IMP CALL FLOW TRAINING NOTES

8/7/2019 IMP CALL FLOW TRAINING NOTES

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1 CALL FLOW Signalling Procedures

The BSS signalling procedures are mainly related to actions and events triggeredby or for the MS. This document describes the signalling procedures, the signalling

flow and the messages used for the various services.

In this part the different phases of the signalling procedures are explained.

Radio access part

Before any signalling event (e.g. MOC or LUP) can take place the MS has to make

a radio access. This consists of three phases, the random access, the channel

activation and the immediate assignment.

The MS will send a RACH burst to the BTS when performing a location update,

originating a call, or answering a page in the case of an MTC. When a RACH is

received, the BTS requests a signalling channel from the BSC. The BSC will

activate an SDCCH in the BTS. The BSC then sends an Immediate Assignment

message (AGCH on Air interface) which will tell the mobile to use the assigned

SDCCH channel.

During radio access the communication is based on a Random Reference Number

produced by the MS. The MS will send a random number with the RACH burst

and the BSC will include this number in the Immediate Assignment Command.

The other RACH related parameters are described in the BCCH description in this

document.


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Establishment part

After the MS has started transmitting on the SDCCH it will send a signallingconnection establishment message, SABM. This message has to be acknowledged

by the BTS with a UA-message. Included in the SABM message is the first MM-

message describing the service required by the MS. Once the signalling connection

between the MS and the BTS has been established, and the MS has requested a

service, the SCCP connection-oriented signalling can begin on the A interface.

Location update or call setup

After the signalling connections have been established the procedure varies

depending on the type of service requested.

Location Update

In the case of a Location Update Request, the MSC will check the MS identity

based on IMSI or TMSI and perform authentication. If this is successful, ciphering

is activated, after which the MS equipment identity can be checked. With the

Location Update Accepted message the MSC will allow the MS to access the

network and a new TMSI is allocated.

Call Setup

After the authentication, ciphering and TMSI reallocation procedures as described

above have been completed, the system has to assign a traffic channel (TCH) to the

MS. All of these procedures may vary, depending on the network settings.

The setup of the call is divided into two parts, traffic channel assignment and

connection of the call. The traffic channel is taken into use during the assignment

procedure. The procedure starts with an Assignment Request and can be split into

three phases. The first phase consists of A-interface TCH allocation and of Air

interface TCH activation. The MSC will inform the BSC which speech circuit will

be used on the A-I/F and the BSC will activate a TCH in the BTS for the MS.

The second phase is to assign the channel to the MS. When the MS switches to the

assigned TCH it will use FACCH mode (stealing mode) to send signalling. The

third phase is to start the signalling connection with SABM. After this, the MS will

use the assigned signalling connection, FACCH, to send an Assignment Complete

message to the MSC.

Once the channels have been successfully allocated between the subscribers, the

second part of call setup takes place. This involves alerting the called party (the

phone rings) and connection (if the phone is answered).


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Conversation part

The conversation part can start when the Connect Acknowledgement message is

received. During the conversation there will be measurement signalling between

the MS, BTS and BSC. If required the BTS can change the Timing Advance of the

MS and the BSC can make decisions on power level modifications or handovers. Itis also possible to send SMS messages on the SACCH.

Release after call or location update

When either the called or the calling party hangs up, the Disconnect message will

be sent. This initiates the release procedure, which can be divided into four phases.

Firstly, the call connection will be released and then the signalling connections

(FACCH and the associated SACCH) can be disconnected. When the logical

resources using the physical TCH have been cleared the RF channel can be

released. Last part of the release is to clear the SCCP connection-orientedsignalling communication between MSC and BSC.

In the case of a Location Update the used resources will be cleared in the same

way. This will happen after the Location Update Accepted message is received by

the MS and the TMSI reallocation is completed. The RF resource used in this case

is an SDCCH with its associated SACCH.


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2 Mobile call signalling

This section describes the signalling message flow of a mobile call. The signallingmessage flow of a mobile originated call differs from that of a mobile terminated

call. The signalling flow will also be affected when the release of the call is made

by the calling or called party. The particular messages are explained in the

signalling examples below.


