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Introduction:
GSM
stands for Global System for Mobile
Communication. It is a digital cellular technology used for
transmitting mobile voice and data services.

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The
concept of GSM emerged from a cell-based mobile radio system at Bell
Laboratories in the early 1970s.

GSM is
the name of a standardization group established in 1982 to create a
common European mobile telephone standard.

GSM is
the most widely accepted standard in telecommunications and it is
implemented globally.

GSM is
a circuit-switched system that divides each 200 kHz channel into
eight 25 kHz time-slots. GSM operates on the mobile communication
bands 900 MHz and 1800 MHz in most parts of the world. In the US,
GSM operates in the bands 850 MHz and 1900 MHz.

GSM
owns a market share of more than 70 percent of the world’s digital
cellular subscribers.

GSM
makes use of narrowband Time Division Multiple Access (TDMA)
technique for transmitting signals.

GSM was
developed using digital technology. It has an ability to carry 64
kbps to 120 Mbps of data rates.

Presently
GSM supports more than one billion mobile subscribers in more than
210 countries throughout the world.

GSM
provides basic to advanced voice and data services including roaming
service. Roaming is the ability to use your GSM phone number in
another GSM network.

Components
of GSM:
A
GSM network comprises of many functional units. These functions and
interfaces are explained in this chapter. The GSM network can be
broadly divided into:

The
Mobile Station (MS)

The
Base Station Subsystem (BSS)

The
Network Switching Subsystem (NSS)

The
Operation Support Subsystem (OSS)

Given below is
a simple pictorial view of the GSM architecture.

The
additional components of the GSM architecture comprise of databases
and messaging systems functions:

Home
Location Register (HLR)

Visitor
Location Register (VLR)

Equipment
Identity Register (EIR)

Authentication
Center (AuC)

SMS
Serving Center (SMS SC)

Gateway
MSC (GMSC)

Chargeback
Center (CBC)

Transcoder
and Adaptation Unit (TRAU)

In a GSM
network, the following areas are defined:

Cell
: Cell is the basic service area; one BTS covers one cell. Each cell
is given a Cell Global Identity (CGI), a number that uniquely
identifies the cell.

Location
Area : A group of cells form a Location Area (LA). This is the
area that is paged when a subscriber gets an incoming call. Each LA
is assigned a Location Area Identity (LAI). Each LA is served by one
or more BSCs.

MSC/VLR
Service Area : The area covered by one MSC is called the MSC/VLR
service area.

PLMN
: The area covered by one network operator is called the Public Land
Mobile Network (PLMN). A PLMN can contain one or more MSCs.

GSM
Services:
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:

Telephony
services or teleservices

Data
services or bearer services

Supplementary
services

Teleservices
The abilities
of a Bearer Service are used by a Teleservice to transport data.
These services are further transited in the following ways:
Voice
Calls:
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.
Videotext
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 Messages:
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.
Bearer
Services:
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.
Supplementary
Services:
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:

Conferencing
: 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.

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.

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.

Call
Barring : Call Barring is useful to restrict certain types of
outgoing calls such as ISD or stop incoming calls from undesired
numbers.

Number
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.

Calling
Line Identification Restriction : A person not wishing their
number to be presented to others subscribes to this service.

Connected
Line Identification Presentation : This service is provided to
give the calling party the telephone number of the person to whom
they are connected.

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.

Conclusion:
The
communication development and the increase of living standard of
people are directly related to the more use of cellular mobile.
Cellular mobile radio-the high end sophisticated technology that
enables every one to communicate anywhere with anybody. The mobile
telephony industry rapidly growing and that has become backbone for
business success and efficiency and a part of modern lifestyles all
over the world.
The features and benefits
expected in the GSM systems are superior speech quality, low
terminal, operational and service costs, a high level security,
providing international roaming support of low power hand portable
terminals and variety of new services and network facilities. In near
forth coming days, the third generation mobile telephony becomes
available whole over the world, which will give the facility of
videoconference in mobile telephone.