Mobile Call - 2.ppt

7/27/2019 Mobile Call - 2.ppt

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GSM CALL FLOW SCENARIOS


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MS enters a new area under the control

of new VLR. MS came from old VLR. MSlisten to LAI (on BCCH) and compare

this LAI to old LAI (in SIM)

1. MS detects a new LA and send channel

request over RACH.

2. BSS receives channel request andallocates a SDCCH and forward channel

assignment on AGCH.

3. MS send Location update request on

SDCCH. In this message are TMSI & old

LAI

4. BSS send update request to MSC.

5. MSC inform VLR for Location update

request. MS can identify itself by IMSI

or TMSI, in this case it is TMSI, and old

LAI.

Channel Request

RACH

Dedicated Signaling

Channel Assignment

AGCH

Location Update

Request (TMSI,old LAI

SDCCH

Location Update


Location Update


MS BSS MSC New VLR

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2

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5

4

BA

Mobile Location Update-Request for Service


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6. VLR analyses that TMSI received is old.For registration the IMSI of MS isrequired. VLR request to MSC to getIMSI

7. MSC forward, request for IMSI to MSthrough BSS.

8. MS reads IMSI and send to BSS over

SDDCH and BSS sends to MSC.

9. MSC forwards the IMSI to VLR

Request IMSI

Request IMSI

IMSI Acknowledge (IMSI)

MS BSS MSC New VLR

6

7

8

9

BA

SDCCH

SDCCH

IMSI Acknowledge (IMSI)


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AUTHENTICATION:-Key Ki is

required it resides is 1-AUC, 2-SIM, Ki

never transmitted on AIR.

10. New VLR sends request to HLR for

authentication parameters for this

IMSI.

11. HLR send request to AUC.

12. AUC using IMSI extracts subs Ki,

AUC then generate a RAND Applies

the Ki, RAND to Authentication

algorithm (A3) and cipher Key

generation algorithm (A8) to

produce SRES, and cipher Key (Kc)

AUC then returns to HLR an

authentication triplets RAND, SRES,

Kc.

13. HLR forward authentication triplets

to VLR.

Get

Authentication

Parameters (IMSI)

MSNew

VLRMSC

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11

12

13

DB

Get

Authentication

Parameters (IMSI)

Authentication

Parameters

(SRES,Kc RAND)

HLR AUC

Authentication

Parameters

(SERES,Kc RAND)


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Authenticate

Mobile Station (RAND)

MSNew

VLRMSC

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16

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DB

Authentication

Response (SRES)

Authentication

Response (SRES)

SDCCH

HLR AUC

14. VLR keeps 2 parameter Kc, SRES for

later use and send message

(including RAND) to MSC for MS

authentication.

15. MSC send authentication request

to MS, MS reads Ki from SIM,

Applies RAND, Ki to algorithm (A3)

and Cipher Key generation

algorithm (A8) to produce SRES

and Kc, MS saves Kc and will use Kc

for ciphering.

16. MS returns the generated SRES to

MSC.

17 MSC send SRES to VLR, VLR

compares 2 SRES. It equal, MS

passes authentication if unequal

then SIM disabled. Now MS is

under the control of new VLR and

MS can be deregistered from oldVLR.

Authenticate

Mobile Station (RAND)

SDCCH


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Update Location (MSRN)

New

VLR HLR

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21

D

De-registerMobile Station

18. VLR allots MSRN. New VLR sends message to HLR

informing it that a given IMSI has changed location and

send I/c call on MSRN.

19. HLR insert the MSRN into the record of IMSI, Now HLR

returns to the VLR a copy of Subs profile.

20. HLR will send a message to old VLR for deleting the old

entry of IMSI.

21. Old VLR frees up the old MSRN and deallocates the VLR

entry for the specified IMSI, and sends an

acknowledgement to HLR

Old

VLR

Location Update

Mobile Station

De-registered

Mobile location update


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Cipher_uplink_Channel

SDCCH

MS BSS

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23

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A

Cipher_Radio_Channel

(Kc)

MSC

Uplink_Channel_Ciphered

SDCCH

26

Cipher_Radio_Channel

(Kc)

B

The HLR&Old VLR have been informed that

MS has been registered with an MSC, under

control of New VLR, New VLR will allocate a

TMSI, before this radio channel is

encrypted.

22. VLR request MSC to Cipher Radio Channel.

Cipher Key is included in this message

23. MSC forward this message to BSS.

24. BSS retrieves the Kc and ask MS to Cipher in

uplink.

