Project report on Gsm

8/13/2019 Project report on Gsm

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GSM

GSM is an acronym that stands for Global System for Mobile Communications. The

original French acronym stands for Groupe Spcial MobileGSM is a digital cellular network.

At the time the standard was developed it offered much higher capacity than the currentanalog systems. It also allowed for a more optimal allocation of the radio spectrum, which

therefore allows for a larger numer of suscriers.

GSM offers a numer of services including voice communications, Short Message Service

!SMS", fa#, voice mail, and other supplemental services such as call forwarding and caller

I$.

%urrently there are several ands in use in GSM. &'( M)*, +'( M), -(( M)*, +(( M)*,

and -(( M)* are the most common ones.GSM makes use of Fre/uency $ivision Multiple

Access !F$MA" and Time $ivision Multiple Access !T$MA".

Uplinks/Downlinks & Reverse Forward

GSM allows for use of duple# operation. 0ach and has a fre/uency range for the uplink !cell

phone to tower" and a separate range for the downlink !tower to the cell phone". The uplink is

also known as theReverseand the downlink also known as theForward. In this report, I will

use the terms uplink and downlink.

Freuency Division Multiple !ccess "FDM!#

GSM divides the allocated spectrum for each and up into individual carrier fre/uencies.

%arrier separation is 1(( k)*.

!bsolute Radio Freuency C$annel %umber "!RFC%#

The A2F%3 is a numer that descries a pair of fre/uencies, one uplink and one downlink.

The uplink and downlink fre/uencies each have a andwidth of 1(( k)*. The uplink and

downlink have a specific offsetthat varies for each and. The offset is the fre/uency

separation of the uplink from the downlink. 0very time the A2F%3 increases, the uplink will

increase y 1(( k)* and the downlink increases y 1(( k)*.

An A2F%3 has an allowed andwidth of 1(( k)*, which corresponds e#actly to the carrier

separation. The fre/uency of the A2F%3 refers to its centre fre/uency. If an A2F%3 has a

fre/uency of -&.+( M)*, then it occupies the fre/uency space from -&.4 M)* to -&.-

M)* !1(( k)* total". 2ememer that this is the allocatedandwidth. 5ecause of the nature

of the modulation method !GMS6" and data rate used in GSM, the actual physical andwidth

will e aout 7'.& k)*. The unused andwidth for each A2F%3 acts as a uffer etweenother A2F%3 to avoid interference.


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The following tale summari*es the fre/uency ranges, offsets, and A2F%3s for several

popular ands.

The following diagram illustrates an A2F%3 with paired uplink and downlink fre/uencies

for A2F%3 in the GSM -(( and.


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Spare "S+#This numer is a check digit known as aLuhn Chec !igit. It is omitted during

transmission within the GSM network.

GSM !RC,*)C*UR)

Mobile Station "MS#

The Moile Station !MS" is made up of two components9

Mobile )uipment "M)#This refers to the physical phone itself. The phone must e ale

to operate on a GSM network. >lder phones operated on a single and only. 3ewer phones

are dual:and, triple:and, and even /uad:and capale. A /uad:and phone has the technicalcapaility to operate on any GSM network worldwide.

0ach phone is uni/uely identified y theInternational Mobile "#uip$ent Identity!IM0I"

numer. This numer is urned into the phone y the manufacturer. The IM0I can usually e

found y removing the attery of the phone and reading the panel in the attery well.

It is possile to change the IM0I on a phone to reflect a different IM0I. This is known as

IM0I spoofing or IM0I cloning. This is usually done on stolen phones. The average user does

not have the technical aility to change a phone8s IM0I.

Subscriber dentity Module "SM#: The SIM is a small smart card that is inserted into

the phone and carries information specific to the suscrier, such asIMSI% &MSI% 'i!used for

encryption", Service ;rovider 3ame !S;3", andLocal (rea Identity!


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-ase *ransceiver Station "-*S#

-ase *ransceiver Station "-*S#: The 5TS is the Moile Station8s access point to the

network. It is responsile for carrying out radio communications etween the network and the

MS. It handles speech encoding, encryption, multiple#ing !&!M(", andmodulation?demodulation of the radio signals. It is also capale of fre/uency hopping. A 5TS

will have etween and @ Transceivers !T2", depending on the geography and user

demand of an area. 0ach T2 represents one A2F%3.

>ne 5TS usually covers a single 1( degree sector of an area. =sually a tower with 7 5TSs

will accommodate all 7@( degrees around the tower. )owever, depending on geography and

user demand of an area, a cell may e divided up into one or two sectors, or a cell may e

serviced y several 5TSs with redundant sector coverage.

