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