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Mobile Originated Call Signalling Example

`

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

AuthenticateDT1Authentication 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 TMSI

TMSI Reallocation Command

TMSI Reallocation Command ( SDCCH )

TMSI Reallocation Complete ( SDCCH )

TMSI Reallocation Complete

TMSI Ack .

Setup ( SDCCH )

DT1 Setup

Send Info for O.G. Call

Complete Call

DT1 Call ProceedingCall Proceeding ( SDCCH )

DT1 Assignment Request

Physical Context Request

Physical Context Confirmed

Channel Activation

Channel Activation Ack .

Assignment Command ( SDCCH )

SABM ( FACCH )

Establish Indication

UA ( FACCH )

Assignment Complete ( FACCH )

DT1 Assignment Complete

RF Channel Release

RF 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 SACCH

DISC ( FACCH )

UA ( FACCH )

Release Indication

RF Channel Release

RF Channel Release Ack .

DT1 ( Clear Complete )

RLSD ( SCCP Released )

RLC ( SCCP Released Ack .)

12

3

4

56

78

91011

12 1314

1516

17

18 19

20 21

2223

24

25 2627

282930

3132

33

3435

3637

38

39

4041

4243

44

454647

48

4950

5152

53

5455

5657

5859

6061

6263

64 65

6667

6869

70

7172

7374

UA (SDCCH)

RADIO

ACCESS

PART

PART

CIPHERING,

N

PART

TCH SEIZED

PART

CM Service Request

Ciphering Mode Command

SABMCR (CM Service Request)

CC


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1. Channel Request (MS to BTS;RACH)

The MS requests a channel by sending a random access burst on a RACH channelto a BTS. The Channel request message contains the establishment cause (3 bits)

which can be response to paging, emergency call or 'other services' e.g. Mobile

Originated Call, Short Message Service or Location Update. Additionally, this

message contains a Random Reference, which consists of 5 bits randomlyselected by the MS. This random reference is used to separate two MSs that are

attempting to access the network at exactly the same time.

2. Channel Request (BTS to BSC;BTSM)

Upon receiving the Channel Request message from the MS, the BTS sends a

Channel-Required message to the BSC, which contains the information containedin the channel request. To this, the BTS adds the TDMA frame number and the

Access Delay, which is the first timing advance estimate made by the BTS.

CHAN RQD (CCh) T=0

Channel Nr

- uplink CCCH (RACH)

- timeslot : 0

Req. Ref

- MOC, SMS

- random reference : 2 (2h)

- N32 : 11 (bh)

- N26 : 14 (eh)

- N51 : 35 (23h)

Access Delay

- value : 0 (00h)


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3. Channel Activation(BSC to BTS;BTSM)

After receiving the Channel-Required message, the BSC allocates an SDCCH-channel for this call. It sends a Channel Activation message to the BTS containing

the following parameters: DTX control, channel description, mobile allocation,

maximum power levels of the MS and BTS and the timing advance as

calculated by the BSC.

CHAN. ACT. (DCh) T=0

Channel Nr

- SDCCH/8 subchannel 1

- timeslot : 1

Act. Type

- immediate assignment procedure

Channel Mode

- length : 4

- downlink DTX not used, uplink DTX not used

- channel type : 03h 01h 00h

Channel Id

- length : 6

- SDCCH/8 subch 1

- timeslot : 1

- training sequence code : 0

- hopping : 0- Frequency band nr : 3

- ARFCN : 92 (5ch)

- frequencies included from CA :

BS Power

- power control level : 14 (eh)

MS Power

- power control level : 0 (0h)

Timing Adv.

- 0 (00h) (0 km)


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4. Channel Activation Ack (BTS to BSC;BTSM)

A response to the Channel Activation message. When the BTS has received thismessage it starts to send and receive on the SACCH channel.

CHAN. ACT. ACK (DCh) T=0

Channel Nr


- timeslot : 1

Frame Number

- N32 : 11 (bh)

- N26 : 24 (18h)

- N51 : 45 (2dh)

5. Immediate Assignment Command(BSC to BTS;BTSM;L3)

The BSC tells the BTS about the characteristics of the SDCCH channel to use.

