part i.ppt

8/10/2019 Part I.ppt

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1

GSM Basics

Annamalai Maheswaran

[email protected]


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2

Cellular Concepts


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3

Cellular Concepts

Cellular concepts involve using a base station

radiating less power and serving a smaller areacalled cell The geographical area to be covered is divided

into large number of such cells

The coverage areas of cells are overlapping Vehicle moving from one cell to another is

handled by the serving base station handing itover to another base station in adjoining cell

Frequencies used in one cell are reused aftersome distance

Neighbouring cells use different frequencies Large capacities can be built by having large

number of smaller cells


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4

7 Cell Frequency Reuse

Pattern Can Be

Replicated

Indefinitely

Many Cells Can ShareSame Frequencies If

Separated In Space

1

2 3

4

5 6

7

1

2 3

4

5 6

7

1

2 3

4

5 6

7

1

2 3

4

5 6

7

1

2 3

4

5 6

7

n

n indicates thefrequency set used

Cell radius

Frequencyreusedistance


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5

3 Cell Reuse

D2

B2

D1

E2

D3

B1

B3

A2

E1

E3

C2

A1

A3

F2

C1

C3

G2

F1

F3

G1

G3


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6

Cellular Concepts Key Factors

Overlapping cells, each covering smaller area

Neigbouring cells use different carrier

frequencies

Reuse of frequencies

Mobility of mobiles handled by handover

Paging for incoming calls

Tracking of idle mobiles


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Cell Clusters

SOURCE: IEC.ORG

Actual Coverage

Area Of Cell 1

Actual CoverageArea Of Cell 3

Cell 1 Overlaps 6 Others

Different Frequencies

Must Be Used In AdjacentCells

Seven Different Sets Of

Frequencies Required
http://www.iec.org/tutorials/cell_comm/topic03.htmlhttp://www.iec.org/tutorials/cell_comm/topic03.html


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Cell Handover

SOURCE: R. C. LEVINE, SMU

As Phone Moves From Cell A To Cell B:

Cell A Must Hand The Call Over To B

Phone Must Change Frequencies

Cell A Must Stop Transmitting

Minimum

performance

contour

Handover threshold

contour

A Bx y

z


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9

Cellular System Architecture

.

.

.

M

S

M

S

M

S

M

S

M

S

MS

MSC

BS1

BS2

BSn

PSTN

Air Interface

.

.


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10

BS1 BS2

1 1

BS1

BS2

. A B .

Level at point A

Level at point B (Call is terminated)

Handover threshold

Minimum acceptable signal

to maintain the call

Improper

Handover

Proper

Handover

Level at point B

Level at which handover is made

(call properly transferred to BS2)

Handover In Cellular Networks


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11

Handover in a Cellular System

User is moving from Cell A to B

BA

Power Received

from B

Power Received

from A

Distance


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12

Capacity & Interference

Capacity of cellular systems is limited by

interference There are two types of interference called co-

channel interference and adjacent channelinterference

Co-channel interference is created by usersoperating at the same set of frequencies in theadjoining clusters

Adjacent channel interference is created by users

operating at different but close by frequencies(or different TDMA slots) due to imperfectreceiver filters that allow these to leak into thereceiver band


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13

A Simplified Network View

PSTNMSC


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14

Concept of Network

Consists of interconnected Network Elements Covers large contiguous geographic area

Multiple networks in one area

Base stations continuously transmit system info

Mobile receives this info and select network

Mobile can transmit, when needed

For making outgoing call

For receiving incoming call

Transmission & reception through wireless medium


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15

Concept of Network (Contd.)

Transmission takes place in two directions

Downlink from Base Station to Mobil Station

Uplink from MS to BS

Physical channel is capable of transmission in onedirection

Either Downlink or Uplink

Subdivided into specialised channels calledlogical channels

Paging channels, traffic channels, etc

MS accesses the network through these channels

Call established by conveying MS identity, diallednumber & other info

Traffic channel used during conversation

Mobility handled by handover


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Challenges In Mobile Communication

System Objectives

Cover large contiguous areas Provide uninterrupted service while moving in a

vehicles

Serve maximum users within allotted spectrum

Provide good grade of service (minimumblocking)

Also less dropped calls

Dropped calls perceived in bad light (asagainst blocked calls)

Achieve reasonable voice quality

Minimise infrastructure cost

Optimise no of base stations

Ability to enhance the service capability on anevolutionary basis


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17

Cellular systems the GSM view

Analog

Cellular

GSMGPRS

EDGEWCDMA

1980s 1990 Late 90s

ETACS

NMT

Digital

systems

Voice Based

Packet

switcheddata

HigherspeedData

NewSpectrum3G

2000 2003

HSPA

Optimisedfor Highspeed Data


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18

Cellular systems the CDMA view

Analog

Cellular

IS-95

CDMA

CDMA

2000

1x-

EVDO

1980s 1990 Late 90s

AMPS

Early

2000

To

come

IS-54

IS-136

1x-

EVDV

Predominantlyvoice and circuitswitched data

Pkt-switchedData support

Optimizedfor Dataonly (HDR)

Co-existence ofData andvoice


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19

GSM Architecture, Subsystems &Interfaces


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History of GSM

1982 - Started As Group Speciale Mobile

Has Been Renamed As Global System for MobileCommunication 1985 - Decision to Design Digital System 1986 - Paris Trial for Field Testing 1987 - MOU Signed by 12 Countries

1988 - GSM Becomes ETSI Committee 1990 - Phase 1 GSM Specifications Frozen 1991 - First GSM Network Launched Continuous Enhancements & Upgrades

Gprs, Edge Has Global Foot Print Including Usa Very Popular for Voice & Data Applications

Current Market Share >80 %


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21

HLR

EIR

AUC

Op & Maint

center

Um

to PSTN

B

S.

C

B

S

C

B

S

C

.

.

.

VLR

M

S

C

M

S

C

VLR

to

PSTN

E1/SS7

.

.

M

S

M

S

M

S

GSM Network Architecture

A

BSS

B

C

.

.

.

BTS

BTS

BTS

BTS


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22

GSM Subsystems & Interfaces

MS BTS BSC MSC HLR AUC

VLROMC

Other

MSCsOther

NetworkEIR

Other

MSCs

VLR

BSSUm

Abis

A

E

G

F

DB

C


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23

GSM Network Elements

Mobile Station (MS)

Consists of Mobile Equipment (ME)& Subscriber

Identity Modlule (SIM)

Base Station Subsystem (BSS)

Base Transceiver Station (BTS)+ Base StationController (BSC)

BTS contains one or more Transmitter / Receiver (TRX)

each covering one or more cells

Network Switching Subsystem (NSS) Consists of one or more Mobile Switching Centre (MSC)

+ Home Location Receiver (HLR)+ Visitor Location

Receiver (VLR)+ Authentication Centre (AuC)+

Equipment Identification Register (EIR)


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Mobile Station (MS)

Mobile Equipment (ME) containing all hardware and

software for the operation of handset

Hardware - battery, antenna, transmit / receive

switch, transmitter, receiver, modulator,

demodulator, processor, memory, keypad, display,

speaker, microphone, a/d and d/a converter, buzzer,

etc.

Software operating system, channel coding, source

coding, various protocols, applications, etc

Subscriber Identification Module (SIM)is a detachable

memory module that contains all the information related to

a specific subscriber this is supplied to subscriber at the

time of subscription


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Mobile Station (MS) (Contd.)

