GSM 3G Basic

1

Agenda, GSM & MPA Training course

• Agenda:

» 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

» Evaluation.

2

Global System

for

Mobile 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

Mobile

Switching

Centre

fixed

medium

Mobile

Station

fixed

location

Variable

Location

Diffuse

Medium

Telephone

SONOFON

M N

Basic concept - 1 GSM 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, Pakistan

Singapore, Hong Kong

Analog Mobile Systems

RC 2000

Italy

France

TACS / ETACS

PCS 1900 GSM at

1900 MHz

C-NET

Analog

450 MHz

UMTS / IMT-2000 (FPLMTS)

CT2

DCS 1800 GSM at

1800 MHz

Cordless

Trunked

mobile radio

(TETRA)

Satellite

(IRIDIUM)

GSM Digital

900 MHz

Mobile

Other systems CT0,CT1

DECT

GSM Digital

900 MHz

NMT

Analog

450/900 MHz

TACS/ETACS

Analog

900 MHz

AMPS

Analog

800 MHz

GSM Digital

900 MHz

DAMPS (TDMA)

GSM Digital

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.

Base

Station

Controller

BSC

Public Switched

Telephone Network

Base Mobile Station

(MS)

Mobile

Switching

Centre

MSC

(PSTN)

Station Subsystem

(BSS)

A-Inter

A-bis

Um

2 Mbit/s PCM

Air 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. Id

Register

EIR

Authen.

Centre

AUC

Visitor

Location

Register

VLR

Home

Location

Register

HLR Mobile

Switching

Centre

MSC

MAP

ISUP /

TUP

MAP

MAP MAP

ISUP /

TUP ISUP /

TUP

MAP

System Overview

Home

Location

Register

Visitor

Location

Register

Mobile

Switching

Centre

Base

Station

Controller

Base

Transceiver

Station

MSC BTS

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

MSC BTS

BSC

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

• 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

MSC BTS

BSC

VLR

HLR

SONOFON

M N

VLR (Visitor Location register)

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.

• Contains the radio transmitters and receivers (transceivers)

covering a certain geographical area of the GSM network

MSC BTS

BSC

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.

MSC BTS

BSC

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)

MSC BTS

BSC

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

Base

Station

Controller

BSC

Public Switched

Telephone Network

Base Mobile Station

(MS)

Mobile

Switching

Centre

MSC

(PSTN)

Station Subsystem

(BSS)

A-Inter

A-bis

Um

2 Mbit/s PCM

Air 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. Id

Register

EIR

Authen.

Centre

AUC

Visitor

Location

Register

VLR

Home

Location

Register

HLR Mobile

Switching

Centre

MSC

MAP

ISUP /

TUP

MAP

MAP MAP

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

BTS BSC MSC

VLR

HLR SONOFON

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

DTAP CM

MM

RR

Sig. layer 2

Layer 1 (air)

Sig. layer 2

Sig. layer 1

MTP

SCCP

BSSMAP RR

(CM+MM)

MS BSC

MTP MTP

SCCP SCCP

CM

MM

BSSMAP TCAP

MAP

I

S

U

P

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)

BTSM BTSM RR'

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

Base

Station

Controller

BSC

Public Switched

Telephone Network

Base

Mobile Station

(MS)

Mobile

Switching

Centre

MSC

(PSTN)

Station Subsystem

(BSS)

A-Inter

A-bis

Um

2 Mbit/s PCM

Air 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. Id

Register

EIR

Authen.

Centre

AUC

Visitor

Location

Register

VLR

Home

Location

Register

HLR Mobile

Switching

Centre

MSC

MAP

ISUP /

TUP

MAP

MAP MAP

ISUP /

TUP ISUP /

TUP

MAP

41












DTAP CM

MM

RR

Sig. layer 2

Layer 1 (air)

Sig. layer 2

Sig. layer 1

MTP

SCCP

BSSMAP RR

(CM+MM)

MS BSC

MTP MTP

SCCP SCCP

CM

MM

BSSMAP TCAP

MAP

I

S

U

P

MSC

Sig. layer 2

Layer 1 (air)

BTS

(CM)

(MM)

(RR)

(CM)

(MM)

(RR)

(CM)

(MM)


Sig. layer 2

Sig. layer 1

(LAPD)

BTSM BTSM RR


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

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”


» 374 carriers



BTS

SONOFON

M N

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.


