GSM+Overview

Call Management in GSM

Overview

Land to Mobile Call Scenario

Mobile to Mobile Call Scenario

Mobile to Land Call Scenario

Detailed Intra-MSC Handover Scenario

Handover Overview

Detailed Inter-MSC Handover Scenario

Objectives

• Recognise and describe the phases of a mobile originated call.

• Recognise and describe the phases of a mobile terminated call.

• Describe the need for handover in GSM and typical handover causes.

• Explain the different types of handover in the GSM system.

• Recognise and describe the phases of different types of handovers.

Mobile-to-LandCall Scenario

Required Facilities for a Mobile-to-Land Call

1. Radio channel between Mobile Station and BTS selected by the BSC 2. BSC – BTS voice trunk selected by the BSC3. MSC – BSC voice trunk selected by the MSC4. MSC – PSTN voice trunk selected by the MSC5. Line from PSTN end switching office to Fixed Station (permanent link)

BSC - Base Station ControllerBTS - Base Transceiver Station MSC - Mobile Switching CentrePSTN - Public Switched Telephone Network

BTS

RadioChannel

Mobile StationBSC

MSC PSTN

BSCVoiceTrunk

VoiceTrunk to PSTN Line

MSCVoiceTrunk

Fixed PublicLand Network

Public LandMobile Network

Phases of a Mobile-to-Land Call

• Request for Service

• Authentication*

• Ciphering*

• Equipment Validation*

• Call Set-up

• Handover(s)*

• Release

* Phase might not occur

Note: Detail for authentication and ciphering is not shown. It is the same as in the location registration update scenario.

Mobile-to-Land CallRequest for Service

NewVLR

BMSCBSSMS

AUm

1

2

3

4

5

Channel Request

Dedicated SignallingChannel Assignment

Service Request TMSI, LAI

Service Request TMSI, LAI

Service Request TMSI, LAI

Mobile-to-Land CallEquipment Validation

6

7

8

9

EIRMSCMS

IMEI Request

IMEI Response

Check IMEI

IMEI Check Results

(IMEI)

Mobile-to-Land Call Set-up

VLRB

MSCBSSMSAUm

10

11

12

13

14

Call Setup RequestDialled DN

Access Subscriber Data

Subscriber Data

Call Proceeding

Assign Trunk & RadioTrunk No.

15

16

17

Assign Radio Channel TCH

Radio Assignment Complete(on TCH)

Trunk & Radio AssignmentComplete TCH

Mobile-to-Land Call Set-upContinued

18

19

20

21

PSTNMSCMS

Network Set-up(Dialled DN, Trunk No.)

Network Alerting

Alerting

Connect (answer)

22

23

Connect

Connect Acknowledgement

Note: Network Set-up, Network Alerting and Connect are generic terms. For SS7, the network set-up message would be Initial Assignment Message (IAM).

Mobile-to-Land CallMobile Initiated Release

PSTNMSCBSSMSAUm

1

2

3

4

5

Disconnect

Network Release

Release

Release Complete

Clear Command

6

7

Channel Release

Clear Complete

Land-to-MobileCall Scenario

Phases of a Land-to-Mobile Call

• Routing Analysis

• Paging

• Authentication*

• Ciphering*

• Equipment Validation*

• Call Set-up

• Handover(s)*

• Release

*Phase might not occur

Note:: Detail for authentication, ciphering and equipment validation is not shown. It is the same as in location registration update and mobile-to-land call scenarios.

Land-to-Mobile CallRouting Analysis

VLR

HLRMSCPSTNC

1

2

3

4

5

Incoming Call MSISDN

Get Route MSISDN

Routing Information MSRN

Incoming Call MSRN

Perform Page

TMSI, LAI

B

Land-to-Mobile CallPaging

VLRB

MSCBSSMSAUm

6

7

8

9

10

Perform Page TMSI

Page TMSI (on PCH)

Channel Request (on RACH)

Dedicated Signalling ChannelAssignment (on AGCH)

Page Response TMSI,LAI (on SDCH)

11

12

Page Response TMSI, LAI

Page Response TMSI, LAI

Land-to-Mobile Call Set-up

13

14

15

16

MSCBSSMS

Call Set-up

Call Set-up Confirm

Assign Trunk & RadioChannel TRUNK

Assign RadioChannel TCH

17

18

Radio Assignment Complete

Trunk & RadioAssignment Complete

U m A

Land-to-Mobile Call Set-upContinued

19

20

21

22

PSTNMSCMS

Mobile Alerting

Network Alerting

Connect (off-hook)