IMM.ASS. CMD (CCh) T=0

Channel Nr

- downlink CCCH (PCH + AGCH)

- timeslot : 0

Imm. Ass. Info

- value (hex) : 06 3F 00 49 03 5C E25C 6E 00 00

IMMEDIATE ASSIGNMENT (RR)

Page Mode

- normal paging

Channel Description


- timeslot : 1


- hopping : 0

- Frequency band nr : 3

- ARFCN : 92 (5ch)

Request Reference

- MOC, SMS


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- random reference : 2 (2h)

- N32 : 11 (bh)

- N26 : 14 (eh)

- N51 : 35 (23h)

Timing Advance

- 0 (00h) (0 km)

Mobile Allocation


6. Immediate Assignment (BS to MS;AGCH)

The BSC informs the MS via the BTS on the AGCH channel the characteristics of

the SDCCH channel to be used. Parameters include the page mode, SDCCH

channel description, SACCH, hopping indicator, the initial timing advance,

and mobile allocation (if frequency hopping applies). Additionally, the requestreference (random reference and the TDMA frame number) originally sent by the

MS is included to identify the relevant MS. The MS is then able to switch to this

SDCCH channel.

7. CM Service Request (MS to BTS;SDCCH)

SABM (LAPDm) After receiving the IMMEDIATEASSIGNMENT message, theMS tunes to the assigned SDCCH and starts to establish the signalling link across

the network. The MS sends the layer2 SABM to the BTS on the SDCCH. The

SABM contains a layer3 service request message indicating the service type

required to the network through the service request message.

8. CM Service Request (BTS to BSC; L3)

Establish Indication (BTSM)

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. Also the BTS identifies the link id as the main signalling

channel and adds received Layer 3 information into this message. The BSC starts

the handover algorithm.

EST. IND (RLL) T=0

Channel Nr


- timeslot : 1

Link Id

- main DCCH (FACCH or SDCCH)

- SAPI : 0

L3 Info


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CM SERVICE REQUEST (MM)

CM Service Type

- value : 1h

Ciphering Key Seq. Nr

- value : 2h

MS Classmark 2

- length : 2 (02h)

- revision level : reserved for phase 1

- encryption algorithm A5

- class 1, vehicle and portable

- frequency band 0

- short message capability present

Mobile Identity

- length : 5h

- TMSI : ca290100

9. Complete L3 Information

(BSC to MSC;BSSMAP)

CM Service Request ( L3 )

The CM Service Request message is forwarded to the MSC

- BSSMAP (length : 22, 16h)

COMPLETE L3 INFORMATION

Cell Identifier

- length : 5 (05h)

- cell identified with LAC + CI

- location area code : 1369 (0559h)

- cell identifier : 174 (00AEh)

Layer 3 Information

-length : 12 (0Ch)

CM SERVICE REQUEST (MM)

CM Service Type

- value : 1h


- value : 2h

MS Classmark 2


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- length : 2 (02h)

- revision level : reserved for phase 1

- encryption algorithm A5

- class 1, vehicle and portable

- frequency band 0

- short message capability present

Mobile Identity

- length : 5h

- TMSI : ca290100

10. UA (BTS to MS;SDCCH LAPDm)

The BTS acknowledges the SABM sent by the MS.

11. Process Access Request (MSC to VLR;CCS7

MSC forwards MS's request for access management from

VLRby Process Access Request message.

12. Authentication (VLR to MSC;CCS7)

VLRinitiates authentication request by sending an Authenticate

Message to MSC.

13. Authentication Request

(MSC to BSC ; L3)

The network sends this message to the mobile to initiate the authenticationof the mobile station identity. The mobile uses the RAND (input)as an inputto the authentication algorithm to calculate the response, SRES.(output)

- DTAP (length : 19, 13h)

- SAPI : 0, main DCCH is used

AUTHENTICATION REQ (MM)


- value : 2h

Auth. Parameter RAND

741D0912FA6493F91D8AC833ACA2075D

14. Authentication Request

(BSC to BTS ;BTSM L3)

(BTS to MS ; SDCCH L3)

DATA REQ (RLL) T=1


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Channel Nr


- timeslot : 1

Link Id


- SAPI : 0

L3 Info

AUTHENTICATION REQ (MM)


- value : 2h

Auth. Parameter RAND

741D0912FA6493F91D8AC833ACA2075D

This element is used to identify a previously calculated and stored ciphering key

(Kc) in the mobile. The mobile stores this sequence number it received from the

network with the corresponding Kc.

