Mobile Communication

IT2402 MOBILE COMMUNICATION
UNIT – III
Dr.A.Kathirvel, Professor and Head, Dept of IT
Anand Institute of Higher Technology, Chennai

Unit - III
MOBILE COMMUNICATION SYSTEMS
GSM-architecture-Location tracking and call setup-
Mobility management- Handover- Security-GSM SMS
–International roaming for GSM- call recording
functions-subscriber and service data mgt –-Mobile
Number portability -VoIP service for Mobile
Networks – GPRS –Architecture-GPRS procedures-
attach and detach procedures-PDP context
procedure-combined RA/LA update procedures-
Billing

Computers for the next decades?
 Computers are integrated
 small, cheap, portable, replaceable - no more separate devices
 Technology is in the background
 computer are aware of their environment and adapt (“location
awareness”)
 computer recognize the location of the user and react appropriately
(e.g., call forwarding, fax forwarding)
 Advances in technology
 more computing power in smaller devices
 flat, lightweight displays with low power consumption
 new user interfaces due to small dimensions
 more bandwidth
 multiple wireless interfaces: wireless LANs, wireless WANs, regional
wireless telecommunication networks etc.

Mobile communication
 Two aspects of mobility:
user mobility: users communicate (wireless) “anytime,
anywhere, with anyone”
device portability: devices can be connected anytime,
anywhere to the network
 The demand for mobile communication creates the need for
integration of wireless networks into existing fixed networks:
local area networks: standardization of IEEE 802.11
Internet: Mobile IP extension of the internet protocol IP
wide area networks: e.g., internetworking of GSM and
ISDN

Applications
 Vehicles
 transmission of news, road condition, weather, music via DAB
 personal communication using GSM
 position via GPS
 local ad-hoc network with vehicles close-by to prevent accidents,
guidance system, redundancy
 vehicle data (e.g., from busses, high-speed trains) can be transmitted in
advance for maintenance
 Emergencies
 early transmission of patient data to the hospital, current status, first
diagnosis
 replacement of a fixed infrastructure in case of earthquakes, hurricanes,
fire etc.
 crisis, war,.

Typical application: road traffic
UMTS, WLAN,
DAB, DVB, GSM,
cdma2000, TETRA, ...
Personal Travel Assistant, Laptop,
GSM, UMTS, WLAN,
Bluetooth, ...

Applications
 Traveling salesmen
 direct access to customer files stored in a central location
 consistent databases for all agents
 mobile office
 Replacement of fixed networks
 remote sensors, e.g., weather, earth activities
 flexibility for trade shows
 LANs in historic buildings
 Entertainment, education, ...
 outdoor Internet access
 intelligent travel guide with up-to-date location dependent information
 ad-hoc networks for multi user games

Location dependent services
 Location aware services
 what services, e.g., printer, fax, phone, server etc. exist in the local
environment
 Follow-on services
 automatic call-forwarding, transmission of the actual workspace to the
current location
 Information services
 push: e.g., current special offers in the supermarket
 pull: e.g., where is the Black Forrest Cherry Cake?
 Support services
 caches, intermediate results, state information etc. follow the mobile
device through the fixed network
 Privacy
 who should gain knowledge about the location

Mobile devices
Pager
• receive only
• tiny displays
• simple text
messages
Mobile phones
• voice, data
• simple graphical displays
PDA
• graphical displays
• character recognition
• simplified WWW
Palmtop
• tiny keyboard
• simple versions
of standard applications
Laptop/Notebook
• fully functional
• standard applications
Sensors,
embedded
controllers
www.scatterweb.net

Effects of device portability
 Power consumption
 limited computing power, low quality displays, small disks due to
limited battery capacity
 CPU: Power Consumption
 Loss of data
 higher probability, has to be included in advance into the design (e.g.,
defects, theft)
 Limited user interfaces
 compromise between size of fingers and portability
 Limited memory
 integration of character/voice recognition, abstract symbols
 limited value of mass memories with moving parts
 flash-memory or ? as alternative

Wireless systems: overview of the development
cellular phones satellites
wireless LANcordless
phones
1992:
GSM
1994:
DCS 1800
2001:
IMT-2000
1987:
CT1+
1982:
Inmarsat-A
1992:
Inmarsat-B
Inmarsat-M
1998:
Iridium
1989:
CT 2
1991:
DECT 199x:
proprietary
1997:
IEEE 802.11
1999:
802.11b, Bluetooth
1988:
Inmarsat-C
analogue
digital
1991:
D-AMPS
1991:
CDMA
1981:
NMT 450
1986:
NMT 900
1980:
CT0
1984:
CT1
1983:
AMPS
1993:
PDC
4G – fourth generation: when and how?
2000:
GPRS
2000:
IEEE 802.11a
200?:
Fourth Generation
(Internet based)

Wireless networks Vs fixed networks
 Higher loss-rates due to interference
 emissions of, e.g., engines, lightning
 Restrictive regulations of frequencies
 frequencies have to be coordinated, useful frequencies are almost all
occupied
 Low transmission rates
 local some MBs, regional currently, e.g., 53kbit/s with GSM/GPRS
 Higher delays, higher jitter
 connection setup time with GSM in the second range, several hundred
milliseconds for other wireless systems
 Lower security, simpler active attacking
 radio interface accessible for everyone, base station can be simulated,
thus attracting calls from mobile phones
 Always shared medium
 secure access mechanisms important

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
– authentication
– media access
– multiplexing
– media access control
– encryption
– modulation
– interference
– frequency
 Application layer
 Transport layer
 Network layer
 Data link layer
 Physical layer

GSM: Overview
 GSM ( http://www.gsmworld.com/index.shtml )
 formerly: Groupe Spéciale Mobile (founded 1982)
 now: Global System for Mobile Communication
 Pan-European standard (ETSI, European Telecommunications
Standardization 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 970.8 million subscribers (Dec 2003)
 more than 73% of all digital mobile phones use GSM
 over 10 billion SMS (Short Message Service) per month in Germany, >
360 billion/year worldwide

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

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 B-
channel (ISDN bearer – ISDN channel that carries the main data)
 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: 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 – data
 Telemetry Services – voice, short message service (SMS)
 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

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 – will be covered
later!

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 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

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)
Short Message Service (SMS)
alphanumeric data transmission to/from the mobile
terminal using the signaling channel, thus allowing
simultaneous use of basic services and SMS2

Supplementary services
 Services in addition to the basic services, cannot be offered
stand-alone
 Similar to ISDN services besides lower bandwidth due to the
radio link
 May differ between different service providers, countries and
protocol versions
 Important services
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)

Architecture of the GSM system
 GSM is a PLMN (Public Land Mobile Network)
several providers setup mobile networks following the GSM standard
within each country
components
MS (mobile station)
BS (base station)
MSC (mobile switching center)
LR (location register)
subsystems
RSS (radio subsystem): covers all radio aspects
NSS (network and switching subsystem): call forwarding,
handover, switching
OSS (operation subsystem): management of the network

GSM: overview
fixed network
BSC
BSC
MSC MSC
GMSC
OMC, EIR,
AUC
VLR
HLR
NSS
with OSS
RSS
VLR

GSM: elements and interfaces
NSS
MS MS
BTS
BSC
GMSC
IWF
OMC
BTS
BSC
MSC MSC
Abis
Um
EIR
HLR
VLR VLR
A
BSS
PDN
ISDN, PSTN
RSS
radio cell
radio cell
MS
AUC
OSS
signaling
O

Um
Abis
A
BSS
radio
subsystem
MS MS
BTS
BSC
BTS
BTS
BSC
BTS
network and
switching subsystem
MSC
MSC
fixed
partner networks
IWF
ISDN
PSTN
PSPDN
CSPDN
SS7
EIR
HLR
VLR
ISDN
PSTN
GSM: system architecture

System architecture: radio subsystem
 Components
 MS (Mobile Station)
 BSS (Base Station Subsystem):
consisting of
BTS (Base Transceiver Station):
sender and receiver
BSC (Base Station Controller):
controlling several transceivers
 Interfaces
 Um : radio interface
 Abis : standardized, open interface
with
16 kbit/s user channels
 A: standardized, open interface
with
64 kbit/s user channels
Um
Abis
A
BSS
radio
subsystem
network and switching
subsystem
MS MS
BTS
BSC MSC
BTS
BTS
BSC
BTS
MSC

System architecture: network and switching subsystem
Components
 MSC (Mobile Services Switching Center):
 IWF (Interworking Functions)
 ISDN (Integrated Services Digital Network)
 PSTN (Public Switched Telephone Network)
 PSPDN (Packet Switched Public Data Net.)
 CSPDN (Circuit Switched Public Data Net.)
Databases
 HLR (Home Location Register)
 VLR (Visitor Location Register)
 EIR (Equipment Identity Register)
network
subsystem
MSC
MSC
fixed partner
networks
IWF
ISDN
PSTN
PSPDN
CSPDN
SS7
EIR
HLR
VLR
ISDN
PSTN

Radio subsystem
 The Radio Subsystem (RSS) comprises the cellular mobile network up
to the switching centers
 Components
Base Station Subsystem (BSS):
Base Transceiver Station (BTS): radio components including
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)
BSS = BSC + sum(BTS) + interconnection
Mobile Stations (MS)

possible radio coverage of the cell
idealized shape of the cell
cell
segmentation of the area into cells
GSM: cellular network
 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

Example coverage of GSM
e-plus (GSM-1800)
T-Mobile (GSM-900/1800) Berlin
O2 (GSM-1800)
Vodafone (GSM-900/1800)

Base Transceiver Station and Base
Station Controller
 Tasks of a BSS
are distributed
over BSC and
BTS
 BTS comprises
radio specific
functions
 BSC is the
switching
center for radio
channels
Functions BTS BSC
Management of radio channels X
Frequency hopping (FH) X X
Management of terrestrial channels X
Mapping of terrestrial onto radio channels X
Channel coding and decoding X
Rate adaptation X
Encryption and decryption X X
Paging X X
Uplink signal measurements X
Traffic measurement X
Authentication X
Location registry, location update X
Handover management X

Mobile station
 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
 SIM (Subscriber Identity Module):
personalization of the mobile terminal, stores user parameters
R S
Um
TE TA MT

Network and switching subsystem
 NSS is the main component of the public mobile network GSM
 switching, mobility management, interconnection to other networks,
system control
 Components
 Mobile Services Switching Center (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
 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

Mobile Services Switching Center
 The MSC (mobile switching center) 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

Operation subsystem
 The OSS (Operation Subsystem) enables centralized operation, management,
and maintenance of all GSM subsystems
 Components
 Authentication Center (AUC)
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)
different control capabilities for the radio subsystem and the network
subsystem

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 µs
577 µs
tail user data TrainingS
guard
space S user data tail
guard
space
3 bits 57 bits 26 bits 57 bits1 1 3
GSM - TDMA/FDMA

GSM - TDMA/FDMA
 GSM time-slot (normal burst)
 Tail are all set to 0 and can be used to enhance the receiver performance.
 The training sequence is used to adapt the parameters and select the
strongest signal.
 A flag S indicates whether the data field contains user or network control
data.
 GSM bursts
 A normal burst for data transmission
 A frequency correction burst allows the MS to correct the local oscillator
to avoid interference
 A synchronization burst with an extended training sequence synchronizes
the MS with BTS in time.
 An access burst is used for the initial connection setup.
 A dummy burst is used if no data is available for a slot.

