本建议|国际标准以抽象的方式定义了供应商提供的外部可见服务 传输层包括: a） 服务的原始动作和事件； b） 与每个基本动作和事件关联的参数数据； c） 这些行为和事件之间的关系以及有效的顺序。 本建议|国际标准中定义的服务是由增强型 通信传输协议（与网络服务结合使用），任何 应用程序协议。服务还可以由其他协议提供，可能每个协议都支持服务的一个子集 此处定义的服务。 本建议|国际标准中规定的原语支持连接模式服务和 无连接服务。在支持增强通信的无连接模式服务的某些情况下，某些 在开始数据传输之前，也可能需要进行操作，例如服务质量协议。 对于连接模式或无连接模式服务的数据传输阶段，可能存在一系列数据排序 特点。 本建议|国际标准中不包含或排除任何以下内容: 上述特征基于本文指定的服务原语。

This Recommendation | International Standard defines in an abstract way the externally visible service provided by the Transport Layer in terms of: a) the primitive actions and events of the service; b) the parameter data associated with each primitive action and event; c) the relationship between, and the valid sequences of, these actions and events. The service defined in this Recommendation | International Standard is that which is provided by the Enhanced Communications Transport Protocol (in conjunction with the Network Service) and which may be used by any application protocol. The service can also be provided by other protocols possibly each supporting a subset of the services defined herein. The primitives specified in this Recommendation | International Standard support a connection-mode service and a connectionless service. In some cases of connectionless-mode service supporting enhanced communications, certain operations may also be necessary prior to the commencement of data transfer, e.g. agreement on quality of service. For the data transfer phase of either connection-mode or connectionless-mode services, there may be a range of dataordering characteristics. No implication is made in this Recommendation | International Standard regarding the inclusion or exclusion of any of the above characteristics given the service primitives specified herein.