25. MS uses Kc already generated (during

authentication) to cipher the Uplink and

sends Confirmation over the cipheredchannel to BSS.

26 BSS sends Ciphered complete message to

MSC.

New

VLR

Ciphering Completed

The BSS Ciphers

The down_link_channel

CIPHERING


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SDCCH

MS BSS

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28

29

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Um A

Location UpdateAccept (TMSI)

MSC

31

Location Update

Accept

B

27. VLR Informs MSC for MS Location

update. In this message New TMSI

included.

28. MSC forward LA updation message

(TMSI) to MS

29. MS stores New TMSI in SIM. MS now

sends update complete message to

MSC.

30. MSC request BSS to release signalling

connection.

31. BSS sends Radio resource channel

release to MS and releases SDCCH.

32. BSS then inform MSC that radio channel

released.

New

VLR

Clear SignalingConnection

Release RadioSignaling Channel

Location UpdateComplete

SDCCH

SDCCH

32

Clear Complete

TMSI-REALLOCATION


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MOBILE TO LAND CALL SCENARIO

FOLLOWING PHASES ARE PERFORMED:-

1. REQUEST FOR SERVICE

2. AUTHENTICATION

3. CIPHERING

4. EQUIPMENT VALIDATION

5. CALL SETUP

6. RELEASE


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MS BSS

1

2

3

4

m A

DedicatedSignaling Channel

AssignmentAGCH

MSC

Channel Request

RACH

B

Assume that MS is registered with system and

has been allocated TMSI

User enter the MSISDN and then presses the

send Key

1. MS send a channel request on RACH.

2. BSS allocates a SDCCH on AGCH. MS NowCommunicate on SDCCH with BSS &

MSC till TCH is allocated

3. MS send Service request to BSS on

SDCCH. In this message are TMSI & LAI.

4. BSS send Service request to MSC

5. MSC forward service request to VLR.

Now Authentication & Ciphering phases

take place.

VLR

Service Request

SDCCH

Service Request

5 Service Request

The Authentication Phase

The Ciphering Phase

MOBILE TO LAND CONNECTION


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IMEI Request

SDCCH

MS MSC

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F

Check IMEI

6. MSC request MS to send IMIE.

7. MS send IMEI.

8. MSC request EIR to Check IMEI. EIR check that IMEI iswithin valid range and valid equipment.

9. EIR returns the results to MSC if results areve then

MSC drop the call. If call continue, then MSC inform the

N/W of the event.

EIR

IMEI Response (IMEI)

SDCCH

IMEI Check Results

EQUIPMENT VALIDATION


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SDCCH

MS BSS

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11

Um A

Call Setup Request)

MSC

Access Subscriber

Data (DD,SI)

B

There are 2 steps in setting a call

- Setting of a voice path between MS &

MSC by allocating a radio traffic channel

& a voice Trunk

- Setting a voice path between MSC &

PSTN.

10. MS send a call setup request to MSC. It

included dialled digit

11. MSC request VLR to supply subs

parameters. Requested message contain

digit dialled (DD) and service indication

(SI).

12. VLR will check for call barring etc. VLR will

supply subs data for call processing.

13 MSC will inform MS that call is

proceeding .

New

VLR

Subscriber Data12

SDCCH

Call Proceeding)13


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MS BSS

Um A

MSCB

14 MSC allocates a trunk to BSS for serving

MS and request the BSS (TN) to allocate

a radio channel (TCH) for MS.

15 BSS allocate Radio channel on SDCCH.

16. MS tunes TCH and send

acknowledgement to BSS

17. BSS connects the radio channel to

assigned trunk of MSC, BSS deallocate

the SDCCH, BSS send trunk & radio

assignment message to MSC.

New

VLR

Assign Trunk &Radio (TN)

Assign

Radio Channel (TCH)

SDCCH

Radio Assignment

Complete

SDCCH16

15

14

17

Trunk & Radio

Assignment Complete


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Networking Setup (DD.)

MS MSC

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21Connect (Answer)

CALL SETUPWITH LAND N/W- A path has been

established between MS & MSC now a path will be established

from MSC to PSTN

18. MSC send a N/W setup message to PSTN. In message are

dialled digit and details of Trunk to be used for call.

19. PSTN inform MSC with networking alerting message. MS will

hear ringing tone from PSTN.

20. MSC inform MS that the destination number is being

alerted.

