3. AUTHENTICATION:
Confirm the true identity of the user(or device).
Ensures that the subscriber is authorized access to
the network.
GOALS:
Protection of the network against unauthorized use.
Protect the operator against the billing fraud.
4. AUTHENTICATION:
Authenticates the identity of the subscriber through the use of a
challenge-response mechanism.
MS requests access to the network.
Forward the IMSI and authentication request to the request authentication
The MSC will forward the IMSI to the HLR and Authentication Center
(AuC).
Triplets.
IMSI
HLR
MS
IMSI
Request authentication Triplets
request Triplets
MSC
BS
AuC
TMSI-Temporary Mobile Subscriber Identity
HLR-Home Location Register
MSC-Mobile Switching Center
IMSI-International Mobile Subscriber Identity
V
f
v
d
e r i
y
a l i
i t y
5. AUTHENTICATION:
The AuC will use the IMSI to look up the Ki associated with
that IMSI.
The Auc will also generate a 128-bit random number called
the RAND.
Ki-Individual subscriber authentication key.
It is a 128-bit number that is paired with an IMSI when the SIM
IMSI
card is created.
Authentication Center
RAND
Ki
6. AUTHENTICATION:
The RAND and the Ki are inputted into the A3 encryption
algorithm as well as A8 encryption algorithm.
The output is the Signed Response (SRES) and Ciphering
key(Kc) correspondingly.
The RAND, SRES, and Kc are collectively known as the
Triplets.
RAND
RAND
Ki
A8
A3
32-bit
SRES
Ki
64-bit
Kc
7. AUTHENTICATION:
Once the AuC has generated the triplets, it forwards them to
theThe HLR subsequently sends them to the requesting
HLR.
MSC. MSC stores the Kc and the SRES but forwards the RAND to the MS
The
and orders it to authenticate.
Triplets
MSC
SRES
HLR
Request triplets
Kc
IMSI
Triplets
IMSI
Request authentication Triplets
MS
AuC
BS
8. AUTHENTICATION:
The MS has the Ki stored on the SIM card.
The A3 and A8 algorithms also reside on the SIM card.
The RAND and Ki are inputted into the A3 and A8 algorithm.
Generate the SRES and the Kc respectively.
RAND
MS
Ki
Ki
RAND
SIM
A3
SRES
A8
Kc
9. AUTHENTICATION:
The MS stores the Kc on the SIM card and sends the generated SRES back to the
network.
Triplets
RAND
MSC
SRES
Kc
IMSI
Request authentication Triplets
IMSI
IF
SRES
=
SRES
AUTHENTICATION SUCCESSFUL
Triplets
Request
TMSI or IMSI
access
Request triplets
MS
HLR
AuC
10. GSM LOCALIZATION:
Kind of cell phone tracking mechanism that's possible
in GSM phones.
The GSM system always knows where a user is
currently located.
Same phone number is valid worldwide.
GSM system performs periodic location updates, even
if the user does not use the MS.
-provided that the MS is still logged on to the GSM
network and is not completely switched off.
12. GSM LOCALIZATION:
HOW?
The HLR contains information about the current
location.
The VLR that is currently responsible for the MS
informs the HLR about the location of the MS when
it changes.
Localization can be done in following four ways..
-Network based
-Handset based
-SIM based
-Hybrid
13. GSM LOCALIZATION :
HYBRID BASED LOCALIZATION:
Uses a combination of Network based, Handset based
& SIM based technologies.
-makes the location more accurate.
Example : Global Positioning System (GPS)
space based satellite navigation system.
allows small electronic
receivers to determine their location
14. GSM LOCALIZATION:
To locate an MS and to address the MS following
numbers are required..
Mobile Station International ISDN Number
(MSISDN) :
Important for GSM user.
Associated with SIM.
Consists of –
Country Code (CC)
National Destination Code(NDC)
Subscriber Number (SN)
15. GSM LOCALIZATION:
International Mobile Subscriber Identity(IMSI) :
GSM uses the IMSI for internal unique identification
of a subscriber.
Consists of –
Mobile Country Code (MCC)
Mobile Network Code(MNC)
Mobile Subscriber Identification Number(MSIN)
16. GSM LOCALIZATION:
Temporary Mobile Subscriber Identity(TMSI):
Give the exact identity of the user signaling over the
air interface.
GSM uses the 4 byte TMSI.
TMSI is selected by the current VLR.
Only valid temporarily and within the location area of
VLR.
17. GSM LOCALIZATION:
Mobile Station Roaming Number(MSRN) :
Temporary address.
Hides the location of a subscriber.
Consists of –
Visitor Country Code(VCC)
Visitor National Destination Code (VNDC)
18. GSM HANDOVER:
Handover is the process of switching a radio connection from
one BS to another in order to maintain seamless radio
connection during mobile station movement.
HANDOVER
BTS
BTS
19. 1 Handover request
GSM HANDOVER:
1
3
5
6
4
2
2 Forward
MSC new BSCa handover request from the old BSC. a handover
The receives handoverthe handover by transmitting
initiates complete
MS sendsthe old radio channels inmessage to the old BSC via new
Releasestothe the request to the new BSC. sends handover bursts to the
the old
MSC forwardsthe MS the connection the MS
In order to
command establish via old BSC.
BSC.
BSC. BSC
new
MSC
3 Handover
2
1
command
4 Handover burst
3
5 Handover
BSC
BSC
5
complete
6 Release
4
5
3
6
HANDOVER SUCCESSFUL
4
BTS
BTS
NEW
OLD