Logical channels and frame hierarchy
 GSM specifies two basic groups of logical channels:
 Traffic channels (TCH): GSM uses a TCH to transmit user data.
 Control channels (CCH): CCHs are used to control medium access,
allocation of traffic channels or mobility management.
Broadcast control channel (BCCH):A BTS uses this channel to signal
information such as the cell identifier, options, and frequencies to all
MSs within a cell.
Common control channel (CCCH): All information regarding connection
setup between MS and BS is exchanged via the CCCH.
Dedicated control channel (DCCH): Before a MS established a TCH with
the BTS, it uses DCCH for signaling.
 Logical frame hierarchy
 26 frame  multi-frame  26 multi-frames + 51 frames or 51 multi-
frames + 26 frames  2048 superframe  hyperframe

GSM hierarchy of frames
0 1 2 204520462047...
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
burst
slot
577 µs
4.615 ms
120 ms
235.4 ms
6.12 s
3 h 28 min 53.76 s

41
What is a location area (LA)?
 A powered-on mobile is informed of an incoming call by a
paging message sent over the PAGCH channel of a cell
 One extreme is to page every cell in the network for each call
- a waste of radio bandwidth
 Other extreme is to have a mobile send location updates at
the cell level. Paging cut to 1 cell, but large number of location
updating messages.
 Hence, in GSM, cells are grouped into Location Areas –
updates sent only when LA is changed; paging message sent
to all cells in last known LA

42
Addresses and Identifiers
 International Mobile Station Equipment Identity (IMEI)
It is similar to a serial number. It is allocated by equipment
manufacturer, registered by network, and stored in EIR
 International Mobile Subscriber Identity (IMSI)
MCC MNC MSIN
MCC: Country Code
MNC: Mobile Network Code
MSIN: Mobile Subscriber Identification Number
When subscribing for service with a network, subscriber receives (IMSI)
and stores it in the SIM (Subscriber Identity Module) card.
The HLR can be identified by a VLR/MSC from the IMSI.

43
 Mobile Subscriber ISDN (MSISDN)
The “real telephone number”: assigned to the SIM
The SIM can have several MSISDN numbers for
selection of different services like voice, data, fax
CC NDC SN
NDC: National Destination Code (NDC identifies operator);
SN: Subscriber Number; CC: Country Code;
Digits following NDC identifies the HLR

44
 Mobile Station Roaming Number (MSRN)
It is temporary location dependent ISDN number
It is assigned by local VLR to each MS in its area.
CC NDC SN
 Temporary Mobile Subscriber Identity (TMSI)
It is an alias of the IMSI and is used in its place for privacy.
It is used to avoid sending IMSI on the radio path.
It is an temporary identity that is allocated to an MS by the
VLR at inter-VLR registration, and can be changed by the VLR
TMSI is stored in MS SIM card and in VLR.

45
TMSI, IMSI, MSRN and MSISDN
 Unlike MSISDN, IMSI is not known to the GSM user. The CC of
MSISDN translates to an MCC of IMSI as follows, e.g, Denmark
CC: 45 MCC: 238
 TMSI is used instead of IMSI during location update to protect
privacy. As user moves, TMSI is used to send location update.
Thus a third party snooping on the wireless link cannot track a
user as he/she moves.
 MSRN is the routing number that identifies the current location
of the called MS.
MSRN is temporary network identity assigned to a mobile
subscriber.
MSRN identifies the serving MSC/VLR.
MSRN is used for call delivery (calls incoming to an MS).
 MSISDN is the dialed number to reach a GSM user

46
 Location Area ID (LAI)
CC: Country Code
MNC:Mobile Network Code
LAC: Location Area Code
LAI is broadcast regularly by Base Station on BCCH
Each cell is identified uniquely as belonging to an LA by its LAI
CC MNC LAC

47
Location management
Set of procedures to:
track a mobile user
find the mobile user to deliver it calls
Current location of MS maintained by 2-level
hierarchical strategy with HLRs and VLRs.

48
Ways to obtain MSRN
 Obtaining at location update – MSRN for the MS is assigned
at the time of each location update, and is stored in the
HLR. This way the HLR is in a position to immediately supply
the routing info (MSRN) needed to switch a call through to
the local MSC.
 Obtaining on a per call basis – This case requires that the
HLR has at least an identification for the currently
responsible VLR. When routing info is requested from the
HLR, it first has to obtain the MSRN from the VLR. This
MSRN is assigned on a per call basis, i.e. each call involves a
new MSRN assignment

49
Abbreviations
 ISC: International switching center
 OMC: Operations and maintenance center
 GMSC: Gateway switching center
 MSC: Mobile switching center
 VLR: Visitor location register
 HLR: Home Location register
 EIR: Equipment Identification register
 AUC: Authentication center
 BSC: Base station controller
 BTS: Base transceiver station
 MS: Mobile subscriber
 TMSI: Temporary Mobile Subscriber Identity
 IMSI: International Mobile Subscriber Identity

50
Routing information: case when MSRN is
selected per call by VLR/MSC
If MSRN is allocated to each subscriber visiting at an MSC, then the number of
MSRNs required is large. If instead, an MSRN is allocated only when a call is to
be established, then the number of MSRNs is roughly equal to number of
circuits at MSC – a much smaller number – hence MSRNs typically allocated per
call by VLR/MSC
MSISDN
GMSC
HLR

MSC/VLR



MSISDNIMSI, VLR number
MSRN

51
Call routing to a mobile station:
case when HLR returns MSRN
GMSC
BSC
BSC
EIR
HLR
AUC
VLR
MSCBTS
BTS
BTS
LA 1
LA 2
ISDN
1
MS
1
MSISDN
6
TMSI
4
MSRN
3
MSRN
2
MSISDN
7
TMSI
7
TMSI
7
TMSI
8
TMSI
5
MSRN
MSC

52
Messages exchanged: call delivery
PSTN
GMSC
HLR
VLR
Target
MSC
Originating
Switch GMSC HLR VLR
Target
MSC
1. ISUP IAM
2. MAP_SEND_ROUTING_INFO
3. MAP_PROVIDE_ROAMING_NUMBER
4. MAP_PROVIDE_ROAMING_NUMBER_ack
5. MAP_SEND_ROUTING_INFO_ack
6. ISUP IAM
1
2 3
45
6

53
Location registration
 MS has to register with the PLMN to get communication services
 Registration is required for a change of PLMN
 MS has to report to current PLMN with its IMSI and receive new
TMSI by executing Location Registration process.
 The TMSI is stored in SIM, so that even after power on or off,
there is only normal Location Update.
 If the MS recognizes by reading the LAI broadcast on BCCH that it
is in new LA, it performs Location Update to update the HLR
records.
 Location update procedure could also be performed periodically,
independent of the MS movement.
 The difference in Location Registration and Location Update is
that in location update the MS has already been assigned a TMSI.

54
Location registration
MS BSS/MSC VLR HLR AUC
IMSI Ki
A3 & A8
Generate
TMSI
Loc.Upd.Req
(IMSI,LAI)
Upd Loc.Area
(IMSI,LAI)
Aut.Par.Req Auth.Info.Req
(IMSI)
(RAND)
Authenticate
(IMSI,Kc,
RAND,SRES)
Aut. Info.
(IMSI)
(RAND)
Authentic.
Req
(IMSI,Kc,
RAND,SRES)
Auth.Info
Auth.Resp.
(SRES)
(SRES)
Auth.Resp
Update
Location
(IMSI,MSRN)
SRES
RANDKi
Kc SRES
Contd...

55
(…contd) Location registration.
A5
Generate
TMSI
(Kc)
Start Ciph.
Ciph.Mod.Com.
Message
M
Kc
Kc(M)
Ins.Subsc.Da
ta
(IMSI)
Forw. New TMSI
(TMSI)
Subs.Dat.Ins.Ac
k
Loc.Upd.Accept
(IMSI)Loc.Upd.Accept
Ciph.Mod.Kc(M)
A5
Kc(M)Kc
M
TMSI Realloc.Ack
TMSI
Realloc.Cmd.
TMSI.Ack
Loc.Upd.Accept
can be combined
New TMSI is received by MS
(TMSI Reallocation) in ciphering mode.

56
Location update
IMSI, TMSI
Ki, Kc, LAI
Start ciphering.
Authentication
Loc.Upd.Req
(TMSI,LAI)
Update
Loc.Area
(TMSI,LAI)
Update Location
(IMSI,MSRN)
Generate
TMSI
Start
ciphering(Kc) IMSI
Insert Subscriber.
data
Subs. Data Insert Ack
(contd..)

57
(..contd) Location update.
(IMSI)
Auth.Info.Req
(IMSI,Kc, RAND,SRES)
Auth.Info
Start ciphering.
Forward new TMSI
Auth. Para. Req
Loc. Upd. Acept
Loc. Upd. Acept
TMSI AckTMSI Reallocation
Complete
TMSI Realloc. Cmd.
(TMSI)
Auth. Info.
(IMSI,Kc, RAND,SRES)
(IMSI)
(IMSI)
Loc. Upd. Acept

58
Types of handover (same as
“handoff”)
 There are four different types of handover in the GSM system.
Handover involves transferring a call between:
Channels (time slots) in the same cell
Cells (Base Transceiver Stations) under the control of the
same Base Station Controller (BSC),
Cells under the control of different BSCs, but belonging to
the same Mobile services Switching Center (MSC), and
Cells under the control of different MSCs.

59
Attributes of radio-link handover
Hard handover
MAHO
Backward
COS selection scheme: static
Cross-over switch: anchor switch

60
Handover (MAHO)
 Handovers are initiated by the BSS/MSC (as a means of traffic
load balancing).
 During its idle time slots, the mobile scans the Broadcast
Control Channel of up to 16 neighboring cells, and forms a list
of the six best candidates for possible handover, based on the
received signal strength.
 This information is passed to the BSC and MSC, at least once
per second, and is used by the handover algorithm.

61
Handover procedures in GSM
BSC
MSC-A
BSC
MSC-B
BTS 1
BTS 3
BTS 2
BSC
MSC-C
BTS 3
Connection route
1
2
34
5
6
7
8
8
9

62
Inter MSC basic handover
MS/BSS 1 MSC-A
Handover
required
HA Indication
MSC-B VLR-B
Radio chan. Ack
Handover report
MS/BSS 2
Allocate Handover number
RLC
ANS
REL
End Signal
HB Indication
HB Confirm
Handover report
Perform
Handover
IAM
ACM
Send End Signal
End of Call

63
Subsequent handover from MSC-B to MSC-A
MS/BSS 1 MSC-A
HB Indication
HB Confirm
MSC-B
VLR-B
Subseq.
Handover
Acknowledge
MS/BSS 2
RLC
REL
End Signal
HA Required
HA Indication
Handover report
Perform
subsequent
Handover
End of Call

64
Subsequent handover from MSC-B to MSC-C
MSC-A
MSC-C
Perform
Handover
Radio chan.
Ack.
MSC-B
Allocate
Handover
Number
MS
IAM
ACM
HA RequestPerform
subsequent
Handover
VLR-C
Send Handover
report
HB Indication
(Contd…)

65
(…contd) Subsequent handover from MSC-B to MSC-C
MSC-A
MSC-C
Send End Signal
Handoff Report
MSC-B MS
REL
RLC
HA Indication
Perform
subsequent
Acknowledge
HB Confirm
ANS
MSC-B VLR-B
End Signal

GSM protocol layers for signaling
CM
MM
RR
MM
LAPDm
radio
LAPDm
radio
LAPD
PCM
RR’ BTSM
CM
LAPD
PCM
RR’
BTSM
16/64 kbit/s
Um Abis A
SS7
PCM
SS7
PCM
64 kbit/s /
2.048 Mbit/s
MS BTS BSC MSC
BSSAP BSSAP

Mobile Terminated Call (Wired
phone call)
PSTN
calling
station
GMSC
HLR VLR
BSSBSSBSS
MSC
MS
1 2
3
4
5
6
7
8 9
10
11 12
13
16
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

Mobile Originated Call
PSTN GMSC
VLR
BSS
MSC
MS
1
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
•

MTC/MOC
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
MTC MOC

4 types of handover
 GSM handover:
Intra-cell: A new frequency needs to be arranged by BSC
because of interference.
Inter-cell, intra-BSC handover: The mobile station moves
from one cell to another. The BSC performs a handover.
Inter-BSC, intra-MSC handover: The handover is controlled
by the MSC.
Inter MSC handover: Both MSCs perform the handover
together.

