GB/T 16976-1997 in English

《GB/T 16976-1997信息技术 系统间远程通信和信息交换 使用X.25提供OSI连接方式网络服务》由TC28（全国信息技术标准化技术委员会）归口，TC28SC6（全国信息技术标准化技术委员会数据通信分会）执行，主管部门为国家标准化管理委员会。
本标准规定了两组规程，并从中引出了三类实现的描述。本标准规定了系统-1984实现要满足的需求。本标准也规定了系统-1980实现要操作的规程。本标准还规定了兼容的实现要满足的需求。

Scope

OSI Connectivity Network Services (CONS) are defined in terms of a set of primitive actions and events and their associated parameters. For a protocol to support such a service, there must be a mapping between the CONS abstract primitives and parameters and the actual elements of the protocol. For the X.25 Packet Layer Protocol (PLP), the main part of this standard provides such a mapping to X.25/PLP-1984 using virtual calls. This standard also provides the mapping of CONS primitives and parameters to X.25/PLP-1980 plus SNDCP (Appendix A). These mappings apply to X.25 virtual call services. In addition, methods for selecting the appropriate mapping, if any, are defined for different combinations of end systems and network layer relay systems implementing one or more mappings (Appendix B). For the permanent virtual circuit PVC service of X.25/PLP-1984 and X.25/PLP-1980, the mapping of CONS primitives and parameters to X.25/PLP is given in Appendix C. This International Standard specifies two sets of procedures from which three types of implementation descriptions derive. The requirements of these procedures apply both to end system operations and to network layer relay half operations. Interrupt operations are involved here, and the two halves of the relay can be of the same or different implementation classes. This standard specifies the procedures by which System-1080 implementations are to operate. Such implementations are designed to operate directly with other System-1980 implementations, including the case of operation over any form of X.25 subnet, but operate less efficiently than System-1984 implementations. This standard also specifies the requirements to be met by compliant implementations. This class of implementations is designed to operate directly with all other implementation types, including over any type of X.25 subnetwork. When placed in this environment, they will effectively take advantage of X.25 (1984). X.25/PLP is generally thought of as an operation between an end system (i.e., "data terminal equipment" in X.25 terminology) and a packet-switched public data subnetwork. However, X.25/PLP can also be used in other environments where OSICONS is provided. Examples of such other uses include: End systems connected to X.25 packet-switched private data subnetworks; End systems connected to local area networks; When the switched public data subnetwork intervenes, the two end systems are directly connected or circuit-switched connected (including the connection through the circuit-switched data subnetwork).