part i.ppt
TRANSCRIPT
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GSM Basics
Annamalai Maheswaran
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Cellular Concepts
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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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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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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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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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Cellular System Architecture
.
.
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M
S
M
S
M
S
M
S
M
S
MS
MSC
BS1
BS2
BSn
PSTN
Air Interface
.
.
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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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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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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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A Simplified Network View
PSTNMSC
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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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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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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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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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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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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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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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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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GSM Entities (Contd.)
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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GSM Entities (Contd.)
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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GSM Entities (Contd.)
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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GSM Entities (Contd.)
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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GSM Entities (Contd.)
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
Purposes Of Various Group of Bits In GSM
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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
Purposes Of Various Group of Bits In GSM
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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
Purposes Of Various Group of Bits In GSM
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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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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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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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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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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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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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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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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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Authentication & Tracking MS
Security Issues
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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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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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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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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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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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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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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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Originated)
Access Request Message
on RACH
MSBSS
Response
on SDCCH
Assign SDCCH
on AGCH
Functions of HLR & VLR
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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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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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Signalling And Call Processing
GSM Functional Planes
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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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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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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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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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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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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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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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1. Same as step 1 in the intra MSC handover
2. Same as step 2 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
6. Same as step 3 in the intra MSC handover
7. Same as step 4 in the intra MSC handover
Messages In Inter Msc Handover(Contd.)
8 Target MSC sends Prepare Handover
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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
14. Same as step8 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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15. Same as step 9 in the intraMSC handover
16. Same as step 10 in the intraMSC handover
17. Same as step 11 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
21. Same as step13 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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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