15. Authentication Response

(MS to BTS; SDCCH L3)

(BTS to BSC; BTSM L3)

The MS responds to the Authentication Request with the Signed Response SRES.

There are two algorithms used in the Authentication procedure, A3 and A8. In the

MS, these algorithms are stored on the SIM card, along with a 32-digit key called

Ki. The same information can be found in the Authentication Centre (AuC). When

the network requests MS Authentication, the AuC/VLR sends a 32 digit RANDom

Number to the MS. The MS calculates the Signed Response (SRES) and sends it

to the VLR. The VLR then compares the MSs SRES with the AuCs SRES and if

they are the same, the call set-up can continue.

Note

The first 8 digits of the Ki are used for Authentication and SRES calculation;

the other 24 are reserved for Ciphering Key (Kc) calculation.


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DATA IND (RLL) T=1

Channel Nr


- timeslot : 1

Link Id


- SAPI : 0

L3 Info

AUTHENTICATION RSP (MM)

Auth. Parameter SRES : 741C0B11

16. Authentication Response

(BSC to MSC; L3)

The BSC forwards the SRES to the VLR.



AUTHENTICATION RSP (MM)

Auth. Parameter SRES : 741C0B11

17. Authentication Response (MSC to VLR)

MSC sends a positive response to Authenticate message.

18. SET_CIPHERING_MODE

VLR sends MSC Set Ciphering Mode message that is used for changing MS-BTS

connection ciphering status.

19. Cipher Mode Command (MSC to BSC;BSSMAP)

The MSC uses this command, which includes Kc to initiate ciphering if the

function is enabled.


CIPHER MODE COMMANDL3 Header Information

- length : 2 (02h)

- protocol discr. : Radio Resources

- transaction id. : 0 (0h)

- message send from originating side


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Encryption Information

- length : 9 (09h)

- GSM user data encr. v. 1

- ciphering key, length : 8 (08h)

FE 61 95 FE E5 73 32 C8

------------------------------------------------------------------------------------------------

Layer 3 Header Information

This element is used to supply the BSS with the necessary information in order tocarry the layer 3 messages to the mobile over the radio interface.

L3 Header Information

length : d (xh)

protocol discriminator pd text

transaction identifier : d (xh)

message sent dir text originating side

Protocol discriminator

value pd text

3h Call Control

5h Mobility Management

6h Radio Resources

9h SMS with call

Bh SMS with out call

Fh GSM test procedures

others Unknown protocol discriminator : d (xh)

The dir text is replaced with "to", if the TI flag is set to one. Otherwise "from" is

displayed.

Encryption information

This element carries the user data encryption information necessary to control the

encryption equipment in the BSS.

------------------------------------------------------------------------------------------------

Encryption information

length : d (xh)

algorithm id text

ciphering key, length : d (xh)

xx xx xx xx xx xx xx xx


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Algorithm idetifier

Phase 1:

Value algorithm id text

1 no encryption required

2 GSM encryption version 1

others Unknown algorithm id : d (xh)

Phase 2:

Bit No algorithm id text

1 no encryption required

2 GSM user data encryption version 1 (A%/1)

3 GSM A5/2

4 GSM A5/3

5 GSM A5/46 GSM A5/5

7 GSM A5/6

8 GSM A5/7

The chipering key bytes shall be displayed in hex in the order they apper in the

information element

20. Ciphering Mode Command (BSC to BTS;L3)

Establishment Command (BTSM)

The BSC stores the Encryption information and forwards the command to the BTS.

If the BTS software contains the algorithm specified by the MSC it can startciphering, otherwise it sends a reject message back to the MSC.

ENCR. CMD (DCh) T=0

Channel Nr


- timeslot : 1

Encr. Info

- lentgh : 9

- GSM A5/1

- ciphering key : FE 61 95 FE E5 73

32 C8

Link Id


- SAPI : 0


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L3 Info

CIPH. MODE COMMAND (RR)

Cipher Mode Setting

- start ciphering

21. Ciphering Mode Command (BTS to MS;SDCCH)

The BTS commands the MS to start ciphering (whether required or not) and starts

receiving in the ciphered mode.

22. Ciphering Mode Complete

(MS to BTS to BSC;SDCCH BTSM L3)

DATA IND (RLL) T=1

Channel Nr


- timeslot : 1

Link Id


- SAPI : 0

L3 Info

CIPH. MODE COMPLETE (RR)

The MS acknowledges the ciphering command in the specified cipher mode. This

message may include the IMEI.(for phase 2)

23. Cipher Mode Complete

(BSC to MSC;BSSMAP)

The BSC forwards the cipher response to the MSC.


CIPHER MODE COMPLETE

24. Access Request Accept (MSC to VLR;CCS7)

VLR sends a positive acknowledge to Process Access Request message.

25. Forward New TMSI (VLR to MSC;CCS7)

VLR requests MSC to perform TMSI reallocation. ( It's optinal, no change in

Beijing now)

25+. Identity Request (MSC to BSC to BTS to MS)



IDENTITY REQUEST (MM)


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Identity Type

25++. Identity Response(MS to BTS to BSC to MSC)

DATA IND (RLL) T=1

Channel Nr


- timeslot : 1

Link Id


- SAPI : 0

L3 Info

IDENTITY RESPONSE (MM)

Mobile Identity

- length : 8h

- IMEI : 495000100676140

26. TMSI Reallocation Command

(MSC to BSC; L3)

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 ReallocationCommand message is sent to the MS by using a RR connection in ciphered mode.

- DTAP (length : 13, 0Dh)


TMSI REALLOC COMMAND (MM)

Location Area Id.

- MCC : 262

- MNC : 09- LAC : 1369 (559h)

Mobile Identity

- length : 5h

- TMSI : ca2a0100


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27. TMSI Reallocation Command

(BSC to BTS to MS;BTSM SDCCH L3)

DATA REQ (RLL) T=1

Channel Nr


- timeslot : 1

Link Id


- SAPI : 0

L3 Info

TMSI REALLOC COMMAND (MM)

Location Area Id.

- MCC : 262

- MNC : 09

- LAC : 1369 (559h)

Mobile Identity

- length : 5h

- TMSI : ca2a0100

----------------------------------------------------------------------------------------

Location Area Identification

The purpose of this element is to uniquely idetify a location area withn GSM

network. This information is broadcast on the BCCH to all mobiles. Mobiles use

this information to decide when there is a need to update the location information

of that mobile to the network.

Location Area Id.

MCC : ddd

MNC : dd

LAC : d (xh)

------------------------------------------------------------------------------------------------

Mobile Identity

length : d (xh)

identity text : dddd

Type of identity

value identy text

0 no identity


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1 IMSI

2 IMEI

3 IMEISV

4 TIMSI

other Unknown identity type : d (xh)

If the number of digits is even, the upper nibble of the last octet is then interpreted

as spare bits. In IMSI, they must be set to one.

28. TMSI Reallocation Complete

(MT to BTS to BSC;SDCCH BTSM L3)

DATA IND (RLL) T=1

Channel Nr


- timeslot : 1

Link Id


- SAPI : 0

L3 Info

TIMSI REALLOC COMP. (mm)

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 thenetwork.

29. TMSI Reallocation Complete

(BSC to MSC ; L3)

TMSI Reallocation Complete message is forwarded to the MSC.



TMSI REALLOC COMPL. (MM)

30. TMSI Ack (MSC to VLR;CCS7)

MSC sends VLR a positive response to reallocation of TMSI.

31. Setup (MS to BTS to BSC ;SDCCH BTSM L3)

After authentication, Identification and Ciphering, the MS is on the SDCCHchannel and ready to start real call setup signalling. The MS sends a Setup

message to the BSC to be forwarded to the MSC


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DATA IND (RLL) T=1

Channel Nr


- timeslot : 1

Link Id


- SAPI : 0

L3 Info

SETUP (CC)

Bearer Capability

- length : 1 (1h)

- info xfer cap : speech

- xfer mode : circuit

- coding std : GSM standardized

- radio ch req: full rate ch required

Called Party BCD Nr

- nr type : 0

- nr plan : 1

- nr : 01772000001

32. Setup (BSC to MSC ; L3)

- DTAP (length : 14, 0Eh)


SETUP (CC)

Bearer Capability

- length : 1 (1h)

- info xfer cap : speech

- xfer mode : circuit

- coding std : GSM standardized

- radio ch req: full rate ch required

Called Party BCD Nr

- nr type : 0

- nr plan : 1

- nr : 01772000001


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------------------------------------------------------------------------------------------------

Called Party BCD number

This element contains the called party BCD number. In a normal call, thiselement contains the dialled digits.

