1
Scope
1.1 General
1.2 Relationship to other
international standards
1.3 References
2 Definitions
3 Abbreviations
4 Establishing an error-corrected
connection
5 Interchange circuits affected by
error correction
6 Overview of error-correcting DCE
operation
6.1 General
6.2 Overview of the control function
6.3 Overview of the error control
function
6.4 Communication between the control
function and the error control function
7 Operation of the control function
7.1 Physical handshake
7.2 Phases of error-correcting
protocol establishment
7.2.1 Detection phase
7.2.2 Protocol establishment phase
7.3 Data transfer
7.3.1 Flow control across the DTE/DCE interface
7.4 Transfer of break signal
7.5 Receipt of break
7.6 Negotiation/Indication of
parameter values and optional procedures
7.7 Orderly release of the
error-corrected connection
7.8 Loop-back test
7.9 Operation of the DTE-DCE interface
after failure to establish error-correcting operation
7.10 Suspension of error correction
procedure
7.10.1 Reception of L-SUSPEND request primitive during the detection phase
7.10.2 Reception of L-SUSPEND request primitive during the protocol
establishment phase or after an error correction connection has been
established
7.11 Resumption of error correction
procedure
8 Operation of the error control
function: LAPM procedures
8.1 General
8.1.1 Frame structure and fields
8.1.2 Format
conventions
8.1.3 Invalid frames
8.1.4 Frame abort
8.1.5 Interframe time fill
8.2 LAPM elements of procedures and
field formats
8.2.1 Address field format
8.2.2 Control field format
8.2.3 Control field parameters and associated state variables
8.2.4 Frame types
8.2.5 Use of timers
8.3 Establishment of the
error-corrected connection
8.3.1 General
8.3.2 Detailed procedures
8.4 Transfer of user data from the
V.24 interface
8.4.1 Transmitting I frames
8.4.2 Receiving I frames
8.4.3 Sending and receiving acknowledgements
8.4.4 Receiving REJ frames
8.4.5 Receiving SREJ frames
8.4.6 Receiving RNR frames
8.4.7 Own-receiver busy condition
8.4.8 Waiting acknowledgement
8.4.9 Termination of the error-corrected connection
8.5 Exception condition reporting and
recovery
8.5.1 N(S) sequence error
8.5.2 N(R) sequence error
8.5.3 Timer-recovery condition
8.5.4 Invalid-frame condition
8.5.5 Frame-rejection condition
8.5.6 Receipt of an FRMR response frame
8.5.7 Unsolicited response frames
8.6 Transfer of user-control
information
8.7 Orderly release of an
error-corrected connection
8.7.1 General
8.7.2 Release procedure
8.7.3 Procedure on expiry of timer T401
8.8 Disconnected state
8.9 Collision of unnumbered commands
and responses
8.9.1 Identical transmitted and received set-mode commands
8.9.2 Different transmitted and received set-mode commands
8.9.3 Unsolicited DM response and SABME or DISC command
8.10 Negotiation/indication of
parameter values and optional procedures
8.10.1 General
8.10.2 Negotiation/Indication procedure
8.10.3 Procedure on expiry of timer T401
8.11 Loop-back test
8.12 Monitoring functions
8.12.1 General
8.12.2 Supervision during the connected state
8.12.3 Connection verification procedures
8.13 Transfer of break
8.13.1 General
8.13.2 State variables and parameters
8.13.3 Break procedures
9 System parameters
9.1 Parameters of the control function
9.1.1 Detection phase timer (T400)
9.2 Parameters of the error control
function
9.2.1 Acknowledgement timer (T401)
9.2.2 Maximum number of retransmissions (N400)
9.2.3 Maximum number of octets in an information field (N401)
9.2.4 Window size (k)
9.2.5 Reply delay timer (T402) –
Optional
9.2.6 Inactivity timer (T403) – Optional
9.2.7 DLCI values
9.3 Other parameters
10 Negotiation of optional procedures
11 Control function-to-control function connection
12 Encoding of information fields
12.1 Information fields in I frames
12.2 Information fields in XID frames
12.2.1 General
12.2.2 Encoding for negotiation/indication of parameter values and optional
procedures
12.3 Information fields in UI frames
12.3.1 Encoding of BRK message
12.3.2 Encoding of BRKACK message
12.4 Information fields in TEST frame
12.5 Information fields in SREJ frames
Annex A – Operation
of the error control function – Alternative procedure
Annex B – Mapping of
character formats to 8-bit format
Appendix I –
Interworking with a non-error correcting DCE
I.1 Interworking with a non-error-correcting
answerer
I.2 Interworking with a non-error-correcting originator
I.3 Disposition of unrecognized bits
Appendix II – Data
forwarding conditions
Appendix III – Additional
information for V.42 implementers regarding robustness of operation
III.1 Transmission of the answerer
detection pattern
III.2 Value of parameter N400 (maximum
number of retransmissions)
III.3 Incomplete XID exchange
III.4 Selective retransmission
III.5 Reject on detection of errored
frames
III.6 Checkpointing
Appendix IV – Factors
for determining the acknowledgement timer
Appendix V –
Potential enhancements to LAPM protocol
Appendix VI –
Additional information for V.42 implementers regarding answerer detection
patterns
VI.1 Alternative answerer detection
patterns
VI.2 Skipping of originator/answerer
detection patterns