Gsm Call Flow With Defination

GSM/DCS BSS

Signalling Examples

Training Document

Document Number/Issue Copyright © Nokia Telecommunications Oy 1 (159)NTC CTXX 0677/1.0 en Training Document

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No. of pages

159/TT

Edited by/Translator

14-May-97Miia Sjögren

Author

14-May-97Pasi Mehtonen

Approved by

14-May-97Philippe Esterman

Previous issue(x) approved

TABLE OF CONTENTS

1. MOBILE ORIGINATED CALL.................................................................

2. MOBILE TERMINATED CALL................................................................

3. LOCATION UPDATE.................................................................................

4. INTERNAL HANDOVER, INTRA CELL.................................................

5. INTERNAL HANDOVER, INTER CELL..................................................

6. EXTERNAL HANDOVER..........................................................................

Mobile Originated Call

1. MOBILE ORIGINATED CALL


MSC BSC BTS MSVLR

Channel Required

Channel Activation

Channel Activation Ack.

Immediate Assigment Command.

Channel Request ( RACH )

Immediate Assigment ( AGCH ).

CM Service Request ( SDCCH)

Establish IndicationCR (CM Service Request)Process Access Request

AuthenticateCC Authentication Request

Authentication Request ( SDCCH )

Authentication Response ( SDCCH )DT1 Authentication Response

Authentication Response

Set Ciphering ModeDT1 Ciphering Mode Command

Encryption Command Ciphering Mode Command ( SDCCH )

Ciphering Mode Complete ( SDCCH )DT1 Ciphering Mode Complete

Access Request Accepted

Forward New TMSITMSI Reallocation Command

TMSI Reallocation Command ( SDCCH )

TMSI Reallocation Complete ( SDCCH )TMSI Reallocation Complete

TMSI Ack.Setup ( SDCCH )

DT1 SetupSend Info for O.G. Call

Complete CallDT1 Call Proceeding

Call Proceeding ( SDCCH )

DT1 Assignment RequestPhysical Context Request

Physical Context Confirmed

Channel Activation


Assignment Command ( SDCCH )

SABM ( FACCH )Establish Indication

UA ( FACCH )

Assignment Complete ( FACCH )DT1 Assignment Complete

Channel Release

Channel Release Ack.DT1 Alerting

Alerting ( FACCH )DT1 Connect

Connect ( FACCH )

Connect Ack.( FACCH )DT1 Connect Ack.

Measurement Report ( SACCH )Measurement Report/Result

Disconnect ( FACCH )DT1 ( Disconnect )

DT1 ( Release )

DT1 ( Release Complete)

DT1 ( Clear Command )

Release ( FACCH )

Release Complete ( FACCH )

Channel Release ( FACCH )

Deactivate SACCHDISC ( FACCH )

UA ( FACCH )Release Indication

RF Channel Release

RF Channel Release Ack.DT1 ( Clear Complete )

RLSD ( SCCP Released )

RLC ( SCCP Released Ack.)

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UA (SDCCH)

RADIOACCESSPART

ESTABLISHMENTPART

CIPHERING,AUTHENTICATIONAND CALL SETUPPART

TCH SEIZED

CONVERSATIONPART

RELEASE BY MS

CM Service Request

Ciphering Mode Command


1. CHANNEL_REQUEST

The MS requests a channel by sending a random access burst on a RACH channel via one BTS. Channel request -message contains the establishment cause. This can be 'Answer for paging', 'emergency call', 'other services (Mobile Originated Call, Short Message Service)' or 'Other', like location update. In addition to, this message contains Random Reference. This is 5 bits randomly selected by MS. The usage of random reference is: when two MSs are accessing to the network exactly the same time, the network can separate these Mobile Stations by using this random reference.


2. CHANNEL_REQUIRED

The BTS sends a channel required message to the BSC. By using this message, BTS delivers further on towards the BSC the channel request generated by MS. In practice Channel Required contains the same information as above but the BTS adds some information into it also. BTS numbers always the channels. In this case, the number of the Uplink CCCH (RACH -burst) is included. Request reference is directly coming from Channel request -message. Then, the first timing advance estimate called Access Delay is added into this message by the BTS.


3. CHANNEL_ACTIVATION

The BSC sends a Channel Activation message to the BTS. After receiving channel required from the BTS, the BSC starts to search and allocate SDCCH -channel for this call on certain terms, the most important is of course which BTS and then the channel configuration of this SDCCH. Parameters: DTX control, channel ID & description & mobile allocation, maximum power levels of the MS and BS and finally, the first timing advance concerning this access calculated by the BSC.

4. CHANNEL_ACTIVATION_ACK


A response to the channel activation message. When BTS has received this message it starts to send and receive SACCH -channel. The reference used in this case is the power levels received in Channel Activation message.

5. IMMEDIATE_ASSIGNMENT_COMMAND

The BSC tells the BTS about the SDCCH channel to be used.