4 types of handover
MSC MSC
BSC BSCBSC
BTS BTS BTSBTS
MS MS MS MS
1
2 3 4

Handover decision
receive level
BTSold
receive level
BTSold
MS MS
HO_MARGIN
BTSold BTSnew

Handover procedure
HO access
BTSold BSCnew
measurement
result
BSCold
Link establishment
MSCMS
measurement
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

Security in GSM
 Security services
 access control/authentication
user  SIM (Subscriber Identity Module): secret PIN (personal identification
number)
SIM  network: challenge response method
 confidentiality
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
 A3 for authentication (“secret”, open interface)
 A5 for encryption (standardized)
 A8 for key generation (“secret”, open interface)
“secret”:
• A3 and A8
available via the
Internet
• network providers
can use stronger
mechanisms

GSM - authentication
A3
RANDKi
128 bit 128 bit
SRES* 32 bit
A3
RAND Ki
128 bit 128 bit
SRES 32 bit
SRES* =? SRES SRES
RAND
SRES
32 bit
mobile network SIM
AC
MSC
SIM
Ki: individual subscriber authentication key SRES: signed response

GSM - key generation and
encryption
A8
RANDKi
128 bit 128 bit
Kc
64 bit
A8
RAND Ki
128 bit 128 bit
SRES
RAND
encrypted
data
mobile network (BTS) MS with SIM
AC
BSS
SIM
A5
Kc
64 bit
A5
MS
data data
cipher
key

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)
 mainly software update on MS and MSC to split a traffic stream into several
streams.
 bundling of several time-slots to get higher AIUR (Air Interface User Rate)
(e.g., 57.6 kbit/s using 4 slots, 14.4 each)
 advantage: ready to use, constant quality, simple
 disadvantage: channels blocked for voice transmission
AIUR [kbit/s] TCH/F4.8 TCH/F9.6 TCH/F14.4
4.8 1
9.6 2 1
14.4 3 1
19.2 4 2
28.8 3 2
38.4 4
43.2 3
57.6 4

Data services in GSM II
 GPRS (General Packet Radio Service)
 packet switching
 using free slots only if data packets ready to send
(e.g., 50 kbit/s using 4 slots temporarily)
 standardization 1998, introduction 2001
 advantage: one step towards UMTS, more flexible
 disadvantage: more investment needed (new hardware)
 GPRS network elements
 GSN (GPRS Support Nodes): GGSN and SGSN
 GGSN (Gateway GSN)
interworking unit between GPRS and PDN (Packet Data Network)
 SGSN (Serving GSN)
supports the MS (location, billing, security)
 GR (GPRS Register)
user addresses

Introduction
 Definition: Short message service (SMS) is a globally accepted wireless
service that enables the transmission of alphanumeric messages
between mobile subscribers and external systems such as electronic
mail, paging, and voice-mail systems.
 SMS appeared on the wireless scene in 1991 in Europe. The European
standard for digital wireless, now known as the Global System for
Mobile Communications (GSM), included short messaging services
from the outset.
 In North America, SMS was made available initially on digital wireless
networks built by early pioneers such as BellSouth Mobility, PrimeCo,
and Nextel, among others. These digital wireless networks are based
on GSM, code division multiple access (CDMA), and time division
multiple access (TDMA) standards.

How it works?
 Messages in Short Message Service (SMS) must be no longer than 160 alpha-
numeric characters and contain no images or graphics.
 Once a message is sent, it is received by a Short Message Service Center (SMSC),
which must then get it to the appropriate mobile device.
 To do this, the SMSC sends a SMS Request to the home location register (HLR) to
find the roaming customer. Once the HLR receives the request, it will respond to
the SMSC with the subscriber's status: 1) inactive or active 2) where subscriber is
roaming.
 If the response is "inactive", then the SMSC will hold onto the message for a period
of time. When the subscriber accesses his device, the HLR sends a SMS Notification
to the SMSC, and the SMSC will attempt delivery.
 The SMSC transfers the message in a Short Message Delivery Point to Point format
to the serving system. The system pages the device, and if it responds, the message
gets delivered.
 The SMSC receives verification that the message was received by the end user,
then categorizes the message as "sent" and will not attempt to send again.
 The number of mobile-phone users expects to reach 500 million worldwide by
2003, and with the help of SMS, 75 percent of all cellular phones will be Internet-
enabled.

Benefits of SMS
 At a minimum, SMS benefits include the following:
 Delivery of notifications and alerts
 Guaranteed message delivery
 Reliable, low-cost communication mechanism for concise information
 Ability to screen messages and return calls in a selective way
 Increased subscriber productivity
 More sophisticated functionality provides the following
enhanced subscriber benefits:
 Delivery of messages to multiple subscribers at a time
 Ability to receive diverse information
 E-mail generation
 Creation of user groups
 Integration with other data and Internet-based applications

Benefits of SMS (cont.)
 The benefits of SMS to the service provider are as follows:
 Ability to increment average revenue per user (due to increased number
of calls on wireless and wireline networks by leveraging the notification
capabilities of SMS)
 An alternative to alphanumeric paging services, which may replace or
complement an existing paging offer
 Ability to enable wireless data access for corporate users
 New revenue streams resulting from addition of value-added services
such as e-mail, voice mail, fax, and Web-based application integration,
reminder service, stock and currency quotes, and airline schedules
 Provision of key administrative services such as advice of charge, over-
the-air downloading, and over-the-air service provisioning
 Protection of important network resources (such as voice channels),
due to SMS’ sparing use of the control and traffic channels
 Notification mechanisms for newer services such as those utilizing
wireless application protocol (WAP)

GSM Short Message Service
 Can contain up to 140 octets, or 160 char.
 To allow messages longer than 160 char.
SMS concatenation
SMS compression
 SDCCH signaling channel
 Two type of GSM SMS
Cell broadcast service
Point-to-point service

SMS Architecture
GSM Network
IWMSC
Originating MS
SM-SC
Short Message
Sender
GSM Network
SMS
GMSC
MSC
MS
SIM
Terminating MS
BSS
SMS GMSC : SMS Gateway MSC
IWMSC : Interworking MSC
SM-SC : Short Message Service Center
MSC : Mobile Switching Center
BSS : Base Station System
SIM : Subscriber Identity Module
MS : Mobile Station
Figure 12.1 GSM short message
service network architecture

SMS Protocol Hierarchy
Short Message
Relay Entity
(SMR)
Short Message
Control Entity
(SMC)
Short Message
Relay Entity
(SMR)
Short Message
Control Entity
(SMC)
Short Message
Application Layer
(SM-AL)
Short Message
Transfer Layer
(SM-TL)
Short Message
Relay Layer
(SM-RL)
Connection
Management
Sublayer (CM-sub)
Short Message
Relay Protocol
(SM-RP)
Short Message
Control Protocol
(SM-CP)
Short Message Transfer Protocol (SM-TP)
MSC IWMSC
MS SM-SC
Lower layers
Figure 12.2 SMS MS-MSC protocol hierarchy (mobile origination)

 Short Message Transfer Layer
 Provides services to transfer SM-AL short msg.
 Generate a reference number SMI (short message identifier)
SM-AL SMI is not carried between the MS and SM-SC
 Four types of transfer protocol data units (TPDUs)
SMS-SUBMIT
SMS-DELIVER
SMS-STATUS-REPORT
SMS-COMMAND

 Short Message Relay Layer
 Provides services to transfer TPDUs and delivery reports for
SM-TL
 Generate SM-RL SMI for every short message
SM-RL SMI is mapped to and from SM-TL SMI
SM-RL SMI at the MS is not carried at the peer entity in the
SM-SC
 SM-RP consists of the following RPDU types:
RP-DATA
RP-SM-MEMORY-AVAILABLE
RP-ACK
RP-ERROR

 Connection Management Sublayer
 Provides services to support the SM-RL
 MS has two SMC entities
 MS-originated (MO) short message service
 MS-terminated (MT) short message service
 SM-CP consists of following protocol elements
 CP-DATA
 CP-ACK
 CP-ERROR
 MNSMS-ESTablish
 To establish an MM-connection and transfer RPDU on that establish
 MNSMS-DATA
 Transfer an RPDU on MM-connection
 MNSMS-RELease
 MNSMS-ABORT
 MNSMS-ERROR

Mobile-Originated Messaging
SM-TL SM-RL CM-Sub CM-Sub SM-RL SM-TL
1. SM-RL-DATA-Req
(SMS-SUBMIT)
3. MM-Connection Establishment
MS MSC
SM-SC
2. MNSMS-EST-Req
(RP-DATA(MO))
4. CP-DATA
5. CP-ACK
5. MNSMS-EST-Req
(RP-DATA) 6. SM-RL-DATA-Ind
(SMS-SUBMIT)
Figure 12.3 Mobile-originated short messaging (part 1)
The logical message path is :
MS -> originating MSC -> IWMSC -> SM-SC

MS MSC VLR
3a. CM_SERV_REQ
3d. CM_ACCEPT
3b. MAP_PROCESS_ACCESS_REQUEST
3c. MAP_PROCESS_ACCESS_REQUEST_ack
Figure 12.4 MM-connection establish for mobile-originated short messaging

MSC IWMSCVLR SM-SC
7. MAP_SEND_INFO_FOR_MO_SMS
8. MAP_SEND_INFO_FOR_MO_SMS_ack
9. MAP_FORWARD_SHORT_MESSAGE
12. MAP_FORWAR_SHORT_MESSAGE_ack
10. Short Message
11. Delivery Report

17. SM_RL_REPORT_Ind
(SMS_STATUS_REPORT)
MS MSC
13. SM_RL_REPORT_Req
(SMS_STATUS_REPORT)
15. CP-DATA
17. MNSMS_REL_Req
14. MNSMS_DATA_Req
(RP_ACK)
18. MM-Connection Release
14. MNSMS_REL_Req
16. MNSMS_DATA_Ind
(RP_ACK)
14. MNSMS_DATA_Req
(RP_ACK)

Mobile-Terminated Messaging
MS
3. MAP_SEND_ROUTING_INFO_FOR_SM_ack
1. Short Message
MSC VLR HLR
SMS
GMSC
SM-SC
2. MAP_SEND_ROUTING_INFO_FOR_SM
4. MAP_FORWARD_SHORT_MESSAGE
5. MAP_SEND_INFO_FOR_MT_SMS
6. MAP_PAGE
7. PAGING_REQUEST
8. PAGING_RESPONSE
9. MAP_PROCESS_ACCESS_REQUEST
10. MAP_SEND_INFO_FOR_MT_SMS_ack
Figure 12.7 Mobile-terminated short messaging (part 1)
The logical massage path is :
SM-SC -> GMSC -> terminating MSC -> MS

MS MSC
11. SM_RL_DATA_Req
(SMS_DELIVER)
14. CP-DATA
12. MNSMS_EST_Req
(RP_DATA(MT))
13. MM-Connection Establishment
15. MNSMS_EST_Ind
(RP_DATA)
(SMR) (SMC) (SMC) (SMR)
20. MM-Connection Release
15. CP_ACK
16. SM_RL_DATA_Ind
(SMS_DELIVER) 16. MNSMS_DATA_Req
(RP_ACK)
17. CP-DATA
18. CP_ACK
16. MNSMS_REL_Req
18. MNSMS_DATA_Ind
(RP_ACK)
19. MNSMS_REL_Req
19. SM_RL_REPORT_Ind
(SMS_STATUS_REPORT)
Figure 12.8 Mobile-terminated short messaging (part2)