Connect

23Connect Acknowledge

Land-to-Mobile CallNetwork Initiated Call Release

PSTNMSCBSSMSAUm

1

2

3

4

5

Disconnect

Release

Release Complete

Clear Command

6

7

Channel Release

Clear Complete

Network Release

Mobile-to-MobileCall Scenario

Phases of a Mobile-to-Mobile Call

•Request for Service

• Authentication*

• Ciphering*

• Equipment Validation*

• Call Setup

• Routing Analysis

• Paging

• Authentication*

• Ciphering*

• Equipment Validation*

• Call Setup

• Handover(s)*

• Release

*Phase might not occur

•

Originating Mobile

Terminating Mobile

Mobile-to-Mobile Call Set-up & Release

BSSA’

MSCVLR

BSSMS-AA

Channel Request

MS-BUm’Um

Service Request

Channel Request

Authentication

Ciphering

Equipment Validation

Paging and Response

Authentication

Ciphering

Equipment Validation

Call Set-up

Handover

Release

Call Set-up

Handover

Release

Routing AnalysisWith HLR

Handover Overview

Handover

• Maintains Call Continuity.

• Controlled by BSS.

• Based on RF subsystem criteria or traffic loading considerations.

• Both MS and BTS provide RF link measurements to the handover process.

• Handover causes are prioritised:RXQUALRXLEVDISTANCEPOWER BUDGET

Handover Types

Four Levels

• within same Base Transceiver Station (Intra-BTS)• between different BTSs served by same BSC (intra-BSS/inter-BTS)• between different BSSs within same MSC (intra-MSC/inter-BSS)• between different MSCs (inter-MSC)

Intra-BTS Handover

Global Cell Identification

BSC3BSC2BSC1

MSC B MSC A PSTN

234 01 100 53

234 01 100 54

234 01 100 55

234 01 100 51

234 01 100 52

234 01 089 20

234 01 089 21

234 01 089 22

234 01 100 50

CountryCode

NetworkCode

Location AreaCode

CellIdentity

Intra-BSS/Inter-BTS Handover

Location AreaCode

Global Cell Identification

BSC3BSC2BSC1

MSC B MSC A PSTN

234 01 100 53

234 01 100 54

234 01 100 55

234 01 100 51

234 01 100 52

234 01 089 20

234 01 089 21

234 01 089 22

234 01 100 50

CountryCode

NetworkCode

CellIdentity

Intra-MSC, Inter-BSS Handover

Global Cell Identification

BSC3BSC2BSC1

MSC B MSC A PSTN

234 01 100 53

234 01 100 54

234 01 100 55

234 01 100 51

234 01 100 52

234 01 089 20

234 01 089 21

234 01 089 22

234 01 100 50

CountryCode

NetworkCode

Location AreaCode

CellIdentity

Intra-BSC, Inter-BTS Handover

Global Cell Identification

BSC3BSC2BSC1

MSC B MSC A PSTN

234 01 100 53

234 01 100 54

234 01 100 55

234 01 100 51

234 01 100 52

234 01 089 20

234 01 089 21

234 01 089 22

234 01 100 50

CountryCode

NetworkCode

Location AreaCode

CellIdentity

Detailed Intra-MSC/Inter-BSS Handover Scenario

Intra-MSC/Inter-BSS Handover Step 1

BSS 1

MSCPSTN

Present Voice Path

BSS 2

Step 1: Handover Request from BSS

Intra-MSC/Inter-BSS Handover Step 2

BSS 1

MSCPSTN

Future Voice Path

BSS 2

Step 2: Allocation of New Resources

Intra-MSC/Inter-BSS Handover Step 3

BSS 1

MSCPSTN

Old Voice Path

BSS 2

Step 3: Handover Execution

New Voice Path

Intra-MSC/Inter-BSS Handover Step 4

BSS 1

MSCPSTN

BSS 2

Step 4: Release of Old Resources

Intra-MSC Handover Signalling

VLRB

MSCBSSMSAUm

1

Signal Strength MeasurementSIG, MEAS

2

Rank-ordered list of target BSSsHAND, REQ

3

Kc, Identity of trunk, LAIHAND, REQ

4

New Radio Channel IDHAND, REQ, ACK

5

New Radio Channel IDHAND, REQ, ACK

6

New Radio Channel IDHAND, REQ, ACK

7HAND, ACC

8On New Radio Channel

PHYS, INFO

9 HAND, DET

10 HAND, COMP

11 HAND, COMP

12 REL, RCH

13 REL, RCH, COMP

Intra-MSC HandoverSignalling (Continued)

