信息技术 提供无连接方式网络服务的协议:协议规范

[中文适用范围]： GB/T 17179的本部分规定了用来提供在GB／T 15126中描述的无连接方式网络服务和执行某些网络层管理功能的协议。该协议依靠实子网方式和／或数据链路提供的低层无连接方式服务。协议假设的低层无连接方式服务，可以直接从尢连接方式实子网获得，也可以间接地在连接方式实子网上，按照G／T 15274—1994中所描述，通过一个适当的依赖于子网的收敛功能(sNDcF)或依赖于子网的收敛协议(sNDCP)的操作来获得。本部分规定了关于统一、抽象的“低层子网服务”协议的操作。其他标准规定了从实子网，如符合GH／T 15629．4—1 997或GB／T 16974—1997的子网中，获得这种“低层子网服务”的方法。这种“低层子网服务”可以从除其他标准专门覆盖的子网以外的其他实子网中获得。 本部分规定了： a) 用于从一个网络实体到另一个对等网络实体的无连接传输数据和控制信息的规程； b) 用于传输数据和控制信息的协议数据单元(PDu)的编码，包括可变长度协议首标格式； c) 用于正确解释协议控制信息的规程； d) 声称与本部分一致的实现的功能要求。 规程依照下面内容来定义： a) 对等网络实体之间通过交换协议数据单元交互作用； b) 网络实体和网络服务用户之间通过交换网络服务原语交互作用； c) 网络实体和抽象低层服务提供者之间通过交换服务原语交互作用。 本部分还提供了本协议的PICS形式表，符合GB／T 17178．1—1997中规定的相关要求和相关指南。 [外文原描述]： This Recommendation | International Standard specifies a protocol that is used to provide the connectionless-mode Network service described in ITU-T Rec. X.213 | ISO/IEC 8348 and to perform certain Network layer management functions. The protocol relies upon the provision of an underlying connectionless-mode service by real subnetworks and/or data links. The underlying connectionless-mode service assumed by the protocol may be obtained either directly, from a connectionless-mode real subnetwork, or indirectly, through the operation of an appropriate Subnetwork Dependent Convergence Function (SNDCF) or Protocol (SNDCP) over a connection-mode real subnetwork, as described in ISO/IEC 8648. This Recommendation | International Standard specifies the operation of the protocol with respect to a uniform, abstract "underlying subnetwork service". Other Recommendations | International Standards specify the way in which this "underlying subnetwork service" is obtained from real subnetworks, such as those which conform to ISO/IEC 8802 or ISO/IEC 8208. The "underlying subnetwork service" may be obtained from real subnetworks other than those that are specifically covered by the other Recommendations | International Standards. This Recommendation | International Standard specifies: a) procedures for the connectionless transmission of data and control information from one Network entity to one or more peer Network entities; b) the encoding of the Protocol Data Units (PDUs) used for the transmission of data and control information, comprising a variable-length protocol header format; c) procedures for the correct interpretation of protocol control information; and d) the functional requirements for implementations claiming conformance to this Recommendation | International Standard. The procedures are defined in terms of: a) the interactions among peer Network entities through the exchange of protocol data units; b) the interactions between a Network entity and a Network service user through the exchange of Network service primitives; and c) the interactions between a Network entity and an abstract underlying service provider through the exchange of service primitives. This Recommendation | International Standard also provides the PICS proforma for this protocol, in compliance with the relevant requirements, and in accordance with the relevant guidance, given in ITU-T Rec. X.290 | ISO/IEC 9646-1