Performs all physical layer related functions source

coding, channel coding, encryption, frequency & time

synchronization, equalization, timing advance, etc.

Supports call management functions to support

transmission of voice & data Monitors of power & signal quality of surrounding cells

for optimum handover (facilitate MAHO)

Performs idle mode procedure Selecting cell

Helping network track MS by registration, location

area updating, power up/down registration


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Functions Of BTS

Serves a single cell

Encodes, encrypts, multiplexes, modulates andfeeds RF signals to the antenna for transmission

Transcoding and rate adaptation

Time and frequency synchronization

Demodulates, decrypts, demultiplexes, decodes thesignal received through antenna

Detecting the random access

Computing timing advance for mobiles

Does slow frequency hopping as per hoppingsequence

Acts as slave to BSC in radio resource management(RRM)


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Functions of BSC

It controls a group of BTS and provides them

connectivity through Abis interface

It is responsible for managing radio resources(RR) of all BTS coming under it like allocation /deallocation of various channels, performing

paging, etc It is responsible for intra BSC handover

It controls frequency hopping

BSC is responsible for allocation of frequencies

among BTSs

It manages power levels of BTSs


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Functions of MSC

MSC covers a geographic area (one and only one

in every area)

It is responsible for tracking mobiles byperforming mobility management (MM) functionsregistration, location updating, TMSI allocation,

authentication, arranging for paging for MS, etc It is responsible for coordination of call set up

(both incoming and outgoing)

It provides interworking functions with different

networks It handles inter BSC handovers

It provides support for billing of MSs in its area


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GSM Entities

Since GSM systems are deployed worldwide in many

countries there is a need to standardise how the

GSM entities (like MS, GSM network, etc.,) will be

addressed in a uniform and consistent manner.

Some of the entities are

PLMN Identity:A Public Land Mobile Network(PLMN) is uniquely identified by a 3 digit Mobile

Country Code (MCC)and a 2 digit Mobile Network

Code (MNC)within the country

MNC(2 digits)

MCC(3 digits)

PLMN Code Format


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Concept Of Location Area

Should a paging message go on PCH channels of

all BTSs? Results in heavy load on PCH

We can reduce load if network knows approximate

location of MS

Concept ofLocation Area LA is a group of neighbouring cells

All cells must belong to same MSC

Can each cell be called a LA?

Will result in too much updating load Compromise is to club 5 to 20 cells as one LA

MS listens to LA ID from BCCH

MS registers itself in the LA with MSC

GSM E titi (C td )


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GSM Entities (Contd.)

Location Area Identity (LAI):The service area of aPLMN is divided into a number of MSC service

areas and each of these is subdivided intolocation areas that consist of a number ofadjacent cells. Each location area is assigned aLocation Area Code (LAC),that can be upto 4hexadecimal digits. LAI identifies the GSM

location area LAI = MCC + MNC + LAC

LAC is used in all messages

MNC

(2 digits)

MCC

(3 digits)

LAC

(2 octets)

LAI

CI

(2 octets)

CGI (Cell Global

Identity)


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Arrangement of Location Areas

(1) Cells belonging to LA1

(MSC!)

(2)

2(3)

2(1)

6(3)

5(3)

4(1)

3(3)

1(1)

3(1)

5(1)

3(2)

4(3)1(2)

1(3)

5(2)

4(2)

2(2)

7(1)

6(2)

6(1)

7(2)

8(1)

MSC1

MSC2

Cells belonging to LA2(MSC1)

(3)Cells belonging to LA3

(MSC2)


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GSM Service Area Hierarchy

cell

Location Area

MSC/VLR

PLMN Service Area(one per operator)

GSM Service Area


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SIM is a small memory package containingpermanent and temporary information about the

mobile user

SIM adds personality to Mobile Equipment

It carries the following information IMSI

Authentication Key (Ki) Subscriber Information Access Control Class Cipher Key (Kc*)

TMSI* Location Area Identity (LAI*) Forbidden PLMN*

* Updated by network


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International Mobile Station Identity(IMSI):This uniquely identifies a MS in anyGSM network

IMSI = MCC + MNC + MSIN

Where the 10 digit BCD number MSIN (MobileSubscriber Identity Number) identifies a MS

in that PLMN. IMSI is allocated by PLMNoperator and entered into permanent memoryof SIM

MCC MNC MSIN (10 digits)

IMSI Format


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Temporary Mobile Station Identity (TMSI):is a 32 bit number that uniquely identifies the

MS within one location area of a PLMN TMSI is a temporary identification and has

only local significance within location area Has no validity after MS has left the

location area

This offers protection against cloning ofTMSI

LAI and TMSI are stored in temporary SIMmemory

Most messages on the Uminterface identify a

MS by TMSI and LAI

TMSI (Max 4 Octets)

GSM Entities (Contd )


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Mobile Station ISDN Number (MSISDN):

This could be upto 15 digits Numbers for routing a call frominternational location & local location

CC NDC SN

International MSISDN (15 digits)

National Mobile Number

CC Country Code 1 to 3 digits

NDC National Destination Code 2 to 3 digits

SN Subscriber Number

GSM Entities (Contd )


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Base Station Identity Code (BSIC)is used

to distinguish between neighbouring BSs - 6 bitconsisting of 3 bits Network Colour Code (NCC)and 3 bits Base Transceiver Colour Code (BCC)

Mobile Subscriber Roaming Number(MSRN)is used to route a call to a mobilestation when this has gone to another network(roaming network)

MSRN = CC + NDC + SN

Identity of RoamingPLMN


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Multiple Identities of MS

External

Networks

MSISDN

GSM

Networks

MobileStation

MSRN(for Roaming MS_


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GSM Air Interface

GSM Air Interface Specifications


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GSM Air Interface Specifications

Parameter SpecificationsUplink Channel Frequency 890-915 MHz

Downlink Channel Frequency 935-960 MHzARFCN Number 0 to 124Tx/Rx Frequency SpacingTx/Rx Time Slot Spacing

45 MHz3 Time Slots

Modulation Data Rate 270.833 kbpsFrame Period 4.615 msecUsers per Frame (Full Rate) 8Time Slot Duration 576.9 msecBit Period 3.692 msec

Modulation 0.3 GMSKARFCN Channel Spacing 200 kHzVoice Coder Bit Rate 13 kbps


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GSM Variants

Variant Uplink (MHz) Downlink

(MHz)

Total

Bandwidth

Duplex-

frequencyseparation

Channels

GSM-400 451-458 and479-486

461-468 and489-496

Twice 14 MHz 10 MHz Twice 72

GSM-900

(primaryband)

890-915 935-960 Twice 25 MHz 45 MHz Twice 124

ExtendedGSM-900

880-915 925-960 Twice 35 MHz 45 MHz Twice 174

GSM-R 876-880 921-925 Twice 4 MHz 45 MHz Twice 19

DCS-1800 1,710-1,785 1,805-1,880 Twice 75 MHz 95 MHz Twice 373

PCS-1900 1,850-1,910 1,930-1,990 Twice 60 MHz 80 MHz Twice 300

Source: Bekkers, 299


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Modulation Scheme In GSM

Data rate in GSM is about 270 kbps & carrier spacing in

GSM is 200 kHz, with bandwidth slightly less than this GSM uses 0.3 GMSK, where 0.3 describes the 3 dB

bandwidth of the Gaussian pulse shaping filter withrelation to the bit rate (BT=0.3)

