GSM dan GPRS basic

1

Agenda, GSM & GPRS Theory

• GSM» Definition and History.» GSM Services.» GSM System architecture.» GSM Functional model.» GSM Radio (Um) Interface.» GSM A-bis.» GSM A-Interface.» GSM A-Interface BSSAP.» GSM A-Interface DTAP.» GSM Inter-MSC Signalling

MAP.» GSM Signalling procedures

• IN Signalling Procedures

• TRAU(Transcoder Rate Adaption Unit

• GPRS» History and definition

» GPRS Network and its new elements

» GPRS Air and A-bis Interface

2

Global SystemforMobile Communication

(Groupe Spéciale Mobile)

GSM

BTS

Definition and History

• Does mobile mean that you have

to be driving in a car ?• Does it work in aeroplanes ?• ………onboard ships in the ocean ?• …….inside buildings ??• ….. everywhere in the nature ?

?

?

?

?

?SONOFON

M N

SONOFON

M N

SONOFON

M N

SONOFON

M N

SONOFON

M N

What is Mobile telephony ??

Local Exchange

MobileSwitchingCentre

fixed medium

Mobile Station

fixed location

Variable Location

Diffuse Medium

Telephone

SONOFON

M N

Basic concept - 1GSM vs. fixed network Telephony

NMT 450/900

C-Netz

RTMS

AMPS

Nordic Countries, France, Belgium, Netherland, Switzerland,Austria, Turkey, Yugoslavia, Thailand, Malaysia, North Africa

West Germany, Portugal

UK, Ireland, Italy, Spain, Austria, Greece, Hong Kong, China,Malaysia, Thailand, Sri Lanka

USA, Canada, Australia, New Zealand, Malaysia, PakistanSingapore, Hong Kong

Analog Mobile Systems

RC 2000

Italy

France

TACS / ETACS

PCS 1900GSM at

1900 MHz

C-NETAnalog

450 MHz

UMTS / IMT-2000 (FPLMTS)

CT2

DCS 1800GSM at

1800 MHz

Cordless

Trunked mobile radio

(TETRA)

Satellite(IRIDIUM)

GSMDigital

900 MHz

Mobile

Other systemsCT0,CT1

DECT

GSMDigital

900 MHz

NMTAnalog

450/900 MHz

TACS/ETACSAnalog

900 MHz

AMPSAnalog

800 MHz

GSMDigital

900 MHz

DAMPS(TDMA)

GSMDigital

900 MHz

CDMA

The evolution

8

• The GSM Standard is divided into phases (phase 1, phase 2 and phase 2+) all the phases has been finalized by ETSI.

• Many of the GSM networks in operation today are currently using the phase 2. However many of the GSM network operators are starting to implement phase 2+.

• The ETSI GSM standard specification is around 5500 pages, and are divided into12 series.

GSM Standard part 1

• Series 00 Preamble• Series 01 General• Series 02 Service aspects• Series 03 Network Aspects• Series 04 BS-MS interface / protocols• Series 05 Physical layer of radio path• Series 06 Speech Encoding• Series 07 Adaptation techniques• Series 08 BS-MSC interface• Series 09 Interworking procedures (network)• Series 10 Interworking between services• Series 11 Equipment and type approval specifications• Series 12 Operation and maintenance procedures

GSM Standard part 2

• GSM 900» The original system

» Widely applied in EUR

• DCS 1800» Typical expansion path when running out of capacity with GSM 900

• PCS 1900» Widely used in the United States

GSM systems today

• Specification start-up: 1980• First network in operation: Jan. 1992 (Radiolinja, Finland)• Forecast in 1995:

» At the ITU's Telecom '95 event, were stated that we will reach 100 million subscribers Worldwide before the year 2000.

• September 1997: ~55 million subscribers.~1 new subscriber each second.~250 networks in 110 countries.

• July 1998:

» More than15 months early then year 2000 the magic figure of 100 million subscribers was reached.

• Today : Over 200 million subscribers. 369 networks in 137 countries.

Status

BTS

GSM Services

BTS

• Telephony• Data services (up to 9600 b/s)• Fax group 3 (special modem)• Short Message Service (SMS)• Supplementary services, e.g.

» Call Forwarding» Call Barring» Call Waiting» Three Party Service» Advice of Charge

Services

BTS

• Integrated voice/data (ISDN)• Improved performance• Improved security

» Digital encryption» Authentication (IMSI)» TMSI assignment

• All types of Mobile Stations• Automatic roaming• Sophisticated radio functions

» Discontinuous transmission - DTX» Frequency hopping

GSM Features

BTS

• Half-rate and enhanced full-rate speech• New supplementary services:

» Display of called and calling user's number» Multi-party conversations (up to 6 parties)» Closed user groups / virtual private networks» Call completion services (busy, no answer etc.)» Intelligent network services (CAMEL)» Roaming between GSM and DCS 1800 (PCS 1900)

• High speed data services:» High Speed Circuit Switched Data (HSCSD)» General Packet Radio Service (GPRS)

Services, phase 2 and 2+

BTS

System architecture.

BaseStation

ControllerBSC

Public Switched

Telephone Network

Base Mobile Station (MS)

MobileSwitching

CentreMSC

(PSTN)

StationSubsystem

(BSS)

A-Inter

A-bis

Um

2 Mbit/s PCMAir Interface

BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Equip. IdRegister

EIR

Authen.CentreAUC

VisitorLocationRegister

VLR

HomeLocationRegister

HLRMobile

SwitchingCentreMSC

MAPISUP / TUP

MAP

MAPMAP

ISUP / TUP

ISUP / TUP

MAP

System Overview

HomeLocation Register

VisitorLocation Register

Mobile Switching Centre

BaseStation Controller

Base TransceiverStation

MSCBTS

BSC

VLR

HLR

SONOFON

M N

System Building Blocks

• “Home Base” of information regarding customers subscribing to

a particular operators GSM network• Keeps track of subscriber profile, conditions and whereabouts

MSCBTSBSC

VLR

HLR

SONOFON

M N

HLR (Home Location register)

BTS

• Subscriber information:» IMSI (International Mobile Subscriber Identity)» MSISDN (International Mobile Station ISDN Number)» MS Category (e.g. payphone)» Authentication vectors (RAND, SRES and Kc: AUC and

SIM)» Allowed services (subscription data)

• Mobile location information:» VLR number» (MSRN - Mobile Station Roaming Number)

HLR contains

BTS

• Subscriber information:» IMSI» TMSI - Temporary Mobile Subscriber Identity» MS category» Authentication vectors» Allowed services

• Mobile location information:» MSRN - Mobile Station Roaming Number» LAI - Location Area Identity

VLR contains.

• Database with information about mobile users

present/active in the network segment served by the MSC• Handles true visitors as well as subscribers of the operator himself

MSCBTSBSC

VLR

HLR

SONOFON

M N

VLR (Visitor Location register)

• Contains the radio transmitters and receivers (transceivers)

covering a certain geographical area of the GSM network

MSCBTSBSC

VLR

HLR

SONOFON

M N

BTS (Base Transceiver Station)

• Controls a group of BTS’s in relation to power control and handover.• The combination of a BSC and its BTS’s is called a Base Station Subsystem (BSS).• The interface between the BTS and the is called the A-bis interface.

MSCBTSBSC

VLR

HLR

SONOFON

M N

BSC (Base Station Controller)

• Serves a number of BSS’s (Base Station Subsystem) via the A-interface.• Responsible for call control (set-up, routing, control and termination of the calls)

• Management of inter-MSC handover and supplementary services, and

for collecting charging/accounting information.• Gateway to other to other GSM networks and public-switched networks)

BSC (Base Station Controller)

MSCBTSBSC

VLR

HLR

SONOFON

M N

26

• Contains the individual subscriber-identification key (also contained in the SIM), and provides the subscriber data to the HLR and VLR used for authentication and encryption of calls.

AUC

HLR

AUC - Authentication Centre

BTS

27

BTS

• Stores information about mobile stations in use and may block calls from a MS if the MS is stolen, not type-approved or has faults which may disturb the network.

• Each MS is identified by a unique International Mobile Station Equipment Identity (IMEI)

MSC

EIR

EIR - Equipment Identity Registration.

• Power:» - Class 1: 20 W Vehicle/» - Class 2: 8 W portable» - Class 3: 5 W Hand-held» - Class 4: 2 W Hand-held» - Class 5: 0.8 W Hand-held

(MS) Mobile Station

BTS

Functional model.

30

BaseStation

ControllerBSC

Public Switched

Telephone Network


MobileSwitching

CentreMSC

(PSTN)

StationSubsystem

(BSS)

A-Inter

A-bis

Um


BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Equip. IdRegister

EIR

Authen.CentreAUC


VLR


HLRMobile

SwitchingCentreMSC

MAPISUP / TUP

MAP

MAPMAP

ISUP / TUP

ISUP / TUP

MAP

The overview of the System.

• Call Management (CM)» Call Control (CC)» SMS » Non Call-related SS

• Mobility Management (MM)

• Radio Resource Management (RR) CM

MM

RR

BTSBSC MSC

VLR

HLRSONOFON

M N

A functional model

32

• DTAP - Direct Transfer Application Part

• BSSMAP - BSS Management Application Part

• CM - Call Management• MM - Mobile Management• RR - Radio Resource Management• BTSM - BTS Management

• SCCP - Signalling Connection Control Part• MAP - Mobile Application Part• TCAP - Transaction Capability Application Part• ISUP - ISDN User Part• MTP - Message Transfer Part

DTAPCM

MM

RR

Sig. layer 2

Layer 1 (air)

Sig. layer 2

Sig. layer 1

MTP

SCCP

BSSMAPRR

(CM+MM)

MS BSC

MTP MTP

SCCP SCCP

CM

MM

BSSMAP TCAP

MAP

ISUP

MSC

Sig. layer 2

Layer 1 (air)

BTS

(CM)

(MM)

(RR)

(CM)

(MM)

(RR)

(CM)

(MM)

(LAPDm) (LAPDm) (LAPD)Sig. layer 2

Sig. layer 1

(LAPD)

BTSMBTSMRR'

Um Interface Abis Interface A Interface Inter-MSC

Layer 1

Layer 2

Layer 3

GSM Protocol Architecture

33

• The Network layer contains the signalling procedures and is divided into:

» CC - Call Management.» MM - Mobility Management.» RR - Radio Resource Management.

Layer 3 Network Layer

BTS

34

BTS

• Call Management takes care of the ordinary call-control procedure:

» Establishment and release of calls, as well as access to services and facilities.

• CM is divided into:» Call Control (CC), short messages services (SMS).» Non-call-related supplementary services (SS).

Layer 3 Call Management (CM)

35

• Mobility Management handles roaming and authentication procedure.

Layer 3 Mobility Management (MM)

BTS

36

• Radio Resource Management comprise:» Paging.» Radio-channel access. » Ciphering.» Handover.» Radio-signal control» Radio-signal measurement BTS

Layer 3 Radio Resource Management (RR)

37

BTS

• The Data Link Protocol is used at the Um and A-bis interface, the Data Link Protocol is based on LAPD (ISDN D-channel layer 2 protocol).

• On the A-Interface MTP and SCCP are used as signaling-transport function.

• On the inter-MSC interface, MTP is used for ISUP, TUP and MTP + SCCP + TCAP is used for MAP.

Layer 2 Data Link Protocol.

38

• Physical Link of the signaling is time slots in the radio carriers and digital PCM lines.

BTS

Layer 1 Physical Link

Um

BTS

Radio (Um) Interface

The System

BaseStation

ControllerBSC

Public Switched

Telephone Network

Base

Mobile Station (MS)

MobileSwitching

CentreMSC

(PSTN)

StationSubsystem

(BSS)

A-Inter

A-bis

Um


BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Equip. IdRegister

EIR

Authen.CentreAUC


VLR


HLRMobile

SwitchingCentreMSC

MAPISUP / TUP

MAP

MAPMAP

ISUP / TUP

ISUP / TUP

MAP

41





DTAPCM

MM

RR

Sig. layer 2

Layer 1 (air)

Sig. layer 2

Sig. layer 1

MTP

SCCP

BSSMAPRR

(CM+MM)

MS BSC

MTP MTP

SCCP SCCP

CM

MM

BSSMAP TCAP

MAP

ISUP

MSC

Sig. layer 2

Layer 1 (air)

BTS(CM)

(MM)

(RR)

(CM)

(MM)

(RR)

(CM)

(MM)


Sig. layer 1

(LAPD)

BTSMBTSMRR


Protocol Architecture

• GSM has been assigned 1000 radio channels in the 900 MHz band. More precisely:

» 890 - 915 MHz “Uplink”» 935 - 960 MHz “Downlink”

• A combination of frequency and time division is used. » 124 carriers» Carrier spacing is 200 kHz» 8 timeslots per carrier

BTS

Downlink

Uplink

Ch1 890

Ch124 915

Ch1 935

Ch124 960

SONOFON

M N

GSM 900 Radio (Um) Interface Physical Channels

• GSM has been assigned 2992 radio channels in the 1800 MHz band. More precisely:

» 1710 - 1785 MHz “Uplink”» 1805 - 1880 MHz “Downlink”


BTS

Downlink

Uplink

SONOFON

M N

Ch374 1785

Ch374 1880

Ch1 1805

Ch1 1710

DCS-1800 Radio (Um) Interface Physical Channels

• Except for the difference in power level range and frequency, PCS-1900 are identical to DCS-1800.