MSC
SMS
GMSC
SM-SC
21. MAP_FORWARD_SHORT_MESSAGE_ack
22. Delivery Report
Figure 12.9 Mobile-terminated short messaging (part 3)

Introduction
GSM supports roaming services that allow a
subscriber in a GSM network to receive mobile
telephony service when the user visits a different
GSM network
GSM networks are within the same country
GSM networks are located in different countries

Introduction
 International roaming issue from the customer’s perspective
John is a subscriber of GSM service in Korea
Suppose that he travels from Korea to Japan ,which have a
GSM roaming agreement
John
Jenny

3 scenarios for call delivery to John
 Scenarios #1
If a person in Korea call John
The caller is charged for a local GSM call
John is charged for an international call from Korea to Japan
 Scenarios #2
If the caller is from a third country (say, Hong Kong)
The caller is charged for an international call from Hong Kong
to Korea
John is charged for an international call from Korea to Japan
 Scenarios #3
If the caller is in Japan
international call
This scenario is in fact a special case of scenario 2, and is
referred to as tromboning

International GSM Call Setup
 The call delivery procedure to a GSM roamer is basically the same
as the procedure described in Chapter 9, except that two
international switch centers (ISCs) are involved in the voice path.
 ISCs offer interworking functions between the national networks
and the international network
 The call path of every international call is composed of three
segments:
one in origination country
another in the international network
the third in the destination country
 These circuit segments are interconnected by two ISCs:
one in the origination country
the other in the destination country

Korea
International call setup procedure (Step 1)
Radio tower
1 2 3
4 5 6
7 8 9
* 8 #
HLR
E
VLR
F
GMSC D
MSC G
Switch
A
ISC B
(Japan)
ISC C
(Korea)
John Jenny
1
JAPAN
Jenny first dials the ISCA
(international switch center
access code), CC (country
code), John’s MSISDN
1.1
Switch A interprets the
ISCA, the first portion of
the dialed digits, it
identifies the call as an
international call, then sets
up the call using the IAM
message to Japan ISC
1.2
Based on country code,
ISC B routes the call to
Korea’s ISC C
ISC C interprets the prefix
of the remaining digits, and
sets up the voice trunk to
GMSC D
1.3

Korea
International call setup procedure(Step 2~6)
Radio tower
1 2 3
4 5 6
7 8 9
* 8 #
HLR
E
VLR
F
GMSC D
MSC G
Switch
A
ISC B
(Japan)
ISC C
(Korea)
John Jenny
1
JAPAN
1.1
1.2
1.3
2
Step 2.
GMSC D queries
HLR E to obtain
the MSRN
Step 3and 4
HLR E queries
VLR F
3.1
3.2
3.3
4.1
4.2
4.3
Step 5
The MSRN is
returned to GMSC
D
5
Step 6
Based on the
MSRN, GMSC D
uses the IAM
message to set up
the trunk to MSC G
6.1
6.2
6.3
6.3
6.3

Reducing the International Call Delivery
Cost
 To avoid unnecessary international trunk setups, an IAM message
should not travel across country boundaries before the destination
is known
 Four solutions that follow this guideline
A basic restriction is that we should not introduce any new
message types to the GSM MAP protocol defined in GSM
specification 09.02.
The solutions utilize only existing messages with the prefix
MAP_
In the first three solutions, we utilize the concept of roamer
location cache (RLC)
In solution 4, we introduce a special dialing code that leads the
call to the GMSC of the visited GSM system

RLC
 The RLC in a visited system maintains a database containing
the records of all international roamers who are presently in
that visited system
From the perspective of a VLR in the visited system, RLC
functions as the HLR of a roamer
From the perspective of the HLR in the home system of the
roamer, RLC serves as the VLR in a visited system

Solution 1 (Registration)
Radio tower
Korea
HLR
VLR
MSC
ISC B
(Japan)
ISC C
(Korea)
JAPAN
RLC
1
1
1
Step 1.
The MS registers to the
VLR
2
Step 2.
The VLR sends
MAP_UPDATE_LOCA
TION to the roamer’s
HLR.
HLR은 외국에
있으므로 ISC B에게
라우트
3
3 5
5
4
Step 3.
ISC B는 메시지를
해석, roamer
등록절차인지를 식별,
The message is
forwarded to Korean
(ISC C) as usual
Step 4.
At the same time, ISC B
duplicates the message
and forwards it to the
RLC.
RLC creates a record to
store the IMSI and
VLR/MSC address
Step 5.
RLC
MAP_RESTORE_DAT
A : HLR MSISDN
MAP_INSERT_SUBSC
RIBER_DATA :
MSISDN

Solution 1 (Call delivery)
Radio tower
VLR
MSC
ISC B
(Japan)
RLC
4
1
2
4
1 2 3
4 5 6
7 8 9
* 8 #
3
PSTN
Switch
A
1
Jenny
John
Step 1.
Jenny first dials the ISCA
code, the CC code, then
John's MSISDN
스위치A는 다이얼의 앞
부분(ISCA+CC)을 해석
국제전화임을 확인하고
ISC B에게 라우트 (IAM
message)
Step 2.
CC code와 남아있는
번호에 근거하여 ISC
B는 국내에서 이뤄지는
통화임을 알게 된다
ISC B는 IAM 메시지에
의해 제공된 MSISDN을
이용하여 RLC를 찾는다
Step 3.
RLC Table에 John
entry가 있는 경우
VLR로 부터 MSRN을
가지고 온다.
Step 4.
By using the MSRN, ISC
B routes the IAM
message to John

Solution 1 (Advantage & Disadvantage)
 Advantage
Only ISC B needs to be modified
Other network elements, such as the VLR and HLR, remain
the same
 Disadvantage
Most ISCs are not equipped with the GSM MAP protocol
(not be able to interpret the GSM MAP message)
ISCs typically belong to an international telephone carrier
different from that of the GSM service provider

Radio tower
Korea
HLR
VLR
MSC
A
ISC B
(Japan)
ISC C
(Korea)
RLC
1
1
1
Step 1.
VLR
3
3 4
4
JAPAN
Switch
D
4
3
2
Step 2.
VLR은 international
roamer의 등록임을 알고,
MAP_UPDATE_LOCATI
ON 메시지를 RLC에게
보낸다
store the IMSI and
VLR/MSC address
Step 3.
RLC sends the
MAP_UPDATE_LOCATI
ON message to the
roamer’s HLR
Step 4.
RLC
MAP_RESTORE_DATA
roamer MSISDN

Solution 2 (Call delivery)
Radio tower
VLR
MSC
RLC
4
1
2
4
1 2 3
4 5 6
7 8 9
* 8 #
3
PSTN
Switch
A
1
Jenny
John
Step 1.
The steps are the same as
those for solution 1.
Except that Jenny dials
the number of Switch D
instead of the country
code
Step 2.
Switch D는 IAM
메시지에 의해 제공된
MSISDN을 이용하여
RLC를 찾는다
Step 3.
RLC Table에 John
entry가 있는 경우
VLR로 부터 MSRN을
가지고 온다.
Step 4.
By using the MSRN, ISC
B routes the IAM
message to John
Switch
D

 Advantage
The modifications are made only within the GSM network
 Disadvantage
Extra modifications to the VLR
The caller must dial the number of Switch D, then the
MSISDN
Dialing process id different from the ordinary international
call dialing procedure
Sophisticated billing procedure

Radio tower
Korea
HLR
VLR
MSC
A
ISC B
(Japan)
ISC C
(Korea)
RLC
1
1
1
Step 1.
VLR
2
2 4
4
JAPAN
Switch
D
4
Step 2.
The VLR sends
MAP_UPDATE_LOCATI
ON to the roamer’s HLR.
HLR은 외국에 있으므로
ISC B에게 라우트
Step 3.
foreign country의 HLR
location update 메시지
보내질 동
store the IMSI and
VLR/MSC address
Step 4.
RLC
MAP_RESTORE_DATA
roamer
MSISDN
2
extrator
3

Advantage
It is transparent to the VLR
Disadvantage
A new network component (i.e., the extractor)

Solution 4
 Dial NDC1+IRAC+CC+NDC2+SN
 NDC1 : NDC or mobile network access code to the visited GSM system
 IRAC : international roamer access code
 CC : country code of the home country
 NDC2 : NDC of the home GSM system
 SN : subscriber number for the roamer
 PSTN routes the call to a GMSC of the visited GSM system
(NDC1)
 GMSC international roaming call (IRAC)
 HLR CC+NDC2+SN MSISDN
 Signaling path between the GMSC and the HLR already exists
 The GMSC query the HLR to obtain the MSRN
 GMSC MSC call MS

HLR VLRGMSC
MSC
PSTN
1 2 3
4 5 6
7 8 9
* 8 #
1
2 3
45
6

Solution 4
GMSC is a general-purpose switching system
Roamer
MSC
Advantage
GSM call delivery procedure is not modified
No new elements are required
Cost-effective (no new network elements)

GSM Operations
Administration, and Maintenance

 To manage the network GSM requires OA&M functions
 Follow the standard Telecommunication Management Network (TMN)
concept
 The TMN Component
 Operations System (OS)
With the operations system function (OSF), the OS is responsible for
the overall TMN management
billing, accounting, management of mobile equipment, HLR
measurement
Reside in an operation and maintenance center (OMC)
 Network Element (NE)
NEs in GSM are HLR, VLR, MSC, AuC, BSC, BTS, EIR
monitored or controlled by the OS
Network Element Functions (NEFs) represent the
telecommunications and support functions to be managed by the OS
Operations, Administration & Maintenance

 Data Communication Network (DCN)
The OSs, NEs, and other TMN elements communicate through DCN by
using data communication function (DCF)
The DCN technology can be WAN, LAN, or others
The GSM OMC typically connects to MSCs and BSCs by X.25
 Mediation Device (MD)
The MD adapts the OS to the specific NEs
Uses the mediation function (MF) to route or pass information between
standardized interface
 Q-Adapter (QA)
Use the Q-adaptor function (QAF) to connect the non-TMN entities
 Workstation (WS)
Interacts the operation/maintenance personnel with the OS through the
workstation functions (WSFs)
With WSFs, staff access the status of the network and monitor the
system parameters

TMN architecture
To another
TMN
Workstation Functions
(WSFs)
Workstations(WS)
Operations System
Functions (OSF)
Operations System(OS)
Mediation Functions
(MFs)
Mediation Device(MD)
Q-Adaptor Functions
(QAFs)
Q-Adaptor(QA)
Network Element Functions
(NEFs)
Network Element(NE)
(f)
(x)
(q3)
(q3)
(qx)
(g)
Data Communications Function (DCF)
To operating staff
To another
TMN
Workstation Functions
(WSFs)
Workstations(WS)
Operations System
Functions (OSF)
Operations System(OS)
Mediation Functions
(MFs)
Mediation Device(MD)
Q-Adaptor Functions
(QAFs)
Q-Adaptor(QA)
Network Element Functions
(NEFs)
Network Element(NE)
Data Communications
Network(DCN)
(f)
(x)
(q3)
(q3)
(qx)
(g)

TMN connection for the base station system
OSF
OS BSC BTS
MF
NEF
NEF
(q3)
(qx)
 The relationship between components of TMN functions are defined by
using the reference points
q3 : connects an OSF to an MF or an NEF
qx : connects an MF to an NEF or a QAF
x : connects an OSF to another OSF , OSF-like functionality in a
different TMN
f : connects an OSF to a WSF
g : connects an WSF to the operating staff

Common Management Function for GSM
 Three categories
 Forwarding of event notifications
Emit event notifications to the OS following Event Report Systems
Management Function
The object class Event Forwarding Discriminator (EFD) in the NE manages
forwarding of event notifications
 Information logging
Information generated by NE may be stored in a record filestore in the NE
Information can be retrieved by NE or OS
Allows the OS to control the logging of selective event notifications
 Bulk data transfer between the OS and the NE
Use Common Management Information Service Element (CMISE) control
of File Transfer Access and Management (FTAM)
The data transfer is controlled by the OS