GMSK is a special type of digital frequency modulation

binary ones and zeros are represented in GSM byshifting the RF carrier by 67.708 kHz

Channel data rate is exactly 4 times this

This minimises the bandwidth occupied by themodulation spectrum

This improves the channel capacity

MSK modulated signal is passed through a Gaussianfilter to smooth the rapid frequency transitions whichwould otherwise spread energy into the adjacentchannels


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GSM Frame & Burst Format

2

One Slot

(156.25 symbols for 576.92msecs)

1 3 4 5 6

One Frame = 4.615msecs (216.66 frames/sec)

70

Normal Slot on DL and UL

Stealing (flag) Bits Tail Bits

TBTBTraining

sequenceGuardBits

3 26 3 8.25

Payload Payload

57 57

1 1


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GSM Frame Arrangement In Downlink & Uplink

21 3 4 5 6

Downlink Transmission

70

Uplink Transmission

21 3 4 5 6

Uplink Frame

70

Downlink Frame

0 1 2

765

Downlink - Uplink Offset(3 Time Slots) Duplex Transmission

Physical & Logical Channels


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Physical & Logical Channels

Physical Channelis a way of specifying a carrierfrequency number (called ARFCN - Absolute RadioFrequency Channel Number), time slot number,TDMA frame number and the direction (DL/UL)

This channel is capable of carrying any payloadconsisting of traffic or control data

Logical Channelrefers to the use to which aparticular physical channel is put

Control Channel- A physical channel that hasbeen logically used for carrying control data -there are many different types of control

channels Broadcast Channelsconsisting of Frequency

Correction Channel (FCCH),SynchronisationChannel (SCH) and Broadcast Control

Channel (BCCH)

Physical & Logical Channels (Contd )


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Physical & Logical Channels (Contd.)

Common Control Channelsconsisting of

Paging Channel (PCH), Random AccessChannel (RACH) and Access Grant Channel(AGCH)

Dedicated Control Channel - Stand-alone

Dedicated Control Channel (SDCCH) Traffic Channel- A physical channel that used

for carrying user traffic (usually voice) andsignalling

Traffic channel can be full rate traffic channel(TCH/F) or half rate traffic channel (TCH/H)

Traffic channel also has associated SlowAssociated Control Channel (SACCH) and FastAssociated Control Channel (FACCH)

C l M l if F


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Control Multiframe Format

Slot 0 of beacon is transmitted continuously by BTS

Empty bursts are filled with dummy data

0 1 2

Broadcast +Paging +

Access Grant 9 10 11 40 41 50

F S F S F SIdle

In slot 0 of specific beacon carriers (frequencies

stored in SIM) with 51-multiframe formatMS can tune to control slot during idle slot evenwhen TCH is present

Frequency Correction Channel (FCCH)


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Frequency Correction Channel (FCCH)

Frames 0, 10, 40 of control multiframe (x 51)

contain FCCH for frequency offset estimation andcorrection

All zero data constant frequency

When MS is turned on, it hunts continuously for

FCCH on beacon of all carriers in its SIM listFCCH allows mobile to acquire the carrier frequencyof the base station

Mobile then looks in the next frame for

Synchronisation Channel

142 all zeros3

TB

3

TB8.25

G

One beacon per cell


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Synchronisation Channel (SCH)

This is the first data reception after turning MS on

Long training sequence (64 bits)

78 bits containing information about framenumber and BSIC

Can determine slot number (SCH is on slot #0), multiframe, and hyperframe numbers

BSICis 6 bit colour code for the beaconfrequency - adjacent cells will have differentcolours (BSICs)

3

TB39

message

64

Training

39

message3

TB

8.25

G

Synchronisation burst

Purposes Of Various Group of Bits In GSM


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p pBurst

The various groups are Training Bits, Tail Bits,

Stealing Bits and Guard Bits Training bits(also called midamble in a normal

burst since this occurs in the middle) are used toallow the receiver to characterise the mobile

channel This is done by transmitting a known sequence

of bits this varies depending upon the type ofchannel and for traffic channel this is 26 bits

long The receiver can model the channel using the

received response through the channel

This process is called equalisation



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p pBurst (Contd.)

Having modeled the channel using the training

sequence, the receiver can demodulate theunknown bits using this model

Since the mobile channel changes all the timedue the mobility of the user, the midamble has

to be transmitted in every burst Also, since the training sequence is in the

middle of the burst, the channel condition atthe middle of the burst is captured, thus

resulting in less RMS error Training sequence is chosen to have good

autocorrelation property



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p pBurst (Contd.)

Tail bitsare used to indicate to the receiver

about the start and end of the burst to help theequaliser in its function tail bit values are allset to 000 in the case of traffic burst

Guard bitsduration is idle period during which

no body should transmit this is a no mansland to facility different entities who are onlyapproximately time synchronised to each otherto have a smooth functioning without any

collision Guard bit in RACH channel is increased toaccommodate mobile that has not beenranged



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p pBurst (Contd.)

Mobiles in traffic state have been ranged (or

they have been told about timing advance totake care of their position relative to BTS)

Stealing bithelps the sender to use thepayload of 57 bits either for traffic (normally) or

for signalling (when the stealing bit is set) The signalling channel obtained by setting

the stealing bits is called FACCH

FACCH is used for emergency situations

like when handover has arisen, when call hasto be disconnected or when an incomingmessage is received during a call

S h i i Ch l M F


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Synchronisation Channel Message Format

NCC(3)

T1Superframe(11)

T2Multiframe(5)

BCC(3)

T3BlockFrame (3)

NCC Network Colour Code

BCC Base Station Colour Code

T1 (11 bits) = Frame Number / 26 x 51 Range from 0 to 2047

T2 (5 bits) = Frame Number mod 26 Range from 0 to 25

T3 (3 bits) = (Frame Number mod 51 1) / 10 Range from 0 to 4

BSIC

Broadcast Control Channel (BCCH)


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Broadcast Control Channel (BCCH)

BCCH is a downlink control channel that is used to

broadcast information such as cell and network

identity (CGI), operating characteristics of the cell

- current control channel structure, channel

availability and congestion BCCH also broadcasts a list of channels that are

currently in use within the cell

Frame 2 through frame 5 in a control multiframe

(4 out of 51 frames) contain BCCH data

BCCH and other control channel are transmitted in

time slot 0 of a particular ARFCN (Absolute Radio

Frequency Number)

Paging Channel (PCH)


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Paging Channel (PCH)

PCH is a downlink channel used by the base station

for paging purpose to inform a MS about an

incoming call

PCH uses 4 consecutive frames to send a

message

PCH transmits TMSI (usually) or IMSI (on rare

occasions)

PCH may also be used to provide cell broadcast

(ASCII text messages) to all subscribers as part of

the SMS feature of GSM

Random Access Channel (RACH)


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Random Access Channel (RACH)

TB TBTraining sequence

8 41 336

AdditionalGuard Bits

60

Message

RACH is uplink channel used by MS to access network

To acknowledge a paging done through PCH

To request a channel to originate a call, send SMS, etc.

MS accesses RACH after acquiring freq & timing sync

This burst includes 48 bit synchronisation sequence and 36bit message

RACH uses slotted ALOHA schemeThis burst has a longer guard period of 58 bits

Allows transmission of MS that has not acquired thetime synchronisation does not collide with other burstsif it is within 35 km ( distance for 58 x 3.69 msec)

8.25

GuardBits

Access Grant Channel (AGCH)


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Access Grant Channel (AGCH)

AGCH is a downlink control channel used by base

station to allocate SDCCH for bidirectionalcommunication path between BS and MS

AGCH instructs the MS to operate in aparticular physical channel (time slot andARFCN)

AGCH is sent in response to a RACH request byMS

This assigns a SDCCH to the MS for carryingthe signaling messages related to call set up,registration, etc.