• The frequency shift is required in US because of presence of some point to point radio links on the 1800 MHz band.


PCS-1900 Radio (Um) Interface Physical Channels

BTS

Downlink

Uplink

SONOFON

M N

Ch1 1850

Ch299 1910

Ch1 1930

Ch299 1990

BTS

TDMA Frame

Time Slot

4.615 msec

3 57 1 26 1 57 3

TB Coded Data C TS C Coded Data TB

8.25

GP

0.577 msec

Duration of 1 bit: 3.692 usec

0 1 2 3 4 5 6 7

TB : Tail bitTS : Training Sequence (setting up the receiver equaliser)GP : Guard PeriodC : Control bit

13 kbit/s user data

TDMA Frame Structure

46

BTS

Physical Channels

TS 5TS 4

TS 3TS2

TS1 TS0

TS 4TS 3

TS2TS0 TS7

TS6

TS 5

TS7TS6

SONOFON

M

N

Control Channels

Control Channels

Traffic Channels

Traffic channels showing three timeslot delays between the down and up links.

Eight TS, or eight physical channels compromise a FRAME

TS 2TS1

TS 0TS7

TS6 TS5

TS 0TS 7

TS6TS5 TS4

TS3

TS 1

TS3TS2

Downlink Uplink

47

FCCH

burst3 142 3

8.25

GuardTailTail

Information

Tail Information Training

3 57+1 (TCH/FACCH) 26 57+ 1 (TCH/FACCH) 3Normal

burst

8.25

GuardTail

Information

Access

burst7 41 36 3

GuardTailTail

68,25

InformationTraining

SCH

burst3 39 64 39 2

8.25

GuardTailTail

Information InformationTraining

» Not illustrated is the “dummy” burst which has the same structure as the “Normal” burst. The dummy burst is sent when no information is transmitted on a TCH

Radio (Um) Interface burst modulation structure

48

• For the “Normal” burst, one of the 58 information bits on each side of the training sequence is a flag bit indicating whether the burst is a TCH - traffic channel (0) or for a FACCH - fast associated control channel (1).

• The burst is converted to FACCH when signalling is required after a TCH has been allocated.

» Note: Each “Normal” burst (TDMA) time slot period consist of 156.25 bits (equal to 33.9 kbit/s per time slot or 270.8 kbit/s per frame carrier), of which 144 (2*57) bits are coded data including forward error correction. All information is transferred in blocks of 456bits divided into four time slot periods (456 = 4*2*57). The maximum net bit rate is 13 kbit/s (Excluding the error correction)

Tail Information Training

3 57+1 (TCH/FACCH) 26 57+ 1 (TCH/FACCH) 3Normal

burst

8.25

GuardTail

Information

Radio (Um) Interface Normal burst

49

• The “access” burst is a shortened burst used by the mobile station when it first access a cell.

• Its short length guarantees it will arrive within the correct time slot at the BTS receiver if the mobile station is no greater than 35km from the BTS.

» 68,25 bits * 3,s (1 bit) = 251s ~ (75Km / 2) = 37,5Km

Access

burst7 41 36 3

GuardTailTail

68,25

InformationTraining

Radio (Um) Interface Access burst

• Downstream: » A series of bits intended for different

users, who must select only the one intended for him and filter out the rest

• Upstream: » Individual bits from each of the users

arrive at the BTS» Strict timing of when the MS should

transmit is required to avoid collisions at the BTS

Time Division Multiple Access burst

Wrong Uplink Timing

BTS

SONOFON

M N

SONOFON

M N

SONOFON

M N

SONOFON

M N

51

15 Km 30 Km 1 Km

BTS

SONOFON

M N

SONOFON

M NSONOFON

M N

TS TS TS TS TS TS

TS

Timing advance

Accessburst

• The transmitted radio burst from BTS must travel whatever the distance is to the mobile station , and then transmitted burst from the mobile station (three burst later) must travel back the same distance. By measuring the time between the last bit in the access burst and the last bit in the TS the mobile then know the distance to the BTS and will adjust its Timing advance to compensate for the distance.

Timing advance (Access burst)

52

Mobile StationTiming advance Measurement Report

Message Type : 3Fh = Immediate assignment--- Channel description --- Time slot number : .....001 Channel type and TDMA offset : 01011... = SDCCH/8 + SACCH/C8 or CBCH (SACCH/8) Training Sequence Code : 011..... Hopping channel : ...0.... = Single RF channel spare : ....00.. Absolute RF Channel Number : 720 --- Request reference --- Random access information : 4 T1 : 7 T3 : 19 T2 : 7 --- Timing advance --- Timing advance value : ..000010 Spare : 00......

Timing advance = 2 The mobile station is 1kmfrom the BTS.

53

• The SCH burst is the synchronization channel burst which carries the the BSIC - Base Station Identity Code and the FN - Frame Number.

• As this is the first burst decoded by the mobile station it has an extended training sequence.

SCH

burst3 39 64 39 2

8.25

GuardTailTail

Information InformationTraining

SCH burst

54

• The FCCH burst is the frequency correction channel burst which is modulated with zero

FCCH

burst3 142 3

8.25

GuardTailTail

Information

FCCH burst

BTS

• Traffic channels (TCH):» Carrying Voice/data» Bm: 13 kbit/s user data» Lm: Half rate (6,5 kbit/s)

• Common control channels (CCCH):» Channels that all Mobile Stations can share

• Dedicated control channels (DCCH):» Control channels for individual Mobile Stations

Radio (Um) Interface Logical Channels

BTS

• Broadcast: BCCH» Carry system info intended for everybody, e.g.

Location Area Identity

• Paging: PCH» To request a specific Mobile User to react/reply, e.g.

when there is a call for him

• Random Access: RACH» Used by the Mobile Station to initiate contact with the

network, e.g. when trying to start a call

• Access Granted: AGCH» Used to respond to the RACH to inform that the

Mobile is now being allowed to access the network

Radio (Um) Interface Common Control Channels

BTS

• Stand-alone Dedicated : SDCCH» Used for settling practicalities such as roaming,

authentication, encryption and call control before allocating the traffic channel

• Slow Associated: SACCH» Associated to a TCH» Used together with the Traffic Channel to deal with

control and measurement of radio signals

• Fast Associated: FACCH» Large bandwidth version of the SACCH» Used for sudden control action such as handovers» Implemented a robbed bits in a TCH

Radio (Um) Interface Dedicated Control Channels

1 hyperframe = 2048 superframes (3h 28min 53s 760ms)

0 1 2 3 4 5 6 7

1 TDMA frame = 8 timeslots (4.615 ms)

0 1 2 3 4 5 62042

2043

2044

2045

2046

2047

0 1 2 3 4 5 6 718

19

20

21

22

23

24

25

1 superframe = 26 (51-frames) or 51 (26-frames) multiframes (6.12s)

0 1 2 3 4 545

46

47

48

49

506

0 1 2 3 4 5 6 718

19

20

21

22

23

24

25

1 (26-frame) multiframe = 26 TDMA frames (120ms)

1 (51-frame) multiframe = 51 TDMA frames (235.38 ms)

0 1 2 3 4 545

46

47

48

49

506

0 1 2 3 4 5 6 7

1 TDMA frame = 8 timeslots (4.615 ms)

Hyper-, Super- and Multiframes

Downlink and Uplink

Bm Bm Bm Bm Bm Bm Bm Bm Bm Bm Bm Bm SA Bm Bm Bm Bm Bm Bm Bm Bm Bm Bm Bm Bm -

0 1 2 3 4 5 6 7TDMA Frame (8 timeslots)

F S BCCH PCH/AGCH F S F S SDCCH/1 SDCCH/2 F S SDCCH/3 SDCCH/4 F S SACCH/1 SACCH/2 -PCH/AGCH PCH/AGCH

F S BCCH PCH/AGCH F S F S SDCCH/1 SDCCH/2 F S SDCCH/3 SDCCH/4 F S SACCH/3 SACCH/4 -PCH/AGCH PCH/AGCH

R R SACCH/1 SACCH/2 R R R R R R SDCCH/1 SDCCH/2R R SDCCH/3 SDCCH/4

R R SACCH/3 SACCH/4 R R R R R R SDCCH/1 SDCCH/2R R SDCCH/3 SDCCH/4

R R R R R R R R

R R R R R R R R

R R R R R R R R

R R R R R R R R

Cyklus: 1 TCH multiframe = 26 TDMA frames = 120 ms

4.615 ms

Downlink:Cyklus: 1 CCH multiframe = 51 TDMA frames = 235.38 ms

F = Frequency correction burst S = Synchronisation burst

R = RACH

R

R

Uplink:

TDMA Frame with 1 combined CCH and 7 TCH

R 5xR

F1 F2

F3F4

F5 F6

F4

Omni-directional BTS

3-directional BTS

Safety distance

BTS

BTS

BTS

BTS • To avoid interference between two cells using the same frequency, a safety distance of about 5 times the cell radius is required.

• A BTS may cover one cell (Omni-directional) or several cells (typical three directional cells).

• Each cell may be served by on or more TRXs depending on the required capacity.

• Note: each TRX controls one carrier with eight TS.

Cell Structure

61

BTS

• Mobile station in IDLE mode» Besides listening to the BCCH and the PCH the mobile

station is measuring for neighbour cells.

• Mobile station in active mode» In active mode the mobile station is using the time

between the down and uplink TS (three TS 2ms) to do neighbour cell measuring.

• The mobile station can measure up to 31 neighbour cells.

» In practice the mobile station measures up to 12 neighbour cells.

» Very often only three or four cells are measured.

Radio (Um) Interface Neighbour Cells

62

Mobile StationNeighbour Cells Measurement Report

--- MEAS REP --- --- MEAS RES ---NO NCELL M : 100b = 4 neighbour cell measurement result RXL NCEL 1 : 36 = minimum received signal level = -75 dBm to -74 dBm BCCH NCEL1 : 1 BSIC NCEL1 : 57 RXL NCEL 2 : 24 = minimum received signal level = -87 dBm to -86 dBm BCCH NCEL2 : 12 BSIC NCEL2 : 63 RXL NCEL 3 : 23 = minimum received signal level = -88 dBm to -87 dBm BCCH NCEL3 : 7 BSIC NCEL3 : 59 RXL NCEL 4 : 16 = minimum received signal level = -95 dBm to -94 dBm BCCH NCEL4 : 2 BSIC NCEL4 : 56 RXL NCEL 5 : 0 = minimum received signal level less than -110 dBm BCCH NCEL5 : 0 BSIC NCEL5 : 0 RXL NCEL 6 : 0 = minimum received signal level less than -110 dBm BCCH NCEL6 : 0 BSIC NCEL6 : 0

63

• IMSI » - International Mobile subscriber Number

• MSISDN » - Mobile Station ISDN Number

• Latest BCCH List» The latest BCCH used last time the mobile station was

connected to the network.

• Preferred Network List.• Forbidden Network List.• KI

» The Key identifier refers to an authentication key for the mobile subscriber.

(MS) Mobile Station SIM Card

BTS

A-bis

The System.

BaseStation

ControllerBSC

Public Switched

Telephone Network


MobileSwitching

CentreMSC

(PSTN)

StationSubsystem

(BSS)

A-Inter

A-bis

Um


BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Equip. IdRegister

EIR

Authen.CentreAUC


VLR


HLRMobile

SwitchingCentreMSC

MAPISUP / TUP

MAP

MAPMAP

ISUP / TUP

ISUP / TUP

MAP

66





DTAPCM

MM

RR

Sig. layer 2

Layer 1 (air)

Sig. layer 2

Sig. layer 1

MTP

SCCP

BSSMAPRR

(CM+MM)

MS BSC

MTP MTP

SCCP SCCP

CM

MM

BSSMAP TCAP

MAP

ISUP

MSC

Sig. layer 2

Layer 1 (air)

BTS

(CM)

(MM)

(RR)

(CM)

(MM)

(RR)

(CM)

(MM)


Sig. layer 1

(LAPD)

BTSMBTSMRR'



TS 1TS 31TS 5 - - - -

16 kbit/s traffic channels

64 kbit/s signalling channels

TS = 64 kbit/s timeslot

TS 2TS 0 TS 3 TS 4

• One 2Mbit/s line may cover several BTSs. This means that

normally several time slots in the same PCM frame are used as

signalling channels.» Three time slots divided into one 64Kbit/s signalling channel and eight

16Kbit/s traffic channels are sufficient to cover one TRX, giving up to 10 TRXs and 10 signaling channels per 2 Mbit/s.

» In practice , the configuration of the transmission lines depends on the actual network structure and the GSM equipment used.