» 299 carriers



PCS-1900 Radio (Um) Interface Physical Channels

BTS

SONOFON

M N

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

TS : Tail bit

TS : Training Sequence (setting up the receiver equaliser)

GP : Guard Period

C : Control bit

13 kbit/s user data

TDMA Frame Structure

46

BTS

Physical Channels

TS 5

TS 4

TS 3

TS2

TS

1 TS0

TS 4

TS 3

TS2

TS

0 TS7 TS6

TS 5

TS7 TS6

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 2

TS1

TS 0

TS7

TS

6 TS5

TS 0

TS 7

TS6

TS

5 TS4 TS3

TS 1

TS3 TS2

Downlink Uplink

47

FCCH

burst 3 142 3

8.25

Guard Tail Tail Information

Tail Information Training

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

burst

8.25

Guard Tail Information

Access

burst 7 41 36 3

Guard Tail Tail

68,25

Information Training

SCH

burst 3 39 64 39 2

8.25

Guard Tail Tail Information Information Training

» 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) 3 Normal

burst

8.25

Guard Tail 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 * 3,7gs (1 bit) = 251gs ~ (75Km / 2) = 37,5Km

Access

burst 7 41 36 3

Guard Tail Tail

68,25

Information Training

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 N SONOFON

M N

TS TS TS TS TS TS

TS

Timing

advance

Access

burst • 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 Station Timing 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 1km

from 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

burst 3 39 64 39 2

8.25

Guard Tail Tail Information Information Training

SCH burst

54

• The FCCH burst is the frequency correction channel burst which

is modulated with zero

FCCH

burst 3 142 3

8.25

Guard Tail Tail 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 6 2042 2043 2044 2045 2046 2047

0 1 2 3 4 5 6 7 18 19 20 21 22 23 24 25

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

(6.12s)

0 1 2 3 4 5 45 46 47 48 49 50 6

0 1 2 3 4 5 6 7 18 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 5 45 46 47 48 49 50 6

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 7 TDMA 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/2 R R SDCCH/3 SDCCH/4

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

F

1

F

2

F3 F4

F

5 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 Station Neighbour 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


BCCH NCEL2 : 12

BSIC NCEL2 : 63


BCCH NCEL3 : 7

BSIC NCEL3 : 59


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.

Base

Station

Controller

BSC

Public Switched

Telephone Network

Base Mobile Station

(MS)

Mobile

Switching

Centre

MSC

(PSTN)

Station Subsystem

(BSS)

A-Inter

A-bis

Um

2 Mbit/s PCM

Air 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. Id

Register

EIR

Authen.

Centre

AUC

Visitor

Location

Register

VLR

Home

Location

Register

HLR Mobile

Switching

Centre

MSC

MAP

ISUP /

TUP

MAP

MAP MAP

ISUP /

TUP ISUP /

TUP

MAP

66












DTAP CM

MM

RR

Sig. layer 2

Layer 1 (air)

Sig. layer 2

Sig. layer 1

MTP

SCCP

BSSMAP RR

(CM+MM)

MS BSC

MTP MTP

SCCP SCCP

CM

MM

BSSMAP TCAP

MAP

I

S

U

P

MSC

Sig. layer 2

Layer 1 (air)

BTS

(CM)

(MM)

(RR)

(CM)

(MM)

(RR)

(CM)

(MM)


Sig. layer 2

Sig. layer 1

(LAPD)

BTSM BTSM RR'