6. IMMEDIATE_ASSIGNMENT

The BSS informs the MS on AGCH channel about the SDCCH channel to be used. In practice, this message is an order from the network to the MS to move to the SDCCH -channel defined before. Page mode, SDCCH channel description, associated SACCH and hopping frequency are included as parameters. In addition, request reference (same as establishment cause), initial timing advance and frequency allocation if frequency hopping applies are also included.

7. CM_SERVICE_REQUEST


The CM Service Request message is sent to the network by the MS to request a service for the connection management sublayer entities, like circuit switched connection establishment, supplementary services activation or short message transfer.

8. ESTABLISH_INDICATION

BTS acknowledges the Immediate Assignment Command by returning Establish Indication message. Establish indication -message has two uses. Firstly, when used in this phase it points out that from the BTS point of view, the MS is now on the SDCCH-channel. Thus, the BTS sends information back


to the BSC that the MS is now on this kind of SDCCH-channel which description is like this etc. Also the BTS identifies the link and adds received Layer 3 information into this message.

9. CM_SERVICE_REQUEST

The CM Service Request message is forwarded to the MSC.

10. UA


UA is normal Layer 2 level acknowledgement when setting up the Layer 2 level link in LAPDm -protocol.

11. PROCESS_ACCESS_REQUEST

MSC forwards MS's request for access management from VLR by Process Access Request message.

12. AUTHENTICATE


VLR initiates authentication request by sending an Authenticate message to MSC.

13. AUTHENTICATION_REQUEST

As a CC (Connection Confirmed) message, the MSC sends an Authentication Request message to the BSC. The message contains the RAND.


The BSC forwards the message via the BTS to the MS.


15. AUTHENTICATION_RESPONSE

The MS responds to the Authentication Request with the Signed Response SRES. The Authentication Response is sent to the BSC via the BTS.

In the MS Authentication procedure, two algorithms, A3 and A8 are used. In the SIM -card (In MS), both of these algorithms and 32 -digit key are stored) and the very same information can be found in Authentication Centre (AuC) also. When MS Authentication is requested by the network, AuC/VLR sends 32 -digit RANDom Number to the MS. MS calculates then Signed Response (SRES and returns that back to the VLR. VLR makes a comparison if received


SRES is same than it has received inside of the Authentication triplet from the AuC before. If these two SRESs are the same, authentication went OK and MS can continue the call setup.

Should you notice, the first 8 digits of the KI are used for Authentication and SRES calculation, the rest 24 are reserved for Ciphering Key calculation.


Inside of this message, the SRES value from the MS is forwarded back to the VLR in order to finalize authentication procedure.


This and all other messages in the A-interface up to the releasing of the SCCP connection are transmitted by using SCCP DT1 (Data Form 1) messages.


MSC sends a positive response to Authenticate message.

18. SET_CIPHERING_MODE

VLR sends MSC Set Ciphering Mode message which is used for changing MS-BTS connection ciphering status.


19. CIPHERING_MODE_COMMAND

The MSC asks the BSC start ciphering on the radio path. This message is sent in the A-interface in case the network wants to initiate ciphering over the radio interface. If the network uses ciphering then MS starts ciphering after receiving this message.

20. ENCRYPTION_COMMAND

The BSC stores the Encryption information to its memory and sends an Encryption command to the BTS to start ciphering mode operations.



The BSS informs the MS about beginning of ciphering , and starts receiving in the ciphered mode.

22. CIPHERING_MODE_COMPLETE

The MS acknowledges ciphering command.



If ciphering is in use, this is the first ciphered message (by the MS) in the Air interface. The BSS acknowledges the Ciphering Command, informs the MSC that MS has started ciphering and starts sending information in ciphered mode.

24. ACCESS_REQUEST_ACCEPTED

VLR sends a positive acknowledge to Process Access Request message.

25. FORWARD_NEW_TMSI


VLR requests MSC to perform TMSI reallocation.

26. TMSI_REALLOCATION_COMMAND

The purpose of the TMSI reallocation procedure is to provide identity confidentiality. Usually the TMSI reallocation is performed at least at each change of location area. MSC initiates the TMSI reallocation procedure by sending TMSI Reallocation command message to the MS. TMSI Reallocation Command message contains a new combination of TMSI and LAI allocated by the network or a LAI and the IMSI if the used TMSI shall be deleted. Usually


the TMSI Reallocation Command message is sent to the MS by using a RR connection in ciphered mode.


TMSI Reallocation Command is forwarded to the MS.

28. TMSI_REALLOCATION_COMPLETE

When the MS receives the TMSI Reallocation Command message, it stores the LAI in the SIM. If the received identity is the IMSI of the MS, it deletes any


previously stored TMSI. If the received identity is a TMSI, the MS stores it in the SIM. In both cases the MS send a TMSI Reallocation Complete message to the network.


TMSI Reallocation Complete message is forwarded to the MSC.