A-bis (A) Layer 1 Structures

68

Flag01111110

Flag0111111016 Bits

CRCInformation

N - BitsControlAddress

16 Bits 8 or 16 Bits

SAPITEI

C/R EA 0EA 1

SAPI value

01166263

Related entity

Radio signallingReserved for packet mode /Q.931Reserved for packet mode /X.25Operation and maintenanceLayer 2 management

TEI value

0-6364-126

For fixed TRX addressesFor additional TRX addresses

User type

All others Reserved for future standardisation

Not used in GSM

Vendor-specific

• SAPI -Service Access Point Identifier• TEI - Terminal End Point Identifier • C/R -Command / Response bit• EA -Address Extension bit

» 0 = Extend 1 = Final

A-bis Layer 2 Structure

Flag

01111110

Flag

0111111016 Bits

CRCInformation

N - Bits

ControlAddress


8 7 6 5 4 3 2 1

0

1

1

0

1

S S

M M

OCTET 1 OCTET 2 + 3 OCTET 4 ( + 5 ) OCTET N

OCTET 4

OCTET 4

OCTET 4M M M

P

P/F

P/F

N ( R )

N ( R )

N ( S )

Control field bits ( modulo 8 )

I format

S format

U format

8 7 6 5 4 3 2 1

0

1

1

0

1

S S

M M

OCTET 4

OCTET 4

OCTET 4 M M M P/F

N ( R )

N ( R )

N ( S )

Control field bits ( modulo 128 )

I format

S format

U format

P5

X X X X

P/F 5

• N(S) - Transmitter send sequence number• N(R) - Transmitter receive sequence number• S -Supervisory function bit• M -Modifier function bit• P/F - Poll bit when issued as a command Poll

bit when issued as a command Final bit when

issued as a response• X - Reserved and set to 0

• I forma - Information transfer format» Used for information transfer

between layer 3 entities• S format - Supervisory format

» Used for control functions• U format - Unnumbered format

» Used for additional control functions and information transfer

A-bis Layer 2 Control Field

Flag

01111110

Flag

0111111016 Bits

CRCInformation

N - Bits

ControlAddress


Message Discriminator

12345678

Octet 1

Octet 2

Octet n

EM Message Type

Information Elements

8 7 6 5 4 3 12

Fixed Length Info. Element Format

Information Element Identifier

Length of Information Elements

Content of Information Elements

Variable Length Info. Element Format

T



T:EM

==

0: Non-transparent message Extension bit (future use)

Message Discriminator0146

8

Other

ReservedRadio Link ManagementDedicated Channel ManagementCommon Channel ManagementTransceiver ManagementReserved for Future Use

A-bis Layer 3 Structure I

Radio Link Layer Management messages DATA REQuest (Transfer of transparent messages in layer 2DATA INDication I-frames on radio interface)ERROR INDication (Indicates protocol error on radio link layer)ESTablish REQuest (Establishment of layer 2 link on radio interface)ESTablish CONFirmESTablish INDicationRELease REQuest (Release of layer 2 link on radio interface)RELease CONFirmRELease INDicationUNIT DATA REQuest (Transfer of transparent messages in layer 2 UI-UNIT DATA INDication frames on radio interface)

0000- - - -0001

0010 0011 0100 0101 0110 0111 1000 1001 1010 1011

Message typeCode

A-bis Messages, MD=1

Dedicated Channel Management messages:CHANnel ACTIVation (Activation of a radio channel)CHANnel ACTIVation ACKnowledgeCHANnel ACTIVation Negative ACKnowledgeCONNection FAILure INDication (Failure on radio connection)DEACTIVATE SACCH ENCRyption CoMmanD (Start of ciphering on radio interface)HANDOver DETection (MS handover to new BTS detected)MEASurement RESult (Radio signal measurement data from BTS/MS)MODE MODIFY REQuest(Change of channel mode, e.g. speech to data)MODE MODIFY ACKnowledgeMODE MODIFY Negative ACKnowledge

A-bis Messages, MD=4, part 1

Message typeCode

001- - - - - 00001 00010 00011 00100 00101 00110 00111 01000 01001 01010 01011

Dedicated Channel Management messages:PHYsical CONTEXT REQuest(Physical context is not specified by ETSI)PHYsical CONTEXT CONFirmRF CHANnel RELease (Release of radio channel)MS POWER CONTROL (Change of MS power level or control limits)BS POWER CONTROL (Change of TRX power level or control limits)PREPROCess CONFIGure(Conveys pre-processing parameters to BTS)PREPROCessed MEASurement RESult (From BTS)RF CHANnel RELease ACKnowledge

001- - - - - 01100 01101 01110 01111 10000 10001 10010 10011

A-bis Messages, MD=4, part 2

Message typeCode

Common Channel Management messages:BCCH INFOrmation (Indicates new information to be sent on BCCH)CCCH LOAD INDication (Indicates load on RACH and PCH)CHANnel REQuired (Reception of RR Channel Request message)DELETE INDication (Deletion of RR Immediate Assign message due to overload on AGCH)PAGING CoMmanD (Requests paging of MS)IMMediate ASSign CoMmanD (Setup of DCCH, answer to CHAN REQ)SMS BroadCast REQuest (Broadcast of SMS-message in cell)

A-bis Messages, MD = 6

Message typeCode

00010 - - -001 010 011 100 101 110 111

TRX Management messages:

RF RESource INDication (Interference level on idle radio channels)SACCH FILLing (New filling information to be used on SACCH)OVERLOAD (Control channel or TRX processor overload)ERROR REPORT (Detection of errored message)

00011 - - -

001 010 011 100

A-bis Messages, MD=8

Message typeCode

- Channel number (Indicates channel on radio interface)- Link identifier (Signalling link and SAPI used on radio interface)- Activation type (Intra-cell, inter-cell or additional assignment CHAN ACTIV)- BS power (BTS/TRX power level)- Channel identification (Description of channels allocated to MS)- Channel mode (Indicates discontinuous transmission and channel type, e.g.

speech)- Encryption information (Encryption algorithm and key)- Frame number (On radio interface, modulo 42432)- Handover reference (Identical to handover reference in RR information elements)- L1 information (MS power level and timing advance)- L3 information (Contains transparent RR, MM or CM message)- MS identity (IMSI or TMSI)- MS power (MS power level)- Paging group (Identifies MS paging group)- Paging load (Load on paging channel, PCH)- Physical context (Not specified)- Access delay (Delay of MS access burst at random access or handover)- RACH load (Load of random access channel, RACH)- Request reference (Random ref. in RR Channel Request message)

A-bis Information Elements, part 1

- Release mode (Normal release or local end release)- Resource information (Interference level for idle TRX channels)- RLM cause (Indicates protocol error on radio link layer)- Starting time (Expressed as Frame Number modulo 42432)- Timing advance (To be used by MS in subsequent communications)- Uplink measurements (Radio signal measurement results from TRX)- Cause (Reason for event/failure)- Measurement result num (For a radio channel; set to 0 at activation)- Message identifier (In ERROR REPORT message: Message type of errored message)- Message indicator (In ERROR REPORT message: Copy of errored message follows)- System info type (Type of RR System Information message)- MS power parameters (Limits set by BSC for BTS control of MS power)- BS power parameters (Limits set by BSC for BTS control of TRX power)- Preprocessing param. (For preproc. of radio measurement data in BTS)- Preprocessed measurements (Preprocessed radio measurement data)- Immediate assign info (Conveys complete RR Immediate Assign msg.)- SMSCB information (SMS-message to be broadcasted in a radio cell)

A-bis Information Elements, part 2

Bm + ACCHsLm + ACCHsSDCCH/4 + ACCHSDCCH/8 + ACCHBCCHUplink CCCH (RACH)Downlink CCCH (PCH + AGCH)

TDMA timeslot number

C5 C4 C3 C2 C1 0 0 0 0 1 0 0 0 1 T 0 0 1 T T 0 1 T T T 1 0 0 0 0 1 0 0 0 1 1 0 0 1 0

TN = 0 - 7

Element identifier

C5 C4 C3 C2 C1 TN

8 7 6 5 4 3 2 1• C5 - C1 (Channel Number )

describes the types of radio

channel used

• TN is the physical TDMA

time slot number that the

radio channel is using. It is

coded 0-7 in binary

representation

(There are 8 timeslots per

TRX)

Channel number information element

Flag01111110

Flag0111111016 Bits

CRCInformation

N - Bits

ControlAddress16 Bits 8 or 16 Bits

Message Discriminator

12345678

Octet 1

Octet 2

Octet n

EM Message Type

Channel Number

T

Message Discriminator := 1 (Radio Link Management)

L3 Information

ProtocolDiscriminator

0 Message Type

Information Elements

Protocol Discriminator3569

11

15

Call control, packet, suppl. serviceMobility managementRadio resources management

Short message services

Non call related suppl. servicesReserved for test procedures

Other Reserved for future use

T := 1 (transparent message)

TIFlag

TIValue

Transaction Identifier

TI-flag := 0 Message is sent from the TI-originating side

TI-flag := 1 Message is sent to the TI-originating side

TI-value := 0-7 ReferenceInformation Elements

• All CM and MM messages as well as most of the RR messages are transferred

across the A-bis interface inside a L3 information element in A-bis layer 3 Radio

Link management messages.

A-bis Layer 3 Structure II

80

BTS

BSCBTS

ENCRyption CoMmanD (Ciphering Mode Command [RR])

ESTablish INDication {MS establishes layer 2 on TCH}

DEACTIVATE SACCH {on BTS}

RF CHANnnel RELease {release of TCH}

DATA REQuest (Release [CM])

DATA INDication (Release Complete [CM])

RF CHANnel RELease {release of SDCCH}

DATA INDication (Assign Complete [RR]) {MS now ready on TCH}

DATA REQuest (Assign Command [RR]) {assigns TCH to MS}

CHANnel ACTIVation ACKnowledge {TCH activ}

DATA INDication (Ciphering Mode Complete [RR])

CHANnel ACTIVation {activation of TCH}

CHANnel REQuired {MS requests DCCH}

CHANnel ACTIVation {activation of SDCCH}

CHANnel ACTIVation ACKnowledge {SDCCH activ}

IMMediate ASSign CoMmanD {assigns SDCCH to MS}

ESTablish INDication (CM Service Request [MM]) {L2 up on SDCCH}

DATA INDication (Setup [CM])

DATA REQuest (Call Proceeding [CM])

DATA REQuest (Alerting [CM]) {call setup continues on TCH}

RELease INDication {MS releases layer 2 on SDCCH}

RF CHANnel RELease ACKnowledge {SDCCH released}

.

RELease INDicaton {MS releases layer 2 on TCH}

DATA INDication (Disconnect [CM]) {MS disconnects call}

DATA REQuest (Channel Release [RR]) {to MS, deactivation of TCH}

RF CHANnel RELease ACKnowledge {TCH released}

Active Call

DATA REQuest (Connect [CM])

DATA INDication (Connect Acknowledge [CM])

DATA REQuest (Authentication Request (RAND) [MM])

DATA INDication (Authentication Response (SRES) [MM])

A-bis signalling example

BTS

A-Interface.

The System.

BaseStation

ControllerBSC

Public Switched

Telephone Network


MobileSwitching

CentreMSC

(PSTN)

StationSubsystem

(BSS)

A-Inter

A-bis

Um


BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Equip. IdRegister

EIR

Authen.CentreAUC


VLR


HLRMobile

SwitchingCentreMSC

MAPISUP / TUP

MAP

MAPMAP

ISUP / TUP

ISUP / TUP

MAP

83





DTAPCM

MM

RR

Sig. layer 2

Layer 1 (air)

Sig. layer 2

Sig. layer 1

MTP

SCCP

BSSMAPRR

(CM+MM)

MS BSC

MTP MTP

SCCP SCCP

CM

MM

BSSMAP TCAP

MAP

ISUP

MSC

Sig. layer 2

Layer 1 (air)

BTS

(CM)

(MM)

(RR)

(CM)

(MM)

(RR)

(CM)

(MM)


Sig. layer 1

(LAPD)

BTSMBTSMRR'



84

BTS

• Based on System 7 MTP and SCCP• Uses Base Station Subsystem Application Part

(BSSAP)» BSS Management Application Part (BSSMAP)

• Radio Resource (RR) and BSC management• Uses SCCP connectionless service

» Direct Transfer Application Part (DTAP)• Transfer of Call Control (CM) messages• Transfer of Mobility Management (MM) messages• Uses SCCP connection-oriented service

A-Interface

85

Signalling System Number 7

MTP Level 3MTP Level 3

PhysicalPhysical

Data LinkData Link

NetworkNetwork

TransportTransport

SessionSession

Presentation Presentation

Application Application

OSI Layer SS7 Levels

7

6

5

4

3

2

1 MTP Level 1MTP Level 1


PhysicalPhysical MTP Level 1MTP Level 1

Data LinkData Link2 MTP Level 2MTP Level 2

MTP Level 3MTP Level 3NetworkNetwork3

ISUP

ISUP

SCCPSCCP

TCAPTCAPTUP

TUP

IN, MAPIN, MAP

ISUP

ISUP

TransportTransport

SessionSession



SCCPSCCP

• Level 4/User Parts

• SCCP

Basic format of MSU - SCCP message

LabelSIFF CKFIB

FSN FBIB

BSNLI > 2SIO

User DataUser Data MTCMTC SLSSLSOriginatingPoint Code

OriginatingPoint Code

DestinationPoint Code


N x 8 bits 8 bits 14 bits 14 bits4 bits

Mandatory fixed partMandatory fixed part

Mandatory variable partMandatory variable part

Optional partOptional part

Service Indicator0 0 1 1

Sub-serviceField

=== MTP === BSN : 66 BIB : 0....... FSN : 4 FIB : 1....... LI : 28 = MSU SPARE : 00...... SIO : 03h = SCCP

87

SCCP message format

• An SCCP Messages contains the following information.