TS 1 TS 31 TS 5 - - - -

16 kbit/s traffic channels

64 kbit/s signalling channels

TS = 64 kbit/s timeslot

TS 2 TS 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

Flag

01111110

Flag

01111110 16 Bits

CRC Information

N - Bits

Control Address

16 Bits 8 or 16 Bits

SAPI

TEI

C/R EA 0

EA 1

SAPI value

0

1

16

62

63

Related entity

Radio signalling

Reserved for packet mode /Q.931

Reserved for packet mode /X.25

Operation and maintenance

Layer 2 management

TEI value

0-63

64-126

For fixed TRX addresses

For 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

01111110 16 Bits

CRC Information

N - Bits

Control Address


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 4 M 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

P 5

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

01111110 16 Bits

CRC Information

N - Bits

Control Address


Message Discriminator

1 2 3 4 5 6 7 8

Octet 1

Octet 2

Octet n

EM Message Type

Information Elements

8 7 6 5 4 3 1 2

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)


0

1

4

6

8

Other

Reserved

Radio Link Management

Dedicated Channel Management

Common Channel Management

Transceiver Management

Reserved for Future Use

A-bis Layer 3 Structure I

Radio Link Layer Management messages

DATA REQuest (Transfer of transparent messages in layer 2

DATA 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 CONFirm

ESTablish INDication

RELease REQuest (Release of layer 2 link on radio interface)

RELease CONFirm

RELease INDication

UNIT 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 type Code

A-bis Messages, MD=1

Dedicated Channel Management messages:

CHANnel ACTIVation (Activation of a radio channel)

CHANnel ACTIVation ACKnowledge

CHANnel ACTIVation Negative ACKnowledge

CONNection 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 ACKnowledge

MODE MODIFY Negative ACKnowledge

A-bis Messages, MD=4, part 1

Message type Code

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 CONFirm

RF 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 type Code

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 type Code

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 type Code

- 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 + ACCHs

Lm + ACCHs

SDCCH/4 + ACCH

SDCCH/8 + ACCH

BCCH

Uplink 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

Flag

01111110

Flag

01111110 16 Bits

CRC Information

N - Bits

Control Address



1 2 3 4 5 6 7 8

Octet 1

Octet 2

Octet n

EM Message Type

Channel Number

T

Message Discriminator := 1 (Radio Link Management)

L3 Information

Protocol

Discriminator

0 Message Type

Information Elements

Protocol Discriminator

3

5

6

9

11

15

Call control, packet, suppl. service

Mobility management

Radio resources management

Short message services

Non call related suppl. services

Reserved for test procedures

Other Reserved for future use

T := 1 (transparent message)

TI

Flag

TI

Value

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 Reference Information 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

BSC BTS

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.

Base

Station

Controller

BSC

Public Switched

Telephone Network

Base Mobile Station

(MS)

Mobile

Switching

Centre

MSC

(PSTN)

Station Subsystem

(BSS)

A-Inter

A-bis

Um

2 Mbit/s PCM

Air 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. Id

Register

EIR

Authen.

Centre

AUC

Visitor

Location

Register

VLR

Home

Location

Register

HLR Mobile

Switching

Centre

MSC

MAP

ISUP /

TUP

MAP

MAP MAP

ISUP /

TUP ISUP /

TUP

MAP

83












DTAP CM

MM

RR

Sig. layer 2

Layer 1 (air)

Sig. layer 2

Sig. layer 1

MTP

SCCP

BSSMAP RR

(CM+MM)

MS BSC

MTP MTP

SCCP SCCP

CM

MM

BSSMAP TCAP

MAP

I

S

U

P

MSC

Sig. layer 2

Layer 1 (air)

BTS

(CM)

(MM)

(RR)

(CM)

(MM)

(RR)

(CM)

(MM)


Sig. layer 2

Sig. layer 1

(LAPD)

BTSM BTSM RR'



