the gsm system

7302019 The GSM System

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Network Switching Subsystem (NSS)

Network Switching Subsystem (NSS) - Contains the elementsMobile Services Switching Centre (MSC)

Home Location Register (HLR)

Visitor Location Register (VLR)

Authentication Centre (AC)

Equipment Identity Register (EIR)The Authentication Centre (AC) and Equipment Identity Register (EIR)

are used to provide security The subscriber and the mobile station

have to be identified and authorised before accessing the network

These functions will be discussed later

Function of NSS

Call control A mobile terminated call requires HLR

enquiry to locate the called subscriber Mobility Management

The HLR always knows in which MSCVLR area a

particular subscriber is located



An MSCVLR knows in which Location Area a subscriber

is located This is enabled by a Location Update of which

there are three types Power On Generic and Periodic

Mobility Management also helps in maintaining ongoingcalls for a moving subscriber by a procedure known as

Handover There are four types of Handovers Intra

Cell Inter Cell-Intra BSC Inter Cell - Inter BSC and

Inter MSC

Subscriber Data handling A subscriberrsquos data is located

in three places the HLR VLR and SIM card

Security Issues Subscriber verification is performed inthe VLR by an authentication process Speech encryption

is carried out between BTS and Mobile Station

Various types of numbers are used in the GSM network

for different functions The most important ones are

IMSI MSISDN MSRN LAI LAC CGI TMSI and

HON

Charging The MSC is responsible for collecting charging

information It is sent to the Billing Centre which

creates bills for the subscriber

Signalling towards Base Station Subsystem and other

networks

The services offered by the GSM network are classified

as MOBILE SWITCHING CENTER (MSC)

MSC performs the switching functions for all mobile stations located in

the geographic covered by its assigned BSSs






mobile subscribers currently located in

the geographical area (ie cells) controlled by the VLR The VLR

allocates the MSRN(when required) a Temporary Mobile SubscriberIdentity (TMSI) for secret identification of mobile subscriber on the

radio link

In summary the VLR contains -(1) Identity of mobile subscriber

(2) Any temporary mobile subscriber identity

(3) ISDN directory number of mobile

(4) Location area where the mobile station is registered(5) Copy of subscriber data from HLR

Equipment Identity Register (EIR)

This database is accessed during the equipment validation procedurewhen a mobile accesses the system it contains the identities of mobile

station equipmentrsquos(called International Mobile Station Equipment

Identity or IMEI) which may be valid suspect or known to fraudulent

This contains

(1) Valid list-list of valid MS equipment identities(2) Suspect list-list of mobiles under observation

(3)Fraudulent list-list of mobiles for which service is barred

Authentication Centre (AUC)

The Authentication Center -

(1) Contains subscriber authentication data called authentication keys(Ki)

(2) Generates security related parameters needed to service using Ki(3)Generate unique data pattern called a cipher key (Kc) needed for

encrypting speech and dataThere are several interfaces in the GSM system which are as follows-









The VLR is the location and management data base for the mobile

subscribers roaming in the area controlled by the associated MSC(s)Whenever the MSC needs data related to a given mobile station

currently located in its area it interrogates the VLR When a mobilestation initiates a location updating procedure with an MSC the MSC

informs its VLR which stores the relevant information This procedure

occurs whenever an MS roams to another location area Also when a

subscriber activates a specific supplementary service or modifies some

data attached to a service the MSC informs (via the VLR) the HLRwhich stores these modifications and updates the VLR if required

C INTERFACE (HLR and the MSC)

The Gateway MSC must interrogate the HLR of the requiredsubscriber to obtain routing information for a call or a short message

directed to that subscriberD INTERFACE (HLR - VLR)

This interface is used to exchange the data related to the location ofthe mobile station and to the management of the subscriber The main

service provided to the mobile subscriber is the capability to set up orto receive calls within the whole service area To support this the

location registers have to exchange data The VLR informs the HLR ofthe location of a mobile station managed by the latter and provides it(either at location updating or at call set-up) with the roaming number

of that station The HLR sends to the VLR all the data needed tosupport the service to the mobile subscriber The HLR then instructs

the previous VLR to cancel the location registration of this subscriber

Exchanges of data may occur when the mobile subscriber requires aparticular service when he wants to change some data attached to his

subscription or when some parameters of the subscription are modifiedby administrative means

