MSC
8
2 9
BTS
channel request
immediate assignment
MS
1
10
BSS
service request
authentication request
authentication response
ciphering command
ciphering complete
setup
call confirmed
assignment command
assignment complete
alerting
connect
4
5
HLR
3 6
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
calling
station 1
PSTN
GMSC
2
7
10
BSS
11
MTC
MS
BTS
VLR
8 9
14 15
MSC
10 13
16
10
BSS
BSS
11
11
10 . paging request
11 12
17
channel request
immediate assignment
paging response
MS
authentication request
authentication response
ciphering command
ciphering complete
call confirmed
assignment command
assignment complete
alerting
connect
connect acknowledge
connect acknowledge
data/speech exchange
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
4 types of handover
1
MS
2
3
4
MS
MS
MS
GSM Mobility Management
BTS
4.1.6 Handovers in GSM
Give reasons for a handover in GSM and the problems associated with it.
What are the typical steps for handover? (Figure 4.10)
What types of handover can occur in GSM?
What measurements have to be done during handover? Who takes the measurements?
How are the measurements processed? (Figure 4.11)
Why is there a need for a handover margin? What are the implications of setting it too high
or low?
Explain Figure 4.12. What are the important conclusions you can make from it?
BTS
BTS
BTS
BSC
BSC
BSC
MSC
MSC
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
11
Handover decision
Handover procedure
receive level
BTSold
receive level
BTSold
MS
BTSold
BSCold
measurement
measurement
report
result
MSC
HO decision
HO required
BSCnew
BTSnew
HO request
resource allocation
ch. activation
HO command
HO command
HO command
HO request ack ch. activation ack
HO access
HO_MARGIN
Link establishment
MS
MS
BTSold
clear command clear command
BTSnew
clear complete
HO complete
HO complete
clear complete
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
Security in GSM
Security services
access control/authentication
GSM Security
4.1.7 Security in GSM
What are the security services offered by GSM?
State the names, location and purpose of all the keys (PIN, PUK, Ki, Kc) and
algorithms (A3, A5, A8) used for GSM security?
Describe the steps involved in the authentication of a GSM user? (Figure 4.13)
Describe the steps involved in the encryption of user data? (Figure 4.14)
How is system security maintained?
confidentiality
user SIM (Subscriber Identity Module): secret PIN (personal
identification number)
SIM network: challenge response method
voice and signaling encrypted on the wireless link (after successful
authentication)
anonymity
temporary identity TMSI
(Temporary Mobile Subscriber Identity)
newly assigned at each new location update (LUP)
encrypted transmission
3 algorithms specified in GSM
“secret”:
• A3 and A8
available via the
Internet
• network providers
can use stronger
mechanisms
A3 for authentication (“secret”, open interface)
A5 for encryption (standardized)
A8 for key generation (“secret”, open interface)
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
12
GSM - authentication
GSM - key generation and encryption
SIM
mobile network
Ki
RAND
128 bit
AC
RAND
128 bit
RAND
Ki
128 bit
Ki
AC
128 bit
A3
MS with SIM
mobile network (BTS)
128 bit
A3
RAND
RAND
RAND
128 bit
Ki
128 bit
128 bit
A8
SIM
A8
SIM
SRES* 32 bit
MSC
SRES* =? SRES
SRES
SRES
32 bit
32 bit
SRES
cipher
key
Kc
64 bit
Kc
64 bit
data
BSS
SRES
data
encrypted
data
MS
A5
Ki: individual subscriber authentication key
A5
SRES: signed response
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
Data services in GSM I
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)
HSCSD
4.1.8 New Data Services (HSCSD only)
What are the limitations of data services offered by GSM networks?
How can the data rates associated with GSM be increased?
Explain the important characteristics of HSCSD?
What is the maximum data rate that can be achieved with HSCSD?
Which resources need to be allocated during handover for data transmission
using HSCSD?
What are the limitations of HSCSD?
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
TCH/F4.8
1
2
3
4
TCH/F9.6
TCH/F14.4
1
1
2
3
4
2
3
4
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
13
Future mobile telecommunication networks
terminal
mobility
MBS
(Mobile Broadband System)
fast
UMTS
mobile
GSM DECT
slow
portable
fixed
SAMBA
MEDIAN
WAND
ISDN
10 kbit/s
B-ISDN
2 Mbit/s
20 Mbit/s
30 Mbit/s
150 Mbit/s
Acknowledgements to Schiller, Nokia, Ericsson, Alcatel, ETSI, 3GPP, IEEE,
Copyright 2011 Prof K.Sandrasegaran. Please report unauthorized usage to kumbes@ieee.org
14