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 3

Physical

Data Link

Network

Transport

Session

Presentation

Application

OSI Layer SS7 Levels

7

6

5

4

3

2

1 MTP Level 1

MTP Level 2

Physical MTP Level 1

Data Link 2 MTP Level 2

MTP Level 3 Network 3

I

S

U

P

SCCP

TCAP

T

U

P

IN, MAP

I

S

U

P

Transport

Session

Presentation

Application

SCCP

• Level 4/User Parts

• SCCP

Basic format of MSU - SCCP message

Label SIF F CK F I B

FSN F B I B

BSN LI > 2 SIO

User Data MTC SLS Originating

Point Code

Destination

Point Code

N x 8 bits 8 bits 14 bits 14 bits 4 bits

Mandatory fixed part

Mandatory variable part

Optional part

Service Indicator

0 0 1 1 Sub-service

Field

=== 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 Label

Message 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 Data MTC SLS Originating

Point Code

Destination

Point Code

N x 8 bits 8 bits 14 bits 14 bits 4 bits

Mandatory fixed part

Mandatory variable part

Optional 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 Request

CC Connection Confirm

CREF Connection Refused

RLSD Released

RLC Release Complete

DT1 Data Form 1

DT2 Data Form 2

AK Data Acknowledgement

UDT Unitdata

UDTS Unitdata Service

ED Expedited Data

EA Expedited Data Acknowledgement

RSR Reset Request

RSC Reset Confirm

ERR Protocol Data Unit Error

IT Inactivity Test

Protocol class

0

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

Message type Code

0000 0001

0000 0010

0000 0011

0000 0100

0000 0101

0000 0110

0000 0111

0000 1000

0000 1001

0000 1010

0000 1011

0000 1100

0000 1101

0000 1110

0000 1111

0001 0000

1 2 3

X

X

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


•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-Interface BSSAP

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 Header

SSN FEh: BSSAP

Discriminator

0 0 0 0 0 0 0 0

1 1

DLCI Data Link Connection Identifier

Discriminator

0 0 0 0 0 0 0 1

OCTET

DLCI

2

3 2 Length

Indicator 1

n n Layer 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


FSN F B I B

BSN LI > 2 SIO

x3h

BTS

A-Interface BSSMAP

104

BTS

BSSMAP Format

Disc. 0 = BSSMAP

Length indicator

BSSMAP message type

BSSMAP message Information 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 type Code


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 type Code


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 type Code


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 type Code

- 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-Interface DTAP

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 message Information 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

MSC BSC

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 Signalling MAP

Base

Station

Controller

BSC

Public Switched

Telephone Network

Base Mobile Station

(MS)

Mobile

Switching

Centre

MSC

(PSTN)

Station Subsystem

(BSS)

A-Inter

A-bis

Um

2 Mbit/s PCM

Air 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. Id

Register

EIR

Authen.

Centre

AUC

Visitor

Location

Register

VLR

Home

Location

Register

HLR Mobile

Switching

Centre

MSC

MAP

ISUP /

TUP

MAP

MAP MAP

ISUP /

TUP ISUP /

TUP

MAP

The System.

118












DTAP CM

MM

RR

Sig. layer 2

Layer 1 (air)

Sig. layer 2

Sig. layer 1

MTP

SCCP

BSSMAP RR

(CM+MM)

MS BSC

MTP MTP

SCCP SCCP

CM

MM

BSSMAP TCAP

MAP

I

S

U

P

MSC

Sig. layer 2

Layer 1 (air)

BTS

(CM)

(MM)

(RR)

(CM)

(MM)

(RR)

(CM)

(MM)


Sig. layer 2

Sig. layer 1

(LAPD)

BTSM BTSM RR'