ACGH uses 4 consecutive frames for sendingacknowledgement message

Stand-alone Dedicated Control Channel


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(SDCCH)

SDCCH is a duplex signalling channel allotted

through AGCH message for carrying signaling data &for user services (like messaging not requiring TCH)

SDCCH enables the base station and MS to remain

connected till the MS identity is verified

SDCCH is deallocated once TCH is assigned

(SACCH becomes available)

SDCCH is used to send authentication and alert

messages SDCCH may be carried on a traffic multiframe basis

or control multiframe basis

Associated Control Channel (ACCH)


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Associated Control Channel(ACCH)

ACCH used for conveying signalling and otherinformation bidirectionally between BS and MSThere are two types of ACCH

Slow Associated Control Channel (SACCH)that is available on frame # 12 in a trafficmultiframe

[184 bits (23 bytes) message + 40 parity bits]

x 2 due to rate 1/2 convolutional code will resultin 456 bits in 480 msecSlow ACCH (184 bits every 480 msec ~380bits/sec)SACCH multiframes for different time slots areoffset to achieve load balancing at BSC

Fast Associated Control Channel (FACCH)ismade use of during handover by setting the stealbits of traffic channel. In every frame there are 2sets of 57 bits and by stealing in 8 slots you get456 bits

Traffic Multiframe Format


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Traffic Multiframe Format

Traffic Channel (TCH/F) transmission occurs in a

particular time slot of every traffic frame except inframe numbers 12 and 25 of traffic multiframe

Speech codec generates 13 kbps data (260 bitsevery 20 msec) and with FEC this gets enhancedto 456 bits

24 bursts every 120 msec with 114 bits perburst gives a pay load of 24 x 114 = 2736 bitswhich equals the data rate of codec (456 x 6)

Traffic

Frame

Number0 . . . . . . 12 13

Signaling idle

251

T affic M ltif ame Fo mat (Contd )


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Traffic Multiframe Format (Contd.)

Signaling (SACCH) is done in frame # 12 and

frame # 25 is not used In the case of half rate traffic channel TCH/H

alternate frames are made use of

Codec rate is 5.6 kbps (112 bits / 20 msec)and this after FEC gets enhanced to 228 bits

One MS uses frame # 12 for signaling withframe # 25 being idle and the other usesframe # 25 with frame # 12 being idle

Downlink frames offset by exactly 3 time slots to

avoid simultaneous transmission and reception inMS

This eliminates the need for duplexer baseddesign

Multiframe Structure


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0 4321 5 49 50

0 1 24 25

Multiframe Structure

0 1 2 3 4 2045 2046 2047

1 hyperframe=2048 superframes (3h 28m 53s 760 msec)

0 1 32 6 754

0 1 2 25 0 1 50

1 frame= 8 slots

traffic multiframe=26 frames Control multiframe = 51 frames

1 superframe = 51 traffic multiframes= 26 control multiframes (6.12 sec)

3T B

57bits

1F

26T

1F

57bits

8.25G

576.92 msec

3T B

TB: Tail Bits

F: Flag

G: Guard

Logical Channels Purposes & Formats


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Logical Channels Purposes & Formats

Name of LogicalChannel & direction

Purpose of Channel Format ofChannel

Frequency CorrectionChannel (FCCH) DL

Enables MS to acquirecarrier frequency ofBTS

142 0s

SynchronizationChannel (SCH) DL

Allows MS to acquireframe synchronisation

& BSIC

39 bits + 64training bits + 39

bitsBroadcast ControlChannel (BCCH) DL

Broadcasts Network &System information

Normal Bursts (4frames)

Paging Channel(PCH) DL

Paging for MS(s) Normal Bursts (4frames)

Random AccessChannel (RACH) - UL

MS sending accessrequest

36 bits + 48training bits + 56extra guard bits

Access Grant Channel

(AGCH) DL

Allocating SDCCH to

MS

Normal Bursts (4

frames)

GSM Logical Channels


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g

Group Channel

Name

Function Direction

Traffic Channel

(TCH)

TCH/F

TCH/H

Full Rate TCH

Hall Rate TCH

UL & DL

UL & DL

Broadcast

Control Channel

BCCH

FCCH

SCH

Broadcast Control

Frequency Correction

Synchronisation

DL

DL

DLCommon

Control Channel

RACH

AGCHPCH

NCH

Random Access

Access GrantPaging

Notification

UL

DLDL

DL

DedicatedControl Channel

SDCCH

SACCHFACCH

Stand-alone ControlChannel

Slow Associated ControlFast Associated Control

UL & DL

UL & DLUL & DL

Summary of Channel Coding


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67

Summary of Channel Coding

Channel

Bits / Block

Data + Parity +Tail

Channel

CodingRate

Coded bits /

block

Sent over

Frames

TCH

Class I

Class II

182+3+4 = 189

78+0+0 = 78

Rate 378

78 = 456

8

FACCH

SACCH

SDCCH

184+40+4=228 Rate 456 4

BCCH

AGCH

PCH

184+40+4=228 Rate 456 4

RACH 8 + 6 + 4 Rate 36 1

SCH 25 + 10 + 4 Rate 78 1

Details Of GSM TDMA Frame Transmission


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Bit time 3.69 msec Smallest unit

Time slot 0.577 msec 156.25 bits

TDMA frame 4.615 msec 8 time slots

Traffic Multiframe 120 msec 26 TDMA frames

Control Multiframe 235.385 msec 51 TDMA frames

Super Frame 6.12 sec 1326 TDMA frames

Hyper Frames 3h 28mt 53.76 s 2048 Superframes

Channel Coding For Voice Bits


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69

g

20msecSpeech(8KHz, 13bitLinear PCM)

RPE-LTPSpeechCoder

3-bitCRC -rate

Convul-UtionalCoderClass-1 bits (182)

50 mostsignificantClass-1 bits 3 bits

4 tail bits

CodedClass-1

378 bits

Class-2 bits (78)

8-burstInter-Leaver

456 bits

2080 bits

Source codinggenerates 13

kbps

Channel coded

datarate is 22.8 kbps

Interleaving Scheme


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70

1 2 3 4 5 6 7 8

Stream of bursts with each burst of 114 bits

1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8

Channel Coder

456 bits

Channel Coder

RPE-LTP Coder

456 bits

RPE-LTP Coder

260 bits260 bits

Expanded burst Data 57 bits Data 57 bits

156.25 bits

Ciphering In TCH/F


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71

Ciphering In TCH/F

TBTBSync.

(Midamble)GuardBits

3 26 3 8.25

Payload Payload

57 57

1 1

114 bit encryption bits obtainedusing A5 algorithm

XOR Block (57bits) XOR Block (57bits)

57 bits each

Outgoing TCH Burst

57 Block A

bits after

Interleaving

57 Block B

bits afterInterleaving

Deciphering In TCH/F


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Deciphering In TCH/F

TBTBSync.