30. TMSI_ACK

MSC sends VLR a positive response to reallocation of TMSI.

31. SETUP

After authentication, Identification and Ciphering, the MS is in the SDCCH channel and ready to start real call setup signaling. The MS sends a Setup message to the BSC to be forwarded to the MSC.

32. SETUP


The BSC sends the Setup message to the MSC in order to inform the MSC about the incoming call.

33. SEND_INFO_FOR_OG_CALL

VLR request for retrieval of call data.

34. COMPLETE_CALL

Call completion acknowledged by VLR for MOC.


35. CALL_PROCEEDING

The MSC responds to the Setup message.

36. CALL_PROCEEDING

When the call control entity of the MS receives a Call Proceeding message, it enters the "Mobile originated call proceeding" state.

37. ASSIGNMENT_REQUEST


This message starts the TCH allocation. In the A- interface, MSC is the master and it hunts the circuit used for this call through the A- interface. This message can contain some optional information according to GSM- recommendations. This optional information is: Priority of the call, Downlink Discontinuous Transmission (DTX), Radio channel identity and Interference band to use.

38. PHYSICAL_CONTEXT_REQUEST

By using this message, the BSC interrogates the actual timing advance from the BTS in order to start TCH allocation through the Abis -interface.


39. PHYSICAL_CONTEXT_CONFIRM

BSC receives the timing advance information from the BTS and starts TCH reservation and allocation. This reservation & allocation procedure is similar to the case of the SDCCH -channel.


After the BSC's internal channel reservation and allocation, it activates the TCH by sending this message towards the BTS. Contents: channel number, activation type, channel mode (DTX/No DTX), channel type (Speech / data: if


speech, then GSM encoding algorithm included, if data, then information about transparency or non-transparency of the channel and data rate), channel identity, encryption information if received, BS & MS power levels as received in 'Physical context confirm' -message and timing advance.

41. CHANNEL_ACTIVATION_ACK.

The BTS returns current TDMA frame number and after that the TCH is activated through the Abis -interface.


42. ASSIGNMENT_COMMAND

The BTS delivers received information further on towards the MS. Contents: channel description, power levels, cell channel description, channel mode (Full / Half) and mobile allocation.

43. SABM (Set Asynchronous Balanced Mode)

This is Layer 2 message and contains some Layer 3 information. Content of this message: service request (look establishment cause!), ciphering key sequence, Mobile Station Classmark and Mobile Identity.



Establish indication -message has two uses. Firstly, when used this phase it points out that from the point of view of the BTS, the MS is now on the FACCH-channel. Thus, the BTS sends information back to the BSC that the MS is now on this kind of FACCH-channel which description is like this etc. Also the BTS identifies the link = main signaling channel and adds received Layer 3 information into this message. This layer 3 information is coming from the MS, of course.

45. UA


UA is normal Level 2 acknowledgement when setting up the Layer 2 level link in LAPDm-protocol.

46. ASSIGNMENT_COMPLETE

The MS informs it is now on the TCH and everything is OK.


The BSS acknowledges the channel seizure to the MSC.


48. CHANNEL_RELEASE

When MS has informed the network it is in the TCH, there is no need to use the SDCCH -channel for this call setup any more. By Channel Release procedure it is released.

49. CHANNEL_RELEASE_ACK.

The BTS acknowledges the Channel Release message.

50. ALERTING


The MSC sends an Alerting message via BSS.

51. ALERTING

The MSC informs the MS that the called subscriber has been alerted. This message can contain also so-called progress indicator IE, which tells that there are in-band announcements or other similar information to be received. In brief, this means that the connection is not end-to-end ISDN connection. If the MS receives this element, it shall through-connect the speech path. In case it is not, the MS generates ringing tone in itself. This information can also be transferred in a Progress message.


52. CONNECT

The MSC sends a Connect message to the MS via the BSS. This message indicates the MS that a connection has been established through the network.

53. CONNECT

When the MS receives a Connect message, it attachs the user connection to the radio path, returns a Connect Acknowledge message, stops any locally generated alerting indication (if applied) and enters the "active" state.


54. CONNECT_ACK.

By using this message, the MS informs the MSC that the MS is now in the "active" state.

55. CONNECT_ACK.

The message is forwarded to the MSC.

56. MEASUREMENT_REPORT


When call is on, the MS sends measurement report concerning mainly the quality of the speech connection two times per second.


57. MEASUREMENT_REPORT/RESULT

If these measurement reports are preprocessed in the BTS then measurement results are sent towards the BSC. If the is no preprocessing in the BTS, then measurement reports are sent. In this phase, Nokia BTS does not make any preprocessing.

58. DISCONNECT

This request is sent by MS. Contents: clear end-to-end connection. This message stops the charging concerning this call connection.


59. DISCONNECT

The Disconnect message is forwarded to the MSC.

60. RELEASE

Actual release is coming from the MSC; real call is just about to end.

