Call Management in GSM

7/29/2019 Call Management in GSM

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Call Management in GSM


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Overview

Land to Mobile Call Scenario

Mobile to Mobile Call Scenario

Mobile to Land Call Scenario

Detailed Intra-MSC HandoverScenario

Handover Overview

Detailed Inter-MSC Handover

Scenario


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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.


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Mobile-to-LandCall Scenario


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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 MSC

4. MSC PSTN voice trunk selected by the MSC

5. Line from PSTN end switching office to Fixed Station (permanent link)

BSC - Base Station Controller

BTS - Base Transceiver Station

MSC - Mobile Switching Centre

PSTN - Public Switched Telephone Network

BTS

RadioChannel

Mobile Station

BSC

MSC PSTN

BSCVoiceTrunk

VoiceTrunk toPSTN Line

MSCVoice

Trunk

Fixed PublicLand Network

Public LandMobile Network


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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.


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Mobile-to-Land Call

Request for Service

New

VLR

BMSCBSSMS

AUm

1

2

3

4

5

Channel Request

Dedicated Signalling

Channel Assignment

Service Request TMSI, LAI




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Mobile-to-Land Call

Equipment Validation

6

7

8

9

EIRMSCMS

IMEI Request

IMEI Response

Check IMEI

IMEI Check Results

(IMEI)


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Mobile-to-Land Call Set-up

VLR

B

MSCBSSMS

AUm

10

11

12

13

14

Call Setup Request

Dialled DN

Access Subscriber Data

Subscriber Data

Call Proceeding

Assign Trunk & Radio

Trunk No.

15

16

17

Assign Radio Channel TCH

Radio Assignment Complete

(on TCH)

Trunk & Radio Assignment

Complete TCH


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Mobile-to-Land Call Set-up

Continued

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).


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Mobile-to-Land Call

Mobile Initiated Release

PSTNMSCBSSMS

AUm

1

2

3

4

5

Disconnect

Network Release

Release

Release Complete

Clear Command

6

7

Channel Release

Clear Complete


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Land-to-MobileCall Scenario


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Phases of a Land-to-Mobile Call

Routing Analysis

Paging

Authentication*

Ciphering*


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.


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Land-to-Mobile Call

Routing Analysis

VLRHLR

MSCPSTN

C

1

2

3

4

5

Incoming Call MSISDN

Get Route MSISDN

Routing Information MSRN

Incoming Call MSRN

Perform Page

TMSI, LAI

B


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Land-to-Mobile Call

Paging

VLR

B

MSCBSSMS

AUm

6

7

8

9

10

Perform Page TMSI

Page TMSI (on PCH)

Channel Request (on RACH)

Dedicated Signalling Channel

Assignment (on AGCH)

Page Response TMSI,

LAI (on SDCH)

11

12

Page Response TMSI, LAI

Page Response TMSI, LAI


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Land-to-Mobile Call Set-up

13

14

15

16

MSCBSSMS

Call Set-up

Call Set-up Confirm

Assign Trunk & Radio

Channel TRUNK

Assign Radio

Channel TCH

17

18

Radio Assignment Complete

Trunk & Radio

Assignment Complete

U m A


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Land-to-Mobile Call Set-up

Continued

19

20

21

22

PSTNMSCMS

Mobile Alerting

Network Alerting

Connect (off-hook)

Connect

23Connect Acknowledge


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Land-to-Mobile Call

Network Initiated Call Release

PSTNMSCBSSMS

AUm

1

2

3

4

5

Disconnect

Release

Release Complete

Clear Command

6

7

Channel Release

Clear Complete

Network Release


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Mobile-to-MobileCall Scenario


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Phases of a Mobile-to-Mobile Call

Request for Service

Authentication*

Ciphering*


Call Setup

Routing Analysis

Paging

Authentication*

Ciphering*


Call Setup

Handover(s)*

Release

*Phase might not occur

Originating Mobile

Terminating Mobile


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Mobile-to-Mobile

Call Set-up & Release

BSS

AMSC

VLR

BSSMS-A

A

Channel Request

MS-B

UmUm

Service Request

Channel Request

Authentication

Ciphering


Paging and Response

Authentication

Ciphering


Call Set-up

Handover

Release

Call Set-up

Handover

Release

Routing Analysis

With HLR


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Handover Overview


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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:

RXQUAL

RXLEV

DISTANCE

POWER BUDGET


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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)


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Intra-BTS Handover

Global Cell Identification

BSC3BSC2BSC1

MSC B MSC A PSTN

Country

Code

Network

Code

Location

Area

Code

Cell

Identity


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Intra-BSS/Inter-BTS Handover

Location

Area

Code


BSC3BSC2BSC1

MSC B MSC A PSTN

Country

Code

Network

Code

Cell

Identity


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Intra-MSC, Inter-BSS Handover