A 5TS is assigned a Cell Identity. The cell identity is @:it numer !doule octet" that

identifies that cell in a particularLocation (rea. The cell identity is part of the %ell Gloal

Identification !%GI", which is discussed in the section aout the Bisitor


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Mobile Switc$in' Centre

Gateway Mobile Switc$in' Centre "GMSC#


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There is another important type of MS%, called a Gateway Moile Switching %entre

!GMS%". The GMS% functions as a gateway etween two networks. If a moile suscrier

wants to place a call to a regular land line, then the call would have to go through a GMS% in

order to switch to the ;ulic Switched Telephone 3etwork !;ST3".

Gateway Mobile Switc$in' Centre

For e#ample, if a suscrier on the %ingular network wants to call a suscrier on a T:Moile

network, the call would have to go through a GMS%.


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Connections between *wo %etworks

The interface etween Moile Switching %entres !MS%" is called the" Interface


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,ome ocation Re'ister ",R#

,ome ocation Re'ister ",R#: The )


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ocation !rea dentity "!#

An


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)uipment dentity Re'ister ")R#: The 0I2 is a dataase that keeps tracks of handsets on

the network using the IM0I. There is only one 0I2 per network. It is composed of three lists.

The white list, the gray list, and the lack list.

The lack list is a list if IM0Is that are to e denied service y the network for some reason.

2easons include the IM0I eing listed as stolen or cloned or if the handset is malfunctioningor doesnCt have the technical capailities to operate on the network.

The gray list is a list of IM0Is that are to e monitored for suspicious activity. This could

include handsets that are ehaving oddly or not performing as the network e#pects it to.

The white list is an unpopulated list. That means if an IM0I is not on the lack list or on the

gray list, then it is considered good and is Don the white listD.

The interface etween the MS% and the 0I2 is called the F Interface.

!ut$entication Centre "!uc#!ut$entication Centre "!uC#: The Au% is responsile for generating the necessary

cryptovariales for authentication and encryption on the network. These variales are the

2A3$, S20S, and 6c. The Auc also stores the 6i for each IMSI on the network. Although it

is not re/uired, the Auc is normally physically collocated with the )


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Full GSM %etwork


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!dvanta'es1

orldwide 2oaming

Since GSM service is otainale in added than 1(( countries, clienteles are capale to roam

gloally without altering their devices or their facility plans. Messaging facilities and otherprogressive services, such as data, too endure otainale. %ellular usinesses sort partnership

contracts with suppliers overseas, so usinesses are capale to roam gloally at reduced

roaming charges.

Security

GSM facilities are e#tremely protected, with skills in place that can defend against oth

snooping and service riding. GSM devices and facilities cannot e duplicated as simply as

other skills. The SIM card or Suscrier recogni*e =nit card which transmits suscrier and

e#change info, secures purchaser info. These cards also permit consumers to handover theirsuscription info and telephone ook info from one receiver to add at any period.

2easonale $evices and Facilities

GSM suppliers switch a huge portion of the cellular marketplace and so are capale to deliver

a huge diversity of reasonale devices and facilities. %onstructors are capale to afford

numerous diverse kinds of devices for reasonale values since the huge capacity of purchases

aids to energy down the trade costs. The change of strategies and facilities re/uest to

consumers as well, since they need to try the latest and ma#imum e#citing yields.

0#tensive Spectrums >tainale

The GSM e#pertise usages five ands of M)* rateH &'(, +'(, -((, +(( and -(( M)*.

5uilders are capale to yield devices that can choice up two or three diverse occurrence

ands. Those receivers can then shift etween those rates routinely as desirale, in order to

preserve a network linking almost wherever. The signals otainale with GSM facility are

effectual, meaning that an e#cessive deal of data can transfer diagonally the fre/uency ands

without dipping the efficiency of the signs.

Disadvanta'es1

2eleased and Missed %alls

%onferring to %ellular 3ewscast, call superiority difficulties, with dropped calls and missed

calls are shared difficulties with GSM e#pertise. These difficulties outcome right from the

e#pertise in use. GSM e#pertise cannot provide accommodations as numerous callers on a

lone cell tower as the more current %$MA technology.

Safety Issues

$3et =6 rumors that GSM has a grave safety flaw, estalished y a hacker who wascapale to interrupt telephone calls from an amount of GSM:ased cellular headphones. The


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2eferences

www.wikipedia.com

www.gsmfordummies.com

www.google.com

Techblog.com
http://www.wikipedia.com/http://www.gsmfordummies.com/http://www.google.com/http://www.wikipedia.com/http://www.gsmfordummies.com/http://www.google.com/

Project report on Gsm

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