• Rec. CCITT Q.921 (11/1988) – ISDN USER-NETWORK INTERFACE – DATA LINK LAYER SPECIFICATION
  • 1 General
  • 2 Frame structure for peer-to-peer communication
    • 2.1 General
    • 2.2 Flag sequence
    • 2.3 Address field
    • 2.4 Control field
    • 2.5 Information field
    • 2.6 Transparency
    • 2.7 Frame check sequence (FCS) field
    • 2.8 Format convention
    • 2.9 Invalid frames
    • 2.10 Frame abort
  • 3 Elements of procedures and formats of fields for data link layer peer-to-peer communication
    • 3.1 General
    • 3.2 Address field format
    • 3.3 Address field variables
    • 3.4 Control field formats
    • 3.5 Control field parameters and associated state variables
    • 3.6 Frame types
  • 4 Elements for layer-to-layer communication
    • 4.1 General
    • 4.2 Primitive procedures
  • 5 Definition of the peer-to-peer procedures of the data link layer
    • 5.1 Procedure for the use of the P/F bit
    • 5.2 Procedures for unacknowledged information transfer
    • 5.3 Terminal endpoint identifier (TEI) management procedures
    • 5.4 Automatic negotiation of data link layer parameters
    • 5.5 Procedures for establishment and release of multiple frame operation
    • 5.6 Procedures for information transfer in multiple frame operation
    • 5.7 Re-establishment of multiple frame operation
    • 5.8 Exception condition reporting and recovery
    • 5.9 List of system parameters
    • 5.10 Data link layer monitor function
  • ANNEX A – Provision of point-to-point signalling connections
  • ANNEX B – SDL for point-to-point procedures
  • B.1 General
  • B.2 An overview of the states of the point-to-point data link layer entity
  • B.3 Cover notes
  • B.4 The use of queues
  • B.5 SDL representation
  • ANNEX C – SDL representation of the broadcast procedures
  • ANNEX D – State transition table of the point-to-point procedures of the data link layer
  • D.1
  • D.2 Key to the state transition table
  • APPENDIX I – Retransmission of REJ response frames
  • I.1 Introduction
  • I.2 Procedure
  • APPENDIX II – Occurrence of MDL-ERROR-INDICATION within the basic states and actions to be taken by the management entity
  • II.1 Introduction
  • II.2 Layout of Table II-1/Q.921
  • II.3 Preferred management actions
  • APPENDIX III – Optional basic access deactivation procedures
  • III.1 Introduction
  • III.2 Description of the Conceptual Model
  • III.3 Deactivation procedure with MPH-DEACTIVATE-IND
  • III.4 Deactivation procedure without MPH-DEACTIVATE-IND
  • APPENDIX IV – Automatic negotiation of data link layer parameters
  • IV.1 General
  • IV.2 Parameter initialization
  • IV.3 Internal parameter initialization
  • IV.4 Automatic notification of data link layer parameter values
  • ABBREVIATIONS AND ACRONYMS USED IN RECOMMENDATION Q.921
  • References