Called Party Number nr type : d

nr plan : d

nr ddddddddddddddd

The meaning of different values for type of number is:

value type of number

0 Unknown

1 international

2 national

3 network specific

4 dedicate PAD access

Other values are reserved.

The meaning of different values for numbering plan is:

value numpering plan

0 Unknown

1 ISDN/telephony

3 data (X.121)

4 telex (F.69)

8 national

9 private

Other values are reserved.

The digits of the party number are displayed in the order as they apper in the

message. Digits from 0 to 9 are displayed as themselves. For other digits thefollowing interpretation shall be used:

Ah ':'

Bh ';'

Ch ''

Fh '?', endmark.

33. Send information for Originated call

(MSC to VLR;CCS7)


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VLR requests forretrieval of call data.

34. Complete call (VLR to MSC ;CCS7)

Call completion acknowledged by VLRfor MOC.

35. Call Proceeding (MSC to BSC ; L3)



CALL PROCEEDING (CC)

The MSC responds to the Setup message.

36. Call Proceeding

(BSC to BTS to MS;BTSM SDCCH L3)

DATA REQ (RLL) T=1

Channel Nr


- timeslot : 1

Link Id


- SAPI : 0

L3 Info

CALL PROCEEDING (CC)

Ready to get TCH

37. Assignment Request (MSC to BSC;BSSMAP)


ASSIGNMENT REQUEST

Channel Type

- length : 3 (03h)

- speech

- TCH/FS

- GSM speech encoding algorithm version 1

L3 Header Information

- length : 2 (02h)

- protocol discr. : Radio Resources

- transaction id. : 0 (0h)

- message send from originating side

Priority


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- length : 1 (01h)

- priority level 3 (3h)

- queueing allowed

- preemption vulnerability indi not allowed

Circuit Identity Code

- pcm multiplex : 1 (001h)

- pcm timeslot : 1 (01h)

This message starts the TCH allocation. In the A- interface, MSC is the master andit 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.


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38. Physical Context Request(BSC to BTS ;BTSM)

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

PHYS. CONTEXT REQ (DCh) T=0

Channel Nr


- timeslot : 1

39. Physical Context Confirm (BTS to BSC ;BTSM)

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.

PHYS. CONTEXT CNF (DCh) T=0

Channel Nr


- timeslot : 1

BS Power


MS Power


Timing Adv.

- 0 (00h) (0 km

40. Channel Activation (BSC to BTS;BTSM)

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.

CHAN. ACT. (DCh) T=0

Channel Nr

- full rate TCH

- timeslot : 6

Act. Type

- normal assignment procedure


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Channel Mode

- length : 4

- downlink DTX not used, uplink DTX not used

- channel type : 01h 08h 01h

Channel Id

- length : 6

- full rate TCH

- timeslot : 6


- hopping : 0


- ARFCN : 92 (5ch)


Encr. Info

- lentgh : 9

- GSM A5/1

- ciphering key : FE 61 95 FE E5 73

32 C8

BS Power


MS Power


Timing Adv.

- 0 (00h) (0 km)

41. Channel Activation Ack (BTS to BSC; BTSM)

The BTS returns current TDMA frame number and after that the TCH is

activated through the Abis-interface

CHAN. ACT. ACK (DCh) T=0Channel Nr

- full rate TCH

- timeslot : 6

Frame Number

- N32 : 12 (ch)


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- N26 : 14 (eh)

- N51 : 46 (2eh)

42. Assignment Command

(BSC to BTS to MS;BTSM SDCCH L3)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.

DATA REQ (RLL) T=1

Channel Nr


- timeslot : 1

Link Id


- SAPI : 0

L3 Info

ASSIGNMENT COMMAND (RR)

Channel Description

- full rate TCH

- timeslot : 6


- hopping : 0


- ARFCN : 92 (5ch)

Power Command

- power level of MS : 0

Channel Mode

- speech FR or HR version 1

43. SABM (MS to BTS ;FACCH)

This is a Layer 2 message.