(Midamble)GuardBits

3 26 3 8.25

Payload Payload

57 57

1 1

114 bit decryption bits obtainedusing A5 algorithm

XOR Block (57bits) XOR Block (57bits)

57 bits each

57 bit block B

data fordeinterleaving

57 bit block A

data fordeinterleaving

Incoming TCH Burst

Block Schematic Of Functions Of MS


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A/D

Conversion

Voice

Coding &

Blocking

Channel

Coding

Inter

leaving

Ciphering

Burst

Formatting

Modulator

Transmitter

D/A

Conversion

Voice

DecodingViterbi

DecodingDeinter

leaving

Deciphering Receiver

Demodulator

Equaliser

Microphone

Earphone

8 kHz 13 bits

13 kbps22.8 kbps

Block Schematic Of Functions Of BTS / BSC


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74

Block Schematic Of Functions Of BTS / BSC

Trans

coding

Voice

Coding &

Blocking

Channel

Coding

Inter

leaving

Ciphering

Burst

Formatting

Modulator

Transmitter

Trans

coding

Voice

DecodingViterbi

DecodingDeinter

leaving

Deciphering Receiver

Demodulator

Equaliser

8 kHz 13 bits

Linear

13 kbps22.8 kbps

64 kbps

PCM

TRAU

Functions

Capacity Enhancement


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75

Capacity can be increased by reducing the cell size

Reducing cell size will increase interference and henceinterference reduction is required for enhancing capacity

Some of the techniques area

Adaptive Power Control:

Less power reduced interference

Key is to transmit just enough power Discontinuous Transmission (DTX):

Speech has long periods of silence and transmittercan be switched off during silence

Slow Frequency Hopping (SFH):

Averages influence of interference by changingcarrier frequency periodically

Sectorising:

Transmitting in a narrow beam

Reduces the number of transmitters directed at MS

Cell Splitting


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76

Macro Cells

Large Sized cells 10s of km

Capacity less

Less handover due to mobility

Can support high speeds

Micro Cells

Medium sized cells few kms

Moderate capacity & speeds

Pico CellsSmall sized cells few 100s ofmeter

High capacity & pedestrian speeds

Hierarchical Layered Cells


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Same area covered by multiple layered cells Macro, Micro & Pico cells

Handover can happenhorizontally (or laterally) orvertically (or hierarchically)

Can handle hot spot regions

Results in improved Coverage Quality Capacity

Disadvantages Increased # sites (cost) Increased signaling load to MSC and hand-offs Stringent power planning necessary

Macro cells,low density

Micro cells,

high density

Pico cells,higher density


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78

Authentication & Tracking MS

Security Issues


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79

Security Issues

Due to vulnerability of air interface

IMSI is rarely used on air interface TMSI is always used in all messages between MS& BS

TMSI has validity only in LAI All critical information like dialed digit, calling

number, etc. exchanged over air are encrypted Two distinct processes exist in GSM

Authentication:This is the process of sendingRAND and challenging MS to return a correctSRES.

Encryption:As part of the authentication aCipher key Kcis produced and this is used inencrypting and decrypting process for all dataexchanged between MS & BS

Authentication & Encryption


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80

yp

Network Mobile station

A3

?

A8

A5

A8

A5

A3

SRES

Ki

Ki

Frame #Kc

RAND (128 bits)

SRES (32 bits)

Encrypted traffic

Frame #

RAND

Ki

RAND

Ki

Kc

Authentication

Encryp

tion

RAND

Authentication & Encryption (Contd.,)


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81

Authentication

Network sends RAND (128 bits)

Kiis secret key

Ki, RAND used with Algorithm A3 to produce

SRES (32 bits) Ki, RAND used with Algorithm A8 to produce Kc

(128 bits)

A3 & A8are operator-dependent

Ki cannot be accessed by user When SRES sent by MS matches MS is

authenticated

Authentication & Encryption (Contd.,)


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82

yp ( ,)

Encryption

Kccipher key (64 bits) Frame number (22 bits), Kcused with

Algorithm A5

Produce two 114-bit sequences (encryption /

decryption bits)

Algorithm A5 is universal to all operators

Each burst has 114 data bits and these bits are

generated by XORing with encryption bits on

data bits

Received 114 bits are XORed with decryption

bits to get the original data

Functions of MS Idle Mode


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83

MS chooses Home PLMN, when present

Tunes to beacon frequencies listed in SIM Chooses the strongest carrier among these

Gets timing information from FCCH

Gets frame information from SCH

Gets PLMN identity, identity of neighbouringBS, configuration of the channels, CGI, etcfrom BCCH

Performs Location Area Update / Authentication/ Registration as needed

Locks on to PCH

If Home PLMN is not available, looks for otherPLMNs and performs above steps

Functions of MS Call Establishment


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84

Functions of MS Call Establishment

When MS wants to make an outgoing call it accessesnetwork through RACH

Network responds though AGCH & allocates SDCCH

MS and BS communicate privately in SDCCH

When call matures TCH is allocated forconversation

Routing due to movement of mobile is handled bymeans of handovers

When an incoming call is received for MS, it is pagedin PCH

MS responds by accessing RACH Steps above are repeated

After completing the call TCH is released and againperforms Idle Mode functions

Call Routing To And From MS


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PLMN must accept incoming calls at one fixed

exchange, called Gateway MSC(GMSC)

GMSC has information about location area of MS

and mobile is paged in this area

Call is completed on MS responding

In case MS is visiting another PLMN area, the

call is forwarded to visited PLMN and call is

completed thereMS can make outgoing calls in Home / Visited PLMN

and these gets routed to nearest interconnect point

Incoming Call to a Roaming MS


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MS

BS Visited

MSCVLR

HLRGMSC

OriginatingSwitch

User dialsMS numbe

IAM (MSISDN)HLR Query

(MSISDN)

HLR Response

(MSRN)IAM (MSRN)

Paging Procedure (Mobile Terminated)


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87

g g ( )

Paging Request Message on PCH

(TMSI or IMSI)

MSBSS

Channel Request on RACH

Response on SDCCH

Assign SDCCH on AGCH

Random Access Channel Procedure (MobileOriginated)


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88

Originated)

Access Request Message

on RACH

MSBSS

Response

on SDCCH

Assign SDCCH

on AGCH

Functions of HLR & VLR


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89

HLR & VLR are data bases

The data in HLR / VLR can be accessed by SS7 queries

Addressing is through Global Title

Absolute address obtained by GT translationfunctionality of SCCP

HLR contains database of all subscribers who are

registered in a PLMN area Usually there is one HLR per PLMN & this can be split

for operational convenience

Data contained include MSISDN, IMSI, IMEI, LAI,

TMSI, Access Profile, Database is of permanent nature

Once created, remains for the life time of MSsubscription

Functions of HLR & VLR (Contd.)