119


MTP Level 3

Physical

Data Link

Network

Transport

Session

Presentation

Application


7

6

5

4

3

2

1 MTP Level 1

MTP Level 2




I

S

U

P

SCCP

TCAP

T

U

P

IN, MAP

I

S

U

P

Transport

Session

Presentation

Application

SCCP

• 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 1

DPC 2

DPC 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 1

DPC 2

DPC 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

MTP Level 3

Physical

Data Link

Network

Transport

Session

Presentation

Application


7

6

5

4

3

2

1 MTP Level 1

MTP Level 2




I

S

U

P

SCCP

TCAP

T

U

P

INAP, MAP

I

S

U

P

Transport

Session

Presentation

Application

SCCP

TCAP

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

SIF F CK F I B

FSN F B I B

BSN LI > 2 SIO

Optional part Mandatory

variable part

Mandatory

fixed part MTC SLS OPC DPC

Messages

Component

Messages

Component Length

Transaction

information element

Messages

Length

Messages

Type Tag

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 tag

Total message length

Transaction portion information element

Component portion tag

Component type tag

Component length

Component portion information

element

Component

Abort Cause

Dialogue Portion

Component Portion

Destination Transaction Identifier

Originating Transaction Identifier

Tag

Length

Contents

Tag

Length

Contents

Invoke ID

Linked ID

Operation Code

Sequence

Error Code

Problem Code

- Unidirectional

- Begin

- End

- Continue

- Abort

- 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

YES NO

NO NO

YES NO

Component portion information element

• 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

MTP Level 3

Physical

Data Link

Network

Transport

Session

Presentation

Application


7

6

5

4

3

2

1 MTP Level 1

MTP Level 2




I

S

U

P

SCCP

TCAP

T

U

P

INAP, MAP

I

S

U

P

Transport

Session

Presentation

Application

SCCP

TCAP

MAP

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 party

address

Message

type

Calling party

address

Protocol

class 0, 1

Pointers

MAP

Info. TCAP part Sub-system Number

(part of the address field)

SCCP User Data

Format of SCCP message for MAP information


FSN F B I B

BSN LI > 2 SIO

x3h

143

MAP information in TCAP

Message type tag

Total message length


Component portion tag

Component type tag

Component length

Component portion information

element

Component

Tag

Length

Contents

Tag

Length

Code

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

Operation Value

1 Update location area

2 Update location

3 Cancel location

4 Provide roaming number

5 Detach IMSI

6 Attach IMSI

7 Insert subscriber data

8 Delete subscriber data

9 Send parameters

10 Register SS

11 Erase SS

12 Activate SS

13 Deactivate SS

14 Interrogate SS

15 Invoke SS

16 Forward SS notification

17 Register password

18 Get password

19 Process unstructured data

MAP Operations Part 1

146

BTS

20 Send info for incoming call

21 Send info for outgoing call

22 Send routing information

23 Complete call

24 Connect to following address

25 Process call waiting

26 Page

27 Search for mobile subscriber

28 Perform handover

29 Send end signal

30 Perform subsequent handover

31 Allocate handover number

32 Send handover report

33 Process access signalling

34 Forward access signalling

35 Note internal handover

36 Register charging information

37 Reset

38 Forward check SS indication


Operation Value

147

BTS

39 Authenticate

40 Provide IMSI

41 Forward new TMSI

42 Set ciphering mode

43 Check IMEI

45 Send routing info for SM

46 Forward short message

47 Set message-waiting data

48 Note MS present

49 Alert service centre

50 Activate trace mode

51 Deactivate trace mode

52 Trace subscriber activity

53 Process access request

54 Begin subscriber activity


Operation Value

148

BTS

Home side

Visited

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

GSM Signalling 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)

MS

BT

S

BS

C

MS

C 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 contact to 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

BTS BTS

SONOFON

M N

SONOFON

M N

SONOFON

M N

TRAU Signaling

Send handover report


MAP signalling

ISUP/TUP signalling

MS

BT

S

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)

ACM Handover 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 BSC

MS

C VLR HLR

GMS

C

ISD

N

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] ACM Connect [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 call Call Proceeding [CM]

Assign Request [RR] Assign Command [RR]

Assign Complete [RR] IAM

ACM

ANM

Alerting [CM]

Connect [CM]

Connect Ack [CM]

CM copy [MM]

MS Channel Request/Required [RR]


MAP signalling

ISUP/TUP signalling

Outgoing Call from MS

161


Level 4/User Parts

INAP

MTP Level 3

Physical

Data Link

Network

Transport

Session

Presentation

Application


7

6

5

4

3

2

1 MTP Level 1

MTP Level 2




I

S

U

P

SCCP

TCAP

T

U

P

INAP, MAP

I

S

U

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Transport

Session

Presentation

Application

SCCP

TCAP

INAP

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.