61. RELEASE

The Release message is forwarded to the MS.


62. RELEASE_COMPLETE

MS informs that it will release the transaction identifier, i.e. call release is proceeding.


The Release Complete message is forwarded to the MSC.

64. CLEAR_COMMAND


This message is coming from the MSC and releases the associated dedicated resources, i.e. BSSAP connection concerning this call.

65. CHANNEL_RELEASE

Deactivation command of the used TCH. This is sent by the BSC towards the MS. Quite often this is also called '3rd layer disconnection'. In case of normal call setup case, the release cause is 'normal'.

66. DEACTIVATE_SACCH


By sending this message to downlink direction, the BSC inhibits system information message sending towards the MS. In fact, there is no use to send/receive any information in the SACCH channel any more, so it will be deactivated.

67. DISC

The MS send Layer 2 frame DISConnect to uplink direction in order to inform the BTS it is stopping the traffic in the TCH/FACCH.

68. UA


The BTS acknowledges DISC -frame. Consequences: the MS starts to listen BCCH -channel again and all the Air interface resources are released.

69. RELEASE_INDICATION

The BTS informs the BSC that the MS has no more any dedicated Air interface resources (i.e. TCH/FACCH) in use.

70. RF_CHANNEL_RELEASE

The BSC tells the BTS to release the rest of the radio resources.


71. RF_CHANNEL_RELEASE_ACK.

All the rest of the radio resources have been released; BTS send an acknowledgment to BSC. These radio resources are: TCH/FACCH and SACCH.

72. CLEAR_COMPLETE

This is acknowledgement to the message SCCP Data (Clear Command). Now the BSC informs the MSC that all radio resources related to this call are released.


73. SCCP_RELEASED

When all radio resources are released, BSSAP connection concerning this call is not needed any more. This message tells the BSC to release this SCCP connection. The message is sent as RLSD message.

74. SCCP_RELEASED_ACK.

BSC informs MSC that now the dedicated SCCP connection concerning this call is released. The message is sent as RLC message.


2. MOBILE TERMINATED CALL


MSC BSC BTS MSVLR

Channel Required

Channel ActivationChannel Activation Ack.




SABM Paging Response(SDCCH)

Establish IndicationCR (Paging Responset)Process Access Request

AuthenticateCC Authentication Request




Set Ciphering ModeDT1 Ciphering Mode Command

Encryption CommandCiphering Mode Command(SDCCH)

Ciphering Mode Complete ( SDCCH )DT1Ciphering Mode Complete


Forward New TMSITMSI Reallocation Command

TMSI Reallocation Command ( SDCCH )

TMSI Reallocation Complete ( SDCCH )

TMSI Reallocation CompleteTMSI Ack.

Setup ( SDCCH )DT1 Setup

Send Info for O.G. Call

Complete CallDT1 Call Proceeding

Call Proceeding ( SDCCH )DT1 Assignment Request

Physical Context Request


Channel Activation

Channel Activation Ack.Assignment Command ( SDCCH )


UA ( FACCH )Assignment Complete (FACCH)

DT1 Assignment CompleteChannel Release

Channel Release Ack.DT1 Alerting Alerting ( FACCH )

DT1 Connect Connect ( FACCH )

Connect Ack.( FACCH )DT1 Connect Ack.


Disconnect ( FACCH )DT1 Disconnect

DT1 Release

DT1 Release Complete

DT1 Clear Command

Release ( FACCH )

Release Complete ( FACCH )

Channel Release (FACCH)



RF Channel Release

RF Channel Release Ack.DT1 Clear Complete

RLSD ( SCCP Released )

RLC ( SCCP Released Ack.)

Paging RequestPaging Command

UDT Paging12

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RADIOACCESSPART

PAGINGPART

UA (SDCCH)

ESTABLISHMENTPART

CIPHERING,AUTHENTICATIONAND CALL SETUPPART

TCH SEIZED

CONVERSATIONPART

RELEASE BY MS

PagingResponse(SDCCH)



1. PAGING

This message is sent by MSC when it has found out the called MS is somewhere under him (= MSC recognizes this is a GSM_END -call). This message contains mainly four kind of information: message type, IMSI of the called subscriber, TMSI of the called subscriber and Cell Identifier list. If TMSI -numbers are defined for use these have the priority one, for security reasons and if the network does not use TMSIs then IMSI -number is included only. The paging is sent as an UDT (Unit Data) message to the BSC.

2. PAGING_COMMAND


The BSC always calculates so called paging group. The idea of this calculation is to find out in which radio time slots the BTS can send the Paging Requests out towards the MS. Reason: in the network, there is a possibility to have at least three different kind of BCCH-TRX -radio time slot configuration and thus logical channel PCH can have at least three different kind of location. If the BSC receives both TMSI and IMSI from the MSC, then it uses always TMSI number when sending paging further on.

3. PAGING_REQUEST

The BTS sends paging on a PCH channel.


