Mobile Call - 2.ppt
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Transcript of 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
Request (TMSI,old LAI
Location Update
Request (TMSI,old LAI
MS BSS MSC New VLR
1
2
3
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
10
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
14
15
16
17
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
18
19
20
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
22
23
24
25
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
27
28
29
30
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
6
7
8
9
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
10
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
18
19
20
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
26
25
24
27
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
13
14
15
16
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
19
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)
26
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.