IN Signalling procedures

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 / WAN IP

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 signalling

INAP 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 ISUP signalling

INAP signalling

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 PlayAnnouncement

Internal IP CON

TC_CONTINUE SpecializedRescourceReport

Setup & PA

AnnCompleted

TC_CONTINUE DisconnectForwardConnection, ReleaseCall

Release Rel

ISUP signalling

INAP signalling

178

Virtual Private Network Call (VPN)

MSC/SSP

(SSF)

SCP

(SCF) MS

ISUP signalling

INAP signalling

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

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

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

SC

P

INAP signalling

InitialDP (CollectInfo)

ApplyCharging (Continue)

BTS

TRAU Transcoder 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

T

R

A

U

BTS BSC MSC

BTS BSC MSC

BTS BSC MSC

T

R

A

U

T

R

A

U

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 bits User 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 32 304 320 Bit

TRAU

frame

16 kbit/s

PCM frame 2 Mbit/s TS 1 TS 2

TRAU Signalling

BTS

GSM 3G

187

• 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

188

• 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?

189

• 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?

190

• 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?

191

• 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.

193

From GSM to GPRS Network

Um MAP

ISUP

MAP MAP

ISUP

GSM

A A-bis

BSS

PSTN/ISDN

R

Gi

Gp

Gb Gs

Gf

Gr

PDN

Private

Backbone

Gn

Gn

GPRS

Gc

PDN

194

• 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)

195

• 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)

196

• 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)

197

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

LA = Location Area.

LAI = MCC+MNC+LAC

RA = Routing Area (Subset of LA)

RAI = LAI+RA

PCU = Packet Control Unit.

CCU = Channel Codec Unit.

LA 1 LA 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 GPRS Air and A-bis Interface

199

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.

200

• 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

201

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.

202

• 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

203

GPRS Protocols

204

• 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)

205

•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

206

• 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

207

• 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)

208

• 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

209

• 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

210

•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

SM IP / X25

SNDCP

GPRS Um protocol stack

= Radio Link Control.

= Medium Access

Control.

= Logical Link Control.

= SubNetwork Dependent Convergence .

GPRS Air Interface

211

• 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

Network

Service

Relay

A-bis protocol stack

BSSGP

Layer1

RLC

MAC

LLC

GMM/SM

Gb protocol stack

GPRS A-bis Interface

212

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):

213

• 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)

214

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)

215

• 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)

216

GPRS Air Interface

R

BTS

SNDPC

LLC

MAC/RLC MAC/RLC Info H Info H Info H

Segment H FSC 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 B B

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.

217

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

MAC

RLC

NS

BSSGP

NS

BSSGP

L2 (PPP)

IP

UDP/TCP

GTP

BSS SGSN Gb

RELAY

RELAY

LLC

LAPG

PLL

RFL

GPRS Gb Interface

SNDCP

218

• 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

219

GPRS Network

Um MAP

ISUP

MAP MAP

ISUP

GSM

A A-bis

BSS

PSTN/ISDN

R

Gi

Gp

Gb Gs

Gf

Gr

PDN

Private

Backbone

Gn

Gn

GPRS

Gc

PDN

220

• 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

221

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 GGSN Gn

RELAY

LLC

LAPG

Gn Interface

SNDCP

222

• 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)

223

• 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

224

I’m still

confused, but

on a higher

level!

Now I know why!

Excellent, I will be

the champ!

To

difficult!

Not good!

How was the course ?

Evaluation

Technology

GSM 3G Basic