This document discusses localization, calling, handover, and security in GSM networks. It explains that GSM uses home location registers (HLR) and visitor location registers (VLR) to track the location of mobile subscribers and enable roaming between networks. When a subscriber moves between locations, their data is sent from the HLR to the new VLR. Handover allows phone calls and data sessions to remain connected as a user moves between different cell sites without disconnecting. Security features in GSM include personal identification numbers, international mobile subscriber identities, and subscriber authentication keys.

1. LOCALIZATION & CALLING,
HANDOVER,SECURITY
N.SURATHAVANI MSc(Information
Technology)
Nadar Saraswathi college of arts
& science.Theni.

2. LOCALIZATION & CALLING:
GSM (Global System for mobile
communication) provides many useful
services in which, one of the most important is
the automatic, worldwide localization of users.
For localization of users, GSM performs
periodic location updates even if a user does
not use the mobile phones or some other
devices but user should not be out of GSM
network and is not completely switched off
their devices.

3. GSM USES TWO TYPES OF
DATABASES:
Home Location Register (HLR)
Visitor Location Register (VLR)

4. HOME LOCATION REGISTER
(HLR):
The Home Location Register is a
database from a mobile network in
which information from all mobile
subscribers is stored.

5. VISITOR LOCATION REGISTER
(VLR):
VLR is responsible for the MS (Mobile
Station) to inform the HLR about
location changes.
As soon as user moves from one
location to another location, the HLR
sends all user data needed to the new
VLR (New Location). Changing of one
VLR to another VLR and their
uninterrupted services is called as
Roaming.

6. ROAMING CAN BE TAKEN PLACE AS
FOLLOWS:
Within the network of one
provider.
Between two providers in one
country (National Roaming).
Different providers in different
countries (International
Roaming)

7. TO LOCATE AN MS NEEDED:
Mobile station international ISDN
number (MSISDN).
International mobile subscriber identity
(IMSI).
Temporary mobile subscriber identity
(TMSI).
Mobile station roaming number (MSRN)

9. HANDOVER:
A handover is a process in
telecommunications and mobile
communications in which a connected
cellular call or a data session is
transferred from one cell site to another
without disconnecting the session.
Cellular services are based on mobility
and handover, allowing the user to be
moved from one cell site range to
another or to be switched to the nearest
cell site for better performance.

10. Handovers are a core element in
planning and deploying cellular
networks.
It allows users to create data sessions or
connect phone calls on the move.
This process keeps the calls and data
sessions connected even if a user
moves from one cell site to another

11. TYPES OF HANDOVERS:
Hard Handover
Soft Handover

12. HARD HANDOVER:
An instantaneous handover in
which the existing connection is
terminated and the connection to
the destination channel is made.
It is also known as a break-before-
make handover. The process is so
instantaneous that the user does
not hear any noticeable
interruption.

13. SECURITY:
The authentication protocols used in
GSM are described in a number of
places, such as (which also describes
the mechanisms in an incompatible
U.S. system).
But the industry tried to keep secret
the cryptographic and other protection
mechanisms that form the core of the
GSM security system.

14. There’s a personal identification
number, which you use to unlock the
card. In theory, this stops stolen mobiles
being used. In practice, many networks
set an initial PIN of 0000, and most
users never change it.
There’s an international mobile
subscriber identification (IMSI), a unique
number that maps on to your mobile
phone number.

15. Finally there is a subscriber
authentication key Ki, a 128-bit number
that serves to authenticate that IMSI
and is known to your home network.
Telecom System Security: