1     General
        1.1     Scope of this Recommendation
        1.2     Application to interface structures
 2     Overview of call control
        2.1     Circuit-switched calls
                  2.1.1     Call states at the user side of the interface
                  2.1.2     Network call states
        2.2     Packet-mode access connections
                  2.2.1     Access connection states at the user side of the interface
                  2.2.2     Access connection states at the network side of the interface
        2.3     Temporary signalling connections
                  2.3.1     Call states at the user side of the interface
                  2.3.2     Network call states
        2.4     States associated with the global call reference
                  2.4.1     Call states at the user side of the interface
                  2.4.2     Call states at the network side of the interface
 3     Message functional definitions and content
        3.1     Messages for circuit-mode connection control
                  3.1.1     ALERTING
                  3.1.2     CALL PROCEEDING
                  3.1.3     CONNECT
                  3.1.4     CONNECT ACKNOWLEDGE
                  3.1.5     DISCONNECT
                  3.1.6     INFORMATION
                  3.1.7     NOTIFY
                  3.1.8     PROGRESS
                  3.1.9     RELEASE
                 3.1.10     RELEASE COMPLETE
                 3.1.11     RESUME
                 3.1.12     RESUME ACKNOWLEDGE
                 3.1.13     RESUME REJECT
                 3.1.14     SETUP
                 3.1.15     SETUP ACKNOWLEDGE
                 3.1.16     STATUS
                 3.1.17     STATUS ENQUIRY
                 3.1.18     SUSPEND
                 3.1.19     SUSPEND ACKNOWLEDGE
                 3.1.20     SUSPEND REJECT
        3.2     Messages for packet-mode connection control
                  3.2.1     ALERTING
                  3.2.2     CALL PROCEEDING
                  3.2.3     CONNECT
                  3.2.4     CONNECT ACKNOWLEDGE
                  3.2.5     DISCONNECT
                  3.2.6     PROGRESS
                  3.2.7     RELEASE
                  3.2.8     RELEASE COMPLETE
                  3.2.9     SETUP
                 3.2.10     STATUS
                 3.2.11     STATUS ENQUIRY
        3.3     Messages for user signalling bearer service control
                  3.3.1     ALERTING
                  3.3.2     CALL PROCEEDING
                  3.3.3     CONGESTION CONTROL
                  3.3.4     CONNECT
                  3.3.5     CONNECT ACKNOWLEDGE
                  3.3.6     INFORMATION
                  3.3.7     RELEASE
                  3.3.8     RELEASE COMPLETE
                  3.3.9     SETUP
                 3.3.10     SETUP ACKNOWLEDGE
                 3.3.11     STATUS
                 3.3.12     STATUS ENQUIRY
                 3.3.13     USER INFORMATION
        3.4     Messages with the global call reference
                  3.4.1     RESTART
                  3.4.2     RESTART ACKNOWLEDGE
                  3.4.3     STATUS
 4     General message format and information elements coding
        4.1     Overview
        4.2     Protocol discriminator
        4.3     Call reference
        4.4     Message type
        4.5     Other information elements
                  4.5.1     Coding rules
                  4.5.2     Extensions of codesets
                  4.5.3     Locking shift procedure
                  4.5.4     Non-locking shift procedure
                  4.5.5     Bearer capability
                  4.5.6     Call identity
                  4.5.7     Call state
                  4.5.8     Called party number
                  4.5.9     Called party subaddress
                 4.5.10     Calling party number
                 4.5.11     Calling party subaddress
                 4.5.12     Cause
                 4.5.13     Channel identification
                 4.5.14     Congestion level
                 4.5.15     Date/time
                 4.5.16     Display
                 4.5.17     High layer compatibility
                 4.5.18     Keypad facility
                 4.5.19     Low layer compatibility
                 4.5.20     More data
                 4.5.21     Network-specific facilities
                 4.5.22     Notification indicator
                 4.5.23     Progress indicator
                 4.5.24     Repeat indicator
                 4.5.25     Restart indicator
                 4.5.26     Segmented message
                 4.5.27     Sending complete
                 4.5.28     Signal
                 4.5.29     Transit network selection
                 4.5.30     User-user
        4.6     Information element for packet communications
                  4.6.1     Closed user group
                  4.6.2     End-to-end transit delay
                  4.6.3     Information rate
                  4.6.4     Packet layer binary parameters
                  4.6.5     Packet layer window size
                  4.6.6     Packet size
                  4.6.7     Redirecting number
                  4.6.8     Reverse charging indication
                  4.6.9     Transit delay selection and indication
 5     Circuit-switched call control procedures
        5.1     Call establishment at the originating interface
