1 DTE/DCE interface characteristics (physical layer)
    1.1 X.21 interface
    1.2 X.21 bis interface
    1.3 V-Series interface
    1.4 X.31 interface
2 Link access procedures across the DTE/DCE interface
    2.1 Scope and field of applications
    2.2 Framing aspects
    2.3 LAPB elements of procedures
    2.4 Description of the LAPB procedure
    2.5 Multilink procedure (MLP) (Subscription-time selectable option)
3 Description of the packet layer DTE/DCE interface
    3.2 Basic structure of packets
    3.3 Procedure for restart
    3.4 Error handling
4 Procedures for virtual circuit services
    4.1 Procedures for virtual call service
    4.2 Procedures for permanent virtual circuit service
    4.3 Procedures for data and interrupt transfer
    4.4 Procedures for flow control
    4.5 Effects of clear, reset and restart procedures on the transfer of packets
    4.6 Effects of the physical layer and the data link layer on the packet layer
5 Packet formats
    5.1 General
    5.2 Call set-up and clearing packets
    5.3 Data and interrupt packets
    5.4 Flow control and reset packets
    5.5 Restart packets
    5.6 Diagnostic packet
    5.7 Packets required for optional user facilities
6 Procedures for optional user facilities (packet layer)
    6.1 On-line facility registration
    6.2 Extended packet sequence numbering
    6.3 D-bit modification
    6.4 Packet retransmission
    6.5 Incoming calls barred
    6.6 Outgoing calls barred
    6.7 One-way logical channel outgoing
    6.8 One-way logical channel incoming
    6.9 Non-standard default packet sizes
    6.10 Non-standard default window sizes
    6.11 Default throughput classes assignment
    6.12 Flow control parameter negotiation
    6.13 Throughput class negotiation facilities
    6.14 Closed user group related facilities
    6.15 Bilateral closed user group related facilities
    6.16 Fast select
    6.17 Fast select acceptance
    6.18 Reverse charging
    6.19 Reverse charging acceptance
    6.20 Local charging prevention
    6.21 Network user identification (NUI) related facilities
    6.22 Charging information
    6.23 ROA related facilities
    6.24 Hunt group
    6.25 Call redirection and call deflection related facilities
    6.26 Called line address modified notification
    6.27 Transit delay selection and indication
    6.28 TOA/NPI address subscription
    6.29 Alternative addressing related facilities
7 Formats for facility fields and registration fields
    7.1 General
    7.2 Coding of facility field in call set-up and clearing packets
    7.3 Coding of the registration field of registration packets
Annex A Range of logical channels used for virtual calls and permanent virtual circuits
Annex B Packet layer DTE/DCE interface state diagrams
B.1 Symbol definition of the state diagrams
B.2 Order definition of the state diagrams
Annex C Actions taken by the DCE on receipt of packets in a given state of the packet layer DTE/DCE ...
Annex D Packet layer DCE time-outs and DTE time-limits
D.1 DCE time-outs
D.2 DTE time-limits
Annex E Coding of X.25 network generated diagnostic fields in clear, reset and restart indication, registration ...
Annex F Applicability of the on-line facility registration facility to other facilities
Annex G ITU-T specified DTE facilities to support the OSI Network service and other purposes
G.1 Introduction
G.2 Coding of the facility code fields
G.3 Coding of the facility parameter field
Annex H Subscription-time optional user facilities that may be associated with a network user identifier ...
Appendix I Examples of data link layer transmitted bit patterns by the DCE and the DTE
Appendix II An explanation of how the values for N1 in subclause are derived
Appendix III Examples of multilink resetting procedures
III.1 Introduction
III.2 MLP reset initiated by either the DCE or the DTE
III.3 MLP reset initiated by both the DCE and the DTE simultaneously
Appendix IV Information on addresses in call set-up and clearing packets
IV.1 Main address and complementary address
IV.2 Addresses in call request packet
IV.3 Addresses in incoming call packets
IV.4 Addresses in call accepted packets
IV.5 Addresses in call connected packets
IV.6 Addresses in clear request packets
IV.7 Addresses in clear indication packets
IV.8 Addresses in clear confirmation packets
IV.9 Addresses in call redirection and call deflection related facilities
Appendix V Guidelines for transmission over channels with long round-trip delay and/or transmission rates higher ...
V.1 Preamble
V.2 Common guidelines
V.3 Guidelines for channels with long round-trip delays operating at 64 000 bit/s
V.4 Guidelines for circuits with long round-trip delays operating at 1920 kbit/s
Appendix VI Format for NUI parameter field