E INTERFACE (MSC ndash MSC)When a mobile station moves from one MSC area to another during a

call handover procedure has to be performed in order to continue the

communication For that purpose the MSCs have to exchange data to



initiate and then to realize the operation After the handover

operation has been completed the MSCs will exchange information totransfer A-interface signaling as necessary When a short message is

to be transferred between a Mobile Station and Short MessageService Centre (SC) in either direction this interface is used to

transfer the message between the MSC serving the Mobile Station and

the MSC which acts as the interface to the SC

F INTERFACE (MSC and EIR)

This interface is used between MSC and EIR to exchange data inorder that the EIR can verify the status of the IMEI retrieved from

the Mobile Station

G INTERFACE (VLR ndash VLR) When a mobile subscriber moves from a VLR area to another Location

Registration procedure will happen This procedure may include theretrieval of the IMSI and authentication parameters from the old VLRH INTERFACE (HLR - AuC)

When an HLR receives a request for authentication and ciphering data

for a Mobile Subscriber and it does not hold the requested data theHLR requests the data from the AuC The protocol used to transfer

the data over this interface is not standardisation

HANDOVER

Handover or handoff as it is called in North America is the switchingof an ongoing call to a different channel or cell There are four

different types of handover in the GSM system which involve

transferring a call betweenChannels (time slots) in the same cell

Cells (Base Transceiver Stations) under the control of the same BaseStation Controller (BSC)

Cells under the control of different BSCs but belonging to the sameMobile services Switching Center (MSC) and

Cells under the control of different MSCs





102 Security

3G networks offer greater security than their 2G predecessors By

allowing the UE (User Equipment) to authenticate the network it is

attaching to the user can be sure the network is the intended one andnot an impersonator 3G networks use the KASUMI block crypto instead of

the older A51 stream cipher However a number of serious weaknesses in

the KASUMI cipher have been identified[19]

In addition to the 3G network infrastructure security end-to-end

security is offered when application frameworks such as IMS are

accessed although this is not strictly a 3G property

103 Applications of 3G

The bandwidth and location information available to 3G devices gives

rise to applications not previously available to mobile phone users Someof the applications are

Mobile TV

Video on demand Video conferencing Tele-medicine

Location-based services

11 Evolution

Both 3GPP and 3GPP2 are currently working on extensions to 3G standardthat are based on an all-IP network infrastructure and using advancedwireless technologies such as MIMO these specifications already

display features characteristic for IMT-Advanced (4G) the successor of3G However falling short of the bandwidth requirements for 4G



(which is 1 Gbits for stationary and 100 Mbits for mobile operation)

these standards are classified as 39G or Pre-4G

3GPP plans to meet the 4G goals with LTE Advanced whereas Qualcomm

has halted development of UMB in favour of the LTE family[5]

On 14 December 2009 Telia Sonera announced in an official press

release that We are very proud to be the first operator in the world

to offer our customers 4G services[20] With the launch of their LTEnetwork initially they are offering pre-4G (or beyond 3G ) services in

Stockholm Sweden and Oslo Nor

ABOUT 4GIn telecommunications 4G is the fourth generation of cellular wireless

standards It is a successor to the 3G and 2G families of standards In

2009 the ITU-R organization specified the IMT-Advanced

(International Mobile Telecommunications Advanced) requirements for4G standards setting peak speed requirements for 4G service at

100 Mbits for high mobility communication (such as from trains and

cars) and 1 Gbits for low mobility communication (such as pedestriansand stationary users)[1]

A 4G system is expected to provide a comprehensive and secure all-IP

based mobile broadband solution to laptop computer wireless modems smartphones and other mobile devices Facilities such as ultra-broadband

Internet access IP telephony gaming services and streamed multimedia

may be provided to users

Pre-4G technologies such as mobile WiMAX and first-release Long term

evolution (LTE) have been on the market since 2006[2] and 2009[3][4][5]

respectively and though often branded as 4G in marketing materials

the current versions of these technologies provide downstream peak

bitrates of 144 Mbits and 100 Mbits respectively and do consequently



not fulfill the original ITU-R requirements of data rates approximately

up to 1 Gbits for 4G systems

IMT -Advanced compliant versions of the above two standards are under

development and called ―LTE Advanced and ―WirelessMAN-Advancedrespectively ITU has decided that ―LTE Advanced and