4. CHANNEL_REQUEST

The MS responds to the paging by sending a random access burst on a RACH channel via one BTS. Channel request -message contains the establishment cause. This can be 'Answer for paging', 'emergency call', 'other services (Mobile Originated Call, Short Message Service)' or 'Other', like location update. In addition to, this message contains Random Reference. This is 5 bits randomly selected by MS. The usage of random reference is: when two MSs are accessing to the network exactly the same time, the network can separate these Mobile Stations by using this random reference.


5. CHANNEL_REQUIRED












The BSS informs the MS on AGCH channel about the SDCCH channel to be used. In practice, this message is an order from the network to the MS to move to the SDCCH -channel defined before. Page mode, SDCCH channel description, associated SACCH and hopping frequency are included as a parameters. In addition, request reference (same as establishment cause), initial timing advance and frequency allocation if frequency hopping applies are also included.

10. PAGING_RESPONSE

The MS responds to the paging on the signaling channel.



BTS acknowledges the Immediate Assignment Command by returning Establish Indication message. Establish indication -message has two uses. Firstly, when used in this phase it points out that from the BTS point of view, the MS is now on the SDCCH-channel. Thus, the BTS sends information back to the BSC that the MS is now on this kind of SDCCH-channel which description is like this etc. Also the BTS identifies the link = main signaling channel and adds received Layer 3 information into this message.

12. PAGING_RESPONSE


The BSC initiates the MSC about the connection by paging response, which is a CR (Connection Request) message.


13. UA



As a CC (Connection Confirmed) message, the MSC sends an Authentication Request message to the BSC. The message contains the RAND.






In the MS Authentication procedure, two algorithms, A3 and A8 are used. In the SIM -card (In MS), both of these algorithms and 32 -digit key are stored) and the very same information can be found in Authentication Centre (AuC) also. When MS Authentication is requested by the network, AuC/VLR sends


32 -digit RANDom Number to the MS. MS calculates then Signed Response (SRES and returns that back to the VLR. VLR makes a comparison if received SRES is same than it has received inside of the Authentication triplet from the AuC before. If these two SRESs are the same, authentication went OK and MS can continue the call setup.





















The purpose of the TMSI reallocation procedure is to provide identity confidentiality. Usually the TMSI reallocation is performed at least at each change of location area. MSC initiates the TMSI reallocation procedure by sending TMSI Reallocation command message to the MS. TMSI Reallocation Command message contains a new combination of TMSI and LAI allocated by the network or a LAI and the IMSI if the used TMSI shall be deleted. Usually the TMSI Reallocation Command message is sent to the MS by using a RR connection in ciphered mode.



TMSI Reallocation Command is forwarded to the MS.


When the MS receives the TMSI Reallocation Command message, it stores the LAI in the SIM. If the received identity is the IMSI of the MS, it deletes any previously stored TMSI. If the received identity is a TMSI, the MS stores it in the SIM. In both cases the MS send a TMSI Reallocation Complete message to the network.



TMSI Reallocation Complete message is forwarded to the MSC.


27. SETUP

After authentication, Identification and Ciphering, the MS is in the SDCCH channel and ready to start real call setup signaling. The MSC sends a Setup message to the BSC to be forwarded to the MS.

28. SETUP

The BSC sends the Setup message to the MS via BTS in order to inform the MS about the incoming call.


29. CALL_PROCEEDING

The MS responds after having checked the compatibility with a requested bearer capability.

30. CALL_PROCEEDING

The information is forwarded to the MSC. This message indicates that the network has received all information that is required for call setup and no more such information will be accepted.


31. ASSIGNMENT_REQUEST

This message starts the TCH allocation. In the A- interface, MSC is the master and it hunts the circuit used for this call through the A- interface. This message can contain some optional information according to GSM- recommendations. This optional information is: Priority of the call, Downlink Discontinuous Transmission (DTX), Radio channel identity and Interference band to use.



By using this message, the BSC interrogates the actual timing advance from the BTS in order to start TCH allocation through the Abis -interface.


BSC receives the timing advance information from the BTS and starts TCH reservation and allocation. This reservation & allocation procedure is similar to the case of the SDCCH -channel.



After the BSC's internal channel reservation and allocation, it activates the TCH by sending this message towards the BTS. Contents: channel number, activation type, channel mode (DTX/No DTX), channel type (Speech / data: if speech, then GSM encoding algorithm included, if data, then information about transparency or non-transparency of the channel and data rate), channel identity, encryption information if received, BS & MS power levels as received in 'Physical context confirm' -message and timing advance.



The BTS returns current TDMA frame number and after that the TCH is activated through the Abis -interface.


The BTS delivers received information further on towards the MS. Contents: channel description, power levels, cell channel description, channel mode (Full / Half) and mobile allocation.





