Gsm
Transcript of Gsm
GSM AUTHINTICATION,LOCALIZATIO
N AND HANDOVER
Prof. A
nirudha Sahoo
3.2
GSM: SYSTEM ARCHITECTURE
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.
AUTHENTICATION:
Authenticates the identity of the subscriber through the use of a challenge-response mechanism.
MS requests access to the network.
MSCRequest
accessTM
SI or
IMSI
The MSC will forward the IMSI to the HLR and request authentication Triplets.
IMSI
Request authentication Triplets
HLR
Verify validity
Forward the IMSI and authentication request to the Authentication Center (AuC).
MS
AuC
req
uest
Trip
lets
IM
SI
Accept req
uest
BS
MSC-Mobile Switching CenterHLR-Home Location RegisterTMSI-Temporary Mobile Subscriber IdentityIMSI-International Mobile Subscriber Identity
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 card is created.
Authentication Center
IMSI
RAND Ki
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.
A3 A8
SRES Kc
RAND Ki RAND Ki
32-bit 64-bit
AUTHENTICATION:
MSC
Request access
TMSI or IMSI
IMSI Request authentication Triplets
HLR
MS
AuC
Once the AuC has generated the triplets, it forwards them to the HLR.The HLR subsequently sends them to the requesting MSC.The MSC stores the Kc and the SRES but forwards the RAND to the MS and orders it to authenticate.
Trip
lets
Request
triple
tsIM
SI
Triplets
RAND
SRES
Kc
accept
request
RAND
BS
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.
A3 A8
RAND RANDKi Ki
MS SIM
SRES Kc
AUTHENTICATION:
MSC
Request accessTMSI or IMSI
IMSI Request authentication Triplets
HLR
MS
AuC
The MS stores the Kc on the SIM card and sends the generated SRES back to the network.
Trip
lets
Request
triple
tsIM
SI
TripletsRAND
SRES
SRES
Kc
SRES SRES
IF
AUTHENTICATION SUCCESSFUL
=
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.
GSM ARCHITECTURE:
GSM LOCALIZATION:
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
GSM uses Hybrid Localization Technique.
HOW?
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
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)
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)
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.
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)
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.
BTS
BTS
HANDOVER
GSM HANDOVER:
BTS
BTS OLD
NEW
BSCBSC
MSC
MSC receives a handover request from the old BSC.1
1
MSC forwards the request to the new BSC.2
2
1Handover request
2 Forward
3
3
3
3
Handover command
4
4
4
In order to establish the connection the MS sends handover bursts to the new BSC
4
Handover burst
MS sends the handover complete message to the old BSC via new BSC.
55
5
5
Handover complete
Releases the old radio channels in the old BSC.
6
6
6
Release
The new BSC initiates the handover by transmitting a handover command to the MS via old BSC.
HANDOVER SUCCESSFUL
Questions ?
THANK YOU