                  5.1.1     Call request
                  5.1.2     B-channel selection – Originating
                  5.1.3     Overlap sending
                  5.1.4     Invalid call information
                  5.1.5     Call proceeding
                  5.1.6     Notification of interworking at the originating interface
                  5.1.7     Call confirmation indication
                  5.1.8     Call connected
                  5.1.9     Call rejection
                 5.1.10     Transit network selection
        5.2     Call establishment at the destination interface
                  5.2.1     Incoming call
                  5.2.2     Compatibility checking
                  5.2.3     B-channel selection – Destination
                  5.2.4     Overlap receiving
                  5.2.5     Call confirmation
                  5.2.6     Notification of interworking at the terminating interface
                  5.2.7     Call accept
                  5.2.8     Active indication
                  5.2.9     Non-selected user clearing
        5.3     Call clearing
                  5.3.1     Terminology
                  5.3.2     Exception conditions
                  5.3.3     Clearing initiated by the user
                  5.3.4     Clearing initiated by the network
                  5.3.5     Clear collision
        5.4     In-band tones and announcements
        5.5     Restart procedure
                  5.5.1     Sending RESTART message
                  5.5.2     Receipt of RESTART message
        5.6     Call rearrangements
                  5.6.1     Call suspension
                  5.6.2     Call suspended
                  5.6.3     Call suspend error
                  5.6.4     Call re-establishment
                  5.6.5     Call resume errors
                  5.6.6     Double suspension
                  5.6.7     Call rearrangement notification controlled by an NT2
        5.7     Call collisions
        5.8     Handling of error conditions
                  5.8.1     Protocol discrimination error
                  5.8.2     Message too short
                  5.8.3     Call reference error
                  5.8.4     Message type or message sequence errors
                  5.8.5     General information element errors
                  5.8.6     Mandatory information element errors
                  5.8.7     Non-mandatory information element errors
                  5.8.8     Data link reset
                  5.8.9     Data link failure
                 5.8.10     Status enquiry procedure
                 5.8.11     Receiving a STATUS message
        5.9     User notification procedure
       5.10     Basic telecommunication service identification and selection
                 5.10.1     Additional procedures at the coincident S and T reference point
                 5.10.2     Procedures for interworking with private ISDNs
       5.11     Signalling procedures for bearer capability selection
                 5.11.1     Procedures for the originating user to indicate bearer capability selection is allowed
                 5.11.2     Procedures for bearer capability selection at the destination side
                 5.11.3     Procedures for interworking with private ISDNs
                 5.11.4     Channel selection
       5.12     Signalling procedures for high layer compatibility selection
                 5.12.1     Procedures for the originating user to indicate high layer compatibility selection is allowed
                 5.12.2     Procedures for high layer compatibility selection at the destination side
                 5.12.3     Procedures for interworking with private ISDNs
 6     Packet communication procedures
        6.1     Outgoing access
                  6.1.1     Circuit-switched access to PSPDN services (Case A)
                  6.1.2     Access to the ISDN virtual circuit service (Case B)
        6.2     Incoming access
                  6.2.1     Access from PSPDN services (Case A)
                  6.2.2     Access from the ISDN virtual circuit service (Case B)
        6.3     X.25 virtual call establishment and release
                  6.3.1     Link layer establishment and release
                  6.3.2     Packet layer virtual call set-up and release
        6.4     Call clearing
                  6.4.1     B-channel access
                  6.4.2     D-channel access
                  6.4.3     Additional error handling information
                  6.4.4     Cause mappings
        6.5     Access collision
 7     User signalling bearer service call control procedures
        7.1     General characteristics
        7.2     Call establishment
        7.3     Transfer of USER INFORMATION messages
        7.4     Congestion control of USER INFORMATION messages
        7.5     Call clearing
        7.6     Handling of error conditions
        7.7     Restart procedures
 8     Circuit-mode multirate (64 kbit/s base rate) procedures
        8.1     Call establishment at the originating interface
                  8.1.1     Compatibility information
                  8.1.2     Channel selection
                  8.1.3     Interworking
        8.2     Call establishment at the destination interface
                  8.2.1     Compatibility information