Figure 14.3 GSM-managed object class containment
Network
plmnNetwork
managedElement
aucFunction
mscFunction
wlrFunction
hlrFunction
bssFunction
Other Object Classes
CommonManagedObegects
Sms_G_JW_Function
elrFunction
callRecording Function(a)
(b)
(c)
(d) (i)
(h)
(g)
(f)
(e)

Call-Recording Functions
 The billing of the mobile subscribers, statistics of service usage, and roaming traffic must
be monitored by the OS
 This information is provided by the NEs
 Managed by the tariff and charging administration
 Administration includes the following services
 Service Provision : introduce new or modified services to the GSM
 Billing : determines the charge for the services
 Accounting
Inter-PLMN:
Required for roaming traffic management, which is settled by means of the
transfer account procedure (TAP)
TAP records are regularly exchanged between GSM network
For visitor from another GSM network
The mobile-originated call charges are calculated and converted to an
agreed accounting currency
 Fixed-network : manage call traffic between MS and the fixed network
 signaling traffic for functions such as location updates
 Customer Administration : handles customer queries such as billing complaints

Tariff and
charging
administration
OSF
Service
Provision
OSF
Billing
OSF
Accounting
Customer
Administration
Tariff
Administra
-tion
Data
Collection
Tariff
Administra
-tion
Online
Tariff
(AoC)
Data
Generation
Control
Tariff
Data
Real-time
Event
Collection
Call-
Recording
Function
Record
Class
Event-
Forwarding
Discriminat
-or
Data
Transfer
Control
Log
Record
Filestore
OSF
Tariff and
Charging
Administration
Telecommunication Events
Log control
Event reporting
Internal event
Record
generation
control
Event
report
Log
record
File transfer
Record
generation
control
Event report
a b c d
e f
g
h
i
j
l
n
k
m
o
AoC parameter (sent to MS)

Tariff Administration
 Tariff administration function provides the tariff administration
information to the Nes
 The OSF uses the tariff class management functions to assign a tariff
class with service, distance, and time-based tariff-dependent charging
parameters
 These dependencies are elaborated next:
 The service charging dependencies are defined based on the
customized AoC
 The AoC (advice of charge) service definition may consist of one or
more
Service types
Radio channel types
Connection type
 The distance dependencies are defined based on the origins,
destinations, and charging zone

Data Collection
 Data collection functions provide the specifications of the collected
data to the NEs through the data generation control in the NEF
(record generation, event reporting, and log control)
 The OSF data collection functions collect the data from these NEs
through the data transfer control
 Call-recording function generates potential call and event records
based on the internal telecommunication events in the NE
 The record generation control determines where the records are
sent:
The records may be forwarded to the record filestore
The records may be saved in a log file
The records may also be passed to the EFDs controlled by the
event-reporting function

Performance Measurement and Management
 Performance of GSM network
 Evaluate based on the data provided by NEs
data : user/signaling traffic levels, quality of service
network configuration verification, resource access measurements
 Measurement job
is created, modified, displayed, suspended, resumed, deleted in the OS
is implemented as a simple Scanner object
is scheduled in a period to accumulate measurement data for inspection
instruct measurement function objects in the NEs to collect the data
hlrFunction
simpleScanner hlrMeasurement
Fuction
(measurement job)
 HLR measurement object class
containment

Fig 5. Measurement attribute modifications in location update
(a) Modify
measurement attribute
attLocationUpdate
(b) Modify
measurement attribute
succLocationUpdate
Location update
operation in HLR
HLR VLR
MAP_UPDATE_LOCATION
MAP_UPDATE_LOCATION_ack

Simple Scanner object
 Measurement types
 attLocationUpdate : number of the attempted location updates
 succlocationUpdate : number of the successful location updates
 Measured network resources : The network resource is HLR
 Measurement function : The simpleScanner specifies one or more
measurement functions in the NEs to collect the desired data
 Measurement schedule :
 specify start time & stop time of the active measurement period
 should be started within 90 days after measurement job is created
 Granularity period :
 specify periodic interval of sending measured data from HLR to OS
 Scan report
 is sent from NE to OS at the end of every granularity period
 include timestamp to indicate when it is sent to OS

Subscriber and Service Data Management
Define management for NEs … AuC, HLR, VLR, and EIR
Managed data in different NEFs may depend on each other
example :
To create a subscriber profile in the HLR, subscriber data
should already exist in the AuC
If it does not, creation in the HLR fails
MSISDNs and IMSIs are managed in HLR
An MSISDN can associate with several basic service
Established between the msisdnHlr object and the
basicServiceInHlr objects
Some supplementary services are specified with parameters
When a subscriber is deleted from the HLR, the corresponding
subscriberInHlr object and all its contained objects are removed

subscriberInHlr msisdnHlr
hlrFunction
basicServiceInHlr basicServiceGroupInHlr
ssInHlrCFNRc ssInHlrBarring ssInHlrCW ssInHlrCUG
ssInHlrCFNRy ssInHlrCFU ssInHlrSimple ssInHlrClir
ssInHlrParmCFNRc
ssInHlrParmBarr
ing
ssInHlrParmSimple
ssInHlrParmCUG
ssInHlrParmCFNRy ssInHlrParmCFB ssInHlrParmCFU
ssInHlrCUGSubscription
ssInHlrCFB
Subsclasses of sslnHlrParameter
b a d c
e
f
g
Subsclasses of supplementary ServiceInHlr
HLR subscriber administration object
class containment

Introduction
 Number portability
Subscriber to keep a “unique” telephone number
Enhance fair competition among telco.
To improve customer service quality
 Three kinds of number portability
Location portability
Service portability
Operator portability
 CLEC (competitive local exchange carrier)
 ILEC (incumbent local exchange carrier)

Fixed-Network Number Portability (1/2)
Switch1 2 3
4 5 6
7 8 9
* 8 #
Switch
Originating Network Donor Network
Switch 1 2 3
4 5 6
7 8 9
* 8 #
Recipient Network
Ported Number
1
2
Switch1 2 3
4 5 6
7 8 9
* 8 #
Switch
Switch 1 2 3
4 5 6
7 8 9
* 8 #
Recipient Network
Ported Number
1
2
Switch1 2 3
4 5 6
7 8 9
* 8 #
Switch
1
2
Switch 1 2 3
4 5 6
7 8 9
* 8 #
Recipient Network
Ported Number
NP
Database
3
Switch1 2 3
4 5 6
7 8 9
* 8 #
Switch
1
2
Switch 1 2 3
4 5 6
7 8 9
* 8 #
Recipient Network
Ported Number
NP
Database
3
4
(a) Call Forwarding (b) Call Drop-back
(c) Query-on-Release (d) All-Call-Query
Signaling path
Trunk setup path

Fixed-Network Number Portability(2/2)
NUMBER PORTABILITY
SOLUTION
ROUTING
INDEPENDENCE
EXTRA CALL
SETUP COST
INITIAL SYSTEM
SETUP COST
Call Forwarding low pct low
Call Drop-back medium cs medium
Query-on-Release medium p (cs + cd) high
All-Call-Query high cs high
 Extra call setup costs
 Initial System Setup Costs
 Customer Transfer Costs

Cost Recovery
NUMBER PORTABILITY
SOLUTION
CUSTOMER
TRANSFER COST
EXTRA CALL
SETUP COST
INITIAL SYSTEM
SETUP COST
Call Forwarding r->d ; c->r o->d own
Call Drop-back r->d ; c->r o->d own
Query-on-Release r->d, db ;c->r o->d, o->db own
All-Call-Query r->db ;c->r o->db own
 r : recipient operator
 d : donor operator
 o : origination operator
 c : customer
 db : the party who manages number portability database

Number Portability for Mobile Networks
 Mobile phone is associated with two number
Directory number (MSISDN in GSM)
Identification number (IMSI in GSM)
MSISDN and IMSI pair is assigned to the user
MIN (mobile identification number) ,MDN ( mobile directory
number) are used in EIA/TIA IS-41 based system
Typically assume that both MIN and MDN have the same value
To support portability, separation of MIN and MDN is required
Location update
Mobile call origination
Mobile call termination

Mobile Number Portability Mechanisms
MSC
1 2 3
4 5 6
7 8 9
* 8 #
Switch PSTN
Visited System
1. Incoming call
Originating switch
4. Trunk Setup
to Serving MSC GMSC
HLR
2. Query
MSRN
3. Return
MSRN
Home System
 Two restriction
 The GMSC must be in the call path for the provision of special
features and services, as well as for billing
 The originating switch does not have the capability of query
the HLR database, which must be done by GMSC
Simplified GSM call termination procedure and tromboning routing

Signaling Relay Approach 1/2 (SRA 1/2)
1 2 3
4 5 6
7 8 9
* 8 #
PSTN
Originating switch
6. Trunk Setup
to Serving MSC
MSC
HLR
3. Query MSRN 4. Return MSRN
Recipient Network
HLR
GMSC
2. Query MSRN
Signaling
Relay
Function
5. MSRN
Donor
Network
Switch
1. Incoming
call
1 2 3
4 5 6
7 8 9
* 8 #
PSTN
Originating switch
6. Trunk Setup
to Recipient MSC
using IRN
GMSCHLR
3. Query IRN
4. Return IRN
Recipient Network
HLR
GMSC
2. Query IRN
Signaling
Relay
Function
5. IRN
Donor
Network
Switch
1. Incoming
call
Gateway
9. Trunk setup
to serving MSC
MSC
7. Query MSRN
8. Return MSRN
SRA 1 SRA 2
IRN (Intermediate Routing Number)

Tromboning trunk setup in SRF 2
1. Incoming
call
GMSC MSC
HLR
Signaling
Relay
Function
HLR
GMSC
Donor
Network
A
2. Qrery IRN 5. IRN
3. Query IRN 4. Return IRN
7. Query MSRN
8. Return MSRN
9. Trunk setup
to serving MSC
Originating
switch
MS q MS p
Recipient Network B
6. Trunk Setup
to Recipient MSC
using IRN

All-Call-Query Approach 1/2 (ACQ 1/2)
1. Incoming call
5. Trunk Setup to
Serving MSC
1 2 3
4 5 6
7 8 9
* 8 #
Originating switch
1. Query MSRN
Switch
NP
Database
PSTN
4. Return MSRN
MSC
HLR
2. Query MSRN 3. Return MSRN
Singaling
Relay
function
ACQ1 ACQ2

Implementation Costs for mobile Number
portability
NUMBER PORTABILITY
SOLUTION
ROUTING
INDEPENDENCE
EXTRA CALL
SETUP COST
INITIAL SYSTEM
SETUP COST
SRA 1 low cs medium
SRA 2 low 2cs + pct medium
ACQ 1 high cs medium
ACQ 2 high cs - ct medium
NUMBER PORTABILITY
SOLUTION
CUSTOMER
TRANSFER COST
EXTRA CALL
SETUP COST
INITIAL SYSTEM
SETUP COST
SRA 1 r->d (db) ; c->r o->d, d->db own
SRA 2 r->d (db) ; c->r o->d, r, d->db own
ACQ 1 r->db ;c->r o->db own
ACQ 2 r->db ;c->r o->db own
Comparison of Mobile Number portability Solution
Cost Recovery mobile number portability solutions

VoIP Service for Mobile Networks

Introduction
 VoIP is considered as a promising trend in telecommunication.
 Integrating mobile phone services with VoIP in particular has
become an important issue.
 Telecommunications and Internet Protocol Harmonization
over Network (TIPHON) specifies the mechanism (i.e. a
mediation gatekeeper) to provide the service control
functions for convergence of IP networks, mobile networks,
fixed wireless networks, and PSTN.
 Several scenario are defined in TIPHON to illustrate different
ways of integrating IP and mobile networks.
 We use GSM as an example of mobile networks to describe
mobile/IP integration, where the mobile signaling protocol is
GSM MAP

TIPHON IP and mobile integration scenario
Signaling
Gateway
MSC
VLR
HLR
Gateway
(VLR)
Mediation
Gatekeeper
Mobile
Network
IP Network
BSC/BTS
BSC/BTS

GSM on the Net
 Based on a concept similar to TIPHON, Ericsson’s GSM on the
Net utilizes a corporate intranet to integrate an enterprise
communication network with the public GSM network
 This system supports both terminal mobility and user mobility.
Terminal mobility : whereby a terminal can be moved
around the service area without losing contact with the
system
User mobility : whereby, using various types of terminals, a
user can move around the service area without losing
contact with the system
 Each of the elements in the corporate network is connected to
a switched Ethernet with 10Mbps bandwidth.
 They communicate with each other using the H.323 family of
protocols.