Establish indication -message has two uses. Firstly, when used this phase it points out that from the point of view of the BTS, the MS is now on the FACCH-channel. Thus, the BTS sends information back to the BSC that the MS is now on this kind of FACCH-channel which description is like this etc. Also the BTS identifies the link = main signaling channel and adds received


Layer 3 information into this message. This layer 3 information is coming from the MS, of course.

39. UA

UA is normal Level 2 acknowledgement when setting up the Layer 2 level link in LAPDm-protocol.


The MS informs it is now on the TCH and everything is OK.



The BSS acknowledges the channel seizure to the MSC.

42. CHANNEL_RELEASE

When MS has informed the network it is in the TCH, there is no need to use the SDCCH -channel for this call setup any more. By Channel Release procedure it is released.

43. CHANNEL_RELEASE_ACK.



44. ALERTING

The MS sends an Alerting message via BSS.

45. ALERTING

The MS informs that the subscriber has been alerted. This message can contain also so-called progress indicator IE, which tells that there are in-band announcements or other similar information to be received. In brief, this means


that the connection is not end-to-end ISDN connection. If the MS receives this element, it shall through-connect the speech path. In case it is not, the MS generates ringing tone in itself. This information can also be transferred in a Progress message.

46. CONNECT

The call is 'accepted' by MS user.

47. CONNECT


Connect -message is end-to-end message and when this message reaches the MSC, charging related to this call starts.

48. CONNECT_ACK.

By using this message, the MSC informs the MS that call is now connected through. Thus, the speech codecs can be opened in the MS, if not already opened, and the logical radio channel changes from FACCH to TCH.

49. CONNECT_ACK.


The message is forwarded to the MS.





If these measurement reports are preprocessed in the BTS then measurement results are sent towards the BSC. If the is no preprocessing in the BTS, then measurement reports are sent. In this phase, Nokia BTS does not make any preprocessing.

52. DISCONNECT

This request is sent by MS. Contents: clear end-to-end connection. This message stops the charging concerning this call connection.


53. DISCONNECT

The Disconnect message is forwarded to the MSC.

54. RELEASE

Actual release is coming from the MSC; real call is just about to end.

55. RELEASE

The Release message is forwarded to the MS.



MS informs that it will release the transaction identifier, i.e. call release is proceeding.


The Release Complete message is forwarded to the MSC.

58. CLEAR_COMMAND



59. CHANNEL_RELEASE





61. DISC


62. UA










66. CLEAR_COMPLETE



67. SCCP_RELEASED





3. LOCATION UPDATE


MSC BSC BTS MSVLR

Channel Required

Channel Activation





Location Update Request

Establish IndicationProcess Access Request

AuthenticateDT1Authentication Request




Set Ciphering ModeDT1 Cipher Mode Command

Encryption Command

Ciphering Mode Command ( SDCCH )

Ciphering Mode Complete ( SDCCH )DT1Cipher Mode Complete


DT1 Location Update Accepted

Location Update Accepted

TMSI reallocation CompleteDT1TMSI Reallocation Complete

DT1 Clear Command

Channel Release ( SDCCH )



RF Channel Release

RF Channel Release Ack.DT1 Clear Complete

RLSD (SCCP Released)

RLC (SCCP Released Ack.)

CR Location Update Req.Request Request UA ( SDCCH )

Identity RequestCC Identity Request

Identity Request ( SDCCH )

Identity Response ( SDCCH )DT1 Identity ResponseIdentity Response

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34

3536

3738

RADIOACCESSPART

IDENTIFICATIONANDAUTHENTICATIONPROCEDURES

CHANNELRELEASE

LOCATIONUPDATEREQUEST

CIPHERING ANDENCRYPTIONPART

LOCATIONUPDATE

Location Update RequestRequest Request SABM (SDCCH)



1. CHANNEL_REQUEST

The MS requests a channel by sending a random access burst on a RACH channel via one BTS. Channel request -message contains the establishment cause. This can be 'Answer for paging', 'emergency call', 'other services (Mobile Originated Call, Short Message Service)' or 'Other', like location update. In addition to, this message contains Random Reference. This is 5 bits randomly selected by MS. The usage of random reference is: when two MSs are accessing to the network exactly the same time, the network can separate these Mobile Stations by using this random reference.


2. CHANNEL_REQUIRED












The BSS informs the MS on AGCH channel about the SDCCH channel to be used. In practice, this message is an order from the network to the MS to move to the SDCCH -channel defined before. Page mode, SDCCH channel description, associated SACCH and hopping frequency are included as a parameters. In addition, request reference (same as establishment cause), initial timing advance and frequency allocation if frequency hopping applies are also included.

7. LOCATION_UPD_REQ


The Location Update Request message is sent by the MS to the network to request update of its location file.


BTS acknowledges the Immediate Assignment Command by returning Establish Indication message. Establish indication -message has two uses. Firstly, when used in this phase it points out that from the BTS point of view, the MS is now on the SDCCH-channel. Thus, the BTS sends information back to the BSC that the MS is now on this kind of SDCCH-channel which


description is like this etc. Also the BTS identifies the link = main signaling channel and adds received Layer 3 information into this message.