                  8.2.2     Channel selection
                  8.2.3     Interworking
        8.3     Call clearing
        8.4     Restart procedures
        8.5     Call rearrangements
 9     List of system parameters
        9.1     Timers in the network side
        9.2     Timers in the user side
Annex A – User side and network side SDL diagrams
Annex B – Compatibility and address checking
        B.1     Introduction
        B.2     Calling side compatibility checking
        B.3     Called side compatibility and address checking
                  B.3.1     Checking of addressing information
                  B.3.2     Network-to-user compatibility checking
                  B.3.3     User-to-user compatibility checking
                  B.3.4     User action tables
        B.4     Interworking with existing networks
Annex C – Transit network selection
        C.1     Selection not supported
        C.2     Selection supported
Annex D – Extensions for symmetric call operation
        D.1     Additional message handling
                  D.1.1     B-channel selection – Symmetric interface
                  D.1.2     Call confirmation
                  D.1.3     Clearing by the called user employing user-provided tones/announcements
                  D.1.4     Active indication
        D.2     Timers for call establishment
        D.3     Call collisions
Annex E – Network-specific facility selection
        E.1     Default provider
        E.2     Routing not supported
        E.3     Routing supported
Annex F – D-channel backup procedures
        F.0     Foreword
        F.1     General
        F.2     D-channel backup procedure
                  F.2.1     Role of each D-channel
                  F.2.2     Switch-over of D-channels
Annex G – Use of progress indicators
Annex H – Message segmentation procedures
        H.1     Introduction
        H.2     Message segmentation
        H.3     Reassembly of segmented messages
Annex I –Low layer information coding principles
        I.1     Purpose
        I.2     Principles
                  I.2.1     Definitions of types of information
                  I.2.2     Examination by network
                  I.2.3     Location of type I information
                  I.2.4     Location of type II and III information
                  I.2.5     Relationship between Bearer capability and Low layer capability information elements
        I.3     Information classification
                  I.3.1     Examples for speech and 3.1 kHz audio bearer services
                  I.3.2     Examples for 64 kbit/s UDI circuit mode bearer service
                  I.3.3     Examples for ISDN virtual-circuit bearer service
        I.4     Scenarios outside the scope of ISDN standardization
                  I.4.1     Examples for speech and 3.1 kHz audio bearer services
                  I.4.2     Examples for 64 kbit/s UDI circuit-mode bearer services
Annex J – Low layer compatibility negotiation
        J.1     General
        J.2     Low layer capability notification to the called user
        J.3     Low layer compatibility negotiation between users
        J.4     Low layer compatibility negotiation options
        J.5     Alternate requested values
Annex K – Procedures for establishment of bearer connection prior to call acceptance
        K.1     General
        K.2     Procedures
Annex L – Optional procedures for bearer service change
Annex M – Additional basic call signalling requirements for the support of private network interconnection for Virtual Private Network applications
        M.1     Introduction
        M.2     Scope
                  M.2.1     Acronyms used in this Annex
                  M.2.2     References
                  M.2.3     Definitions
        M.3     Basic call states
        M.4     Additional messages and content
                  M.4.1     SETUP message
                  M.4.2     CONNECT message
        M.5     Additional information elements and coding
                  M.5.1     Called party number
                  M.5.2     Calling party number
                  M.5.3     Connected number
                  M.5.4     Connected subaddress
                  M.5.5     Progress indicator
                  M.5.6     Transit counter
                  M.5.7     VPN indicator
        M.6     Additional basic call control procedures
                  M.6.1     Distinction between public network and VPN context
                  M.6.2     Procedures applicable for signalling in a public network
                  M.6.3     Procedures applicable for signalling in a VPN context
        M.7     System parameters
Appendix M.I – Discrimination of calls in a VPN context by means of the Network-specific facilities information element
Annex N – Flexible channel selection
Appendix I – Definition of causes values
Appendix II – Example message flow diagrams and example conditions for cause mapping
       II.1     Example message flow diagrams
                 II.1.1     Key to the figures
       II.2     Example conditions for cause mapping
Appendix III – Summary of assigned information element identifier and message type code points for the Q.93x-series and Q.95x-series of Recommendations
      III.1     Acronyms used in this Recommendation
      III.2     References