GSM on the Net
Service
node
MSC
VLR
HLR
Gateway
Access
node
GSM Network
Corporate offices
GSM/BTS
BSC/BTS
Intranet
IP Phone/PC

GSM on the Net
 Service node
Enables user mobility.
Controls calls among different types of terminals.
Translates addresses between PSTN and GSM on the Net.
Provides authentication, resource management, least-cost
routing, and administration for user identity and service profile.
 Access node
Resembles the MSC, VLR, and BSC to manage connection,
mobility, and radio resources.
Does not provide trunks; instead, controls only the
communication between the endpoints.
Consist of network access controller (NAC), and the radio
network server (RNS)

GSM on the Net
 GSM/BTS
Provides wireless access for a GSM MS in the IP network
 Gateway
Provides interfaces between GSM on the Net and other
networks (particularly the GSM network)
Consists of both voice and SS7 gateway functionality
 Terminal equipment
Can be an IP phone, PC, DECT phone, or GSM mobile
station.

The iGSM Wireless VoIP solution
 We proposes the iGSM service that realizes another TIPHON
scenario supporting user mobility for GSM subscribers to
access VoIP service.
 iGSM solution is different from GSM on the Net
 Unlike GSM on the Net, iGSM is a value-added service to
the public GSM Networks.
iGSM network does not introduce wireless access
equipment in the IP network; rather, iGSM service is
implemented using standard platforms(general IP gateway
/ gatekeeper)

The iGSM Wireless VoIP solution
 We describe the iGSM architecture and the protocols for
location update and call delivery.
 We discuss how the tromboning effect in standard GSM
systems can be avoided when accessing the IP Network.
 We investigate the problem of misrouting a call caused by
user mobility.

H.323 Network
H.323
Gatekeeper
H.323
Gateway
H.323
Multipoint
Control Unit
MC
MC
MC
MP
MP
MP
MC
ISDN
LAN
PSTN
H.323 Terminal
(phone or PC)
The iGSM system consists of the GSM and H.323 (IP) networks.
<H.323 Architecture>
ITU-T H.323 covers the technical requirements for multimedia
communications Over packet-based networks that may not provide a
guaranteed quality of service

H.323 architecture
 Terminal
Customer premises equipment (CPE) that provides audio, video, and
data communications capability for point to point or multipoint
conferences in the H.323 network
 Gateway
Perform call control function and the communication protocol
translation mechanism between an H.323 endpoint and endpoint of a
circuit-switched network, such as ISDN,PSTN
 Gatekeeper
Optional in an H.323 network
May be colocated with a terminal, gateway or multipoint control unit
Provide these functions that address translation, admissions control,
bandwidth control, and zone management.

H.323 architecture
 Multipoint control unit (MCU)
Utilizes multipoint controllers to support multipoint
conferences
 Multipoint controller
Provides control functions to support conferences between
three or more endpoints in a multipoint conference.
Every MCU contains an MC.
 Multipoint process (MP)
Receives audio, video, and data streams from the endpoints
involved in a multipoint conference.
An MP is optionally included in a gateway, gatekeeper, or MCU

The iGSM Architecture
 iGSM gateway is implemented to perform two major functions
besides the standard H.323 mechanisms
GSM MAP and H.225 RAS (registration, admission, status)
protocol translation.
GSM/PSTN/IP call setup and release
 An iGSM gatekeeper is implemented to serve as the VLR for iGSM
subscribers who visit the IP network.
Every iGSM gatekeeper is assigned an ISDN number that can be
recognized by the HLR.
The iGSM gatekeeper maintains a list of all iGSM subscribers.
Based on this list, the gatekeeper performs MSISDN-to-
transport address translation and GSM roaming management
procedures for the iGSM subscribers.

iGSM architecture
GSM
IP networkMSC
VLR
HLR
iGSM
Gateway
Gatekeeper
iGSM VLR
BTS/BSC
H.323 Terminal
MS

iGSM procedures and Message Flows
 Every iGSM subscriber has a record in the datebase.
MSISDN of the MS
Transport address of the H.323 terminal for the subscriber in
the IP network.
Password of the iGSM subscriber
HLR address of the iGSM subscriber
IMSI of the MS
User profile which indicates the service features and
restrictions the iGSM subscriber
Presence indication of the iGSM subscriber in the IP network.

HLR deregistration
oldVLRMAP_CANCEL_LOCATION
oldVLR oldVLR iGSM MS
Registration
H.323 terminal
GSM
IP networkMSC
VLR
HLR
iGSM
Gateway
Gatekeeper
iGSM VLR
BTS/BSC 1
2
4
7,8
MS
3
6 5
3
4
6
5

Message flow for iGSM registration
H.323
terminal
Gatekeeper
(new VLR) Gateway HLR Old VLR
2
3
3
4
4
5
5
6
6
6
7
8
PRQ(MSISDN)
IRQ
MAP_UPDATE_LOCATIO
N
MAP_INSERT_SUBSCRIBERDATA
MAP_CANCEL_LOCATIO
N
MAP_CANCEL_LOCATION_ac
k
IRQ
IRR
MAP_INSERT_SUBSCRIBER_DATA_ac
k
MAP_UPDATE_LOCATION_ack
IRR
RCF

Deregistration
H.323 terminal
HLR Gateway
Gatekeeper
(old VLR)
MAP_CANCEL_LOCATION(IMSI)
MAP_CANCEL_LOCATION_ack
IRR (CanLoc, IMSI)
IACK (CanLocAck)
URQ(unregister Request)
UCF(Unregister
Confirmation)
2
2
2
1
1
1
 In this case of the iGSM gatekeeper is the “OLD VLR”
 iGSM subscriber moves from the IP Network to the GSM Network.

H.323 terminal gatekeeper
ARQ and ACF message
ARJ(Admission Reject)
Call delivery to the IP network
H.323 terminal
GSM
IP network
Gateway
MSC
HLR
iGSM
Gateway
Gatekeeper
iGSM VLR
1
SwitchOriginating
PSTN
2 3
1
3
2
3
24
6
5
7
8
10
9
12
11

Message flow for iGSM call setup

Implementation Issues
 iGSM
 Reducing GSM Tromboning Effect
 Investigating misrouting of user mobility

Reducing GSM Tromboning Effect
 Tromboning occurs when the caller and the called MS are in
the same city but the GMSC is in another city.
 Both GSM MSCs and iGSM gateways can serve as GMSCs for
iGSM subscribers
If an iGSM subscriber is assigned a GSM MSC as his GMSC,
call delivery follows the procedure iGSM call delivery and
tromboning occurs.
 If an iGSM subscriber is assigned a iGSM gateway as his
GMSC, call delivery tromboning can be avoided

PSTN iGSM IP network
Switch
iGSM
Gateway
Gatekeeper
iGSM VLR
1
2
caller
3 4
5
iGSM user
IP Network iGSM IP network
iGSM
Gateway
Gatekeeper
iGSM VLR
1
2
iGSM user
caller
 Two kinds of subscribers are anticipated in iGSM
 The GMSCs of the iGSM subscribers are standard GSM MSCs. In this case,
the subscibers typically subscribe to the standard GSM services at the
beginning, and determine to include the iGSM service later
 The GMSC of the subscribers is the iGSM gateway. In this case, the
subscribers typically subscribe to the iGSM service from the beginning
<PSTN-to-IP Cal Setup>
<IP-to-IP Cal Setup>

 The first kind of subscribers
call delivery follows the standard GSM procedure
A subscriber visits the IP network, tromboning may occur
as in traditional GSM networks
The GSM operator would prefer this scenario if the iGSM
gateway and gatekeeper are owned by other ISPs.
 The second kind of subscribers
Call-delivery tromboning avoided when the subscriber
visits the IP network.
The GSM operator is likely to own the iGSM gateway and
gatekeeper

Misrouting Due to User Mobility
 To support user mobility, the subscriber needs to explicitly
perform registration to inform the system in which location
area he resides when the terminal has been changed.
 Missing  call deliveries may be misrouted
 This problem can be eliminated if the subscriber always turns
off the MS when he moves to the H.323 terminal
 The turn-off action results in a GSM detach message, which
deregisters the MS.

GSM VoIP network
MSC
GSM
VoIP
Gateway
VLR
B
HLR
p A
VLR
A
p
IP Phone
HLR
p B
GSM MS
1
4
2
VLR
A
VLR
B
p
3
step1step2step3

 The misrouting problem is avoided if the subscriber explicitly or
implicitly registers with the GSM MS step3.
 Implicit registration occurs in two cases
The subscriber originates a call. In this case, VLR A finds that
the VLR record for the subscriber does not exit. VLR A will ask
the MS to perform a registration operation, as described in
the VLR failure restoration procedure
The subscriber moves to another LA in the GSM network.
Registration is automatically initiated by the GSM MS.
 Both case, after the HLR has modified the subscriber’s record, it
also cancels the subscriber’s VLR record in VLR B

General Packet Radio Service
(GPRS)

What is GPRS ?
Part of GSM phase 2+
General Packet Radio Service
General -> not restricted to GSM use (DECT ?, 3rd generation systems ?)
Packet Radio -> enables packet mode communication over air
Service, not System -> existing BSS (partially also NSS) infrastructure is
used
Requires many new network elements into NSS
Provides connections to external packet data networks (Internet, X.25)
Main benefits
Resources are reserved only when needed and charged accordingly
Connection setup times are reduced
Enables new service opportunities

GPRS access interfaces and reference
points
Gi reference point
GPRS network 1
GPRS network 2
PDNs or
other networksTE MT
Gp
UmR reference point
MS
GPRS provides packet switched connections from MS to packet
data networks (PDN)
Different operator’s GPRS networks are connected through Gp
interface

How is GPRS seen by external networks
and GPRS users?
Local
area
network
Router
Corporate 2
Local
area
network
Router
Corporate 1
Packet
networkData
network
(Internet)
GPRS
SUBNETWORK
SUBNETWORK
155.222.33.XXX
SUBNETWORK
131.44.15.XXX
SUBNETWORK
191.200.44.XXX
HOST
191.200.44.21
HOST
131.44.15.3
HOST
155.222.33.55
"Router"

Air interface resources
0
2
4
6
8
10
12
14
16
1:00 PM 1:15 PM 1:30 PM 1:45 PM
TCH
An example of occupied TCH
capacity by CS traffic during
busy hour with n% blocking
0
2
4
6
8
10
12
14
16
3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00
TCH
Capacity occupied by CS traffic
Free
Capacity
GPRS "steals" any TCH
capacity not used by CS
traffic

GPRS characteristics
 GPRS uses packet switched resource allocation
resources allocated only when data is to be
sent/received
 Flexible channel allocation
one to eight time slots
available resources shared by active users
up and down link channels reserved separately
GPRS and circuit switched GSM services can use same
time slots alternatively
 Traffic characteristics suitable for GPRS
Intermittent, bursty data transmissions
Frequent transmissions of small volumes of data
Infrequent transmission of larger volumes of data