» Routing label.» Messages type.» Mandatory fixed part.» Mandatory variable part.» Optional part.

Pointer to parameter P

Length Indicator of parameter M

Parameter M

Length Indicator of parameter P

Parameter P

Parameter name = X

Length Indicator of parameter X

Parameter X

Routing LabelMessage Type Code

Mandatory parameter A

Pointer to start of optional part

Mandatory parameter F

Pointer to parameter M

End of optional parameters

Parameter name = Z

Length Indicator of parameter Z

Parameter Z

User DataUser Data MTCMTC SLSSLSOriginatingPoint Code

OriginatingPoint Code



N x 8 bits 8 bits 14 bits 14 bits4 bits

Mandatory fixed partMandatory fixed part

Mandatory variable partMandatory variable part

Optional partOptional part

Signalling Connection Control Part (SCCP)• The SCCP itself has users called Subsystems (SS).

• The SCCP provides additional functions to the MTP for an OSI network service. » In particular, the non circuit related data transfer between signalling

end points is supported by the SCCP.

• Special protocol functions are provided by SCCP.» Segmentation.

• Allows messages of any great length to be transmitted.

» Addressing and Routing.

89

SCCP four classes of service

• Basic connectionless Class (Class 0).» Data are transparent independently of each other and may therefore be

delivered out of sequence. This corresponds to a pure connectionless network service.

• Sequenced connectionless Class (Class 1).» In protocol class 1 the features of class 0 are complemented by a sequence

control.

• Basic Connection-oriented Class (Class 2).» Bi-directional transfer of NSDUs is done by setting up a temporary or

permanent signalling connection. This corresponds to a simple connection- oriented network service.

• Flow control connection-oriented Class (Class 3).» In protocol class 3 the features of class 2 are complemented by the

inclusion of flow control.

90

Connection-oriented Data Transfer

Data Transfer Data Transfer

= Release Resource = Reserved Resource

CR

CC CC CR

RLC

RLSD RLSD

RLC

91

Connectionless Data Transfer

UDT

UDT

UDT

UDT

BTS

• UDT (Unitdata) Class 0 » Used by a SCCP wanting to send data in a

connectionless mode.

• DT1 (Data Form 1) Class 2 » A Data Form 1 message is sent by either end of a

signalling connection to pass transparently SCCP user data between two SCCP nodes.

• Note: Only point to point signalling route is used in at the A-inter phase, meaning that the MTP does not have to contain the functions related to the signalling transfer point (STP) and multiple signalling-route management.

SCCP Message Types, for A-Interface Class 0 and 2

CR Connection RequestCC Connection ConfirmCREF Connection RefusedRLSD ReleasedRLC Release CompleteDT1 Data Form 1DT2 Data Form 2AK Data AcknowledgementUDT UnitdataUDTS Unitdata ServiceED Expedited DataEA Expedited Data AcknowledgementRSR Reset RequestRSC Reset ConfirmERR Protocol Data Unit ErrorIT Inactivity Test

Protocol class

0

XX

XXXXXX

XX

XXXXX

XX

XXXXXX

Message type Code

0000 00010000 00100000 00110000 01000000 01010000 01100000 01110000 10000000 10010000 10100000 10110000 11000000 11010000 11100000 11110001 0000

1 2 3

XX

SCCP Message Types

94

• Message type code• Destination local reference• Source local reference• Called party address• Calling party address• Protocol class• Segmenting/reassembling• Release cause• Return cause• Error cause• Refusal cause• Data• End of optional parameters

BTS

SCCP Information elements

95

Short descriptions SCCP Message Types, Class 2 and 3.Part 1

•Connection Request (CR ). » A connection Request message is

sent by a calling SCCP to a called SCCP to request the setting up of a signalling connection between the two entities. The required characteristics of the signalling connection are carried in various parameter fields. On reception of a Connection Request message, the called SCCP initiates the setup of the signalling connection if possible.

•Connection Confirm (CC )» A connection confirm message is sent

by the called SCCP to indicate to the calling SCCP that it has performed the setup of the signalling connection. On reception of a Connection confirm message, the calling SCCP completes the setup of the signalling connection if possible.

•Connection Refused (CREF)» A Connection Refused message is sent

by the called SCCP or an intermediate node to indicate to the calling SCCP that the setup of the signalling connection has been refused.

96

Short descriptions SCCP Message Types, Class 2 and 3.Part 2•Released (RLSD).

» A released message is sent, in the forward or backward direction, to indicate that the sending SCCP wants to release a signalling connection and the associated resources at the sending SCCP have been brought into the disconnect pending condition. It also indicates that the receiving node should release the connection and any other associated resources as well.

•Release Complete (RLC).» A Release Complete message is sent

in response to the Released message indicating that the Released message has been received, and the appropriate procedures have been completed.

•Data Form1 (DT1). » A Data Form 1 message is sent by

either end of a signalling connection to pass transparently SCCP user data between two SCCP nodes.

97


•Data Form 2 (DT2). » A Data Form 2 message is sent

by either end of a signalling connection to pass transparently SCCP user data between two SCCP nodes and to acknowledge message flowing in the other direction.

•data acknowledgement (AK).» A Data Acknowledgement

message is used to control the window flow control mechanism, which has been selected for the data transfer phase.

•Expedited Data (ED).» An Expedited Data message functions

as a Data Form 2 message but includes the ability to bypass the flow control mechanism which has been selected for the data transfer phase. It may be sent by either end of the signalling connection.

•Expedited Data acknowledgement (EA). » An Expedited Data Acknowledgement

message is used to acknowledge an Expedited Data message.Every ED message has to be acknowledged by an EA message before another ED message may be sent.

98

Short descriptions SCCP Message Types, Class 2 and 3.Part 4•Reset Request (RSR).

» A Reset Request message is sent to indicate that the sending SCCP wants to initiate a reset procedure (re-initialization of sequence numbers) with the receiving SCCP.

•Reset Confirm (RSC).» A Reset Confirm message is sent

in response to a Reset Request message to indicate that Reset Request has been received and the appropriate procedure has been completed.

•Protocol Data Unit Error (ERR).» A Protocol Data Unit Error message is

sent on detection of any protocol errors.

•Inactivity Test (IT). » An Inactivity Test message may be

sent periodically by either end of a signalling connection to check if this signalling connection is active at both ends, and to audit the consistency of connection data at both ends.

•Extended Unitdata (XUDT).» An Extended Unitdata message is used

by the SCCP wanting to send data along with optional parameters in a connectionless mode. It can also be used by a SCCP to send data without optional parameters.

99


•Extended Unitdata Service (XUDTS). » An Extended Unitdata Service

message is used to indicate to the originating SCCP that a XUDT with optional parameters cannot be delivered to its destination. A XUDTS message is sent only when the option field in the XUDT message is set to "return on error".

•Long Unitdata (LUDT).» A Long Unitdata message is used by

the SCCP to send data (along with optional parameters) in a connection mode, when MTP-3b capabilities are present. It allows sending of NSDU sizes up to 3952 octets without segmentation.

•Long Unitdata Service (LUDTS).» A long Unitdata Service message is

used to indicate to the originating SCCP that a LUDT cannot be delivered to its destination. A LUDTS message is sent only when the return option in the LUDT is set.

BTS

A-InterfaceBSSAP

101

• ETSI has specified an SS7 Base Station Subsystem Application Part (BSSAP) as the user of the SCCP/MTP transport service.

» SCCP subsystem number for BSSAP is FEh.

BTS

Base Station Subsystem Application Part (BSSAP)

SCCP Information elements

SCCP HeaderSSN FEh: BSSAP

Discriminator0 0 0 0 0 0 0 0

1 1

DLCI Data Link Connection Identifier

Discriminator0 0 0 0 0 0 0 1

OCTET

DLCI 2

3 2Length Indicator 1

n nLayer 3 Messages Octet

Length Indicator 1

Layer 3 Um Interface Octet

Bit no.: 8 7 6 5 4 3 2 1 C2 C1 0 0 0 S3 S2 S1

C2 C1 identifies signaling-radio channel(00: SDCCH/FACCH, 01: SACCH)

S3-S1 is the SAPI on the radio interface

BSSMAP DTAP

LabelSIFF CKFIB

FSN FBIB

BSNLI > 2SIOx3h

BTS

A-InterfaceBSSMAP

104

BTS

BSSMAP Format

Disc. 0 = BSSMAP

Length indicator

BSSMAP message type

BSSMAP messageInformation Element Identifier







OCTET 1

OCTET 2

OCTET n

BSSMAP Messages, part 1

Assignment messages: (Setup of traffic channels)- Assignment request- Assignment complete- Assignment failure

Release messages:- Clear command (Release of traffic channels)- Clear complete- Clear request- SAPI "n" clear command (Control of layer 2 links with SAPI not equal- SAPI "n" clear complete to 0 on the radio interface)- SAPI "n" reject

0000- - - -0001

0010 0011

0010- - - - 0000 0001 0010 0011 0100 0101

Message typeCode


Handover messages:- Handover request (To BSC: Request for handover to that BSC)- Handover required (To MSC: Inter-BSC/MSC handover required)- Handover request ack (To MSC: Acknowledge of Handover request)- Handover command (To BSC: Contains the new radio channel/BTS to which the MS should switch)- Handover complete (To MSC: Commanded handover complete)- Handover failure (To MSC: Commanded handover unsuccessful)- Handover performed (To MSC: BSC has performed intern. handover)- Handover candidate (To BSC: MSC requests list of MS that could enquire be handed over to another cell)- Handover candidate (To MSC: Answer to Handover candidate response enquire)- Handover required reject (To BSC: Required handover unsuccessful)- Handover detect (To MSC: Commanded handover successful)

0001- - - -0000

0001 0010 0011

0100 0110 0111 1000

1001

1010 1011

Message typeCode


General messages:- Reset (Initialisation of BSS or MSC due to failure)- Reset Acknowledge- Overload (Processor or CCCH overload)- Trace invocation (Start production of trace record)- Reset Circuit (Initialisation of single circuit due to failure)- Reset Circuit acknowledge

Terrestrial resource messages:- Block (Management of circuits/time slots- Blocking acknowledge between MSC and BTS) - Unblock- Unblocking acknowledge

0011- - - - 0000 0001 0010 0011 0100 0101

0100- - - - 0000 0001 0010 0011

Message typeCode


Radio resource messages:- Resource request (Available radio channels in the BSS cells)- Resource indication- Paging (Paging of MS)- Cipher mode command (Commands start of cyphering)- Classmark update (Change of MS power class)- Cipher mode complete (Ciphering is successfully initiated)- Queuing indication (Indicates delay in assignment of traffic channel)- Complete layer 3 (Contains first message received from MS; information sets up SCCP-connection at A-interface)

0101- - - -0000 0001 0010 0011 0100 0101 0110

0111

Message typeCode

- Circuit identity code (Traffic channel on A-interface)- Radio channel identity (Description of channels allocated to MS)- Resource available (Available radio channels in a cell)- Cause (Reason for event/failure)- Cell identifier (Identity of radio cell)- Priority (Indicates the priority of a request)- Layer 3 header (Protocol discriminator and transaction identifier information to be used on the radio interface)- IMSI- TMSI- Encryption information (Encryption algorithm and key)- Channel type (Speech, data incl. speed or signalling; full or half rate)- Periodicity (Defines periodicity of a particularly procedure)- Number of MSs (No. of handover candidates to be sent to MSC)- Current radio environment (Measurement data on radio cells for handover)- Environment of BS “n” (Data in order of priority on the n preferred new cells

for handover)

BSSMAP Information Elements, part 1

BSSMAP Information Elements, part 2

- Classmark information type 2 (MS power class + SMS capability)- Interference band to be used (Indicates acceptable interference level)- RR Cause (Reason for RR release)- Trace number (Reference number for a trace record)- Layer 3 information (Contains transparent RR, MM or CM message)- DLCI (Indicates the layer 2 link to be used on the radio

interface)- Downlink DTX flag (Disabling of discontinuous transmission)- Cell identifier list (Identifies the cells within a BSS)- Response request (Requests a response on a Handover required

messages)- Resource indication method (How the BSS shall transfer resource info)- Classmark information type 1 (MS power class)

BTS

A-InterfaceDTAP

112

• The Direct Transfer Application sub-Part (DTAP) is used to transfer call control and mobility management messages to and from the MS;

» The layer-3 information in these messages is not interpreted by the BSS.

