BS ISO/IEC 7776:1995 Information technology. Telecommunications and information exchange between systems. High-level data link control procedures. Description of the X.25 LAPB-compatible DTE data link procedures
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This International Standard defines an application of the following HDLC Standards: ISO/IEC 3309, ISO/IEC 4335, ISO 7478, and ISO/IEC 7809. When there is difficulty in the interpretation of a reworded requirement from one of the other International Standards, the original requirement of ISO/IEC 3309, ISO/IEC 4335, ISO 7478 or ISO/IEC 7809 is definitive. It also defines the structure, elements and procedures for the Operation of a DTE using the X.25 LAPB protocol as specified in ITU-T Recommendation X.25.1) The procedures are applicable to data interchange between a DTE and a DCE, or between two DTEs. The procedures are defined for use on duplex links, using synchronous transmission or start/stop transmission. Clause 3 describes two frame structures: one for basic (modulo 8) Operation and one for extended (modulo 128) Operation. Basic (modulo 8) Operation is the ISO/IEC balanced asynchronous class of procedure with optional functions 2 and 8 (BAC, 2, 8). Extended (modulo 128) Operation is the ISO/IEC balanced asynchronous class of procedure with optional functions 2, 8 and 10 (BAC, 2, 8, 10). For those DTE/DCE connections that support both basic (modulo 8) Operation and extended (modulo 128) Operation, the choice is made at subscription-time only. For those DTE/remote DTE connections that support both basic (modulo 8) Operation and extended (modulo 128) Operation, the choice is made by bilateral agreement.
NOTE - The procedure herein described as basic (modulo 8) Operation is the only one available in all public data networks.
Clause 3 also describes two methods for encoding the frames, as sequences of bits when synchronous transmission is used, and as sequences of octets when start/stop transmission is used. The start/stop encoding specifies optional mechanisms, for use in environments that are sensitive to transmission of octets with values that could be interpreted as ISO/IEC 646 control characters, and/or in environments that support transfer of only seven data bits per start/stop Character. The choice of encoding is made by bilateral agreement, or other suitable means, to suit the data transmission characteristics of the environment.
Clause 4 describes the elements of procedures. Same aspects are only operable for the basic (modulo 8) Operation and some for the extended (modulo 128) Operation.
Clauses 5 and 6 describe the Single link procedure (SLP) which is derived fror-n the frame structure and the elements of procedures, and an optional multilink procedure (MLP), respectively. The SLP is used for data interchange over a Single data link and the MLP is used for data interchange over a multiple of parallel SLPs. An MLP is required if the effects of individual SLP failures are not to disrupt the higher layer Operation. An MLP tan also be used over a Single SLP by Prior bilateral agreement. For DTE/DCE connections the choice of an MLP Operation or not is made at subscription-time only. For DTE/remote DTE connections, the choice is made by bilateral agreement.
Where choices among alternative actions are indicated in the procedures, a recommended choice is usually indicated. Unless specifically stated otherwise, the choice of action does not affect interoperability with other implernentations of this International Standard although efficiency of Operation may be affected. Where such choices do affect interoperability, the procedures explicitly state that Prior bilateral
ICS 35.200 Interface and interconnection equipment
Language:
English
Subject Keywords:
Data transmission control procedures; Packet switching networks; Data layout; Data transmission; Data link layer (OSI); Interfaces (data processing); Conformity; Synchronous transmission; Open systems interconnection; Computer-computer communications; Frames (data transmission); Computer terminals; Computer networks; Information exchange; Data transfer; High-level data link control; Communication procedures; LAPB
BS ISO/IEC 7776:1995 Information technology. Telecommunications and information exchange between systems. High-level data link control procedures. Description of the X.25 LAPB-compatible DTE data link procedures