Applications
Standard data network protocol based
IP based applications
WWW, FTP, Telnet, ...
Any conventional TCP/IP based applications
X.25 based applications
Packet Assembly/Disassembly (PAD) type approach
GPRS specific protocol based
Point-to-point applications
Toll road system, UIC train control system
Point-to-multipoint applications
Weather info, road traffic info, news, fleet management
SMS delivery (GPRS as a bearer for SMS)

MAP-F
Gi
Gn
Gb
Gc
MAP-D
MAP-CMAP-H
Gp
Gs
Signalling and Data Transfer Interface
Signalling Interface
MSC/VLR
TE MT BSS TEPDN
R Um
Gr
A
HLR
Other PLMN
SGSN
GGSN
Gd
SM-SC
SMS-GMSC
SMS-IWMSC
GGSN
EIR
GPRS architecture

Functional view on GPRS
Local
area
network
Server
Router
Local
area
network
Server
Router
Corporate 2
Corporate 1
Intra-PLMN
backbone
network
(IP based)
Serving GPRS
Support Node
(SGSN)
Point-To-
Multipoint
Service
Center
(PTM SC)
Gateway GPRS
Support Node
(GGSN)
GPRS
INFRASTRUCTURE
HLR/AuC
MSC
BSCBTS Packet
networkPSTN
Packet
networkSS7
Network
Packet
network
Data
network
(Internet)
Packet
network
Data
network
(X.25)
Packet
network
Inter-PLMN
Backbone
network
Border
Gateway (BG)
Gb
Gr Gd
Gi.IP
Gi.X.25
Firewall
Firewall
Firewall
Um
R/S
SMS-GMSC
Gr Gd
Gs
Gs
Gp
Gn
Gn
EIR
MAP-F

Function MS BSS SGSN GGSN HLR
Network Access Control:
Registration X
Authentication and Authorisation X X X
Admission Control X X X
Message Screening X
Packet Terminal Adaptation X
Charging Data Collection X X
Packet Routeing & Transfer:
Relay X X X X
Routeing X X X X
Address Translation and Mapping X X X
Encapsulation X X X
Tunnelling X X
Compression X X
Ciphering X X X
Mobility Management: X X X X
Logical Link Management:
Logical Link Establishment X X
Logical Link Maintenance X X
Logical Link Release X X
Radio Resource Management:
Um Management X X
Cell Selection X X
Um-Tranx X X
Path Management X X
Assignment of functions to general
logical architecture

Subscription of GPRS service (1/2)
 Subscription storage: HLR
 Supports Multiple Subscriber Profile (MSP)
 Mobile identification: IMSI
 One or several PDP addresses per user
Each subscribed configuration contains
PDP type (e.g., IP, X.25)
PDP address (static, e.g. 128.200.192.64)
Subscribed QoS (level 1…4)
Dynamic address allowed
VPLMN address allowed
GGSN address
Screening information (optional)

Subscription of GPRS service (2/2)
 Subscription is copied from HLR to SGSN during GPRS Attach
 Part of PDP context is copied to relevant GGSNs when a PDP
address is activated
 Possible PDP address allocation alternatives
 Static address allocated from HPLMN
 Dynamic address allocated from HPLMN
 Dynamic address allocated from VPLMN
 HPLMN operator specifies which alternatives are possible

Gateway GPRS Support Node
 GGSN
 Typically located at one of the MSC sites
 One (or few) per operator
 Main functions
Interface to external data networks
Resembles to a data network router
Forwards end user data to right SGSN
Routes mobile originated packets to right destination
Filters end user traffic
Collects charging information for data network usage
Data packets are not sent to MS unless the user has
activated the PDP address

Serving GPRS Support Node
 SGSN
 Functionally connected with BSC, physically can be at MSC
or BSC site
 One for few BSCs or one (or few) per every BSC
 One SGSN can support BSCs of several MSC sites
 Main functions
 Authenticates GPRS mobiles
 Handles mobile’s registration in GPRS network
 Handles mobile’s mobility management
 Relays MO and MT data traffic
TCP/IP header compression, V.42bis data compression,
error control MS- SGSN (ARQ)
Collect charging information of air interface usage

Other elements
 BG (Border Gateway)
 (Not defined within GPRS)
 Routes packets from SGSN/GGSN of one operator to a SGSN/GGSN of an
other operator
 Provides protection against intruders from external networks
 DNS (Domain Name Server)
Translates addresses from ggsn1.oper1.fi -format to 123.45.67.89
format (i.e. as used in Internet)
 Charging Gateway
Collects charging information from SGSNs and GGSNs
 PTM-SC (Point to Multipoint -Service Center)
PTM Multicast (PTM-M): Downlink broadcast; no subscription; no
ciphering
PTM Group call (PTM-G): Closed or open groups; Down/up -link;
ciphered
Geographical area limitation

GPRS backbones
 Enables communication between GPRS Support Nodes
 Based on private IP network
IPv6 is the ultimate protocol
IPV4 can be used as an intermediate solution
 Intra-PLMN backbone
Connects GPRS Support Nodes of one operator
Operator decides the network architecture
LAN, point-to-point links, ATM, ISDN, ...
 Inter-PLMN backbone
Connects GPRS operators via BGs
Provides international GPRS roaming
Operators decide the backbone in the roaming
agreement

GPRS mobile types
 Class A:
Simultaneous GPRS and conventional GSM operation
Supports simultaneous circuit switched and GPRS data transfer
 Class B:
Can be attached to both GPRS and conventional GSM services
simultaneously
Can listen circuit switched and GPRS pages (via GPRS)
Supports either circuit switched calls or GPRS data transfer but
not simultaneous communication
 Class C:
Alternatively attached in GPRS or conventional GSM
No simultaneous operation
‘GPRS only’ mobiles also possible (e.g. for telemetric
applications)

GPRS multislot capabilities
0MS RX
MS TX
Monitor
1 2 3 4 5 6 7 0 1
0 2 3 4 5 65 6 7 1
MS RX
MS TX
Monitor
0 1 2 3 4 5 6 7 0 1
0 2 3 4 5 65 6 7 1
MS RX
MS TX
Monitor
0 1 2 3 4 5 6 7 0 1
0 2 3 4 5 65 6 7 1
3 slots: 4th slot: 5th slot:
1-slot
2-slot
3-8 -slot

Security: Based on GSM phase 2
Authentication
SGSN uses same principle as MSC/VLR:
Get triplet, send RAND to MS, wait for SRES from MS, use Kc
MS can’t authenticate the network
Key management in MS
Kc generated same way from RAND using Ki as in GSM
Ciphering
Ciphering algorithm is optimized for GPRS traffic (‘GPRS - A5’)
Ciphering is done between MS and SGSN
User confidentiality
IMSI is only used if a temporary identity is not available
Temporary identity (TLLI) is exchanged over ciphered link

GPRS Attach
 GPRS Attach function is similar to IMSI attach
Authenticate the mobile
Generate the ciphering key
Enable the ciphering
Allocate temporary identity (TLLI)
Copy subscriber profile from HLR to SGSN
 After GPRS attach
The location of the mobile is tracked
Communication between MS and SGSN is secured
Charging information is collected
SGSN knows what the subscriber is allowed to do
HLR knows the location of the MS in accuracy of SGSN

Data transfer: Basic rules (1/4)
SGSN:
Does not interpret user data, except
SGSN may perform TCP/IP header compression
Does not interpret source or destination addresses
Sends all packets to specified GGSN that handles the PDP
context
GGSN:
Performs optional filtering
Decides where and how to route the packet

Data transfer (2/4)
Mobile originated (left when MS in HPLMN, right when in
VPLMN, no filtering/screening)
Local
area
network
Server
Router
SGSN
GGSN
BG
BSCBTS
Intra-PLMN
backbone
network
(IP based)
SGSN
GGSN
BG
BSC BTS
Intra-PLMN
backbone
network
(IP based)
Packet
network
Inter-PLMN
backbone
network
Packet
network
Data
network
(Internet)
Corporate
HPLMN VPLMN

Data transfer (3/4)
Mobile terminated (left when MS in HPLMN, right when in
VPLMN, with/without filtering/screening)
Local
area
network
Server
Router
SGSN
GGSN
BG
BSCBTS
Intra-PLMN
backbone
network
(IP based)
SGSN
GGSN
BG
BSC BTS
Intra-PLMN
backbone
network
(IP based)
Packet
network
Inter-PLMN
backbone
network
Packet
network
Data
network
(Internet)
Corporate
HPLMN VPLMN

Data transfer (4/4)
Mobile originated and terminated (left MSs in same PLMN,
right MSs in different PLMN)
Local
area
network
Server
Router
SGSN
GGSN
BG
BSCBTS
Intra-PLMN
backbone
network
(IP based)
SGSN
GGSN
BG
BSC BTS
Intra-PLMN
backbone
network
(IP based)
Packet
network
Inter-PLMN
backbone
network
Packet
network
Data
network
(Internet)
Corporate
HPLMN VPLMN
BSCBTS
SGSN

Mobility management (1/3)
 Instead of Location Area, GPRS uses Routing Areas to group cells.
RA is a subset of LA.
 IDLE:
MS is not known by the network (SGSN)
 STANDBY:
MS’s location is known in accuracy of Routing Area
MS can utilize DRX (to save battery)
MS must inform its location after every Routing Area change
(no need to inform if MS changes from one cell to another
within same Routing Area)
Before the network can perform MT data transfer MS must
be paged within the Routing Area
MS may initiate MO data transfer at any time

READY:
MS’s location is known in accuracy of cell
MS must inform its location after every cell change
MS can initiate MO data transfer at any time
SGSN does not need to page the MS before MT data
transfer
MS listens continuously GPRS PCCCH channel
DRX in READY state is optional

Mobility management messages:
Cell update (implicit, with any message)
When MS changes the cell within a Routing Area in READY state
Routing Area update
When MS changes the cell between two Routing Areas in READY or STANDBY
state
Two types of Routing Area Updates (from MS’s point of view only one type)
Intra-SGSN Routing Area Update
Inter-SGSN Routing Area Update
Periodic Routing Area updates are applicable

Interworking with GSM services (1/3)
GPRS can interwork with GSM services through Gs-interface
If no Gs interface exists:
Type of the location update procedure is indicated by the network in the
response message to MS
Effects on different MS classes if Gs does not exist:
A-class mobiles must use conventional GSM services via normal GSM
channels
B-class mobiles won’t get simultaneous support from the network.
Depending on MS design
MS can try listen both paging channels simultaneously by themselves
MS does IMSI detach and use only GPRS service
No effect on C-class mobiles as simultaneous services are not supported

 Combined GPRS and IMSI attach
To save radio resources
MS indicates its request for combined attach
MS sends combined GPRS and IMSI attach to SGSN
SGSN may authenticate the MS
SGSN informs MSC/VLR about the new MS
 Combined Location and Routing Area update
To save radio resources
MS indicates its request for combined update
This is done when both Location Area and Routing Area
changes at the same time
Combined Location and Routing Area update is not done if MS
has CS connection

Paging CS services via GPRS network
MSC/VLR gets MT call or SMS
In VLR, presence of SGSN address tells that the MS
is in GPRS attached state
MSC/VLR sends the paging request to SGSN
address (not to BSC)
SGSN checks the location of MS (identified by
IMSI)
SGSN pages the MS via GPRS channels indicating
“CS page” status
MS replies to the page using normal GSM channels

Special issues: SMS support
 MO and MT SMSs can be carried via GPRS network
 HLR stores and returns two SS7 addresses to GMSC:
SGSN address
MSC/VLR address
 Primary route:
Via SGSN, if available
 Secondary route:
Via MSC/VLR, if available and primary failed

Special issues:
GPRS charging of PTP (1/2)
 SGSN gathers charging:
usage of radio resources (packets, bits)
usage of packet data protocols (time)
usage of general GPRS resources
e.g. signaling messages, GPRS backbone
 GGSN gathers charging :
based on destination/source of data packets
usage of external data networks (packets, bits)
 Operator selects what information is used for billing

Special issues:
GPRS charging of PTM (2/2)
 SGSN gathers usage of:
usage of radio resources
amount of data
geographical areas
number of repetition
 PTM Service Center gathers charging :
usage of general GPRS resource
usage of PTM-G groups

Special issues:
Operation and management
 GSM related parts can be handled with Q3
 GPRS backbone network is based on IP network
IP network uses Simple Network Management Protocol (SNMP)
SGSN
GGSN
IP
ROUTER
BSC
BTS
GPRS
backbone
network
(IP based)
Packet
network
Inter-operator
backbone
network
Packet
network
Data
network
(Internet)
GPRS/GSM OMC
Operator A's GPRS
backbone management
Inter-operator's GPRS
backbone management
Data network
management
Operator B's GPRS
backbone management

Special issues: Supplementary services
 Most of the conventional GSM supplementary
services are not applicable for GPRS
E.g., Call forwarding when busy, Calling line
identification, Call waiting
 Some supplementary services may be applicable
Advice of charge (can be difficult to realize)
Closed user group (can be implemented as
part of external data network)
 GPRS has its own supplementary services
Barring of GPRS Interworking Profile(s)

Quality of Service
Precedence class (1,2,3)
Delay class (1-4)
Reliability class
Peak throughput class; and
Mean throughput class.