9. LOCATION_UPD_REQ

The Location Update Request message is forwarded to the MSC as a CR (Connection Request) message.

10. UA



11. IDENTITY_REQUEST

Actually this is an Identification procedure used for IMEI -checking. IMEI = International Mobile Equipment Identity. This kind of request is generated by Equipment Identity Register in order to control MS Hardware Parts. Normally, this is not made in every call setup; quite typical value (set inside the VLR) is that IMEI is checked every 20th time when MS is making call setup. The network may also require IMSI of the subscriber in case it cannot be obtained


from the network side. An example is that MS tries to establish a call with TMSI, but the network has lost TMSI. In this case the network has no other possibility to identify the subscriber than to ask the MS. The Identity Request message is sent as a CC (Connection Confirm) message.


12. IDENTITY_REQUEST

The BSS forwards the Identity Request message to the MS.

13. IDENTIFICATION_RESPONSE

The MS sends a response to the Identity Request containing its mobile identity information.

14. IDENTIFICATION_RESPONSE


The message is forwarded to the MSC.


As a DT1 (Data Form 1) message, the MSC sends an Authentication Request message to the BSC. The message contains the RAND.






In the MS Authentication procedure, two algorithms, A3 and A8 are used. In the SIM -card (In MS), both of these algorithms and 32 -digit key are stored) and the very same information can be found in Authentication Centre (AuC) also. When MS Authentication is requested by the network, AuC/VLR sends 32 -digit RANDom Number to the MS. MS calculates then Signed Response (SRES and returns that back to the VLR. VLR makes a comparison if received


SRES is same than it has received inside of the Authentication triplet from the AuC before. If these two SRESs are the same, authentication went OK and MS can continue the call setup.



















24. LOCATION_UPD_ACC

The MSC sends the Location Updating Accep message to the MS to indicate that updating has been completed.

25. LOCATION_UPD_ACC


The Location Updating Accept message is forwarded to the MS by the BSS.

26. TMSI_REALLOC_COMPL

The TMSI Reallocation Complete message is sent to the network to indicate, that reallocation of new TMSI has taken place.

27. TMSI_REALLOC_COMPL

The TMSI Reallocation Complete message is forwarded to the MSC.


28. CLEAR_COMMAND



29. CHANNEL_RELEASE





31. DISC


32. UA










36. CLEAR_COMPLETE



37. SCCP_RELEASED






4. INTERNAL HANDOVER, INTRA CELL


BSC BTS MSMSC

Receiver Ready ( FACCH )


DT1 ( HO Performed )

RF Channel Release

RF Channel Release Ack.

Physical Context Request


Channel Activation


Assignment Command (FACCH )


UA ( FACCH )

Assignment Complete ( FACCH )

12

3

4

5

6

7

8910

111213

1415

NEWTCHRESERVATIONANDACTIVATION

OLDTCHRELEASE

HOMEASUREMENTS

PHYSICALCONTEXTINFORMATION

SIGNALLING ONFACCH NEW

SIGNALLINGON FACCH OLD






If these measurement reports are preprocessed in the BTS then measurement results are sent towards the BSC. If the is no preprocessing in the BTS, then measurement reports are sent.





The BSC sends a Channel Activation message to the BTS. After receiving Handover Request from the MSC, the BSC starts to search and allocate TCH for this call on certain terms, the most important is of course which BTS and then the channel configuration of this BTS. Parameters: DTX control, channel ID & description & mobile allocation, maximum power levels of the MS and BS and finally, the first timing advance concerning this access calculated by the BSC.



A response to the Channel Activation message. When BTS has received this message it starts to send and receive TCH/SACCH. The reference used in this case is the power levels received in Channel Activation message.






BTS acknowledges the Immediate Assignment Command by returning Establish Indication message. Establish indication -message has two uses. Firstly, when used in this phase it points out that from the BTS point of view, the MS is now on the new TCH. Thus, the BTS sends information back to the BSC that the MS is now on this kind of TCH which description is like this etc.


Also the BTS identifies the link = main signaling channel and adds received Layer 3 information into this message.

10. UA




This message is sent by the MS to the network to indicate, that the MS has established the main signalling link successfully.

12. RR

The BTS sends a Receive Ready message to the MS.

13. HO_PERFORMED


The Handover Complete message is forwarded to the MSC. When the Handover Complete message is received, the network releases the old channels.


When MS has informed the network it is in the TCH, there is no need to use the old TCH for this call setup any more. By Channel Release procedure it is released.





