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ITU-T

Q.931

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INTERNATIONAL TELECOMMUNICATION UNION

ITU-T Q.931

TELECOMMUNICATION (03/93)

STANDARDIZATION SECTOR

OF ITU

DIGITAL SUBSCRIBER SIGNALLING SYSTEM

No. 1

NETWORK LAYER

DIGITAL SUBSCRIBER SIGNALLING

SYSTEM No. 1 (DSS 1) – ISDN

USER-NETWORK INTERFACE LAYER 3

SPECIFICATION FOR BASIC CALL

CONTROL

ITU-T Recommendation Q.931

(Previously “CCITT Recommendation”)

Recommendation Q.931 (03/93) i

CONTENTS

Recommendation Q.931 (03/93)

Page

1 General........................................................................................................................................................... 1

1.1 Scope of the Recommendation ......................................................................................................... 1

1.2 Application to interface structures.................................................................................................... 1

2 Overview of call control................................................................................................................................. 1

2.1 Circuit switched calls........................................................................................................................ 2

2.2 Packet-mode access connections ...................................................................................................... 4

2.3 Temporary signalling connections.................................................................................................... 6

2.4 States associated with the global call reference................................................................................ 8

3 Message functional definitions and content ................................................................................................... 9

3.1 Messages for circuit mode connection control.................................................................................. 10

3.2 Messages for packet mode connection control ................................................................................. 28

3.3 Messages for user signalling bearer service control.......................................................................... 37

3.4 Messages with the global call reference ........................................................................................... 50

4 General message format and information elements coding............................................................................ 52

4.1 Overview........................................................................................................................................... 52

4.2 Protocol discriminator....................................................................................................................... 53

4.3 Call reference.................................................................................................................................... 54

4.4 Message type .................................................................................................................................... 56

4.5 Other information elements .............................................................................................................. 58

4.6 Information element for packet communications ............................................................................. 116

5 Circuit-switched call control procedures........................................................................................................ 128

5.1 Call establishment at the originating interface.................................................................................. 128

5.2 Call establishment at the destination interface.................................................................................. 133

5.3 Call clearing...................................................................................................................................... 140

5.4 In-band tones and announcements.................................................................................................... 143

5.5 Restart procedure.............................................................................................................................. 143

5.6 Call rearrangements.......................................................................................................................... 145

5.7 Call collisions ................................................................................................................................... 148

5.8 Handling of error conditions............................................................................................................. 148

5.9 User notification procedure............................................................................................................... 154

5.10 Basic telecommunication service identification and selection.......................................................... 154

5.11 Signalling procedures for bearer capability selection ....................................................................... 155

5.12 Signalling procedures for high layer compatibility selection............................................................ 157

6 Packet communication procedures................................................................................................................. 159

6.1 Outgoing access................................................................................................................................ 160

6.2 Incoming access................................................................................................................................ 162

6.3 X.25 virtual call establishment and release....................................................................................... 167

6.4 Call clearing...................................................................................................................................... 169

6.5 Access collision ................................................................................................................................ 173

7 User signalling bearer service call control procedures................................................................................... 173

7.1 General characteristics...................................................................................................................... 173

7.2 Call establishment............................................................................................................................. 174

7.3 Transfer of USER INFORMATION messages................................................................................. 175

7.4 Congestion control of USER INFORMATION messages................................................................ 175

7.5 Call clearing...................................................................................................................................... 175

ii Recommendation Q.931 (03/93)

Page

8 Circuit-mode multirate (64 kbit/s base rate) procedures ................................................................................ 175

8.1 Call establishment at the originating interface.................................................................................. 176

8.2 Call establishment at the destination interface.................................................................................. 177

8.3 Call clearing...................................................................................................................................... 179

8.4 Restart procedures............................................................................................................................. 179

8.5 Call rearrangements.......................................................................................................................... 179

9 List of system parameters............................................................................................................................... 179

9.1 Timers in the network side................................................................................................................ 179

9.2 Timers in the user side...................................................................................................................... 179

Annex A – User side and network side SDL diagrams.............................................................................................. 187

Annex B – Compatibility and address checking........................................................................................................ 260

B.1 Introduction....................................................................................................................................... 260

B.2 Calling side compatibility checking.................................................................................................. 260

B.3 Called side compatibility and address checking ............................................................................... 260

B.4 Interworking with existing networks ................................................................................................ 261

Annex C – Transit network selection ........................................................................................................................ 263

C.1 Selection not supported..................................................................................................................... 263

C.2 Selection supported........................................................................................................................... 263

Annex D – Extensions for symmetric call operation................................................................................................. 264

D.1 Additional message handling............................................................................................................ 264

D.2 Timers for call establishment............................................................................................................ 265

D.3 Call collisions ................................................................................................................................... 265

Annex E – Network specific facility selection .......................................................................................................... 265

E.1 Default provider................................................................................................................................ 265

E.2 Routing not supported....................................................................................................................... 265

E.3 Routing supported............................................................................................................................. 266

Annex F – D-channel backup procedures.................................................................................................................. 266

F.0 Foreword........................................................................................................................................... 266

F.1 General.............................................................................................................................................. 266

F.2 D-channel backup procedure ............................................................................................................ 267

Annex G – Use of progress indicators....................................................................................................................... 269

Annex H – Message segmentation procedures.......................................................................................................... 270

H.1 Introduction....................................................................................................................................... 270

H.2 Message segmentation...................................................................................................................... 270

H.3 Reassembly of segmented messages................................................................................................. 271

Annex I – Low layer information coding principles.................................................................................................. 277

I.1 Purpose ............................................................................................................................................. 277

I.2 Principles .......................................................................................................................................... 277

I.3 Information classification ................................................................................................................. 279

I.4 Scenarios outside the scope of ISDN standardization....................................................................... 282

Annex J – Low layer compatibility negotiation......................................................................................................... 283

J.1 General.............................................................................................................................................. 283

J.2 Low layer capability notification to the called user.......................................................................... 284

J.3 Low layer compatibility negotiation between users.......................................................................... 284

J.4 Low layer compatibility negotiation options .................................................................................... 284

J.5 Alternate requested values................................................................................................................ 284

Annex K – Procedures for establishment of bearer connection prior to call acceptance........................................... 285

K.1 General.............................................................................................................................................. 285

K.2 Procedures......................................................................................................................................... 285

Annex L – Optional procedures for bearer service change........................................................................................ 286