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90

VLR contains database of all subscribers who are

currently located in a MSC area One VLR can serve one MSC or multiple MSCs

Data contained will be similar to VLR database

This database is dynamically updated

New entries are made when new subscribervisits MSC area

Entries deleted as a result of LA updating ortime out

HLR and VLR play complementary roles

VLR / HLR track movement of MS

HLR helps in routing incoming calls to MS

VLR helps in handling outgoing calls from MS

Tracking MS


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MS can freely roam in GSM coverage area

Due to reasons of security, MS uses TMSI inmessages in clear (unciphered) mode

IMSI is used in exceptional cases

MS updates network about Location Area (LA)

Location Area is group of contiguous cellscoming under one MSC

MS updates whenever it moves into new LA andacquires a new TMSI

This is done by revealing its previous identity(TMSI & LAI)

Since it is not possible to track MS to cell level, MSis tracked to level of Location Area (LA)

Location Area Updating


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MS captures LAI and TMSI in its SIM

Whenever it enters a new cell area, it compares LAIcontained in BCCH with LAI stored in SIM

Initiates a Location Area Updating if these aredifferent

Sends access request in RACH & getting SDCCH

assigned Conveys the previous LAI & TMSI on SDCCH

and requests a new TMSI

Network allocates new TMSI

HLR captures this information (LAI & TMSI) forrouting incoming calls

Now MS can freely roam in the new LA since it canmake and receive calls in this area

Different Scenarios of Location Updating


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Scene 1:MS movement within same MSC area

LA updating done in the same VLR and new TMSIassigned & HLR updated

Scene 2:MS movement from one MSC to anotherMSC within same PLMN

LA updating results in message flow between VLRs New TMSI assigned by new visited VLR and entry

deleted in old visited VLR

HLR entry updated

Scene 3:MS movement from one PLMN to anotherPLMN

May need fresh authentication in the new PLMN

Same procedure as Scene 2


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94

Signalling And Call Processing

GSM Functional Planes


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95

OAM

CM

MM

RR

transmission

operator user

CM

MM

RR

trans

MS BTS BSC MSC/

VLR

HLR

GMSC

BTS BSC MSC

VLR HLR GMSC

GSM Signaling Protocol Architecture


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96

BSSAP

MM

CM

BSSAP

CM

BTS

MS BSC MSC

AUm Abis B/C/D/E/F

MTP

SCCP

MTP

SCCPSCCP

MM

RRM

RRM

RRM

LAPDLAPDLAPDmLAPDmSignaling

Layer1

Signaling

Layer1

Signaling

Layer1

Signaling

Layer1

BTSM BTSM

I

S

U

P

M

A

P

TCAP

Relay

MTP

GSM System Model Signaling View


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VLR

VLR

MAP/G

MAP/BMAP/C

MAP/D

MAP

MAP/F

MAP/E / ISUP

EIR

MAP /

ISUP

MAP /ISUP

MSC

BSC

BTS

MS

PSTN/

ISDN

PLMN

BSSAP /

Q.931

BSS

LAPD / Q.931

LAPDm / Q.931

MSC

HLR AUC

What Are RRM Functions?


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98

RRM functions cover all activities related to

physical layer (air interface) These relate functions like

Channel assignment

Channel release

Channel change and handover Change of channel frequencies, hopping

sequences (algorithms) and frequency tables

Measurement reports from the MS

Power control and Time Advance Modification of channel modes (speech and

data)

Cipher mode setting

Some RRM Messages


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Name ofMessage

Sent by &sent to

Carried onChannel

Purpose of Message

AssignmentCommand

BSC to MS SDCCH Allocation of TCH(ARFCN & TS#)

AssignmentComplete

MS to BSC SDCCH Acknowledge forAssignment Command

Channel Request MS to BSC RACH Request for channel

Channel Release BSC to MS SDCCH orTCH

Release of SDCCH orTCH

Cipher ModeCommand

BSC to MS SDCCH To indicate to MS thatciphering will start

Some RRM Messages (Contd.)


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Name of Message Sent by &sent to

Carried onChannel

Purpose of Message

Cipher ModeComplete

MS to BSC SDCCH Acknowledge that MSwill also startciphering

ImmediateAssignment

Command

BSC to MS AGCH Allocation of TCH(ARFCN & TS#)

Paging Request BSC to MS PCH To inform MS aboutincoming call / SMS

Paging Response MS to BSC SDCCH To respond to pagingby revealing MSidentity (TMSI)

SystemInformationMessages

BSC to allMSs

BCCH To broadcast CGI,System information,neighbouring celldescription

Some RRM Messages (Contd.)


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Name of Message Sent by &sent to

Carried onChannel

Purpose of Message

MeasurementReport

MS to BSC SACCH MS reporting onsignal strengthmeasurement

HandoverCommand

BSC to MS FACCH /SACCH

Change of MS channelallocation (will include

new ARFCN & TS#)

Handover Access MS to BSC(new)

FACCH /SACCH

Initial message senton the new TCH aboutpresence of MS

HandoverComplete

MS to BSC(new)

FACCH /SACCH

MS informs new BSCthat handover hasbeen completed

Handover Failure MS to BSC(old)

SACCH /FACCH

MS indicates thathandover has failed

What Are MM Functions?


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All activities connected with mobility of MS are

MM functions Location updating

Periodic registration

Authentication procedure

IMSI attach procedure (on power up a MS willpresent its IMSI to network and get a TMSI)

IMSI detach ( on power off of a MS, detachprocedure to tell network it is no longer inservice.

TMSI reallocation

Identification

Some MM Messages


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Name ofMessage

Sent by &sent to

Carried onChannel

Purpose of Message

AuthenticationRequest

MSC toMS

SDCCH Sending RAND forauthenticating MS

AuthenticationResponse

MS toMSC

SDCCH MS response bysending SRES

AuthenticationReject

MSC toMS

SDCCH MSC informing MSthat authenticationhas failed

LocationUpdating

Request

MS toMSC

SDCCH To update location byincluding TMSI and

LAILocation UpdateAccept Command

MSC toMS

SDCCH To indicate thatlocation updating hasbeen done

Some MM Messages (Contd.)N f S b & C i d P f M


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Name ofMessage

Sent by &sent to

Carried onChannel

Purpose of Message

TMSIReallocationCommand

MSC to MS SDCCH To indicate that locationupdating has been doneand will include new TMSI

TMSIReallocation

Complete

MS to MSC SDCCH Acknowledgement ofTMSI Reallocation

Command by MSIMSI DetachIndication

MS to MSC SDCCH Indication to MSC that itsidentity be removed fromMSC/VLR

IMSI Attach

Command

MS to MSC SDCCH To inform MSC that MS is

again powered upIdentityRequest

MSC to MS SDCCH MSC requesting MS tosend its identity (IMSI)

IdentityResponse

MS to MSC SDCCH MS sends its identity(IMSI)

What are CM Functions?


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CM functions relate to establishing, releasing call

and status indication

Call establishment for mobile-originated calls

Call establishment for mobile-terminated calls

Indication of status Changes of transmission mode during an

ongoing call

Call reestablishment after interruption of anMM connection

Dual-tone multifrequency (DTMF) controlprocedure for DTMF transmission

Flow of CM Messages


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MSC /GMSC

PSTN /

PLMN

MS A

NNIISUP messages

UNI

Q.931 messages

Interface between MS and MSC is called User to

Network Interface (UNI)Q.931 messages are used in this interface

Interface between MSC / GMSC and externalnetwork is called Network to Network Interface(NNI)

ISUP messages are used in this interface

M T itt d b

Call Management Messages


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Message name

Starting a call

Transmitted by

SETUP

EMERGENCY SETUPCALL PROCEEDING

PROGRESS

CALL CONFIRMED

ALERTING

CONNECT

MS/MSC

MSMSC

MSC

MS

MS/MSC

MS/MSC

During a callSTART DTMF

STOP DTMF

MODIFY

USER INFORMATION

MS

MS

MS/MSC

MS/MSC

Ending a call

DISCONNECTRELEASE

RELEASE COMPLET

MS/MSCMS/MSC

MS/MSC

Abnormal conditions

STATUS

STATUS ENQUIRY

CONGESTION CONROL

MS/MSC

MS/MSC

MS/MSC

Important ISUP Messages


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There are 3 important ISDN User Part (ISUP)

messages IAM(Initial Address Message) is sent by the

calling network to initiate a call sendingcomplete information about the call callingnumber, called number, type of call and other

information ACM(Address Complete Message) is sent by

terminating network to confirm that the callednumber is free and is being alerted