44. Establish Indication (BTS to BSC ;BTSM)

Establish indication -message has two uses. Firstly, when used this phase it points

out that from the point of view ofthe BTS, the MS is now on the FACCH-


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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 signalling channel and adds

received0020Layer 3 information into this message. This layer 3 information is

coming from the MS, of course. (L3 information is optional)

EST. IND (RLL) T=0

Channel Nr

- full rate TCH

- timeslot : 6

Link Id


- SAPI : 0

45. UA (BTS to MS ;FACCH)

UA is normal Level 2 acknowledgement when setting up the Layer 2 level link in

LAPDm-protocol.

46. Assignment Complete

(MS to BTS to BSC;FACCH BTSM L3)

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

DATA IND (RLL) T=1

Channel Nr

- full rate TCH

- timeslot : 6

Link Id


- SAPI : 0

L3 Info

ASSIGNMENT COMPLETE (RR)

RR Cause

- normal


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47. Assignment Complete (BSC to MSC ; L3)

The BSS acknowledges the channel seizure to the MSC.


ASSIGNMENT COMPLETE

RR Cause

- norma

48. RF Channel Release (BSC to BTS ;BTSM)

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 RF Channel Release

procedure it is released.

RF CHANNEL REL. (DCh) T=0

Channel Nr- SDCCH/8 subchannel 1

- timeslot : 1

49. RF Channel Release Ack.(BTS to BSC ;BTSM)

The BTS acknowledges the RF Channel Release message.

RF CH. REL. ACK (DCh) T=0

Channel Nr

- SDCCH/8 subchannel 1- timeslot : 1

(Paging the other end;MS power control; ccch load)

50. Alerting (MSC to BSC ; L3)

This message is sent to the originating side during call set up to inform that the

alerting of the called party has been started.



ALERTING (CC)

Progress Indicator

- value (hex) :E0 88


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51. Alerting (BSC to BTS to MS ;BTSM FACCH L3)

The MSC informs the MS that the called subscriber has been alerted. Thismessage 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 MSgenerates ringing tone in itself. This information can also be transferred in a

Progress message.

DATA REQ (RLL) T=1

Channel Nr

- full rate TCH

- timeslot : 6

Link Id


- SAPI : 0

L3 Info

ALERTING (CC)

Progress Indicator


52. Connect (MSC to BSC ; L3)

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.



CONNECT (CC)

53. Connect (BSC to BTS to MS;BTSM FACCH L3)

When the MS receives a Connect message, it attaches 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.

DATA REQ (RLL) T=1

Channel Nr

- full rate TCH

- timeslot : 6

Link Id


- SAPI : 0


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L3 Info

CONNECT (CC)

54. Connect Ack.

(MS to BTS to BSC;FACCH BTSM L3)

By using this message, the MS informs the MSC that the MS is now in the

"active" state.

DATA IND (RLL) T=1

Channel Nr

- full rate TCH

- timeslot : 6

Link Id


- SAPI : 0

L3 Info

CONNECT ACKNOWLEDGE (CC)

55. Connect Ack. (BSC to MSC ; L3)

The message is forwarded to the MSC.



CONNECT ACKNOWLEDGE (CC)

This is the point at which speech is connected & conversation starts.

56. Measurement Report (MS to BTS ;SACCH L3)

When call is on, the MS sends measurement report concerning mainly the quality

of the speech connection two times per second.

57. Measurement Report (BTS to BSC ;BTSM L3)

If these measurement reports are pre-processed in the BTS then measurement

results are sent towards the BSC. If the is no pre-processing in the BTS, then

measurement reports are sent. In this phase, Nokia BTS does not make any pre-

processing.


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MEAS. RES. (DCh) T=0

Channel Nr

- full rate TCH

- timeslot : 6

Meas.Res. Nr

- value : 42 (2ah)

Uplink Meas.

- length : 3 (3h)

- downlink DTX not used

- rxlev_full : 43 (-68 - -67 dBm)

- rxlev_sub : 43 (-68 - -67 dBm)

- rxqual_full : 0

- rxqual_sub : 0

BS Power


L1 Info

- MS power control level : 1 (1h)

- actual TA : 0 (00h) (0 km)

L3 Info

MEASUREMENT REPORT (RR)

Measurement Results

- BCCH allocation sequence number : 0

- DTX was not used

- serving cell rxlev_full : 31 (-80 - -79 dBm)

- serving cell rxlev_sub : 32 (-79 - -78 dBm)

- measurement results are valid

- serving cell rxqual_full : 0

- serving cell rxqual_sub : 0- no neighbour cell meas results

Conversation


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58. Disconnect

( MS to BTS to BSC;BTSM FACCH L3)

This request is sent by MS. Contents: clear end-to-end connection. This message

stops the charging concerning this call connection.

