GSM is the dominant global standard for mobile communications. It uses GSMK modulation and operates in the 900MHz or 1800MHz bands. Key elements of GSM architecture include the BTS for radio transmission/reception, BSC for managing multiple BTSs, MSC for call routing, HLR for permanent subscriber data, VLR for temporary subscriber data, AUC for authentication, and EIR for equipment identity registration. Together, these elements allow GSM networks to provide mobile voice and data services on a large scale.

1. GSM & MNP
Peshwa Acharya
1

2. GSM
-­‐
Some
facts
• GSM stands for Global System for Mobile Communications
• It is estimated that 80% of the global mobile market uses
this standard.
• GSM evolved because of the need for a standard mobile
telephone system that could be deployed across Europe
• It uses the Gaussian Minimum Shift Keying [ GMSK ]
technique for modulation
• GSM networks operate in the 900 MHz or 1800 MHz bands

3. Why
GSM?
• Dominant global market share
• Large number of infrastructure and handset vendor’s
giving advantage in terms of price and other commercial
terms
• Wide choice of handsets
• Seamless interoperability between networks and handsets
• Global footprint for international roaming including SMS,
data and other value added services

4. GSM
Architecture
PSTN
GMSC
VLR
HLR
MSC
AUC
Network
Switching
EIR
System
BSC
BTS
Mobile
Station
BTS
BTS
BSS

5. Mobile
Station
(MS)
Mobile
Sta+on
Subscriber
IdenAty
Mobile
Equipment
Module
[
SIM
]
 Mobile
staAon
provides
user
access
to
GSM
network
for
Voice
&
Data
 Subscriber
data
is
read
from
a
SIM
card
that
plugs
into
MS
 Each
MS
has
a
unique
number
called
as
IMEI
number,
 Mobile
Transmit
and
Receive
voice
at
13
KB/s
over
air
interface

6. Base
Transceiver
Station
(BTS)
 Air
interface
signalling

Ciphering
 Speech
processing
(channel
coding,
interleaving,
and
burst
formaTng)

GeneraAon
of
alarms
and
staAsAcs

Baseband/Radio
frequency
transformaAon

7. BSC
-­‐
Base
Station
Controller
• ConnecAon
establishment
between
the
MS
and
the
NSS
•
Mobility
management
•
StaAsAcal
raw
data
collecAon
•
Several
BTSs
are
connected
to
the
BSC
•
BSC
Manages
channel
allocaAon,
handovers
and
release
of
channels
at
connected
BTSs

8. MSC – Mobile Switching Centre
•
Exchange
where
calls
are
established,
maintained
and
released
•
Database
for
all
subscribers
and
their
associated
features.
•
Communicates
with
the
BSCs
•
MSC
is
weighted
on
the
number
of
subscribers
it
can
support.

9. HLR
-­‐
Home
Location
Register
• MSC
has
all
subscriber
database
stored
in
HLR
• HLR
has
all
permanent
subscriber
database
• MSC
communicates
with
HLR
to
get
data
for
subscribers
on
call
MSC
HLR
• HLR will have the series of all subscriber numbers, which
may not be activated or issued .

10. VLR – Visiting Location Register
• A
subscripAon
when
acAvated
is
registered
in
VLR
• VLR
has
all
the
subscriber
numbers
which
are
acAve.
• VLR
has
a
temporary
database
of
all
acAve
subscribers
(on/
off,
locaAon
informaAon)
HLR
MSC
VLR

11. VLR – Visiting Location Register
HLR
MSC
VLR
VLR
MSC
• MSC
communicates
with
HLR
for
subscribers
coming
from
different
MSCs.
If
the
subscriber
is
found
valid,
then
it
registers
the
subscriber
in
the
VLR

12. AUC – Authentication Centre
• AuthenAcaAon
is
a
process
by
which
a
SIM
is
verified
• Secret
data
and
the
verificaAon
process
algorithm
are
stored
in
AUC
• AUC
is
the
element
which
carries
out
the
verificaAon
of
the
SIM
• AUC
is
associated
with
the
HLR
MS
MSC
HLR
AUC

13. EIR
(Equipment
Identity
Register)
• EIR
is
the
Mobile
Equipment
Database
which
has
a
series
of
IMEIs
• MSC
asks
the
Mobile
to
send
its
IMEI
• MSC
then
checks
the
validity
of
IMEI
with
the
EIR
• All
IMEIs
are
stored
in
EIR
with
relevant
classificaAons
EIR
MSC