BTS

Direct Transfer Application sub-Part (DTAP)

113

BTS

Disc. 1 = DTAP

Length indicator

BSSMAP message type

BSSMAP messageInformation Element Identifier







OCTET 1

OCTET 2

OCTET n

DTAP Format

114

BTS

• Layer 3 of the DTAP messages has the same format as BSSMAP messages.

• The DTAP messages and information elements are identical to the the transparent MM and CM listed in the A-bis section.

DTAP messages and elements

115

BTS

MSCBSC

SCCP CR (BSSMAP Comp layer 3 info (CM Service Request

SCCP CC (BSSMAP Cipher mode command)

SCCP DT1 (BSSMAP Cipher mode complete)

SCCP DT1 (DTAP (Setup [CM]))

SCCP DT1 (DTAP (Call Proceeding [CM]))

SCCP DT1 (BSSMAP Assignment request)

SCCP DT1 (BSSMAP Assignment complete)

SCCP DT1 (DTAP (Alerting [CM]))

SCCP DT1 (DTAP (Connect [CM]))

SCCP RLC

SCCP DT1 (DTAP (Disconnect [CM]))

SCCP DT1 (DTAP (Release [CM]))

SCCP DT1 (DTAP (Release Complete [CM]))

SCCP DT1 (BSSMAP Clear command)

SCCP DT1 (BSSMAP Clear complete)

SCCP RLSD

.

.

.

.

..

.

.

.Active call

A-Interface signalling example

[MM]))

BTS

Inter-MSC SignallingMAP

BaseStation

ControllerBSC

Public Switched

Telephone Network


MobileSwitching

CentreMSC

(PSTN)

StationSubsystem

(BSS)

A-Inter

A-bis

Um


BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Base Transceiver

Station BTS

Equip. IdRegister

EIR

Authen.CentreAUC


VLR


HLRMobile

SwitchingCentreMSC

MAPISUP / TUP

MAP

MAPMAP

ISUP / TUP

ISUP / TUP

MAP

The System.

118





DTAPCM

MM

RR

Sig. layer 2

Layer 1 (air)

Sig. layer 2

Sig. layer 1

MTP

SCCP

BSSMAPRR

(CM+MM)

MS BSC

MTP MTP

SCCP SCCP

CM

MM

BSSMAP TCAP

MAP

I

SUP

MSC

Sig. layer 2

Layer 1 (air)

BTS

(CM)

(MM)

(RR)

(CM)

(MM)

(RR)

(CM)

(MM)


Sig. layer 1

(LAPD)

BTSMBTSMRR'



119



PhysicalPhysical

Data LinkData Link

NetworkNetwork

TransportTransport

SessionSession




7

6

5

4

3

2






ISUP

ISUP

SCCPSCCP

TCAPTCAPTUP

TUP

IN, MAPIN, MAP

ISUP

ISUP

TransportTransport

SessionSession



SCCPSCCP

• Level 4/User Parts

• SCCP

Signalling Connection Control Part (SCCP)• The SCCP itself has users called Subsystems (SS).

• The SCCP provides additional functions to the MTP for an OSI network service. » In particular, the non circuit related data transfer between signalling

end points is supported by the SCCP.

• Special protocol functions are provided by SCCP.» Segmentation.

• Allows messages of any great length to be transmitted.

» Addressing and Routing.• See next slide.

SCCP Addressing and Routing.

• The SCCP provides its own routing function. » As address parameter the SCCP can use.

• DPC and SSN› Routing based on MTP DPC and SSN in Global title (GT).

• Global title (GT)› Routing based on global title

• E.g. Routing based on MTP DPC and SSN in Global title.Link Set Link Set A

Link Set B

DPC 1DPC 2DPC 3

First Route Second Route

Link set A

Link set B

Link set B

Link set B Link set A

Link set A

MTP DPC = 2

SCCP Addressing and Routing.

» When global title (GT) is used different information cant be available.• Translation type, numbering plan, encoding scheme, nature of address,

Address and Point Code.

• If for example , a destination number of the ISDN or IMSI numbering plan is used, then the SCCP defines the DPC on the basis of a “GT Translation Table” that is available within the signalling point.

Link Set Link Set A

Link Set B

DPC 1DPC 2DPC 3

First Route Second Route

Link set A

Link set B

Link set B

Link set B Link set A

Link set A

GT = 3

DPC 2

DPC 1

DPC 3

GT 3

GT 2

GT 1

123

SCCP Subsystem number (SSN)

• SSN 01h = SCCP Management message (SCMG).

• The MAP layer consist several of Application Service Elements, so more than one SSN are alocated.

» The SSN for MAP are:• 05h = MAP

• 06h = HLR

• 07h = VLR

• 08h = MSC

• 09h = EIR

• 0Ah = AUC

• Within a INAP node, it is the choice of the network operator to which SSN(s) he will assigned to INAP.

» Any addressing scheme supported and not reserved by the SCCP may be used.

• 91h = GMLC• 93h = gsmSCF• 94h = SIWF• 95h = SGSN• 96h = GGSN

124

SCCP Management message (SCMG)

• The SCCP management function (SCGM). » SCMG are taking care of handling of errors and other problems on

subsystems level.• Subsystem-Prohibited.• Subsystem-Status-Test.• Subsystem-Out-of-Service.• Subsystem Congested.

» The SCMG messages (SSA, SSP, SST, SOR, SOG) contain mandatory fixed parameters. These parameters are defined in the data field of the UDT and XUDT message.

125

SCCP four classes of service

• Basic connectionless Class (Class 0).» Data are transparent independently of each other and may therefore be

delivered out of sequence. This corresponds to a pure connectionless network service.

• Sequenced connectionless Class (Class 1).» In protocol class 1 the features of class 0 are complemented by a sequence

control.

• Basic Connection-oriented Class (Class 2).» Bi-directional transfer of NSDUs is done by setting up a temporary or

permanent signalling connection. This corresponds to a simple connection- oriented network service.

• Flow control connection-oriented Class (Class 3).» In protocol class 3 the features of class 2 are complemented by the

inclusion of flow control.

126

Short descriptions SCCP Message Types, Class 0 and 1.

•Unitdata (UDT). » Used by a SCCP wanting to send

data in a connectionless mode.

•Unitdata Service (UDTS). » A Unitdata Service message is

used to indicate to the originating SCCP that a UDT it sent cannot be delivered to its destination. A UDTS message is sent only when the option field in that UDT is set to "return on error".

•TCAP uses the connectionless protocol classes of SCCP only.» In connection with INAP the protocol class 1 is used exclusively.» In connection with MAP the protocol class 0 and 1 is used.

127

Connectionless Data Transfer

UDT

UDT

UDT

UDT

128


Level 4/User Parts

TCAP


PhysicalPhysical

Data LinkData Link

NetworkNetwork

TransportTransport

SessionSession




7

6

5

4

3

2






ISUP

ISUP

SCCPSCCP

TCAPTCAPTUP

TUP

INAP, MAPINAP, MAP

ISUP

ISUP

TransportTransport

SessionSession



SCCPSCCP

TCAPTCAP

Transaction Capabilities Application Part (TCAP)

• Definition» The overall objective of TCAP is to provide means for the transfer of

information between nodes, and to provide generic services to applications, while being independent of any of these.

» Transaction Capabilities in the SS7 protocol are functions that control non-circuit-related information transfer between two or more signalling nodes via a signalling network.

• For use between» Exchanges

» An exchange and a network service centre

» Network service centres

130

TCAP / SCCP classes

• ITU-T has only specified the use of SCCP class 0 and 1 (connectionless transfer) This means that the intermediate service part (ISP) is empty/not needed because no layer 4, 5 and 6 functions are required for control of SCCP.

131

The ASN.1 notation

• TCAP is build on ANS.1 abstract notation.

• The ASN.1, abstract syntax notation one, is a formal language for defining high level protocol information by means of user defined data types. It was standardized by CCITT in 1984 but is now also adopted by ISO in conjunction with BER as part of OSI applications. ASN.1`s prime use has been in the definition of application protocols, but is also used in definition of presentation protocols. The grammar of the syntax is the Backus-Naur Form (BNF) as used in other programming languages.

TCAP Applications

• Mobile services (MAP)» e.g.

• Location updating/roaming• Non-call related supplementary services• Charging information

• Supplementary services (INAP/CAMEL)» e.g.

• Number conversion (800, VPN).• Credit check.• Prepaid/calling card• Prepaid roaming.

• Operation and Maintenance (OMAP)

Messages Structure when TCAP is used.

• TCAP is an user of SCCP.

MAXIMUM 272 OCTETS

SIFSIFFF CKCKFIB

FIB FSNFSN FF

BIB

BIB BSNBSNLI > 2LI > 2SIOSIO

Optional partOptional part Mandatory variable part

Mandatory variable part

Mandatory fixed part

Mandatory fixed part MTCMTC SLSSLS OPCOPC DPCDPC

Messages Component

Messages Component

Messages Component Length

Messages Component Length

Transaction information element

Transaction information element

MessagesLength

MessagesLength

Messages Type Tag

Messages Type Tag

Higher layer (INAP, CAMEL or MAP)Higher layer (INAP, CAMEL or MAP)

The messages type (MTC)

is always UDT or UDTS, if the

higher layer is MAP CAMEL or INAP

MTP

SCCP

TCAP

TCAP sub-layers

• TCAP is divided into two sub-layers

• Transaction sub-layer» Is a simple transport service for the component sub-layer

(comparable to an “envelope” containing a group of components to be processed at the remote end)

• Component sub-layer» Deals with individual actions or data, called components

(e.g. one mobile phone)

TCAP Message types

• Transaction Sub-layer» Unidirectional (used when no need to establish a transaction)

» Begin (initiate transaction)

» End (terminate transaction)

» Continue (continue transaction)

» Abort (terminate transaction in abnormal situation)

• Component Sub-layer» Invoke (request operation to be performed at remote end)

» Return Result(last) (successful completion of operation, contains last/only result)

» Return Error (reports unsuccessful completion of operation)

» Reject (incorrect component received at remote end)

» Return Result (contains part of result of operation)

136

TCAP Structure

Message type tagTotal message length

Transaction portion information element

Component portion tag

Component type tagComponent length

Component portion information element

Component

Abort CauseDialogue PortionComponent Portion

Destination Transaction IdentifierOriginating Transaction Identifier

TagLength

Contents

TagLength

Contents

Invoke ID Linked IDOperation CodeSequenceError CodeProblem Code

- Unidirectional- Begin- End - Continue- Abort

- Unidirectional- Begin- End - Continue- Abort

- Invoke- Return Result (Last) Return Result - (Not Last)Return Error -Reject -

Invoke - Return Result - (Last)- Return Result (Not Last)- Return Error- Reject

• The table shows where ORIG and DEST TID is used.


• The application on higher layer (MAP and INAP) are using the ORIG and DEST TID within the “Transaction portion info element” to differ between the transactions send to and from the application.

» ORIG TID (Originating Transaction Identifier).• The originating transaction ID is assigned by the node sending a message, and is

used to identify the transaction at that end.

» DEST TID (Destination Transaction Identifier).• The destination transaction ID identifies the transaction at the receiving end.

Unidirectional

Begin

Continue

End

Transaction

Abort

ORIG ID DEST ID

YES NO

YES YES

YESNO

NONO

YESNO


• The application on higher layer (MAP, CAMEL and INAP) are using the Invoke ID and Linked ID within the “Component portion info element” to correlate the question and answer within transactions send to and from the application. » Invoke ID

• An Invoke ID is used as a reference number to identify uniquely an operation. It is present in the Invoke component and in any reply to the Invoke (Return Result, Return Error or Reject), enabling the reply to be correlated with the invoke.

» Linked ID• A Linked ID is included in an invoke component by a node when it

responds to an operation invocation with a linked operation invocation. The node receiving the Linked ID uses it for correlation purposes, in the same way that it uses the invoke ID in Return Result, Return Error and Reject components.

139

TCAP Signaling Example.

BEGIN ORIG TID: 75 INVOKE INVOKE ID: 0

CONTINUE ORIG TID: 18 DEST TID: 75 INVOKE INVOKE ID: 0

CONTINUE ORIG TID: 75 DEST TID: 18 RET RES L INVOKE ID: 0





END DEST TID: 75 INVOKE INVOKE ID: 0

Application Begin

Data send

Data received

Data send

Data send

Data received

Data received

Application End

140

BTS


Level 4/User Parts

MAP


PhysicalPhysical

Data LinkData Link

NetworkNetwork

TransportTransport

SessionSession




7

6

5

4

3

2






ISUP

ISUP

SCCPSCCP

TCAPTCAPTUP

TUP

INAP, MAPINAP, MAP

ISUP

ISUP

TransportTransport

SessionSession



SCCPSCCP

TCAPTCAP

MAPMAP

BTS

• MAP = Mobile Application Part

• Users: MSC, HLR, VLR, EIR

• Applications:» Location updating/roaming» Incoming call routing information (MSRN)» Subscriber service information» Non-call related supplementary services» Short message service delivery» MS equipment identity (IMEI)» Charging information

MAP

Called partyaddress

Messagetype

Calling partyaddress

Protocolclass 0, 1

Pointers

MAPInfo.