ANM(ANswer with Metering) is sent byterminating network once the called subscriberanswers the call. Now the conversation canbegin and metering starts

Important Q.931 Messages


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There are 3 important ISDN User Part (ISUP)

messages Setupmessage is sent by user or network

(originating side) to initiate a call by sendinginformation about the call calling number,

called number, type of call and otherinformation this is equivalent to IAM

Alertingis sent by the other side (terminatingside) to confirm that the called number is freeand is being alerted this is equivalent to ACM

Connectmessage is sent by the terminatingside that the called subscriber has answered thecall this is equivalent to ANM

Mobile Originated Call


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MS BSC MSC VLR PSTN

Setup(dialled digits + encryption)

Assignment of TCH (SDCCH)

Assignment Complete

Assignment Complete

(voice path from MS to MSC)

Assignment of trunk

on A channel

Call Proceed(on SDCCH)

Send infofor Outgoing Call(call restriction query)l

Alerting

Connect

Connect Acknowledge

Complete Call

Route Establishment

Answer

1

2

3

4

5

6

7

8

9

10

11

12

13

14

ringback heard by MS

Call Establishmentto PSTN no. (IAM)

(ACM)

(ANM)

Messages In Mobile Originated Call


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1. When user dials the number and presses ok

button MS sends Setupmessage transferring thisinfo to MSC

2. MSC sends a message to VLR for accessingsubscription information of MS

3. VLR checks the database of MS to determine

whether the call can be allowed or not and returnsa message

4. MSC send Call Proceedingmessage to MS

5. MSC allocates a trunk between BSC &MSC and

asks BSC to assign TCH for MS6. BSC allocates TCH, sendsAssignmentmessage

to MS

7. MS tunes to the TCH and sendsAssignmentCompletemessage to BSC

Messages In Mobile Originated Call


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8. BSC deallocates SDCCH, connects TCH to thetrunk and sendsAssignment Complete

message to MSC9. MSC sends Initial Address Message (IAM) to

PSTN containing the digits dialed

10. PSTN sets up the call and returns Address

Complete Message(ACM)11. MSC informs MS that destination number is being

alerted, subscriber hears ringing tone

12. When called subscriber answers PSTN sends

Answermessage13. MSC informs MS that connection has been

established through the Connectmessage

14. MS returns a Connect Acknowledgemessage

and conversation can proceed

Mobile Terminated CallGMSC


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Page Request(TMSI)

Alerting

Call Confirmed

Page Messageto

appropriate BSCs

Setup

Connect

Connect Acknowledge

Setup Complete

Answer

Channel Request(on RACH)

SDCCHAssignment (on AGCH)

Page Responseon SDCCHPage Response

Process Access Request

Complete Call

Page

LA & TMSI

Send infofor Incoming Call

Routing Information

Send Routing Information(VLR)1

2

3

4

5

6

7

89

10

11

12

13

14

151617

18

1920

21

MS BSC VLR PSTNHLR

end of MSC-VLR

dialogue

Call EstablishmentMessage

MSC

(IAM)

(ACM)

(ANM)

Messages In Mobile Terminated Call


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1. GMSC receivesIAMfor an incoming call fromPSTN to MS with directory no MSISDN

2. MSC requests routing information from HLRthrough Routing Information Message byincluding MSISDN

3. HLR acknowledges by returning MSRN / MSISDNand address of serving VLR

4. MSC queries VLR with Send Info for IncomingCall message

5. VLR responds with a Pagemessage that specifiesthe LAI & TMSI of MS

If incoming calls are barred VLR will inform theMSC and MSC would connect to an appropriateannouncement

Messages In Mobile Terminated Call (Contd.)

MSC d t i th BSC i LAI d d


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6. MSC determines the BSCs covering LAI and sendsthe Pagemessage to each of the BSCs

7. Each BSC broadcasts TMSI of MS in Page Requestmessage in PCH

8. MS responds with Channel Requestmessage inRACH

9. BSC allocates SDCCH, sends Channel Assignmentmessage to MS over AGCH

10. MS sends Page Responsemessage (containingMSs TMSI & LAI) over SDCCH

11. BSC forwards Page Responsemessage to MSC12. MSC sends Process Access Requestmessage to

VLR

Messages In Mobile Terminated Call (Contd.)

3 VLR esponds ith a Complete Call message


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116

13. VLR responds with a Complete Callmessage

14. MSC sends Setupmessage to MS

15. MS responds with Call Confirmedmessage16. MS sendsAlertingmessage to MSC indicating

the subscriber is being alerted about incomingcall

17. MSC returnsACMto PSTN18. When user answers, MS sends Connect

message to MSC

19. MSC returns Connect Acknowledge messageto MS

20. MSC sendsAnswer message to PSTN

21. VLR closes the dialog with MSC by returningSend Info for Incoming Call Acknowledgemessage

INTRA MSC HANDOVER


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MS MSC

Handover Command

Handover Command

+ new BSIC, TCH

Trunk Assignmenton A I/F +Handover Request(BSIC, encr. Key)

1

2

3

4

5

6

7

8

9

10

11

12

13

Periodic Measurement Report

Handover Access(on new TCH)

Physical Information

Handover Request

with ranking of target BTSs

Handover Detected

Handover RequestAcknowledge

new TCH ID

Handover Completed(after timing advance, power control)

Release

Release Complete

Handover Completed

Serving

BSCTarget

BSC

Messages In Intra Msc Handover

1 When MS determines that a handover is required


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118

1. When MS determines that a handover is required,it sends Measurement Reportmessagecontaining signal strength measurements

2. Serving BSC sends a Handover Requestmessage to MSC containing rank ordered list oftarget BTSs

3. MSC identifies the best candidate cell &determines whether the handover is intra MSC orinter MSC and checks about availability of trunkand radio resources and sends HandoverRequestmessage to target BSC

4. Target BSC sends Handover RequestAcknowledge message indicating the radio

channel5. MSC sends Handover Commandmessage to

serving BSC6. Serving BSC forwards this message to MS

MESSAGES IN INTRA MSC HANDOVER(Contd.)

7 MS tunes to the new channel and sends Handover


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119

7. MS tunes to the new channel and sends HandoverAccessmessage to BSC on the new radio channel

8. Target BSC sends Physical Informationmessageto MS.

9. Target BSC informs MSC when it begins detectingthe MS handing over with the Handover Detectedmessage

10. After MS and target BSC establish signalingconnection MS sends Handover Completedmessage to target BSC

11. Target BSC sends Handover Completed messageto MSC

12. MSC sends a Release messageto the serving BSCto release the old radio TCH

13. Serving BSC releases all resources with MS andsends Releases Completemessage to MSC

Serving Target TargetTarget

INTER MSC HANDOVER

Serving


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120

Prepare Handover

Send Handover Request

1

2

3

4

5

6

7

89

10

11

12

13

14

151617

18

1920

21

22

MSServing

BSC

Target

MSC

Target

VLR

Target

BSC

Serving

MSC

Measurement Report

Handover Request

Allocation Handover Number

Handover Request

Handover RequestAcknowledge

Prepare HandoverAcknowledge

Send Handover AcknowledgeHandover Command

Handover Command

Send HandoverAcknowledge

Handover Access

Physical Information

Handover Completed

Handover Detected

Handover Completed

Send End Signal

Process AccessSignaling

Send End Signal

Release Complete

Release

Messages In Inter MSC Handover


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121

1. Same as step 1 in the intra MSC handover


3. MSC identifies the target MSC associated with the

best candidate cell and sends Prepare Handover

message4. Target MSC sends anAllocate Handover

message to its VLR to assign the TMSI

5. Target VLR sends the TMSI in Send Handover

Requestmessage



Messages In Inter Msc Handover(Contd.)