Reliability Class
Data reliability is defined in terms of the
residual error rates for the following cases
(see GSM 02.60):
Probability of data loss
Probability of data delivered out of sequence
Probability of duplicate data delivery
Probability of corrupted data

Throughput classes
Peak Throughput Class Peak Throughput in octets per second
1 Up to 1 000 (8 kbit/s).
2 Up to 2 000 (16 kbit/s).
3 Up to 4 000 (32 kbit/s).
4 Up to 8 000 (64 kbit/s).
5 Up to 16 000 (128 kbit/s).
6 Up to 32 000 (256 kbit/s).
7 Up to 64 000 (512 kbit/s).
8 Up to 128 000 (1 024 kbit/s).
9 Up to 256 000 (2 048 kbit/s).
Mean Throughput Class Mean Throughput in octets per hour
1 Best effort.
2 100 (~0.22 bit/s).
3 200 (~0.44 bit/s).
4 500 (~1.11 bit/s).
5 1 000 (~2.2 bit/s).
6 2 000 (~4.4 bit/s).
7 5 000 (~11.1 bit/s).
8 10 000 (~22 bit/s).
9 20 000 (~44 bit/s).
10 50 000 (~111 bit/s).
11 100 000 (~0.22 kbit/s).
12 200 000 (~0.44 kbit/s).
13 500 000 (~1.11 kbit/s).
14 1 000 000 (~2.2 kbit/s).
15 2 000 000 (~4.4 kbit/s).
16 5 000 000 (~11.1 kbit/s).
17 10 000 000 (~22 kbit/s).
18 20 000 000 (~44 kbit/s).
19 50 000 000 (~111 kbit/s).

Performance (1/3)
 Example: SGSN that handles 2 Mbps up and downlink traffic
 Average packet size 500 octets (4000 bits)
 Each packet must be processed totally every 1 milliseconds
IP stack in backbone
possible UDP (de)fragmentation, IP checksums
GTP header processing, finding the right context
possible paging of the MS
compression in SNDCP level, possible segmentation
LLC CRC, LLC acknowledges, LLC timers
handle GPRS ciphering/deciphering
BSSGP protocol
Frame relay protocol

Performance (2/3)
 Background tasks
Ensuring the QoS for every mobile
Scheduling pending packets to time horizon
Rescheduling everything after MS has changed the cell
Handling charging data collection
Performance monitoring
Handle SGSN operating system, task switching, etc.
Handle diagnostics of the network element
 If SGSN handles 65 Mbps, instead of 2 Mbps?
=> SGSN has just about 30 micro seconds to do all above

Performance 3/3
 Solution: Each network element has limited capacity (x
packets/second)
 If operator needs more capacity (e.g. 50x)
use 50 parallel boxes
for example,
every GGSN boxes are really independent of each other
each SGSN handles its own area (list of cells)
 Capacity grows linearly but complexity in each box remains
the same
 Reliability? Configuration?

What must be invested to get GPRS up
and running?
 Updates on existing network elements
 BTS, BSC, MSC/HLR, O&M, billing system, network planning
 New network elements
 Totally new network for GPRS backbone, based on IP
 New packet network nodes
 A lot of Internet "stuff" (routers, DNS servers, firewalls, …)
 Totally new skills needed
 "Internet way" of thinking
 New mobiles and new type of users
 New type of business thinking

How to launch GPRS with minimized
incremental cost
 A single SGSN/GGSN combined functional unit
 BTSs support basic GPRS services with software update only,
BSCs need HW upgrade to add connection to SGSN
 Use existing paging and control channels for GPRS
 Limit the number of radio channels available for GPRS
 Gs interface can be deleted => no MSC developments

How to make money with GPRS?
 New users
More subscribers
 New services
New ways to get money from users
New instances to pay instead of the users (e.g. advertisers)
 New applications
New ways to get money from users
 More data traffic
More data traffic
Small payments per packet, but huge number of packets

Users' benefits of GPRS
 GPRS Selling arguments:
Higher capacity Internet access
Up to 171,2 kbps in theory, 40 kbps in practice
Quicker access to Internet
No set up time, Iternet access all the time available
Lower cost
Flat rate or volume based billing
Or no cost
via anonymous access (somebody else pays the bill)

Business model (1/2)
 If the users are paying little (or nothing), how does this make
profit to the operator?
Not the high cost per time but the large number of packets
Somebody else may pay the bill (e.g. anonymous access)
# sub- QoS level Monthly Cost/kB Volume/ Monthly Total annual Total data
scribers fee (FIM) FIM day (FIM) cost/subs cost (MFIM) volume (GB)
Business users 100000 High 50 0,02 1000 650 780 36500
"Normal" users 1000000 Normal 25 0,01 20 31 372 7300
Web surfers 1000000 Best effort 50 0 250 50 600 91250
Computers 100000 High 50 0,1 20 110 132 730
Total 2200000 1884 135780
Example business model

Business model (2/2)
Average data per day 372 GB/d
volume per hour 15,5 GB/h
per sec 4,3 MB/s
per sec 34,3 Mbps
Peak hour data per year 43800 GB/a
volume per day 120 GB/d
per hour 30 GB/h all data in 4 busy hours
per sec 8,3 MB/s
per sec 66,7 Mbps
Number of time 6667 TSs average 10 kbps/TS
slots needed
Carrier 833 Carriers
Volume calculations

GPRS Standardization
 GPRS Phase 1: Release 97
Basic set of GPRS functionality
Optional features
 GPRS Phase 2: GPRS for UMTS
Certain issues defined in stage 1
documents are not included in the first
release of the GPRS standard
New requirements have been pointed out
for UMTS
Standard was approved March/June 1998

220
GPRS Procedures : Attach
• Attach : register with a SGSN before using services
MS BSS New SGSN Old SGSN GGSN HLR VLR
1.1. Attach Request
1.2. Identification_Request
1.2. Identification_Request
RA/LA Update
1.3. Attach Accept
Attach message flow

221
GPRS Procedures : Detach
Detach : disconnect the GPRS network
MS BSS New SGSN GGSN HLR VLR
2.2. Detach Rdquest
2.1. MAP_CANCEL_LOCATION
2.3. Delete_PDP_Context Request
2.5. Detach Accept
2.3. Delete_PDP_Context Response
2.4. GPRS_Detach_Indication
2.6. MAP_CANCEL_LOCATION-ack
Detach message flow

222
PDP Context Procedures : Activation
MS BSS GGSN
1.1. Active PDP context Request
1.2. Create_PDP_Context_Rquest
1.2. Create_PDP_Context_Response
PDP context activation message flow
SGSN
1.3. Activate PDP Context Accept

223
PDP Context Procedures : Update
MS BSS GGSN
2.2. Modify PDP Context Request
2.1. Update_PDP_Context_Request
2.1. Update_PDP_Context_Response
PDP context update message flow
SGSN
2.2. Modify PDP Context Response

224
PDP Context Procedures: Deactivation
MS BSS GGSN
3.2. Deactivate PDP Context Request
3.1. Delete_PDP_Context_Request
3.1. Delete_PDP_Context_Response
PDP context deactivation message flow
SGSN
3.2. Deactivate PDP Context Response

225
RA/LA Update (1/2)
MS BSS New SGSN Old SGSN GGSN New VLR HLR
1. Routing Area Update Request
2. SGSN_Context_Request
2. SGSN_Context_Request
(Packet forwarding)
2. SGSN_Context_ACknowledge
3. Update_PDP_Context_Request
3. Update_PDP_Context_Request

226
RA/LA Update (2/2)
MS BSS New SGSN Old SGSN GGSN New VLR HLR
4. MAP_UPDATE_LOCATION
4. MAP_CANCEL_LOCATION
4. MAP_CANCEL_LOCATION_ack
4. MAP_INSERT_SUBSCRIBER_DATA
4. MAP_INSERT_SUBSCRIBER_DATA_ack
4. MAP_UPDATE_LOCATION_ack
5. GPRS_Location_Updating_Request
5. GPRS_Location_Updating_Accept
6. Routing Area Update Accept
Standard GSM
Inter-VLR
Location Update

227
GPRS Billing (1/2)
 MSC collect the billing records in GSM , but SGSN and GGSN in GPRS
 SGSN : Charging information for an MS
 Location information
 The amount of data transmitted
 The amount of time an MS occupies a PDP address
 The amount of GPRS-related network resources and the GPRS
network activity
 GGSN
 The addresses of the destination and the source defined
 The amount of data delivered between the MS and the external data
network
 The period that the MS has used the PDP addresses

228
GPRS Billing (2/2)
 The data volume counted
 SNDCP level in SGSN
 GTP level in GGSN
 CDR(Call Detail Record) types
 S-CDR is generated in the SGSN for the radio usage
 G-CDR is generated by the GGSN for the external data network
usage
 M-CDR is generated by the GGSN for mobility management activity
 CCF (Charging Gateway Function)
 Support charging information collection, immediate storage, and
CDR transfer
 CCF is either implemented in a separate network node or is
distributed among the GSNs

229
Evolving from GSM to GPRS
ELEMENT SOFTWARE HARDWARE
MS Upgrade required Upgrade required
BTS Upgrade required No change
BSC Upgrade required PCU interface
TRAU No change No change
MSC/VLR Upgrade required No change
HLR Upgrade required No change
SGSN New New
GGSN New New

230
Two Phases in GPRS (1/2)
 Phase 1 : implements basic GPRS features
Standard packet services delivery ; that is , point-to-point packet
bearer service
Support for CS-1 and CS-2 channel coding schemes
GPRS internal network interfaces such as Gn, Gb, Gp, and Gs
Flexible radio resource allocation
Support for Classes B and C MSs
GPRS charging
GSM-based services, such as SMS over GPRS
IP and X.25 interfaces to packet data network
Static and dynamic IP address allocation
Anonymous access
Security ; authentication and ciphering

231
Two Phases in GPRS (2/2)
 Phase 2
Enhanced QoS support in GPRS
Unstructured octet stream GPRS PDP type
Access to ISPs and intranets
GPRS prepaid
GPRS advice of charge
Group call
Point to multipoint services

Mobile Communication

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