TCAP part Sub-system Number(part of the address field)

SCCP User Data

Format of SCCP message for MAP information

LabelSIFF CKFIB

FSN FBIB

BSNLI > 2SIOx3h

143

MAP information in TCAP

Message type tagTotal message length


Component portion tag

Component type tagComponent length


Component

TagLength

Contents

TagLengthCode

Parameter

• The inter-MSC interface are:» The MSC-VLR interface. » The MSC-HLR interface.» The HLR-VLR interface.» The MSC-MSC interface.» The MSC-EIR interface.» The VLR-VLR interface.» The MSC-ISDN/telephone network interface.

BTS

Inter-MSC Signalling

145

BTS

OperationValue

1 Update location area2 Update location3 Cancel location4 Provide roaming number5 Detach IMSI6 Attach IMSI7 Insert subscriber data8 Delete subscriber data9 Send parameters10 Register SS11 Erase SS12 Activate SS13 Deactivate SS14 Interrogate SS15 Invoke SS16 Forward SS notification17 Register password18 Get password19 Process unstructured data

MAP Operations Part 1

146

BTS

20 Send info for incoming call21 Send info for outgoing call22 Send routing information23 Complete call24 Connect to following address25 Process call waiting26 Page27 Search for mobile subscriber28 Perform handover29 Send end signal30 Perform subsequent handover31 Allocate handover number32 Send handover report33 Process access signalling34 Forward access signalling35 Note internal handover36 Register charging information37 Reset38 Forward check SS indication


OperationValue

147

BTS

39 Authenticate40 Provide IMSI41 Forward new TMSI42 Set ciphering mode43 Check IMEI45 Send routing info for SM46 Forward short message47 Set message-waiting data48 Note MS present49 Alert service centre50 Activate trace mode51 Deactivate trace mode52 Trace subscriber activity53 Process access request54 Begin subscriber activity


OperationValue

148

BTS

Home sideVisited side

INVOKE (Update Location)

BEGIN

INVOKE (Insert Subscriber Data)

CONTINUE

RETURN RESULT

CONTINUE

(Update Location)

END

(Insert Subscriber Data)

RETURN RESULT

MAP - signalling Location Updating example

BTS

GSMSignalling procedures

BTS

• Call Management» Ordinary Call Control (as usual)

• Mobility Management » Location Updating (Roaming)» Authentication

• Radio Resource Management» Paging» Network Access» Encryption» Radio Signal Control» Radio Signal Measurements» Handover

Special signalling procedures for GSM

Area 1

Area 2

BTS BTS

BTS BTS

•An MM procedure•Reasons for roaming:

» MS has detected that it has entered into a new location area (by listening to Broadcast system info)

•Types of roaming:» Inside same VLR area

• The HLR does not need to know

» Another VLR area• In this case the

HLR is informed

MSC

VLR

MSC

VLR

SONOFON

M N

Location Updating (Roaming)

MSBTS

BSC

MSC VLR 1 VLR 2 HLR

Location Update Request (old LAI, TMSI) [MM]Update Location Area (old LAI, new LAI, TMSI)

Send Parameters (old LAI, TMSI)

Send Parameters Result (IMSI)

Update Location (IMSI, MSRN, VLR no)

Cancel Loc (IMSI, VLR' no)

Cancel Location Ack

Update Location Ack

Insert Subscriber Data (IMSI, service inf)

Subscriber Data Acknowledge

Update Location Area Ack

Forward New TMSI (TMSI)Location Update Accept (new LAI, TMSI) [MM]

TMSI Reallocation Complete [MM]TMSI Ack

Channel Release [RR] Clear Command [RR]

Um/A-bis/A signalling

MAP signalling

Location Updating (Roaming)

• A RR procedure• The Handover process is the situation where a Mobile Station changes from being served by one Antenna to another • Handovers take place during a call• Handover are done automatically• Crossing the boundary of two adjacent cells is the typical example of a Handover

Handovers.

BTS BTS

• Major types of handovers

» Intra BSC» Inter BSC» Inter MSC

• Purpose of handover» Poor quality

connection• Avoid loosing

contactto the mobile station

» Fault in the MS or BTS/BSC

» Network management

Intra BSC

Inter BSC

Inter MSC

BSC

MSC - A

MSC - B

BSC

BSC

BTS

BTS

BTSBTSSONOFON

M N

SONOFON

M N

SONOFON

M N

TRAU Signaling

Send handover report


MAP signalling

ISUP/TUP signalling

MSBTS

BSC-A

MSC-A

BSC-B

MSC-B

VLR-B

Handover Required (new BTS) [RR]Perform handover (new BTS, Ch type)

Handover Request (new BTS)

Handover Req Ack (Radio Ch)Allocate handover number

(MSRN)

(MSRN)

Radio Ch Ack (Radio Ch, MSRN)

IAM (MSRN)

ACMHandover Command (Radio CH) [RR]

Handover Complete [RR]

Clear Command[RR]

Clear Complete[RR]

Send End Signal

Answer

Measurement Result [RR]

Handover, example

BTS

• A CM procedure• Distinguish two types

» Mobile Terminating Call • i.e. a call from the fixed network to a Mobile

Station» Mobile Originating Call

• i.e. a call from a Mobile Station to the fixed network

Call Setup

BTS

• Problems and answers » Where in the world is the Mobile Station

• Look it up in the HLR • (The HLR may have to ask the VLR)

» How to Make the Mobile Station Aware that a call is waiting

• Page it in the cell where it is located » What does the MS do when being paged ?

• Asks for a Radio channel• Tells the system that it is ready

• Now the usual setup flow follows

Mobile Terminating Call

IAM (MSISDN, service)

BTS BSCMSC VLR HLR

GMSC

ISDN

Send Routing Info (MSISDN)

Roaming Number (MSRN)Routing Info (MSRN)

Provide Roaming Number (IMSI)

IAM (MSRN, service)

Send Info Incoming Call (MSRN, service)

Page (IMSI, TMSI, LAI)Paging Request (TMSI) [RR]

Paging Response (TMSI) [RR]Page Result

Complete Call (service)

Channel Request [RR]Immediate Assign [RR]

SETUP (service) [CM]

Call Confirm [CM]

Assign Command [RR] Assign Req [RR]

Assign Complete [RR]Alerting [CM] ACMConnect [CM] ANM

Connect Ack [CM]Complete Call Result

MS


MAP signalling

ISUP/TUP signalling

Incoming Call

BTS

• Problems and Answers» How the mobile gets in contact with the network

• Switch the MS on• Request a channel• Tell the network what kind of service is wanted

» How does the network respond• Verifies the Mobile identity (authentication)• Assigns a traffic channel

• And then everything proceed as usual

Mobile Originating Call

BTS BSC MSC VLR ISDN

Immediate Assign [RR]

CM Service Req (IMSI, transact) [MM] Process Access Request

Authenticate (RAND)Authentication Request (RAND) [MM]

Authentication Response (SRES) [MM] Authentication Response (SRES)

Set ciphering mode (key)

Ciphering Mode Command (key) [RR]

Ciphering Mode Complete [RR]

Access Request Ack

SETUP (service, called number) [CM] Send info for o/g (service, called number)

Complete callCall Proceeding [CM]

Assign Request [RR]Assign Command [RR]

Assign Complete [RR]IAM

ACM

ANM

Alerting [CM]

Connect [CM]

Connect Ack [CM]

CM copy [MM]

MSChannel Request/Required [RR]


MAP signalling

ISUP/TUP signalling

Outgoing Call from MS

161


Level 4/User Parts

INAP


PhysicalPhysical

Data LinkData Link

NetworkNetwork

TransportTransport

SessionSession




7

6

5

4

3

2






ISUP

ISUP

SCCPSCCP

TCAPTCAPTUP

TUP

INAP, MAPINAP, MAP

ISUP

ISUP

TransportTransport

SessionSession



SCCPSCCP

TCAPTCAP

INAPINAP

CS1 / IN / INAP

• Abbreviations.» CS1 = Intelligent Network Capability Set 1.» IN = Intelligent Network.» INAP = Core Intelligent Network Application Part

• The intelligent Network (IN) is a control architecture for telecommunication network service.» The goal of the IN service control architecture is to provide a

framework, which allows the Network Operator to create , to control and to manage services more efficiently, economically and rapidly as the present network architecture allows.

CS1 / IN / INAP

• INAP supports interactions between the following three Functions » - Service Switching Function (SSF).» - Service Control Function (SCF).» - Specialized Resource Function (SRF).

• INAP provides a set of predefined Messages and parameters that can be used in the intelligent Network predefined functions, however Extension Fields is allowed.» Those parameter are operator specific, and therefore not known by the

MPA.

• INAP is not like the MAP where all transactions shall be ended by TC_END. In INAP a TC_END shall no longer be maintained if both part involved in the transaction knows that no more data is required.» Those cases are called pre-arranged end. The MPA doesn't know

those cases, and therefore not able to to make a correct sequence recording.

164

Short descriptions INAP Operations Part 1

•Initial DP. Direction: SSF -> SCF» This operation is used after a TDP to indicate request for service.

•Assist Request Instructions. Direction: SSF -> SCF or SRF -> SCF» This operation is used when there is an assist or a hand-off procedure and may be

sent by the SSF or SRF to the SCF. This operation is sent by the SSF or SRF to the SCF, when the initiating SSF has set up a connection to the SRF or to the assisting SSF as a result of receiving an Establish Temporary Connection or Connect (in case of hand-off) operation from the SCF.

•Establish Temporary Connection. Direction: SCF -> SSF» This operation is used to create a connection to a resource for a limited period of

time (e.g. to play an announcement, to collect user information); it implies the use of the assist procedure.

•Disconnect Forward Connection. Direction: SCF -> SSF» This operation is used to disconnect a forward temporary connection or a

connection to a resource.

165


•Connect To Resource. Direction: SCF -> SSF» This operation is used to connect a call from the SSP to the PE containing the SRF.

•Connect. Direction: SCF -> SSF» This operation is used to request the SSF to perform the call processing actions to

route or forward a call to a specified destination. To do so, the SSF may or may not use destination information from the calling party (e.g., dialed digits) and existing call setup information (e.g., route index to a list of trunk groups), depending on the information provided by the SCF.

•Release Call. Direction: SCF -> SSF» This operation is used to tear down an existing call at any phase of the call for all

parties involved in the call.

•Request Report BCSM Event. Direction: SCF -> SSF» This operation is used to request the SSF to monitor for a call-related event (e.g.,

BCSM events such as busy or no answer), then send a notification back to the SCF when the event is detected.

166


•Event Report BCSM. Direction: SSF -> SCF» This operation is used to notify the SCF of a call-related event (e.g., BCSM events

such as busy or no answer) previously requested by the SCF in a Request Report BCSM Event operation.

•Request Notification Charging Event. Direction: SCF -> SSF» This operation is used by the SCF to instruct the SSF on how to manage the

charging events which are received from other FEs and not under control of the service logic instance. The operation supports the capabilities to cope with the interactions concerning charging.

•Event Notification Charging. Direction: SSF -> SCF» This operation is used by the SSF to report to the SCF the occurrence of a specific

charging event type as previously requested by the SCF in a Request Notification Charging Event operation. The operation supports the capabilities to cope with the interactions concerning charging.

167


•Collect Information. Direction: SCF -> SSF» This operation is used to request the SSF to perform the originating basic call

processing actions to prompt a calling party for destination information, then collect destination information according to a specified numbering plan (e.g., for virtual private networks).

•Continue. Direction: SCF -> SSF» This operation is used to request the SSF to proceed with call processing at the DP

at which it previously suspended call processing to await SCF instructions (i.e., proceed to the next point in call in the BCSM). The SSF continues call processing without substituting new data from SCF.

•Initiate Call Attempt. Direction: SCF -> SSF» This operation is used to request the SSF to create a new call to one call party using

address information provided by the SCF.

•Reset Timer. Direction: SCF -> SSF» This operation is used to request the SSF to refresh an application timer in the SSF.

168


•Furnish Charging Information. Direction: SCF -> SSF» This operation is used to request the SSF to generate, register a call record or to

include some information in the default call record. The registered call record is intended for off-line charging of the call.

•Apply Charging. Direction: SCF -> SSF» This operation is used for interacting from the SCF with the SSF charging

mechanisms. The Apply Charging Report operation provides the feedback from the SSF to the SCF.

•Apply Charging Report. Direction: SSF -> SCF» This operation is used by the SSF to report to the SCF the occurrence of a specific

charging event as requested by the SCF using the Apply Charging operation.

•Call Gap. Direction: SCF -> SSF» This operation is used to request the SSF to reduce the rate at which specific

service requests.

169


•Activate Service Filtering. Direction: SCF -> SSF» When receiving this operation, the SSF handles calls to destination in a specified

manner without sending queries for every detected call. It is used for example for providing Tele-voting or mass calling services. Simple registration functionality (counters) and announcement control may be located at the SSF. The operation initializes the specified counters in the SSF.

