1

Channel Overview

3 Types

1. Broadcast Control Channel: Point to Multipoint, Downlink (BTS) to MS)

(A) BCCH (Board cast Control Channel) It inform the Mobile about system confirmation parameter (LAI, Cell -Identity, Neighbouring Cell Identity. MS select best cell to attach BCCH on full power, never Frequency hopped.

(B) FCCH (Frequency Correction Channel) Which is used to allow a MS to accurately tune to a BS; FCCH Transmits a constant

frequency burst of the Radio carrier that is used by the MS for frequency correction.

2

(C) SCH (Synchronization Channel);- SCH is used to synchronizetime. SCH carries TDMA Frame number and BSIC (Base

Station Identity Code)

2. CCCH (Common Control channel). They are Point To Multi Point and UP or Down link and carry signaling information necessary for Access Management function (e.g. allocation of dedicated control channels.) This include ---

1. PCH (Paging Channel)- Down Link, used for paging when Incoming call.

2. RACH (Random Access Channel)- Used by MS to request allocation of a specific dedicated control channel. (SDCCH)

either in response to a paging message or for call Origination/Registration from the MS. This is an uplink Channel and Point to Point.

3. AGCH- Down Link- To assign a specific dedicated control channel (SDCCH) to MS (When MS request on RACH). It is Down Link Channel.

3

Dedicated Control Channel

Full Duplex, Point, For Signalling between BTS, & Certain MS.

(A) SACCH- (Slow Associated Control Channel)

(B) FACCH- (Fast Associated Control Channel)

(C) SDCCH- (Stand Alone Dedicated Control Channel) Duplex chl.which is always allocated to TCH or SDCCH.

SACCH- Slow Associated Control Channel.

It is used for:

- Radio link supervision measurement

- Power Control

- Timing Advance Information

In 26 Frame Traffic Multiframe 13th frame (frame no. 12) is used fro SACCH. SACCH – for NON URGENT PROCEDURES.

4

(II) FACCH – Fast Associated Control

- Used for Urgent Signalling; like handover during a call.

- During call data is transmitted over TCH instead of Traffic data, this is marked by a flag known as stealing Flag.

(III) SDCCH – Stand alone dedicated Control Channel.

- Duplex, P to P used for Signalling in Higher Layer.

- Carry all Signals when no TCH is allocated to MS.

- Used for Service request, location update, Subscribers Authentication, Ciphering , Equipment

Validation, Assignment of a TCH

5

MS enters a new area under the control of new VLR. MS came from old VLR. MS listen 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 and allocates 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 SignalingChannel Assignment AGCH

Location UpdateRequest (TMSI,old LAI

SDCCHLocation Update

Request (TMSI,old LAI

Location UpdateRequest (TMSI,old LAI

MS BSS MSC New VLR

1

2

3

5

4

Um BA

Mobile Location Update-Request for Service

6

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

7. MSC forward, request for IMSI to MS through 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

Um BA

SDCCH

SDCCH

IMSI Acknowledge (IMSI)

7

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)

MS NewVLR

MSC

10

11

12

13

DB

Get

Authentication

Parameters (IMSI)

Authentication

Parameters

(SRES,Kc RAND)

HLR AUC

Authentication

Parameters

(SERES,Kc RAND)

8

Authenticate

Mobile Station (RAND)

MS NewVLR

MSC

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 old VLR.

Authenticate

Mobile Station (RAND)

SDCCH

9

Update Location (MSRN)

NewVLR HLR

18

19

20

21

D D

De-register

Mobile 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

OldVLR

Location Update

Mobile Station

De-registered

Mobile location update

10

Cipher_uplink_Channel

SDCCH

MS BSS

22

23

24

25

Um 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 ciphered channel to BSS.

26 BSS sends Ciphered complete message to MSC.

NewVLR

Ciphering Completed

The BSS Ciphers

The down_link_channel

CIPHERING

11

SDCCH

MS BSS

27

28

29

30

Um A

Location Update Accept (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.

NewVLR

Clear Signaling Connection

Release Radio Signaling Channel

Location Update Complete

SDCCH

SDCCH

32Clear Complete

TMSI-REALLOCATION

12

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

13

MS BSS

1

2

3

4

Um A

Dedicated Signaling Channel

Assignment

AGCH

MSC

Channel Request

RACH

B

Assume that MS is registered with system and has been allocated TMSI User enter the MSISDN and them presses the “send” Key

1. MS send a channel request on RACH.

2. BSS allocates a SDCCH on AGCH. MS Now Communicate 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

14

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 is within valid range and valid equipment.

9. EIR returns the results to MSC if results are – ve 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

15

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 .

NewVLR

Subscriber Data 12

SDCCH

Call Proceeding)13

16

MS BSSUm 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.

NewVLR

Assign Trunk &

Radio (TN)

Assign

Radio Channel (TCH)

SDCCH

Radio Assignment

Complete

SDCCH16

15

14

17

Trunk & Radio

Assignment Complete

17

Networking Setup (DD.)

MS MSC

18

19

20

21Connect (Answer)

CALL SETUP – WITH 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

18

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 is completed.

PSTN

Disconnect

TCH

Release

TCH

Release CompleteTCH

26

25

24

27

Networking Release

Clear Command28

Channel Release29TCH

Clear Command30

RELEASE OF CALL

19

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

20

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 is roaming is 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

21

Home MSC

C

If MS is barred for I/c calls, then VLR inform MSC accordingly, them 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 (MSRN0

Perform Page

(LAI, TMSI)

VLRDVisited

MSC

22

BSSA

6. MSC used LAI given by VLR to determine which 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 Signaling Channel Assignment

AGCH

10Page Response (TMSI,LAI)

SDCCH

11Page Response

PAGING

12Page Response

23

BSSA

Authentication Ciphering, Equipment validation are 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 VLRB Home or

Visited MSCUm

The Authentication The Cipher phaseThe Equipment Validation N/W

24

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 use SDCCH 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 & Radio Assignment Complete

Home or Visited MSC

SDCCH

Call Setup Confirm

SDCCH

17

Radio Assignment Complete

SDCCH

25

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

Connect Acknowledge

TCH

PSTN

Mobile Alerting

TCH

Start Billing

26

BSSA

24. MSC receives a Release message from the 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 in cleared.

29. The Traffic channel is released.

30. The recourses are completely released.

MS

Network Release

Disconnect)

26

25

24

27

Release

TCH

28Clear Command

PSTNUm

Home or Visited MSC

TCH

TCH

Clear Command

Clear Command

30

29

RELEASE

27

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

Phase might not occur

Originating Mobile

Terminating Mobile

28

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.