5. INTERNAL HANDOVER, INTER CELL


BSC BTS 2 BTS 1 MSMSC

Handover Command

Handover Detect

HO Command ( FACCH )

HO Access ( FACCH )

Establish Indication

Physical Info ( FACCH )

SABME ( FACCH )

Handover Complete

Handover Complete ( FACCH )

UA ( FACCH )



Channel Activation


DT1 ( HO Performed )RF Channel Release


12

45 6

789

1011

1314

3

15

12

1617

18

TCHRESERVATION ANDACTIVATION IN BTS2

HO MEASUREMENTS

SIGNALLINGON FACCH IN BTS1

SIGNALLINGON FACCH IN BTS2

TCH RELEASE INBTS1








The BSC sends a Channel Activation message to the BTS. After receiving Handover Request from the MSC, the BSC starts to search and allocate a TCH for this call on certain terms, the most important is of course which BTS and then the channel configuration of this BTS. Parameters: DTX control, channel ID & description & mobile allocation, maximum power levels of the MS and


BS and finally, the first timing advance concerning this access calculated by the BSC.




5. HO_COMMAND

Handover Command message is sent from the BSC to the BTS to change the dedicated channel configuration and timing adjustment needeed.

6. HO_COMMAND

The BTS forwards the message to the MS.

7. HO_ACCESS


The MS sends a Handover Access message in random mode to the new BTS.

8. HO_DETECT

The new BTS informs the BSC, that it has detected a handover access message.

9. PHYSICAL_INFO

The Physical Information message contains various physical layer related information, allowing a proper transmission by the MS.





BTS acknowledges the Immediate Assignment Command by returning Establish Indication message. Establish indication -message has two uses. Firstly, when used in this phase it points out that from the BTS point of view,


the MS is now on the new TCH. Thus, the BTS sends information back to the BSC that the MS is now on this kind of TCH which description is like this etc. Also the BTS identifies the link = main signaling channel and adds received Layer 3 information into this message.

12. UA


13. HO_COMPLETE




14. RR


15. HO_COMPLETE

The Handover Complete message is sent to the BSC.

16. HO_PERFORMED




When MS has informed the network it is in the new TCH, there is no need to use the old TCH for this call setup any more. By Channel Release procedure it is released.





6. EXTERNAL HANDOVER


BSC1 BTS 2 BTS 1 MSMSC

Handover Detect

HO Command ( FACCH )

HO Access ( FACCH )

Establish Indication

Physical Info ( FACCH )

SABME ( FACCH )

Handover Complete

Handover Complete ( FACCH )

UA ( FACCH )



Channel Activation


DT1 ( HO Detection )

RF Channel Release


12

45

6

7

89

1011

13

1415

12

16

18

TCHRESERVATION ANDACTIVATION IN BSS2

HOMEASUREMENTSANDDECISION

DISCONNECTIONAND TCH RELEASEIN BSS1

BSC2

3

CC ( HO_Req.Ack )

CR ( HO_Request )

DT1 ( HO Required )

DT1

17

19DT1 ( HO Complete)20

Handover Command

2122

DT1 Clear Command

23

24DT1 ( Clear Complete)







3. HO_REQUIRED

The BSC informs the MSC, that according to the measurement results, a handover is needed.

4. HO_REQUEST


The MSC sends a Handover Request message to the new BSC, which starts channel activation.



The BSC sends a Channel Activation message to the BTS. After receiving Handover Request from the MSC, the BSC starts to search and allocate a TCH for this call on certain terms, the most important is of course which BTS and then the channel configuration of this BTS. Parameters: DTX control, channel ID & description & mobile allocation, maximum power levels of the MS and BS and finally, the first timing advance concerning this access calculated by the BSC.




7. HO_REQUEST_ACK

After channel activation the new BSC sends a Handover Request Acknowledge message to the MSC to indicate, that the channel activation procedure is executed.

8. HO_COMMAND


Handover Command message is sent from the MSC to the BSC to change the dedicated channel configuration and timing adjustment needeed.

9. HO_COMMAND


10. HO_ACCESS

The MS sends a Handover Access message in random mode to the new BTS.


11. HO_DETECT

The new BTS informs the BSC, that it has detected a handover access message.

12. HO_DETECTION

The new BSC sends a Handover Detection message to the MSC, which starts channel establishment procedure on the new BSS.

13. PHYSICAL_INFO


The Physical Information message contains various physical layer related information, allowing a proper transmission by the MS.





BTS acknowledges the Immediate Assignment Command by returning Establish Indication message. Establish indication -message has two uses. Firstly, when used in this phase it points out that from the BTS point of view,


the MS is now on the new TCH. Thus, the BTS sends information back to the BSC that the MS is now on this kind of TCH which description is like this etc. Also the BTS identifies the link = main signaling channel and adds received Layer 3 information into this message.

16. UA


17. HO_COMPLETE



18. RR


19. HO_COMPLETE



20. CLEAR_COMMAND




When MS has informed the network it is in the TCH, there is no need to use the old TCH for this call setup any more. By Channel Release procedure it is released.




23. CLEAR_COMPLETE



Documents

Gsm Call Flow With Defination