―WirelessMAN-Advanced should be accorded the official designation

of IMT-Advanced On December 6 2010 ITU announced that current

versions of LTE WiMax and other evolved 3G technologies that do not

fulfill IMT-Advanced requirements could be considered 4G

provided they represent forerunners to IMT-Advanced and asubstantial level of improvement in performance and capabilities with

respect to the initial third generation systems now deployed[6]

In all suggestions for 4G the CDMA spread spectrum radio technology used

in 3G systems and IS-95 is abandoned and replaced by OFDMA and otherfrequency-domain equalization schemes[citation needed ] This is combined with MIMO

(Multiple In Multiple Out)

25G and 3G systems rely on double core network infrastructures traditional circuit-switchednetwork nodes (switching points) for telephony and packet-switched GPRS nodes for various

OVERVIEW OF GPRS TECHNOLOGY

111 Services offered

GPRS extends the GSM Packet circuit switched data capabilities and

makes the following services possible

SMS messaging and broadcasting

File manipulation functions

Active process block process Always on internet access

Multimedia messaging service (MMS)



Push to talk over cellular (PoC)

Instant messaging and presencemdashwireless village Internet applications for smart devices through wireless application

protocol (WAP) Point-to-point (P2P) service inter-networking with the Internet (IP)

Point-to-Multipoint (P2M) service point-to-multipoint multicast and

point-to-multipoint group calls

If SMS over GPRS is used an SMS transmission speed of about 30

SMS messages per minute may be achieved This is much faster than

using the ordinary SMS over GSM whose SMS transmission speed isabout 6 to 10 SMS messages per minute

12 Usability

The maximum speed of a GPRS connection offered in

2003 was similar to a modem connection in an analog

wire telephone network about 32-40 kbits

depending on the phone used Latency is very highround-trip time (RTT) is typically about 600-700 ms

and often reaches 1 s GPRS is typically prioritized

lower than speech and thus the quality of connection

varies greatly

Devices with latencyRTT improvements (via for

example the extended UL TBF mode feature) are

generally available Also network upgrades offeatures are available with certain operators With

these enhancements the active round-trip time can

be reduced resulting in significant increase in

application-level throughput spe





the general system health and rough orbits of all GPS satellites (the

almanac)

The receiver uses the messages it receives to determine the transit

time of each message and computes the distance to each satelliteThese distances along with the satellites locations are used with the

possible aid of trilateration depending on which algorithm is used tocompute the position of the receiver This position is then displayed

perhaps with a moving map display or latitude and longitude elevation

information may be included Many GPS units show derived information

such as direction and speed calculated from position changes

Three satellites might seem enough to solve for position since spacehas three dimensions and a position near the Earths surface can beassumed However even a very small clock error multiplied by the very

large speed of light[31] mdash the speed at which satellite signals propagate mdash

results in a large positional error Therefore receivers use four or

more satellites to solve for the receivers location and time The very

accurately computed time is effectively hidden by most GPSapplications which use only the location A few specialized GPS

applications do however use the time these include time transfer trafficsignal timing and synchronization of cell phone base stations

Although four satellites are required for normal operation fewer applyin special cases If one variable is already known a receiver can

determine its position using only three satellites For example a ship oraircraft may have known elevation Some GPS receivers may use

additional clues or assumptions (such as reusing the last known altitude

dead reckoning inertial navigation or including information from the vehiclecomputer) to give a less accurate (degraded) position when fewer than

four satellites are visible



14 Applications

While originally a military project GPS is considered a dual-use

technology meaning it has significant military and civilian applicationsGPS has become a widely deployed and useful tool for commercescientific uses tracking and surveillance GPSs accurate time

facilitates everyday activities such as banking mobile phone

operations and even the control of power grids by allowing well

synchronized hand-off switching[38]

141 Civilian

See also GNSS applications and GPS navigation device

This antenna is mounted on the roof of a hut containing a scientific

experiment needing precise timing



Many civilian applications use one or more of GPSs three basic

components absolute location relative movement and time transfer

Clock synchronization The accuracy of GPS time signals (plusmn10 ns)[51] is

second only to the atomic clocks upon which they are based Cellular telephony Clock synchronization enables time transfer which

is critical for synchronizing its spreading codes with other basestations to facilitate inter-cell handoff and support hybrid