8 Target MSC sends Prepare Handover


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122

8. Target MSC sends Prepare Handover(acknowledge)message to the serving MSC

indicating that it is ready for the handover9. Serving MSC sends the Send Handover

(acknowledge) message to the target MSC

10. Target MSC sends a Send Handover Request

(acknowledge)message to the target VLR11. Same as step 5 in the intra MSC handover

12. Same as step 6 in the intra- MSC handover

13. Same as step7 in the intra MSC handover


Messages In Inter MSC Handover (Contd.)

15 Same as step 9 in the intra MSC handover


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123

15. Same as step 9 in the intraMSC handover



18. Target MSC sends a Process Access Signallingmessage to the serving MSC

19. At this point the handover has been

completed,and the target MSC sends a SendEnd Singlingmessage to the serving MSC

20. Same as step 12 in the intra-MSC handover


22. Serving MSC sends a Send End Signal(acknowledge)message to the target MSC

Call Release Mobile Initiated


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124

MS BSC PSTNMSC

1

2

3

4

5

6

7

8

Disconnect

Clear Command

Release Complete

Release

Release

Channel release

Release Complete

Clear Complete

Messages In Call Release Mobile Initiated

1 MS sends the Disconnect message to the MSC


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1. MS sends theDisconnect message to the MSC2. MSC sends a Release message to PSTN to release

the call.3. MSC sends Releasemessage asking MS to begin

clearing procedure4. MS performs clearing procedure and informs MSC

through Release Completemessage

5. PSTN sends a Release Completemessage toMSC6. MSC sends Clear Commandmessage to BSC

requesting release of allocated resources for agiven SCCP connection

7. BSC sends Channel Releasemessage to MS torelease the TCH8. BSC sends Clear Completemessage to MSC

informing that all allocated resources have beenreleased

Location Updating Procedure


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Mobile

station

Base

station

Category LogicalChannel

SYNC CHANNEL INFORMATION

Carrier sine wave

SYSTEM INFORMATION TYPE3

CHANNEL REQUEST

IMMEDIATE ASSIGNMENT

LOCATION UPDATING REQUEST

AUTHENTICATION REQUEST

CIPHERING MODE COMMAND

CIPHERING MODE ACK

LOCATION UPDATING ACCEPT

TMSI ALLOCATION COMPLETE

AUTHENTICATION RESPONSE

CHANNEL RELEASE

RRM

RRM

RRM

RRM

MM

MM

MM

MM

MM

RRM

RRM

RRM

FCCH

SCH

BCCH

RACH

AGCH

SDCCH

SDCCHSDCCH

SDCCH

SDCCH

SDCCH

SDCCH

SDCCH

Mobilestation

Basestation

Category LogicalChannel

C i i

Mobile Terminated Call Sequence


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RRM

RRM

RRMRRM

RRM

RRM

MM

MM

RRM

RRMCM

CM

CM

RRM

RRM

CM

CM

CM

CM

RRM

FCCH

SCH

BCCH

PCH

RACH

AGCH

SDCCH

SDCCH

SDCCH

SDCCH

SDCCHSDCCH

SDCCH

SDCCH

SDCCH

SDCCH

SDCCH

FACCHTCH

TCH

FACCH

FACCH

FACCH

FACCH

Carrier sine wave

SYNC CHANNEL INFORMATION

SYSTEM INFORMATION

PAGING REQUESTCHANNEL REQUEST

IMMEDIATE ASSIGNMENT

PAGING RESPONSE

AUTHENTICATION REQUEST

AUTHENTICATION RESPONSE

CIPHERING MODE

CIPHERING MODE ACKSETUP

CALL CONFIRMED

ALERTING

CONNECT

ASSIGNMENT COMMAND

ASSIGNMENT ACK

CONNECT ACKconversation

conversation

conversation

DISCONNECT

RELEASE

RELEASE COMPLETE

CHANNEL RELEASE

Mobile Assisted Handover

Mobile Base Logical


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ob estation station

gChannel

TCH

TCHSACCH

TCHTCHTCHSACCHTCHFACCH

new TCHTCHTCHTCH

FACCHTCH

TCHSACCHTCHTCHTCHSACCHTCH

conversation

conversation

MEASUREMENT REPORT

conversation

conversation

conversation

MEASUREMENT REPORT

conversation

HANDOVER COMMAND

HANDOVER ACCESS

HANDOVER ACCESS

HANDOVER ACCESS

PHYSICAL INFORMATION

HANDOVER COMPLETE

conversation

conversation

MEASUREMENT REPORT

conversation

conversation

conversation

MEASUREMENT REPORT

conversation

Short Message Services


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Short Message Service (SMS) is a very important

and popular service Message delivery is by using SDCCH rather a

light load on network resources

There are two types of services

Point to Point

Cell Broadcast (Point to Multipoint)

This service is supported through Type 0 MS &

SMSC (SMS Center)

SMSC can be a separate external element or

could be built into MSC

SMS Network Elements

Short Messaging Entity (SME) is any device


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Short Messaging Entity (SME) is any devicecapable of sending and receiving short messages

This may be located in fixed network, mobilenetwork or could be another service centre

Short Message Service Centre (SMSC) isresponsible for relaying, storing and forwarding

between an SME and MS SMS Inter Working MSC (SMS-IWMSC) is an MSC

capable of receiving short messages from themobile network and submitting it to SMSC

SMS Gateway MSC (SMS-GMSC) is an MSC that iscapable of receiving short messages andinterrogating HLR for location information fordelivery

Architecture Of SMS


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Mobile Network

SMSCMSC /

VLRMS

Gateway or

I/W MSC

HLR

MS Originated Short Message Message Flow

SMSC SMS HLR MSC VLR MS


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Message

Transfer

Delivery

forwardShortMessage

sendInfoFor-

MO-SMS

Message Transfer

Delivery ReportDelivery

Report

Report

SMSC SMS-IWMSC

HLR MSC VLR

Access Request

Authenticate

MS

MS Terminated Short Message Message Flow

SMSC GMSC HLR MSC VLR MS


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Message

TransfersendRoutingInfo-

Delivery

ForShortMsg

forwardShortMessage

sendInfoFor-

MT-SMS

Message TransferDeliver Report

SM-DeliveryReportStatus

Report

SMSC GMSC HLR MSC VLR

Page

Authenticate

MS

Half Rate Traffic Channels (TCH/H)

Half rate traffic Channel (TCH/H) is allocating a time


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Half rate traffic Channel (TCH/H) is allocating a timeslot to 2 users with each one using alternate frames

User1 is given all odd frames and User2 is givenall even frames of the same time slot

Speech coding is done at lower rate resulting insomewhat lower quality of speech

TCH/H allocation is resorted to support two users pertime slot during peak hours of the day or duringemergencies

Frame

Number 0 . . . . . . 12 13 251 2

User2idle Signaling

part i.ppt

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