•Service Filtering Response. Direction: SSF -> SCF» This operation is used to send back to the SCF the values of counters specified in a

previous Activate Service Filtering operation.

•Call Information Report. Direction: SSF -> SCF » This operation is used to send specific call information for a single call to the SCF as

requested by the SCF in a previous call Information Request.

•Call Information Request. Direction: SCF -> SSF» This operation is used to request the SSF to record specific information about a

single call and report it to the SCF (with a call Information Report operation).

170


•Send Charging Information. Direction: SCF -> SSF» This operation is used to instruct the SSF on the charging information to be sent by

the SSF. The charging information can either be sent back by means of signalling or internal if the SSF is located in the local exchange. In the local exchange this information may be used to update the charge meter or to create a standard call record. The charging scenario supported by this operation is scenario 3.2 (refer to Annex B where these are defined).

•Play Announcement. Direction: SCF -> SRF» This operation is to be used after Establish Temporary Connection (assist procedure

with a second SSP) or a Connect to Resource (no assist) operation. It may be used for in-band interaction with an analogue user, or for interaction with an ISDN user. In the former case, the SRF is usually collocated with the SSF for standard tones (congestion tone etc.) or standard announcements. In the latter case, the SRF is always collocated with the SSF in the switch. Any error is returned to the SCF. The timer associated with this operation must be of a sufficient duration to allow its linked operation to be correctly correlated.

171


•Prompt And Collect User Information. Direction: SCF -> SRF» This operation is used to interact with a user to collect information.

•Specialized Resource Report. Direction: SRF -> SCF» This operation is used as the response to a Play Announcement operation when the

announcement completed report indication is set.

•Cancel. Direction: SCF -> SRF or SCF -> SSF» This generic operation cancels the correlated previous operation or all previous

requests. The following operations can be cancelled ”Play Announcement and Prompt And Collect User Information”.

•Activity Test. Direction: SCF -> SSF» This operation is used to check for the continued existence of a relationship

between the SCF and SSF. If the relationship is still in existence, then the SSF will respond. If no reply is received, then the SCF will assume that the SSF has failed in some way and will take the appropriate action.

172

Intelligent Network Signalling Procedures

IN

The System.

• SSF = Service Switching Function• SCF = Service Control Function• SRF = Specialized Resource

Function• SSP = Service Switching Point• SMP = Service management Point.• SCP = Signalling Control Point

Local exchange

Local exchange

LAN / WANIP

ISUP

ISUP

ISU

P

ISUP

INAP

INAP

INAP

IP

SSF

SSF

SCF

SRF

IP

Mobile switching Center

The System

• Service Management Point (SMP).» Management of

• data.• statistic.

» Introduction of new services.» Administration of the SCP.

• Service Switching Point (SSP)» Access point for the service user. *» Execution of service functions.

* service user: A user of an IN Service, the so-called customer.

• Service Control Point (SCP).» Call control and routing.

• Selection code dependent, origin dependent, state dependent.

• Intelligent Periphery (IP).» Announcement.

» Speech recognition.• E.g. voice dialling.

» Speech synthesis.

175

Simple IN call service

• The dialled number will be translated into anther number.» Process:

• The service user are dialling e.g. 800 or free number.• At the the IN the number is converted into an E.164 number.• The call is then forwarded to the destination.

SSP (SSF)SCP

(SCF)Local Exchange

IAM (CLD CLG)TC_BEGIN InitialDP (CLD CLG)

TC_END Connect(CLD CLG)

IAM (CLD CLG)

ISUP signallingINAP signalling

176

Simple IN call service with Busy/No answer Monitoring

• The dialled number will be translated into anther number.» Process:

• Same as last slide, but in case of busy or No answer. The call will be forwarded to an alternative number (e.g another phone or voice mail)

SSP (SSF)SCP

(SCF)Local Exchange


TC_CONTINUE RequestReportBCSMEvent, connect

IAM (CLD CLG)

REL(Busy)

TC_CONTINUE EventReportBCSMEvent(Busy)

TC_CONTINUE Connect (New CLD)

IAM (New CLD CLG)

CON


177

Simple IN call service with announcement.

» Process:• Same as last slide, but in this case the call are forwarded to an

(e.g. Waiting announcement or voice mail)

SSP (SSF)Local Exchange


TC_CONTINUE ConnectToResource PlayAnnouncementInternal IPCON

TC_CONTINUE SpecializedRescourceReport

Setup & PA

AnnCompleted

TC_CONTINUE DisconnectForwardConnection, ReleaseCall

ReleaseRel


178

Virtual Private Network Call (VPN)

MSC/SSP (SSF)

SCP (SCF)MS


IAM (CLD:6198 CLG: 26126134) TC_BEGIN InitialDP (CLD:26126198 CLG: 26126134 ORIG CLD 6198

TermAttemptAuthorized 26126198)

TC_END Connect (CLD:26126198 ORIG: CLD 6198

CLG: 6138 ORIG CLG: 26126134)

IAM (CLD:26126198, CLG: 6138, ORIG: CLD 6198, ORIG CLG: 26126134)

ACM

ANM

Now the usual Call flow follows

179

Outgoing Prepaid Call from MS

MSC VLR

ISDN

CM Service Req (IMSI, transact) [MM] Process Access

RequestAuthenticate (RAND)

Authentication Request (RAND) [MM]

Authentication Response (SRES) [MM]

Authentication Response (SRES)

Set ciphering mode (key)Ciphering Mode Command (key) [RR]Ciphering Mode Complete [RR]

Access Request Ack

SETUP (service, called number) [CM] Send info for o/g (service, called number)

Complete call

Call Proceeding [CM]Assign Command [RR]Assign Complete [RR] IAM

ACM

ANM

Alerting [CM]Connect [CM]Connect Ack [CM]

CM copy [MM]

MS


MAP signalling

ISUP/TUP signalling

SCP

INAP signalling

InitialDP (CollectInfo)

ApplyCharging (Continue)

BTS

TRAUTranscoder Rate Adaptation Unit

BTS

• TRAU - Transcoder / Rate Adaptation Unit Functions:

» Conversion of speech from 64 kbit/s on PCM (A-law) to 13/6.5 kbit/s on the GSM radio interface

» Intermediate rate adoption of data from V.110 frames to the special TRAU frames on the A-bis interface

TRAU

182

13Kbit/s speech channel

TRAU

BTS BSC MSC

BTS BSC MSC

BTS BSC MSC

TRAU

TRAU

Um A-bis A-Interface

Possible Locations of the TRAU.

BTS

• Bandwidth: 13 kbit/s• Encoding algorithm: Regular Pulse Excitation

with Long Term Prediction (RPE LTP):» Speech is sampled 8000 times per second» Each sample is converted into a 13 bit digital value» Every 20 ms a 260 bit segment is generated (13 kbit/s)» The segment is divided by importance into 182 class 1

bits and 78 class 2 bits» For protection, the 182 class 1 bits are mapped into

378 bits» The resulting 456 bits (378 + 78) are divided into 8x57

bits» The data are transmitted in 4 consecutive TDMA

blocks

• Resulting overall delay is 57.5 msec.

GSM Speech Encoding

BTS

• TRAU is controlled by BTS

• In-band signalling used, if TRAU not at BTS

• Control functions:» Shift between speech and data» Shift between full rate and half rate channels» Timing of speech frames (BSS - MS)» Comfort noise (Discontinuous Transmission)

Control of TRAU

Synchronization

0000000000000000 D/C/T - Bits

user data/control bitsUser data bits

D - Bits

Control bits

1 C1 - - - - - - - - - - C15

TS 0 TS 31

C1 - C4

C5

C6 - C11

C12 - C15

Frame type: Speech/Idle speech/Data/O&M

Channel type: Full rate/half rate

Speech: Time alignment (250/500 us)

Data: Intermediate RA (8 or 16 kbit/s)

Speech: Frame indicators (BFI, SID, TAF)

C16

C17 - C21

T1 - T4

Speech: Spare

Speech: Time alignment bits

Speech: Frame indicator (SP)

0 16 32 304 320Bit

TRAU

frame

16 kbit/s

PCM frame 2 Mbit/s TS 1 TS 2

TRAU Signalling

186

General Packet Radio Service

GPRS

BTS

GPRS History and definition

188

• As early as 1994, a Special Mobile Group started to think about a High Speed Data upgrade for GSM.

• The first step was HSCSD (High Speed Circuit Switched Data).» HSCSD is a circuit-switched extension to GSM.

• The next step was GPRS.» GPRS is a packet-switched extension to GSM.

History

189

• HSCSD (High Speed Circuit Switched Data).» HSCSD invented the principle of timeslot bundling to achieve higher

throughput rates. » HSCSD is the simplest high speed data upgrade for GSM.» HSCSD provides GSM users with a bandwidth of up to 57.6 Kbps.

» HSCSD does not require a hardware upgrade within BSS or core network (NSS), but different mobile stations.

• Even though HSCSD is easy to implement into the GSM network hardly any operator have decided to implement it.

» The commercial implementations of HSCSD barely exceed a speed of 38.4 Kbps.

» The most common implementation is 14,4 Kbps which only requires one full rate TCH.

What is HSCSD?

190

• GPRS (General Packet Radio Service) is a packet oriented data service for IP and X.25 over GSM networks.

• GPRS provides data speeds up to 170 Kbps.» Normally GSM only provides 9.6 Kbps, however, HSCSD provides GSM

users with a bandwidth up to 57.6 Kbps.

• GPRS provides an “always on” functionality, without continuous consumption of resources.

• GPRS is a step stone to 3rd generation networks.» EDGE. Almost similar to GRPS, but three times faster.» UMTS.

What is GPRS?

191

• EDGE is mainly concerned with the modulation scheme on the Air-Interface.

» Originally, EDGE was the abbreviation for Enhanced Data rates for GSM Evolution. Nowadays, EDGE is the acronym for Enhanced Data rates for Global Evolution.

• EDGE is using frequency modulation scheme 8-PSK in order to increase the Data speed.

» Applying 8-PSK-modulation to such a network implies shrinking of the cell size.

» GSM and GPRS are using the same modulation scheme GPSK.

• Not only is a new core network required, but also additional BTSs and a new cell structure.

» EDGE requires a major hardware upgrade and this is extremely costly to the operator.

Why not choose EDGE if it is almost similar to GRPS?

192

• Introduction of a new modulation technique – 8PSK, 8 Phase Shift Keying. 8PSK enables air interface bitrates roughly 3 times higher than traditional GMSK (Gaussian Minimum Shift Keying)

• However, the major disadvantage of 8-PSK modulation is that it includes amplitude modulation.

Q

I

Start

+90(same bit)

-90(diff bit)

Q

I(1,1,1)

(0,1,1)

(1,0,0)

(1,0,1)

(0,0,1)

(0,0,0)(0,1,0)

(1,1,0)

8PSK: 1 Symbol = 3 bits GMSK: 1 Symbol = 1 bit

EGPRS (Enhanced GPRS)

BTS

The GPRS network and it’s new elements.

194

From GSM to GPRS Network

UmMAPISUP

MAPMAPISUP

GSM

AA-bis

BSS

PSTN/ISDN

R

Gi

Gp

Gb Gs

Gf

GrPDN

PrivateBackbone

Gn

Gn

GPRS

Gc

PDN

195

• Handles:» PDP contexts for Mobile Stations.» Determines Quality of Service assigned to the user.» Routes packets to Mobile Stations.» “Pages” Mobile Stations when data is to be sent.

• Stores:» Subscriber data for all Mobile Stations in the location area.

• Security:» Authentication by means of identity or equipment check.» P-TMSI is allocated by SGSN.» Ciphering. (Not only in ”Um as in GSM” but all the way down to SGSN).

SGSN (Service GPRS Support Node)

196

• Handles:» Gateway to the Internet.» Routes IP packets to the appropriate SGSN.

• If the Mobile Station changes the SGSN during ready mode, the GGSN is used as data packet buffer.

• Stores:» Subscriber data for active Mobile Stations.

• Security:» Firewall.» Screening.

GGSN (Gateway GPRS Support Node)

197

• New fields have been added to HLR in order to serve the GPRS Network.

» IMSI is still the reference key.• SGSN Number.

› The SS7 address of SGSN currently serving the MS.• SGSN Address.

› The IP address of SGSN currently serving the MS.• MS purged for GPRS.

› Indicates that MM and PDP context of the MS are deleted from SGNS.• GGSN List.

› The GGSN number and optional IP address are related to the GGSN which will be contacted when activity from the MS is detected.

• Each IMSI “subscriber” record contains zero or more of the following PDP context.

› PDP Type. (e.g.. X25 or IP).› PDP Address. (Note: This field will be empty if dynamic IP add is used.).› QoS Profile. (Qos profile for this PDP context).› VPLMN Address allowed.› Access Point name. (A label according DNC naming list).

HLR (Home Location Register)

198

• In GPRS, LA is divided into RA. Each RA contains one or more cells.

LA = Location Area.LAI = MCC+MNC+LACRA = Routing Area (Subset of LA)RAI = LAI+RAPCU = Packet Control Unit.CCU = Channel Codec Unit.