DATA REQ (RLL) T=1Channel Nr

- full rate TCH

- timeslot : 6

Link Id


- SAPI : 0

L3 Info

DISCONNECT (CC)

Cause

- length : 2

- coding standard : GSM

- location : user

- normal event

- cause: normal clearing

Progress Indicator


59. Disconnect (BSC to MSC ; L3)

The Disconnect message is forwarded to the MSC.



DISCONNECT (CC)

Cause

- length : 2


- location : user

- normal event


Progress Indicator



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60. Release (MSC to BSC ; L3)

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



RELEASE (CC)

Cause

- length : 2


- location : user

- normal event


61. Release ( BSC to BTS to MS;BTSM L3)

The Release message is forwarded to the MS.

DATA IND (RLL) T=1

Channel Nr

- full rate TCH

- timeslot : 6

Link Id


- SAPI : 0

L3 Info

RELEASE (CC)

Cause

- length : 2


- location : user

- normal event


62. Release Complete

( MS to BTS to BSC ;BTSM FACCH L3)


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

proceeding.

DATA REQ (RLL) T=1

Channel Nr

- full rate TCH

- timeslot : 6

Link Id


- SAPI : 0

L3 Info

RELEASE COMPLETE (CC)

63. Release Complete (BSC to MSC ; L3)

The Release Complete message is forwarded to the MSC.



RELEASE COMPLETE (CC)

64. Clear Command (MSC to BSC;BSSMAP)

This message is coming from the MSC and releases the associated dedicated

resources, i.e. BSSAP connection concerning this call.


CLEAR COMPLETE

65. Channel Release

(BSC to BTS to MS ;BTSM FACCH L3)

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

setup case, the release cause is 'normal'.

DATA REQ (RLL) T=1

Channel Nr

- full rate TCH

- timeslot : 6

Link Id



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- SAPI : 0

L3 Info

CHANNEL RELEASE (RR)

RR Cause

- normal

66. Deactivate SACCH (BSC to BTS;BTSM)

By sending this message to downlink direction, the BSC inhibits systeminformation 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.

DEACT. SACCH (DCh) T=0

Channel Nr

- full rate TCH

- timeslot : 6

67. DISC (MS to BTS;FACCH )

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 (BTS to MS ;FACCH)

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(BTS to BSC ;BTSM)

The BTS informs the BSC that the MS has no more any dedicated Air

interface resources (i.e. TCH/FACCH) in use.

REL IND (RLL) T=0

Channel Nr

- full rate TCH

- timeslot : 6

Link Id


- SAPI : 0

70. RF Channel Release (BSC to BTS ;BTSM)

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

RF CHANNEL REL. (DCh) T=0


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Channel Nr

- full rate TCH

- timeslot : 6

71. RF Channel Release Ack.

All the rest of the radio resources have been released; BTS send an

acknowledgement to BSC. These radio resources are TCH/FACCH and SACCH.

RF CH. REL. ACK (DCh) T=0

Channel Nr

- full rate TCH

- timeslot : 6

72. Clear Complete (BSC to MSC ; BSSMAP)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.


CLEAR COMPLETE

73. SCCP Released (MSC to BSC;SCCP)

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.

RLSD - RELEASED

Routing Label

- DPC : 432 (01B0h) OPC : 12600 (3138h)

- SLC : 11 (0Bh)

Destination Local Reference

- 0D8056h

Source Local Reference

- 4B814Ch

Release Cause

- SCCP user originated

74. SCCP Released Ack. (BSC to MSC ;SCCP)

BSC informs MSC that now the dedicated SCCP connection concerning this call

is released. The message is sent as RLC message.


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RLC - RELEASE COMPLETE

Routing Label

- DPC : 12600 (3138h) OPC : 432 (01B0h)

- SLC : 13 (0Dh)

Destination Local Reference

- 4B814Ch

Source Local Reference

- 0D8056h

Documents

IMP CALL FLOW TRAINING NOTES