GPScellular position detection for mobile emergency calls and other

applications The first handsets with integrated GPS launched in the late

1990s The US Federal Communications Commission (FCC) mandated thefeature in either the handset or in the towers (for use in

triangulation) in 2002 so emergency services could locate911 callers Third-party software developers later gained access to

GPS APIs from Nextel upon launch followed by Sprint in 2006 andVerizon soon thereafter

Disaster reliefemergency services Depend upon GPS for location and

timing capabilities

Geofencing Vehicle tracking systems person tracking systems and pet

tracking systems use GPS to locate a vehicle person or pet These

devices are attached to the vehicle person or the pet collar Theapplication provides continuous tracking and mobile or Internet

updates should the target leave a designated area[52]

Geotagging Applying location coordinates to digital objects such as

photographs and other documents for purposes such as creating map

overlays GPS Aircraft Tracking GPS tours Location determines what content to display for instance

information about an approaching point of interest

Map-making Both civilian and military cartographers use GPSextensively

Navigation Navigators value digitally precise velocity and orientationmeasurements



Phasor measurement units GPS enables highly accurate timestamping of

power system measurements making it possible to compute phasors Recreation For example geocaching geodashing GPS drawing and

waymarking Surveying Surveyors use absolute locations to make maps and

determine property boundaries

Tectonics GPS enables direct fault motion measurement inearthquakes

Telematics GPS technology integrated with computers and mobilecommunications technology in automotive navigation systems

Fleet Tracking The use of GPS technology to identify locate and

maintain contact reports with one or more fleet

vehicles in real-time

1411 Restrictions on civilian use

The US Government controls the export of some civilian receivers All

GPS receivers capable of functioning above 18 kilometres (11 mi)

altitude and 515 metres per second (1001 kn)[53] are classified as

munitions (weapons) for which US State Department export licenses arerequired These limits attempt to prevent use of a receiver in a ballistic

missile They would not prevent use in a cruise missile because their

altitudes and speeds are similar to those of ordinary aircraft

This rule applies even to otherwise purely civilian units that only

receive the L1 frequency and the CA (ClearAcquisition) code andcannot correct for Selective Availability (SA) etc

Disabling operation above these limits exempts the receiver fromclassification as a munition Vendor interpretations differ The rule

targets operation given the combination of altitude and speed whilesome receivers stop operating even when stationary This has caused



problems with some amateur radio balloon launches that regularly

reach 30 kilometres (19 mi)

142 Military

Attaching a GPS guidance kit to a dumb bomb March 2003

As of 2009 military applications of GPS include

Navigation GPS allows soldiers to find objectives even in the dark

or in unfamiliar territory and to coordinate troop and supplymovement In the United States armed forces commanders use theCommanders Digital Assistant and lower ranks use the Soldier

Digital Assistant [54][55][56][57] Target tracking Various military weapons systems use GPS to track

potential ground and air targets before flagging them as

hostile[citation needed ] These weapon systems pass target coordinates toprecision-guided munitions to allow them to engage targets accurately

Military aircraft particularly in air-to-ground roles use GPS to findtargets (for example gun camera video from AH-1 Cobras in Iraq show

GPS co-ordinates that can be viewed with specialized software)

Missile and projectile guidance GPS allows accurate targeting of

various military weapons including ICBMs cruise missiles and precision-

guided munitions Artillery projectiles Embedded GPS receivers able towithstand accelerations of 12000 g or about 118 kms2 have been

developed for use in 155 millimetres (61 in) howitzers[58]

Search and Rescue Downed pilots can be located faster if theirposition is known

Reconnaissance Patrol movement can be managed more closely

GPS satellites carry a set of nuclear detonation detectors

consisting of an optical sensor (Y-sensor) an X-ray sensor adosimeter and an electromagnetic pulse (EMP) sensor (W-sensor)



that form a major portion of the United States Nuclear Detonation

Detection System[59][60]

15 Communication

The navigational signals transmitted by GPS satellites encode a variety

of information including satellite positions the state of the internalclocks and the health of the network These signals are transmitted on

two separate carrier frequencies that are common to all satellites in

the network Two different encodings are used a public encoding that

enables lower resolution navigation and an encrypted encoding used bythe US military






























Function of NSS













Inter MSC








HON





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radio link









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HON





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timing capabilities





































142 Military






















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142 Military






















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142 Military






















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timing capabilities





































142 Military






















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15 Communication






the gsm system

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