LA 1LA 2 RA 1

RA 3

RA 5

RA 2

RA 4

BTS + CCU

• In a RA, the RAI is broadcasted as System Information.

• When an MS is crossing an RA border the MS will initiate an RA update procedure.

• New elements (CCU , PCU) are added to the BSS in order to support new coding schemes introduced by GPRS.

BSS

BTS

The GPRS Air and A-bis Interface

200

BTS

CS-4

CS-3

CS-2

CS-1

Coding Schemes in GPRS

• To achieve higher throughput rates per timeslot than plain GSM, GPRS introduces three new coding schemes.

» CS-1. Throughput =< 8kbit/s. Also provided by GSM.» CS-2. Throughput =< 12kbit/s.» CS-3. Throughput =< 14.4kbit/s.» CS-4. Throughput =< 20kbit/s.

• Due to unpredictable environment of the radio transmission the distance between MS and the cell impacts the QoS.

» The different CS are therefore not always available.

201

• Channel Codec Unit (CCU).» The existing CCU used in GSM is upgraded to handle GPRS.

• CH Coding (CS-2 …. CS-4).• Radio Channel Management (Signal, Strength, Quality and TA).

• Packet Control Unit (PCU).» The PCU is a very important function for the interfaces in GPRS.

• Communication with CCU using in-band signalling. (One can say that the PCU is the TRAU of the GPRS network).

• PDCH scheduling.• Segmentation (LLC to RLC blocks).• Error Handling (Retransmission of data packets).

TA = Timing Advance. PDCH = Packet Data Channel.TRAU = Transcoder Rate Adaptation Unit (Part of a GSM Network). LLC = Logical Link Control which is part of the GPRS protocol stack..RLC = Radio Link Control which is part of the GPRS protocol stack..

CCU & PCU

202

PCU (Packet Control Unit)

• Interface the new GPRS core network to the existing GSM BSS. » Converting packet data coming from the SGSN in so called PCU-frames that

have the same format as TRAU-frames. These PCU-frames are transparently routed through the BSC and towards the BTS. The BTS needs to determine the respective coding scheme and other options before processing a PCU-frame.

• Takes over all GPRS radio related control functions from the BSC.

203

• Three different classes of mobile stations have been defined.

• Class A.» The Mobile Station class A supports simultaneous monitoring and operation of

packet-switched and circuit-switched services. • Class B.

» The Mobile Station class B supports simultaneous monitoring but not simultaneous operation of circuit-switched and packet-switched services.

• Class C.» The Mobile Station class C supports either circuit-switched or packet-switched

monitoring and operation at a given time.

The Mobile Station

204

GPRS Protocols

205

• Like MM in GSM, GMM are used to keep track of the current location of an MS and to initiate security procedures.

• GMM is a function that is mainly handled between the mobile station and the SGSN. However, the HLR is also involved.

• There are various scenarios defined in GPRS to update a subscriber's location within the network. The most important ones are:

» Routing Area Update (Intra-SGSN and Inter-SGSN)» GPRS Attach and Detach» Cell Update (only while in GMM-Ready State)

• The GMM cell update procedure replaces in GPRS what is known as handover procedure in circuit-switched GSM.

• Due to the fact that a GPRS MS is not constantly “connected” to the network, the GMM has introduced a new state, called “Ready State”.

GMM (GPRS Mobility Management)

206

•Like MM in GSM, GMM handles the roaming and authentication procedure. However, due to the fact that a GPRS MS is not constantly using the resources in Um, the GMM has introduced a new state, called “Ready State”. • Idle Mode. (MS off or not attached yet.).

» If the MS is on, and is a Class B or Class C MS, the MS will listen to the network, but not make any updating of where the MS is. It is not possible to page an MS.

• Ready Mode. (MS is able to send and receive data).

» Cell updating is necessary.

» If no activity within the timer (T3314 / Default = 44s) the MS will fall back to a stand-by state.

» NOTE: an MS can be forced back to standby mode due to lack of recourses.

• Standby Mode. (MS is listening to the Network).

» Only RA update and periodic update is necessary.

» It is possible to page the MS.

Idle

Ready

Standby

GPRS Attach

GPRS Detach

Ready Timer expired

Data transfer or reception

GPRS Mobility Management

207

• GPRS Attach/Detach» Made towards the SGSN» The MS must provide its identity (P-TMSI/IMSI) and an indication of which type

of attach that is to be executed (GPRS / combined GPRS/IMSI)» After GPRS attach the MS is in ”Ready” state and MM contexts are established

in the MS and the SGSN.

• Routing Area Update» When a GPRS-attached MS detects a new RA (Routing Area)» When the periodic RA update counter has expired

• Cell Update» When the MS enters a new cell inside the current RA and the MS is in ”Ready”

state

• Combined RA/LA update» Only if option Gs-interface i simplemented

GMM Procedures

208

• Allow transfer of user data packets between the MS and some external packet data network.

• Before data transmission start, SM involves a handshaking procedure between the MS, SGSN and teh GGSN.

» Establish a PDP context between the MS and the GGSN (includes the negotiated QoS profile)

Session Management (SM)

209

• Identifies the transaction parameters of an active session of a GPRS mobile station.

» Note that a GPRS mobile station may support multiple simultaneous sessions and activated PDP-contexts

• Can be initiated by the network or the MS (in ”Standby” or ”Ready” state)

• Cannot be activated before a GMM context exists. (A GPRS mobile station first needs to register itself towards the SGSN before a PDP context activation procedure can be initiated).

• Can be deactivated on request of the MS or the SGSN or the GGSN by means of the PDP context deactivation procedure

PDP Context Activation

210

• Takes care of the allocation and maintenance of radio communication paths

• Paging» The paging procedure moves the MM state to ”Ready” to allow the SGSN to

forward downlink data to the BSS

• TBF Establishment/Release» A Temporary Block Flow (TBF) is a physical connection used by two RR entities

to support unidirectional transfer of user data or signalling.» The TBF is an allocated radio resource on one or more Packet Data Channels

(PDCH)» A TBF is temporary and is maintained only for the duration of the data transfer.

Radio Resource (RR) Management Procedures

211

•In GPRS, the RLC protocol, and the MAC Protocol is in charge of all radio related control functions on the air interface. •In GPRS, the LLC Protocol is in charge of transmission between SGSN and the Mobile Station.

» Delivery of data units to the higher layer in the correct sequence.

•In GPRS, the SNDCP Protocol is in charge of Segmentation and compression of Data.

» SNDCP represents the highest layer of the GPRS protocol stack. Therefore, SNDCP provides an interface function between the GPRS protocol stack and the different packet data protocols.

Physical Layer

MAC

LLC

GMM

RLC

SMIP / X25

SNDCP

GPRS Um protocol stack

= Radio Link Control.

= Medium Access Control.

= Logical Link Control.

= SubNetwork Dependent Convergence .

GPRS Air Interface

212

• In GSM the A-bis is a well known structured protocol.• In GPRS the A-bis has more or less become the wild west for the

vendors. » Each vendor is making his own version of the A-bis protocol.

• Due to the principle of PTCH bundling as well as the new GMM the known BTMS (BTS Management Protocol for GSM) has been changed to BSSGP.

= BSS GPRS.

= Frame Relay

Layer1

NetworkService

Relay

A-bis protocol stack

BSSGP

Layer1

RLC

MAC

LLC

GMM/SM

Gb protocol stack

GPRS A-bis Interface

213

Physical Layer (GSM RF)

• The channel coding fucntions (see fig. Below)• Cell selcetion/reselection• Setting of Timing Advance• Perform measurements on the neighbouring cells• Four channel coding schemes are defined (CS1-4):

214

• The RLC/MAC protocol is defined between the mobile station and the PCU (Packet Control Unit).

• In charge of all radio related control functions on the air interface. • Performs segmentation of LLC frames into radio blocks

RLC/MAC (Radio Link Control/Medium Access Control)

215

LLC (Logical Link Control)

• LLC provides different types of services to different upper layer applications, namely SNDCP GMM/SM and SMS.

• Provides the transport frames for the data transfer between MS and SGSN

• Encapsulation of higher layer protocol data units into LLC data units. (This applies in particular to data units from SNDCP which are tailored to fit into one LLC data unit. )• Delivery of data units to the higher layer in the correct sequence. • Ciphering and Deciphering (if enabled)

216

• Interface function between the GPRS protocol stack and the different packet data protocols like IP.

• The SNDCP is applicable between the MS and the SGSN. » Within the SGSN, there is a relay function from the SNDCP towards the

GPRS Tunneling Protocol (GTP).

• Segmentation of user data packets (max. 1520 octets)» Compression of Packet Data (optional)

• Relies completely on the error recovery and transmission capabilities of LLC and therefore provides no means for these functions

• nn

SNDCP (Sub-Network Dependent Convergence Protocol)

217

GPRS Air Interface

R

BTS

SNDPC

LLC

MAC/RLC MAC/RLCInfo H Info H Info H

Segment HFSC Towards the SGSN.

E.g. WWW or E-mail IP

Segmentation and compressing

H = Header.B = Normal Burst, see the GSM recommendation. FSC = Frame Check Sequence.

Towards the PCU

Physical Layer 1.

B B BB

LLC frame Max size 1600 octets.Encryption, error detecting and retransmission.

RLC Block 20 to 50 octets of data

Into normal radio bursts (58bit*8) = 456bit.

218

L1bis (WAN) L1 (LAN)L1bis (WAN)

MAC

RLC

NS

BSSGP

NS

BSSGP

L2 (PPP)

IP

UDP/TCP

GTP

BSS SGSNGb

RELAY

RELAY

LLCLAPG

PLLRFL

GPRS Gb Interface

SNDCP

219

• BSSGP (Base Station Subsystem GPRS Protocol)» Transparent transfer of signaling and data PDU's between the SGSN and the

PCU» Administration of the packet-switched link resources between SGSN and PCU. » Initiation of packet-switched paging for a particular mobile station if requested

by the SGSN.

• NS (Network Service) - consists of two sublayers:» The Network Service Control Protocol.

• Provides for virtual connections (NS-VC) between the SGSN and the PCU. These virtual connections need to be administrated by the Network Service protocol

» The Frame Relay Protocol.• The Network Service is a packet-switched protocol: A single virtual

connection may use resources from 0 kbit/s up to the entire bandwidth of the transmission link

» Transports BSSGP PDUs between BSS and SGSN.

Gb protocol layers

220

GPRS Network

UmMAPISUP

MAPMAPISUP

GSM

AA-bis

BSS

PSTN/ISDN

R

Gi

Gp

Gb Gs

Gf

GrPDN

PrivateBackbone

Gn

Gn

GPRS

Gc

PDN

221

• Gn - GSN backbone network » Private IP network intended for GPRS data/signalling only» Connects the GPRS Support Nodes (GSNs) together within a GPRS PLMN

• Gp – inter-PLMN backbone network» PLMN to PLMN connection (i.e. roaming) via Border Gateways (BG)» Packet data Network (public Internet or leased line)

• Gi » Interface to external packet data network (IP)

• Gs – SGSN to MSC/VLR» Used to perform IMSI attach and GPRS attach simultaneously» Combined paging procedures, where all paging is done form SGSN

• Gr – SGSN to HLR» SGSN must contact the HLR whenever a new subscriber enters one of its

Routing Areas

• Gd – SGSN to SMS» Used if SMS is forwarded over GPRS channels

• Gf – SGSN to EIR» Used to check the IMEI number

Other GPRS interfaces

222

L1 (LAN)L1bis (WAN) L1 (LAN)

Frame Relay

BSSGP

L2 (PPP)

IP

UDP/TCP

GTP

L2 (PPP)

IP

UDP/TCP

GTP

IP/X.25

SGSN GGSNGn

RELAY

LLCLAPG

Gn Interface

SNDCP

223

• Allows multi-protocol packets to be tunnelled through the GPRS backbone between GPRS Support Nodes (GSNs).

• Responsible for the transmission of both, signaling information and application data.

• Based on an IP-protocol stack and uses UDP as transport layer (OSI layer 4)

• Also takes care of the transfer of charging information. In that function, GTP is called GTP'

GTP (GPRS Tunnel Protocol)

224

• TCP (Transmission Control Protocol) » Manages the segmentation of a message or file into smaller packets that are

transmitted over the Internet and received by a TCP layer that reassembles the packets into the original message.

» A connection-oriented protocol, which means that a virtual connection is established between the two peers of a TCP-transaction.

» Usually, TCP is used together with IP.

• UDP (User Datagram Protocol )» Offers a limited amount of service compared to TCP. Most importantly:: UDP

does not provide segmentation or sequencing functions. The application needs to take of these functions.

» UDP is an alternative to TCP if network applications need to save processing time.

UDP/TCP

225

I’m still I’m still confused, but confused, but on a higher on a higher level! level!

Now I know why!Now I know why!

Excellent, I will be Excellent, I will be the champ!the champ!

Too Too difficult!difficult!

Not good!Not good!

How was the course ?How was the course ?

Evaluation

Education

GSM dan GPRS basic