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Aim: To prepare
the case study for GSM (Global System for Mobile Communications).

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GSM (Global System for Mobile Communications) is a standard developed by
the European Telecommunications Standards Institute (ETSI) to describe the
protocols for 2G digital cellular networks used by mobile devices such as tablets;
it has become the global standard for mobile communications.

is a trademark owned by the GSM Association (GSMA). It may also refer to the
(initially) most common voice codec used, Full Rate.

According to the
GSMA, which represents the interests of the worldwide mobile communications
industry, it is approximated that 80% of the world uses GSM technology when
placing wireless calls.



Improved spectrum efficiency

International roaming

SIM phonebook management

Fixed dialling number (FDN)

Real time clock with alarm management

High-quality speech

Uses encryption to make phone
calls more secure

Short message service (SMS)

Compatibility with integrated
services digital network (ISDN)

Support for new services.

Block Diagram: The following diagram shows the GSM network along with the added


The generic
GSM network architecture is composed of three main subsystems as the Radio
Subsystem (RSS), the network and Switching Subsystem (NSS) and the Operation
Subsystem (OSS). The subscriber carries the Mobile Station, which is part of

Radio Substation (RSS)

consists of the components that are necessary in order to allocate the radio
resources to the individual subscribers. It principally consists of the mobile
terminals (mobile phone or mobile station, MS) & the base station subsystem

Network switching subsystem (NSS) (or GSM core network)

It is the
component of a GSM system that carries out call switching and mobility
management functions for mobile phones roaming on the network of base stations.
It is owned & deployed by mobile phone operators and allows mobile devices
to communicate with each other and telephones in the wider public switched
telephone network (PSTN). The architecture contains specific features &
functions which are needed because the phones are not fixed in one location.

originally consisted of the circuit-switched core network, used for traditional
GSM services such as voice calls, SMS, and circuit switched data calls. It was
extended with overlay architecture to provide packet-switched data services
known as the GPRS core network. This allows mobile phones to have access to
services such as WAP, MMS & the Internet.

Mobile Station (MS)

MS is
basically mobile equipment (the handset) which comprises all user equipment and
software needed for mobile communication & a smart card called the
Subscriber Identity Module (SIM). The MS, which contain a SIM, card in the form
of a very small chip beside the equipment.

The Subscriber
Identity Module (SIM) contains all subscriber information necessary for
identifying GSM subscriber. Broadly, it holds a subscriber’s International
Mobile Subscriber Identity (IMSI), authentication key & algorithm. SIM is
independent of the device or handset in which it is being used because an MS
can be identified via International Mobile Equipment Identity (IMEI). As soon
as the SIM is inserted into handset, it becomes immediately programmed for use.
Therefore, it can be inserted into any handset. Typically, mobile stations have
transmitted power from 2 W to 1W depending upon the cell size, If cell size is
smaller, the transmitted power will be less.

Home Location Register (HLR)

The HLR in
telecom is the reference database for subscriber parameters. Various
identification numbers & addresses are stored, as well as authentication
parameters. This information is entered into the database by the network
provider when a new subscriber is added to the system.

The Basic
Parameters stored in the HLR in telecom are listed below:

Subscriber ID (IMSI and MSISDN)

Subscriber Status (Registered
or Deregistered)

Authentication Key and AUC

Mobile Subscriber Roaming

Current Subscriber VLR (Current

Supplementary Services
Subscriber to (Caller Tone, Missed Call Alert, Any Other Services etc.)

Visitor Location Register (VLR)

contains a copy of most of the data stored at the HLR. It is, however,
temporary data which exists for only as long as the subscriber is “active” in
the particular area covered by the VLR.

database will therefore contain some duplicate data as well as more precise
data relevant to the subscriber remaining within the VLR coverage (here
coverage means status of customer of last LAC (location area code) updation ).

The additional
data stored in the VLR in telecom is listed below:

Location Area Identity (LAI).

Temporary Mobile Subscriber
Identity (TMSI).

Mobile Station Roaming Number

Mobile status (busy/free/no
answer etc.).

and Support System (OSS)

The implementation of OMC is called the operation and support system
(OSS).The OSS is the functional entity from which the network operator monitors
& controls the system. The purpose of OSS is to offer the customer
cost-effective support for centralized, regional and local operational and
maintenance activities that are required for a GSM network. An important
function of OSS is to provide a network overview & support the maintenance
activities of different operation and maintenance organizations.

Authentication Center (AUC)

Separate AUC is defined to protect User ID and data transmission. A
database which contains the International Mobile Subscriber Identity (IMSI),
the Subscriber Authentication key and the defined algorithms for encryption.

Identity Register (EIR)

A database
which contains information about the identity of mobile equipment in order to
prevent calls from stolen, unauthorized, or defective mobile stations.


GSM services
are classified as either teleservices or data services. Teleservices include
standard mobile telephony & mobile-originated traffic. Data services
include computer to computer communication & packet switched traffic. User
services may be divided into three major categories:

A. Telephone
services: These include emergency calling & facsimile. GSM
also supports Videotex and Teletex.

B. Bearer
services or data services: These are limited to layer 1, 2 and
3 of the open system interconnection (OSI) reference model. Supported services
include packet switched protocols and data rates from 300 bps to 9.6 kbps. Data
may be transmitted using transparent or non transparent mode.

C. Supplementary
ISDN services: These are digital in nature and include call
diversion, closed user groups and caller identification, and are not available
in analog mobile networks. Supplementary services also include short messaging
service (SMS) which allows GSM subscribers and base station to transmit
alphanumeric pages of limited length while simultaneously carrying normal voice
traffic. SMS provides cell broadcast also can be used for safety & advisory
applications such as the broadcast of highway or weather information to all GSM


Thus, we have
studied and prepared the case study for GSM (Global System for Mobile Communications).

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