CCITT Rec. V.42 (11/1988) – ERROR-CORRECTING PROCEDURES FOR DCES USING ASYNCHRONOUS-TO-SYNCHRONOUS CONVERSION
CONTENTS
1 Scope
1.1 General
1.2 Relationship to other international standards
2 Definitions
2.1 DCE
2.2 error-Correcting DCE
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
7.3 Data transfer
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
8 Operation of the error control function: LAPM procedures
8.1 General
8.2 LAPM elements of procedures and field formats
8.3 Establishment of the error-corrected connection
8.4 Transfer of user data from the V.24 interface
8.5 Exception condition reporting and recovery
8.6 Transfer of user-control information
8.7 Orderly release of an error-corrected connection
8.8 Disconnected state
8.9 Collision of unnumbered commands and responses
8.10 Negotiation/indication of parameter values and optional procedures
8.11 Loop-back test
8.12 Monitoring functions
8.13 Transfer of break
9 System parameters
9.1 Parameters of the control function
9.2 Parameters of the error control function
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
12.3 Information fields in UI frames
12.4 Information fields in TEST frame
References
ANNEX A – Operation of the error control function - Alternative procedure
A.1 General
A.2 Format conventions
A.3 Start-stop, octet-oriented framing mode
A.4 Bit-oriented framing mode
A.5 Invalid frames
A.6 Alternative elements of procedure and field formats
A.7 Description of the error-correcting 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 – Cross-reference with CCITT Recommendations Q.920 and Q.921
APPENDIX IV – Factors for determining the acknowledgment timer
APPENDIX V – Potential enhancements to LAPM protocol
V.1 Data compression
V.2 Forward error correction
V.3 Statistical multiplexing
V.4 End-to-end transport of interface state information
V.5 Issues related to control function-to-control function information exchange
V.6 Rate negotiation
V.7 Operation over an asymmetric or half-duplex physical connection
V.8 Multiple frame reject
V.9 Character format indication/negotiation
V.10 Preservation of framing/parity errors
V.11 Encryption
V.12 ISDN compatibility