BSC3BSC2BSC1

MSC B MSC A PSTN

Country

Code

Network

Code

Location

Area

Code

Cell

Identity


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Intra-BSC, Inter-BTS Handover


BSC3BSC2BSC1

MSC B MSC A PSTN

Country

Code

Network

Code

Location

Area

Code

Cell

Identity


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Detailed Intra-MSC/Inter-BSS HandoverScenario


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Intra-MSC/Inter-BSS

Handover Step 1

BSS 1

MSCPSTN

Present Voice Path

BSS 2

Step 1: Handover Request from BSS


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Intra-MSC/Inter-BSS

Handover Step 2

BSS 1

MSCPSTN

Future Voice Path

BSS 2

Step 2: Allocation of New Resources


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Intra-MSC/Inter-BSS

Handover Step 3

BSS 1

MSCPSTN

Old Voice Path

BSS 2

Step 3: Handover Execution

New Voice Path


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Intra-MSC/Inter-BSS

Handover Step 4

BSS 1

MSCPSTN

BSS 2

Step 4: Release of Old Resources

I MSC H d Si lli


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Intra-MSC Handover Signalling

VLR

B

MSCBSSMS

AUm

1

Signal Strength Measurement

SIG, MEAS

2

Rank-ordered list of target BSSs

HAND, REQ

3

Kc, Identity of trunk, LAI

HAND, REQ

4

New Radio Channel ID

HAND, REQ, ACK

5


HAND, REQ, ACK

6


HAND, REQ, ACK

7HAND, ACC

8

On New Radio Channel

PHYS, INFO

9HAND, DET

10HAND, COMP

11HAND, COMP

12REL, RCH

13REL, RCH, COMP

I t MSC H d


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Intra-MSC Handover

Signalling (Continued)

VLR

B

MSCBSSMS

AUm

1

Signal Strength Measurement

SIG, MEAS

2

Rank-ordered list of target BSSs

HAND, REQ

3

Kc, Identity of trunk, LAI

HAND, REQ

4


HAND, REQ, ACK

5


HAND, REQ, ACK

6


HAND, REQ, ACK

7HAND, ACC

8

On New Radio Channel

PHYS, INFO

9HAND, DET

10HAND, COMP

11HAND, COMP

12REL, RCH

13REL, RCH, COMP


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Detailed Inter-MSC Handover Scenario

B i I t MSC H d St


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Basic Inter-MSC Handover Steps

BSS A

MSC A

PSTN

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

B i I t MSC H d St


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Basic Inter-MSC Handover Steps

Continued

BSS A

MSC A

PSTN

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

I t MSC H d


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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 Di t N b S t


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MSC Directory Number Spectrum

Local

Exchange

Directory Number Spectrum

MSC

MSC

PSTN

MSISDN

MSRN

MSHN Used to reference

Inter-MSC handovers

Trunks

Trunks

I t MSC Si lli


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Inter-MSC Signalling

Two 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 Part

TUP Telephone User Part

Basic Inter MSC Handover


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Basic Inter-MSC Handover

Initial Condition

MSC A

BSS A

PSTN

Talk Path

Dialled Number

720-1234

Serving Cell

Global Cell ID

234-01-235-43720-1234

MSC B

BSS B

Candidate Cell

Global Cell ID

234-02-120-65

VLR B



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Handover Number Allocation

MSC A

BSS A

PSTN

Perform Handover

(234-02-120-65, Kc)

720-1234

Serving Cell

Global Cell ID

234-01-235-43720-1234

MSC B

BSS B

Candidate Cell

Global Cell ID

234-02-120-65

VLR B

Perform Handover

(234-02-120-65, Kc)

E Interface

PSTN/ISDN Interface

SS7

PSTN



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Inter-MSC Trunk Set-up

MSC A

BSS A

PSTN720-1234

Serving Cell

Global Cell ID

234-01-235-43720-1234

MSC B

BSS B

Candidate Cell

Global Cell ID

234-02-120-65

VLR B

Network Set-up

(219-9221)

Set-up Complete

E InterfaceSS7



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Events 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


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Inter-MSC Handover Signalling

Serving

BSSMS

1

Signal Strength

Measurement

SIG, MEAS

Target

MSC

Serving

MSC

Target

VLR

Target

BSS

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



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(Continued)Serving

BSSMS

9 NET_SETUP

Target

MSC

Serving

MSC

Target

VLR

Target

BSS

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



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(Continued)Serving

BSSMS

17 HAND_COMP

Target

MSC

Serving

MSC

Target

VLR

Target

BSS

22 END_SIGNAL

18 SEND_ENDSIG

19 ANSWER

20

21

23 NET_REL

24 REL_HAND_NUM

REL_RCH_COMP

REL_R CH

Documents

Call Management in GSM