VLRB

MSCBSSMSAUm

1

Signal Strength MeasurementSIG, MEAS

2

Rank-ordered list of target BSSsHAND, REQ

3

Kc, Identity of trunk, LAIHAND, REQ

4

New Radio Channel IDHAND, REQ, ACK

5

New Radio Channel IDHAND, REQ, ACK

6

New Radio Channel IDHAND, REQ, ACK

7HAND, ACC

8On New Radio Channel

PHYS, INFO

9 HAND, DET

10 HAND, COMP

11 HAND, COMP

12 REL, RCH

13 REL, RCH, COMP

Detailed Inter-MSC Handover Scenario

Basic Inter-MSC Handover Steps

BSS A

MSC APSTN

Future Talk Path

BSS B

Step 2: Allocation of New Resources

MSC B

BSS A

MSC APSTN

Present Talk Path

BSS B

Step 1: Handover Request from BSS

MSC B

Present Talk Path

Basic Inter-MSC Handover StepsContinued

BSS A

MSC APSTN

BSS B

Step 4: Release of Old Resources

MSC B

BSS A

MSC APSTN

Old Talk Path

BSS B

Step 3: Handover Execution

MSC B

New Talk Path

Inter-MSC Handover Voice Facilities

MSC A

MSC B

MSC C

MSC D

PSTN

Inter-MSC Trunks (dedicated)

PSTN Trunks

MSC A

MSC B

MSC C

MSC D

PSTN

MSC Directory Number Spectrum

LocalExchange

Directory Number Spectrum

MSC

MSC

PSTN

MSISDN

MSRN

MSHN Used to referenceInter-MSC handovers

TrunksTrunks

Inter-MSC SignallingTwo Signalling Paths

MSC B

E

Mobile Application Part (MAP)(Defined in GSM Specification 09.02)

MSC A

PSTN

Dedicated Trunk Group

or

Inter-office Signalling such as ISDN-UP or TUP(Outside scope of GSM specification)

SS7

ISDN-UP – ISDN User PartTUP – Telephone User Part

Basic Inter-MSC HandoverInitial Condition

MSC A

BSS A

PSTN

Talk Path

Dialled Number720-1234

Serving CellGlobal Cell ID234-01-235-43

720-1234

MSC B

BSS B

Candidate CellGlobal Cell ID234-02-120-65

VLR B

Basic Inter-MSC HandoverHandover Number Allocation

MSC A

BSS A

PSTN

Perform Handover(234-02-120-65, Kc)

720-1234

Serving CellGlobal Cell ID234-01-235-43720-1234

MSC B

BSS B

Candidate CellGlobal Cell ID234-02-120-65

VLR B

Perform Handover(234-02-120-65, Kc)

E Interface

PSTN/ISDN Interface

SS7

PSTN

Basic Inter-MSC HandoverInter-MSC Trunk Set-up

MSC A

BSS A

PSTN720-1234

Serving CellGlobal Cell ID234-01-235-43720-1234

MSC B

BSS B

Candidate CellGlobal Cell ID234-02-120-65

VLR B

Network Set-up(219-9221)

Set-up Complete

E InterfaceSS7

Basic Inter-MSC HandoverEvents After Handover Command

MSC A

BSS A

PSTN720-1234

720-1234

MSC B

BSS B

VLR B

Send End Signal

E Interface

Answer

PSTN/ISDN Interface

New Talk Path

Inter-MSC Handover Signalling

ServingBSSMS

1

Signal Strength MeasurementSIG, MEAS

TargetMSC

ServingMSC

TargetVLR

TargetBSS

6 HAND, REQ

2Rank-ordered list of

Target BSSs

3 HAND, PER

4 HAND, NUM

5 HAND, NUM, COMP

7New Radio Channel ID

HAND, REQ, ACK

8 HAND, PER, ACK

Inter-MSC Handover Signalling(Continued)

ServingBSSMS

9 NET_SETUP

TargetMSC

ServingMSC

TargetVLR

TargetBSS

14 PHYS_INFO

10 SETUP_COMP

11

New Radio Channel ID

HAND_COMP

12

13

15 HAND_DET

16 HAND_COMP

New Radio Channel ID

HAND_COMP

On New Radio Channel

HAND_ACC

Inter-MSC Handover Signalling(Continued)

ServingBSSMS

17 HAND_COMP

TargetMSC

ServingMSC

TargetVLR

TargetBSS

22 END_SIGNAL

18 SEND_ENDSIG

19 ANSWER

20

21

23 NET_REL

24 REL_HAND_NUM

REL_RCH_COMP

REL_RCH