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Study On GSM


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System for Mobile Communications is a standard developed by
the European Telecommunications Standards Institute (ETSI) to
describe the protocols for second-generation digital cellular
networks used by mobile devices such as tablets, first deployed in
Finland in December 1991.As of 2014, it has become the global
standard for mobile communications – with over 90% market share,
operating in over 193 countries and territories.
uses a variation of time division multiple access (TDMA) and is the
most widely used of the three digital wireless telephony technologies
(TDMA, GSM, and CDMA). GSM digitizes and compresses data, then sends
it down a channel with two other streams of user data, each in its
own time slot. It operates at either the 900 MHz or 1800 MHz
frequency band.

of GSM Module:

spectrum efficiency


with integrated services digital network (ISDN)

phonebook management

dialing number (FDN)

time clock with alarm management


encryption to make phone calls more secure

Short message
service (SMS)

Block Diagram of GSM:

provides recommendations, not requirements. The GSM specifications
the functions and interface requirements in detail but do not address
the hardware. The reason for this is to limit the designers as little
as possible but still to make it possible for the operators to buy
equipment from different suppliers.
GSM network is divided into three major systems: the switching system
(SS), the base station system (BSS), and the operation and support
system (OSS).

Switching System
switching system (SS) is responsible for performing call processing
and subscriber-related functions. The switching system includes the
following functional units:

Location Register (HLR). The HLR is a database used for storage and
management of subscriptions. The HLR is considered the most important
database, as it stores permanent data about subscribers, including a
subscriber’s service profile, location information, and activity
status. When an individual buys a subscription from one of the PCS
operators, he or she is registered in the HLR of that operator.

Services Switching Center (MSC)
MSC performs thetelephony switching functions of the system. It
controls calls to and from other telephone and data systems. It also
performs such functions as toll ticketing, network interfacing,
common channel signaling, and others.

Location Register (VLR)
VLR is a database that contains temporary information about
subscribers that is needed by the MSC in order to service visiting
subscribers. The VLR is always integrated with the MSC. When a mobile
station roams into a new MSC area, the VLR connected to that MSC will
request data about the mobile station from the HLR. Later, if the
mobile station makes a call, the VLR will have the information needed
for call setup without having to interrogate the HLR each time.

Center (AUC)
unit called the AUC providesauthentication and encryption parameters
that verify the user’s identity and ensure the confidentiality of
each call. The AUC protects network operators from different types of
fraud found in today’s cellular world.

Identity Register (EIR)
EIR is a database that contains information about the identity of
mobile equipment that prevents calls from stolen, unauthorized, or
defective mobile stations. The AUC and EIR are implemented as
stand-alone nodes or as a combined AUC/EIR node.

Base Station System (BSS)

radio-related functions are performed in the BSS, which consists of
base station controllers (BSCs) and the base transceiver stations

BSC provides all the control functions and physical links between the
MSC and BTS. It is a high-capacity switch that provides functions
such as handover, cell configuration data, and control of radio
frequency (RF) power levels in base transceiver stations. A number of
BSCs are served by an MSC.

BTS handles the radio interface to the mobile station. TheBTS is the
radio equipment (transceivers and antennas) needed to service each
cell in the network. A group of BTSs are controlled by a

Operation and Support System
operations and maintenance center (OMC) is connected to all equipment
switching system and to the BSC. The implementation of OMC is called
and support system (OSS). The OSS is the functional entity from which
network operator monitors and controls the system. The purpose of OSS
is to
the customer cost-effective support for centralized, regional, and
and maintenance activities that are required for a GSM network. An
function of OSS is to provide a network overview and support the
activities of different operation and maintenance organizations.

Serivces offered by
GSM offers much more than
just voice telephony. Contact your local GSM network operator to the
specific services that you can avail.
GSM offers three basic
types of services:

services or teleservices

services or bearer services


The abilities of a Bearer
Service are used by a Teleservice to transport data. These services
are further transited in the following ways:
The most basic Teleservice
supported by GSM is telephony. This includes full-rate speech at 13
kbps and emergency calls, where the nearest emergency-service
provider is notified by dialing three digits.
and Facsmile
Another group of
teleservices includes Videotext access, Teletex transmission,
Facsmile alternate speech and Facsmile Group 3, Automatic Facsmile
Group, 3 etc.
Short Text
Short Messaging Service
(SMS) service is a text messaging service that allows sending and
receiving text messages on your GSM mobile phone. In addition to
simple text messages, other text data including news, sports,
financial, language, and location-based data can also be transmitted.
Data services or Bearer
Services are used through a GSM phone. to receive and send data is
the essential building block leading to widespread mobile Internet
access and mobile data transfer. GSM currently has a data transfer
rate of 9.6k. New developments that will push up data transfer rates
for GSM users are HSCSD and GPRS now available.
Supplementary services are
additional services that are provided in addition to teleservices and
bearer services. These services include caller identification, call
forwarding, call waiting, multi-party conversations, and barring of
outgoing (international) calls, among others. A brief description of
supplementary services is given here:

: It allows a mobile subscriber to establish a multiparty
conversation, i.e., a simultaneous conversation between three or
more subscribers to setup a conference call. This service is only
applicable to normal telephony.

Call Waiting
: This service notifies a mobile subscriber of an incoming call
during a conversation. The subscriber can answer, reject, or ignore
the incoming call.

Call Hold :
This service allows a subscriber to put an incoming call on hold and
resume after a while. The call hold service is applicable to normal

Call Forwarding
: Call Forwarding is used to divert calls from the original
recipient to another number. It is normally set up by the subscriber
himself. It can be used by the subscriber to divert calls from the
Mobile Station when the subscriber is not available, and so to
ensure that calls are not lost.

Call Barring
: Call Barring is useful to restrict certain types of outgoing calls
such as ISD or stop incoming calls from undesired numbers. Call
barring is a flexible service that enables the subscriber to
conditionally bar calls.

Identification : There are following supplementary services
related to number identification:

Calling Line
Identification Presentation : This service displays the
telephone number of the calling party on your screen.

Connected Line
Identification Presentation : This service is provided to give
the calling party the telephone number of the person to whom they
are connected. This service is useful in situations such as
forwarding’s where the number connected is not the number dialled.

Connected Line
Identification Restriction : There are times when the person
called does not wish to have their number presented and so they
would subscribe to this person. Normally, this overrides the
presentation service.

Malicious Call
Identification : The malicious call identification service was
provided to combat the spread of obscene or annoying calls. The
victim should subscribe to this service, and then they could cause
known malicious calls to be identified in the GSM network, using a
simple command.

Advice of Charge
(AoC) : This service was designed to give the subscriber an
indication of the cost of the services as they are used.
Furthermore, those service providers who wish to offer rental
services to subscribers without their own SIM can also utilize this
service in a slightly different form. AoC for data calls is provided
on the basis of time measurements.

Closed User
Groups (CUGs) : This service is meant for groups of subscribers
who wish to call only each other and no one else.

supplementary services data (USSD) : This allows
operator-defined individual services.


Thus we have studied the
Features, Block Diagram and different Services offered by GSM.