21. When B. party go off-hook, PSTN will inform the MSC of this

event. Billing start, MS is connected to the destination

party.

22. MSC informs the MS that the Connection has been

established.

23. MS acknowledges the receipt of the connect message.

PSTN

Alerting

TCH

Networking Alerting

22Connect

TCH

23

Connect

Acknowledgment

TCH


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MS BSSUm A

MSCB

24. MS initiate the release of call by pressing

end button. MS will send the Disconnect

message to MSC.

25. MSC send Release message to PSTN End

to END connection is terminated.

26. MSC send Release message to MS.

27. MS send Release Complete message.

28. Voice Trunk between MSC & BSS is

released.

29. The Traffic channel is cleared.

30. The Release of the Resources iscompleted.

PSTN

Disconnect

TCH

Release

TCH

Release Complete

TCH

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Networking Release

Clear Command28

Channel Release29TCH

Clear Command30

RELEASE OF CALL


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LAND TO MOBILE CALL

PHASES OF A LAND TO MOBILE CALL.

1. ROUTING ANALYSIS

2. PAGING

3. AUTHENTICATION

4. CIPHERING

5. EQUIPMENT VALIDATION

6. CALL SETUP

7. RELEASE


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Home

MSC

CHLR

Assume that MS is already registered and

allocated TMSI and MS in his home system

1. PSTN subscriber dials MS ISDN.

2. GMSC request HLR to provide routing

information about this MS.

3. HLR provide MSRN to GMSC, if MS isroaming in its home MSC area then

MSRN = MS ISDN, if roaming in different

MSC area then MS ISDN & MSRN are

different. Assume that MS roaming in

Home MSC area.

4. MSC inform VLR for a call to MS, In the

message is MSRN.

5. VLR respond to MSC by LAI & TMSI.

PSTN

Incoming Call (MSISDN)

Get Route (MSISDN)

3

2

1

4

Routing Information

(MSRN)

5

Incoming call (MSRN)

Perform Page

(LAI, TMSI)

VLR ROUTING ANALYSIS


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Home

MSC

C

If MS is barred for I/c calls, then VLR inform

MSC accordingly, then MSC will connect

announcement.

IF MS ROAMING IN ANOTHER MSC

AREA.

4. The call is routed from home MSC to the

visited MSC and MSRN is transmitted

then to the VLR

5. The VLR sends a message to the visited

MSC asking it to performs paging by

passing to it the new LAI & TMSI of the

MS.

PSTN

Route the Call (MSRN)

5

4

Incoming call (MSRN)

Perform Page

(LAI, TMSI)

VLRD Visited

MSC


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BSSA

6. MSC used LAI given by VLR to determinewhich BSS should page, included in the

message is the TMSI.

7. BSS broadcast TMSI, of MS in paging

channel (PCH).

8. MS detects TMSI, or IMSI on paging

channel MS asks channel request on

RACH.

9. BSS allocates SDCCH on AGCH. Now

onwards MS communicate as SDCCH till

MS gets a TCH.

10. MS responds paging on SDCCH, in the

message MS sends TMSI, LAI.

11. BSS send this message to MSC.

12. MSC informs its VLR that MS has

responded.

MS

Perform Page (TMSI)

7

6

Page

PCH

Channel Request

RACH

Home or

Visited VLR

B Home or

Visited MSC

Um

8

9

Dedicated SignalingChannel Assignment

AGCH

10Page Response (TMSI,LAI)

SDCCH

11Page Response

PAGING

12Page Response


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BSSA

Authentication Ciphering, Equipment validationare done in same manner as in Mobile to Land call.

In the case, the MS is visiting a new MSC area,

the authentication and Equipment Validation are

performed as follows.

- The Visited VLR request the authentication

parameters from the Home AUC through the

Network connecting the two MSCs and then

through the HOME HLR.

- The Equipment Validation phase involves the

visited MSC & the HOME EIR.

There are again two steps in setting up a voice

path for a call from a mobile to a PSTN

subscriber.- The call setup with the mobile :- A voice path is

created between MS & MSC by allocating a TCH

and a voice trunk.

- The call setup with the land N/W:- Where a

voice path is established between the MSC & a

PSTN N/W

MSHome or

Visited VLR

BHome or

Visited MSC

The Authentication

The Cipher phase

The Equipment Validation N/W


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Call Setup

MS BSS

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13. MSC inform MS that a call can be setup.

14. MS perform compatibility check it acknowledges the call

setup message by setup confirm.

15. MSC selects a trunk to BSS and request BSS to allot a radio

channel (TCH).

16. BSS allot TCH and transmits an Assignment command over

SDCCH to MS.

17. MS tunes to TCH and transmits an assignment complete

message back to BSS. MS user phone rings. MS do not useSDCCH after it gets TCH.

18. BSS on receiving assignment complete message connects

the TCH to Trunk. SDCCH is free now and send Assignment

Complete Message to MSC.

Assign Radio Channel

SDCCH

Assign Trunk &

Radio Channel

18

Trunk & RadioAssignment Complete

Home or

Visited MSC

SDCCH

Call Setup Confirm

SDCCH

17

Radio AssignmentComplete

SDCCH


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MS

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20

21

22

19. MS got TCH, MS begin alerting the user after if receives a

TCH. A alerting message is sent to MSC.

20. MSC on getting alerting indication from MS will generate

ringing to calling party and send a N/W alerting to PSTN.

21. Mobile subscribers answers, MS stops alerting and send

connect message to MSC.

22. MSC removes audible tone to PSTN, and connects PSTN

trunk to BSS trunk and send connect message to PSTN,

Billing start.

23. MSC send a connect acknowledge to MS.

Connect (off-hook)TCH

Network Alerting

Connect

Home or

Visited MSC

23

ConnectAcknowledge

TCH

PSTN

Mobile Alerting

TCH

Start Billing


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BSSA

24. MSC receives a Release message fromthe N/W to terminate the end to end

connection.

25. MSC send disconnect message to MS.

26. MS send Release to MSC

27. MSC send Release complete to MS.

28. Voice trunk between MSC & BSS is

cleared.

29. The Traffic channel is released.

30. The recourses are completely released.

MS

Network Release

Disconnect)

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25

24

27

ReleaseTCH

28Clear Command

PSTNHome or

Visited MSC

TCH

TCH

Clear Command

Clear Command

30

29

RELEASE


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Phase of a Mobile to Mobile call

- Request for Service

- Authentication*

- Ciphering*

- Equipment Validation*

- Call Setup

- Release

- Routing Analysis

- Paging

- Authentication*

- Ciphering*

- Equipment Validation*

- Call Setup

- Release

OriginatingMobile

Terminating

Mobile


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Mobile to Mobile call phase divided in 2 parts

Originating Mobile Point

1. MS to MSC is same as part of MS to Land call.

2. Terminating Mobile part same as land to Mobile call, i.e. PSTN to MSC Part.


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INTERFACES

GSM Interfaces are briefly explained below:

Um :

The air interface is used for exchanges between a

MS and a BSS.

LAPDm, a modified version of the ISDN LAPD, is usedfor signaling.

Abis :

This is a BSS internal interface linking the BSC and aBTS, and it has not been standardized.

The Abis interface allows control of the radio

equipment and radio frequency allocation in the BTS.


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A :

The A interface is between the BSS and the MSC.

The A interface manages the allocation of suitableradio resources to the MSs and mobility management.

B :

The B interface between the MSC and the VLR uses theMAP/B Protocol.

Most MSCs are associated with a VLR, making the B

interface internal .

Whenever the MSC needs access to data regarding a

MS located in its area, it interrogates the VLR using the

MAP/B protocol over the B interface.


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C :

The C interface is between the HLR and a GMSC or a

SMS-G. Each call originating outside of GSM (i.e. a MS

terminating call from the PSTN) has to go through aGateway to obtain the routing information required to

complete the call, and the MAP/C protocol over the Cinterface is used for this purpose.

Also, the MSC may optionally forward billinginformation to the HLR after call clearing.

D : The D interface is between the VLR and HLR, and uses

the MAP/D protocol to exchange the data related tothe location of the MS and to the management of the

subscriber.


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E :

The E interface interconnects two MSCs.

The E interface exchanges data related to handoverbetween the anchor and relay MSCs using the MAP/E

protocol.

F :

The F interface connects the MSC to the EIR, and uses

the MAP/F protocol to verify the status of the IMEI

that the MSC has retrieved from the MS.

G: The G interface interconnects two VLRs of different

MSCs and uses the MAP/G protocol to transfer

subscriber information, during e.g. a location update

procedure .


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H :

The H interface is between the MSC and the SMS-G ,

and uses the MAP/H protocol to support the transferof short messages.

I :

The I interface is the interface between the MSC andMS.

Messages exchanged over the I interface are relayed

transparently through the BSS.

Mobile Call - 2.ppt

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